A Raman scattering study of GaAs: As films lifted off GaAs substrate

We performed Raman scattering investigations on low-temperature-grown (LTG) films of GaAs that had been lifted off the GaAs substrate. The Raman measurements unambiguously show the effects of excess arsenic on phonon scattering from LTG films of GaAs. The larger downwards shift of the LO phonon frequency for unannealed free-standing films is explained by invoking the elimination of mismatch strain. The Raman signal due to precipitates of elemental arsenic in the annealed GaAs : As films is determined. It is confirmed that the arsenic clusters formed by rapid thermal annealing are mainly amorphous, giving rise a broad Raman peak in the range 180-260 cm(-1).

Morphological defects and uniformity issues of 4H-SiC homoepitaxial layers grown on off-oriented (0001)Si faces

The morphological defects and uniformity of 4H-SiC epilayers grown by hot wall CVD at 1500 degrees C on off-oriented (0001) Si faces are characterized by atomic force microscope, Nomarski optical microscopy, and Micro-Raman spectroscopy. Typical morphological defects including triangular defects, wavy steps, round pits, and groove defects are observed in mirror-like SiC epilayers. The preparation of the substrate surface is necessary for the growth of high-quality 4H-SiC epitaxial layers with low-surface defect density under optimized growth conditions. (c) 2006 Elsevier Ltd. All rights reserved.

Homoepitaxial growth and MOS structures of 4H-SiC on off oriented n-type (0001)Si-faces

Homoepitaxial growth of 4H-SiC on off-oriented n-type Si-face (0001) substrates was performed in a home-made hot-wall low pressure chemical vapor deposition (LPCVD) reactor with SiH4 and C2H4 at temperature of 1500 C and pressure of 20 Torr. The surface morphology and intentional in-situ NH3 doping in 4H-SiC epilayers were investigated by using atomic force microscopy (AFM) and secondary ion mass spectroscopy (SIMS). Thermal oxidization of 4H-SiC homoepitaxial layers was conducted in a dry O-2 and H-2 atmosphere at temperature of 1150 C. The oxide was investigated by employing x-ray photoelectron spectroscopy (XPS). 4H-SiC MOS structures were obtained and their C-V characteristics were presented.

Pipeline Architecture and Parallel Computation-Based Real-Time Stereovision Tracking System for Surgical Navigation

This paper studies the development of a real-time stereovision system to track multiple infrared markers attached to a surgical instrument. Multiple stages of pipeline in field-programmable gate array (FPGA) are developed to recognize the targets in both left and right image planes and to give each target a unique label. The pipeline architecture includes a smoothing filter, an adaptive threshold module, a connected component labeling operation, and a centroid extraction process. A parallel distortion correction method is proposed and implemented in a dual-core DSP. A suitable kinematic model is established for the moving targets, and a novel set of parallel and interactive computation mechanisms is proposed to position and track the targets, which are carried out by a cross-computation method in a dual-core DSP. The proposed tracking system can track the 3-D coordinate, velocity, and acceleration of four infrared markers with a delay of 9.18 ms. Furthermore, it is capable of tracking a maximum of 110 infrared markers without frame dropping at a frame rate of 60 f/s. The accuracy of the proposed system can reach the scale of 0.37 mm RMS along the x- and y-directions and 0.45 mm RMS along the depth direction (the depth is from 0.8 to 0.45 m). The performance of the proposed system can meet the requirements of applications such as surgical navigation, which needs high real time and accuracy capability.

Pipeline Architecture and Parallel Computation-Based Real-Time Stereovision Tracking System for Surgical Navigation

This paper studies the development of a real-time stereovision system to track multiple infrared markers attached to a surgical instrument. Multiple stages of pipeline in field-programmable gate array (FPGA) are developed to recognize the targets in both left and right image planes and to give each target a unique label. The pipeline architecture includes a smoothing filter, an adaptive threshold module, a connected component labeling operation, and a centroid extraction process. A parallel distortion correction method is proposed and implemented in a dual-core DSP. A suitable kinematic model is established for the moving targets, and a novel set of parallel and interactive computation mechanisms is proposed to position and track the targets, which are carried out by a cross-computation method in a dual-core DSP. The proposed tracking system can track the 3-D coordinate, velocity, and acceleration of four infrared markers with a delay of 9.18 ms. Furthermore, it is capable of tracking a maximum of 110 infrared markers without frame dropping at a frame rate of 60 f/s. The accuracy of the proposed system can reach the scale of 0.37 mm RMS along the x- and y-directions and 0.45 mm RMS along the depth direction (the depth is from 0.8 to 0.45 m). The performance of the proposed system can meet the requirements of applications such as surgical navigation, which needs high real time and accuracy capability.

Structural ordering and interface morphology in symmetrically strained (GaIn)As/Ga(PAs) superlattices grown on off-oriented GaAs(100)

In this work we investigate the structural properties of symmetrically strained (GaIn)As/GaAs/Ga(PAs)/GaAs superlattices by means of x-ray diffraction, reciprocal-space mapping, and x-ray reflectivity. The multilayers were grown by metalorganic vapor-phase epitaxy on (001) GaAs substrates intentionally off-oriented towards one of the nearest [110] directions. High-resolution triple-crystal reciprocal-space maps recorded for different azimuth angles in the vicinity of the (004) Bragg diffraction clearly show a double periodicity of the x-ray peak intensity that can be ascribed to a lateral and a vertical periodicity occurring parallel and perpendicular to the growth surface. Moreover, from the intensity modulation of the satellite peaks, a lateral-strain gradient within the epilayer unit cell is found, varying from a tensile to a compressive strain. Thus, the substrate off-orientation promotes a lateral modulation of the layer thickness (ordered interface roughness) and of the lattice strain, giving rise to laterally ordered macrosteps. In this respect, contour maps of the specular reflected beam in the vicinity of the (000) reciprocal lattice point were recorded in order to inspect the vertical and lateral interface roughness correlation, A semiquantitative analysis of our results shows that the interface morphology and roughness is greatly influenced by the off-orientation angle and the lateral strain distribution. Two mean spatial wavelengths can be determined, one corresponding exactly to the macrostep periodicity and the other indicating a further interface waviness along the macrosteps. The same spatial periodicities were found on the surface by atomic-force-microscopy images confirming the x-ray results and revealing a strong vertical correlation of the interfaces up to the outer surface.

Origin of flat-band voltage sharp roll-off in metal gate/high-k/ultrathin- SiO2/Si p-channel metal-oxide-semiconductor stacks

The origin of the flat band voltage roll-off (V-FB roll-off) in metal gate/high-k/ultrathin-SiO2/Si metal-oxide-semiconductor stacks is analyzed and a model describing the role of the dipoles at the SiO2/Si interface on the V-FB sharp roll-off is proposed. The V-FB sharp roll-off appears when the thickness of the SiO2 interlayer diminishes to below the oxygen diffusion depth. The results derived using our model agree well with experimental data and provide insights to the mechanism of the V-FB sharp roll-off.

Numerical study on NOx/CO emissions in the diffusion flames of high-temperature off-gas of steelmaking converter

The combustion of high-temperature off-gas of steelmaking converter with periodical change of temperature and CO concentration always leads to CO and NOx over-standard emissions. In the paper, high-temperature off-gas combustion is simulated by adopting counterflow diffusion flame model, and some influencing factors of CO and NOx emissions are investigated by adopting a detailed chemistry GRI 3.0 mechanism. The emission index of NOx (EINOx) decreases 1.7–4.6% when air stoichiometric ratio (SR) increase from 0.6 to 1.4, and it dramatically increases with off-gas temperature at a given SR when the off-gas temperature is above 1500 K. High-concentration CO in off-gas can result in high NOx emissions, and NOx levels increase dramatically with CO concentration when off-gas temperature is above 1700 K. Both SR and off-gas temperature are important for the increase of CO burnout index (BICO) when SR is less than 1.0, but BICO increase about 1% when off-gas temperature increases from 1100 K to 1900 K at SR > 1.0. BICO increases with CO concentration in off-gas, and the influence of off-gas temperature on BICO is marginal. BICO increases with the relative humidity (RH) in air supplied, but it increases about 0.5% when RH is larger than 30%.

Fast simulation of the forward tracking detector of HPLUS

The necessity of installing a forward tracking detector stack is discussed for the Hadron Physics LanzhoU Spectrometer(HPLUS). A local tracker is developed to solve the multi-track finding problem. The track candidates are searched iteratively via Hough Transform. The fake tracks are removed by a least square fitting process. With this tracker we have studied the feasibility of pp -> pp + phi(-> K+K-), a typical physical channel proposed on HPLUS. The single track momentum resolution due to the uncertainty of the positioning in FTD is 1.3%. The multiple scattering effect contributes about 20% to the momentum resolution in the FTD coverage. The width and the signal-to-background ratio of the reconstructed phi are 1.51 MeV and 4.36, respectively, taking into account the direct Kaon channel pp -> pp + K+K- as background. The geometry coverage of FTD for phi events is about 85.4%. Based on the current fast simulation and estimation, the geometrical configuration of FTD meets the physical requirement of HPLUS under the current luminosity and multiplicity conditions. The tracker is applicable in the full simulation coming next and is extendable to other tracking component of HPLUS.

eta production off the proton in a Regge-plus-chiral quark approach

A chiral constituent quark model approach, embodying s- and u-channel exchanges, complemented with a Reggeized treatment for the t channel is presented. A model is obtained allowing data for pi(-)p ->eta n and gamma p ->eta p to be described satisfactorily. For the latter reaction, recently released data by the CLAS and CBELSA/TAPS Collaborations in the system total energy range 1.6 less than or similar to W less than or similar to 2.8 GeV are well reproduced by the inclusion of Reggeized trajectories instead of simple. and. poles. The contribution from "missing" resonances, with masses below 2 GeV, is found to be negligible in the considered processes.