摘要:

In this paper a study is made of the heat transfer inside cylindrical resistance diffusion and low‐pressure chemical vapor deposition furnaces, aimed at developing an improved temperature controller. A model of the thermal behavior is derived which also covers the important class of furnaces equipped with semitransparent quartz process tubes. The model takes into account the thermal behavior of the thermocouples. It is shown that currently used temperature controllers are highly inefficient for very large scale integration applications. Based on the model an alternative temperature controller of the linear‐quadratic‐Gaussian type is proposed which features direct wafer temperature control. Some simulation results are given.

ISSN:0021-8979    

DOI:10.1063/1.345519

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The feasibility of direct measurement of temperature in shock‐loaded, nonmetallic solids within microseconds using a foil thermocouple of 200 A˚ thickness has been studied over a range of pressure from 0.5 to 4 GPa. The foil thermocouple and thermopile (200 A˚ thickness) were designed and used to measure the temperature rise in shock‐compressed polymethylmethacrylate (PMMA). The method used to manufacture the gauges is spelled out in detail in this paper. The results agree with calculated PMMA temperatures when the shock pressure is below 2.2 GPa. Above this pressure the measured temperature rise is far higher than the calculated values. This result appears to be very similar to that obtained earlier by Bloomquist and Sheffield.

ISSN:0021-8979    

DOI:10.1063/1.345520

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Phase locking of two high‐power virtual cathode oscillators (vircators) has been achieved. The vircators interact directly by common connection through a short waveguide. Reproducible phase locking occurs for ∼45 ns. The time required to establish phase coherence is &bartil;10 ns. The peak power is ∼1.6 GW.

ISSN:0021-8979    

DOI:10.1063/1.345521

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Characterizations of the interaction of intense ultraviolet laser radiation (&lgr;=248 nm) with small solid aerosols are presented. Interaction dynamics, velocity measurements of expelled material, and thresholds for plasma formation are presented for aluminum, calcium fluoride, glass, silicon carbide, and tungsten particles. An excimer laser operating with a krypton fluoride gas mixture was used to irradiate small solid aerosol particles (≊5–50 &mgr;m) under atmospheric and vacuum conditions down to 10−5Torr. Focused laser radiation intensities varied from 107W/cm2to a maximum of 2×1011W/cm2. Interactions of the laser radiation with the solid aerosols were recorded in real time by an ultraviolet laser imaging system. Velocities between 250 and 2000 m/s were measured for material ejected from particles undergoing laser interaction. Laser intensity thresholds for visible plasma emission ranged from a maximum of 650 MW/cm2for aluminum to a minimum of 59 MW/cm2for tungsten. Thresholds for plasma formation were determined to be relatively independent of ambient pressure.

ISSN:0021-8979    

DOI:10.1063/1.345522

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Local measurements of the saturated laser‐induced fluorescence (LIF) signal from pulsed laser excitation of the 63P1resonance state of Hg have been obtained in a high‐pressure metal halide lamp. Hg atoms were excited at 436 nm (63P1→73S1) and the laser‐induced fluorescence was detected at 546 nm (73S1→63P2). The LIF signals were obtained as a function of radial position and the ac phase angle. The LIF signals were corrected for the optical depth of the fluorescence. The LIF measurements were made under saturated conditions to minimize the spatial dependence of the fluorescence quantum efficiency in the discharge. The 63P1density was a maximum at the arc center and monotonically decreased towards the wall. The relative 63P1profile was broader at the current zero crossing than at the current maximum. The 63P1density was undermodulated during the ac phase at the arc center compared to predictions based on the Hg 577‐nm emission, suggesting a departure from local thermodynamic equilibrium. At a reduced radius of 0.62, the 63P1density was almost independent of phase angle. Estimates of the 63P2density were obtained from the optical depth. LIF measurements were also obtained by exciting the 63P2level of Hg at 546 nm and detecting the fluorescence at 436 nm. The spatial and phase angle dependence of the LIF signals from a mercury discharge were very similar to the results from a metal halide lamp.

ISSN:0021-8979    

DOI:10.1063/1.345523

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An experimental study of the etching of tungsten with SF6has been performed in a microwave multipolar plasma using an electron cyclotron resonance excitation with an independent low dc biasing. The anisotropy and etch rate of tungsten have been measured as a function of atomic fluorine concentration in the plasma and compared with silicon characteristics. The etching mechanisms of tungsten are analyzed in light of published data on the fluorine‐tungsten interaction, and the results are explained in terms of the diffusion model for plasma etching developed for the Si‐F system. Atomic fluorine adsorption on tungsten appears to be monolayerlike, whereas it is of multilayer type on silicon, and associative desorption of WF6occurs from WF3and/or WF4adspecies in nearest‐neighbor positions.

ISSN:0021-8979    

DOI:10.1063/1.345524

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Illumination uniformity in laser‐pellet interactions is investigated for small kilojoule‐range laser systems that are capable of symmetrically illuminating spherical targets. We address a variety of options that might be used to control the illumination uniformity on such targets, including the number of beams, pulse energy, laser wavelength, temporal pulse shape, and beam spatial profile shape. We consider only laser beams that are optically smoothed using methods such as induced spatial incoherence or random phase plates. The parameters that are most important for providing good uniformity are identified. We find that the most important parameters governing the uniformity are the number of beams and the shape of the beam profile. Configurations with a small number of beams (e.g., six) are much more sensitive to the beam profile; using techniques such as splitting the focal spots provides an additional degree of freedom that can significantly increase the illumination uniformity. Additionally, we show that the hydrodynamics of the plasma is important in determining the uniformity, although it is not so easily controlled. Quantitatively, we find nonuniformities (measured by peak‐to‐valley ablation pressure differences) can be less than 10% for six‐beam kilojoule‐level 1/4 ‐&mgr;m laser wavelength systems, and of the order of a few percent for comparable 24‐beam systems.

ISSN:0021-8979    

DOI:10.1063/1.345525

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Transmission electron diffraction (TED) was used to observe extra diffraction spots in the TED patterns of molecular beam epitaxial GaAs1−ySbylayers withy=0.25, 0.50, and 0.71 grown at 520 °C on (001) GaAs substrates. Half‐order diffraction spots in the TED patterns indicated ordering on the (1¯11) and (11¯1) planes of the Group V sublattice, and streaks with subsidiary spots indicated a modulation in the [110] direction with a periodicity of ∼4d110. Streaks in the [001] direction indicated monolayer disruptions of the {111} ordering and the [110] modulation in the [001] direction. As the composition parameteryvaried, there were progressive changes in the {111} ordering, the [110] modulation, and the [001] disruptions, and these correlated with corresponding changes in the reconstruction of the dangling bonds at the growing layer surface, as determined by reflection high‐energy electron diffraction. A model is proposed to explain the observed effects in terms of ordered atomic arrangements of the Group V atoms resulting from the surface reconstruction being incorporated into the bulk epitaxial layers.

ISSN:0021-8979    

DOI:10.1063/1.345526

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Laser‐annealed and further thermally annealed arsenic implanted silicon specimens have been investigated in a range of doses from 1×1016to 5×1016As/cm2, with different experimental techniques: electrical measurements, transmission electron microscopy (TEM), double‐crystal x‐ray diffractometry (DCD), and extended x‐ray absorption fine structure analysis (EXAFS). On the as laser‐annealed samples, in the whole range of doses examined, a lattice contraction of the doped layer has been evidenced by DCD, whereas, on the same specimens, EXAFS measurements have shown the presence of a local expansion around substitutional As atoms. The relationship between strain and carrier concentration has been found to be approximately linear and can be described by the presence of a size and an electronic effect, as recently proposed in the literature. The former effect represents the atomic size contribution, while the latter is the strain induced by the variation of the conduction‐band minima due to the doping. After a subsequent thermal annealing in a low‐temperature range (350–550 °C), a strong deactivation of the dopant has been evidenced by electrical measurements. From the experimental results, a new model of the first step of the As deactivation phenomenon at low temperature is proposed. It is described by the capture of two electrons from a pair of As atoms in the second neighbor position in the Si lattice, leading to the formation of a positively charged arsenic‐vacancy cluster (As2V)+, and to the emission of a negatively charged Si self‐interstitialI−. This model takes into account the main phenomena that are experimentally observed simultaneously to the As deactivation, i.e., the transition from a contraction to a dilatation of the strain observed by DCD and the formation of interstitial loops. At relatively high temperatures (650–900 °C), the hypothesis of the coexistence of the clusters and of the observed precipitates has to be taken into account in order to explain the nature of the inactive As. However, whether clustering or precipitation is the dominant phenomenon still remains an open question.

ISSN:0021-8979    

DOI:10.1063/1.345527

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The amorphous alloy Fe60Co20Si10B10has been shown to display a high electrocatalytic activity for the hydrogen evolution in 30 wt. % KOH at 70 °C. We present, in this paper, a structural study of the crystallization process and an attempt to correlate the observed changes to the electrocatalytic behavior. The results for crystalline samples of the same average composition obtained from the melt at a lower cooling rate are also presented. Our results show that the amorphous structure is the best suited for the production of hydrogen and that the changes observed can be related in some part to the different processes of surface oxidation.

ISSN:0021-8979    

DOI:10.1063/1.345528

出版商:AIP    

年代:1990

数据来源: AIP