Ion beam applications for precision infrared optics

Ion beam applications for precision infrared optics

Classified abstracts 5688-5696 sizes are directly measured by a combined sharp-edge and Faraday cup method. This optical system is well suited for ...

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Classified

abstracts

5688-5696

sizes are directly measured by a combined sharp-edge and Faraday cup method. This optical system is well suited for variable energy microprobe applications. (Japan) T ishitani et al, J Vat Sci Technol, 20 (I), 1982, 80-83. 36 5688. Low-voltage, high-current electron gun. (USA) A simple, high-performance, electrostatically focused electron gun, which is useful over an energy range extending from a few electron volts to at least 500 eV, is described. The current is delivered in a beam - 1 mm in diameter, with ~50 mrad angular divergence and typically has a current over 1 mA at 100 eV. The design is small, compact, and rugged. This electron gun has been used succ&sfully in both l&oratory and sounding rocket experiments. Peter W Erdman and Edward C Zipf, Rev Sci Instrum, 53 (2), 1982, 225221. 36 5689. Ion beam applications for precision infrared optics. (GB)

In applications involving steering optical beams, the wavefront rms distortion introduced by the optical train strongly influences the system deviation from diffraction-limited, which in turn determines the system performance in focusing, imaging, etc. Substrate surface figures better than i/l0 (2 in the visible) are sometimes required; for optical coatings, uniformities of 2% or better can be essential. These can be severe requirements, particularly for large diameter optics. Ion beam techniques can be applied to improve the surface figure of metal and glass substrates as well as dielectric coating materials. This is done at the expense of increased surface roughness. Results are presented illustrating the increase of surface roughness with an amount of ion beam milling for a variety of materials. Other parameters are described which determine the effectiveness of the process. Ion beam milling techniques have been employed for adjusting the performance of an optical coating in situ without breaking vacuum. Used with an optical monitor, the technique can be a diagnostic to analyse coating performance. J R McNeil and W C Herrmann Jr, J Vat Sci Technol, 20 (3), 1982, 324326. 36 5690. Simple and efiicient monoenergetic electron source. (USA) A source of monoenergetic electrons giving a high electron current (3 x lo-’ A) simultaneously with a good energy resolution (30 meV) is described. It has been ascertained that the emitted electron beam is not superimposed on a background which normally appears when an electron beam is scattered on deflecting electrodes within the instrument. This double 127’ cylindrical selector is especially suitable for experiments where relatively high intensities in conjunction with high quality beams are essential and where stable electron currents over periods of several days or weeks are required. Such a stability is observed in the case where the gas pressure inside the selectors is as high as IO-’ torr. (Canada) M Proulx et al, Ret Sci Insrrum, 53 (6). 1982, 778-780. 36 5691. Plasma studies on a hollow cathode, magnetic multipole ion source for neutral beam injection (USA) A series of Langmuir probe studies has been undertaken on the hydrogen plasma of an 8 x 8 cm extraction area hollow cathode, magnetic multipole ion source intended for use in neutral beam injection systems. Five movable probes were utilized to measure plasma density, electron temperature, plasma potential and primary electron density as a function of position in the plasmagenerator and performance of the ion source. The measurements indicate that at discharge current below 150 A, a fairly uniform plasma over the source volume, with a potential positive with respect to the anode, is generated. The performance of the plasma generator at low currents resembles the filament discharge, magnetic multipole confinement ion source. The ion source in this case has good efficiency and plasma uniformity, but atomic species fractions of less than 70%. As the discharge current is increased, the plasma separates into a high-density, high-ionization, positive potential region near the cathode, and a lower-density, negative potential plasma near the extraction grids. This plasma near the acceleration electrodes is characterized by a relatively low primary electron to plasma electron density ratio of about 2 %. The performance of the source significantly increases over the uniform volume plasma case with atomic species outpit of typically 85% and gas utilization efficiencies of 40-65X. The high-current, hollow cathode discharge produces a plasma c&figuration and output performance similar to that of the duoPIGatron ion source, but with lower noise levels. D M Goebel and A T Forrester, Ret Sci insrrum, 53 (6), 1982, 81&815. 424

36 5692. Reduction of gas flow into a hollow cathode ion source for a neutral beam injector. (USA) Experimental studies have been made on the reduction of the gas flow rate into ion sources which utilize a hollow cathode. The electron emitter of the hollow cathode was a barium oxide impregnated porous tungsten tube. The hollow cathode was mounted to a circular or a rectangular bucket source and the following results were obtained. There was a tendency for the minimum gas flow rate for the stable source operation to decrease with increasing orifice diameter of the hollow cathode up to 10 mm. A molybdenum button with an appropriate diameter set in front of the orifice reduced the minimum gas flow rate to one half of that without button. An external magnetic field applied antiparallel to the field generated by the heater current stabilized the discharges and reduced the minimum gas flow rate lo one half of that without field. Combination of the button and the antiparallel field reduced the minimum gas flow rate from the initial value (9.5 torr I s-l) to 2.4 torr I s- ‘. The reason for these effects was discussed on the basis of the theory for arc starvation. (Japan) Shigeru Tanaka et al, Reu Sci Instrum, 53 (7), 1982, 1038-1048. 37. VACUUM INSTRUMENTATION

FOR SURFACE STUDIES

37 5693. In siru investigation of metallic surfaces by surface plnsmon ATR spectroscopy, electrical resistance measurements (GB)

and Auger spectroscopy.

We describe an experimental ultra-high vacuum set-up which allows the performance of optical reflectivity and dc resistance measurements as well as Auger spectroscopy on thin metallic films prepared in situ. The use of surface plasmon excitation in attenuated total reflection (ATR) configuration, combined with the two other methods, is of particular interest for investigation ofsurface phenomena at metallic surfaces. As an illustration, we present and discuss results for bare metallic films and for films covered with very thin metallic layers. (France) T Lopez-R& and G Vuye, J Phys E: Sci Instrum, 15 (4), 1982,456-461. 37 5694. Imaging of surfaces in LEED instruments. (GB) A new technique to obtain a magnified image of a surface with a lowenergy electron diffraction instrument with central electron gun is described. It is achieved by scanning the primary electron beam by means of two pairs of Helmholtz coils externally attached to the apparatus. The technique can be used to analyse selected grains of polycrystalline samples by both LEED and AES. (West Germany) H E Bauer et al, .I Phys E: Sci Insrrum, 15 (3). 1982, 277-278. 37 5695. Principles and applications of ion-induced Auger electron emission from solids. (USA) We review critically the field of Auger electron emission from slow ion impact on surfaces (Auger neutralization and de-excitation), and Auger emission from the decay of inner-shell holes created by impact with energetic ions. We show how the inspection of the basic formalism of transition rates for Auger neutralization, reveals the basic physical mechanisms involved, and provides the foundation for the method of Ion Neutralization Spectroscopy (INS) created by Hagstrum and co-workers. We describe the necessary experimental techniques, and show some of the most prominent applications of INS. We then present background information from electron-excited Auger Electron Spectroscopy (AES), we review the basic physics of inner-shell excitation by energetic light-ions (Born approximation and leading corrections lo it), the case of inner-shell electron promotion in heavy ion collisions, and specific solid state effects. Finally, we discuss experimental aspects and specific examples of ioninduced Auger spectra from low Z targets, and point to possible applications. Rail A Baragiola, Rad Eficrs, 61, 1982, 47-72. 37 56%. High sensitivity surface crystallographyillustative LEED analyses of Cu(lO0) and Ag(ll0). (GB) Results obtained from studies of the Cu( 100) and Ag( 110) surfaces indicate that LEED structural analyses ofclean metallic surfaces can be sensitive to changes on the order of 0.02 A in atomic spacing. This sensitivity was achieved by placing particular emphasis on both obtaining a reliable experimental data base and studying the effects of nonstructural parameters which are used in dynamical LEED calculations. Error reduction in the experimental I-V profiles was accomplished by using a technique where nonspecular profiles, collected for normal incidence, were