Thin films of Ln1−xSrxCoO3 (Ln=La, Nd and Gd) and SrRuO3 by nebulized spray pyrolysis

Thin films of La_1−xSr_xCoO₃, Nd_0.5Sr_0.5CoO₃, Gd_0.5Sr_0.5CoO₃ and SrRuO₃ have been deposited on Si(100), LaAlO₃(100) and SrTiO₃(100) single crystal substrates by nebulized spray pyrolysis. The films deposited on Si are generally polycrystalline, but they are highly oriented on the oxide substrates. The cobaltate films are generally not metallic, but exhibit low resistivity specially when x=0.3 and 0.5, the latter also exhibiting ferromagnetic characteristics. Films of La_0.7Sr_0.3CoO₃ show negative magnetoresistance of 35% around 180 K. Films of SrRuO₃ are metallic on Si and LaAlO₃ substrates but show an insulator–metal transition on SrTiO₃ around 130 K, around which temperature negative magnetoresistance is observed.     

Fabrication of polycrystalline La2NiMnO6 thin films on Si (1 0 0) substrates by chemical solution deposition

Polycrystalline double perovskite La₂NiMnO₆ thin films are successfully deposited on Si (1 0 0) substrates via chemical solution deposition. The X-ray diffraction and Raman scattering spectroscopy are used to characterize all the films, it is found that all films are single phase and polycrystalline. The field-emission scanning electron microscopy shows that the films are relatively smooth and dense. The magnetic measurements indicate that one sample exhibits a Curie temperature of about 271 K, which is close to that of the bulk material. Moreover, the low-temperature magnetization of the films is lower than that of the films deposited on LaAlO₃ (1 0 0) substrates, which can be attributed to the large mismatch between the films and the Si substrates.     

Surface modification of thermoplastics by atomic layer deposition of Al2O3 and TiO2 thin films

Al₂O₃ and TiO₂ thin films were deposited by atomic layer deposition at 80-250 °C on various polymeric substrates such as polymethylmethacrylate (PMMA), polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE) and ethylenetetrafluoroethylene (ETFE). The films were studied with FESEM, EDX, XRD, contact angle measurements and adhesion tests. The film growth rates on the thermoplastics were close to the corresponding growth rates on Si substrates. The adhesion of the films was good on PEEK and poor on PTFE. All coated surfaces showed lower water contact angles than the uncoated thermoplastics. Furthermore, the water contact angles on all TiO₂-coated surfaces decreased upon UV illumination, most efficiently with crystalline TiO₂ coatings.     

Structural study of lanthanum nickelate thin films deposited on different single crystal substrates

Fabrications of La₂NiO_4+δ thin film layers by liquid-injection metalorganic chemical vapor deposition were tried on different single crystals substrates: (001)Si, (001)MgO, (001)LaAlO₃ and (001)SrTiO₃. As results of structural characterizations, polycrystalline dendritic layers of La₂NiO_4+δ tetragonal (or orthorhombic) phase were observed on (001)Si substrates while layers of a perovskite-like cubic structure were observed on the other single crystal substrates. From a high-resolution TEM study of a layer deposited on (001)MgO, such a perovskite-like cubic structure exhibits many planar structural faults likely similar to planes of oxygen vacancies of the La₂NiO_4+δ orthorhombic structure. A thin intermediate epitaxial layer of NiO phase was also identified. Using a X-ray texture diffractometer, the layer structure on (001)MgO, (001)LaAlO₃ and (001)SrTiO₃ was confirmed to be of cubic structure with 〈100〉 axes parallel to those of the substrate. The T dependence of the resistivity of a layer deposited on (001)MgO substrate was found to be of a semi-conducting behavior.     

LiNbO3 and LiTaO3 thin films deposited by chemical and/or physical processes

Lithium niobate LiNbO₃ thin films were deposited onto silicon (111) Si and sapphire (001) AI₂O₃ single crystal substrates by the pyrosol and/or r.f. sputtering processes. A matrix of experiments was designed to determine the effects of several experimental parameters on the resulting film quality (stoichiometry, crystallization state) and properties. Under optimized conditions, requiring the combination of the two above-mentioned deposition techniques, <001 > oriented polycrystalline LiNbO₃ films were grown which exhibit homogeneous and columnar grain structures with the <c > -polar axis normal to the substrate surface.     

Effect of substrate on phase formation and surface morphology of sol-gel lead-free KNbO3, NaNbO3, and K0.5Na0.5NbO3 thin films

Environmentally acceptable lead-free ferroelectric KNbO₃ (KN) or NaNbO₃ (NN) and K_0.5Na_0.5NbO₃ (KNN) thin films were prepared using a modified sol-gel method by mixing potassium acetate or sodium acetate or both with the Nb-tartrate complex, deposited on the Pt/Al₂O₃ and Pt/SiO₂/Si substrates by a spin-coating method and sintered at 650°C. X-ray diffraction (XRD) analysis indicated that the NN and KNN films on the Pt/SiO₂/Si substrate possessed a single perovskite phase, while NN and KNN films on the Pt/Al₂O₃ substrate contained a small amount of secondary pyrochlore phase, as did KN films on both substrates. Scanning electron microscopic (SEM) and atomic force microscopic (AFM) analyses confirmed that roughness R _q of the thin KNN/Pt/SiO₂/Si film (?? 7.4 nm) was significantly lower than that of the KNN/Pt/Al₂O₃ film (?? 15 nm). The heterogeneous microstructure composed of small spherical and larger needle-like or cuboidal particles were observed in the KN and NN films on both substrates. The homogeneous microstructure of the KNN thin film on the Pt/SiO₂/Si substrate was smoother and contained finer spherical particles (?? 50 nm) than on Pt/Al₂O₃ substrates (?? 100 nm). The effect of different substrates on the surface morphology of thin films was confirmed.     

Oriented SrFe12O19 thin films prepared by chemical solution deposition

Thin films of SrFe₁₂O₁₉ (SrM) were prepared from a solution of iron and strontium alkoxides through the chemical solution deposition method on both amorphous (glassy SiO₂), and single crystal substrates (Si(100), Si(111), Ag(111), Al₂O₃(001), MgO(111), MgAl₂O₄(111), SrTiO₃(111)) substrates. The process of crystallization was investigated by means of powder diffraction, atomic force microscopy and scanning electron microscopy. Magnetization measurements, ferromagnetic and nuclear magnetic resonance were used for evaluation of anisotropy in the films. Whilst amorphous substrates enabled growth of randomly oriented SrM phase, use of single crystal substrates resulted in samples with different degree of oriented growth. The most pronounced oriented growth was observed on SrTiO₃(111). A detailed inspection revealed that growth of SrM phase starts through the breakup of initially continuous film into isolated grains with expressive shape anisotropy and hexagonal habit. A continuous film with epitaxial relations to the substrate was produced by repeating recoating and annealing.     

Synthesis and microstructural TEM investigation of CaCu3Ru4O12 ceramic and thin film

CaCu₃Ru₄O₁₂ (CCRO) is a conductive oxide having the same structure as CaCu₃Ti₄O₁₂ (CCTO) and close lattice parameters. The later compound is strongly considered for high density parallel plates capacitors application due to its so-called colossal dielectric constant. The need for an electrode inducing CCTO epitaxial growth with a clean and sharp interface is therefore necessary, and CCRO is a good potential candidate. In this paper, the synthesis of monophasic CCRO ceramic is reported, as well as pulsed laser deposition of CCRO thin film onto (001) NdCaAlO₄ substrate. Structural and physical properties of bulk CCRO were studied by transmission electron microscopy and electron spin resonance. CCRO films and ceramic exhibited a metallic behavior down to low temperature. CCRO films were (001) oriented and promoted a CCTO film growth with the same orientation.     

The influence of A-site rare-earth for barium substitution on the chemical structure and ferroelectric properties of BZT thin films

Rare-earth (RE) doped Ba(Zr,Ti)O₃ (BZT) thin films were prepared by rf-magnetron sputtering from a Ba_0.90Ln_0.067Zr_0.09Ti_0.91O₃ (Ln=La, Nd) target. The films were deposited at a substrate temperature of 600 °C in a high oxygen pressure atmosphere. X-ray diffraction (XRD) patterns of RE-BZT films revealed a 〈001〉 epitaxial crystal growth on Nb-doped SrTiO₃, 〈001〉 and 〈011〉 growth on single-crystal Si, and a 〈111〉-preferred orientation on Pt-coated Si substrates. Scanning electron microscopy (SEM) showed uniform growth of the films deposited, along with the presence of crystals of about half-micron size on the film's surface. Transmission electron microscopy (TEM) evidenced high crystalline films with thicknesses of about 100 nm for 30 min of sputtering. Electron-probe microanalysis (EPMA) corroborated the growth rate (3.0-3.5 nm/min) of films deposited on Pt-coated Si substrates. X-ray photoelectron spectroscopy (XPS), in depth profile mode, showed variations in photoelectron Ti 2p doublet positions at lower energies with spin-orbital distances characteristic of BaTiO₃-based compounds. The XPS analysis revealed that lanthanide ions positioned onto the A-site of the BZT-perovskite structure increasing the MO₆-octahedra distortion (M=Ti, Zr) and, thereby, modifying the Ti-O binding length. Polarization-electric field hysteresis loops on Ag/RE-doped BZT/Pt capacitor showed good ferroelectric behavior and higher remanent polarization values than corresponding non-doped system.     

Fabrication and electron transport properties of epitaxial films of electron-doped 12CaO·7Al2O3 and 12SrO·7Al2O3

Epitaxial growth and electron doping of 12CaO·7Al₂O₃ (C12A7) and 12SrO·7Al₂O₃ (S12A7) are reported. The C12A7 films were prepared on Y₃Al₅O₁₂ (YAG) single-crystal substrates by pulsed laser deposition at room temperature and subsequent thermal crystallization. X-ray diffraction patterns revealed the films were grown epitaxially with the orientation relationship of (001)[100] C12A7 || (001)[100] YAG. For S12A7, pseudo-homoepitaxial growth was attained on the C12A7 epitaxial layer. Upon electron doping, metallic conduction was achieved in the C12A7 film and the S12A7/C12A7 double-layered films. Analyses of optical absorption spectra for the S12A7/C12A7 films provided the densities of free electrons in each layer separately. Hall measurements exhibited larger electron mobility in the S12A7/C12A7 film than those in C12A7 and S12A7 films, suggesting free electrons may be accumulated at the S12A7/C12A7 interface due presumably to a discontinuity of the cage conduction bands.     

Fabrication and optical conductivities of strained epitaxial NaxCoO2 thin films: x=0.5, 0.7

Epitaxial γ phase-Na_xCoO₂ thin films were deposited on (001) sapphire by the pulsed laser deposition method. To fabricate epitaxial Na_0.5CoO₂ thin films, we used a solution of iodine-dissolved acetonitrile and obtained an epitaxial Na_0.5CoO₂ thin film with a high crystallinity because of Na deintercalation of epitaxial Na_0.7CoO₂. From the spectroscopic ellipsometry analysis, we obtained the optical constants as well as the optical conductivities for the Na_0.5CoO₂ and Na_0.7CoO₂ thin films. The energy splitting between e_g and a_1g increased because of the structural strain of the Na_0.7CoO₂ thin film. It is inferred that the structural strain is the source for the lower resistivity and the preservation of the strongly correlated system up to 200 K for the Na_0.7CoO₂ thin film. On the other hand, the strain in the Na_0.5CoO₂ thin film was not affected, and the charge-ordering state and the Na content (x=0.5) only cause the charge-ordering state.     

Chemical solution deposited silver tantalate niobate, Ag x (Ta0.5Nb0.5)O3? y , thin films on (111)Pt/Ti/SiO2/(100)Si substrates

Silver tantalate niobate films are candidates for temperature stable microwave dielectrics. In this work, a chemical solution deposition synthesis method was developed for Ag _x (Ta_0.5Nb_0.5)O_3−y films on Pt-coated Si substrates. Stable solutions with a range of silver stoichiometries were prepared using 2-methoxyethanol and pyridine as solvents, from AgNO₃ and Nb and Ta ethoxide precursors. It was extremely difficult to prepare phase-pure perovskite films of Ag(Ta_0.5Nb_0.5)O₃ on Pt-coated Si subtrates; instead a mixture of perovskite and natrotantite phases was identified. Such mixed phase films had dielectric constant ɛ _r and dielectric loss tanδ values ranging from 200±20 to 270±25 and 0.006±0.002 to 0.002±0.001 at 100 kHz, respectively, depending on the firing temperature. For Ag₂(Ta_0.5Nb_0.5)₄O₁₁, Ag_0.8(Ta_0.5Nb_0.5)O_2.9, Ag_0.85(Ta_0.5Nb_0.5)O_2.925 and Ag_0.9(Ta_0.5Nb_0.5)O_2.95 films, mainly the natrotantite phase was observed. The ɛ _r values of these films were between 70±10 and 130±15 with tan δ values of 0.008±0.002 at 100 kHz.     

Phase separation morphology of thin films of polystyrene/polyisoprene blends

We present the results of a study of the morphology of phase separation in a thin film blend of polystyrene (PS) and polyisoprene (PI) in a common solvent of toluene. The blend is quenched by rapid solvent evaporation using a spincoating technique rather than a temperature quench. The mass fraction of polystyrene is varied to determine the effect of the substrate on thin film phase separation morphology. We compare the phase separation morphology for very thin films of the PS/PI blend cast onto three different substrates: Si(001) with a native oxide layer (Si (SINGLEBOND) SiO_x), Si(001) etched in hydrofluoric acid (Si-H), and a Au/Pd alloy sputtered onto Si(001). We observe large differences between the morphologies of 1000 Å thick blend films on the Si(SINGLEBOND) SiO_x and Si-H substrates as the mass fraction is varied due to the difference in the wetting properties of PS on the two substrates. Smaller differences are observed between the films on the Si(SINGLEBOND) SiO_x and Au/Pd substrates only for film thicknesses h < 600 Å. © 1996 John Wiley & Sons, Inc.     

Crystallization of textured PbTiO3 films deposited from gels

Sol-gel processed PbTiO₃ thin films have been deposited by spin coating onto different subtrates; Si[111], Si/Al, Si/SiO₂/Cr/Pt, MgO[100], SrTiO₃[100] and sapphire. Interactions between the substrate and PbTiO₃ films after heat treatment have been studied by X-ray diffraction and Rutherford Back Scattering. When deposited onto sapphire and Si[111], PbTiO₃ films exhibit a preferred orientation with (101) perpendicular to the substrate. These films become oriented along (100) onto MgO and (001) onto SrTiO₃[100] substrates. A strong channelling effect is observed by the RBS technique when the film is oriented along the c axis on SrTiO₃[100] suggesting that these films are epitaxially grown. The diffusion of metal atoms during the thermal treatment gives rise to the formation of lead silicate on Si[111] substrates. As a result a pyrochlore phase is formed. Lead titanate films on Si/SiO₂/Cr/Pt and Si/Al substrates are polycrystalline and do not exhibit any texture.     

Magnetoelectric Bi3.25Nd0.75Ti3O12–La0.6Ca0.4MnO3 composite thin films derived by SOL–GEL method

Magnetoelectric (ME) Bi_3.25Nd_0.75Ti₃O₁₂–La_0.6Ca_0.4MnO₃ (BNT–LCMO) composite thin films were deposited on Pt/Ti/SiO₂/Si(100) substrates by a simple SOL–GEL method and spin-coating process with two different deposition sequences: BNT/LCMO/Pt/Ti/SiO₂/Si(BLP) and LCMO/BNT/Pt/Ti/SiO₂/Si(LBP). Our results show the composite thin films exhibit both good ferroelectric and magnetic properties, as well as a ME effect. BLP thin films have larger maximum ME voltage coefficient values than LBP structured thin films. The deposition sequence has a notable effect on the ferroelectric and magnetic properties and ME coupling behavior of the bi-layer thin films.     

Growth of iron cobalt oxides by atomic layer deposition

Thin films of iron cobalt oxides with spinel-type structure are made by the atomic layer deposition (ALD) technique using Fe(thd)3 (Hthd = 2,2,6,6-tetramethylheptane-3,5-dione), Co(thd)2, and ozone as precursors. Pulse parameters for ALD-type growth are established and such growth can be achieved at deposition temperatures between 185 and 310 degrees C. Films have been deposited on amorphous soda-lime glass and single-crystalline substrates of Si(100), MgO(100), and alpha-Al2O3(001) which all provide crystalline films, but with various orientations and crystallite sizes. Application of an external magnetic field during the film growth does not influence film growth characteristics (growth rate, crystallinity, topography etc.). Magnetization data are reported for phase-pure films of spinel-type structure with composition Fe2CoO4.     

Metal-Organic Chemical Vapor Deposition (MOCVD) Synthesis of Heteroepitaxial Pr0.7Ca0.3MnO3 Films: Effects of Processing Conditions on Structural/Morphological and Functional Properties

Calcium-doped praseodymium manganite films (Pr_0.7Ca_0.3MnO₃, PCMO) were prepared by metal-organic chemical vapor deposition (MOCVD) on SrTiO₃ (001) and SrTiO₃ (110) single-crystal substrates. Structural characterization through X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) analyses confirmed the formation of epitaxial PCMO phase films. Energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) characterization was used to confirm lateral and vertical composition and the purity of the deposited films. Magnetic measurements, obtained in zero-field-cooling (ZFC) and field-cooling (FC) modes, provided evidence of the presence of a ferromagnetic (FM) transition temperature, which was correlated to the transport properties of the film. The functional properties of the deposited films, combined with the structural and chemical characterization collected data, indicate that the MOCVD approach represents a suitable route for the growth of pure, good quality PCMO for the fabrication of novel spintronic devices.     

Substrate dependent structure and in-plane dielectric properties of Ba(Sn0.15Ti0.85)O3 thin films

The structure, microstructure and in-plane dielectric properties of Barium tin titanate Ba(Sn_0.15Ti_0.85)O₃ (BTS) thin films grown on (100) LaAlO₃ (LAO) and (100) MgO single crystal substrates through sol–gel process were investigated. The films deposited on (100) LAO substrate exhibited a strong (100) preferred orientation while the film deposited on (100) MgO substrate showed polycrystalline structure. The in-plane ɛ–T measurements reveal that the films grown on (100) LAO substrate exhibited an obvious room-temperature ferroelectric state, while the film grown on MgO substrate showed paraelectric state in the temperature range of 10–130 °C. A high tunability of 52.11% was observed for the BTS films deposited on (100) LAO substrate at the frequency of 1 MHz with an applied electric field of 80 kV/cm, which is about two times larger than that of the BTS films deposited on (100) MgO substrate. The obvious differences in the dielectric properties could be attributed to the stress in the films, which come from lattice mismatch and difference in the thermal expansion coefficients between the film and substrates. This work clearly reveals the highly promising potential of BTS films for application in tunable devices.     

Textured PLCT Thin Films Prepared on Pt/Ti/SiO2/Si Substrate by Metal-Organic Decomposition

Textured calcium modified (Pb,La)TiO₃ (PLCT) films were deposited on Pt/Ti/SiO₂/Si substrates by using a metal-organic decomposition (MOD) process. The PLCT films exhibit good ferroelectric properties, a very low leakage current and a sharp PLCT/Pt interface. The (100) texture of the PLCT film is growth-controlled; the (100) oriented grains grow preferentially so as to minimize the surface energy. Particularly, the (100) preferred orientation is easy to form in the PLCT film with a layered structure for which the substrate almost does not affect the nucleation and growth of the film.     

Structure formation in yttrium-barium cuprate superconductor films obtained from solutions of methacrylates on lanthanum aluminate substrates

Nanoscale structuring of YBa₂Cu₃O₇ high-temperature superconductor films on a lanthanum aluminate LaAlO₃ substrate was studied after annealing at 200–850°C. For this purpose, a 0.5% aerosol of Y, Ba, and Cu methacrylates was deposited on the substrate. A general scheme of the mechanism of complex oxide film formation from chemical solutions is suggested. The formation of complex oxide film structures from solutions was found to be a three-stage process irrespective of the deposition procedure. It included the liquid-phase, pyrolytic, and high crystallization stages.