摘要:

The transient sheath expansion around square and cross‐shaped targets is simulated numerically with a two‐dimensional fluid model. The angular distribution of the ions impinging on the target surface and the nonuniformity of the incident ion dose are calculated. The incident ion dose peaks near, but not at, the convex corner and has a minimum at the concave corner. The dip of the dose profile at the convex corner is shown to be caused by the product of a decreasing normal velocity profile and an increasing ion density profile along the target surface from the center to the corner. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360464

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A 193 nm excimer laser and a custom fabricated cylindrical lens system is used to produce a plasma sheet of 8 cm×30 cm×0.4 cm in tetrakis(dimethylamino)ethylene (TMAE), a low ionization energy organic gas. Plasma density variation due to photon absorption is studied by scanning the filling pressure of TMAE between 12 and 150 mTorr. A high density (n≥2.0×1013cm−3), low temperature (Te≊0.8 eV) plasma sheet of 4 mm thickness is obtained with less than 50% spatial density variation over the 30 cm axial length. Charge recombination is found to be the dominant process for t≤1.2 &mgr;s with the plasma diffusion playing a perturbational role. A one‐dimensional plasma model is utilized to model the experimental plasma data by treating the diffusion as a perturbation. This study shows that the recombination coefficient is 1.8±0.1×10−7cm3 s−1and the diffusion coefficient is 2.8±0.4×104cm2 s−1. The plasma sheet has attractive properties for a microwave agile mirror. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360773

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Microstructural changes that occur in a GeSbTe film during repetitious overwriting in phase‐change optical recording were investigated. The GeSbTe active layer was melted by a focused laser diode (LD) beam during each overwriting process over amorphous mark formation. The repetitious solidification and liquefaction process in such a short time as 50–200 ns resulted in microstructural changes in the active layer: a segregation, sink, and void formations. The sink was formed in the low‐density active layer due to the shrinking of the volume during the resolidification process. Sink formation could be suppressed when a high‐density active layer, having more than 80% of the bulk density, was used. Such a high‐density GeSbTe film, however, resulted in a void formation of the size of 0.1 &mgr;m. The voids were thought to be nucleated by residual vacancies and Ar precipitation, since the active layer contained a high concentration of Ar impurities, due to the atomic peening effect. The subsequent void coalescence and migration processes across the beam scanning direction could result in the formation of thermally discontinuous grooves at the edges of the written marks. The voids could also migrate along the LD beam scanning direction, accompanied by a material flow of the active layer in the opposite direction. These phenomena were also found to depend on the material used to fabricate the protective layers which sandwiched the active layer. A TaOxprotective layer enhanced the void migration across the track, resulting in the removal of voids from the center of the track. Use of the ZnS:SiO2compound protective layer confined voids to the center of the track. The ZnS:SiO2protective layer also promoted the formation of thermally discontinuous grooves at the edges of amorphous marks. The material flow along the track resulted in a thicker active layer at the start of the consecutive LD irradiation, and also in a high void density region at the final edge of the irradiation having a length on the order of 10 &mgr;m. This tendency was found for both the ZnS:SiO2and TaOxsandwiching media. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360465

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

CaF2single crystals have been irradiated atT=21 K and at 0 °C with electrons of 0.5 and 1 MeV energy. The low‐temperature irradiated samples exhibit electron‐spin‐resonance (ESR) spectra with signals due to F‐centers and an unchanged real component of the dielectric constant &egr;′. The room temperature irradiated crystals, on the other hand, present ESR‐spectra due to VF‐, U‐, and, possibly, to metallic‐colloid (g=2.003) centers as well as an increased (dose dependent) &egr;′. The introduced defects and the radiation‐induced &Dgr;&egr;′ are investigated in a thermal annealing treatment up to 900 °C. Their recovery behaviour is complex and can be interpreted as a competition between growth and annihilation processes of metallic clusters estimated to have initially a radius of ∼200 A˚. Thus, the appearance of a new ESR‐line nearg=2.000 after an anneal at 200 °C indicates the possible transformation of colloids to larger units before vanishing. The annealing spectrum of &Dgr;&egr;′ and the dose dependence of its substages support the ESR findings. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360466

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An influence of Te doping on the lattice parameter and the thermal expansion of AlxGa1−xAs epitaxial layers was examined by high‐resolution x‐ray diffractometry over a temperature range 77–673 K. For doped AlxGa1−xAs layers the thermal expansion coefficients were found to be larger relative to undoped samples of the same Al content. This phenomenon is attributed to the change of anharmonic part of lattice vibrations by free electrons and/or ionized tellurium atoms. An increase of thermal expansion caused by doping is a factor which should be taken into account in lattice constant measurements at 295 K. We propose an interpretation of the lattice expansion (examined at room temperature by other authors and by us) of GaAs caused by Te doping in terms of three factors: (i) ‘‘size’’ effect (bigger Te atoms with respect to As), (ii) free electrons via the deformation potential of the conduction‐band minimum occupied by these electrons, (iii) increase of the thermal expansion. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360467

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In this work we used Raman spectroscopy to investigate the structural characteristics of as‐deposited amorphous and micro‐crystalline silicon films. For amorphous silicon films, the order (or disorder) of the silicon network was quantified using properties of the Raman spectra that were related to key deposition conditions. We found that a strong relationship exists between the structural order of the silicon matrix and the deposition temperature and deposition rate. A quantitative model was proposed relating the intensity ratio of transverse optical phonon peak to longitudinal optical phonon peak to the surface diffusion length, a parameter that was calculated from available data. It was found that optimization of the as‐deposited silicon microstructure is possible by selecting deposition conditions yielding peak–ratio values in the vicinity of 0.53. For as‐deposited micro‐crystalline silicon films, Raman spectroscopy was used to estimate the initial crystalline fraction of the film and monitor the crystallization process during annealing. These data were used to confirm the crystallization mechanism in mixed‐phase silicon films and identify the effect of different process parameters on the crystallization time of the annealed films. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360468

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A theoretical modeling of the threshold voltage of short‐channel silicon metal–oxide–semiconductor field‐effect transistors (MOSFETs) taking into consideration the focused ion‐beam technology for the direct implantation of dopants into semiconductor substrates has been performed. Based on a quasitwo‐dimensional solution of Poisson’s equation, the surface potential distribution along the channel of a MOSFET has been derived. For this, implanted channel doping concentration is varied linearly along the channel and in a Gaussian‐type fashion in a direction perpendicular to the channel. The threshold voltage has been determined from a knowledge of the minimum surface potential in the channel. The effects of finite source and drain junction depths have been included by modifying the depletion capacitance beneath the gate. Short‐channel effects on the threshold voltage are thus taken into consideration. The model provides important insight of the physics controling the threshold voltage of a MOSFET. It is noted that a nonuniform doping with density lower in the drain end of the channel and higher in the source end of the channel, and a proper tailoring of the doses, straggles, and energy of implantation are keys to the improvement of the electrical characteristics of a MOSFET. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360469

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Polycrystalline &bgr;‐SiC samples were implanted with 50 keV15N ions with fluences ranging from 3×1017to 1.5×1018ions/cm2at elevated temperature up to 1100 °C. Nitrogen depth profiles were measured as a function of implantation temperature and annealing temperature using nuclear reaction analysis, Rutherford backscattering spectroscopy, and Auger electron spectroscopy. It was found that the maximum concentration and the width of nitrogen depth profiles implanted at 1100 °C were reduced distinctly in comparison with the profiles implanted below 930 °C or annealed at 1100 °C. The redistribution of nitrogen implanted in SiC at 1100 °C was ascribed to the formation of &bgr;‐Si3N4crystallites in SiC, which was confirmed by x‐ray diffraction at glancing incidence. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360470

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Shock waves are generated in thin films of glycidyl azide polymer (GAP) by pulsed laser vaporization of a thin aluminum film. The rapidly expanding aluminum plasma launches a shock wave into the adjacent layer of GAP, initiating chemical reactions. The shock velocity has been measured by use of a velocity interferometer as a function of the thickness of the GAP layer and the fluence of the Nd:YAG laser pulse. Shock pressures as high as 8 GPa have been generated in this manner. Detonation of thick GAP samples has been observed, providing important information about the chemical reaction rates and the thickness of the reaction zone. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360471

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Nonlinear features of dislocation emission processes under mode II loads are explored from an atomic scale. Crack tip atom string models coupling with the continuum mechanics analysis are devised. Dynamic analysis shows that the atom motion at the crack tip changes from periodic to chaotic, as the mode II stress intensity factor increases. The chaotic atom motion dictates the dislocation nucleation process at the crack tip. Study on the dislocation emission band reveals the phenomenon of cloudlike drifting of the dislocation core ahead of the crack tip. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360472

出版商:AIP    

年代:1995

数据来源: AIP