Function Of Ag Coverage Research Articles

Ag adsorption on Cd-terminated CdS (0 0 0 1) and S-terminated CdS (0 0 0 1̄) surfaces: First-principles investigations

First-principles calculations are performed to study the adsorption of Ag at Cd-terminated CdS (0 0 0 1) and S-terminated CdS (0 0 0 1̄) surfaces as a function of Ag coverage. Our results reveal that Ag adsorption at Cd-terminated (0 0 0 1) has a large binging energy than at S-terminated (0 0 0 1̄) surface. For Ag adsorption at Cd-terminated (0 0 0 1) surface, T4 structure is more favorable and the Ag–Cd bond posses an ionic-like character. While for Ag adsorption at S-terminated (0 0 0 1̄) surface, the H3 structure is most stable and the bonding between Ag–S is covalent. It is found that the magnitude and the sign of surface dipole moment are partly determined by the difference between the electronegativities of Ag and the host atom bonding with Ag. The adsorption energy changes as a function of Ag coverage. In addition, related properties of Ag cluster adsorption at Cd-terminated (0 0 0 1) surface are also discussed.

Ag-induced spin-reorientation transition of ultrathin Fe films on Pt(111)

The spin-reorientation transition (SRT) was observed when Ag overlayers deposited on Fe∕Pt(111) by magneto-optical Kerr effect measurements. The easy axis of the magnetization changes completely from the in-plane to out-of-plane direction after the coverage of Ag is 1 ML. The polar Kerr intensity and its coercivity as a function of Ag coverage are investigated during SRT. The easy axis of magnetization can be reversed back to the in-plane direction after the Ag overlayers are removed by sputtering. The chemical compositions of the interfaces are measured by Auger electron spectroscopy. The mechanism of SRT induced by Ag is discussed.

Ag-induced spin-reorientation transition of Co ultrathin films on Pt(111)

The surface magneto-optical Kerr effect was used to study the magnetic properties of Co ultrathin films deposited on Pt(111). The easy axis of the magnetization changes from the out-of-plane to the in-plane direction after the coverage of Co is larger than 3.5 ML. The spin can reorient to the normal of the surface when the proper thickness of Ag overlayers is deposited on Co/Pt(111) with the in-plane magnetization. The out-of-plane magnetization and its coercivity as a function of Ag coverage were investigated during the spin-reorientation transition. The easy axis of the magnetization can shift back to the in-plane direction after the Ag overlayers are sputtered out. The chemical compositions of the interfaces were measured by Auger electron spectroscopy. The mechanism of the spin-reorientation transition induced by Ag is discussed.

Photoelectron spectroscopy of the Ag/Pd(110) system

Silver interaction with a Pd(110) surface was investigated, in a wide range of Ag coverages, by means of UPS, XPS and TDS. Our XPS measurements of the 3d levels of both Ag and Pd show significant shifts of the Ag signal as a function of Ag coverage, while the Pd level position remains constants. Both, silver and palladium 3d level binding energies were found to be dependent on the thermal treatment of the Ag/Pd system. XPS and UPS measurements strongly suggest that annealing at 500 K induces interdiffusion at the Ag/Pd interface. For the silver multilayers, the interdiffusion of Ag and Pd, due to the annealing at 500 K, is accompanied by structural changes of the silver overlayer (i.e., the formation of silver 3D crystallites). In the valence band spectrum of a silver multilayer annealed at 500 K we have identified a virtual bound state (VBS), derived from the hybridization of the Pd4d level and the silver valence (sp) band, indicating the presence of small concentration of Pd atoms diffused into the silver overlay. With increasing annealing temperature the Pd concentration in the Ag overlay increases causing a broadening of the VBS due to the Pd d-d interaction. At temperatures beyond 800 K desorption of Ag atoms from the palladium surface takes place.

The application of photoemission, molecular orbital calculations, and molecular mechanics to the silver–poly(p-phenylene sulfide) interface

The interfacial chemistry between evaporated Ag and poly(p-phenylene sulfide) (PPS) has been investigated with x-ray photoelectron spectroscopy (XPS). The initial stages of nucleation and growth of Ag in the subatomic-layer regime were monitored. The PPS core level spectra exhibit no detectable changes as a function of Ag coverage; however, the Ag 3d5/2 peak position shifts ∼0.6 eV to higher binding energy at low Ag coverages. At low Ag coverages, the valence band spectra consist of two main features centered at 2.5 and 5.9 eV. Unrestricted Hartree–Fock (UHF) molecular orbital calculations suggest that the 5.9 eV band consists of weakly perturbed Ag 4d orbitals and bonding Ag 4d–S 3p hybrid orbitals. The 2.5 eV band consists of antibonding Ag 4d–S 3p hybrid orbitals. Molecular mechanics results suggest that the sulfur atom transforms from a bent to either a trigonal pyramidal or trigonal planar configuration after bonding with Ag. Both the molecular orbital calculations and molecular mechanics results suggest that the trigonal pyramidal configuration is more favorable.

Synchrotron radiation photoemission study of the formation of the Ag/GaSb(110) interface

We have studied the chemistry and electronic properties of the Ag/GaSb(110) interface formed at room and low temperature with high resolution core level photoemission spectroscopy. The Ga 3d and Sb 4d core level spectra are deconvolved into bulk, surface, and reacted components. The relative changes in intensities of these components as a function of Ag coverage at room temperature (RT) and low temperature (LT) are studied in terms of interface morphology and chemistry. At LT, the Ga 3d and Sb 4d surface components disappear with about one monolayer of Ag coverage, confirming the two dimensional Ag growth. At RT, on the other hand, the surface components persist up to coverages of several monolayers, indicating a Volmer–Weber growth mode. At higher coverages, both the Ga 3d and the Sb 4d spectra are dominated by reacted components with lower binding energy. The intensity of the Ga 3d core level decays faster as a function of Ag coverage than that of Sb 4d, indicating out diffusion of Sb. Out diffusion is reduced at 80 K. Band bending at the GaSb surface is extracted from the shift of the bulk components. The final position of EF is found to be within 50 meV of the valence band maximum, in good agreement with previous ultraviolet photoemission results.

Structural change of Si(100) and (111) surfaces after Ag deposition studied by MeV ion channeling

The structural change of Si(100) and (111) surfaces associated with the deposition of Ag thin films (0–5 ML thickness) has been studied by high energy ion channeling and low energy electron diffraction (LEED). The variation of the Si and Ag surface peak intensities has been measured using a 1 MeV He + ion beam as a function of Ag coverage ( gq) and heat treatment. With Ag deposition the reconstructed Si(100)2x1 structure relaxes to the bulk-like structure and the Si surface peak intensity decreases in the normal direction. In the case of Si(111), the Si surface peak intensity remains almost constant with Ag deposition over the range of film thicknesses examined.

Investigation of the Ag/InP(110) interface formation

Photoemission yield spectroscopy (PYS), low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) measurements are performed on a set of UHV cleaved InP(110) surfaces from n- and p-type crystals as a function of Ag coverage θ which is varied from about 10 −3 monolayer (ML) to 100 ML. Ag is shown to form an abrupt interface and no pseudo epitaxy of Ag is observed below 100 ML. The variations upon interface formation of the atomic structure, the work function φ, the ionization energy Φ and the semiconductor band bending are analysed together with the changes of the density of filled surface states in the gap and in the valence band within about 0.6 eV from the top. The pinning of the Fermi level observed on n-type samples at ≅4.8 eV, giving then a band bending of 0.35 eV, and the decrease of the work function on p-type samples with θ are related to the observed interface states the possible origin of which is discussed and compared to the AgGaAs(110) system.

The adsorption of ethanol on silver clusters supported on alumina

The adsorption of ethanol on islands of Ag supported on a surface of Al 2O 3 has been investigated utilizing both inelastic electron tunneling spectroscopy (IETS) to probe the vibrational structure of the adsorbed species, and transmission electron microscopy to characterize some of the physical properties of the solid surface. Results are reported for the number and average size of Ag clusters on the surface as the amount of Ag is varied up to a statistically-averaged coverage of approximately 10 Å. Vibrational spectra are shown for saturation coverage of ethanol as a function of Ag coverage. Peak shifts expected to arise due to the difference in electronegativities between Al and Ag are observed for the surface ethoxide species which form upon adsorption.