Rigid random surfaces at large d

A model of two-dimensional random surfaces with extrinsic curvature energy is studied in the limit where the dimension of bulk space d is large. The large-d effective potential is constructed. For large surface tension the ground state is homogeneous and its properties are studied. For small enough surface tension, non-perturbative instabilities which break translation invariance in the plane of the membrane are shown to occur for large but finite wavelength. The relationships between this model, the bosonic string, the Liouville model and lattive random surface models are discussed.     

Remarks on the Gibbs adsorption equation and the van der Waals,Cahn-Hilliard theory of interfaces

The common statements of the Gibbs adsorption equation, and a phenomenological theory of interfaces (van der Waals, Cahn-Hilliard theory), are summarized, and then two remarks are made. The first is that only certain identifications of the local energy and entropy densities are admissible in the phenomenological theory if it is to be consistent with the adsorption equation. The second is a generalization to any of the relative adsorptions Γ_i(j) in a c-component system, of a microscopic interpetation that Leng, Rowlinson, and Thompson recently gave to Γ₂₍₁₎ in a one-component system, where 2 and 1 refer to the densities of energy and matter, respectively.     

Finite-size crossover in systems with slab geometry

A renormalization group study of the finite-size (dimensional) crossover is carried out with the help pf ε = 4 − d and ε₀ = 3 − d expansion techniques. The finite-size crossover and the invariance relation for the length scale transformation are proven up to the two-loop approximation. The formal equivalence between the finite-size crossover in classical systems and the quantum-to-classical dimensional crossover in certain quantum statistical models is emphasized and exploited. The finite-size corrections to the fluctuation shift of the critical temperature and the width of the critical region are investigated. It is shown that the shift exponent λ describing the fractional rounding of the critical temperature obeys the relation λ = D − 2, where D is the dimensionality of the system.     

Atomic structures and electronic properties of interfaces between aluminum and carbides/nitrides: A first-principles study

We perform a first-principles investigation of the atomic structures and electronic properties of interfaces between aluminum and four kinds of ceramics, TiC, TiN, VC and VN, under three orientations (001), (110) and (111). We find that the stable interfaces are those with bonding between Al atom and metalloid C (or N) atom, which is attributed to the overlap of p states of Al and d states of metalloid atoms at Femi level forming covalent components. Among the interfaces with the three orientations, the (111) interfaces are found to possess the largest adhesion energy in that the stacking of atoms follows intrinsic atomic distribution and this interfacial bonding is relatively strong. It is also found that the interfaces between Al and metal carbides (TiC and VC) are more stable than those between Al and metal nitrides (TiN and VN).     

Hydrogen sorption in titanium alloys with a symmetric Σ5(310) tilt grain boundary and a (310) surface

The hydrogen sorption in intermetallic B2 TiM (M = Ni, Co, Pd) with a symmetric ??5(310) tilt grain boundary and a (310) surface is studied by density functional theory methods. The effect of hydrogen on the electronic characteristics of the alloys is analyzed as a function of a sorption position at the interfaces. The hydrogen sorption energy is shown to depend on the local environment of hydrogen; on the whole, hydrogen at the interfaces prefers titanium-rich positions. The hydrogen sorption energy in metal-rich positions decreases when the d shell of the second alloy component is filled with electrons. The grain-boundary energy, the surface energy, and the hydrogen segregation energies to the interfaces are calculated. Hydrogen sorption in titanium alloys is shown to decrease Griffith work and to favor brittle fracture along tilt grain boundaries.     

Helical turbulent spectra in the presence of energy and helicity fluxes

On the basis of asymptotic approach, the behavior of helicity spectra in turbulent flows has been studied. The obtained expressions relate these spectra to energy spectra on the condition that energy flux ε and helicity flux η are nonzero both in the inertial and dissipative intervals.     

Modification of the electronic structure and formation of an accumulation layer in ultrathin Ba/n-GaN and Ba/n-AlGaN interfaces

The electronic structure of the n-GaN(0001) and Al _x Ga_{1 ? x} N(0001) (x = 0.16, 0.42) surfaces and the Ba/n-GaN and Ba/AlGaN interfaces is subjected to in situ photoemission investigations in the submonolayer Ba coverage range. The photoemission spectra of the valence band and the spectra of the surface states and the core 3d level of Ga, the 2p level of Al, and the 4d and 5p levels of Ba are studied during synchrotron excitation in the photon energy range 50–400 eV. A spectrum of the surface states in Al _x Ga_{1 ? x} N (x = 0.16, 0.42) is found. The electronic structure of the surface and the near-surface region is found to undergo substantial changes during the formation of the Ba/n-GaN and Ba/AlGaN interfaces. The effect of narrowing the photoemission spectrum in the valence band region from 10 to 2 eV is detected, and surface eigenstates are suppressed. The Ba adsorption is found to induce the appearance of a new photoemission peak in the bandgap at the Fermi level in the Ba/n-GaN and Ba/n-Al_0.16Ga_0.84N interfaces. The nature of this peak is found to be related to the creation of an accumulation layer due to a change in the near-surface potential and enriching band bending. The energy parameters of the potential well of the accumulation layer are shown to be controlled by the Ba coverage.     

A study of the first order transition in a compressible Ising magnet by the renormalization group trajectory integral method

The free energy of an Ising magnet coupled to an isotropic elastic medium in d = 4 ? ε dimensions is calculated. Renormalization group predictions of a first order transition in this system are verified and the phase diagram is constructed.     

ε-expansion for the density of states of a disordered system near an Anderson transition

The density of states for the Schrödinger equation with a Gaussian random potential is calculated in a space of dimension d=4?ε in the entire energy range, including the vicinity of an Anderson transition.     

ITO: Zr bi-layers deposited by reactive O2 and Ar plasma with high work function for silicon heterojunction solar cells

We report the influence of reactive oxygen (O₂) and argon (Ar) plasma based ITO:Zr bi-layers for silicon heterojunction (SHJ) solar cells. The purpose of reactive O₂ sputtered ITO:Zr was to improve the Hall mobility and work function while the Ar based ITO:Zr films play an important role to maintain good electrical characteristics. The thickness of reactive O₂ based ITO:Zr films was fixed at 15 nm while Ar based films was varied from 65 to 125 nm, respectively. ITO:Zr bi-layers with the thickness of 15/105 nm deposited by O₂ and Ar plasma, respectively, showed lowest resistivity of 2.358 × 10⁻⁴ Ω cm and high Hall mobility of 39.3 cm²/V · s. All ITO:Zr bi-layers showed an average transmittance of above 80% in the visible wavelength (380–800 nm) region. Work function of ITO:Zr bi-layers was calculated from the X-ray photoelectron spectroscopic (XPS) data. The ITO:Zr work function was enhanced from 5.3 eV to 5.16 eV with the variation of ITO:Zr bi-layers from 15/65 to 15/125 nm, respectively. Front barrier height in SHJ solar cells can be modified by using TCO films with high work function. The SHJ solar cells were fabricated by employing the ITO:Zr bi-layer as front anti-reflection coating. The SHJ solar cells fabricated on ITO:Zr bi-layer with the thickness of 15/105 nm showed the best photo-voltage parameters as; V_oc = 739 mV, J_sc = 39.12 mA/cm², FF = 75.97%, η = 21.96%.     

Electroreflectance of bound excitonic states in semiconductors

While first-derivative spectroscopy (thermoreflectance, piezoreflectance, wavelength derivative modulation) has a general validity, no matter whether one is studying interband or excitonic transitions (involving also bound states), things are more complex in the case of electroreflectance (ER). As a matter of fact, Aspnes and Rowe's third-derivative theory does not include bound excitonic states. Using a phenomenological approach one can see that only in the case of a strong mixing between d³ε_r/dE³ and d³ε₁/dE³ it is possible to observe a qualitative agreement between Δε and d³ε/dE³ in some particular cases where Wannier excitonic series gives a predominant contribution to the optical spectra.     

Extended perturbation formulae for Jahn-Teller molecules

The effect of the Jahn-Teller interaction on a symmetric top molecule with a threefold axis of symmetry in a ^2S + 1E state has been investigated by perturbation theory. Contributions up to sixth order are included. Explicit formulae for various quantities have been derived on the assumption that there is only one Jahn-Teller active mode of vibration; both linear and quadratic Jahn-Teller interactions are considered. The quantities concerned are (i) the vibronic energy levels, (ii) the orbital quenching factor d_t, (iii) the correction to the A-rotational constant, (iv) the correction to the spin-spin dipolar coupling term, and (v) the correction to the spin-rotation coupling constant ε_aa. Because the perturbation expansion converges slowly, the results are only applicable to molecules subject to a weak Jahn-Teller effect. There are several examples of this type of molecule which have been studied experimentally.     

Surface critical exponents using the renormalization group ϵ-expansion

A Ginzburg-Landau-Wilson (GLW) model extended to include surface energy terms is used to discuss the surface critical behaviour of a system of interacting spins. A straightforward extension of the bulk renormalization group transformation is worked out to first order in ε = 4 ? d (where d is the number of spatial dimensions). In contrast to previous work, the coefficients of the quadratic (r) and quartic (u) terms in the GLW free energy are allowed to depend on the distance from the surface. To lowest order in ε, we show that the fixed point $\text{u}{}^1\text{(z)}$ is given by the usual bulk value. The RG recursion formula we obtain has a line of possible fixed points $\text{r}{}^1\text{(z)}$ associated with both the “special” and “ordinary” transitions. The fact that the GLW model can only describe systems with short-range interactions allows one to select the correct fixed point, in which $\text{r}{}^1\text{(z)}$ is given by its bulk value up to atomic distances from the surface. We discuss the ordinary and special transitions in a unified way. The correlation functions involving surface spins are worked out and the critical exponents η_| and η_⊥ are evaluated to O(ε). Our results agree with those of Lubensky and Rubin (ordinary transition) and Bray and Moore (special transition), who used less transparent methods of carrying out the RG transformation.     

Modeling and computation of two phase geometric biomembranes using surface finite elements

Biomembranes consisting of multiple lipids may involve phase separation phenomena leading to coexisting domains of different lipid compositions. The modeling of such biomembranes involves an elastic or bending energy together with a line energy associated with the phase interfaces. This leads to a free boundary problem for the phase interface on the unknown equilibrium surface which minimizes an energy functional subject to volume and area constraints. In this paper we propose a new computational tool for computing equilibria based on an L² relaxation flow for the total energy in which the line energy is approximated by a surface Ginzburg–Landau phase field functional. The relaxation dynamics couple a nonlinear fourth order geometric evolution equation of Willmore flow type for the membrane with a surface Allen–Cahn equation describing the lateral decomposition. A novel system is derived involving second order elliptic operators where the field variables are the positions of material points of the surface, the mean curvature vector and the surface phase field function. The resulting variational formulation uses H¹ spaces, and we employ triangulated surfaces and H¹ conforming quadratic surface finite elements for approximating solutions. Together with a semi-implicit time discretization of the evolution equations an iterative scheme is obtained essentially requiring linear solvers only. Numerical experiments are presented which exhibit convergence and the power of this new method for two component geometric biomembranes by computing equilibria such as dumbbells, discocytes and starfishes with lateral phase separation.