Vacuum Phase Research Articles

Microstructural changes and elemental diffusion of sputtered NiCrAlY coating on a Ni-base SC superalloy subjected to high temperature

Microstructural changes and elemental diffusion of sputtered NiCrAlY coating on the Ni-base SC superalloy were investigated. Tests were conducted by exposing coated specimens both in vacuum and in still air at 1000 °C. XRD and SEM were used to analyze phases and microstructures. EPMA was used to characterize the distribution of elements in the coating interdiffusion layers and substrates. It was found that the as-sputtered NiCrAlY coating showed homogeneous element distribution with abrupt change of constituent at the interface between the substrate and the coating. After vacuum heat treatment, microstructural and phase changes occurred in the coating because of interdiffusion between the substrate and the coating—an interdiffusion layer and two new phases emerged. After 200 h oxidation at 1000 °C in air, the interdiffusion layer thickened and a diffusion influenced layer emerged below the interdiffusion layer in the substrate. Some of the Al in the γ′-Ni 3Al phase was replaced by Ta, resulting in an increase of the lattice parameter a 0 of γ′ phase.

Thermal stability of nitride coatings formed by ion–plasma deposition

Titanium nitride and chromium nitride coatings were formed on a gray cast iron by condensation from a plasma phase in vacuum with the ion bombardment of the sample surface by titanium or chromium plasma flows in a residual nitrogen atmosphere. The element and phase composition of coatings were studied before and after annealing for 1–43 h in air at temperature 700 °C using Auger electron spectroscopy (AES) and X-ray diffraction (XRD). It is established that titanium nitride coatings are single-phase TiN system with a (1 1 1) preferred growth orientation, and chromium nitride coatings—a two-phase system: CrN and Cr 2N phases. The annealing of coatings at the atmospheric pressure and the temperature of 700 °C in the range of 1–43 h results in the deceleration of the oxidation process of the material substrate for chromium nitride with respect to titanium nitride coatings.

Investigation of n-GaN/p-SiC/n-SiC heterostructures

With the use of sublimation epitaxy in vacuum and hydride vapor phase epitaxy (HVPE) a heterostructure n-GaN/p-6H-SiC/n-SiC on base top of n+6H-SiC substrate was developed. The electrical properties of the n-GaN/p-6H-SiC heterojunction was investigated and prototype of hetero bipolar transistor (HBT) was fabricated. It was shown that this device can work up to ∼350 °C. It was concluded that device parameters can be improved by further optimization.

False vacuum bubble nucleation due to a nonminimally coupled scalar field

We study the possibility of forming the false vacuum bubble nucleated within the true vacuum background via the true-to-false vacuum phase transition in curved spacetime. We consider a semiclassical Euclidean bubble in the Einstein theory of gravity with a nonminimally coupled scalar field. In this paper we present the numerical computations as well as the approximate analytical computations. We mention the evolution of the false vacuum bubble after nucleation.

Deconfinement in dense two-color QCD

We study SU(2) lattice gauge theory with two flavors of Wilson fermion at non-zero chemical potential μ and low temperature on a 83×16 system. We identify three régimes along the μ-axis. For μ≲mπ/2 the system remains in the vacuum phase and all physical observables considered remain essentially unchanged. The intermediate régime is characterised by a non-zero diquark condensate and an associated increase in the baryon density, consistent with what is expected for Bose–Einstein condensation of tightly bound diquarks. We also observe screening of the static quark potential here. In the high-density deconfined régime we find a non-zero Polyakov loop and a strong modification of the gluon propagator, including significant screening in the magnetic sector in the static limit, which must have a non-perturbative origin. The behaviour of thermodynamic observables and the superfluid order parameter are consistent with a Fermi surface disrupted by a BCS diquark condensate. The energy per baryon as a function of μ exhibits a minimum in the deconfined régime, implying that macroscopic objects such as stars formed in this theory are largely composed of quark matter.

Nonlinear coupling between breathing and quadrupole-like oscillations in the transport of mismatched beams in continuous magnetic focusing fields

A nonlinear analysis of the transport of breathing beams considering nonaxisymmetric perturbations is performed. It is shown that large-amplitude breathing oscillations of an initially round beam may couple nonlinearly to quadrupole-like oscillations, such that the excess energy initially constrained to the axisymmetric breathing oscillations is allowed to flow back and forth between breathing and quadrupole-like oscillations. In this case, the beam develops an elliptical shape with a possible increase in its size along one direction as the beam is transported. This is a highly nonlinear phenomenon that occurs for large mismatch amplitudes on the order of 100% and is found to be particularly relevant for space-charge-dominated beams with K≳k0ϵ, where K is the beam perveance, k0 is the vacuum phase advance per unit axial length, and ϵ is the emittance of the beam. A simple model based on mapping techniques is used to clarify the mechanism that leads to the energy exchange between the modes and is tested against results from direct integration of the envelope equations.

Global Monopole and C-Field

It is well known that a C-field, generated by a certain source equation leads to interesting changes in the cosmological solutions of Einstein's equations. It is argued that different types of topological objects may have been created by the vacuum phase transitions in the early universe. In the cosmological arena, the defects have been put forward as a possible mechanism for structure formation. A global monopole is a heavy object formed in the phase transition of a system composed of a self coupling scalar field triplet φa whose original global 0(3) symmetry is spontaneously broken to U(1). In this article, we find a special solution for the space-time of a global monopole in presence of C-field. It is shown that the nature of the solution remains the same as in general relativity case i.e. monopole exerts no gravitational force on the matter surrounding it but space around it has a deficit solid angle.

Coating Single-Walled Carbon Nanotubes with Phospholipids

Single-walled carbon nanotubes (SWNTs), being hydrophobic by nature, aggregate in water to form large bundles. However, isolated SWNTs possess unique physical and chemical properties that are desirable for sensing and biological applications. Conventionally isolated SWNTs can be obtained by wrapping the tubes with biopolymers or surfactants. The binding modes proposed for these solubilization schemes, however, are less than comprehensive. Here we characterize the efficacies of solubilizing SWNTs through various types of phospholipids and other amphiphilic surfactants. Specifically, we demonstrate that lysophospholipids, or single-chained phospholipids offer unprecedented solubility for SWNTs, while double-chained phospholipids are ineffective in rendering SWNTs soluble. Using transmission electron microscopy (TEM) we show that lysophospholipids wrap SWNTs as striations whose size and regularity are affected by the polarity of the lysophospholipids. We further show that wrapping is only observed when SWNTs are in the lipid phase and not the vacuum phase, suggesting that the environment has a pertinent role in the binding process. Our findings shed light on the debate over the binding mechanism of amphiphilic polymers and cylindrical nanostructures and have implications on the design of novel supramolecular complexes and nanodevices.

Thermal testing and numerical simulation of a prototype cell using light wallboards coupling vacuum isolation panels and phase change material

Light envelopes are more and more frequently used in modern buildings but they do not present sufficient thermal inertia. A solution to increase this inertia is to incorporate a phase change material (PCM) in this envelope. This paper presents the performance of a test-cell with a new structure of light wallboards containing PCMs submitted to climatic variation and a comparison is made with a test-cell without PCMs. To improve the wallboard efficiency a vacuum insulation panel (VIP) was associated to the PCM panel. This new structure allows the apparent heat capacity of the building to be increased, the solar energy transmitted by windows to be stored without raising the indoor cell temperature, and the thickness of the wallboard to be decreased compared with that of traditional wallboards. An experimental study was carried out by measuring temperature and heat fluxes on and through the wallboards. The indoor temperature, which has a special importance for occupants, was also measured. A numerical simulation with the TRNSYS software was carried out in adding a new module representing the new wallboard. It showed a good agreement with experimental results. This new tool will allow users to simulate the thermal behaviour of buildings having walls with PCMs.

Simulation of the surface structure of butylmethylimidazolium ionic liquids

Molecular dynamics simulations of the liquid/vacuum surfaces of the room temperature ionic liquids [bmim][PF(6)], [bmim][BF(4)] and [bmim][Cl] have been carried out at various temperatures. The surfaces are structured with a top monolayer containing oriented cations and anions. The butyl side chains tend to face the vacuum and the methyl side chains the liquid. However, as the butyl chains are not densely packed, both anions and rings are visible from the vacuum phase. The effects of temperature and the anion on the degree of cation orientation is small, but the potential drop from the vacuum to the interior of the liquid is greater for liquids with smaller anions. We compare the simulation results with a range of experimental observations and suggest that neutron reflection from samples with protiated butyl groups would be a sensitive probe of the structure.

The fundamental-electroweak scale hierarchy in the standard model

The multiple-point principle, according to which several vacuum states with the same energy density exist, is put forward as a fine-tuning mechanism predicting the ratio between the fundamental and electroweak scales in the Standard Model (SM). It is shown that this ratio is exponentially huge: ∼e 40. Using renormalization group equations for the SM, we obtain the effective potential in the two-loop approximation and investigate the existence of its postulated second minimum at the fundamental scale. The investigation of the evolution of the top-quark Yukawa coupling constant in the two-loop approximation shows that, with initial values of the top-quark Yukawa coupling in the interval h(M t )=0.95±0.03 (here, M t is the top-quark pole mass), a second minimum of the SM effective potential can exist in the region ϕmin2≈1016−1022 GeV. A prediction is made of the existence of a new bound state of six top quarks and six antitop quarks, formed owing to Higgs boson exchanges between pairs of quarks-antiquarks. This bound state is supposed to condense in a new phase of the SM vacuum. This gives rise to the possibility of having a phase transition between vacua with and without such a condensate. The existence of three vacuum states (new, electroweak, and fundamental) solves the hierarchy problem in the SM.

41.5L: Late-News Paper: Deposition of PEDOT:PSS Films by Infrared Laser Vaporization

Thin films of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) were deposited by resonant infrared laser vaporization from a frozen PEDOT:PSS target. The deposited films were continuous, and exhibited morphological and structural properties similar to those of the starting material, as measured by scanning electron microscopy and Fourier-transform infrared spectroscopy, suggesting that vacuum phase deposition may be practical.

Evaluation of Density Functional Theory Methods for Studying Chemisorption of Arsenite on Ferric Hydroxides

Understanding adsorption of arsenic on ferric hydroxide surfaces is important for predicting the fate of arsenic in the environment and in designing treatment systems for removing arsenic from potable water. This research investigated the binding of arsenite to ferric hydroxide clusters using several density functional theory methods. Comparison of calculated and experimentally measured As-O and As-Fe bond distances indicated that As(III) forms both bidentate and monodentante corner-sharing complexes with Fe(III) octahedra. Edge-sharing As(III) complexes were less energetically favorable and had As-O and As-Fe distances that deviated more from experimentally measured values than corner-sharing complexes. The hydrated bidentate complex was the most energetically favorable in the vacuum phase, while the monodentate complex was most favored in the aqueous phase. Structures optimized using the Harris and Perdew-Wang local functionals were close to both experimental data and structures optimized using the nonlocal Becke-Lee-Yang-Parr (BLYP) functional. Binding energies calculated with the gradient-corrected BLYP functional were only weakly dependent on the method used for geometry optimization. The approach of using low-level structures coupled with higher level single-point energies was found to reduce computational time by 75% with no loss in accuracy of the computed binding energies.

Mechanical properties of C 60 single crystals

The Vickers microhardness H V of C 60 single crystals grown from the vapor phase in vacuum has been measured in the temperature range 77–300 K. The temperature dependence of H V manifests two distinct features: a step-wise change in the microhardness of about 30% in the temperature region of the face-centered cubic–simple cubic (fcc → sc) transition ( T c ≈ 260 K) and a kink in the H V( T) dependence at T 0 ≈ 180 K. The influence of structural defects, environmental factors (light, atmosphere), and helium intercalation on the microhardness was investigated. Besides, the crystals were subjected to compressive deformation along 〈1 1 0〉 at room temperature. The yield stress was about 2.85 MPa and the activation volume determined by the stress relaxation technique was about 60 b 3. It is assumed that the dislocation glide is controlled by the local high-density defects or by the lattice potential relief. The fracture of crystals was often caused by the splitting along the {1 1 1} planes, which are the cleavage planes in fullerite C 60.

A New Phase of the c(4 × 2) Superstructure of Alkanethiols Grown by Vapor Phase Deposition on Gold

A self-assembled monolayer of dodecanethiol is grown onto (111) oriented gold by vacuum phase deposition and studied by ultrahigh vacuum scanning tunneling microscopy (STM). The films consist of domains that exhibit the c(4 x 2) over-structure of the hexagonal (square root of 3 x square root of 3)R30 of alkanethiols on gold. The domain size is only limited by the terrace size of the underlying gold. By higher resolution scans a new phase of the c(4 x 2) structure consisting of four inequivalent molecules that display different heights in the STM images is discovered.

Parametric studies of image-charge effects on an intense beam in a small-aperture alternating-gradient focusing system

The image-charge effects on an intense charged-particle beam propagating through an alternating-gradient focusing channel with a small aperture, circular, perfectly conducting pipe are studied using a test-particle model. For a well-matched elliptical beam with the Kapchinskij–Vladimirskij (KV) distribution, it is found that halo formation and beam loss are induced by nonlinear fields due to image charges on the wall. The halo formation and chaotic particle motion is found to depend sensitively on the system parameters: the occupancy of the quadrupole focusing field, the vacuum phase advance, the beam perveance, and the ratio of the beam size to the aperture. Furthermore, the percentage of beam loss to the conductor wall is calculated as a function of propagating distance and aperture.

Conformational analysis of methylphenidate: comparison of molecular orbital and molecular mechanics methods

Methylphenidate (MP) binds to the cocaine binding site on the dopamine transporter and inhibits reuptake of dopamine, but does not appear to have the same abuse potential as cocaine. This study, part of a comprehensive effort to identify a drug treatment for cocaine abuse, investigates the effect of choice of calculation technique and of solvent model on the conformational potential energy surface (PES) of MP and a rigid methylphenidate (RMP) analogue which exhibits the same dopamine transporter binding affinity as MP. Conformational analysis was carried out by the AM1 and AM1/SM5.4 semiempirical molecular orbital methods, a molecular mechanics method (Tripos force field with the dielectric set equal to that of vacuum or water) and the HF/6-31G* molecular orbital method in vacuum phase. Although all three methods differ somewhat in the local details of the PES, the general trends are the same for neutral and protonated MP. In vacuum phase, protonation has a distinctive effect in decreasing the regions of space available to the local conformational minima. Solvent has little effect on the PES of the neutral molecule and tends to stabilize the protonated species. The random search (RS) conformational analysis technique using the Tripos force field was found to be capable of locating the minima found by the molecular orbital methods using systematic grid search. This suggests that the RS/Tripos force field/vacuum phase protocol is a reasonable choice for locating the local minima of MP. However, the Tripos force field gave significantly larger phenyl ring rotational barriers than the molecular orbital methods for MP and RMP. For both the neutral and protonated cases, all three methods found the phenyl ring rotational barriers for the RMP conformers/invertamers (denoted as cte, tte, and cta) to be: cte, tte > MP > cta. Solvation has negligible effect on the phenyl ring rotational barrier of RMP. The B3LYP/6-31G* density functional method was used to calculate the phenyl ring rotational barrier for neutral MP and gave results very similar to those of the HF/6-31G* method.

Intermolecular interaction studies of winter flounder antifreeze protein reveal the existence of thermally accessible binding state.

The physical nature underlying intermolecular interactions between two rod-like winter flounder antifreeze protein (AFP) molecules and their implication for the mechanism of antifreeze function are examined in this work using molecular dynamics simulations, augmented with free energy calculations employing a continuum solvation model. The energetics for different modes of interactions of two AFP molecules is examined in both vacuum and aqueous phases along with the water distribution in the region encapsulated by two antiparallel AFP backbones. The results show that in a vacuum two AFP molecules intrinsically attract each other in the antiparallel fashion, where their complementary charge side chains face each other directly. In the aqueous environment, this attraction is counteracted by both screening and entropic effects. Therefore, two nearly energetically degenerate states, an aggregated state and a dissociated state, result as a new aspect of intermolecular interaction in the paradigm for the mechanism of action of AFP. The relevance of these findings to the mechanism of function of freezing inhibition in the context of our work on Antarctic cod antifreeze glycoprotein (Nguyen et al., Biophysical Journal, 2002, Vol. 82, pp. 2892-2905) is discussed.

DFT and metal-metal bonding: a dys-functional treatment for multiply charged complexes?

Density functional theory (DFT) calculations are reported for 16 binuclear transition-metal complexes. Structural motifs studied include face-shared and edge-shared bioctahedra, carboxylate-bridged "paddlewheel" complexes, and nonbridged dimers possessing direct metal-metal bonds. Most of these structure types are represented both by multiply charged (tri- and tetra-anionic, and tetracationic) and by neutral or singly charged examples. Geometry optimizations for these species, in the vacuum phase, use the "broken-symmetry" approach coupled with nine different DFT methods. We find a clear dichotomy in the performance of different DFT approaches. For the eight neutral or singly charged complexes, orthodox gradient-corrected DFT methods such as BP and PBE perform generally very well in reproducing in vacuo the complex geometries obtained from X-ray crystallographic studies. In contrast, these orthodox approaches fail to reliably mimic the crystalline geometries for more highly charged complexes such as Mo(2)Cl(9)(3-), Cr(2)(CH(3))(8)(4-), and Rh(2)(NCCH(3))(10)(4+). Much closer agreement with experimental condensed-phase structures for the multiply charged dinuclear complexes is seen for two "local-density-approximation" approaches, X alpha and VWN, and for VWN+B-LYP, an unorthodox combination of the VWN local and B-LYP nonlocal density functionals. The very good performance of the latter approaches arises from an essentially fortuitous cancellation of errors: while the generally overbinding nature of these approaches suggests that they will not reliably describe true gas-phase structures, this overbinding compensates very well for the coulombic distortion expected when complexes are removed from the charge-stabilizing environment of the crystalline or solvated state. We recommend that, as an alternative to the (computationally expensive) incorporation of solvent-field corrections, VWN+B-LYP is the preferred method for structural characterization of triply or more highly charged dinuclear complexes, while orthodox approaches such as PBE perform best for neutral or mildly charged complexes.

Expansion ratio and color improvement of dried vegetables texturized by a new process “Controlled Sudden Decompression to the vacuum”: Application to potatoes, carrots and onions

A procedure, Controlled Sudden Decompression (Détente Instantanée Contrôlée DIC ®) has been developed to impart a porous structure to partially dried pieces of food by expanding them. In this paper, the DIC cycle was optimized for use with special food products. The establishment of an initial vacuum phase prior to the steam treatment, a treatment by step-wise increases in temperature and an atmospheric air injection phase enabled us to process product pieces in a thick layer, very heat-sensitive products or other food products with a low hardening temperature. The physical attributes evaluated were the expansion ratio and color of three vegetables: potatoes, carrots and onions.