摘要:

This paper gives a theoretical and experimental treatment of the subject. It is shown that the capture of single atoms can be related to catchment areas associated with stable and critical nuclei. It is then shown that for the materials and conditions used in evaporation work the size of the smallest stable cluster is normally a pair.Two equations describing the initial stages of growth are then derived dependent on whether the lifetime of single atoms is determined by reevaporation or by capture. For the reevaporation case, it is predicted that nucleation proceeds exponentially to a saturation densityNsof islands, and thatNsincreases with temperatureTand is independent of incidence rateR. For the capture case, condensation is initially complete andNsincreases withRand decreases withT. Experimental results with gold on vacuum cleaved rocksalt show reasonable agreement with the predicted behavior. Modified growth conditions are also examined experimentally, and the results are interpreted in terms of the parameters of the theoretical expressions. Growth using gold ejected from a sputtered single crystal suggests an increased effective condensate temperature. Normal evaporation with simultaneous electron bombardment of the substrate gives results which can be ascribed to lower mobility of migrating atoms.

ISSN:0022-5355    

DOI:10.1116/1.1492548

出版商:American Vacuum Society    

年代:1967

数据来源: AIP

摘要:

The collection efficiency of a plane acting as a pump in a vacuum system can be determined by measuring the rate at which molecules of a given species strike and the rate at which they return from that plane. This paper discusses an experimental vacuum system incorporating a movable partial-pressure analyzer capable of making such measurements. The experimental procedure discussed here provides a means for evaluating parameters affecting the pumping efficiency. Efficiency values obtained by the present approach are compared with values obtained from kinetic theory and from speed-factor measurements. The experimental data show that much of the deviation of reported pumping efficiencies can be explained by fragmentation of the test-gas molecules and by a pressure anisotropy in the test dome. A means of calibrating the analyzer with vapor-pressure data is also discussed.

ISSN:0022-5355    

DOI:10.1116/1.1492549

出版商:American Vacuum Society    

年代:1967

数据来源: AIP

摘要:

An experimental technique is described in which both the kinetics of nucleation of vapor deposits and certain of the related physical processes, such as the thermal accommodation of vapor at the substrate surface and the adsorptive properties of the nucleant species, can be measured simultaneously. The technique described is based on the use of a small mass spectrometer to monitor the flux of vapor molecules leaving the substrate while adsorption or nucleation processes are taking place. Results obtained for cadmium vapor impinging on an atomically clean tungsten surface indicate the formation of two distinct adsorbed phases. A primary phase, obeying the relationτa=0.94×10−10exp(41100/RT),forms on initial exposure of the clean substrate to the vapor. At lower temperatures a secondary phase, which obeys the relationτa=1.42×10−10exp(21200/RT),forms on top of the primary phase. Measurements of the critical supersaturation required for crystal nucleation indicate. that adsorbed layers, several monolayers thick, are present on the surface prior to crystal nucleation. Thus the nucleation process in this case cannot be described in terms of current theories.

ISSN:0022-5355    

DOI:10.1116/1.1492550

出版商:American Vacuum Society    

年代:1967

数据来源: AIP

摘要:

The gas calibrations of the Explorer 32 satellite atmospheric density experiment provided comparisons of the operation of the following five kinds of ionization gauges: (1) flight type, glass enveloped, cold cathode, magnetron gauge (model NRC-528), (2) flight type, metal enveloped, cold cathode, magnetron gauge (model GCA-R5), (3) commercially available, glass enveloped, “Redhead gauge” (model NRC-552), (4) flight type, metal enveloped, warm cathode, magnetron gauge (WCM), and (5) commercially available, metal enveloped, Penning-type gauge (model GE-22GT210).The nitrogen pressure responses of these gauges are compared in terms of the conversion constant (C). C is the ratio of the cathode current to the pressure and is related to the number of ions produced per neutral particle in the gauge. The 552 and R5 gauges exhibit values of C which axe maximum between10−10and10−9Torr and decrease at higher pressures. In contrast to this behavior the 528 and 22GT210 gauges exhibit primarily increasing C values with pressure, and the C values of the warm cathode magnetron are constant at low pressures. Experimental results which can be interpreted in terms of the behavior of the negative space charge in the gauges are briefly discussed. A high sensitivity of the R5 gauge response characteristics to anode voltage is demonstrated in terms of C values, oscillation regions, and discontinuities.

ISSN:0022-5355    

DOI:10.1116/1.1492551

出版商:American Vacuum Society    

年代:1967

数据来源: AIP

摘要:

A new vacuum-gauge calibration method is described. Tile pressure ratio generated by the molecular flow of gas through two known, fixed, series conductances is applied repeatedly, serially in time, to establish a progression of increasing chamber pressures. A single pressure indication serves as the higher value in one ratio and the lower value in the succeeding ratio, thereby correlating the calibration pressures by a fixed known factor. Calibration pressures can be calculated after one of them is sufficiently high to be measured accurately by a reference system. In one modification, gauges are calibrated on a symmetrical, well-baffled chamber connected directly to the pump by a large conductance, thus significantly reducing the possible interaction between the establishment of new calibration pressures, and the pumping or outgassing of gauges being calibrated. A simple, single-pump apparatus suffices for calibrating from10−3Torr to within a decade of the system ultimate pressure. Re-producibility in the order of 2% is achieved in the10−9Torr decade.

ISSN:0022-5355    

DOI:10.1116/1.1492552

出版商:American Vacuum Society    

年代:1967

数据来源: AIP

摘要:

Inert gas ions of energies between 100 eV and 2 KeV have been injected into polycrystalline tungsten and gold. The subsequent thermal desorption of entrapped ions from these targets has distinct peak structures, and an attempt has been made to correlate the energies associated with these peaks in the desorption spectrum with normal defect-migration processes in the target materials.

ISSN:0022-5355    

DOI:10.1116/1.1492553

出版商:American Vacuum Society    

年代:1967

数据来源: AIP

摘要:

The conventional first-order linear differential equation for the partial pressures of the residual gases in an ultrahigh vacuum system has been tested experimentally and found to be satisfactory for He,CH4,N2, and Ar but unsatisfactory forH2and CO. Two simultaneous first-order linear differential equations, based upon a model postulating a surface phase obeying Henry’s Law, are suggested forH2and CO. The solutions to these simultaneous equations yield greatly improved but not complete agreement with experiment. Qualitative suggestions are made for further improvement of the model. Literature concerning quantitative measurements ofH2and CO in ultrahigh vacuum systems and based upon the conventional pressure equation is reexamined critically in terms of the new system of equations.

ISSN:0022-5355    

DOI:10.1116/1.1492554

出版商:American Vacuum Society    

年代:1967

数据来源: AIP

ISSN:0022-5355    

DOI:10.1116/1.1492555

出版商:American Vacuum Society    

年代:1967

数据来源: AIP

ISSN:0022-5355    

DOI:10.1116/1.1492556

出版商:American Vacuum Society    

年代:1967

数据来源: AIP

ISSN:0022-5355    

DOI:10.1116/1.1492557

出版商:American Vacuum Society    

年代:1967

数据来源: AIP