Showing papers on "Pulsed laser deposition published in 2002"

Realization of band gap above 5.0 eV in metastable cubic-phase MgxZn1−xO alloy films

Abstract: We report on the realization of wide band gap (5–6 eV), single-phase, metastable, and epitaxial MgxZn1−xO thin-film alloys grown on sapphire by pulsed laser deposition We found that the composition, structure, and band gaps of the MgxZn1−xO thin-film alloys depend critically on the growth temperature The structural transition from hexagonal to cubic phase has been observed for (Mg content greater than 50 at %) (1⩾x⩾05) which can be achieved by growing the film alloys in the temperature range of 750 °C to room temperature Interestingly, the increase of Mg content in the film has been found to be beneficial for the epitaxial growth at relatively low growth temperature in spite of a large lattice mismatch between sapphire and cubic MgZnO alloys

Ferroelectric Bi3.25La0.75Ti3O12 Films of Uniform a-Axis Orientation on Silicon Substrates

Abstract: The use of bismuth-layered perovskite films for planar-type nonvolatile ferroelectric random-access memories requires films with spontaneous polarization normal to the plane of growth. Epitaxially twinned a axis–oriented La-substituted Bi4Ti3O12 (BLT) thin films whose spontaneous polarization is entirely along the film normal were grown by pulsed laser deposition on yttria-stabilized zirconia-buffered Si(100) substrates using SrRuO3 as bottom electrodes. Even though the (118) orientation competes with the (100) orientation, epitaxial films with almost pure (100) orientation were grown using very thin, strained SrRuO3 electrode layers and kinetic growth conditions, including high growth rates and high oxygen background pressures to facilitate oxygen incorporation into the growing film. Films with the a-axis orientation and having their polarization entirely along the direction normal to the film plane can achieve a remanent polarization of 32 microcoulombs per square centimeter.

Observation of saturated polarization and dielectric anomaly in magnetoelectric BiFeO3 thin films

Abstract: We report here synthesis of phase-pure magnetoelectric BiFeO3 thin films with controlled oxygen stoichiometry on Pt/TiO2/SiO2/Si substrate using pulsed-laser deposition technique. Saturated ferroelectric hysteresis loop has been observed in phase-pure and highly resistive BiFeO3 thin films. The dielectric response study of the films with temperature indicates an anomaly in dielectric constant e(T), in the vicinity of Neel temperature (∼380 °C). This anomaly in e(T) is explained as an influence of vanishing magnetic ordering on electric ordering of magnetoelectric BiFeO3 sample.

Photoluminescence of size-separated silicon nanocrystals: Confirmation of quantum confinement

Abstract: Silicon nanocrystals with diameters between 2.5 and 8 nm were prepared by pulsed CO2 laser pyrolysis of silane in a gas flow reactor and expanded through a conical nozzle into a high vacuum. Using a fast-spinning molecular-beam chopper, they were size-selectively deposited on dedicated quartz substrates. Finally, the photoluminescence of the silicon nanocrystals and their yield were measured as a function of their size. It was found that the photoluminescence follows very closely the quantum-confinement model. The yield shows a pronounced maximum for sizes between 3 and 4 nm.

Magnetic properties of epitaxially grown semiconducting Zn1−xCoxO thin films by pulsed laser deposition

Abstract: We have characterized Zn1−xCoxO (x=0.25) films grown on sapphire (0001) substrates by pulsed laser deposition using various growth conditions to investigate the growth condition dependence of properties of Co-doped ZnO films. The substrate temperature (TS) was varied from 300 to 700 °C and the O2 pressure (PO2) from 10−6 to 10−1 Torr. When TS is relatively low (≲600 °C), homogeneous alloy films with a wurtzite ZnO structure are grown and predominantly paramagnetic, whereas inhomogeneous films of wurtzite ZnO phase mixed with rock-salt CoO and hexagonal Co phases form when TS is relatively high and PO2 is fairly low (≲10−5 Torr). The presence of Co clusters leads to room temperature ferromagnetism in inhomogeneous films. The temperature dependence of the magnetization for the homogeneous Zn1−xCoxO (x=0.25) films shows spin-glass behavior at low temperature and high temperature Curie–Weiss behavior with a large negative value of the Curie–Weiss temperature, indicating strong antiferromagnetic exchange coupl...

Formation of Co nanoclusters in epitaxial Ti0.96Co0.04O2 thin films and their ferromagnetism

Abstract: Anatase Ti0.96Co0.04O2 films were grown epitaxially on SrTiO3 (001) substrates by using pulsed laser deposition with in-situ reflection high-energy electron diffraction. The oxygen partial pressure, PO2, during the growth was systematically varied. As PO2 decreased, the growth behavior was changed from a two-dimensional layer-by-layer-like growth to a three-dimensional island-like one, which resulted in an increase in the saturation magnetization. These structural and magnetic changes were explained in terms of the formation of cobalt clusters whose existence was proved by transmission-electron-microscope studies. Our work clearly indicates that the cobalt clustering will cause room-temperature ferromagnetism in the Co-doped TiO2 films.

MgO-mixed Ba0.6Sr0.4TiO3 bulk ceramics and thin films for tunable microwave applications

Abstract: The dielectric properties of Ba0.6Sr0.4TiO3 (BST) and 1.0, 20.0, 40.0, and 60.0 wt % MgO-mixed BST bulk ceramics and thin films were investigated for tunable microwave applications. The effects of MgO mixing with BST on BST phase transitions were examined. It is observed that Mg substitution into BST causes a shift in the cubic-tetragonal BST phase transition peak to a lower temperature. Mg-substituted BST and MgO-mixed phases exhibit depressed and broadened BST phase transition peaks, resulting in decreased dielectric constants and dielectric losses at room temperature. BST and 1.0, 20.0, 40.0, and 60.0 wt % MgO-mixed BST thin films (∼0.3 μm thick) were deposited on (100) MgO single-crystal substrates at 750°C in an oxygen ambient pressure of 200 mTorr by pulsed laser deposition. The MgO–BST composite thin films showed a relatively high dielectric Q (=1/tan δ) compared to the pure BST and Mg-substituted BST thin films while retaining useful dielectric tuning.

Deposition of film layers by alternately pulsing a precursor and high frequency power in a continuous gas flow

Abstract: A method of film layer deposition is described. A film layer is deposited using a cyclical deposition process. The cyclical deposition process consists essentially of a continuous flow of one or more process gases and the alternate pulsing of a precursor and energy to form a film on a substrate structure.

Chemical vapor deposition methods, atomic layer deposition methods, and valve assemblies for use with a reactive precursor in semiconductor processing

Abstract: The invention includes chemical vapor deposition methods, including atomic layer deposition, and valve assemblies for use with a reactive precursor in semiconductor processing. In one implementation, a chemical vapor deposition method includes positioning a semiconductor substrate within a chemical vapor deposition chamber. A first deposition precursor is fed to a remote plasma generation chamber positioned upstream of the deposition chamber, and a plasma is generated therefrom within the remote chamber and effective to form a first active deposition precursor species. The first species is flowed to the deposition chamber. During the flowing, flow of at least some of the first species is diverted from entering the deposition chamber while feeding and maintaining plasma generation of the first deposition precursor within the remote chamber. At some point, diverting is ceased while feeding and maintaining plasma generation of the first deposition precursor within the remote chamber. Other aspects and implementations are contemplated.

Dependence of the excitonic transition energies and mosaicity on residual strain in ZnO thin films

Abstract: The mosacity and optical properties of ZnO on (0001) Al2O3 grown by pulsed-laser deposition have been studied by x-ray diffraction and spectroscopic ellipsometry. Strong dependence has been found between the grain size and the residual strain along the c axis, ezz, as well as the film texture. In general, strain relieves and texture improves at larger grain size regardless of the growth conditions. The excitonic transition energies are also found to vary in the presence of strain field. It is observed that the transition energies increase with increasing strain and eventually they are resolved into two well-defined bands at the strain of 1.63%. By taking into account of the biaxial strain, the theoretical band structure of ZnO has been considered by solving the Luttinger–Kohn Hamiltonian. Reasonable agreement is found between the theory and experiment.

Hot-filament chemical vapor deposition chamber and process with multiple gas inlets

Abstract: A thin film deposition method uses a vacuum confinement cup that employs a dense hot filament and multiple gas inlets. At least one reactant gas is introduced into the confinement cup both near and spaced apart from the heated filament. An electrode inside the confinement cup is used to generate plasma for film deposition. The method is used to deposit advanced thin films (such as silicon based thin films) at a high quality and at a high deposition rate.

S doping in ZnO film by supplying ZnS species with pulsed-laser-deposition method

Abstract: S-doped ZnO (ZnO:S) film was fabricated by supplying ZnS species from laser ablation of a ZnS target during ZnO growth. Variations of lattice constants and band gaps with respect to S content did not follow Vegard’s law. The ZnO:S film showed semiconducting behavior with lower activation energy and resistivity than those of ZnO owing to higher carrier concentration. Despite the absence of magnetic elements, the large magnetoresistance amount of 26% was observed at 3 K from ZnO:S film.

Effects of Thickness Variation on Properties of ZnO Thin Films Grown by Pulsed Laser Deposition

Abstract: A series of ZnO films with various thicknesses were prepared on (0001) sapphire substrate by pulsed laser deposition (PLD) Scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis were utilized to investigate the effects of thickness variation on the surface morphology and the crystallinity The electrical and optical properties of the films were also investigated as a function of the film thickness It was found that the crystalline quality, electrical and optical properties of the films depended on the film thickness and were improved with increasing the film thickness This is attributed to the fact that the films thinner than 4000 A are under the severe misfit strain, which decreases with increasing the film thickness further

Mo/Si multilayers with different barrier layers for applications as extreme ultraviolet mirrors

Abstract: Pulsed laser deposition (PLD) and magnetron sputter deposition (MSD) have been used to prepare different types of Mo/Si multilayers for the extreme ultraviolet (EUV) spectral range. In the case of PLD prepared Mo/Si multilayers the deposition of 0.3?0.5 nm thick carbon barrier layers at the interfaces leads to a substantial improvement of the interface quality. This can be deduced from Cu-K? reflectivity measurements and HRTEM observations. Consequently the EUV reflectivity has been substantially increased. For pure Mo/Si-multilayers prepared by MSD the deposition parameters have been optimized so that a normal incidence reflectivity of REUV=68.7% could be realized. Although this is one of the best experimental results achieved so far, there is still a gap between this experimental value and the theoretical limit (REUV=75.5%). One of the main reasons for this discrepancy is the formation of intermixing zones at the interfaces. With B4C and C barrier layers at the interfaces interdiffusion can be reduced. The resulting EUV reflectivity of this new type of EUV multilayers is 69.8% (?=13.42 nm, ?=1.5?) and 71.4% (?=12.52 nm, ?=22.5?).

Method for depositing refractory metal layers employing sequential deposition techniques

Abstract: A method for forming a tungsten layer on a substrate surface is provided. In one aspect, the method includes positioning the substrate surface in a processing chamber and exposing the substrate surface to a boride. A nucleation layer is then deposited on the substrate surface in the same processing chamber by alternately pulsing a tungsten-containing compound and a reducing gas selected from a group consisting of silane (SiH 4 ), disilane (Si 2 H 6 ), dichlorosilane (SiCl 2 H 2 ), derivatives thereof, and combinations thereof. A tungsten bulk fill may then be deposited on the nucleation layer using cyclical deposition, chemical vapor deposition, or physical vapor deposition techniques.

Comparison between ZnO films grown by femtosecond and nanosecond laser ablation

Abstract: We have studied the structural properties of ZnO thin films grown on Al2O3 (00.1) single-crystal substrates by pulsed-laser deposition using either a femtosecond or a nanosecond laser. Although hexagonal ZnO films deposited on sapphire substrate were epitaxially grown in both cases, the crystalline quality was found to be very different: ZnO films grown with the femtosecond laser are characterized by a higher mosaicity, a smaller crystallite size, a larger content of defects but also smaller residual stresses than ZnO films obtained by nanosecond laser ablation. These differences can be explained according to the kinetic energy of the species evolved during laser ablation as deduced from plasma characterization with a charged-coupled device camera: close to 1 KeV in the femtosecond regime for the population species emitted from the target with the highest velocity, versus a few hundreds of eV in the case of nanosecond pulses. The high energy species irradiation associated with a femtosecond laser is likely to induce a large structural disorder together with stress relaxation during ZnO films growth.

Epitaxial thin films of the giant-dielectric-constant material CaCu3Ti4O12 grown by pulsed-laser deposition

Abstract: Pulsed-laser deposition has been used to grow epitaxial thin films of the giant-dielectric-constant material CaCu3Ti4O12 on LaAlO3 and SrTiO3 substrates with or without various conducting buffer layers. The latter include YBa2Cu3O7, La1.85Sr0.15CuO4+δ, and LaNiO3. Above 100–150 K, the thin films have a temperature independent dielectric constant as do crystals. The value of the dielectric constant is of the order of 1500 over a wide temperature region, potentially making it a good candidate for many applications. The frequency dependence of its dielectric properties below 100–150 K indicates an activated relaxation process.

Epitaxial Thin Films of the Giant-Dielectric-Constant Material CaCu_3Ti_4O_{12} Grown by Pulsed-laser Deposition

Abstract: Pulsed-laser deposition has been used to grow epitaxial thin films of the giant-dielectric-constant material CaCu_3Ti_4O_{12} on LaAlO_3 and SrTiO_3 substrates with or without various conducting buffer layers. The latter include YBa_2Cu_3O_7, La_{1.85}Sr_{0.15}CuO_{4+\delta} and LaNiO_3. Above 100K - 150K the thin films have a temperature independent dielectric constant as do single crystals. The value of the dielectric constant is of the order of 1500 over a wide temperature region, potentially making it a good candidate for many applications. The frequency dependence of its dielectric properties below 100K - 150K indicates an activated relaxation process.

Epitaxial growth and electronic structure of LaTiOx films

Abstract: LaTiOx films have been grown on (001) perovskite oxide substrates by pulsed-laser deposition. Both single-phase perovskite LaTiO3 and layered La2Ti2O7 films could be stabilized by varying the oxygen partial pressure and substrate temperature during growth. We have obtained a crystallographic and electronic phase diagram for LaTiOx films, demonstrating the ability to vary the titanium valence from 3+ to 4+ in thermodynamically unfavorable growth conditions by utilizing interface energies.