Outgassing of vacuum materials—II

Classified abstracts 1562-1573 correlation between current and the work-functions of the metals was found. The current can be explained in terms of electron transfer induced by the contact of substances having different work-functions. (Canda) J Hart et al, J Phys D: Appl Phys, 8 (16), 1975, 1941-1947. 34 1562. An optimized Faraday cage design for electron beam current measurements. (GB) We describe a Faraday cage detector for measuring electron beam intensity for use with energies up to 1.2 MeV, with the present data taken at 100 keV. The design features a readily changeable limiting aperture and detector cup geometry, and a secondary electron suppression grid. The detection efficiency of the cage is shown to be limited only by primary backscatter through the detector solid angle of escape, which is optimized with respect to primary backscattered electrons and secondary electron escape. The geometry and stopping material of the detection cup are varied, and the results show that for maximum detection efficiency with carbon as the stopping material, the solid angle of escape must be equal to or less than 0.05= sr. The experimental results are consistent within the d=2% accuracy of the detection electronics, and are not limited by the Faraday cage detection efficiency. (USA) J N Turner et al, JPhys E: Scient Instrum, 8 (I 1), 1975, 954-957. 28 1563. A cryostat for Hall effect measurements under ultrahigh vacuum conditions. (GB) The design and the construction of an apparatus for measuring the Hall effect in ultrahigh vacuum conditions is discussed. R V Aldridge and P J Whyman, JPhys E: Scient hlstrum, 8 (12), 1975, 994-996. 34 1564. Carbon fibres as field emitters. (GB) Electron microscope and field emission microscope studies of carbon fibre field emitters are reported. The total field emission current from the fibres is reasonably stable for many days in vacua of the order of 10 -7 torr; short-term fluctuations are of the order of d=3 % of the current. The half-width of the energy distribution of the emitted electrons is comparable with that for tungsten. Carbon fibres field emit even when not specially sharpened. To explain the emissioncurrent stability in poor vacuum, we propose a mechanism of selfregeneration. E Braun et al, Vacuum, 25 (9/10), 425-426.

35. PROCESSING OF MATERIALS 35 1565. Diffusion profiles of zinc in indium phosphide. (GB) A series of experiments is described in which radio-tracer Zn was diffused into n-type InP over a wide range of experimental conditions. Diffusions were carried out in the temperature range 650-900°C, for varying times of diffusion, and for a variety of ambient vapour pressures. Both chemical and isoconcentration diffusions were performed, and it was found that the diffusion constants for chemical diffusion are much smaller than those for isoconcentration experiments. A detailed consideration of the shapes of the profiles shows that a time-dependent process occurs in the diffusion, giving rise to a concave section in some of the profiles. A model is proposed in which most of the Zn occurs in the InP in the form of the complex (VpZn~. I/p). Zn atoms also occupy In sites, giving rise to the observed p-type conductivity and, in addition, exist in a fast-diffusing interstitial state. It is shown that the results of this and of previous work are in good qualitative agreement with the model. B Tuck and A I-looper, J Phys D: Appl Phys, g (15), 1975, 1806-1821. 35 1566. Ontgassing of vacuum materials---H. (GB) Part II of this two part account examines the methods available for the measurement of outgassing rate. It recounts the results obtained for some selected materials and in particular examines methods for reducing the outgassing rates of materials for use in ultrahigh vacuum. Finally it presents outgassing rates for various materials in tabulated form. R J Elsey, Vacuum, 25 (8), 1975, 347-361.

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36 1567. An apparatus for measuring surface potentials. (GB) An apparatus for measuring surface potentials ranging from a few millivolts to a few kilovolts is described; its principle is derived from Kelvin's method. The measurements can be performed in vacuum or under any controlled atmosphere. The spatial resolution of the apparatus is evaluated, and an example of its use in the investigation of dielectric breakdowns in electrophotographic layers is given. (USSR) S Sakalauskas et al J Phys E: Scient lnstrum, 8 (10), 1975, 837-839.

(In French) 36 1568. Inelastic scattering effects in quantitative Auger electron spectroscopy. (GB) lnelastically transmitted Auger electrons are shown to make a significant contribution to the observed oxygen KLL Auger spectrum from thick magnesium oxide films. A method of inelastic background removal is presented in order that this type of spectrum can be interpreted quantitatively in terms of an inelastic mean free path. A D Martin, J Phys D: Appl Phys, 8 (17), 1975, 2074-2078. 36 1569. The nature of field emission sites. (GB) A probe-hole technique for measuring and mapping electron emission from metal surfaces (e.g. contacts from used vacuum switches) has been developed for use ill situ in a scanning electron microscope. A single emitting region can be selected and its voltage/current characteristic measured. The specific site of the emission source can be predicted, to an accuracy of better than ± 10 p.m, using an electron beam tracking technique; then this site can be examined with the microscope. Visual evidence is shown of 'conditioning' an electrode by voltage breakdown. The link between the source of pre-breakdown current and the site of a spark is confirmed in experiment which demonstrates the accuracy of predicting the position of emission sites. The ambiguity of the Fowler-Nordheim method of analysing voltage/current characteristics is shown by the failure to correlate size predictions with visual observation of certain types of emitter. B M Cox, J Phys D: Appl Phys, 8 (17), 1975, 2065-2073. 36 1570. Inelastic electron scattering spectrometer. (USA) The design and construction of an inelastic electron scattering spectrometer for the study of electronic excitations of solids is described. The spectrometer features high beam energy (300 keV) and fine energy loss resolution (<0.1 eV). Energy loss spectra in the range 0-1000 eV may be measured with momentum transfer from 0to2~ -t. P C Gibbons et al, Rev Scient hlstrum, 46 (11), 1975, 1546-1554. 36 1571. Apparatus for the measurement of angle-resolved spectra of electrons emerging from single crystals. (LISA) An apparatus to measure inelastic low-energy electron diffraction (ILEED) and energy- and angular-dependent secondary electron emission (EADSEE), is described. The apparatus can measure EADSEE for incident beam energies of up to 200 eV and ILEED for beam energies up to 50 eV, with energy and angular resolutions of about 0.15 eV and 1.5 °, respectively. General design criteria are discussed, and detail is provided where a little-known technique has been employed. P E Best, Rev Scient lnstrum, 46 (!1)', 1975, 1517-1521. 36 1572. Determination of concentration in depth profiles of thin films with Secondary Ion Mass Spectrometry. (German) The method of Secondary Ion Mass Spectrometry (SIMS) for the determination of concentration in depth profiles of thin-solid surface layers is briefly presented and discussed. An apparatus for the measurement of depth profiles is described. Some results obtained with diffusion and implantation profiles in a semiconductor and an insulator are reported. The results demonstrate that the SIMS method is still applicable at concentrations which are not detectable with other surface analytical methods. Von R. Buhl et al, Vakuum-Tech, 24 (7), 1975, 189-194. (hz German). 36 1573. Interdiffusions in thin-film Au on Pt on GaAs (100) studied with Auger spectroscopy. (USA) It has been proposed that interdiffusion of Pt, Au, and GaAs constitutes one major source of instability in GaAs microwave devices