1x1 Surface Research Articles

Growth of Sb[formula omitted]Te[formula omitted] thin films on Ge(111) sample by thermal deposition: Morphological and electronic properties

Sb2Te3 is a well-known thermoelectric material and a topological insulator and its utilization is foreseen for many applications, such as quantum computing, mode-locking of laser systems, and cooling systems. Various methods have been used to grow thin Sb2Te3 films on different substrates, such as molecular beam epitaxy or electrodeposition. Often, such methods require performing laborious and rigid steps in order to optimize film growth and reduce the amount of defects. For this reason, we investigate a simplified growth method: thermal deposition starting from Sb2Te3 lumps followed by annealing. By means of various surface science techniques (LEED, STM, XPS), we show that it is possible to obtain a single crystalline Sb2Te3 film on a Ge(111) substrate. The film, which is amorphous after deposition, undergoes a phase transition and becomes crystalline after annealing at 573 K. This is clearly shown by a 1x1 surface termination typical of a (0001) surface with hexagonal lattices. The presence of several quintuple-layer steps was observed by scanning tunneling microscopy. Photoelectron spectroscopy characterization confirms that the grown chalcogenide film presents the expected stoichiometry (Te/Sb=1.5). The proposed method simplifies the growth phase and seems to reduce the number of defects induced by the growth technique, major advantages for many applications.

Field Ion Scanning Tunneling Microscopy and Its Application to Oxygen Adsorption on the Ag(110) 1x1 Surface

Field Ion Scanning Tunneling Microscopy and Its Application to Oxygen Adsorption on the Ag(110) 1x1 Surface

Epitaxial Graphene on SiC(0001): a photoelectron diffraction study

A flat, single layer of graphite known as graphene has become the focus of studies due to its exceptional properties and fascinating applications. Large scale graphene layers for a possible application can be grown epitaxially on SiC by Si sublimation [1]. Even before the interest in graphene, the surface of SiC was already extensively studied [2],[3]. It exhibits a large variety of surface reconstructions and these reconstructions are very dependent of sample preparation and orientation (0001) or (000-1). In this study, we show a investigation of the structural properties of graphene layers on SiC (0001) by photoelectron diffraction (XPD). The surfaces were prepared by heating the 1x1 surface to temperatures of about 1150 in high ultra vacuum and the various reconstructions were monitored by Low Energy Electron Diffraction (LEED) and X-Ray Photoelectron Spectroscopy (XPS). In particular for the Si terminated surface, that is SiC(0001), the interface between graphene and SiC is characterized by the so-called (6Sqrt(3) × 6Sqrt(3))R30◦ reconstruction (buffer layer). The interpretation of this reconstruction, which is the initial stage of graphitization, has lead to controversy in the literature [2]. We will further discuss the buffer layer structure in terms of the XPD results. The XPD experiments were performed at SGM beam line at LNLS using photons with 450 eV probing the Si2p and C1s core level. The C1s signal was separate in to contributions from volume and surface and compares the experimental results with photoelectron multiple scattering calculations performed with the MSCD package [4].

Preparation of ordered 1x1 surface of rutile TiO<sub>2</sub> (001) for surface x-ray diffraction study

Preparation of ordered 1x1 surface of rutile TiO<sub>2</sub> (001) for surface x-ray diffraction study

X-ray Photoelectron Diffraction Study of bias-treatment for the growth of 1-inch-diameter Hetero-Epitaxial diamond (001) thick films

Bias-treatment (BT) is widely used as an initial seeding process of chemical vapor deposition (CVD) growth of diamonds. In a BT, substrates are negatively biased by an order of hundred volts so that positive ions in the plasma of CVD gas source bombard the substrate to form 'seeds' of diamond growth. Bias-treated 1-inch-diameter (ϕ) Ir(001)/MgO(001) substrates were used as the substrates of the CVD growth of 1-inch- ϕ diamond (001) thick films. XPS (X-ray Photoelectron Spectroscopy) spectra and C 1s and Ir 4f XPD (X-ray Photoelectron Diffraction) patterns were measured for the BT 1-inch- ϕ samples. 5 typical portions on the sample were measured; one at the central portion and the other 4 were peripheral portions, 90° apart from each other and ~4 mm from the edge of the sample. The uniformity of the result over the 5 portions was confirmed. The coverage of carbon layers on the sample after BT was evaluated to be ~ 50 ML in the unit of monolayer of Ir(001)1x1 surface. A quantitative measure of the effect of BT, A45° (the degree of variation of XPD pattern as defined as Imax−Imin/Ia, where Imax, Imin and Ia are the maximum, minimum and average intensities of photoelectrons in an azimuthal diffraction pattern at the polar angle of 45°, respectively), was examined for C 1s and Ir 4f core-levels for the 1-inch- ϕ BT samples. The A45° values appeared to be ~3% and ~17% for C 1s and Ir 4f, respectively. The results were compared with those for other bias-treated smaller samples reported so far. The A45° value of ~3% for C 1s is found to be very small compared to the corresponding values for the smaller samples reported so far. Thus, the method of BT for the present 1-inch- ϕ sample was found to have a large margin of improvement in terms of A45° for C 1s XPD.

Density Functional Theory Study of the Geometry, Energetics, and Reconstruction Process of Si(111) Surfaces

We report the structures and energies from first principles density functional calculations of 12 different reconstructed (111) surfaces of silicon, including the 3x3 to 9x9 dimer-adatom-stacking fault (DAS) structures. These calculations used the Perdew-Burke-Ernzerhof generalized gradient approximation of density functional theory and Gaussian basis functions. We considered fully periodic slabs of various thicknesses. We find that the most stable surface is the DAS 7x7 structure, with a surface energy of 1.044 eV/1x1 cell (1310 dyn/cm). To analyze the origins of the stability of these systems and to predict energetics for more complex, less-ordered systems, we develop a model in which the surface energy is partitioned into contributions from seven different types of atom environments. This analysis is used to predict the surface energy of larger DAS structures (including their asymptotic behavior for very large unit cells) and to study the energetics of the sequential size change (SSC) model proposed by Shimada and Tochihara for the observed dynamical reconstruction of the Si(111) 1x1 structure. We obtain an energy barrier at the 2x2 cell size and confirm that the 7x7 regular stage of the SSC model (corresponding to the DAS 7x7 reconstruction) provides the highest energy reduction per unit cell with respect to the unreconstructed Si111 1x1 surface.

Photoemission study for Mg/Si(111)1×1 surface

The interface and silicide formation on Si(111)7x7 surface at 300°C by Mg deposition was studied using low energy electron diffraction and synchrotron radiation photoelectron emission spectroscopy. At 300°C only Mg/Si(111)1x1 structure was observed, which is different structure from the Mg/Si(111)1x1 surface formed at room temperature. A disordered Mg film was formed for further Mg deposition. We observed that the thin silicide layer between Mg film and Si substrate play a role as interdiffusion barrier for Mg atoms.

Vibrational energy relaxation dynamics of SH stretching modes on stepped H/Si(111)1x1 surfaces

The vibrational energy relaxation rates of excited SiH stretching modes on the monohydride step of miscut H/Si(111)1x1 surfaces are calculated using Bloch-Redfield theory combined with classical molecular dynamics (MD) simulation. The structure and vibrational frequencies of the surface are first investigated using the Car-Parrinello ab initio MD method. The calculated SiSiH bending frequencies and relaxed structures are then used to refine the empirical potential for the classical MD simulations. The lifetime of the excited SiH stretching mode at the step is found to be shorter than the modes on the rerrace. Both the magnitude and the trend of the calculated results agree well with the experimental measurement on the 9° monohydride stepped surface. The vibrational relaxation rate of the SiH stretching modes on the 15° monohydride stepped surface are also calculated and predicted to have a slightly shorter lifetime than for the 9° surface.