4,810 research outputs found
Extrahepatic toxicity of acetaminophen: critical evaluation of the evidence and proposed mechanisms
Structural perfection in poorly lattice matched heterostructures
Continuum elastic theory is applied to the formation of misfit dislocations and point defects in strained layer structures. Explicit calculations of the energies of misfit dislocations in the doubleâ and singleâkink geometries yield line tensions below which strained films are stable with respect to defect formation. Our results yield a mismatchâdependent stability limit which, in the double kink case, differs from the MatthewsâBlakeslee model by a geometrical factor and by the addition of a stress term associated with climb of the misfit dislocation. While our calculations yield equilibrium stability limits which may not correspond to observed critical thicknesses, the calculated stresses may be applied to descriptions of the kinetics of strain relief in films grown beyond these limits. Last, calculations of strainârelated contributions to the free energy of formation of point defects suggest a contribution âÎG_(strain)â â0.25 eV for a 5% lattice mismatch. This suggests a means of suppressing or enhancing the formation of vacancies or interstitials in semiconductors favoring these defects
Electronic properties of deep levels in pâtype CdTe
DLTS and associated electrical measurements were made on unintentionally doped CdTe crystals obtained from several vendors, on Cuâdoped CdTe, and on Teâannealed CdTe. All of the crystals were pâtype. Four majority carrier deep levels were observed in the temperature range from 100â300 K with activation energies relative to the valence band of 0.2, 0.41, 0.45, and 0.65 eV. Two of these levels were specific to certain crystals while the other two were seen in every sample and are attributed to common impurities or native defects. Fluctuations in the concentrations of levels across samples and as a result of modest sample heating (400 K) were also observed
Professionalism in residency training: A compilation of desirable behaviors and a case-based comparison between pathologists in training and practice
Professionalism is one of the most important competencies for physicians but is also the most difficult to teach, assess, and manage. To better understand professionalism in pathology, we surveyed practicing pathologists and pathology residents and fellows in training. We identified 12 key desirable attributes of professionalism. In addition, 8 case scenarios highlighting unprofessional behavior were presented, and results between pathologists in practice and in training were compared. No significant differences between attending pathologists and residents were identified in how these cases should be managed. Our study demonstrated remarkable concordance between practicing pathologists and residents as to what constitutes professionalism and how to manage unprofessional behavior. Our case-based approach can be a useful technique to teach professionalism to both pathologists in practice and in training
New negative differential resistance device based on resonant interband tunneling
We propose and demonstrate a novel negative differential resistance device based on resonant interband tunneling. Electrons in the InAs/AlSb/GaSb/AlSb/InAs structure tunnel from the InAs conduction band into a quantized state in the GaSb valence band, giving rise to a peak in the current-voltage characteristic. This heterostructure design virtually eliminates many of the competing transport mechanisms which limit the performance of conventional double-barrier structures. Peak-to-valley current ratios as high as 20 and 88 are observed at room temperature and liquid-nitrogen temperature, respectively. These are the highest values reported for any tunnel structure
Nickel layers on indium arsenide
We report here on the preparation and characterization of InAs substrates for in situ deposition of ferromagnetic contacts, a necessary precursor for semiconductor devices based on spin injection. InAs has been grown on InAs(111)A and (100) substrates by molecular-beam epitaxy and then metalized in situ in order to better understand the mechanisms that inhibit spin injection into a semiconductor. Initial x-ray characterization of the samples indicate the presence of nickel arsenides and indiumânickel compounds forming during deposition at temperatures above room temperature. Several temperature ranges have been investigated in order to determine the effect on nickel-arsenide formation. The presence of such compounds at the interface could greatly reduce the spin-injection efficiency and help elucidate previous unsuccessful attempts at measuring spin injection into InAs
Observation of large peak-to-valley current ratios and large peak current densities in AlSb/InAs/AlSb double-barrier tunnel structures
We report improved peak-to-valley current ratios and peak current densities in InAs/AlSb double-barrier, negative differential resistance tunnel structures. Our peak-to-valley current ratios are 2.9 at room temperature and 10 at liquid-nitrogen temperatures. Furthermore, we have observed peak current densities of 1.7Ă10^5 A/cm^2. These figures of merit are substantially better than previously reported values. The improvements are obtained by adding spacer layers near the barriers, thinner well regions, and thinner barriers
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