Effect of the doped nitrogen on the optical properties of β-Ga2O3 nanowires

In this study, optical properties of the nitrogen-doped β-Ga₂O₃ nanowires (N-doped β-Ga₂O₃ NWs) were synthesized by exposing β-Ga₂O₃ NWs under high input power nitrogen plasma (2 kW), using a microwave plasma enhanced chemical vapor deposition (MPECVD) system. The nitrogen contents in the NWs were as-prepared about 7.4, 8.9, 9.7, 13.9, 19.3, and 26.6 at.%, respectively. Low temperature (10 K) cathodoluminescence (CL) spectra exhibit significantly different optical properties for the different nitrogen contents. The CL result of the N-doped β-Ga₂O₃ NWs (210 s N₂ plasma treatment) exhibited four distinct emission peaks at 378, 516, 759, and 970 nm. The possible light emission mechanism including the effect of the nitrogen dopant was discussed.     

Control of macrostress σ in reactively sputtered Mo-Al-N films by total gas pressure

This article reports on the effect of the energy delivered to a growing film by bombarding ions and fast neutrals on the macrostress σ and the structure of sputtered films. To demonstrate this effect, we selected Mo-Al-N films with a low (?20 at.%) Al content reactively sputtered using an unbalanced dc magnetron with a target of 100 mm diameter at a high total pressure , low substrate bias and a high substrate ion current density . The main goal of this study was to show the reduction of σ in films sputtered at high pressures of several Pa. Under the conditions given above approximately 4 μm thick Mo-Al-N films with enhanced hardness H≈35 GPa and a very low (?−0.5 GPa) macrostress σ were successfully prepared. This result demonstrates that the enhanced hardness H of Mo-Al-N films is not caused by σ but is due to its nanostructure as shown in the XRD patterns of these films. The Mo-Al-N films with enhanced hardness are composed of a mixture of grains of different crystallographic orientations.     

MOCVD growth of HfSixOy films from hafnium β-diketonato silylamides and siloxides

New hafnium β-diketonato-silylamide and siloxides namely Hf(thd)₂[N(SiMe₃)₂]₂ (1), Hf(thd)₂(OSiMe₃)₂ (2) and Hf(thd)₂(OSi^tBuMe₂)₂ (3) (thd=2,2,6,6-tetramethyl-3,5-heptanedionate) were investigated as single-source precursors for low-pressure pulsed liquid injection MOCVD of HfSi_xO_y thin films on Si(1 0 0) and R-plane sapphire. Films were characterized by XRD, XPS and AFM. The growth rate increased in order 1>2>3 in agreement with the decreasing precursor thermal stability. The activation energy was ∼80-100 kJ/mol. The as-deposited at 550-800 °C films were essentially amorphous; hafnia reflections appeared after 1 h annealing at 900 °C probably due to phase separation into amorphous Si-rich silicate and crystallized HfO₂. The surface of the films showed similar amounts of Hf and Si (∼1:1) and was overstoichiometric in oxygen (ratio O/(Hf+Si) >2). The bulk of the films was Hf-rich (70-85% of Hf/ Hf+Si) and slightly oxygen-deficient. The new complexes are attractive single-source precursors for the deposition of pure and very smooth (R_a∼0.7 nm, <1% relative to thickness) HfSi_xO_y films. Dielectric constant 11.3 and leakage current density 8×10⁻⁴ A/cm² (at −1 V) were measured for a 22 nm thick film.     

Role of chlorine on the opto-electronic properties of β-In2S3 thin films

Effect of chlorine doping on the opto-electronic properties of β-In₂S₃ thin film, deposited by spray pyrolysis technique is studied for the first time. Chlorine was incorporated in the spray solution, using HCl. Pristine sample prepared using In(NO₃)₃ and thiourea as the precursors showed very low photosensitivity. But upon adding optimum quantity of chlorine, the photosensitivity increased by 3 orders. X-ray analysis revealed that crystallinity was also increasing up to this optimum level of Cl concentration. It was also observed that samples with high photosensitivity were having higher band gap. The present study proved that doping with chlorine was beneficial as this could result in forming crystalline and photosensitive films of indium sulfide.     

The photoluminescence of SiCN thin films prepared by C implantation into α-SiNx:H

SiCN thin films were prepared by high-dosage (2 × 10¹⁷ cm^− 2) C⁺ ion implantation into α-SiN_x:H films. The prepared films were then processed by thermal annealing for 2 h at 800 °C, 1000 °C and 1200 °C respectively. The composition and bond structure of SiCN were analyzed by X-ray photoemission spectroscopy, Auger electron spectroscopy, Raman spectroscopy and X-ray diffraction, and photoluminescence. Ternary structure with N bridging C and Si of the film annealed at 800 °C was found. The luminescent properties of SiCN have also been studied by synchrotron radiation at 20 K. Four emission bands were observed, corresponding to 2.95, 2.58, 2.29 and 2.12 eV at 20 K, respectively. In this paper, we report the experimental results and try to explain them.     

γ-Irradiation-induced changes at the electrical characteristics of Sn/p-Si Schottky contacts

We studied electrical parameters of Sn/p-Si Schottky barrier diodes (SBDs) by using in situ current-voltage (I-V) and capacitance-voltage (C-V) measurements under γ-irradiation at room temperature. The devices were held under zero bias during γ-irradiation with dose rate 0.25 kGy/h, and the total dose range was 0-45 kGy. Irradiation results indicated that these devices may have applications as radiation sensors in order to detect the low-energy γ radiation.     

Effect of the sintering temperature on the properties of Ce0.85La0.10Ca0.05O2−δ electrolyte material

Rare earth and alkaline earth co-doped Ce_0.85La_0.10Ca_0.05O_2−δ electrolyte material with the powder obtained by solid-state reaction method was sintered at 1300, 1400, 1500 and 1600 °C respectively. The results showed that the ionic conductivity of the sample sintered at 1400 °C was slightly lower compared to that sintered at 1500 °C in the temperature range of 300-550 °C, while the sample sintered at 1400 °C showed the highest ionic conductivity in all the samples above 550 °C. The ionic conductivity of ∼0.021 S/cm at 600 °C and the relative density of 98.2% were observed for the sample sintered at 1400 °C. In addition, the highest flexural strength with 145 MPa was also obtained for the sample sintered at 1400 °C. It suggested that the sintering temperature for Ce_0.85La_0.10Ca_0.05O_2−δ electrolyte may be reduced to as low as 1400 °C with desired properties.     

Effect of oxidation behavior on visible–infrared property of TiN films

Journal of Materials Science: Materials in Electronics - TiN films were oxidized at different temperatures (300, 400, 500, and 600&nbsp;°C) for different times (1, 10, 50, and100 h), and...     

Microstructure, magnetic and electronic transport properties of polycrystalline γ′-Fe4N films

The single-phase γ′-Fe₄N films were fabricated using reactive sputtering. The x-ray diffraction peaks from γ′-Fe₄N(111), (200) and (311) indicate that the films are γ′-Fe₄N. The grain size increases with the increase of film thickness (t), and the grains grow with a columnar structure. All of the films are soft ferromagnetic at room temperature. The saturation magnetization decreases with the increasing temperature, and satisfies the modified Bloch's spin wave theory. The electrical transport properties show a metallic conductance mechanism, and the room-temperature resistivity decreases with the increasing t, revealing that the electron scattering increases with the decrease of t. The magnetoresistance (MR) evolves from positive to negative with the increase of temperature, and the transition temperature decreases with the increase of t. The positive MR at 5 K increases with the increasing t. The complex MR should be dominated by Lorentz force effect, the suppression of the electron scattering, and the shift of minority and majority spin bands under a magnetic field.     

A study concerning the reduction of emittance via non-uniform dipoles under the βmin constraint

Low emittance is a primary goal of electron storage ring based light sources. Optics with low emittance always require low beta functions in dipoles, which implies that strong quadrupoles are needed and that natural chromaticity arises. The work presented in this paper demonstrates that by introducing dipoles with a longitudinal dipolar field-variation, the minimum emittance can be lowered even if the minimum beta function is constrained.     

Aging response of the Ti–Nb system biomaterials with β-stabilizing elements

Effects of aging temperature and the contents of β-stabilizing elements on the composition of martensite α′′ in two Ti–Nb alloys and the resulting mechanical properties were investigated for biomedical applications. The microstructures were examined by means of optical microscopy (OM) and X-ray diffraction (XRD). Vickers hardness, compressive elastic modulus and the yield strength have been measured. The results show that the decomposition mode of the martensite α′′ in two studied alloys depends on aging treatment and the contents of β-stabilizing elements. Various microstructures such as α, (α + β) and (β + ω) phases were observed to precipitate in the studied alloys after the aging treatments performed at 523 K, 773 K, 883 K and 1023 K for 0.5 h, respectively. Afterwards, the Ti–24Nb–6Zr–7.5Sn–2Fe alloy was aged at 773 K for 1 h. The compressive elastic modulus and mechanical properties of the two alloys are found to be sensitive to the microstructural change caused by aging temperature. For the Ti–24Nb–6Zr–7.5Sn–2Fe alloy, after aging at 773 K for 1 h, its yield strength, compressive elastic modulus and Vickers hardness reach 846 MPa, 26 GPa and 398 HV, respectively. This aged alloy exhibits proper comprehensive mechanical property and strength-to-modulus ratio for biomedical implant applications.     

Measurement of the surface resistance of YBa2Cu3O7?x thin films using stripline resonators

We review methods of measuring surface resistance (R _s ) of thin films using stripline resonators, and present our measurements of theR _s of YBa₂Cu₃O_7–x films as a function of frequency, temperature, and r.f. magnetic field. The films were deposited on LaAlO₃ substrates by two methods: (1) electron-beam coevaporation of Y, BaF, and Cu followed by annealing in O₂, and (2) single-targetin situ sputtering. The measurements were obtained at frequencies from 0.4 to 10 GHz, temperatures from 4 to 90 K, and an r.f. magnetic field range from 0 to 30 Oe. At low temperature and low r.f. field at 0.4 GHz, theR _s values obtained for the two deposition methods are approximately 7×10^–6 and 4×10^–6 , respectively.     

On the development of high temperature ammonia–water hybrid absorption–compression heat pumps

Ammonia–water hybrid absorption–compression heat pumps (HACHP) are a promising technology for development of efficient high temperature industrial heat pumps. Using 28 bar components HACHPs up to 100 °C are commercially available. Components developed for 50 bar and 140 bar show that these pressure limits may be possible to exceed if needed for actual applications. Feasible heat supply temperatures using these component limits are investigated. A feasible solution is defined as one that satisfies constraints on the COP, low and high pressure, compressor discharge temperature, vapour water content and volumetric heat capacity. The ammonia mass fraction and the liquid circulation ratio both influence these constraining parameters. The paper investigates feasible combinations of these parameters through the use of a numerical model. 28 bar components allow temperatures up to 111 °C, 50 bar up to 129 °C, and 140 bar up to 147 °C. If the compressor discharge temperature limit is increased to 250 °C and the vapour water content constraint is removed, this becomes: 182 °C, 193 °C and 223 °C.     

The influence of different electrodeposition E/t programs on the photoelectrochemical properties of α-Fe2O3 thin films

In this work morphological, structural and photoelectrochemical properties of n-type α-Fe₂O₃ (hematite) thin films synthetized by means of two different electrochemical procedures: potential cycling electrodeposition (PC) and potential pulsed electrodeposition (PP) have been studied. The X-ray diffraction measurements showed that the films obtained after a thermal treatment at 520 °C present a nanocrystalline character. Scanning electron microscopy allowed finding that hematite films obtained by PP technique exhibit nanostructured morphology. The electrochemical and capacitance (Mott-Schottky and parallel capacitance) measurements showed that when in the PC and PP procedures the anodic limit E_λ,A is being made more anodic, a decrease of the majority carriers concentration (N_D) and the surface states number has been observed. The photovoltammetry measurements indicated that the hematite films formed with the PP technique present a photocurrent one order of magnitude higher than the ones exhibited by the iron oxide films formed by PC. For instance, PP hematite films exhibit photovoltaic conversion efficiencies of 0.96% which are 2.5 times higher than the corresponding to the PC ones (0.38%). The maximum incident photon-to-current efficiency measured at λ = 370 and 600 nm was observed for hematite films grown by the PP procedure. By means of the photocurrent transient technique a decrease in the recombination process for those samples synthesized by PP was observed. The results obtained are discussed considering the influence of the anodic limit of the potential employed during the preparation of the iron oxyhydroxide (β-FeOOH) precursor film, all of this related to a decrease of the oxygen defects in this material and to a decrease of Fe(II) amount that is formed during the electrodeposition process.     

Dependence of microwave surface resistance on the structure of laser-deposited YBa2Cu3O7?x thin films

The effect of the structure YBa₂Cu₃O_7-x superconducting thin films on microwave surface resistance was investigated. The electon channeling patterns (ECPs) and X-ray experimental results showed that the microwave surface resistanceR _s is strongly correlated with the perfection of the thin films. The films were deposited on LaAlO₃(100) and YSZ(100) substrates. For thin film withR _s of 280, the crystallinity of the thin film shown byw-scanning and-scanning was excellent and the ECPs were very sharp. For thin film with highR _s of 98 m, only bands from the major zone were visible in the ECPs, which suggested poor crystallinity of the film. From this investigation it was shown that the more perfect the thin films, the lower theR _s.     

Point defect chemistry of YBa2Cu3O6.5+δ

A novel mathematical approach for defect concentration calculations proposed by Poulsen [F.W. Poulsen, Solid State Ionics, 129 (2000) 145] for oxides with rather small deviations from stoichiometry also applies to perovskite-type oxides with large ranges of oxygen nonstoichiometry. Point defect chemistry calculations have been performed for YBa₂Cu₃O_6.5+δ for which experimental equilibrium oxygen partial pressure isotherms are well known. The model applied in this work describes experimental results very well in the p_O2 range of 10⁻⁵ to 10 bar and for temperatures between 450 and 800 °C.     

Low temperature magnetoresistance properties of Ag2+δSexTe1−x nanocrystalline thin films

Ag_2+δSe_xTe_1−x (x = 0-1) nanocrystals (NCs) with different Se and Te content are prepared by a simple hydrothermal process using a Se_xTe_1−x NC template. Both rod- and dot-shaped NCs are obtained, a variation from the rod-shaped Se_xTe_1−x template. The Ag_2+δSe_xTe_1−x NC thin films are dense with an atomic ratio δ between Ag and Se_xTe_1−x that can be controlled in the range of δ = 0.1-0.3. The MR effect of Ag_2+δSe_xTe_1−x NCs is found to be related to the composition as well as annealing temperature. MR of the Ag_2.2Se_0.2Te_0.8 NC thin films shows a rapid increase to 68% at 239 K and 8 T, an observation providing very useful fundamental information necessary for future applications in the fabrication of high-quality MR sensors and other electronic devices.     

Study on the chemical stability of Y-doped BaCeO3 − δ and BaZrO3 − δ films deposited by aerosol deposition

Barium cerate (BaCeO₃) has high proton conductivity but rather poor chemical stability in CO₂-containing atmospheres. Barium zirconate (BaZrO₃), in contrast, is a rather stable material, but exhibits poor sinterability. In the present work, powders of Y-doped BaCeO₃ and BaZrO₃ were synthesized via the solid solution reaction method, and dense ceramic membranes with BaCe_0.9Y_0.1O₃ and BaZr_0.85Y_0.15O₃ were prepared by the aerosol deposition method at room temperature. Aerosol deposition method is a technique that enables the fabrication of ceramic films at room temperature with a high deposition rate as well as strong adhesion to the substrate. The powders and aerosol-deposited membranes were characterized by X-ray diffraction, particle size analysis, scanning electron microscopy, and X-ray elemental mapping. The chemical stability of powders and aerosol-deposited membranes with BaCe_0.9Y_0.1O₃ and BaZr_0.85Y_0.15O₃ against water and carbon dioxide has been investigated, and it was found that BaZr_0.85Y_0.15O₃ materials showed a better chemical compatibility.     

Influence of platinum nano-particles on the photocatalytic activity of sol–gel derived TiO2 films

Different 1-step or 2-step photo-platinization methods have been implemented to load sol–gel TiO₂ photocatalytic thin films with platinum nano-particles. These methods enable flexible variations in the amount of loaded particles, and they strongly influence the structure and size of these particles and the morphology of derived platinized films. The photocatalytic activity of platinized films has been studied. It is shown that optimal platinization conditions allow envisaging thin film photocatalysts with enhanced properties. Best performances are reached when the films are loaded with platinum particles for 30 or 60 min using a 1-step platinization method, which yields photocatalytic activities about 4 times greater than that of non-platinized films. Photocatalytic activity differences induced by the 1-step or 2-step photo-platinization methods are discussed in relation to the amount of loaded platinum together with structural and morphological features.