Growth of epitaxial γ-Al2O3 films on rigid single-crystal ceramic substrates and flexible,single-crystal-like metallic substrates by pulsed laser deposition

Epitaxial γ-Al₂O₃ thin films were grown on diverse substrates using pulsed laser deposition. The high quality of epitaxial growth and cubic structure of γ-Al₂O₃ films was confirmed by X-ray diffraction. SrTiO₃ and MgO single crystal substrates were used to optimize the growth conditions for epitaxial γ-Al₂O₃ film. Under the optimized conditions, epitaxial γ-Al₂O₃ thin films were grown on flexible, single-crystal-like, metallic templates. These included untextured Hastelloy substrates with a biaxially textured MgO layer deposited using ion-beam-assisted-deposition and biaxially textured Ni-W metallic tapes with epitaxially grown and a biaxially textured, MgO buffer layer. These biaxially textured, γ-Al₂O₃ films on flexible, single-crystal-like substrates are promising for subsequent epitaxial growth of various complex oxide films used for electrical, magnetic and electronic device applications.     

Epitaxial thin films of topological insulator Bi2Te3 with two-dimensional weak anti-localization effect grown by pulsed laser deposition

We have grown high quality epitaxial topological insulator Bi₂Te₃ thin films on silicon (111) substrates by pulsed laser deposition. Systematic structural characterization of the films using X-ray diffraction and transmission electron microscopy has demonstrated that a low laser pulse rate is the key to achieving epitaxial films. The films show n-type metallic behavior, consistent with Te deficiency as determined by Rutherford backscattering spectrometry measurements. The A_1g longitudinal optical phonon mode of Bi₂Te₃ was detected by time-resolved reflectivity measurements. A 2-dimensional (2-D) weak-antilocalization effect was also observed at low temperatures, which indicates the existence of topologically protected 2-D surface states in our thin films. This growth and characterization effort paves the way to fabricate multi-layer heterostructures of topological insulators along with ferromagnetic oxides and high temperature superconductors by the same growth technique in the search for physics arising from their interfacial couplings.     

Epitaxial-Strain Effects on Electronic Structure and Magnetic Properties of Hexagonal YMnO3 Thin Films Studied by Femtosecond Spectroscopy

In this paper, (001)-oriented hexagonal YMnO₃ (h-YMO) thin films with various nominal strain states were deposited on MgO(100), MgO(111), and YSZ(111) substrates by pulsed laser deposition. The in-plane orientation alignment and substrate-induced epitaxial strain between the h-YMO films and substrates are examined by X-ray diffraction (XRD) θ–2θ, Φ, and ω scans. The effects of epitaxial strain on the on-site Mn d–d transition energy E _dd (T), and the Néel temperature (T _N) in these thin films are investigated by wavelength-tunable ultrafast pump-probe techniques. We find that the changes of E _dd (T) and T _N depend on the type and magnitude of the epitaxial strain. The possible mechanisms for the observed strain effect on the electronic structure and associated magnetism are discussed.     

Fabrication of epitaxial conductive LaNiO3 films on different substrates by pulsed laser ablation

LaNiO₃ (LNO) thin films were deposited on (1 0 0) MgO, SrTiO₃ (STO) and LaAlO₃ (LAO) crystal substrates by pulsed laser deposition (PLD) under 20 Pa oxygen pressure at different substrate temperatures from 450 to 750 °C. X-ray diffraction (XRD), ex situ reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM) were employed to characterize the crystal structure of LNO films. LNO films deposited on STO and LAO at a temperature range from 450 to 700 °C exhibit high (0 0 l) orientation. XRD ψ scans and RHEED observations indicate that LNO films could be epitaxially grown on these two substrates with cubic-on-cubic arrangement at a wide temperature range. LNO films deposited at 700 °C on MgO (1 0 0) substrate have the (l l 0) orientation, which was identified to be bicrystalline epitaxial growth. La₂NiO₄ phase appears in LNO films deposited at 750 °C on three substrates. The epitaxial LNO films were tested to be good metallic conductive layers by four-probe method.     

Epitaxial growth of thin gold films onto pure and doped NaCl and KCl substrates

The influence of impurities such as calcium, strontium or silver ions present in the substrates on the structural growth features of continuous gold thin films, vacuum evaporated at constant deposition rates onto NaCl and KCl substrates heated in the temperature range from 90 to 300 °C, was studied by transmission electron microscopy and transmission electron diffraction. The epitaxial growth of gold thin films is inhibited by the presence of 5 × 10^-1 mol.% strontium or calcium ions in the KCl and NaCl substrates. The presence of 1.7 × 10^-1 mol.% silver ions in the NaCl substrates enhances the epitaxial growth of the gold thin films even at a substrate temperature of 120 °C. An enhancement of the gold thin film epitaxial growth is also obtained with NaCl-2 × 10^-2mol.%Ag-5 × 10^-1mol.%Ca and NaCl-1.7 × 10^-1mol.%Ag-5 × 10^-1mol.%Ca substrates.     

Chemical solution deposition and transport properties of epitaxial CuFeO2 thin films

In this paper, chemical solution deposition is used to prepare CuFeO₂ thin films on Al₂O₃ (001) substrates by nitrate-based precursors. The derived films are characterized by X-ray diffraction and field-emission scanning electron microscopy. The derived thin film is epitaxial growth. The lowest resistivity is 0.58 Ω cm at 300 K, which is comparable to the single crystals, indicating the chemical solution deposition is an effective route to obtain the CuFeO₂ films. The high- and low-temperature transport mechanisms are attributed to thermal activation and Mott variable range hopping type, respectively. The result will provide a feasible route to prepare epitaxial CuFeO₂ thin films using chemical solution deposition.     

Laser molecular beam epitaxy growth and properties of SrTiO3 thin films for microelectronic applications

Dielectric SrTiO₃ thin films were deposited on LaAlO₃ and Si substrates using laser molecular beam epitaxy. The correlations between the deposition parameters of SrTiO₃ thin films, their structural characteristics, and dielectric properties were studied. The conditions for achieving epitaxial SrTiO₃ thin films were found to be limited to deposition conditions such as deposition temperature. We show that the SrTiO₃ films with single (110) orientation can be grown directly on Si substrates. The nature of epitaxial growth and interfacial structures of the grown films were examined by various techniques, such as Laue diffraction and X-ray photoelectron spectroscopy. The SrTiO₃/Si interface was found to be epitaxially crystallized without any SiO₂ layer. Furthermore, we have measured dielectric properties of the grown SrTiO₃ multilayer suitable for tunable microwave device. A large tunability of 74.7%, comparable to that of SrTiO₃ single-crystal, was observed at cryogenic temperatures. Such STO thin films will be very promising for the development of microelectronic device applications.     

Epitaxial growth of SrRuO<Subscript>3</Subscript> thin films by RF sputtering and study of surface morphology

We report on the epitaxial growth of SrRuO₃ (SRO) thin films on Pt (111)/γ-Al₂O₃ (111) nSi (111) substrates. The grown thin films are crystalline and epitaxial as suggested by RHEED and XRD experiments. With the use of γ-Al₂O₃ (001)/nSi (001) and γ-Al₂O₃ (111)/nSi (111) substrates, crystalline but not epitaxial films have grown successfully. This result implies that lattice mismatch between nSi and SRO prevents the epitaxial growth of SRO film directly on nSi. However, the buffer Pt (111) layer mitigates lattice mismatch that provides to grow epitaxial film on nSi of quality. Morphological study shows a good surface with moderate roughness. Film grown at 700°C is smoother than the film grown at 750°C, but the variation of temperature does not affect significantly on the epitaxial nature of the films.     

Fabrication of single crystal PZT thin films on glass substrates

 We have successfully transferred heteroepitaxial Pb(Zr,Ti)O₃ (PZT) thin films from MgO substrates on to glass substrates. The transferred PZT thin films exhibit single crystal structure with ferroelectric properties similar to the as-grown epitaxial films. The transferring process comprises coating of Cr-metallized surface of epitaxial PZT thin films, pressing and cementing the Cr-metallized surface on to the glass substrates by silicone rubber, and removing the MgO substrates by chemical etching. This process realizes a fabrication of high-temperature processed PZT thin films onto the glass at room temperature. The process is also available for the transformation of PZT thin films on organic film sheet. The present transfer process reduces the effects of the inevitable strain and/or constraint to rigid substrates for heteroepitaxial growth and has a potential for integration of single crystal piezoelectric PZT devices onto a wide variety of MEMS.     

Superconducting characteristics and epitaxial-growth analyses of YBa2Cu3O7−x thin films by direct-current magnetron sputtering

Using direct-current magnetron sputtering deposition, we have successfully prepared highquality epitaxial YBa₂Cu₃O_7–x thin films, on (1 0 0) and (1 1 0) ZrO₂, SrTiO₃ and LaAlO₃ substrates. The films reached zero resistance at about 90 K and had a critical current density, J _c (at 77 K, H=O), above 10⁶ Acm^–2. Electrical measurements showed that the films had a small microwave surface resistance. The epitaxial structure of the films was studied by X-ray diffraction (XRD), Rutherford backscattering (RBS) and channeling spectroscopy, X-ray double-crystalline diffraction and transmission electron microscopy (TEM). It was found that the c-axis of the film grown on the (1 0 0) substrates under optimum deposition conditions was perpendicular to the substrate surface. But on the (1 1 0) substrates, epitaxial growth was along the (1 1 0) or (1 0 3) direction. The experimental results indicate that the films had excellent superconducting properties and complete epitaxial structure.     

Epitaxial growth and magnetic properties of <Emphasis Type="Italic">h</Emphasis>-LuFeO<Subscript>3</Subscript> thin films

In this paper, the epitaxial hexagonal LuFeO₃ (h-LuFeO₃) thin films with c-axis-oriented single phase, smooth surface were grown on YSZ (111) substrates by pulsed laser deposition method. Furthermore, a structural distortion of increased lattice constant of c is found in the epitaxial h-LuFeO₃ thin films. Moreover, the epitaxial h-LuFeO₃ thin films show room-temperature ferromagnetism. The coercive field and remnant magnetization of the epitaxial h-LuFeO₃ thin film decrease with the increase in the test temperature from 50 to 300 K. The study would be of benefit to the room-temperature single-phase multiferroic materials.     

Epitaxial growth of SrRuO3 thin films by RF sputtering and study of surface morphology

We report on the epitaxial growth of SrRuO₃ (SRO) thin films on Pt (111)/γ-Al₂O₃ (111) nSi (111) substrates. The grown thin films are crystalline and epitaxial as suggested by RHEED and XRD experiments. With the use of γ-Al₂O₃ (001)/nSi (001) and γ-Al₂O₃ (111)/nSi (111) substrates, crystalline but not epitaxial films have grown successfully. This result implies that lattice mismatch between nSi and SRO prevents the epitaxial growth of SRO film directly on nSi. However, the buffer Pt (111) layer mitigates lattice mismatch that provides to grow epitaxial film on nSi of quality. Morphological study shows a good surface with moderate roughness. Film grown at 700°C is smoother than the film grown at 750°C, but the variation of temperature does not affect significantly on the epitaxial nature of the films.     

Compositionally graded Pb(Zr,Ti)O3 thin films with different crystallographic orientations

Compositionally graded ferroelectric PbZr_xTi_1−xO₃ (PZT) films were deposited using a sputtering method and crystallized in situ at 500 °C. The films showed purely (100) or (111) crystallographic orientation when grown on Si/SiO₂/TiO₂/Pt substrates, while they exhibited c-axis epitaxial microstructure when prepared on MgO/Pt substrates. Their crystallographic orientation was controlled owing to a thin TiO_x layer sputtered on substrates prior to PZT deposition. Analysis performed by Auger depth profile clearly confirmed the variation of composition in the films. Coercive fields from 80 kV/cm to 200 kV/cm and remnant polarization as large as 45 μC/cm² were obtained. However, no typical offset was observed on hysteresis loops, unlike previous works related to graded PZT films.     

Preparation and Characterization of Nanometer Grained High Temperature Superconducting High-Quality Epitaxial Bi-2223 Thin Films Grown by DC Sputtering

Bi₂Sr₂Ca₂Cu₃O_10+?? HTSC epitaxial thin films with thickness in the order of 6.0?nm were prepared onto (100) aligned SrTiO₃ single-crystal substrates by DC sputtering from stoichiometric targets. As-grown samples were characterized by X-ray diffraction, AC-susceptibility and scanning electron microscopy. X-ray diffraction patterns show that all obtained superconducting thin films were c-axis oriented with a Bi-2223 phase. All reflections (except the substrate ones) can be assigned to the (00l) reflections of the film material (h=k=0, l??0), indicating that the films were grown preferentially with the c-axis normal to the film plane. In order to investigate the crystal quality of these Bi-2223 films, the rocking curves of the (0012) peaks were explored by ??-scans. The rocking curve of the (0012) reflection had a full width at half maximum (FWHM) of 0.30??. This demonstrates that our prepared Bi-2223 thin films have good crystalline quality and high degree of c-axis orientation. The grain size has well known important effects in the magnetic, optical, and electrical properties of metals and alloys. High temperature superconducting thin films, obtained in this work, have nanometer grain size. The mean size of the grains of the samples were determined by X-ray diffraction (XRD) and found to be in the order of 34.8?nm. The superconducting transitions temperature of several Bi-2223 samples is about 103?K. Surface morphology of the films and chemical composition were studied using scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis (EDX).     

Preparation and microstructure of nanocrystalline Rb0.5Cs0.5Ag4I5 thin films on NaCl substrates

Nanocrystalline Rb_0.5Cs_0.5Ag₄I₅ thin films were prepared by vacuum thermal evaporation on NaCl single crystal substrates. The microstructure and the electronic energy states of the thin films were examined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The results showed that the obtained Rb_0.5Cs_0.5Ag₄I₅ layer has an epitaxial orientation relationship with the NaCl substrate, and the unit cell of nanocrystalline grain Rb_0.5Cs_0.5Ag₄I₅ thin films belongs to cubic crystal system. The principal X-ray diffraction peaks at d=3.7666, 3.4557, 3.3759, 2.3026, 2.1839, 2.1385, 1.9968, and 1.9624 Å are probably related to new quaternary compound Rb_0.5Cs_0.5Ag₄I₅ thin films structure. Based on which, it can be approximately concluded that the lattice constant is a=11.31 Å.     

Thickness dependent microstructural changes in La0.5Ca0.5MnO3 thin films deposited on (111) SrTiO3

The epitaxial strain can modify the physical properties of complex oxide thin films considerably. The strain effect is expected to be less pronounced for relatively thick films and the physical properties should resemble to the bulk material. However, it has been recently observed that the electronic and magnetic properties of La_0.5Ca_0.5MnO₃ thin films deposited on (111) SrTiO₃ substrates thicker than a threshold value differ considerably from the bulk material. This observation is a hint for some interesting microstructural features in these films. In the present study, the microstructure of La_0.5Ca_0.5MnO₃ thin films on (111) SrTiO₃ substrates is investigated by X-ray diffraction and high resolution transmission electron microscopy.     

Realization of nonpolar a-plane ZnO films on r-plane sapphire substrates using a simple single-source chemical vapor deposition

Nonpolar (112?0) ZnO thin films (a-plane ZnO) have been grown on (11?02) sapphire substrates (r-plane sapphire) by a simple atmospheric pressure single-source chemical vapor deposition (SSCVD) approach. The crystallinity, surface morphology and optical property of the films were investigated using high-resolution X-ray diffraction (HRXRD), scanning electron microscope (SEM) and transmission spectrum, respectively. XRD results revealed that the ZnO films were grown on the substrates epitaxially along (112?0) orientation, and the epitaxial relationship between the ZnO films and the substrates was determined to be (112?0)ZnO∥(11?02) Al2O3, and [1?101]ZnO∥[022?1]Al₂O₃. The SEM image exhibited that the a-plane ZnO films showed a high density of well-aligned ZnO sheets with rectangular structure. The transmission spectrum showed that the ZnO films were highly transparent in the visible region.     

Preparation of epitaxial DyFeO3 thin films and magnetodielectric coupling

Multiferroic DyFeO₃ thin films deposited on (001) Nb-doped SrTiO₃ (NSTO) substrates are prepared by pulsed laser deposition. We demonstrate the epitaxial deposition of DyFeO₃ thin films on the substrates with the DyFeO₃(001)//NSTO(001) out-of-plane and DyFeO₃[100]//NSTO[110] in-plane epitaxial relationship. In addition, the weak ferromagnetism and significant magnetodielectric coupling effect at low temperature are revealed. It is indicated that the DyFeO₃ thin films have very different properties from the DyFeO₃ single crystals in term of multiferroicity.     

Precursor chemistry for the solution deposition of epitaxial La0.66Sr0.33MnO3 (LSMO) thin films

A new chemical solution deposition method for the epitaxial growth of La_0.66Sr_0.33MnO₃ (LSMO) thin films from metal acetates, acetylacetonates and propionic acid is presented. Using this method, epitaxial LSMO thin films were grown on (001) SrTiO3 (STO) single crystalline substrates in the temperature range from 800 °C to 1100 °C, both in air and in oxygen atmosphere. The LSMO thin films exhibit good structural and electrical properties. The FWHM of the ω-scan for the (002) peak has a mean value of 0.06°. The Curie temperature of the LSMO thin films is about 320 K and 350 K for the annealed in oxygen and air, respectively.     

Oxygen pressure dependent VO2 crystal film preparation and the interfacial epitaxial growth study

High quality VO₂ crystal films have been prepared on sapphire substrates by pulsed laser deposition method and the effects of oxygen pressure on the crystal phase structure are investigated. Results indicate that the phases and microstructures of VO₂ films are strongly sensitive to oxygen pressure. High oxygen pressure tends to form coarse B-VO₂ nanocrystals while low pressure favors a flat M1-VO₂ film epitaxial growth. X-ray diffraction φ-scan patterns confirm the [020] epitaxial growth orientation of the M1-VO₂ film and the in-plane lattice epitaxial relationship at the interface is also examined. Raman spectra indicate that M1-VO₂ phase has much stronger Raman scattering modes than B-VO₂, and the clear phonon modes further confirm the idea stoichiometry of VO₂ crystal film. Infrared transmittance spectra as the function of temperature are recorded and the results show that M1-VO₂ crystal films undergo a distinct infrared transmittance variation across metal insulator transition boundary, while B-VO₂ exhibits negligible thermochromic switching properties in the temperature range concerned. The pronounced phase transition behavior of the M1-VO₂ crystal film makes it a promising candidate for optical filter/switch and smart window applications in the future.