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At least 343 records · Page 19Linked to original sources
PubMed2005

Vibration sensitivity of the scanning near-field optical microscope with a tapered optical fiber probe.

In this paper the Rayleigh-Ritz method was used to study the scanning near-field optical microscope (SNOM) with a tapered optical fiber probe's flexural and axial sensitivity to vibration. Not only the contact stiffness but also the geometric parameters of the probe can influence the flexural and axial sensitivity to vibration. According to the analysis, the lateral and axial contact stiffness had a significant effect on the sensitivity of vibration of the SNOM's probe, each mode had a different level of sensitivity and in the first mode the tapered optical fiber probe was the most acceptive to higher levels of flexural and axial vibration. Generally, when the contact stiffness was lower, the tapered probe was more sensitive to higher levels of both axial and flexural vibration than the uniform probe. However, the situation was reversed when the contact stiffness was larger. Furthermore, the effect that the probe's length and its tapered angle had on the SNOM's probe axial and flexural vibration were significant and these two conditions should be incorporated into the design of new SNOM probes.

Algorithms↗
PubMed2003

Monitoring cell movements and volume changes with pulse-mode scanning ion conductance microscopy.

Here we describe the use of pulse-mode scanning ion conductance microscopy (SICM) to observe volume changes and cell membrane movements during the locomotion of cultured cells in the range of minutes to several hours. The microscope is based on the pulse-mode SICM previously developed for stable imaging of single cells in culture. Our instrument uses current pulses to control the distance between cell surface and electrode tip as well as a back-step mode to prevent contact of tip and membrane during lateral movements of the probe. We performed repeated scans of cell surfaces using feedback-controlled piezoactors to position the electrode. Using patch-clamp-type electrode tips the height of cells could reproducibly be measured with a standard deviation of 50 nm. To quantify and separate changes in cell position and volume occurring between consecutive scans, a program was written to subtract images and calculate volume changes. Examples of repeated scans show that membrane movements in the range of 30 min to a few hours can be quantitatively monitored with a lateral resolution of 500 nm using difference images and that faster movements in the range of minutes can be recorded at defined cell sections using the line scan mode. Difference images indicate that volume changes can affect cell surfaces inhomogeneously, emphasizing the role of the cytoskeleton in the stabilization of cell shape.

Animals↗
PubMed2004

Shape control of near-field probes using dynamic meniscus etching.

Dynamic etching methods for fabricating fibre optic tips are explored and modelled. By vertically translating the fibre during etching by an HF solution under an organic protective layer, a variety of tip shapes were created. The probe taper lengths, cone angles and geometrical probe shapes were measured in order to evaluate the dynamic meniscus etching process. Fibre motion, etching rate, meniscus distortion and etching time were all found to be important variables that can be used to control the final probe shape.

Equipment Design↗
PubMed2003

In situ electrical measurements and manipulation of B/N-doped C nanotubes in a high-resolution transmission electron microscope.

B/N-doped multiwalled C nanotubes were electrically probed by means of a tungsten needle attached to a piezo-driven stage of a high-resolution transmission electron microscope holder. Two-terminal transport measurements were performed in a 'W needle-nanotube-ground' circuit. The I-V curves were recorded in situ while viewing the nanotubes in the imaging mode of the microscope. This allows us to trace nanotube array morphological changes under applied voltage (up to 50 V). Specific manipulation with nanotube assemblies was found to be possible under applied electrical field: attachment of a tiny nanotube bundle to the W needle and extraction of a given nanotube fragment from an entangled complex bunch were achieved. The electrically-probed B/N-doped C nanotubes exhibited alternating B-rich and C-rich B-C-N domains within tubular layers, as revealed by elemental mapping during energy-filtered TEM (Omega filter). At room temperature the nanostructures displayed resistivity (rho) of approximately 1.8 x 10(-5) omegam and linear I-V curves. The key role of a given contact between the probing needle and a nanotube during electrical measurements was particularly verified.

Electricity↗
PubMed2005

Design of metal-cladded near-field fiber probes with a dispersive body-of-revolution finite-difference time-domain method.

A dispersive body-of-revolution finite-difference time-domain method is developed to simulate metal-cladded near-field scanning optical microscope (NSOM) probes. Two types of NSOM probe (aperture and plasmon NSOM probes) are analyzed and designed with this fast method. The influence of the metal-cladding thickness and the excitation mode on the performance of the NSOM probes is studied. We introduce a new scheme of illumination-mode NSOM by employing the plasmon NSOM probe with the TM01 mode excitation. Such a NSOM probe is designed, and we demonstrate its advantages over the conventional aperture NSOM probe by scanning across a metallic object.

Algorithms↗
PubMed2004

Near-field microscopy by elastic light scattering from a tip.

We describe ultraresolution microscopy far beyond the classical Abbe diffraction limit of one half wavelength (lambda/2), and also beyond the practical limit (ca. lambda/10) of aperture-based scanning near-field optical microscopy (SNOM). The 'apertureless' SNOM discussed here uses light scattering from a sharp tip (hence scattering-type or s-SNOM) and has no lambda-related resolution limit. Rather, its resolution is approximately equal to the radius a of the probing tip (for commercial tips, a < 20 nm) so that 10 nm is obtained in the visible (lambda/60). A resolution of lambda/500 has been obtained in the mid-infrared at lambda = 10 microm. The advantage of infrared, terahertz and even microwave illumination is that specific excitations can be exploited to yield specific contrast, e.g. the molecular vibration offering a spectroscopic fingerprint to identify chemical composition. S-SNOM can routinely acquire simultaneous amplitude and phase images to obtain information on refractive and absorptive properties. Plasmon- or phonon-resonant materials can be highlighted by their particularly high near-field signal level. Furthermore, s-SNOM can map the characteristic optical eigenfields of small, optically resonant particles. Lastly, we describe theoretical modelling that explains and predicts s-SNOM contrast on the basis of the local dielectric function.

Equipment Design↗
PubMed2005

Surface-potential reversibility of an amino-terminated self-assembled monolayer based on nanoprobe chemistry.

Nanoprobe chemistry offers a promising approach for the construction of nanostructures consisting of organic molecules by employing the tip of a scanning probe microscope. In a previous report, we demonstrated that a nitroso-terminated surface on an organosilane self-assembled monolayer could be converted into an amino-terminated surface by applying such a nanoprobe electrochemical technique. This paper reports on surface-potential reversibility originating from a reversible chemical reaction between amino and nitroso groups. In addition, we demonstrate surface-potential memory based on this chemical reversibility. Amino-terminated SAMs were prepared from p-aminophenyl-trimethoxysilane through chemical vapor deposition. Surface potentials were acquired by Kelvin force microscopy. When scanning probe lithography was conducted with a gold tip at positive-bias voltages, the surface potential of the scanned area shifted dramatically in the negative direction. Scanning with negative-bias voltages led to positive shift in the surface potential of the scanned area. The surface potential could be recovered even after multiple scannings with positive and negative applied bias voltages. On the basis of this discovery, we also succeeded in demonstrating surface-potential memory via our nanoprobe electrochemical technique.

Journal Article↗
PubMed2002

Pulse-mode scanning ion conductance microscopy--a method to investigate cultured hippocampal cells.

Scanning ion conductance microscopy (SICM) takes advantage of the increase in the resistance which occurs if a glass microelectrode is closely approached to a poorly conducting membrane (Science 243 (1989) 641) and has been shown to be a promising technique to study membranes of living cells (Biophys J 73 (1997a) 653; J Microsc 188 (1997b) 17). Based on a newly designed set-up on top of an inverted light microscope in combination with a speed optimized low noise intracellular amplifier, a novel mode for control of the distance between the probe and surface has been developed. By application of current pulses, the change in the resistance is monitored independently from electrode drift and parasitic DC currents. We demonstrate the applicability by showing first high-resolution images of neural cells produced with the pulse-mode operated SICM.

Animals↗
PubMed2003

A novel light source for SICM-SNOM of living cells.

We have developed a novel light source for use in a scanning near-field optical microscope (SNOM or NSOM) based on a nanopipette whose distance from the sample surface is controlled using scanning ion conductance microscopy. The light source is based on the general principle of the chemical reaction between a fluorophore in the pipette and ligand in the bath, to produce a highly fluorescent complex that is continually renewed at the pipette tip. In these experiments we used fluo-3 and calcium, respectively. This complex is then excited with an Ar+ laser, focused on the pipette tip, to produce the light source. This method overcomes the transmission problem of more traditional SNOM probes and has been used to acquire simultaneous high-resolution topographic and optical images of biological samples in physiological buffer. A resolution of approximately 220 nm topographic and approximately 190 nm optical was determined through imaging fixed sea-urchin sperm flagella. Live A6 cells were also imaged, demonstrating the potential of this system for SNOM imaging of living cells.

Aniline Compounds↗
PubMed2003

Scanning probe evolution in biology.

Twenty years ago the first scanning probe instrument, the scanning tunneling microscope, opened up new realms for our perception of the world. Atoms that had been abstract entities were now real objects, clearly seen as distinguishable individuals at particular positions in space. A whole family of scanning probe instruments has been developed, extending our sense of touching to the scale of atoms and molecules. Such instruments are especially useful for imaging of biomolecular structures because they can produce topographic images with submolecular resolution in aqueous environments. Instruments with increased imaging rates, lower probe-specimen force interactions, and probe configurations not constrained to planar surfaces are being developed, with the goal of imaging processes at the single-molecule level-not only at surfaces but also within three-dimensional volumes-in real time.

Biology↗
PubMed1993

Identification of the physical modification threshold of dentin induced by neodymium and holmium YAG lasers using scanning electron microscopy.

Laser application to dentin has been advocated to modify the dentin substrate for restorative procedures. We examined the minimum energy density required to physically modify the dentin surface using 1.06 microns and 1.32 microns Neodymium:Yttrium-Aluminum-Garnet (Nd:YAG) and 2.10 microns Holmium-YAG (Ho:YAG) lasers. Three millimeter thick dentin sections from the middle occlusal third of crowns of third molars were used. To determine the effect of surface preparation, the sections were ground to 240, 320, 400, 600 grit or polished to 0.5 micron. Smear layer was removed using 0.5 M EDTA for 2 minutes. Five single pulse repetitions at each laser parameter were performed. Power (W) and energy per pulse (mJ/p) were increased for each wavelength until a physical modification occurred. The energy density (J/cm2) was then held constant and the threshold was confirmed using 200, 320 and 550 microns diameter quartz contact probes. Scanning electron microscopy (SEM) was used to verify the physical modification of the dentin. The physical threshold remained constant for ground and polished surfaces. Similar surface modifications were found for the three wavelengths tested. The threshold modifications occurred at 207, 165, and 83 J/cm2 for the 1.06 microns, 1.32 microns and 2.10 microns lasers, respectively. For all emission wavelengths tested the physical threshold modification occurred at relatively low energy densities. These lasers show promise for surface modification of dentin.

Aluminum↗
PubMed2003

Fabrication of near-field optical apertures in aluminium by a highly selective corrosion process in the evanescent field.

A simple, one-step process to fabricate high-quality apertures for scanning near-field optical microscope probes based on aluminium-coated silicon nitride cantilevers is presented. A thin evanescent optical field at a glass-water interface was used to heat the aluminium at the tip apex due to light absorption. The heat induced a breakdown of the passivating oxide layer and local corrosion of the metal, which selectively exposed the front-most part of the probe tip from the aluminium. Apertures with a protruding silicon nitride tip up to 72 nm in height were fabricated. The height of the protrusion was controlled by the extent of the evanescent field, whereas the diameter depended on the geometry of the probe substrate. The corrosion process proved to be self-terminating, yielding highly reproducible tip heights. Near-field optical resolution in a transmission mode of 85 nm was demonstrated.

Aluminum↗
PubMed2006

Unravelling single metalloprotein electron transfer by scanning probe techniques.

This review is intended to account for the experimental and theoretical achievements obtained in a period of about 15 years on the investigation of the electron transport through single redox metalloproteins by scanning probe techniques. A highly focussed research effort has been deployed by the scientists active in this particular field towards measuring and interpreting electronic current signals flowing via blue copper, redox metalloproteins (e.g. azurin). The field has taken a remarkable advantage of the use of electrochemically assisted scanning tunnelling microscope (EC-STM) which has allowed to probe single molecule signals under full control of all the potential values involved in the experiments. This experimental activity has both triggered more comprehensive theoretical interpretations and has been, in its turn, stimulated by theoreticians to test always new predictions. The authors hope to have succeeded in providing the reader with a valuable appraisal of this fascinating field.

Electric Conductivity↗
PubMed2001

Scanning force images through the 'Milliscope'--a probe microscope with very wide scan range.

The effectiveness and adequacy of a home-built scanning force microscope (SFM) able to cover a volume of approximately 1.2 x 1.2 x 0.13 mm(3) (X x Y x Z) were tested on calibrating objects, as well as on cytological and histological samples. The instrument was designed for matching the magnification range of an optical microscope (approximately 20-1200x) but its dynamics were one or two orders of magnitude higher, thanks to a lateral resolution of about 10 nm. Images ranging in size from 1.2 x 1.2 mm(2) to 1 x 1 microm(2) showed a quality comparable to that given by other SFMs on similar materials. The 'Milliscope' is a curious but effective imaging tool whose operating range overlaps at one extreme with a goldsmith's eyepiece, and at the other with an electron microscope. The intrinsic limits of scanning probe techniques and of the available SFM cantilevers prevented us taking complete advantage of the wide height range of our scanner. However, our results show that an instrument having a very wide scan area, obtained through simple, inexpensive and intrinsically linear techniques, can give a good performance even at small scan sizes. This encourages us to develop wide scan instruments, which could further increase the already extensive use of scanning force microscopy in biology.

Humans↗
PubMed2005

Kelvin probe force microscopy study on conjugated polymer/fullerene bulk heterojunction organic solar cells.

We conducted a comprehensive Kelvin probe force microscopy (KPFM) study on a classical organic solar cell system consisting of MDMO-PPV/PCBM blends. The KPFM method yields the information of topography and local work function at the nanometer scale. Experiments were performed either in the dark or under cw laser illumination at 442 nm. We identified distinct differences in the energetics on the surface of chlorobenzene and toluene cast blend films. Together with high-resolution scanning electron microscopy (SEM) experiments we were able to interpret the KPFM results and to draw some conclusions for the electron transport toward the cathode in the solar cell configuration. The results suggest that surfaces of toluene cast films exhibit a morphologically controlled hindrance for electron propagation toward the cathode, which is usually evaporated on top of the films in the solar cell device configuration.

Electric Power Supplies↗
PubMed2003

Photoplastic near-field optical probe with sub-100 nm aperture made by replication from a nanomould.

Polymers have the ability to conform to surface contours down to a few nanometres. We studied the filling of transparent epoxy-type EPON SU-8 into nanoscale apertures made in a thin metal film as a new method for polymer/metal near-field optical structures. Mould replica processes combining silicon micromachining with the photo-curable SU-8 offer great potential for low-cost nanostructure fabrication. In addition to offering a route for mass production, the transparent pyramidal probes are expected to improve light transmission thanks to a wider geometry near the aperture. By combining silicon MEMS, mould geometry tuning by oxidation, anti-adhesion coating by self-assembled monolayer and mechanical release steps, we propose an advanced method for near-field optical probe fabrication. The major improvement is the possibility to fabricate nanoscale apertures directly on wafer scale during the microfabrication process and not on free-standing tips. Optical measurements were performed with the fabricated probes. The full width half maximum after a Gaussian fit of the intensity profile indicates a lateral optical resolution of approximately 60 nm.

Aluminum↗
PubMed2006

Microfabricated torsion levers optimized for low force and high-frequency operation in fluids.

We developed a mass production fabrication process for making symmetrically supported torsion cantilevers/oscillators with highly compliant springs. These torsion probes offer advantages in atomic force microscopy (AFM) because they are small, have high optical gain, do not warp and can be made with two independent axes. Compared to traditional AFM cantilevers, these probes have higher frequency response, higher Q, lower noise, better optics (since the mirror does not bend) and two data channels. Soft small levers with sub-pN force resolution can resonate cleanly above 10 kHz in water. When fabricated with a ferromagnetic coating on the rigid reflecting pad, they can be driven magnetically or serve as high-resolution magnetometers. Asymmetric levers can be tapping mode probes or high-resolution accelerometers. The dual axis gimbaled probes with two orthogonal axes can operate on a standard AFM with single beam illumination. These probes can be used as self-referencing, drift free, cantilevers where one axis senses the substrate position and the other the sample position. These levers can be optimized for differential contrast or high-resolution friction imaging.

Gold↗
PubMed2005

Imaging a single-electron quantum dot.

Images of a single-electron quantum dot were obtained in the Coulomb blockade regime at liquid He temperatures using a cooled scanning probe microscope (SPM). The charged SPM tip shifts the lowest energy level in the dot and creates a ring in the image corresponding to a peak in the Coulomb-blockade conductance. Fits to the line shape of the ring determine the tip-induced shift of the energy of the electron state in the dot. SPM manipulation of electrons in quantum dots promises to be useful in understanding, building, and manipulating circuits for quantum information processing.

Arsenicals↗