Optimized La0.6Sr0.4CoO3–δ Thin‐Film Electrodes with Extremely Fast Oxygen‐Reduction Kinetics

La_0.6Sr_0.4CoO_3–δ (LSC) thin‐film electrodes are prepared on yttria‐stabilized zirconia (YSZ) substrates by pulsed laser deposition at different deposition temperatures. The decrease of the film crystallinity, occurring when the deposition temperature is lowered, is accompanied by a strong increase of the electrochemical oxygen exchange rate of LSC. For more or less X‐ray diffraction (XRD)‐amorphous electrodes deposited between ca. 340 and 510 °C polarization resistances as low as 0.1 Ω cm² can be obtained at 600 °C. Such films also exhibit the best stability of the polarization resistance while electrodes deposited at higher temperatures show a strong and fast degradation of the electrochemical kinetics (thermal deactivation). Possible reasons for this behavior and consequences with respect to the preparation of high‐performance solid oxide fuel cell (SOFC) cathodes are discussed.     

Fabrication and Electrochemical Properties of Epitaxial Samarium‐Doped Ceria Films on SrTiO3‐Buffered MgO Substrates

Thin films of samarium‐oxide‐doped (20 mol%) ceria (SDC) are grown by pulsed‐laser deposition (PLD) on (001) MgO single‐crystal substrates. SrTiO₃ (STO) prepared by PLD is used as a buffer layer on the MgO substrates to enable epitaxial growth of the fluorite‐structured SDC film; the STO layer provides a proper crystalline match between SDC and MgO, resulting in highly crystalline, epitaxial SDC films grown in the (001) orientation. Film conductivity is evaluated by electrochemical impedance spectroscopy measurements, which are performed at various temperatures (400–775 °C) in a wide range of oxygen partial pressure (pO₂) values (10^?25?1 atm) in order to separate ionic and electronic conductivity contributions. At 700 °C, SDC/STO films on (100) MgO exhibit a dominant ionic conductivity of about 7 × 10^?2 S cm^?1, down to pO₂ values of about 10^?15 atm. The absence of grain boundaries make the SDC/STO/MgO heterostructures stable to oxidation‐reduction cycles at high temperatures, in contrast to that observed for the more disordered SDC/STO films, which degraded after hydrogen exposure.     

Indium Tin Oxide Thin Films Grown on Polyethersulphone (PES) Substrates by Pulsed‐Laser Deposition for Use in Organic Light‐Emitting Diodes

High quality indium tin oxide (ITO) thin films were grown by pulse laser deposition (PLD) on flexible polyethersulphone (PES) substrates. The electrical, optical, and surface morphological properties of these films were examined as a function of substrate temperature and oxygen pressure. ITO thin films, deposited by PLD on a PES substrate at room temperature and an oxygen pressure of 15 mTorr, have a low electrical resistivity of 2.9×10^?4 Ω cm and a high optical transmittance of 84 % in the visible range. They were used as the anode in organic light‐emitting diodes (OLEDs). The maximum electro luminescence (EL) and current density at 100 cd/m² were 2500 cd/m² and 2 mA/cm², respectively, and the external quantum efficiency of the OLEDs was found to be 2.0 %.     

Properties of Flame Sprayed Ce0.8Gd0.2O1.9‐δ Electrolyte Thin Films

Thin films of Ce_0.8Gd_0.2O_1.9‐δ (CGO) are deposited by flame spray deposition with a deposition rate of about 30 nm min^?1. The films (deposited at 200 °C) are dense, smooth, and particle‐free and show a biphasic amorphous/nanocrystalline microstructure. Isothermal grain growth and microstrain are determined as a function of dwell time and temperature and correlated to the electrical conductivity. CGO films annealed for 10 h at 600 °C present the best electrical conductivity of 0.46 S m^?1 measured at 550 °C. Reasons for the superior performance of films annealed at low temperature over higher‐temperature‐treated samples are discussed and include grain‐size evolution, microstrain relaxation, and chemical decomposition. Nanoindentation measurements are conducted on the CGO thin films as a function of annealing temperature to determine the hardness and elastic modulus of the films for potential application as free‐standing electrolyte membranes in low‐temperature micro‐SOFCs (solid oxide fuel cells).     

Dielectric properties of low loss Ba<Subscript>6−3x</Subscript>Nd<Subscript>8+2x</Subscript>Ti<Subscript>18</Subscript>O<Subscript>54</Subscript> thin films prepared by pulsed laser deposition for microwave applications

Ba_6−3xNd_8+2xTi₁₈O₅₄ with x=0.25 (BNT-0.25, or simply, BNT) dielectric thin films with a thickness of 320 nm have been prepared on Pt-coated silicon substrates by pulsed laser deposition (PLD) at the substrate temperature of 650°C in 20 Pa oxygen ambient. X-ray analysis showed that the as-deposited films are amorphous and the films remain amorphous after a postannealing at 750°C for 30 min. The dielectric constant of the BNT films has been determined to be about 80 with a low loss tan δ of about 0.006 at 1 MHz. The capacitance-voltage (C-V), capacitance-frequency, and capacitance-temperature characteristics of a BNT capacitor with Pt top electrode were measured. A low leakage-current density of 4×10⁻⁶ A/cm² at 6 V was measured, and a preliminary discussion of the leakage-current mechanism is also given. It is proposed that amorphous BNT-0.25 thin films will be a potential dielectric material for microwave applications.     

Impact of vacuum and nitrogen annealing on HVE SnS photoabsorber films

Researchers worldwide focus on new earth abundant and cheap absorber materials for use in thin film solar cells that allow wider use of photovoltaics in energy production. SnS is one of such promising absorber materials that comprises earth abundant elements (Sn, S). We describe here the effect of annealing of high vacuum evaporated (HVE) SnS thin films in vacuum and nitrogen atmosphere with relatively high pressures of nitrogen. SnS thin films with a thickness of 500 nm were deposited onto the surface of glass by HVE at a substrate temperature of 300 °C. The as-deposited SnS thin films were annealed at 500 °C and 550 °C for 1 h in vacuum as well as in nitrogen with respect to ambient (N₂) pressure that varied in the range of 500–2000 mbar. We analyze crystalline quality, crystal structure, elemental and phase compositions, and electrical properties of SnS films before and after the annealing process and their changes. Our results show that the use of pressurized inert ambient, such as nitrogen, improves the crystalline quality as well as the electrical properties of SnS thin films. The enhanced growth of crystals and modification of microstructural properties of SnS thin films as a function of annealing conditions (type of ambient, annealing temperature and ambient pressure) are discussed in detail.     

Integration of Self‐Assembled Epitaxial BiFeO3–CoFe2O4 Multiferroic Nanocomposites on Silicon Substrates

Perovskite‐spinel epitaxial nanocomposite thin films are commonly grown on single crystal perovskite substrates, but integration onto a Si substrate can greatly increase their usefulness in devices. Epitaxial BiFeO₃–CoFe₂O₄ nanocomposites consisting of CoFe₂O₄ pillars in a BiFeO₃ matrix are grown on (001) Si with two types of buffer layers: molecular beam epitaxy (MBE)‐grown SrTiO₃‐coated Si and pulsed‐laser‐deposited (PLD) Sr(Ti_0.65Fe_0.35)O₃/CeO₂/yttria‐stabilized ZrO₂/Si. The nanocomposite grows with the same crystallographic orientation and morphology as that observed on single crystal SrTiO₃ when the buffered Si substrates are smooth, but roughness of the Sr(Ti_0.65Fe_0.35)O₃ promoted additional CoFe₂O₄ pillar orientations with 45° rotation. The nanocomposites on MBE‐buffered Si show very high magnetic anisotropy resulting from magnetoelastic effects, whereas the hysteresis of nanocomposites on PLD‐buffered Si can be understood as a combination of the hysteresis of the Sr(Ti_0.65Fe_0.35)O₃ film and the CoFe₂O₄ pillars.     

Non‐stoichiometry in Oxide Thin Films: A Chemical Capacitance Study of the Praseodymium‐Cerium Oxide System

While the properties of functional oxide thin films often depend strongly on their oxygen stoichiometry, there have been few ways to extract this information reliably and in situ. In this work, the derivation of the oxygen non‐stoichiometry of dense Pr_0.1Ce_0.9O_2?δ thin films from an analysis of chemical capacitance obtained by impedance spectroscopy is described. Measurements are performed on electrochemical cells of the form Pr_0.1Ce_0.9O_2?δ/Y_0.16Zr_0.84O_1.92/Pr_0.1Ce_0.9O_2?δ over the temperature range of 450 to 800 °C and oxygen partial pressure range of 10^?5 to 1 atm O₂. With the aid of a defect equilibria model, approximations relate chemical capacitance directly to non‐stoichiometry, without need for fitting parameters. The calculated non‐stoichiometry allows extraction of the thermodynamic constants defining defect generation. General agreement of these constants with bulk values derived by thermogravimetric analysis is found, thereby confirming the suitability of this technique for measuring oxygen non‐stoichiometry of thin oxide films. Potential sources of error observed in earlier chemical capacitance studies on perovskite structured oxide films are also discussed.     

Making Large‐Area Titanium Disulfide Films at Reduced Temperature by Balancing the Kinetics of Sulfurization and Roughening

The synthesis of large‐area TiS₂ thin films is reported at temperatures as low as 500 °C using a scalable two‐step method of metal film deposition followed by sulfurization in an H₂S gas furnace. It is demonstrated that the lowest‐achievable sulfurization temperature depends strongly on the oxygen background during sulfurization. This dependence arises because Ti? O bonds present a substantial kinetic and thermodynamic barrier to TiS₂ formation. Lowering the sulfurization temperature is important to make smooth films, and to enable integration of TiS₂ and related transition metal dichalcogenides—including metastable phases and alloys—into device technology.     

Growth of Heteroepitaxial ZnO Thin Films on GaN‐Buffered Al2O3 (0001) Substrates by Low‐Temperature Hydrothermal Synthesis at 90 °C

Heteroepitaxial ZnO films are successfully grown on nondoped GaN‐buffered Al₂O₃ (0001) substrates in water at 90 °C using a two‐step process. In the first step, a discontinuous ZnO thin film (ca. 200 nm in thickness) consisting of hexagonal ZnO crystallites is grown in a solution containing Zn(NO₃)·6 H₂O and NH₄NO₃ at ca. pH 7.5 for 24 h. In the second step, a dense and continuous ZnO film (ca. 2.5 μm) is grown on the first ZnO thin film in a solution containing Zn(NO₃)·6 H₂O and sodium citrate at ca. pH 10.9 for 8 h. Scanning electron microscopy, X‐ray diffraction, UV‐vis absorption spectroscopy, photoluminescence spectroscopy, and Hall‐effect measurement are used to investigate the structural, optical, and electrical properties of the ZnO films. X‐ray diffraction analysis shows that ZnO is a monocrystalline wurtzite structure with an epitaxial orientation relationship of (0001)[11 0]_ZnO∥(0001)[11 0]_GaN. Optical transmission spectroscopy of the two‐step grown ZnO film shows a bandgap energy of 3.26 eV at room temperature. A room‐temperature photoluminescence spectrum of the ZnO film reveals only a main peak at ca. 380 nm without any significant defect‐related deep‐level emissions. The electrical property of ZnO film showed n‐type behavior with a carrier concentration of 3.5 × 10¹⁸ cm^–3 and a mobility of 10.3 cm² V^–1 s^–1.     

Room-temperature ferromagnetic ordering in Mn-doped ZnO thin films grown by pulsed laser deposition

The ferromagnetic ordering in Mn-doped ZnO thin films grown by pulsed laser deposition (PLD) as a function of oxygen pressure and substrate temperature has been investigated. Room-temperature ferromagnetic behaviors in the Mn-doped ZnO films grown at 700°C and 800°C under 10⁻¹ torr in oxygen pressure were found, whereas ferromagnetic ordering in the films grown under 10⁻³ torr disappeared at 300 K. The large positive magnetoresistance (MR), ∼10%, was observed at 5 K at low fields and small negative MR was observed at high fields, irrespective of oxygen pressure. In particular, anomalous Hall effect (AHE) in the Mn-doped ZnO film grown at 700°C under 10⁻¹ Torr has been observed up to 210 K. In this work, the observed AHE is believed to be further direct evidence demonstrating that the Mn-doped ZnO thin films are ferromagnetic.     

Single‐Crystalline Films of the Homologous Series InGaO3(ZnO)m Grown by Reactive Solid‐Phase Epitaxy

Single‐crystalline thin films of the homologous series InGaO₃(ZnO)_m (where m is an integer) are fabricated by the reactive solid‐phase epitaxy (R‐SPE) method. Specifically, the role of ZnO as epitaxial initiator layer for the growth mechanism is clarified. High‐temperature annealing of bilayer films consisting of an amorphous InGaO₃(ZnO)₅ layer deposited at room temperature and an epitaxial ZnO layer on yttria‐stabilized zirconia (YSZ) substrate allows for the growth of single‐crystalline film with controlled chemical composition. The epitaxial ZnO thin layer plays an essential role in determining the crystallographic orientation, while the ratio of the thickness of both layers controls the film composition.     

Deposition and characterization of Pb TiO3 thin films on silicon wafers using metalorganic sources

Ferroelectric PbTiO₃ thin films were deposited on bare silicon and Pt/SiO₂/Si substrates by metalorganic chemical vapor deposition in a temperature range from 270 to 550°C. The deposition of a single phase PbTiO₃ thin film did not occur on bare silicon substrates. Instead a double layer of lead-silicate and PbTiO₃ was formed owing to a serious diffusion of lead and oxygen ions into silicon substrates. But on Pt/SiO₂/Si substrates, a single phase PbTiO₃ oriented parallel to a-and c-axis was grown at a substrate temperature as low as 350°C even without a high temperature post-annealing. To get an optimal film, a precise control of input gas composition and also a deposition in a low temperature range from 350 to 400°C are necessary.     

Synthesis and characterization of phosphorus-doped ZnO and (Zn,Mg)O thin films via pulsed laser deposition

The transport and optical properties of phosphorus-doped (Zn,Mg)O thin films grown via pulsed laser deposition (PLD) are studied. The carrier type of as-deposited (Zn,Mg)O:P films converts from n-type to p-type with increasing oxygen partial pressure. All the films exhibit good crystallinity with c-axis orientation. This result indicates the importance of oxidation conditions in realizing p-type (Zn,Mg)O:P films. The as-deposited ZnO:P film properties show a strong dependence on the deposition ambient at different growth temperatures. The resistivity of the samples deposited in O₃/O₂ mixture is two orders of magnitude higher than the films grown in oxygen and O₂/Ar/H₂ mixture. The room-temperature photoluminescence (PL) of the as-deposited films has been shown that growing in the O₂/Ar/H₂ mixture ambient significantly increases the band edge emission while inhibiting the visible emission. The enhanced ultraviolet (UV) emission in the films grown in O₂/Ar/H₂ mixture may result from hydrogen passivation of the deep level emission centers. The annealed ZnO:P films are n-type with nonlinear dependence of resistivity on annealing temperature. The resistivity increases in the films with annealing at 800°C while decreasing with further increasing annealing temperature. Strong visible light emission is observed from the ZnO:P films annealed in oxygen.     

Hierarchically Ordered Nano‐Heterostructured PZT Thin Films with Enhanced Ferroelectric Properties

Realization of ferroelectric (FE) devices based on the polarization effects of Pb(Zr_0.52Ti_0.48)O₃ (PZT) has reinforced the investigation of this material in multiple dimensions and length scales. Multi‐level hierarchical nanostructure engineering in PZT thin films offer dual advantages of variable length‐scale and dimensionality. Here, the growth of hierarchically ordered PZT nano‐hetero­structures (Nhs) from PZT seed‐layer deposited on SrTiO₃:Nb (100) substrates, using a physical/chemical combined methodology involving pulsed laser deposition (PLD) and hydrothermal processes, is reported. Systematic SEM, TEM, and Raman spectroscopy studies reveal mixed hetero‐ and homo‐epitaxial growth mechanism. In the final stage, 3D Nh units cross‐link and form a dense network‐like Nh PZT thin‐film. FE polarizations are measured without using any polymer fill‐layer which otherwise introduces huge dielectric losses and lowers the polarization values for a FE device. In benefit, well saturated and symmetric FE hysteresis loops are observed with high degree of squareness and a high remnant polarization (54 μC cm^‐2 at a coercive field of 237 kV cm^‐1). This work provides a pathway towards preparing hierarchical PZT Nhs offering coherent design of high‐performance FE capacitors for data storage technologies in future.     

Micro Solid Oxide Fuel Cells on Glass Ceramic Substrates

Miniaturized solid oxide fuel cells are fabricated on a photostructurable glass ceramic substrate (Foturan) by thin film and micromachining techniques. The anode is a sputtered platinum film and the cathode is made of a spray pyrolysis (SP)‐deposited lanthanum strontium cobalt iron oxide (LSCF), a sputtered platinum film and platinum paste. A single‐layer of yttria‐stabilized zirconia (YSZ) made by pulsed laser deposition (PLD) and a bilayer of PLD–YSZ and SP–YSZ are used as electrolytes. The total thickness of all layers is less than 1 µm and the cell is a free‐standing membrane with a diameter up to 200 µm. The electrolyte resistance and the sum of polarization resistances of the anode and cathode are measured between 400 and 600 °C by impedance spectroscopy and direct current (DC) techniques. The contribution of the electrolyte resistance to the total cell resistance is negligible for all cells. The area‐specific polarization resistance of the electrodes decreases for different cathode materials in the order of Pt paste > sputtered Pt > LSCF. The open circuit voltages (OCVs) of the single‐layer electrolyte cells ranges from 0.91 to 0.56 V at 550 °C. No electronic leakage in the PLD–YSZ electrolyte is found by in‐plane and cross‐plane electrical conductivity measurements and the low OCV is attributed to gas leakage through pinholes in the columnar microstructure of the electrolyte. By using a bilayer electrolyte of PLD–YSZ and SP–YSZ, an OCV of 1.06 V is obtained and the maximum power density reaches 152 mW cm⁻² at 550 °C.     

Recent Advances in ZnO Films Prepared by Pulsed Laser Deposition

Pulsed laser deposition （PLD） is emerging as the most rapid and efficient technique for fabricating the many compound films. ZnO thin films can be prepared under various deposition conditions by PLD. The effects of various substrate temperature, oxygen partial pressure, annealing temperature, substrate, buffer layers thickness and film thickness on micro-structural, optical and electrical properties of ZnO films grown by PLD technology are reviewed. ZnO films with special function can grow under proper conditions by PLD.     

Impacts of surface sulfurization on Cu(In1−x,Gax)Se2 thin‐film solar cells

In this work, the impacts of surface sulfurization of high‐quality Cu(In_1−x,Ga_x)Se₂ (CIGS) thin films deposited by three‐stage process on the film properties and the cell performance were investigated. The CIGS thin films were sulfurized at 550 °C for 30 min using H₂S gas. The X‐ray photoelectron spectroscopy analysis revealed that sulfur atoms diffused into the CIGS surface layer and that the valence band minimum was lowered by the film sulfurization. The open circuit voltage (V_oc) drastically increased from 0.590 to 0.674 V as a result of the sulfurization process. Temperature‐dependent current–voltage and capacitance–frequency measurements also revealed that interface recombination was drastically decreased by the lowering of the defect's activation energy level at the vicinity of the buffer/CIGS interface after the sulfurization. Copyright © 2014 John Wiley & Sons, Ltd.     

Room‐Temperature Printing of Organic Thin‐Film Transistors with π‐Junction Gold Nanoparticles

Printing semiconductor devices under ambient atmospheric conditions is a promising method for the large‐area, low‐cost fabrication of flexible electronic products. However, processes conducted at temperatures greater than 150 °C are typically used for printed electronics, which prevents the use of common flexible substrates because of the distortion caused by heat. The present report describes a method for the room‐temperature printing of electronics, which allows thin‐film electronic devices to be printed at room temperature without the application of heat. The development of π‐junction gold nanoparticles as the electrode material permits the room‐temperature deposition of a conductive metal layer. Room‐temperature patterning methods are also developed for the Au ink electrodes and an active organic semiconductor layer, which enables the fabrication of organic thin‐film transistors through room‐temperature printing. The transistor devices printed at room temperature exhibit average field‐effect mobilities of 7.9 and 2.5 cm² V^?1 s^?1 on plastic and paper substrates, respectively. These results suggest that this fabrication method is very promising as a core technology for low‐cost and high‐performance printed electronics.