Effect of Mg doping on optical and electrical properties of SnO2 thin films: An experiment and first-principles study

Transparent Mg-doped p-type conductive SnO₂ thin films were fabricated on quartz substrates by sol–gel method. Effect of Mg doping on structural, morphological, optical, and electrical properties of SnO₂ films were investigated. A single phase of tetragonal rutile structure was observed in Mg-doped SnO₂ films. The optical bandgap energy of the Mg-doped SnO₂ films showed a systematical redshift with respect to the undoped SnO₂ film, and the resistivity significantly increased with the increase of Mg concentration. A conduction type transform from n to p was also observed. The strong ultraviolet and comparatively weak blue/green emissions were observed in room temperature photoluminescence, suggesting the dipole-forbidden rule of bulk SnO₂ is broken in Mg-doped SnO₂ films. These results were supported by first-principles electronic structure calculations.     

Fabrication of N-doped TiO2 thin films by laser ablation method: Mechanism of N-doping and evaluation of the thin films

N-doped TiO₂ thin films were prepared by the laser ablation method under an N₂ gas atmosphere. Properties of the films such as color, the relative amount of N doped and the crystal structure strongly depended on substrate temperature and N₂ gas pressure. XPS data indicated that the amount of doped N unexpectedly increases with decreasing N₂ gas pressure in the range of ca. 40–270 Pa. We proposed that the N-doping occurred when N species and TiO₂ particles collide on the substrate. The decomposition of methylene blue using the N-doped TiO₂ thin film was also performed under visible light irradiation.     

Non-isothermal micromixing in turbulent liquids: Theory and experiment

Partial segregation of reagents occurs when reaction rates exceed mixing rates and frequently causes product distributions to be mixing-dependent. A simultaneous temperature segregation, whereby the temperature in a reaction zone differs from that in its surroundings, has rarely been considered when mixing reagents in the liquid phase. The Prandtl number is usually sufficiently small that engulfment, not thermal conduction, determines the local temperature. The engulfment model of micromixing can then be extended by a heat balance to specify this temperature. To evaluate this model, a new pair of fast competitive reactions (neutralisation and acetal hydrolysis) has been characterised thermochemically and kinetically. A Mettler RC1 calorimeter was operated under isothermal and adiabatic conditions with various stirrer speeds and HCl was slowly added to a mixture of NaOH and 2,2-dimethoxypropane. Measured hydrolysis yields compared quite well with the extended engulfment model, although temperature segregation was of minor importance. It was also unimportant in other reaction systems (simultaneous neutralisation and ester hydrolysis; diazo coupling) employed earlier to study micromixing. Suggestions for further work are made.     

Growth of thin epitaxial films

A new theoretical model for prediction of the mechanism of growth of thin epitaxial films is developed. The model is not based on the classical nucleation theory as this is the case of the approach of Bauer to the problem. The thermodynamic conditions for occurrence of island growth, layer-by-layer growth, multilayer growth and Stranski—Krastanov mechanism consisting of layer-by-layer growth followed by islands are found. The influence of the lattice misfit and the surface alloying on the mode of growth is discussed. The effect of the crystallographic orientation of the substrate is also studied. The theoretical results are applied to the case of electrocrystallization of metals on single crystal metal substrates. A comparison with experimental data is carried out whenever possible.     

Nanoindentation of GaSe thin films

ABSTRACT: The structural and nanomechanical properties of GaSe thin films were investigated by means of X-ray diffraction (XRD) and nanoindentation techniques. The GaSe thin films were deposited on Si(111) substrates by pulsed laser deposition. XRD patterns reveal only the pure (000?l)-oriented reflections originating from the hexagonal GaSe phase and no trace of any impurity or additional phases. Nanoindentation results exhibit discontinuities (so-called multiple 'pop-in' events) in the loading segments of the load-displacement curves, and the continuous stiffness measurements indicate that the hardness and Young's modulus of the hexagonal GaSe films are 1.8?±?0.2 and 65.8?±?5.6?GPa, respectively.     

ZnO薄膜的制备及其性能

用脉冲激光沉积(PLD)法在SiO2基片上制备了ZnO薄膜和Zn1-xMnxO薄膜。X射线衍射、原子力显微镜、紫外-可见分光光度计对ZnO薄膜的测试结果表明:薄膜具有(103)面的择优取向,表面比较平坦;SiO2基片上制备的薄膜在387nm附近存在明显的吸收边,且薄膜的吸收对基片温度变化不明显。通过对Zn1-xMnxO薄膜的吸收光谱分析得出:Mn离子的掺杂改变了ZnO薄膜的禁带宽度,随Mn离子的掺杂量的增加,薄膜禁带宽度增加;薄膜的光吸收也从直接跃迁过渡为间接跃迁过程。     

Preparation and characterization of catalyst thin films

Many devices used in catalysis are based on high surface area materials in which catalytic reactions are carried out inside pores, channels and other confined cavities for which the deposition of catalyst thin films is required. This paper provides an overview of the methods in use for the preparation and characterization of catalyst thin films, and focuses more specifically on thin films involved in the electropromotion of catalysis (EPOC). In fact, EPOC or NEMCA (Non-Faradic Electrochemical Modification of Catalytic Activity) have shown the importance of being able to combine electrical contacts between catalytic metals and ion conducting oxide layers as well as to develop in the same system catalytic materials with large specific surface area. The different aspects of thin film preparation and characterization are described in relation to catalyst thin films deposition. Multimodal and hierarchic porous structures can be obtained from the assembly of catalyst thin films with various carrier materials, anticipating more efficient catalytic systems. Chemical and physical coating techniques are compared with a special attention on those useful for the preparation of thin films with controlled porous structure and morphology. With regard to EPOC systems, electrode and electrolyte materials of interest for electrochemical catalytic devices are listed and typical examples of systems based on electrocatalyst thin films are given.     

Electrohydrodynamic instabilities of polymer thin films: Filler effect

The influence of various nanoparticles with different dimension, density, dielectric constant, and surface property on electrohydrodynamic (EHD) instabilities of polymer/nanoparticle nanocomposite thin films was examined as a function of nanoparticle concentration. Transmission electron microscopy (TEM) images of polystyrene (PS)/nanoparticles (NPs) thin films demonstrated that all the nanoparticles were uniformly distributed in polymer matrix and the homogeneous dispersions of nanoparticles were not affected by thermal annealing above glass transition temperature. Optical microscopy (OM) observations indicated that thin films of polystyrene containing silica (SiO₂), gold (Au), cadmium selenide (CdSe), and titania (TiO₂) nanoparticles showed electrohydrodynamic instability patterns similar to those seen in pure polystyrene, up to 3 vol% nanoparticles. The presence of nanoparticles changed the dielectric constant of the thin films, which led to systematic variations in the wavelengths of the surface instabilities, which were consistent with calculated values. Cross-sectional transmission electron microscopy (TEM) images showed that migration or aggregation of the nanoparticles occurred only for silica contrary to other nanoparticles. This work points to a simple route to reduce the scale of final well-ordered columnar structures.     

Microstructure of c-BN thin films deposited on diamond films

Diamond films were used as substrates for cubic boron nitride (c-BN) thin film deposition. The c-BN films were deposited by ion beam assisted deposition (IBAD) using a mixture of nitrogen and argon ions on diamond films. The diamond films exhibiting different values of surface roughness ranging from 16 to 200 nm (in R_rms) were deposited on Si substrates by plasma enhanced chemical vapor deposition. The microstructure of these c-BN films has been studied using in situ reflexion electron energy loss spectroscopy analyses at different primary energy values, Fourier transform infrared spectroscopy and high resolution transmission microscopy. The fraction of cubic phase in the c-BN films was depending on the roughness of the diamond surface. It was optimized in the case of the smooth surface presenting no particular geometrical effect for the incoming energetic nitrogen and argon ions during the deposition. The films showed a nanocrystalline cubic structure with columnar grains while the near surface region was sp² bonded. The films exhibit the commonly observed layered structure of c-BN films, that is, a well textured c-BN volume lying on a h-BN basal layer with the (00.2) planes perpendicular to the substrate. The formation mechanism of c-BN films by IBAD, still involving a h-BN basal sublayer, does not depend on the substrate nature.     

Doping graphene thin films with metallic nanoparticles: Experiment and theory

Precise doping of graphene at nanoscale resolution is vital for a number of applications in nanoelectronics and sustainable energy. Although large metallic contacts are presumed to move the Fermi level of graphene above or below the Dirac point, little has been done to study these effects when graphene is in contact with nanoscale metallic objects of specific sizes and concentrations and to investigate if such phenomena are associated with some forms of doping as in conventional semiconductors. As a case study we determine here the local effect of copper nanoparticles (Cu-NPs) on the Fermi energy of graphene domains in large-area graphene thin films. Tight-binding calculations corroborate our Kelvin-probe force microscopy experiments indicating that the Fermi level shifts in the presence of Cu-NPs (corresponding to 0.2 eV at 20% graphene area coverage by Cu) which break the electron-hole symmetry of graphene due to its weak Van der Waals interactions with Cu even in the absence of chemical bonding and charge transfer, in contrast to previous predictions for large and flat metallic contacts.     

New photoimageable dielectric insulating copolyester thin films: Synthesis and characterization

In this article, we describe the synthesis and characterization of a new family of photoimageable dielectric insulating polymer films. Four different photoimageable thin films have been prepared from all-aromatic and aromatic/aliphatic copolyesters, which exhibit good photospeed (10–180 s, 15.5 mW/cm² intensity), resolution and line width (10 μm), thermal stability (330–400°C), adhesion on different substrates, mechanical strength, and reasonable glass transition temperature (120–150°C). One feature of the new photoimageable copolyester is the formation of a low dielectric constant film (2.5 at 1 kHz, 25°C) upon curing at temperatures up to 280°C. The low dielectric constant is a result of foaming arising from evolution of by-products during curing. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1199–1211, 1997     

SHS reaction and explosive crystallization in thin films: Resemblance and distinction

The SHS waves in multilayer Ni/Al nanofilms and the explosive crystallization waves in Sb films deposited onto a thin copper substrate were comparatively explored by IR imaging and SEM. Despite a markedly lower thermal effect of crystallization, the waves of chemical reaction and crystallization were found to have much in common in their temperature–time histories: warmup rate, temperature gradient in the wave front, and duration of heat release. Observed was a micro-scintillation mode of the propagation of explosive crystallization wave in Sb films.     

Superconductivity in polycrystalline diamond thin films

Superconductivity was discovered in heavily boron-doped diamond thin films deposited by the microwave plasma assisted chemical vapor deposition (MPCVD) method. Advantages of the MPCVD deposited diamond are the controllability of boron concentration in a wide range, and a high boron concentration, especially in (111) oriented films, compared to that of the high-pressure high-temperature method. The superconducting transition temperatures are determined to be 8.7 K for T_c onset and 5.0 K for zero resistance by transport measurements. And the upper critical field is estimated to be around 7 T.     

Characterization of aluminium nitride thin films

Aluminium nitride (AlN) thin films have been synthesized by evaporation of aluminium and simultaneous irradiation with nitrogen ions, ion-vapour deposition method, at the substrate temperature of room temperature or 473K. The kinetic energy of the incident nitrogen ion beam has been kept at 0.5 keV and the deposition rate has been varied from 0.075 to 0.28 nm/s. The structure of the synthesized films has been examined by X-ray diffraction (XRD) and the surface morphology has been characterized by atomic force microscopy (AFM). In the XRD patterns of both films synthesized at room temperature and 473K, the diffraction lines due to the AlN(10.0), (00.2) and (10.1) planes have been discerned. AFM observations reveal that the surface of the films synthesized at 473K becomes rough as compared with the films synthesized at room temperature. This may be attributed to growth of AlN particles on the substrate kept at 473K. Furthermore, in the films synthesized at the 473K substrate, several aggregated protrusions can be observed on the relatively smooth surface at the deposition rate of 0.28 nm/s, while the surface of the films is uniform on nanometre scale at the deposition rate of less than 0.12 nm/s. The present results suggest that the synthesis of the AlN films with uniform surface is feasible by controlling the substrate temperature and the deposition rate.     

Sol-gel processed barium titanate thin films

Ferroelectric barium titanate (BaTiO₃) thin films have been prepared by sol-gel technique from barium acetate [Ba(CH₃COO)₂] and titanium (IV) isopropoxied [Ti(CH₃)₂CHO)₄] precursors. The as-grown films were found to be amorphous which crystallized to tetragonal phase after annealing at 700°C for one hour in air. The room temperautre dielectric constant (ε) and loss tangent (tanδ) of the films were found to be 370 and 0.02 respectively. The values of the spontaneous polarization (P_s), remanent polarization (P_r) and coercive field (E_c) of the films determined from the polarization-field (P-E) hysteresis were found to be 14.0, 3.2μC-cm^-2 and 53KV-cm^-1 respectively. The coercive field of the film determined from the capacitance-voltage (C-V) characteristics is slightly lower than that determined from the P-E hysteresis loop.