Interface Disorder Research Articles

TOPICAL NEPAFENAC AS AN ALTERNATE TREATMENT FOR CYSTOID MACULAR EDEMA IN STEROID RESPONSIVE PATIENTS

To evaluate the use of nepafenac 0.1% in patients with cystoid macular edema who are known steroid responders. Patients (N = 15) with clinical and angiographic cystoid macular edema (> or = 2 months) and a history of increased intraocular pressure following administration of topical corticosteroids participated in this prospective, open-label, pilot study. All patients were treated with nepafenac 0.1% four times daily for 6 weeks and the dose was tapered off over the ensuing 6 weeks. The total treatment duration was 12 weeks. Visual acuity and retinal thickness were measured. For the entire population, there was a mean significant improvement in visual acuity and retinal thickness at 4 weeks and 12 weeks posttreatment compared with baseline (P < 0.0001). A subgroup analysis revealed that patients with pseudophakic cystoid macular edema (n = 11) had a mean significant improvement in visual acuity and retinal thickness compared with baseline at 4 weeks and 12 weeks posttreatment (P < 0.0001). Although the improvement in the vitreoretinal interface disorders group was not statistically different from baseline (probably due to the outlier), three of the four patients with vitreoretinal interface disorders had improvement in visual acuity and retinal thickness. Nepafenac was well tolerated. Nepafenac may be an effective and safe therapy for treating chronic cystoid macular edema in patients who are steroid responders.

MeV-ion beam analysis of the interface between filtered cathodic arc-deposited a-carbon and single crystalline silicon

Amorphous carbon ( a-C) films were deposited on Si(1 0 0) wafers by a filtered cathodic vacuum arc (FCVA) plasma source. A negative electrical bias was applied to the silicon substrate in order to control the incident energy of carbon ions. Effects of the electrical bias on the a-C/Si interface characteristics were investigated by using standard Rutherford backscattering spectrometry (RBS) in the channeling mode with 2.1-MeV He 2 + ions. The shape of the Si surface peaks of the RBS/channeling spectra reflects the degree of interface disorder due to atomic displacement from the bulk position of the Si crystal. Details of the analysis method developed are described. It was found that the width of the a-C/Si interface increases linearly with the substrate bias voltage but not the thickness of the a-C film.

Abnormal temperature behavior of photoluminescence in CdSe/ZnSe self-assembled quantum dots

We report on the temperature dependence of photoluminescence (PL) of CdSe/ZnSe self-assembled quantum dots (QDs). In the temperature range of 19–120 K, although the energy gap of CdSe shrinks by 25 meV, the PL of CdSe QDs does not show any line shift or shape change. According to the equilibrium theories of heteroepitaxial growth, a model involving the presence of interface disorders is suggested to be responsible for this invariant PL. In the temperature range of 120–300 K, the PL peak of CdSe QDs initially blue-shifts and then red-shifts with increasing temperature arising from the thermally activated detrapping of carriers.

Observation of exchange bias and spin-glass-like ordering in ɛ-Fe2.8Cr0.2N nanoparticles

Nanoparticles of ɛ-Fe2.8Cr0.2N system exhibit the exchange bias phenomenon due to the exchange coupling of the spins of the antiferromagnetic (AF) oxide/oxynitride surface layer and the ferromagnetic (FM) nitride core. Exchange bias is observed at 10 K both in the absence and presence of cooling field. Due to the interface disorder, a mixture of parallel and anti-parallel/perpendicular coupling of the AF and FM spins is observed. The roughness of AF-FM interface induces disorder due to the random exchange anisotropy. The saturation magnetization is also found to be drastically lowered as compared to parent ɛ-Fe3N. Below 58 K, the broad peak (T E ≅ T f ) in zero-field cooled (ZFC) magnetization curves indicates the presence of unidirectional anisotropy and spinglass-like ordering, that arises from the freezing of localized frustrated spins.

Magnetic behaviour of superconductor/ferromagnet metallic and perovskite based superlattices

AbstractWe present a study of the magnetic behaviour of superconducting/ferromagnetic superlattices, both for metallic and perovskite based systems. In the first case we find that the response is determined by the ferromagnetic layer regime. If these layers are very thin, no ferromagnetism is observed, but the superconducting layers are decoupled, and the superlattice behaves as a stack of independent superconducting films. For thicker ferromagnetic films, ferromagnetism is established and the effective field resulting from the superposition of stray and applied fields dominates the superconducting response of the superlattice. For the perovskite based superlattices, the physical properties are more affected by interface disorder. In this case we have found that the behaviour can be interpeted as charge carrier transfer between both materials, inducing a change in the magnetic character of the manganite. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Electronic transport in normal-conductor/graphene/normal-conductor junctions and conditions for insulating behavior at a finite charge-carrier density

We investigate the conductance of normal-conductor/graphene/normal-conductor (NGN) junctions for arbitrary on-site potentials in the normal and graphitic parts of the system. We find that a ballistic NGN junction can display insulating behavior even when the charge-carrier density in the graphene part is finite. This effect originates in the different $\mathbf{k}$ intervals supporting propagating modes in graphene and a normal conductor, and persists for moderate levels of bulk, edge, or interface disorder. The ensuing conductance thresholds could be used as an electronic tool to map out details of the graphene band structure in absolute $\mathbf{k}$ space.

Interface effects on layer doping in [YBa2Cu3O7/LaMnO3] superlattices

Format This is a copy of the slides presented at the meeting but not formally written up for the volume. Abstract The growth of heterostructures combining oxide materials is a new strategy to design novel artificial multifunctional materials with interesting behaviors ruled by the interface. There has been increasing interest in heterostructures combining oxides with different functionalities and ground states competing at the interface. In structures involving oxides, interfaces are especially complex and various factors like interface disorder and roughness, epitaxial strain, polarity mismatch etc., are responsible for modified properties at the interface over nanometer length scales. In this presentation we will focus on cuprate / manganite heterostructures made of YBa2Cu3O7 (YBCO) and La1-xCaxMnO3 (LCMO), where the Ca content is varied over a wide range. The manganite grows epitaxially on the superconductor with different degrees of strain depending on the Ca content. For x=0.3 the manganite is ferromagnetic what causes a strong depression of the superconducting order parameter at the YBCO side. Interestingly, there is also a depression of the ferromagnetic moment at the interface suggesting charge transfer (electrons) from the manganite into the YBCO. This is confirmed growing superlattices combining YBCO with the parent manganite compound with x=0, which is nominally an AF insulator. Actually, for LMO thickness below 6 unit cells (2,4 nm) the layers are non magnetic and insulating as expected. However, above this LMO thickness (6 unit cells) we show that superconductivity is strongly suppressed and ferromagnetism is induced at the interface providing a strong evidence for the charge transfer scenario. The control of layer bulk doping by charge transfer at the interface opens new possibilities of tailoring the electronic states at the interface for the design of novel functionalities and devices. Work supported by CICYT MAT2005 06024 C02-02 and DOE.

Effect of interface disorder on quantum well excitons and microcavity polaritons

The theory of the linear optical response of excitons in quantum wells and polaritons inplanar semiconductor microcavities is reviewed, in the light of the existing experiments.For quantum well excitons, it is shown that disorder mainly affects the excitoncentre-of-mass motion and is modelled by an effective Schrödinger equation in twodimensions. For polaritons, a unified model accounting for quantum well roughness andfluctuations of the microcavity thickness is developed. Numerical results confirm thatpolaritons are mostly affected by disorder acting on the photon component, thusconfirming existing studies on the influence of exciton disorder. The polaritonlocalization length is estimated to be in the few-micrometres range, dependingon the amplitude of disorder, in agreement with recent experimental findings.

Diamagnetic shift of disorder-localized excitons in narrowGaAs∕AlGaAsquantum wells

A correlation between the diamagnetic shift and transition energy of disorder-localized excitons is observed in magnetomicrophotoluminescence $(\ensuremath{\mu}\mathrm{PL})$ on narrow $\mathrm{GaAs}∕{\mathrm{Al}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}$ quantum wells (QW's). The QW's were grown by molecular-beam epitaxy without growth interruption at the interfaces. $\ensuremath{\mu}\mathrm{PL}$ spectra were obtained in a confocal setup with the magnetic field applied normal to the QW plane. The lowest-energy exciton states have the smallest diamagnetic coefficients; the exciton diamagnetic shift in the localized exciton tail of the QW emission spectra increases by a factor of 2 as a function of transition energy. The positive correlation between diamagnetic shift and emission energy reveals exciton localization by short-range correlated interface disorder.

Influence of roughness and disorder on tunneling magnetoresistance

A systematic, quantitative study of the effect of interface roughness and disorder on the magnetoresistance of FeCo$|$vacuum$|$FeCo magnetic tunnel junctions is presented based upon parameter-free electronic structure calculations. Surface roughness is found to have a very strong effect on the spin-polarized transport while that of disorder in the leads (leads consisting of a substitutional alloy) is weaker but still sufficient to suppress the huge tunneling magneto-resistance (TMR) predicted for ideal systems.

Interface disorder and layer transitions in Ising thin films

AbstractThe disorder and layer transitions in the interface between an Ising spin‐1/2 film denoted (n ), and an Ising spin‐1 film denoted (m ), are studied using Monte Carlo simulations. The effects of both an external magnetic field, acting only on the spin‐1/2 film, and a crystal magnetic field acting only on the spin‐1 film, are studied for a fixed temperature and selected values of the coupling constant J p between the two films. It is found that for large values of the constant J p, the layers of the film (n ), as well as those of the film (m ), undergo a first order layering transition. On the other hand, the only disordered layer of the film (n ) is that one belonging to the interface films (n )/(m ), for any values of the crystal field Δ . We show the existence of a critical value of the crystal field Δ c, above which this particular layer of the film (n ) is disordered. We found that Δ c depends on the values of the constant coupling J p between the two films. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

General medical and psychiatric perspectives on somatoform disorders: separated by an uncommon language

While Diagnostic and Statistical Manual of Mental Disorders-IV provided updated definitions and diagnostic criteria for the diagnoses subsumed under the category of somatoform disorders, various nosological questions are still unresolved. We assessed current research activity on important key concepts related to nosology, validity, and reliability of the Diagnostic and Statistical Manual of Mental Disorders-IV somatoform diagnoses. The initial Medline search for articles from 2000 through 2005 yielded a total of 912 articles. After checking for redundancy and excluding publications using other than Diagnostic and Statistical Manual of Mental Disorders-IV diagnostic criteria, a total of 101 articles was further reviewed. Heterogeneity of papers precluded statistical approaches; thus, a descriptive and narrative review was pursued. It appears that applying the specific categories and criteria as proposed by Diagnostic and Statistical Manual of Mental Disorders-IV only captures a small proportion of the phenomena of interest at the interface of medicine and psychiatry. A paradigm shift towards 'general medical/psychiatry interface disorders' in exchange for the current dichotomy of 'mind' vs. 'body' disorders, may reduce stigma associated with current diagnostic labeling, improve user acceptability, and stimulate research in this important but still fragmented clinical area that still lacks agreed-upon diagnostic definitions.

First-principles scattering matrices for spin transport

Details are presented of an efficient formalism for calculating transmission and reflection matrices from first principles in layered materials. Within the framework of spin density functional theory and using tight-binding muffin-tin orbitals, scattering matrices are determined by matching the wave functions at the boundaries between leads which support well-defined scattering states, and the scattering region. The calculation scales linearly with the number of principal layers $N$ in the scattering region and as the cube of the number of atoms $H$ in the lateral supercell. For metallic systems for which the required Brillouin zone sampling decreases as $H$ increases, the final scaling goes as ${H}^{2}N$. In practice, the efficient basis set allows scattering regions for which ${H}^{2}N\ensuremath{\sim}{10}^{6}$ to be handled. The method is illustrated for $\mathrm{Co}∕\mathrm{Cu}$ multilayers and single interfaces using large lateral supercells (up to $20\ifmmode\times\else\texttimes\fi{}20$) to model interface disorder. Because the scattering states are explicitly found, ``channel decomposition'' of the interface scattering for clean and disordered interfaces can be performed.

Proton-induced damage in gallium nitride-based Schottky diodes

Proton irradiation decreases the doping concentration and increases the ideality factor and series resistance, but has very little effect on the Schottky barrier height in n-Gallium nitride Schottky diodes. 1.0-MeV protons cause greater degradation than 1.8-MeV protons because of their higher nonionizing energy loss. The displacement damage recovers during annealing. Comparison between Schottky diodes and high electron-mobility transistors suggests that the degradation in both types of devices is predominantly due to carrier removal and mobility degradation caused by radiation-induced defect centers in the crystal lattice, with interface disorder playing a relatively insignificant part in overall device degradation.

Differences between solid superheating and liquid supercooling

The thermodynamic and kinetic behaviors for solid superheating and liquid supercooling were critically examined and compared via molecular-dynamics simulations. It is shown that the large elastic energy associated with internal melting and solid-liquid interface disorder play important roles in superheating. The growth rate is anisotropic for supercooling, but isotropic for superheating. Supercooling can be well described by the classical nucleation theory, whereas superheating shows many exceptions. The underlying mechanisms for these differences are discussed.

Nature and extent of melting in superheated solids: Liquid-solid coexistence model

The nature and extent of superheating in solids have remained an open problem for nearly a century. Using a liquid-solid coexistence model, we critically examined melting in the superheating regime. It is found that the solid/liquid density difference and the interface disordering at melting are two key factors determining the nature of the transition and the extent of superheating. A nucleation forbidden gap is found due to the density difference. The nucleation barrier rising from the interface is reduced by the interface disordering. The results obtained from the theoretical model are in excellent agreement with those in atomistic simulations.

Applicability of the coherent potential approximation for transmission through disordered interfaces

We present a study of ballistic conductance through substitutionally disordered Fe–Cr(100) interfaces. The effects of interface disorder on the conductance are investigated using (a) a supercell approach (SA) where disorder is approximated by randomly generated configurations within large two-dimensional supercells and (b) the layer adapted coherent potential approximation (CPA). The SA gives simultaneously the specular and diffuse part of the transmission. The CPA, on the other hand, accounts only for specular transmission. We observe excellent agreement between the CPA result and the specular part of the transmission obtained via the SA. However, the CPA, in the absence of vertex corrections does not account for the diffuse transmission and therefore cannot be used to describe phenomena such as current perpendicular to the plane giant magnetoresistance (CPP GMR).

Effect of interwall surface roughness correlations on optical spectra of quantum well excitons

We show that the correlation between morphological fluctuations of two interfaces confining a quantum well strongly suppresses a contribution of interface disorder to inhomogeneous line width of excitons. We also demonstrate that only taking into account these correlations one can explain all the variety of experimental data on the dependence of the line width upon thickness of the quantum well.

Effect of electron-nuclear spin interactions for electron-spin qubits localized in InGaAs self-assembled quantum dots

The effect of electron-nuclear spin interactions on qubit operations is investigated for a qubit represented by the spin of an electron localized in an InGaAs self-assembled quantum dot. The localized electron wave function is evaluated within the atomistic tight-binding model. The electron Zeeman splitting induced by the electron-nuclear spin interaction is estimated in the presence of an inhomogeneous environment characterized by a random nuclear spin configuration, by the dot-size distribution, alloy disorder, and interface disorder. Due to these inhomogeneities, the electron Zeeman splitting varies from one qubit to another by the order of 10−6, 10−6, 10−7, and 10−9eV, respectively. Such fluctuations cause errors in exchange operations due to the inequality of the Zeeman splitting between two qubits. However, the error can be made lower than the quantum error threshold if an exchange energy larger than 10−4eV is used for the operation. This result shows that the electron-nuclear spin interaction does not hinder quantum-dot based quantum computer architectures from being scalable even in the presence of inhomogeneous environments.

On the role of the interface charge in non-ideal metal–semiconductor contacts

The bias dependent interface charge is considered as the origin of the observed non-ideality in current–voltage and capacitance–voltage characteristics. Using the simplified model for the interface electronic structure based on defects interacting with the continuum of interface states, the microscopic origin of empirical parameters describing the bias dependent interface charge function is investigated. The results show that in non-ideal metal–semiconductor contacts the interface charge function depends on the interface disorder parameter, density of defects, barrier pinning parameter and the effective gap center. The theoretical predictions are tested against several sets of published experimental data on bias dependent ideality factor and excess capacitance in various metal–semicoductor systems.