Showing papers on "Thin film published in 1999"

"Dip-Pen" Nanolithography

Abstract: A direct-write “dip-pen” nanolithography (DPN) has been developed to deliver collections of molecules in a positive printing mode. An atomic force microscope (AFM) tip is used to write alkanethiols with 30-nanometer linewidth resolution on a gold thin film in a manner analogous to that of a dip pen. Molecules are delivered from the AFM tip to a solid substrate of interest via capillary transport, making DPN a potentially useful tool for creating and functionalizing nanoscale devices.

Organic-inorganic hybrid materials as semiconducting channels in thin-film field-effect transistors

Abstract: Organic-inorganic hybrid materials promise both the superior carrier mobility of inorganic semiconductors and the processability of organic materials A thin-film field-effect transistor having an organic-inorganic hybrid material as the semiconducting channel was demonstrated Hybrids based on the perovskite structure crystallize from solution to form oriented molecular-scale composites of alternating organic and inorganic sheets Spin-coated thin films of the semiconducting perovskite (C(6)H(5)C(2)H(4)NH(3))(2)SnI(4) form the conducting channel, with field-effect mobilities of 06 square centimeters per volt-second and current modulation greater than 10(4) Molecular engineering of the organic and inorganic components of the hybrids is expected to further improve device performance for low-cost thin-film transistors

Modeling photocurrent action spectra of photovoltaic devices based on organic thin films

Abstract: We have modeled experimental short-circuit photocurrent action spectra of poly(3-(4′-(1″,4″,7″-trioxaoctyl)phenyl)thiophene) (PEOPT)/fullerene (C60) thin film heterojunction photovoltaic devices. Modeling was based on the assumption that the photocurrent generation process is the result of the creation and diffusion of photogenerated species (excitons), which are dissociated by charge transfer at the PEOPT/C60 interface. The internal optical electric field distribution inside the devices was calculated with the use of complex indices of refraction and layer thickness of the materials as determined by spectroscopic ellipsometry. Contributions to the photocurrent from optical absorption in polymer and fullerene layers were both necessary to model the experimental photocurrent action spectra. We obtained values for the exciton diffusion range of 4.7 and 7.7 nm for PEOPT and C60, respectively. The calculated internal optical electric field distribution and resulting photocurrent action spectra were used in or...

Electrical, optical, and structural properties of indium–tin–oxide thin films for organic light-emitting devices

Abstract: High-quality indium–tin–oxide (ITO) thin films (200–850 nm) have been grown by pulsed laser deposition (PLD) on glass substrates without a postdeposition annealing treatment. The structural, electrical, and optical properties of these films have been investigated as a function of target composition, substrate deposition temperature, background gas pressure, and film thickness. Films were deposited from various target compositions ranging from 0 to 15 wt % of SnO2 content. The optimum target composition for high conductivity was 5 wt % SnO2+95 wt % In2O3. Films were deposited at substrate temperatures ranging from room temperature to 300 °C in O2 partial pressures ranging from 1 to 100 mTorr. Films were deposited using a KrF excimer laser (248 nm, 30 ns full width at half maximum) at a fluence of 2 J/cm2. For a 150-nm-thick ITO film grown at room temperature in an oxygen pressure of 10 mTorr, the resistivity was 4×10−4 Ω cm and the average transmission in the visible range (400–700 nm) was 85%. For a 170-n...

Silver-based crystalline nanoparticles, microbially fabricated

Abstract: One mechanism of silver resistance in microorganisms is accumulation of the metal ions in the cell. Here, we report on the phenomenon of biosynthesis of silver-based single crystals with well-defined compositions and shapes, such as equilateral triangles and hexagons, in Pseudomonas stutzeri AG259. The crystals were up to 200 nm in size and were often located at the cell poles. Transmission electron microscopy, quantitative energy-dispersive x-ray analysis, and electron diffraction established that the crystals comprise at least three different types, found both in whole cells and thin sections. These Ag-containing crystals are embedded in the organic matrix of the bacteria. Their possible potential as organic-metal composites in thin film and surface coating technology is discussed.

Oxide thin film

Abstract: An object of the invention is to provide an oxide thin film which exhibits a widegap or transparency and p-type conductivity although it has heretofore been very difficult to form. The oxide thin film formed on a substrate contains copper oxide and strontium oxide as a main component and exhibits p-type conductivity at a bandgap of at least 2 eV.

Excitonic singlet-triplet ratio in a semiconducting organic thin film

Abstract: A technique is presented to determine the spin statistics of excitons formed by electrical injection in a semiconducting organic thin film. With the aid of selective addition of luminescent dyes, we generate either fluorescence or phosphorescence from the archetype organic host material aluminum tris (8-hydroxyquinoline) $({\mathrm{Alq}}_{3}).$ Spin statistics are calculated from the ratio of fluorescence to phosphorescence in the films under electrical excitation. After accounting for varying photoluminescent efficiencies, we find a singlet fraction of excitons in ${\mathrm{Alq}}_{3}$ of $(22\ifmmode\pm\else\textpm\fi{}3)%.$

Crystallite coalescence: A mechanism for intrinsic tensile stresses in thin films

Abstract: We examined the stress associated with crystallite coalescence during the initial stages of growth in thin polycrystalline films with island growth morphology. As growing crystallites contacted each other at their bases, the side-walls zipped together until a balance was reached between the energy associated with eliminating surface area, creating a grain boundary and straining the film. Our estimate for the resulting strain depends only on interfacial free energies, elastic properties, and grain size and predicts large tensile stresses in agreement with experimental results. We also discuss possible stress relaxation mechanisms that can occur during film growth subsequent to the coalescence event.

Optical properties of epitaxially grown zinc oxide films on sapphire by pulsed laser deposition

Abstract: ZnO thin films were epitaxially grown on c-sapphire substrates by pulsed laser deposition at substrate temperatures of 500–800 °C. The crystal structure of ZnO films follow the epitaxial relationship of (0001)ZnO∥(0001)Al2O3(1010)ZnO∥(1120)Al2O3. Both room temperature and cryogenic temperature photoluminescence showed a remarkable band-edge transition, and clear excitonic structures could be seen at cryogenic temperature. The optical refractive index was measured in the range of 375–900 nm by varying angle spectroscopic ellipsometry. The simulation was carried out using a Sellmeier equation.

p-Type Electrical Conduction in ZnO Thin Films by Ga and N Codoping.

Abstract: We report the realization of p-type behavior in ZnO thin films, which are prepared by codoping method using Ga (donor) and N (acceptor) as the dopants. Especially, using active N formed by passing N2O gas through an electron cyclotron resonance (ECR) plasma source is quite effective for the acceptor doping. We have observed a room temperature resistivity of 2 Ωcm and a hole concentration of 4×1019 cm-3. These values are enough high for practical applications in various oxide electronic devices.

Photoluminescence and ultraviolet lasing of polycrystalline ZnO thin films prepared by the oxidation of the metallic Zn

Abstract: We report a simple method for preparing polycrystalline ZnO thin films with good luminescent properties: the oxidization of metallic Zn films. In photoluminescence (PL) studies at room temperature for wavelengths between 370 and 675 nm, we have observed a single exciton peak around 390 nm without any deep-level emission and a small PL full width at half maximum (23 meV), indicating that the concentrations of the defects responsible for the deep-level emissions are negligible. We have also observed optically pumped lasing action in these films. The threshold intensity for lasing was ∼9 MW/cm2.

ZnO quantum particle thin films fabricated by electrophoretic deposition

Abstract: Thin films of quantum size ZnO particles were fabricated by electrophoretic deposition from stable colloidal suspensions. The average particle size and hence the optical properties can be tailored by controlling the aging time and temperature of the suspensions. Thin films prepared by electrophoretic deposition exhibit optical properties characteristic of the quantum size particles. Both the band-to-band and visible photoluminescence were progressively blue shifted with decreasing particle size in the film.

Large Magnetoresistance of Electrodeposited Single-Crystal Bismuth Thin Films

Abstract: Single-crystal bismuth thin films 1 to 20 micrometers thick were fabricated by electrodeposition and suitable annealing. Magnetoresistance up to 250 percent at 300 kelvin and 380,000 percent at 5 kelvin as well as clean Shubnikov-de Haas oscillations were observed, indicative of the high quality of these films. A hybrid structure was also made that showed a large magnetoresistive effect of 30 percent at 200 oersted and a field sensitivity of 0.2 percent magnetoresistance per oersted at room temperature.

Role of nitrogen in the formation of hard and elastic CN x thin films by reactive magnetron sputtering

Abstract: Carbon nitride films, deposited by reactive dc magnetron sputtering in Ar/N2 discharges, were studied with respect to composition, structure, and mechanical properties. CNx films, with 0

Growth of a Single Freestanding Multiwall Carbon Nanotube on each Nanonickel Dot

Abstract: Patterned growth of freestanding carbon nanotube(s) on submicron nickel dot(s) on silicon has been achieved by plasma-enhanced-hot-filament-chemical-vapor deposition (PE-HF-CVD). A thin film nickel grid was fabricated on a silicon wafer by standard microlithographic techniques, and the PE-HF-CVD was done using acetylene (C2H2) gas as the carbon source and ammonia (NH3) as a catalyst and dilution gas. Well separated, single carbon nanotubes were observed to grow on the grid. The structures had rounded base diameters of approximately 150 nm, heights ranging from 0.1 to 5 μm, and sharp pointed tips. Transmission electron microscopy cross-sectional image clearly showed that the structures are indeed hollow nanotubes. The diameter and height depend on the nickel dot size and growth time, respectively. This nanotube growth process is compatible with silicon integrated circuit processing. Using this method, devices requiring freestanding vertical carbon nanotube(s) such as scanning probe microscopy, field emissi...

The correlation between mechanical stress and magnetic anisotropy in ultrathin films

Abstract: The impact of stress-driven structural transitions and of film strain on the magnetic properties of nm ferromagnetic films is discussed. The stress-induced bending of film-substrate composites is analysed to derive information on film stress due to lattice mismatch or due to surface-stress effects. The magneto-elastic coupling in epitaxial films is determined directly from the magnetostrictive bending of the substrate. The combination of stress measurements with magnetic investigations by the magneto-optical Kerr effect (MOKE) reveals the modification of the magnetic anisotropy by film stress. Stress-strain relations are derived for various epitaxial orientations to facilitate the analysis of the substrate curvature. Biaxial film stress and magneto-elastic coupling coefficients are measured in epitaxial Fe films in situ on W single-crystal substrates. Tremendous film stress of more than 10 GPa is measured in pseudomorphic Fe layers, and the important role of film stress as a driving force for the formation of misfit distortions and for inducing changes of the growth mode in monolayer thin films is presented. The direct measurement of the magneto-elastic coupling in epitaxial films proves that the magnitude and sign of the magneto-elastic coupling deviate from the respective bulk value. Even a small film strain of order 0.1% is found to induce a significant change of the effective magneto-elastic coupling coefficient. This peculiar behaviour is ascribed to a second-order strain dependence of the magneto-elastic energy density, in contrast to the linear strain dependence that is valid for bulk samples.

Organic el element

Abstract: PROBLEM TO BE SOLVED: To provide an organic EL element (electro luminescence) having a structure suitable for fine pattern SOLUTION: An organic resist film 62 is formed on a surface of a glass substrate 60 formed with a transparent wiring film 61 by vacuum evaporation method, the exposure and development by heating by ultraviolet rays are performed to form a resist pattern 63, and then the EL thin films 65A, 65B and the metal wiring films 66A, 66B are formed A width of a surface of the resist pattern 63 is larger than a width of a bottom face, so that the metal vapour does not deposited to the side faces, whereby the metal wiring films 66A, 66B are separated and insulated from each other Since the development and removal of the resist film with the organic solvent and plasma are unnecessary, the transparent wiring film 61 and the EL thin films 65A, 65B will not deteriorate, and an organic EL element 3 of good characteristics can be obtained

Properties of aluminum nitride thin films for piezoelectric transducers and microwave filter applications

Abstract: Aluminum nitride thin films have been grown by reactive magnetron sputter technique using a pulsed power supply. The highly (002)-textured columnar films deposited on platinized silicon substrates exhibited quasi-single-crystal piezoelectric properties. The effective d33 was measured as 3.4 pm/V, the effective e31 as 1.0 C/m2. The pyroelectric coefficient turned out to be positive (4.8 μC m−2 K−1) due to a dominating piezoelectric contribution. Thin-film bulk acoustic resonators (TFBAR) with fundamental resonance at 3.6 GHz have been fabricated to assess resonator properties. The material parameters derived from the thickness resonance were a coupling factor k=0.23 and a sound velocity vs=11 400 m/s. With a quality factor Q of 300, the TFBARs proved to be apt for filter applications. The temperature coefficient of the frequency could be tuned to practically 0 ppm/K.

Long‐Range Electron Transfer through DNA Films

Abstract: Regardless of its position within the DNA film, cross-linked daunomycin (DM) is efficiently reduced electrochemically, indicating that the electron transfer exhibits a shallow distance dependence. Upon the introduction of an intervening cytosine-adenine (CA) mismatch, the electrochemical response is dramatically attenuated (shown schematically). Therefore, the DNA double helix can facilitate long-range electron transfer, but only in the presence of a well-stacked pathway.