Laser-chemical vapor deposition of W Schottky contacts on GaAs\ud using WF6 and SiH4

Reports on the deposition of tungsten on gallium arsenide (GaAs) using a low-temperature laser-chemical vapor deposition process. Induction of metallic W formation from a gas mixture; Columnar structure shown by scanning electron microscopy of the W films; Schottky diodes obtained during a laser based resistless projection patterning process on GaAs

Fabrication and Sub-Band-Gap Absorption of Single-Crystal Si Supersaturated with Se by Pulsed Laser Mixing

Selenium supersaturated silicon layers were fabricated by pulsed excimer laser induced liquid-phase mixing of thin Se films on Si(001) wafers. Sufficiently low Se coverage avoids destabilization of rapid epitaxial solidification, resulting in supersaturated solid solutions free of extended defects, as shown by transmission electron microscopy. The amount of retained Se depends on the original film thickness, the laser fluence, and the number of laser pulses irradiating the same spot on the surface. Using this method, Se has incorporated into the topmost 300 nm of the silicon with a concentration of 0.1 at.%. Channeling Rutherford backscattering spectrometry measurements show that the substitutional fraction can be as high as 75% of the total retained Se. These alloys exhibit strong sub-band-gap absorption with optical absorption coefficient ranging up to about 104 cm−1, thus making them potential candidates for applications in Si-based optoelectronic devices.Physic

Unilateral vs. bilateral STN DBS effects on working memory and motor function in Parkinson disease

Bilateral subthalamic nucleus deep brain stimulation (STN DBS) can reduce working memory while improving motor function in Parkinson disease (PD), but findings are variable. One possible explanation for this variability is that the effects of bilateral STN DBS on working memory function depend in part on functional or disease asymmetry. The goal of this study was to determine the relative contributions of unilateral DBS to the effects seen with bilateral DBS. Motor (Unified Parkinson Disease Rating Scale Part III, UPDRS) and working memory function (Spatial Delayed Response, SDR) were measured in 49 PD patients with bilateral STN DBS while stimulators were Both-off, Left-on, Right-on and Both-on in a randomized, double-blind manner. Patients were off PD medications overnight. Effects of unilateral DBS were compared to effects of bilateral STN DBS. Mean UPDRS and SDR responses to Left-on vs. Right-on conditions did not differ (p>.20). However, improvement in contralateral UPDRS was greater and SDR performance was more impaired by unilateral DBS in the more affected side of the brain than in the less affected side of the brain (p=.008). The effect of unilateral DBS on the more affected side on contralateral UPDRS and SDR responses was equivalent to that of bilateral DBS. These results suggest that motor and working memory function respond to unilateral STN DBS differentially depending on the asymmetry of motor symptoms

Fabrication and subband gap optical properties of silicon supersaturated with chalcogens by ion implantation and pulsed laser melting

Topographically flat, single crystal silicon supersaturated with the chalcogens S, Se, and Te was prepared by ion implantation followed by pulsed laser melting and rapid solidification. The influences of the number of laser shots on the atomic and carrier concentration-depth profiles were measured with secondary ion mass spectrometry and spreading resistance profiling, respectively. We found good agreement between the atomic concentration-depth profiles obtained from experiments and a one-dimensional model for plane-front melting, solidification, liquid-phase diffusion, with kinetic solute trapping, and surface evaporation. Broadband subband gap absorption is exhibited by all dopants over a wavelength range from 1 to 2.5 microns. The absorption did not change appreciably with increasing number of laser shots, despite a measurable loss of chalcogen and of electronic carriers after each shot.One of the authors M.T. acknowledges the financial support of the Fulbright Program. This research was supported in part by the U.S. Army ARDEC under Contract No. W15QKN-07- P-0092