Effect of environment and heat treatment on the optical properties of RF-sputtered SnO2 thin films

Thin films of SnO₂ were deposited by RF-magnetron sputtering on quartz substrates at room temperature in an environment of Ar and O₂. The XRD pattern shows amorphous nature of the as-deposited films. The optical properties were studied using the reflectance and transmittance spectra. The estimated optical band gap (E_g) values increase from 4.15 to 4.3 eV as the Ar gas content decreases in the process gas environment. The refractive index exhibits an oscillatory behavior that is strongly dependent on the sputtering gas environment. The Urbach energy is found to decrease with increase in band gap. The band gap is found to decrease on annealing the film. The role of oxygen defects is explored in explaining the variation of optical parameters.     

Characteristics of sputtered Ta-B-N thin films as diffusion barriers between copper and silicon

Ta-B-N thin films were prepared by rf-magnetron sputtering from a TaB₂ target in N₂/Ar reactive gas mixtures and then used as diffusion barriers between Cu and Si substrates. In order to investigate the performance of Cu/Ta-B-N/Si contact systems, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), four-point probe measurement, scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (XTEM), and Auger electron spectroscopy (AES) depth profile were used. Results of this study indicate that the barrier characteristics are significantly affected by the nitrogen content. In addition, the failure mechanism for the Cu/Ta-B-N/Si contact systems is also discussed herein.     

Influence of deposition pressure and power on characteristics of RF-Sputtered Mo films and investigation of sodium diffusion in the films

Mo films deposited by DC sputtering are widely used as back contact in CIGS and CZTS based thin film solar cells. However, there have been only a few studies on the deposition of Mo films by RF sputtering method. In this context, Mo films on SLG substrates were prepared as a function of deposition pressure and power by using RF magnetron sputtering method to contribute to this shortcoming. Mo films were deposited at 250 °C substrate temperature by using 20, 15, 10 mTorr Ar pressures at 120 W RF power and 10 mTorr Ar pressure at 100 W RF power. Structural, morphological and reflectivity properties of RF-sputtered Mo films were clarified by XRD, AFM, FE-SEM and UV–Vis measurements. In addition, due to sodium incorporation from SLG substrate to the absorber layer through Mo back contact layer is so essential in terms of improving the conversion efficiency values of CIGS and CZTS thin film solar cell devices, the effects of Na diffusion in the films were analyzed with SIMS depth profile. The electrical properties of the films such as mobility, carrier density and resistivity were determined by Hall Effect measurements. It was found that Mo films prepared at 120 W, 10 mtorr and 250 °C substrate temperature and then annealed at 500 °C for 30 min, had resistivity as low as 10⁻⁵ Ω cm, as well as higher amount of Na incorporation than other films.     

Effect of hydrogen gas on the growth process of PbS nanorods grown by a CVD method

PbS nanostructures were grown by sulfuration of two lead sheets in a tube furnace under nitrogen (N₂) and argon/hydrogen (Ar/H₂) conditions. All conditions, such as the sheet temperature, sulfur powder temperature, and the carrier gas rate, were the same for two samples. Field emission scanning electron microscope (FESEM) images showed that the nanostructures with rod morphology were formed on the sheets. However, the nanorods that were grown under N₂ gas, were denser, more compact, and a different shape and size in comparison to another sample. In addition, the nanorods grown under N₂ gas exhibited a rectangular shape, while another sample showed nanorods that were tapered. X-ray diffraction (XRD) patterns indicated that these nanorods were PbS with a cubic phase. Furthermore, Raman measurements confirmed the XRD results, and indicated three Raman active modes of PbS phase. The optical characterization results showed a band gap for the PbS nanorods in the infrared region.     

Preparation of Fe/Pt Films with Perpendicular Magnetic Anisotropy

We have investigated the microstructures and magnetic properties of L1₀ ordered equi-atomic FePt thin films prepared by ion beam sputtering and subsequent annealing. It is observed from X-ray reflectivity and X-ray diffraction measurements that the mixing at Fe/Pt interfaces starts to occur with annealing and leading to the FePt alloy phase formation. The rapid increase in the coercivity values above 275°C, obtained from vibrating sample magnetometer (VSM) measurements, confirms the formation of the ordered L1₀ FCT FePt phase.     

Effect of ambient gas on structural and optical properties of titanium oxynitride films

Titanium oxynitride films have been deposited on glass substrates by reactive RF magnetron sputtering of titanium target. The influence of oxygen partial pressure in N₂ + Ar and N₂ + He mixtures was examined on structural and optical properties of titanium oxynitride films. The prepared samples were characterized by X-ray diffraction, EDS, surface profilometer, AFM and contact angle measurement system. With increase in oxygen partial pressure, the grain size decreases from ∼70 nm to ∼50 nm in N₂ + Ar mixture, while from ∼60 nm to ∼37 nm in N₂ + He mixture. The thickness calculated from optical transmission data and surface profilometer is in good agreement with each other. The deposited samples are hydrophobic by nature and the contact angle was found to decrease with increase in oxygen partial pressure. Samples prepared in oxygen partial pressure ≥5.5% show transmittance of about 97% in the visible region of the spectrum in both N₂ + Ar and N₂ + He mixtures. The atomic mass of the sputtering gas (Ar and He) significantly affects the primary crystallite size, orientation as well as band gap. We were able to relate the better crystallisation of titanium atoms with low partial pressure of oxygen when films are deposited in helium instead of argon due to Penning ionization.     

Structure, magnetic and magnetostrictive properties of as-deposited Fe-Ga thin films

Polycrystalline Fe_100−xGa_x (19?x?23) films were grown on Si(1 0 0) substrates at different partial pressures of sputtering gas ranging from 3 to 7 μbar. Microstructural, magnetic and magnetostrictive properties were studied using X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and magneto-optic Kerr effect (MOKE) magnetometry respectively. X-ray diffraction showed that all films have the body-centered cubic (bcc) Fe-Ga phase with the 〈1 1 0〉 direction out of the film plane. Magnetic characterization of the films showed that the films prepared at 3 μbar had weak uniaxial anisotropy whereas films grown at Ar pressures in the range 4-7 μbar were magnetically isotropic. The effective saturation magnetostriction constants (λ_eff) of the films were measured using the Villari effect. It was found that effective saturation magnetostriction constants were almost constant over the Ga composition range achieved by varying the sputtering pressure. The measured effective magnetostriction constants fit closely to the calculated saturation magnetostriction constants of 〈1 1 0〉 textured polycrystalline films with the 〈1 1 0〉 directions slightly canted with respect to the normal to the sample surface. It was found that a high pressure of the sputtering gas effected the magnetic softness of the films. The saturation field increased and remanence ratio decreased with increase in pressure.     

Superfluid transition in a chiron gas

Low temperature measurements of the magnetic susceptibility of LaCuO₄ doped with Sr (LSCO) suggest that superconducting transition is associated with the disappearance of the vortex liquid. This note draws attention to the possibility that these vortices can be identified with the soliton-like charge carriers introduced in a previous theory of spin–orbit localization in layered poor conductors. In two-dimensions, these solitons are vortex-like, while in three-dimensional systems they are monopole-like. In either case, there is a natural mechanism for the pairing of spin-up and spin-down solitons. At low temperatures, there is a also cross-over transition which is a function of carrier density between a state where the solitons can move independently and a condensate state where the spin-up and spin-down solitons in neighbouring layers are paired.     

Spin polarization and spin-dependent transmittance in II–VI diluted magnetic semiconductorheterostructure

In this work, we carried out detailed investigation of a Cd_1?xMn_xTe/CdTe/Cd_1?xMn_xTe diluted magnetic semiconductor based quantum well. Our theoretical results are based on an accurate self-consistent resolution of the one-dimension Schrödinger and Poisson’s equations in the framework of the mean-field approximation for spin-up and spin-down orientations of carriers coupled via the sp–d exchange interaction. From the calculation of spin-dependent carrier densities for ferromagnetic and anti-ferromagnetic coupling, we evidence the spin-up and spin-down space separation for holes in quantum well for different values of band offsets. From deduced spin polarizations, we show that the CdTe region acts as a layer of spin rearrangement and spin reversal, respectively, in the ferromagnetic and anti-ferromagnetic coupling. The transmittance coefficients T₊ and T_? of injected spin-up and spin-down carriers are evaluated as a preliminary work to assess the spin-dependent currents in devices consisting of alternatively layers of non-magnetic and diluted magnetic semiconductors.     

Effects of the oxygen partial pressure and annealing atmospheres on the microstructures and optical properties of Cu-doped ZnO films

Cu-doped zinc oxide (ZnO:Cu) films were deposited on p-Si (1 0 0) substrates at 200 °C under various oxygen partial pressures by using radio frequency reactive magnetron sputtering. The properties of the films were characterized by the X-ray diffraction spectroscopy (XRD), energy dispersive spectrometer, X-ray photoelectron spectroscopy (XPS) and fluorescence spectrophotometer with the emphasis on the evolution of microstructures, element composition, valence state of Cu, optical properties. The results indicated that the properties of ZnO:Cu films were significantly affected by oxygen partial pressures. XRD measurements revealed that the sample prepared at the ratio of O₂:Ar of 15:10 sccm had the best crystal quality among all ZnO:Cu films. XPS analysis results suggested that the valence of Cu in the ZnO films was a mixed state of +1 and +2, and the integrated intensity ratio of Cu²⁺ to Cu⁺ increased with the increment of oxygen partial pressure. The photoluminescence measurements at room temperature revealed a violet, two blue and a green emission. We considered that the origin of green emission came from various oxygen defects when the ZnO:Cu films grew in oxygen poor and enriched environment. Furthermore, the influence of annealing atmosphere on the microstructures and optical properties of ZnO:Cu films were discussed.     

Properties of MgxZn1−xO thin films sputtered in different gases

Mg_xZn_1−xO alloy films were prepared on sapphire substrates using Ar and N₂ as the sputtering gases. The effect of the sputtering gas on the structural, optical and electrical properties of the Mg_xZn_1−xO films was studied. By using N₂ as the sputtering gas, the Mg_xZn_1−xO film shows p-type conductivity and the band gap is larger than that employing Ar as the sputtering gas. The reason for this phenomenon is thought to be related to the reaction between N-O or N-Zn, and the N-doping.     

Quantized magnetic flux through the ground-state orbit of the hydrogen atom

We have investigated the spin-dependent quantized magnetic fluxes through the ground-state electronic orbit of the hydrogen atom. We show that the corresponding fluxes are (1/2)Φ₀ for the spin-up case and (3/2)Φ ₀ for the spin-down case, respectively, where Φ₀ = hc/e is the flux quantum. Using the energy-flux proportionality, we also show that the spin-up case (where the electron spin is antiparallel to the proton spin, resulting in zero total spin) is the spin-dependent ground state of the hydrogen atom. The present result helps to understand the spin flip-flop in excitonic transitions in nanostructures.     

Vibrational spectroscopy characterization of magnetron sputtered silicon oxide and silicon oxynitride films

Vibrational (infrared and Raman) spectroscopy has been used to characterize SiO_xN_y and SiO_x films prepared by magnetron sputtering on steel and silicon substrates. Interference bands in the infrared reflectivity measurements provided the film thickness and the dielectric function of the films. Vibrational modes bands were obtained both from infrared and Raman spectra providing useful information on the bonding structure and the microstructure (formation of nano-voids in some coatings) for these amorphous (or nanocrystalline) coatings. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis have also been carried out to determine the composition and texture of the films, and to correlate these data with the vibrational spectroscopy studies. The angular dependence of the reflectivity spectra provides the dispersion of vibrational and interference polaritons modes, what allows to separate these two types of bands especially in the frequency regions where overlaps/resonances occurred. Finally the attenuated total reflection Fourier transform infrared measurements have been also carried out demonstrating the feasibility and high sensitivity of the technique. Comparison of the spectra of the SiO_xN_y films prepared in various conditions demonstrates how films can be prepared from pure silicon oxide to silicon oxynitride with reduced oxygen content.     

Study of hydrogenated amorphous silicon nitride films prepared by RF magnetron sputtering

Hydrogenated amorphous silicon nitride films have been deposited by the rf magnetron sputtering method with non-stoichiometric and stoichiometric compositions using a poly-Si target and a mixture of Ar, H₂ and N₂ as the sputtering gas. Data on optical and infrared absorption, electrical conductivity, breakdown voltage, capacitance measurements and thermal evolution of hydrogen have been presented as a function of nitrogen concentration in the films, especially in the stoichiometric region of composition. Attempts have been made to identify the roles of hydrogen and nitrogen in determining the electrical and optical properties and thermal stability exhibited by the films. Properties relevant for device application of the material have been shown to be comparable to those obtained by glow discharge or electron cyclotron resonance plasma chemical vapour deposition methods of deposition. RF magnetron sputtering has therefore been suggested as a viable alternative to the more widely adopted CVD methods for device applications of silicon nitride, where the use of hazardous process gases can be avoided.     

Effects of N2 addition on nanocrystalline diamond films by HFCVD in Ar/CH4 gas mixture

Nanocrystalline diamond (NCD) films were grown on silicon substrates by hot filament chemical vapor deposition in Ar/N₂/CH₄ gas mixtures. The effects of seeding process prior to deposition, the total gas pressure, and concentration of nitrogen on the grain size, morphology and bonding nature in HFCVD technique were investigated. The results indicated that a low total gas pressure is favorable for nanosized diamond crystallites. Films micrograph obtained from scanning electron microscopy showed diamond nanograins elongated with the addition of nitrogen in the plasma. Crystal structure investigations were carried out by X-ray diffraction measurements for deposited films. An increase in the size of crystallite is also observed from XRD measurements in NCD film when nitrogen was added in plasma. From Raman spectra, it was observed that the relative intensity of G peak increases indicating more graphite content after nitrogen added in the plasma. The effects of the nitrogen incorporation in nanocrystalline films in HFCVD are discussed.     

Influence of reactive gas and temperature on structural properties of magnetron sputtered CrSiN coatings

CrSiN coatings were deposited on stainless steel (Grade: SA304) and silicon Si(1 0 0) substrates, with varying argon-nitrogen gas proportions and deposition temperature, using reactive magnetron sputtering technique in the present work. The influence of sputtering (Ar) and reactive gas proportions (N₂) and temperature on the structural properties of the CrSiN coating was investigated. A small amount of silicon content (3.67 at.% Si) plays a crucial role in addition to the nitrogen content for the formation of different phases in the CrSiN coatings as observed in the present work. For example, the coating with comparatively low nitrogen content, 40% N₂, during deposition, formed a crystalline structure consisting of nano-crystalline CrN which is separated by an amorphous SiN phase, as evident from X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The formation of CrN(1 1 1) and Cr₂N(1 1 1) phases has occurred at 30% N₂ with 3.67% Si content, which transformed in to CrN(1 1 1) and CrN(2 0 0) with increase in N₂ content but with same Si content. The surface topography and morphology of the coatings were analyzed by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM), respectively. A less columnar growth is observed in CrSiN coatings deposited at low argon content, Ar:N₂ (20:80), and with 3.67 at.% Si in the coatings. However, it becomes dense with increase in nitrogen content and temperature. The XRD analysis showed that the intensity of a dominating peak (1 1 1) is decreasing from (80:20) to (60:40) argon:nitrogen environment. With a further increase of nitrogen content, from (60:40), in the sputtering gas mixture, to (40:60) argon-nitrogen, there is a sudden increase in (1 1 1) peak and above (40:60), the peak reduction rate is very slow than the previous one. The (1 1 1) and (2 0 0) peak intensity variations are very limited due to high nitrogen content, above 50%, and considerable amount of Si atoms, 3.67 at.%, present in the CrN coatings.     

Half-metallic properties of Ti2FeSi full-Heusler compound

In this study, the electronic structure and magnetic properties of novel half-metallic Ti₂FeSi full-Heusler compound with CuHg₂Ti-type structure were examined by density functional theory (DFT) calculations. The electronic band structures and density of states of the Ti₂FeSi compound show the spin-up electrons are metallic, but the spin-down bands are semiconductor with a gap of 0.45 eV, and the spin-flip gap is of 0.43 eV. Fe atom shows only a small magnetic moment and its magnetic moment is antiparallel to that of Ti atoms, which is indicative of ferrimagnetism in Ti₂FeSi compound. The Ti₂FeSi Heusler compound has a magnetic moment of 2 μ_B at the equilibrium lattice constant a=5.997 Å.     

Role of oxygen impurity in growth and magnetic properties of Ni83Fe17 permalloy thin films

To study the influence of oxygen impurities in the sputtering atmosphere on microstructure, and the magnetic and magnetotransport properties, thin films of Ni₈₃Fe₁₇ were deposited under dc magnetron sputtering technique into which regulated oxygen gas was introduced. The partial pressure of oxygen was varied from 2×10⁻⁷ to 3×10⁻⁶ mbar. X-ray diffraction patterns indicate the reduction of grain growth with increasing the oxygen partial pressure. The grain microstructure and the composition were confirmed through high resolution transmission electron microscopy attached with Scanning Transmission Electron Microscopy (STEM). Transition from canted to rectangular magnetic hysteresis loop was observed through magnetization measurements for samples prepared under higher oxygen partial pressure which implies the structural changes in the magnetic domain formation. These observations were further confirmed through the measurements of anisotropic magnetoresistance properties.     

Evolution of the structural and optical properties of silver oxide films with different stoichiometries deposited by direct-current magnetron reactive sputtering

Nitrogen doping of silver oxide(AgxO) film is necessary for its application in transparent conductive film and diodes because intrinsic AgxO film is a p-type semiconductor with poor conductivity.In this work,a series of AgxO films is deposited on glass substrates by direct-current magnetron reactive sputtering at different flow ratios(FRs) of nitrogen to O2.Evolutions of the structure,the reflectivity,and the transmissivity of the film are studied by X-ray diffractometry and sphectrophotometry,respectively.The specular transmissivity and the specular reflectivity of the film decreasing with FR increasing can be attributed to the evolution of the phase structure of the film.The nitrogen does not play the role of an acceptor dopant in the film deposition.     

直流磁控溅射YBCO非晶薄膜的卢瑟福背散射研究

利用直流磁控溅射(D.C.Magnetron Sputtering)法,选取总气压为80Pa,沉积时间为60min,溅射靶尺寸为φ80,在磁场强度、靶与基片之间的距离及Ar/O₂比等参数变化的情况下,制备了四组YBCO/Al₂O₃非晶薄膜样品。用MeV Li卢瑟福背散射(RBS)分析技术,测量了各块样品中Ba和Cu相对Y的含量和薄膜厚度随基片的横向分布。分析结果表明:在不同的沉积条件下,薄膜中各点的Ba和Cu相对浓度差别较大,薄膜厚度分布也 关键词：