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Podosomes are unique cellular entities specifically found in macrophages and involved in cell--matrix interactions, matrix degradation, and 3D migration. They correspond to a core of F-actin surrounded at its base by matrix receptors. To investigate the structure/function relationships of podosomes, soft lithography, atomic force microscopy (AFM), and correlative fluorescence microscopy were used to characterize podosome physical properties in macrophages differentiated from human blood monocytes. Podosome formation was restricted to delineated areas with micropatterned fibrinogen to facilitate AFM analyses. Podosome height and stiffness were measured with great accuracy in living macrophages (578 [+ or -] 209 nm and 43.8 [+ or -] 9.3 kPa) and these physical properties were independent of the nature of the underlying matrix. In addition, time-lapse AFM revealed that podosomes harbor two types of overlapping periodic stiffness variations throughout their lifespan, which depend on F-actin and myosin II activity. This report shows that podosome biophysical properties are amenable to AFM, allowing the study of podosomes in living macrophages at nanoscale resolution and the analysis of their intimate dynamics. Such an approach opens up perspectives to better understand the mechanical functionality of podosomes under physiological and pathological contexts. cytoskeleton | Young's modulus | microcontact printing doi/ 10.1073/pnas.1007835107

Strong confinement of charges in few-electron systems such as in atoms, molecules, and quantum dots leads to a spectrum of discrete energy levels often shared by several degenerate states. Because the electronic structure is key to understanding their chemical properties, methods that probe these energy levels in situ are important. We show how electrostatic force detection using atomic force microscopy reveals the electronic structure of individual and coupled self-assembled quantum dots. An electron addition spectrum results from a change in cantilever resonance frequency and dissipation when an electron tunnels on/off a dot. The spectra show clear level degeneracies in isolated quantum dots, supported by the quantitative measurement of predicted temperature-dependent shifts of Coulomb blockade peaks. Scanning the surface shows that several quantum dots may reside on what topographically appears to be just one. Relative coupling strengths can be estimated from these images of grouped coupled dots. nanoelectronics | single-electron charging | shell structure | electrostatic force microscopy www.pnas.org/cgi/doi/10.1073/pnas.0912716107

We have studied the deposition of Zn metal onto a polished gold-coated quartz crystal with in situ tapping-mode atomic force microscopy (AFM), while simultaneously recording chronoamperometric and acoustic impedance quartz crystal microbalance (QCM) measurements. We are able to demonstrate good correlation between the three techniques. Modeling of the chronoamperometric dam recorded for the initial nucleation process of the same experiment suggests that nucleation initially occurred via a progressive mechanism. Crystallites of different sizes were clearly visible from the AFM images throughout the whole deposition time monitored, suggesting that sustained nucleation also occurs via a progressive mechanism. 10.1021/ac901329e

Resolving individual atoms has always been the ultimate goal of surface microscopy. The scanning tunneling microscope images atomic-scale features on surfaces, but resolving single atoms within an adsorbed molecule remains a great challenge because the tunneling current is primarily sensitive to the local electron density of states dose to the Fermi level. We demonstrate imaging of molecules with unprecedented atomic resolution by probing the short-range chemical forces with use of noncontact atomic force microscopy. The key step is functionalizing the microscope's tip apex with suitable, atomically well-defined terminations, such as CO molecules. Our experimental findings are corroborated by ab initio density functional theory calculations. Comparison with theory shows that Pauli repulsion is the source of the atomic resolution, whereas van der Waals and electrostatic forces only add a diffuse attractive background.

We study the physical origins of phase contrast in dynamic atomic force microscopy (dAFM) in liquids where low-stiffness microcantilever probes are often used for nanoscale imaging of soft biological samples with gentle forces. Under these conditions, we show that the phase contrast derives primarily from a unique energy flow channel that opens up in liquids due to the momentary excitation of higher eigenmodes. Contrary to the common assumption, phase-contrast images in liquids using soft microcantilevers are often maps of short-range conservative interactions, such as local elastic response, rather than tip-sample dissipation. The theory is used to demonstrate variations in local elasticity of purple membrane and bacteriophage [phi]29 virions in buffer solutions using the phase-contrast images. atomic force microscopy | liquid environments | energy dissipation | higher eigenmodes | momentary excitation

Dynamic force spectroscopy probes the kinetic and thermodynamic properties of single molecules and molecular assemblies. Here, we propose a simple procedure to extract kinetic information from such experiments. The cornerstone of our method is a transformation of the rupture-force histograms obtained at different force-loading rates into the force-dependent lifetimes measurable in constant-force experiments. To interpret the force-dependent lifetimes, we derive a generalization of Bell's formula that is formally exact within the framework of Kramers theory. This result complements the analytical expression for the lifetime that we derived previously for a class of model potentials. We illustrate our procedure by analyzing the nanopore unzipping of DNA hairpins and the unfolding of a protein attached by flexible linkers to an atomic force microscope. Our procedure to transform rupture-force histograms into the force-dependent lifetimes remains valid even when the molecular extension is a poor reaction coordinate and higher-dimensional free-energy surfaces must be considered. In this case the microscopic interpretation of the lifetimes becomes more challenging because the lifetimes can reveal richer, and even nonmonotonic, dependence on the force. atomic force microscope | optical tweezers | nanopore unzipping Kramers theory | rupture force distribution

Restoration of lung homeostasis following injury requires efficient wound healing by the epithelium. The mechanisms of lung epithelial wound healing include cell spreading and migration into the wounded area and later cell proliferation. We hypothesized that mechanical properties of cells vary near the wound edge, and this may provide cues to direct cell migration. To investigate this hypothesis, we measured variations in the stiffness of migrating human bronchial epithelial cells (16HBE cells) ~2 h after applying a scratch wound. We used atomic force microscopy (AFM) in contact mode to measure the cell stiffness in 1.5-[micro]m square regions at different locations relative to the wound edge. In regions far from the wound edge (>2.75 mm), there was substantial variation in the elastic modulus in specific cellular regions, but the median values measured from multiple fields were consistently lower than 5 kPa. At the wound edge, cell stiffness was significantly lower within the first 5 [micro]m but increased significantly between 10 and 15 [micro]m before decreasing again below the median values away from the wound edge. When cells were infected with an adenovirus expressing a dominant negative form of RhoA, cell stiffness was significantly decreased compared with cells infected with a control adenovirus. In addition, expression of dominant negative RhoA abrogated the peak increase in stiffness near the wound edge. These results suggest that cells near the wound edge undergo localized changes in cellular stiffness that may provide signals for cell spreading and migration. wound healing; ventilator-induced lung injury; Rho-GTPases

The cell envelope of gram-negative bacteria is responsible for many important biological functions: it plays a structural role, it accommodates the selective transfer of material across the cell wall, it undergoes changes made necessary by growth and division, and it transfers information about the environment into the cell. Thus, an accurate quantification of cell mechanical properties is required not only to understand physiological processes but also to help elucidate the relationship between cell surface structure and function. We have used a novel, atomic force microscopy (AFM)-based approach to probe the mechanical properties of single bacterial cells by applying a constant compressive force to the cell under fluid conditions while measuring the time-dependent displacement (creep) of the AFM tip due to the viscoelastic properties of the cell. For these experiments, we chose a representative gram-negative bacterium, Pseudomonas aeruginosa PAO1, and we used regular V-shaped AFM cantilevers with pyramid-shaped and colloidal tips. We find that the cell response is well described by a three-element mechanical model which describes an effective cell spring constant, [k.sub.1], and an effective time constant, [tau], for the creep deformation. Adding glutaraldehyde, an agent that increases the covalent bonding of the cell surface, produced a significant increase in [k.sub.1] together with a significant decrease in [tau]. This work represents a new attempt toward the understanding of the nanomechanical properties of single bacteria while they are under fluid conditions, which could be of practical value for elucidating, for instance, the biomechanical effects of drugs (such as antibiotics) on pathogens.

The image quality in electron microscopy often suffers from lens aberration. As a result of lens aberrations, critical information appears distorted at the atomic scale in high-resolution transmission electron microscopy (HRTEM). In scanning TEM (STEM), the spatial resolution of images and the quality of spectroscopic data are greatly reduced. With the recent introduction of aberration-corrected lenses and monochromators, new and exciting images with sub-0.1-nm spatial resolution are now recorded routinely, and electron energy loss data has been used to determine the location of a single atom in an atomic column. As a result of the decreased focal depth of an aberration-corrected lens used in STEM, the dream of three-dimensional (3-D) atomic resolution is one step closer and for HRTEM it was shown that 3-D imaging with atomic resolution is feasible. However, understanding imaging and spectroscopy in HRTEM and STEM still requires refined modeling of the underlying electron scattering processes by multislice image simulation. Since research into the physics and technology of nanoelectronic devices has already moved into sub-10-nm transistor gate lengths, the need for well-understood imaging and spectroscopy at nanoscale dimensions is already upon us. Fortunately, nanowires and other nanotechnology materials serve as useful test samples as well as being potential materials for future nanoelectronics. This enables early development of microscopy methods that will be used to investigate future generations of integrated circuits. Index Terms--Defects, nanowire, simulation, transmission electron microscopy (TEM).

The occurrence of scanning electron microscopy (SEM) and atomic force microscopy (AFM) side-by-side is becoming increasingly common in analytical research. This article shows microscopy techniques to image Bacillus spores, to measure spore dimensions, and to demonstrate how these methods provide supplementary information to study plasma torch effects. This paper demonstrates that observed morphologies of spores before and after exposure to a plasma torch are remarkably different. The use of SEM and AFM as a tool complex enables examination of spore morphology and dimensions as well as their alterations during decontamination using plasma torch. Index Terms--Atomic force microscopy (AFM), Bacillus cereus, decontamination, plasma torch, scanning electron microscopy (SEM).

This paper investigates nanomachining of single-crystal silicon using an atomic force microscope with a diamond-tip cantilever To enable nanomachining of silicon, a nanomachining cantilever with a pyramidal diamond tip was developed using a combination of photolithography and hot-filament chemical vapor deposition. Nanomachining experiments on silicon using the cantilever are demonstrated under various machining parameters. The silicon surface can be removed with a rate of several tens to hundreds of nanometers in ductile mode, and the cantilever shows superior wear resistance. The experiments demonstrate successful nanomachining of single-crystal silicon. [DOI: 10.1115/1.2163364] Keywords: nanomachining, atomic force microscope, cantilever, single-crystal silicon

The mechanism by which mechanical force regulates the kinetics of a chemical reaction is unknown. Here, we use single-molecule force-clamp spectroscopy and protein engineering to study the effect of force on the kinetics of thiol/disulfide exchange. Reduction of disulfide bonds through the thiol/disulfide exchange chemical reaction is crucial in regulating protein function and is known to occur in mechanically stressed proteins. We apply a constant stretching force to single engineered disulfide bonds and measure their rate of reduction by DTT. Although the reduction rate is linearly dependent on the concentration of DTT, it is exponentially dependent on the applied force, increasing 10-fold over a 300-pN range. This result predicts that the disulfide bond lengthens by 0.34 [Angstrom] at the transition state of the thiol/disulfide exchange reaction. Our work at the single bond level directly demonstrates that thiol/disulfide exchange in proteins is a force-dependent chemical reaction. Our findings suggest that mechanical force plays a role in disulfide reduction in vivo, a property that has never been explored by traditional biochemistry. Furthermore, our work also indicates that the kinetics of any chemical reaction that results in bond lengthening will be force-dependent. atomic force microscopy | mechanochemistry

The elastic properties of capsids of the cowpea chlorotic mottle virus have been examined at pH 4.8 by nanoindentation measurements with an atomic force microscope. Studies have been carried out on WT capsids, both empty and containing the RNA genome, and on full capsids of a salt-stable mutant and empty capsids of the subE mutant. Full capsids resisted indentation more than empty capsids, but all of the capsids were highly elastic. There was an initial reversible linear regime that persisted up to indentations varying between 20% and 30% of the diameter and applied forces of 0.6-1.0 nN; it was followed by a steep drop in force that is associated with irreversible deformation. A single point mutation in the capsid protein increased the capsid stiffness. The experiments are compared with calculations by finite element analysis of the deformation of a homogeneous elastic thick shell. These calculations capture the features of the reversible indentation region and allow Young's moduli and relative strengths to be estimated for the empty capsids. atomic force microscopy | cowpea chlorotic mottle virus | finite element analysis | biomechanics

One of the major thrusts in proximal probe techniques is combination of imaging capabilities with simultaneous measurements of physical properties. In tapping mode atomic force microscopy (TMAFM), the most straightforward way to accomplish this goal is to reconstruct the time-resolved force interaction between the tip and surface. These tip-sample forces can be used to detect interactions (e.g., binding sites) and map material properties with nanoscale spatial resolution. Here, we describe a previously unreported approach, which we refer to as scanning probe acceleration microscopy (SPAM), in which the TMAFM cantilever acts as an accelerometer to extract tip-sample forces during imaging. This method utilizes the second derivative of the deflection signal to recover the tip acceleration trajectory. The challenge in such an approach is that with real, noisy data, the second derivative of the signal is strongly dominated by the noise. This problem is solved by taking advantage of the fact that most of the information about the deflection trajectory is contained in the higher harmonics, making it possible to filter the signal by 'comb' filtering, i.e., by taking its Fourier transform and inverting it while selectively retaining only the intensities at integer harmonic frequencies. Such a comb filtering method works particularly well in fluid TMAFM because of the highly distorted character of the deflection signal. Numerical simulations and in situ TMAFM experiments on supported lipid bilayer patches on mica are reported to demonstrate the validity of this approach. atomic force microscopy | Fourier transform atomic force microscopy | nanoaccelerometry

Abstract: Some of the most important trafficking processes in cells involve transport across the nuclear envelope. Whether it is the import of transcription factors or the export of RNA, the [...]

An optimization procedure is applied to the physically more rigorous solvation model, the generalized Born with surface area (GB/SA) together with the all-atom AMBER force field. There were no significant differences in performance among the 3 GB/SA studied and the differences are not very large and for certain individual loops are reversed.

The combination of in situ ellipsometry with atomic force microscopy (AFM) in the liquid study of adsorption of creatine phosphokinase (CPK) was presented. The thickness, the adsorbed amount, and the topography of the immobilized CPK layer onto silicon (Si) wafers were obtained under different pH conditions, the nature of interactions between CPK and Si wafers associated with the hydration forces control the degree of CPK unfolding upon adsorbing.

An investigation is presented of the nanotribological properties of C60 single crystal (111) and (100) surfaces around its orientational order-disorder phase transition temperature by atomic force microscopy and frictional force microscopy (AFM/FFM) in high vacuum. Results reveal that for both surfaces across the phase transition temperature, the friction force and the adhesive force between a C60 coated AFM tip and the C60 crystal surfaces exhibit discontinuous behavior.

The 5-H[T.sub.3] receptor is a cation-selective ligand-gated ion channel of the Cys-loop superfamily. The receptor is an important therapeutic target, with receptor antagonists being widely used as antiemetics in cancer therapy. The two known receptor subunits, A and B, form homomeric 5-H[T.sub.3A] receptors and heteromeric 5-H[T.sub.3A/B] receptors. The heteromeric receptor has the higher single-channel conductance and more closely mimics the properties of the native receptor. We have used atomic force microscopy to study the architecture of 5-H[T.sub.3A] and 5-H[T.sub.3A/B] receptors. We engineered different epitope tags onto the A- and B-subunits and imaged receptors that were doubly liganded by anti-epitope antibodies. We found that, for the 5-H[T.sub.3A/B] receptor, the distribution of angles between antibodies against the A-subunit had a single peak at [approximately equal to] 144[degrees], whereas the distribution for antibodies against the B-subunit had two peaks at [approximately equal to] 72[degrees] and 144[degrees]. Our results indicate that the subunit stoichiometry is 2A:3B and that the subunit arrangement around the receptor rosette is B-B-A-B-A. This arrangement may account for the difference between the agonist Hill coefficients and the single-channel conductances for the two types of receptor. ligand-gated ion channel | receptor structure

Protein conformational diseases, including Alzheimer's, Huntington's, and Parkinson's diseases, result from protein misfolding, giving a distinct fibrillar feature termed amyloid. Recent studies show that only the globular (not fibrillar) conformation of amyloid proteins is sufficient to induce cellular pathophysiology. However, the 3D structural conformations of these globular structures, a key missing link in designing effective prevention and treatment, remain undefined as of yet. By using atomic force microscopy, circular dichroism, gel electrophoresis, and electrophysiological recordings, we show here that an array of amyloid molecules, including amyloid-[beta](1-40), [alpha]-synuclein, ABri, ADan, serum amyloid A, and amylin undergo supramolecular conformational change. In reconstituted membranes, they form morphologically compatible ion-channel-like structures and elicit single ion-channel currents. These ion channels would destabilize cellular ionic homeostasis and hence induce cell pathophysiology and degeneration in amyloid diseases. atomic force microscopy | protein conformational disease | peptide ion channel | misfolding protein | 3D structure

Nanofiber structures of some peptides and proteins as biological materials have been studied extensively, but their molecular mechanism of self-assembly and reassembly still remains unclear. We report here the reassembly of an ionic self-complementary peptide RADARADARADARADA (RADA16-I) that forms a well defined nanofiber scaffold. The 16-residue peptide forms stable [beta]-sheet structure and undergoes molecular self-assembly into nanofibers and eventually a scaffold hydrogel consisting of >99.5% water. In this study, the nanofiber scaffold was sonicated into smaller fragments. Circular dichroism, atomic force microscopy, and rheology were used to follow the kinetics of the reassembly. These sonicated fragments not only quickly reassemble into nanofibers that were indistinguishable from the original material, but their reassembly also correlated with the rheological analyses showing an increase of scaffold rigidity as a function of nanofiber length. The disassembly and reassembly processes were repeated four times and, each time, the reassembly reached the original length. We proposed a plausible sliding diffusion model to interpret the reassembly involving complementary nanofiber cohesive ends. This reassembly process is important for fabrication of new scaffolds for 3D cell culture, tissue repair, and regenerative medicine. atomic force microscopy | circular dichroism | dynamic behaviors | ionic self-complementary peptides | nanofiber hydrogels

A method to measure charge within a molecular circuit that shows negative differential resistance by conducting probe atomic force microscopy is presented. It is observed that the voltage region over which conduction was enhanced correlated strongly with the region over which the scanning probe tip experienced capacitive attraction to the surface.

The study created random parallel nanostuctures by scattering gold thin films deposited on glass slides. Atomic force microscope (AFM) images concluded that the width of the substructures within the scratches were of the order of a few hundred nanometers.

A major cause of magnetic spacing losses in data tape systems is pole tip recession (PTR). This study is an investigation of PTR in a linear data tape recording system and identification of the mechanisms responsible for these effects, but the results have implications for any head where the tape bearing surface is [Al.sub.2][O.sub.3]/TiC, AlTiC. Tape cycling experiments were performed using the linear tape open system as the experimental platform with metal particle tape. All experiments were conducted within a matrix of pressure and humidity, which encompassed the system operating extremes. Atomic force microscopy was used to analyze the surface topography of the heads. Auger electron spectroscopy and x-ray photoelectron spectroscopy were employed to analyze the chemical changes on the surface of the heads and tapes. Environment was found to have a significant influence on the head/tape interface. Head wear and PTR was highest at high temperature and humidity. Water vapor was found to transform the surface layers on the TiC grains in the tape-bearing surface to Ti[O.sub.2]. This process results in the production of Ti[O.sub.2] fragments that become trapped in the recessed pole tip region, acting as three-body abrasive particles. The Ti[O.sub.2] present on the TiC grains and on the surface of heads increases with the water content after cycling against tapes. The hypothesis is supported by the presence of Ti on the poles.

Dynamic numerical simulation of a protein-ligand molecular chain connected to a moving atomic force microscope (AFM) has been studied. A sinusoidal base excitation of the cantilevered beam of the AFM is considered in some detail. A comparison between results for a single molecule and those for multiple molecules has been made. For a small number of molecules, multiple stable static equilibrium positions are observed and chaotic behavior may be generated via a period-doubling cascade for harmonic base excitation of the AFM. For many molecules in the chain, only a single static equilibrium position exists. To enable these calculations, reduced-order (dynamic) models are constructed for fully linear, combined linear/nonlinear and fully nonlinear systems. Several distinct reduced-order models have been developed that offer the option of increased computational efficiency at the price of greater effort to construct the particular reduced-order model. The agreement between the original and reduced-order models (ROM) is very good even when only one mode is included in the ROM for either the fully linear or combined linear/nonlinear systems provided the excitation frequency is lower than the fundamental natural frequency of the linear system. The computational advantage of the reduced-order model is clear from the results presented.

Atomic force microscopy is a powerful and widely used imaging technique that can visualize single molecules and follow processes at the single-molecule level both in air and in solution. For maximum usefulness in biological applications, atomic force microscopy needs to be able to identify specific types of molecules in an image, much as fluorescent tags do for optical microscopy. The results presented here demonstrate that the highly specific antibody--antigen interaction can be used to generate single-molecule maps of specific types of molecules in a compositionally complex sample while simultaneously carrying out high-resolution topographic imaging. Because it can identify specific components, the technique can be used to map composition over an image and to detect compositional changes occurring during a process.

A long-standing question in anesthesia is that of the molecular mechanism. Do anesthetics target proteins or change membrane properties or both? We used temperature-dependent magnetic A/C mode atomic force microscopy (AFM) to study interaction of the volatile anesthetics halothane and ethanol with model membranes made from supported planar bilayers (SPBs) of 1,2-dioleoyl-sn-3-glycero-3-phosphocholine (DOPC), dioleoyltrimethylammonium propane (DOTAP), or 1,2-dipalmitoyl-sn-3-glycero-3-phosphocholine (DPPC). We found that the incorporation of halothane or ethanol induces structural changes in the bilayer. These compounds cause thickness reduction in [L.sub.[alpha]] bilayers (either globally or in domains) and the formation of domains with reduced thickness in [L.sub.[beta]] phase bilayers. We propose that an anesthetic-induced increased area per lipid drives local chain disorder, thus promoting local phase change. The characteristics of SPBs with halothane or ethanol incorporated were compared with characteristics of the [L.sub.[alpha]] and [L.sub.[beta]] phases of anesthetic-free SPBs. Key words: atomic force microscopy, anesthesia, lipid bilayer domains, phase transition Le mecanisme moleculaire de l'anesthesie n'a toujours pas ete resolu. On se demande encore est-ce que les produits anesthesiques s'attaquent anx proteines ou s'ils changent les proprietes des membranes ou agissent-ils sur les deux fronts. On a fait appel a la microscopie de forces atomiques (MFA) en mode A/C magnetique et dependante de la temperature pour etudier l'interaction d'anesthesiques volatiles, tels l'halothane et l'ethanol, avec des membranes modeles faites a partir de bicouches planaires supportees (BPS) de 1,2-dioleoyl-sn-3-glycero-3-phosphocholine (DOPC), de dioleoyltrimethylammonium propane (DOTAP) ou de 1,2-dipalmitoyl-sn-3-glycero-3-phosphocholine (DPPC). On a observe que l'incorporation d'halothane ou d'ethanol induit des changements structuraux dans la bicouche. Ces composes provoquent une reduction de l'epaisseur des bicouches [L.sub.[alpha]] (globalement ou dans les domaines) accompagnee de la formation de domaines comportant des epaisseurs reduites dans les bicouches de la phase [L.sub.[beta]]. On suggere qu'une surface par lipide accrue, induite par l'anesthesique, provoque un desordre de cha'/ne local qui induit un changement de phase local. On a compare les caracteristiques des BPS dans lesquelles on a incorpore de l'halothane ou de l'ethanol avec les caracteristiques des phases [L.sub.[alpha]] et [L.sub.[beta]] de BPS ne contenant pas d'anesthesique. Mots cles : microscopie de forces atomiques, anesthesie, domaines de bicouches lipidiques, transition de phase. [Traduit par la Redaction]

Design, fabrication, and characterization of near-field microwave scanning probes compatible with an atomic force microscope (AFM) for imaging of embedded nanostructures are discussed. The microwave probe discussed here bridges the frequency gap between the existing local probe microscopy systems, and enables localized microwave spectroscopy and imaging of molecules and nanostructures. The probe consists of a coaxially shielded heavily doped silicon tip, and an aluminum (AI) coplanar waveguide. The coaxial tip structure was formed by a thick photoresist and plasma etching process, enabling the silicon apex to protrude through a well-defined aperture in the AI layer. Using this technique, probes with 10-[micro]m-high coaxial tips of 5-nm apex radius and 500-nm aperture radius were realized. The aperture confines the electromagnetic fields in the exposed tip region, allowing microwave measurements with high spatial resolution. The mechanical and electrical characterizations of the microwave probes were performed to ensure their compliance with the requirement of an AFM, as well as that of the microwave measurements. Finally, simultaneous AFM and microwave imaging of standard AFM samples with grid structures was performed for the first time. The lateral spatial resolution of the microwave scans was approximately 50 nm at 2.8 GHz, compared to 100 nm for the AFM scans. The ability of the microwave signal to penetrate inside the sample opens new possibilities in hyperspectral and multimodal imaging of nanostructures. Correlations between AFM images and the microwave images enable proper registration and referencing of the microwave properties to landmarks in the topographic AFM images. Index Terms--Atomic force microscope (AFM), cantilever beams, coaxial probes, scanning local probe microscopy (SLPM), scanning near-field microwave microscope (SNMM), silicon-on-insulator (SOI).

The effect of humidity on quantitative atomic force acoustic microscopy (AFAM) measurements of elastic properties is investigated in this research. The results indicate that environmental conditions can influence quantitative AFAM measurements of nanoscale elastic properties, at least for some materials.

Limitation effects involving the breakdown (BD) of ultrathin SiO[subscript 2] layers is analyzed at a nanometric scale using a conductive atomic force microscope (C-AFM).

In situ atomic force microscopy (AFM) was used to follow the far-from-equilibrium dissolution of the {001} cleavage surface of natural gibbsite in nitric acid. The main dissolution mechanism was the retreat of straight monolayer steps, the edges of which are paraallel to the , , and directions. The stability of these steps can be expressed as > > . The results are explained in terms of the positions of the terminal O atoms and their associated A1 atoms at the steps. New steps were formed at etch pits that opened where screw dislocations emerged on the surface. The dissolution rates were calculated from the change in size of pits and islands. The values obtained were 9.5 x [10.sup.-9] - 2.3 x [10.sup.-8] mol/[m.sup.2].s, normalized to the total surface area, and 1.8 - 3.6 x [10.sup.-7] mol/[m.sup.2].s, normalized to the surface area of the step fronts. The rates of dissolution calculated using only the surface area of the step fronts are similar to literature values obtained by other methods.

The electroformation of a Cu2S phase, obtained by sulfidization of a thin film of copper placed by the coating technique onto the gold surface of a gold/quartz crystal that is part of an electrochemical quartz crystal microbalance is studied. Atomic force microscopy revealed that the Cu2S phase electroformed on the gold/crystal quartz electrode is deposited as hemispherical particles on the terraces and in the cavities present in the gold film.

Atomic force microscopy (AFM) is a technique used routinely in material science to image substances at a submicron (including nm) scale. We apply this technique to analysis of the fine structure of organic-walled Precambrian fossils, microscopic sphaeromorph acritarchs (cysts of planktonic unicellular protists) permineralized in [approximately equal to] 650-million-year-old cherts of the Chichkan Formation of southern Kazakhstan. AFM images, backed by laser-Raman spectroscopic analysis of individual specimens, demonstrate that the walls of these petrified fossils are composed of stacked arrays of [approximately equal to] 200nm-sized angular platelets of polycyclic aromatic kerogen. Together, AFM and laser-Raman spectroscopy provide means by which to elucidate the submicron-scale structure of individual microscopic fossils, investigate the geochemical maturation of ancient organic matter, and, potentially, distinguish true fossils from pseudofossils and probe the mechanisms of fossil preservation by silica permineralization.

Rapid and accurate determination of the surface area of three kaolinite clay standards, taking into account the complex microtopography of the particles, was achieved using atomic force microscopy images and computerized image analysis. All surface areas were determined to within 3%. Edge surface area is 18.2-30.0% of the total surface area depending on the particular kaolinite standard. Specific surface areas agree to within 4% of published values determined by the BET method. The approach can be applied to clay and nanoparticle samples too small in quantity for BET analysis, since it requires ~11 orders of magnitude less material.

Under a stretching force, the sugar ring of polysaccharide molecules switches from the chair to the boat-like or inverted chair conformation. This conformational change can be observed by stretching single polysaccharide molecules with an atomic force microscope. In those early experiments, the molecules were stretched at a constant rate while the resulting force changed over wide ranges. However, because the rings undergo force-dependent transitions, an experimental arrangement where the force is the free variable introduces an undesirable level of complexity in the results. Here we demonstrate the use of force-ramp atomic force microscopy to capture the conformational changes in single polysaccharide molecules. Force-ramp atomic force microscopy readily captures the ring transitions under conditions where the entropic elasticity of the molecule is separated from its conformational transitions, enabling a quantitative analysis of the data with a simple two-state model. This analysis directly provides the physico-chemical characteristics of the ring transitions such as the width of the energy barrier, the relative energy of the conformers, and their enthalpic elasticity. Our experiments enhance the ability of single-molecule force spectroscopy to make high-resolution measurements of the conformations of single polysaccharide molecules under a stretching force, making an important addition to polysaccharide spectroscopy.

A detailed study of GaN pillar arrays by atomic force microscopy (AFM), Raman spectroscopy, and photoluminescence (PL) spectroscopy is presented. AFM is used to characterize the shape of the GaN pillars and revealed a large roughness of etched pillar surfaces.

The objective of this paper is to formulate the equations of motion and to investigate the vibrations of the atomic force microscope (AFM), which is divided into the contact and noncontact types. First, the governing equations of the AFM including both base oscillator and piezoelectric actuator are obtained using Hamilton's principle. In the dynamic analysis, the piezoelectric layer is treated as a sensor to measure the deflection and as an actuator to excite the AFM via an external voltage. The repulsive force and van der Waals (vdW) force are considered in the contact and noncontact types of the AFM, respectively. Some important observations are made from the governing equations and boundary conditions. Finally numerical results using a finite element method are provided to illustrate the excitation effects of base oscillator and piezoelectric actuator on the dynamic responses. [DOI: 10.1115/1.1389084]

Research describing the tapping mode dynamics of atomic force microscopy is presented. In particular power and harmonic balance techniques are investigated for identifying tip-sample interaction.

Atoms can be observed and determined for positions on nonconductive surfaces with the advent and progress of atomic force microscopy (AFM) technique. For the first time the array and orientation of the adsorbed molecules on zeolite surfaces could be determined.

The capacitive force acting on the tip of an atomic force microscope has been computed and compared with the the corresponding van der Waals force. Results indicate that the force measured for tip-surface distance larger than 10 nm cannot be given in terms of van der Waals forces and have to be stated in terms of capacitive forces. This finding shows that electrostatic forces are dominant for a tip-surface distance larger than half of the tip radius of curvature.

Experimental and theoretical characterizations of the detection sensitivity of atomic force microscopes equipped with optical beam deflection for small cantilevers are presented. It is demonstrated that the signal-to-noise ratio of the detection can be raised considerably with the use of an adjustable aperture. The findings show that the aperture has increased the signal-to-noise ratio of the optimal beam deflection detection by a factor of 1.5 to almost 3.

A comparison was made between atomic force microscopes (AFM) and scanning tunneling microscope (STM) nanolithography techniques based on local oxidation of silicon. Findings showed that the STM mode is not a suitable tool for lithography on silicon, while the AFM in contact mode (CM-AFM) allows high speed and can provide thick oxide. The best compromise between STM and CM-AFM appeared to be AFM in tapping mode, which keeps fine patterns as narrow as 20 nm with relative high speed.

The limit to the resolution when optically sensing the displacements of a mechanical cantilever utilizing the the knife edge detection procedure implemented with a quasimonochromatic thermal-like optical source was theoretically examined. Results showed that superluminescent diodes can provide a minimum detectable displacement of the cantilever about 5 dBs above the shot noise for 1 mW of optical power. Also, the source induced noise is smaller than the thermal-vibration noise of the cantilever in many of the cases of practical importance.

The tip of an atomic force microscope has been used to manipulate multiwalled carbon nanotubes on a passivated silicon surface. Multiwalled carbon nanotuves were dissolved in methylene chloride using an ultrasonic bath and the solution was dissolved dispersed on a H-passivated Si(100) surface. The results showed that the interaction between the nanotubes and the substrate can stabilize highly strained nanotube configurations, with the resulting distortion inducing changes on the electronic structure and electron transport properties.

A combination of atomic force microscopy, scanning election microscopy, transmission electron microscopy, energy dispersive spectroscopy, electron diffraction, and X-ray diffraction were used to study reactions of 0.5-500 mg/L aqueous Pb with [Ca.sub.5][([PO.sub.4]).sub.3]OH, hydroxylapatite (HAP), at pH 6 and 22 [degrees] C. Following 2 h reaction time, concentrations of [Pb.sub.aq] ([[Pb.sub.aq]]) decreased from 500 mg/L to [is less than] 100 mg/L, and from 0.5- 100 mg/L to [is less than] 15 [micro]g/L. This loss of [Pb.sub.aq] from solution (i.e.. sorption) resulted partially from simultaneous dissolution of HAP and precipitation of [Pb.sub.5][([PO.sub.4]).sub.3]OH, hydroxypyromorphite (HPY), or another solid Pb phase. The initial saturation state with respect to HPY (defined as the ratio of the ion activity product to equilibrium solubility product) influenced strongly precipitation processes. At a high degree of saturation (initial [[Pb.sub.aq]] [is greater than] 100 mg/L), small nuclei or aggregates of poorly crystalline HPY precipitated homogeneously in solution. At intermediate saturation (initial [[Pb.sub.aq]] ~10-100 mg/L), large, euhedral needles of HPY precipitated homogeneously in solution. At a low degree of saturation (initial [[Pb.sub.aq]] [is less than] 10 mg/L), a needle-like Pb-containing phase grew heterogeneously on HAP These results agree well with concepts derived from nucleation and growth theories and demonstrate that initial saturation state influences strongly the sorption process.

A novel atomic force microscope with a magnetically oscillated tip has provided unprecedented resolution of small DNA fragments spontaneously adsorbed to mica and imaged in situ in the presence of divalent ions. Kinks (localized bends of average angle 78 [degrees]) were observed in axially strained minicircles consisting of tandemly repeated d[(A).sub.5] and d(GGGCC[C]) sequences. The frequency of kinks in identical minicircles increased 4-fold in the presence of 1 mM [Zn.sup.2+] compared with 1 mM [Mg.sup.2+]. Kinking persisted in mixed [Mg.sup.2+]/[Zn.sup.2+] electrolytes until the [Zn.sup.2+] concentration dropped below 100 [[micro]mol], indicating that this type of kinking may occur under physiological conditions. Kinking appears to replace intrinsic bending, and statistical analysis shows that kinks are not localized within any single sequence element. A surprisingly small free energy is associated with kink formation.

An investigation on the validity of the profiles gathered from preferential etching and atomic force microscopy (AFM) imaging of etched optical fibers and waveguides was conducted. The optical fiber's measured geometry and the position of its lateral features were found to be independent of the etch time. Results from the study of an elliptical core fiber indicate that the refractive index profile was in qualitative agreement with the preform index profile. However, measurements obtained through AFM reveal that during the drawing process, the ellipticity of the core changed.

Computation of the eigenfrequencies of a rectangular cantilever clamped at a rigid support for the atomic force microscope (AFM) for a vacuum and for corrected flow showed a relative error less than 4% given a thickness T less than 1/20 of cantilever width. Measurements for both fluid and gaseous medium also indicated a node requirement of at least four for the eigenmode, assuming that the cantilever followed a z direction.