PACS. 81.15.Hi -Molecular, atomic, ion, and chemical beam epitaxy. PACS. 68.65.-k -Low-dimensional, mesoscopic, and nanoscale systems: structure and nonelectronic properties. PACS. 78.67.Lt -Quantum wires.Abstract. -An original mechanism is described for the self-assembly of nanometer-sized structures in the silicon germanium material system. The self-organized formation of vertical Si-rich quantum wells (VSQW) is obtained during the growth of Si1−xGex on narrow line-shaped Si mesa, which are oriented in 150 on the Si (001) surface. The occurrence of the VSQW is accompanied by the formation of {15 3 23} facets on top of the mesa. Detailed structural insights have been gathered by cross-sectional transmission electron microscopy, secondary electron microscopy and photoluminescence measurements. Ge quantum wires are embedded into the VSQW forming a superlattice containing SiGe and Ge wires. Intense low-temperature photoluminescence, which can be assigned to this one-dimensional superlattice, has been observed.

Amorphous and polycrystalline boron nitride (BN) films were deposited on n‐type Si substrates using a B2H6‐NH3‐H2 system. During deposition of the BN film, boron diffuses into the Si; a BN film deposited at temperatures below about 1000°C acts as an infinite diffusion source of boron in Si. The maximum values of boron surface concentration give solid solubility of boron in Si at each temperature. A thin layer of BN (below 80Å) gives a surface concentration of boron in the range between 1016 and 1020 cm−3, by varying the heat‐treatment conditions. Amorphous BN decomposes easily when heated in a nitrogen atmosphere. This can be used for planar diode processes using only one photomask. An MIS‐memory diode with normalAl‐BN‐SiO2‐normalSi structure, shows an anomalous C‐V shift due to the formation of borosilicate glass between BN and SiO2 .

We present a detailed study on the effect of bottom-and top-oxide thicknesses on the current conduction and the dielectric breakdown of oxide/nitride/oxide (ONO) multi-layer dielectrics. An abrupt reduction in current is observed when the oxide that is contiguous to the anode is thicker than 3 nm. This leads us to conclude that the thick oxide (>3 nm) impedes hole injection from anode into nitride. The injected charge-to-breakdown (QBD) and the time-to-breakdown (TBD) are measured to study the breakdown mechanism. We observe that a substantial increase in TBD occurs in spite of the reduction in QBD when the thick oxide is contiguous to anode. This phenomenon is explained by a hole-induced breakdown model for the ONO structure with thin bottom-and top-oxides (<3 nm). Hole injection is suppressed by the thick oxide that is contiguous to anode. The increase in TBD is attributed to the reduction in injected holes. We conclude that the dielectric breakdown of the ONO structure with the thin oxides is induced by injected holes. We also observe that the thermal activation energy of the TSD changes at 3 nm in bottom-oxide thickness under negative gate bias. Therefore, this value of 3 nm is determined as a threshold thickness for the change of the breakdown mechanism.

While it is well-known that faces provide linguistically relevant information during communication, most efforts to identify the visual correlates of the acoustic signal have focused on the shape, position and luminance of the oral aperture. In this work, we extend the analysis to full facial motion under the assumption that the process of producing speech acoustics generates linguistically salient visual information, which is distributed over large portions of the face. Support for this is drawn from our recent studies of the eye movements of perceivers during a variety of audiovisual speech perception tasks. These studies suggest that perceivers detect visual information at low spatial frequencies and that such information may not be restricted to the region of the oral aperture. Since the biomechanical linkage between the facial and vocal tract systems is one of close proximity and shared physiology, we propose that physiological models of speech and facial motion be integrated into one audiovisual model of speech production. In addition to providing a coherent account of audiovisual motor control, the proposed model could become a useful experimental tool, providing synthetic audiovisual stimuli with realistic control parameters.3

A model is proposed to explain the dependence of the substrate hole current in n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) on applied electric field and on oxide thickness. Two types of devices were prepared: n-channel MOSFETs with gate oxides of 67, 86, and 131 Å and p-channel MOSFETs in which gate oxide thicknesses were almost equal to those in the n-channel MOSFETs. The carrier-separation technique was used in the p-channel MOSFETs, and the average energy of hot electrons entering the silicon substrate was obtained. The average energy of the hot electrons is related to the energy distribution of hot holes created by hot electrons emitted from the oxide into the n+ polysilicon gate during the Fowler–Nordheim electron tunneling in the n-channel MOSFETs. The substrate hole current is numerically modeled as thermionic emission of the hot holes overcoming the energy barrier at the oxide-n+ polysilicon interface. For the gate oxides ranging from 67 to 131 Å, the dependence of the substrate hole current on the electric field and on oxide thickness is explained by using the average energy of the hot electrons and the thermionic hole emission model.

We propose a hybrid neural network model of aimed arm movements that consists of a feedforward controller and a postural controller. The cascade neural network of Kawato, Maeda, Uno, and Suzuki (1990) was employed as a computational implementation of the feedforward controller. This network computes feedforward motor commands based on a minimum torque-change criterion. If the weighting parameter of the smoothness criterion is fixed and the number of relaxation iterations is rather small, the cascade model cannot calculate the exact torque, and the hand does not reach the desired target by using the feedforward control alone. Thus, one observes an error between the final position and the desired target location. By using a fixed weighting parameter value and a limited iteration number to simulate target-directed arm movements, we found that the cascade model generated a planning time-accuracy trade-off, and a quasi-power-law type of speed-accuracy trade-off. The model provides a candidate neural mechanism to explain the stochastic variability of the time course of the feedforward motor command. Our approach also accounts for several invariant features of multijoint arm trajectories, such as roughly straight hand paths and bell-shaped speed profiles.

Etching yields of SiO2 by mass-separated F+, CF+, CF2+, CF3+, and Ar+ ions have been measured at low ion energies ranging from 80 to 350 eV. CF3+ and CF2+ ions have higher etching yields than CF+ and F+ ions. At low ion energies, SiO2 cannot be etched and some film deposition is observed on the SiO2 surface. For example, in the case of CF+ ions, SiO2 can be etched at ion energies above 200 eV. This film deposition is caused by reactions of CFx+ ions at the SiO2 surface, and neutrals coming from the ion source also have some effect on this deposition.

Boron monophosphide (BP) was epitaxially grown on Si substrates with (100), (110) and (111) faces, by thermal decomposition of a B2H6-PH3 mixture in hydrogen in the temperature range of 950°C to 1050°C. The crystallographic orientation of the BP was the same as that of the Si substrates. n- and p-type BP were obtained under different growth conditions. The carrier concentrations without any additional doping were from 1018 to 1021 cm-3 and their mobilities were from 150 to 80 cm2/Vsec.