Parallel syntheses and thermoelectric properties of Ce-doped SrTiO3 thin films

Thermoelectric properties of single crystalline Ce_xSr_1−xTiO₃ films (0 ≤ x ≤ 0.5) have been studied by using combinatorial pulsed-laser deposition. Temperature gradient method was used for identifying an optimum growth temperature for SrTiO₃ homoepitaxial growth, at which both oxygen stoichiometry and persisting layer-by-layer growth mode could be accomplished. Electrical conductivity (σ) and Seebeck coefficient (S) were measured at room temperature for the composition-spread films grown at the optimized temperature and found to be considerably higher than those reported for bulk poly-crystalline compounds. Hall measurement revealed that carrier density linearly increased with increasing x, suggesting that a trivalent Ce ions substituted divalent Sr ions to supply electrons. A maximum power factor (S²σ) was obtained for the x = 0.2 film, being 7 and 14 μW/K² cm at 300 and 900 K, respectively.     

TbMnO3 epitaxial thin films by pulsed-laser deposition

Epitaxial TbMnO₃ films have been fabricated on SrTiO₃(001) and LaAlO₃(001) substrates by pulsed laser deposition (PLD), the structure and surface morphology of the films were characterized by X-ray diffraction with Cu K_α radiation and atomic force microscopy. The electrical transport and magnetic properties of the TbMnO₃ films and bulk were examined, the resistivity and the forbidden band width E_g change with epitaxial orientation, semiconductor transport properties are found in the films and bulk, the average of the E_g of the films on SrTiO₃ and on LaAlO₃ is equal to the E_g of the bulk. The two TMO films have different magnetization mode, the magnetization of the film on SrTiO₃ have an analogy to that of TbMnO₃ single crystal.     

Opto-electrical properties of Ti-doped In2O3 thin films grown by pulsed laser deposition

By ablating titanium containing In₂O₃ target with a KrF excimer laser, highly conducting and transparent films on quartz were obtained to investigate the effects of growth temperature and oxygen pressure on the structural, optical and electrical properties of these films. We find that the transparency of the films depends more on the growth temperature and less on the oxygen pressure. Electrical properties, however, are found to be sensitive to both the growth temperature and oxygen pressure. We report in this paper that a growth temperature of 500 °C and an oxygen pressure of 7.5 × 10⁻⁷ bar lead to titanium-doped indium oxide films which have high mobility (up to 199 cm² V⁻¹ s⁻¹), low resistivity (9.8 × 10⁻⁵ Ω cm), and relatively high transmittance (∼88%).     

Pulsed laser deposition and characterization of nitrogen-substituted SrTiO3 thin films

Nitrogen-substituted cubic perovskite-type SrTiO₃ thin films were deposited in a one-step process using pulsed reactive crossed beam laser ablation (PRCLA) and RF-plasma assisted pulsed laser deposition (RF-PLD). Both techniques yield preferentially oriented films on SrTiO₃(0 0 1), LaAlO₃(0 0 1) and MgO(0 0 1) substrates with the unit cell parameters within 0.390(5) < a < 0.394(9) nm. The nitrogen content is higher in films deposited by PRCLA (0.84-2.40 at.%) as compared to films deposited by RF-PLD with nitrogen plasma (0.10-0.66 at.%). PRCLA with an ammonia gas pulse leads to a higher nitrogen content compared to the films grown with a nitrogen gas pulse, while films deposited by RF-PLD with ammonia plasma reveal only minor nitrogen contents (<0.10 at.%). The amount of the incorporated nitrogen can be tuned by adjusting the deposition parameters. Films deposited by PRCLA have a lower roughness of 1-3 nm compared to 12-18 nm for the films grown by RF-PLD. PRCLA yields partially reduced films, which exhibit electronic conductivity, while films deposited by RF-PLD are insulating. There is also a pronounced influence of the substrate material on the resistivity of the films deposited by PRCLA: films grown on SrTiO₃ substrates exhibit a metallic-like behaviour, while the corresponding films grown on MgO and LaAlO₃ substrates reveal a metal-to-semiconductor/insulator transition. Nitrogen incorporation into the SrTiO₃ films results in an increased optical absorption at 370-500 nm which is associated with N(2p) localized states with the energy about 0.7 eV higher than the valence band energy in strontium titanate. The optical band gap energies in the studied N-substituted SrTiO₃ films are 3.35-3.40 eV.     

Pulsed laser deposition of (110) oriented semiconductive SrFeO3−x thin films

 The semiconductive perovskite-type oxide SrFeO_3-x (x<0.16) (SFO) thin films have been directly fabricated on (001)SrTiO₃ and (001)LaAlO₃ single crystal substrates by pulsed laser deposition(PLD) under high oxygen partial pressure of 100 Pa. The SFO thin films were (110) oriented. The x-ray photoelectron spectroscopy (XPS) analysis showed that the surface of SFO thin film has strong gas absorption capability. The resistance versus temperature has been measured in the temperature range from 77 K to 300 K. The SFO thin film showed typical semiconductive property. Dependence of resistance of SFO thin film on oxygen pressure was measured and result showed that the SFO thin film had better oxygen sensitive property. Received: 14 May 1996/Accepted: 15 August 1996     

Preparation of transparent conductive TiO2:Nb thin films by pulsed laser deposition

This study investigated the optical and electrical properties of Nb-doped TiO₂ thin films prepared by pulsed laser deposition (PLD). The PLD conditions were optimized to fabricate Nb-doped TiO₂ thin films with an improved electrical conductivity and crystalline structure. XRD analyses revealed that the deposition at room temperature in 0.92 Pa O₂ was suitable to produce anatase-type TiO₂. A Nb-doped TiO₂ thin film attained a resistivity as low as 6.7 × 10⁻⁴ Ω cm after annealing at 350 °C in vacuum (<10⁻⁵ Pa), thereby maintaining the transmittance as high as 60% in the UV-vis region.     

Pulsed laser deposition of Bi2Te3 thermoelectric films

Bi₂Te₃ is one of the most used materials for thermoelectric applications at ambient temperature. An improvement of thermoelectric performances through a suitable modification of electron and phonon transport mechanisms is predicted for low dimensional or nanostructured systems, but this requires a control of the material structure down to the nanoscale. We show that pulsed laser deposition provides control on film composition, phase and structure, necessary for a comprehension of the relationship between structure and thermoelectric properties. We have explored the role of deposition temperature, background inert gas type and pressure, laser fluence and target-to-substrate distance and we found the experimental condition ranges to obtain crystalline films containing the Bi₂Te₃ phase only, by comparing energy dispersive X-ray spectroscopy, Raman spectroscopy and X-ray diffraction analysis. Variations of substrate temperature and deposition gas pressure prove to be crucial also for the control of film morphology and crystallinity. Substrate type has no influence on film stoichiometry and crystallinity, but highly oriented growth can be achieved on mica due to van der Waals epitaxy.     

Planar Hall effect and magnetoresistance in Ni81Fe19 and Co square shaped thin films

Ni₈₁Fe₁₉ and Co thin films have been fabricated and their transport properties have been investigated for potential applications in ultra sensitive magnetic field sensors. The Ni₈₁Fe₁₉ films exhibit an anisotropic magnetoresistance (AMR) of 2.5% with a coercivity 2.5 Oe and the Co films exhibit an AMR of 0.7% with coercivity 11 Oe. Large planar Hall effect magnetoresistance values at room temperature are reported for both cases. An unbalanced Wheatstone bridge model is proposed to describe quantitatively the observed experimental Planar Hall Effect data.     

Wide band gap Cd0.83Mg0.15Al0.02O thin films by pulsed laser deposition

Magnesium and aluminum doped CdO thin films were deposited on quartz substrate using pulsed laser deposition technique. Magnesium is used to widen the band gap and aluminum is used to increase carrier concentration of CdO films. The effect of growth temperature on structural, optical, and electrical properties was studied. These films are crystalline in nature and their preferred orientation depends on growth temperature. These films are highly transparent (∼86%) in visible region. The band gap of the films varies from 3.1 eV to 3.4 eV. The electrical conductivity and carrier concentration were found to decrease with increase in growth temperature.     

Pulsed laser deposition of ZnO as conductive buffer layer of (001)-LiNbO3 thin films

1 (LO) mode peak at 579 cm^-1, indicating oxygen deficiency in the films. Significant dependence of the electrical property for the films on substrate temperature was shown. The I–V relation of the films exhibited non-ohmic behavior. Whereas the films deposited above 500 °C showed a metal-like property, at a lower substrate temperature semiconducting thin films were achieved. The (001)-oriented LiNbO₃/ZnO heterostructure was successfully prepared on quartz fused and (001) sapphire plates. Received: 6 April 1998/Accepted: 26 May 1998     

利用脉冲激光沉积技术在双轴织构的Ni基带上外延CeO2薄膜

利用脉冲激光沉积技术在氢还原气氛下成功地在双轴织构的Ni基带上外延了高质量的CeO₂薄膜. x射线衍射θ—２θ扫描和ω扫描结果表明，CeO₂薄膜在Ni基带上呈c轴方向生长，存在很强的平面外织构；极图和φ扫描显示它具有良好的平面内织构. Ni基片上织构的CeO₂薄膜为进一步在其上外延高质量的YBa₂Cu₃O_7-x超导薄膜提供了很好的模板. 关键词： 双轴织构的Ni基带 2薄膜')" href="#">CeO₂薄膜 脉冲激光沉积     

The photoemission study of NdNiO3/NdGaO3 thin films, through the metal-insulator transition

The electronic structure of thin films NdNiO₃/NdGaO₃ with various thicknesses (from 17 nm to 150 nm), have been studied by photoemission spectroscopy at 300 K and 169 K. The XPS results are consistent with the literature ab initio calculations of the NdNiO₃ electronic structure. A noticeable variation attributed to the metal-insulator (MI) transition has been found only for the films with relatively high thickness (150 nm). Furthermore, the photoemission spectra and their temperature dependence have been discussed with regard to the results of dc electrical resistivity measurements which also exhibit large thickness dependence. Finally, these new results support a possible large hetero-epitaxial effect on the thinnest sample (17 nm) which could stress the NdNiO₃ structure and consequently makes its electronic structure nearly stabilized.     

Pulsed laser deposition of oxide thin films

The pulsed laser deposition (PLD) process was studied in detail during oxide thin film growth by constructing a sophisticated PLD chamber combined with an energy-stable excimer laser. It was revealed that the transmitting laser energy at the entrance view port decreased exponentially with deposition runs, roughly by A e^−0.02x%, where A is the original transmission and x is the run number, and transmission loss could become considerable (up to 90%) in 100 deposition runs. In addition, area of the focused spot on the target was found a function of charging high voltage, which is a parameter of excimer laser operation, even through a slit forming rectangular sharp-edge beam profile. Laser energy density is one of the most important parameter governing grown film properties, and therefore accurate laser energy and spot area calibration is vital for reproducible film growth. In course of this study, the importance of spot area as well as the energy density is discussed in the view of deposition rate.     

Pulsed laser deposition of BiCuOSe thin films

Undoped and 10% Ca-doped BiCuOSe thin films are prepared by pulsed laser deposition without ex-situ processing. The influence of the preparation conditions on structure and properties of Bi_0.9Ca_0.1CuOSe thin films on amorphous silica substrates is studied. The highest achieved concentration and mobility of free holes (3.9×10²⁰ cm⁻³ and 3.5 cm²/Vs) was close to that measured in strongly c-axis oriented samples on SrTiO₃ substrates (4.0×10²⁰ cm⁻³ and 7.5 cm²/Vs). The Bi_0.9Ca_0.1CuOSe films on SrTiO₃ show almost temperature-independent Seebeck coefficient and their resistivity increases with increasing temperature. The Seebeck coefficient of undoped BiCuOSe films on SrTiO₃ increases below 150°K, and the resistivity shows a flat plateau centered at this temperature. Optical measurements suggest that BiCuOSe has an indirect bandgap of 0.8 eV and a strong absorption edge at 1.45 eV. Ab-initio calculations of the electronic band structure, effective masses and optical properties of BiCuOSe are also presented.     

Electrical and structural properties of Ce0.9CoFe3Sb12 thermoelectric thin films

In this work, we show experimental results for growth conditions of thermoelectric Ce_0.9CoFe₃Sb₁₂ thin films. An rf-magnetron sputtering system has been used to grow the films on single crystal substrates of sapphire (Al₂O₃), silicon (Si), and magnesium oxide (MgO) at different substrate temperatures between 250 and 450 °C. The films were thermoelectrically characterized with resistivity and thermopower measurements as functions of temperature. The results show linear behavior of resistivity with temperature, and thermopower growth with the temperature increase. Such behavior is typical for metallic materials. The structure and surface morphology of the samples were analyzed by X-ray diffraction pattern and atomic force microscopy (AFM), respectively.     

Properties of Sr2FeMoO6 thin films fabricated by the chemical solution deposition method

We fabricated the ordered Sr₂FeMoO₆ (SFMO) thin film with a double perovskite structure using the chemical solution deposition (CSD) method. The highly c-axis oriented SFMO thin film with a high degree of Fe/Mo ordering was successfully synthesized on an MgO (001) substrate by optimizing processing conditions. The precise preparation process control of the SFMO precursor solution leads to a typical magnetoresistance effect in a low magnetic field at room temperature.     

Epitaxial growth and characterization of CaVO3 thin films

Epitaxial thin films of CaVO₃ were synthesized on SrTiO₃, LaAlO₃ and (La_0.27Sr_0.73)(Al_0.65Ta_0.35)O₃ substrates by pulsed laser deposition. All CaVO₃ films, independent of epitaxial strain, exhibit metallic and Pauli paramagnetic behavior as CaVO₃ single crystals. X-ray absorption measurements confirmed the 4+ valence state for Vanadium ions. With prolonged air exposure, an increasing amount of V³⁺ is detected and is attributed to oxygen loss in the near surface region of the films.     

Photocarrier injection and the I-V characteristics of La0.8Sr0.2MnO3/SrTiO3:Nb heterojunctions

Oxide heterojunctions made of p-type La_0.8Sr_0.2MnO₃ (LSMO) and niobium-doped n-type SrTiO₃ (STO:Nb) have been fabricated by the pulsed laser deposition (PLD) technique and characterized under UV light irradiation by measuring the current-voltage, photovoltaic properties and the junction capacitance. It is shown that the heterojunctions work as an efficient UV photodiode, in which photogenerated holes in the STO:Nb substrate are injected to the LSMO film. The maximum surface hole density Q/e and external quantum efficiency γ are estimated to be 8.3×10¹² cm⁻² and 11% at room temperature, respectively. They are improved significantly in a p-i-n junction of LSMO/STO/STO:Nb, where Q/e and γ are 3.0×10¹³ cm⁻² and 27%, respectively.     

Hall effect in a GdBa2Cu3O7−δ/La0.75Sr0.25MnO3 perovskite bilayer

We present results on the Hall coefficient R_H in the normal state for a GdBa₂Cu₃O_7−δ/La_0.75Sr_0.25MnO₃ bilayer and a La_0.75Sr_0.25MnO₃ film grown by dc magnetron sputtering on (1 0 0) SrTiO₃. We find that the electric transport on the bilayer can be qualitatively described using a simple parallel layers model. The GdBa₂Cu₃O_7−δ layer presents a carrier density approximately equal to that reported for 7 − δ = 6.85 oxygen doping. Also we observe an unexpected presence of two Hall resistivity regimes, effects that may be associated with the internal magnetic field induced on the superconducting layer by the ferromagnetic layer.     

Effect of CO2 laser irradiation on the transport properties of La0.67Ba0.33MnO3 thin film

The effect of CO₂ laser irradiation on La_0.67Ba_0.33MnO₃ epitaxial thin film was investigated. Epitaxial thin films grown by pulsed laser deposition were irradiated by a CO₂ laser in air for 10-60 s. It is shown that after CO₂ laser irradiation treatment, the crystallinity of the film is strongly enhanced. It is found that a dramatic decrease in the resistivity of the CO₂-laser-irradiated film is accompanied by a remarkable increase in its insulator-metal transition temperature and the temperature coefficient of resistance. This significant improvement of its structure and properties is achieved in several dozens of seconds and surpasses that observed in films annealed in an oxygen atmosphere at 900 ^°C for 12 h, suggesting that CO₂ laser irradiation is a new and effective tool to optimize CMR manganites for bolometric applications.