Monte Carlo simulation on layered polymeric films

Thin films of polymer blends composed of alternating copolymer, diblock copolymer and/or homopolymer are studied using Monte Carlo simulation. A multilayer morphology is observed in the film, that is, the blended polymers assemble into individual domains arranged from interior to the surfaces of the film. The coexisting components residing throughout the neighboring domains in the film make no distinguishable interface between any neighboring domains. By this means, it forms a vertical composition gradient in the polymeric film. Being different from layer-by-layer deposition of polyelectrolyte or hydrogen bonding approach etc., the layered structure in this study is formed by polymer blending in one step. Alternating copolymers are found to be essential components to form vertical composition gradient （layered structure） in thin films.     

Equilibrium behavior of confined triblock copolymer films

Using a two-dimensional self-consistent field calculation, we determine the equilibrium morphology of thin films of ABC triblock copolymers confined between hard, smooth plates. The B segment is chosen to be the central block and all the blocks are incompatible. The chains microphase-segregate into a lamellar phase, with the stripes either perpendicular or parallel to the walls. When all the monomer-surface interactions are identical, the perpendicular orientation has the lowest free energy. When a repulsion is introduced between the surface and the A and C monomers. The surface interactions further stabilize the perpendicular orientation. At strong surface interactions, the morphology of the perpendicular structure is controlled by the overall thickness of the molten layer. In comparing diblocks to triblocks as candidates for forming laterally patterned films, our work indicates that triblocks possess distinct advantages over diblocks. First, no special effort needs to be taken to establish neutral surfaces. Second, the film does not have to be confined between two substrates. Thus, triblocks can be used to fabricate patterned polymer surfaces, which can be used for novel optical or electronic applications.     

不对称两嵌段共聚物熔体在平板狭缝中微相分离的Monte Carlo模拟

采用改进的键长涨落空穴扩散算法对平板狭缝中不对称两嵌共聚高分子熔体的微相分离进行了Monte Carlo模拟。模拟结果表明：在吸引壁条件下，靠近壁面处将形成平等于壁面的层状相；在弱吸引壁条件下，靠近壁面处将形成垂直于壁面的层状相；不对称共聚物在远离壁面处有丰富的微区形态。从结构因子上分析可知，弱吸引壁条件下不对称共聚物的结构比强吸引壁条件下更接近对称共聚物。     

Spontaneous pattern formation by dip coating of colloidal suspensions on homogeneous surfaces

We study the slow withdrawal of a partially wet vertical plate at velocity U from a suspension of well-wet particles. Periodic horizontal striped assemblies form spontaneously at the three-phase contact line on energetically uniform surfaces. Stripe width and spacing depend on the withdrawal velocity U relative to a transition velocity Ut. Thick stripes separated by large spaces form for UUt, thin stripes separated by small spaces form. The stripe spacing is reduced by an order of magnitude and varies weakly with U until a maximum velocity is reached at which the stripes fail to form. A partially wet surface can entrain a meniscus. For UUt, we infer that a film of thickness h is entrained above the meniscus. When h is smaller than the particle diameter D, particles aggregate where the entrained film thickens to match up to the wetting meniscus. When an entrained particle becomes exposed to air by evaporation, it becomes the new pinning site from which the next film is entrained. The film thickness h increases with U; at some velocity, h becomes comparable to D. Particles flow into the film and deposit there in a disordered manner. A diagram summarizing particle deposition is developed as a function of D, U, and h.     

Pattern formation and dewetting in thin films of liquids showing complete macroscale wetting: from "pancakes"to "swiss cheese"

Based on the complete 3D numerical solutions of the nonlinear thin film equation, we address the problems of surface instability, dynamics, morphological diversity and evolution in unstable thin films of the liquids that display complete macroscale wetting. The twin constraints of complete macroscale wettability and nanoscale instability produce a variety of microscopic morphological phases approximating sharp crystal surfaces with flat tops resembling a mesa or a micro "pancake" or a slice of Swiss cheese. While the maximum thickness of flat regions is found to be independent of the initial film thickness, the precise lateral morphology of microdomains formed depends on the film thickness. As the film thickness is increased, the initial pathway of evolution changes from the formation of small spherical droplets, to long mesas (parapets) and islands, to circular holes, all of which eventually resolve by ripening into a collection of round pancakes at equilibrium. However, beyond a certain transition thickness, a novel metastable honeycombed morphology, resembling a membrane or a slice of Swiss cheese, is uncovered, which is produced by an abrupt "freezing" of the evolution during hole growth. In contrast, the spinodal dewetting in thin films of partially wettable systems always engenders spherical droplets at equilibrium. The equilibrium dewetted area from simulations, as well as from simple mass balance, is shown to decline linearly with the initial film thickness.     

Grazing-incidence transmission small angle X-ray scattering from thin films of block copolymers

Thin films of lamellar and cylindrical block copolymers are popular systems for low-cost nanolithography. To be useful as nanoscale templates, the lamellae or cylinders must be oriented perpendicular to the substrate. Domain orientations are usually characterized by microscopy measurements of the film surface, but these techniques cannot detect tilted, bent, or tortuous domains in the film interior. We report a simple method to quantify out-of-plane disorder in thin films of block copolymers based on a variant of grazing-incidence small angle X-ray scattering (GI-SAXS). A typical GI-SAXS experiment illuminates the center of a substrate-supported film at a grazing angle of incidence (near the film/substrate critical angle), and the strong reflected signal is interpreted with the distorted-wave Born approximation. In a new approach, the beam footprint is moved to the far edge of the sample, allowing the acquisition of a transmission pattern. The grazing-incidence transmission data are interpreted with the simple Born approximation, and out-of-plane defects are quantified through analysis of crystal truncation rods and partial Debye-Scherrer rings. Significantly, this study demonstrates that grazing-incidence transmission small angle X-ray scattering can detect and quantify the buried defect structure in thin films of block copolymers. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Pattern formation in PMMA film induced by electric field

Micro‐sized patterns were created on thin poly(methyl methacrylate) (PMMA) films by the effect of external field, perpendicular to the film surface. The PMMA film, prepared by spin‐coating onto Si wafer, was heated to the fluid temperature (275 °C) and a linear pattern was created by the effect of electric field produced by a strip electrode. In another experiment, a round pattern was created as a result of local laser heating of the PMMA film under homogenous electrical field. The created patterns were analyzed by optical microscopy and profile meter. The dependence of the form and size of the created patterns on the intensity of the electric field, exposure time, and initial film thickness was examined. Wave guiding property of a linear pattern, produced by the above technique, was examined in a simple experiment. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1131–1135, 2009     

聚丙烯表面的计算机模拟

用计算机模拟的方法详细研究了聚丙烯薄膜表面分子级别的结构 .采用无定形本体聚丙烯产生初始的随机父链 ,将一条随机父链在二维边界条件下进行塌陷 ,研究薄膜在真空中的构型 .用 10 0个重复单元的父链生成厚度为 3 5nm的薄膜 .发现薄膜内部密度等于聚丙烯的本体密度 ,而离自由表面 0 8nm处薄膜的密度开始跌落 .主链键在内部随机取向 ,在自由表面附近则明显沿薄膜表面平面取向 ,键开始有序取向的程度大致与质量密度相对于本体密度的减小一致 .与聚丙烯本体相比 ,薄膜表面中CH2 CH 的反式结构和旁式结构是增加的 ,这是因为分子链能更好的沿薄膜平面舒展 .同时通过聚丙烯无定形本体 (3D周期性 )和薄膜 (2D周期性 )中的链的能量的差异计算了薄膜内部能量对表面能量的贡献 .     

Polarization inscription in ferroelectric (111) PZT and (100) SBT films

Ferroelectric thin films form an equilibrium domain structure compatible with their respective crystallographic symmetry. In tetragonal (111) PZT, 90° domains prevail; in (pseudo-tetragonal) (100) SBT both 90° and 180° domains are present. The size of 90° domains has been measured for e.g., PZT as slabs of 15 nm width. Domain size is a result of stress minimization in the film during the paraelectric (PE) → ferroelectric (FE) transition. A precise and regular domain pattern for (111) PZT and (100) SBT films has been investigated in detail by TMSFM. Single domains can be addressed mechanically with the tip of an AFM. Such single domain switching corresponds to a data storage density of 200 Gbit/inch². Applications of ferroelectric and high- paraelectric materials for e.g., non-volatile data storage replacing DRAM devices or as sensors in infrared cameras are increasingly becoming popular.     

Enhancement of thin film tin oxide negative electrodes for lithium batteries

Thin films of pure SnO₂, of the Sn/Li₂O layered structure, and of Sn/Li₂O were fabricated by sputtering method, while a `lithium-reacted tin oxide thin film' was assembled by the evaporation of lithium metal onto a SnO₂ thin film. Film structure and charge/discharge characteristics were compared. The lithium-reacted tin oxide thin film, the Sn/Li₂O layered structure, and the Sn/Li₂O co-sputtered thin films did not show any irreversible side reactions of forming Li₂O and metallic Sn near 0.8 V vs Li/Li⁺. The initial charge retention of the Sn/Li₂O layered structure and Sn/Li₂O co-sputtered thin films was about 50% and a similar value was found for the lithium-reacted tin oxide thin film (more than 60%). Sn/Li₂O layered structure and Sn/Li₂O co-sputtered thin films showed better cycling behavior over 500 cycles than the pure SnO₂ and lithium-reacted tin oxide thin film in the cut-off range from 1.2 to 0 V vs Li/Li⁺.     

Fabrication of metal structures with nanometer-scale lateral dimensions by sectioning using a microtome

This Communication describes the fabrication of planar structures comprising metallic features with nanometer-scale lateral dimensions in polymer prepared by sectioning a thin metallic film, embedded in a polymer matrix, in a plane perpendicular to the metallic film. This procedure converts a structure that is thin along the z-axis into a structure that is thin along the x-axis. The embedded thin metal film is still conductive and can be used as a nanoelectrode. The structure and composition of the exposed nanoedge can be easily tuned by changing the structure of the surface supporting the metal film, and the composition and the thickness of that film.     

Two‐Dimensional Boronate Ester Covalent Organic Framework Thin Films with Large Single Crystalline Domains for a Neuromorphic Memory Device

Despite the recent progress in the synthesis of crystalline boronate ester covalent organic frameworks (BECOFs) in powder and thin‐film through solvothermal method and on‐solid‐surface synthesis, respectively, their applications in electronics, remain less explored due to the challenges in thin‐film processability and device integration associated with the control of film thickness, layer orientation, stability and crystallinity. Moreover, although the crystalline domain sizes of the powder samples can reach micrometer scale (up to ≈1.5 μm), the reported thin‐film samples have so far rather small crystalline domains up to 100 nm. Here we demonstrate a general and efficient synthesis of crystalline two‐dimensional (2D) BECOF films composed of porphyrin macrocycles and phenyl or naphthyl linkers (named as 2D BECOF‐PP or 2D BECOF‐PN ) by employing a surfactant‐monolayer‐assisted interfacial synthesis (SMAIS) on the water surface. The achieved 2D BECOF‐PP is featured as free‐standing thin film with large single‐crystalline domains up to ≈60 μm² and tunable thickness from 6 to 16 nm. A hybrid memory device composed of 2D BECOF‐PP film on silicon nanowire‐based field‐effect transistor is demonstrated as a bio‐inspired system to mimic neuronal synapses, displaying a learning–erasing–forgetting memory process.     

Polymer Crystallization Influenced by Initial Orientation of Cylindrical Diblock Copolymers in Thin Films

The effect of the initial states (disordered perpendicular cylinder structure vs. parallel cylinder structure) on the crystallization of polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO) thin films during cyclohexane annealing was investigated. The cylindrical domains perpendicular or parallel to the surface were obtained by controlling the film thickness. During solvent annealing, for the film with the perpendicular cylinders, the ordering degree of cylinders was increased. The enthalpic increase is large enough for the forming of square‐shaped crystals, and subsequently the square‐shaped single crystals surrounded by the ordered hexagonally packed perpendicular cylinders evolved to the dendrite ones. For the film with the parallel cylinders, the parallel cylinders were translated to the perpendicular ones. The increased enthalpy was not large enough for the formation of square‐shaped single crystals. Instead, the dendrite‐like crystals started at the edge of terraces.

     

电子背散射衍射法研究马氏珠母贝珍珠层中文石择优取向

贝壳珍珠层中的文石相对于在自然环境中生长的文石来说具有更优异的力学性能,这种力学性能取决于其独特的晶体排布方式。通过电子背散射衍射（EBSD）技术获得了马氏珠母贝中不同文石的结晶学取向信息,结果表明珍珠层中文石晶体的c轴均垂直于珍珠层层面,而a、b轴在平行珍珠层方向上具有两级取向畴结构：在初级畴结构内,相邻畴绕c轴偏转,导致不同畴之间a轴或b轴的取向差约64°。在次级畴结构内,文石板片围绕c轴偏转,导致不同畴之间a轴或b轴取向差在10°或20°左右。这种畴结构为我们认识珍珠层中文石的生长机理提供了有益线索。     

电子背散射衍射法研究马氏珠母贝珍珠层中文石择优取向

贝壳珍珠层中的文石相对于在自然环境中生长的文石来说具有更优异的力学性能,这种力学性能取决于其独特的晶体排布方式。通过电子背散射衍射(EBSD)技术获得了马氏珠母贝中不同文石的结晶学取向信息,结果表明珍珠层中文石晶体的c轴均垂直于珍珠层层面,而a、b轴在平行珍珠层方向上具有两级取向畴结构:在初级畴结构内,相邻畴绕c轴偏转,导致不同畴之间a轴或b轴的取向差约64°。在次级畴结构内,文石板片围绕c轴偏转,导致不同畴之间a轴或b轴取向差在10°或20°左右。这种畴结构为我们认识珍珠层中文石的生长机理提供了有益线索。     

The equilibrium fraction of bridging chains and the swelling behavior of ABA triblock copolymer mesophases

The physical cross-linked network due to B blocks bridging different A domains of a microphase separated melt formed by an ABA copolymer in the strong-segregation limit is examined. The system is considered to consist of swollen elements of the same size, each containing an A domain and a B layer anchored to the A domain as loops or bridges. A lattice model and a generator-matrix method are employed to calculate the equilibrium fraction of the bridging B chains of the ABA mesophase and the equilibrium swelling concentration of the B layer in a selective solvent for the planar, cylindrical and spherical A domain structures. The effects of chain length and of two-dimensional surface density of the AB joints are discussed. The equilibrium fraction of the bridging chains as a function of chain stiffness and the equilibrium swelling concentration as a function of the fraction of bridging chains and of the interaction parameter are calculated. In addition, the segment density distributions of both loop and bridging chains for both the pure ABA and the swollen ABA mesophases are provided.     

Atomic force microscopy measurements of topography and friction on dotriacontane films adsorbed on a SiO2 surface

We report comprehensive atomic force microscopy (AFM) measurements at room temperature of the nanoscale topography and lateral friction on the surface of thin solid films of an intermediate-length normal alkane, dotriacontane (n-C32H66), adsorbed onto a SiO2 surface. Our topographic and frictional images, recorded simultaneously in the contact mode, reveal a multilayer structure in which one to two layers of molecules adsorb adjacent to the SiO2 surface oriented with their long axis parallel to the interface followed by partial layers of molecules oriented perpendicular to the surface. The thicknesses of the parallel and perpendicular layers that we measured with the AFM agree with those inferred from previous x-ray specular reflectivity measurements on similarly prepared samples. We also observe bulk dotriacontane particles and, in contrast with our previous measurements, are able to determine their location. Above a minimum size, the bulk particles are separated from islands of perpendicularly oriented molecules by regions of exposed parallel layers that most likely extend underneath the particles. We find that the lateral friction is sensitive to the molecular orientation in the underlying crystalline film and can be used effectively with topographic measurements to resolve uncertainties in the film structure. We measure the same lateral friction on top of the bulk particles as on the perpendicular layers, a value that is about 2.5 times smaller than on a parallel layer. Scans on top of parallel layers indicate a constant height but reveal domains having different sublevels of friction. We explain this by the domains having different azimuthal orientations of the molecules.     

Nanoscale phenomena in synthetic functional oxide heterostructures.

This paper reviews nanoscale phenomena such as polarization relaxation dynamics and piezoelectric characterization in model ferroelectric thin films and nanostructures using voltage-modulated scanning force microscopy. Using this technique we show the three-dimensional reconstruction of the polarization vector in lead zirconate titanate (PZT) thin films. Second, the time-dependent relaxation of remanent polarization in epitaxial PZT ferroelectric thin films, containing a uniform two-dimensional grid of 90 degrees domains (c-axis in the plane of the film), has been investigated extensively. The 90 degrees domain walls preferentially nucleate the 180 degrees reverse domains during relaxation. Relaxation occurs through the nucleation and growth of reverse 180 degrees domains, which subsequently coalesce and consume the entire region as a function of relaxation time. In addition we also present results on investigation of the relaxation phenomenon on a very local scale, where pinning and bowing of domain walls has been observed. We also show how this technique is used for obtaining quantitative information on piezoelectric constants and by engineering special structures, and how we realize ultrahigh values of piezoconstants. Last, we also show direct hysteresis measurements on nanoscale capacitors, where there is no observable loss of polarization in capacitors as small as 0.16 microm2 in area.     

A microporous structure of a thin film made of an ion-exchangeable layered compound

A thin film made of an ion-exchangeable layered compound, K₄Nb₆O₁₇, was prepared by a novel method. Fine particles of K₄Nb₆O₁₇ obtained by wet-grinding of the powder were coated on a substrate and calcined. Recrystallization of the fine particles at 1073 K was confirmed by XRD and SEM, and very flat and large crystals with the b-axis perpendicular to the substrate surface were obtained. The obtained thin film had a layered structure and an ion-exchange property similar to that of K₄Nb₆O₁₇ powder. The adsorption of CO was investigated for the thin film calcined at 1073 K by IR spectroscopy. The initially IR-inactive H⁺ species were suggested to be transformed into OH groups as a result of CO adsorption at the interlayer space.     

A set of homologous hetarylenediyne macrocycles by oxidative acetylene-acetylene coupling

The synthesis of a set of bipyridine-containing macrocycles by oxidative acetylene-acetylene dimerization is described. The cycles are separated by preparative GPC, and the smallest homologue is analyzed by single-crystal X-ray diffraction, which shows a layered structure with channels that are partially filled with parts of the flexible chains of adjacent macrocycles. The cyclic trimer has a D3h symmetry and is a possible candidate for the formation of metal organic supramolecular assemblies on surfaces.