Search results for "layer"
showing 10 items of 2667 documents
Bright Beaches of Nanoscale Potassium Islands on Graphite in STM Imaging
2008
We demonstrate, via scanning tunneling microscopy (STM) measurements performed at 48 K, the existence of "bright beaches" at the edges of K islands (diameter approximately 5-500 nm) on the graphite surface. The enhanced tunneling current is only observed in monolayer-high islands on graphite, and not in islands of similar geometry on top of a K monolayer film. First-principles density functional calculations and STM simulations suggest that this is an STM field effect, which appears as the positive tip attracts donated electrons back to the metallic K islands. The restored charge accumulates preferentially at the island edges.
Reconstructed bcc Co films on the surface
2007
Abstract Ultrathin epitaxial Co films on Cr ( 1 1 0 ) are examined by scanning tunneling microscopy and spectroscopy (STM and STS). At room temperature Co grows as pseudomorphic bcc layers for the first two monolayers and forms close-packed Co layers with stacking faults for thicker coverages. A periodic lattice distortion appears in two equivalent (3 × 1) reconstruction domains in combination with a regular lattice of dislocation lines oriented along the in-plane close-packed row directions bcc [ 1 1 ¯ 1 ] and bcc [ 1 ¯ 1 1 ] . The reconstruction and the occurrence of dislocation lines are caused by the epitaxial strain. The local density-of-states function is mapped by scanning tunneling …
Real-time observation of the intravalley spin-flip process in single-layer WS2
2019
We use helicity-resolved transient absorption spectroscopy to track intravalley scattering dynamics in monolayer WS2. We find that spin-polarized carriers scatter from upper to lower conduction band by reversing their spin orientation on a sub-ps timescale.
Deformation profile in GaN quantum dots: Medium-energy ion scattering experiments and theoretical calculations
2005
Medium energy ion scattering (MEIS) has been used to measure at the scale of the monolayer the deformation profile of self-organized GaN quantum dots grown on AlN by molecular-beam epitaxy. The effect of capping the GaN dots by a thin layer of AlN has also been studied. It is shown that GaN dots are partially relaxed in every situation. Capping them with AlN has little effect on the basal plane, as expected, but strongly modifies the strain of the upper part of dots. The experimental results are compared with theoretical calculations, allowing one to conclude that GaN quantum dots experience a nonbiaxial strain, which drastically decreases when going from the basal plane up to the apex of t…
Ab initio thermodynamics for the growth of ultra-thin Cu film on a perfect MgO(001) surface
2005
Controlled growth of thin metallic films on oxide substrates is important for numerous micro-and nanoelectronic applications. Our ab initio study is devoted to the periodic slab simulations for a series of ordered 2D Cu superlattices on the regular MgO(001) substrate. Submonolayer and monolayer substrate Cu coverages were calculated using the DFT-GGA method, as implemented into the CRYSTAL-98 code. The results of ab initio calculations have been combined with thermodynamic theory which allows us to predict the growth mode of ultra-thin metal films (spinodal decomposition vs. nucleation-and-growth regime) as a function of the metal coverage and the temperature, and to estimate the metal dens…
Electrical switching of perpendicular magnetization in a single ferromagnetic layer
2020
We report on the efficient spin-orbit torque (SOT) switching in a single ferromagnetic layer induced by a new type of inversion asymmetry, the composition gradient. The SOT of 6- to 60-nm epitaxial FePt thin films with a $L{1}_{0}$ phase is investigated. The magnetization of the FePt single layer can be reversibly switched by applying electrical current with a moderate current density. Different from previously reported SOTs which either decreases with or does not change with the film thickness, the SOT in FePt increases with the film thickness. We found the SOT in FePt can be attributed to the composition gradient along the film normal direction. A linear correlation between the SOT and th…
Amorphous silica between confining walls and under shear: a computer simulation study
2002
Molecular dynamics computer simulations are used to investigate a silica melt confined between walls at equilibrium and in a steady-state Poisseuille flow. The walls consist of point particles forming a rigid face-centered cubic lattice and the interaction of the walls with the melt atoms is modelled such that the wall particles have only a weak bonding to those in the melt, i.e. much weaker than the covalent bonding of a Si-O unit. We observe a pronounced layering of the melt near the walls. This layering, as seen in the total density profile, has a very irregular character which can be attributed to a preferred orientational ordering of SiO4 tetrahedra near the wall. On intermediate lengt…
Glass transition in confined geometry.
2010
Extending mode-coupling theory, we elaborate a microscopic theory for the glass transition of liquids confined between two parallel flat hard walls. The theory contains the standard MCT equations in bulk and in two dimensions as limiting cases and requires as input solely the equilibrium density profile and the structure factors of the fluid in confinement. We evaluate the phase diagram as a function of the distance of the plates for the case of a hard sphere fluid and obtain an oscillatory behavior of the glass transtion line as a result of the structural changes related to layering.
Numerical analysis of the influence of ultrasonic vibration on crystallization processes
2011
The challenge in the future fabrication of semiconductor bulk crystals is the improvement of the crystal quality with a simultaneous increase of the yield. For that, a proper control of mass transfer within the fluid phase is required. Besides the damping of violent convective fluctuations, the thickness of the diffusion boundary layer, causing morphological instability, has to be decreased. The influence of ultrasound in molten Germanium was analyzed by numerical simulations. The simulations were provided by applying commercial software packages ANSYS ® and FLUENT ® . ANSYS ® was used to model the ultrasonic wave propagation in the whole growth system consisting of melt and crystal, crucib…
Crystal Reorientation and Amorphization Induced by Stressing Efficient and Stable P–I–N Vacuum‐Processed MAPbI 3 Perovskite Solar Cells
2021
Herein, the long-term stability of vacuum-deposited methylammonium lead iodide (MAPbI(3)) perovskite solar cells (PSCs) with power conversion efficiencies (PCEs) of around 19% is evaluated. A low-temperature atomic layer deposition (ALD) Al2O3 coating is developed and used to protect the MAPbI(3) layers and the solar cells from environmental agents. The ALD encapsulation enables the MAPbI(3) to be exposed to temperatures as high as 150 degrees C for several hours without change in color. It also improves the thermal stability of the solar cells, which maintain 80% of the initial PCEs after aging for approximate to 40 and 37days at 65 and 85 degrees C, respectively. However, room-temperature…