Sol–gel derived nanostructured nickel oxide films: Effect of solvent on crystallographic orientations

Nickel oxide films were deposited onto glass substrates by sol–gel dip coating method using solvents of different polarities without any catalysts, templates or surfactants. Methanol, 1,4-butanediol, ethanol, and 2-propanol were used as solvents. The structural, optical and electrical properties of NiO films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible spectroscopy and Hall effect measurements, respectively. Nickel oxide thin films with cubic phase crystal structure of various preferred orientations were obtained in the different solvents. The XRD results showed that films deposited from solution using higher polar solvents develop a (1 1 1) preferred orientation, while the (2 0 0)-orientated films were obtained using lower polar solvents. The average particle size increases with viscosity of solvents. Surface morphology of the nickel oxide film consisted of nanoparticles with uniform coverage of the substrate surface. The solvent of higher viscosity induced larger particle size. Band gap narrowing from 4.42 to 3.87 eV was observed using different solvents. The lower resistivity and Hall coefficient was obtained for prepared NiO films using higher polar solvents. The relationships between solvent physicochemical properties, preferred orientation, structural, optical and electrical properties of NiO films were investigated.     

磁控溅射制备择优取向氮化铝薄膜

AlN薄膜;磁控反应溅射;磁控溅射制备择优取向氮化铝薄膜;晶面取向;X射线衍射     

Evaporated thin films of insulating poly-(tetrabromo-p-phenylenediselenide)

It has been shown that thin insulating film at the interface transparent conductive oxide/organic electroluminescent film could improve the performance of organic electroluminescent diodes (OLED). Such insulating film can be inorganic or organic. Poly-(tetrabromo-p-phenylenediselenide) (PBrPDSe) has been proved to be an efficient insulating film in OLED. The properties of these evaporated PBrPDSe thin films have been systematically studied by IR absorption, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, electron spin resonance and optical transmission measurements. It is shown that, when the deposition temperature is kept below the decomposition temperature of the polymer, tetrabromo-p-phenylenediselenide molecule is preserved during the deposition process. However the polymer, which is insoluble in powder form, becomes soluble after deposition. It can be concluded that films are mainly composed of oligomers of tetrabromo-p-phenylenediselenide.The electrical properties of SnO₂/PBrPDSe/Al thin films structures have been studied. The current-voltage characteristics exhibit a rectifying behaviour with a forward direction corresponding to a positive bias of the transparent conductive oxide film, the SnO₂.     

Layer-by-layer growth of polar MgO(111) ultrathin films

By alternate deposition of Mg and exposure of O2, layer-by-layer growth, polar MgO(111) ultrathin films with Mg-terminated or O-terminated surfaces have been successfully fabricated on Mo(110) substrate. The surface geometric structure and electronic structures of the polar MgO(111) films were investigated using surface analysis techniques including low-energy electron diffraction and photoelectron emission and electron energy loss spectroscopies. The results indicate that the O-terminated surface is of an insulating character, while for Mg-terminated surface, a prominent new surface state at 2-3 eV and appreciable density of states near Fermi level have been observed. The polar oxide films provide ideal model surfaces for further investigation of support-particle system.     

Thiocyanate-capped nanocrystal colloids: vibrational reporter of surface chemistry and solution-based route to enhanced coupling in nanocrystal solids

Ammonium thiocyanate (NH(4)SCN) is introduced to exchange the long, insulating ligands used in colloidal nanocrystal (NC) synthesis. The short, air-stable, environmentally benign thiocyanate ligand electrostatically stabilizes a variety of semiconductor and metallic NCs in polar solvents, allowing solution-based deposition of NCs into thin-film NC solids. NH(4)SCN is also effective in replacing ligands on NCs after their assembly into the solid state. The spectroscopic properties of this ligand provide unprecedented insight into the chemical and electronic nature of the surface of the NCs. Spectra indicate that the thiocyanate binds to metal sites on the NC surface and is sensitive to atom type and NC surface charge. The short, thiocyanate ligand gives rise to significantly enhanced electronic coupling between NCs as evidenced by large bathochromic shifts in the absorption spectra of CdSe and CdTe NC thin films and by conductivities as high as (2 ± 0.7) × 10(3) Ω(-1) cm(-1) for Au NC thin films deposited from solution. NH(4)SCN treatment of PbTe NC films increases the conductivity by 10(13), allowing the first Hall measurements of nonsintered NC solids, with Hall effect mobilities of 2.8 ± 0.7 cm(2)/(V·s). Thiocyanate-capped CdSe NC thin films form photodetectors exhibiting sensitive photoconductivity of 10(-5) Ω(-1) cm(-1) under 30 mW/cm(2) of 488 nm illumination with I(photo)/I(dark) > 10(3) and form n-channel thin-film transistors with electron mobilities of 1.5 ± 0.7 cm(2)/(V·s), a current modulation of >10(6), and a subthreshold swing of 0.73 V/decade.     

Evolution of surface topography and optical band gap of ZnO film deposited on NiO/Si(100)

Evolution of surface features and optical band gap of ZnO thin films deposited on different NiO/Si(100) are reported. In order to create different initial microstructure, we first deposited NiO film on Si(100) at 3 different temperatures (400°C, 650°C, and 700°C) by pulsed laser deposition. These NiO/Si(100) films are used as substrate for the deposition of ZnO films. Combining the results obtained from grazing incidence X‐ray diffraction, atomic force microscope, and UV‐Visible characterization, our study indicated that the microstructure of the substrate takes the important role in dictating properties of the film. Our study also indicated that one needs to choose appropriate synthesis condition to achieve good quality ZnO films.     

Optimization of large area pulsed laser deposition of YBaCuO thin films by SNMS depth profiling and rutherford backscattering

The scaling up of established deposition techniques like pulsed laser deposition (PLD) to larger substrate diameter is a main condition for the technological application of high-T_c superconducting (HTSC) thin films. SNMS depth profiling and RBS have been used to control the homogeneity of film thickness and stoichiometry of Au/YBaCuO/CeO₂ thin film systems deposited on 3-inch sapphire wafers by PLD. A systematic dependence has been found for the relative SNMS sensitivity factors (RSF) on the structural state of YBaCuO. Therefore, a calculation of the composition of the epitaxial YBaCuO thin films is not possible using RSF determined from polycrystalline YBaCuO target material. The interdiffusion of thin films and substrate has been investigated in dependence on the deposition temperature by SNMS depth profiling. The obtained homogeneity of film thickness and stoichiometry over the entire 3-inch diameter proofs the suitability of PLD for in-situ deposition of 3-inch wafers by YBaCuO thin film systems for microwave applications.     

Electrochemical Deposition of Gold Metal Particles into 3‐Dimensional Polypyrrole Film Deposited on a Highly Oriented Pyrolytic Graphite

Electrochemical techniques and lateral friction microscopy (LFM) are exploited to characterize the deposition of gold metal particles onto the 3‐dimensional (3‐D) polypyrrole (PPy) film deposited on 2‐dimensional (2‐D) highly oriented pyrolytic graphite (HOPG) substrate surface in an aqueous solution involving 0.01 M pyrrole and 0.1 M LiClO₄? 3H₂O. Cyclic voltammetry is utilized to find the gold deposition potential onto the PPy film from 0.001 M KAu(CN)₂/KOH solution. The gold deposition potential is found to be in the range of ?1.2 V to ?1.4 V. Chronoamperometry is used to find out the nucleation and growth mechanism of gold metal particles onto PPy film. When the PPy film is thin, the mechanism follows the 3‐D instantaneous and moved towards 3‐D progressive as the film thickness increases. Considering the high resistance of thick PPy film and insulating and compact nature of the film at more cathodic potentials, it is suggested that the gold nuclei are formed first on the HOPG substrate surface, move to the PPy film surface and then distributed inside the PPy matrix. Since the friction of gold and the PPy film is different, the LFM is found to be an effective tool to see the distribution of gold particles in the domain boundaries of the PPy film.     

Instabilities during the formation of electroactive polymer thin films

The solvent-induced film structure of poly(n-vinyl carbazole) (PVK) thin films on indium tin oxide (ITO)-coated glass was examined. PVK thin films were prepared via spin-coating using five different solvents. We investigated the relationship between the solvent characteristics and film properties, including surface roughness and structure, film thickness, and density. The spin-coated polymer thin films are not in thermodynamic equilibrium; rather, the film properties are affected by the dynamics of the spin-coating process. We found that water present in tetrahydrofuran (THF) induces dewetting of PVK films during the spin-coating process. Solvents with a high evaporation rate lead to high surface roughness due to Marangoni convection. The results show that the surface roughness and structure of the films are dominated by the dynamics of the film formation process, rather than thermodynamic interactions between the polymer and solvents.     

分散溶剂对PEMFC催化层中超薄Nafion离聚物质子传导的影响

质子交换膜燃料电池(PEMFC)商业化应用的瓶颈仍然是贵金属催化剂导致的成本问题。然而,目前对于催化层中纳米尺度全氟磺酸离聚物(以Nafion为代表)薄膜中质子传导的问题研究不足,无法完善三相界面的成型规律,进而指导催化层设计。在催化层浆料制备过程中,分散溶剂对Nafion的分散形态有直接影响,可能对催化层成型后附着在催化剂颗粒表面Nafion薄膜的微观结构有潜在影响,进而影响Nafion薄膜的质子传导能力。因此,在本文中利用分子自组装技术模拟催化层离聚物薄膜的聚集过程,于模型基底上制备厚度精确可控的纳米尺度Nafion薄膜,并通过微观测试表征技术探索并建立纳米尺度Nafion离聚物的微观结构模型,阐明分散溶剂对Nafion薄膜微观结构及质子传导的影响。研究发现Nafion薄膜在纳米尺度下的质子电导率比体相膜的质子电导率低一个数量级,使用介电常数较小的醇类溶剂可以使Nafion薄膜形成更有利于质子传导的微观结构,使Nafion薄膜的质子电导率得到提高。相关研究结果为优化PEMFC催化层结构,改善PEMFC催化层中质子传导问题提供给了依据。     

一种含有偶氮磺酸基与吡啶基的高分子氢键自组装及自组装超薄膜

静电自组装是指将带相反电荷的聚电解质，于水溶液中交替沉积在片基上，制备多层超薄膜的技术．由于它在水溶液进行，技术简单，无需专用设备，再加上静电力比范德华力强，因此静电自组装膜比传统的LB(Langmuir—Blodget)膜稳定，在近年来得到很大发展．现在自组装成膜驱动力已从最初的静电力扩展到氢键、电荷转移相互作用、疏水相互作用等；用于组装的组分也从聚电解质扩展到多官能团小分子、胶体粒子、无机纳米     

ITO基底上ZnO薄膜的制备以及刻蚀图形的扫描电化学显微镜表征

在氧化铟锡(ITO)导电玻璃的衬底上,利用直接电沉积方法制备了ZnO纳米线或ZnO薄膜.然后利用存储有HCI刻蚀剂的琼脂糖微图案印章对其进行了化学刻蚀以形成不同的图形.利用扫描电子显微镜(SEM)、X射线衍射(XRD)和扫描电化学显微镜(SECM)分别对ITO衬底上的ZnO薄膜的结构、形貌和电化学性质进行表征.     

Synthesis,assembly, and thin film transistors of dihydrodiazapentacene: an isostructural motif for pentacene

The study below details the synthesis, assembly, and thin film transistors from dihydrodiazapentacenes. These molecules have the same molecular shape as pentacene but are much easier to prepare and have much greater environmental stability. Thin films made from the dihydrodiazapentacene behave as field effect transistors with mobilities and on/off ratios high enough to be useful in certain applications. X-ray diffraction and AFM experiments on these films show that the molecules stack in layers with their long axis upright from the surface. Some of the derivatives synthesized for this study have unexpectedly high solubility in polar solvents such as DMF and DMSO. The crystal structure from DMF reveals self-assembled channels with each of the aniline functionalities forming a hydrogen bond with solvent. In more nonpolar solvents, the solid-state assembly switches to a herringbone motif characteristic of the linear acenes.     

Initiated chemical vapor deposition of trivinyltrimethylcyclotrisiloxane for biomaterial coatings

Organosilicon polymers show great utility as both biocompatible and electrically insulating materials. In this work, thin films of a novel organosilicon polymer are synthesized by initiated chemical vapor deposition utilizing trivinyltrimethylcyclotrisiloxane as a monomer and tert-butyl peroxide as a free-radical-generating initiator. Use of an initiator allows for the formation of polymer films at filament temperatures as low as 250 degrees C, significantly lower than those required to thermally polymerize the monomer species. The mild reaction conditions allow for the retention of all siloxane ring moieties within the resulting polymer. Films deposited at filament temperatures of 600 degrees C or higher exhibit damage to this moiety. The all-dry deposition process generates a highly cross-linked matrix material in which over 95% of the vinyl moieties present on the monomer units have been reacted out to form linear polymerized hydrocarbon chains. While each hydrocarbon backbone chain averages 8.9 monomer units in length, as evaluated by X-ray photoelectron spectroscopy analysis, each monomer unit is involved in three independent chains, resulting in polymer films of such high molecular weight that they are completely insoluble. Kinetic analysis of the deposition process indicates that the film formation rate is limited by the adsorption of reactive species to the deposition substrate, with an apparent activation energy of -23.2 kJ/mol with respect to the substrate temperature. These results are consistent with a surface growth mechanism, ideal for the coating of nonuniform or high aspect ratio substrates.     

Influence of fluid flow on the deposition of soluble surfactants through receding contact lines of volatile solvents

Soluble surfactants are often deposited from volatile solvents through moving contact lines. In this study, we demonstrate that altering the flow field near such a contact line fundamentally changes the deposited surfactant structure. At slow contact line speeds, the substrate emerges dry. A densely packed, tilted monolayer of surfactant is deposited along the solid-vapor interface from the rolling fluid motion at the contact line. At faster speeds, the substrate emerges with an evaporating thin film entrained on its surface. Surfactant is confined in the film in a constantly increasing concentration environment. Monodisperse crystalline islands nucleate and grow on the surface with sizes and shapes controlled by varying the deposition conditions. These results contrast with disordered deposits that result from evaporation at a pinned contact line. Our results suggest that dip-coating with control of dipping speed and evaporation rate may provide better control of deposition through contact lines of evaporating solvents.     

超声搅拌化学浴沉积法制备大颗粒和致密的CdS薄膜

采用超声搅拌化学浴法(UCBD)在SnO2:F透明导电玻璃衬底上制备了CdS薄膜.研究了退火和CdCl2处理对UCBD-CdS薄膜的表面形貌、晶体结构和直接带隙的影响,比较了沉积时间对UCBD-CdS薄膜中CdS聚集体颗粒大小和堆积致密性的影响.结果表明,CdCl2处理可使CdS聚集体中的小颗粒重新熔合在一起,但CdS聚集体的大小并没有改变.在UCBD-CdS薄膜的沉积过程中,CdS薄膜的横向和纵向生长速率之比会随着沉积时间的不同而改变,且沉积时间是获得大颗粒的CdS聚集体和致密的UCBD-CdS薄膜的重要影响因素.当沉积时间为40min时,获得的UCBD-CdS薄膜较致密,CdS聚集体的大小为180nm,膜厚为80.8nm,适合作为薄膜太阳电池的窗口层.     

Electrical conductivity of alternate layer deposition of pentancene and tetracene superlattices

Superlattice thin films of pentacene (PEN) and tetracene (TET) were fabricated by alternate layer deposition using the sublimation method. The film showed a highly crystalline structure that was due to the strong aggregation tendency of polyacene compounds to form a layered monomolecular column structure. The crystalline structure of the films was drastically changed by doping with iodine. The doped films showed a highly ordered structure where an iodine monomelecular layer was intercalated between molecular columns of acene compounds in both PEN and TET. The doped films exhibited a large lateral conductivity of 10 Ω^?1 cm^?1 and attained giant anisotropy above 10¹². This indicated that molecular columns of TET remained insulating upon doping to form a perfect two-dimensional conductor in the superlattice thin films.     

Characterization and electrochemical deposition of natural melanin thin films

Melanin is an important class of biological pigments because of its distinct chemical and physical properties. The electrochemical deposition of natural melanin thin films was studied using two different techniques; constant potential and cyclic voltammetry along with a deposition time of five hours. The thin films deposited electrochemically on a fluorine-doped tin oxide conductive glass substrate using the constant potential method, exhibited faster growth rate and better adhesion to the fluorine-doped tin oxide working electrodes than those deposited using the cyclic voltammetry method. The thin films deposited on the fluorine-doped tin oxide conductor glass using the constant potential method were also more homogeneous than those deposited via the cyclic voltammetry technique. The increase of film thickness is related to the increase of electrochemical deposition time. Interestingly, the electrochemical deposition using the constant potential method had the advantage of consuming less electric charge. The physical and chemical structures of the melanin thin films were characterized using ultraviolet–visible absorption spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction analysis. The ultraviolet–visible absorption spectra showed the correlation between the variation of deposition rates of melanin and the type of electrochemical technique employed as well as the thickness of the film. The average thickness of the film is 500 nm which absorb 40% of light in both type of films. The atomic force microscopy images illustrated the homogeneous deposition of the melanin molecules on the fluorine-doped tin oxide conductive glass substrate, indicating that the thickness of the thin films can be controlled. We estimated an average grain size of 14.093 Å. The ease of preparing such thin films of organic materials can open new avenues towards the use of soft conductors, in contrast to the complex preparation of industrial semiconductors.     

Growth of organic n-conductors on thin polymer films for use in organic field effect transistors

Thin films of different polymers - poly(styrene) (PS), poly(methylmethacrylate) (PMMA), poly(vinylcarbazole) (PVCz), poly(vinylchloride) (PVC) and poly(vinylidene fluoride) (PVDF) - were deposited by spin-coating or by vapor deposition. On these polymers, thin films of (hexadecafluorophthalocyaninato)-oxovanadium (F₁₆PcVO) were prepared by physical vapor deposition. The growth of these films was monitored in situ by optical spectroscopy. The optical absorbance spectra were analyzed based on the coupling of transition dipoles to obtain information on the intermolecular arrangement of chromophores in the films. In all of these samples, the molecules are oriented with their molecular plane preferentially perpendicular to the substrate surface. This gives the desired overlap of the π-systems for electric conductance parallel to the substrate. Differences in the interactions were detected when deposition temperatures below or above the glass transition temperature of a given polymer were compared. The morphology of the polymer films and the deposited semiconductors were investigated by atomic force microscopy and scanning electron microscopy. The influence of the chosen substrate on the film structure is determined. The optical and electric properties of the films could thereby be influenced and the applicability of such films as active layers in organic thin film transistors is discussed.     

电喷雾离子化技术制备FeNi(OH)x薄膜及电催化水氧化性能

采用电喷雾离子化沉积技术, 在氟掺杂锡氧化物(FTO)衬底上制备了均匀的无定形铁镍双金属氢氧化物薄膜. 与浸泡法制备的薄膜相比, 该薄膜具有更高的纯度、 更大的比表面积和较高的电催化水氧化性能, 在10 mA/cm ²时的过电位为290 mV, 并在催化反应中表现出良好的稳定性, 为可控合成高催化活性的过渡金属氢氧化物薄膜提供了一种新方法.