Cytocompatibility of novel tin oxide thin films

The capacity of tin oxide films to support cell growth was investigated. Three substrates were used for the test: glass coverslips, glass coverslips spin coated with tin oxide and commercially available 316 stainless steel. The wettabilities and surface roughness of the three surfaces were measured before seeding 3T3 fibroblasts onto the samples. The behaviour of the cells grown on the tin oxide was compared to the uncoated glass and the steel and results showed that the cell growth on tin oxide compared favourably with the other substrates. The surface wettability appeared to have the strongest effect on cell adhesion to tin oxide.     

Optical, structural and electrical properties of Mn doped tin oxide thin films

Mn doped SnO_x thin films have been fabricated by extended annealing of Mn/SnO₂ bilayers at 200°C in air for 110 h. The dopant concentration was varied by controlling the thickness of the metal layer. The overall thickness of the film was 115 nm with dopant concentration between 0 and 30 wt% of Mn. The films exhibit nanocrystalline size (10-20 nm) and presence of both SnO and SnO₂. The highest transmission observed in the films was 75% and the band gap varied between 2.7 and 3.4 eV. Significantly, it was observed that at a dopant concentration of ∼4 wt% the transmission in the films reached a minimum accompanied by a decrease in the optical band gap. At the same value of dopant concentration the resistivity also reached a peak. This behaviour appears to be a consequence of valence fluctuation in Sn between the 2+ and 4+ states. The transparent conductivity behaviour fits into a model that attributes it to the presence of Sn interstitials rather than oxygen vacancies alone in the presence of Sn^{2 +}.     

Investigation on structural, electrical and optical properties of tungsten-doped tin oxide thin films

Tungsten-doped tin oxide (SnO₂:W) transparent conductive films were prepared on quartz substrates by pulsed plasma deposition method with a post-annealing. The structure, chemical states, electrical and optical properties of the films have been investigated with tungsten-doping content and annealing temperature. The lowest resistivity of 6.67 × 10^− 4 Ω cm was obtained, with carrier mobility of 65 cm² V^− 1 s^− 1 and carrier concentration of 1.44 × 10²⁰ cm^− 3 in 3 wt.% tungsten-doping films annealed at 800 °C in air. The average optical transmittance achieves 86% in the visible region, and approximately 85% in near-infrared region, with the optical band gap ranging from 4.05 eV to 4.22 eV.     

Electroluminescence from CdSe microcrystals-doped indium tin oxide thin films

When the DC voltage (4 V cm–1) was applied to the CdSe microcrystals doped indium tin oxide (ITO) thin film prepared by RF-magnetron sputtering method, the red colour luminescence was observed. The luminescence spectrum had two peaks of about 710 and 880 nm, and the ascending tail at longer than 900 nm. It was considered that the luminescence at 710 and 880 nm is electroluminescence, which may be attributable to the surface defect of CdSe microcrystals.     

Modeling the optical properties of tin oxide thin films

Searching the many papers reporting on the optical characteristics of tin oxide thin films, an obvious question arises: what is the origin of the very large differences in the reported optical and electrical properties of these films? The objective of the present work is to resolve this question by applying a modeling approach, simulating the refractive index of SnO, SnO₂, SnO + SnO₂, and porous tin oxide films in the visible range of the spectrum under various structure and composition conditions. Using the semi-empirical model of Wemple and DiDomenico for the dielectric function below the interband absorption edge of ionic and covalent solids, and the effective-medium theory of Bruggeman, the refractive indices of SnO, SnO₂, several mixtures of SnO and SnO₂ and various porous tin oxide films were calculated. The resulting data are compared with some published data to suggest the compositional and structural characteristics of the reported oxides. The correlation between the optical properties of the studied thin films and film composition is also indicated. It is proposed that the large spread in reported optical data is possibly a spread in the composition of the samples.     

Indium tin oxide thin films for metallization in microelectronic devices

The use of sputtered indium tin oxide (ITO) thin films as metal layers in silicon-based electronic circuits has been investigated. The ITO films were sputtered directly from In₂O₃/SnO₂ targets under inert ambient in an r.f. sputtering system. The films were characterized as functions of process parameters such as r.f. power, substrate temperature and post-deposition annealing treatments. The properties studied included sheet resistance, transparency, thickness uniformity, composition and structure, step coverage, and etchability. In addition, the suitability of these ITO films as interconnects in microelectronic devices was examined by fabricating MOSFET devices using fine line patterned ITO for the metallization.     

Preparation of complex oxide thin films under hydrothermal and hydrothermal-electrochemical conditions

Thin-film growth of complex oxides including BaTiO₃, SrTiO₃, BaZrO₃, SrZrO₃, KTaO₃, and KNbO₃ were studied by the hydrothermal and the hydrothermal-electrochemical methods. Hydrothermal-electrochemical growth of ATiO₃ (A = Ba, Sr) thin films was investigated at temperatures from 100° to 200°C using a three-electrode cell. Current efficiency for the film growth was in the range from ca. 0.6% to 3.0%. Tracer experiments revealed that the ATiO₃ film grows at the film/substrate interface. AZrO₃ (A = Ba, Sr) thin films were also prepared on Zr metal substrates by the hydrothermal-electrochemical method. By applying a potential above ca. +2 V vs. Ag/AgCl to the Zr substrates, AZrO₃ thin films were formed uniformly. KMO₃ (M = Ta, Nb) thin films were prepared on Ta metal substrates by the hydrothermal method. Perovskite-type KTaO₃ thin films were formed in 2.0 M KOH at 300°C. Pyrochlore-type K₂Ta₂O₆ thin films were formed at lower temperatures and lower KOH concentrations. Morphotropic phase changes were also revealed in the hydrothermal system KTaO₃-KNbO₃.     

Thermal stability of indium tin oxide thin films co-sputtered with zinc oxide

The thermal stability of indium tin oxide (ITO) films and ITO co-sputtered with zinc oxide (ZnO) films at different zinc atomic ratios in various atmospheres are investigated. The resistivity of the annealed ITO films decreased with increased annealing temperatures. The improved electrical properties were attributed mainly to the increase in carrier concentration originating from the significant formation of oxygen vacancies in the ITO films. In contrast, due to the lower oxidation potential of zinc ions, the resistivity of the annealed co-sputtered films showed no significant reduction and an increase with annealing temperatures. The film decomposition due to the high degree outdiffusion of oxygen atoms and aggregation of In atoms observed from the metal-like In phase in the diffraction patterns was responsible for the drastic thermal degradation in the electrical and optical properties of the samples annealed at elevated temperatures in reducing gas atmosphere. In contrast, the superior thermal stability of the co-sputtered films, at an atomic ratio of 60% annealed in reducing gas atmospheres, was ascribed to the stable Zn₃In₂O₆ crystalline structure that appeared in the diffraction pattern. The absorption edge observed from the optical transmittance of these annealed films also showed evidence of carrier concentration evolution in various annealing atmospheres. The lower oxidation potential of the zinc atoms introduced into the ITO films was concluded to be efficient in compensating for the formation of oxygen vacancies resulting in the alleviated decomposition behavior during thermal annealing.     

Refractive indices of textured indium tin oxide and zinc oxide thin films

The refractive indices of textured indium tin oxide (ITO) and zinc oxide (ZnO) thin films were measured and compared. The ITO thin film grown on glass and ZnO buffered glass substrates by sputtering showed distinct differences; the refractive index of ITO on glass was about 0.05 higher than that of ITO on ZnO buffered glass in the whole visible spectrum. The ZnO thin film grown on glass and ITO buffered glass substrates by filtered vacuum arc also showed distinct differences; the refractive index of ZnO on glass was higher than that of ZnO on ITO buffered glass in the red and green region, but lower in the blue region. The largest refractive index difference of ZnO on glass and ITO buffered glass was about 0.1 in the visible spectrum. The refractive index variation was correlated with the crystal quality, surface morphology and conductivity of the thin films.     

Eu-doped indium tin oxide thin films fabricated by sol-gel technique

We have fabricated Eu-doped indium tin oxide thin films via the conventional sol-gel technique, and confirmed that the doped Eu atoms were chemically incorporated into the indium tin oxide lattice by substituting the In sites. Optical spectra indicated that the Eu-doped films were free of any impurities leading to additional vibrational effects. Valence states of Eu ions in our Eu-doped indium tin oxide films were discussed in connection with Eu concentration.     

Characterization of tin oxide thin films deposited by reactive sputtering

SnO_x Thin films deposited by reactive sputtering are characterized by conversion electron Mössbauer spectroscopy, X-ray diffraction, nuclear resonant scattering and Rutherford backscattering analyses and sheet resistance measurements. The samples were submitted to thermal annealing and exposed to butane gas. The highly disordered as-deposited thin film is modified under thermal processing and gas exposure, changing the oxygen vacancy concentration. This behaviour should affect the steady state response of tin oxide sensors.     

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.     

High frequency characteristics of tin oxide thin films on Si

High frequency characteristics of tin oxide (SnO₂) thin films were studied. SnO₂ thin films have been successfully grown on n-type Si (111) substrates by using a spray deposition technique. The capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of the metal-oxide-semiconductor (Au/SnO₂/n-Si) Schottky diodes were investigated in the high frequency range from 300 kHz to 5 MHz. It has been shown that the interface state density, D_it, ranges from 2.44 × 10¹³ cm⁻² eV⁻¹ at 300 kHz to 0.57 × 10¹³ cm⁻² eV⁻¹ at 5 MHz and exponentially decreases with increasing frequency. The C-V and G/ω-V characteristics confirm that the interface state density and series resistance of the diode are important parameters that strongly influence the electrical parameters exhibited by the metal-oxide-semiconductor structure.     

Lanthanum concentration dependence of electrical properties in tin oxide thin films

Lanthanum doped tin oxide thin films were prepared on boron-silicon glass substrates by spray pyrolysis. Lanthanum concentration was varied from 0 to 1.0 wt%. The microstructures, sheet resistance and thermal stabilities of the lanthanum doped tin oxide thin films have been investigated in order to determine the role of this dopant on electrical properties. X-ray diffraction (XRD) result shows the deposited thin film is mainly rutile SnO₂. And atomic force microscopy (AFM) reveals that the thin film has smooth surface with no cracks and defects. And it exhibits a typical bimodal grain size distribution with an average grain size of 95 nm. The sheet resistances of the thin films have a complex dependence on the lanthanum concentration. With increasing lanthanum concentration, the sheet resistances of tin oxide thin films were slightly increased and then abruptly decreased. Moreover, when the lanthanum concentration of 0.5 wt% was reached, the specimen exhibits excellent electrical properties. Because of its effectiveness in improving homogeneity of operating surface temperature and thermal stability, lanthanum appears to be an attractive additive for the tin oxide thin films.     

Pulsed laser deposition of conductive indium tin oxide thin films

Thin indium tin oxide (ITO) films have been grown on quartz glass substrates by pulsed laser deposition. The influence of ablation target composition and deposition conditions on the growth rate, optical transmission spectra, and carrier mobility and concentration of the films has been examined. The average surface roughness of the ITO films grown at substrate temperatures above 300°C is 2 nm. The films grown at an oxygen partial pressure of 5 mTorr using ablation targets with Sn/(In + Sn) = 5% possess high transmission (85-95%) in the visible range and low resistivity (1.8 × 10⁻⁴ Ω cm).     

Excimer laser deposition and characteristics of tin oxide thin films

ArF excimer laser assisted chemical vapor deposition of tin oxide thin films on Si was obtained using SnCl₄ and O₂ as precursors. Experimental measurements revealed that the deposition rate increases with incident laser energy density. The composition, structure and ultraviolet-to-visible spectra of the thin films were investigated by means of XPS, SEM, XRD and a UV–Vis techniques. It was shown that SnO₂ and SnOCl₂ coexisted in the thin films, and SnOCl₂ was almost completely converted into SnO₂ after annealing. The SnO₂ thin films deposited at room temperature were amorphous in structure and the grain size of the films became larger after annealing. The transmittance of the SnO₂ thin films is above 90%, the absorption edge is 355 nm and the energy gap is 3.49 eV.     

Sol-gel preparation and characterisation of mixed metal tin oxide thin films

Mixed metal oxide stannates were prepared by sol-gel methods and coated onto solid titanium substrates as thin films using spin and dip coating methods. Metal oxides such as Sb₂O₅, ZrO₂, CuO, MnO_x and PdO were introduced into a SnO₂ host matrix using sol-gel technology. The mixed metal tin oxide materials prepared via the sol-gel route were extensively characterised in terms of surface characterisation and chemical composition. Thermogravimetric analysis was performed to confirm that at 600 °C (the calcination temperature) no further structural changes due to mass loss occur. UV spectroscopy of the liquid gels allowed the determination of the band gap energy. The surface morphology of the thin film electrodes were characterised by atomic force microscopy and scanning electron microscopy and the effect of the coating method employed i.e. spin or dip coating could be clearly seen in the estimated values of surface roughness. These techniques were also able to confirm the thickness of the films in the nano range. Combined nuclear beam techniques such as Rutherford backscattering spectroscopy and particle induced X-ray emission provided some insight into the chemical composition of the mixed metal tin oxides and confirmed the presence of the dopant element in the SnO₂ host material.