Crystal bridge formation marks the transition to rigidity in a thin lubrication film

We report that the rheological transition in a thin lubrication film of dodecane from bulk to high viscosity states as the thickness is decreased is the result of a novel structural transition. Using nonequilibrium molecular dynamics simulations we find that the initial increase in viscosity as the film thins is due to the formation of isolated crystalline bridges between the surfaces. As the thickness decreases further, these bridges increase in number and organize themselves into a tetratic order in the plane of the surface. We show that this ordered state melts at a temperature of 350 K.     

Statistical-thermodynamic theory of ordering in a binary film deposited on the surface of a monocrystal

The ordering of a binary monolayer deposited on the surface of a monocrystal is studied. In the case when the structure of the film is equivalent to that of the crystal surface, the ordering in the film is qualitatively similar to that in the bulk of the sample: When the ordering energy is positive there exists an order-disorder phase transition at a certain temperature and for a certain concentration interval. If the structure of the film is different from the structure of the surface, then the film is ordered at all temperatures, independently of the sign of the ordering energy. In this case, in addition to the equilibrium ordered state in the region T < T_* (T_* is a certain temperature which is determined by the composition of the alloy and by the magnitude of the energy shift of the atoms of the film in the field of the substrate), there exists a metastable ordered state in which there is a jump-like change in the ordering at the point T_*, analogous to a first-order phase transition. Possible methods of experimental study of the ordering in films are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 53–57, May, 1987.     

Polarization of light transmitted through a polymer film with nanosized droplets of liquid crystal

A method is developed for analyzing the state of polarization of a plane wave transmitted through a polymer-dispersed liquid-crystal (PDLC) film with nanosized liquid-crystal (LC) droplets. This method is based on the anisotropic-dipole approximation for describing scattering by a separate droplet and on the Foldy-Twersky approximation for describing propagation of light in a film. Equations are obtained that relate the ellipsometric parameters of coherent (direct) light transmitted through a PDLC film to the order parameters that characterize the morphological and structural properties of the film. Elliptic and circular polarizations and the rotation of the plane of polarization of a wave transmitted through a film are investigated under the normal illumination of the PDLC film by a linearly polarized plane wave. The order parameters of the PDLC film are determined as a function of a control field under the transition from a partially ordered structure of optical axes of LC droplets to a homeotropic structure.     

模板法自组装银团簇阵列的制备和性质研究

利用自组装的嵌段聚合物有序图案为模板来制备有序金属颗粒纳米阵列是人们关注的热点之一。本文概述了最近利用团簇束流沉积系统将银团簇淀积在聚苯乙烯-聚丁二烯-聚苯乙烯(SBS)三嵌段聚合物自组装形成的有序图案上,制备了有序的银纳米颗粒阵列材料,如线形银团簇颗粒阵列和二维银团簇颗粒阵列。利用自编的径向分布函数计算程序对线形银团簇颗粒阵列进行了定量分析,进一步定标了这种线形阵列的有序度,发现在同一线形阵列内有小部分银团簇是近接排列的,大部分团簇颗粒是等间距排列的。同时探讨了这些有序阵列形成的机制。并讨论了利用紫外-可见分光光度计和拉曼谱仪研究这些有序阵列所得到的相关性质。     

Crystallization of polycarbonate from the glassy state. part I. Thin films cast from solution

The morphology of glassy amorphous thin polycarbonate film cast from solution is affected by thermal treatments. Annealing above 80° C and below T_g results in an increase in the size of the ordered regions, nodules, up to several hundred Angströms. The crystallization process from the glass, taking place at 145° C, is divided into three major steps. At first the nodules merge into patches which aggregate to form lamellar planar structures. In some cases the planar structures are well-formed single crystals. Following this, spherulitic arms develop from the planar structures as centers. These arms at first consist of aggregates of large nodules which recrystallize to form lamellae; the final morphology is spherulitic in nature. The effect of film thickness and of several substrates on the morphology has been observed. Applying stress at room temperature to the crystalline film results in a breaking up of the lamellae into small blocks.     

Stick-slip friction and energy dissipation in boundary lubrication

Shearing of a simple nonpolar film, right after the liquid-to-solid phase transition under nanometer confinement, is studied by using a liquid-vapor molecular dynamics simulation method. We find that, in contrast with the shear melting and recrystallization behavior of the solidlike phase during the stick-slip motion, interlayer slips within the film and wall slips at the wall-film interface are often observed. The ordered solidified film is well maintained during the slip. Through the time variations of the frictional force and potential energy change within the film, we find that both the friction dissipation during the slip and the potential energy decay after the slip in the solidified film take a fairly large portion of the total energy dissipation.     

Edge Effects on Growth of Ordered Stress Relief Patterns in Free Sustained Aluminum Films

An unusual form of ordered stress relief patterns is observed in a nearly free sustained aluminum film system deposited on liquid substrates by the therm~l evaporation method. The edge effects on the growth of the ordered patterns are systematically studied. It is found that the patterns initiate from the film edges, preexisting ordered patterns, or other imperfections of the film. When the patterns extend in the film regions, they decay gradually and finally disappear. If they develop along the boundaries, however, the sizes are almost unchanged over several millimeters. The stress relief patterns look like rectangular waves in appearance, which are proven to evolve from sinusoidal to triangular waves gradually. The morphological evolution can be well explained by the general theory of buckling of plates.     

Transition to spatiotemporal chaos in a two-dimensional hydrodynamic system

We study the transition to spatiotemporal chaos in a two-dimensional hydrodynamic experiment where liquid columns take place in the gravity induced instability of a liquid film. The film is formed below a plane grid which is used as a porous media and is continuously supplied with a controlled flow rate. This system can be either ordered (on a hexagonal structure) or disordered depending on the flow rate. We observe, for the first time in an initially structured state, a subcritical transition to spatiotemporal disorder which arises through spatiotemporal intermittency. Statistics of numbers, creations, and fusions of columns are investigated. We exhibit a critical behavior close to the directed percolation one.     

Electronic transport properties of the charge ordered manganite-based heterojunction

The charge ordered Bi_0.4Ca_0.4Sr_0.2MnO₃ (BCSMO) film has been grown on (011) SrTiO₃: Nb (STON) (0.05 wt%) substrate. The charge ordering (CO) transition is realized at ～336 K. The BCSMO/STON heterojunction shows excellent rectifying behavior. Through the capacitance measure of the junction, it is found that the built-in potential of the heterojunction is affected by the CO transition. A upward shift of the built-in potential of the junction appears around the CO transition temperature, which is ascribed to the change of the Fermi level in BCSMO film.     

Microscopic field in nanocrystalline ferromagnetic metal films and the opportunity for studying it by the μSR method

The relation of the microscopic (local) field in nanocrystalline ferromagnetic metal films to macroscopic characteristics (the external magnetic field, average magnetization, saturation magnetization) is determined for the case where a nanocrystalline ferromagnetic film consists of crystallographically ordered grains separated by disordered regions and where the dimensions of grains along a normal to the film plane are much smaller than those in the film plane. In the case of a strong external field (? ? M), the magnetization direction is determined in grains in the form of oblate ellipsoids for metals with uniaxial or cubic magnetocrystalline anisotropy. Expressions are derived for the spin polarization of an ensemble of rapidly diffusing and nondiffusing muons in nanocrystalline ferromagnetic films. It is shown that experiments with “slow” positive muons make it possible to measure all parameters of such structures and to obtain important information for studying phase transition physics.     

156Gd基态SU(3)→O(6)相变的一种微观理解

γ射线能量自旋曲线指认156Gd核基态具有SU(3)和O(6)两种对称性。 基于微观sdIBM-max方案和单粒子能量实验值, 用两组核子之间的对作用、 四极对作用、 四极 四极作用的等效强度参数, 都很好地再现了这两种能谱及其演化过程。 计算结果揭示出对基态相变的一种新理解: SU(3)的基准态是低激发 低有序态, 而O(6)基准态则是高激发 高有序的, 它们有临界区6+1—8+1态; 当核退耦到临界区时, 高有序基准态释放多余的有序结构能, 导致低有序基准态重组, 实现减速旋转驱动高有序核向着低有序核过渡的量子相变。最后用156Gd核的势能曲面作了直观说明。 The γ ray energy over spin curves identifies that there are the SU(3) and O(6) symmetries in the ground states of the 156Gd nucleus; by means of the microscopic sdIBM max approach and signal particle experimental energies the spectra of those two symmetries and their transient process are successfully reproduced through two parameters of nucleon nucleon effective interaction with pairing plus quadrupole pairing plus quadrupole quadrupole forces. The calculated results reveal a new way to recognize ground states quantum phase transition, in which the basic state of the SU(3) symmetry is a low lying and low ordered state, while one of the O(6) are a high lying and high ordered state, their critical region is between 6+1—8+1 states, the high ordered basic state releases spare ordered structure energy, reducing rotation speed, thus causing the restructure of low ordered basic state and accomplishing the quantum phase transition from the high ordered phase into the low ordered phase, the shape phase transition takes place along the yrast line of nucleus when it de excited to the critical region. Because the structural phase transition takes place by no obvious charge of boson structure constants in the critical region it is a benignancy and calm transition with respect to its macroscopic behave. The potential energy surface of 156Gd nucleus has been illustrated to visualize.     

Simulation of flux lines with columnar pins: bose glass and entangled liquids

Using path integral Monte Carlo we simulate a 3D system of up to 1000 magnetic flux lines by mapping it onto interacting bosons in (2+1)D. With increasing temperatures we find first order melting from an ordered solid to an entangled liquid signaled by a finite entropy jump and sharp discontinuities of the defect density and the structure factor S(G). For a particular density of strong columnar pins the crystal is transformed into a Bose glass phase with patches of crystalline order disrupted by the trapped vortices at the pinning sites but with no overall positional or orientational order. This glassy phase melts into a defected entangled liquid through a continuous transition.     

Fourier Transform Infrared Transmission Spectral Study on the Thermal Stability of Multilayer Langmuir-Blodgett Film of Stearic Acid

Fourier transform infrared (FTIR) transmission spectra at elevated temperatures of the 21-layer LB film of stearic acid have been recorded to study the thermal-induced order-disorder transition of the film. The transition was found to take place around 65°C (T _c), which results in the introduction of gauche conformers into the ordered zigzag alkyl chains, and the transformation of the trans dimers of the carboxylic groups to the cis ones while both configurations coexist below T _c. It was found that the mobility and the orientational disorder of the alkyl chains begin to increase before their conformational disorder occurs., The temperature-dependent spectra of the bulk stearic acid were also measured for comparison. The cyclic thermal treatment of the LB film indicates that the structural changes caused by the order-disorder transition is largely irreversible, although the conformation of the alkyl chains and the dimeric configuration of the carboxylic groups return to the corresponding states at room temperature.     

Study of solid-state reactions and order-disorder transitions in Pd/α-Fe(001) thin films

The formation of the hard-magnetic ordered L1₀-FePd phase in thin bilayer Pd/α-Fe(001) films has been experimentally studied. Solid-state reactions initiated by thermal heating in bilayer Pd/α-Fe(001) films with a thickness of 50–60 nm (the atomic ratio Pd: Fe ≈ 50: 50) separated from the substrate have been studied using the in situ electron diffraction methods. It has been shown that the solid-state reaction between the palladium and iron layers in Pd/α-Fe(001) starts at 400°C with the formation of the disordered Fe-Pd phase. At 480°C, the ordered L1₀-FePd phase is formed. The order-disorder phase transition has been studied. It has been established that the transition of the ordered L1₀-FePd phase to the disordered FePd phase starts at 725°C. At 740°C, only the disordered FePd phase is present over the whole volume of the film. The observed temperature of the order-disorder phase transition is shifted from the equilibrium value by 35°C to higher temperatures. This effect is assumingly associated with the higher concentration of palladium atoms at the boundaries of the Fe-Pd crystal grains owing to the grain-boundary adsorption.     

Effect of nanopatches on electrical behavior of Ni/n-type Si Schottky diode

Topological surface measurement of thin metal film using a conducting probe atomic force microscope (C-AFM) shows that thin metal film deposited on Ni/n-Si Schottky diode (SD) consists of patches. These patches are sets of parallel connected and electrically cooperating nano-contacts of size between 50 and 100nm. Every individual patch acts as an individual diode with different I-V curve, barrier height (BH) and ideality factor (n). Between these diodes or patches, there are spot field distributions; the patches with different local work functions are in direct electric contact with surrounding patches. As a result, a potential difference between surfaces of patches, the so-called electrostatic spot field E_f, is formed. It is shown that in real metal-semiconductor (MS) contacts, patches with quite different configurations, various geometrical sizes and local work functions are randomly distributed on the surface of metal; hence direction and intensity of spot field are non-uniformly distributed along the surface of metal. There is a linear dependence between barrier height and ideality factor, which is the consequence of reduction of distance of the maximum of BH from the interface. This dependency is the sign of reduction of contribution of a peripheral current.     

Critical behavior of three-dimensional frustrated helimagnets

The critical properties of classical frustrated helimagnets with different numbers of chiral order parameters are studied in three dimensions. The model of an antiferromagnet on a simple cubic lattice is considered with additional competing exchange interactions between spins of the first and the third range orders. In this model, helicoidal ordered phases exist with one, two, and three independent chiral order parameters. In all cases, it was found that a transition from an ordered to a disordered phase is a single first-order transition in the absence of partially ordered phases.     

Robust and Flexible Colloidal Photonic Crystal Films with Bending Strain–Independent Structural Colors for Anticounterfeiting

Colloidal photonic crystals (PCs) possess iridescent and metallic structural color, making them an attractive candidate for anticounterfeiting. However, traditional colloidal PC-based anticounterfeiting materials usually have bending-induced color-switching characteristics or poor flexible stability, significantly affecting their color reproducibility and durability. Here, a novel robust colloidal PC film with bending strain–independent structural color and high flexible stability has been developed through the self-assembly of SiO₂ particles into the poly(ethylene glycol) diacrylate (PEGDA) matrix. The unique microstructure of the colloidal PC film contains ordered and disordered arrays of SiO₂ nanoparticles embedded into the flexible PEGDA matrix, which is crucial to achieving bending strain–independent structural color. In fact, during the bending process, the colorless disordered arrays act as the buffer space, avoiding deformation of the colored ordered arrays and thus maintaining its original structural color. Remarkably, the film retains its structural and optical integrity after 10 000 times bending, supporting its high flexible stability and robustness. In addition, the film shows high transparency so that it can easily achieve an invisible and visible state transition under switch of weak and strong light. The film is potentially useful for applications in anticounterfeiting and encryption.     

Growth of nanorods and mesoscale stars prior to an orientation transition in thin Bi films on graphite

We report on the growth of unusual star shaped Bi islands and ordered arrays of nanorods on highly ordered pyrolitic graphite (HOPG) substrates. The rods and stars grow with {0 1 2}_Bi||{0 0 1}_HOPG and are preferentially aligned with the high symmetry directions of the substrate. As more Bi is deposited, the film undergoes a transition to the {0 0 1} orientation. These features are a result of a complex interplay between kinetics, thermodynamics, and the crystallography of the substrate and island material.     

Theory of radiation-induced self-organization of defect structures

During high-dose electron irradiation of thin Ni foils at 520 K, groups of about 10 Stacking-Fault Tetrahedra (SFT) are formed, which are referred to as patches. Within the patches the SFT occupy the sites of a square lattice whose sides are parallel to the two 100 directions of the crystalline host lattice in the foil plane. A theory of this planar square lattice of SFT is the subject matter of the preceding paper (Part I). The patches themselves are arranged in a planar face-centred cubic lattice that also shares its orientation with the host lattice. In the present paper (Part II) a mesoscopic theory is presented that accounts for this ordering of SFT-lattice patches in terms of an instability of disordered patch arrangements that results from a point-defect-mediated dynamic patch-patch interaction. This interaction arises from the competition of SFT-lattice patches for static crowdions migrating one-dimensionally along close-packed host lattice directions and for three-dimensionally diffusing vacancies and dumbbell interstitials. The so far exclusive occurrence of ordered SFT-lattice patches in Ni is related to the low packing density of this material, which leads to a high stability of the static crowdions and thus to a long range of the dynamic interaction between SFT-lattice patches.     

Ordered porous TiO2 films obtained by freezing and the application in dye sensitized solar cells

TiO₂ films with ordered porous structure were prepared by freezing. By simply freezing wet TiO₂ film on a cold copper plate, ice crystals could grow from bottom of film. Removing such ice crystals then led to ordered, micro-sized pores in the films. With assistance of scanning electron microscopy and N₂ adsorption–desorption isotherms, micro-structural properties of the films were studied. Coarsening behavior of ice crystals was analyzed based on evolvement of the micro-structure. It was found that, both larger film thickness and longer freezing time were beneficial for the formation of ordered porous structure, which was caused by enhanced ice crystals growth. The films were then used to fabricate photoanode of dye sensitized solar cells, of which the photo-to-electric power conversion efficiency was evaluated. It was observed that, solar cell made of ordered porous TiO₂ film came out with 13% larger photo-current density comparing to that made of conventional doctor blading method, which is due to the enhanced light scattering by the ordered porous structure.