Atomic Layer Deposited Ti2O3 Thin Films

Ti₂O₃ thin films have been prepared through atomic layer deposition and subjected to electrical resistivity measurements as a function of temperature. The as-prepared films were stable for up to three weeks. In Ti₂O₃ thin films, the insulator-metal transition is observed at ∼80 K, with nearly 3–4 orders of magnitude change in resistivity. The anomalous increase in electrical resistivity in the films is in accordance with the two-band model. However, the energy interval between the bands depending on the crystallographic c/a ratio leads to a change in electrical resistivity as a function of temperature.     

Sol-Gel Deposited Sb-Doped Tin Oxide Films

The structural, electrical and optical properties of single sol-gel derived antimony-doped tin oxide (ATO) films sintered at 550°C have been measured. The reproducibility of both the preparation and the characterization procedures have been tested by a round-robin test involving eight laboratories within a Concerted European Action (CEA) project. The resistivity measured as a function of Sb content has been obtained by electric and reflectance and transmission measurements. Their differences are discussed in terms of structural and grain boundary effects. An increase of Sb content results in a decrease of the crystallite size (7.0 to 5.4 nm) and a greater influence of the grain boundary.     

Electrical Percolation During Gelation of Lithium Doped Siloxane-Poly(oxyethylene) Hybrids

Gelation mechanisms of lithium-doped Siloxane-Poly(oxyethylene) (PEO) hybrids containing polymer of two different molecular weight (500 and 1900 g/mol) were investigated through the evolution of the electrical properties during the solgel transition. The results of electrical measurements, performed by in-situ complex impedance spectroscopy, were correlated with the coordination and the dynamical properties of the lithium ions during the process as shown by ⁷Li NMR measurements. For both hybrids sols, a decrease of the conductivity is observed at the initial gelation stage, due to the existence of an inverted percolation process consisting of the progressive separation of solvent molecules containing conducting species in isolated islands during the solid network formation. An increase of conductivity occurs at more advanced stages of gelation and aging, attributed to the increasing connectivity between PEO chains promoted by the formation of crosslinks of siloxane particles at their extremities, favoring hopping motions of lithium ions along the chains.     

Preparation and characterization of a polyimide membrane

Two different polyimide semipermeable membranes have been prepared from two base polyimides of PMDA/ODA and BTDA/ODA by incorporation of lithium chloride with the respective poly(amic acids) and subsequently leaching out the maximum possible lithium chloride by water at slightly elevated temperature. The water and various organic vapor permeability of the lithium chloride modified films has been found to be better compared to the respective control films. BTDA/ODA based polyimide films show overall lower permeability.     

Doping of C60 fullerene peapods with lithium vapor: Raman spectroscopic and spectroelectrochemical studies

Raman spectroscopy and in situ Raman spectroelectrochemistry have been applied to the study of the lithium vapor doping of C60@SWCNTs (peapods; SWCNT=single-walled carbon nanotube). A strong degree of doping was proven by the disappearance of the radial breathing mode (RBM) of the SWCNTs and by the attenuation of the tangential (TG) band intensity by two orders of magnitude. The lithium doping causes a downshift of the Ag(2) mode of the intratubular C60 by 27 cm(-1) and changes the resonance condition of the encapsulated fullerene. In contrast to potassium vapor doping, the strong downshift of the TG band was not observed for lithium doping. The peapods treated with lithium vapor remained partially doped even when they were exposed to humid air. This was reflected by a reduction in the intensity of the nanotube and the fullerene modes and by the change in the shape of the RBM band compared with that of the undoped sample. The Ag(2) mode of the intratubular fullerene was not resolved after contact of the lithium-doped sample with water. Lithium insertion into the interior of a peapod and its strong interaction with the intratubular fullerene is suggested to be responsible for the air-insensitive residual doping. This residual doping was confirmed by in situ spectroelectrochemical measurements. The TG band of the lithium-doped peapods did not undergo an upshift during the anodic doping, which points to the formation of a stable exohedral metallofullerene peapod.     

STRUCTRE AND PROPERTIES OF COMPOSITE Ni/HARD CARBON FILMS PREPARED BY PLASMA DEPOSITION

IntroductionHardcarbonfilmsprcparcdb}'vari0usplasmaprocesscsareofc0nsidcrablcinterestbccauscofthcirunusualmcchanical-opticalandelcctricalpropertiesll~3l.Rccently,ithasReceive(IJl111c5,l9`)5;,.`,1iis()tI1ie)\tioII,1'ceil'edJtl1)'l4,l995*'I11isprojectiss[1pportcdh}tl1cNatiol1a1Nat[lntlScicl1ccI`()ul1dati()l1ofCl1il1aal1dtl1eI,aboraton'ofSolidI,ubricati()l1,l.al1/l10ulnstitutcofCl1cn1icalPh\'sics,111cChincscAcadcl11\'ofScicnccs.benfoundthattheinc0rporati0nofmetaIintocarbonfilmscangrcatl}'…     

Thickness dependence of the structural,mechanical and electrical properties of Ni films deposited on polyimide by ion beam‐assisted deposition (IBAD)

Ni thin films with different thicknesses were deposited on pre‐treated polyimide substrates by ion beam‐assisted deposition. Dependence of structural, mechanical and electrical properties of the Ni films on their thickness was investigated. The results showed a clear correlation between film properties and film thickness. The inter‐diffusion at the interface regions of the films with different deposition time were demonstrated by transmission electron microscopy and X‐ray photoelectron spectroscopy. With increasing film thickness, surface roughness of the Ni films firstly decreased and then increased, while the grain size gradually increased. Residual stress of the Ni thin films decreased with increasing Ni film thickness up to 202 nm and then slightly increased as the film thickness further increased. Resistivity decreased, and temperature coefficient of resistivity (TCR) increased with increasing film thickness due to the enhancement of crystallization degree and the increase in grain size. The decrease in surface roughness and residual stress also contributed to the decrease of resistivity and the increase of TCR of the films. An optimal film thickness is suggested, which yielded a relatively high TCR value and low levels of both surface roughness and residual stress. Copyright © 2012 John Wiley & Sons, Ltd.     

Tuning the surface hydrophobicity of polymer/nanoparticle composite films in the Wenzel regime by composition

Surface hydrophobicity of composite films containing polymer and nanoparticles has been studied as a function of composition. We show that the hydrophobicity can be tuned by adjusting the amount of particles in the two-component system. A sharp transition from a polymer-rich surface to a nanoparticles-rich surface was observed with increasing mass fraction of particles in spin-coated thin films. Water drops on the films did not slide down even at tilt angles of 90 degrees . Contact angle hysteresis increased with the mass fraction of particles indicating that the surface roughness increased as the surfaces remained in the Wenzel regime. Contact angle hysteresis data were quantitatively consistent with predictions of a recent theory.     

Resistivity control in the semiconductive region for carbon-black-filled polymer composites

It is known that the electrical volume resistivity of insulating polymers filled with conductive fillers, such as metal particles and/or carbon black (CB) particles, suddenly decreases at a certain content of the filler. Therefore, it is very difficult to control the resistivity in the semiconductive region for the CB-filled composites. We examined two effects to control the electrical volume resistivity in the semiconductive region for CB-filled polymer composites. One is the effect of fluorination of the CB surface on the percolation behavior using surface-fluorinated CB particles as a filler. The other is the effect of copolymerization of polyethylene (PE) with a vinyl acetate (VA) functional group on the percolation behavior using poly(ethylene-co-VA) (EVA) as a matrix. By immersion heat measurements, it was found that the London dispersive component turned out to be the predominant factor of the surface energy of fluorinated CBs. The London dispersive component of the surface energy significantly decreased, while the polar component slightly increased on increasing the fluorine content. The resistivity of fluorinated a CB-filled low-density PE composite showed that the percolation threshold increased, and the transition from the insulating state to the conductive state became sluggish, on increasing the fluorine content. In the case of using EVA as a matrix, on the other hand, the percolation curve was moderated with the increase in the VA content. Therefore, copolymerization of PE with VA is also suitable for the design of a semiconductive polymer composite as well as for fluorination of the CB surface. The total surface area per unit mass of dispersed CB particles in the EVA matrix estimated from small-angle X-ray scattering decreased with increasing CB content. Further, the decrease in the surface area is moderated with an increase in VA content. It was found that the difference in the percolation curve is due to the difference in the dispersive state of CB particles.     

Study of the interaction polymer/organic solvents/salt in microporous PVdF separator for lithium batteries

Interactions between microporous PVdF and polar liquid electrolytes have been investigated. PVdF separators are an attractive alternative to microporous apolar polyolefins, such as polyethylene, whose poor wetting by these electrolytes induces a significant resistivity increase in lithium batteries. The swelling study of polymer/electrolyte interactions has shown that the resistivity increase induced by microporous PVdF is moderate and will enable the electrolyte composition to be optimized. Existence of a shut-down effect is an asset for the battery safety.     

Bismuth sulfide thin films with low resistivity on self-assembled monolayers

Using self-assembled monolayers (SAMs), highly crystalline bismuth sulfide thin films with low electrical resistivity have been prepared from aqueous solution at low temperature (40-70 degrees C). The nucleation and growth process of Bi2S3 thin films was investigated in detail by XPS, AES, SEM, XRD, SAED, and HRTEM. Solution conditions have marked effects on the microstructure, growth rate, and mechanism of Bi2S3 films. Increased solution temperature resulted in a higher growth rate and a shorter induction time due to a higher supersaturation degree. In the solution of pH 1.12, homogeneous nucleation and the attachment process dominated the formation of Bi2S3 films. In contrast, at pH 0.47 Bi2S3 thin films were formed via heterogeneous nucleation and growth. The c-axial orientation of bismuthinite films was enhanced with the increase of reaction time. By controlling the solution supersaturation and reaction duration, highly crystalline Bi2S3 films composed of closely packed and coalescent crystallites could be realized, whose dark electrical resistivity could reach as low as 0.014 Omega cm without any post-treatment.     

Surface morphology and electrical properties of copper thin films prepared by MOCVD

Thin copper films have been grown in a vertical MOCVD (Metal-Organic Chemical Vapor Deposition) reactor using bis(2,2,6,6-tetramethyl-3,5-heptanedionato) copper(II), Cu(thd)₂, as precursor. Deposition has been carried out in a pure hydrogen atmosphere (pressure: 3, 20 mbar) at different substrate temperatures (350–750 ° C). The films have been investigated by profilometry, four-point resistivity measurements, ESCA, AES, XRD, AFM, and Normarsky microscopy. An unusual dependence of the film thickness with deposition time has been observed. Rapid growth occurred in the first minutes resulting in badly conducting films (thickness below 1000 Å). Good electrical resistivities have been obtained above 2000 Å. AFM has been used to gain information about the surface morphology of the films with different thicknesses. The grain size and surface roughness increased with increasing film thickness. Small grains grew in the beginning and the electrical properties have been governed by the highly Ohmic bridges between the individual grains.     

Asymmetric Ni/PVC films for high-performance electromagnetic interference shielding

A novel asymmetric Ni/PVC film has been developed by solution casting method. The structure, electrical conductivity, electromagnetic interference(EMI) shielding, and impact resistance were investigated. The results showed that the Ni particles were asymmetrically distributed along the thickness direction in the film. The top surface resistivity increased with film thickness, while the bottom surface exhibited the different trend. EMI shielding effectiveness(SE) depended on formation of closed packed conductive Ni network, which was influenced by both Ni content and film thickness. A linear relationship was observed between EMI SE and film thickness. The films with lower Ni content showed the faster increasing rate of EMI SE with film thickness. Some of the films show appreciably high EMI SE( 40 d B), indicating the promising application in EMI shielding field. Moreover, the films exhibit different impact performance under different impacting directions. All the experimental facts demonstrate that the asymmetric structure endows the film achieving high-performance EMI shielding function.     

Studies on nanocrystalline cadmium sulphide (CdS) thin films deposited by spray pyrolysis

Cadmium chalcogenides with appropriate band gap energy have been attracting a great deal of attention because of their potential applications in optoelectronic devices. CdS in the form of thin film is prepared at different substrate temperatures by a simple and inexpensive chemical spray pyrolysis technique. The as-deposited thin films have been characterized by XRD, SEM, EDAX and electrical resistivity measurement techniques. The XRD patterns show that the films are polycrystalline with hexagonal crystal structure irrespective of substrate temperature. SEM studies reveal that the grains are uniform with uneven spherically shaped, distributed over the entire surface of the substrates. Compositional analysis reveals that the material formed is stoichiometric at the optimized substrate temperature. The optical band gap energy is found to be 2.44 eV with direct allowed band-to-band transition for film deposited at 300°C. The electrical resistivity measurement shows that the films are semiconducting with a minimum resistivity for film deposited at 300°C. The thermoelectric power measurement shows that films exhibit n-type of conductivity.     

Effects of substrate temperature on properties of ITO-ZnO composition spread films fabricated by combinatorial RF magnetron sputtering

We have fabricated ITO-ZnO composition spread films to investigate the effects of substrate temperature on their electrical and optical properties by using combinatorial RF magnetron sputtering. It turned out by X-ray measurement that the film with zinc contents above 16.0 at% [Zn/(In+Zn+Sn)] showed amorphous phase regardless of substrate temperature. The amorphous ITO-ZnO film had lower resistivity than polycrystalline films. When the films were deposited at 250 °C, the minimum resistivity of 3.0×10⁻⁴ Ω cm was obtained with the zinc contents of 16.0 at%. The indium content could be reduced as high as ~30 at% compared to that of ITO for the films having similar resistivity (~10⁻⁴ Ω cm). However, a drastic increase of resistivity was observed for the ITO-ZnO films deposited at 350 °C, having zinc contents below 15.2 at%.     

Growth of porous anodic alumina films in hot phosphate–glycerol electrolyte

Growth of porous anodic alumina films has been examined at 10 V in hot phosphate-containing glycerol electrolyte containing 0.1 to 0.57 mass% water. The growth rate of the films is highly dependent upon the water content of the electrolyte, reducing markedly at a water content of 0.1 mass%, an opposite trend to that found previously for the formation of porous films on titanium and niobium. Chemical dissolution of the anodic alumina is also suppressed in electrolyte of low water content. GDOES depth profiles revealed that an increased water content of the electrolyte promoted the incorporation of phosphorus species into the films, although chemical dissolution reduced the amounts of phosphorus in the outer regions. Carbon species also appeared to be present in films, particularly at lower water content. Using a niobium oxide outer layer to suppress chemical dissolution resulted in films that were about 1.2 times the thickness of the consumed aluminium for an electrolyte containing 0.25 mass% water. The expansion suggests a possible contribution of field-assisted flow of film material in the growth of the porous anodic film.     

Interaction of water with self-assembled monolayers of alkylsilanes on mica

The interaction of water with self-assembled alkylsilane monolayers on mica substrates has been studied using an atomic force microscope operated in contact, noncontact, and electrical polarization modes. Complete monolayer films were found to be effective in blocking water adsorption. On partially covered surfaces water was found to produce large changes in the conductivity and surface potential of the exposed mica regions. It was also found that water could penetrate films near defects and at island edges.     

High-throughput screening for combinatorial thin-film library of thermoelectric materials

A high-throughput method has been developed to evaluate the Seebeck coefficient and electrical resistivity of combinatorial thin-film libraries of thermoelectric materials from room temperature to 673 K. Thin-film samples several millimeters in size were deposited on an integrated Al2O3 substrate with embedded lead wires and local heaters for measurement of the thermopower under a controlled temperature gradient. An infrared camera was used for real-time observation of the temperature difference Delta T between two electrical contacts on the sample to obtain the Seebeck coefficient. The Seebeck coefficient and electrical resistivity of constantan thin films were shown to be almost identical to standard data for bulk constantan. High-throughput screening was demonstrated for a thermoelectric Mg-Si-Ge combinatorial library.     

Effect of Fluorine Doping on Semiconductor to Metal-Like Transition and Optical Properties of Cadmium Oxide Thin Films Deposited by Sol–Gel Process

Highly conducting fluorine doped n-type cadmium oxide thin films have been synthesized by sol–gel dip coating process on glass and Si substrates for various fluorine concentrations in the films. X-ray diffraction pattern confirmed the cubic CdO phase formation and SEM micrograph showed fine particles of CdO with size ~0.3 m. F concentration in the films was varied from 1.8% to 18.7% as determined from energy dispersive X-ray analysis (EDX). The resistivity of the CdO films decreased with increase of F doping and increase of temperature below 14.6% of F, as usual for semiconductors. Above this F concentration the resistivity increased with increase of temperature like metals. Hall measurement showed very high carrier concentrations in the films lying in the range of ~2.93 × 10²⁰ cm^–3 to 4.56 × 10²¹ cm^–3. UV-VIS-NIR spectrum of the films showed the optical bandgap energy increased with increase of F doping and corresponding carrier concentrations obtained from Burstein-Moss shift also support the Hall measurement results.     

Interactions in water-alcohol mixtures: Conductance of lithium picrate in solutions of water and isomeric pentanols at 25°C

Conductance measurements of lithium picrate in solutions of water in n-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol and 3-methyl-1-butanol have been carried out at 25°C. Ionic association and conductance were found to change with water content and with the molecular structure of the alcohols (i.e. position of the OH group and degree of branching of the alkyl chain). These results indicate that both conductance and ion pair formation are not the consequence of the simple motion of ions in the electrical field as required by the continuum model. A more realistic approach, involving the internal structure of the solvent mixtures, has been considered.