Tunneling magnetoresistance in a Eu<Subscript>0.7</Subscript>Pb<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> (single crystal)-Fe (film) structure

We have studied the magnetoresistive properties of a structure comprising single crystal manganite Eu_0.7Pb_0.3MnO₃ covered with an epitaxial iron film. At temperatures below T _C of the manganite crystal, the structure exhibits positive magnetoresistance. The behavior of the resistance as a function of the magnetic field is characteristic of a tunneling junction with ferromagnetic electrodes separated by a thin insulating film. The observed effect is related to the formation of a transition layer at the manganite-Fe interface, which is depleted of oxygen and possesses dielectric properties. The sensitivity of the resistance with respect to the magnetic field is determined both by the negative magnetoresistance of the manganite crystal and by the tunneling contribution to the conductivity, whereby the tunneling current depends on the mutual orientation of magnetic moments of the electrodes (Eu_0.7Pb_0.3MnO₃ crystal and Fe film).     

Mechanical properties of HfB2 whiskers

Nanoindentation has been used to study mechanical behavior of HfB₂ whiskers 10–20μm in diameter in a directionally reinforced ceramics. For comparison a bulk (0001) HfB₂ single crystal 5 mm in diameter has been tested. For both the samples a pop-in due to the nucleation of dislocations in a previously dislocation-free region under the indent has been observed. It has been shown that for a HfB₂ whisker in reinforced ceramics the critical load of the elastoplastic transition is twice as high as for a bulk HfB₂ single crystal and, the maximum shear stress, at which the nucleation of the first dislocation loop in a HfB₂ whisker occurs, approaches to the theoretical shear strength value. The observed effect has been caused by the higher structural perfection of whiskers as compared with a bulk sample. Hardness and elastic modulus of the HfB₂ whisker are higher than that of the bulk crystal by 10 and 3%, respectively.     

Effects of bottom electrodes on dielectric properties of epitaxial 2% Mn doped Ba(Zr<Subscript>0.2</Subscript>Ti<Subscript>0.8</Subscript>)O<Subscript>3</Subscript> thin films

2 mol% Mn doped Ba(Zr_0.2Ti_0.8)O₃ (Mn-BZT) thin films were prepared by pulsed laser deposition (PLD) on single crystal oxide substrates LaAlO₃(001) and MgO(001), with conductive oxide bottom electrodes LaNiO₃ and SrRuO₃, respectively. Both the Mn-BZT films and the bottom electrode films could be c-axial oriented with a cube-on-cube arrangement on the corresponding substrates. The dielectric properties measured with parallel plate capacitor configurations of Au/Mn-BZT/LNO and Au/Mn-BZT/SRO revealed that the Mn-BZT film on LNO bottom electrode exhibited comparatively higher dielectric constant, larger dielectric tunability and lower dielectric loss than that on SRO. It could be mainly attributed to the better epitaxial growth characteristics and mismatch stress of Mn-BZT thin film on LNO, as well as less misfit dislocation and the better morphology of LNO bottom electrode.     

Anomalous magnetic hysteresis in La<Subscript>0.6</Subscript>Sr<Subscript>0.2</Subscript>Mn<Subscript>1.2</Subscript>O<Subscript>3−δ</Subscript> manganites with a perovskite structure

We have observed an anomalous magnetic hysteresis in polycrystalline (ceramic) and single crystal (film) samples of La_0.6Sr_0.2Mn_1.2O_3−δ manganites with a perovskite structure. The anomaly is explained by the coexistence and interaction of two magnetic phases (ferromagnetic and antiferromagnetic) in these lanthanumcontaining manganites.     

Electric resistance and magnetoresistance of a two-layer epitaxial heterostructure (30 nm)La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript>/(30 nm)La<Subscript>0.67</Subscript>Ba<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript>

Two-layer epitaxial heterostructures (30 nm)La_0.67Ca_0.33MnO₃/(30 nm)La_0.67Ba_0.33MnO₃ (LCMO/LBMO) have been grown by laser deposition on single crystal (001)LaAlO₃ (LAO) substrates. In this system, the upper (LCMO) layer occurs under the action of tensile stresses in the substrate plane, whereas the lower (LBMO) layer exhibits biaxial compression. The formation of a 30-nm-thick LCMO film on the surface of the 30-nm-thick LBMO layer leads to an increase in the level of mechanical stresses in the latter layer. The maximum electric resistivity ρ of the (30 nm)LCMO/(30 nm)LBMO/LAO structure was observed at a temperature 25–30 K below that corresponding to the maximum of the ρ(T) curve for a single (30 nm)LBMO film on the same LAO substrate.     

Preparation and ferroelectric properties of (124)-oriented SrBi<Subscript>4</Subscript>Ti<Subscript>4</Subscript>O<Subscript>15</Subscript> ferroelectric thin film on (110)-oriented LaNiO<Subscript>3</Subscript> electrode

A (124)-oriented SrBi₄Ti₄O₁₅ (SBTi) ferroelectric thin film with high volume fraction of was obtained using a metal organic decomposition process on SiO₂/Si substrate coated by (110)-oriented LaNiO₃ (LNO) thin film. The remanent polarization (P _r) and coercive field (E _c) for (124)-oriented SBTi film are 12.1 μC/cm² and 74 kV/cm, respectively. No evident fatigue of (124)-oriented SBTi thin film can be observed after 1 × 10⁹ switching cycles. Besides, the (124)-oriented SBTi film can be uniformly polarized over large areas using a piezoelectric-mode atomic force microscope. Considering that the annealing temperature was 650 °C and the thickness of each deposited layer was merely 30 nm, a long-range epitaxial relationship between SBTi(124) and LNO(110) facets was proposed. The epitaxial relationship was demonstrated based on the crystal structures of SBTi and LNO.     

MnGeP<Subscript>2</Subscript> Thin Films Grown by Molecular Beam Epitaxy

Growth conditions for MnGeP₂ thin films have been investigated by using molecular beam epitaxy (MBE) method. Mn and Ge were evaporated by K-cells, and P₂ was supplied by decomposing tertialybutylphosphine (TBP). GaAs (001) and InP (001) single crystals were used as substrates. An X-ray diffraction peak, which can be assigned to (008) peak of MnGeP₂, was observed at nearly the same position as the (004) peak of GaAs. The lattice constant of the MnGeP₂ thin film was determined to be 1.13 nm assuming its crystal structure is a c-axis oriented chalcopyrite type structure. Secondary phases such as GeP, MnGe _x and MnP were observed for beam fluxes of Mn and Ge as high as 1×10^?8 Torr.     

Optical band gap of Sn<Subscript>0.2</Subscript>Bi<Subscript>1.8</Subscript>Te<Subscript>3</Subscript> thin films

Sn_0.2Bi_1.8Te₃ thin films were grown using the thermal evaporation technique on a (001) face of NaCl crystal as a substrate at room temperature. The optical absorption was measured in the wave number range 500–4000 cm⁻¹. From the optical absorption data the band gap was evaluated and studied as a function of film thickness and deposition temperature. The data indicate absorption through direct interband transition with a band gap of around 0.216 eV. The detailed results are reported here.     

Template Engineering of CuBi2O4 Single‐Crystal Thin Film Photocathodes

To develop strategies for efficient photo‐electrochemical water‐splitting, it is important to understand the fundamental properties of oxide photoelectrodes by synthesizing and investigating their single‐crystal thin films. However, it is challenging to synthesize high‐quality single‐crystal thin films from copper‐based oxide photoelectrodes due to the occurrence of significant defects such as copper or oxygen vacancies and grains. Here, the CuBi₂O₄ (CBO) single‐crystal thin film photocathode is achieved using a NiO template layer grown on single‐crystal SrTiO₃ (STO) (001) substrate via pulsed laser deposition. The NiO template layer plays a role as a buffer layer of large lattice mismatch between CBO and STO (001) substrate through domain‐matching epitaxy, and forms a type‐II band alignment with CBO, which prohibits the transfer of photogenerated electrons toward bottom electrode. The photocurrent densities of the CBO single‐crystal thin film photocathode demonstrate ?0.4 and ?0.7 mA cm^?2 at even 0 V_RHE with no severe dark current under illumination in a 0.1 m potassium phosphate buffer solution without and with H₂O₂ as an electron scavenger, respectively. The successful synthesis of high‐quality CBO single‐crystal thin film would be a cornerstone for the in‐depth understanding of the fundamental properties of CBO toward efficient photo‐electrochemical water‐splitting.     

Electric resistance of La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> films biaxially strained during growth on lattice-mismatched substrates

We have studied the electric resistance of 20-nm-thick La_0.67Ca_0.33MnO₃ films coherently grown on single crystal substrates with considerable (negative) and almost zero lattice mismatch. The unit cell volume in the growing film depends on the substrate lattice parameter. At T<200 K and μ₀H=0, the resistance of manganite films on (001)LaAlO₃ substrates was several orders of magnitude greater than the value for an analogous film grown on (001)La_0.29Sr_0.71Al_0.65Ta_0.35O₃. The observed decrease in resistance of the elastically strained (biaxial compression) manganite films is related to a superstoichiometric (≈45%) relative concentration of Mn⁴⁺ ions in the film volume.     

A robust and self-assembled route to synthesis of CdZn(Se<Subscript>1−x</Subscript>Te<Subscript>x</Subscript>)<Subscript>2</Subscript> photoanodes as light harvesters for photoelectrochemical solar cells

This work reports on the development of CdZn(Se_1?xTe_x)₂ thin films utilized as the photoanode for photoelectrochemical cells (PECs). It was found that the incorporation of tellurium plays an important role in determining the optostructural, morphological, compositional and PEC performance of thin films. XRD measurements showed that the deposited thin films are in the mixed phases with a nanocrystalline nature. SEM images indicated that the surface morphology is favourable for effective light absorption in the solar spectrum. The EDS spectrum confirmed that thin film deposition occured in a stoichiometric manner. A detailed quantitative study was also executed using XPS and revealed the presence of Cd²⁺, Zn²⁺, Se^2? and Te^2? elements in the deposited thin film. Finally, the deposited thin films were tested for their photoelectrochemical (PEC) performance. The PEC study illustrated that CdZn(Se_1?xTe_x)₂ thin film showed the highest power conversion efficiency (η) of 1.13% among reported values.     

SnO<Subscript>2</Subscript>-based thin films with excellent photocatalytic performance

SnO₂ semiconductor is a new-typed promising photocatalyst, but wide application of SnO₂-based photocatalytic technology has been restricted by low visible light utilization efficiency and rapid recombination of photogenerated electrons–holes. To overcome these drawbacks, we prepared B/Fe codoped SnO₂–ZnO thin films on glass substrates through a simple sol–gel method. The photocatalytic activities of the films were evaluated by degradation of organic pollutants including acid naphthol red (ANR) and formaldehyde. UV–Vis absorption spectroscopy and photoluminescence (PL) spectra results revealed that the B/Fe codoped SnO₂–ZnO film not only enhanced optical absorption properties but also improved lifetime of the charge carriers. X-ray diffraction (XRD) results indicated that the nanocrystalline SnO₂ was a single crystal type of rutile. Field emission scanning electron microscopy (FE-SEM) results showed that the B/Fe codoped SnO2–ZnO film without cracks was composed of smaller nanoparticles or aggregates compared to pure SnO2 film. Brunauer–Emmett–Teller (BET) surface area results showed that the specific surface area of the B/Fe codoped SnO₂–ZnO was 85.2 m² g^?1, while that of the pure SnO₂ was 20.7 m² g^?1. Experimental results exhibited that the B/Fe codoped SnO₂–ZnO film had the best photocatalytic activity compared to a pure SnO₂ or singly-modified SnO₂ film.     

Piezoelectric and optical properties of ZnO thin films deposited using various O<Subscript>2</Subscript>/(Ar+O<Subscript>2</Subscript>) gas ratios

In this study, ZnO thin films were fabricated on a Pt(111)/TiO_x/SiO₂/Si substrate using the RF magnetron sputtering method. Then, the effect of the crystallization orientation and microstructure on the piezoelectric and optical properties of the ZnO thin film was investigated for various O₂/(Ar+O₂) gas ratios. When the O₂/(Ar+O₂) gas ratio was 50%, the intensity of the (002) peak corresponding to the preferred orientation of the ZnO thin film was a maximum and the minimum FWHM value of 0.56° was observed. The surface roughness of the ZnO thin film measured using AFM also had a minimum value of 16.43 °C at an O₂/(Ar+O₂) gas ratio of 50%. The piezoelectric characteristics of the ZnO thin film were measured using the pneumatic loading method (PLM) and the corresponding constant had the largest value of 11.9 pC/N at an O₂/(Ar+O₂) gas ratio of 50%. The transmittance of the ZnO thin film obtained from the transmittance curve using a spectrophotometer was slightly greater than 80% in the human visible light region at an O₂/(Ar+O₂) gas ratio of 50%. By using the refractive index data obtained from the transmittance curve and the Sellmeir dispersion relation, we can also predict the refractive index at a wavelength of 400 nm. When the O₂/(Ar+O₂) gas ratio was 50%, the refractive index was 2.043 and, at other gas ratios, the corresponding refractive indices were 2.004∼2.006. The band gap energies of the ZnO thin film were 3.27∼3.33 eV depending on the O₂/(Ar+O₂) gas ratio and were little affected by the variation of the oxygen inflow volume.     

Laser ablated lead free (Na,K) NbO<Subscript>3</Subscript> thin films with excess alkali-content

Lead free (Na_0.5K_0.5) NbO₃ (NKN) being hygroscopic in nature is very difficult to be fabricated with enhanced properties in thin films. To maintain stoichiometry 0, 5 and 10% mole excess of Na on A-site were added on NKN bulk targets. The perovskite ABO₃ crystal structure incorporating 0, 5 and 10% excess alkali ions were grown on Pt/Ti/SiO2/Si substrate by pulsed laser deposition, using stoichiometric high density ceramic targets. X-ray diffraction peaks and Raman scattering spectra suggest the formation of single phase of the film in monoclinic phase. The dielectric properties and leakage current is improved with increasing amount of Na concentration. The reduction in leakage current with addition of excess Na concentration may be due to increase in grain size decrease in the connection of grain boundaries with grains. The impedance spectra of the film shows single dielectric relaxation which is non-debye type and the relaxation frequency is shifted to higher side at higher frequency.     

Optimization of Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> thin film absorber layer growth without sulphurization using triethanolamine as complexing agent for thin film solar cells applications

Quaternary kesterite Cu₂ZnSnS₄ (CZTS) thin films have been prepared via a simple spin-coating technique based on a sol–gel precursor of 2-methoxyethanol solution with metal salts and thiourea. Solution processed CZTS thin film growth parameters using complexing agent triethanolamine (TEA) have been investigated. Effects of complexing agent TEA on structural, morphological, optical, electrical and photovoltaic properties of CZTS thin films were systematically investigated. X-ray diffraction and Raman spectroscopy studies reveal that amorphous nature of CZTS thin film changes into polycrystalline with kesterite crystal structure with optimized TEA concentartion. Surface morphology of CZTS films were analyzed by field emission scanning electron microscope and atomic force microscope, which revealed the smooth, uniform, homogeneous and densely packed grains and systematic grain growth formation with varying TEA concentrations. UV–Vis spectra revealed a direct energy band gap ranging from 1.78 to 1.50 eV, which was found to depend upon the TEA concentration. X-ray photoelectron spectroscopy demonstrated stoichiometric atomic ratios of multicationic quaternary CZTS thin film grown without sulphurization. p-type conductivity was confirmed using Hall measurements and the effect of varying concentartion of TEA on electrical and photovoltaic properties are studied. The SLG/FTO/ZnO/CZTS/Al thin film solar cell is fabricated with the CZTS absorber layer grown at optimized TAE concentration of 0.06 M. It shows a power conversion efficiency of 0.87% for a 0.16 cm² area with V_oc = 0.257 mV, J_sc = 8.95 mA/cm² and FF?=?38%.     

Electrical behavior of Y-doped Ba<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>TiO<Subscript>3</Subscript> thin films

Ba_0.6Sr_0.4TiO₃ (BST) and 1.5 at% Y-doped Ba_0.6Sr_0.4TiO₃ (Y-BST) thin films have been deposited on single-crystal (100) oriented LaAlO₃ substrates using pulsed-laser deposition technique (PLD), respectively. X-ray diffraction (XRD) scanning revealed that the two kinds of films could be epitaxially grown in pure single-oriented perovskite phases, but Y-BST thin films showed an enhanced crystallization effect. The dielectric properties of the pure and Y-BST thin films were measured at 10 kHz and 300 K with a parallel-plate capacitor configuration. The results revealed that the addition of Y as an acceptor doping is very effective to increase dielectric tunability, and to reduce leakage current of BST thin films. The figure-of-merit (FOM) factor value increases from 17.32 for BST to 25.84 for Y-BST under an applied electric field of 300 kV/cm. The leakage current density of the BST thin films at a negative bias field of 300 kV/cm decreases from 2.45 × 10⁻⁴ A/cm² to 1.55 × 10⁻⁶ A/cm² by Y doping. The obtained results indicated that the Y-doped BST thin film is a promising candidate material for tunable microwave devices.     

Growth of highly oriented iridium oxide bottom electrode for Pb(Zr,Ti)O<Subscript>3</Subscript> thin films using titanium oxide seed layer

Due to its low resistivity and excellent thermal stability, IrO₂ has attracted attention as an alternative for electrode material in ferroelectric integrated circuit applications. Oriented growth of IrO₂ electrode film was investigated with the goal to control the texture of the PZT thin film. IrO₂ films were prepared by DC reactive sputtering. PZT film was prepared by RF magnetron sputtering single target deposition method. The whole layer stack was grown onto amorphous thermal oxide of a silicon wafer. The results indicate that IrO₂ thin film was preferentially (200) oriented when a TiO₂ seeding layer was used. The orientation relationships along the whole PZT(111)/IrO₂(200)/TiO₂(200)/Ti structure was discussed.     

Structural and optical characterization of c-axis textured BaTiO<Subscript>3</Subscript> thin films on MgO fabricated by RF magnetron sputtering

In this paper, BaTiO₃ thin films were prepared by RF magnetron sputtering on MgO substrates and their properties such as the crystal structure and optical waveguide properties were investigated. The optimum deposition parameters, such as substrate temperature, deposition pressure, gas flow ratio, the RF power and the after annealing temperature, were obtained in order to get the best BaTiO₃ film quality. The XRD results show that highly c-axis textured BaTiO₃ thin films were successfully grown on MgO substrate. Films obtained under the optimum deposition parameters, substrate temperature of 650°C, RF power of 50 W, deposition pressure 18 mTorr and gas flow ratio O₂/(Ar+ O₂) of 15% namely, reaches a full width at half maximum intensity (FWHM) of BaTiO₃ (002) XRD peak of 0.25°. The FWHM of BaTiO₃ (002) XRD peak was further reduced to 0.24° via post-treatment with furnace annealing (at 800°C for 2 h) which indicates the film crystal quality is further improved. The bright and sharp TE modes measured by m-line spectroscopy of the BaTiO₃ film were observed indicating its possible application in optical waveguide.     

Effect of excess Bi content on electrical properties of BiFe<Subscript>0.95</Subscript>Cr<Subscript>0.05</Subscript>O<Subscript>3</Subscript> thin films

The Bi_1?+?xFe_0.95Cr_0.05O₃ (BFCO) (x?=?0, 5, 10, 15 and 20%) thin films are fabricated on FTO/glass substrate using a chemical solution deposition method and sequential-layer annealing process. The effects of the excess Bi content on crystalline structure, morphology, and electrical performance of BFCO thin films are investigated. All the BFCO thin films are crystallized into polycrystalline perovskite structure and belonging to the space group of R3c. The BFCO thin films with 5 and 10% excess Bi contents possess no impurity phase. Especially, a dense surface morphology and columnar crystal structure can be obtained for the film with 5% excess Bi content. Especially, the one possesses superior ferroelectricity with a relative high remnant polarization (P _r) of 69.8 µC/cm² and low coercive electric field (E _c) of 291 kV/cm at 1 kHz due to the relatively low leakage current density of 3.04?×?10^??5 A/cm² at 200 kV/cm.     

Epitaxial YBa<Subscript>2</Subscript>Fe<Subscript>3</Subscript>O<Subscript>8</Subscript> Films Prepared by Chemical Solution Deposition Method

YBa₂Fe₃O₈(YBFO) epitaxial films are prepared on (100) SiTrO₃ single crystal substrate by polymer-assisted non-fluorine chemical solution deposition (CSD) method. The influence of firing temperature on texture degree, microstructure, and physical properties of YBFO films is systematically investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and SQUID magnetometer. YBFO film fired at 1070 °C exhibits best epitaxial quality with FWHM value of (103) phi-scan and (005) omega-scan is 0.19° and 0.45°, respectively, and highly dense and smooth morphology. A weak ferromagnetism transition was observed at 68 K in the YBFO film.