Island coalescence and diffusion along kinked steps on Cu(0 0 1): Evidence for a large kink Ehrlich-Schwoebel barrier

Using temperature-variable scanning tunneling microscopy, we studied the coalescence of vacancy islands on Cu(0 0 1) in ultra-high vacuum. From the temperature dependence of the relaxation of merged vacancy islands to the equilibrium shape we obtain an activation energy of the island coalescence process of 0.76 eV. From that value we deduce an activation energy for the atomic hopping coefficient of E_Γh=0.89 eV. Comparing our result with previous STM data on step fluctuations with dominant diffusion along straight step segments (E_Γh=0.68 eV; [M. Giesen, S. Dieluweit, J. Mol. Catal. A: Chem. 216 (2004) 263]) and step fluctuations with kink crossing (E_Γh=0.9 eV; [M. Giesen-Seibert, F. Schmitz, R. Jentjens, H. Ibach, Surf. Sci. 329 (1995) 47]), we conclude that there is a large extra barrier for diffusion of atoms across kinks on Cu(0 0 1) of the order of 0.23 eV. This is the first direct experimental evidence for the existence of a large kink Ehrlich-Schwoebel barrier on Cu(0 0 1).     

Annealing effect on CdS/SnO2 films grown by chemical bath deposition

The extensive investigation of the annealing effect in nitrogen atmosphere on the structural optical and electrical properties of chemically deposited CdS films on SnO₂ has been performed. The as-deposited film shows 2.45 eV band gap (E_g) and decreases with increasing annealing temperature. The film annealed at 623 K having pure hexagonal phase (a = 4.14 Å, c = 6.71 Å for [1 0 0] plane) and E_g = 2.36 eV shows 10 times higher conductivity for all temperature range, and shows two different activation energies E_a = 0.114 eV and E_a = 0.033 eV for the temperature range 395 K ≤ T ≤ 515 K and 515 K ≤ T ≤ 585 K, respectively. The structural parameters such as dislocation density, strain and optical parameters such as absorption and extinction coefficient are calculated and compared for all the films.     

K-shell core-electron binding energies for phosphorus- and sulfur-containing molecules calculated by density functional theory

In this paper, 1s ionization energies for P- and S-containing molecules were calculated using energy-difference method by DFT. Using observed core-electron binding energies (CEBEs) as reference, we found that the Becke00x(xc) exchange-correlation functional (E_xc) is the best choice for CEBEs(P1s), with an average absolute deviation (AAD) of 0.20 eV, and that the best choice for CEBEs(S1s) is E_xc = BmTau1, with an average absolute deviation (AAD) of 0.22 eV. However, the best single functional for calculation of both P and S is E_xc = VS98, resulting in the weighted AAD of 0.43 eV. Our results are also showing that the quality of AAD changes slightly with the apparent orbital hybridization of the atom.     

Photoluminescence in germanium with a quasi-equilibrium dislocation structure

The dislocation-related photoluminescence of n-Ge single crystals with a quasi-equilibrium structure of 60° dislocations is investigated at a temperature of 4.2 K. It is shown that the dislocation-related photoluminescence spectra are described by a set involving from 8 to 13 Gaussian lines with a width of less than 15 meV. With due regard for the data available in the literature, the Gaussian lines with maxima at energies in the range 0.47 < E _m ≤ 0.55 eV are assigned to the emission of 90° Shockley partial dislocations involved in quasiequilibrium segments of 60° dislocations with different values of the stacking fault width Δ (Δ = Δ₀, Δ < Δ₀, and Δ > Δ₀). It is revealed that the d8 line at the energy E _m = 0.513 eV, which corresponds to the emission of straight segments with the equilibrium stacking fault width Δ₀, dominates in the photoluminescence spectra only at dislocation densities N _D < 10⁶ cm^?2. As the dislocation density N _D increases, the intensity of the d8 line decreases with the d7 line (E _m ≈ 0.507 eV) initially and the d7 and d6 lines (E _m ≈ 0.501 eV) then becoming dominant in the photoluminescence spectrum. The d7 and d6 lines are attributed to the emission of segments with stacking fault widths Δ < Δ₀. Possible factors responsible for the formation of stacking faults with particular widths Δ ≠ Δ₀ for quasi-equilibrium dislocations are discussed.     

Atomistic modeling of β-Sn surface energies and adatom diffusivity

Energies for low number Miller index surfaces of β-Sn (b.c.t. structure) were computed and the (1 0 0) plane was found to have the lowest un-relaxed energy of 0.0497 eV/Ų. We then used the Dimer method to find mechanisms and corresponding activation energies, E_A, for a Sn adatom moving on a β-Sn (1 0 0) surface. After extensive dimer searches and comparison to long molecular dynamics simulations, we conclude that two simple hopping mechanisms dominate transitions on this surface. For each, we determined hopping rates of the adatom using transition state theory and computed its tracer diffusivity. A hop of the adatom in the lattice c-direction gives D_300 K = 1.893 × 10⁻⁰⁶ cm²/s (E_A = 0.1493 eV), while in the lattice a-direction D_300 K = 3.994 × 10⁻⁰⁶ cm²/s (E_A = 0.1138 eV). When compared to studies on the existence of low energy multi-atom adatom diffusion on Cu and Al (1 0 0), we assert that β-Sn's successive (2 0 0) plane layering in the [1 0 0] direction provides for significantly lower activation energies and may contribute to the inability to locate any concerted atomic motion mechanisms.     

Temperature dependent photoluminescence of PECVD a-SiOx:H (x<2)

The temperature dependent visible photoluminescence (PL) property of a-SiO_x:H (x<2) samples prepared in a PECVD system by using SiH₄+CO₂ gas mixture is investigated at a temperature range of 20 K-400 K. One of the two explicitly distinguished PL bands, with varying peak photon energies between 1.70 and 2.05 eV, can be detected at only low temperatures below 200 K, which is attributed to tail-to-tail radiative recombination. Thermal quenching parameter (T_L) of the tail-to-tail PL band is calculated as varying between 120 and 280 K as the atomic oxygen concentration ([O]at.%) of the samples increases. Stokes shift (ΔE_Stokes) of the tail-to-tail PL band is found to change from 85 meV to 420 meV due to band tail widening. The other PL band emerges at 2.1 eV and can be detected at higher temperatures with thermal activation behavior. The activation energies calculated about room temperature vary in the range of 8 meV-50 meV with oxygen concentration. Thermal activation of the 2.1 eV PL band is attributed to the behavior of thermally activated incoherent hopping migration of electrons. These electrons combine with self trapped holes (STHs) to form self trapped excitons (STEs). STEs are localized at intrinsic defects of SiO₂ structure such as oxygen vacancies (E′ centers) and non-bridging oxygen hole centers (NBOHC).     

The peculiarities of the low-energy ion scattering by polycrystal targets

In the present work, experimental and computer simulation studies of low-energy (E₀ = 80-500 eV) Cs⁺ ions scattering on Ta, W, Re target surfaces and K⁺ ions scattering on Ti, V, Cr target surfaces have been performed for more accurate definition of mechanism of scattering, with a purpose of evaluation of an opportunity of use of slow ions scattering as a tool of surface layers analysis. The choice of the targets was based on the fact that the ratios of atomic masses of target atoms and ions μ = m₂/m₁ were almost the same for all cases considered and greater than 1 (direct mass ratio) however, the difference of binding energies of target atoms in the cases of Cs⁺ and K⁺ scattering was almost twice as much. It has been noticed that the dependencies of the relative energy retained by scattering ions at the maximum of energy distribution versus the initial energy E_m/E₀ (E₀) have a similar shape in all cases. The relative energy retained by scattering ions increases while the initial energy of incidence ions decreases. The curves are placed above each other relative to the binding energies of target atoms, to show what this says about the influence of binding energy on a process of scattering of low-energy ions. The correlation between value of energy change maintained by an ion for different values of E₀ in the case of scattering by targets with different masses of atoms and its binding energies is experimentally established. The contrary behavior of the E_m/E₀ (E₀) dependencies concerning the target atom binding energy quantity E_b for cases with direct (μ > 1) and inverse (μ < 1) mass ratio of colliding particles is established. The comparison of experimental energy distributions with calculated histograms shows that the binary collision approximation cannot elucidate the abnormally great shift in the maxima of relative energy distributions towards greater energy retained by scattering ions.     

Refractive index, oscillator parameters and temperature-tuned energy band gap of Tl4In3GaS8-layered single crystals

Transmission and reflection measurements in the wavelength region 450-1100 nm were carried out on Tl₄In₃GaS₈-layered single crystals. The analysis of the room temperature absorption data revealed the presence of both optical indirect and direct transitions with band gap energies of 2.32 and 2.52 eV, respectively. The rate of change of the indirect band gap with temperature dE_gi/dT=-6.0×10⁻⁴ eV/K was determined from transmission measurements in the temperature range of 10-300 K. The absolute zero value of the band gap energy was obtained as E_gi(0)=2.44 eV. The dispersion of the refractive index is discussed in terms of the Wemple-DiDomenico single-effective-oscillator model. The refractive index dispersion parameters: oscillator energy, dispersion energy, oscillator strength and zero-frequency refractive index were found to be 4.87 eV, 26.77 eV, 8.48×10¹³ m⁻² and 2.55, respectively.     

Ionic thermocurrents in sodium fluoride thin film

Ionic thermocurrent (ITC) in NaF thin film deposited between gold electrodes has been investigated in situ in the temperature region 300–500 K. The thermally stimulated polarization current (TSPC) and thermally stimulated depolarization current (TSDC) obtained under low electric field pf polarization (E_p) at a lower temperature of polarization (T_p) exhibited current-peak temperatures (T_M) about 420 K and 450 K. The activation energies associated with the first and the second current peaks were 1.15 + 0.05 eV and 0.65 + 0.02 eV, which are assigned to cation vacancy blocking at the grain boundary barrier and the electrode contact interface barrier respectively. Polarization under a strong electric field (E_p > MV m₋₁) at T_p > 480 K causes a quasi-stable shift of the ITC peak positions to higher temperature. The current peak positions and magnitudes then depend upon the polarity of the electrode metal during polarization, and activation energies associated with the first peak positions are 0.90 + 0.02 eV and 0.79 + 0.02 eV for positive and negative bias at the counter electrode respectively, which may be attributed to the clustering of the cation vacancies and the dislocation networks at the interfaces.     

Characterization of defects introduced in Sb doped Ge by 3 keV Ar sputtering using deep level transient spectroscopy (DLTS) and Laplace-DLTS (LDLTS)

We have used deep level transient spectroscopy (DLTS), and Laplace-DLTS to investigate the defects created in antimony doped germanium (Ge) by sputtering with 3 keV Ar ions. Hole traps at E_V+0.09 eV and E_V+0.31 eV and an electron trap at E_C−0.38 eV (E-center) were observed soon after the sputtering process. Room temperature annealing of the irradiated samples over a period of a month revealed a hole trap at E_V+0.26 eV. Above room temperature annealing studies revealed new hole traps at E_V+0.27 eV, E_V+0.30 eV and E_V+0.40 eV.     

Density functional theory calculation of 2p core-electron binding energies of Si,P, S,Cl, and Ar in gas-phase molecules

Density functional theory (DFT) calculations have been performed on the gas-phase 2p core-electron binding energies (CEBEs) of Si, P, S, Cl, and Ar in 145 cases using the following procedure: ΔE_KS (scalar-ZORA + E_xc)/TZP//HF/6-31G(d). ΔE_KS is the difference in the total Kohn–Sham energies of the 2p-ionized cation and the neutral parent molecule calculated by DFT using different exchange-correlation functionals E_xc with triple-zeta polarized basis set, at molecular geometry optimized by HF/6-31G(d), and relativistic effects have been estimated by scalar zeroth-order regular approximation. Among the 26 functionals tested, the form of E_xc giving the best overall performance was found to be the combination of OPTX exchange and LYP correlation functionals. For that functional, the average absolute deviation (AAD) of the 145 calculated CEBEs from experiment is 0.26 eV. There are seven other exchange-correlation functionals that led to AADs of less than 0.30 eV. Some functionals give lower AADs than E_xc = OPTX-LYP for some individual elements. In the case of Si, for example, the combination of either mPW91-PBE or Becke88-Perdew86 led to an AAD of only 0.10 eV for 56 silicon-containing molecules. Another example is the case of the argon atom, for which the choice of E_xc = OPTX-Perdew86 yields a value for CEBE equal to the experimental value.     

The density of quenched gold

A precision hydrostatic differential method for measuring small density differences of solid bodies was used to determine the activation energy of vacancy formation and migration in quenched gold. The values were found to beE _f =0·76 eV, andE _m =0·51 eV.E _f is substantially lower than the well established value 0·96 eV, whereasE _m is close to the value 0·56 eV determined by Jeannette and Machlin for oxygen-free gold.The concentration of vacancies determined from our measurement is of the same order as the absolute calorimetric determination by DeSorbo.A short communication was read at the Conference on Point Defects in Quenched Metals, ANL, June 1964.     

Short-living absorption and emission of CsI(Na)

This paper investigates the short-living absorption and the emission of CsI(Na) under a pulsed electron beam (Е_e=0.25 MeV, t_1/2=15 ns and W=0.003…0.16 J/cm²). The bands of singlet self-trapped excitons, as well as Na⁰ and V_k color centers have been detected in the transient absorption spectrum of CsI(Na). It has been found that the activator luminescence spectrum, peaking at 3.0 eV, fits a Gaussian (E_m=3.0 eV and FWHM=0.44±0.02 eV at 80 K) and remains the same at different time delays within 10⁻⁸-10⁻³ s. The decay kinetics of the 3.0 eV emission has one nanosecond exponential component and two microsecond ones with time constants 1.0 and 3.0 μs, which remain unchanged within 78-150 K. It is concluded that the activator emission is due to the radiative annihilation of sodium-perturbed two halide excitons from the non-relaxed singlet state. The pathways of such excitons creation are discussed.     

Core-level shifts at the Pt/W(1 1 0) monolayer bimetallic interface

We have measured W and Pt 4f_7/2 core-level photoemission spectra from interfaces formed by ultrathin Pt layers on W(1 1 0), completing our core-level measurements of W(1 1 0)-based bimetallic interfaces involving the group-10 metals Ni, Pd, and Pt. With increasing Pt coverage the sequence of W spectra can be described using three interfacial core-level peaks with binding-energy (BE) shifts (compared to the bulk) of −0.220 ± 0.015, −0.060 ± 0.015, and +0.110 ± 0.010 eV. We assign these features to 1D, 2D pseudomorphic (ps), and 2D closed-packed (cp) Pt phases, respectively. For ∼1 ps ML the Pt 4f_7/2 BE is 71.40 ± 0.02 eV, a shift of +0.46 ± 0.09 eV with respect to the BE of bulk Pt metal. The W 4f_7/2 core-level shifts induced by all three adsorbates are semiquantitatively described by the Born-Haber-cycle based partial-shift model of Nilsson et al. [39]. As with Ni/W(1 1 0), the difference in W 4f_7/2 binding energies between ps and cp Pt phases has a large structural contribution. The Pt 4f lineshape is consistent with a small density of states at the Fermi level, reflective of the Pt monolayer having noble-metal-like electronic structure.     

Inductively coupled plasma induced deep levels in epitaxial n-GaAs

The electronic properties of defects introduced by low energy inductively coupled Ar plasma etching of n-type (Si doped) GaAs were investigated by deep level transient spectroscopy (DLTS) and Laplace DLTS. Several prominent electron traps (E_c—0.046 eV, E_c—0.186 eV, E_c—0.314 eV. E_c—0.528 eV and E_c—0.605 eV) were detected. The metastable defect E_c—0.046 eV having a trap signature similar to E1 is observed for the first time. E_c—0.314 eV and E_c—0.605 eV are metastable and appear to be similar to the M3 and M4 defects present in dc H-plasma exposed GaAs.     

Valence band and surface core-level shift studies of the oxygen-induced p(3 × 1) reconstruction of the W(1 0 0) surface

Using synchrotron radiation, W 4f_7/2 and valence-band (VB) photoelectron spectroscopy was used to study the oxidation states of the p(3 × 1) reconstructed surface of W(1 0 0) produced by oxygen adsorption at 1500 K. The W 4f_7/2 study showed two features at 0.40 and 1.50 eV higher binding energies relative to the bulk feature which represent shifts to lower binding energies compared to the W 4f_7/2 features of the as-grown oxygen films on W(1 0 0). Co-existence of these features is a characteristic of the formation of the p(3 × 1) structure. The VB studies of this system and as-grown oxygen films at room temperature (RT) showed an oxygen-induced feature for the p(3 × 1) structure for which the peak maximum had shifted by 0.9 eV to higher binding energies compared to the as-grown films. The direction of shifts in the W 4f_7/2 and VB spectra for the p(3 × 1) structure confirmed the reduction of the charge transfer from W to oxygen compared to the as-grown films. A study of the VB changes with photon energy shows that the main component of the oxygen-induced feature in the p(3 × 1) VB at 6.6 ± 0.2 eV is related to a hybridized state between W 5d and O 2p electrons.     

The effect of a weak magnetic field on the mobility of dislocations in silicon

The magnetoplastic effect in dislocation silicon is discovered. It is shown that in the presence of tensile stresses (up to 20 MPa), the mechanically activated path of surface dislocation half-loops is limited mainly by the dynamics of defects in various slip systems relative to the applied load. The activation barriers for the motion of dislocations controlled by various conditions in the temperature range T=850–950 K are E _aF=2.1±0.1 eV and E _aS=1.8±0.1 eV. An increase in the path of surface dislocation half-loops and a change in the activation barriers are detected (E _aF=1.4±0.1 eV and E _aS=1.6±0.1 eV) after subjecting silicon to a magnetic field (B=0.7 T) for 30 min. Possible reasons behind the observed effects are discussed.     

Nanoindentation on carbon thin films obtained from a C60 ion beam

Raman spectra, atomic force microscope (AFM) images, hardness (H) and Young's modulus (E) measurements were carried out in order to characterize carbon thin films obtained from a C₆₀ ion beam on silicon substrates at different deposition energies (from 100 up to 500 eV). The mechanical properties were studied via the nanoindentation technique. It has been observed by Raman spectroscopy and AFM that the microstructure presents significant changes for films deposited at energies close to 300 eV. However, these remarkable changes have not been noticeable on the mechanical properties: apparently H and E increase with higher deposition energy up to ∼11 and ∼116 GPa, respectively. These values are underestimated if the influence of the film roughness is not taken into account.     

Kinetics of slow collapse process: Thermodynamic description of rate constants

Insoluble monolayer formed at the air/water interface compressed at a surface pressure above the equilibrium spreading pressure is unstable. In presented paper the classical theory for homogeneous nucleation is modified adding the activation energy term. It allows quantitative thermodynamic interpretation of the slow collapse phase transformation. The collapse of stearic acid Langmuir films has been carried out by systematic measurements of the area loss-time isobaric dependencies at various temperatures and isothermal dependencies at various pressures. Activation energies (activation enthalpies) and activation entropies have been evaluated for the nucleation (E_α = 1.32 eV) and the growth (E_β = 1.55 eV) processes. The experimental data for various pressures are discussed on the basis of the Gibbs energy analysis.     

A supersymmetric extension of the Weinberg-Salam model

By use of Slavnov's procedure, a supersymmetric extension of the Weinberg-Salam model of lepton interactions is obtained. At low energies (E ? m_W), that model is approached very closely. In addition, we get four heavy leptons (m?m_W) and a number of heavy scalars, plus a normally unobservable new neutrino.