The recrystallization and epitaxial regrowth of amorphous silicon layers on molecular beam epitaxial (MBE) silicon at 650 °C is described. MBE silicon layers were deposited at 650 °C followed by deposition of amorphous layers at 100–400 °C. Subsequent solid phase epitaxial regrowth of these layers has been achieved at 650 °C.
The dissolution of metal sulfides, such as ZnS, is an important biogeochemical process affecting fate and transport of trace metals in the environment. However, current studies of in situ dissolution of metal sulfides and the effects of structural defects on dissolution are lacking. Here we have examined the dissolution behavior of ZnS nanoparticles synthesized via several abiotic and biological pathways. Specifically, we have examined biogenic ZnS nanoparticles produced by an anaerobic, metal-reducing bacterium Thermoanaerobacter sp. X513 in a Zn-amended, thiosulfate-containing growth medium in the presence or absence of silver (Ag), and abiogenic ZnS nanoparticles were produced by mixing an aqueous Zn solution with either H2S-rich gas or Na2S solution. The size distribution, crystal structure, aggregation behavior, and internal defects of the synthesized ZnS nanoparticles were examined using high-resolution transmission electron microscopy (TEM) coupled with X-ray energy dispersive spectroscopy. The characterization results show that both the biogenic and abiogenic samples were dominantly composed of sphalerite. In the absence of Ag, the biogenic ZnS nanoparticles were significantly larger (i.e., ∼10 nm) than the abiogenic ones (i.e., ∼3–5 nm) and contained structural defects (e.g., twins and stacking faults). The presence of trace Ag showed a restraining effect on the particle size of the biogenic ZnS, resulting in quantum-dot-sized nanoparticles (i.e., ∼3 nm). In situ dissolution experiments for the synthesized ZnS were conducted with a liquid-cell TEM (LCTEM), and the primary factors (i.e., the presence or absence structural defects) were evaluated for their effects on the dissolution behavior using the biogenic and abiogenic ZnS nanoparticle samples with the largest average particle size. Analysis of the dissolution results (i.e., change in particle radius with time) using the Kelvin equation shows that the defect-bearing biogenic ZnS nanoparticles (γ = 0.799 J/m2) have a significantly higher surface energy than the abiogenic ZnS nanoparticles (γ = 0.277 J/m2). Larger defect-bearing biogenic ZnS nanoparticles were thus more reactive than the smaller quantum-dot-sized ZnS nanoparticles. These findings provide new insight into the factors that affect the dissolution of metal sulfide nanoparticles in relevant natural and engineered scenarios, and have important implications for tracking the fate and transport of sulfide nanoparticles and associated metal ions in the environment. Moreover, our study exemplified the use of an in situ method (i.e., LCTEM) to investigate nanoparticle behavior (e.g., dissolution) in aqueous solutions.
Radiation effects were measured in GaAs FETs using 1.1 MeV alpha particles. With the devices under bias, degradation in current/ voltage characteristics and charge collection efficiency was observed during irradiation. Failure analysis revealed burnout in some, but not all, devices that appeared to be initiated by local melting of the GaAs under the gate.
Amorphous Si:H and Si1−xGex:H films were prepared by mixing electron beam evaporated silicon with a molecular beam of germanium from a Knudsen cell and with a beam of ionized hydrogen produced by a 0–3 keV ion source. Aluminum Schottky barriers on two types of samples of (1) amorphous Si1−xGex:H with 0.15<x<0.85 and (2) modulated structures of 50×100 Å layers of amorphous Si:H/a-Si0.8Ge0.2:H (10−5 Torr PH hydrogen) were investigated. Barrier height was found to depend on the Ge concentration and possible Fermi level pinning due to the dangling bond deep level. The modulated structures showed a negative resistance region and a barrier height determined only by the composition of the first layer.
Three types of commercially available GaAs FETs were studied under high power gate pulses to simulate the radar environment of transceivers which share the same antenna. Both single pulses and pulse trains of 10 ns and 1 μs pulse widths were used to gain an understanding of the physics of failure in these devices. Gradual degradation of the DC and RE characteristics was observed allowing study of the failure mechanisms before massive damage could occur to the channel region. Failures occurred primarily by electromigration from sharp points and other irregularities along the gate. Electromigration can be reduced by using gate and ohmic contact metallizations without sharp protrusions. These sharp protrusions and the resulting high fields lead to increased electromigration, particularly when the gate-source distance is very small.
A low-temperature surface preparation technique for molecular beam epitaxial growth of silicon on sapphire and silicon is described. Thermal desorption of regrown oxide has been accomplished at 850 °C and epitaxial growth at 650 °C. A comparison of two surface treatment techniques for silicon (100) and sapphire (11̄02) substrates is reported.
n‐MOSFET channel lengths have been determined from SEM cross‐sectional examination and utilizing two different chemical etchants. The two etchants are (i) to stain and (ii) to etch source/drain n‐doped regions. Agreement with electrical measurements of the effective channel lengths was obtained only with the staining method.
A new class of polymeric materials [1] synthesized from fluorinated precursors to produce network molecules of epoxies and polyurethanes has been analyzed as a hybrid encapsulation material. Using test structures, a microthin film (Au-Al 2 O 3 ) moisture sensor and Auger/SIMS analysis, the moisture penetration kinetics for the fluorinated network polymeric materials (FNP) has been determined. It was determined that the activation energy for moisture penetration varied from 0.7 to 1.1 eV at relative humidity (RH) between 20-95 percent. Interdigitated test structures were utilized in order to study the migrative resistive short (MGRS) phenomenon in the hybrids encapsulated with the FNP material. The results show that for a surface ionic contamination level of 10 14 Na + /cm 2 on the encapsulant surface, RH of 95 percent and temperature cycle of +100 to -10°C migrative resistance shorts were not observed after 100 cycles of total duration of 4 h per cycle.
