Paul M. Adams

First use of an airborne thermal infrared hyperspectral scanner for compositional mapping

In May 1999, the airborne thermal infrared hyperspectral imaging system, Spatially Enhanced Broadband Array Spectrograph System (SEBASS), was flown over Mormon Mesa, NV, to provide the first test of such a system for geological mapping. Several types of carbonate deposits were identified using the 11.25-μm band. However, massive calcrete outcrops exhibited weak spectral contrast, which was confirmed by field and laboratory measurements. Because the weathered calcrete surface appeared relatively smooth in hand specimen, this weak spectral contrast was unexpected. Here we show that microscopic roughness not readily apparent to the eye has introduced both a cavity effect and volume scattering to reduce spectral contrast. The macroroughness of crevices and cobbles may also have a significant cavity effect. The diminished spectral contrast is important because it places higher signal-to-noise ratio (SNR) requirements for spectroscopic detection and identification. This effect should be factored into instrumentation planning and interpretations, especially interpretations without benefit of ground truth. SEBASS had the required high SNR and spectral resolution to allow us to demonstrate for the first time the ability of an airborne hyperspectral thermal infrared scanner to detect and identify spectrally subtle materials.

Low temperature pulsed laser deposition of titanium carbide on bearing steels

This study focuses on the room temperature pulsed laser deposition (PLD) of titanium carbide (TiC), as a wear-resistant coating on 52100 and 440C bearing steels. The TiC films have been characterized using a variety of analytical techniques. Atomic force and scanning electron microscopy have revealed the deposition of extremely smooth TiC films, having very high uniformity over large areas. Selected area electron diffraction in transmission electron microscopy has shown an excellent correlation between the observed lattice spacings in the deposited films and the reported literature values of TiC. The crystallite size of these films has been established by dark field transmission electron microscopy. The chemical composition and mechanical properties of these films were also investigated. Room-temperature PLD has been successful in depositing high-quality TiC films on bearing steel components, thus avoiding numerous problems that arise during conventional high-temperature deposition of such coatings on steels.

Integrated TiC coatings for moving MEMS

The application of wear-resistant coatings to microelectromechanical systems (MEMS) devices offers the potential of addressing the reliability of moving MEMS devices. However, coating non-line-of-sight, concealed surfaces in fully released 3D MEMS structures, especially those behind micron-sized apertures, is a difficult problem to overcome with most deposition techniques. A practical and viable solution to this problem is the direct integration of wear-resistant coatings into the MEMS fabrication process. Using this approach we have inserted pulsed-laser-deposited titanium carbide (TiC) coatings between critical polysilicon interfaces during fabrication of a MEMS device. This paper describes the details of inserting laser-ablated TiC coatings into a user-friendly surface micromachining process for MEMS to protect key sliding Si surfaces in MEMS motors. This hybrid technology is an effective way of inserting wear-resistant coatings such as TiC into the MEMS fabrication scheme.

Liquid Crystal Orientation on Carbon Fibers

Abstract The orientation of 4-methoxybenzylidene-4′-n-butylaniline (MBBA) on four different carbon fibers has been investigated by X-ray diffraction. The diffraction patterns show that the MBBA liquid crystal is oriented in the direction of the fiber for all of the fibers studied. Scanning electron microscopy (SEM) of the fiber surfaces reveals grooves along the fiber axis which may cause orientation of the MBBA. The degree of MBBA orientation seems independent of the size and parallelism of the grooves. These results suggest that the preparation of composites with oriented polymer matrices is possible by using liquid crystalline monomers.

Optical and structural characterization of heavily boron-implanted CdTe

Abstract CdTe single crystals were subjected to multiple-energy boron ion implants with total doses up to 1.5×10 16 B + ions/cm 2 . Various diagnostic techniques were used to assess the structural and electronic properties of these crystals in their as-implanted condition and after anneals under vacuum. The degradation of crystallinity following the boron implants was clearly evident. Annealing temperatures up to 500°C were not effective to remove the damage from these heavy dose implants. The chosen boron implant conditions and annealing procedures have not produced substitutional boron donor centers. Excellent correlations were obtained for model calculations of boron projected range and implant damage profiles with the corresponding experimental parameters.

Studies of interdiffusion in Ge m Si n strained layer superlattices

We present the results on the characterization and interdiffusion behavior of GemSin strained layer superlattices (SLS’s) composed of alternating monolayers of pure Ge and pure Si. Such GemSin SLS’s were grown on top of thick relaxed GeySi1-y buffer layers so as to symmetrize the strain distribution and to maintain the pseudomorphic growth of the superlattices. Samples with different superlattice periodicities (i.e. d = dGe + dSi and different layer thickness ratios (i.e. dGe:dSi were prepared for comparison. Raman scattering spectroscopy and x-ray diffraction were used to characterize these samples. Initial results on thermal stability of these GemSin SLS’s are also reported

Pulsed laser deposited Si on multilayer graphene as anode material for lithium ion batteries

Pulsed laser deposition and chemical vapor deposition were used to deposit very thin silicon on multilayer graphene (MLG) on a nickel foam substrate for application as an anode material for lithium ion batteries. The as-grown material was directly fabricated into an anode without a binder, and tested in a half-cell configuration. Even under stressful voltage limits that accelerate degradation, the Si-MLG films displayed higher stability than Si-only electrodes. Post-cycling images of the anodes reveal the differences between the two material systems and emphasize the role of the graphene layers in improving adhesion and electrochemical stability of the Si.

Investigation of the electromagnetic interference shielding of titanium carbide coated nanoreinforced liquid crystalline polymer

The development and analysis of electrical and electromagnetic interference shielding effectiveness of titanium carbide (TiC)-coated carbon nanofiber (CNF) reinforced liquid crystalline polymer composites are presented. The studied samples consisted of different weight percentages (5, 10, and 15 wt %) of CNFs distributed and dispersed homogeneously within the polymeric matrix. A titanium carbide layer was deposited using pulsed laser deposition, and was conducted at room temperature, which eliminated possible thermal degradation of the polymer matrix. The effect of the thickness of the TiC layer on the electrical properties of the polymeric composites was analyzed. A synergistic behavior between the TiC coating and the polymer composite was observed for samples containing 10 wt % of NFs (within the percolation range), and the ability of the composite to shield electromagnetic interference was increased by 20–30 db.

Alignment of Nematic and Smectic A Liquid Crystals on Carbon, Organic and Inorganic Fibers

Abstract The spontaneous alignment of nematic and smectic A liquid crystals on oriented and unoriented fibers has been investigated. The alignment of two nematic liquid crystals, 4-methoxybenzylidene-4′-n-bu-tylaniline (MBBA) and 4′-pentyl-4-biphenylcarbonitrile (5CB), and a commercial smectic A liquid crystal mixture, BN/75A, on a series of carbon, organic and inorganic fibers has been characterized by X-ray diffraction. We have discovered that all of the liquid crystals aligned uniformly parallel to the axes of oriented carbon and organic fibers (coaxial alignment), but were unaligned on the unoriented inorganic fibers. We hypothesize that the uniform alignment of the liquid crystals resulted from the influence of oriented microscopic grooves and/or oriented nanoscale features such as polymer crystallites or carbon fiber basal plane edges. All of the oriented fibers except Kevlar 49 have both surface grooves visible at 5000X and a high degree of molecular orientation. The alignment of the liquid crystal...

Surface functionalization of graphenelike materials by carbon monoxide atmospheric plasma treatment for improved wetting without structural degradation

Oxygen plasma treatment has been extensively used to functionalize the surface of graphenelike materials. However, functionalization is usually accompanied by degradation of the structure, which may affect mechanical and electrical performance. Atmospheric plasma treatment (APT) of HOPG was performed to compare the effect of surface modification using carbon monoxide (CO) as the active gas, in comparison to O2. Both Raman and STM demonstrated nanoscale degradation of the structure when using the O2 treatment. CO treated specimens exhibited no observable damage to the material with high levels of oxygen incorporation. Instead, a well ordered monolayer of oxygen-containing film was observed on the surface of the specimens which could accommodate high levels of surface oxygen. Changes in surface characteristics were analyzed using x-ray photoelectron spectroscopy (XPS) as a function of duration. The results indicated that the use of O2 plasma resulted in only a limited oxygen uptake (O/C = 0.11), while CO AP...