Probing Lattice Vibrations at SiO_2/Si Surface and Interface with Nanometer Resolution

Recent advances in monochromatic aberration corrected electron microscopy make it possible to detect the lattice vibrations with both high-energy resolution and high spatial resolution. Here, we use sub-10 meV electron energy loss spectroscopy to investigate the local vibrational properties of the SiO_2/Si surface and interface. The energy of the surface mode is thickness dependent, showing a blue shift as z-thickness(parallel to the fast electron beam)of SiO_2 film increases, while the energy of the bulk mode and the interface mode keeps constant. The intensity of the surface mode is well-described by a Bessel function of the second kind. The mechanism of the observed spatially dependent vibrational behavior is discussed and compared with dielectric response theory analysis. Our nanometer scale measurements provide useful information on the bonding conditions at the surface and interface.     

晶格失配对InAsxP1-x/InP发光特性的影响

采用低压金属有机化学气相沉积(LP-MOCVD)技术,在掺Fe的半绝缘InP衬底上制备了InAs_0.157P_0.843 外延层。利用变温光致发光研究了InAs_0.157P_0.843外延层在13~300 K温度范围内的发光特性,通过理论分析与计算,证实了在应力作用下InAs_0.157P_0.843外延层价带顶的轻重空穴带发生了劈裂,并研究了导带底与价带顶轻空穴带之间形成的复合发光峰在应力作用下随温度的变化规律。     

Lattice resistance to dislocation motion at the nanoscale

In this Letter, we propose a model that demonstrates the effect of a free surface on the lattice resistance experienced by a moving dislocation in nanodimensional systems. This effect manifests in an enhanced velocity of dislocation due to the proximity of the dislocation line to the surface. To verify this finding, molecular dynamics simulations for an edge dislocation in bcc molybdenum are performed, and the results are found to be in agreement with the numerical implementations of this model. The reduction in this effect at higher stresses and temperatures, as revealed by the simulations, confirms the role of lattice resistance behind the observed change in the dislocation velocity.     

Elastic Wave Reflection at the Interface at Preset Stresses

Russian Physics Journal - The problem of elastic wave reflection at the interface at preset constant stresses is discussed. Under the conditions where the reflection laws are fulfilled, analytical...     

Trees at an Interface

A lattice tree at an interface between two solvents of different quality is examined as a model of a branched polymer at an interface. Existence of the free energy is shown, and the existence of critical lines in its phase diagram is proven. In particular, there is a line of first order transitions separating a positive phase from a negative phase (the tree being predominantly on either side of the interface in these phases), and a curve of localization–delocalization transitions which separate the delocalized positive and negative phases from a phase where the tree is localized at the interface. This model is generalized to a branched copolymer which is examined in a certain averaged quenched ensemble. Existence of a thermodynamic limit is shown for this model, and it is also shown that the model is self-averaging. Lastly, a model of branched polymers interacting with one another through a membrane is considered. The existence of a limiting free energy is shown, and it is demonstrated that if the interaction is strong enough, then the two branched polymers will adsorb on one another.     

Lattice dynamics of molybdenum at high pressure

We have determined the lattice dynamics of molybdenum at high pressure to 37 GPa using high-resolution inelastic x-ray scattering. Over the investigated pressure range, we find a significant decrease in the H-point phonon anomaly. We also present calculations based on density functional theory that accurately predict this pressure dependence. Based on these results, we infer that the likely explanation for the H-point anomaly in molybdenum is strong electron-phonon coupling, which decreases upon compression due to the shift of the Fermi level with respect to the relevant electronic bands.     

Quantum Lattice Models at Intermediate Temperature

We analyze the free energy and construct the Gibbs-KMS states for a class of quantum lattice systems, at low temperature and when the interactions are almost diagonal, in a suitable basis. The models we study may have continuous symmetries, our results, however, apply to intermediate temperatures where discrete symmetries are broken but continuous symmetries are not. Our results are based on quantum Pirogov–Sinai theory and a combination of high and low temperature expansions. Received: 6 December 2000 / Accepted: 18 July 2001     

Lattice relaxation at alkali metal surfaces

The surface relaxation of the first interlayer spacing for both the (110) and (100) faces of alkali metals has been calculated selfconsistently using the density functional formalism and a new density matrix method which obviates the use of wavefunctions. For the (110) surfaces of all alkali metals we find no or only very small relaxation. The (100) surfaces show bigger relaxation effects and these vary from 3.5% inward for Li to 1% outward for Cs. These findings are consistent with general trends found in LEED or Ion scattering studies. Force constants for the movement of the last atomic layer are also determined.     

Accommodation and adsorption of gases on solid surfaces at low temperatures

The present state of the quantum theory of accommodation and adsorption of gases on solid surfaces, in the limit of low temperatures, is considered, and it is concluded that there have been no significant advances since the author's paper in J. Chem. Phys. 55 (1971) 5742. Using the work of that paper, power series in temperature are presented for the adsorption probability and for the bound-state and continuum-state contributions to the energy accommodation coefficient, α. The qualitative agreement of the bound-state contribution to α with recent calculations of Garcia, Celli and Manson is discussed, as is the strong disagreement of the result for α with existing experimental data.     

Lattice QCD at finite temperature and density

QCD at finite temperature and density is becoming increasingly important for various experimental programmes, ranging from heavy ion physics to astro-particle physics. The non-perturbative nature of non-abelian quantum field theories at finite temperature leaves lattice QCD as the only tool by which we may hope to come to reliable predictions from first principles. This requires careful extrapolations to the thermodynamic, chiral and continuum limits in order to eliminate systematic effects introduced by the discretization procedure. After an introduction to lattice QCD at finite temperature and density, its possibilities and current systematic limitations, a review of present numerical results is given. In particular, plasma properties such as the equation of state, screening masses, static quark free energies and spectral functions are discussed, as well as the critical temperature and the QCD phase structure at zero and finite density.     

Lattice dynamics of CuCl at 4.2°K

The deformable-ion model in the dipole approximation is used to calculate the phonon dispersion curves of CuCl at 4.2°K. A very good agreement with the neutron scattering data is obtained with only six adjustable parameters and the model parameters are quite reasonable.     

Lattice Yang-Mills theory at nonzero temperature and the confinement problem

We discuss finite temperature lattice Yang-Mills theory with special attention to the confinement problem. The relationship between the confinement criteria of Wilson, Polyakov, and 't Hooft is clarified by establishing a string of inequalities between the corresponding string tensions. The close connection between finite temperature Yang-Mills models and spin models is exploited to obtain new and rather sharp upper bounds for the critical coupling constant above which there is confinement. This same analogy also allows us to establish infrared bounds for the gauge models that yield a lower bound for this critical coupling and thereby show the existence of a weak coupling regime without confinement at nonzero temperature in three or more space dimensions. Finally we discuss extension of our results to other forms of the lattice action, the Hamiltonian lattice models of Kogut and Susskind and 't Hooft'sN → ∞ limit.     

十八胺单分子膜的研究

通过测定在纯水和CdCl2 溶液亚相上十八胺单分子膜的平衡、循环π～A等温线及其动态弹性 ,发现在亚相中加入Cd2 + 可以使膜的液态相凝聚性增强 ,固态相凝聚性减弱 .液态的单分子膜在两种亚相上有较好的可回复性 ,而在固态膜中则不然 .这可归因于在水面上十八胺分子间可形成氢键 ,而在CdCl2 水溶液亚相上的十八胺则与Cd2 + 发生配位 ,形成了多配位络合物 ,两种情况下十八胺分子在高膜压区都会发生稳定的聚集 .静、动态弹性的比较表明 ,膜障的振动不利于十八胺分子与Cd2 + 间的配位作用     

Interface of transition metal oxides at the atomic scale

Remarkable phenomena arise at well-defined heterostructures, composed of transition metal oxides, which is absent in the bulk counterpart, providing us a paradigm for exploring the various electron correlation effects. The functional properties of such heterostructures have attracted much attention in the microelectronic and renewable energy fields. Exotic and unexpected states of matter could arise from the reconstruction and coupling among lattice, charge, orbital and spin at the interfaces. Aberration-corrected scanning transmission electron microscopy (STEM) is a powerful tool to visualize the lattice structure and electronic structure at the atomic scale. In the present study some novel phenomena of oxide heterostructures at the atomic scale are summarized and pointed out from the perspective of electron microscopy.     

Transfer Matrices and Lattice Fermions at Finite Density

I discuss the connection between the Hamiltonian and path integral approaches for fermionic fields. I show how the temporal Wilson projection operators appear naturally in a lattice action. I also carefully treat the insertion of a chemical potential term.     

Lattice thermal conductivity of polyvinyl acetate at low temperatures

The lattice thermal conductivity of a non-crystalline polymer has been studied at low temperatures in the frame of the density fluctuation model by calculating the total lattice thermal conductivity of polyvinyl acetate in the temperature range 0.1–4K as an example and a very good agreement has been reported between the calculated and the experimental values of the lattice thermal conductivity in the entire temperature range of study. It is also found that at low temperatures, the lattice thermal resistivity of a non-crystalline polymer is mainly due to scattering of phonons by empty spaces.     

Lattice Green's Function for the Diamond Lattice

An expression for the Green's function (GF) of diamond lattice is evaluated analytically and numerically for a single impurity interacting with the first nearest-neighboring host atoms. The density of states (DOS), phase shift and scattering cross-section are expressed in terms of complete elliptic integrals of the first kind.     

Lattice fermions at non-zero temperature and chemical potential

We study the free fermion gas at finite temperature and chemical potential in the lattice regularized version proposed by Hasenfratz and Karsch and by Kogut et al. Special emphasis is placed on the identification of the particle and antiparticle contributions to the partition function. In the case of naive fermions we show that the partition function no longer separates into particle-antiparticle contributions in the way familiar from the continuum formulation. The use of Wilson fermions, on the other hand, eliminates this unpleasant feature, and leads, after subtracting the vacuum contributions, to the familiar expressions for the average energy and charge densities.