Variety Of Surface Morphologies Research Articles

Carbon-infiltrated carbon nanotubes inhibit the development of Staphylococcus aureus biofilms

Staphylococcus aureus forms biofilms that cause considerable morbidity and mortality in patients who receive implanted devices such as prosthetics or fixator pins. An ideal surface for such medical devices would inhibit biofilm growth. Recently, it was reported that surface modification of stainless steel materials with carbon-infiltrated carbon nanotubes (CICNT) inhibits the growth of S. aureus biofilms. The purpose of this study was to investigate this antimicrobial effect on titanium materials with CICNT coated surfaces in a variety of surface morphologies and across a broader spectrum of S. aureus isolates. Study samples of CICNT-coated titanium, and control samples of bare titanium, a common implant material, were exposed to S. aureus. Viable bacteria were removed from adhered biofilms and quantified as colony forming units. Scanning electron microscopy was used to qualitatively analyze biofilms both before and after removal of cells. The CICNT surface was found to have significantly fewer adherent bacteria than bare titanium control surfaces, both via colony forming unit and microscopic analyses. This effect was most pronounced on CICNT surfaces with an average nanotube diameter of 150 nm, showing a 2.5-fold reduction in adherent bacteria. Since S. aureus forms different biofilm structures by isolate and by growth conditions, we tested 7 total isolates and found a significant reduction in the biofilm load in six out of seven S. aureus isolates tested. To examine whether the anti-biofilm effect was due to the structure of the nanotubes, we generated an unstructured carbon surface. Significantly more bacteria adhered to a nonstructured carbon surface than to the 150 nm CICNT surface, suggesting that the topography of the nanotube structure itself has anti-biofilm properties. The CICNT surface possesses anti-biofilm properties that result in fewer adherent S. aureus bacteria. These anti-biofilm properties are consistent across multiple isolates of S. aureus and are affected by nanotube diameter. The experiments performed in this study suggest that this effect is due to the nanostructure of the CICNT surface.

The efficiency of Australian grindstones for processing seed: A quantitative experiment using reproduction implements and controlling for morphometric variation and grinding techniques

This paper presents a controlled experimental examination of the efficiency of Australian Aboriginal grindstones with a variety of surface morphologies in milling seeds into meal. Several replicate sandstone grindstones (large and small millstones with functional surfaces ranging in length from 43cm to 16cm and a mortar) were employed to process three domesticated commercial grains that serve as viable proxies for native grains. These were processed in 10min grinding sessions. Our results show that large millstones significantly outperform both the small millstones and the small mortar in the net output of ground grain. We also find that other factors may influence productivity, including the amount of wear and the seed being processed. These variations are of sufficient magnitude to have possibly influenced crucial economic decisions.

Light Trapping in Isotextured Silicon Wafers

We present an experimental investigation into light trapping within isotextured wafers. Measurements of reflectance and transmittance are performed on Si wafers both before and after the deposition of thin films on their surfaces. The wafers have a variety of surface morphologies that were created by varying the isotexture etch duration. We find that, unlike external reflectance, light trapping in isotextured wafers depends only weakly on the isotexture etch time (for practical etch durations). We also find that the light trapping induced by isotexture is similar to that induced by random pyramids. Moreover, we conclude that the spherical-cap model, which is extended to account for internal rays within the isotexture, can be applied to predict the transmittance and escape reflectance and, hence, the light trapping in isotextured wafers. By way of quantification, the model predicts the AM1.5g generation current to within ±1% and the reflectance and transmittance to within ±2% absolute for λ < 1100 nm (and to within ±4% for λ < 1200 nm for most samples). With an established light-trapping model, photovoltaic researchers can more accurately predict the behavior of isotextured solar cells for various antireflection coatings, encapsulants, and light sources.

Distal ejecta from lunar impacts: Extensive regions of rocky deposits

Lunar Reconnaissance Orbiter (LRO) Diviner Radiometer, Mini-RF, and LRO Camera data were used to identify and characterize rocky lunar deposits that appear well separated from any potential source crater. Two regions are described: 1) A ∼18,000 km2 area with elevated rock abundance and extensive melt ponds and veneers near the antipode of Tycho crater (167.5°E, 42.5°N). This region has been identified previously, using radar and imaging data. 2) A much larger and more diffuse region, covering ∼730,000 km2, centered near 310°E, 35°S, containing elevated rock abundance and numerous granular flow deposits on crater walls. The rock distributions in both regions favor certain slope azimuths over others, indicating a directional component to the formation of these deposits. The spatial distribution of rocks is consistent with the arrival of ejecta from the west and northwest at low angles (∼10–30°) above the horizon in both regions. The derived age and slope orientations of the deposits indicate that the deposits likely originated as ejecta from the Tycho impact event. Despite their similar origin, the deposits in the two regions show significant differences in the datasets. The Tycho crater antipode deposit covers a smaller area, but the deposits are pervasive and appear to be dominated by impact melts. By contrast, the nearside deposits cover a much larger area and numerous granular flows were triggered. However, the features in this region are less prominent with no evidence for the presence of impact melts. The two regions appear to be surface expressions of a distant impact event that can modify surfaces across wide regions, resulting in a variety of surface morphologies. The Tycho impact event may only be the most recent manifestation of these processes, which likely have played a role in the development of the regolith throughout lunar history.

Fabrication of broadband anti-reflective sub-micron structures using polystyrene sphere lithography on a Si substrate

Anti-reflective coatings are widely used on the surfaces of solar cells to increase the efficiency of photoelectric conversion. Sub-wavelength structures have gradually replaced conventional anti-reflective (AR) thin films due to their broadband AR properties. This paper successfully fabricated structures with a variety of surface morphologies on Si substrate using polystyrene sphere lithography in conjunction with two-step inductive coupling plasma (ICP) and high density plasma (HDP) etching processes. We successfully fabricated various sub-micron structures with heights of 700nm and above. Experimental results show that the sub-micron pyramidal structure has the best anti-reflection performance with the average reflectance effectively suppressed to below 1% across the spectral range of 300–1200nm.

Formation of pyramid-like nanostructures in MBE-grown Si films on Si(001)

The growth of Si homoepitaxial layers on Si(001) substrates by molecular beam epitaxy is analyzed for a set of growth conditions in which diverse nanometer-scale features develop. Using Si substrates prepared by exposure to HF vapor and annealing in ultra-high vacuum, a rich variety of surface morphologies is found for different deposited layer thicknesses and substrate temperatures in a reproducible way, showing a critical dependence on both. Arrays of 3D islands (truncated pyramids), percolated ridge networks, and square pit (inverted pyramid) distributions are observed. We analyze the obtained arrangements and find remarkable similarities to other semiconductor though heteroepitaxial systems. The nanoscale entities (islands or pits) display certain self assembly and ordering, concerning size, shape, and spacing. Film growth sequence follows the ‘islands–coalescence–2D growth’ pathway, eventually leading to optimum flat morphologies for high enough thickness and temperature.

Review Article: Hydrogen blistering of silicon: Progress in fundamental understanding

AbstractThe understanding of blistering mechanisms at the fundamental, atomic‐scale level is still not complete, but large strides towards that goal have been made in the last decade. In this issue's Review Article [1] Bernard Terreault gives a comprehensive survey of this progress, discussing the current questions as well as outlining suggestions for future work.The related cover picture shows atomic force micrographs of a variety of surface morphologies obtained by hydrogen ion implantation into silicon followed by rapid thermal annealing. In this particular case, the ions were implanted through PMMA masks of decreasing width (from left to right, 6 μm, 1 μm, 600 nm and 150 nm) [2]. This is but one application of blistering, the most common being ion‐cutting and layer transfer as used in the commercial production of silicon‐on‐insulator wafers.The author is Honorary retired Professor at the EMT (Energy, Materials, Telecom) Center of the Institut National de la Recherche Scientifique (Université du Québec).Another feature included in the current issue is the Editor's Choice contribution ‘Optical and micro‐analytical study of a copper–conjugated polymer composite’ by Kaushik Mallik et al. [3], where the authors investigate a nanoscale fiber network for potential application in microelectronic systems.

X-ray diffraction mapping of strain fields and chemical composition of SiGe:Si(001) quantum dot molecules

A variety of surface morphologies can be formed by controlling kinetic parameters during heteroepitaxial film growth. The system reported is a ${\mathrm{Si}}_{0.7}{\mathrm{Ge}}_{0.3}$ film grown by molecular beam epitaxy at $550\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ and a $1\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}∕\mathrm{s}$ deposition rate, producing quantum dot molecule (QDM) structures. These nanostructures are very uniform in size and shape, allowing strain mapping and chemical composition evaluation by means of anomalous x-ray diffraction in a grazing incidence geometry. Tensile and compressed regions coexist inside QDMs, in accordance with the finite-element calculations of lattice relaxation. The Ge content was found to vary significantly within the structures, and to be quite different from the nominal composition.

Influence of deposition parameters on morphological properties of biomedical calcium phosphate coatings prepared using electrostatic spray deposition

In order to deposit biomedical calcium phosphate (CaP) coatings with a defined surface morphology, the electrostatic spray deposition (ESD) technique was used since this technique offers the possibility to deposit ceramic coatings with a variety of surface morphologies. A scanning electron microscopical study was performed in order to investigate the influence of several deposition parameters on the final morphology of the deposited coatings. The chemical characteristics of the coatings were studied by means of X-ray diffraction and Fourier-transform infrared spectroscopy. Regarding the chemical coating properties, the results showed that the coatings can be described as crystalline carbonate apatite coatings, a crystal phase which is similar to the mineral phase of bone and teeth. The morphology of CaP coatings, deposited using the ESD technique, was strongly dependent on the deposition parameters. By changing the nozzle-to-substrate distance, the precursor liquid flow rate and the deposition temperature, coating morphologies were deposited, which varied from dense to highly porous, reticular morphologies. The formation of various morphologies was the result of an equilibrium between the relative rates of CaP solute precipitation/reaction, solvent evaporation and droplet spreading onto the substrate surface.

Microstructure and properties of CVD tungsten carbide from tungsten hexafluoride and dimethyl ether

Tungsten carbide was deposited from tungsten hexafluoride, dimethyl ether, and hydrogen using a horizontal, cold-wall reactor. The effects of substrate temperature, reactor pressure, and reagent ratio on the coating growth rate, morphology, composition, and microhardness were studied. Under most conditions, the solid deposit was primarily W 3C with minor amounts of W. The tungsten carbide growth rate data fit an Arrhenius rate expression for temperatures from 425 to 550°C and had an activation energy of 24kcal/mol at 70mmHg total pressure and a WF 6/DME ratio of 6.3. A variety of surface morphologies and microstructures were observed. The microhardness of the coated substrates increased with coating thickness to a maximum value of 2400kg/mm 2.

Reactions between Clay Volatiles and Calcite Reinvestigated

AbstractCalcite crystals exposed to clay volatiles react with some components of these volatiles, giving rise to a variety of surface morphologies. F, Cl, and S in different proportions were detected by electron microprobe analysis of the calcite surfaces. Under identical experimental conditions, volatiles from every clay mineral examined caused a specific morphology and chemical composition of the calcite surfaces, but these varied with temperature of the calcite. Changes in pH values and mass spectra of the volatiles after passage through calcite demonstrate that even on rapid heating some clay volatile-calcite reactions occur at temperatures as low as 150°C. Species other than those detectable by electron microprobe analysis also participate in the reactions in which CO2 is liberated.