Perovskite oxide films inclusive of high Tc cuprates were fabricated by pulsedlaser deposition (PLD) under both conventional Po2(0.01∼1Torr) and high vacuum(≤10−6 Torr) conditions and their surface morphology, crystal quality, and conductivity were evaluated. Under optimized conventional PLD conditions, we obtained high quality YBa2Cu3O7−δ (YBCO) films that showed clear energy gaps and atomically flat surface image in the small area (4x4nm) STM/STS measurements. AFM and SEM ana!yscs on wider film surfaces (∼1x1μm), however, revealed granular structure of about 250nm grains with their root mean square roughness of 5nm.

Under high vacuum PLD, i.e. laser MBE conditions, not only epitaxial but also two dimensional growth has been verified for such films as SrTiO3−x, SrVO3−y, and (AE)CuO2−z(AE=alkaline earth metal) by the RHEED observation of fine streak patterns and intensity oscillations. AFM demonstrated atomically flat surfaces of these films. Oxgen or nitric oxide pressure at the laser MBE growth gave crucial effects on the electrical conductivity of SrTiO3−x. and predominant crystal phase of SrCuO2−z.

Insulating BaTiO3 films with atomically flat surfaces could be fabricated by both conventional and high vacuum PLD conditions. RBS channeling measurements revealed very high epitaxial quality (χmin−2%) of our SrTiO3 and BaTiO3 films. The factors controlling the surface morphology and electrical properties of perovskite oxide epitaxial films,are discussed.

Reflection high-energy electron diffraction (RHEED) oscillations during pulsed laser ablation of YBCO on SrTiO3(100) substrates were measured. We found that the oscillations are modulated by the laser-pulse repetition frequency, due to diffuse scattering by the initially disordered YBCO material. Since the disordered YBCO crystallizes the specular intensity recovers exponentially with time. An estimate of the diffusion length was obtained by measuring RHEED oscillations during deposition on slightly misoriented SrTiO3(100). From the rise time of the RHEED signal and the mean diffusion length a diffusion constant of 1.4*10−2cm2/sec was determined [1].

Secondary Neutrals Mass Spectrometry SNMS was used to investigate interdiffusion processes in laser deposited BiSrCaCuO HTSC thin films on various substrate materials. The in-situ deposition of epitaxial Bi2Sr2Ca1Cu2O8+x films requires a substrate temperature just below the decomposition temperature of the 2212 -phase of BiSrCaCuO. This high substrate temperature of about 850°C seems to be the reason for interdiffusion processes of BiSrCaCuO films and MgO(100), YSZ(100) and Si(100) with YSZ or SrTiO3 buffer layers as substrate materials. Therefore, Tc(R=0) of BiSrCaCuO films on silicon with buffer layer is not higher than 70 K at present. SNMS depth profiling gives a more detailed insight into interdiffusion phenomena than other analytical techniques.

The growth of (001)-textured, biaxially-aligned yttria-stabilized zirconia (YSZ) intermediate layers on amorphous or randomly-oriented polycrystalline substrates is desirable for subsequent YBa2Cu3O7–x (YBCO) c-axis thin film growth. Laser deposition of YSZ on polycrystalline metal substrates (Haynes Alloy #230) in 1.0 millitorr oxygen at 70°C produces partial (001) texture but no alignment of in-plane axes. Highly-textured biaxially-aligned layers are obtained by using an ion beam to assist growth. Similar layers are obtained on amorphous silica and polycrystalline alumina substrates. The effects of ion-beam parameters including incident angle, source gas, and beam voltage and current are presented. Highly c-axis-oriented, biaxiallyaligned YBCO thin films have been deposited in situ on these YSZ layers, with Tc(R=0) ∼ 92K and Jc(77K) = 6 × 105 A/cm2. Angular magnetoresistance data shows a dip in resistance with magnetic field normal to the film, in contrast to films grown epitaxially on single crystal substrates, which have maximum resistance with field normal.

The lead based superconductor Pb2Sr2Y0.5Ca0.5Cu3O8+δ is a most complex material. If any oxygen is present in the PbO-CuOδ-PbO sandwich layer (i.e. if δ>0) the superconductivity deteriorates. This is also a most difficult material to grow not only because of the large number of cation stoichiometries which have to be precisely balanced but also because of the tendency for multiple phases to form. Pulsed laser deposition (PLD) has been applied to prepare thin films of the 2213-phase on MgO (100) single crystal substrates at low temperature (300°C) in low oxidizing atmospheres. A basic set of ex-situ growth conditions has been determined which produce for the first time good quality films of this material as characterized by DC resistivity using the Van der Pauw method, as well as EDX and XRD. The layers are reasonably c-axis oriented and display a superconducting onset transition temperature of 79K and zero resistance at 65K after subsequent annealing in a nitrogen ambient.

Several attempts have been made by different groups to grow (110) YBa2Cu3O7−δ thin films on (110) substrates. In most of the cases, both (103) and (110) orientations of YBa2Cu3O7−δ have been found in the film. The substrate temperature during deposition is one of the major factors that determines the crystal orientation of the YBa2Cu3O7−δ. In our experiment, effort is made to examine the influence of the initial substrate temperature from 595 °C to 660 °C on the relative amount of (110) and (103) oriented grains. The orientations are determined by x-ray analysis with a Weissenberg camera. The amount of (103) oriented YBa2Cu3O7−δ is reduced systematically with decreasing substrate temperature. At the lowest deposition temperatures we find only (110) oriented growth.

Superconducting YBa2Cu3Ox (YBCO) thin films have been deposited on Si(100) substrates with yttria-stabilized zirconia (YSZ) buffer layers by laser ablation. Buffers have been obtained by laser ablation as well. The films have been characterized by scanning electron microscopy, x-ray diffractometry, secondary ion mass spectrometry, and four-contact electrical resistivity measurements. Secondary ion mass spectrometry results indicate very low interdiffusion between Si, YSZ and YBCO. The best YBCO films are textured with c axis perpendicular to the substrate and their resistance shows a normal state metallic behavior with zero resistance at temperatures higher than 80 K. The properties of YBCO films have been related with the substrate temperature and oxygen partial pressure during deposition.

Using scanning tunneling microscopy (STM) and reflection high energy electron diffraction (RHEED) we have examined the growth morphology, surface structure, and surface degradation of laser ablated YBa2Cu3O7−δ thin films. Films from 5 nm to ltm thick were studied. The films were deposited on MgO and LaAlO3 substrates using two different excimer laser ablation systems. Both island nucleated and spiral growth morphologies were observed depending on the substrate material and deposition rate used. The initial growth mechanism observed for a 5–10 nm thick film is replicated through different growth layers up to thicknesses of 200 run. Beyond 200 rnm, the films show some a-axis grains and other outgrowths. The thinnest films (5–10 nm) show considerable surface roughness on the order of 3–4 nm. For both growth mechanisms the ledge width remains approximately constant (∼ 30 nm) and the surface roughness increases as the film thickness increases. The films with spiral growth have streaked RHEED patterns despite having considerable surface roughness, while the films with island growth have more of a three dimensional diffraction pattern. RHEED patterns were obtained after the film surfaces were degraded by exposure to air, KOH developer, a Br-methanol etch, and a shallow ion mill. Exposure to air and KOH developer caused only moderate degradation of the RHEED pattern whereas a shallow (I nm deep) 300 V ion mill completely destroyed the RHEED pattern.

We have prepared high-quality superconducting YBa2Cu3O7−δ (YBCO) thin films on Si(100) with TiN as a buffer layer using in-situ multitarget deposition system. Both TiN and YBCO thin films were deposited sequentially by KrF excitner laser ( λ = 248 nm ) at substrate temperature of 650°C. Thin films were characterized using X-ray diffraction (XRD), four-point-probe ac resistivity, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Rutherford backscattering (RBS). The TiN buffer layer was epitaxial and the epitaxial relationship was found to be cube on cube with <100> TiN // <100> Si. YBCO thin films on Si with TiN buffer layer showed the transition temperature of 90–92K with Tco (zero resistance temperature) of ∼84K. We have found that the quality of the buffer layer is very important in determining the superconducting transition temperature of the thin film. The effects of processing parameters and the correlation of microstructural features with superconducting properties are discussed indetail.

Silicon oxide and oxynitride films are deposited, at low temperature (≤ 450°C) by pulsed ArF excimer laser ablation from silicon, silicon monoxide, fused silica and silicon nitride targets, performed under vacuum and in oxygen atmosphere. We investigate in this paper the specific influence of laser fluence, target materials, substrate temtperature and oxygen pressure on the composition and final properties of SiOxNy grown layers. The synthesis of good quality SiO2 films is demonstratedx. By contrast, the preparation of stoichiometric Si7N4 layers by laser ablation has to be optimized.

ABSTRACTPulsed laser deposition of compressed Si3N4 powder has been used to grow thin SiNx films on a variety of substrates at substrate temperatures ranging from room temperature to 350°C. Film composition was analyzed by Auger electron spectroscopy. The SiN0.33 films have a band gap of 5.60 eV as measured by UV absorption. The FT-IR spectrum shows an absorption characteristic of Si-N. The Si/N ratio in the deposited films corresponding to various substrate temperatures has also been determined.

Reactive pulsed laser deposition of titanium targets in a nitrogen atmosphere has been used to deposit thin titanium oxynitride films on Si substrates. The gold coloured layers exhibited a smooth, featureless surface and good chemical resistance in HF-HNO3 mixtures. The films had a high oxygen content which was responsible for relatively high electrical resistivity, measured to be 200–600 μΩ cm. This new method can easily be applied to the growth of other important nitrides such as ZrN, WN, HfN or the deposition of multilayer structures such as TiN/Ti on a variety of substrates.

Epitaxial growth of TiN films on GaAs(100) by pulsed laser deposition has been studied. Excimer KrF laser (λ=248 nm, τ=30 ns) has been used for deposition of TiN films in a chamber maintained at vacuum of ≤ 10−6 torr. The microstructure of TiN films has been characterized by x-ray diffraction and transmission electron microscopy (TEM). Cross-sectional high resolution TEM showed a smooth unreacted interface between the single crystalline TiN film and GaAs. The predominant epitaxial relationship was found to be [110]TiN//[010]GaAs, (220)TiN//(040)GaAs at a substrate temperature of 350°C. Modelling of epitaxial growth showed that the interfacial energy is an important term responsible for 45° rotation of the TiN unit cell with respect to that of GaAs. The high strain energy associated with the coherent epilayer is reduced by domain epitaxial growth. These films were characterized using high-resolution TEM techniques, and experimental results were rationalized by thin film growth modeling.

We have synthesized epitaxial TiN films having low resistivity on (100) silicon substrates using pulsed laser deposition method. The TiN films were characterized using X-ray diffraction, Rutherford back-scattering, four-point-probe ac resistivity, high resolution transmission electron microscopy techniques and epitaxial relationship was found to be <100> TiN // <100> Si. TiN films showed 10–20% channeling yield. In the plane, four unit cells of TiN match with three unit cells of silicon with less than 4.0% misfit. This domain matching epitaxy provides a new mechanism of epitaxial growth in systems with large lattice misfits. Room-temperature resistivity of these films was found to be about 15 μΩ-cm. Implications of low-resistivity epitaxial TiN in silicon device fabrication are discussed.

The pulsed laser deposition process is a powerful tool for investigating prototype epitaxial structures. This report outlines recent developments in epitaxial structures which may usefully serve as ferroelectric optical waveguides. Emphasis is given to structures on semiconductor substrates, motivated by hybrid optical/semiconductor integration. Earlier pulsed laser deposited structures, such as BaTiO3/MgO/GaAs (100) are discussed in conjunction with current results on Z-lithium niobate on GaAs (111)A and GaAs (111)B. BaTiO3/MgO/GaAs (100) grows with cube-on-cube crystallography. The epitaxial system z-lithium niobate on GaAs (111)A and GaAs (111)B has been demonstrated both with and without intermediate MgO (111) layers. The in-plane epitaxial relationships are LiNbO3 [110] // GaAs [211] and [211] indicating the existence of 180° boundaries in the LiNbO3 with and without the MgO layer, which grows cube-on-cube with the GaAs. Out-of-plane texture is typically 1.0° and 1.2° for the MgO and LiNbO3 layers respectively. In-plane texture is typically 2.8° and 4.5° for MgO and LiNbO3 layers respectively. These and similar epitaxial systems may be useful for monolithic electro-optic or frequency doubling applications in conjunction with semiconductor laser sources.

We have formed epitaxial LiNbO3 thin films on sapphire substrates (001),(110) and (012) using an excmer-laser ablation technique. We have fabricated surface acoustic wave (SAW) filters on the films and evaluated SAW properties. It is demonstrated that the LINbO3 thin films on the sapphire substrates are candidates for a high frequency SAW filter because of their high velocities of propagation (5300–5600m/s).

Potassium tantalate niobate [K(Ta1−x Nbx )O3 or KTNJ films were deposited by pulsed laser deposition (PLD) on (100)MgO substrates from targets of KTN with x=0.45. The effects of substrate temperature (300–700°C) and ambient oxygen pressure (50 and 300 mTorr) on the characteristics of films were investigated. At 500°C and 300 mTorr, films were amorphous with a few isolated, randomly-oriented crystalline grains of perovskite and pyrochlore. At 600°C and 300 mTorr, the films comprised a columnar microstructure consisting of a mixture of amorphous phase with (100) perovskite. At 650°C, films were almost entirely (100) perovskite. At 700°C, the films were predominantly (100) perovskite, but contained a much higher fraction of pyrochlore. At 50 mTorr, pyrochlore was found in significant fractions up to 650°C. At 700°C, films were predominantly (100) perovskite. Rutherford Backscattering analysis of the chemical composition showed that all the films were potassium-deficient and the tantalum to niobimn ratio exceeded that found in the targets for all deposition conditions. There appeared to be a relationship between oxygen pressure during deposition and the amount of potassium retained in the films.

The study of oxide solid-state reactions is a natural application for pulsed-laser ablation (PLA) because high quality films of virtually any oxide composition can be fabricated. In this study, the effect of interfacial morphology on reaction kinetics in the model oxide system of nickel oxide (NiO) and alumina (α-Al2O3) is investigated. Thin films of NiO have been grown on single-crystal substrates of basal (0001) α-Al2O3 by PLA in order to study the initial stages of the nickel-aluminate spinel (NiAl2O4) phase transformation. The initial state, a 100 nm NiO film on (0001) α-Al2O3, is characterized with both plan-view and cross-section transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The final state of the spinel reaction layer between the NiO and α-Al2O3 after various heat-treatments is also characterized by the same techniques.

BaTiO3 (BT) thin films deposited using pulsed laser ablation on substrates of (100) Si and (100) Si with 0.3 μm Ge were examined. For one set of samples, approximately 2000 Å of BT was deposited at 70°C at O2 pressures of 0, 1.0 and 10.0 mT. In a second set, O2 pressures of 0 and 1.0 mT were used during deposition of 200 Å of BT at 450°C followed by a 5 minute anneal and deposition of an additional 2000 Å at 750°C. This gave a total sample matrix of 10 samples. Cross-sectional TEM revealed that an interfacial layer formed in the BT on Si samples but not in the BT on Ge samples. HREM analysis of the interfaces showed that the interfacial layer was amorphous. On Ge, the BT films were found to have large areas of epitactic growth along the interface. This was confirmed by diffraction tilt angle experiments which showed a strong preferred orientation of BT on Ge. No preferred orientation was found for BT on Si. Statistical grain size analysis of the films using multiple regression showed that the film microstructures were affected most strongly by the substrate type (Ge or Si) followed by the deposition temperature of the substrate. Only a weak effect of O2 pressure was observed.

Ferroelectric Bi4Ti3O12 thin films have been deposited using second harmonics of a Q-switched Nd:YAG laser. Various single crystal substrates, including SrTiO3(100), SrTiO3(110). MgO(100), and MgO(110), were used. Structural and electro-optic properties of the films were investigated using XRD, x-ray pole figure, and linear birefringence measurements. It is found that substrate kinds and their surface orientations are important growth parameters which determine crystal axis orientation and electro-optic properties of the Bi4Ti3O12 thin films.