Zn Adatoms Research Articles

Specific anion adsorption in the course of upd of Zn2+ ions on platinum

Abstract The specific anion adsorption accompanying the upd of Zn 2+ ions on platinum electrodes has been studied by the radiotracer technique using 15 S labelled sulphate species and 36 Cl labelled Cl − ions. It has been found that sulphate ions adsorb readily on the top of Zn adatoms while the adsorption strength of Cl −1 ions on the Zn adlayer is significantly lower than that of HSO 4 −1 (SO 4 2− ) ions. Indirect radiotracer evidence obtained from competitive adsorption studies is presented concerning the relatively high adsorbability of H 2 PO 4 ions. It follows from the experimental results obtained that the calculation of mass and charge balance (involving the determination of the so-called electrosorption valence) requires the knowledge of the extent of the anion adsorption on the adatom layer.

The chemical properties of bimetallic surfaces: bonding between CO and Zn on Ru(001)

The adsorption of CO on Zn/Ru(001) surfaces has been studied using thermal desorption mass spectroscopy, core and valence level photoemission and Auger spectroscopy. At 80 K, CO does not adsorb on thick Zn films under ultra-high vacuum conditions. In contrast, adsorption of the molecule is observed on Zn atoms bonded to Ru(001). Bimetallic bonding induces a reduction of ∼ 0.5 eV in the binding energy of the core and valence levels of Zn. This shift probably increases the strength of the ZnCO bond. CO molecules adsorbed on Zn adatoms show an O(1s) binding energy close to 535.2 eV and a desorption temperature of ∼ 125 K. Both properties indicate that π-backbonding is very weak in the ZnCO bond. For CO chemisorption on Zn/Ru(001) surfaces, Zn blocks Ru sites approximately on a one-to-one basis and induces a weakening of the RuCO bond.

The chemical properties of bimetallic surfaces: bonding between CO and Zn on Ru(001)

The adsorption of CO on Zn/Ru(001) surfaces has been studied using thermal desorption mass spectroscopy, core and valence level photoemission and Auger spectroscopy. At 80 K, CO does not adsorb on thick Zn films under ultra-high vacuum conditions. In contrast, adsorption of the molecule is observed on Zn atoms bonded to Ru(001). Bimetallic bonding induces a reduction of ∼ 0.5 eV in the binding energy of the core and valence levels of Zn. This shift probably increases the strength of ZnCO bond. CO molecules adsorbed on Zn adatoms show an O(1s) binding energy close to 535.2 eV and a desorption temperature of ∼ 125 K. Both properties indicate that π-backbonding is very weak in the ZnCO bond. For CO chemisorption on Zn/Ru(001) surfaces, Zn blocks Ru sites approximately on a one-to-one basis and induces a weakening of the RuCO bond.

Reflection high energy electron diffraction study on adatom desorption from ZnSe surface under electron beam irradiation and light irradiation

Effects of electron-beam and light irradiation on the desorption and adsorption processes of Zn and Se adatoms on ZnSe(100) surfaces were studied using the intensity variation of the specular spot of RHEED. The desorption rate constants of physisorbed and chemisorbed atoms were obtained and discussed.

Photo-assisted MBE growth of ZnSe on GaAs substrates

ZnSe epilayers have been grown by photo-assisted MBE on GaAs substrates at various substrates temperatures and under various molecular beam intensity ratios of group VI to group III element. A He-Cd laser with 441.6 mm wavelength was used as a light source. From the temperature dependence of the photo-desorption rate constants, the activation energies of photo-desorption of Zn and Se adatoms from the physical adsorption state ( E P Zn, E P Ss) and from the chemical adsorption state ( E C) are obtained, that is, E P Zn =7.8 kcal/ mol, E P Se =6.7 kcal/mol and E C =16.1 kcal/mol. Thus, the photo-desorption observed is photo-enhanced “thermal” desorption. ZnSe epilayers have been successfully grown at a temperature as low as 150°C. A sharp and strong free-excition emission is observed in photoluminescence spectra at 11 K in the low-temperature grown samples, which shows that the crystallinity is almost comparable with that of the unirradiated epilayer grown at 340°C (the optimum growth temperature without irradiation).

Morphological instability of Zn crystals grown by VLS mechanism from Zn-Bi monotectic droplets

Disk-like or bowl-like Zn crystals were grown by the VLS mechanism just below the monotectic point, using the monotectic Zn-Bi system. These morphologies have not been observed in eutectic systems. During the VS growth after the cessation of the VLS growth, pulley-like crystals were grown from many of these crystals by morphological instability. It seems that the morphological instability of these crystals is due to the surface diffusion of Zn ad-atoms, on flat basal faces, to edges of the curved lateral surface.

Observation of ALE growth process of ZnTe by RHEED.

The ALE growth process of ZnTe is investigated with RHEED intensity observation. It is found that when the substrate temperature is sufficiently low, physisorbed Zn and Te adatoms are present on the Zn and Te-coverd surfaces, respectively. The ZnTe layers not less than monolayer grow during one cycle of ALE by the presence of these excess adatoms. Evaporation of the surface atoms occurs during growth suspension. First, the excess adatoms desorb, and then Zn and Te atomic layers sublime with different sublimation time constants. At high temperatures, the layer-by-layer evaporation occurs, as is verified by RHEED intensity oscillation during the sublimation process.