Scanning Probe Microscopy Techniques Research Articles

Surface Characterization of Poly(ε-caprolactone)-Based Nanocomposites

This work deals with the preparation and the surface characterization of biodegradable nanocomposites made of poly(e-caprolactone) (PCL) and a montmorillonite-type clay. Nanocomposites with different relative compositions of PCL and montmorillonite, either natural or organo-modified by various alkylammonium cations, are prepared by melt intercalation and in situ intercalative polymerization. The goal of this study is to characterize the dispersion of the clay layers in PCL, which is a critical parameter governing the final physical properties of the obtained nanocomposites. Morphological studies of PCL nanocomposites are carried out by means of scanning probe microscopy techniques while surface analysis is performed both by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The results demonstrate that the dispersion of the clay layers is strongly dependent on both the synthetic route and the type of alkylammonium chains used for the cationic exchange. Whereas the melt-intercala...

Combined scanning probe microscopy and electron microscopy study of microstructure evolution in copper processed by equal channel angular pressing

Abstract We produced submicrocrystalline Cu using the equal channel angular pressing technique with four passes. The as-deformed samples exhibited a high yield strength > 400 MPa and a poor elongation before failure < 20%. The majority of the grain boundaries after equal channel angular pressing were of the low-angle type. A series of heat treatments in the temperature range 220–300°C was performed and partly recrystallized microstructures with different fractions of recrystallized grains were obtained. The microstructures were analyzed by a combination of transmission electron microscopy, orientation image microscopy, light microscopy and scanning probe microscopy. The increase in ductility in partly recrystallized samples was accompanied by a decrease in the yield strength. It was suggested that to obtain a bulk nanocrystalline material which is both strong and ductile the majority of the grain boundaries should be of the high-angle type. It is shown that the scanning probe microscopy technique allows o...

Two‐Dimensional Supramolecular Self‐Assembly Probed by Scanning Tunneling Microscopy

AbstractFor Abstract see ChemInform Abstract in Full Text.

Preparation of smooth siloxane surfaces for AFM visualization of immobilized biomolecules

Development of scanning probe microscopy (SPM) techniques during past decade has made possible to study bioprocesses at a molecular level. Common protocols for immobilization of biomolecules for SPM studies are based on their adsorption to alkylsiloxane monolayers on hydroxylated surfaces. The same procedure is also widely used for DNA chip and biosensor fabrication. For SPM studies of immobilized biomolecules smooth carrier surfaces are mandatory. Several studies refer to the lack of reproducibility in formation of smooth silanized surfaces. In this work a new method based on carrier treatment with linearly polymerized 3-aminopropyltrimethoxysilane for preparation of reproducibly smooth silanized surfaces is proposed.

Two-dimensional supramolecular self-assembly probed by scanning tunneling microscopy.

Supramolecular chemistry has a very large impact on chemistry of current interest and the use of non-covalent but directional forces is appealing for the construction of 'supramolecular architectures'. The invention of scanning probe microscopy techniques has opened new doorways to study these concepts on surfaces. This review deals with recent progress in the study of two-dimensional supramolecular self-assembly on surfaces probed by scanning tunneling microscopy, with a special emphasis on structure, dynamics and reactivity of hydrogen bonded systems.

Superhard materials in the B/C/N system and modern micro system technology: synergistic effects

Diamond-like materials from the B/C/N system (e.g. diamond, tetrahedral amorphous carbon, cubic boron nitride (c-BN)) possess a great number of outstanding properties. Accordingly, they are very promising candidates for applications as active or passive layers in modern micro or nano systems, e.g. in probes for scanning probe microscopies (SPM). On the other hand, specially designed micro systems, in general, and SPM techniques especially, may help to overcome current problems in the optimization of existing thin films from the B/C/N system and in developing new ones by providing new techniques of material characterization, in the ideal case in situ during deposition. Therefore, synergistic effects may come into play, leading to a mutual improvement of both, the thin films and their properties, and the micro or nano systems. Although this ideal case has not yet been reached for films from the B/C/N system, we will present examples from our current research, which may eventually help to reach this aim. Fabrication of all-diamond tips and cantilevers for AFM applications, and of humidity sensors including carbon nitride films show the applicability of thin B/C/N films in micro systems, while the in situ characterization of diamond nucleation and growth by STM measurements and the measurements of the stress of c-BN films by micromachined silicon cantilevers demonstrate the usefulness of material characterization by modern micro systems.

Controlled modification and direct characterization of multimode-fiber refractive-index profiles.

A combination of controlled annealing and characterization by scanning probe microscopy (SPM) is used to demonstrate that the refractive-index proffle of a commercially available silica-based optical fiber can be accurately reconfigured for use as an evanescent field sensor. The process relies on the controlled relocation of the silica glass dopants across the fiber cross section through heat treatment and the accurate measurement of the resulting dopant redistribution with SPM and differential etching techniques. The effect of variable annealing along a length of fiber is to produce a mode transformer to couple light from a laser source into the sensing region of the fiber.

Phase Characterization and Morphology Control of Electrospun Nanofibers of Pani/Pmma Blends

ABSTRACTElectrospinning derived from electro spraying is a process by which sub-micron polymer fibers can be produced using an electrostatically driven jet of polymer solution. The fibers are collected as non-woven mat and offer a high surface to volume ratio. Polyaniline is an organic conducting polymer and can be used to fabricate conducting nano fibers by blending with suitable polymers like poly methyl methacrylate. In this present work we have explored the effects of electrospinning parameters on the formation of PANI/PMMA fibers and the phase morphology of the electrospun fibers using advanced electron microscopy and scanning probe microscopy techniques.

Surface viscoelasticity studies of Gd 2O 3, SiO 2 optical thin films and multilayers using force modulation and force–distance scanning probe microscopy

The single and multilayer of Gd 2O 3 and SiO 2 thin films deposited through reactive electron beam evaporation have been studied for their viscoelasticity properties and optical spectral stability using multimode scanning probe microscope and spectrophotometric techniques. A conspicuous changes in viscoelasticity properties and surface topographies have been observed with the Gd 2O 3 films deposited under various oxygen pressures. The scanning probe measurements on the multilayer filters fabricated using these film materials for laser wavelengths of 248 nm (KrF) and 355 nm (Nd:Yag-III) have shown superior viscoelasticity property, which is not the case with the most conventional multilayers. The results were correlated with the long-term spectral stability that has been studied by recording transmittance spectra of these filters at a time interval of 10 months. Both the multilayer filters have shown excellent temporal spectral stabilities with a relatively better result for the 248 nm reflection filter. Further analysis has shown a very good co-relationship in the spectral stability and viscoelasticity properties in these multilayers.

Direct imaging of the depletion region of an InP p–n junction under bias using scanning voltage microscopy

We directly image an InP p–n junction depletion region under both forward and reverse bias using scanning voltage microscopy (SVM), a scanning probe microscopy (SPM) technique. The SVM results are compared to those obtained with scanning spreading resistance microscopy (SSRM) measurements under zero bias on the same sample. The SVM and SSRM data are shown to agree with the results of semiclassical calculations. The physical basis of the SVM measurement process is also discussed, and we show that the measured voltage is determined by the changes in the electrostatic potential and the carrier concentration at the SVM tip with and without the applied bias.

Tunneling spectroscopy of palladium-barium emitters

The surface of a palladium-barium cathode was studied using scanning probe microscopy techniques. Data from the tunneling spectroscopy showed the pattern of the electron work function distribution over a microscopic region on the emitter surface. This pattern is compared to the distribution of various phases in the palladium-barium alloy employed.

Electrical microcharacterization of dislocation-related charges in GaN-based single layers by scanning probe microscopy techniques

Threading dislocations in differently doped GaN single layers grown by metalorganic vapor phase epitaxy on (0 0 0 1) sapphire were investigated by tapping-mode atomic force microscopy (AFM) and by scanning surface potential microscopy (SSPM) with respect to their local electrical properties. In Mg-doped and in some undoped GaN layers, surface potential variations of about 0.1 V due to additional negative coulomb charges appear around the dislocation/surface intersections. In contrast, in Si-doped and in some other undoped layers, the surface pits are electrically neutral without any systematic surface potential signal. These differences in charge state are attributed to decoration effects of the dislocation core with other defects.

Adsorption of Individual Polyacrylamide Molecules Studied by Atomic Force Microscopy

Adsorption of Individual Polyacrylamide Molecules Studied by Atomic Force Microscopy

Nanometer structure of carbon fibers studied by different scanning probe microscopy techniques: a comparative investigation

The capability of several different scanning probe microscopy techniques with different sorts of tips for the study of carbon fibers is compared. The objective is to establish the limitations of the available methods to reveal the nanostructure of these materials, although the results will be widely applicable not only to carbon fibers, but to carbon materials in general and many others of a different nature. Scanning tunneling microscopy provided the best results in terms of resolution, followed by tapping mode atomic force microscopy. Contact mode atomic force microscopy yielded a poorer resolution with evident distortions in the observed features. The results are discussed in terms of the finite size and morphology of the probing tips and are additionally supported by numerical simulations of the atomic force microscopy imaging process for the case of a strictly geometrical interaction between tip and surface.

Quantitative voltage measurement of high-frequency internal integrated circuit signals by scanning probe microscopy

This article describes a scanning probe microscopy technique for quantitative high-speed voltage wave form measurement inside an operating integrated circuit. Internal signals are determined by sensing the local electrostatic force on a noncontacting micromachined probe cantilever that is closely positioned above the circuit test point. Amplitude modulation based downconversion is employed to measure repetitive high-frequency signals which can have a bandwidth much greater than the mechanical response of the probe. A force-nulling technique is used to obtain accurate absolute voltages without the need for complex calibration or precise probe positioning, and enables direct measurement of passivated circuits. A method of eliminating dc offset errors, such as that due to material work function differences, is described. Measurement of signals on the passivated interconnects of a wideband distributed amplifier is presented. The instrument demonstrates a voltage accuracy of &amp;lt;30 mV over a dynamic range of 2.5 V.

Creatingchiral architectures at metal surfaces

The adsorption of complex organic molecules at a metal surfaceprovides a means of introducing the ultimate selectivity function ofchirality to a metal surface. Here, the adsorption ofR, R-tartaric acid (R standing for rectus), which possessestwo chiral centres, on a Cu(110) surface is reviewed. Using acombination of vibrational, surface diffraction, and scanning probemicroscopy techniques, a detailed molecular picture of theorganic/metal interface has been constructed. This reveals that anumber of different phases can be created which vary in terms of thelocal chemistry and bonding of the organic unit and in terms of thelong-range-ordered architectures that are created. Of the variousphases created, two possess the special quality of extendedchirality, where a truly chiral surface which is non-superimposableon its mirror image, is created. Three constraints are shown to beimportant for sustaining a single chiral domain across the entiresurface: local chirality of the adsorbate, a rigid and definedadsorption geometry, and the presence of anisotropic lateralinteractions.

Influence of Gold Substrate Topography on the Voltammetry of Cytochrome c Adsorbed on Carboxylic Acid Terminated Self-Assembled Monolayers

Interfacial investigations of a protein monolayer electrochemical system, equine cytochrome c (cyt c) adsorbed to carboxylic acid terminated self-assembled monolayer (COOH SAM) modified gold electrodes, were performed. Electrochemical, spectroscopic, and scanning probe microscopy techniques were utilized to explore the influence of gold topography in the cyt c/COOH SAM/gold system. COOH SAMs were prepared from 14-mercaptotetradecanoic acid and 11-mercaptoundecanoic acid on a variety of substrates including evaporated, bulk, single crystal, and epitaxially grown gold on mica. These substrates encompassed a wide range of surface roughness. As the topography of the gold became smoother, SAMs exhibited an increased ability to block a solution probe molecule, indicative of a lower level of defectiveness. At the same time, after exposure to equine cyt c deposition solutions, the extent of adsorption and the magnitude of the electrochemical response of the adsorbed cyt c decreased significantly with increasingly smooth substrates. The results show cyt c adsorption and electrochemistry to be intimately related to the density of defects in the SAM, which in turn are largely dictated by the topography of the gold substrate. This hypothesis is supported by experiments in which the density of defects in the SAMs was controlled on each type of gold substrate using intentional roughening/smoothing procedures as well as through the use of mixed SAMs. Results are interpreted in terms of the topographically dependent acid/base properties of the COOH SAMs, which can limit the electrostatically driven adsorption of cyt c and the effectiveness of the protein's electronic coupling at the differently textured SAM surfaces.

Investigation of the electrostatic forces in scanning probe microscopy at low bias voltages

AbstractThe electrostatic force between a gold tip and an atomically flat highly oriented pyrolytic graphite substrate has been measured as a function of tip– sample separation distance for low bias voltages (&lt;1 v). The experiments involve phase‐sensitive detection of the reflected laser beam off a stiff oscillating cantilever as it approaches the sample. The results are compared with the theoretical model in which the tip– sample geometry is described by confocal hyperboloids of revolution. The general behaviour of the force curve was found to be in agreement with theoretical expectations only for distances of &gt;600 Å. The deviations at smaller distances probably could be due to extraneous material such as graphite nanoflakes or a conducting liquid column present between tip and sample. The results have direct bearing on understanding the interaction forces in scanning probe microscopy techniques in which tip– sample junctions are biased. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Heterodyne electrostatic imaging of polarization due to a surface acoustic wave

We describe a technique that enables us to obtain a stroboscopic image of surface polarization associated with a surface acoustic wave. The surface polarization has been imaged as it travels across the exposed substrate of a surface acoustic wave filter operating at 434 MHz. The high-frequency polarization signals were recovered using a heterodyne electrostatic force scanning probe microscopy technique.

Transparent and conductive Sb-doped tin oxide SPM tips prepared by sol–gel method

The rapid progress in scanning probe microscopy (SPM) techniques in the last decade has induced an increasing need for manufacturing advanced SPM tips. One important case is conductive and transparent tips. For such tips, only a few techniques have been proposed, which are either expensive or have poor reproducibility. We here propose a simple and cheap sol–gel technique to prepare fibers with a suitably sharp apex so that they can be used as SPM tips. The fibers were spinned off from a high-viscosity solution of tin alkoxide and SbCl 3 hydrolysed in humid air and baked at 520 °C for several hours. The radii of the resulting tips were estimated by transmission electron microscopy to be less than 50 nm. The resistivity of the transparent fibers was measured using different Sb-doping (0.5–1 wt.%) of the tin oxide. The temperature dependence of the conductivity and light absorption were investigated down to liquid He temperatures.