Microstructure and electrical conductivity of Au-MgF2 nanoparticle cermet films

Au-MgF₂ nanoparticle cermet films with Au volume fraction of 6-50% were prepared by radio-frequency magnetron co-sputtering and analyzed by X-ray diffraction, X-ray photoelectron spectroscopy and temperature-varying four-wire technique. Microstructure analysis shows that the films are composed of mainly amorphous MgF₂ matrix with embedded fcc Au nanoparticles with a mean size of 9.8-21.4 nm. The electrical properties of the films from 54 to 300 K were measured. The results show that the electrical percolation threshold occurs between Au 40 vol.% and 50%, and around the percolation threshold the electrical conductivity of the films changes by four orders.     

Amorphous Films of Ternary Zinc and Tin Oxides for Transparent Electronics

Amorphous films of two varieties of zinc stannate (ZnSnO₃ and Zn₂SnO₄) have been considered that were fabricated by radio-frequency sputtering of ceramic compound targets containing ZnO and SnO₂ in 1: 1 and 2: 1 ratios. The elemental and phase compositions of the films and their optical and electrical parameters were determined. The transparency of the films in the visible spectral range is on average 87%. Zinc stannate amorphous films have a high electrical conductivity in contrast to amorphous ZnO and SnO₂. This phenomenon, which makes it possible to use zinc stannate amorphous films in transparent and flexible electronics, is explained.     

Effect of annealing on molybdenum doped indium oxide thin films RF sputtered at room temperature

Thin films of molybdenum doped indium oxide (IMO) were deposited on glass at room temperature using an in-built three-source RF magnetron sputtering. The films were studied as a function of oxygen volume percentage (O₂ vol. %; ranging from 0.0 to 17.5%) in the sputtering chamber. The as-deposited amorphous films were crystallized on post-annealing. The as-deposited films are low conducting and Hall coefficients were undetectable; whereas post-annealed films possess fairly high conductivity. The lowest transmittance (11.96% at 600 nm) observed from the films deposited without oxygen increased to a maximum of 88.01% (3.5 O₂ vol. %); whereas this transmittance was decreased with the increasing O₂ vol. % to as low as 81.04% (15.6 O₂ vol. %); a maximum of 89.80% was obtained from the films annealed at 500 °C in open air (3.5 O₂ vol. %). The optical band gap of 3.80 eV obtained from the films deposited without oxygen increased with increasing O₂ vol. % to as high as 3.91 eV (17.5 O₂ vol. %). A maximum of 3.92 eV was obtained from the films annealed at 300 °C in N₂:H₂ gas atmosphere (17.5 O₂ vol. %).     

In situ electrical conductivity and the amorphous-crystalline transition in vacuum deposited thin films of Se80Te20 alloy

The electrical conductivity of thin films of Se₈₀Te₂₀ polycrystalline alloy vacuum-deposited at room temperature on glass substrates has been studied duringin situ heating and cooling cycles. From the electron diffraction of as-grown films it is seen that the studied films are amorphous at room temperature. The electrical conductivity and electron diffraction studies showed that the as-grown amorphous thin films undergo an amorphous-crystalline transition in the temperature range 340 to 360 K. Upon cooling, the films appear to undergo a crystalline crystalline transition around the same temperatures. There does not appear to be any dependence of the amorphous-crystalline transition temperature on the thickness of the films. However, high-resistance films (thinner films) have a well-defined transition temperature while the low-resistance films (thicker films) have a broader transition. The electrical conductivity of polycrystalline Se₈₀Te₂₀ films above 360 K appears to be an exponential function of reciprocal temperature.     

Development of transparent and conductive ZnO films by spray pyrolysis

Indium-doped zinc oxide (IZO) films were deposited on Corning 7059 substrates by the spray pyrolysis technique. To achieve higher electrical conductivity both the zinc acetate concentration and indium concentration in the solution were varied. The films were characterized for their structural and electrical properties. Film stability in H₂ plasma was also checked for possible use in amorphous and microcrystalline silicon related fields. It was observed that the films can be sustained in a hydrogen plasma, and hence IZO films of high conductivity can be used for the development of amorphous and microcrystalline silicon solar cells.     

In situ electrical conductivity and amorphous-crystalline transition in vacuum-deposited thin films of Se20Te80 alloy

In situ electrical conductivity measurements have been carried out on vacuum-deposited thin films of Se₂₀Te₈₀ alloy during heating and cooling cycles. The electrical conductivity and X-ray diffraction studies show that the as-grown Se₂₀Te₈₀ films are amorphous and, upon heating, undergo an irreversible amorphous-crystalline transition between 315 and 350 K. The observation that the as-grown thin films (deposited at room temperature on glass substrates) are amorphous is in contrast to earlier observations by other workers who find that they are polycrystalline. Above the transition temperature, the electrical conductivity of the polycrystalline Se₂₀Te₈₀ films changes as an exponential function of reciprocal temperature. The amorphous-crystalline transition in Se₂₀Te₈₀ thin films is broad, with films of high initial resistance having lower transition temperatures and low-resistance films having higher transition temperatures. The observation of a broad transition in the case of the present Se₂₀Te₈₀ thin films has to be contrasted with our earlier observations of sharp transitions in the case of Se₈₀Te₂₀ and Se₅₀Te₅₀ thin films.     

A study of crystallographic phases in non-stoichiometric (oxygen deficiency) indium oxide thin films

Indium oxide is a well-known transparent conductive oxide (TCO) in its stoichiometric composition (In₂O₃). Its electrical and optical properties are strongly influenced by the chemical composition. This work focuses on an experimental investigation of the crystallographic phases in non-stoichiometric (oxygen deficiency) compositions of indium oxide thin films. The thin films were deposited at 300 °C by reactive sputtering of pure indium target at different oxygen gas flow rates on Si substrates. Two different phases are identified only in the non-stoichiometric compositions: metallic indium- and crystalline indium-rich oxide. The metallic indium phase appears as nano-crystals, a few nano-meters in diameter, evenly dispersed and occupies only 1 vol. % of the film. These metallic nano-particles have a negligible effect on the optical transparency and electrical conductivity of the films. The indium-rich oxide (In_xO_y) phase which occupies about 99 vol. % of the film has the bixbyite crystallographic structure and average grain size of about 50 nm. This phase has a pronounced effect on improving the TCO figure-of-merit (FM) relative to stoichiometric crystalline In₂O₃ films due to a higher increase of the electrical conductivity than the decrease of the optical transparency.     

Thin film fabrication of nano-porous 12CaO·7Al2O3 crystal and its conversion into transparent conductive films by light illumination

Thin film fabrication of crystalline 12CaO·7Al₂O₃ (C12A7) with zeolitic structure was examined, and their electrical and optical properties were measured. Polycrystalline thin films were prepared by post-annealing of amorphous films in oxygen atmosphere at temperatures above 800 °C. Choice of substrates was crucial for obtaining single-phase thin films. Although various oxide substrates (single crystals of Al₂O₃, Y-stabilized ZrO₂, MgO and silica glass) were examined, single-phase films were obtained only for MgO substrates and the other substrates reacted with the CaO component in the films during post-annealing. The optical band gap of C12A7 was evaluated to be 5.9 eV. Hydride ions were incorporated into the film by a thermal treatment in a hydrogen atmosphere at 1200 °C. The resulting transparent thin films were converted into transparent persistent electronic conductors exhibiting an electrical conductivity 6.2×10⁻¹ S cm⁻¹ at 300 K by ultraviolet light illumination. This is the first example of transparent conductive thin film in which conductive areas can be patterned directly by light.     

Phase formation and morphology control of niobium oxide nanopillars

Nanopillar metal oxide thin films offer versatility as ultra high surface area supports and conductors. Metal oxide properties (e.g. stability, conductivity) can be tuned via phase and composition control to achieve desired application-specific functionality. Here we demonstrate phase control of high surface area thin films grown by glancing angle deposition and transformed to desired phases through high temperature annealing in a reducing environment. The post-annealed properties such as stoichiometry, phase, and morphology are shown to be largely dependent on initial film structure and hydrogen forming gas flow rate. Initially amorphous films of approximate stoichiometry Nb₂O₅ are transformed to NbO₂ or NbN_xO_1−x through annealing. Transformation to oxygen-deficient phases is more easily achieved for films of higher initial porosity. Higher forming gas flow rates result in both increased oxygen removal and significantly less physical degradation of nanostructures. A phase map is included as a guide to phase formation and morphology control in annealed nanopillar niobium oxide films.     

Synthesis and electrical properties of mixed-layer Aurivillius phases

Polycrystalline samples of the mixed-layer Aurivillius phases Bi₁₀Ti₃W₃O₃₀, Bi₇Ti₄NbO₂₁, Bi₇Ti₄TaO₂₁, SrBi₆Ti₃Nb₂O₂₁, BaBi₆Ti₃Nb₂O₂₁, SrBi₈Ti₇O₂₇, and BaBi₈Ti₇O₂₇ (ferroelectrics with high oxygen-ion conductivity) have been prepared by solid-state reactions, and their electrical properties have been studied. All of the compounds undergo a second-order ferroelectric phase transition at temperatures from 500 to 800°C and have high electrical conductivity. Of particular interest is the compound Bi₁₀Ti₃W₃O₃₀, whose conductivity exceeds that of the other mixed-layer Aurivillius phases by more than one order of magnitude and reaches 5 × 10^?2 S/cm at 800°C.     

Impedance spectroscopy and relaxation phenomena of (Na,K) excess Na0.5K0.5NbO3 thin films grown by chemical solution deposition

Na_0.5K_0.5NbO₃ (NKN) and 10 mol% (Na,K) excess Na_0.5K_0.5NbO₃ (NKN10) thin films on Pt/Ti/SiO₂/Si substrate were prepared by chemical solution deposition. Crystallization of NKN10 thin films was confirmed by X-ray diffraction. The (Na,K) excess Na_0.5K_0.5NbO₃ thin film shows a ferroelectric P-E hysteresis loop. Dielectric properties and impedance spectroscopy of thin films were investigated in the frequency range from 0.1 Hz to 100 kHz and the temperature range of 25 ~ 500 °C. By analyzing the complex impedance relaxation with Cole-Cole plots, we found impedance relaxations for the thin film. The contribution of electrical conduction is discussed in relation to grain, grain boundary, and interface effects.     

Structural, electrical and optical properties of Bi2Se3 and Bi2Se(3−x)Tex thin films

Thin films of Bi₂Se₃, Bi₂Se_2.9Te_0.1, Bi₂Se_2.7Te_0.3 and Bi₂Se_2.6Te_0.4 are prepared by compound evaporation. Micro structural, optical and electrical measurements are carried out on these films. X-ray diffraction pattern indicates that the as-prepared films are polycrystalline in nature with exact matching of standard pattern. The composition and morphology are determined using energy dispersive X-ray analysis and scanning electron microscopy (SEM). The optical band gap, which is direct allowed, is 0.67 eV for Bi₂Se₃ thin films and the activation energy is 53 meV. Tellurium doped thin films also show strong optical absorption corresponding to a band gap of 0.70-0.78 eV. Absolute value of electrical conductivity in the case of tellurium doped thin film shows a decreasing trend with respect to parent structure.     

Effect of laser power on electrical conductivity 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 the electrical conductivity of the BaTi₅O₁₁ films was investigated. The electrical resistivity of the grains was much higher than that of the grain boundaries, which indicated that the electrical conductivity along the grain boundary was dominant. For the BaTi₅O₁₁ films, the conduction was mainly attributed to oxygen vacancies, and the electrical conductivity was strongly affected by their microstructures and the concentration of the charge carriers. With increasing the P _L, the grain size increased and the grain-boundary density decreased, which resulted in the decrease of the electrical conductivity. At the same time, the increase of T _dep led to higher concentration of charge carriers, which resulted in the increase of electrical conductivity.     

Formation of high-conductivity regions in nanostructured SnO2-AOx (A = Ti4+, Zr4+, Sb3+, Sb5+) films exposed to UV radiation or H2

Data are presented on the composition, structure, and electronic properties of SnO₂ films doped with Ti, Zr, and Sb oxides. The films were prepared by thermohydrolytic decomposition of SnCl₂, TiCl₄, ZrCl₄, and SbCl₃ solutions and were found to contain nanoscale regions of crystalline SnO₂-based solid solutions and amorphous SnO₂ containing Sn²⁺ or Sb³⁺ ions and located on the surface of crystallites or between them. As distinct from SnO₂ sensors containing no noble metals, the films exhibit high sensitivity to H₂ adsorption and/or UV radiation at 20°C (conductivity increase by 5 orders of magnitude). The results on the nanostructure, electronic spectra, and conductivity indicate that, in the three systems studied, UV irradiation and H₂ adsorption give rise to the formation of high-conductivity, metallic regions responsible for the low-temperature H₂ sensitivity of the films.     

Electronic conduction in thin amorphous MoO3/SiO films deposited by co-evaporation

A study of the effects of changes in composition and temperature on the electrical properties of MoO₃/SiO thin amorphous films is presented. The high-field conduction is probably due to the Poole-Frenkel effect as it is in simple SiO. At low temperature and low field the electron hopping process is dominant but conduction at higher temperatures is a contact-limited process. The decrease in conductivity with increasing concentration of SiO in MoO₃ may be attributed to the increasing number of trapping centres introduced in MoO₃/SiO films during the evaporation process. The increase in conductivity in MoO₃/SiO films with increasing temperature is attributed to the increasing concentration and higher mobility of charge carriers.     

Preparation of delafossite CuFeO2 thin films by rf-sputtering on conventional glass substrate

CuFeO₂ is a delafossite-type compound and is a well known p-type semiconductor. The growth of delafossite CuFeO₂ thin films on conventional glass substrate by radio-frequency sputtering is reported. The deposition, performed at room temperature leads to an amorphous phase with extremely low roughness and high density. The films consisted of a well crystallized delafossite CuFeO₂ after heat treatment at 450 °C in inert atmosphere. The electrical conductivity of the film was 1 mS/cm. The direct optical band gap was estimated to be 2 eV.     

Electrical conductivity,thermoelectric power and optical absorption studies of amorphous and crystalline gallium antimonide thin films

Amorphous films (240–1740 Å thick) of gallium antimonide were formed by vacuum evaporation onto goldseal glass slides and onto sodium chloride crystals. They were annealed in successive cycles to obtain the ideal amorphous state. The heat treatment was continued until the crystalline phase was obtained. The electrical conductivity, the thermoelectric power with respect to bulk silver and the optical absorption were measured in all these films before and after crystallization. The electron diffraction patterns of the as-deposited, the annealed and the crystalline films were obtained using a transmission electron microscope. The activation energy for conduction ΔE, the amorphous-to-crystalline transition temperature, the density of states at the Fermi level N(_EF) and the optical energy gap E_o were evaluated.     

Influence of the reactive N2 gas flow on the properties of rf-sputtered ZnO thin films

Nitrogen (N)-doped ZnO thin films were RF sputtered with different N₂ volume (ranging from 10% to 100%) on sapphire (001) substrates. The influence of N₂ vol.% on the properties of ZnO films was analyzed by various characterization techniques. The X-ray diffraction studies showed that the films grow along the preferential (002) crystallographic plane and the crystallinity varied with varying N₂ vol.%. The films sputtered with 25 vol.% N₂ showed better crystallinity. The transmittance was decreased with increasing N₂ volume until 25% and was almost constant above 25%. A maximum optical band gap (2.08 eV) obtained for 10 vol.% N₂ decreased with increasing N₂ volume to reach a minimum of 1.53 eV at 100%. The compositional analysis confirmed the incorporation of N into ZnO films, and its concentration increased with increasing N₂ volume to reach a maximum of ∼ 3.7 × 10²¹ atom/cm³ at 75% but then decreased slightly to 3.42 × 10²¹ atoms/cm³. The sign of Hall coefficient confirmed that the films sputtered with ≤ 25 vol.% N₂ possess p-type conductivity which changes to n-type for > 25 vol.% N₂.     

Electrical characteristics of mixed Zr-Si oxide thin films prepared by ion beam induced chemical vapor deposition at room temperature

Mixed Zr-Si oxide thin films have been prepared at room temperature by ion beam decomposition of organometallic volatile precursors. The films were flat and amorphous. They did not present phase segregation of the pure single oxides. A significant amount of impurities (-C-, -CH_x, -OH, and other radicals coming from partially decomposed precursors) remained incorporated in the films after the deposition process. This effect is minimized if the Ar content in the O₂/Ar bombarding gas is maximized. Static permittivity and breakdown electrical field of the films were determined by capacitance-voltage and current-voltage electrical measurements. It is found that the static permittivity increases non-linearly from ~ 4 for pure SiO₂ to ~ 15 for pure ZrO₂. Most of the dielectric failures in the films were due to extrinsic breakdown failures. The maximum breakdown electrical field decreases from ~ 10.5 MV/cm for pure SiO₂ to ~ 45 MV/cm for pure ZrO₂. These characteristics are justified by high impurity content of the thin films. In addition, the analysis of the conduction mechanisms in the formed dielectrics is consistent to Schottky and Poole-Frenkel emission for low and high electric fields applied, respectively.     

Towards large area deposition of Cr2AlC on steel

Cr₂AlC belongs to the MAX phases, which are promising materials for protective coatings on steel due to their unique combination of properties like corrosion and oxidation resistance, good electrical conductivity, low friction coefficient, damage tolerance, and high temperature stability. Here the deposition of Cr₂AlC thin films has been carried out by magnetron sputtering of a Cr₂AlC compound target. The effect of the substrate temperature on the constitution was investigated. It was found that the MAX phase structure is stable in a substrate temperature range between 1123 K and 723 K. At lower substrate temperatures, the structure of the film is X-ray amorphous. A temperature of approximately 870 K was determined for the transition from amorphous to crystalline Cr₂AlC using differential scanning calorimetry. A phase purity of more than 90% MAX phase in the films was reached and the equilibrium volume is in excellent agreement with our ab initio calculations. The here presented deposition method provides a pathway towards large area deposition of MAX phase Cr₂AlC coatings on steel.