Effect Of Interface Structure Research Articles

Heteroepitaxy of dissimilar materials: effect of interface structure on strain and defect formation

Differences in crystal symmetry, bonding, and lattice parameter play important roles in the epitaxy of dissimilar materials. We emphasize on how these differences influence the interface structure and the resulting epitaxial growth. Case studies are presented including the hexagonal MnAs–cubic GaAs and hexagonal GaN–tetragonal LiAlO 2 systems. The interfaces are structurally analyzed and reveal low-energy configurations promoting the epitaxial alignment. The results are explained with an extended coincidence model considering strain and defect formation.

Effect of interface structure on magnetic and magnetoresistive properties of Fe/Cr multilayers

The influence of growth temperature on atomic and magnetic interface structure was traced in Fe/Cr multilayers grown with MBE at different substrate temperatures in the range 20–480°C. Proper growth was found to be possible only in a narrow temperature range about 140–180°C, deviations from optimal temperature causing drastic increase in interface roughness. Giant magnetoresistive effect was shown to be in close correlation with the interface structure.

Low resistance magnetic tunnel junctions and their interface structures

Effects of interface structure and oxidation state were studied in stacked magnetic tunnel junction (MTJ) structures with top and bottom antiferromagnetic layers to obtain optimum resistance and high tunneling magnetoresistance (TMR) ratios for read heads. The roughness of the NiFe surface and the Al coverage were significantly improved by introduction of O2 surfactant gas on the Ta-seed-layer surface, which increased TMR ratios of the MTJ with low resistance area (RA) products of less than 10 Ω μm2. Furthermore, it was found that avoidance of Ni oxidation and Co oxidation at the tunnel barrier interface is essential to obtaining high TMR ratios, and that a good Al coverage and Fe–oxide formation may enhance TMR ratios when Fe-rich magnetic materials are used. For the top-type and bottom-type structures, a TMR ratio of 12%–17% with RA products of 6–7 Ω μm2 was obtained, which provides sufficient performance for read heads.

Influence of the exchange reaction on the electronic structure of GaN/Al junctions

Ab-initio calculations have been used to study the influence of the interface morphology and, notably, of the exchange reaction on the electronic properties of Al/GaN (100) interfaces. In particular, the effects of interface structure (i.e. interfacial bond lengths, semiconductor surface polarity, and reacted intralayers) on the SBH at the Al/GaN (001) junction are specifically addressed. The electronic structure of the following atomic configurations have been investigated theoretically: (i) an abrupt, relaxed GaN/Al interface; (ii) an interface which has undergone one monolayer of exchange reaction; and interfaces with a monolayer-thick interlayer of (iii) AlN and (iv) Ga$_{0.5}$Al$_{0.5}$N. Intermixed interfaces are found to pin the interface Fermi level at a position not significantly different from that of an abrupt interface. Our calculations also show that the interface band line--up is not strongly dependent on the interface morphology changes studied. The p-type SBH is reduced by less than 0.1 eV if the GaN surface is Ga-terminated compared to the N-terminated one. Moreover, we show that both an ultrathin Ga$_x$Al$_{1-x}$N ($x$ = 0, 0.5) intralayer and a Ga$\leftrightarrow$Al atomic swap at the interface does not significantly affect the Schottky barrier height.

Electronic spectra of dipolar solutes at liquid/liquid interfaces: Effect of interface structure and polarity

Molecular dynamics computer simulations are used to elucidate the role of solvent polarity and interface structure in determining the electronic absorption and fluorescence line shapes for model dipolar solutes at the interface between water and one of four different organic liquids. The different organic liquids represent a range of molecular structure and polarity: 1-octanol, 1,2-dichloroethane, n-nonane, and carbon tetrachloride. The solute is represented by two rigidly connected Lennard-Jones spheres. The different electronic states correspond to different charges on the two Lennard-Jones centers. In each interfacial system, different choices of solute charge distribution and solute location relative to the interface (including the bulk region) are considered and provide insight into different microscopic factors that influence the electronic line shape. For the water/1,2-dichloroethane and water/CCl4 interfaces, all of the calculations are repeated while the interface is externally constrained to be smooth in order to investigate the role of surface roughness. The calculated electronic line shapes are Gaussians whose peak positions reflect solvent polarity, interface structure, and probe location. Their widths are in general agreement with the prediction of linear response theory. Although continuum electrostatic models predict qualitatively correct behavior, they miss interesting interfacial effects.

Effect of interface structure and amino groups on water splitting and rectification effects in bipolar membranes

Bipolar membranes consist of a layered structure involving a cation selective membrane joined to an anion selective membrane. This is of practical interest in a new process for the commercial production of acids and bases. In this study, the mechanism of water splitting and the characteristics of the bipolar membranes were examined. It was suggested that water splitting occurred due to the second Wien effect in the intermediate region, because the potential drop was very large. If amines exist in the intermediate region, the water splitting is accelerated, because protonation and deprotonation reactions occur between H 2O and the amines. Current—voltage characteristics were correlated with water splitting effects. The efficiency of water splitting was increased by controlling the positions of the amino groups in the anion-selective polymer.

Interface structure effects on coupled transport of Cu(II) ions through binary liquid membranes

The structure of the aqueous donor phase/membrane interface in membrane transport systems was investigated by considering the variation in interfacial tension with experimental conditions. For the first time a new approach based on the use of binary membranes is proposed, which can be used to obtain finer detail of interface phenomena. As an example, an attempt was made to explain the different behaviour of membrane permeation and membrane exit rates in non-steady-state transport of Cu(II) ions through binary liquid membranes.

The fracture resistance of metal-ceramic interfaces

The effects of interface structure and microstructure and microstructure on the fracture energy Γ i of metal-ceramic interfaces are reviewed. Some systems exhibit a ductile fracture mechanism and others fail by brittle mechanisms. In the absence of either interphases or reaction products, Γ i is dominated by plastic dissipation (for both fracture mechanisms), leading to important effects of metal thickness h, and yield strength σ 0. Additionally, Γ i is larger when fracture occurs by ductile void growth (for the same h and σ 0). A fundamental understanding now exists for the ductile fracture mechanism. However, some basic issues remain to be understood when fracture occurs by brittle bond rupture, particularly with regard to the role of the work of adhesion W ad. Interphases and reaction products have been shown to have an important effect on Γ i. A general trend found by experiments is that Γ i scales with the fracture energy of the interphase itself, wherein Γ i tends to increase for the interphase sequence amorphous oxides >crystalline oxides>intermetallics. However, there also appear to be important effects of the residual stresses in the interface (which influence the fracture mechanism) and the layer thickness.

The fracture resistance of metal-ceramic interfaces

The effects of interface structure and microstructure on the fracture energy, Γi, of metal-ceramic interfaces are reviewed. Some systems exhibit a ductile fracture mechanism and others fail by brittle mechanisms. In the absence of either interphases or reaction products, Γi is dominated by plastic dissipation (for both fracture mechanisms), leading to important effects of metal thickness, h, and yield strength, σ0. Additionally, Γi is larger when fracture occurs by ductile void growth (for the same h and σ0). A fundamental understanding now exists for the ductile fracture mechanism. However, some basic issues remain to be understood when fracture occurs by brittle bond rupture, particularly with regard to the role of the work of adhesion, Wad. Interphases and reaction products have been shown to have an important effect on Γi. A general trend found by experiment is that Γi scales with the fracture energy of the interphase itself, wherein Γi tends to increase for the interphase sequence: amorphous oxides > crystalline oxides > intermetallics. However, there also appear to be important effects of the residual stresses in the interface (which influence the fracture mechanism and the layer thickness.

Nucleation and Morphology of TiSi2 on Si

ABSTRACTThis study explores the nucleation and surface and interface morphology of TiSi2 films formed on Si (100) and (111) surfaces. Titanium suicide films were formed on atomically clean Si(111) and (100) surfaces by UHV deposition of Ti followed by in situ anneals. The TiSi2 formation process was characterized is itu using AES and LEED, and the interface structure was determined post preparation by HRTEM. The metastable C49 and stable C54 TiSi2 phases have been identified from Raman spectroscopy measurements. The islands were partially recessed into the substrate, and the shape and degree of recession was different for the islands on (111) and (100) substrates. On (111) substrates epitaxial islands were observed which exhibited different interface structures and epitaxial alignments. The contact angles of the islands were measured and the surface and interface energies of the different configurations were deduced. The mechanisms pertaining to island formation and interface morphology are described in terms of the wetting properties of a liquid-liquid system, with the effects of interface structures causing deviations from the model.

Effect of interface structure on the X-ray double crystal rocking curve peak position from very thin layers in the highly asymmetric Bragg geometry

Double crystal rocking curves from a thin epitaxial layer of GalnAsP on InP have been studied in the highly asymmetric, glancing incidence, Bragg geometry. While a simulation based on a single layer fits the data quite well, a slightly better fit to the data is obtained by assuming the presence of a thin, highly mismatched, interface layer. The interface layer, however, significantly affects the main layer peak position. Very similar rocking curves are found for substantially different structures. We examine the implications for the determination of main layer composition from mismatch measurement.

Formation and characteristics of LaB 6/GaAs(001) Schottky barrier

The effects of interface structure on the formation and characteristics of a LaB 6/chemically etched GaAs(001) Schottky barrier have been investigated using current-voltage measurements, high energy ion scattering and X-ray photoelectron spectroscopy. Barrier heights are 0.7 eV for as-deposited samples and 0.9 eV after annealing at 400–800°C. Annealing above 400°C causes reduction of GaAs native oxides and relaxation of interface disorder. This interface structure is found to determine the pinning position of the Fermi level.

Effect of interface structure on photoluminescence of InGaAs/GaAs pseudomorphic single quantum wells

Photoluminescence studies have been carried out on InGaAs pseudomorphic single quantum wells grown on GaAs by molecular beam epitaxy. Linewidths as narrow as 2.0 meV have been observed. The spectra typically consist of two peaks which on certain samples can be explained by intrawell thickness variations of one monolayer. On other samples the results are more consistent with exciton trapping at islands having a smaller lateral extent than the exciton Bohr radius.