Showing papers on "Thin film published in 1994"
01 Jan 1994
TL;DR: Pulsed laser deposition of high-temperature superconducting thin films for active and passive device applications is discussed in this article, with a focus on the commercial scale-up of Pulsed Laser Deposition.
Abstract: Partial table of contents: History and Fundamentals of Pulsed Laser Deposition (J. Cheung). Diagnostics and Characteristics of Laser--Produced Plasmas (D. Geohegan). Particulates Generated by Pulsed Laser Ablation (L.--C. Chen). Angular Distribution of Ablated Material (K. Saenger). Film Nucleation and Film Growth in Pulsed Laser Deposition of Ceramics (J. Horwitz & J. Sprague). Processes Characteristics and Film Properties in Pulsed Laser Plasma Deposition (S. Metev). Commercial Scale--Up of Pulsed Laser Deposition (J. Greer). Pulsed Laser Deposition: Future Trends (T. Venkatesan). Comparison of Vacuum Deposition Techniques (G. Hubler). Pulsed Laser Deposition of High--Temperature Superconducting Thin Films for Active and Passive Device Applications (R. Muenchausen & X. Wu). Pulsed Laser Deposition of Metals (J. Kools). Appendix. References. Index.
3,228 citations
TL;DR: In this article, the metastable phase anatase has been shown to have a wider optical absorption gap than rutile thin films, which is consistent with the high mobility, bandlike conduction observed in anatase crystals.
Abstract: Electrical and optical spectroscopic studies of TiO2 anatase thin filmsdeposited by sputtering show that the metastable phase anatase differs in electronic properties from the well‐known, stable phase rutile. Resistivity and Hall‐effect measurements reveal an insulator–metal transition in a donor band in anatase thin films with high donor concentrations. Such a transition is not observed in rutile thin films with similar donor concentrations. This indicates a larger effective Bohr radius of donor electrons in anatase than in rutile, which in turn suggests a smaller electron effective mass in anatase. The smaller effective mass in anatase is consistent with the high mobility, bandlike conduction observed in anatase crystals. It is also responsible for the very shallow donor energies in anatase. Luminescence of self‐trapped excitons is observed in anatase thin films, which implies a strong lattice relaxation and a small exciton bandwidth in anatase. Optical absorption and photoconductivity spectra show that anatase thin films have a wider optical absorption gap than rutile thin films.
1,560 citations
TL;DR: In this paper, a simple technique for measuring trace-metal concentrations in situ in water is described, where an ion exchange resin is separated from the solution by an ion-permeable gel membrane.
Abstract: RELIABLE measurement of trace species in natural waters is essential for studies of pollution or trace-element cycling, but is difficult, partly because the distribution of chemical species often changes during sampling and storage1. In situ measurements can overcome these problems, but the few measurements made previously have involved complicated systems that cannot be used routinely1,2. Here we describe a simple technique for measuring trace-metal concentrations in situ in water. The technique incorporates an ion-exchange resin separated from the solution by an ion-permeable gel membrane. Mass transport through the gel is diffusion-controlled and thus well defined, making it possible to obtain quantitative data on concentration and speciation over relatively short time periods (from one hour to several weeks). We present measurements of zinc concentrations in sea water using this technique which agree well with electrochemical measurements. In principle, our technique should be applicable to any inorganic or organic diffusing species.
1,140 citations
TL;DR: The authors measured the thickness dependence of thin films of poly(methyl methacrylate) by using spectroscopic ellipsometry to detect the discontinuity in thermal expansivity occurring at Tg.
Abstract: We have measured the thickness dependence of the glass-transition temperature (Tg) of thin films of poly(methyl methacrylate)(PMMA) by using spectroscopic ellipsometry to detect the discontinuity in thermal expansivity occurring at Tg. We studied films on two surfaces: the native oxide of silicon, and evaporated gold. The Tg of PMMA on a gold surface decreases with decreasing film thickness, in accordance with previous results for polystyrene on silicon. We suggest that at the air surface a liquid-like layer exists whose size diverges as Tg is approached from below. For films of PMMA on the native oxide of silicon, however, we find a slight increase in Tg with decreasing thickness. We speculate that hydrogen bonding at the interface restricts mobility and leads to an increase in Tg, outweighing the effect of the free surface.
922 citations
TL;DR: In this article, surface and interface stresses in solids are defined and their role in the thermodynamics of solids is presented, along with a review of selected theoretical calculations and experimental measurements.
852 citations
Book•
01 May 1994
TL;DR: In this paper, the authors present thin film technology, thin film characterisation, and high energy techniques for thin film. But they do not discuss the effects of these technologies on the performance of the film.
Abstract: Thin Film Technology. Gas Kinetics. Vacuum Technology. Evaporation. Deposition. Epitaxy. Chemical Vapor Deposition. High-Energy Techniques. Plasma Processes. Film Characterization.
736 citations
TL;DR: Here, studies are presented of molecular order and organization in thin films of fatty acid salts, the prototypical system of Katharine Blodgett, which presents both a challenge and an opportunity for future molecular design of organic thin-film devices.
Abstract: The controlled transfer of organized monolayers of amphiphilic molecules from the airwater interface to a solid substrate was the first molecular-scale technology for the creation of new materials. However, the potential benefits of the technology envisioned by Langmuir and Blodgett in the 1930s have yet to be fully realized. Problems of reproducibility and defects and the lack of basic understanding of the packing of complex molecules in thin films have continued to thwart practical applications of Langmuir-Blodgett films and devices made from such films. However, modern high-resolution x-ray diffraction and scanning probe microscopy have proven to be ideal tools to resolve many of the basic questions involving thin organic films. Here, studies are presented of molecular order and organization in thin films of fatty acid salts, the prototypical system of Katharine Blodgett. Even these relatively simple systems present liquid, hexatic, and crystalline order; van der Waals and strained layer epitaxy on various substrates; wide variations in crystal symmetry and interfacial area with counterions; modulated superstructures; and coexisting lattice structures. The wide variety of possible structures presents both a challenge and an opportunity for future molecular design of organic thin-film devices.
690 citations
Book•
01 Jan 1994
TL;DR: In this paper, the authors present an overview of the role of plasma-assisted and plasma-enhanced chemical vapor deposition processes in the development of thin films and coatings, as well as their application in a variety of applications.
Abstract: Deposition Technologies: An Overview * Plasmas in Deposition Processes * Surface Preparation For Film and Coating Deposition Processes * Evaporation: Processes, Bulk Microstructures And Mechanical Processes * Sputter Deposition Processes * Ion Plating * Chemical Vapor Deposition * Plasma-Enhanced Chemical Vapor Deposition * Plasma-Assisted Vapor Deposition Processes: Overview * Deposition from Aqueous Solutions: An Overview * Advanced Thermal Spray Deposition Techniques * Non-Elemental Characterization of Films and Coatings * Film Growth and Structure of PVD Deposits * Metallurgical Applications * Characterization of Thin Films And Coatings.
639 citations
TL;DR: In this paper, Ga and Se were coevaporated to form precursor films of (Inx,Ga1−x)2Se3, which were then converted to CuInxGa 1−xSe2 by exposure to a flux of Cu and Se. The final films were smooth, with tightly packed grains, and had a graded Ga content as a function of film depth.
Abstract: In, Ga, and Se were coevaporated to form precursor films of (Inx,Ga1−x)2Se3. The precursors were then converted to CuInxGa1−xSe2 by exposure to a flux of Cu and Se. The final films were smooth, with tightly packed grains, and had a graded Ga content as a function of film depth. Photovoltaic devices made from these films showed good tolerance in device efficiency to variations in film composition. A device made from these films resulted in the highest total‐area efficiency measured for any non‐single‐crystal, thin‐film solar cell, at 15.9%.
584 citations
TL;DR: In this article, the normal load method is used to measure the coefficients for PZT thin films with various compositions prepared by the solgel technique or by organometallic chemical vapor deposition (OMCVD).
Abstract: This article presents measurements of piezoelectric coefficients of lead zirconate titanate (PZT) thin films. The normal load method is used to measure the coefficients for PZT films with various compositions prepared by the sol‐gel technique or by organometallic chemical vapor deposition (OMCVD). The as‐deposited OMCVD films have a piezoelectric coefficient of 20–40×10−12 m/V, whereas the unpoled sol‐gel films are not piezoelectric. After poling the thin films having a composition near the morphotropic phase boundary; these values increase to 200×10−12 m/V for OMCVD films and 400×10−12 m/V for sol‐gel films. The difference may arise from an incomplete poling of the OMCVD films.
547 citations
TL;DR: High-quality, dense polycrystalline films of oxides, hydroxides, and sulfides have now been prepared from "biomimetic" synthesis techniques, well suited to the production of organic-inorganic composites.
Abstract: Processing routes have been developed for the production of thin ceramic films through precipitation from aqueous solutions. The techniques are based on crystal nucleation and growth onto functionalized interfaces. Surface functionalization routes have been developed by the mimicking of schemes used by organisms to produce complex ceramic composites such as teeth, bones, and shells. High-quality, dense polycrystalline films of oxides, hydroxides, and sulfides have now been prepared from "biomimetic" synthesis techniques. Ceramic films can be synthesized on plastics and other materials at temperatures below 100 degrees C. As a low-temperature process in which water rather than organic solvents is used, this synthesis is environmentally benign. Nanocrystalline ceramics can be produced, sometimes with preferred crystallite orientation. The direct deposition of high-resolution patterned films has also been demonstrated. The process is well suited to the production of organic-inorganic composites.
TL;DR: Scattering of phonons at the interface between the a-Si:H film and the substrate places a simple upper limit on the heat transport by long-wavelength phonons and facilitates the comparison of the experimental data to recent numerical solutions of a Kubo formula using harmonic vibrations.
Abstract: The thermal conductivity of sputtered a-Si:H thin films for a hydrogen content of 1--20 % and a film thickness of 0.2--1.5 \ensuremath{\mu}m is determined in the temperature range 80--400 K using an extension of the 3\ensuremath{\omega} measurement technique. The reliability of the method is demonstrated on 1-\ensuremath{\mu}m-thick a-${\mathrm{SiO}}_{2}$ thermally grown on Si. Scattering of phonons at the interface between the a-Si:H film and the substrate places a simple upper limit on the heat transport by long-wavelength phonons and facilitates the comparison of the experimental data to recent numerical solutions of a Kubo formula using harmonic vibrations.
TL;DR: In this paper, the authors developed temperature dependent stability maps that predict the stable domain structure that forms during the paraelectric to ferroelectric transition (PE→FE) and discussed the role of dislocation stabilization of domain patterns.
Abstract: Possible mechanisms for strain relaxation in ferroelectric thin films are developed. The models are applicable to tetragonal thin film ferroelectrics grown epitaxially on (001) cubic single crystal substrates. We assume growth at temperatures in excess of the Curie temperature (Tc). The extent of strain accommodation by misfit dislocations is considered at the growth temperature (Tg). On cooling to Tc, further misfit dislocation generation is possible due to differences in thermal expansion behavior of the film and substrate. During the paraelectric to ferroelectric transition (PE→FE) additional strains develop in the film. The total strain for the FE phase may be relieved either by further misfit generation or by domain formation. We have developed temperature dependent stability maps that predict the stable domain structure that forms during the PE→FE transition. The stability maps incorporate the role of the following parameters: (i) substrate lattice parameter, (ii) differential thermal expansion characteristics between the film and substrate, (iii) cooling rate, and (iv) depolarizing fields and electrode geometry. Further, the role of dislocation stabilization of domain patterns is discussed.
TL;DR: In this article, a new metallization process for achieving low resistance ohmic contacts to molecular beam epitaxy grown n−GaN (∼1017 cm−3) using an Al/Ti bilayer metallisation scheme was reported.
Abstract: We report a new metallization process for achieving low resistance ohmic contacts to molecular beam epitaxy grown n‐GaN (∼1017 cm−3) using an Al/Ti bilayer metallization scheme. Four different thin‐film contact metallizations were compared during the investigation, including Au, Al, Ti/Au, and Ti/Al layers. The metals were first deposited via conventional electron‐beam evaporation onto the GaN substrate, and then thermally annealed in a temperature range from 500 to 900 °C in a N2 ambient using rapid thermal annealing techniques. The lowest value for the specific contact resistivity of 8×10−6 Ω cm2, was obtained using Ti/Al metallization with anneals of 900 °C for 30 s. X‐ray diffraction and Auger electron spectroscopy depth profile were employed to investigate the metallurgy of contact formation.
Patent•
29 Nov 1994
TL;DR: In this article, an electron hole transporting layer is used to form an organic electroluminescent element as a prescribed thin film, which enhances heat resistance and light emitting brightness characteristics.
Abstract: PURPOSE:To enhance heat resistance and light emitting brightness characteristics by forming an electron hole transporting layer to form an organic electroluminescent element as a prescribed thin film. CONSTITUTION:A positive electrode A of a transparent electrode, an electron hole transporting layer B, a light emitting layer C and a negative electrode D are layered on a transparent board E, and an organic electroluminescent element is formed. This layer B is composed of a thermal decomposition polyimide thin film containing Si in a structure formed by thermal decomposition after a polyimide thin film is formed. Thereby, an organic electroluminescent element whose heat resistance and light emitting brightness characteristics are enhanced more than a luminescent element having a hole transporting layer composed of a polyimide thin film, is formed.
TL;DR: In this article, a thorough discussion of today's understanding of the growth of thin metal films and related atomistic mechanisms responsible for intrinsic stress is presented, where the intrinsic stress either originates from strained regions within the films (grain boundaries, dislocations, voids, impurities, etc.) or at the film/substrate (lattice mismatch, different thermal expansion, etc).
Abstract: It is well known that thin films develop large intrinsic stress during their preparation. The intrinsic stress either originates from strained regions within the films (grain boundaries, dislocations, voids, impurities, etc.) or at the film/substrate (lattice mismatch, different thermal expansion, etc) and film/vacuum interfaces (surface stress, adsorption, etc.) or is due to dynamic processes (recrystallization, interdiffusion, etc). Since the magnitude of most of these stress contributions is directly related to film morphology, important structural information can be extracted from measurements of the intrinsic stress. This article presents a thorough discussion of today's understanding of the growth of thin films and reviews the related atomistic mechanisms responsible for intrinsic stress. On the basis of these ideas recent experimental results on the intrinsic stress of UHV deposited polycrystalline and epitaxial thin metal films are discussed. Depending on the respective growth mode of the films-Volmer-Weber, Stranski-Krastanov and Frank-Van der Merwe modes-characteristic stress behaviours are observed. In situ intrinsic stress measurements are therefore a promising new technique to gain additional insight into film growth.
TL;DR: In this article, the influence of the process parameters on the optical properties of TiO2 films, such as index of refraction, scattering of light, and absorption, is discussed.
IBM1
TL;DR: In this article, the thermodynamics of irreversible processes were used to examine spontaneous interfacial reaction at room temperature in bimetallic Cu-Sn thin films, where the volume change in forming the compound produces a biaxial compressive stress in the Sn film, resulting in the growth of Sn whiskers to accompany the reaction.
Abstract: Using the thermodynamics of irreversible processes, we examine spontaneous interfacial reaction at room temperature in bimetallic Cu-Sn thin films. The reaction forms an intermetallic compound and is interfacial reaction limited. The volume change in forming the compound produces a biaxial compressive stress in the Sn film. The stress results in the growth of Sn whiskers to accompany the reaction. This is a case of an irreversible process of involving the interaction of chemical affinity and mechanical stress. However, the atomic mobility can significantly affect the reaction product and morphology. If the reaction temperature is raised above 100 \ifmmode^\circ\else\textdegree\fi{}C, the compound formation becomes so fast that there is no time to grow whiskers, instead hillocks form. To model the whisker growth (or hillock growth), we assume that whiskers grow at weaker spots on the Sn surface where the surface oxide has been broken. These spots become localized stress relief centers, and they are surrounded by a long-range stress gradient needed for whisker growth.
TL;DR: In this paper, thin films of transparent conducting aluminum-doped ZnO have been deposited using a sol-gel process and the dependence of electrical characteristics upon aluminum concentration in the films and upon post-deposition heat treatment in vacuum was examined.
TL;DR: In this article, the photovoltaic effect in diode structures formed with thin films (100 nm) of the conjugated polymer poly(p-phenylene vinylene), PPV, sandwiched between electrodes of indium/tin oxide, ITO, and either aluminium, magnesium or calcium.
Abstract: We report measurements of the photovoltaic effect in diode structures formed with thin films (100 nm) of the conjugated polymer poly(p-phenylene vinylene), PPV, sandwiched between electrodes of indium/tin oxide, ITO, and either aluminium, magnesium or calcium. Under illumination incident through the ITO contact, large open-circuit voltages were measured, which saturated at approximately 1.2 V for Al and Mg devices, and approximately 1.7 V for Ca devices. Quantum efficiencies (short-circuit current/incident photon flux) of order 1% were measured at low intensities (0.1 mW cm-2). The spectral response of the photocurrent demonstrates that photon absorption near the electron-collecting electrode optimizes the photocurrent, indicating that device performance is limited by low electron mobilities in the bulk PPV. The photocurrent exhibits a weak temperature dependence, with an activation energy that is a function of the electric field in the polymer. We have used these measurements to estimate an exciton binding energy in PPV of approximately 0.4 eV.
TL;DR: In this paper, it was shown that the coercive field is independent of thickness having a value of 2.4 V/μm and the ratio ebl/dbl is in the range 20−28 nm−1; the voltage across the blocking layer is proportional to the polarization, Vbl=cP, where c=4.1±0.5 Vm2/C; and (iv) the polarization depends on the electric field in the PZT layer.
Abstract: Ferroelectric capacitors having Pt bottom and top electrodes and a ferroelectric film of composition PbZr0.51Ti0.49O3 (PZT) were fabricated and investigated. The PZT films of thicknesses varying from 0.12 to 0.69 μm were prepared by organometallic chemical‐vapor deposition. Annealed capacitors were investigated by capacitance, hysteresis, and pulse switching measurements. It is found that the thickness dependence of the reciprocal capacitance, the coercive voltage, and the polarization measured by pulse switching can all be explained by a blocking layer model, in which a dielectric layer of thickness dbl and relative permittivity ebl is situated between the PZT film and an electrode. It is shown that (i) the coercive field is independent of thickness having a value of 2.4 V/μm; (ii) the ratio ebl/dbl is in the range 20–28 nm−1; (iii) the voltage across the blocking layer is proportional to the polarization, Vbl=cP, where c=4.1±0.5 V m2/C; and (iv) the polarization depends on the electric field in the PZT layer, independent of thickness. Pulse switching endurance measurements showed that in the saturation range the fatigue for these ferroelectric capacitors is determined by the pulse voltage and is independent of the thickness.
TL;DR: In this paper, a colossal magnetoresistance effect with more than a thousandfold change in resistivity (ΔR/RH=127 000% at 77 K, H=6 T) has been obtained in epitaxially grown La•Ca•Mn•O thin films.
Abstract: A colossal magnetoresistance effect with more than a thousandfold change in resistivity (ΔR/RH=127 000% at 77 K, H=6 T) has been obtained in epitaxially grown La‐Ca‐Mn‐O thin films. The effect is negative and isotropic with respect to the field orientations. The magnetoresistance is strongly temperature dependent, and exhibits a sharp peak that can be shifted to near room temperature by adjusting processing parameters. Near‐room‐temperature ΔR/RH values of ∼1300% at 260 K and ∼400% at 280 K have been observed. The presence of grain boundaries appears to be detrimental to achieving very large magnetoresistance in the lanthanum manganite films. The orders of magnitude change in electrical resistivity could be useful for various magnetic and electric device applications.
TL;DR: In this paper, the atomic processes taking place during deposition are described in terms of rate and diffusion equations; the concept of competitive capture is outlined, where adatoms are forced to choose between competing sinks.
TL;DR: In this article, it was shown that the suppressed polarization can be restored to essentially its initial polarization value by injecting electronic charge carriers into the ferroelectric, which strongly suggests that all three forms of degradation involve locking domains by electronic charge trapping centers.
Abstract: Switchable polarization can be significantly suppressed in Pb(Zr,Ti)O3 thin films by optical, thermal, and electrical processes. The optical (thermal) suppression effects occur by biasing the ferroelectric near the switching threshold and illuminating the material with band‐gap light (heating the material to ≊100 °C). The electrical suppression effect, commonly known as electrical fatigue, occurs by subjecting the ferroelectric to repeated polarization reversals. It is found that the suppressed polarization in all three cases can be restored to essentially its initial polarization value by injecting electronic charge carriers into the ferroelectric. This strongly suggests that all three forms of degradation involve locking domains by electronic charge trapping centers.
TL;DR: In this article, the effects of pyrolysis temperature, post-pyrolyisation thermal treatments, and excess lead addition on the growth and orientation of lead zirconate titanate thin films prepared from organometallic precursor solutions by spin coating on (111) oriented platinum substrates and crystallized by rapid thermal annealing was investigated.
Abstract: The nucleation, growth, and orientation of lead zirconate titanate thin films prepared from organometallic precursor solutions by spin coating on (111) oriented platinum substrates and crystallized by rapid thermal annealing was investigated. The effects of pyrolysis temperature, post-pyrolysis thermal treatments, and excess lead addition are reported. The use of post-pyrolysis oxygen anneals at temperatures in the regime of 350–450 °C was found to strongly affect the kinetics of subsequent amorphous-pyrochlore-perovskite crystallization by rapid thermal annealing. The use of such post-pyrolysis anneals allowed films of reproducible microstructure and textures [both (100) and (111)] to be prepared by rapid thermal annealing. It is proposed that such anneals and pyrolysis temperature affect the oxygen concentration/average Pb valence in the amorphous films prior to annealing. Such changes in the Pb valence state then affect the stability of the transient pyrochlore phase and thus the kinetics of perovskite crystallization.
TL;DR: In this paper, the authors used reactive rf magnetron sputtering of Sn, Sb, or Mo in Ar+O2(+CF4) onto glass heated to a temperature up to 530 °C. Optimized deposition parameters gave SnOx:(Sb,F) films with high luminous transmittance, low luminous absorptance, high infrared reflectance, and dc resistivity down to 9.1×10−4 Ω
Abstract: Tin oxide films doped with oxygen vacancies, F, Sb, or Mo were made by reactive rf magnetron sputtering of Sn, Sn‐Sb, or Sn‐Mo in Ar+O2(+CF4) onto glass heated to a temperature up to 530 °C. Electrical dc resistivity, mobility, free‐electron density, spectral optical properties, and microstructure were investigated as a function of sputtering parameters. Optimized deposition parameters gave SnOx:(Sb,F) films with high luminous transmittance, low luminous absorptance, high infrared reflectance, and dc resistivity down to 9.1×10−4 Ω cm. Refractive index n and extinction coefficient k were evaluated from spectrophotometric transmittance. In the luminous range, the films had 1.90
TL;DR: In this paper, the authors investigated the electrical and photoelectrical properties of non-doped and doped zinc oxide films coated on glass plates by the dip-coating method at room temperature in various ambient atmospheres.
Abstract: Electrical and photoelectrical properties of nondoped and doped zinc oxide films coated on glass plates by the dip-coating method are investigated at room temperature in various ambient atmospheres. The dark conductivity of the nondoped films exponentially decreased with decreasing film thickness while the conductivity under illumination of 350 nm light was almost constant at 100 Scm-1 irrespective of the film thickness. Consequently thinner films showed larger photoresponse than thicker films. This thickness dependence is explained by the variation of ZnO particle size with the film thickness (fine particle model) and the additional effect of the Schottky barrier generated between the film and gold electrodes.
TL;DR: It is demonstrated that one of the most common methods used to determine surface energies from thin-film total-energy calculations introduces a computational error that increases linearly with the thickness of the film.
Abstract: It is demonstrated that one of the most common methods used to determine surface energies from thin-film total-energy calculations introduces a computational error that increases linearly with the thickness of the film. This linear divergence is shown to have had a major impact on a recent calculation of the Li(111) surface energy, using one- to five-layer-thick films.