An Investigation on Starvation Onset of Rough Surface Line Contacts

Utilizing a computational approach, this study quantifies the onset of lubrication starvation for line contacts of rough surfaces operating under typical ranges of automotive gearing applications. The response parameter is selected as the critical film thickness supply, at which starvation initiates. The potential influential parameters (predictors) considered include normal force density, rolling velocity, sliding, lubricant viscosity, and surface roughness amplitude. A non-Newtonian thermal mixed lubrication model is employed to determine the critical lubricant supply under various operating and surface roughness conditions. General linear regression is implemented to reach an easy-to-use equation (R-squared value higher than 97%), facilitating the quantification of starvation dependence on the predictors that are statistically significant.

Влияние напряжения смещения и скорости осаждения на структуру и коэрцитивность пленок NiFe

Influence of the bias voltage Ub and the deposition rate  on the structure, grain size D, and coercivity Hc of NiFe films with the thickness d from 30 to 980 nm, grown onto Si / SiO2 substrates by DC magnetron sputtering, was studied. In the case Ub = 0, the decrease of  from ≈ nm/min to ≈ 7 nm/min is accompanied by the increase of the critical film thickness dcr from dcr ≈ 220 nm to dcr ≈ 270 nm. In this case, Hc in the films with d < dcr is characterized by the dependence Hc ~ D6 and varies from ~ 1 to ~ 20 Oe. In the case of Ub = -100 V, the effect of the deposition rate on the coercivity is much more noticeable. At ν = 7 and 14 nm / min, the films demonstrate soft magnetic properties (Нс ≈ 0.15 - 1.4 Oe) and the absence of dcr for the entire range of studied thicknesses. The films obtained at ν = 21 and 27 nm / min turn into the “supercritical” state at d ≥ dcr ≈ 520 nm, and, in the region d < dcr, they are characterized by the dependence Hc ~ D3 and by the increase of coercivity from ~ 0.35 to ~ 10 Oe.

Quantum Spin Hall Insulators in Tin Films: Beyond Stanene

Large-gap quantum spin Hall (QSH) insulators were previously predicted in stanene and its derivatives. Beyond stanene that is the thinnest [Formula: see text]-Sn(111) film, we propose to explore QSH insulators in [Formula: see text]-Sn films with different crystallographic orientations. Our first-principles calculations reveal that the thickness-dependent band gap of [Formula: see text]-Sn(100) and [Formula: see text]-Sn(110) films does not show a monotonic decrease as typically expected by quantum confinement, but displays an oscillating change behavior, an indicative of topological quantum phase transition. While these films are normal insulators in the ultrathin limit, the QSH phase emerges above a critical film thickness of around 10 layers. Remarkably, the QSH insulators are obtainable within a wide thickness range and their energy gaps are sizable (even [Formula: see text][Formula: see text]0.1[Formula: see text]eV), which facilitates experimental realization of the high-temperature QSH effect.

Effect of Nanostructures and Wettability on the Instability of Thin Water Films on a Solid Surface: A Molecular Dynamics Study

Molecular dynamics simulations are performed to investigate the stability of thin water films on square gold nanostructures of varying depth and wavelength. The critical film thickness of breakup is shown to increase linearly with nanostructure depth, and is not affected by nanostructure wavelength. In addition, the wettability of the gold surface is controlled from superhydrophilic to hydrophobic by altering the energy parameter of the solid-liquid potential, and the equilibrium contact angle for each energy parameter is calculated using a droplet spreading simulation. Four different energy parameters of the solid-liquid potential are investigated. The ratio of the energy parameter to the energy parameter of water and gold is 1, 0.5, 0.25 and 0.1. The case for ratio of 1 represents water on superhydrophilic gold surfaces. The relationship between the critical film thickness of breakup and the equilibrium contact angle is demonstrated. The results of the present work will provide guidelines for nanostructure design for controlling thin film stability.

A Molecular Dynamics Study for Stability of Thin Water Films on Nanostructured Surfaces

The stability of thin water films on a variety of gold nanostructures was simulated by molecular dynamics simulations. The critical film thickness to prevent a film break-up was investigated as a function of the characteristic length of the nanostructures. Layering of water molecules adjacent to the gold substrate was observed as a result of the strong van der Waals interactions between the water molecules and the gold atoms. A model for the critical film thickness in the presence of nanostructures is developed based on the stability analysis. The model prediction is compared with molecular dynamics simulations with good agreement.

Electrical and structural properties of ABO3/SrTiO3 interfaces

ABSTRACTElectrical transport and microstructure of interfaces between nm-thick films of various perovskite oxides grown by pulsed laser deposition (PLD) on TiO2- terminated SrTiO3 (STO) substrates are compared. LaAlO3/STO and KTaO3/STO interfaces become quasi-2DEG after a critical film thickness of 4 unit cell layers. The conductivity survives long anneals in oxygen atmosphere. LaMnO3/STO interfaces remain insulating for all film thicknesses and NdGaO3/STO interfaces are conducting but the conductivity is eliminated after oxygen annealing. Medium-energy ion spectroscopy and scanning transmission electron microscopy detect cationic intermixing within several atomic layers from the interface in all studied interfaces. Our results indicate that the electrical reconstruction in the polar oxide interfaces is a complex combination of different mechanisms, and oxygen vacancies play an important role.

Thin Film Electronic Properties of Ternary Topological Insulator

ABSTRACTUsing an ab initio density functional theory (DFT), we study thin film electronic properties of topological insulators (TIs) based on ternary compounds of Tl (thallium) and Bi (bismuth). We consider TlBiX2 (X=Se, Te) and Bi2X2Y (X, Y=Se, Te) compounds. Here we discuss the nature of surface states, their locations in the Brillouin Zone (BZ) and their interactions within the bulk region. Our calculations suggest a critical film thickness to maintain the Dirac cone which is smaller than that in binary Bi-based compounds. Atomic relaxations are found to affect the Dirac cone in some of these compounds. We discuss the penetration depth of surface states into the bulk region.