Highly Electrical Conductivity of Hybrid Langmuir-Blodgett Films of Transition Metal Dichalcogenide and Amphiphilic Compounds

Abstract

Hybrid alternate layered films of transition metal dichalcogenides and amphiphilic compounds were prepared by Langmuir-Blodgett (LB) technique. The conductivity at room temperature depended on the transition metal dichalcogenide species, showing the highest value for the hybrid LB films of MoS₂ system. This methodology was successfully applied to the fabrication of the hybrid LB films using various organic amphiphiles such as cyanine dyes, phthalocyanines, azobenzene, and ferrocene derivatives. The conductivity depended on the interlayer spacing: the conductivity decreased with increasing interlayer spacing of the film. The highest electrical conductivity of the hybrid LB films was over 100 Scm^?.     

Supramolecular structure formation of Langmuir-Blodgett films of comblike precursor and polyimide

The surface structure of Langmuir-Blodgett films of a comblike polyimide precursor—a rigid-chain polyamic acid alkylamine salt bearing multichains of tertiary amine—and films of the corresponding polyimide were studied by atomic force microscopy (AFM). An analysis of the images of the surface of three-layer films revealed a domain structure. It was found that the Langmuir-Blodgett film formation of the precursor occurs as a result of the layer-by-layer deposition of two-dimensional domains (composed of polyamic acid salt molecules on the water surface) onto a substrate. The formation of domains in a monolayer is associated with the chemical structure of the precursor, to be more precise, with the rigidity of the main chain and the presence of closely spaced aliphatic side chains in the polymer chain, whose total cross-section area is close to the surface area of the projection onto the plane of the repeating unit of the main chain. Polyimide films inherit the domain structure of the precursor films; the inhomogeneity of the film thickness substantially decreases, whereas the domain size and character of their distribution in the film remain unchanged.     

Complex study of mechanical properties of a-Si:H and a-SiC:H boron doped films

The aim of the present work is to provide the complex study of the mechanical properties of p-doped a-Si:H and a-SiC:H thin films prepared under different plasma conditions. For the investigation of the samples we used mainly the continuous depth sensing indentation technique (DSI), pin-on-disc test and internal stress measurement. The morphology of the thin film surface and the indentation prints are studied using optical microscopy, scanning electron microscopy (SEM) and topography mode of atomic force microscopy (AFM). The dependence of the mechanical parameters upon the deposition conditions were compared with the optoelectronic properties of studied films.     

On two-dimensional ferroelectricity in layered polymer films on substrates

A simple model for describing structural phase transitions in thin ferroelectric copolymer films on solid substrates obtained by the Langmuir-Blodgett method has been suggested. It is shown that the polymer-substrate interaction and surface tension considerably influence these transitions and, in particular, can induce additional low-temperature first-and second-order phase transitions depending on the material parameters and the film thickness. The main dimensionless parameter and its critical value, which control the formation of the additional order in very thin films, are determined.     

Study of polymorphous silicon and germanium as thermo-sensing films for infrared detectors

In this work we present a comparative study on the electrical characteristics of polymorphous silicon (pm-Si:H) and polymorphous germanium (pm-Ge:H) thin films deposited by low frequency plasma enhanced chemical vapor deposition (LF-PECVD), aiming to use them as thermo sensing elements in un-cooled microbolometers.We studied the effect of the deposition pressure on the film characteristics that are important for IR detection, as the activation energy (E_a), the thermal coefficient of resistance (TCR), the room temperature conductivity (σ_RT) and the film responsivity with IR radiation.Our results indicate that polymorphous films have advantages over boron doped a-Si:H, material which is currently employed as thermo-sensing element in commercial microbolometer arrays.     

Preparation of indium tin oxide thin films without external heating for application in solar cells

Indium tin oxide (ITO) films were grown without external heating in an ambient of pure argon by RF-magnetron sputtering method. The influence of argon ambient pressure on the electro-optical properties of as-deposited ITO films was investigated. The morphology, structural and optical properties of ITO films were examined and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and UV–VIS transmission spectroscopy. The deposited ITO films with a thickness of 300 nm show a high transparency between 80% and 90% in the visible spectrum and 14–120 Ω/□ sheet resistance under different conditions. The ITO films deposited in the optimum argon ambient pressure were used as transparent electrical contacts for thin film Cu(In,Ga)Se₂ (CIGS) solar cells. CIGS solar cells with efficiencies of the order of 7.0% were produced without antireflective films. The results have demonstrated that the developed ITO deposition technology has potential applications in thin film solar cells.     

Synthesis and characterization of manganese sulphide thin films deposited by spray pyrolysis

Manganese sulphide (MnS) thin films have been deposited onto glass substrate by a low cost spray‐pyrolysis technique at 220 °C. The as‐deposited MnS thin films have been characterized using scanning electron microscopy (SEM), energy dispersive X‐ray (EDX) spectroscopy, atomic force microscopy (AFM), X‐ray diffraction, UV visible spectroscopy and photo electrochemical (PEC) measurement. The SEM and AFM images showed that the MnS thin films were well covered onto the substrate surface. The as‐deposited raw thin film was found to be amorphous in nature and perfectly crystalline phase after annealing the sample. Optical band gap of the MnS thin films was found to vary from 3.1 to 3.21 eV and the band gap decreases with the increase in film thickness. Optical constants such as refractive index, extinction coefficient have been evaluated using reflectance and absorbance data. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spectroscopic and microscopic study of aggregate formation in the nano-dimensional Langmuir-Blodgett films of perylene with a fatty acid/polymer

Perylene (PYL) mixed with Behenic acid (BA) and Polymethyl methacrylate (PMMA) separately have been incorporated in the Langmuir-Blodgett film. The surface pressure versus area per molecule area isotherms are measured at various molar ratios. Stability of the mixed monolayer of PYL and BA/PMMA and their collapse pressure are much higher than that of pure PYL. Negligible amount of hysteresis observed in the compression-decompression isotherms indicate the formation of stable monolayer. Miscibility of the mixed systems is found to vary with the film composition. The formation of PYL aggregates in the mixed films is investigated using UV-Vis absorption spectroscopy, emission spectroscopy and atomic force microscopy (AFM).     

Influence of annealing on the physical properties of filtered vacuum arc deposited tin oxide thin films

Tin oxide (SnO₂) thin films were deposited on UV fused silica (UVFS) substrates using filtered vacuum arc deposition (FVAD). During deposition, the substrates were at room temperature (RT). As-deposited films were annealed at 400 and 600 °C in Ar for 30 min. The film structure, composition, and surface morphology were determined as function of the annealing temperature using X-ray diffraction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The XRD patterns of the SnO₂ thin films deposited on substrates at RT indicated that the films were amorphous, however, after the annealing the film structure became polycrystalline. The grain size of the annealed films, obtained from the XRD analysis, increased with the annealing temperature, and it was in the range 8-34 nm. The AFM analysis of the surface revealed an increase in the film surface average grain size from 15 nm to 46 nm, and the surface roughness from 0.2 to 1.8 nm, as function of the annealing temperature. The average optical transmission of the films in the visible spectrum was >80%, and increased by the annealing ∼10%. The films’ optical constants in the 250-989 nm wavelength range were determined by variable angle spectroscopic ellipsometry (VASE). The refractive indexes of as-deposited and annealed films were in the range 1.83-2.23 and 1.85-2.3, respectively. The extinction coefficients, k(λ), of as-deposited and annealed films were in the range same range ∼0-0.5. The optical energy band gap (E_g), as determined by the dependence of the absorption coefficient on the photon energy at short wavelengths, increased with the annealing temperature from 3.90 to 4.35 eV. The lowest electrical resistivity of the as-deposited tin oxide films was 7.8 × 10⁻³ Ω cm, however, film annealing resulted in highly resistive films.     

Study of the growth and switching kinetics on ferroelectric nanocrystals of copolymer vinylidene fluoride and trifluoroethylene on an atomic force microscope

The growth of nanocrystals obtained from Langmuir-Blodgett films of ferroelectric copolymer consisting of 70% vinylidene fluoride and 30% trifluoroethylene has been investigated by atomic force microscopy (AFM). The radius and concentration of nanocrystals are found to depend on the annealing time of the film. A model for nanocrystal growth is proposed which yields adequate time dependences for nanocrystal size parameters. The switching kinetics of individual ferroelectric nanocrystals with an average diameter of 100–200 nm and a height of 15–20 nm has been investigated in the piezoelectric response mode. It is shown that the switching of nanocrystals has an activation character.     

The role of the pressure in pulsed laser deposition of bioactive glass films

Effects of the Ar pressure on the morphology, structure, bonding configuration and deposition rate of the bioglass thin films were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and crystal lattice monitor. Ar pressure has an influence on the quantity and shapes of the particles generated in the PLD process. The target bonding configuration is not correctly transferred to the films. This effect is attributed to the network rearrangement during the film growth, which is associated to special structure of glass and complex physical mechanisms of PLD. Deposition rate decreases as the pressure increases following a linear dependence.     

机械磨抛对CdZnTe薄膜阻变特性的影响

采用磁控溅射法在ITO玻璃上制备了CdZnTe薄膜,探究机械磨抛对CdZnTe薄膜阻变特性的影响。通过对XRD图谱、Raman光谱、AFM显微照片等实验结果分析阐明了机械磨抛影响CdZnTe薄膜阻变特性的物理机制。研究结果表明,磁控溅射制备的薄膜为闪锌矿结构,F43m空间群。机械磨抛提高了CdZnTe薄膜的结晶质量;CdZnTe薄膜粗糙度(Ra)由磨抛前的3.42 nm下降至磨抛后的1.73 nm;磨抛后CdZnTe薄膜透过率和162 cm^-1处的类CdTe声子峰振动峰增强;CdZnTe薄膜的阻变开关比由磨抛前的1.2增加到磨抛后的4.9。机械磨抛提高CdZnTe薄膜质量及阻变特性的原因可能是CdZnTe薄膜在磨抛过程中发生了再结晶。     

Production and shaping of high performance phosphors by using the sol–gel process: Yttrium aluminum garnet (Y3Al5O12)

Luminescent Y₃Al₅O₁₂:Tb³⁺ (YAG:Tb³⁺) phosphor thin films and powders have been successfully prepared by the sol–gel route from alkoxide precursors. Advanced coatings were produced by spray and dip-coating from stabilized sols. X-ray diffraction (XRD), attenuated total reflectance/Fourier transform infrared spectroscopy (ATR/FTIR) and atomic force microscopy (AFM) were used to investigate the structure and morphology of layers. YAG phases of high purity were obtained for both powders and films. AFM study revealed coatings of homogeneous topography, whatever the deposition technique. However, dip-coated samples exhibited a much smoother topography, characterized by a root mean square (rms) roughness much lower than that of spray-coated ones. Laser induced emission spectra and decay times of Tb³⁺ ions in a spray-coated film were recorded. Measurements exhibit the characteristic green emission of Tb³⁺. Effectiveness of the Tb³⁺ doped coatings under UV excitation is also illustrated by pictures.     

Microstructural and optoelectrical properties of transparent conducting ZnO:Al thin films for organic solar cells

The Al‐doped zinc oxide (ZnO:Al) thin films were grown on glass substrates by the magnetron sputtering technique. The films were characterized with X‐ray diffractometer, four‐point probe and optical transmission spectroscopy, respectively. The dependence of microstructural, electrical and optical properties on deposition temperature was investigated. The results show that all the films have hexagonal wurtzite structure with highly c‐axis orientation. And the microstrural and optoelectrical properties of the films are observed to be subjected to the deposition temperature. The ZnO:Al film prepared at the deposition temperature of 650 K possesses the best optoelectrical properties, with the lowest electrical resistivity (6.1×10⁻⁴ Ω·cm), the highest average visible transmittance (85.3%) and the maximum figure of merit (0.41 Ω⁻¹). The optical energy gap of the films was estimated from Tauc's law and observed to be an increasing tendency with the increment of the deposition temperature. Furthermore, the refractive index of the films was determined by the optical characterization methods and the dispersion behavior was studied by the single electronic oscillator model.     

氩氧流量比对CeOx-SnOx膜微观结构及光学性能的影响

采用磁控反应共溅射的方法,以金属Ce和Sn为金属源,成功地制备出CeOx-SnOx薄膜.利用扫描电子显微镜(SEM)、X射线衍射(XRD)、透射电子显微镜(TEM)和X射线光电子能谱(XPS)等测试手段对薄膜的结构、表面形貌及成分进行了分析和表征.结果表明薄膜以岛状模式生长,随氩氧比降低,结晶性增强,出现CeO2和SnO相.此外,利用紫外-可见分光光度计对薄膜的光学性能进行了研究,测试结果表明薄膜对紫外光有极强的吸收作用.当氩氧流量比为3∶1时,紫外光平均透过率仅为5.80;,而可见光平均透过率为81.48;.     

PEM控制合成碳掺杂钛氧薄膜的成分结构研究

采用等离子体发射监测(PEM)系统实现闭环控制反应气体流量,使反应溅射稳定在滞回曲线过渡区,并以气相CO2和O2为碳源和氧源制备了碳掺杂钛氧(C∶Ti-O)薄膜.采用原子力显微镜、掠入射X射线衍射和X射线光电子能谱表征薄膜的表面形貌、结构、成分,紫外-可见分光光度计测试薄膜透射率并用Tauc作图法计算薄膜的带隙宽度.结果表明,随着辉光强度设定点(SP)的增大,沉积速率增大,薄膜中Ti-C键含量增多,带隙宽度降低,薄膜的结晶性增强且有利于金红石相的形成.     

固溶体半导体碲硫锌多晶薄膜的制备及发光特性研究

ZnS1-x Tex薄膜具有高效的发光特性.样品可观测到强烈的光致发光,随着Te含量x的不同,发射光的颜色从深蓝到黄变化,使其成为制作短波长光波段光电子器件和紫外探测器的理想材料.本文介绍了ZnS1-x Tex多晶薄膜真空蒸发制备的情况,并用X射线衍射仪对淀积在玻璃、石英玻璃和单晶硅衬底上的多晶薄膜进行结构分析,用紫外-可见分光光度计、荧光光谱分析仪对样品的光吸收和发光性质进行研究.分析表明,该薄膜的结构符合闪锌矿的特征.紫外-可见吸收光谱显示该样品在紫外光区有一个强烈的吸收峰,可见光区的吸收很微弱.光致发光光谱表明,样品在可见光区有一个以470nm为中心的发射峰,发射光肉眼可见.该多晶薄膜基本保持了单晶薄膜的紫外吸收、光致发光等良好特性.     

Preparation and characterisation of Ag incorporated Al2O3 nanocomposite films obtained by sol‐gel method

Sol‐gel route has been applied for a deposition of the thin films of aluminum oxide and Ag embedded in Al₂O₃ films. The films are spin‐coated on Si and quartz substrates with the film thickness of 120 nm. XRD analysis has been used for the determination of the film structure. FTIR spectroscopy is applied for studying vibrational properties of the obtained coatings. Optical characterization is done by UV‐VIS spectroscopy. The formation of Ag nanoparticles has been confirmed by XRD and optical data. The sol‐gel process is found to be useful technology for incorporation of Ag nanoparticles in the metal oxide matrices. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Surface biofunctionalization of nanostructured GeSbSe chalcogenide glass thin films

Thin nanostructured chalcogenide films were grown using the oblique angle deposition (OAD) technique and subsequently polymerized with thin poly(amino-p-xylylene) (PPX) films. Our objective was twofold, i.e., to use deposited polymeric thin films to allow the attachment of biomolecules to chalcogenide glass thin films, and at the same time, to increase surface area by OAD to enhance surface functionality. The effectiveness of this approach was evaluated by Fourier transform infrared spectroscopy (FTIR), together with a combination of fluorescent protein immobilization and confocal microscopy characterization. It is shown that the presence of amine groups on the surface of the polymer coated chalcogenide thin films yield a notable increment of surface coverage with proteins at large evaporation oblique angles which is expected to enhance detection performance of the film in biosensor applications.     

Structure of Polycrystalline Cu Films as Solar Selective Coatings

Copper thin films (5–150 nm) were prepared by vacuum deposition with different rates (0.7, 1.5 and 3 nm/s). The position, intensity and profile of X-ray diffraction lines were analysed to study the phases, the crystallographic preferred orientation as well as the residual strain and crystallite size. The fcc polycrystalline Cu phase was revealed and no oxide phases were identified. The films were highly oriented with 〈111〉 fiber texture. The ratio of P₁₁₁/P₂₀₀ increased with the film thickness. Thus, in case of amorphous substrate, the type of the crystallographic texture of a film depends mainly on the structure of the deposited material. The crystallite size increases while the residual strain decreases, as the film thickness or the deposition rate is increased. The crystallite size was very small compared with the film thickness. The effect of deposition rate was pronounced specially from 0.7 to 1.5 nm/s.