Electrical transport and magnetoresistance in La2/3Sr1/3MnO3 polycrystalline composite thin films

The manganite La_2/3Sr_1/3MnO₃ (LSMO)/CuO and LSMO/Al₂O₃ polycrystalline composite thin films are deposited on Si (111) substrates in a magnetron sputtering system, using the tandem deposition method. The electrical transport and magnetoresistance properties of the films have been systematically investigated. By considering two parallel conduction channels at the grain boundary, we obtain a general expression for the temperature dependency of the resistance that agrees with the experimental data measured in LSMO polycrystalline composite thin films at whole temperature region of 300 K-10 K under the condition of zero magnetic field. Also, the resistance vs. temperature curve under an external magnetic field can be obtained by only varying one parameter in the model. It provides an effective way to obtain the high-temperature grain boundary magnetoresistance in the polycrystalline manganite.     

Spray Pyrolysis of MgO Templates on 321-Austenitic Stainless Steel Substrates for YBa2Cu3O7 Deposition by PLD

Spray pyrolysis was used to deposit MgO films on polycrystalline 321-austentic stainless steel substrates using magnesium nitrates and magnesium acetates as precursors. The MgO films deposited from the nitrate precursors were amorphous; however, MgO (200) oriented films were obtained when the acetates precursors were used. The texture of the films was improved with increasing the concentration and the deposition temperature. To evaluate the performance of the MgO buffers, PLD was used to deposit YBCO on MgO-buffered 321 substrates. Only the smoothest MgO films were found as good buffers for the deposition of c-axis oriented YBCO films. The superconducting transition temperature was broad and the T _C onset was 83.6 K. Austenitic 321 steel is an alternative for C276 as a substrate for thin film deposition.     

Low Field Magnetoristance and Inhomogenieties in La2/3Ca1/3MnO3 Films

La_2/3Ca_1/3MnO₃ films were prepared using a conventional paint-on method on alumina and monocrystalline TiSrO₃ substrates. A significant difference between the peak resistivity temperature T _p=178 K and the magnetic transition temperature T _c=240 K was found in contrast to single crystal samples. The behavior of the magnetoresistance with temperature also differs from that found in bulk samples. Although the films show significant granular morphology differences, their transport and magnetoresistive properties are very similar. Maximum magnetoresistance ratios of 16% and 10% at 0.3 T and 77 K were obtained for films deposited on alumina and TiSrO₃ substrates, respectively. Magnetization measurements above T _c show a nonlinear behavior, consistent with the presence of ferromagnetic inhomogeneities within the paramagnetic phase. These results suggest that, in addition to the importance of grain boundary scattering in determining the magnetoresistance at low fields, microscopic inhomogeneity plays a role in determining magnetotransport properties.     

Effect of strain and grain boundaries on dielectric properties in La0.7Sr0.3MnO3 thin films

High dielectric constant and its dependence on structural strain and grain boundaries (GB) in La_0.7Sr_0.3MnO₃ (LSMO) thin films are reported. X-ray diffraction, magnetization, and magneto-transport measurements of the LSMO films, made by pulsed laser deposition on two different substrates—MgO and SrTiO₃ (STO), were compared to co-relate magnetic properties with dielectric properties. At room temperature, in the ferromagnetic phase of LSMO, a high dielectric constant (6 × 10⁴) was observed up to 100 kHz frequency for the films on MgO, with polycrystalline properties and more high-angle GB related defects, while for the films on STO, with single-crystalline properties but strained unit cells, high dielectric constant (≈10⁴) was observed until 1 MHz frequency. Also, a large dielectric relaxation time with significant broadening from the Debye single-dielectric relaxation model has been observed in samples with higher GB defects. Impedance spectroscopy further shows that large dielectric constant of the single-crystalline, strained LSMO film is intrinsic in nature while that in the polycrystalline films are mainly extrinsic due to higher amount of GBs. The presence of high dielectric constant value until high frequency range rules out the possibility of “apparent giant dielectric constant” arising from the sample-electrode interface. Coexistence of ferromagnetism and high dielectric constant can be very useful for different microelectronic applications.     

Effect of internal strain on magnetic properties of La0.7Sr0.3MnO3 films

Oriented La_0.7Sr_0.3MnO₃ (LSMO) films were grown on (100) LaAlO₃ (LAO) and SrTiO₃ (STO) substrates by the method of radio frequency magnetron sputtering. X-ray diffraction patterns of LSMO films deposited on LAO and STO substrates showed a slight shift of diffraction peaks as compared to the corresponding peaks of the bulk LSMO. The shift of diffraction peaks was believed to result from the in-plane lattice mismatch between the film and substrate. The distinguished strain effects of substrates were found to be effective on the magnetic properties and the surface morphology of LSMO films on both substrates. The results indicate that STO substrate may be the promising candidate for room-temperature applications of LSMO film.     

Synthesis and Characterization of MgB2 Thin Films Prepared by?2.4?Mhz Ultrasonic Spray Pyrolysis System

Nano-sized B and Mg powders have been successfully deposited onto single crystal MgO(100) and Al₂O₃(001) substrates using 2.4 MHz ultrasonic spray pyrolysis system and an appropriate solution to obtain thin films of MgB₂ superconductors. After an in-situ heating process, ??600?C1000 nm thick superconductor films were obtained. The microstructure, electrical, and magnetic properties were characterized by means of particle size analyzer, XRD, SEM?CEDX, R?CT, and M?CH analysis. The effect of particle concentration in the solution, spraying time, and heating temperature on the quality of the MgB₂ films were discussed. The best T _c and T _zero results were obtained to be 39.5 and 37.4 K, respectively, for the film deposited on the Al₂O₃(001) substrates. Magnetic properties of the MgB₂ films were investigated at 3 different temperatures and up to 5 T. Symmetric hysteresis loops for all temperature and field cases were obtained and maximum $J_{c}^{\mathrm{mag}}$ value was calculated to be 4.0×10⁶ A?cm^?2 at 10 K for 0 T for the film deposited on the Al₂O₃(001) substrates. The results obtained were found to be highly dependant on the particle concentration in the solution, heating temperature of substrates and carrier gas flow rate during spraying.     

Magnetic properties of NiFe2O4 thin films grown on La0.7Sr0.3MnO3-buffered Si substrate

Nickel ferrite NiFe₂O₄ (NFO) thin films have been prepared on a Si substrate (NFO/Si) and La_0.7Sr_0.3MnO₃ (LSMO)-coated Si (100) substrate (NFO/LSMO/Si) by RF magnetron sputtering. The microstructures and magnetic properties of the two films were systematically investigated. X-ray diffraction (XRD) and atomic force microscopy (AFM) revealed that highly (331)-oriented NFO films with a smooth surface were grown on the LSMO/Si substrate. The magnetization of the films was measured at room temperature. It showed a clear hysteresis loop in both samples, with the magnetic field applied in the plane. However, no hysteresis loop is seen with the magnetic field applied perpendicular to the film plane. This indicates the presence of an anisotropy favoring the orientation of the magnetization in the direction parallel to the film plane. A study of magnetization hysteresis loop measurements indicates that the LSMO buffer layer may improve the magnetic properties of NFO thin films, and that the saturation magnetization increases from 4.15 × 10⁴ to 3.5 × 10⁵ A/m.     

Growth and characterization of La1 − xAxMnO3 (A = Ag and K, x = 0.33) epitaxial and polycrystalline manganite thin films derived by sol-gel dip-coating technique

Manganite La_0.67Ag_0.33MnO₃ (LAgMO) and La_0.67K_0.33MnO₃ (LKMO) films have been obtained on a single-crystal of LaAlO₃ (100) and quartz substrates using sol-gel dip-coating technique. Structural, electrical, magnetic and magnetoresistance properties of the films have been investigated. X-ray diffraction patterns of the films grown on LaAlO₃ (100) substrate showed to be highly oriented in the direction of (100) and the films grown on the quartz substrate have perovskite with rhombohedral structure. The oriented films exhibited typical transport properties, whereas the polycrystalline films showed significantly different behaviors of the temperature dependent resistivity, magnetization and magnetoresistance (MR). The epitaxial films of the LAgMO and LKMO showed different metal-insulator transition temperature (T_MI) and the paramagnetic-ferromagnetic phase transition temperature (T_C). This was mainly due to the different ionic radius size of Ag¹⁺ and K¹⁺. The variation of T_MI and T_C was due to the different annealing temperatures and grain size effect in the polycrystalline films. The polycrystalline films showed a higher MR than the corresponding epitaxial films. An extrinsic MR has been observed at low temperatures (< 100 K) for the polycrystalline films due to the spin dependent scattering of conduction electrons at grain boundaries.     

Magnetic properties of NiFe2O4 thin films grown on La0.7Sr0.3MnO3-buffered Si substrate

Nickel ferrite NiFe₂O₄ (NFO) thin films have been prepared on a Si substrate (NFO/Si) and La_0.7Sr_0.3MnO₃ (LSMO)-coated Si (100) substrate (NFO/LSMO/Si) by RF magnetron sputtering. The microstructures and magnetic properties of the two films were systematically investigated. X-ray diffraction (XRD) and atomic force microscopy (AFM) revealed that highly (331)-oriented NFO films with a smooth surface were grown on the LSMO/Si substrate. The magnetization of the films was measured at room temperature. It showed a clear hysteresis loop in both samples, with the magnetic field applied in the plane. However, no hysteresis loop is seen with the magnetic field applied perpendicular to the film plane. This indicates the presence of an anisotropy favoring the orientation of the magnetization in the direction parallel to the film plane. A study of magnetization hysteresis loop measurements indicates that the LSMO buffer layer may improve the magnetic properties of NFO thin films, and that the saturation magnetization increases from 4.15 × 10⁴ to 3.5 × 10⁵ A/m.     

Combined effect of substrate temperature and laser energy density on laser ablated BiFeO3 thin films

Bismuth ferrite (BiFeO₃) thin films were prepared on Pt(111)/Ti/SiO₂/Si substrates by laser ablation deposition at various substrate temperature (T _sub) and laser energy density (D _L). The combined effect of T _sub and D _L on crystalline phase, preferential orientation and surface morphology of the films were investigated. The microstructure and morphology of the films showed a strong dependence on T _sub and D _L simultaneously. BiFeO₃ thin films with single phase could be prepared at T _sub-D _L of 893 K?1 J/cm², 943 K?2 J/cm² and 963 K?3 J/cm², respectively. Film deposited at T _sub = 963 K and D _L = 3 J/cm² exhibited better ferroelectric property due to the combination of high (111) preferential orientation, dense surface morphology and less Fe²⁺ content.     

Substrate dependent structural and magnetic properties of pulsed laser deposited Fe3O4 thin films

Nanocrystalline iron oxide thin films have been deposited on various substrates such as quartz, MgO(100), and Si(100) by pulsed laser deposition technique using excimer KrF laser (248 nm). The orientations, crystallite size and lattice parameters were studied using X-ray diffraction. The XRD results show that the films deposited on MgO and Si substrates are highly oriented and show only (400) and (311) reflections respectively. On the other hand, the orientation of the films deposited on quarts substrate changed from (311) to (400) with an increase in the substrate temperature from 400 degrees C to 600 degrees C, indicating thereby that the film growth direction is highly affected with nature of substrate and substrate temperature. The surface morphology of the deposited films was studied using Atomic Force Microscopy (AFM) and spherical ball like regular features of nanometer size grains were obtained. The magnetic properties were studied by Superconducting Quantum Interference Device (SQUID) magnetometer in the magnetic field +/- 6 Tesla. The magnetic field dependent magnetization (M-H) curves of all the Fe3O4 thin films measured at 5 K and 300 K show the ferrimagnetic nature. The electrochemical sensing of dopamine studied for these films shows that the film deposited on MgO substrate can be used as a sensing electrode.     

Growth and properties of highly orientated Sr0.75Ba0.25Nb2O6 thin films on silicon substrates with MgO or TiN buffer layers

Sr_0.75Ba_0.25Nb₂O₆ (SBN75) thin films were deposited on silicon substrate with MgO (100) or TiN (100) buffer layer by radio-frequency magnetron sputtering technique. X-ray diffraction confirmed that a 900 °C annealed SBN self-buffer layer introduced before SBN deposition can lead to the highly c-axis orientation of SBN75 thin film on MgO buffer layer. Energy-dispersive spectrometry analysis showed that the SBN75 films had target-film composition transfer and the TiN buffer layer was partially oxidized during SBN growth. The refractive index of SBN films on both MgO/Si and TiN/Si substrates was determined by fitting the measured reflectance curves with Sellmeier dispersion model in the visible region and the micro-structures were studied by scanning electron microscopy. In this paper, the conditions for SBN/MgO/Si treated as waveguide structure were also discussed.     

On the compositional,optical and electrical characteristics of vacuum‐deposited GaAs1‐xPx films prepared by a successive evaporatron method

Abstract

GaAs_1‐xP_x thin films have been deposited onto glass substrates at a rate of 50Å/min. in a vacuum of 5 x 10^‐5 Torr using a successive evaporation method. Thin films of various compositions (X = 0.3–0.9) were obtained at gallium source temperature T_Ga = 870°C, arsenic source temperature T_As = 275°C, phosphorus source temperature T_P = 330°‐363°C and substrate temperature T_sub = 265°‐330°C. Compositional, optical (absorption) and electrical properties of the films in a thickness range of 1300–1900 Å were determined by using an X‐ray diffractometer, a grating spectrometer and an electrometer respectively. The experimental results were compared with those for simultaneous evaporation and discussed from the atomistic viewpoints.

The values of △X/△T_sub are ‐ 7 x 10^‐3 and ‐1 x 10^‐3 °C^‐1 for successive and simultaneous evaporation respectively, the difference of which can be explained by the absorption effect of a predeposited Ga layer in successive evaporation. The value of △X/△Tp is about +7 x 10^‐3°C^‐1 for the two evaporation methods, however, it levels off more distinctly at higher substrate temperatures. Absorption edge shift and relatively low resistivity suggest that successively vacuum‐deposited films have much more phosphorus vacancies and/or impurities than simultaneously vacuum‐deposited and chemically vapor‐deposited films.     

The Rectification Studies on the P+-Ion Implanted C60/Si Films

Abstract

N-type doping of the C₆₀ films deposited on Si substrates has been achieved by 80 keV P⁺-ion implantation with doses of 2×10¹⁴ cm^?2 at room temperature. The heterostructures composed of the n-type doped C₆₀ films and n- or p-type Si(111), Si(100) substrates are studied in view of semiconductor heterojunctions. The rectification and other electrical characteristics of the P⁺-ion implanted n-C₆₀/n-(p-)Si heterostructures are disclosed by the current-voltage (I-V) measurements at room temperature. The n-C₆₀/p-Si heterostructures show stronger rectification than n-C₆₀/n-Si heterostructures and Si(111) substrates are found to be more suitable for forming n-C₆₀/Si heterostructures than Si(100) substrates.     

Chemical Bath Deposition of Zinc Sulfide Films Doped With Copper

Zinc sulfide (ZnS) films are doped with low copper concentrations by the chemical bath deposition (CBD) technique on glass substrates. The basic chemical bath contains ZnSO₄, KOH, NH₄NO₃, and thiourea as chemical reagents. Different volumes of copper chloride solution (0.004 M) were included into the basic solution for doping. Doped films were deposited in a chemical solution at 363 K and deposition times from 30 to 90 min. The chemical solution and films present changes, from pale to dark-brown, in their color when the Cu doping is increased. The bandgap energy of the undoped and doped films ranged from 3.68 to 3.72 eV, meanwhile the crystalline structure suffers an amorphization with doping. The Cu-doped ZnS was verified with the photoluminescence technique.     

Microstructural and transport properties of LaNiO3−δ films grown on Si (111) by chemical solution deposition

Electrically conductive LaNiO_3−δ (LNO) thin films with typical thickness of 200 nm were deposited on Si (111) substrates by a chemical solution deposition method and heat-treated in air at 700 °C. Structural, morphological, and electrical properties of the LNO thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), field-emission scanning electron microscopy (FEG-SEM), and electrical resistivity ρ(T). The thin films have a very flat surface and no droplet was found on their surfaces. The average grain size observed by AFM and FEG-SEM was approximately 100 nm in excellent agreement with XRD data. The ρ(T) data showed that these thin films display a good metallic character in a large range of temperature. These results suggest the use of this conductive layer as electrode in the integration of microelectronic devices.     

Hot wire chemical vapor deposited multiphase silicon carbide (SiC) thin films at various filament temperatures

Influence of filament temperature (T_Fil) on the structural, morphology, optical and electrical properties of silicon carbide (SiC) films deposited by using hot wire chemical vapor deposition technique has been investigated. Characterization of these films by low angle XRD, Raman scattering, XPS and TEM revealed the multiphase structure SiC films consisting of 3C–SiC and graphide oxide embedded in amorphous matrix. FTIR spectroscopy analysis show an increase in Si–C, Si–H, and C–H bond densities and decrease in hydrogen content with increase in T_Fil. The C–H bond density was found higher than the of Si–H and Si–C bond densities suggesting that H preferably get attached to C than Si. AFM investigations show decrease in rms surface roughness and grain size with increase in T_Fil. SEM studies show that films deposited at low T_Fil has spherulites-like morphology while at high T_Fil has cauliflower-like structure. Band gap values E_Tauc and E₀₄ increases from 1.76 to 2.10 eV and from 1.80 to 2.21 eV respectively, when T_Fil was increased from 1500 to 2000 °C. These result show increase in band tail width (E₀₄–E_Tauc) of multiphase SiC films. Electrical properties revealed that σ_Dark increases from ~7.87 × 10^?10 to 1.54 × 10^?5 S/cm and E_act decreases from 0.67 to 0.41 eV, which implies possible increase in unintentional doping of oxygen or nitrogen due to improved crystallinity and Si–C bond density with increase in T_Fil. The deposition rate for the films was found moderately high (21 < r_dep < 30 Å/s) over the entire range of T_Fil studied.     

Analysis of current conduction mechanism in CZTSSe/n-Si structure

In this study, Cu₂ZnSn(S,Se)₄ (CZTSSe) thin films were deposited by the single step thermal evaporation process using the sintered powder of CZTSSe on soda lime glass (SLG) and Si wafer substrates. The structural, optical, and electrical properties of deposited films were investigated. Current–voltage (I–V) in the temperature range of 250–350 K, capacitance–voltage(C–V) and conductance–voltage (G/w–V) measurements at room temperature were carried out to determine electrical properties of CZTSSe/n-Si structure. The forward bias I–V analysis based on thermionic emission (TE) showed barrier height inhomogeneity at the interface and thus, the conduction mechanism was modeled under the assumption of Gaussian distribution of barrier height. The mean barrier height \(({\bar {\Phi }_{B0}})\) and standard deviation \(({\sigma _0})\) at zero bias were obtained as 1.27 eV and 0.18 V, respectively. Moreover, Richardson constant was obtained as 120.46 A cm^?2 K^?2 via modified Richardson plot and the density of interface states (D_it) profile was determined using the data obtained from forward bias I–V measurements. In addition, by the results of frequency dependent C–V measurements, characteristics of the interface state density were calculated applying high-low frequency capacitance (C_HF ? C_LF) and Hill–Coleman methods.     

Fabrication of a novel SnO2:Al/ZnO:F bi-layer for opto-electronic applications

Single layered aluminium doped tin oxide (ATO), fluorine doped zinc oxide (FZO) and bi-layered ATO/FZO thin films were deposited onto preheated glass substrates (T_s = 340 ± 5 °C) using a low-cost and simplified spray pyrolysis technique. The structural, optical, electrical and surface morphological properties of the bi-layered ATO/FZO thin films were studied and compared with that of the single layered films. The average optical transmittance of the bi-layer film in the visible range was found to be around 80 %. The bi-layered ATO/FZO films possessed both better transmittance in the visible range and sharp absorption edge, the unique desirable features of ATO and FZO films, respectively. The optical band gap (E_g) value of the bi-layer coating (3.22 eV) was found to lie between the E_g values of single layered ATO (3.71 eV) and FZO (3.20 eV) films. Sheet resistance values of ATO and FZO single layer films were 3.47 and 11.2 kΩ/sq., respectively. The bi-layered ATO/FZO thin films exhibited a sheet resistance of 4.42 kΩ/sq. which was very much close to that of ATO films and three times less than that of FZO film. The AFM images showed the good packing density and homogeneity of the surface of the bi-layer films. The annealing studies clearly showed that the ATO over layer remarkably improved the thermal stability of the bi-layered film.     

Influence of Interfacial LSMO Nanoparticles/Layer on the Vortex Pinning Properties of YBCO Thin Film

YBa₂Cu₃O_7?δ (YBCO) thin films have been deposited on bare and La_0.67Sr_0.33MnO₃ (LSMO) modified single crystal SrTiO₃ (STO) substrates. The effect of randomly distributed ferromagnetic LSMO nanoparticles and a complete LSMO layer, present at STO/YBCO interface, on the superconducting properties of YBCO thin films has been investigated by temperature dependent magnetization studies. The YBCO thin film on LSMO nanoparticles decorated STO substrate shows significant improvement in the critical current density and pinning force density as compared to the YBCO thin film deposited on bare STO substrate and this improvement is more significant at higher applied magnetic field. However, the LSMO/YBCO bilayer showed the improved flux pinning properties only up to a magnetic field of 1.5 T above which it deteriorates. In the case of LSMO/YBCO bilayer, the underlying LSMO layer gives rise to magnetic inhomogeneities due to domain structure, which leads to improved flux pinning properties limited to lower field. However, in the case of LSMO nanoparticles decorated substrate, the presence of LSMO nanoparticles at YBCO/STO interface seems to introduce magnetic inhomogeneities as well as structural defects, which might be acting as correlated pinning sites leading to improved flux pinning properties of the YBCO thin film over a wide range of applied magnetic field.