J Hastie | PubMed Health

PubMed2002

Characterization of nitride thin films by electron backscatter diffraction.

Thin films incorporating GaN, InGaN and AlGaN are presently arousing considerable excitement because of their suitability for UV and visible light-emitting diodes and laser diodes. However, because of the lattice mismatch between presently used substrates and epitaxial nitride thin films, the films are of variable quality In this paper we describe our preliminary studies of nitride thin films using electron backscattered diffraction (EBSD). We show that the EBSD technique may be used to reveal the relative orientation of an epitaxial thin film with respect to its substrate (a 90 degrees rotation between a GaN epitaxial thin film and its sapphire substrate is observed) and to determine its tilt (a GaN thin film was found to be tiltedby 13 +/- 1 degrees towards [1010]GaN), where the tilt is due to the inclination of the sapphire substrate (cut off-axis by 10 degrees from (0001)sapphire towards (1010)sapphire). We compare EBSD patterns obtained from As-doped GaN films grown by plasma-assisted molecular beam epitaxy (PA-MBE) with low and high As4 flux, respectively. Higher As4 flux results in sharper, better defined patterns, this observation is consistent with the improved surface morphology observed in AFM studies. Finally, we show that more detail can be discerned in EBSD patterns from GaN thin films when samples are cooled.

Journal Article↗

PubMed2001

The Alaska Native diabetes program.

OBJECTIVES: To provide optimum health care to indigenous people with diabetes, to prevent diabetes, and to monitor the epidemiology of diabetes and selected complications. The purposes of this paper are to describe the program and to present data that highlights the major problems and successes. STUDY DESIGN: Descriptive epidemiology report of diabetes and population service program based on yearly chart review data. METHODS: Almost half of Alaska Natives with diabetes have no direct access to physicians or hospitals. Health care delivery is now managed by the tribes themselves. Program emphases include maintenance of a population-based registry, formal training for village health aides, physical activity programs, patient education, primary prevention activities and adherence to standards of care to prevent complications. A centralized registry is maintained to assure that epidemiological data is available and patients are not lost to follow-up. Each year a random sample of charts at each major facility is audited against nationally standardized care guidelines. RESULTS: The prevalence of diabetes among Alaska Natives increased 80% over the 13 years from 1985 to 1998 (15.7/1000 to 28.3/1000, age adjusted to U.S. 1980 population). For the years 1986-1998 the incidence rates of lower extremity amputation and end stage renal disease were 6.1/1000 and 2.0/1000 respectively. The level of care provided to Alaska Native patients is comparable to that provided to the general diabetic patient population seen in Alaskan urban clinics. CONCLUSIONS: In spite of logistic challenges, care provided to Alaska Native people with diabetes compares favorably to that provided in other settings. Incidence rates of lower extremity amputation and end stage renal disease also remain comparable to or lower than those in other U.S. populations. Many aspects of our system could be extended to other chronic disease programs serving isolated indigenous populations. Primary prevention of diabetes remains a major challenge as life styles change.

Alaska↗