Z. Wolfram

Atomic force microscopy of Au/Hg alloy formation on thin Au films

Abstract Atomic force microscopy was applied to the study of thin Au films deposited under ultra-high vacuum conditions on a glass support maintained at 78 K. A variety of thin gold film structures were thus determined and characterized ranging from (i) nanometric isolated gold islands, (ii) nanometric gold structures, to (iii) continuous gold films, all depending on the amount of Au deposited. The influence of the amalgamation process on the thin Au films topography was studied. The fundamental importance of surface defects on the rate of amalgamation was clearly seen. The movement of small Au islands on glass obtained as the result of thermal decomposition of Au Hg alloys was observed.

Incorporation of positively and negatively polarized hydrogen and deuterium adspecies from the surface into the bulk of thin palladium films

The incorporation of hydrogen and deuterium adspecies from the surface of a thin palladium film into the bulk has been studied measuring simultaneously the surface potential changes by means of high sensitivity (± 1 mV), short response time (0.1 s) static capacitor system, and pressure by means of the ultrasensitive Pirani type gauge. It has been found that the positively polarized β+ adspecies of hydrogen incorporate quickly at 78 K and 87 K. via a tunneling mechanism, with a diffusion coefficient of 3 × 10−13 cm2s. The β+ adspecies of deuterium incorporate with slightly increasing diffusion coefficient with the temperature increase: 1 × 10−13 cm2s at 78 K and 2 × 10−13 cm2s at 87 K. The negatively polarized adspecies β−, which strongly predominate and at 160 K, slowly incorporate in the bulk of palladium.

Surface phenomena in titanium hydride formation

Surface phenomena which occur during hydrogen interaction with thin titanium films within the pressure interval 10−10−10−2 Torr, at the temperature range 78–298 K, have been studied through measurement of surface potential changes by means of high sensitivity, short response time static capacitor system, with simultaneous recording of pressure by means of an ultra-sensitive Pirani-type gauge. At the beginning of adsorption negatively polarized adspecies stable on the surface, named β+ formed. With the increase of the population they are followed by the creation of positively polarized adspecies named β−. The β− adspecies are incorporated quickly below the surface forming percipitates of titanium hydride in a thin titanium film matrix. The activation energy for β+ adspecies incorporation has been estimated to be 6kJ/mol H2. On a titanium hydride surface, positively polarized, weakly adsorbed (Ed < 20 kJ/mol) hydrogen adspecies exist.

Investigation of atomic deuterium (hydrogen) emission from the surface of some transition metal deuterides (hydrides)

Abstract Deuterium desorption from the surface of decomposing palladium deuteride was studied while monitoring the atomic component of the desorbing gas by means of an adsorption method. A thin gold film was applied as an adsorbent active for D adsorption, but inert against interaction with D2. The deuterium deposit thereby collected on the Au surface was analysed by means of thermal desorption mass spectrometry (TDMS). The atomic component of deuterium arising by desorption from decomposing PdDy was clearly detected. The experimental results obtained for PdDy are compared with those observed during the decomposition of PdHx, as well as the decomposition of other hydrides including TiHz and VHu.

Oxygen interaction with palladium hydride and titanium hydride surfaces

Abstract Oxygen interaction with thin palladium hydride (PdH x ) and titanium hydride (TiH y ) films obtained in situ under controlled conditions in UHV apparatus has been studied. The surface potential (SP) measurements have been carried ut to distinguish between elementary steps of surface processes during hydrides formation, oxygen adsorption on Pd (Ti) and O 2 reaction with PdH x and TiH y , Mass spectrometry has been applied to determine gas phase composition. It has been found that O 2 interaction with PdH x at 195 K leads to H 2 O formation with the hydride decomposition. O 2 interaction with TiH y within a temperature range of 78–195 K causes hydrogen replacement on the surface and in the subsurface region by oxygen. Hydrogen is removed to the gas phase.

Atomic hydrogen desorption from thin palladium hydride films

It has been proved that hydrogen atoms desorb from the surface of a decomposing thin palladium hydride film. A thin gold film deposited and sintered in situ was used as a selective adsorbent for atomic hydrogen. The TDMS (thermal desorption mass spectrometry) technique was applied to detect the adsorption of hydrogen on gold and to determine the amount adsorbed.

Deuterium adsorption on thin nickel films

Abstract Adsorption states arising upon interaction of deuterium with thin nickel films at 298 and 78 K were distinguished by simultaneous surface potential and pressure measurements. Rapid recording, sensitive and nondisturbing methods (static capacitor and ultrasensitive Pirani-type gauge) were applied. Negatively polarized β- adspecies are formed at 298 K, while at 78 K the β- state arising at low coverage is followed by the positively polarized β+ state. The features of the β+ state are described. The isotope effect is shown.

Atomic hydrogen adsorption on sintered thin copper films

Abstract Atomic hydrogen adsorption on thin copper films deposited under UHV conditions was examined by means of Thermal Desorption Mass Spectrometry (TDMS) and measurements of corresponding relative resistance changes ( ΔR R ). It was found that at 78 K, within a coverage interval 0.02 θ ΔR R with increasing θ. TD spectra showed a large TD peak with a temperature maximum T m at 300 K and traces of a very small TD peak (with θ on the order of 10 −4 ) at a T m of 170 K. At θ > 0.3 a weakly bound, inferred to be an induced form of the adsorbate was seen with a T m at 230 K. No traces of molecular hydrogen adsorption could be observed until the H 2 pressure, P , was below 0.1 Torr.

Surface phenomena in the process of vanadium hydride formation

Abstract Surface phenomena associated with the formation of vanadium hydride VH x were studied by measuring both the surface potential of thin V films and the H 2 pressure during hydrogen interaction with vanadium. It has been found that hydrogen forms two different adspecies here referred to as β − and β + . The β + adspecies forms a precursor in the fast incorporation process of atoms from the surface into the bulk of the metal. The bcc to fcc phase transition which occurs during the VH x formation alters the kinetics of β + incorporation. On the surface of VH 0.6 a weakly bound atomic hydrogen adsorbate was found at 87 K under a H 2 pressure of the order of 10 −1 Pa.

Decomposition of thin palladium hydride films as a source for low temperature atomic hydrogen emission

Abstract Atomic hydrogen emission from the surface of thin palladium hydride films PdH x during their decomposition was studied using thin Au films as a selective adsorbent for H atoms from a desorbing (H + H 2 ) mixture. The influence upon this phenomenon of Pd films sintering and the population of weakly bound atomic hydrogen adspecies on a PdH x surface was examined.