Showing papers on "Thin film published in 1987"

Preparation of Y‐Ba‐Cu oxide superconductor thin films using pulsed laser evaporation from high Tc bulk material

Abstract: We report the first successful preparation of thin films of Y‐Ba‐Cu‐O superconductors using pulsed excimer laser evaporation of a single bulk material target in vacuum. Rutherford backscattering spectrometry showed the composition of these films to be close to that of the bulk material. Growth rates were typically 0.1 nm per laser shot. After an annealing treatment in oxygen the films exhibited superconductivity with an onset at 95 K and zero resistance at 85 and 75 K on SrTiO3 and Al2O3 substrates, respectively. This new deposition method is relatively simple, very versatile, and does not require the use of ultrahigh vacuum techniques.

Characterization of diamondlike carbon films and their application as overcoats on thin‐film media for magnetic recording

Abstract: This paper reviews and analyzes the literature on thin carbon layers with emphasis on their use as protective overcoats for thin‐film magnetic media. We discuss carbon as a material, its preparation as a thin film, and review and evaluate various techniques for characterizing its thin‐film properties.

Interface roughness scattering in GaAs/AlAs quantum wells

Abstract: We study experimentally and theoretically the influence of interface roughness on the mobility of two‐dimensional electrons in modulation‐doped AlAs/GaAs quantum wells. It is shown that interface roughness scattering is the dominant scattering mechanism in thin quantum wells with a well thickness Lw<60 A, where electron mobilities are proportional to L6w, reaching 2×103 cm2/V s at Lw∼55 A. From detailed comparison between theory and experiment, it is determined that the ‘‘GaAs‐on‐AlAs’’ interface grown by molecular beam epitaxy has a roughness with the height of 3–5 A and a lateral size of 50–70 A.

Femtosecond electronic heat-transport dynamics in thin gold films.

Abstract: We have observed ultrafast heat transport in thin gold films under femtosecond laser irradiation. Time-of-flight (from-pump back-probe) measurements indicate that the heat transit time scales linearly with the sample thickness, and that heat transport is very rapid, occurring at a velocity close to the Fermi velocity of electrons in Au.

Time-resolved observation of electron-phonon relaxation in copper.

Abstract: Amplified 150--300-fs laser pulses are applied to monitor the thermal modulation of the transmissivity of thin copper films. Non- equilibrium electron-lattice temperatures are observed. The process of electron-phonon energy transfer was time resolved and was observed to be 1--4 ps increasing with the laser fluence.

Ion beam modification of insulators

Abstract: 1. Ion Ranges and Energy Deposition in Insulators (J.P. Biersack). 2. The Sputtering of Insulators (R. Kelly). 3. Characterization Techniques for Ion Bombarded Insulators (J.A. Borders). 4. Defect Creation in Ion Bombarded Inorganic Insulators (A. Perez, P. Thevenard). 5. Ion Beam Modification of Glasses (G.W. Arnold, P. Mazzoldi). 6. The Mechanical and Tribological Properties of Ion Implanted Ceramics (C.J. McHargue). 7. Synthesis of Dielectric Layers in Silicon by Ion Implantation (I.H. Wilson). 8. Ion Beam Effects in Organic Molecular Solids and Polymers (T. Venkatesan, L. Calcagno, B.S. Elman, G. Foti). 9. Condensed Gases (W.L. Brown). 10. Optoelectronic Materials (G. Gotz). 11. Ferromagnetic Garnets (P. Gerard). 12. Nuclear Waste Materials (Hj. Matzke). 13. Role of Defects on the Aqueous Dissolution of Ion-Bombarded Insulators (G. Della Mea, J.-C. Dran, J.-C. Petit). 14. Chemical Effects of Ion Bombardment (G.K. Wolf, K. Roessler). 15. Ion Beam Effects on Thin Film Adhesion (J.E.E. Baglin). 16. Astrophysical Implications of Ions Incident on Insulators (L.J. Lanzerotti, R.E. Johnson). Subject Index. Appendix: Tables of Ion Ranges in Insulators.

Reproducible technique for fabrication of thin films of high transition temperature superconductors

Abstract: We report on a new process to make films of Y1Ba2Cu3O7 using coevaporation of Y, Cu, and BaF2 on SrTiO3 substrates. The films have high transition temperatures (up to 91 K for a full resistive transition), high critical current densities (106 A/cm2 at 81 K), and a reduced sensitivity to fabrication and environmental conditions. Because of the lower reactivity of the films, we have been able to pattern them in both the pre‐annealed and post‐annealed states using conventional positive photoresist technology.

Low‐temperature growth of silicon dioxide films: A study of chemical bonding by ellipsometry and infrared spectroscopy

Abstract: This paper presents a spectroscopic study using the techniques of ellipsometry and infrared (IR) absorption spectroscopy of the chemical bonding in silicon dioxide (SiO2) films grown in dry oxygen ambients at temperatures between 550 and 1000 °C. We find that the index of refraction at 632.8 nm increases and the frequency of the dominant IR active bond‐stretching vibration at about 1075 cm−1 decreases as the growth temperature is decreased below 1000 °C. Comparing the properties of these films with suboxides (SiOx, x<2) grown by plasma‐enhanced chemical vapor deposition, and compacted bulk silica has lead us to conclude: (i) that films grown at temperatures at or below 1000 °C are homogeneous stoichiometric oxides (SiO2); and (ii) that the systematic and correlated variations in the index of refraction and the IR frequency result from increases in the film density with decreasing growth temperature. We present a microscopic model that accounts for (i) the increases in the density and the index of refracti...

An intrinsic stress scaling law for polycrystalline thin films prepared by ion beam sputtering

Abstract: The intrinsic stresses of Al, Ti, Fe, Ta, Mo, W, Ge, Si, AlN, TiN, and Si3N4 films prepared by ion beam sputtering were investigated at low Td/Tm values. The intrinsic stress is compressive and its origin is explained in terms of the ion peening model. Knock‐on linear cascade theory of forward sputtering is applied to derive a simple scaling law with the film’s physical properties. The results show that the stress is directly proportional to the elastic energy/mole, given by the quantity Q=EM/(1−ν)D, where E is Young’s modulus, M the atomic mass, D the density, and ν Poisson’s ratio. Stress data taken from the literature for a variety of materials deposited by low‐pressure magnetron sputtering, and rf and ion beam sputtering also fit the correlation with Q. Furthermore, the model predicts a square‐root dependence on the incident ion energy, suggesting that the stress is momentum rather than energy driven.

Quantum interference devices made from superconducting oxide thin films

Abstract: We have fabricated superconducting quantum interference devices (dc SQUID’s) from thin films of the superconducting oxide YBa2Cu3Oy. The devices were made by first lithographically patterning an ion implant mask containing a 40 by 40 μm loop and two 17‐μm‐wide weak links over a ∼1‐μm‐thick oxide film. Ion implantation was then used to destroy the superconductivity in the film surrounding the device without actually removing material, resulting in a completely planar structure for the SQUID’s. The SQUID’s were operated in the temperature range from 4.2 to 68 K. The superconducting flux quantum was measured to be h/2e in these materials.

Modeling of reactive sputtering of compound materials

Abstract: An experimentally verified useful new model for reactive sputtering is presented. By considering the total system (target erosion, gas injection, chamber wall deposition, reactive gas gettering at all surfaces, etc.) during deposition it is possible to evaluate quite simple relationships between processing parameters. We have expanded earlier treatments to include these phenomena. The model involves that gettering of the reactive gas takes place at the target and at the walls opposite to the target. Arguments are also presented for how the sputtered materials (elemental target atoms and the formed compound) contribute to the formation of the surface composition of the walls opposite to the sputtering electrode. The mass flow of the reactive gas has been chosen as the independent parameter in this presentation. Results for partial pressure and sputter rate are presented. The theoretical values are compared with experimental results from reactive sputtering of TiN. It is also pointed out that the calculated...

Properties of Fe single‐crystal films grown on (100)GaAs by molecular‐beam epitaxy

Abstract: Single‐crystal (100)Fe films 90–330 A thick have been grown on etch‐annealed (100)GaAs substrates by molecular‐beam‐epitaxy techniques. Ferromagnetic resonance data indicate that the two in‐plane 〈110〉 directions are inequivalent and, together with magnetometry data, show that the average film magnetization decreases as the thickness decreases. The inequivalence is attributed to the nature of the interface bonding at a (100) zinc‐blende surface. The decreased magnetization is attributed to the formation of Fe2As microclusters in the film due to As diffusion which is supported by Auger and electron diffraction studies. In general, the Fe films grown to date on etch‐annealed (100)GaAs substrates are significantly inferior to those grown on (110)GaAs.

Recrystallization of amorphized polycrystalline silicon films on SiO2: Temperature dependence of the crystallization parameters

Abstract: This paper presents a theoretical and experimental study of the recrystallization behavior of polycrystalline silicon films amorphized by self‐implantation. The crystallization behavior was found to be similar to the crystallization behavior of films deposited in the amorphous state, as reported in the literature; however, a transient time was observed, during which negligible crystallization occurs. The films were prepared by low‐pressure chemical vapor deposition onto thermally oxidized silicon wafers and amorphized by implantation of silicon ions. The transient time, nucleation rate, and characteristic crystallization time were determined from the crystalline fraction and density of grains in partially recrystallized samples for anneal temperatures from 580 to 640 °C. The growth velocity was calculated from the nucleation rate and crystallization time and is lower than values in the literature for films deposited in the amorphous state. The final grain size, as calculated from the crystallization param...

Largely Anisotropic Superconducting Critical Current in Epitaxially Grown Ba2YCu3O7-y Thin Film

Abstract: Ba2YCu3O7-y (BYCO) thin films have been epitaxially grown on SrTiO3 substrates by magnetron sputtering. The films exhibit zero resistance at 84 K, with a transition width of 6 K. The resistivity along the basal plane is one order of magnitude smaller than that along the c-axis, and the transport property is more metallic in the former direction. Furthermore, the critical current density is two order of magnitudes larger in the former direction than in the latter direction. These results strongly suggest a quasi-two-dimensional electronic structure in BYCO. The maximum critical current at the liquid nitrogen temperature has reached 1.8×106 A/cm2.

Thin film electrical devices with amorphous carbon electrodes and method of making same

Abstract: Thin film electrical structures, such as threshold switching devices and phase change memory cells, preferably utilizing electrically stable, relatively inert, conductive electrodes including a non-single-crystal deposited film of carbon material, are disclosed. The film of carbon material, which preferably is amorphous and substantially pure, is disposed adjacent to a layer of active material such as an amorphous semiconductor, and serves to prevent undesired degradation of the active material, especially when the device is carrying appreciable current in its on-state. A method of making such structures with high quality interfaces between the semiconductor layer and the conductive carbon barrier layers adjacent thereto by successively depositing such layers in a continuously maintained partial vacuum is disclosed. The method may include a step performed in the vacuum for hermetically sealing all of, or at least the electrically switchable portion of, the active layer against subsequent contamination. Thin film structures suitable for threshold switching or memory applciations and employing insulating pores having substantially sloped side walls are also disclosed.

Growth of diamond thin films by dc plasma chemical vapor deposition

Abstract: Diamond thin films have been formed by dc plasma chemical vapor deposition with a high growth rate (∼20 μm/h). The diamond has been grown from methane (CH4) and hydrogen (H2) mixed gases on Si and α‐Al2O3 substrates at a pressure of 200 Torr without surface scratching by diamond or c‐BN powder. The obtained films have good crystallinity in the sense of electron and x‐ray diffraction. Vicker’s hardness of the film is the same as that of natural diamond (∼10 000 kg/mm2). The influence of the dc discharge in a low vacuum (∼200 Torr) on diamond synthesis will be discussed briefly.

Epitaxial ordering of oxide superconductor thin films on (100) SrTiO3 prepared by pulsed laser evaporation

Abstract: Thin films of Y‐Ba‐Cu‐O superconductors on (100) SrTiO3 were prepared using the pulsed excimer laser evaporation technique. After an annealing treatment in oxygen the films exhibited superconductivity with zero resistance at 85 K with transition widths (90%–10%) as narrow as a 2 K. A considerable amount of orientation of the films with respect to the substrates was observed by x‐ray diffraction and ion channeling techniques. Interface reaction revealed by Rutherford backscattering and Auger electron spectrometry resulted in a thickness dependence of the superconducting properties of the films.

Stress and microstructure of sputter‐deposited thin films: Molecular dynamics investigations

Abstract: In magnetron sputter deposition the intrinsic mechanical stress of films of refractory metals passes a tensile stress maximum, decreases and then becomes compressive with decreasing working gas pressure. To elucidate the dependence of internal tensile stress on film growth and microstructure, a two‐dimensional molecular dynamics simulation is employed. The evolving structure is determined at an atomic level and the stress is calculated as a function of the kinetic energy of adatoms and fast neutralized inert gas atoms which arrive at the film surface. These energies are dependent on the deposition geometry and the working gas pressure. The theoretical results are in qualitative agreement with experiment and reveal that the initial increase in tensile stress with increasing adatom and neutral incident kinetic energy is caused by a microstructural change from microcolumnar growth to a more densely packed atomic network with closed micropores. Interatomic attractive forces producing tensile stress can act mo...

Variation of the critical layer thickness with In content in strained InxGa1−xAs‐GaAs quantum wells grown by molecular beam epitaxy

Abstract: The critical width Lc for misfit dislocation generation has been determined for molecular beam epitaxy grown strained InxGa1−xAs (0.1

Observation of atomic corrugation on Au(111) by scanning tunneling microscopy.

Abstract: Premiere observation de l'ondulation atomique pour une surface metallique a empilement compact

Magnetic properties and structure of Pd/Co and Pd/Fe multilayers

Abstract: Pd/Co and Pd/Fe multilayer films containing ultrathin Co and Fe layers were prepared by vapor deposition on substrates at room temperature. Their modulated structure, even for films containing 2‐A‐thin Co and Fe layers, was proved by x‐ray diffraction and transmission electron microscopy. Below a Co layer thickness of about 8 A, the Pd/Co multilayers acquire an easy magnetic axis perpendicular to the film, which is mainly caused by magnetic interface anisotropy. This leads for multilayers containing Co monolayers to almost rectangular hysteresis loops, by which these films may be very suitable as a perpendicular magnetic recording medium. Pd/Fe multilayers also have a perpendicular interface anisotropy, but the shape anisotropy dominates. Per unit Co volume the Pd/Co multilayers have a higher saturation magnetization than pure Co, which is attributed to an induced ferromagnetism on Pd interfacial atoms.

A review of recent advances in solid film lubrication

Abstract: Thin, adherent sputtered MoS2 and ion plated metallic (Au, Ag, Pb) lubricating films are primarily used in precision contacting triboelement surfaces where wear debris formation is critical and high reliability requirements have to be satisfied. Detailed structural and compositional characterization of solid film lubricants is of prime importance. It is this information from the nano–micro–macro level which is needed to interpret and improve the frictional behavior and assure long endurance lives. The purpose of this paper is to summarize in a concise review the solid lubricant film structure and morphology and their effects on the tribological properties of the lubricant systems. The tribological performance of thin lubricating films has significantly advanced through progressive understanding of the film parameters such as adhesion, cohesion, interface formation, nucleation and microstructural growth, critical film thickness and substrate finish, and temperature. Sputtered MoS2 and ion plated Au, Ag, an...

Mechanistic Studies of Chemical Vapor Deposition

Abstract: Chemical vapor deposition (CVD) is a process whereby gas phase mol­ ecules are decomposed in some manner to leave behind solid materials. In this review we consider only CVD processes used to prepare thin films of electronic materials. CVD processes can be used to deposit a wide range of conducting, semiconducting, and insulating materials necessary for the fabrication of integrated circuits. Figure I shows a schematic of a bipolar transistor used in computer logic circuitry. The caption details which materials have been deposited by CVD techniques. As device dimensions shrink into the submicron region and material requirements and deposition conditions become more stringent, CVD processes must be understood at an increasingly detailed mechanistic level. This realization has led to rapid growth in applied and fundamental studies of CVD and has opened a whole new area of exciting and intriguing chemical problems. A schematic representation of the macroscopic and some of the micro­ scopic events that might occur in a generalized CVD process for the deposition of silicon from silane is shown in Figure 2. The goal of mech­ anistic studies is to determine which microscopic processes occur, to what extent they occur, and how they affect the macroscopic properties of the deposited films. As seen below, this goal has yet to be achieved for any CVD system, owing in no small part to the chemical complexity of even a relatively simple CVD process. Figure 2 also serves as an outline for this review. First we describe "classical" CVD studies, i .e. studies in which the experimental observable is the film, and discuss the mechanistic models that have been developed,

Effects of radiation damage in ion‐implanted thin films of metal‐oxide superconductors

Abstract: The effects of ion implantation into thin films of the superconductor YBa2Cu3Ox have been studied. Using oxygen and arsenic ions, the superconducting transition temperature Tc, the change in room‐temperature electrical properties from conducting to insulating, and the crystalline to amorphous structural transition in the films were studied as a function of ion dose. The deposited energy required to change Tc was found to be 0.2 eV/atom, while 1–2 eV/atom was required to affect the room‐temperature conductivity, and 4 eV/atom to render the film amorphous. This hierarchy of effects is discussed in terms of the damage mechanisms involved.

Epitaxial growth and electric characteristics of cubic SiC on silicon

Abstract: Single crystals of cubic SiC were heteroepitaxially grown by chemical vapor deposition (CVD) using a SiH4‐C3H8‐H2 system on silicon substrates. To reduce the large lattice mismatch between cubic SiC and silicon, a buffer layer was made by carbonizing the surface of a Si substrate in the CVD system. An optimum condition for the buffer layer formation was determined by x‐ray rocking curve measurements, reflection electron diffraction, and Auger electron spectroscopy. Electrical properties of the epitaxial cubic SiC layer were measured, and the mobilities on the Si(111) substrate were found to be larger than those on the Si(100) substrate. Diode characteristics of epitaxially grown p‐n junctions were also investigated.

Synthesis of diamond films in a rf induction thermal plasma

Abstract: Microcrystals and microcrystalline films of diamond were prepared on molybdenum substrates in a thermal plasma which was produced by rf inductive heating in an argon‐hydrogen‐methane mixture gas under 1 atm pressure. The deposition rate amounted to 1 μm/min.

High‐resolution electron microscopy study of x‐ray multilayer structures

Abstract: Multilayered structures containing thin (1–12 nm) layers of W or Mo, alternating with C or Si, have been prepared to produce thin cross‐sectional specimens, and direct structural information on the atomic scale has been obtained using an ultrahigh resolution electron microscope. Layer thickness and flatness have been analyzed—the average layer thickness varies by up to 0.6 nm from the average value, and the flatness of the layers depends on the quality of the substrate surface. The degree of crystallinity and crystal orientation within the layers has also been examined. This information should enable more accurate theoretical models to be proposed for the multilayer materials and their x‐ray optical properties. The results for the Mo/Si multilayers suggest a model for their growth when prepared by sputtering.

Thin-film synthesis of the high-Tc oxide superconductor YBa2Cu3O7 by electron-beam codeposition

Abstract: The successful synthesis of high-Tc YBa2Cu3O7 films by means of electron-beam codeposition are reported. Several important growth parameters have been surveyed in a preliminary way. The substrates investigated include Al2O3, ZrO2, MgO, and SrTiO3, The films were characterized by resistivity measurements, x-ray diffraction, microprobe, and Rutherford backscattering analysis. Some TEM and critical current density studies were also carried out. The best results to date have been obtained on SrTiO3 substrates with which polycrystalline epitaxial growth has been achieved. Resistive superconducting transitions with zero resistance at 89.5 K and a 2 K width have been observed in these films.