Field emission patterns and emission characteristics concerning single crystal tips of LaB₆, CeB₆, PrB₆, NdB₆ and SmB₆ were studied. The (001) oriented cathode tips were prepared by means of the flux technique and the electrolytic etching method. MeB₆ cathodes showed symmetrical field emission patterns either by flashing operation with some definite temperature range (for example, 1400-1500°C for a La, cathode), or by field desorption cleaning. These emitters displayed characteristic patterns easily correlated with the body-centered cubic crystal structure. Most crystals gave (001) built-up patterns by the heat treatment of 800°C× 30-40 min. with the anode voltage applied. Emission characteristics for a period of about an hour after the flashing treatment were mainly governed by adsorption, desorption and migration of residual gas molecules on the cathode surface.

View full abstract

A new technique specially designed to use Auger electron spectroscopy for the measurement of very low sputtering yield has been applied for low energy (0.1-6 keV) proton sputtering of molybdenum and pyrolytic graphite. In molybdenum the sputtering yield above 1 keV is about three times as large as the experimental one obtained by Finfgeld, and below 1 keV it rapidly decreases with decreasing energy. In graphite physical sputtering yield at 500°C is about an order of magnitude larger than that of molybdenum, whereas the energy dependence is very similar to the molybdenum case. But the energy dependence is very different from the theory of Weissmann and Sigmund. The measured temperature dependence of the chemical sputtering yield for pyrolytic graphite at 1 keV shows the maximum value of about 0.08 CH₄ molecules/ion near 750 K.

View full abstract

Using the FEM method adsorption of CO on tungsten tips has been studied at adsorption temperatures of 300 K, 200 K and 80 K. A proposed model of adsorbed species has been used to analyze the observed FEM images. The low-temperature (below200 K) CO layer and the high-temperature (200 K-300 K) CO layer are shown to have no differences, except that weakly-bound CO species are additionally populated as the temperature of adsorption is lowered. At saturation the CO layer over a tungsten tip below 300 K is interpreted to be a superposition of seven states which are attributed to those seven intrinsic sites over a tip of a b.c.c. crystal which are given by considering not only the outermost atomic arrays of surface planes but also atomic arrays below the outermost ones. An interpretation of “pseudoclean pattern” is made that if all the above types of adsorption are completely surface-dependent the relative situation of the saturated tip is not different from that of the clean tip. The occupation at 80 K is found to be attained most completely, which seems to permit the image the most clever imitation of the clean pattern.

View full abstract