Trends in surface roughening: analysis of ion-sputtered GaAs(110)

The effects of diffusion kinetics on surface roughness were investigated by measuring the dependence of surface width and step density on the amount of material removed for GaAs(110) sputtered at different temperatures (T). Surfaces after the removal of ten monolayers of material at 625 K were rougher on a small scale than those at 725 K, but they were smoother on a large scale. The increased large-scale roughness at high T was caused by increased diffusion on terraces and along step-edges, but insufficient cross-step transport. The high step-density created at low T enhanced cross-step transport. This mechanism, first proposed for the re-entrant layer-by-layer growth, is expected to cause the long-range roughness to increase with T for many solid surfaces after substantial sputtering or deposition over a certain range of T.     

Diffusion kinetics in the Pd/Cu(001) surface alloy

We use atom-tracking scanning tunneling microscopy to study the diffusion of Pd in the Pd/Cu(001) surface alloy as a function of temperature. By following the motion of individual Pd atoms incorporated in the surface, we show that Pd diffuses by a vacancy-exchange mechanism. We measure an activation energy for the diffusion of incorporated Pd atoms of 0.88 eV, which is in good agreement with our ab initio calculated energy of 0.94 eV.     

Atomic mechanisms and kinetics of self-diffusion on the Pd(001) surface

The atomic mechanisms and kinetics of self-diffusion of Pd adatoms on a single-crystal Pd(001) surface are investigated using molecular dynamics simulation. It is shown that the migration of Pd adatoms on the Pd(001) surface predominantly occurs through the relay-race mechanism with the participation of substrate atoms. The activation energy for an elementary event of relay-race self-diffusion is calculated from the kinetic equation describing the change in the concentration of surface adatoms labeled at the initial instant of time.     

Initial surface roughening in Ge/Si(001) heteroepitaxy driven by step-vacancy line interaction

The initial surface roughening during Ge epitaxy on Si(001) is shown to arise from an effective repulsion between S(A) surface steps and dimer vacancy lines (VLs). This step-VL interaction gradually inactivates a substantial fraction of adatom attachment sites at the growth front, causing a rapid increase in the rate of two-dimensional island nucleation. The mutual repulsion hinders the crossing of S(A) surface steps over VLs in the second layer, thus organizing the developing surface roughness into a periodic array of anisotropic 2D terraces. Isolated (105) facets forming at specific sites on this ordered template mediate the assembly of first 3D Ge islands.     

Cl chemisorption on the Pd(001) surface: A self-consistent LCAO calculation of electronic structure

The total and partial densities of states and work functions for the clean Pd(001) surface and for a c(2×2) Cl overlayer on this surface are calculated using a self consistent Gaussian LCAO technique. The adlayer increases the work function of the clean surface by 0.8 eV and leads to a distinct split off feature in the total density of states. The band structure of the bands composing this feature are compared to the bands of the isolated Cl layer.     

Scaling and universality of roughening in thermal oxidation of Si(001)

By analyzing atomic force microscopy images, we derive a continuum equation that quantitatively explains the roughening at the Si(001)-SiO2 interface during thermal oxidation at the temperature at 1200 degrees C in an Ar atmosphere containing a small fraction of O2. We also show that there is a phase transition in the universality class from a disordered to step-terrace structure at the interface at oxidation temperatures between 1150 and 1380 degrees C with the miscut angle of the substrate as the scaling parameter.     

Els and leed study of CO adsorption on Pd(001) and Pd(001) 6° [110]

LEED studies indicate that both CO and carbon adsorb differently on Pd(001) surfaces with and without steps. However, electron energy loss spectra for Pd(001) samples with and without ordered steps show no detectible surface structural sensitivity to CO adsorption. For both samples an additional loss feature at 13.5 eV appears upon CO adsorption. This feature is identified as a (1π?5σ) to 2π^★ type intramolecular electronic excitation, and it appears to be a universal feature of molecular CO adsorption on metals. A second loss expected in the 6–7 eV range associated with a d to 2π^★ type charge-transfer excitation was not detected. Either the transition probability is low for this excitation or hybridization with surface plasmons may obscure its identification.     

3d过渡金属原子单层在Pd(001)表面磁性的第一性原理研究

用第一性原理基础上的超软赝势方法的总能计算，研究了3d过渡金属(Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn)在Pd(001)表面的单层p(1×1)和c(2×2)结构的表面磁性和总能. 所得结果表明：对于Sc, Ti, V和Cr只存在p(1×1)的铁磁性结构，而Mn只有c(2×2)的反铁磁结构存在. Fe, Co和Ni这三种元素上述两种结构都存在，但是总能上p(1×1)的铁磁结构要低些，因此是比较稳定的结构. 而Cu和Zn在该表面上的单层中不存在上述两种结构. 对于V的p(1×1)铁磁结构，计算得到的每个V原子磁矩为2.41μ_B，大于用全电子方法得到的0.51μ_B. 两种计算方法得到其他金属原子 (Cr，Mn，Fe，Co，Ni)的表面磁矩比较相近，都比孤立原子磁矩略小. 关键词： Pd(001)表面 过渡金属原子单层 表面磁性     

New structure model for the GaAs(001)-c(4x4) surface

The surface structure of the As-stabilized GaAs(001)-c(4 x 4) surface has been studied. We show that the seemingly established three As-dimer model is incompatible with experimental data and propose here a new structure model which has three Ga-As dimers per c(4 x 4) unit cell. This mixed dimer model, confirmed by the rocking-curve analysis of reflection high-energy electron diffraction and first-principles calculations, resolves disagreements in the interpretation of several previous experiments. A good agreement between the observed scanning tunneling microscopy image and the simulated one further confirms the newly proposed model.     

A RHEED and AFM study of the epitaxial growth of Pd on Pd(001)

The homoepitaxial growth of Pd on a Pd(001) single crystal surface was studied by the RHEED and AFM methods. The values of surface width obtained by both the methods were compared to each other. Generally, we observed that at the room temperature and at the deposition rate of 1nm/min the surface roughness increases with the mass thickness of the deposited layer. Up to the mass thickness of 10nm the values of surface width ₀ calculated on the basis of measurements carried out by the RHEED and AFM methods are in relatively good mutual agreement. If the values of the mass thickness are higher than 10nm, surface polycrystalline phase develops.