Pulsed laser deposition of BiFeO3 thin films with large polarization on Pt(111)/Ti/SiO2/Si by controlling substrate temperature

Bismuth ferrite (BiFeO₃) thin films with large polarization were grown on Pt(111)/Ti/SiO₂/Si by optimizing the substrate temperatures (T _sub). The BiFeO₃ thin films were prepared by pulsed laser deposition and the effects of T _sub (T _sub = 853–913 K) on crystallization orientation, surface morphology and properties of the films were investigated. The microstructure and morphology of the films showed a strong dependence on T _sub. The film prepared at T _sub = 893 K had a relatively high degree of (111) preferential orientation and densely packed morphology. A large polarization with the maximum remanent polarization of 108 μC/cm² was obtained, which was due to the high degree of preferential orientation and the dense surface morphology at the optimum substrate temperature.     

Fabrication of Cu(In,Ga)Se2 thin films by ion beam sputtering deposition from a quaternary target at different substrate temperatures

Cu(In, Ga)Se₂ (CIGS) thin films were fabricated by ion beam sputtering deposition from a single quaternary target at different substrate temperatures (T _sub). The thin films were characterized with X-ray diffractometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy and four-point probe technique to study the microstructures, surface morphology, composition and electrical properties, respectively. The results show that the films grown above 400?°C are of chalcopyrite structure. Cu(In_0.7Ga_0.3)Se₂ thin film was obtained when T _sub is 550?°C. The Cu and Se atomic percentage when T _sub is above 500?°C is higher than when T _sub is below 500?°C. With the increase in T _sub, the surfaces morphology of the films is denser and the resistivity of the films decreases.     

Study on Mn-induced Jahn–Teller distortion in BiFeO3 thin films

Present work reports Raman spectroscopy study of single-phase Mn-doped BiFeO₃ [BiFe_1?x Mn _x O₃ (0 ≤ x ≤ 0.20)] polycrystalline thin films carried out in backscattering geometry. De-convolution of Raman spectra showed a gradual transition in the crystal symmetry from rhombohedral (?R) to multiphase [rhombohedral (?R) + tetragonal (?T)] structure with increasing Mn doping concentration in BiFe_1?x Mn _x O₃ (BFMO) thin films. X-ray diffraction (XRD) along with Le-Bail extraction refinement confirms that the structural symmetry lowering in BFMO thin films occurs at about 10 % Mn doping concentration. A blue shift is observed in the direct energy band gap of BFMO thin films from 2.53 to 2.87 eV (at T = 295 K) and is attributed to the local symmetry lowering and local induced strain in Fe³⁺ environment resulted from Jahn–Teller distortion in (MnFe)³⁺O₆ octahedral unit. Second-derivative analysis of FTIR spectra in the spectral regions (420–470) cm^?1 and (480–680) cm^?1 further indicates the favourable structure distortion leading to the simultaneous exhibition of enhanced ferromagnetic and ferroelectric properties owing to Mn substitution in host BiFeO₃ lattice.     

Electrical and optical properties of MoSe2 films prepared by r.f. magnetron sputtering

The electrical resistivity of MoSe₂ films prepared by r.f. magnetron sputtering was measured between 300 and 10 K. The main sputtering parameter governing the physical properties of the films was found to be the substrate temperature T_sub. The room temperature resistivity of the as-sputtered films increased from $\text{1.7 × 10}{}^{-1}\text{Ω}\text{cm}$(T_sub = -70 °C) to $\text{1.4 × 10}{}^1\text{Ω}\text{cm}\text{(T}{}_{\mathrm{<mtext>sub</mtext>}}\text{= 150 °}\text{C}\text{)}$. A check of the thermo-electrical response showed that the majority charge carriers are holes except for films deposited at T_sub = 150 °C which are n type. Hall effect measurements indicated very low Hall mobilities (3–5 cm² V^-1 s^-1). Thermal annealing increased the room temperature resistivities by more than one order of magnitude for the specimens sputtered at a low substrate temperature. The optical properties were weakly influenced by the process conditions. The optical gap was determined to be 1.06 eV.     

Structural and optical properties of BaTi2O5 thin films prepared by pulsed laser deposition at different substrate temperatures

BaTi₂O₅ thin films were prepared on MgO (1 0 0) substrates by pulsed laser deposition. The effect of substrate temperature (T_sub) on the structural and optical properties of the films, such as crystal phase, preferred orientation, crystallinity, surface morphology, optical transmittance and bandgap energy, was investigated. The preferred orientation of the films changed form (7 1 0) to (0 2 0) depending on T_sub, and the b-axis oriented BaTi₂O₅ thin film could be obtained at T_sub = 973–1023 K. The surface morphology of the films was different with changing T_sub, which showed a dense surface with an elongated granular texture at T_sub = 973–1023 K. The crystallinity and surface roughness increased at the elevated substrate temperatures. The as-deposited BaTi₂O₅ thin films were highly transparent with an optical transmittance of ～70%. The bandgap energy was found to decrease with increasing substrate temperature, from 3.76 eV for T_sub = 923 K to 3.56 eV for T_sub = 1023 K.     

Effects of In-situ and Ex-situ Heat-Treatment Procedures on?the?Transport Properties of the MgB2 Superconducting Thin Films Fabricated by Ultrasonic Spray Pyrolysis (USP) System

Superconducting MgB₂ thin films have been prepared using Ultrasonic Spray Pyrolysis (USP) system. 2.4 MHz USP system and various solutions which contain different Mg, B and de-ionized water and LAPSA concentrations and gas atmospheres were used to obtain 500 nm to 1.0 ??m thick MgB₂ films. Some of the films produced were heat treated in-situ in the spraying chamber during deposition and some of them were annealed ex-situ in the tube furnace under Mg vapor. T _c and T _zero of the samples were obtained to be 39.5 K and 37.4, 39.5 and 37.0 for ex-situ and in-situ prepared films, respectively. The highest critical current density was obtained to be 4.12×10⁶ A?cm^?2 for ex-situ annealed films and 4.01×10⁶ A?cm^?2 for in-situ produced films. The result obtained indicated that the ex-situ preparation method provides improvement in the transport and magnetic properties.     

Thickness Dependence of Critical Current Density in MgB2 Films Prepared by Thermal Evaporation Method

MgB₂ films with the thickness of 350 to 1150 nm have been prepared on the Al₂O₃ (001) single crystal substrates from high purity B and Mg powder by the thermal evaporation method. Films were then heat treated ex-situ under Mg vapor at 950?°C to achieve actual MgB₂ stoichiometry. Thickness of the films, so the deposition time, was varied to investigate its influence on critical current density of the films. The films fabricated were analyzed by means of microstructural, transport, and magnetic properties. The best T _c and T _zero values were obtained to be 39.5 K and 38 K, respectively, and decreased with increasing the thickness. We found that the critical current density of the films prepared is highly thickness dependent. The maximum $J_{c}^{\mathrm{mag}}$ value was calculated to be 3.18×10⁶ A?cm^?2 at 10 K and zero field for 1150 nm thick films but dropped drastically by thickness.     

Fabrication of BSCCO Films on SrTiO3 Substrates Using Ultrasonic Spray Pyrolysis (USP) Technique

In this study, the BiSrCaCuO (Bi-2212) films on SrTiO₃ substrates were fabricated using an ultrasonic spray pyrolysis technique (USP). Structural, electrical, magnetic, and critical current density, J _c, properties of the films fabricated were investigated under different heat treatment conditions. XRD analysis showed that the films mainly consisted of the Bi-2212 phase, but the Bi-2223 phase was also detected. T _c values of the films were found between 81 K and 88 K, depending on the heat treatment conditions. J _c values of the films were calculated using the Beans’ equation. Highest J _c value was found to be 2.93×10⁵ A?cm^?2 at 5 K and 0 T for Film C. The results obviously showed that USP method is a very effective technique for fabrication of the HT _c films having high J _c values as well as its simplicity, low cost, and easily coating.     

Structure transition and enhanced ferroelectric properties of (Mn, Cr) co-doped BiFeO3 thin films

Pure BiFeO₃ (BFO) and (Mn, Cr) co-doped BiFe_0.96?yMn_0.04Cr_yO₃ thin films were prepared on FTO/glass (SnO₂:F) substrates by using a sol–gel method. The effects of (Mn, Cr) co-doped on the microstructure and electric properties of the BiFeO₃ thin films were studied. The result indicates that the co-doped BiFe_0.94Mn_0.04Cr_0.02O₃ (BFMCO) thin film has a structure transition and better ferroelectric properties compared with the pure BFO thin film. The Rietveld refined XRD patterns of BFO and BFMCO thin films conform the trigonal (R3c:H) and the biphasic (R3c:H + R3m:R) structure, respectively. The co-existence of two phases and the mixed valences of Cr^3+/6+ and Mn^2+/3+, which apparently improves the electric properties of the (Mn, Cr) co-doped BFMCO thin films. The remnant polarization (P _r) of the BFMCO thin film was 93.58 μC/cm² at 1 kHz in the applied electric field of 636 kV/cm. At an applied electric field of 100 kV/cm, the leakage current density of (Mn, Cr) co-doped BFMCO thin film is 6.2 × 10^?6 A/cm². It is about three orders much lower than that of the BFO thin film (1.43 × 10^?3 A/cm²).     

Effect of laser power on microstructure and dielectric properties of BaTi5O11 films prepared by laser chemical vapor deposition method

BaTi₅O₁₁ films were prepared on Pt/Ti/SiO₂/Si substrates by a laser chemical vapor deposition method. The effect of laser power (P _L) on microstructure and dielectric properties of the BaTi₅O₁₁ films was investigated. With increasing P _L from 62 to 108?W, the deposition temperature (T _dep) monotonously increased from 872 to 951?K. At T _dep?=?920?K (P _L?=?90?W), the BaTi₅O₁₁ film had $ (\overline{3} 01) $ preferred orientation. At T _dep?≥?938?K (P _L?≥?98?W), the preferred orientation changed to $ (\overline{3} 22)/(\overline{2} 23) $ . The deposition rate (R _dep) was 154.8–177.6?μm?h^?1. With increasing T _dep, the surface morphologies changed from rectangular to pyramidal, and the dielectric constant (ε _r) increased from 18.3 to 21.4 at 1?MHz and 300?K.     

Epitaxial layers of CuInSe2 on GaAs

CuInSe₂ single-crystal films with (112) orientation and with thicknesses in the range 800–1200 Å were deposited onto semi-insulating (111)A-oriented GaAs substrates by flash evaporation under controlled growth conditions. Epitaxial growth began at a substrate temperature T_sub = 720 K and twins in the 〈221〉 direction were detected in reflection high energy electron diffraction investigations. The twin concentration decreased with increasing growth temperature. At T_sub = 870 K a change of the structure from chalcopyrite to sphalerite was observed. Films produced at T_sub ? 720 K showed n-type conductivity whereas at higher growth temperatures the films were always p type and showed a rapid increase in hole concentration with increasing substrate temperature. Two different acceptor levels with ionization energies of 92 meV and about meV were found.     

Structure transition and multiferroic properties of Mn-doped BiFeO3 thin films

Pure BiFeO₃ (BFO) and Mn-doped BiFe_1?yMn_yO₃ thin films were prepared on FTO/glass (SnO₂: F) substrates by using a sol–gel method. The effects of Mn-doping on the structure and electric properties of the BFO thin films were studied. The X-ray diffraction (XRD) analysis reveals a structure transition in the Mn-doped BiFe_0.96Mn_0.04O₃ (BFMO) thin film. The Rietveld refined XRD patterns conform the trigonal (R3c: H) and tetragonal (P422) symmetry for the BFO and BFMO thin films, respectively. The structure transition and the mixed valences of Mn ions substantially improve the electric properties of the BFMO thin film. The remnant polarization (P _r) of the BFMO thin film was 105.86 μC/cm² at 1 kHz in the applied electric field of 865 kV/cm. At an applied electric field of 150 kV/cm, the leakage current density of BFMO thin film is 1.42 × 10^?5 A/cm². It is about two orders of magnitude lower than that of the pure BFO thin film (1.25 × 10^?3 A/cm²). And the enhanced saturated magnetization of the BFMO thin film is 4.45 emu/cm³.     

Growth and characterization of La5/8Sr3/8MnO3 thin films prepared by pulsed laser deposition on different substrates

Colossal magnetoresistance La_5/8Sr_3/8MnO₃ (LSMO) thin films were directly grown on MgO(100), Si(100) wafer and glass substrates by pulsed laser deposition technique. The films were characterized using X-ray diffraction (XRD), field emission-scanning electron microscope and atomic force microscopy (AFM). The electrical and magnetic properties of the films are studied. From the XRD patterns, the films are found to be polycrystalline single-phases. The surface appears porous and cauliflower-like morphology for all LSMO films. From AFM images, the LSMO films deposited on glass substrate were presented smooth morphologies of the top surfaces as comparing with the films were deposited on Si(100) and MgO(100). The highest magnetoresistance (MR) value obtained was ?17.21 % for LSMO/MgO film followed by ?15.65 % for LSMO/Si and ?14.60 % for LSMO/Cg films at 80 K in a 1T magnetic field. Phase transition temperature (T_P) is 224 K for LSMO/MgO, 200 K for LSMO/Si and above room temperature for films deposited on glass substrates. The films exhibit ferromagnetic transition at a temperature (T_C) around 363 K for LSMO/MgO, 307 K for LSMO/Si and 352 K for LSMO/Cg thin film. T_C such as 363 and 352 K are the high T_C that has ever been reported for LSMO films deposited on MgO substrate with high lattice mismatch parameter and glass substrates with amorphous nature.     

Superconducting Properties of Ag and Sb Substitution on Low-Density YBa2Cu3O δ Superconductor

The effects of silver (Ag) and antimony (Sb) substitution on low-density YBa₂Cu₃O _δ (YBCO) superconductor were investigated. Two series of sample with a nominal composition of YBa_2?x Ag _x Cu₃O _δ and YBa_2?x Sb _x Cu₃O _δ where x=0.05, 0.10, 0.15, 0.20, 0.30, 0.40 and 0.50 were synthesized and characterized. All Ag-doped samples showed metallic behavior at the normal state and T _C?onset was found at 90 K. T _C?zero decreased as the Ag concentration increased. Optimum Ag concentration was achieved at x=0.20 where T _C?zero has the highest value of 87 K and J _C at 70 K is 16.50 A/cm². For Sb-doped case with x≤0.30, the samples showed metallic behavior above T _C?onset while semiconducting behavior was shown for x≥0.40. The optimum Sb concentration was achieved at x=0.15 where T _C?zero is 85 K and J _C value measured at 70 K is 2.75 A/cm². T _C?onset and T _C?zero were found to decrease toward higher Sb concentration. The crystallographic structure transformed to tetragonal in Sb-doped samples of x≥0.30 while other samples remain orthorhombic.     

Optimizing phase and microstructure of chemical solution-deposited bismuth ferrite (BiFeO3) thin films to reduce DC leakage

Polycrystalline bismuth ferrite (BiFeO₃ or BFO) thin films were prepared by chemical solution deposition to explore the impact of processing conditions including annealing temperature, percent excess bismuth, and gel drying temperature on film microstructure and properties. Incorporating 0–5 % excess Bi and annealing at 550 °C in air produced stoichiometric single-phase BiFeO₃ films. Deviation from this temperature yielded the bismuth-rich Bi₃₆Fe₂O₅₇ phase at temperatures below 550 °C or the bismuth-deficient Bi₂Fe₄O₉ phase at temperatures above 550 °C, both of which contributed to higher DC leakage. However, even single-phase BiFeO₃ films produced at 550 °C show high DC leakage (~1.2 × 10^?1 A/cm² at 140 kV/cm) due to a porous microstructure. We have thus investigated unconventional thermal treatments that significantly increase film densification while maintaining phase purity. Under these revised thermal treatment conditions, room temperature leakage current values are reduced by three orders of magnitude to ~1.0 × 10^?4 A/cm² at 140 kV/cm.     

Structure,conduction mechanisms and multiferroic properties of (Sm,Cr) co-doped Bi0.89Sm0.11Fe0.97Cr0.03O3–NiFe2O4 composition thin films

(Sm, Cr) co-doped Bi_0.89Sm_0.11Fe_0.97 Cr_0.03O₃ (BSFC)–NiFe₂O₄ (NFO) composition thin films were successfully prepared on FTO/glass (SnO₂:F) substrates via a sol–gel method. The structure, surface morphology, leakage current, ferroelectricity and ferromagnetism of BSFC–NFO composition thin film have been investigated. X-ray diffraction analysis indicates that the thin film is polycrystalline and consisted of a rhombohedral perovskite (R3m space group) BiFeO₃ phase and a cubic (Fd-3m space group) inverse spinel NiFe₂O₄ phase. The BSFC–NFO composition thin film is promising in practical application because of its well saturated ferromagnetic (Ms = 19.45 emu/cm³) and ferroelectric (Pr = 39 µC/cm²) hysteresis loops with low order of leakage current density (J = 6.73 × 10^?6 A/cm², at an applied electric field of 100 kV/cm). Which suggest the ferroelectric and ferromagnetic properties can be improved by this composition thin film structure. Moreover, the various conduction mechanisms of BSFC–NFO composition thin film have also been studied.     

Preparation of rare earth CeO<Subscript>2</Subscript> thin films using metal organic decomposition method for metal-oxide–semiconductor capacitors

Investigation of metal organic decomposed rare earth cerium oxide thin films deposited on Si substrate by sol–gel spin coating technique was carried out. The structural properties have been examined by using XRD, Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The XRD confirms the cubic phase of CeO₂ thin films with (111) plane observed at 28.54°. The FTIR and EDAX spectra confirm the formation of CeO₂ films with atomic percentage of 19.39 and 54.82% of Ce and O₂, respectively. Thickness of 60.11 nm of CeO₂ film measured by cross sectional FESEM image, the average roughness of ~0.6 nm of 400?°C annealed CeO₂ films were observed from AFM micrograph. The MOS capacitors were fabricated by using Ti/Au bilayer metal contact depositing by E-beam evaporator on CeO₂/Si thin film for electrical measurements. Capacitance and conductance voltage measurement was carried out to determine the effective oxide charges (Q_eff), interface trap density (D_it) and dielectric constant (k) and are 2.48?×?10¹² cm^?2, 1.26?×?10¹² eV^?1cm^?2 and ~39, respectively. The effective metal work function of 5.68 for Ti/Au bilayer is observed to be higher than the work function of Ti or Au metals in vacuum.     

Spin Coherence Time T 2 in Metallic P-doped Si at Very Low Temperature

We report NMR measurements of transverse relaxation rate 1/T ₂ of the ³¹P nuclear spins in metallic Si:P (concentration of dopant P, n=18×10¹⁸ and 56×10¹⁸ cm^?3) at temperatures between 45 mK and 5 K in a magnetic field of 7 T. Above 1.4 K, 1/T ₂ is constant independent of temperature as well as concentration and is determined by magnetic dipolar interaction between the ³¹P and ²⁹Si nuclear spins. As temperature decreases below 1.4 K, 1/T ₂ increases over the dipolar-determined value by an order of magnitude and levels off around 0.6 K. The concentration dependence of 1/T ₂ at low temperatures suggests that 1/T ₂ below 1.4 K is determined by the coupling between the ³¹P nuclear spins. We understand 1/T ₂ at low temperatures originates from the RKKY interaction. We explain the temperature dependence of 1/T ₂ between 0.6 K and 1.4 K by the motional-narrowing expression of 1/T ₂ with a temperature-dependent correlation time of the fluctuating local field due to the RKKY interaction.     

Effects of High Pressure on the Physical Properties of MgB2

The synthesis of MgB₂-based materials under high pressure gave the possibility to suppress the evaporation of magnesium and to obtain near theoretically dense nanograined structures with high superconducting, thermal conducting, and mechanical characteristics: critical current densities of 1.8?C1.0×10⁶ A/cm² in the self-field and 10³ A/cm² in a magnetic field of 8 T at 20 K, 5?C3×10⁵ A/cm² in self-field at 30 K, the corresponding critical fields being H _c2=15 T at 22 K and irreversible fields H _irr=13 T at 20 K, and H _irr=3.5 T at 30 K, thermal conduction of 53±2 W/(m?K), the Vickers hardness H _V =10.12±0.2 GPa under a load of 148.8 N and the fracture toughness K _1C =7.6±2.0 MPa?m^0.5 under the same load, the Young modulus E=213 GPa. Estimation of quenching current and AC losses allowed the conclusion that high-pressure-prepared materials are promising for application in transformer-type fault current limiters working at 20?C30 K.     

Characterization of Microstructure and Performance of YBa2Cu3O7−x Films Synthesized Through Sol–Gel Aqueous Precursors with DEA/TEA Addition

YBa₂Cu₃O_7?x (YBCO) superconducting thin films are synthesized through non-fluorine sol–gel aqueous processes. Diethanolamine (DEA) and triethonalamine (TEA), which have similar molecular structures but different complexation abilities and molecular weights, are separately used as chelating agents. Compare to DEA, the precursor with TEA additive exhibits higher stability and yields films of superior microstructure and surface morphology. Finally, the YBCO film produced from the TEA precursor displays a sharp superconducting transition, with a J _c of 1.7 MA/cm² estimated at 77 K in self field.