Structural and optical studies on dc reactive magnetron sputtered Cu2O films

Cuprous oxide (Cu₂O) thin films were deposited by dc reactive magnetron sputtering technique onto glass substrates by sputtering of pure copper target in a mixture of argon and oxygen gases under various oxygen partial pressures in the range 8 × 10^− 3–1 × 10^− 1 Pa at a constant substrate temperature of 473 K and a sputtering pressure of 4 Pa. The dependence of cathode potential on the oxygen partial pressure was explained in terms of cathode poisoning effect. The influence of oxygen partial pressure on the structural and optical properties of Cu₂O films was systematically studied. Single phase films of Cu₂O were obtained at an oxygen partial pressure of 2 × 10^− 2 Pa. The films formed at an oxygen partial pressure of 2 × 10^− 2 Pa were polycrystalline with cubic structure and exhibited an optical band gap of 2.04 eV.     

Effect of oxygen partial pressure on microstructural and optical properties of titanium oxide thin films prepared by pulsed laser deposition

Nanocrystalline titanium oxide (TiO₂) thin films were deposited on silicon (1 0 0) and quartz substrates at various oxygen partial pressures (1 × 10⁻⁵ to 3.5 × 10⁻¹ mbar) with a substrate temperature of 973 K by pulsed laser deposition. The microstructural and optical properties were characterized using Grazing incidence X-ray diffraction, atomic force microscopy, UV–visible spectroscopy and photoluminescence. The X-ray diffraction studies indicated the formation of mixed phases (anatase and rutile) at higher oxygen partial pressures (3.5 × 10⁻² to 3.5 × 10⁻¹ mbar) and strong rutile phase at lower oxygen partial pressures (1 × 10⁻⁵ to 3.5 × 10⁻³ mbar). The atomic force microscopy studies showed the dense and uniform distribution of nanocrystallites. The root mean square surface roughness of the films increased with increasing oxygen partial pressures. The UV–visible studies showed that the bandgap of the films increased from 3.20 eV to 3.60 eV with the increase of oxygen partial pressures. The refractive index was found to decrease from 2.73 to 2.06 (at 550 nm) as the oxygen partial pressure increased from 1.5 × 10⁻⁴ mbar to 3.5 × 10⁻¹ mbar. The photoluminescence peaks were fitted to Gaussian function and the bandgap was found to be in the range ∼3.28–3.40 eV for anatase and 2.98–3.13 eV for rutile phases with increasing oxygen partial pressure from 1 × 10⁻⁵ to 3.5 × 10⁻¹ mbar.     

Optical nonlinearities of BaTiO3 matrix-embedded Au nanoparticles

Composite thin films Au/BaTiO₃ comprising nanometer-sized gold particles embedded in BaTiO₃ matrices were synthesized on MgO(1 0 0) substrates by co-depositing Au and BaTiO₃ targets using pulsed laser deposition technique. The nanostructure of the films and the size distributions of the Au particles were analyzed by high-resolution transmission electron microscopy. Crystal lattice fringes from the Au nanocrystals and BaTiO₃ matrices were observed. The nonlinear optical properties of the Au/BaTiO₃ films were measured using z-scan method at the wavelength of 532 nm with a laser duration of 10 ns. The nonlinear refractive index n₂ and the nonlinear absorption coefficient β were determined to be 2.72 × 10⁻⁶ esu and −1.1 × l0⁻⁶ m/W, respectively.     

Deposition and DC electrical characterisation of rf magnetron sputtered silicon nitride thin films

Silicon nitride (Si₃N₄) is an important insulator, frequently used in VLSI technology and for encapsulation. Conventionally it is prepared by low pressure and plasma-enhanced chemical vapour deposition, but may also be successfully deposited by RF sputtering. In the present work the sputtering process was characterised, together with some measurements on the high-field DC electrical properties in sandwich samples with Au electrodes. Films were Ar-sputtered using a Si₃N₄ sputtering target at gas pressures up to 2.12 Pa and RF discharge powers of 60–200 W. The deposition rate R was in the range 0.03–0.19 nm s^− 1 and was directly proportional to the discharge power and varied linearly with the pressure. Au electrodes formed sandwich structures with thicknesses of 50 nm–1 μm. Conductivity was essentially ohmic below 300 nm, while for the thicker films space-charge limited conductivity, dominated by an exponential distribution of traps, was observed. A mobility value of μ = 2.89 × 10^− 6 m² V^− 1 s^− 1 was derived from temperature measurements, and further analysis of the J–V data indicated a thermally generated electron concentration of 3.23 × 10¹⁹ m^− 3 and a trap concentration of 1.57 × 10²⁴ m^− 3. It was concluded that this method is suitable for the deposition of thin films, which have similar electrical properties to those prepared by chemical vapour deposition methods.     

Evolution of different structural phases of TiO2 films with oxygen partial pressure and Fe doping and their electrical properties

We have studied the influence of oxygen partial pressure (OPP; 250 mTorr–1 × 10^?5 Torr) and Fe doping (2 and 4 at.%) on structural and electrical properties of TiO₂ thin films on LaAlO₃ substrates. X-ray photoelectron spectroscopy suggests that Fe is not in metal cluster form. It is found that the evolution of the three phases; anatase, rutile and brookite of TiO₂ as well as the magneli phase (Ti_nO_2n?1) strongly depends on the OPP and Fe doping concentration. All the films grown at 250 mTorr show insulating behavior, whereas films grown at 1 × 10^?2 and 1 × 10^?4 Torr reveal high temperature metallic to low temperature semiconducting transition. Interestingly, films deposited at 1 × 10^?5 Torr reveal charge ordering, which is contributed to the magneli phase of TiO₂. The present study suggests that functionality of TiO₂ thin film based devices can be tuned by properly selecting the OPP and dopant concentration.     

Negative thermal expansion in silicalite-1 and zirconium silicalite-1 having MFI structure

In situ high temperature X-ray diffraction (HTXRD) studies on monoclinic silicalite-1 (S-1, silica polymorph of ZSM-5) and an orthorhombic metallosilicate molecular sieve, zirconium silicalite-1 (ZrS-1) with MFI structure (Si/Zr = 50) have been carried out using a laboratory X-ray diffractometer with an Anton Parr HTK 1600 attachment. While the structure of the S-1 collapsed at 1123 K forming α-cristobalite. S-1 and ZrS-1 showed a complex thermal expansion behavior in the temperature range 298–1023 K, ZrS-1 was stable. Powder X-ray diffraction (PXRD) data taken in this region have shown strong negative lattice thermal expansion coefficient, α_V = −6.75 × 10⁻⁶ and −17.92 × 10⁻⁶ K⁻¹ in the temperature range 298–1023 K⁻¹ for S-1 and ZrS-1 samples, respectively. The thermal expansion behavior of S-1 and ZrS-1 is anisotropic, with the relative strength of contraction along a axis is more than that along b and c axes. Three different thermal expansion regions could be identified in the overall temperature range (298–1023 K) studied, corroborating with the three steps of weight loss in the TG curve of ZrS-1 sample. While the region between 298 and 423 K, displays positive thermal expansion coefficient with α_V = 2.647 × 10⁻⁶ and 4.24 × 10⁻⁶ K⁻¹, the second region between 423 and 873 K shows strong negative thermal expansion (NTE) coefficient α_V = −7.602 × 10⁻⁶ and −15.04 × 10⁻⁶ K⁻¹, respectively, for S-1 and ZrS-1 samples. The region between 873 and 1023 K, shows a very strong NTE coefficient with α_V = −12.08 × 10⁻⁶ and −45.622 × 10⁻⁶ K⁻¹ for S-1 and ZrS-1, respectively, which is the highest in the whole temperature range studied. NTE seen over a temperature range 298–1023 K could be associated with transverse vibrations of bridging oxygen atoms in the structure which results in an apparent shortening of the Si–O distances.     

Optical and thermal properties of crystalline Tb: KLu(WO4)2

A single crystal of Tb: KLu(WO₄)₂ with dimensions of 40 mm × 40 mm × 18 mm has been grown by the top-seeded solution growth (TSSG) method. The color of the crystal is brown. Absorption and fluorescence spectra were measured at room temperature. The measured specific heat is a little lower than that of Yb: KLW (0.365 J/g K) at 90 °C. The measured mean linear coefficients of thermal expansion are α_a = 17.1643 × 10^− 6 K^− 1_, α_a^⁎ = 14.0896 × 10^− 6 K^− 1, α_b = 8.7938 × 10^− 6 K^− 1, α_c = 23.1745 × 10^− 6 K^− 1, α_c^⁎ = 20.2866 × 10^− 6 K^− 1. The results indicate that the crystal has a large anisotropy. The refractive index was measured.     

Effect of strain amplitude on the low-cycle fatigue behavior of a new Fe–15Mn–10Cr–8Ni–4Si seismic damping alloy

The low-cycle fatigue (LCF) properties and post-fatigue microstructure of a Fe–15Mn–10Cr–8Ni–4Si austenitic alloy were investigated under an axial strain control mode with total strain amplitudes, Δε_t/2, ranging from 2.5 × 10⁻³ to 2 × 10⁻². The fatigue resistance of the alloy was described by Coffin–Manson’s and Basquin’s relationships, and the corresponding fatigue parameters were evaluated. In addition, the Masing behavior, which is associated with a constant deformation mode during fatigue, was revealed at the examined strain amplitudes. Microstructural observations of the fatigue fractured samples showed that the strain induced ε-martensitic transformation accompanied by a planar slip of the Shockley partial dislocations in the austenite is the main deformation mode controlling the fatigue behavior of the studied alloy at Δε_t/2 < 2 × 10⁻². However, at Δε_t/2 = 2 × 10⁻², the formation of a cell structure was found in the austenite in addition to ε-martensitic transformation. The LCF resistance of the alloy was compared with conventional Cr–Ni austenitic stainless steels, ferrous base TRIP and TWIP steels and low yield point damping steels. It was found that at the studied strain amplitudes the alloy possessed a higher LCF resistance compared to conventional Fe-base alloys and steels. Remarkably, the fatigue ductility coefficient, ε_f′, of the studied alloy is 1.3–6 times higher than that of the stainless steels because of a cyclic deformation-induced ε-martensitic transformation. The results showed that the ε-martensitic transformation that occurred in the studied alloy during LCF is the main reason for the improved LCF resistance.     

Tungsten-doped tin oxide thin films prepared by pulsed plasma deposition

Transparent conductive oxide tungsten-doped tin oxide thin films were deposited on glass substrates from ceramic targets by the pulsed plasma deposition method. The structural, electrical and optical properties have been investigated as functions of tungsten doping content and oxygen partial pressure. The lowest resistivity of 2.1 × 10^? 3 Ω?cm was reproducibly obtained, with carrier mobility of 30 cm²V^? 1s^? 1 and carrier concentration of 9.6 × 10¹⁹ cm^? 3 at the oxygen partial pressure of 1.8 Pa. The average optical transmission was in excess of 80% in the visible region from 400 to 700 nm, with the optical band gap ranging from 3.91 to 4.02 eV.     

Effect of solvent ratio on the properties of highly oriented sprayed fluorine-doped tin oxide thin films

Transparent conducting thin films of F:SnO₂ have been deposited onto preheated glass substrates by a spray pyrolysis technique using pentahydrate stannic chloride (SnCl₄·5H₂O) and ammonium fluoride (NH₄F) as precursors and mixture of water and propane-2-ol as solvent. The concentration of SnCl₄·5H₂O and NH₄F is kept fixed and the ratio of water and propane-2-ol solvent in the spraying solution is varied. A fine spray of the source solution using air as a carrier gas has grown films of thickness up to 995 nm. Optical absorption, X-ray diffraction, Van der Pauw technique for measurement of a sheet resistance and Hall effect measurements at room temperature for determination of carrier density and conductivity have been used. The as-deposited films are of polycrystalline SnO₂ with a tetragonal crystal structure and are preferentially having orientation along the (200) direction with texture coefficient as high as 6.16. The average grain size for the as-deposited sample is found to be of the order of 44 nm. The films have moderate optical transmission (up to 70–85% at 550 nm). The figure of merit (ϕ) values vary from 1.95 · 10^− 3 to 35.68 · 10^− 3 Ω^− 1. The films are heavily doped, degenerate and exhibit n-type electrical conductivity. The lowest sheet resistance (R_s) for the optimized sample is 5.1 Ω. The films have a resistivity of 5.43 · 10^− 4 Ω cm and mobility around 7.38 cm² V^− 1 s^− 1.     

Compression behaviour and micro-structure evaluation of Zr57Nb5Cu15.4Ni12.6Al10 bulk metallic glass under high pressure

Compression behaviour and micro-structure evaluation of Zr₅₇Nb₅Cu_15.4Ni_12.6Al₁₀ bulk metallic glass is investigated at room temperature up to 32.8 GPa using in-situ high pressure energy dispersive X-ray diffraction with a synchrotron radiation source. The equation of state of the bulk metallic glass is − ΔV / V = 0.012P − 2.49 × 10^− 4P² − 9.5 × 10^− 7P³ + 5.02 × 10^− 8P⁴. The result shows that the nearest atom pair of the as-quenched bulk metallic glass corresponds to Zr–Zr correlations. And with pressure increasing, the nearest atom pair changes to a new one at 32.8 GPa.     

Third-order nonlinear optical properties of bis(tetrabutylammonium)bis(4,5-dithiolato-1,3-dithiole-2-thione)copper

Bis(tetrabutylammonium)bis(4,5-dithiolato-1,3-dithiole-2-thione)copper (BCDT) was synthesized and its third-order optical nonlinearity was characterized using picosecond Z-scan at 1064 nm. The Z-scan spectra reveal a large negative nonlinear refraction coefficient n₂ as high as 4.0 × 10⁻¹⁸ m²/W and a slight two-photon absorption β, which is determined to be 3.4 × 10⁻¹² m/W. The molecular second-order hyperpolarizability γ was calculated to be 6.5 × 10⁻³² esu. All these results suggest that this material has potential for the application of all-optical switching.     

Studies on the electrochemical preparation of MgCeCo alloy thin films on Cu substrates in urea–DMSO system

Cyclic voltammetry was used to investigate the electrochemical behaviors of Mg(II), Ce(III) and Co(II) in 3.00 mol L^− 1 urea–DMSO (dimethylsulfoxide). The electrode processes of Mg(II), Ce(III) and Co(II) reducing on Pt electrodes were irreversible steps. The transfer coefficient of Mg(II), Ce(III) and Co(II) in 3.00 mol L^− 1 urea–DMSO system was calculated as 0.07, 0.05 and 0.05 at 298.15 K, respectively. The diffusion coefficient of Mg(II), Ce(III) and Co(II) in 3.00 mol L^− 1 urea–DMSO system was calculated as 2.27 × 10^− 10, 1.77 × 10^− 10 and 3.16 × 10^− 10 m² s^− 1 at 298.15 K, respectively. The MgCeCo alloy thin films with smooth, uniform and metallic luster were obtained on Cu substrates by cyclic electrodeposition in 0.01 mol L^− 1 Mg(ClO₄)₂–0.01 mol·L^− 1 Ce(CH₃SO₃)₃₋0.01 mol L^− 1 CoCl₂–3.00 mol L^− 1 urea–DMSO system. The potential sweep rate was found to be important with respect to the adhesion of the thin films.     

Electroresistance and magnetoresistance in La0.9Ba0.1MnO3 thin films

The electroresistance and magnetoresistance effects have been investigated in La_0.9Ba_0.1MnO₃ epitaxial thin films. Tensile strain caused by substrate mismatch makes the Curie temperature T_C of the film at ∼300 K. The influence of an applied dc-current on the resistance in the absence of a magnetic field was studied. Significant change of the peak resistance at different currents was found. The reduction of the peak resistance reaches ∼27% with an electric current density up to 1.3 × 10⁵ A cm⁻². We also studied colossal magnetoresistance (CMR) effect in the films. Applying a magnetic field of 2 T could lead to a magnetoresistance as large as 42%. The reduction of resistance caused by a current density ∼1.3 × 10⁵ A cm⁻² was found to be equivalent to the CMR effect caused by 1.5 T near T_C. The phenomenon that the resistance in CMR manganites could be easily controlled by the electric current should be of high interest for both fundamental research and practical applications.     

Growth and characterization of (Pb,La)TiO3 films with and without a special buffer layer prepared by RF magnetron sputtering

The (Pb, La)TiO₃ (PLT) ferroelectric thin films with and without a special buffer layer of PbO_x have been deposited on Pt/Ti/SiO₂/Si(100) substrates by RF magnetron sputtering technique at room temperature. The microstructure and the surface morphology of the films annealed at 600 °C for 1 h have been investigated by X-ray diffraction (XRD) and atomic force microscope (AFM). The surface roughness of the PLT thin film with a special buffer layer was 4.45 nm (5 μm × 5 μm) in comparison to that of 31.6 nm (5 μm × 5 μm) of the PLT thin film without a special buffer layer. Ferroelectric properties such as polarization hysteresis loop (P–V loop) and capacitance–voltage curve (C–V curve) of the films were investigated. The remanent polarization (P_r) and the coercive field (E_c) are 21 μC/cm² and 130 kV/cm respectively, and the pyroelectric coefficient is 2.75 × 10^− 8 C/cm² K for the PLT film with a special buffer layer. The results indicate that the (Pb, La)TiO₃ ferroelectric thin films with excellent ferroelectric properties can be deposited by RF magnetron sputtering with a special buffer layer.     

Synthesis and dc conductivity of Nd2/3TiO2.988

The A-site deficient perovskite Nd_2/3TiO_3 − δ was synthesized under an H₂–CO₂ gas mixture. The sample was found to have slight oxygen deficiency of δ∼0.012. The crystal structure was assigned to a double perovskite structure with orthorhombic space group Pmmm, as in the case of La_2/3TiO_3 − δ. Electrical conductivity measurement has also been performed. The temperature dependence of conductivity shows that electronic transport in Nd_2/3TiO_2.988 is well described by Emin–Holstein adiabatic small polaron model. The polaron density extracted from the conductivity measurement is ∼1.96 × 10²⁰ cm^− 3. This result agrees well with nominal polaron density for Nd_2/3TiO_2.988, ∼2.1 × 10²⁰cm^− 3. We have also derived important quantities for transport in Nd_2/3TiO_2.988.     

Effects of ZnO addition on electrical and structural properties of amorphous SnO2 thin films

Amorphous Zn–Sn–O (ZTO) thin films with relative Zn contents (= [at.% Zn]/([at.% Zn] + [at.% Sn])) of 0, 0.08 and 0.27 were fabricated by co-sputtering of SnO₂ and ZnO targets at room temperature. Changes in structural, electrical and optical properties together with electron transport properties were examined upon post-annealing treatment in the temperature range from 200 to 600 °C in vacuum and in air. Characterization by XRD showed that an amorphous ZTO thin film crystallized at higher temperatures with increasing Zn content. Crystallized ZTO films with a relative Zn content of 0.27 might not contain a single SnO₂ phase which is observed in the films of the other compositions. Amorphous ZTO films showed decreasing electrical resistivities with increasing annealing temperature, having a minimum value of 1 × 10^− 3 Ω cm. Upon crystallization, the resistivities increased drastically, which was attributed to poor crystallinity of the crystallized films. All the ZTO films were found to be degenerate semiconductors with non-parabolic conduction bands having effective masses varying from 0.15 to 0.3 in the carrier concentration range of 6 × 10¹⁸ to 2 × 10²⁰ cm^− 3. As for a ZTO film with a relative Zn content of 0.27, the degree of non-parabolicity was much lower compared with films of the other compositions, leading to a relatively stable mobility over a wide range of carrier concentration.     

High-temperature electrical resistivity and heat capacity studies on nano-crystalline geikielite

We report here for the first time the temperature dependence of the electrical resistivity and heat capacity of nano-crystalline MgTiO₃ geikielite of up to 1000 K. The temperature dependence of heat capacity of nano-crystalline geikielite expressed as C_p = 46.44(5) + 0.0502(2)T − 4.56 × 10⁶T² + 1.423 × 10³T^− 0.5 − 8.672 × 10^− 6T^− 2, where C_p = is specific heat expressed in J/mol. K and T is the temperature in K. Both the electrical resistivity and heat capacity behaviour show that the geikielite (both the natural and synthetic nano-crystalline samples) are stable and remains electrically insulating up to 1000 K.     

Spectroscopic properties of Tm3+/Al3+ co-doped sol–gel silica glass

Tm³⁺/Al³⁺ co-doped silica glass was prepared by sol–gel method combined with high temperature sintering. Glasses with compositions of xTm₂O₃–15xAl₂O₃–(100 − 16x) SiO₂ (in mol%, x = 0.1, 0.3, 0.5, 0.8 and 1.0) were prepared. The high thulium doped silica glass was realized. Their spectroscopic parameters were calculated and analyzed by Judd–Ofelt theory. Large absorption cross section (4.65 × 10⁻²¹ cm² at 1668 nm) and stimulated emission cross section (6.00 × 10⁻²¹ cm² at 1812 nm), as well as low hydroxyl content (0.180 cm⁻¹), long fluorescence lifetime (834 μs at 1800 nm), large σ_em × τ_rad (30.05 × 10⁻²¹ cm² ms) and large relative intensity ratio of the 1.8 μm (³F₄ → ³H₆) to 1.46 (³H₄ → ³F₄) emissions (90.33) are achieved in this Tm³⁺/Al³⁺ co-doped silica glasses. According to emission characteristics, the optimum thulium doping concentration is around 0.8 mol%. The cross relaxation (CR) between ground and excited states of Tm³⁺ ions was used to explain the optimum thulium doping concentration. These results suggest that the sol–gel method is an effective way to prepare Tm³⁺ doped silica glass with high Tm³⁺ doping and prospective spectroscopic properties.     

Low temperature growth of SnO2 nanowires by electron beam evaporation and their application in UV light detection

For the first time, high quality tin oxide (SnO₂) nanowires have been synthesized at a low substrate temperature of 450 °C via vapor–liquid–solid mechanism using an electron beam evaporation technique. The grown nanowires have shown length of 2–4 μm and diameter of 20–60 nm. High resolution transmission electron microscope studies on the grown nanowires have shown the single crystalline nature of the SnO₂ nanowires. We investigated the effect of growth temperature and oxygen partial pressure on SnO₂ nanowires growth. Variation of substrate temperature at a constant oxygen partial pressure of 4 × 10⁻⁴ mbar suggested that a temperature equal to or greater than 450 °C was the best condition for phase pure SnO₂ nanowires growth. The SnO₂ nanowires grown on a SiO₂ substrate were subjected to UV photo detection. The responsivity and quantum efficiency of SnO₂ NWs photo detector (at 10V applied bias) was 12 A/W and 45, respectively, for 12 μW/cm² UV lamp (330 nm) intensity on the photo detector..