Transformation of CaSi overgrowth domains to the CaSi2 crystal phase via vacuum annealing

The phase transformation of overgrown CaSi crystal on an (00l)-oriented epitaxial CaSi2 film was studied using high-angle annular dark-field scanning transmission electron microscopy. After annealing at 450°C under vacuum conditions, the CaSi domain transformed to the CaSi2 phase with thin Si layers. The transformed CaSi2 crystal formed epitaxially along the under-layer epitaxial CaSi2 film. The results suggest that Ca atoms in the overgrown CaSi domain diffused to the outermost passivated silicon oxide layer during the low-temperature vacuum anneal.

Hydrogen-Induced Passivation of Grain-Boundary Defects in Polycrystalline Silicon

The influence of the hydrogen content in the amorphous starting material on hydrogen bonding and defect passivation in laser annealed polycrystalline silicon is investigated. The samples are characterized using electron paramagnetic resonance and hydrogen effusion measurements. After laser dehydrogenation and crystallization the samples contain a residual H concentration of up to 8×1021 cm-3. During a vacuum anneal at least 1.5×1021 cm-3 are mobile of which only 3.7×1018 cm-3 H atoms passivate preexisting Si dangling bonds. It is shown that a vacuum anneal can cause the vast majority of H atoms to accumulate in platelet-like structures. Defect passivation and platelet nucleation and growth occur spatially separated requiring long range H diffusion.

Analytical Electron Microscopy of V-4%Ti-4%Cr Alloys

An important aspect in the consideration of V-4%Ti-4%Cr alloys as structural materials for proposed fusion reactors, especially for weldments, is the sensitivity of mechanical behavior to oxygen content. Following a 1-h anneal at 1200°C, sheet specimens were subjected to extended (16h to 43h) anneals at 500°C in 5 to 8 x 10-6 torr oxygen, followed by an homogenization vacuum anneal of 100 h at 600°C. Weight gains indicated ∼200 to >1400 wppm oxygen doping. Specimens were also subjected to an additional vacuum anneal for 4 h at 950°C. Specimens were prepared by standard double-jet electropolishing for TEM characterization with a Philips CM30 (LaB6) equipped with a Gatan Imaging Filter (GIF), and with a Philips CM200FEG equipped with Oxford EDS, GIF, and Emispec Vision integrated acquisition system.Following oxygen doping and homogenization, high concentrations of nanoscale G.P.-zone-like clusters on ﹛001﹜ were observed in the matrix, with a ∼200-nm-wide precipitate free zone (PFZ) at grain boundaries.

Anelastic Creep Phenomena in Thin Metal Plated Cantilevers for MEMS

ABSTRACTDuring the past several years, we have developed high displacement sensitivity tunneling accelerometers using surface micromachining and metal electroplating techniques. These devices consist of a Au tunneling tip fabricated below a 1-2 μm thick metal cantilever beam of electroplated Ni or Au. A thin film of e-beam evaporated Au on the underside of the cantilever serves as the tunneling counter electrode. In operation, a 100mV bias is applied across the tunneling gap. A larger turn-on voltage is also applied between the cantilever and a control electrode, located on the substrate, to deflect the cantilever and maintain a constant tunneling current of 1 or 10 nA. Typical deflections of the end of 100 μm-long and 250 μm-long cantilevers are 0.5μm during operation. We have observed that the turn-on voltage decreases over time for most devices with a larger drop observed for the Au cantilevers. In all cases, the initial decay of the turn-on voltage was almost completely recoverable after the device was turned off for 24 hrs. This decay was not found to be strongly dependent on the magnitude of the tunneling current, but could be significantly reduced by pre-stressing the cantilever before operation. Finally, a vacuum anneal at 100°C influences the measured temperature dependence of the turn-on voltage. The observed effects appear to be consistent with fatigue and creep phenomena in the cantilevers. These effects are reversible at room temperature and are dependent on the stress and temperature history of the devices. A comparison is made between metal plated and all-Si structures.