ARL-WMRD

The tribological behavior of titanium carbide (Tic) thin films grown by excimer pulsed laser deposition (PLD) was investigated. The purpose of this work was to evaluate the effects of film deposition temperature, substrate hardness, and counterface hardness on the friction and wear behavior of the TiC films. Films were grown at room temperature (RT) and at 300°C. Substrate hardness was varied by selecting the heat treatments of the 440C stainless steel (SS) disks; the counterface. hardness was varied through materials selection (e.g. hardened 440C SS and sapphire). Friction coefficients and wear lives were determined for each film/substrate/ counterface configuration. The wear surfaces were investigated by optical and scanning electron microscopy.

Films of MoS2 were grown at various thicknesses onto silicon substrates at room temperature using pulsed laser deposition. Planar and cleaved cross-sectional samples examined in a scanning electron microscope showed that very thick films (thicker than about 450 nm) transitioned from being fully dense to having extensive porosity. The porosity is directly correlated with the accumulated incorporation of spherical particles within the film. Transmission electron microscopy (TEM) results from samples of differential thicknesses, acquired from early and later stages of deposition, showed that the volume fraction of the particles increased with the thickness. Decreasing the energy density of the laser beam by underfocusing relative to the target was shown to decrease dramatically the number of particles. Simulation of the deposition process by adding digitized, binary TEM images of the differential thickness samples, to an equivalent thickness of 450 nm, indicated that the porosity begins at a total particle projected area fraction of about 35%.

Pulsed laser deposition was used to produce hydrogen-free amorphous diamondlike carbon (a-C) and hydrogenated amorphous diamondlike carbon (a-C:H) from graphite and polycarbonate targets, respectively. Films were grown under identical conditions in high vacuum at low temperatures onto steel and Si substrates. The a-C films were uniform, while a-C:H films contained a great number of particles ejected from the target surface. The a-C films have hydrogen contamination about 0.1 at. %, while a-C:H have about 25 at. % H and 10 at. % O. High percentages of sp 3 bonding were found in both films. Film densities were estimated to be 3.0 g cm Ϫ3 for a-C films and 2.2 g cm Ϫ3 for a-C:H films. Chemical and structural characteristics of the films were correlated with their thermal stability and mechanical properties. Temperatures for starting graphitization were about 500°C for a-C and 350°C for a-C:H. The presence of hydrogen reduced film hardness from 60 GPa for a-C films to 14 GPa for a-C:H films. Hydrogen was also associated with dependence of a-C:H films friction coefficient on environment and with higher wear rates of a-C:H films in comparison to a-C films.

The growth of low temperature (LT) GaAs by molecular beam epitaxy has been studied using ellipsometryo Different regimes of growth were observed in the data, depending on film thickness. Epitaxial growth ofpseudomorphic LT-GaAs occurred immediately above the substrate, followed by a layer with changing dielectric properties. This upper layer can be modeled as a two-phase region consisting ofepitaxial LT-GaAs and small grained, polycrystalline GaAs, which increases in volume fraction with increasing layer thickness. For sufficiently thick LT layers, cross-sectional transmission electron microscopy analysis showed pyramidal defects that were composed primarily of highly twinned regions. The ellipsometry data showed a deviation from the homogeneous growth model at a thickness less than the thickness at which the pyramidal defects nucleated in all samples.

Current generation field emission SEM have resolutions around 1 nm at 15 kV and a few namometres at 1 kV. These capabilities allow the critical imaging of nanostructures, many of which are poor or non-conductive. Consequently conductive coatings are now required to have minimal or no resolvable structure at the nanometre scale. These conductive films also need to be both stable for a reasonable period of time and insensitive to plasma cleaning. This project presents results of the study of a range of thin film metal coatings using FEG SEM and FEG TEM.

Sample preparation for cross-sectional examination of coatings and thin films by transmission electron microscopy (TEM) is the most critical step of this characterization technique. Without a sufficiently thin sample with a minimum of artifacts, some of the high-resolution imaging and analytical techniques available in the modern analytical TEM cannot be utilized. Frequently, the cross-sectional TEM (XTEM) sample preparation step requires special instrumentation, extensive technical skills, and long lead times. The small angle cleavage technique (SACT) has been successfully applied to various semiconductor materials. It has the advantage of being a very fast, inexpensive, and easy technique for XTEM sample preparation. In addition, it produces a sample with very clean surfaces without ion milling. In this paper, the technique will be briefly described. The technique can be easily accommodated into any specimen preparation laboratory. Results for single-layered and multi-layered coatings and thin films deposited on semiconductor and non-semiconductor substrates including Si, GaAs, sapphire, quartz, SiC, and glass are shown to illustrate the flexibility of the technique. The technique does not always work. Examples of materials systems in which it was not possible to make a suitable sample are given, and the reasons for the failure are discussed. Published by Elsevier Science S.A.

Precipitation in alloy 718, a Ni-Cr-Fe based superalloy with Nb additions, was studied as a function of heat treatment with specific reference to grain boundary precipitation. Three different heat treatments were studied; a low temperature precipitation treatment (1 h at 650 °C) typical of age hardening, a high temperature precipitation treatment (1 h at 930 ° C) typical of solution anneal and a homogenization treatment (1 h at 1100 ° C). It was observed that grain boundary precipitation was dependent on the location of the boundary relative to the dendritic solidification pattern of the alloy. The same grain boundary exhibited a change in precipitation behavior as it passed from a dendritic core into the interdendritic region. In general, niobium carbides (NbC) were observed to be located on the grain boundaries in the Nb-depleted core region, while Nb-rich precipitates which included NiaNb (8), Ni3Nb (3/'), laves, and NbC were observed in the Nb-enriched interdendritic region. The grain boundaries in the interdendritic region contained 8 precipitated in a discontinuous manner.

Résume: Cet article est un compte rendu des premières étapes de nos travaux concernant la capture de l'hydrogène par les défauts du réseau métallique. Les imperfections de structure, ainsi que l'hydrogène, sont introduits par implantation ionique. La plupart des résultats tournent autour de la caractérisation des défauts structuraux par utilisation des techniques FIM et TEM. La faisabilité de l'application de 1'IAP à l'étude de l'interaction hydrogène/défaut est aussi discutée.

Phyllosilicates are difficult phases to characterize using electron backscatter diffraction (EBSD), as they tend to yield poor diffraction patterns. The underlying cause of this problem is under debate, however, prior studies point to poor sample surface preparation and problems inherent in the phyllosilicate structure. Traditional protocol for sample surface preparation for EBSD involves stepwise mechanical polishing followed by chemical mechanical polishing. Although variations of this procedure have proven relatively successful, problems still exist when preparing polyphase materials that pair soft and hard phases, i.e. mica and quartz. Ion milling is a technique ideally suited for EBSD sample preparation as it offers the ability to smooth sample surface topography and remove subsurface damage induced by mechanical polishing. We explore the viability of this method as a final step in preparing polyphase, mica-bearing geological materials for EBSD analysis. We prepared a suite of ...

Cellulose nanofibrils (CNFs) are a class of cellulosic nanomaterials with high aspect ratios that can be extracted from various natural sources. Their highly crystalline structures provide the nanofibrils with excellent mechanical and thermal properties. The main challenges of CNFs in nanocomposite applications are associated with their high hydrophilicity, which makes CNFs incompatible with hydrophobic polymers. In this study, highly transparent and toughened poly(methyl methacrylate) (PMMA) nanocomposite films were prepared using various percentages of CNFs covered with surface carboxylic acid groups (CNF-COOH). The surface groups make the CNFs interfacial interaction with PMMA favorable, which facilitate the homogenous dispersion of the hydrophilic nanofibrils in the hydrophobic polymer and the formation of a percolated network of nanofibrils. The controlled dispersion results in high transparency of the nanocomposites. Mechanical analysis of the resulting films demonstrated that...

With the new "L" brackets that are available for the Tripod Polisher™ (South Bay Technology, Inc.) which allow the sample to be easily backlit with room lights, it is relatively easy to grind away most of the material to be removed when polishing the second side of a sample. The following steps outline the procedure that I have been using for rapidly removing material and getting the samples very thin prior to starting the final wedge polishing. The samples that I have been preparing with this technique are approximately 1µm thick, pulsed laser deposited ZnO-WS2 films on SiC substrates.

The Small Angle Cleavage Technique (SACT) developed by John McCaffrey is an extremely easy and cost-effective technique for producing superior cross sectional TEM samples from semiconductor and other single crystal materials. In the original technique, a special jig is required to be made in order to make too cuts in a 2 x 0.5 mm slotted capper TEM grid to create vertical tabs to mount the cleaved samples. This jig is not commercially available and the actual cutting and bending of the grids require a significant amount of manual dexterity. (Fat fingered fellows, like myself, need not apply.) Early on, John proposed a design for a commercial grid that could easily be bent into the required shape with no cutting, but the electron microscopy supply houses passed on the idea. Until now, microscopists wanting to experiment with the technique had to invest in the cost of having one of these jigs made.

Clostridium acetobutylicum has traditionally been used for production of acetone, butanol, and ethanol (ABE). Butanol is a commodity chemical due in part to its suitability as a biofuel; however, the current yield of this product from biological systems is not economically feasible as an alternative fuel source. Understanding solvent phase physiology, solvent tolerance, and their genetic underpinning is key for future strain optimization of the bacterium. This study shows the importance of a [NiFe]-hydrogenase in solvent phase physiology. C. acetobutylicum genes ca_c0810 and ca_c0811, annotated as a HypF and HypD maturation factor, were found to be required for [NiFe]-hydrogenase activity. They were shown to be part of a polycistronic operon with other hyp genes. Hydrogenase activity assays of the ΔhypF/hypD mutant showed an almost complete inactivation of the [NiFe]-hydrogenase. Metabolic studies comparing ΔhypF/hypD and wild type (WT) strains in planktonic and sessile conditions i...