SLIT-WAVE MODEL FOR BAND STRUCTURES IN SOLID STATE PHYSICS

The reason behind the entire development in silicon technology was band models in solid state physics. However, the theories postulated in order to give response to this phenomenon do not explain all kinds of materials. In a bid to overcome this limitation, we approach the problem from another point of view. In this work, the wave properties of the electrons from the external orbitals of the atoms and its diffraction patterns through the lattice structure of the material have been used to explain the band structure of metals, semiconductor and insulators. In order to probe this hypothesis, a simulation has been used and according to the relation between the lattice constant and the atomic diameter, the splitting of the bands have been observed for different kind of materials, showing a strong correlation between the simulation and the experimental results.

A Molecular Dynamics Study on the Static and Dynamic Properties of Lubricant PFPE in Hard Disk Driver

The static and dynamic properties of lubricant PFPE are important for the service durability and reliability of the computer head-disk device. Thus molecular dynamic simulations based on a coarse-grained, bead-spring model are adopted to study those properties. On the one hand, we investigate the static properties and infer the structure of both nonpolar and polar PFPE films. For a nonpolar PFPE film, there is a layering structure in the surface layer. And for a polar PFPE film, besides layering structure, there is a bi-polymer structure in the bulk layer. On the other hand, we investigate the dynamic properties and find that for nonpolar PFPE film, a precursor film around one atomic diameter thickness develops according to layering structure; while for polar PFPE film, besides a precursor film, a much steeper and slower spreading shape appears according to bi-polymer structure.

The first coordination number for liquid metals

A simple and absolute method for the calculation of the first coordination number for any pure, isotropic liquid element is presented. The liquid density and the position for the first peak of the radial distribution function, assumed to be the atomic diameter, are the only parameters required. The coordination number for liquid metals that exhibit a BCC (body-centred cube) solid structure averages 7.4 while the first coordination number for liquid metals with a FCC (face-centred cube) or CPH (close-packed hexagonal) solid structure averages 7.1. Those liquid elements that have less closed-packed solid structures have a first coordination number less than 7.0. The calculation also correctly predicts the first coordination number for liquid Se to be 2.4, consistent with its chain-like structure. The calculated values for the liquid element coordination numbers are consistent with the decrease in density of a few percent that occurs upon melting and appear to be related to the Engel–Brewer valence of the solid, which suggests that the electron structure of the solid may be retained upon melting. The first coordination numbers for liquid Ge and Si were calculated to be 5.0 and 4.7, respectively, larger than the value of 4.0 for solid structures. The increase in coordination number upon melting accounts for the increase in density of Ge and Si that occurs upon melting.PACS No.: 61.20.Gy

X-Ray and Neutron Diffraction with Amorphous Ti67Si33, V67Si33, and Cr67Si33

The amorphous alloys Ti67Si33 , V67Si33 , and Cr67Si33 were produced by sputtering. Their structure was investigated by X-ray and neutron diffraction. X-ray diffraction showed that the structure of the three metallic glasses is not isomorphous. Neutron diffraction showed that Si-Si atomic pairs occur preferentially with distances distinctly larger than the atomic diameter of the Si atoms. For T67Si33 partial pair correlation functions could be evaluated from combination of the X-ray and the neutron data.The structural results are compared with the structure of amorphous Mn74Si23P3 .

Computer Simulations of Epitaxial Interfaces

The embedded-atom method was applied in computer simulations to study epitaxial Cu/Ag interfaces in cube-on-cube orientation relationship. Coherent and semicoherent interfaces were studied with inclinations parallel to (001), (011) and (111). The coherent boundary energy depends strongly on the predicted enthalpy of mixing. The interfacial energy for semicoherent boundaries was highly anisotropic, having its largest value (549 mJ/m2) for the (011) interface and its smallest value (231 mJ/m2) for the (111) interface. The periodic elastic relaxations correspond to networks of misfit dislocations lying in the plane of the interface; the maximum displacement in the (011) interface is about one-third the atomic diameter, but only one-eighth the atomic diameter in the (111) interface.

Polymer decoration : Principle and uses in surface science

The vaporization and condensation of gold particles introduced by G. A. Basset has become a classical method in surface investigation by electron microscopy. The “gold decoration” of small drops reveals steps of atomic diameter on the surface of alkali halides.Recently, an original decoration technique has been introduced, which is similar in its principle and experimental set up to gold decoration, but uses polymer molecules rather than gold as the marker. The vaporized polymer (typically polyethylene) has a molecular weight of ∼ 1300, i.e. is an elongated cylinder about 100 Å long and 5 Å diameter; this shape makes it a directional marker, in sharp constrast to gold atoms. The molecules build up small rods (in essence, polymer lamellae seen edge on) visible by conventional electron microscopy. The pattern of these rods (the “polymer decoration“) reveals some of the substrate structural features and can be used to analyze polymer-substrate interactions.

Atomistic Simulations of Surface Relaxations in Ni, Al, and Their Ordered Alloys

ABSTRACTWe have performed a series of simulations to examine the atomistic nature of surface relaxations in pure metals and ordered alloys. The surface relaxations (∆dn, n+1) are shown to be oscillatory and to decay rapidly into the bulk. The period and form of the oscillation may be determined by simple geometrical arguments. The oscillation wavelength is always of the order of an atomic diameter. In pure metals, the surface layer of atoms always displaces inward. However, in the ordered alloys the larger atom may displace outward. On planes composed of more than one atom types, rippling occurs.

A Simple Model for Liquid or Amorphous Metals

The structure of liquid or amorphous metals is described by means of an harmonic approxima­ tion where atoms vibrate around the equilibrium positions of a random hard sphere network. This model depends on three parameters, of which the only adjustable one is the atomic vibration frequency, which is shown to be proportional to the Debye frequency of the corresponding crystalline phase. The atomic diameter is deduced from the position of the structure factor first peak and turns out to be equal to the Goldschmidt diameter. The packing fraction temperature variations are at­ tributed to presence of a variable number of randomly distributed atomic holes and deduced from density measurements. Good agreement with experimental structure factor determinations is found for a wide variety of liquid metals.