Labyrinthine island growth during Pd/Ru(0001) heteroepitaxy

Using low energy electron microscopy we observe that Pd deposited on Ru only attaches to small sections of the atomic step edges surrounding Pd islands. This causes a novel epitaxial growth mode in which islands advance in a snakelike motion, giving rise to labyrinthine patterns. Based on density functional theory together with scanning tunneling microscopy and low energy electron microscopy we propose that this growth mode is caused by a surface alloy forming around growing islands. This alloy gradually reduces step attachment rates, resulting in an instability that favors adatom attachment at fast advancing step sections.     

Surface states of Sc(0001) and Ti(0001)

Calculated electronic properties are compared for 11-layer Sc(0001) and Ti(0001) films. Prominent surface states are found whose locations conform to expectations based on the respective bulk band structures establishing a roughly rigid band picture of the surface bands. Surface core-level shift and work function results are qualitatively explained.     

Band structure of Au layers on the Ru(0001) and graphene/Ru(0001) surfaces

The electronic structures of Au monolayers on the Ru(0001) and graphene-coated Ru(0001) surfaces have been calculated by DFT method using the supercell (repeated-slab) approach. The local densities of states (LDOS) and band structures of the monolayer and bilayer Au films adsorbed on the graphene/Ru(0001) and those of free hexagonal Au layers are found to be very similar. This result indicates that the monolayer graphene almost completely screens the Au layers from the Ru(0001) substrate surface, so that electronic properties of Au films adsorbed on graphene are determined predominantly by the electronic structure of the Au adlayers, essentially independent on the electronic structure of the substrate surface.     

Angle-resolved photoemission study of Pd(111) and Co/Pd(111)

Electronic structure of epitaxial Co films on Pd(111) has been investigated as a function of the Co overlayer thickness, by using angle-resolved photoemission spectroscopy (ARPES). It is found that experimental band structures for Pd(111) and work functions for Co/Pd(111) agree reasonably well with the results of band structure calculations. Compared to Pd(111), valence band ARPES spectra of Co/Pd(111) support the existence of the induced magnetic polarization of Pd atoms near the interface, suggesting large hybridization between Co 3d and Pd 4d states near the interface.     

Pd对O吸附在ZnO（0001）面上的影响的第一性原理研究

本文用第一性原理方法计算了Pd 在ZnO(0001)面上的吸附、Pd对O吸附的影响及Pd替代表面Zn原子能量的变化.结果表明：(1) Pd的吸附位置不随覆盖度变化,Pd稳定吸附位为H3位;(2)Pd在1/4单层吸附时比1个单层吸附时稳定;(3)Pd的存在增强了氧在ZnO(0001)面上的吸附,O原子可以扩散到Pd吸附层的下,Pd处于最上面, 具有催化作用.     

Magnetic properties of (Co Pd ) superstructures on Pd(100) and Pd(111)

The magnetic properties of (Co_nPd_m)_r superstructures on Pd(100) and Pd(111) are evaluated using the fully-relativistic spin-polarized screened Korringa-Kohn-Rostoker method. It is found that only in the case of a Pd(111) substrate such superstructures exhibit perpendicular magnetism, while on a Pd(100) substrate the magnetization is oriented in-plane. Also investigated is the effect of interdiffusion in repeated superstructures. By using the inhomogeneous coherent potential approximation (CPA) for layered systems the effect of ordering into (repeated) superstructures can be described in an ab-initio-like manner. It is found that already small amounts of interdiffusion can be decisive for the actual value of the magnetic anisotropy energy. Received 3 November 1999 and Received in final form 18 January 2000     

Adsorption and desorption of fullerene on graphene/SiC(0001)

Adsorption and desorption of fullerene on a single layer of graphene grown on SiC(0001) were investigated by photoemission spectroscopy (PES). No significant change in the band structure of graphene was observed after fullerene deposition on the graphene layer under vacuum conditions, and subsequent exposure to the air. After annealing the fullerene layer at 275 °C in a vacuum, complete desorption of fullerene was observed without any resulting damage to the graphene structure. The desorption temperature of fullerene was significantly higher than that of pentacene, indicating that fullerene layers show higher stability than pentacene as protection layers of graphene-based devices.     

Interfacial potential approach for Ag/ZnO （0001） interfaces

Systematic approaches are presented to extract the interfacial potentials from the ab initio adhesive energy of the interface system by using the Chen–M ¨obius inversion method. We focus on the interface structure of the metal（111）/Zn O（0001）in this work. The interfacial potentials of Ag–Zn and Ag–O are obtained. These potentials can be used to solve some problems about Ag/Zn O interfacial structure. Three metastable interfacial structures are investigated in order to check these potentials. Using the interfacial potentials we study the procedure of interface fracture in the Ag/Zn O（0001） interface and discuss the change of the energy, stress, and atomic structures in tensile process. The result indicates that the exact misfit dislocation reduces the total energy and softens the fracture process. Meanwhile, the formation and mobility of the vacancy near the interface are observed.     

Transparent CdO/n-GaN(0001) heterojunction for optoelectronic applications

Undoped CdO films were prepared by sol–gel method. Transparent heterojunction diodes were fabricated by depositing n-type CdO films on the n-type GaN (0001) substrate. Current–voltage (I–V) measurements of the device were evaluated, and the results indicated a non-ideal rectifying characteristic with I_F/I_R value as high as 1.17×10³ at 2 V, low leakage current of 4.88×10⁻⁶ A and a turn-on voltage of about 0.7 V. From the optical data, the optical band gaps for the CdO film and GaN were calculated to be 2.30 eV and 3.309 eV, respectively. It is evaluated that interband transition in the film is provided by the direct allowed transition. The n-GaN (0001)/CdO heterojunction device has an optical transmission of 50–70% from 500 nm to 800 nm wavelength range.     

Ferromagnetic hcp chromium in Cr/Ru(0001) superlattices

We report the first observation of a weak ferromagnetic state of Cr in Cr/Ru(0001) superlattices, based on magnetic hysteresis and corroborated by x-ray magnetic circular dichroism at the CrL(2,3) edges. In situ reflection high-energy electron diffraction, x-ray diffraction, and Cr K-edge polarized x-ray absorption investigations have shown that the Cr layers thinner than 8 angstroms adopt a slightly distorted hcp structure, accompanied by a large atomic volume expansion of up to 14% compared to the bcc packing volume. The expanded hcp structure clearly induces the observed ferromagnetism, in agreement with theory.     

Phase transitions in physisorbed films on cadmium (0001): comparison with graphite (0001)

Physical adsorption of simple molecules has been studied experimentally on cadmium (0001). Adsorption isotherms of Kr and CF₄ at 77.3 K show a first-order phase transition in the first layer, characteristic of adsorption on uniform substrates.

The nature of the phase transition on cadmium (0001) in the first layer is investigated for Kr and CF₄ by a thermodynamic approach in comparison with results obtained earlier on graphite (0001).

From the comparison between the two uniform substrates, we show that (1) cadmium (0001) has a less attractive force field than graphite (0001); and (2) like graphite (0001), cadmium (0001) is a very uniform surface suitable for studying two-dimensional phases according to the Gibbsian formulation.     

Comparative study of adsorption characteristics of Cs on the GaN （0001） and GaN （0001） surfaces

The adsorption characteristics of Cs on GaN （0001） and GaN （0001） surfaces with a coverage from 1/4 to 1 monolayer have been investigated using the density functional theory with a plane-wave uttrasoft pseudopotential method based on first-principles calculations. The results show that the most stable position of the Cs adatom on the GaN （0001） surface is at the N-bridge site for 1/4 monolayer coverage. As the coverage of Cs atoms at the N-bridge site is increased, the adsorption energy reduces. As the Cs atoms achieve saturation, the adsorption is no longer stable when the coverage is 3/4 monolayer. The work function achieves its minimum value when the Cs adatom coverage is 2/4 monolayer, and then rises with Cs atomic coverage. The most stable position of Cs adatoms on the GaN （000i） surface is at H3 site for 1/4 monolayer coverage. As the Cs atomic coverage at H3 site is increased, the adsorption energy reduces, and the adsorption is still stable when the Cs adatom coverage is 1 monolayer. The work function reduces persistently, and does not rise with the increase of Cs coverage.     

Chemically driven diffusion of Pd in the surface region of Zn(0001): An ultraviolet photoemission investigation

The diffusion of deposited Pd through the (0001) surface region of zinc has been studied with photoemission at hν = 21.2 eV by following the time evolution of the Zn 3d and Pd 4d peaks for a Pd initial coverage of 1, 3, 10 and 15 monolayers. The time decay of the Pd 4d signal is explained with a model where the diffusion coefficient D is not constant; it is (4.6 ± 0.5) × 10^?19 cm² s^?1 for t?7000s, then decreases to (5.5 ± 1) × 10^?20 cm² s^?1 for t ? 15,000 s. The D values correlate well with the spectroscopic results on the valence state evolution during diffusion. At short times (higher D) the spectra show an electron energy gain of Pd atoms during diffusion while at higher time (lower D) this gain is negligible. The initial diffusion is chemically driven while at longer times the diffusion becomes gradually entropic.