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A study has been conducted on the pulsed laser deposition (PLD) of transition metal carbides in order to examine alloying and phase formation in binary systems. Alternating layers of TiC/ZrC and ZrC/VC were deposited at 400 C and 5 mTorr Ar with nominal period thicknesses of 0.6 nm, 10.0 nm, and 50.0 nm. ZrC/VC x-ray diffraction analysis showed that the alloys were amorphous and the TiC/ZrC alloys were crystalline. The thicker films showed a higher degree of phase separation of the two compounds. Transmission electron microscopy confirmed the amorphous structure in the 0.6 nm ZrC/VC film, while the 50.0 nm film showed a layered structure and extremely fine grain size.

InGaN layers grown by molecular beam epitaxy are investigated in terms of their compositional homogeneity using transmission electron microscopy and cathodoluminescence spectroscopy performed with high spatial resolution. Strong fluctuations of the indium content were found in bulk-like layers, which could be partially reduced by modulating the indium flux during growth, i. e. by nominally growing a short period GaN/InGaN superlattice. For indium compositions above x ≠ 0.1 this approach fails. Strained InGaN in quantum wells exhibits lateral fluctuations on an atomic scale and on a scale of several hundred nanometers. The results are discussed in view of the origin of inhomogeneous indium incorporation.

The ability to tailor thin film interface structure is illustrated by the growth of thin ferric oxide films using different deposition parameters. Low-pressure chemical vapor deposition (CVD) has been used to grow α-Fe2O3 on sapphire while pulsed-laser ablation (PLA) followed by low temperature oxidation has been used to grow γ-Fe2O3 on MgO. The structure of the films and of the film-substrate interfaces has been characterized using transmission electron microscopy (TEM) and selected-area diffraction (SAD) in plan view. The different deposition techniques lead not only to the growth of two different polymorphs of ferric oxide but also to different growth mechanisms and film-substrate interface structures. In addition, changes in the thermodynamic conditions during deposition can give rise to different interface structures between the individual structural domains of the film.

Appropriate selection of long endurance materials is critical to the cost effective use of fuel cell technology for near-term commercial and defense applications. To effectively transition this technology from laboratory prototype to fielded system, the durability of all fuel cell subsystems must be addressed. Material selection based upon a thorough understanding of system performance requirements, operational environments, and user interfaces not only provides high reliability and enhanced safety, but also lowers life cycle costs. This paper discusses the development of an Aluminum Fuel Cell Power System (FCPS) for the Advanced Research Projects Agency (ARPA) Unmanned Underwater Vehicle (UUV) program, focusing on the operational endurance testing that was conducted to evaluate candidate materials for cell stack, electrolyte, and coolant subsystems. The FCPS is a 15 kW closed aluminum-oxygen fuel cell system that provides up to 1.1 MWh energy. Loral has completed small-scale bench tests and is currently fabricating a full-scale system to be demonstrated in 1995. Requirements that strongly influenced material selection included: chemical compatibility - 4M KOH electrolyte pumped at 50°C, with dissolved aluminum and hydrargillite; system operational objectives - time between refueling and maintenance ranging from daily startup / shutdown to three weeks continuous; ARPA program objectives - commercial components, rapid prototyping, low life cycle costs. A materials / component endurance test program was established and conducted early in the design phase of the FCPS program. To date, Loral has completed over 3000 operational test hours, with nearly 8000 hours of accumulated exposure to KOH. Results of these tests have been incorporated into the FCPS detailed design, and are expected to significantly enhance the performance of the fielded system. This program is sponsored by ARPA Maritime Systems Technology Office under NASA contract NAS3-26715.

We discuss changes in electronic structure and the topography of a graphite surface undergoing by a single ion impact. Protrusion-like regions (PLRs) found in a scanning tunneling microscope image disappeared in the same view of a noncontact atomic force microscope image. We measured tunneling current versus voltage characteristics to determine the density-of-states change in PLRs. We found that the density of states at the Fermi level of PLRs was greater than that of the intact surface. We therefore concluded that the PLRs were not actual topographical changes, but originated from electronic structural changes in semimetal to metal transition.

In an effort to develop an emissivity independent temperature measurement technique for the AST Rapid Thermal Processor (RTP), AST has conceived of the Hot Liner™. The Hot Liner is a silicon nitride coated silicon wafer which is permanently installed in the process chamber, immediately below the wafer. The pyrometer, which is calibrated to a production wafer, views the constant emissivity Hot Liner to produce repeatable temperatures on product wafers regardless of their backside emissivity. Given the repeatability of the Hot Liner, the wafer temperature uniformity must then be optimized in order to achieve 0.25μm capable processing. AST has developed a methodology which incorporates process monitors (ion implanted test wafers) to establish process uniformity in addition to multiple thermocouple wafers to verify across wafer temperature uniformity. The process monitors are used to separately optimize the ramp and steady state steps in the production recipe. Utilizing the AST methodology to optimize processing with the Hot Liner has allowed AMD to significantly improve its RTA processing. The Hot Liner greatly decreases backside and pyrometer effects which yields limited wafer to wafer variation (<5C, 3σ). In combination with the optimization process this results in excellent within wafer uniformity (<3C, 3σ).

In this letter we report the transition from self-assembled InAs quantum-wires to quantum-dots grown on (100) InP substrates. This transition is obtained when the wires are annealed at the growth temperature. Our results suggest that the quantum-wires are a metastable shape originated from the anisotropic diffusion over the InP buffer layer during the formation of the first InAs monolayer. The wires evolve to a more stable shape (dot) during the annealing. The driving force for the transition is associated with variations in the elastic energy and hence in the chemical potential produced by height fluctuations along the wire. The regions along the wires with no height variations are more stable allowing the formation of complex, self-assembled nanostructures such as dots interconnected by wires.

Fe0.1Sc0.9N with a thickness of ˜~ 380 nm was grown on top of a ScN(001) buffer layer of ˜~ 50 nm, grown on MgO(001) substrate by radio-frequency N-plasma molecular beam epitaxy (rf-MBE). The buffer layer was grown at TS ˜~ 800 °C, whereas the Fe0.1Sc0.9N(001) film was grown at TS ~˜ 420 °C. In-situ reflection high-energy electron diffraction measurements show that the Fe0.1Sc0.9N film growth starts with a combination of spotty and streaky pattern [indicative of a combination of smooth and rough surface]. After ˜~ 10 minutes of growth, the pattern converts to a spotty one [indicative of a rough surface]. Towards the end of the Fe0.1Sc0.9N film growth, the spotty patterns transform into even spottier, but also ring-like indicating a polycrystalline behavior. Superconducting quantum interference device magnetic measurements show a ferromagnetic to paramagnetic transition of TC ˜~ 370–380 K. We calculated a magnetic moment per atom of μ(Fe0.1Sc0.9N) = 0.037 Bohr magneton/Fe-atom. Based on the carrier concentration measurements (nS (Fe0.1Sc0.9N) = 2.086 × 1019 /cm3), we find that iron behaves as an acceptor. Comparisons are made with similar MnScN (001)/ScN(001)/MgO(001) system.