摘要:

A significant fraction of the energy deposited by electron beams in gases results in heating of the gas, which causes a transient pressure rise in the cell. When the pressure rise is uniform across the height and length of the cell, but varies across the depth, one‐dimensional unsteady flow theory applies. Then a fast‐response pressure measurement at the back wall of the cell can be interpreted to give the initial spatial pressure distribution. We describe the relationship between time and space coordinates for both low and medium levels of excitation in the cell. Experiments are discussed which illustrate the application of this technique. Analytical predictions using the SANDYL 3‐D electron scattering code show basic agreement with the experimental results, but indicate some areas for improvements in the calculations. Intermediate‐response pressure measurements are shown to be inadequate to determine the local deposition when the deposition varies markedly across the cell.

ISSN:0021-8979    

DOI:10.1063/1.328018

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Single‐crystal films of ZnO have been epitaxially grown on the (0001) and (011¯2) planes of sapphire by rf sputtering. Crystalline structures and electrical properties of the films were investigated. Surface acoustic wave (SAW) properties, including a phase velocity, a coupling coefficient, a propagation loss, and a temperature coefficient of delay, were measured for SAW propagating along thec‐axis of the ZnO films, on the (011¯2) planes of sapphire. Availability of this structure for high‐frequency SAW devices has been demonstrated by a filter with a 1050‐MHz center frequency.

ISSN:0021-8979    

DOI:10.1063/1.328019

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

This paper gives the coefficient of performance for a heat pump operated at minimum input power for given output heat power.

ISSN:0021-8979    

DOI:10.1063/1.328020

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The damage threshold for brittle materials impacted by water drops has been studied by using a combination of analytic and numerical approaches to obtain solutions for the impact stress fields and dynamic stress intensity factors. It has been shown that expressions for the damage threshold, which consists of the activation of preexistent surface microcracks, can be derived from these solutions. The expressions identify three types of behavior, depending upon the adjacence of the preexistent cracks to the impact center, vis‐a‐vis their size, and describe the respective roles of the three important target parameters, the fracture toughness, the elastic wave velocity, and the preexistent flaw size. Anabsolutedamage threshold has also been defined. The conditions at this threshold are demonstrated to be reasonably consistent with available threshold measurements.

ISSN:0021-8979    

DOI:10.1063/1.328021

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A theoretical model describing time‐dependent cataphoretic gas separation in a direct‐current glow discharge with end volumes present is formulated for a binary gas mixture. It is shown how this theoretical model differs from the previous model developed by Shair and Remer. Computed results of the axial impurity density profile for three different end volume configurations based on the new model are presented and discussed. The results indicate that optimum cataphoretic gas separation is attained for large cathode to anode end volume ratios.

ISSN:0021-8979    

DOI:10.1063/1.327970

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A study has been made regarding the influence of end volumes on time‐dependent cataphoretic gas separation in the positive column of a dc glow discharge containing 0.05% neon in helium. The neon 5400‐A˚‐line intensity was monitored at several fixed points within the positive column of the discharge. The experimental data are compared with theoretical predictions based on the model formulated in the concurrent paper. The simplified model predicts the general features of time‐dependent cataphoretic gas separation for the two end volume configurations considered.

ISSN:0021-8979    

DOI:10.1063/1.328022

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Frequency‐jump effects associated with nonlinear mode competition are investigated in an oscillator configuration consisting of a passive linear resonance system coupled to an active nonlinear resonance system. These effects give rise to a hysteresis pattern whose height and width can be related to system parameters such as the resonance frequencies, dissipation, coupling coefficient, etc. It is noted that these effects offer a novel means of determining these parameters in cases in which conventional techniques may not be desirable or as advantageous. The analysis provides a qualitative explanation of empirical observations in a recent nuclear magnetic resonance experiment [R.S. Timsit and J.M. Daniels, Rev. Sci. Instrum. 47, 953 (1976)]. The results also apply to other nonlinear resonance systems such as lasers, microwave generators, and electronic oscillators.

ISSN:0021-8979    

DOI:10.1063/1.328023

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Mass spectrometric sampling of the positive ions from the rf discharge in an 80 mole % helium‐20 mole % flourine mixture showed the principal ions to be F+2and F+. Impurity ions observed in the specially constructed discharge vessel were O+2and CF+3accounting for 10 –15% of the total ions. Very high ion flux was obtained from the discharge in the helium‐flourine mixture, relative to discharge in pure gases. This effect was also found for mixtures of helium with oxygen, nitrogen, and argon. Floating double probe measurements showed that the average electron energy is higher in the helium mixtures than in the pure gases for comparable pressure and power input. Probe measurements also showed that the degree of ionization was higher in the helium mixtures, but the variations were not as large as the mass spectrometric measurements indicated. Some evidence was found to indicate that F−modifies the sheath, but retardation measurements clearly show the charged particle loss from helium‐flourine plasma to be controlled by positive ion‐electron ambipolar diffusion.

ISSN:0021-8979    

DOI:10.1063/1.328024

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The etching of SiO2on Si in a plasma containing 80% helium/20% fluorine has been studied using direct ion sampling. Ionic species in the discharge show the transition from the SiO2surface to the Si surface, and reflect changes in the gas composition in the region adjacent to the specimen very strongly. SiO2etched at a rate of 90–100 A˚/min when mounted on the ground electrode and at 350–450 A˚/min when mounted on the rf electrode. Silicon etches at 2000 A˚/min on the ground electrode and at 6000 A˚/min on the rf electrode. The enhanced etch rates for the rf electrode are attributed to the increased kinetic energy of the ion bombardment. Reactive ion etching could account for the SiO2removal rate, but not for the Si removal rate. A more dilute He‐Fe2mixture was used to etch polycrystalline Si with some degree of anisotropy, and with minimal attack on the photoresist mask.

ISSN:0021-8979    

DOI:10.1063/1.327971

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

This paper presents the investigation of the partial conversion of two ordinary EM waves of frequencies &ohgr;1and &ohgr;2into an extraordinary wave at the difference frequency &ohgr;1∼&ohgr;2in a collisionless hot magnetoplasma. The effect of changing the strength of the static magnetic field is to modify the ratio of the electrostatic and EM parts of the extraordinary wave being generated.

ISSN:0021-8979    

DOI:10.1063/1.327972

出版商:AIP    

年代:1980

数据来源: AIP