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Notes: Alfvén resonances, where the local flow speed relative to the boundary is equal to the local Alfvén speed, introduce novel dynamical features in a differentially rotating plasma. The spatial structure and dynamics of current sheets in such plasmas is investigated analytically as well as numerically. The current sheets at Alfvén resonances tend to power-law singularities. The growth of current sheets is algebraic in time in the linear regime and saturates in the presence of dissipation without the intervention of nonlinear effects. These results have significant implications for forced reconnection and Alfvén wave dissipation in laboratory and space plasmas. © 1998 American Institute of Physics.

Notes: Considering the effect of the finite ion gyroradius, the kinetic Alfvén wave in an anisotropic medium driven by a parallel velocity flow was investigated and the full dispersion relation was given. In deducing the dispersion relation, the coupling between electrostatic and electromagnetic oscillations, effects of the resonant electrons and the longitudinal motion of ions are considered. Based on the analytical and numerical calculations, two instability boundaries are found. They are 1〈(k⊥dV0/dx)/kzωci〈νA2/(Ti⊥/mi) and (k⊥dV0/dx)/kzωci〉νA2/(Ti/mi). Resonant electrons serve as the main energy source in these two regimes, while the ion longitudinal motion only suppresses the mode in the second regime. In the boundary layer of the magnetopause, the temperature anisotropy also modifies the instability by lowering the frequency and reducing the growth rate. The above results show that the low-frequency Alfvén waves with the scale of perpendicular wavelengths greater than the ion gyroradius in the magnetopause can be efficiently driven by a velocity-sheared flow. © 1998 American Institute of Physics.

Notes: In this article, we showed the significant reduction of the energy spacing between ground state and excited state emissions from InAs/GaAs quantum dots (QDs) due to interface interdiffusion induced by thermal treatment. In addition, the strong narrowing of the luminescence linewidth of the ground state and excited state emissions from the InAs dot layers for the annealed samples indicates an improvement of the size distribution of the QDs. Large blueshift of the energy positions of both emissions was also observed. High resolution x-ray diffraction experiments give strong evidence of the interface atom interdiffusion in the annealed samples. This work shows the ability to tune the wavelength for applications like infrared detectors and lasers based on intrasubband transitions of self-assembled QDs. © 1999 American Institute of Physics.

Notes: The high voltage and electromagnetic field environment poses a big challenge to a control system for plasma immersion ion implantation (PIII). The automation process must be immune to electric field interference produced by the high voltage power supply, modulator, radio-frequency or microwave plasma generator, MEVVA plasma sources, and so on. We have recently designed and installed a distributed control system, PIIIDCS, to automate the operation of our PIII facility. Programmable logic controllers are used as the field control stations because of their good anti-interference ability and good real time response. A DH-485 network is used as the communication link between the field controllers and the management station in order to improve the robustness and reliability of the system. The newly developed interface is designed to work in a graphic mode in Microsoft Windows 95. Test runs have shown that the system is reliable, flexible, and easy to operate. The development of this novel control system will expedite the development of commercial PIII instrumentation. © 1998 American Institute of Physics.

Notes: A missteered beam safety monitor (MBSM) has been designed to protect the accelerator ring of the Advanced Photon Source against incursions of the missteered synchrotron radiation. When the orbit of the particle beam in the accelerator shifts out of its safety limits, the photon beam from the bending magnet will pass through the square apertures on the cooled mask of the MBSM and will heat up a very thin tungsten wire (0.025 mm in diameter) behind the mask. Acting as a resistance thermometer, the electrical resistance of the tungsten wire increases proportionally with temperature rise. As soon as the electrical resistance of the tungsten wire reaches a preset point, a signal is triggered immediately to dump the particle beam in the accelerator. The tungsten wire is inclined to the photon beam at 4.5 degrees in the vertical direction to prevent it from being overheated by the high power photon beam. Detailed mechanical design and thermal analysis are presented. © 1996 American Institute of Physics.

Notes: Probe techniques employed in ohmic, rf, and H-mode Phaedrus-T tokamak plasmas are discussed. The floating potentials of nonemitting probes are found to be insensitive to plasma potential fluctuations at the rf frequency. Both Langmuir and emissive probes have been swept. The Langmuir probes were swept into electron saturation where a low-frequency oscillation was sometimes observed. Large probes (biased electrodes) have been used to perturb the plasma into an H mode. The biased electrode I-V characteristics differ from those of nonperturbing Langmuir probes and can be used to help identify the H mode. Probe behavior during the H mode is discussed. Two novel reciprocating probe designs have been developed. The faster of the two achieves average speeds of 5 m/s, which to our knowledge makes it the world's fastest. © 1995 American Institute of Physics.

Notes: Co2ScSn crystallizes with the cubic L21 Heusler structure and is an itinerant ferromagnet with Tc=238 K. X-ray diffraction measurements show that Co2−xSc1+xSn retains the L21 crystal structure with an essentially unchanged lattice constant for 0≤x≤0.15. However, Tc determined from the magnetization measurements decreases monotonically with increasing Sc concentration from 238 K for x=0 to 40 K for x=0.11, and then remains at 40 K from x=0.11 to 0.14. The electronic specific heat coefficient γ is enhanced from 13 mJ/mole-K2 for Co2ScSn (x=0) to 30 mJ/mole-K2 for x=0.13 (Co1.87Sc1.13Sn). In addition, the C/T versus T2 plot shows a leveling-off behavior at low temperatures for the x=0.13 sample. The γ enhancement and level-off behavior observed when a system approaches a magnetic instability are discussed in terms of the self-consistent renormalization theory of spin fluctuations for weak itinerant ferromagnets and nearly magnetic systems. © 1996 American Institute of Physics.

Notes: Three kinds of textures, i.e., (200), (111), and (220) of TiN films prepared by filtered arc deposition have been continuously observed with varying film thickness and bombarding energy of the deposited particles. The evolution of the texture from (200) to (111), then to (220) is discussed on the basis of the so-called overall energy which consists of the surface energy, the strain energy, and the stopping energy of the films. © 1996 American Institute of Physics.

Notes: The evolution of surface morphologies of films prepared by ion-based deposition techniques has been investigated by atomic force microscopy. Two deposition processes, filtered arc deposition (FAD) and ion-beam-assisted deposition, where low-energy (〈100 eV) ion irradiation and high-energy (several tens of keV) ion-beam bombardment concurrent with film growth were involved, respectively, have been employed to prepare TiN and Al films. Comparative studies on the effect of energetic ions on the development of topography have been performed between the low-ion-energy regime and high-ion-energy regime. In addition, the relationship between topography and mechanical properties of thin films has been revealed, by involving thin films prepared by thermal evaporation deposition (TED), where almost all depositing particles are neutral. In the images of the TED TiN and Al films, a large number of porous and deep boundaries between columnar grains was observed, suggesting a very rough and loose surface. In contrast, the FAD films exhibited much denser surface morphologies, although still columnar. The root-mean-square roughness of the FAD films was less than 1 A(ring). Hardness test and optical parameter measurement indicated that the FAD films were much harder and, in the case of optical films, much more transparent than the TED films, which was considered to arise from the denser surface morphologies rather than crystallization of the films. The high density and super smoothness of the FAD films, and the resultant mechanical and optical properties superior to those of the TED films, were attributed to the enhancement of surface migration of the deposited adatoms in the FAD process, which could provide intensive low-energy ion irradiation during film growth. As for topography modification by high-energy ion-beam bombardment concurrent with film growth, in addition to the increase of surface diffusion due to elastic collision and thermal spikes, physical sputtering must be considered while explaining the development of the film topography. Both surface migration enhancement and sputtering played important roles in the case of high-energy heavy-ion-beam bombardment, under which condition surface morphology characterized by dense columns with larger dimension and deep clean boundaries was formed. However, under high-energy light-ion-beam bombardment, the sputtering was dominant, and the variation of sputtering coefficient with position on the surface of growing film led to the formation of cones. © 1996 American Institute of Physics.

Notes: We have measured χ(T) for oxygen-annealed YBa2Cu3Ox samples and observed a glass-like behavior at low magnetic fields which can be explained in terms of a Josephson weak link effect. The glass transition temperature Tg depends on the oxygen annealing temperature and sample pellet pressure. Tg disappears when a sample was powdered after receiving an oxygen anneal, indicating that the Josephson weak link effect occurs between intergranular boundaries. In addition, Tc shifts from 93 K for the air-sintered samples to 90 K for the oxygen-annealed materials. Under vacuum annealing, Tg disappears and Tc first shifts back to 93 K. Prolonged vacuum annealing or vacuum annealing at higher temperatures depresses Tc to below 90 K. The temperature dependence of the specific heat shows a single anomaly for samples sintered in air or annealed under high vacuum. But a double-peak specific heat anomaly occurs for the oxygen-annealed samples. © 1996 American Institute of Physics.