The phenomenon of decrease in the friction force upon transition to the superconducting state

A simple explanation is given to the phenomenon of decrease in the friction force between an adsorbed gas film and the surface of a metal, which is observed when the metal is cooled below the superconducting transition temperature. It is pointed out that, below the critical temperature, the friction force must exhibit a characteristic extremum corresponding to the equality of the heat capacities of superconducting and normal phases.     

Order formation of colloidal nanoparticles adsorbed on a substrate with friction

We examine the adsorption process and order formation of colloidal nanoparticles on a planar surface with friction. We perform Brownian dynamics simulations with a three-dimensional cell model in which the particle–particle and particle–substrate interactions are modeled on the DLVO theory, and examine the effects of the friction acting between the adsorbed particles and the substrate on the adsorbed structure formed on the substrate. The results obtained are as follows: when the friction is so strong that the adsorbed particles are stuck to the substrate, ordered structures never form, which seems to be quite natural. However, when the magnitude of the frictional force is moderate, an ordered structure can form even with low coverage because the frictional force aids order formation. This is because the friction counterbalances the particles’ Brownian motion, which would otherwise disturb the ordered structure. Furthermore, through a detailed examination of the distribution of the Brownian motion, it is demonstrated that an increase in the friction has a similar effect as a decrease in temperature.     

Fluctuational-electromagnetic interaction of a moving nanoparticle with walls of a flat dielectric gap

General expressions for the tangential and normal components of the force of interaction and the rate of heat exchange between a neutral spherical nanoparticle (atom) and dielectric walls of a flat vacuum gap are obtained for the first time in a nonrelativistic nonretarded approximation of the fluctuational electromagnetic field theory. In the general case, the walls have a temperature different from that of the particle and possess arbitrary permittivities.     

Growth behavior and surface topography of different silane coupling agents adsorbed on the silicon dioxide substrate (0001) for vapor phase deposition

The growth behavior and surface topography of the deposited films formed from silane coupling agents on silicon dioxide substrate (0001) via vapor phase deposition was investigated using atomic force microscopy (AFM). The surface topography of the films adsorbed on the silicon dioxide substrates is dissimilar with different silane coupling agents and different deposition conditions: (1) the films adsorbed on the silicon dioxide substrate become smoother with the increasing temperature of the silicon dioxide substrate; (2) the surface roughness of the films increases with the increasing concentration of the silane coupling agent solutions; (3) with the increasing temperature of the carrier gas, the surface roughness of the films decreases firstly and then increases; (4) with the increasing time of deposition, the surface roughness of the films increases firstly, then decreases and subsequently increases again. In experiments, the films adsorbed on the silicon dioxide substrate was rinsed ultrasonically with toluene, the results indicate that the silane coupling agent adsorbed on the substrate by physisorption and chemisorption: the chemisorbed coupling agents present island morphology and the physisorbed coupling agents are deposited on the substrate between the islands to decrease the surface roughness of the film.     

High-density silver nanoparticle film with temperature-controllable interparticle spacing for a tunable surface enhanced Raman scattering substrate

The formation of high-density silver nanoparticles and a novel method to precisely control the spacing between nanoparticles by temperature are demonstrated for a tunable surface enhanced Raman scattering substrates. The high-density nanoparticle thin film is accomplished by self-assembling through the Langmuir-Blodgett (LB) technique on a water surface and transferring the particle monolayer to a temperature-responsive polymer membrane. The temperature-responsive polymer membrane allows producing a dynamic surface enhanced Raman scattering substrate. The plasmon peak of the silver nanoparticle film red shifts up to 110 nm with increasing temperature. The high-density particle film serves as an excellent substrate for surface-enhanced Raman spectroscopy (SERS), and the scattering signal enhancement factor can be dynamically tuned by the thermally activated SERS substrate. The SERS spectra of Rhodamine 6G on a high-density silver particle film at various temperatures is characterized to demonstrate the tunable plasmon coupling between high-density nanoparticles.     

Controlled layer-by-layer formation of ultrathin TiO2 on silver island films via a surface sol-gel method for surface-enhanced Raman scattering measurement

A surface sol-gel process has been demonstrated to be an effective method for the surface modification of silver island films as unique SERS substrates for monitoring molecular adsorption on a dielectric titania surface. This layer-by-layer approach allows control of the thickness of the dielectric surface with a monolayer precision on silver surfaces. The enhancement of Raman scattering from adsorbed Rhodamine 6G molecules is inversely proportional to the thickness of the titania film, which is consistent with the decay of electromagnetic enhancement. Despite a reduction in the sensitivity of the film, a substantial improvement in the film was achieved as a result of the enhanced stability of this substrate compared to the silver island film without a TiO(2) coating.     

钛金属薄膜上两种短链自组装分子膜的制备与摩擦特性

采用自组装技术在钛金属薄膜上制备了两种分子链长相同、官能团不同的自组装分子膜,并对其进行了不同时间的紫外照射,对钛金属薄膜和自组装分子膜进行了表征和摩擦特性测试,研究了紫外照射、官能团、滑动速度和载荷对自组装分子膜摩擦特性的影响,结果表明:通过紫外照射钛金属薄膜表面羟基化、自组装分子水解及自组装分子缩合可在钛金属薄膜上制备结构致密的自组装分子膜,制备的两种短链自组装分子膜可降低钛金属薄膜的摩擦特性,APS自组装分子膜的摩擦特性优于MPS自组装分子膜的摩擦特性,紫外照射5 min的自组装分子膜表面吸附的有机杂质被蒸发掉,对针尖的黏着力减小,从而导致针尖的变形减小,摩擦力最低,而紫外照射15 min的自组装分子膜致密的网状结构被破坏,减弱了自组装分子膜的润滑效应,两种自组装分子膜的摩擦力随着滑动速度的增加略呈上升趋势,随着载荷的增加略呈下降趋势,但是变化不大.     

Optical forces in hybrid plasmonic waveguides

We demonstrate that in a hybrid plasmonic system the optical force exerted on a dielectric waveguide by a metallic substrate is enhanced by more than 1 order of magnitude compared to the force between a photonic waveguide and a dielectric substrate. A nanoscale gap between the dielectric waveguide and the metallic substrate leads to deep subwavelength optical energy confinement with ultralow mode propagation loss and hence results in the enhanced optical forces at low input optical power, as numerically demonstrated by both Maxwell's stress tensor formalism and the coupled mode theory analysis. Moreover, the hybridization between the surface plasmon modes and waveguide modes allows efficient optical trapping of single dielectric nanoparticle with size of only several nanometers in the gap region, manifesting various optomechanical applications such as nanoscale optical tweezers.     

The surface energy of a metal nanoparticle in the presence of a vacuum gap between this particle and a dielectric medium

The surface energy of an alkali metal nanoparticle surrounded by a dielectric medium is calculated in the jelly approximation taking into account a vacuum gap between the particle surface and the medium.     

Adsorption of a microtubule on a charged surface affects its disassembly dynamics

The dynamics of disassembly of microtubules deposited on surfaces is shown to be strongly dependent on the electrostatic interaction between the microtubule and the substrate. Fluorescence microscopy of microtubules adsorbed on a Poly-L-Lysine film and immersed in pure water show a drastic decrease in disassembly velocity compared to the microtubules in bulk water solutions. While microtubules suspended in pure water disassemble in seconds, the dissociation velocity of microtubules adsorbed on a Poly-L-Lysine film ranges from 0.8 to 1.0 microm/min in pure water. Kinetic Monte Carlo simulations of the microtubule dynamics indicate that a decrease in the dissociation velocity of unstable microtubules can be achieved by reducing the heterodimer dissociation rate constant of tubulin heterodimers constituting a single protofilament, adsorbed to the Poly-L-Lysine film. This model suggests that the reduction of the dissociation velocity originates from the electrostatic interactions between the positively charged amino groups of the Poly-L-Lysine film and the negatively charged microtubule surface.     

Effects of thermal treatment on the tribological characteristics of thermoplastic polymer film

Friction tests were carried out using a microtribometer to investigate the effect of thermal treatment on microscale friction and wear between poly(methyl methacrylate) (PMMA) film and a fused silica lens. Two films were examined: one that was baked at 413 K for 2 min and one that was baked at 433 K for 24 h. The friction forces on the PMMA films were measured under atmospheric conditions as the temperature of the films was increased from 300 K to 443 K. The contact area between the films and the lens was also examined. As the temperature increased, the friction force increased for both films. The slope of the friction force with temperature and the contact area varied, depending on the state of the film surface; glassy, rubbery, and viscous flow states. The baking conditions also affected the slope, contact area, and wear generation. For temperatures at which the samples were in a glassy state, wear particles were not generated on the sample baked for 24 h. The results demonstrate that the tribological characteristics can be altered by the thermal treatment of the PMMA film as well as the temperature. When the film contains some residual solvent, the residual solvent in the PMMA film can diffuse to the PMMA surface due to heating and thus decrease the friction force under room-temperature conditions.     

Processing and performance of organic insulators as a gate layer in organic thin film transistors fabricated on polyethylene terephthalate substrate

Fabrication of organic thin film transistor (OTFT) on flexible substrates is a challenge, because of its low softening temperature, high roughness and flexible nature. Although several organic dielectrics have been used as gate insulator, it is difficult to choose one in absence of a comparative study covering processing of dielectric layer on polyethylene terephthalate (PET), characterization of dielectric property, pentacene film morphology and OTFT characterization. Here, we present the processing and performance of three organic dielectrics, poly(4-vinylphenol) (PVPh), polyvinyl alcohol (PVA) and poly(methyl methacrylate) (PMMA), as a gate layer in pentacene-based organic thin film transistor on PET substrate. We have used thermogravimetric analysis of organic dielectric solution to determine annealing temperature for spin-coated films of these dielectrics. Comparison of the leakage currents for the three dielectrics shows PVA exhibiting lowest leakage (in the voltage range of ?30 to +30 V). This is partly because solvent is completely eliminated in the case of PVA as observed by differential thermogravimetric analysis (DTGA). We propose that DTGA can be a useful tool to optimize processing of dielectric layers. From organic thin film transistor point of view, crystal structure, morphology and surface roughness of pentacene film on all the dielectric layers were studied using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). We observe pyramidal pentacene on PVPh whereas commonly observed dendritic pentacene on PMMA and PVA surface. Pentacene morphology development is discussed in terms of surface roughness, surface energy and molecular nature of the dielectric layer.     

The Effect of Gravity and Shear Stress on a Liquid Film Driven in a Horizontal Minichannel at Local Heating

The present study is focused on the investigation of gravity effect on thermocapillary deformations in a film flowing under action of co-current gas flow, which creates the tangential force on the gas–liquid interface. The influence of local heating intensity on the heater at a substrate is also investigated. Effects of surface tension, temperature dependent viscosity and thermocapillarity are taken into account. Investigations have shown that gravity has a significant effect on the film deformations and pattern. Decreasing of gravity level leads to a flow destabilization. 3D liquid film pattern noticeably changes in spanwise direction. Increasing of heat flux leads to increasing of liquid film deformations. Dependence of film thinning on heat flux is strongly nonlinear. The most dangerous deformations (regions of minimum film thickness with possible disruption of liquid) take place behind the downstream edge of the heater at any gravity conditions.     

联合载荷下无裂纹DLC薄膜的内应力有限元分析

本文用有限元分析的方法,对受法向和切向联合载荷作用下的无裂纹类金刚石(DLC)薄膜系统内部应力进行了模拟计算,分析了不同摩擦系数和膜厚比对于内部应力的影响,数值模拟结果表明:较大的摩擦系数可以使得界面处剪切应力和Mises等效应力以及y轴Mises等效应力显著增大,而对于界面处的y向压应力影响不是很大。在一定的范围内(0相似文献   

Dielectric Behavior of the Film Formed on Mica Cleaved in Moist Air

Water adsorbed on a freshly peeled mica crystal causes the loss tangent, D, to increase by 1 to 2 orders of magnitude. The nature of the film is investigated as a function of relative humidity by the measurement of D for the frequency range 100 to 50,000 c/s with a capacitor comprising concentric, parallel, circular electrodes of different diameter on opposite sides of the dielectric sheet. This geometry is then analyzed as consisting of the two regions of that within the plates where the electric field, E, is normal to the dielectric plane and that at the edge where tangential E exists. The first is considered in terms of an equivalent circuit for a two layered dielectric. The second is considered in terms of transmission line concepts. It is predicted and verified that the adsorbed film causes the first component to vary as 1/t and the second as √t where t is the thickness of the crystal. Numerical solutions are used to derive the behavior of D, R, and C of the adsorbed film itself. D for the normal direction is ~0.4 and follows a frequency dependency like fresh snow. Resistivities normal to and parallel to cleavage are considerably different while C is much less than expected for a surface film. It is suggested that the surface film is not continuous but instead is localized in patches.     

Effects of substrate temperatures on the structure and properties of hafnium dioxide films

Different HfO2 monolayers under different deposition conditions, such as substrate temperature and oxygen partial pressure, were prepared from metal hafnium using the reactive electron beam evaporation method. X-ray diffraction was applied to determine the crystalline phase of these films, the surface morphology of the samples was examined by atomic force microscopy, and the optical properties were analyzed using a spectrophotometer and the surface thermal lens technique. The relationship between substrate temperature and film characteristic was investigated, and the correlation between the observed film properties and the laser damage threshold was also discussed.     

Analysis of accuracy in prism coupling methods and a proposal of two simple ways for coupling to guided waves and/or for exciting surface plasmon resonance

The stationarity of the coupling spot in relation with different shapes of couplers is discussed. The accuracy in measuring the effective index by various couplers is analyzed. Two simple methods are proposed to couple light into guided waves and/or to excite surface plasmon resonance (SPR). One uses an optical block as a coupler and the incident beam falls onto it in two perpendicular directions. This method is particularly useful for exciting SPR at an interface between metal and anisotropic dielectric media, but also can be used to couple light into guided waves. Another method does not need any coupler. The incident beam is directly launched into the sample from the sustrate side. When a thin metal film is deposited on the substrate and covered either by air or another dielectric layer, SPR can be excited at the interface of metal/air of metal/dielectric. This method can be viewed as an alternative of Kretschmann configuration.     

Influence substrate temperature on structural properties of TiN/TiC bilayers produced by pulsed arc techniques

This paper presents an investigation regarding influence of substrate temperature during deposition on the characteristics of TiN/TiC bilayers grown by plasma-assisted pulsed arc discharge. The substrate temperatures were 50, 100 and 150 °C. The gases used in the experiment were N₂ for TiN and CH₄ for TiC. These coatings were studied by X-ray diffraction techniques determining the variation of the lattice parameters for each film. The Scherrer equation was used to calculate the crystallite size and the micro-strain. The X-rays analysis showed an increase in the substrate temperature made the formation of TiC in (2 0 0) orientation favorable. The sample grown at 50 °C presented low crystallinity and it was increased as the substrate temperature increases. Using a scanning probe microscopy, with atomic force microscopy, phase detection microscopy and force modulation microscopy modes, the morphology of the deposited layer was studied and macro-particles were observed using gray scales to identify differences in the friction coefficient and material composition in the coatings. It has been found that the increment of the substrate temperature decreases the condensation of microdroplets on the surface. Lateral force microscopy was used to calculate friction coefficient of the TiN and TiC monolayers and we found that the friction coefficient is smaller for TiC than for TiN.     

Graphene synthesis by cold implantation of carbon recoil atoms

A new method of introducing carbon into catalytic metal films for graphene synthesis is proposed. The method is based on the phenomenon of carbon recoil atoms from a layer of methane molecules that are adsorbed on a metal film being incorporated into this film under the action of bombardment with inert gas ions. To increase the thickness of adsorbed methane layer, the substrate is cooled down to ?190°C. The proposed method has been implemented on a polycrystalline nickel film. After the final annealing, Raman spectroscopy showed the presence of numerous fragments of multilayer graphene on the film surface.