Spectroscopic ellipsometry and magneto-transport investigations of Mn-doped ZnO nanocrystalline films deposited by a non-vacuum sol–gel spin-coating method

Nanocrystalline Zn_1?xMn_xO films (x = 0, 0.05, 0.1, 0.15, and 0.2) were deposited onto corning glass substrates by a non-vacuum sol–gel spin coating method. All of the films were annealed at 450 °C for 2 h. The structural, optical and magneto-transport properties were investigated by X-ray diffraction, spectroscopic ellipsometry and a system for the measurement of the physical properties. X-ray diffraction analysis of the films reveals that the Mn-doped ZnO films crystallize in the form of a hexagonal wurtzite-type structure with a crystallite size decreases with an increase of the Mn concentration. It was also found that the microstrain increases with the increase of the Mn content. Evidence of nanocrystalline nature of the films was observed from the investigation of surface morphology using transmission, scanning electron microscopy and atomic force microscopy. The optical constants and film thicknesses of nanocrystalline Zn_1?xMn_xO films were obtained by fitting the spectroscopic ellipsometric data (ψ and Δ) using a three-layer model system in the wavelength range from 300 to 1200 nm. The refractive index was observed to increase with increasing Mn concentration. This increase in the refractive index with increasing Mn content may be attributed to the increase in the polarizability due to the large ionic radius of Mn²⁺ compared to the ionic radius of Zn²⁺. The optical band gap of the nanocrystalline Mn–ZnO films was determined by an analysis of the absorption coefficient. The direct transition of the series of films was observed to have energies increasing linearly from 3.17 eV (x = 0) to 3.55 eV (x = 0.2). Magnetoresistance (MR) was measured from 5 K to 300 K in a magnetic field of up to 6 T. Low-field positive MR and high-field negative MR were detected in Mn-doped ZnO at 5 K. Only negative MR was observed for temperatures above 200 K. The positive MR in Mn-doped ZnO films was observed to decrease drastically when the temperature increased from 5 K to 100 K. The isothermal MR of Zn_1?xMn_xO films with different Mn concentrations at 5 K reveals that the increase of the Mn content induces a giant positive MR above x = 0.05 and reaches up to 55% at an applied field of 30 kOe for x = 0.2.     

A comprehensive study of structural and magnetic properties of sputter deposited nickel–silica thin films

The present work reports the formation of Ni nanoparticles inside the SiO₂ matrix and deals with the influence of Ni concentration on structural and magnetic properties of Ni–SiO₂ nanocomposite thin films. The films with varying Ni concentration (20–55 at% measured by Rutherford back scattering spectroscopy) were deposited using DC/RF magnetron co-sputtering. TEM and XRD analysis reveal the formation of FCC Ni nanoparticles in all the samples. The particle size varies from 3 to 10 nm as a function of Ni concentration. The surface roughness of the films is also found to increase with increase in nickel concentration. Magnetic measurements show that the Ni nanoparticles behave as superparamagnets when their size is ≤6 nm, in spite of their large volume fractions. The results show that the magnetic properties of the nanoparticles can be controlled by their size and Ni concentration in the samples.     

Structural and optical properties of Cu–N codoped ZnO thin films deposited by magnetron cosputtering

ZnO films codoped by copper and nitrogen were prepared by magnetron cosputtering. The effects of this codoping on the structural and optical properties of ZnO films were systematically studied. The results show that Cu–N codoping didn’t affect the optimal orientation. Cu–N codoping can enlarge the grain size, enhance the crystallinity, reduce the stress and lead to denser and smoother surface. A significant red shift of absorption edge and gap-narrowing effect resulting from codoping were found in ZnO films. Cu-doping, N-doping, and oxygen vacancy are the main factors leading to property modification of the ZnO films. By Cu–N codoping, we can modulate the microstructure and optical properties of ZnO films in a wider range.     

Microstructure and properties of nc-TiC/a-C∶H films deposited by radio frequency reactive sputtering

Abstract

Amorphous carbon films containing titanium carbide (nc-TiC/a-C∶H) were deposited onto n-type silicon (100) by radio frequency reactive sputtering titanium target in an Ar–CH₄ mixed atmosphere. The composition and microstructure of the films were characterised by means of X-ray photoelectron spectroscopy, field emitted SEM, XRD and Raman spectra. The mechanical and tribological properties of the films were measured by a nanoindentation tester and a ball-on-disc UMT–2MT tribometer. By adjusting the CH₄ flowrate, Ti content in the films could be controlled, and a transition in structures of the films from loose polymer-like to glassy and dense nanostructure was observed. The density of coatings was improved by the introduction of TiC nanocrystalline particles. The mechanical and lubricious properties were different accordingly.     

Structural and electronic properties of hydrogen adsorptions on BC₃ sheet and graphene: a comparative study

We have systematically investigated the effect of hydrogen adsorption on a single BC? sheet as well as graphene using first-principles calculations. Specifically, a comparative study of the energetically favorable atomic configurations for both H-adsorbed BC? sheets and graphene at different hydrogen concentrations ranging from 1/32 to 4/32 ML and 1/8 to 1 ML was undertaken. The preferred hydrogen arrangement on the single BC? sheet and graphene was found to have the same property as that of the adsorbed H atoms on the neighboring C atoms on the opposite sides of the sheet. Moreover, at low coverage of H, the pattern of hydrogen adsorption on the BC? shows a proclivity toward formation on the same ring, contrasting their behavior on graphene where they tend to form the elongated zigzag chains instead. Lastly, both the hydrogenated BC? sheet and graphene exhibit alternation of semiconducting and metallic properties as the H concentration is increased. These results suggest the possibility of manipulating the bandgaps in a single BC? sheet and graphene by controlling the H concentrations on the BC? sheet and graphene.     

Influence of Fe dopant concentration and annealing temperature on the structural and optical properties of ZnO thin films deposited by sol–gel method

Nanostructured Fe doped ZnO thin films were deposited onto glass substrates by sol–gel spin coating method. Influence of Fe doping concentration and annealing temperature on the structural, compositional, morphological and optical properties were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV–Vis spectroscopy and photoluminescence (PL) measurements. XRD analysis showed that all the films prepared in this work possessed a hexagonal wurtzite structure and were preferentially oriented along the c-axis. Pure ZnO thin films possessed extensive strain, whereas Fe doped films possessed compressive strain. In the doped films, least value of stress and strain was observed in the 0.5 at.% Fe doped thin film, annealed at 873 K. Average crystallite size was not significantly affected by Fe doping, but it increased from 15.57 to 17.79 nm with increase in annealing temperature from 673 to 873 K. Fe ions are present in +3 oxidation state as revealed by XPS analysis of the 0.5 at.% Fe doped film. Surface morphology is greatly affected by changes in Fe doping concentration and annealing temperature which is evident in the SEM images. The increase in optical band gap from 3.21 to 3.25 eV, with increase in dopant concentration was attributed to Moss–Burstein shift. But increase in annealing temperature from 673 to 873 K caused a decrease in band gap from 3.22 to 3.20 eV. PL spectra showed emissions due to excitonic combinations in the UV region and defect related emissions in the visible region in all the investigated films.     

Single-step synthesis of nanocrystalline CdS/polyacrylamide composites by γ-irradiation

-Irradiation has been used to prepare nanocrystalline composites—CdS/polyacrylamide with 18 wt % cadmium sulfide at room temperature, in which the inorganic phase displays uniformity of size and nearly uniform dispersion. The formation of nanocrystalline CdS and the polymerization of acrylamide are in a single step. X-ray Powder Diffraction and Infrared Spectra were used to characterize the product. Its morphology was determined by Transmission Electron Microscopy.     

Nucleation study of hydrogenated microcrystalline silicon (μc-Si:H) films deposited by VHF-ICP

Nucleation in the initial stage of hydrogenated microcrystalline silicon (μc-Si:H) film deposition by VHF inductivity-coupled plasma (ICP) has been investigated. When the SiH₄ concentration (R_SiH4 = [SiH₄] / ([SiH₄] + [H₂])) is 6%, the crystallization in the initial 1.1-2.4 nm film deposition is observed at the substrate temperature of 320 °C, while it is decreased to 150 °C by reducing the R_SiH4 to 3%. Furthermore, the nucleation is significantly promoted by H₂ plasma pretreatment as long as 90 s prior to μc-Si:H film deposition. The crystallinity was improved from 33 to 54% and the grain density was increased from 8.0 × 10¹⁰ to 1.7 × 10¹¹ cm^− 2 by the pretreatment. We confirmed no significant change in SiO₂ surface micro roughness after the H₂ plasma pretreatment. The chemical bond states at the SiO₂ surface before film deposition play an important role in nucleation.     

Corrosion resistance of nanocrystalline Mg–Cr alloys deposited by magnetron sputtering

Nanocrystalline Mg–Cr alloys were formed by dc magnetron sputtering in a wide range of concentrations. Structure, composition and grain sizes of the deposits were studied by XRD and XPS. EIS and dc-voltammetry showed that small chromium concentrations (2–8 at.%) had detrimental effect, while high corrosion resistance was observed when chromium content reached one third or so. Chromium refinement effect on alloy crystalline structure was found by XRD. The values of grain sizes were determined as follows: Mg–3Al (chromium-free) – over 100 nm, Mg–2Cr – 60.5 nm, Mg–8Cr – 44.6 nm, Mg–20Cr – 31.0 nm, Mg–45Cr, Mg–53Cr – ∼11.0 nm and ∼15 nm for sputtered Cr. Mott–Schottky plots showed that the spontaneous oxide layers formed on the alloys with high Cr content (Mg–36Cr, Mg–53Cr) were highly doped semiconductors of n-type. A conductivity change n–p was observed at E = 0.0 V (Ag/AgCl) in a buffer solution (pH 9.9). The conductivity change was also confirmed by photo-electrochemical measurements. Surface enrichment by chromium during initial stages of corrosion was determined, which promote corrosion resistance and provides an opportunity of surface auto-protection (self-healing) in damaged locations.     

Combinatorial growth and analysis of Ti-In-Zn-O films deposited by radio‐frequency and direct-current magnetron co-sputtering system

The compositional dependence of co-sputtered Ti-In-Zn-O film properties was investigated by means of a combinatorial technique. The X-ray diffraction result showed that the amorphous Ti-In-Zn-O films were fabricated regardless of the Ti contents [Ti / (Ti + In + Zn), at.%] of 4.5-34.4 at.%. The surface of amorphous Ti-In-Zn-O film is quite smooth. The obtained surface roughness (R_RMS) values ranged from 0.5 nm to 1.7 nm. The superior resistivity of 3.8 × 10^− 4 Ω cm and the transmittance of 92% (at 550 nm) was obtained for the Ti-In-Zn-O film with the elemental composition ratio of 18.6/68.5/12.9 at.% [Ti/In/Zn, at.%]. The indium quantity actually could be reduced to as high as ~ 15 at.% compared to that of commercial indium tin oxide or indium zinc oxide having similar resistivity value of ~ 10^− 4 Ω cm. Overall, the amorphous Ti-In-Zn-O films may serve as a viable, low-cost alternative for flexible transparent conducting electrode applications.     

A comparative study of microstructure and mechanical behavior of CO2 and diode laser deposited Cu–38Ni alloy

Cu–38Ni alloy was deposited on C71500 (Cu–30Ni) substrates by a laser-aided direct metal deposition technique using CO₂ and diode lasers. Structure–property relationships of deposited specimens were investigated by optical microscopy, electron microscopy, X-ray diffraction techniques, and microhardness and tensile measurements. Laser-deposited specimens’ microstructures were primarily dendritic, forming columnar grains growing epitaxially from the substrate and subsequent layers along the preferred crystallographic growth. The grain growth pattern and grain size distribution was significantly different in both specimens. The lattice parameter of the solid solution phase was relatively larger in diode laser-formed specimen; CO₂ laser-formed specimens showed relatively higher but non-uniform hardness distribution whereas a very uniform hardness distribution was observed in diode laser formed specimens. Diode laser formed specimens showed higher tensile properties compared to CO₂ laser formed specimens which were comparable to C71500 substrates. Microstructure and mechanical behavior were explained based on laser processing parameters.     

Influence of precursor source on sol–gel deposited ZnO thin films properties

Zinc oxide thin films were deposited by sol gel technique on glass substrates using different precursors (zinc acetate, zinc nitrate and zinc chloride). In the present work we investigate the precursor nature influence on structural, morphological, optical, electrical properties and photocatalytic activity of ZnO thin films. For this purpose we have used X-rays diffraction (XRD), atomic force microscopy (AFM), UV–visible spectroscopy and Hall effect measurements for films characterization. The obtained results indicated that ZnO films properties are strongly influenced by the nature of the used precursor as reactant. Films photocatalytic activity was evaluated by the photo-degradation of methylene blue (MB) dissolved in aqueous solution under UV-A light. The obtained results indicated that ZnO thin films prepared from zinc acetate are more efficient than those prepared from zinc nitrate and zinc chloride.     

Evaporated Thin Films of CdS and CdTe: Optimization for Photovoltaic Applications

Thin films of cadmium sulphide and cadmium telluride have been prepared by thermal evaporation under various conditions of deposition. These films have been characterized optically. electrically and for structure determination. The results of these characterizations along with the initial results of all thin film CdS/CdTe solar cells are presented in this paper     

The microstructure and mechanical properties of Fe–Cu materials fabricated by pressure-less-shaping of nanocrystalline powders

The microstructure of Fe-40%_wtCu nanocrystalline powders, prepared by mechanical alloying, was studied before and after the consolidation process. Pressure-less-shaping (PS) was used to consolidate the powders. The PS technique, similar to metal injection moulding (MIM), does not require external pressure in order to fill up the mould. The key factor of the process of consolidation is the use as binder a hybrid inorganic–organic monomer, formed by the reaction of zirconium propoxide and 2-hydroxy ethyl methacrylate. This type of monomer, mixed with the metallic powders, formed slurry having low viscosity, which was easily poured into mould. The binder stiffened upon polymerization. Some pieces were produced through debinding and sintering, both performed under inert atmosphere in order to avoid metal oxidation. Different microstructure and density were observed depending on the maximum sintering temperatures, ranging from 904 to 1,120 °C. In the sample sintered at 1,120 °C, the crystalline domains of the copper phase were of about 40 nm.     

Size quantization effects in optical and electrical properties of II–VI semiconductor films in nanocrystalline form

The electrical properties of CdTe and optical properties of ZnS in nanocrystalline thin film form are studied with a view to have a clearer understanding of the optical processes and the carrier transport mechanisms in nanocrystalline II–VI semiconductors, in general. Nanocrystalline ZnS and CdTe films were deposited by magnetron sputtering of respective targets in argon plasma. The optical absorption data of nanocrystalline ZnS films (thickness 10–40 nm) could be explained by the combined effects of phonon and inhomogeneity broadening along with optical loss due to light scattering at the nanocrystallites. The conductivity of CdTe (grain size within 4–4·7 nm) showed (T ₀/T) ^p dependence withp ∼ 0·5 indicating the presence of a Coulomb gap near the Fermi level. The width of the Coulomb gap varied within 0·02–0·04 eV depending on the deposition condition. The existing theoretical models were used for estimating hopping energy (0·02–0·04 eV) and hopping distance (2·8–5·1 nm) in nano CdTe films.     

Giant phase transition properties at terahertz range in VO₂ films deposited by sol-gel method

VO(2) films were fabricated on high-purity single-crystalline silicon substrate by the sol-gel method, followed by rapid annealing. The composition and microstructure of the films were investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM). The results indicated a polycrystalline nature with high crystallinity and compact nanostructure for the films, and the concentration of +4 valence vanadium is 79.85%. Correlated with these, a giant transmission modulation ratio about 81% of the film was observed by terahertz time domain spectroscopy. The experimentally observed transmission characteristics were reproduced approximately, by a simulation at different conductivities across the phase transition. According to the effective-medium theory, we assumed that it is important to increase the concentration of +4 valence vanadium oxide phases and improve the compactness of the VO(2) films for giant phase transition properties. The sol-gel-derived VO(2) films with giant phase transition properties at terahertz range, and the study on their composition and microstructure, provide considerable insight into the fabrication of VO(2) films for the application in THz modulation devices.     

Variation in boron doping by planar diffusion – a comparative study of computational hydrodynamics and experimental observations

Abstract

Resistivity maps for Si wafers processed using BN solid sources and hydrogen injection were compared to convective flow patterns predicted computationally. The convective flow patterns were found to mirror the resistivity maps, with low velocity flow domains being associated with high resistivity regions on the wafer and high velocity flow with low resistivity regions. Subtle changes in both the flow patterns and resistivity maps as a function of location within the furnace were consistently reflected in both computed flow domains and measured resistitivies. Finally, axially eccentric placement of the wafer–source stack was found to promote convection between wafer–source pairs by as much as a factor of five.     

Electrical and optical properties of µc-SiH films

Microcrystalline silicon films have been found quite useful in amorphous silicon solar cells as a contact material in n-i-p cells. Microcrystalline silicon films are obtained when amorphous silicon films are prepared by R.F. glow discharge of SiH₄ + H₂ at higher power ratings. These films possess higher conductivity as well as high transmission than amorphous silicon films. The present paper reports the preparation technique ofμc-SiH films using R.F. capacitive glow discharge of hydrogen-diluted silane. X-ray studies andtem studies of the films indicate microcrystallinity of the films. The electrical and optical properties are also reported.