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DOI： 10.1088/1361-6641/ac8309

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During visual search, attention is guided by specific features, including shape. Our understanding of shape guidance is limited to specific attributes (closures and line terminations) that do not fully explain the richness of preattentive shape processing. We used a novel genetic algorithm method to explore shape space and to stimulate hypotheses about shape guidance. Initially, observers searched for targets among 12 random distractors defined, in radial frequency space, by the amplitude and phase of 10 radial frequencies. Reaction time (RT) was the measure of "fitness." To evolve toward an easier search task, distractors with faster RTs survived to the next generation, "mated," and produced offspring (new distractors for the next generation of search). To evolve a harder search, surviving distractors were those yielding longer RTs. Within eight generations of evolution, the method succeeds in producing visual searches either harder or easier than the starting search. In radial frequency space, easy distractors evolve amplitude × frequency spectra that are dissimilar to the target, whereas hard distractors evolve spectra that are more similar to the target. This method also works with naturally shaped targets (e.g., rabbit silhouettes). Interestingly, the most inefficient distractors featured a combination of a body and ear distractors that did not resemble the rabbit (visually or in spectrum). Adding extra ears to these distractors did not impact the search spectrally and instead made it easier to confirm a rabbit, once it was found. In general, these experiments show that shapes that are clearly distinct when attended are similar to each other preattentively.

DOI： 10.1167/jov.22.1.7

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DOI： 10.1016/j.asoc.2022.108811

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Other Link： https://dblp.uni-trier.de/db/journals/asc/asc122.html#TakahashiSSCPZZ22

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Ion implantation is a fundamental processing step in electronic device manufacturing. However, it can give rise to electrically active defects, in the crystal, that can undermine the functionality of devices. In this study, we carried out an electrical characterization study of defects in ion implanted n-type GaN. We found several levels in the 0.2–1.2 eV below the conduction band edge. The nature of these defects is discussed in the light of the ion mass, tilt angle and dose dependence of the concentration of the detected levels.

DOI： 10.1016/j.nimb.2020.12.010

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Chlorine-based reactive ion etching (RIE) is a fundamental processing step for the manufacturing of GaN semiconductor devices. As impurities can be unintentionally incorporated in the crystal during processing, the electronic properties of chlorine in GaN are investigated. Density functional theory calculations of substitutional Cl and related complexes (with a vacancy or a dopant) are carried out. It is found that Cl and its complexes explain the reported effects of Cl RIE-treated GaN on hole density and ohmic contact resistivity.

DOI： 10.1002/pssb.202000303

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER INTERNATIONAL PUBLISHING AG  

Recognizing seismic waves immediately is very important for the realization of efficient disaster prevention. Generally, these systems consist of a network of seismic detectors that send real time data to a central server. The server elaborates the data and attempts to recognize the first sign of an earthquake. The problem with this approach is that it exists a critical trade-off between sensitivity of the system and error rate. To overcame this problem, an artificial neural network based intelligent learning system can be used. However, conventional supervised ANN systems are difficult to train, CPU intensive and prone to false alarms. To surpass these problems, here we attempt to use a next-generation unsupervised cortical algorithm hierarchical temporal memory (HTM). This novel approach does not learn particular waveforms, but adapts to continuously fed data reaching the ability to discriminate between normality (seismic sensor background noise in no-earthquake conditions) and anomaly (sensor response to a jitter or an earthquake). Main goal of this study is to test the ability of the HTM algorithm to be used to signal earthquakes automatically in a feasible disaster prevention system. We describe the methodology used and give the first qualitative assessments of the recognition ability of the system. Our preliminary results show that the cortical algorithm used is very robust to noise and that it can successfully recognize synthetic earthquake-like signals efficiently and reliably.

DOI： 10.1007/978-3-030-01174-1_67

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Public Library of Science ({PLoS})  

Birdsong is a complex learned behavior regulated by Neuromuscular coordination of different muscle sets necessary for producing relevant sounds. We developed a heterogeneous and stochastically connected neural network representing the pathway from the high vocal center (HVC) to the robust nucleus of the arcopallium (RA) neurons that drive the muscles to generate sounds. We show that a single active neuron is sufficient to initiate a chain of spiking events that results to excite the entire network system. The network could synthesize realistic bird sounds spectra, with spontaneous generation of intermittent sound bursts typical of birdsong (song syllables). This study confirms experiments on animals and on humans, where results have shown that single neurons are responsible for the activation of complex behavior or are associated with high-level perception events.

DOI： 10.1371/journal.pone.0200998

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics Inc.  

Magnesium (Mg) is the p-type doping of choice for GaN, and selective area doping by ion implantation is a routine technique employed during device processing. While electrically active defects have been thoroughly studied in as-grown GaN, not much is known about defects generated by ion implantation. This is especially true for the case of Mg. In this study, we carried out an electrical characterization investigation of point defects generated by Mg implantation in GaN. We have found at least nine electrically active levels in the 0.2-1.2 eV energy range, below the conduction band. The isochronal annealing behavior of these levels showed that most of them are thermally stable up to 1000 °C. The nature of the detected defects is then discussed in the light of the results found in the literature.

DOI： 10.1063/1.5029254

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Language：English   Publisher：OPTICAL SOC AMER  

Surface exciton polaritons (SEPs) are very important for the realization of novel sensors and next-generation optical devices. Here we propose for the first time, to the best of our knowledge, a Kretschmann-Raether device that is able to induce SEPs propagating along the interface between a J-aggregate cyanine dye and air at room temperature. This configuration has the advantages of being straightforward to realize and easy to study because the Kretschmann-Raether approach is the most simple and fundamental from the theoretical point of view. Here a J-aggregate cyanine dye produces strong binding energy due to Frenkel excitons, and this enables the observation of SEPs easily at room temperature. One of the advantages of the use of the J-aggregate cyanine dye is the simple device preparation. This is because the J-aggregate cyanine dye can be easily deposited on any arbitrary substrates with a spincoating or dip-coating technique from its aqueous solution in ambient condition. We observed SEPs at room temperature, and the deepest resonant peak was obtained for a 94 nm thick 5,6-dichloro-2-[[5,6-dichloro-1-ethyl-3(4-sulfobutyl)-benzimidazol-2-ylidene]-propenyl]-1-ethyl-3(4-sulfobutyl)-benzimidazolium hydroxide film at 532 nm wavelength. Our results may pave the way for the realization of novel SEP biosensors in a simple and straightforward way at room temperature. (C) 2017 Optical Society of America

DOI： 10.1364/OL.42.003876

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：BEILSTEIN-INSTITUT  

The occurrence of plasmon resonances on metallic nanometer-scale structures is an intrinsically nanoscale phenomenon, given that the two resonance conditions (i.e., negative dielectric permittivity and large free-space wavelength in comparison with system dimensions) are realized at the same time on the nanoscale. Resonances on surface metallic nanostructures are often experimentally found by probing the structures under investigation with radiation of various frequencies following a trial-and-error method. A general technique for the tuning of these resonances is highly desirable. In this paper we address the issue of the role of local surface patterns in the tuning of these resonances as a function of wavelength and electric field polarization. The effect of nanoscale roughness on the surface plasmon polaritons of randomly patterned gold films is numerically investigated. The field enhancement and relation to specific roughness patterns is analyzed, producing many different realizations of rippled surfaces. We demonstrate that irregular patterns act as metal-dielectric-metal local nanogaps (cavities) for the resonant plasmonic field. In turn, the numerical results are compared to experimental data obtained via aperture scanning near-field optical microscopy.

DOI： 10.3762/bjnano.8.97

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：OSA - The Optical Society  

We propose two types of plasmon-induced broadband light absorbers consisting of randomly arranged bumps or holes. The absorbers with bumps shows 3-octave band absorption. The absorber with holes replaces the transparent electrode of solar cells.

DOI： 10.1364/PV.2017.JW5A.25

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Language：English   Publisher：CELL PRESS  

DOI： 10.1016/j.bpj.2015.11.3381

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

Toward the development of ecotoxicology methods to investigate microbial markers of impacts of hydrocarbon processing activities, DNA adductomic analyses were conducted on a sphingomonad soil bacterium. From growing cells that were exposed or unexposed to acrolein, a commonly used biocide in hydraulic fracturing processes, DNA was extracted, digested to 2′-deoxynucleosides and analyzed by liquid chromatography-positive ionization electrospray-tandem mass spectrometry in selected reaction monitoring mode transmitting the [M + H]+ &gt
[M + H - 116]+ transition over 100 transitions. Overall data shown as DNA adductome maps revealed numerous putative DNA adducts under both conditions with some occurring specifically for each condition. Adductomic analyses of triplicate samples indicated that elevated levels of some targeted putative adducts occurred in exposed cells. Two exposure-specific adducts were identified in exposed cells as 3-(2′-deoxyribosyl)-5,6,7,8-tetrahydro-6-hydroxy-(and 8-hydroxy-)pyrimido[1,2-a]- purine-(3H)-one (6- and 8-hydroxy-PdG) following synthesis of authentic standards of these compounds and subsequent analyses. A time course experiment showed that 6- and 8-hydroxy-PdG were detected in bacterial DNA within 30 min of acrolein exposure but were not detected in unexposed cells. This work demonstrated the first application of DNA adductomics to examine DNA damage in a bacterium and sets a foundation for future work.

DOI： 10.1002/mbo3.283

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Language：English  

DOI： 10.1002/mbo3.283

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

InGaN alloys and, in particular, InGaN monolayer quantum wells (MLQWs) are attracting an increasing amount of interest for opto-electronic applications. Impurities, incorporated during growth, can introduce electronic states that can degrade the performance of such devices. For this reason, we present a density functional and group theoretical study of the electronic properties of C, H, or O impurities in an InGaN MLQW. Analysis of the formation energy and symmetry reveals that these impurities are mostly donors and can be held accountable for the reported degradation of InGaN-based devices. (C) 2015 AIP Publishing LLC.

DOI： 10.1063/1.4919787

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TRANS TECH PUBLICATIONS LTD  

The photoluminescence from III-V wide band-gap semiconductors as InGaN is characterized by localized large intensity fluctuations, known as 'blinking', that, despite decades of research, is not yet completely understood. In structures where there is a three-dimensional confinement, as for example semiconductors nano-crystals, the phenomena is supposed to be related to temporary quenching due to highly efficient non-radiative recombination processes (for example, Auger). Nevertheless, in typical InGaN devices, the band structure is an infinitely wide quantum well, so the understanding of the blinking phenomenon remains elusive. We present experimental data and a model that suggests that the discussed optical fluctuations are a general phenomena caused by the slow beating between THz thermal vibrations of the Quantum Well. These minuscule displacements are occurring naturally all over the device, the displacements along the growth direction induce a modulation of the matrix elements that drives the optical emission process; this have measurable effect on the device photo-luminescence. In presence of impurities or gradient of concentration, the vibrations have locally slight frequency differences on adjacent domains, this give rise to a band of beats, and we observe the lower frequency tail of this band.

DOI： 10.4028/www.scientific.net/AMM.541-542.253

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The photoluminescence of III-V wide band-gap semiconductors InGaN is characterized by local intensity fluctuations, known as "blinking points", which despite decades of research are not yet completely understood. In this study, we report the experimental data and a theoretical interpretation that suggests that they are caused by the interference of thermal vibrations of the quantum well lattice. With far-field optical tests we could observe the lower frequency tail of these interference waves and study their dynamics as they propagate up to distances of several tens of microns. (C) 2013 AIP Publishing LLC.

DOI： 10.1063/1.4826088

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER-VERLAG BERLIN  

In this paper, we present a visual support system the visually impaired. Our detection algorithm is based on the well known Histograms of Oriented Gradients (HOG) method, due to its high detection rate and versatility[5]. However, the accuracy of object recognition rate is reduced because of high false detection rate. In order to solve that, multiple parts model and triple phase detection have been implemented. These additional filtering stages were conducted by separate action on different area of the sample, considering deformations and translations. We demonstrated that this approach has raised the accuracy and speed of calculation. Through an evaluation experiment based on a large dataset, we found that false detection has been improved by 18.9% in respect to standard HOG detectors. Experimental tests have also shown the system ability to estimate the distance of the pedestrian by the use of a simple perspective model. The system has been tested on several photographic datasets and have shown excellent performances also in ambiguous cases.

DOI： 10.1007/978-3-642-41190-8_3

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Other Link： http://dblp.uni-trier.de/db/journals/corr/corr1210.html#journals/corr/abs-1210-7282

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InGaN/GaN devices are currently used for many applications, for example, full color display, white (RGB) illumination systems and for the realization of shorter wavelength emitters for optical data storage. We previously reported a blinking phenomenon in the photo-luminescence of InGaN device ready single quantum well materials. In this study we observe in high resolution this optical instability with a near-field nano-probe. The phenomenon appears only in local confined domains and does not seem to behave as a bistable state process like reported on quantum dots generated photo-luminescence. We investigated by a modified scanning near-field optical microscope (SNOM) and studied the time/intensity profile of the optical signal with a resolution in the range of 100nm. The dynamics of the blinking was time-resolved and its behaviour studied with Fourier analysis. Despite the intensity oscillations were found to have chaotic component (autocorrelation coefficient is about 0.63), the optical oscillations appear to include regular characteristics. Fourier analysis of the light intensity from confined domains exhibit peaks in the range of 4-5 s. The emergence of these intriguingly slow and partially regular dynamics should shed light on the inner mechanism that are involved in the fundamental processes of optical emission in these devices. © 2011 Optical Society of America.

DOI： 10.1364/OME.1.000158

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

The transition to maximum photoluminescence of InGaN single quantum wells is a phenomena that has time constants in the range of few seconds. Using a systematic illumination/darkening procedure we found that these characteristics are related to previous stimulations as if the sample has a memory of past illumination events. Choosing opportune time sequences, time constants were observed to vary more than 100%. These facts suggest the presence of carrier trapping/de-trapping processes that act beyond the single illumination event, accumulating over time in a complex effect. (C) 2009 Optical Society of America

DOI： 10.1364/OE.17.022855

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We study the optical polarization properties of confined structures in InGaN/GaN single quantum well devices. Using a near-field optical setup we investigated the photoluminescence maps with a polarization-modulation method. If the optical emissions have a preferred polarization orientation, our apparatus yields a signal that is proportional to the degree of polarization. We could demonstrate that within the quantum well there are localized submicrometer centers that emit strongly oriented light. This points toward the existence of quantum-dot like confined asymmetric domains hidden within the quantum well.

DOI： 10.1063/1.3265732

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Surface plasmon resonance sensors exploit the high sensitivity to local perturbations of plasma waves in a thin metal layer. These devices have a wide range of applications as biomedical, environmental, industrial, and homeland security. We concentrate on the theoretical aspects of the sensing principle. By calculations at various indexes of refraction we proved that using substrate material of higher index, sensitivity and dynamics range improve conspicuously. Finally, we show experimental data taken using a special transparent ceramic material of exceptionally high index of refraction n= 2.04. Tests demonstrate sensitivity about one order of magnitude better than those obtained with conventional BK7 glass. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.3005584

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

Epitaxial Laterally overgrown (ELOG) InGaN materials are investigated using a polarization modulated scanning near-field optical microscope. The authors found that luminescence has spatial inhomogeneities and it is partially polarized. Near-field photoluminescence shows polarization phase fluctuation up to 45 degrees over adjacent domains. These results point toward the existence of asymmetries in carrier confinement due to structural anisotropic strain within the framework of the ELOG structure. (C) 2008 Optical Society of America.

DOI： 10.1364/OE.16.006889

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The authors have devised an optical multireflection system to detect nanometer-scale mechanical vibrations in a very simple and cost effective manner. The system is based on a planar glass, reflecting laser light internally a number of times in near critical angular conditions. Any small angular displacement results in an abrupt change of reflectivity. Monitoring the light at the exit of the device results in extremely high sensitivity to small mechanical vibrations. Calibrated tiny vibrations of 2.4 nm were resolved corresponding to an angular shift of about 2x10(-7) rad. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2747676

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The objective of this study is to model a polarization modulation scanning near-field optical microscope set-up (PM-SNOM) and demonstrate how the influence of real instruments as photodetector and lock-in produces a coupling between signals that generates intrinsic artefacts on experimental data. A simple polar coordinates mathematical framework has been used to derive an analytical expression of the relevant signals. A simulation of typical experimental cases is presented and contrast artefacts more than 100% are demonstrated. This study is effective for an accurate analysis of PM-SNOM tests and it is of general use for the discussion of artefacts in polarization modulation systems.

DOI： 10.1088/1464-4258/9/5/001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Optical Society of American (OSA)  

The Scanning Near-field Optical Microscope (SNOM) is able to detect tiny vertical movement on the cell membrane in the range of only 1 nanometer or less, about 3 orders of magnitude better than conventional optical microscopes. Here we show intriguing data of cell membrane nanometer-scale dynamics associated to different phenomena of the cell's life, such as cell cycle and cell death, on rat pheochromocytoma line PC12. Working in culture medium with alive and unperturbed samples, we could detect nanometer-sized movements
Fourier components revealed a clear distinct behavior associated to regulation of neurite outgrowth and changes on morphology after necrotic stimulus. © 2007 Optical Society of America.

DOI： 10.1364/OE.15.005589

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

The Scanning Near-field Optical Microscope ( SNOM) is able to detect tiny vertical movement on the cell membrane in the range of only 1 nanometer or less, about 3 orders of magnitude better than conventional optical microscopes. Here we show intriguing data of cell membrane nanometer-scale dynamics associated to different phenomena of the cell's life, such as cell cycle and cell death, on rat pheochromocytoma line PC12. Working in culture medium with alive and unperturbed samples, we could detect nanometer-sized movements; Fourier components revealed a clear distinct behavior associated to regulation of neurite outgrowth and changes on morphology after necrotic stimulus. (c) 2007 Optical Society of America.

DOI： 10.1364/OE.15.005589

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Diamond grown by chemical vapor deposition (CVD) was investigated using a polarization modulated scanning near field optical microscope. The authors found that the luminescence has spatial inhomogeneities and it is partially polarized. Confined emission shows differences in polarization angle up to 90 degrees. The study reveals a peculiar confined dichroic behavior in CVD materials and suggests that local crystal aggregates play a role in it. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2338581

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

In the development of a hybrid STM-SNOM apparatus, we studied the influence of the illumination on the tip-sample system. Classically, the only effect measurable should be a thermal expansion and a nano-sized mechanical displacement due to a tiny radiation pressure on the tip. However, we observed different kind of perturbations that we had difficulties to explain. We demonstrated that the phenomenon appears to be strongly related to the surface properties of the sample, so we believe that it is not a direct effect of the thermal expansion, nor mechanical movement induced by the irradiation. We describe here the nature of the phenomenon examined, we give details on the experimental condition and setup parameters and we attempt to rigorously discuss the result obtained showing relation to an electro-capacitive coupling of the system at the surface interface. We believe this observation may shed light on the proximity processes that occurs under the STM probe in the presence of light and improve the fundamental understanding of nano-sized interfaces. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.colsurfa.2005.08.021

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We investigate a peculiar optical instability (blinking) phenomena associated with spatial inhomogeneity in InxGa(1-x)N single quantum well systems. We studied the time dependence of this dynamic phenomenon and tested a "quantum jump" single exponential model on the system. A comparative analysis of the behavior of different samples suggests that indium-rich localized centers participate in the mechanism of blinking and that the instability behavior differs with the excitation wavelength. Our study indicates that the trapping and de-trapping process between the localized-luminescent centers and surrounding less luminous regions plays important roles in the carrier recombination mechanism. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2172144

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SCIENTIFIC PUBLISHERS  

We derived a simple method to fabricate STM-SNOM hybrid probes obtained from commercial cheap communication optical fibers. The tips are fabricated by a methodology that combines two well-known techniques: the selective attack by a buffered solution and the protected layer chemical etching, in a single new one-step technique. The tailored probes are then sputtered by metal and mounted on a STM setup. The usual difficulties of integrating the optical fiber in the STM head are solved originally with a particular home made mount described in details. We will show that the resulting probes reach atomic resolution on both vertical and horizontal scale, and that the optical imaging is free of artifacts and satisfactory with a lateral resolution in the order of lambda/20, as far as we know the finest resolution obtained with a system based on a hybrid fiber probe. We believe that our methodology is very interesting for its simplicity of realization and for the good resolving power in both SNOM and STM modes.

DOI： 10.1166/jnn.2006.109

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OPTICAL SOC AMER  

In an effort to improve and simplify refractive index sensors, we identified a basic operation mode at the critical angle. Sensitivity to the refractive index is higher than in standard surface plasmon resonance sensors, and we have been able to demonstrate analytically that it is virtually an unbounded value. We describe this approach and submit a complete analytical study demonstrating its unlimited sensing power. To test the approach, we constructed an economical and basic sensor. Despite its simplicity, we demonstrated the discrimination capability to be of the order of 10(-6), as far as we know close to the best sensitivity ever recorded. This detection method is generally applicable to any optical system and may pave the way for the next generation of optical sensing devices. (c) 2006 Optical Society of America.

DOI： 10.1364/OL.31.000205

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High-resolution analysis of activities of live cells is limited by the use of non-invasive methods. Apparatuses such as SEM, STM or AFM are not practicable because the necessary treatment or the harsh contact with system probe will disturb or destroy the cell. Optical methods are purely non-invasive, but they are usually diffraction limited and then their resolution is limited to approximately I gm. To overcome these restrictions, we introduce here the study of membrane activity of a live cell sample using a Scanning Near-field Optical Microscope (SNOM). A near field optical microscope is able to detect tiny vertical movement on the cell membrane in the range of only 1 nm or less, about 3 orders of magnitude better than conventional optical microscopes. It is a purely non-invasive, non-contact method, so the natural life activity of the sample is unperturbed. In this report, we demonstrated the nanometer-level resolving ability of our SNOM system analyzing cardiomyocytes samples of which membrane movement is known, and then we present new intriguing data of sharp 40 mn cell membrane sudden events on rat pheochromocytoma. cell line PC12. All the measurements are carried out in culture medium with alive and unperturbed samples. We believe that this methodology will open a new approach to investigate live samples. The extreme sensitivity of SNOM allows measurements that are not possible with any other method on live biomaterial paving the way for a broad range of novel studies and applications. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.bpc.2005.04.018

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SCIENTIFIC PUBLISHERS  

Noncontact scanning near-field optical microscope (SNOM) systems can be used to optically resolve samples in atmospheric conditions at theoretical resolutions comparable to those of transmission electron microscope and atomic force microscope systems. SNOM systems are also increasingly used to image biological samples. In this study we custom built a SNOM system with the aim of further demonstrating the potential applications of near-field optical examination of biological material. In this study we were able to image both fixed whole-cell samples in air and liquid environments and live whole-cell samples in liquids. The images acquired were of a relatively low resolution, but this work has shown that SNOM systems can be used to monitor the dynamics of living cells at subnanometric resolutions in the z axis and for fluorescent imaging of whole cells in a liquid medium.

DOI： 10.1166/jnn.2003.202

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：GORDON AND BREACH SCIENCE PUBL  

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We report the observation of live-cc dynamics by noncontact scanning near-field optical microscopy (SNOM) modified to work with living biological samples that are fully immersed in liquid. We did not use the SNOM setup in strictly near-field conditions (we used 1-mu m constant-height mode); however, we could examine the dynamics of rhythmically beating cardiac myocytes in culture with extremely high vertical sensitivity below the nanometric range. We could halt scans at any point to record localized contraction profiles of the cell membrane. We show that the contractions of the organisms changed shape dramatically within adjacent areas. We believe that the spatial dependency of the contractions arises because of the measurement system's ability to resolve the behavior of individual submembrane actin bundles. Our results, combining imaging and real-time recording in localized areas, reveal a new, to our knowledge, noninvasive method for using SNOM setups for studying the dynamics of live biological samples. (C) 1999 Optical Society of America.

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We report on the high-resolution observation of biological samples in water with a collection-mode near-field optical microscope (c-mode NOM) operating under optical feedback control. With rapidly decreasing evanescent field power used as the feedback signal, for the first time to our knowledge, an image of straight-type flagellar filaments of salmonella in water has been obtained. The estimated diameter of a single filament is around 55 nm with a pixel size of 10 nm. A comparison with its nominal value of 25 nm obtained from electron microscope observations under high vacuum confirms that our c-mode NOM performs high-resolution imaging in water. © 1997 Optical Society of America.

DOI： 10.1364/AO.36.001681

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Language：English   Publisher：ELSEVIER SCIENCE BV  

We show for the first time that photoluminescence of InGaN single quantum wells (SQW) devices is related to the gas pressure in which the sample is immersed, also we give a model of the phenomena to suggest a possible cause. Our model shows a direct relation between experimental behavior and molecular coverage dynamics. This strongly suggests that the driving force of photoluminescence decrease is oxygen covering the surface of the device with a time dynamics that depends on the gas pressure. This aims to contribute to the understanding of the physical mechanism of the so-called optical memory effect and blinking phenomenon observed in these devices. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2016.08.075

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We studied the role of noise in neural networks, especially focusing on its relation to the propagation of spike activity in a small sized system. We set up a source of information using a single neuron that is constantly spiking. This element called initiator x(o) feeds spikes to the rest of the network that is initially quiescent and subsequently reacts with vigorous spiking after a transitional period of time. We found that noise quickly suppresses the initiator's influence and favors spontaneous spike activity and, using a decibel representation of noise intensity, we established a linear relationship between noise amplitude and the interval from the initiator's first spike and the rest of the network activation. We studied the same process with networks of different sizes (number of neurons) and found that the initiator xo has a measurable influence on small networks, but as the network grows in size, spontaneous spiking emerges disrupting its effects on networks of more than about N = 100 neurons. This suggests that the mechanism of internal noise generation allows information transmission within a small neural neighborhood, but decays for bigger network domains. We also analyzed the Fourier spectrum of the whole network membrane potential and verified that noise provokes the reduction of main. and a peaks before transitioning into chaotic spiking. However, network size does not reproduce a similar phenomena; instead we recorded a reduction in peaks' amplitude, a better sharpness and definition of Fourier peaks, but not the evident degeneration to chaos observed with increasing external noise. This work aims to contribute to the understanding of the fundamental mechanisms of propagation of spontaneous spiking in neural networks and gives a quantitative assessment of how noise can be used to control and modulate this phenomenon in Hindmarsh-Rose (H-R) neural networks.

DOI： 10.1088/1751-8113/49/28/285601

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We propose a new kind of organic solar cell (OSC) that substitutes the standard indium tin oxide (ITO) electrode with a silver layer with randomly arranged circular nanoholes (plasmonic electrode). The quasi-random structure in the silver layer efficiently converts wideband incident light into surface plasmon polaritons propagating along the surface of the silver film. In this way, the converted surface plasmon polaritons enhance light absorption in the active layer. We describe in detail the fabrication process we used and we give a thorough report of the resulting optical characteristics and performances. Although the transmittance of the plasmonic electrode is approximately one-third of that of the ITO electrodes, the power conversion efficiency of the OSCs with our plasmonic electrode is comparable to that of conventional inverted solar cells using ITO electrodes. Moreover, the obtained incident photon to current efficiency was better than that of the inverted solar cells in the wavelength regions around 400 nm and over 620 nm.

DOI： 10.1088/0022-3727/49/18/185106

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© 2016 Education and Upbringing Publishing.The influence and effect of connection strength between neurons is difficult to predict in complex networks and a complete and exhaustive analytical theory does not exist because of the extremely non-linearity of neural models, so numerical simulation of complex network are the sole reliable method. Here we devised a minimalistic approach, in which two linked neurons are studied and the role of connection strength between them is made apparent. We found that if the post-synaptic neuron has no external stimuli, correlation remains low until a discontinuity threshold that occurs about w = 0. 15 or w = 0. 4 depending on the neurons type tested. After the threshold, correlation grows in a quasi-linear trend ending on a plateau, depending again on the neurons type. Testing bursting and non-bursting neurons, we demonstrated that bursts favour better and quicker correlation between the two cells. In fact in all our tests, a pre-synaptic bursting neuron promote faster correlation against the other type of non-bursting neurons (regular and fast spiking). The presence of a discontinuous dependence of connection strength is a previously known phenomenon, but has been studied here for the first time in controlled and systematic conditions for isolated neuron pairs and for different classes of neurons. When the bursting is stimulating cells in presence of a constant external input, a differentiation between neurons with strong frequency adaptation and other types of cells emerges.

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Language：English   Publisher：IEEE  

The most important part of the neural network research is the learning. The process of learning in our brain is essentially several adjustment processes of connection strength between neurons. It is very difficult to figure out how this mechanism works in the complex network and how the connection strength influences brain functions. In this research, we study the minimal elements block of a learning system. We made a model with only two coupled neurons and studied the influence of connection strength between them. In particular, we found that if the post-synaptic neuron has no external stimuli, correlation remains low until a threshold that occurs about w = 0.15 or w = 0.4 depending on the neuron type testes. Varying types of neurons we find that spike bursts favours synchronization. In fact in all our tests, a pre-synaptic bursting neuron promote faster correlation against the other type of non-bursting neurons tested (regular and fast spiking). The presence of a threshold of connection strength w is a very interesting and previously unknown phenomenon that has implications of the fundamental process in learning and plasticity.

DOI： 10.1109/SICE.2015.7285437

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Language：Japanese   Publisher：一般社団法人日本物理学会  

CiNii Books

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Language：Japanese   Publisher：一般社団法人日本物理学会  

CiNii Books

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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2014.2.0_905

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We use a probabilistic transition matrix methodology to realize an algorithm for the autonomous navigation of Robots. This is achieved without the necessity to set any symbolic or empiric rules, but with a learning strategy based on a purely stochastic approach. The system is tested for its abilities to exit a maze in a minimized time, results show that collisions are avoided with very high percentage of error, nearly 100%. Moreover, goals are reached in a randomly generated maze in a time range better than 80% shorter than with a non-trained algorithm. The robot it is not aware of its position nor it knows the location of the goals. The simple training with one dimensional, no memory Markovian model demonstrates the emergence of the ability to solve the maze in minimal time, a feature that we perceive as intelligent behaviour. The model is very simple to implement, does not require the definition of particular rules nor is related to a specific problem. In fact, this approach can be applied generally to any other situation where there are transitions between a finite set of internal or external states defined by sensors or actuators.

DOI： 10.1109/InfoSEEE.2014.6947882

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Language：Japanese   Publisher：公益社団法人 応用物理学会  

DOI： 10.11470/jsapmeeting.2013.2.0_3370

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Publishing type：Internal/External technical report, pre-print, etc.  

We studied the influence of mechanical vibrotactile signals in the acoustic<br />
range to the visual perception of flickering images. These images are shown on<br />
a CRT screen intermittent at about 75 Hz, without external perturbations are<br />
perceived as constant and stable. However, if presented together with a<br />
controlled acoustical vibration an illusion is perceived. The images appears to<br />
float out of the screen, while the rest of the room is still perceived<br />
normally. The acoustical signal given to the subjects were of very low<br />
frequency (below 100Hz) and low amplitude (almost inaudible). The stimu...

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Language：English   Publisher：OPTICAL SOC AMER  

InGaN/GaN devices are currently used for many applications, for example, full color display, white (RGB) illumination systems and for the realization of shorter wavelength emitters for optical data storage. We previously reported a blinking phenomenon in the photo-luminescence of InGaN device ready single quantum well materials. In this study we observe in high resolution this optical instability with a near-field nano-probe. The phenomenon appears only in local confined domains and does not seem to behave as a bistable state process like reported on quantum dots generated photo-luminescence. We investigated by a modified scanning near-field optical microscope (SNOM) and studied the time/intensity profile of the optical signal with a resolution in the range of 100nm. The dynamics of the blinking was time-resolved and its behaviour studied with Fourier analysis. Despite the intensity oscillations were found to have chaotic component (autocorrelation coefficient is about 0.63), the optical oscillations appear to include regular characteristics. Fourier analysis of the light intensity from confined domains exhibit peaks in the range of 4-5 s. The emergence of these intriguingly slow and partially regular dynamics should shed light on the inner mechanism that are involved in the fundamental processes of optical emission in these devices. (C) 2011 Optical Society of America

DOI： 10.1364/OME.1.000158

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Nowadays there is a big interest in the research of cell behaviour in different sciences, like biology, physics, and medicine. For this reason, many interdisciplinary research projects have been developed in many countries. The main goal of the realization of the proposed biosensor is to obtain a super high resolution optical detection of nano-scaled movements of live cells. We used a very straightforward principle, the interference of laser light with the membrane of the cells under investigation. The laser light is focused on the target cell, while observing the picture through an optical microscope. The laser light creates an interference image (speckle pattern) that is projected on a screen and monitored by a CCD camera. This interference pattern is perturbed by any movement or displacement of the cells, and this interaction is recorded in real time by the CCD. While the contrast in standard optical microscopy is very low, the advantage of this approach is that the coherence of laser light produce constructive or destructive patterns that can be detected with very high signal-to-noise ratio. The displacement resolution we can achieve is better than /30, that is in the order of 20nm. © 2011 IEEE.

DOI： 10.1109/ISSNIP.2011.6146594

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We demonstrate analytically that discontinuity at critical angle can be used to reach extremely high sensitivities against any optical properties that modify this angular value. To test in practice the approach we fabricated cheap and basic sensors by which we could demonstrate extremely high index of refraction discrimination ability in the range of one part over a million. Moreover, we constructed a similar apparatus to detect in a very simple and low-cost manner nanometer scale mechanical vibrations. Also in this case we obtained very high sensitivity, tiny vibrations of 2.4nm were resolved, this correspond to an angular shift of about 50 * 10-6 deg, as far as we know the best angular sensitivity recorded so far. The critical angle detection method discussed in this paper is applicable generally to any optical system and may pave the way for next generation optical sensing devices. © 2010 Optical Society of America.

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Language：English   Publisher：AMER INST PHYSICS  

Surface plasmon resonance sensors exploit the high sensitivity to local perturbations of plasma waves in a thin metal layer. These devices have a wide range of applications as biomedical, environmental, industrial, and homeland security. We concentrate on the theoretical aspects of the sensing principle. By calculations at various indexes of refraction we proved that using substrate material of higher index, sensitivity and dynamics range improve conspicuously. Finally, we show experimental data taken using a special transparent ceramic material of exceptionally high index of refraction n= 2.04. Tests demonstrate sensitivity about one order of magnitude better than those obtained with conventional BK7 glass. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.3005584

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Epitaxial Laterally overgrown (ELOG) InGaN materials are investigated using a polarization modulated scanning near-field optical microscope. The authors found that luminescence has spatial inhomogeneities and it is partially polarized. Near-field photoluminescence shows polarization phase fluctuation up to 45 degrees over adjacent domains. These results point toward the existence of asymmetries in carrier confinement due to structural anisotropic strain within the framework of the ELOG structure. (C) 2008 Optical Society of America.

DOI： 10.1364/OE.16.006889

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Language：English   Publisher：AMER INST PHYSICS  

The authors have devised an optical multireflection system to detect nanometer-scale mechanical vibrations in a very simple and cost effective manner. The system is based on a planar glass, reflecting laser light internally a number of times in near critical angular conditions. Any small angular displacement results in an abrupt change of reflectivity. Monitoring the light at the exit of the device results in extremely high sensitivity to small mechanical vibrations. Calibrated tiny vibrations of 2.4 nm were resolved corresponding to an angular shift of about 2x10(-7) rad. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2747676

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Language：English   Publisher：IOP PUBLISHING LTD  

The objective of this study is to model a polarization modulation scanning near-field optical microscope set-up (PM-SNOM) and demonstrate how the influence of real instruments as photodetector and lock-in produces a coupling between signals that generates intrinsic artefacts on experimental data. A simple polar coordinates mathematical framework has been used to derive an analytical expression of the relevant signals. A simulation of typical experimental cases is presented and contrast artefacts more than 100% are demonstrated. This study is effective for an accurate analysis of PM-SNOM tests and it is of general use for the discussion of artefacts in polarization modulation systems.

DOI： 10.1088/1464-4258/9/5/001

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The Scanning Near-field Optical Microscope ( SNOM) is able to detect tiny vertical movement on the cell membrane in the range of only 1 nanometer or less, about 3 orders of magnitude better than conventional optical microscopes. Here we show intriguing data of cell membrane nanometer-scale dynamics associated to different phenomena of the cell's life, such as cell cycle and cell death, on rat pheochromocytoma line PC12. Working in culture medium with alive and unperturbed samples, we could detect nanometer-sized movements; Fourier components revealed a clear distinct behavior associated to regulation of neurite outgrowth and changes on morphology after necrotic stimulus. (c) 2007 Optical Society of America.

DOI： 10.1364/OE.15.005589

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Diamond grown by chemical vapor deposition (CVD) was investigated using a polarization modulated scanning near field optical microscope. The authors found that the luminescence has spatial inhomogeneities and it is partially polarized. Confined emission shows differences in polarization angle up to 90 degrees. The study reveals a peculiar confined dichroic behavior in CVD materials and suggests that local crystal aggregates play a role in it. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2338581

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Metal-coated, "pulled," and conically shaped fiber probes used in scanning near-field optical microscopy (SNOM) typically undergo a thermal expansion when injected with laser light, due to partial energy absorption by the metallic film. Here, we report investigations into the thermal behavior of fiber probes produced by selective chemical etching that in our experience provide high light throughputs (10(-3)-10(-4) vs 10(-6) for the pulled fibers). Unexpectedly, we find a shortening of such probes in response to "high-power" laser injection (&gt;1 mW). Thermal stress due to prolonged high-power laser injection (similar to 9 mW at 325 nm; compared to powers &lt; 1 mW often used in SNOM experiments) determines permanent alterations of the probes, after which their thermomechanical behavior reverts to the commonly observed elongation in response to laser injection. Scanning electron microscopy after high-power irradiation on such probes shows partial detachment of the metallic coating near the fiber termination. This, however, does not appear to compromise the probe's performance in terms of light confinement outside the aperture area, suggesting that the detachment only affects the coating over the fiber cladding and confirming the operational robustness of these probes. In comparison, tube-etched, conical probes display substantial damage of the coating, up to several microns from the apex, after being injected with a comparable high-power laser beam (&gt;10 mW at 633 nm). Although the vertical feedback mechanism of the microscope can compensate for dilations/contractions of the probes, these findings are of general importance to the field. More specifically they are significant for the achievement of a detailed understanding of apertured-SNOM operation, for the selection and operation of near-field probes, and for preventing potential artifacts in imaging and lithography, due to uncontrolled alteration of the probe properties and/or light leakage from cracks of the opaque coating induced by thermal fatigue. In addition, our results demonstrate that it is important for probe design to also consider the probe's thermal regime during operation, so as to prevent cracks in the functional parts of the coating and thus spurious, undesired sample illumination from regions other than the probe intended aperture. (C) 2006 American Institute of Physics.

DOI： 10.1063/1.2188250

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We realized a planar multireflection glass system to investigate the localized surface plasmon resonance (LSPR) of gold nanoparticles. These nanospheres were realized it? situ using an original and simple chemical growth method that is described. We were able to observe resonance phenomena as reflected by variations in the spectrum and as enhancements in the refractive index sensing ability. The system was able to clearly discern 2% sucrose solution and demonstrated outstanding linearity and reproducibility. We believe this study could be useful for elucidating the fundamental processes in nanoparticle LSPR and contribute to the realization of new and more efficient sensors.

DOI： 10.1088/1464-4258/8/3/007

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We realized a planar multireflection glass system to investigate the localized surface plasmon resonance (LSPR) of gold nanoparticles. These nanospheres were realized it? situ using an original and simple chemical growth method that is described. We were able to observe resonance phenomena as reflected by variations in the spectrum and as enhancements in the refractive index sensing ability. The system was able to clearly discern 2% sucrose solution and demonstrated outstanding linearity and reproducibility. We believe this study could be useful for elucidating the fundamental processes in nanoparticle LSPR and contribute to the realization of new and more efficient sensors.

DOI： 10.1088/1464-4258/8/3/007

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We investigate a peculiar optical instability (blinking) phenomena associated with spatial inhomogeneity in InxGa(1-x)N single quantum well systems. We studied the time dependence of this dynamic phenomenon and tested a "quantum jump" single exponential model on the system. A comparative analysis of the behavior of different samples suggests that indium-rich localized centers participate in the mechanism of blinking and that the instability behavior differs with the excitation wavelength. Our study indicates that the trapping and de-trapping process between the localized-luminescent centers and surrounding less luminous regions plays important roles in the carrier recombination mechanism. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2172144

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Language：English   Publisher：ELSEVIER SCIENCE BV  

In the development of a hybrid STM-SNOM apparatus, we studied the influence of the illumination on the tip-sample system. Classically, the only effect measurable should be a thermal expansion and a nano-sized mechanical displacement due to a tiny radiation pressure on the tip. However, we observed different kind of perturbations that we had difficulties to explain. We demonstrated that the phenomenon appears to be strongly related to the surface properties of the sample, so we believe that it is not a direct effect of the thermal expansion, nor mechanical movement induced by the irradiation. We describe here the nature of the phenomenon examined, we give details on the experimental condition and setup parameters and we attempt to rigorously discuss the result obtained showing relation to an electro-capacitive coupling of the system at the surface interface. We believe this observation may shed light on the proximity processes that occurs under the STM probe in the presence of light and improve the fundamental understanding of nano-sized interfaces. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.colsurfa.2005.08.021

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In an effort to improve and simplify refractive index sensors, we identified a basic operation mode at the critical angle. Sensitivity to the refractive index is higher than in standard surface plasmon resonance sensors, and we have been able to demonstrate analytically that it is virtually an unbounded value. We describe this approach and submit a complete analytical study demonstrating its unlimited sensing power. To test the approach, we constructed an economical and basic sensor. Despite its simplicity, we demonstrated the discrimination capability to be of the order of 10(-6), as far as we know close to the best sensitivity ever recorded. This detection method is generally applicable to any optical system and may pave the way for the next generation of optical sensing devices. (c) 2006 Optical Society of America.

DOI： 10.1364/OL.31.000205

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Language：English   Publisher：AMER SCIENTIFIC PUBLISHERS  

We derived a simple method to fabricate STM-SNOM hybrid probes obtained from commercial cheap communication optical fibers. The tips are fabricated by a methodology that combines two well-known techniques: the selective attack by a buffered solution and the protected layer chemical etching, in a single new one-step technique. The tailored probes are then sputtered by metal and mounted on a STM setup. The usual difficulties of integrating the optical fiber in the STM head are solved originally with a particular home made mount described in details. We will show that the resulting probes reach atomic resolution on both vertical and horizontal scale, and that the optical imaging is free of artifacts and satisfactory with a lateral resolution in the order of lambda/20, as far as we know the finest resolution obtained with a system based on a hybrid fiber probe. We believe that our methodology is very interesting for its simplicity of realization and for the good resolving power in both SNOM and STM modes.

DOI： 10.1166/jnn.2006.109

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Language：English   Publisher：OPTICAL SOC AMER  

In an effort to improve and simplify refractive index sensors, we identified a basic operation mode at the critical angle. Sensitivity to the refractive index is higher than in standard surface plasmon resonance sensors, and we have been able to demonstrate analytically that it is virtually an unbounded value. We describe this approach and submit a complete analytical study demonstrating its unlimited sensing power. To test the approach, we constructed an economical and basic sensor. Despite its simplicity, we demonstrated the discrimination capability to be of the order of 10(-6), as far as we know close to the best sensitivity ever recorded. This detection method is generally applicable to any optical system and may pave the way for the next generation of optical sensing devices. (c) 2006 Optical Society of America.

DOI： 10.1364/OL.31.000205

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We investigate on the photoluminescence spatial unhomogeneities of InGaN/GaN interface with a Polarization Modulation Scanning Near-field Tunneling Microscope. We could demonstrate for the first time nanometer sized domains that present polarization-changing properties. © 2006 IEEE.

DOI： 10.1109/CLEO.2006.4628640

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DOI： 10.1166/jnn.2006.109

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We investigate on the photoluminescence spatial unhomogeneities of InGaN/GaN interface with a Polarization Modulation Scanning Near-field Tunneling Microscope. We could demonstrate for the first time nanometer sized domains that present polarization-changing properties. © 2006 IEEE.

DOI： 10.1109/CLEO.2006.4628640

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In continuation of our research on carbon nanotube/P(VDF-TrFE) nano-composites [1], total x-ray fluorescence (TXRF) is engaged in a novel characterization of these materials regarding their compositions, purities, and structural analysis. Samples such as single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), P(VDF-TrFE) copolymer, SWCNT/P(VDF-TrFE), and MWCNT/P(VDF-TrFE) were analyzed by TXRF. The synthetic quartz used as a substrate was analyzed as reference material for the TXRF measurements. The ethanol and the dimethylformamide (DMF) used as solvents for carbon nanotubes and copolymers respectively were also analyzed by TXRF to determine whether they have an influence or not on the TXRF of the previous material. The preliminary results showed that single-walled and multi-walled carbon nanotubes prepared by the arc-discharge method contain catalytic particles such as Fe, Co, and Ni used to obtain SWCNT while there were no metal or impurities in MWCNT. The TXRF spectrum of CNT/P(VDF-TrFE) showed the same results as we found previously with background due to the P(VDF-TrFE) copolymer scattered signal. ©2005 Springer Science+Business Media, Inc.

DOI： 10.1007/s10812-005-0147-9

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High-resolution analysis of activities of live cells is limited by the use of non-invasive methods. Apparatuses such as SEM, STM or AFM are not practicable because the necessary treatment or the harsh contact with system probe will disturb or destroy the cell. Optical methods are purely non-invasive, but they are usually diffraction limited and then their resolution is limited to approximately I gm. To overcome these restrictions, we introduce here the study of membrane activity of a live cell sample using a Scanning Near-field Optical Microscope (SNOM). A near field optical microscope is able to detect tiny vertical movement on the cell membrane in the range of only 1 nm or less, about 3 orders of magnitude better than conventional optical microscopes. It is a purely non-invasive, non-contact method, so the natural life activity of the sample is unperturbed. In this report, we demonstrated the nanometer-level resolving ability of our SNOM system analyzing cardiomyocytes samples of which membrane movement is known, and then we present new intriguing data of sharp 40 mn cell membrane sudden events on rat pheochromocytoma. cell line PC12. All the measurements are carried out in culture medium with alive and unperturbed samples. We believe that this methodology will open a new approach to investigate live samples. The extreme sensitivity of SNOM allows measurements that are not possible with any other method on live biomaterial paving the way for a broad range of novel studies and applications. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.bpc.2005.04.018

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In continuation of our research on carbon nanotube/P(VDF-TrFE) nano-composites [1], total x-ray fluorescence (TXRF) is engaged in a novel characterization of these materials regarding their compositions, purities, and structural analysis. Samples such as single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), P(VDF-TrFE) copolymer, SWCNT/P(VDF-TrFE), and MWCNT/P(VDF-TrFE) were analyzed by TXRF. The synthetic quartz used as a substrate was analyzed as reference material for the TXRF measurements. The ethanol and the dimethylformamide (DMF) used as solvents for carbon nanotubes and copolymers respectively were also analyzed by TXRF to determine whether they have an influence or not on the TXRF of the previous material. The preliminary results showed that single-walled and multi-walled carbon nanotubes prepared by the arc-discharge method contain catalytic particles such as Fe, Co, and Ni used to obtain SWCNT while there were no metal or impurities in MWCNT. The TXRF spectrum of CNT/P(VDF-TrFE) showed the same results as we found previously with background due to the P(VDF-TrFE) copolymer scattered signal. ©2005 Springer Science+Business Media, Inc.

DOI： 10.1007/s10812-005-0147-9

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Language：English   Publisher：KOREAN PHYSICAL SOC  

Distributed Bragg Beffectors (DBRs) have been found to be very effective in increasing the efficiency of light emitting diodes and semiconductor laser devices, By using polarization-modulated scanning near-field optical microscopy (PM-SNOM), we investigate the optical response to different illumination polarization states of a DBR. structure that consists of a, stack of quarter wavelength thick slabs of dielectrics with alternating high and low refractive index. The DBR has been optically characterized in the near-field at different wavelengths in illumination- and in collection- mode with light excitation orthogonal to the probe axis, for fixed as well as for modulated polarization. We have found that the optical signal does not follow the morphological structure of the slabs, as expected but it shows a different spatial periodicity related to the excitation properties and to the interplay of the different DBR. planes.

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Surface plasmon resonance (SPR) sensors are high sensitive optical system often used for investigations on organic samples or in general for other fundamental research topics. Normally a SPR sensor is based on a prism on which a thin layer of gold has been deposited. These sensors are usually full-size optical devices, heavy and difficult to transport. In the effort to miniaturize and make more flexible and light SPR sensors we developed a novel system based on a metal-coated optical fiber. Its optical and sensing characteristics were studied using an analytical approach and with the aid of a numerical Monte Carlo method. We will describe the fabrication of an actual sensor and the development of an experimental setup realized for sensing tests. We experimentally demonstrated the ability of the optical fiber sensor to detect the presence of a 2 nm octadecane thiol organic film; measurements showed good S/N ratio and rapid response of few seconds time. As far as we know, our system is the fastest SPR sensor realized so far. (c) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.sna.2004.10.036

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Perylene-acetonitrile solution with tetra-n-butyl-ammonium perchlorate (TBAP) is a substance that tends to electro-crystallize and form particular needle-like structures. These perylene materials are studied extensively for their peculiar electrical and optical properties and for the interest in the fundamental phenomena occurring in the electro crystallization process. We introduce here a novel methodology to orient the needle-like crystals by means of electro crystallization in presence of a weak magnetic field. We report details on the technique we used and we present several exceptional SEM pictures of the aggregates growing vertically from the substrate by the effect of the magnetic field. The method introduce a new simple way to control the growth of these intriguing materials and the approach is potentially the basis for the fabrication of new miniaturized devices. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2004.08.006

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DOI： 10.1016/j.bpc.2005.04.018

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The photoluminescence (PL) emission properties of InGaN Single Quantum Well (SQW) systems it's important for the realization of new optical devices as LED, or semiconductor Laser. Scanning Near-field optics has been used recently to investigate with resolution better that wavelength these devices, however polarization properties cannot be recognized with this method. We modified a SNOM setup in order to realize a Polarization Modulation system able to extract a near-field map of PL emission and simultaneously capable to detect the polarization properties of it. Firstly we present a comprehensive theoretical description of the apparatus in order to discuss how the data should be interpreted. We will then show results demonstrating that emission from the InGaN SQWs present, locally, strong polarization properties.

DOI： 10.1109/IQEC.2005.1561023

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We have investigated the heating phenomena occurring in near-field experiments using metal-coated apertured optical fibers. We demonstrate heat transfer from the probe to the sample surface and permanent modification of the probe parameters.

DOI： 10.1109/IQEC.2005.1561047

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Many researches on InxGa(i-x)N systems are focused on their optical characteristics, and in particular on their behaviour in very small time scale range. Conversely, in this report we studied optical phenomena that have long-range time constants. In particular, we studied samples where a thin InGaN/GaN interface defines a single quantum well (SQW) structure in the crystal. Tiny fluctuation of the Indium concentration in the SQW induces localized regions of high Photoluminescence (PL) emission. We established conditions by which temporal instabilities in the PL optical signal were detected and characterized. In this study we will present details on these measurements, in particular we will show how locally indium-rich centers seem to be directly involved in the blinking phenomena. We will report too on the dependence of the temporal behaviour with large-scale (bulk) Indium concentration, and we will show how an epitaxially laterally overgrown GaN (ELOG) substrate influence the PL temporal instabilities.

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Language：English   Publisher：ELSEVIER SCIENCE BV  

Spatial distribution of InGaN photoluminescence (PL) at room temperature has been examined by observation through an illumination-transmission mode scanning near-field optical microscope (SNOM). The near-field PL mapping revealed a disuniform pattern of sharp or blunt emission peaks from few hundreds of nanometer extension to the micrometer scale range. The peaks' average amplitude size and distances from neighboring peaks have been measured in a large number of experiments for three different samples at dissimilar indium doses, and their results compared. A general trend has been found and the influence of indium concentration is shown in a final plot. We describe the experimental approach adopted and present full details on the results obtained. Data were gathered from more than 100 different measurements; low-cost optical SNOM nanoprobes were originally fabricated and we briefly explain the fabrication procedure. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2004.02.025

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Language：English   Publisher：ELSEVIER SCIENCE BV  

We report on the direct observation of highly confined transition molecular switch on azobenzene based monolayer. The transition was induced by UV light through the optical field enhancement occurring in the proximity of a sharp STM probe. A 0.5 nm reduction of the thickness of the azobenzene monolayer is detected in real time on a minute nearly circular region of about 50 nm of diameter. We demonstrated that the thickness change is compatible with rigorous molecular modelling of the polymer used. The area of collective molecular switching, is actually a small bit of information, functional to high-density optical storage investigations. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2004.01.014

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Language：English   Publisher：ELSEVIER SCIENCE BV  

The combination of scanning tunneling microscopy (STM) with time-of-flight mass system (TOF-MS) adds new information to STM imaging. In this study, an STM system has been combined with laser excitation and was used for desorption and ionization of surface molecules, without the use of any other external stimulus. Desorbed ions from confined areas were accelerated and detected by a TOF chamber. We demonstrate in this paper that the technique proposed enables desorption of superficial structures within a small area of approximately 5 nm diameter and simultaneous mass spectroscopy of the desorbed atoms. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0169-4332(03)00174-0

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Language：English   Publisher：SPRINGER-VERLAG  

A perylene-acetonitrile solution with TBAP (tetra-n-butylammonium perchlorate) electrocrystallizes on the electrode surface, under opportune conditions. It forms particular needle-like microcrystals that have been studied recently for their peculiar electrical and optical properties and for the fundamental processes involved in the electron transfer responsible for the electrocrystallization. These intriguing structures present various fractal-like morphological organizations and diverse crystal shapes on the same deposition process. Up to now these formations have been studied optically by conventional standard microscopy. We introduce here a novel methodology to collect information on the actual orientation and crystal structure by a near field optical setup with originally fabricated probes. We performed, for the first time on these samples, near field fluorescence imaging showing evidence that the perylene aggregations actually have a distinct optical orientation.

DOI： 10.1007/s00396-002-0739-3

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Language：English   Publisher：OPTICAL SOC JAPAN  

This work describes a groundbreaking process that provides a direct highly localized measurement of the atomic mass on surfaces at room temperature. Employing an original system that joins a scanning tunneling microscopy (STM) device and a time of flight (TOF) mass analyzer, we could previously ionize surface atoms by the combination of an optical laser pulse and an electric pulse at the STM tip. Desorbed ions from a localized area were accelerated and detected by a TOF chamber. We will demonstrate in this paper that high localization and mass discrimination can be obtained even without the aid of an electric pulse from the tip. We reduced the angle of incidence of the laser beam to zero (laser beam parallel to the sample surface). In this condition we were able to demonstrate for the first time ionic desorption at a confinement level of the order of 5-10 nm, an order of magnitude better than previous configurations.

DOI： 10.1007/s10043-002-0277-8

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Language：English   Publisher：AMER INST PHYSICS  

This study describes a ground-breaking process that provides a direct highly localized measurement of the atomic mass on surfaces at room temperature. Employing an original system that joins a scanning tunneling microscopy (STM) device and a time-of-flight (TOF) mass analyzer, we could locally ionize surface atoms by the combination of an optical laser pulse and an appropriate voltage variation between the sample and the STM tip. Desorbed ions were accelerated and detected by a TOF chamber. Detection and discrimination of single atomic species from nanolocalized area have been demonstrated for the first time. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1499764

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Language：English   Publisher：ELSEVIER SCIENCE BV  

Semiconductive polythiophene derivate polymers show electroluminescence (EL) properties if excited under opportune conditions and can be used as active element in novel efficient light-emitting diodes (LEDs) or in photovoltaic applications as detectors or solar cells. These intriguing and innovative materials are so far studied in bulk condition, under the excitation of two macroscopic electrodes, averaging the optical phenomena over a large region. To realize a better understanding of the spatial distribution of the EL on the films and its optical properties, we modified a scanning near-field optical microscope (SNOM) setup in order to measure the EL signal of poly-3-(2-(5-chlorobenzotriazolo)ethyl)thiophene. The film were deposited over a macroscopic electrode substrate (a transparent indium tin oxide (ITO) treated glass), while a sharp aluminum coated glass probe worked as a nano-sized Al electrode, realizing an Al/polymer/ITO light emitting device in a highly confined region. We describe in detail the methodology we used for the novel EL measurements and we will show the first resulting high-resolution EL emission mapping, as well as other spectroscopic and morphological characterization of the film used. (C) 2001 Published by Elsevier Science B.V.

DOI： 10.1016/S0030-4018(01)01393-1

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Language：English   Publisher：ELSEVIER SCIENCE BV  

We derived a simple method to fabricate scanning near field optical microscopes (SNOMs) optical probes from commercial cheap communication optical fibers. The tips are etched in one single step at the oil-acid interface of a HF solution. The resulting probes are then coated with acrylic paint in order to screen the light and a small optical aperture is spontaneously formed at the apex. The method is straightforward and requires a few hours for a number of ready to use probes. The original use of paint simplifies strongly the procedure of screening of the fiber that usually has been performed by costly and time consuming metal coating technique. We show that the tips are fully operational and we demonstrate a good optical resolving power (100 nm). As far as we know, our method makes the cheapest SNOM probes within this resolution range. (C) 2001 Published by Elsevier Science B.V.

DOI： 10.1016/S0030-4018(00)01147-0

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We report the observation of live-cell dynamics by noncontact scanning near-field optical microscopy (SNOM) modified to work with living biological samples that are fully immersed in liquid. We did not use the SNOM setup in strictly near-field conditions (we used 1-μm constant-height mode); however, we could examine the dynamics of rhythmically beating cardiac myocytes in culture with extremely high vertical sensitivity below the nanometric range. We could halt scans at any point to record localized contraction profiles of the cell membrane. We show that the contractions of the organisms changed shape dramatically within adjacent areas. We believe that the spatial dependency of the contractions arises because of the measurement system&#039;s ability to resolve the behavior of individual submembrane actin bundles. Our results, combining imaging and real-time recording in localized areas, reveal a new, to our knowledge, noninvasive method for using SNOM setups for studying the dynamics of live biological samples. © 1999 Optical Society of America.

DOI： 10.1364/AO.38.006648

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Books

CiNii Research

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Language：Japanese   Publisher：The Surface Science Society of Japan  

A scanning near-field optical microscope (SNOM) combined with a scanning tunneling microscope (STM) is used to investigate nanoscopic optical phenomena both in the near-field region and in the proximity. The system is realized by introducing a doubly metal-coated optical fiber tip with an extremely small aperture, on which metal-coating is performed to obtain a half-transparent conducting tip. A simultaneous SNOM/STM observation is performed for an Au (111) surface, where the evanescent field standing on the tip vicinity through the aperture is scattered by the local structures of the sample and the far-field component of the scattered light is collected as an optical signal. The distance con-trol is carried out under constant current condition in order to separate the optical properties from surface topography. &lambda;/100 optical resolution and the identical channel transport both for electrons and photons are achieved.

DOI： 10.1380/jsssj.20.509

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Language：English   Publisher：JAPAN J APPLIED PHYSICS  

Scanning near-field optical microscope (SNOM) is hybridized with a Scanning tunneling microscope (STM) to investigate nanoscopic optical phenomena in both the near-field region and its proximity. The system is realized by introducing a doubly metal-coated optical fiber tip with an extremely small aperture (&lt; 100 nm); where the metal is coated on the aperture to obtain a half-transparent conducting tip after the fabrication of an "aperture probe." A simultaneous SNOM/STM observation is performed for an Au (111) surface, where the evanescent field at the tip vicinity through the aperture is scattered by the local structures of the sample and the far-field component of the scattered light is collected as an optical signal. The distance control is carried out under the constant-current condition in order to separate the optical properties from surface topography. An optical resolution of lambda/100 and identical channel transport for both electrons and photons are achieved. The intensity changes, as a function of the gap distance, are also measured in the far-field and the near-field regions and the proximity.

DOI： 10.1143/JJAP.38.3949

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Language：English   Publisher：JAPAN J APPLIED PHYSICS  

Scanning near-field optical microscope (SNOM) is hybridized with a Scanning tunneling microscope (STM) to investigate nanoscopic optical phenomena in both the near-field region and its proximity. The system is realized by introducing a doubly metal-coated optical fiber tip with an extremely small aperture (&lt; 100 nm); where the metal is coated on the aperture to obtain a half-transparent conducting tip after the fabrication of an "aperture probe." A simultaneous SNOM/STM observation is performed for an Au (111) surface, where the evanescent field at the tip vicinity through the aperture is scattered by the local structures of the sample and the far-field component of the scattered light is collected as an optical signal. The distance control is carried out under the constant-current condition in order to separate the optical properties from surface topography. An optical resolution of lambda/100 and identical channel transport for both electrons and photons are achieved. The intensity changes, as a function of the gap distance, are also measured in the far-field and the near-field regions and the proximity.

DOI： 10.1143/JJAP.38.3949

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Language：English   Publisher：OPTICAL SOC JAPAN  

We describe an original scanning near field optical microscope setup developed to examine rhythmically beating cardiac myocytes fully immersed in culture media. Scans could be halted at any point to record localized contraction profiles, Contractions could be detected with high sub nanometric vertical sensitivity and changed shape dramatically within adjacent sub micron-sized areas. We believe that the spatial dependency of contractions arises because of system's ability to resolve the dynamic behavior of individual sub membrane actin bundles. Our results, combining imaging and real time recording in localized areas, reveal a new, non-invasive method for studying sub micron morphological activity in live biological samples.

DOI： 10.1007/s10043-999-0268-0

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Language：English   Publisher：ELSEVIER SCIENCE BV  

In order to improve the spatial resolution in scanning near-field optical microscopy (SNOM), we designed a hybrid system of illumination mode SNOM integrated with scanning tunnelling microscopy (STM) by introducing a metal-coated optical fiber tip with a nanometer-scale aperture. The aperture is also covered with a thin metal layer, thus the top of the aperture acts as an STM tip. We employed several materials to show the capability of our hybrid SNOM/STM system as a tool to investigate nanoscopic phenomena. We present a simultaneous SNOM/STM imaging of Bu(111), where the SNOM image has a lateral resolution of the order of nanometers, quite comparable to that of the STM image. An azobenzene dye molecule embedded in liquid crystalline cyanobiphenyl molecules on MoS(2) was also investigated. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0169-4332(98)00858-7

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Language：English   Publisher：ELSEVIER SCIENCE BV  

We describe a versatile scanning near-field optical microscope (SNOM) integrated with a shear force (SF) sample probe separation controller. The system works with special tapered optical fibers as the probing element. These fibers are fabricated by using a technique proposed earlier by Ohtsu et al. [M. Ohtsu, Optoelectronic devices and technology, 10 (2) (1995) 147]. We describe here the SNOM system we developed giving details on the fabrication of the fibers. Then we show the first direct bi-dimensional mapping of the optical emission of these tips as measured by our system in an original 2 tip configuration mode. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0169-4332(98)00857-5

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Language：English   Publisher：Optical Society of Japan  

We describe an original scanning near field optical microscope setup developed to examine rhythmically beating cardiac myocytes fully immersed in culture media. Scans could be halted at any point to record localized contraction profiles. Contractions could be detected with high sub nanometric vertical sensitivity and changed shape dramatically within adjacent sub micron-sized areas. We believe that the spatial dependency of contractions arises because of system's ability to resolve the dynamic behavior of individual sub membrane actin bundles. Our results, combining imaging and real time recording in localized areas, reveal a new, non-invasive method for studying sub micron morphological activity in live biological samples.

DOI： 10.1007/s10043-999-0268-0

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Language：English   Publisher：GORDON BREACH SCI PUBL LTD  

Scanning near-field optical microscope (SNOM) is hybridized with scanning tunneling microscope (STM) in order to achieve a higher spatial resolution by introducing a doubly metal-coated optical fiber tip with a nm-scale aperture. The result of a simultaneous SNOM/STM imaging of Au(lll) indicates the boundary-sensitive detection in SNOM mode, which is not an artifact caused by z-motion crosstalk.

DOI： 10.1080/10587259908026823

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Language：English   Publisher：GORDON BREACH PUBLISHING, TAYLOR & FRANCIS GROUP  

In order to overcome one of the drawbacks in scanning near-field optical microscopy (SNOM), i.e., a low spatial resolution caused by a rather poor sample-probe distance control, we are designing a hybrid system of SNOM with scanning tunneling microscopy (STM) by introducing a metal-coated optical fiber tip with an apex of a nanometer-scale aperture. We present the recent developments of our homemade hybrid SNOM/STM system.

DOI： 10.1080/10587259808030225

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Language：English   Publisher：OPTICAL SOC AMER  

We report on the high-resolution observation of biological samples in water with a collection-mode near-field optical microscope (c-mode NOM) operating under optical feedback control. With rapidly decreasing evanescent field power used as the feedback signal, for the first time to our knowledge, an image of straight-type flagellar filaments of salmonella in water has been obtained. The estimated diameter of a single filament is around 55 nm with a pixel size of 10 nm. A comparison with its nominal value of 25 nm obtained from electron microscope observations under high vacuum confirms that our c-mode NOM performs high-resolution imaging in water. (C) 1997 Optical Society of America.

DOI： 10.1364/AO.36.001681

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Language：English  

We present here a simple technique for depositing wide monolayers of submicron-sized latex particles. The method is straightforward and does not require any special apparatus. We also studied the quality of the arrays formed, giving information on either the large scale structure or the small scale one. With this technique we succeeded to deposit arrays of 42 nm sized latex spheres, as far as we know, the smallest regular monolayer array ever deposited. © 1995, American Chemical Society. All rights reserved.

DOI： 10.1021/la00009a012

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Language：English   Publisher：ELSEVIER SCIENCE BV  

A photon scanning tunneling microscope (PSTM) with longitudinal resolution in the subnanometer range is described. It operates by monitoring the reflected rather than transmitted tight intensity. The most remarkable differences, as compared to other PSTMs are its possibility to scan over opaque samples and to allow an easier interpretation of the images since one can use, with good approximation, the plane wave theory. This instrument is extremely sensitive to the specimen profile and the measurements show that a variation in profile height of one nanometer gives a variation in the signal amplitude that is twice the long-term reproducibility. Lateral resolution, however, is the same as in classical optical microscopes.

DOI： 10.1016/0030-4018(93)90664-Q

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X-ray diffraction results in magnetically oriented samples of aqueous solutions of the sodium salt of the dinucleoside phosphate G2 in the cholesteric N* phase are presented. The symmetry of the diffraction confirms a model of stacking of tetrameric disks forming cylindrical aggregates in the N* phase. A weak band at 7 Å not previously observed gives further information on the inner structure of the cylindrical aggregates. Analysis of the diffraction peak position in low angle evidences a change in functional behaviour of the distance α between cylinder axes as a function of the volume concentration cv of G2. In the H phase, a α cv−1/2 as it should for infinite cylinders; in the N* phase, a α cv−1/3, typical of finite cylinders. The cross-over of functional behaviour occurs at the N*‒H phase transition. There is therefore cylinder growth along the N* phase. © 1992 Taylor &amp; Francis Group, LLC.

DOI： 10.1080/02678299208032807

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Language：Japanese   Presentation type：Oral presentation (general)  

File： Kishino_CSS_38.pdf

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File： NanoOptics_05232012.pdf

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File： micheletto_37.pdf

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Language：Japanese   Presentation type：Oral presentation (general)  

File： 2014takatori-1.pdf

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File： img-takatoripre-62901.pdf

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File： MNC_2013_takatori.pdf

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