Showing papers on "Thin film published in 2003"

Epitaxial BiFeO3 multiferroic thin film heterostructures.

Abstract: Enhancement of polarization and related properties in heteroepitaxially constrained thin films of the ferroelectromagnet, BiFeO3, is reported. Structure analysis indicates that the crystal structure of film is monoclinic in contrast to bulk, which is rhombohedral. The films display a room-temperature spontaneous polarization (50 to 60 microcoulombs per square centimeter) almost an order of magnitude higher than that of the bulk (6.1 microcoulombs per square centimeter). The observed enhancement is corroborated by first-principles calculations and found to originate from a high sensitivity of the polarization to small changes in lattice parameters. The films also exhibit enhanced thickness-dependent magnetism compared with the bulk. These enhanced and combined functional responses in thin film form present an opportunity to create and implement thin film devices that actively couple the magnetic and ferroelectric order parameters.

Small molecular weight organic thin-film photodetectors and solar cells

Abstract: In this review, we discuss the physics underlying the operation of single and multiple heterojunction, vacuum-deposited organic solar cells based on small molecular weight thin films. For single heterojunction cells, we find that the need for direct contact between the deposited electrode and the active organics leads to quenching of excitons. An improved device architecture, the double heterojunction, is shown to confine excitons within the active layers, allowing substantially higher internal efficiencies to be achieved. A full optical and electrical analysis of the double heterostructure architecture leads to optimal cell design as a function of the optical properties and exciton diffusion lengths of the photoactive materials. Combining the double heterostructure with novel light trapping schemes, devices with external efficiencies approaching their internal efficiency are obtained. When applied to an organic photovoltaic cell with a power conversion efficiency of 1.0%±0.1% under 1 sun AM1.5 illuminati...

Growth of Arrayed Nanorods and Nanowires of ZnO from Aqueous Solutions

Abstract: A novel approach to the rational fabrication of smart and functional metal oxide particulate thin films and coatings is demonstrated on the growth of ZnO nanowires and oriented nanorod arrays The synthesis involves a template-less and surfactant-free aqueous method, which enables the generation of, at large-scale, low-cost, and moderate temperatures, advanced metal oxide thin films with controlled complexity The strategy consists of monitoring of the nucleation, growth, and aging processes by means of chemical and electrostatic control of the interfacial free energy It enables the control of the size of nano-, meso-, and microcrystallites, their surface morphology, orientations onto various substrates, and crystal structure

Efficient bulk heterojunction photovoltaic cells using small-molecular-weight organic thin films

Abstract: The power conversion efficiency of small-molecular-weight and polymer organic photovoltaic cells has increased steadily over the past decade This progress is chiefly attributable to the introduction of the donor–acceptor heterojunction1,2 that functions as a dissociation site for the strongly bound photogenerated excitons Further progress was realized in polymer devices through use of blends of the donor and acceptor materials3,4,5: phase separation during spin-coating leads to a bulk heterojunction that removes the exciton diffusion bottleneck by creating an interpenetrating network of the donor and acceptor materials The realization of bulk heterojunctions using mixtures of vacuum-deposited small-molecular-weight materials has, on the other hand, posed elusive: phase separation induced by elevating the substrate temperature inevitably leads to a significant roughening of the film surface and to short-circuited devices Here, we demonstrate that the use of a metal cap to confine the organic materials during annealing prevents the formation of a rough surface morphology while allowing for the formation of an interpenetrating donor–acceptor network This method results in a power conversion efficiency 50 per cent higher than the best values reported for comparable bilayer devices, suggesting that this strained annealing process could allow for the formation of low-cost and high-efficiency thin film organic solar cells based on vacuum-deposited small-molecular-weight organic materials

The Effect of Calcination Temperature on the Surface Microstructure and Photocatalytic Activity of TiO2 Thin Films Prepared by Liquid Phase Deposition

Abstract: TiO2 thin films were prepared on fused quartz by the liquid-phase deposition (LPD) method from a (NH4)2TiF6 aqueous solution upon addition of boric acid (H3BO3) and calcined at various temperatures. The as-prepared films were characterized with thermogravimetry (TG), Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD), UV−Visible spectrophotometry (UV−Vis), scanning electron microscopy (SEM), photoluminescence spectra (PL), and X-ray photoelectron spectroscopy (XPS), respectively. The photocatalytic activity of the samples was evaluated by photocatalytic decolorization of methyl orange aqueous solution. It was found that the as-prepared TiO2 thin films contained not only Ti and O elements, but also a small amount of F, N, and Si elements. The F and N came from the precursor solution, and the amount of F decreased with increasing calcination temperature. Two sources of Si were identified. One was from the SiF62- ions, which were formed by a reaction between the treatment solution and quartz ...

LnCuO(S,Se,Te)monocrystalline thin film, its manufacturing method, and optical device or electronic device using the monocrystalline thin film

Abstract: Disclosed is a method of producing an LnCuOX single-crystal thin film (wherein Ln is at least one selected from the group consisting of lanthanide elements and yttrium, and X is at least one selected from the group consisting of S, Se and Te), which comprises the steps of growing a base thin film on a single-crystal substrate, depositing an amorphous or polycrystalline LnCuOX thin film on the base thin film to form a laminated film, and then annealing the laminated film at a high temperature of 500° C. or more. While a conventional LnCuOX film produced by growing an amorphous film through a sputtering process under appropriate conditions and then annealing the film at a high temperature was unexceptionally a polycrystalline substance incapable of achieving high emission efficiency and electron mobility required for a material of light-emitting devices or electronic devices, the method of the present invention can grow a thin film with excellent crystallinity suitable as a single crystal to an building black of light-emitting diodes, semiconductor leasers, filed-effect transistors, or a hetero-bipolar transistors.

Semiconductor device in which zinc oxide is used as a semiconductor material and method for manufacturing the semiconductor device

Abstract: A semiconductor device having excellent crystallinity and excellent electric characteristics includes a ZnO thin film having excellent surface smoothness. ZnO-based thin films (an n-type contact layer, an n-type clad layer, an active layer, a p-type clad layer, and a p-type contact layer) primarily including ZnO are formed sequentially by an ECR sputtering method or other suitable method on a zinc-polar surface of a ZnO substrate. A transparent electrode and a p-side electrode are formed by an evaporation method or other suitable method on a surface of the p-type contact layer, and an n-side electrode is formed on an oxygen-polar surface of the ZnO substrate.

Wide band gap ferromagnetic semiconductors and oxides

Abstract: Recent advances in the theory and experimental realization of ferromagnetic semiconductors give hope that a new generation of microelectronic devices based on the spin degree of freedom of the electron can be developed. This review focuses primarily on promising candidate materials (such as GaN, GaP and ZnO) in which there is already a technology base and a fairly good understanding of the basic electrical and optical properties. The introduction of Mn into these and other materials under the right conditions is found to produce ferromagnetism near or above room temperature. There are a number of other potential dopant ions that could be employed (such as Fe, Ni, Co, Cr) as suggested by theory [see, for example, Sato and Katayama-Yoshida, Jpn. J. Appl. Phys., Part 2 39, L555 (2000)]. Growth of these ferromagnetic materials by thin film techniques, such as molecular beam epitaxy or pulsed laser deposition, provides excellent control of the dopant concentration and the ability to grow single-phase layers. T...

Atomic Layer Deposition Chemistry: Recent Developments and Future Challenges†

Abstract: New materials, namely high-k (high-permittivity) dielectrics to replace SiO2, Cu to replace Al, and barrier materials for Cu, are revolutionizing modern integrated circuits. These materials must be deposited as very thin films on structured surfaces. The self-limiting growth mechanism characteristic to atomic layer deposition (ALD) facilitates the control of film thickness at the atomic level and allows deposition on large and complex surfaces. These features make ALD a very promising technique for future integrated circuits. Recent ALD research has mainly focused on materials required in microelectronics. Chemistry, in particular the selection of suitable precursor combinations, is the key issue in ALD; many interesting results have been obtained by smart chemistry. ALD is also likely to find applications in other areas, such as magnetic recording heads, optics, demanding protective coatings, and micro-electromechanical systems, provided that cost-effective processes can be found for the materials required.

Microstructural optimization of a zeolite membrane for organic vapor separation.

Abstract: A seeded growth method for the fabrication of high-permeance, high-separation-factor zeolite (siliceous ZSM-5, [Si 96 O 192 ]-MFI) membranes is reported. The method consists of growing the crystals of an oriented seed layer to a well-intergrown film by avoiding events that lead to a loss of preferred orientation, such as twin overgrowths and random nucleation. Organic polycations are used as zeolite crystal shape modifiers to enhance relative growth rates along the desirable out-of-plane direction. The polycrystalline films are thin (∼1 micrometer) with single grains extending along the film thickness and with large in-plane grain size (∼1 micrometer). The preferred orientation is such that straight channels with an open diameter of ∼5.5 angstroms run down the membrane thickness. Comparison with previously reported membranes shows that these microstructurally optimized films have superior performance for the separation of organic mixtures with components that have small differences in size and shape, such as xylene isomers.

Pentacene thin film transistors on inorganic dielectrics: Morphology, structural properties, and electronic transport

Abstract: The structural and transport properties of evaporated pentacene organic thin film transistors (TFTs) are reported, and they show the influence of the deposition conditions with different inorganic dielectrics. Dielectrics compatible with large area fabrication were explored to facilitate low cost electronics on glass or flexible plastic substrates. X-ray diffraction and atomic force microscopy show a clear correlation between the morphology and the structure of the highly polycrystalline films for all dielectrics investigated. The roughness of the dielectric has a distinct influence on the morphology and the structural properties, whereas the films on smooth thermal oxide are in general highly ordered and independent of the deposition conditions. The ordered films exhibit a “thin film” and a bulk phase, and the bulk phase volume fraction increases with the deposition temperature and the film thickness. Careful control of the deposition conditions gives virtually identical films on thermal oxide and silico...

Highly Reversible Lithium Storage in Nanostructured Silicon

Abstract: Anode materials of nanostructured silicon have been prepared by physical vapor deposition and characterized using electrochemical methods. The electrodes were prepared in thin-film form as nanocrystalline particles (12 nm mean diameter) and as continuous amorphous thin films (100 nm thick). The nanocrystalline silicon exhibited specific capacities of around 1100 mAh/g with a 50% capacity retention after 50 cycles. The amorphous thin-film electrodes exhibited initial capacities of 3500 mAh/g with a stable capacity of 2000 mAh/g over 50 cycles. We suggest that the nanoscale dimensions of the silicon circumvents conventional mechanisms of mechanical deterioration, permitting good cycle life.

Atomic layer deposition of transition metals

Abstract: Atomic layer deposition (ALD) is a process for depositing highly uniform and conformal thin films by alternating exposures of a surface to vapours of two chemical reactants. ALD processes have been successfully demonstrated for many metal compounds, but for only very few pure metals. Here we demonstrate processes for the ALD of transition metals including copper, cobalt, iron and nickel. Homoleptic N,N'-dialkylacetamidinato metal compounds and molecular hydrogen gas were used as the reactants. Their surface reactions were found to be complementary and self-limiting, thus providing highly uniform thicknesses and conformal coating of long, narrow holes. We propose that these ALD layers grow by a hydrogenation mechanism that should also operate during the ALD of many other metals. The use of water vapour in place of hydrogen gas gives highly uniform, conformal films of metal oxides, including lanthanum oxide. These processes should permit the improved production of many devices for which the ALD process has previously not been applicable.

Photoelectrochemical and Optical Properties of Nitrogen Doped Titanium Dioxide Films Prepared by Reactive DC Magnetron Sputtering

Abstract: Nanocrystalline porous nitrogen doped titanium dioxide (TiO2) thin films were prepared by DC magnetron sputtering. Films were deposited in a plasma of argon, oxygen, and nitrogen, with varying nitrogen contents. The films were characterized by X-ray diffraction, scanning electron microscopy, and optical- and photoelectrochemical (PEC) measurements. These studies showed that the films were porous and displaying rough surfaces with sharp, protruding nodules having a crystal structure varying from rutile to anatase depending on the nitrogen content. All nitrogen doped films showed visible light absorption in the wavelength range from 400 to 535 nm. The PEC properties of the thin film electrodes were determined on as-deposited as well as dye-sensitized films. The nitrogen doped TiO2 generated an incident photon-to-current efficiency response in good agreement with the optical spectra. The PEC measurements on dye-sensitized films showed that the electron-transfer properties in the conduction band were similar ...

Realization of p-type ZnO thin films via phosphorus doping and thermal activation of the dopant

Abstract: A p-type ZnO was prepared on a sapphire substrate using P2O5 as a phosphorus dopant. As-grown n-type ZnO films doped with phosphorus showed electron concentrations of 1016–1017/cm3 and these films were converted to p-type ZnO by a thermal annealing process at a temperature above 800 °C under a N2 ambient. The electrical properties of the p-type ZnO showed a hole concentration of 1.0×1017–1.7×1019/cm3, a mobility of 0.53–3.51 cm2/V s, and a low resistivity of 0.59–4.4 Ω cm. The phosphorus-doped ZnO thin films showed a strong photoluminescence peak at 3.35 eV at 10 K, which is closely related to neutral acceptor bound excitons of the p-type ZnO. This thermal activation process was very reproducible and effective in producing phosphorus-doped p-type ZnO thin films, and the produced p-type ZnO was very stable.

High electron mobility of epitaxial ZnO thin films on c-plane sapphire grown by multistep pulsed-laser deposition

Abstract: A multistep pulsed-laser deposition (PLD) process is presented for epitaxial, nominally undoped ZnO thin films of total thickness of 1 to 2 μm on c-plane sapphire substrates. We obtain reproducibly high electron mobilities from 115 up to 155 cm2/V s at 300 K in a narrow carrier concentration range from 2 to 5×1016 cm−3. The key issue of the multistep PLD process is the insertion of 30-nm-thin ZnO relaxation layers deposited at reduced substrate temperature. The high-mobility samples show atomically flat surface structure with grain size of about 0.5–1 μm, whereas the surfaces of low-mobility films consist of clearly resolved hexagonally faceted columnar grains of only 200-nm size, as shown by atomic force microscopy. Structurally optimized PLD ZnO thin films show narrow high-resolution x-ray diffraction peak widths of the ZnO(0002) ω- and 2Θ-scans as low as 151 and 43 arcsec, respectively, and narrow photoluminescence linewidths of donor-bound excitons of 1.7 meV at 2 K.

Conformal Coating on Ultrahigh-Aspect-Ratio Nanopores of Anodic Alumina by Atomic Layer Deposition

Abstract: Anodic alumina (AA) membranes are composed of highly uniform, nanometer-scale pores arranged in a hexagonal close-packed array. Depositing conformal films inside the nanopores is extremely difficult because the nanopores have an ultrahigh aspect ratio of L/d ≈ 103. Atomic layer deposition (ALD) is a thin film growth technique that can deposit highly uniform films on high-aspect-ratio substrates with monolayer thickness control. In this study, AA membranes were coated with Al2O3 and ZnO ALD films and subsequently analyzed using cross-sectional scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). SEM analysis of individual nanopores revealed that the AA membranes with nanopore diameters of d = 65 nm and lengths of L = 50 μm could be coated conformally by Al2O3 ALD using sufficient reactant exposure times. Zn concentration profiles measured by EPMA following ZnO ALD showed the progressive infiltration of the ZnO ALD into the nanopores with increasing exposure times for aspect ratios as...

Large-area nanoenabled macroelectronic substrates and uses therefor

Abstract: A method and apparatus for an electronic substrate having a plurality of semiconductor devices is described. A thin film of nanowires is formed on a substrate. The thin film of nanowires is formed to have a sufficient density of nanowires to achieve an operational current level. A plurality of semiconductor regions are defined in the thin film of nanowires. Contacts are formed at the semiconductor device regions to thereby provide electrical connectivity to the plurality of semiconductor devices. Furthermore, various materials for fabricating nanowires, thin films including p-doped nanowires and n-doped nanowires, nanowire heterostructures, light emitting nanowire heterostructures, flow masks for positioning nanowires on substrates, nanowire spraying techniques for depositing nanowires, techniques for reducing or eliminating phonon scattering of electrons in nanowires, and techniques for reducing surface states in nanowires are described.

Atomic layer deposition of metal and nitride thin films: Current research efforts and applications for semiconductor device processing

Abstract: Atomic layer deposition (ALD) has been studied for several decades now, but the interest in ALD of metal and nitride thin films has increased only recently, driven by the need for highly conformal nanoscale thin films in modern semiconductor device manufacturing technology. ALD is a very promising deposition technique with the ability to produce thin films with excellent conformality and compositional control with atomic scale dimensions. However, the applications of metals and nitrides ALD in semiconductor device processes require a deeper understanding about the underlying deposition process as well as the physical and electrical properties of the deposited films. This article reviews the current research efforts in ALD for metal and nitride films as well as their applications in modern semiconductor device fabrication.

Self-organized nanostructures in the Ti–Al–N system

Abstract: The phenomenon of age hardening could be evidenced in thin film applications. A model system, Ti1-xAlxN was chosen as such coatings are known for their excellent wear resistance enabling improved m ...

Sensors for sub-ppm NO2 gas detection based on carbon nanotube thin films

Abstract: Carbon nanotubes (CNTs) deposited by plasma-enhanced chemical vapor deposition on Si3N4/Si substrates have been investigated as resistive gas sensors for NO2. Upon exposure to NO2, the electrical resistance of the CNTs was found to decrease. The maximum variation of resistance to NO2 was found at an operating temperature of around 165 °C. The sensor exhibited high sensitivity to NO2 gas at concentrations as low as 10 ppb, fast response time, and good selectivity. A thermal treatment method, based on repeated heating and cooling of the films, adjusted the resistance of the sensor film and optimized the sensor response to NO2.

Domain epitaxy: A unified paradigm for thin film growth

Abstract: We present a unified model for thin film epitaxy where single crystal films with small and large lattice misfits are grown by domain matching epitaxy (DME). The DME involves matching of lattice planes between the film and the substrate having similar crystal symmetry. In this framework, the conventional lattice matching epitaxy becomes a special case where a matching of lattice constants or the same planes is involved with a small misfit of less than 7%–8%. In large lattice mismatch systems, we show that epitaxial growth of thin films is possible by matching of domains where integral multiples of major lattice planes match across the interface. We illustrate this concept with atomic-level details in the TiN/Si(100) with 3/4 matching, the AlN/Si(100)with 4/5 matching, and the ZnO/α−Al2O3(0001) with 6/7 matching of major planes across the film/substrate interface. By varying the domain size, which is equal to intregral multiple of lattice planes, in a periodic fashion, it is possible to accommodate addition...

Dynamics of ferroelastic domains in ferroelectric thin films.

Abstract: Dynamics of domain interfaces in a broad range of functional thin-film materials is an area of great current interest. In ferroelectric thin films, a significantly enhanced piezoelectric response should be observed if non-180° domain walls were to switch under electric field excitation. However, in continuous thin films they are clamped by the substrate, and therefore their contribution to the piezoelectric response is limited. In this paper we show that when the ferroelectric layer is patterned into discrete islands using a focused ion beam, the clamping effect is significantly reduced, thereby facilitating the movement of ferroelastic walls. Piezo-response scanning force microscopy images of such islands in PbZr0.2Ti0.8O3 thin films clearly point out that the 90° domain walls can move. Capacitors 1 μm2 show a doubling of the remanent polarization at voltages higher than ∼15 V, associated with 90° domain switching, coupled with a d33 piezoelectric coefficient of ∼250 pm V−1 at remanence, which is approximately three times the predicted value of 87 pm V−1 for a single domain single crystal.

High Capacity, Reversible Silicon Thin-Film Anodes for Lithium-Ion Batteries

Abstract: The properties of amorphous 250 nm and 1 μm silicon films deposited by radio-frequency (rf) magnetron sputtering on copper foil are investigated using X-ray diffractιon, scanning electron microscopy (SEM), and electrochemical methods. Galvanostatic half-cell electrochemical measurements conducted between 0.02 and 1.2 V using a lithium counter electrode have shown that the 250 nm Si thin films exhibit an excellent reversible specific capacity of nearly 3500 mAh/g when tested for 30 cycles. The high reversible capacity and excellent cyclability of the 250 nm sputtered silicon thin films suggest excellent adhesion between Si and Cu leading to high capacity retention. SEM analysis conducted on the 250 nm Si films after the 30th charge suggests the good adhesion of the ∼2 μm diam "plates" of silicon to the copper substrate.