Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userStructure Stability and Electronic Property for Alkaline-Earth Metals Induced Si(111)-3x2 Surfaces
168
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Structural stability and electronic properties of alkaline-earth metals (Ca, Sr, Ba) induced Si(111)-3x2 surfaces have been comprehensively studied by means of ab initio calculations. Adsorption energy and charge density difference calculations show the high structural stability due to the strong chemical bonding. Analysis of electronic band structures and band-decomposed charge density distributions indicates that the third valence band is deriving from top Si and metal atoms, while the top most two valence bands are deriving from the bulk silicon. These results suggest a larger surface band gap of 1.65-1.68 eV, which is good consistent with the recent experimental finding for Sr/Si(111)-3x2 surface. These results reveal a natural explanation for the relevant experimental observation and stimulate further experimental and theoretical exploration on the surface science.
rate research
Read More
The electronic structure in alkaline earth AeO (Ae = Be, Mg, Ca, Sr, Ba) and post-transition metal oxides MeO (Me = Zn, Cd, Hg) is probed with oxygen K-edge X-ray absorption and emission spectroscopy. The experimental data is compared with density functional theory electronic structure calculations. We use our experimental spectra of the oxygen K-edge to estimate the bandgaps of these materials, and compare our results to the range of values available in the literature.
We study current-induced step bunching and wandering instabilities with subsequent pattern formations on vicinal surfaces. A novel two-region diffusion model is developed, where we assume that there are different diffusion rates on terraces and in a small region around a step, generally arising from local differences in surface reconstruction. We determine the steady state solutions for a uniform train of straight steps, from which step bunching and in-phase wandering instabilities are deduced. The physically suggestive parameters of the two-region model are then mapped to the effective parameters in the usual sharp step models. Interestingly, a negative kinetic coefficient results when the diffusion in the step region is faster than on terraces. A consistent physical picture of current-induced instabilities on Si(111) is suggested based on the results of linear stability analysis. In this picture the step wandering instability is driven by step edge diffusion and is not of the Mullins-Sekerka type. Step bunching and wandering patterns at longer times are determined numerically by solving a set of coupled equations relating the velocity of a step to local properties of the step and its neighbors. We use a geometric representation of the step to derive a nonlinear evolution equation describing step wandering, which can explain experimental results where the peaks of the wandering steps align with the direction of the driving field.
The studies of electronic and magnetic properties of V-Pc molecule adsorbed onto Au(111) surface are based on ab-initio calculations in the framework of density functional theory. We compute adsorption energies, investigate interaction mechanisms between constituents of the hybrid system consisting of V-Pc molecule and Au surface, and determine geometry changes in the system, particularly in the grafted molecule. We find out that the energetically most stable configuration of the V-Pc/Au(111) occurs when V-Pc is grafted to the Au surfaces fcc site, which leads to the reduction of the point group symmetry of the hybrid system in comparison to the free standing V-Pc molecule. Further, our studies reveal that the electronic structure and magnetic properties of the V-Pc change significantly after adsorption to the Au(111). Generally, these studies shed light on physical mechanisms of the V-Pc adsorption to metallic surfaces and open up new prospects for design of novel spintronic devices.
We have used Low Energy Electron Diffraction (LEED) I-V analysis and ab initio calculations to quantitatively determine the honeycomb chain model structure for the Si(111)-3x2-Sm surface. This structure and a similar 3x1 recontruction have been observed for many Alkali-Earth and Rare-Earth metals on the Si(111) surface. Our ab initio calculations show that there are two almost degenerate sites for the Sm atom in the unit cell and the LEED I-V analysis reveals that an admixture of the two in a ratio that slightly favours the site with the lower energy is the best match to experiment. We show that the I-V curves are insensitive to the presence of the Sm atom and that this results in a very low intensity for the half order spots which might explain the appearance of a 3x1 LEED pattern produced by all of the structures with a 3x2 unit cell.
The electronic structure of Si(110)16 x 2 double-domain, single-domain and 1 x 1 surfaces have been investigated using spin- and angle-resolved photoemission at sample temperatures of 77 K and 300 K. Angle-resolved photoemission was conducted using horizontally- and vertically-polarised 60 eV and 80 eV photons. Band-dispersion maps revealed four surface states ($S_1$ to $S_4$) which were assigned to silicon dangling bonds on the basis of measured binding energies and photoemission intensity changes between horizontal and vertical light polarisations. Three surface states ($S_1$, $S_2$ and $S_4$), observed in the Si(110)16 x 2 reconstruction, were assigned to Si adatoms and Si atoms present at the edges of the corrugated terrace structure. Only one of the four surface states, $S_3$, was observed in both the Si(110)16 x 2 and 1 x 1 band maps and consequently attributed to the pervasive Si zigzag chains that are components of both the Si(110)16 x 2 and 1 x 1 surfaces. A state in the bulk-band region was attributed to an in-plane bond. All data were consistent with the adatom-buckling model of the Si(110)16 x 2 surface. Whilst room temperature measurements of $P_y$ and $P_z$ were statistically compatible with zero, $P_x$ measurements of the enantiomorphic A-type and B-type Si(110)16 x 2 surfaces gave small average polarisations of around 1.5% that were opposite in sign. Further measurements at 77 K on A-type Si(110)16 x 2 surface gave a smaller value of +0.3%. An upper limit of $sim1%$ may thus be taken for the longitudinal polarisation.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
