Ionization-stimulated annealing effects on displacement damage in magnesium oxide

Classified

abstracts

Classified abstracts on this page 3299-3306

Editor’s note The label immediately following that at the end of each abstract

I. General

vacuum

science

3299-3365 the title of each item denotes country or origin of publication, indicates country of origin of work (where known).

and engineering

11. GASES AND SOLIDS 11 3299. Diffusive release of gas from a solid in the presence of traps using a linear tempering schedule. (GB) The effect of permanent trapping on the surface evolution rate of gas released from a semi-infinite solid is examined for the case of a linear tempering schedule. Analytical expressions are obtained for the rate maximum, the temperature at which the maximum occurs and the temperature width of the evolution rate transient for gas initially located in a specific plane below the surface. In addition, precise plots of the evolution rate transients are obtained for initial planar concentrations and for an extended distribution, by numerical solution of the appropriate diffusion equations. S E Donnelly and D G Armour, Vacuum, 27 (1), 1977,21-25. 11 3300. AES-LEED study of adsorption of common gases on the (100) planes of W and Nb. (GB) The adsorption of Oz, Nz and CO on W(lO0) and that of O2 and N2 on Nb(100) at room temperature were studied with LEED-AES techniques and by the measurement of work function changes using the retarding potential method and the Kelvin technique. The LEED pattern changes due to adsorption on W(100) were similar to earlier reports except for heavy doses of nitrogen which produced a (5 x 1) structure. On Nb(lOO), oxygen adsorption caused a ~(2x2). For heavy exposure of nitrogen, a superstructure with four satellite spots positioned crosswise around (01) beams appeared. The work function change was plotted against the Auger peak height of the various adsorbates and a remarkably linear relationship existed for O,/W(lCO) and for N,/W(lOO) but not for CO/W(lOO) or O1/Nb (100). The 26 eV Auger peak of Nb(100) disappeared at an oxygen exposure of IOL, while the same Auger peak was reduced by only l/5 following saturation with nitrogen. (Japan) S Usami et al, Vacuum, 27 (1), 1977, 1I-16. 11 3301. Einetics of the generation of atomic hydrogen and its adsorption on Si(ll0). (USA) The rate of change of uv photoemission spectroscopy (UPS) spectral features accompanying formation of the monohydride phase on Si(llO)5 x 1 has been measured as a function of Hz pressure and W filament temperature in a thermal activation source. It is shown that an equilibrium thermodynamic calculation can reproduce the observed rates only if the adsorbing species produced at the hot filaments is atomic H and not vibrationally excited Hz*. An approximate calculation of absolute rates makes sense only if the sticking probability of atomic hydrogen on clean, room-temperature Si (110) 5 X 1 is near unity. J Sakurai et al, J Vuc Sci Technol, 14 (1), 1977,397-399. 11 3302. Chemical implantation of 10 keV H+ and D+ in rutile. (USA) Rutile (TiO,) implanted with 10 keV H+ and D+ exhibits broad ir absorption bands at 3400 and 2505 cm-‘, respectively. The D+ implantation also includes a sharp band at 2438 cm-‘. This 2438 cm-’ band corresponds to the sharp hydroxyl absorption peak at 3277 cm-t typically present in flame-grown rutile crystals. In addition the bombardment induces a broad absorption at 900 nm, which is attributed to delocalized electrons resulting from direct chemical reduction of the rutile by the implanted hydrogen or deuterium and which is similar to the well-known 1500 mm free-carrier absorption in rutile heated in a reducing atmosphere. The absence of such an absorption after 10 keV He+ or Ar+ bombardment implies that reduction by preferential sputtering does not significantly contribute to this band. Evidence is adduced to support the view that the 900 nm absorption, which appears to the eye as a blue color, is

and

associated with chemically implanted D+. Using projected ranges for 10 keV D+ and experimentally determined transition moments for O-D stretch intensities leads to a value for the oscillator strength of the “blue” band of 4.1. The large f value supports the assignment of the “blue” band to free-carrier absorption rather than to a d-d transition localized at a Ti3+ site. B Siskind et al, J Vuc &i Tech&, 14 (l), 1977,537-542. 11 3303. Ionization-stimulated annealing effects on displacement damage in magnesium oxide. (USA) The effects of ion bombardment into MgO were investigated by measuring resulting volume changes with a cantilever beam technioue and by monitoring the F band absorption induced in the uv region of the spectrum. Single crystals of MgO were bombarded near (lOO> with 500 keV argon, which resulted in an expansion of the implanted near-surface layer due to the ion-induced lattice damage. Under subsequent 100 keV proton irradiation, however, a large fraction of this expansion is relieved since the material compacts. This seems to indicate that defects with different charge states are produced in MgO by heavy-ion bombardment and that electronic processes account for the volume changes observed during subsequent irradiation with the primarily ionizing radiation from the 100 keV H+ implantation. Identical behavior was found earlier for the highly ionic A1203 while no such effect was observed in the predominantly covalent SiOZ. The present results thus corroborate our model of the existence of defects with different charge states in ionic materials. This behavior of MgO and A120s is of considerable interest since both materials are candidates for first-wall application in CTR environments. G B Ereft, J Voc Sci Tech@ 14 (1), 1977,533-536. 11 3304. The role of gaseous impurities in the hydrogensmhrifflement of steel. (USA) The effect of the presence of gaseous hydrogen on the mechanical properties of steels is presented. This phenomenon, generally known as hydrogen embrittlement, is shown to be dependent on the ability of the steel to absorb hydrogen. A series of crack-growth and adsorption experiments clearly show that the supply of hydrogen at the metal surface can be chemically controlled. This chemical control can be used to either accelerate or retard crack growth in a 4340 steel specimen. V Srikrishnan and P J Ficalora, J Vat Sci Tech&, 14 (!), 1977, 588592. 11 3305. Chemisorption on a surface segregated Pt-Au alloy. (USA) Segregation of Au to the surface of polycrystalline Pt-5% Au was studied. This alloy was chosen as an example of a simple regular solution alloy of catalytic interest. At 600°C the equilibrium surface concentration is essentially a monolayer of Au. This behavior is consistent with the broken-bond theory for surface segregation but incompatible with the size-difference theory. The effect of the segregation on the CO/H2 chemisorption has been studied. Small amounts of gold appreciably reduce the adsorption. The shape of the flash desorption spectra for HZ is not altered by the presence of Au on the Pt surface, however the CO spectra are changed. J A Schwan et al, J Vuc Sci Technol, 14 (l), 1977,457460. 11 3306. Molecular-beam study of the nucleation of water on silver iodide. (USA) A molecular heam of water vapor is impinged onto a polycrystalline silver iodide substrate. The beam temperature is 273 K and the beam flux at the substrate is approximately 1.5X lOL4 molecules crnm2 s-r. The substrate is held at a temperature T, between 145 and 163.5 K. The reflection coefficient (1 -y) of water vapor hitting the 87