Changes In Tip Shape Research Articles

Percutaneous Treatment of Coronary Chronic Total Occlusion Part 2: Technical Approach.

Dual injection is recommended for nearly all chronic total occlusion (CTO) percutaneous coronary intervention (PCI) to determine the optimal crossing strategy and guide wire advancement into the distal true lumen. Strategies that provide enhanced guide catheter support (such as long sheaths, large-bore guiding catheters, use of guide catheter extensions, and anchor techniques) are important for maximising the success rate and efficiency of CTO PCI. Use of a microcatheter or over-the-wire balloon is strongly recommended in CTO PCI for enhancing the penetrating power of the guidewire, enabling change in tip shape and allowing guidewire change (stiff CTO guidewires are not optimal for crossing non-occluded coronary segments). Adherence to a procedural strategy that standardises CTO technique and facilitates procedural success is recommended. Such a strategy would permit stepwise decision-making for antegrade and retrograde methods; inform guidewire selection; and incorporate alternative approaches for instances of initial failure. Given the paucity of long-term outcomes with use of novel crossing techniques (antegrade dissection/re-entry and retrograde), antegrade wire escalation is the preferred CTO crossing technique, if technically feasible. Using measures to minimise radiation exposure (including but not limited to use of 7.5 frames per second fluoroscopy and use of low magnification) and contrast administration is recommended. CTO PCI is best performed at centres with dedicated CTO PCI experience and expertise. Use of crossing difficulty prediction tools, such as the J-CTO score, can facilitate the selection of cases with a high likelihood of quick crossing that can be attempted at less experienced centres.

Calibrating a nanoindenter for very shallow depth indentation using equivalent contact radius

Nanoindenter tips are usually modelled as axisymmetric cones, with calibration involving finding a fitting function that relates contact area to contact depth. For accurate calibration of shallow depth indentation, this is not ideal because it means that deeper indents tend to dominate the fitting function. For an axisymmetric object, it is always possible to define an equivalent contact radius (which, in the case, of nanoindentation is linearly related to the reduced modulus) and to obtain a fitting function that relates this equivalent contact radius to indentation depth. The equivalent contact radius approach is used here to provide shallow depth calibration of a nanoindenter tip at three separate times. The advantage of the equivalent contact radius methodology is that it provides a clearer physical interpretation of the changes in tip shape than a conventional area-based fit. We also show that the minimum depth for a reliable hardness measurement is obtainable and increases as the tip blunts with age but that consistent measurements of very near surface elastic moduli can be made if the blunting of the tip over time is fully accounted for in the tip area function calibration.

Contact mechanics and tip shape in AFM-based nanomechanical measurements

Stiffness–load curves obtained in quantitative atomic force acoustic microscopy (AFAM) measurements depend on both the elastic properties of the sample and the geometry of the atomic force microscope (AFM) tip. The geometry of silicon AFM tips changes when used in contact mode, affecting measurement accuracy. To study the influence of tip geometry, we subjected ten AFM tips to the same series of AFAM measurements. Changes in tip shape were observed in the scanning electron microscope (SEM) between individual AFAM tests. Because all of the AFAM measurements were performed on the same sample, variations in AFAM stiffness–load curves were attributed to differences in tip geometry. Contact-mechanics models that assumed simple tip geometries were used to analyze the AFAM data, but the calculated values for tip dimensions did not agree with those provided by SEM images. Therefore, we used a power-law approach that allows for a nonspherical tip geometry. We found that after several AFAM measurements, the geometry of the tips at the very end is intermediate between those of a flat punch and a hemisphere. These results indicate that the nanoscale tip-sample contact cannot easily be described in terms of simple, ideal geometries.

Atomic-Scale Roughness Effect on Capillary Force in Atomic Force Microscopy

We study the capillary force in atomic force microscopy by using Monte Carlo simulations. Adopting a lattice gas model for water, we simulated water menisci that form between a rough silicon-nitride tip and a mica surface. Unlike its macroscopic counterpart, the water meniscus at the nanoscale gives rise to a capillary force that responds sensitively to the tip roughness. With only a slight change in tip shape, the pull-off force significantly changes its qualitative variation with humidity.

Influence of Tip Wear on Atomic Force Acoustic Microscopy Experiments

ABSTRACTTip wear and its corresponding change in geometry is a major impediment for quantifying atomic force acoustic microscopy (AFAM). To better understand the process of tip wear and its influence on AFAM measurements of material elastic properties, we have performed a series of experiments and compared tip geometries calculated from experimental data with direct tip visualization in the scanning electron microscope (SEM). Using a sample with known elastic properties, the tip-sample contact stiffnesses for several different cantilevers were determined. Hertz and Derjaguin-Müller-Toporov (DMT) contact-mechanics models were applied to calculate values of the tip radius R from the experimental data. At the same time, values for R before and after each sequence of AFAM measurements were obtained from SEM images. Both methods showed that the tip radius increased with use. However, values of R calculated with the theoretical models varied indeterminately from those obtained from the SEM images. In addition, in some cases analysis of the AFAM measurements suggested a hemispherical tip, while the corresponding SEM images showed that the end of the tip was flat. We also observed other changes in tip shape, such as an increase in the tip width. By combining theoretical models for contact mechanics with visual information on the tip geometry we hope to better understand contact characteristic in AFM-based systems.Contribution of NIST, an agency of the US government; not subject to copyright.

Stability of alkyl monolayers on chemomechanically scribed silicon to air, water, hot acid, and X-rays

Abstract We report the stability of alkyl monolayers on scribed silicon to air, water, boiling 0.1 M H 2 SO 4 , and X-rays. Monolayers (ML) were prepared by scribing silicon surfaces in the presence of 1-pentene, 1-octene, 1-decene, 1-hexadecene, 1-chlorooctane, 1-bromopentane, 1,4-dibromobutane, methyl iodide, 1-iodopentane, 1-iododecane, 1-butanol, and 1-octanol with a computer-controlled, diamond-tipped instrument. In all cases some initial oxidation of the silicon substrate was observed by X-ray photoelectron spectroscopy (XPS), which increased with time, first rapidly, and then more slowly. Oxidation appears to proceed more quickly for silicon scribed under 1-haloalkanes than 1-alkenes, and more quickly for silicon scribed under 1-haloalkanes that were stored in air than in water. In the case of silicon scribed under an iodoalkane, the resulting iodine to silicon XPS ratio decreased with time, but even after extended exposures to air or water some iodine remained on the surfaces. Steric hindrance and/or hydrophobic effects appear to influence the degree of surface oxidation and halogen loss. The C 1s/Si 2p XPS ratios of surfaces prepared from 1-alkenes and 1-haloalkanes remain nearly constant after all exposures to air, water, hot acid and X-rays. Water capacities of hydrophobic corrals were measured in a semi-automated fashion with a Gilson 215 Liquid Handler and showed trends similar to the XPS results. Hydrophobic corrals generally retained significant fractions of their capacities to hold water with time. Sample-to-sample variation in corral capacity was attributed to variation in the scribing procedure, including possible changes in tip shape. To within experimental error no change in the amount of C, O, or Br at the surfaces was observed by XPS after nearly 4 h of illumination with monochromatic Al Kα X-rays.

Studies of tip wear processes in tapping mode™ atomic force microscopy

Tip integrity is crucial to atomic force microscope image quality. Tip wear not only compromises image resolution but also introduces artifacts. However, the factors that govern wearing have not been systematically studied. The results presented here of tip wearing on a rough titanium surface were determined by monitoring changes in tip shape and the evolution of histograms of complex surface curvatures under different control parameters. In contrast with the common assumption that operating at a low set point (the ratio of tapping amplitude to free oscillation amplitude) wears the tip quickly, we observed that a low set point actually minimizes tip wear on a hard surface regardless of the free amplitude. The results can be interpreted qualitatively with theoretical calculations based on momentum exchange at tapping impact. Operating at a low set point allows more robust scanning than with a high set point (tapping near free amplitude), providing a method to slow down tip wear. Another advantage of a low set point is that amplitude error grows faster than with a high set point by nearly an order of magnitude, permitting an increase in scanning speed.

Characterization of biomolecule immobilization by scanning force microscopy using a wet‐masking technique

AbstractThe assemblage of molecular layers was investigated using scanning force microscopy (SFM). A wet‐masking technique was used for the preparation of monolayer steps by partial masking of the substrate with an elastomeric mask during incubation in the modification buffers. The subsequent adsorption of biotin, streptavidin, and biotiny lated beads onto a gold substrate was investigated by SFM visualization of the created steps. The molecular layers were characterized based on measurements of step height and surface roughness. The simultaneous visualization of the surface before and after modification minimizes artifacts introduced by changes in tip shape or imaging parameters.

Nanowelding: tip response during STM modification of Au surfaces

We have studied the response of the tunnel current and the feedback circuit during surface modification by an STM tip. Our studies show that several classes of events occur when “writing” by applying voltage pulses. We have studied W and Au tips on Au surfaces and PtRh tips on Pt surfaces. Strong correlation is found between the tunnel current response and the kind of surface change that occurs. One dramatic discovery is the formation of a wire between the tip and surface, which is characterized by an electrical shorting of the tip to the surface until the feedback circuit of the tip retracts enough to break the wire. Using a sophisticated graphics display system and allowing pulse placement by pointing at the desired location, we are able to distinguish easily between changes in surface morphology and changes in tip shape and length.

Diversity of macrociliary size, tooth patterns, and distribution in Beroe (Ctenophora)

Macrocilia are compound ciliary feeding organelles found inside the mouth of beroid ctenophores. Each macrocilium contains multiple 9+2 axonemes surrounded by a common membrane and bears a distinct capping structure at the distal end. The cap consists of extensions of axonemal microtubules that are embedded in an electron-dense matrix to form pointed projections or teeth. The teeth change from a straight to a hooked configuration during the beat cycle of macrocilia, and these changes in tip shape are thought to aid ingestion and/or breakup of prey. Using light and electron microscopy we found a remarkable diversity in macrociliary size, tooth pattern, and distribution among “traditional” morphospecies of Beroe. These differences distinguish two major groups of Beroida. Group 1 includes most of the described nominal species [B. cucumis, B. abyssicola, B. ovata, B. gracilis, and B. sp. (Gloria)]. Their macrocilia are relatively small (typically 25–30 μm long, 5 μm diameter) and are restricted to a band around the inside of the lips. Two main types of macrociliary tooth patterns are found: 3–12 equally-sized teeth [B. cucumis (Mon), B. ovata, B. sp. (Gloria)] or 3 teeth with the middle tooth being larger (B. cucumis (CC), B. gracilis) or smaller (B. abyssicola). Group 2 species (B. forskali, B. mitrata) have greatly flattened bodies and wide mouths. Their macrocilia cover an extensive area of the stomodaeal cavity, and are longer and stouter (80–100 μm long, 12–15 μm in diameter). The shaft of the macrocilium is not hexagonal in transverse section, as in Group 1 species, but is wedge-shaped, being broader on the recovery-stroke (oral) side. The macrociliary tips are blunt and finely serrated, bearing one or more rows of 10–12 short teeth running at right angles to the beat plane. This diversity in macrociliary patterns is apparently related to differences in diet, feeding methods, and/or mechanism of prey digestion among various species. However, direct evidence for the functional significance of macrociliary diversity has not yet been obtained. The macrociliary patterns may be useful for clarifying problems of species identification and relationships within the Beroida. In particular, macrociliary differences found between and within traditionally distinguished morphospecies of Beroe raise the possibility of the existence of complexes of sibling species in this group.

Design of Ultra High Vacuum Scanning Electron Microscope Combined with Scanning Tunneling Microscope

AbstractAn ultra high vacuum (UHV) scanning electron microscope (SEM) combined with a scanning tunneling microscope (STM) has been designed and constructed to solve problems, arising from STM surface imaging and nanofabrication using STM tips, such as difficulty in probe tip location and change in tip shape. The system facilitates to image and/or to modify a wide range of area from submicron down to subnanometer. A ZrO/W thermal emitter in a Schottky mode has been used for an electron gun to obtain a low energy spread with a high angular current density. Minimum beam spot diameters of 6 and 12 nm with currents of 100 pA and 4 nA are estimated by optical property calculation for high resolution (SEM) and high current (fabrication) modes, respectively.