Preparation of ZnSe light-emitting diodes by metalorganic chemical vapor deposition using trisdimethylaminoarsine as a p-type doping source

Trisdimethylaminoarsine was used in atmospheric-pressure metalorganic chemical vapor deposition growth of ZnSe on GaAs. The metalorganic precursors employed for ZnSe growth were diethylzinc and diethylselenide, and ethyliodide was used as then-type dopant. P-on-n light emitting diode (LED) structures were prepared, and molecular beam epitaxially deposited HgTe layers were used as ohmic contacts to the p-type ZnSe. Blue LEDs were fabricated on p-on-n samples. Preliminary LED data and the material characterization data are presented.     

Hematogenous osteomyelitis with inflammatory cyst formation mimicking a soft-tissue tumor

Reported is a case of hematogenous osteomyelitis of the femur with inflammatory cyst formation mimicking a soft-tissue tumor. A 15-year-old boy with a three-year history of a gradually enlarging soft-tissue mass of his left thigh was found to have an aborted acute hematogenous osteomyelitis complicated by an inflammatory cyst that was probably caused by inadequate antibiotic therapy. The osteomyelitis and its inflammatory cyst were treated with excisional debridement and six weeks of antibiotic therapy. The patient remains well five years later, with no clinical or radiologic evidence of recurrence. This is a new variant of chronic osteomyelitis that has not previously been reported.     

Development of respirable aerosol samplers using porous foams

Workplace aerosols must be sampled to assess the degree of health hazard caused by the particulate matter. By adjusting the sampling flow rate, most of the samplers can match the 50% cutoff size, but not the slope of the respirable convention defined by the American Conference of Governmental Industrial Hygienists, the International Organization for Standardization, and the European Committee for Standardization (CEN). Combinations of foams (or other porous material) of different nominal sizes (10-100 ppi) and thicknesses (5-35 mm) were employed to overcome this bias. A foam disk 25 mm in diameter was placed in an asbestos sampling cowl. Dioctylphthalate was the liquid test agent. An aerodynamic particle sizer and an Aerosizer were calibrated against a settling chamber and were employed to measure the aerosol number concentrations and size distributions upstream and downstream of the foams. The sampling efficiency data showed that the 50% cutoff size could be met for foams in series, but that the slope remained sharper than the new definition. Foams in parallel showed great flexibility and many of the parallel combinations flattened the slope, closer to that of the new international respirable convention. For instance, when the total flow rate is set at 10.1 L/min the aerosol penetration through foams in parallel (100 ppi, 20 mm thick, diameter 25 mm + 10 ppi, 20 mm thick, diameter 13 mm) nearly matched the new international standard for respirable fraction. This sampler can be further miniaturized for smaller sampling flow rates to fit the capacity of personal sampling pumps.     

Algorithms for scheduling imprecise computations

The imprecise computation technique, which prevents timing faults and achieves graceful degradation by giving the user an approximate result of acceptable quality whenever the system cannot produce the exact result in time, is considered. Different approaches for scheduling imprecise computations in hard real-time environments are discussed. Workload models that quantify the tradeoff between result quality and computation time are reviewed. Scheduling algorithms that exploit this tradeoff are described. These include algorithms for scheduling to minimize total error, scheduling periodic jobs, and scheduling parallelizable tasks. A queuing-theoretical formulation of the imprecise scheduling problem is presented     

Activation of arsenic as an acceptor in Hg1−xCdxTe under equilibrium conditions

Arsenic is an amphoteric impurity in Hg_1−xCd_xTe. Under tellurium-rich conditions, it tends to occupy metal-sublattice sites and act as a donor; while under mercury-rich conditions, it tends to occupy the tellurium sublattice and act as an acceptor. In this process, mercury from the ambient, first, displaces an arsenic atom (donor) occupying a metal-sublattice site. This arsenic atom, in turn, displaces a tellurium atom, taking residence on the tellurium sublattice (acceptor). A second mercury atom combines with this excess tellurium atom at a surface or other crystalline discontinuity. A quantitative knowledge of the equilibrium reaction is important both to understand point defects and doping in HgCdTe. An investigation of this equilibrium under selected mercury pressures spanning the entire range from the tellurium-saturated phase limit to the mercury-saturated phase limit reveals that a majority of the arsenic remains on the sites in the tellurium sublattice even under tellurium-saturated conditions for arsenic concentrations less than 2×10¹⁶ cm⁻³. With increasing mercury pressure, the relative population of the arsenic atoms on sites in the tellurium sublattice monotonically increases, reaching 100% for the mercury-saturated limit.     

A study of the effects of solder volume on the interfacial reactions in solder joints using the differential scanning calorimetry technique

The differential scanning calorimetry (DSC) technique was employed to understand the interfacial reactions during soldering by simulating the soldering process as well as analyzing the interfacial reactions. The measurement of peak temperatures and heat involved provides useful information about the interfacial reactions, such as the amount of intermetallic compounds (IMCs) formed and the amount of Cu dissolved. Tin-plated Cu balls with different Sn thicknesses were used to investigate the solder-volume effect. As the Sn-layer thickness decreases, the amount of the IMC formed during reflow increases in general. This suggests IMC formation depends on the Sn volume. In addition, a Ni layer (electroless and electroplated), introduced as a diffusion barrier between Cu and Sn, was found effective in reducing Cu out diffusion. The results from the DSC study were confirmed by conventional metallography, scanning electron microscopy (SEM), and energy dispersive x-ray (EDX) techniques.