Secondary electron spectra of graphene on Ni(111) surface

We report on kinetic energy distributions of electrons emitted during bombardment of graphene adsorbed on a Ni(111) surface by 0.5-0.9 keV electrons. The spectra reveal several peaks superimposed on the background of cascade electrons. The position of these peaks does not depend significantly on primary electron energy but show a remarkable angular dependence, indicating that they are directly related to the empty bands above the vacuum level of the sample.     

Low-temperature epitaxy of transferable high-quality Pd(111) films on hybrid graphene/Cu(111) substrate

Nano Research - The continuous pursuit of miniaturization in the electronics and optoelectronics industry demands all device components with smaller size and higher performance, in which thin metal...     

Yield and shape selection of graphene nanoislands grown on ni(111)

The catalytic decomposition of hydrocarbons on transition-metal surfaces has attracted increasing interest as a method to prepare high quality graphene layers. Here, we study the optimal reaction path for the preparation of graphene nanoislands of selected shape using controlled decomposition of propene on Ni(111). Scanning tunneling microscopy performed at different stages of the reaction provides insight into the temperature and dose-dependent growth of graphene islands, which precedes the formation of monolayer graphene. The effect of postreaction annealing on the morphology of the islands is studied. By adjusting the initial propene dose, reaction temperature, and postannealing procedure, islands with a triangular or hexagonal shape can be selectively obtained.     

Structural properties of InN on PbTiO3 (111) surfaces

The surface stability of the polar PbTiO₃ (111) surfaces was systematically studied by the first-principle calculations. The surface grand potential was calculated and compared as a function of the relative chemical potential. Both PbO₃ and Ti terminations can exist simultaneously in perovskite PbTiO₃ ceramics. The specific adsorption sites at the initial growth stage and the atomic structure of InN on the PbTiO₃ (111) substrate have been systematically investigated. The In adsorption atoms are more favorable than the N atoms for the PbTiO₃ (111) surface. The In/PbO₃ interface is energetically favorable among the atomic arrangements of the InN/PbTiO₃ (111) interfaces. Substitutional defects may act as a potential source for p-type behavior of Mg- or Zn-doped InN on the Ti-terminated PbTiO₃ (111) surface.     

Visualizing local doping effects of individual water clusters on gold(111)-supported graphene

The local charge carrier density of graphene can exhibit significant and highly localized variations that arise from the interaction between graphene and the local environment, such as adsorbed water, or a supporting substrate. However, it has been difficult to correlate such spatial variations with individual impurity sites. By trapping (under graphene) nanometer-sized water clusters on the atomically well-defined Au(111) substrate, we utilize scanning tunneling microscopy and spectroscopy to characterize the local doping influence of individual water clusters on graphene. We find that water clusters, predominantly nucleated at the atomic steps of Au(111), induce strong and highly localized electron doping in graphene. A positive correlation is observed between the water cluster size and the local doping level, in support of the recently proposed electrostatic-field-mediated doping mechanism. Our findings quantitatively demonstrate the importance of substrate-adsorbed water on the electronic properties of graphene.     

Structural and optical properties of wurtzite InN grown on Si(111)

We report the structural and optical properties of InN films on Si(111) prepared by ion-beam-assisted filtered cathodic vacuum arc technique. X-ray diffraction and Raman spectroscopy measurements indicated that all the InN films were hexagonal crystalline InN. The InN films deposited at substrate temperature of 475 °C exhibited highly (0001) preferred orientation and texturing (cratered) surface morphology. The oxygen incorporated in the InN films was segregated in the form of amorphous indium oxide or oxynitride phases at the grain boundaries. Photoluminescence emission of ∼ 1.15 eV was observed at room temperature from the InN films.     

Long-range ordered single-crystal graphene on high-quality heteroepitaxial Ni thin films grown on MgO(111)

Large-area single crystal monolayer graphene is synthesized on Ni(111) thin films, which have flat terraces and no grain boundaries. The flat single-crystal Ni films are heteroepitaxially grown on MgO(111) substrates using a buffer layer technique. Low-energy electron diffraction and various spectroscopic methods reveal the long-range single crystallinity and uniform monolayer thickness of the graphene. When transferred onto an insulating wafer, continuous millimeter-scale single domain graphene is obtained.     

Structural phase control in self-catalyzed growth of GaAs nanowires on silicon (111)

Au free GaAs nanowires with zinc blende structure, free of twin planes and with remarkable aspect ratios, have been grown on (111) Si substrates by molecular beam epitaxy. Nanowires with diameters down to 20 nm are obtained using a thin native oxide layer on the Si substrates. We discuss how the structural phase distribution along the wire length is controlled by the effective V/III ratio and temperature at the growth interface and explain how to obtain a pure twin plane free zinc blende structure.     

Initial epitaxial growth of (111) Au/(111) Cu and (111) Cu/(111) Au

The room temperature modes of growth of Au/(111) Cu and Cu/(111) Au are described. For the former growth mode initial deposits (2.4 Å) of gold on copper form smooth flat islands delineated by coincidence lattice misfit dislocations. For 6.0 Å of gold deposit, both thick and thin gold areas were observed with almost complete substrate coverage. For a 10 Å deposit, surface coverage was complete. Strain measurements and dislocation densities obtained on the (111) Au/(111) Cu films suggest the presence of two separate misfit dislocation networks at the interface. The coincidence lattice networks were large enough for transmission electron microscopy observation but contributed little to total overlayer strain. The (van der Merwe) natural lattice misfit dislocations were too closely spaced for direct observation but their presence was inferred because of the strain measurements. The initial epitaxy of Cu/(111) Au was similar to the Stranski-Krastanov model: the initial monolayer of copper (also delineated by coincidence misfit dislocations) grew smoothly on the gold; additional copper formed essentially stress-free “nuclei” on top of the initial copper layer.     

Structural study of CH3S self-assembled monolayers on Au(111)

We present preliminary results of an experimental investigation of ordered phases of CH₃S chemisorbed on Au(111). The self-assembled monolayer has been grown by dosing dimethyl disulfide in ultrahigh vacuum at different substrate temperatures between 200 K and 320 K and following different protocols. The monolayers have been characterized by means of low-energy He atom scattering with time-of-flight detection in a temperature range between 150 K and 300 K. The observed diffraction patterns show that the main periodicity is well-described by the (3 × 4) overlayer of the Au(111) lattice, coexisting with the (√3 × √3) periodicity, in agreement with previous results obtained by means of low-energy electron diffraction.     

Structural Properties of Doped GaN on Si(111) Studied by X-Ray Diffraction Techniques

X-ray diffraction (XRD) is a non-destructive technique which is widely used in material characterization, particularly to determine structure, crystalline quality and orientation of samples. Two representative samples are used in this work, these samples are sample I (Si-doped GaN/AlN/Si) nominally consisted of 284 nm AlN followed by 152 nm of Si-doped GaN, and sample II (Mg-doped GaN/AlN/Si), grown with 194 nm AlN followed by 136 nm of Mg-doped GaN. Both doped GaN films were investigated by high resolution X-ray diffraction (HRXRD) with rocking curve (RC) measurement around the symmetrical (0002) and asymmetrical (10 $\overline{1}$ 2) diffraction peaks. The phase analysis result revealed that monocrystalline GaN was obtained. The XRD pattern show sharp and well separated (000l) reflections of doped GaN and AlN indicating complete texture with GaN[0?0?0?2] ∥ AlN[0?0?0?2] ∥ Si[1?1?1]. From the HRXRD RC ω/2θ scans of (10 $\overline{1}$ 2) and (0002) plane, we determined both a and c lattice parameters of the doped GaN. The symmetrical and asymmetrical RC full width at half maximum (FWHM) of doped GaN were obtained.     

Mn atomic layers under inert covers of graphene and hexagonal boron nitride prepared on Rh(111)

Intercalation of metal atoms into the interface of graphene and its supporting substrate has become an intriguing topic for the sake of weakening the interface coupling and constructing metal atomic layers under inert covers. However, this novel behavior has rarely been reported on the analogous hexagonal boron nitride (h-BN) synthesized on metal substrates. Here, we describe a comparative study of Mn intercalation into the interfaces of graphene/Rh(111) and h-BN/Rh(111), by using atomically-resolved scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The intercalation was performed by annealing as-deposited Mn clusters, and the starting temperature of Mn intercalation into h-BN/Rh(111) was found to be ～80 °C higher than that for graphene/Rh(111). Moreover, the intercalated islands of h-BN/Mn/Rh(111) usually possess more irregular shapes than those of graphene/Mn/Rh(111), as illustrated by temperature-dependent STM observations. All these experimental facts suggest a stronger interaction of Mn with h-BN/Rh(111) than that with graphene/Rh(111).      

High-quality epitaxial Bi(111) films on Si(111) by isochronal annealing

Bi(111) films grown on Si(111) at room temperature show a significantly higher roughness compared to Bi films grown on Si(100) utilizing a kinetic pathway based on a low-temperature process. Isochronal annealing steps of 3 min duration each with temperatures up to 200 °C cause a relaxation of the Bi films' lattice parameter toward the Bi bulk value and yield an atomically flat Bi surface. Driving force for the relaxation and surface reordering is the magic mismatch of 11 Bi atoms to 13 Si atoms that emerges at annealing temperatures above 150 °C and reduces the remaining strain to less than 0.2%.     

Structural properties of the formation of yttrium germanides thin films on the Si(111) surface

We have performed first principles total energy calculations to investigate the deposit of yttrium digermanide on the Si(111) surface. We have used the periodic density functional theory as implemented in the Quantum-ESPRESSO package. For the adsorption of a monolayer of yttrium digermanide on the Si(111)-(1 × 1) surface, we have found that the most stable geometry corresponds to a configuration with Y atoms occupying the T4 site above a second layer Si atom, and with a Ge bilayer on top of the structure. The atomic structure of the Ge bilayer is similar to that of Si (Ge) in the bulk but rotated 180° with respect to the crystal. For the three dimensional growth of a few layers of yttrium digermanide on Si(111) we have considered a hexagonal structure with (√3 × √3) periodicity, similar to the one found in the growth of few layers of YSi₂ on Si(111): graphite-like Ge planes (with vacancies) intercalated with yttrium planes. As in the case of a single layer of YGe₂, there is a formation of a Ge bilayer on top of the structure. In this case, the Ge_down atoms of the bilayer, which are on top the vacancies, move down towards the vacancy, while Ge atoms in the graphitic layer, which are below the Ge_up atoms of the bilayer, are displaced towards the vacancy.     

Structural comparison of GdF3 films grown on CaF2 (111) and SiO2 substrates

Wide bandgap metal fluorides are the materials of choice for optical coating applications at 193 nm. Low loss and environmentally stable optics requires a mitigating fluoride film structure on a nanometer scale. To understand the growth mechanism of fluoride materials, GdF(3) films grown on CaF(2) (111) and SiO(2) substrates were investigated. Film inhomogeneity and surface roughness were modeled by fitting ellipsometric data with an effective medium approximation, indicating a correlation between film inhomogeneity and surface roughness. The modeled surface roughness was compared with the atomic force microscope measurement. Film inhomogeneity was correlated to the cone-shaped columnar structure revealed by cross-sectional images from a scanning electron microscope. The film crystalline structure was determined by x-ray diffraction measurement, suggesting a different growth mechanism of GdF(3) films on crystalline and amorphous substrates.     

Self-assembly of rubrene on Cu(111)

We performed an ultra-high vacuum scanning tunneling microscopy (STM) investigation of the self-assembly of rubrene at room temperature on Cu(111), a metal surface with threefold symmetry. Rubrene self-assembles into two different structures called row and trimer. Both are different than the structures already observed on Cu(110) and Cu(100). Row and trimer structures have comparable molecular packing densities and are equally distributed across the surface. In the row structure the molecules are oriented with their backbone along the same high symmetry directions of the surface: [[Formula: see text]], [[Formula: see text]] or [[Formula: see text]]. The trimer structure is composed of units of three rubrene molecules, oriented along the high symmetry surface directions. These units are chiral, as revealed by height profile measurements by STM, and self-assemble in domains containing only one type of enantiomer.