Where physics meets chemistry: Thin film deposition from reactive plasmas

Functionalising surfaces using polymeric thin films is an industrially important field. One technique for achieving nanoscale, controlled surface functionalization is plasma deposition. Plasma deposition has advantages over other surface engineering processes, including that it is solvent free, substrate and geometry independent, and the surface properties of the film can be designed by judicious choice of precursor and plasma conditions. Despite the utility of this method, the mechanisms of plasma polymer growth are generally unknown, and are usually described by chemical (i.e., radical) pathways. In this review, we aim to show that plasma physics drives the chemistry of the plasma phase, and surface-plasma interactions. For example, we show that ionic species can react in the plasma to form larger ions, and also arrive at surfaces with energies greater than 1000 kJ?mol^–1 (>10 eV) and thus facilitate surface reactions that have not been taken into account previously. Thus, improving thin film deposition processes requires an understanding of both physical and chemical processes in plasma.     

One-dimensional confinement in crystallization of P(VDF-TrFE) thin films with transfer-printed metal electrode

The crystallization of thin polymer film depends on surface/interface properties, due to the fact that molecular chain motion is affected by the presence of the surface. In this work, we measured the ferroelectric properties, crystallinity, chain conformation and surface morphologies of one-dimensionally confined P(VDF-TrFE) thin films using transfer-printed Au film, annealed at elevated temperatures, from just below melting temperature up to 200 °C. Crystallization at low temperature, i.e., below melting temperature, the confinement effect has been found to be negligible. At high temperatures, however, confined crystallization has led to superior ferroelectric properties, compared to samples annealed without confinement. These observations have led to two- or three-layer model for those crystallized thin films with or without confinement, respectively. Further, the transfer-printing of metal as a confining surface has been found to be beneficial, compared to vacuum evaporation, due to deposition-induced damages on organic polymer. This confinement-induced retention of ferroelectricity in P(VDF-TrFE) thin films above its melting temperature can extend processing temperature in organic devices using the ferroelectric polymer, such as non-volatile organic memory devices.     

Influence of initiators on the growth of poly(ethyl 2-cyanoacrylate) nanofibers

The type of anionic initiator used to polymerize ethyl 2-cyanoacrylate was found to influence the morphology of the polymer formed via vapor phase polymerization. Depending upon the type of initiator, polymerization of ethyl 2-cyanoacrylate resulted in either the formation of neat polymer nanofibers (～200 nm in diameter) or thin films. Based on the classification of anions using Hard Soft Acid Base principles, we found that harder anions favored polymer film formation while softer ones favored polymer nanofibers. Infrared (IR) spectroscopy, scanning electron microscopy (SEM) and gel permeation chromatography (GPC) were used to characterize the structure, morphology and molecular weight of the synthesized polymers, respectively. Finally, a mechanism of formation of different polymer morphologies is proposed.     

Light-directed nanosynthesis: near-field optical approaches to integration of the top-down and bottom-up fabrication paradigms

The integration of top-down (lithographic) and bottom-up (synthetic chemical) methodologies remains a major goal in nanoscience. At larger length scales, light-directed chemical synthesis, first reported two decades ago, provides a model for this integration, by combining the spatial selectivity of photolithography with the synthetic utility of photochemistry. This review describes attempts to realise a similar integration at the nanoscale, by employing near-field optical probes to initiate selective chemical transformations in regions a few tens of nm in size. A combination of near-field exposure and an ultra-thin resist yields exceptional performance: in self-assembled monolayers, an ultimate resolution of 9 nm (ca. λ/30) has been achieved. A wide range of methodologies, based on monolayers of thiols, silanes and phosphonic acids, and thin films of nanoparticles and polymers, have been developed for use on metal and oxide surfaces, enabling the fabrication of metal nanowires, nanostructured polymers and nanopatterned oligonucleotides and proteins. Recently parallel lithography approaches have demonstrated the capacity to pattern macroscopic areas, and the ability to function under fluid, suggesting exciting possibilities for surface chemistry at the nanoscale.     

Formation of conductive polyaniline nanoarrays from block copolymer template via electroplating

Nanostructured thin films have drawn extensive attention because of their unique properties resulting from nanoscale features. One of the convenient ways to generate nanostructured thin films is to use pattern with nanoscale texture as a template for the reactions carrying out within the template. In this study, nanoporous thin film template was obtained from the self-assembly of degradable block copolymer, polystyrene-b-poly(l-lactide) (PS-PLLA) with PLLA cylinder nanostructure, at which the PLLA block can be hydrolyzed to form the nanopatterns with cylinder nanopores on conductive substrate (i.e., ITO substrate). The nanoporous PS thin film template was stabilized by modification of substrate using hydroxyl terminated PS so as to enhance the adhesion with substrate for following electroplating process. Combining a pulse electroplating method with the control of micro current, polyanilines can be successfully synthesized within the template to fabricate well-defined of conductive polymer nanoarrays.     

PS-b-P4VP的合成及其薄膜的微相分离形貌

通过原子转移自由基聚合（ATRP）方法制备了聚苯乙烯-b-聚（4-乙烯基吡啶）二嵌段共聚物（PS-b-P4VP）,使用核磁共振（1H NMR）和凝胶渗透色谱（GPC）对嵌段共聚物进行了表征。将PS-b-P4VP/三氯甲烷溶液旋涂成膜,使用原子力显微镜（AFM）观察热处理条件对薄膜微相分离形貌的影响。结果表明,PS-b-P4VP薄膜会发生微相分离,形成以PS链段为分散相、P4VP链段为连续相基体的纳米尺度微相分离形貌。热处理条件的改变使薄膜呈现不同程度的微相分离形貌结构,提高热处理温度以及延长热处理时间均有利于促进嵌段共聚物的微相分离,使微相分离程度加大。在150℃、24 h的热处理条件下,PS-b-P4VP薄膜形成了PS微相区以规则的柱状形态在薄膜表面突起的微相分离形貌,且分布均匀,界面清晰。     

Influence of process conditions on structural and electrochemical properties of lithium phosphorus oxynitride thin films

Lithium phosphorus oxynitride (LiPON) is the most representative solid electrolyte in thin film battery applications. In addition, it has been used as an interfacial protective layer to improve the stability of cathode and anode materials. In this article, we review the effect of the process conditions on the structural and electrochemical properties of LiPON thin films. A common method to form LiPON thin films is radiofrequency (RF) sputtering; much research has been conducted to optimize the corresponding process parameters, such as RF power density, working pressure in nitrogen atmosphere, substrate temperature, substrate bias power, post-annealing, and sputtering target. Many studies have characterized LiPON films obtained with various process parameters, but significant differences have been observed in the reported trends. The most representative difference involves the N_t/N_d ratio, which has been reported to be either directly or inversely proportional to the ionic conductivity. Recently, controversial results have been obtained on the N-based local structure of LiPON thin films. The structural argument relies on the idea that nitridation promotes cross-linking via the formation of doubly and triply coordinated N bridges between P atoms. In addition to further research to clarify these issues, it is necessary to introduce new methods for the interpretation of data based on it.     

Quantitative 3D measurement of the nanostructural features that dictate mesoscale performance properties of nanocomposites

Mesoscale performance properties of nanocomposites are dictated by the nanoscale structure developed in the composite during processing, combining nanoscale contributions over a mesoscale volume. In this artilce, for the first time, we present a procedure that deduces the fully 3D process‐induced nanostructural features of carbon nanofiber/polymer composites responsible for the mesoscale performance. In particular, we have developed a method for obtaining the nanofiber orientation in 3D Euclidean space from 2D projections provided by a transmission electron microscope. The 3D Euler angles we obtain are used to construct orientation tensors, the measure of nanostructure that has the most significant influence on mesoscale performance properties. Our measurement method is benchmarked by using numerically generated 3D samples to compare orientation tensor components known a priori with those generated using our procedure. A significant contribution of the procedure is its ability to produce quantitative 3D measurements of the evolution of nanostructure in space and time. The method is successfully applied to observe the effect of extensional rheology on nanofiber orientation. It is shown that orientation tensor data obtained from our experimental method accurately fits the predictions of the fiber orientation evolution equation proposed by Folgar and Tucker. POLYM. COMPOS., 31:1495–1503, 2010. © 2009 Society of Plastics Engineers     

Polyaniline nanofibers: a unique polymer nanostructure for versatile applications

Known for more than 150 years, polyaniline is the oldest and potentially one of the most useful conducting polymers because of its facile synthesis, environmental stability, and simple acid/base doping/dedoping chemistry. Because a nanoform of this polymer could offer new properties or enhanced performance, nanostructured polyaniline has attracted a great deal of interest during the past few years. This Account summarizes our recent research on the syntheses, processing, properties, and applications of polyaniline nanofibers. By monitoring the nucleation behavior of polyaniline, we demonstrate that high-quality nanofibers can be readily produced in bulk quantity using the conventional chemical oxidative polymerization of aniline. The polyaniline nanostructures formed using this simple method have led to a number of exciting discoveries. For example, we can readily prepare aqueous polyaniline colloids by purifying polyaniline nanofibers and controlling the pH. The colloids formed are self-stabilized via electrostatic repulsions without the need for any chemical modification or steric stabilizer, thus providing a simple and environmentally friendly way to process this polymer. An unusual nanoscale photothermal effect called "flash welding", which we discovered with polyaniline nanofibers, has led to the development of new techniques for making asymmetric polymer membranes and patterned nanofiber films and creating polymer-based nanocomposites. We also demonstrate the use of flash-welded polyaniline films for monolithic actuators. Taking advantage of the unique reduction/oxidation chemistry of polyaniline, we can decorate polyaniline nanofibers with metal nanoparticles through in situ reduction of selected metal salts. The resulting polyaniline/metal nanoparticle composites show promise for use in ultrafast nonvolatile memory devices and for chemical catalysis. In addition, the use of polyaniline nanofibers or their composites can significantly enhance the sensitivity, selectivity, and response time of polyaniline-based chemical sensors. By combining straightforward synthesis and composite formation with exceptional solution processability, we have developed a range of new useful functionalities. Further research on nanostructured conjugated polymers holds promise for even more exciting discoveries and intriguing applications.     

Morphological factors affecting the permeation resistance of nanocomposite blend films

The micro‐ and nanoscale morphologies of thin nanocomposite films comprising an immiscible nylon 6/polyethylene blend reinforced with modified sodium montmorillonite were found to substantially affect water vapor transmission rates (WVTRs). Maleic anhydride‐grafted high‐density polyethylene was incorporated as a compatibilizer between the nylon and polyethylene phases. Preferential incorporation of an organosilicate nanoclay in the nylon phase had a secondary effect on the overall blend morphology and thermal properties. Different degrees of phase continuity in the nanocomposite blend system were studied for their effect on WVTRs by varying the relative viscosities of the polymer phases. Transmission electron and atomic force microscopy were utilized to reveal the morphologies of the nanocomposite blends. POLYM. ENG. SCI., 54:1341–1349, 2014. © 2013 Society of Plastics Engineers     

Transitions of morphological patterns of crystallizing polycarbonate in thin films

This article reports the transitions of morphological patterns of polycarbonate crystals in thin films by solvent‐induced crystallization (SINC). As a substrate (silica glass) deposited with an amorphous and micron‐thick bisphenol A polycarbonate polymer film is partially dipped into a liquid acetone bath, acetone penetrated rapidly through the polymer film. The rate of acetone penetration is significantly higher than the predicted by Fickian diffusion or anomalous diffusion model, indicating that the capillary force through stress‐induced cracks may have played a major role in the upward transport of acetone through the polymer films. The morphologies of polycarbonate at different vertical positions on a substrate surface were analyzed by scanning electron microscopy and atomic force microscopy. It was observed that depending on the local acetone concentration the polymer morphologies showed quite diverse patterns ranging from stress‐induced cracks to fully developed three‐dimensional spherulites. The diverse morphologies developed during the thin film SINC may serve as a useful platform for further detailed mechanistic analysis of structures and crystallization kinetics. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Patterning High Explosives at the Nanoscale

For the first time, we have shown that spin coating and Dip pen nanolithography (DPN^TM) are simple methods of preparing energetic materials such as PETN and HMX on the nanoscale, requiring no heating of the energetic material. Nanoscale patterning has been demonstrated by the DPN method while continuous thin films were produced using the spin coating method. Results are presented for preparing continuous PETN thin films of nanometer thickness by the spin coating method and for controlling the architecture of arbitrary nanoscale patterns of PETN and HMX by the DPN method. These methods are simple for patterning energetic materials and can be extended beyond PETN and HMX, opening the door for fundamental studies at the nanoscale.     

Functionalization of polymer multilayer thin films for novel biomedical applications

The design of functional polymer multilayer thin films with nanometer scale control is of great interest for biomedical applications such as tissue engineering, targeted drug delivery, controlled release system, and regenerative medicine. Various functions and properties of polymer thin films can be easily programmed and realized by the layer-by-layer assembly strategy, which is a facile and versatile deposition method to prepare well-defined biomedical multilayer platforms due to its benign process to prepare films under mild conditions and the capability of incorporating bioactive materials at a desired location within the films. Particularly, the fine tuning of physicochemical and biological properties of multilayer thin films is significantly important for designing novel biomedical platforms capable of adjusting the cellular functions. In this review, we focus on the overall background of the layer-by-layer assembly as well as the tuning of multilayer film properties and the programming of biological functions into the polymer thin films with a view on the control of cellular functions. Furthermore, we highlighted the recent achievements toward the design of novel biomedical platforms based on functionalized polymer multilayer thin films.     

Field-assisted heating of Gd-doped ceria thin film

Flash sintering has recently been used to sinter various bulk ceramics under reduced sintering temperatures and sintering time by applying an electric field across the sample. In this work, we have demonstrated field-assisted heating of 10 mol% Gd-doped CeO₂ thin films deposited by pulsed laser deposition. Microstructure analysis revealed the elongated grains aligned in the out-of-plane direction which is perpendicular to the direction of electric field. The overall microstructure of the flash-heated thin film also contained a matrix of porous and clustered regions, which are distributed throughout the thin film from the anode to cathode electrode regions. The flash-heated thin film showed significantly different conductivity and optical permittivity compared to the as-grown thin films. This demonstration suggests a feasible approach for post-deposition synthesis of thin films using field-assisted heating toward novel morphologies and properties.     

Study of the time evolution of the surface morphology of thin asymmetric diblock copolymer films under solvent vapor

The time development of the surface morphology of asymmetric polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) thin films ‘annealing’ in methanol vapor, a selective solvent for minority P4VP block, was investigated by atomic force microscopy(AFM). For PS-b-P4VP with cylindrical structure in bulk, as annealing time progressed, the surface morphology underwent structural transitions from featureless topography to hybrid morphology of cylindrical and spherical pits, to cylinders, to nanoscale depressions, back to cylinders again. The different film thickness made the number of the transitions observed, at any given annealing time, different. The thicker the film is the more transitions at a given annealing time can be observed. If the film was not thick enough, depressions appeared. For PS-b-P4VP with spherical structure in bulk, it displayed nanoscale depressions with the annealing time increasing. A possible mechanism of the transition of morphologies during solvent annealing was proposed.     

Crystallization and morphology of ultrathin films of homopolymers and polymer blends

Ultrathin films of thicknesses below 100 nm are now considered in different areas of applications. Their behavior in term of kinetics of crystallization is very different from that of bulk samples due to the film confinement in two-dimensions, and their morphologies are unique. In this review, recent advances in the crystallization of ultrathin films of homopolymers and miscible polymer blends will be described, with an emphasis on morphologies and, in the case of blends, on mixtures made of two crystalline polymers.     

Structure of glow discharge polysilazane thin films

Thin polysilazane films have been prepared by glow discharge polymerization of hexamethylcyclotrisilazane in an electrode static system. An increase in pressure in the reaction system observed during polymerization indicated that the monomer underwent fragmentation in the glow discharge. The structures of thin polysilazane films prepared at various current densities have been determined by elementary analysis, infra-red spectroscopy and gas chromatography. It has been found that fragmentation of hexamethylcyclotrisilazane takes place mainly through the cleavage of SiC bonds and that methyl group content in the polymer film structure decreases with increasing current density. The mechanisms of reactions leading to polysilazane film formation have been discussed.     

Effect of poly(vinyl acetate) on structure and property of bismuth-doped strontium titanate thin films derived by sol–gel method

Bismuth-doped strontium titanate thin films with pure perovskite phase have been successfully deposited on Pt (1 1 1)/Ti/SiO₂/Si substrate by polymer-assisted sol–gel method. Poly(vinyl acetate) (PVAc) in precursor solution promoted the formation of perovskite phase during the heat treatment. SEM results revealed an increasing thickness from 40 to 80 nm every single layer and a porous structure with the addition of PVAc. The addition of polymer made the dielectric constant decrease from 140 to 40 and the tunability slightly increase compared with films without polymer in precursor.     

静电雾化沉积制备PbTiO3薄膜的研究

采用静电雾化沉积技术制备了PbTiO3薄膜,探索了沉积温度和沉积时间对所制备薄膜的结构和形貌的影响.通过调节制备工艺,制备了多孔和致密的PbTiO3薄膜.测试了所制备钛酸铅薄膜的介电频率特性,在100kHz的介电常数和介电损耗分别为222和0.0247.     

Role of solute and solvent on the deposition of ZnO thin films

ZnO thin films have been deposited on SnO₂:F coated transparent conducting oxide (TCO) glass substrates, using a simple electrochemical (galvanic) technique, from different electrolytic solutions. A detailed investigation on the effect of different solute and solvent on the deposition process has been made. We have established that galvanically obtained ZnO thin films can be deposited with various morphologies depending on the nature of the solute and solvent used. ZnO formation can happen either directly or through an intermediate mixed phase following different reaction paths. Structural, morphological, compositional and optical characterizations of the films developed under different conditions were carried out to study such effects. The films were also tested for their potential use as methane sensor.