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Advancing age is a well-known risk factor for tendon disease. Energy-storing tendons [e.g., human Achilles, equine superficial digital flexor tendon ( SDFT)] are particularly vulnerable and it is thought that injury occurs following an accumulation of micro-damage in the extracellular matrix ( ECM). Several authors suggest that age-related micro-damage accumulates due to a failure of the aging cell population to maintain the ECM or an imbalance between anabolic and catabolic pathways. We hypothesized that ageing results in a decreased ability of tendon cells to synthesize matrix components and matrix-degrading enzymes, resulting in a reduced turnover of the ECM and a decreased ability to repair micro-damage. The SDFT was collected from horses aged 3-30 years with no signs of tendon injury. Cell synthetic and degradative ability was assessed at the mRNA and protein levels. Telomere length was measured as an additional marker of cell ageing. There was no decrease in cellularity or relative telomere length with increasing age, and no decline in mRNA or protein levels for matrix proteins or degradative enzymes. The results suggest that the mechanism for age-related tendon deterioration is not due to reduced cellularity or a loss of synthetic functionality and that alternative mechanisms should be considered. [ABSTRACT FROM AUTHOR]

Presents a study which demonstrated a heterojunction bipolar transistor using a novel compound collector design that allows a low-knee voltage and high-breakdown voltage to be obtained simultaneously. Advantages of double-heterojunction bipolar transistors; Methodology; Results.

The influence of surface chemical treatments and of deposition of a SiO[sub 2] surface passivation layer on carrier distributions and mobility in Al[sub x]Ga[sub 1-x]N/GaN heterostructure field-effect-transistor epitaxial layer structures is investigated. Surface chemical treatments are found to exert little influence on carrier distribution and mobility. Deposition of a SiO[sub 2] surface passivation layer is found to induce an increase in electron concentration in the transistor channel and a decrease in mobility. These changes are largely reversed upon removal of the SiO[sub 2] layer by wet etching. These observations are quantitatively consistent with a shift in Fermi level at the Al[sub x]Ga[sub 1-x]N surface of approximately 1 eV upon deposition of SiO[sub 2], indicating that the Al[sub x]Ga[sub 1-x]N/SiO[sub 2] interface has a different, and possibly much lower, density of electronic states compared to the Al[sub x]Ga[sub 1-x]N free surface. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ga-As-In-As superalloy has been grown by atomic epitaxy on InP substrates. This has been achieved by sequential exposure of the substrate to trimethylgallium, arsine, triethylindium, and arsine. The thickness of the deposited film is in excellent agreement with the predicted value based on the number of exposure cycles. These results demonstrate that atomic layer epitaxy offers the ultimate control for depositing thin films. The superalloy films have been characterized by transmission electron microscopy and photoluminescence. [ABSTRACT FROM AUTHOR]

We report on the successful growth of ordered GaInP by atomic layer epitaxy on a GaAs substrate. The growth was achieved by alternate exposures to TEI, PH3, TMGa, and PH3 fluxes, and epilayers were found to closely match the GaAs substrate irrespective of the growth conditions. Room-temperature photoreflectance results indicate a band gap of 1.78 eV, the lowest value yet reported for such ordered alloys. Photoluminescence shows an anomalous temperature dependence behavior and transmission electron microscopy studies indicate that ordering takes place preferentially on (111) alternating planes. [ABSTRACT FROM AUTHOR]

Atomic layer epitaxy has been used for the low-temperature deposition of planar-doped structures using organometallic sources AsH3 and H2Se. Carrier concentration in the 1019/cm3 range was achieved, with a sharp concentration profile comparable to the best reported for equivalent structures by molecular beam epitaxy. A set of planar-doped Se sheets, separated by 50 Å of GaAs, was used for nonalloyed contacting layers to n-GaAs films with contact resistivity in the low 10-6 Ω cm2 range. Finally, a planar-doped field-effect transistor (FET) was fabricated with planar-doped sidewall source and drain contacting layers, giving a performance comparable to that of reported planar-doped structures by other techniques. This is considered to be the first demonstration of a planar-doped FET using organometallic sources. [ABSTRACT FROM AUTHOR]

Atomic layer epitaxy (ALE) has successfully been used to grow epitaxial layers over chemically etched grooves and dry etched sidewalls formed on GaAs(100) substrates. GaAs/InGaAs multilayers were deposited on V-shaped and inverted trapezoid-shaped grooves that were 4–5 μm deep and 8–20 μm wide. Growth conforming to the original sidewall surfaces was accomplished both on the chemically etched and on ion beam assisted etched surfaces. These features show distinct improvement over similar attempts by metalorganic chemical vapor deposition or molecular beam epitaxy. The ability of ALE to proceed in a self-limiting fashion on such structures is expected to lead to the realization of novel device concepts. [ABSTRACT FROM AUTHOR]

Ballistic-electron-emission microscopy (BEEM) and spectroscopy have been used to investigate the properties of Au/GaN interfaces. The effects of in situ and ex situ annealing on the starting GaN surface were examined, with the aim of increasing the surprisingly low value of interface electron transmission observed in previous BEEM measurements. BEEM imaging and spectroscopy have demonstrated that much higher, more uniform transmission across the Au/GaN interface can be achieved. However, while methods were identified that increase transmission by more than an order of magnitude, BEEM spectroscopy indicates that annealing can substantially alter the Schottky barrier height. These barrier height changes at moderate temperatures are attributed to vacancy diffusion. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ballistic-electron-emission microscopy (BEEM) spectroscopy and imaging have been applied to the Au/GaN interface. In contrast to previous BEEM measurements, spectra yield a Schottky barrier height of 1.04 eV that agrees well with the highest values measured by conventional methods. A second threshold is observed in the spectra at about 0.2 V above the first threshold. Imaging of the Au/GaN interface reveals transmission in nearly all areas, although the magnitude is small and varies by an order of magnitude. BEEM of other GaN material shows no transmission in any areas. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]