Solid-state dewetting of Pt on (100) SrTiO3

Continuous thin films of Pt on (100) SrTiO₃ substrates were dewetted to form Pt particles at 1,150 °C, using an oxygen partial pressure of 10^?20 atm. After retraction of thick (50 or 100 nm) Pt films, SrTiO₃ anisotropic rods, slightly depleted in Ti, were found on the surface of the substrate. Rods did not form after dewetting of thinner (10 nm) Pt films. After dewetting, a ~10 nm thick interfacial phase was found between the Pt and the SrTiO₃. The interfacial phase, based on Sr and containing ~25 at% oxygen, is believed to be a transient state, formed due to Ti depletion from the substrate, resulting in a Pt(Ti) solution in the particles. The interfacial phase forms due to the low oxygen partial pressure used to equilibrate the system, and is expected to influence the electrical properties of devices based on Pt–SrTiO₃.     

Electric-field thermopower modulation in SrTiO3-based field-effect transistors

Electric-field thermopower modulation method is demonstrated in detail using SrTiO₃-based field-effect transistor structure as an example. Using water-infiltrated nanoporous 12CaO·7Al₂O₃ glass “CAN” as the gate insulator, carrier electrons up to ~10¹⁵ cm^?2 can accumulate within an extremely narrow 2D electron gas (~2 nm), leading to an unusually large enhancement of thermopower. Our electric field-effect approach should be applicable to fully verify the performance of thermoelectric materials with complicated crystal structures. This approach may accelerate the development of nanostructures of high performance thermoelectric materials.     

Structural,electrical, optical properties and reliability of ultra-thin tin doped indium oxide films for touch panels

Ultra-thin ITO films with thickness of 4–56 nm were deposited on glass by dc magnetron sputtering using 5 wt% SnO₂ doped ITO target. The effect of film thickness on the structural, electrical, optical properties and reliability was investigated for its application to touch panels. The 4 nm thick ITO film shows amorphous structure and other films present polycrystalline structure and the (222) preferred orientation. The ultra-thin ITO films show smooth surface with low Ra surface roughness smaller than 1 nm. The sheet resistance and visible transmittance of the ITO films decrease with the increase in film thickness. The 4 nm thick ITO film shows the highest resistivity (3.08 × 10^?3 Ω cm) with low carrier density and Hall mobility, and other films have excellent conductivity (<4.0 × 10^?4 Ω cm). The ITO films show high transmittance (>85 %) in visible light range and do not generate interference ripples between film and substrate interface. The ITO films with thickness of 18–56 nm show stable reliability under high temperature, high temperature & high humidity and alkaline environmental conditions. The only electrical degradation corresponds to the increase of sheet resistance in the ITO films with thickness of 4–12 nm.     

Depositions of SrRuO3 thin films on oxide substrates with liquid-delivery spin MOCVD

Systematic variations of the deposition conditions for thin epitaxial SrRuO₃ films with a liquid-delivery spin MOCVD were performed in order to get a detailed understanding of the physical and chemical issues in the growth process. We have observed that at very low as well as at high growth rates the structural ordering of the films and the lattice strain is low, while for optimized conditions (∼ 0.14-0.2 nm/min) films can be grown under high compressive strain on SrTiO₃ and under tensile strain on DyScO₃, showing an electrical resistivity of ∼ 250 μΩcm. Films on NdGaO₃ are nearly totally plastically relaxed. In contrast to PLD, step-flow growth could not be detected due to significantly higher carbon incorporation.     

Enhanced energy-storage properties of SrTiO3 doped (Bi1/2Na1/2)TiO3–(Bi1/2K1/2)TiO3 lead-free antiferroelectric ceramics

The energy-storage properties of SrTiO₃-doped (15, 20, 25, and 30 mol%) 0.80Bi_1/2Na_1/2TiO₃–0.20Bi_1/2K_1/2TiO₃ lead-free antiferroelectric ceramics were investigated by two-step sintering method. The ceramics with higher SrTiO₃ content had smaller grain sizes and a more homogeneous distribution. About 25 mol% SrTiO₃ doping induced antiferroelectric properties, showing a typical double hysteresis loops, accompanied by a large energy density. The first sintering temperature of the ceramics had main impact on the relative density, and the high relative density possessed large external breakdown strength. The optimum electrical performances with a low remanent polarization (P_r = 1.9 μC/cm²), a low coercive field (E_c = 1.7 kV/cm) and a large energy density (W = 0.97 J/cm³) at 10 Hz were obtained at 1,190 °C for a SrTiO₃ content of 25 mol%.     

Microstructural study of YBa2Cu3O7/SrTiO3/YBa2Cu3O7 heteroepitaxial trilayer films grown on (100) SrTiO3 substrates

Detailed transmission electron microscopic study has been carried out on heteroepitaxial YBa₂Cu₃O₇/SrTiO₃/YBa₂Cu₃O₇ trilayer thin films grown on (100)SrTiO₃ substrates prepared by DC and RF magnetron sputtering. The microstructural results showed the existence of somea-axis-oriented YBCO grains 20–90 nm wide in thec-axis-oriented YBCO matrix. Some of thea-axis grains in the lower YBCO thin film layer have protruded into the above SrTiO₃ layer, which may cause short circuit between the two YBCO superconducting layers. This is unsuitable for the application of trilayer thin films for microelectronic devices. The defects on the surface of the substrates would also influence the growth quality of the YBCO thin films.     

Nonlinear Optical Characteristics of C60 Thin Films

Abstract

The results of investigation of the real and imaginary parts of third‐order nonlinear susceptibility (χ⁽³⁾) of C₆₀ thin films (～100 nm) at the wavelength of Nd: YAG laser radiation (532 nm, τ = 55 ps) are presented using Z‐scan technique. Our studies show that the sign of Reχ⁽³⁾ changes from negative, at pulse repetition rate of 2 Hz to positive, at 0.5 Hz. Sign variations of the real part of the third‐order susceptibility were attributed to the influence of the thermal lens.     

New intelligent multifunctional SiO2/VO2 composite films with enhanced infrared light regulation performance,solar modulation capability,and superhydrophobicity

Abstract

Highly transparent, energy-saving, and superhydrophobic nanostructured SiO₂/VO₂ composite films have been fabricated using a sol–gel method. These composite films are composed of an underlying infrared (IR)-regulating VO₂ layer and a top protective layer that consists of SiO₂ nanoparticles. Experimental results showed that the composite structure could enhance the IR light regulation performance, solar modulation capability, and hydrophobicity of the pristine VO₂ layer. The transmittance of the composite films in visible region (T_lum) was higher than 60%, which was sufficient to meet the requirements of glass lighting. Compared with pristine VO₂ films and tungsten-doped VO₂ film, the near IR control capability of the composite films was enhanced by 13.9% and 22.1%, respectively, whereas their solar modulation capability was enhanced by 10.9% and 22.9%, respectively. The water contact angles of the SiO₂/VO₂ composite films were over 150°, indicating superhydrophobicity. The transparent superhydrophobic surface exhibited a high stability toward illumination as all the films retained their initial superhydrophobicity even after exposure to 365 nm light with an intensity of 160 mW^.cm^?2 for 10 h. In addition, the films possessed anti-oxidation and anti-acid properties. These characteristics are highly advantageous for intelligent windows or solar cell applications, given that they can provide surfaces with anti-fogging, rainproofing, and self-cleaning effects. Our technique offers a simple and low-cost solution to the development of stable and visible light transparent superhydrophobic surfaces for industrial applications.     

Epitaxial growth and exchange coupling of spinel ferrimagnet Ni0.3Zn0.7Fe2O4 on multiferroic BiFeO3

Thin films of the zinc nickel ferrite, Zn_0.7Ni_0.3Fe₂O₄ (ZNFO), were deposited by the RF magnetron sputtering on a number of substrates, including (001) oriented single crystals of LaAlO₃ (LAO) and SrTiO₃ (STO), polycrystalline Pt/Si, and epitaxial films of BiFeO₃ (BFO) and LaNiO₃ (LNO). Except for the films on Pt/Si, the ZNFO films grown on other substrates were epitaxial and their magnetic properties were affected by the heteroepitaxy induced strains. Typically, the coercivity (H_c) was increased with the strain, i.e. H_c varied from 31 Oe for the 150 nm thick polycrystalline films grown on Pt/Si, to 55 Oe and 155 Oe for the 20 nm thick epitaxial films grown on BFO and LAO, respectively. The saturation magnetization of the epitaxial films was reduced accordingly to about 470 emu/cm³ from 986 emu/cm³ in the polycrystalline films. The all-oxide architecture allowed field-annealing to perform at the temperature above the Neel temperature of BFO (~ 370 °C), after which clear exchange bias was observed.     

Simple chemical solution deposition and thermoelectric properties of epitaxial La0.95Sr0.05CoO3 thin films

In this paper, simple chemical solution deposition method is used to prepare La_0.95Sr_0.05CoO₃ thin films on SrTiO₃ (001) substrates by acetate-based precursors. The derived film is characterized by x-ray diffraction, field-emission scanning electron microscopy and transmission electronic microscopy. The derived film is epitaxial growth with < 001>[100] La_0.95Sr_0.05CoO₃||<001>[100] SrTiO₃, indicating that the chemical solution deposition is an effective route to obtain the cobalt-based films. The resistivity, Seebeck coefficient and thermal power factor are 0.05Ω cm, 250 μV/K and 0.21 mWK^− 2m^− 1 at 300 K, respectively, which is higher than these of the ceramics, indicating epitaxial thin film is an effective route to enhance the thermoelectric properties of La_0.95Sr_0.05CoO₃.     

Local structure and electron spin resonance of copper-doped SrTiO3 ceramics

We report X-ray diffraction and electron spin resonance (ESR) measurements of the effect of SrTiO₃ ceramics doping using Cu²⁺ ions. ESR measurements reveal two kinds of Cu²⁺ centers in weakly (0.2–0.5 mol% Cu) doped SrTiO₃. Both kinds of centers have been attributed to Cu²⁺ at octahedral Ti sites and possibly associated either with a nearest-neighboring oxygen vacancy (center #1) or some other positively charged defect (center #2). The ESR spectra of the above centers are described by the following spin Hamiltonian parameters: g _‖ = 2.263(1), g _⊥ = 2.041(1), A _‖ = 170(1) × 10^?4 cm^?1, A _⊥ = 27(1) × 10^?4 cm^?1 (center #1) and g _‖ = 2.334(1), g _⊥ = 2.059(1), A _‖ = 137(1) × 10^?4 cm^?1, A _⊥ ≈ 0(1) × 10^?4 cm^?1 (center #2). For copper concentration larger than 2 mol%, the antiferromagnetic SrCu₃Ti₄O₁₂ (SCTO) phase has been detected by both X-ray diffraction and ESR. Its volume increases with increase of Cu concentration reaching about 17 % at Cu doping of 20 mol%. The composite SrTiO₃–SCTO ceramics exhibits substantial magnetocapacitance effect, which could be enhanced by electrostriction of SrTiO₃.     

Enhanced electrical characteristics of sol–gel-derived amorphous SrTiO<Subscript>3</Subscript> films

Amorphous SrTiO₃ thin films were fabricated on Pt (100)/Ti/SiO₂/Si substrates by sol–gel and spin-coating technology and their surface and cross-section morphology were characterized by using field emission scanning electron microscopy. A broad absorption band at about 3390 cm^?1 owing to the stretching vibrations of hydroxyl groups in the absorbed water was observed from fourier transform infrared spectroscopy. J–E measurements were used to investigate the electrical characteristics of SrTiO₃ films. The breakdown characteristics and leakage current are strongly dependent upon their electrode materials. SrTiO₃ films with Al top electrodes exhibit significantly higher breakdown strength and much lower leakage current than those with Au top electrodes. Moreover, samples with Al electrodes exhibit distinct electrical characteristics when a negative voltage was applied under different testing conditions. The surface chemical state of aluminum was analyzed by using X-ray photoelectron spectroscopy, indicating that the 45 nm thick Al electrode was completely transformed into aluminum oxide layer when a positive voltage was applied. These results show that the anodic oxidation of the Al electrodes and films is suggested to be responsible for the enhanced electrical characteristics of SrTiO₃ thin films.     

Growth and characterization of (Pb,La)(Zr,Ti)O3 thin film epilayers on SrTiO3-buffered Si(001)

Ferroelectric Pb_0.92La_0.08Zr_0.4Ti_0.6O₃ (PLZT) thin films were deposited on SrTiO₃-buffered Si(001) substrate by on-axis radio frequency magnetron sputtering. X-ray diffraction analysis revealed epitaxial growth of monocrystalline PLZT films, with an (001) rocking curve full width at half maximum of ∼ 0.3°. φ-scans showed 45° in-plane orientation of the perovskite unit cell relative to that of silicon. The elemental composition of the thin film heterostructure was examined by Auger sputter depth profiling measurements. The recorded profiles suggest that the SrTiO₃ buffer layer serves not only as a template for epitaxial growth, but also as a barrier suppressing Pb-Si interdiffusion between the PLZT layer and the Si substrate. The surface roughness of the PLZT layer was measured at ∼ 4 nm for films with ∼ 500 nm thickness. Wavelength dispersions for the refractive index (n) and the extinction coefficient (k) were obtained from spectroscopic ellipsometry measurements, with n ∼ 2.48 at the main communication wavelength λ = 1550 nm and k < 0.001 for λ > 650 nm. Recorded polarization vs. electric field loops for the PLZT epilayer, with a SrRuO₃ electrode layer interposed between PLZT and SrTiO₃, showed a remnant polarization P_r ≈ 40 µC/cm² and coercive field E_c ≈ 100 kV/cm. These findings suggest that the sputter-deposited PLZT thin films retain the functional properties critical to ferroelectric and electro-optic device applications, also when integrated on a semiconductor substrate.     

Properties of (K,Na)NbO3-based lead-free piezoelectric films prepared by pulsed laser deposition

To investigate the properties of (K,Na)NbO₃-based lead-free piezoelectric films at the morphotropic phase boundary composition, we fabricated epitaxial [(K_0.5Na_0.5)_0.97Li_0.03] (Nb_0.8Ta_0.2)O₃ films on (001), (110) and (111)-oriented single crystal SrTiO₃ substrates by pulsed laser deposition. The structure and electrical properties of the films were studied. Dielectric constants of 540, 390 and 300 and remnant polarizations of 4.00, 1.05, and 0.35 μC/cm² were observed for the (001), (110) and (111) oriented films, respectively.     

Improved thermoelectric performance of PEDOT:PSS films prepared by polar-solvent vapor annealing method

To improve thermoelectric performance, polar-solvent vapor annealing (PSVA) method was introduced into the preparation of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films. The solvent vapors included dimethyl sulfoxide, ethylene glycol, N,N-dimethylformamide, N-methyl-2-pyrrolidone, and deionized water (H₂O). The PSVA-treated PEDOT:PSS films exhibited significantly enhanced electrical conductivity and the maximum value was up to 496 S cm^?1. Especially, utilizing the PSVA method, H₂O could also remarkably enhance the electrical conductivity of pristine PEDOT:PSS film from 0.2 to 57 S cm^?1. There was no distinct change for the Seebeck coefficient of PSVA-treated films with the significantly enhanced electrical conductivity, thereby a maximum power factor of 9.47 μW m^?1 K^?2 at room temperature was obtained. The effects of PSVA method on thermoelectric performance of PEDOT:PSS films were also investigated systematically by analyzing the changes in morphology, carrier mobility and carrier concentration. The results confirmed that PSVA-treated PEDOT:PSS films could obtain smoother morphologies and realize the simultaneous increase of carrier mobility and carrier concentration, which results in the improvement of the thermoelectric performance.     

Hydrothermal synthesis and photoluminescence properties of cerium-doped cadmium tungstate nanophosphor

The present paper reports synthesis and photoluminescence studies of cadmium tungstate (CdWO₄) and cerium-doped cadmium tungstate. The samples were synthesised by low cost and low temperature hydrothermal method and characterised by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and photoluminescence analysis. XRD pattern reveals that the CdWO₄ has monoclinic wolframite structure. The FTIR spectrum of cerium-doped CdWO₄ exhibits broadband below 700 cm^?1 which is due to the δ (Ce–O–C) mode. The TEM images show that size of particle is approximately 60–120 nm in both samples. A broad intense peak was observed at 474 nm when the samples were excited with 263 nm. A broad intense peak was observed at 475 nm when the samples were excited with 600 nm. The intensity of the 474 nm peak decreases with increase in cerium doping concentration. The observation of 475 nm peak when excited with 600 nm is upconversion luminescence. This upconversion emission is due to energy transfer upconversion process involving Cd²⁺ ions and [WO₆]^6? ions. Ce³⁺ ion is responsible for the peak shift of 6 nm.     

Luminescent impurity ion probe and low temperature phase of SrTiO3 nanoparticles

Abstract

Optical absorption and photoluminescence of Cr³⁺ impurity ion probe were studied on nanocrystalline SrTiO₃/Cr(0·1%) powders with an average particle size between 13 and 100 nm prepared by the Pechini type polymeric sol–gel method. Only O_h¹ cubic perovskite phase was revealed in the powders at room temperature. The optical absorption edge and the position of the zero-phonon emission R-line of the octahedral Cr³⁺ centres shifted to higher energies with decreasing particle size. The temperature shift of the R-line position appeared for all powders nearly the same as the 'dielectric related' one in the bulk crystals, evidencing that SrTiO₃ retains quantum paraelectric behaviour down to a particle size of about 10 nm. However, behaviour of the R-line position was unstable at low temperatures in powders with a particle size of about 13 and 20 nm. This instability was speculated as a manifestation of a possible low temperature ferroelectric phase transition in small enough SrTiO₃ nanoparticles.     

Ferroelectricity of ultrathin ferroelectric Langmuir-Blodgett polymer films on conductive LaNiO3 electrodes

LaNiO₃ (LNO) films with a surface roughness rms of 0.384 nm and a sheet resistance of about 200 Ω were prepared on SrTiO₃ and Si/SiO₂ substrates respectively by rf magnetron sputtering technique. The surface of LNO on Si/SiO₂ substrate is smoother than that on SrTiO₃ substrate. A nominal 2-monolayer (ML) poly(vinylidenefluoride-trifluoroethylene) film with a thickness of about 3 nm was deposited on LNO coated Si/SiO₂ substrate by Langmuir-Blodgett (LB) technology. Piezoresponse force microscopy (PFM) measurements show that the LB films demonstrate an obvious feature of polarization switching and good voltage durability. The results suggest that the ultrathin polymer films may be utilized to explore ferroelectric tunnel junctions.     

Glassy Behavior of La0.8Ca0.2MnO3 Nanoparticles

Magnetic and transport properties of La_0.8Ca_0.2MnO₃ nanoparticles with average size of 18 nm and Curie temperature T _C??231 K have been studied. Pronounced irreversibility of magnetization below T _irr??208 K has been observed. Studied particles have shown memory effects in zero-field-cooled and field-cooled magnetization. The resistivity has a semiconducting character at 150<T<300 K and exhibits relaxation and memory effects below the Curie temperature. The results suggest that superspin-glass features in ensembles of interacting 18 nm La_0.8Ca_0.2MnO₃ particles appear along with superferromagnetic-like features.     

Molecular beam epitaxy growth of BaTiO3 thin films and crucial impact of oxygen content conditions on the electrical characteristics

In this study, high quality crystalline BaTiO₃ films were fabricated in different oxygen content conditions on Nb-doped SrTiO₃ (001) substrates by molecular beam epitaxy (MBE). BaTiO₃ epitaxial film presents a critical thickness of 6.4 nm and is almost entirely relaxed on SrTiO₃ with a thickness of ~ 50 nm. The electrical properties of 50 nm strain-free BaTiO₃ films were investigated by both macro- and microscopic measurements. Their electrical characteristics were found to be strongly influenced by different oxygen content conditions used during the preparation or annealing of the samples. Limited molecular oxygen partial pressure in a MBE chamber probably leads to a great amount of oxygen vacancies in the oxide film and results in rectification behavior of the oxygen-deficient BaTiO_3-x/SrTiO₃:Nb interface. Several approaches such as using atomic oxygen ambiance during the growth, annealing under elevated oxygen pressure were employed in order to decrease the oxygen vacancy density and these approaches eventually permit obtaining BaTiO₃ films with good ferroelectric characteristics.