摘要:

Nucleation of thin films was simulated by a Monte Carlo computer technique, assuming nucleation commences with the formation of a critical nucleus consisting of one atom. The population densities of adatoms, paired atoms, and larger clusters, as functions of surface coverage, were determined for this model at several incident fluxes and with and without reevaporation of adatoms. The results are compared to current atomistic nucleation theory.

ISSN:0022-5355    

DOI:10.1116/1.1314473

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

Given an imperfect crystal and an imperfect apparatus to measure the scattered intensity of low-energy electrons, the general problem is to determine the location of all atoms on, and in, diperiodic surface layers relative to a three-dimensional crystalline substrate. The immediate problem is to identify characteristic features in the experimental data (intensity profiles) that will indicate how the complete dynamic analysis may be reduced to yield a most probable structure in a given case; that is, how to identify the geometric signal in a background of multiple scattering “noise”? Recently proposed techniques for averaging out the primary effects of multiple scattering do, indeed, promise to provide the mechanism for unambiguous structure determination. With effective atomic scattering factors for low-energy electrons (also from averaging techniques) surface physics and chemistry can proceed on the same terms as solid state physics.

ISSN:0022-5355    

DOI:10.1116/1.1314474

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

The advent of high-efficiency, high-power lasers, operating at various vibrational-rotational transitions of the carbon dioxide molecule in the vicinity of 10 μm, has created a need for mirrors which have high reflectivity in this region. Reflectivities between 98% and 99% can be realized with metallic mirrors of copper, silver, or gold; however, in the case of silver and copper (which have the highest reflectivities) dielectric protective coatings are required to prevent atmospheric degradation of reflectivity and to permit cleaning of the mirror. Reflectivities greater than 99% can be achieved with “enhanced metallic reflectors,” which consist of metals coated with pairs of alternating, quarter-wavelength thick, low and high index of refraction dielectrics or semiconductors. In principal this type of mirror can have a reflectivity approaching 99.9%, as has been achieved for multilayer dielectric mirrors for use at the 0.633-μm He-Ne laser line in the visible. Performance is limited, however, by the difficulty of finding materials which have suitable physical and optical properties when used in quarter-wavelength thicknesses. The present paper includes a discussion of experimental equipment for making accurate and reproducible measurements of absorption in high-reflectivity mirrors at 10.6 μm, of comparative absorption data on a variety of metals produced in different ways, and of the problems involved in producing enhanced dielectric mirrors along with some preliminary results.

ISSN:0022-5355    

DOI:10.1116/1.1314475

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

All upward, inverted-cone extension to all oil diffusion pump cold cap appears to provide a method for reducing amplitude and frequency of pressure bursts in a continuously pumped vacuum system. Indications are that the pressure fluctuations are a result of oil dripping from the cold cap and/or the liquid nitrogen trap directly over the diffusion pump, then reevaporating and backstreaming into the vacuum system. Oil drip wires are shown as necessary to guide the condensed oil to the pump inner walls rather than into the hot vapor stream. The erratic behavior of these bursts and the difficulties in pinpointing their behavior is given in considerable detail.

ISSN:0022-5355    

DOI:10.1116/1.1314476

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

A highly reliable, automatic liquid nitrogen level control system using an integrated circuit is described. Inexpensive standard components are used in the device. Construction of the system is simple and straightforward.

ISSN:0022-5355    

DOI:10.1116/1.1314477

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

A simple, demountable glass field-ion microscope design is described which utilizes a series arrangement of liquid nitrogen cooled zeolite pellet sorption traps that actively pump during operation. This scheme allows atomic surface features of etched wire tips to be continuously observed in a clean He image gas environment with good resolution at liquid nitrogen temperature. The complete design details and operational procedures are outlined to allow the results presented to be duplicated with a minimum effort, and for an investment below $3500. Typical results are illustrated with images of W and W-3% Re.

ISSN:0022-5355    

DOI:10.1116/1.1314478

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

Studies of the angular distribution of scattered atomic and molecular beams from single crystal surfaces give detailed information about the gas-solid interaction. An ultrahigh vacuum system combining molecular beam scattering within situobservation of the same crystal surface by low-energy electron diffraction is described. A rotating quadrupole mass spectrometer and lock-in detection of the modulated (150 Hz) incident beam provide density profiles of the scattered gases. The scattering of thermal energy helium and oxygen beams from the (100) face of a platinum single crystal is given to demonstrate the types of surface studies that may be carried out in such an apparatus. Data are presented showing the effects of CO adsorption and surface roughness on the scattered beam intensity, and the scattering of various molecular beams from clean and contaminated surfaces.

ISSN:0022-5355    

DOI:10.1116/1.1314479

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

An atmospheric pressure leak detector has been constructed for finding leaks in vacuum and pressurized systems, using a thermistor as a sensing element. Heat transfer calculations for the thermistor in free air to determine its biasing point have been undertaken with the aid of a computer. The current through the thermistor at a given temperature, as determined theoretically and experimentally, is in agreement to within 8%.

ISSN:0022-5355    

DOI:10.1116/1.1314480

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

Equations which express evaporated film thickness ratios at various locations on nonplanar surfaces as a function of the substrate tilt angle are derived. The dependence of these ratios on the angle between the plane-normal and the direction of a uniform, unidirectional vapor stream is determined, as is the integrated effect of rotation of the plane about a normal. The conditions for improved coverage of step edges and on the plane between steps are indicated.

ISSN:0022-5355    

DOI:10.1116/1.1314481

出版商:American Vacuum Society    

年代:1971

数据来源: AIP

摘要:

Thermal transpiration—the phenomenon in which, at low pressures, a pressure difference is maintained across a small bore tube (or orifice) by a temperature difference—has been studied experimentally and theoretically for almost a century. In spite of this, the phenomenon is subject to neither physical explanation nor mathematical analysis in the transition regime. In the present work, the model for thermal transpiration in the near continuum regime is reviewed and extended to include a current model for velocity slip at the wall including thermal creep. The mathematical model formulated has been tested against recent experimental data for the thermal transpiration effect. It is shown that this model predicts both the trends and magnitudes of the effects of overall pressure level, overall temperature ratio, and gas on the thermal transpiration pressure ratio, as long as the pressure level is reasonably high, i.e., as long as the flow is in the near continuum regime.

ISSN:0022-5355    

DOI:10.1116/1.1314482

出版商:American Vacuum Society    

年代:1971

数据来源: AIP