D.C. Cameron

Aluminum-doped zinc oxide transparent conductors deposited by the sol-gel process

Abstract Thin films of transparent conducting aluminum-doped ZnO have been deposited using a sol-gel process. The dependence of electrical characteristics upon aluminum concentration in the films and upon post-deposition heat treatment in vacuum was examined. The effect of changing the aluminum-to-zinc ratio from 0% to 4.5% (atomic) and the heat treatment temperature in vacuum has been thoroughly investigated. Resistivities of (7–10) × 10−4 Ω cm have been achieved for ZnO:Al films with Al/Zn ratios of 0.8 at.% heated to 450 °C in vacuum. Transmittance in the visible region is above 90%. Similar results were obtained using aluminum chloride and aluminum nitrate as the aluminum precursor.

Optical and electrical properties of transparent conductive ITO thin films deposited by sol–gel process

Indium tin oxide (ITO) thin films have been deposited onto quartz glass substrates by a sol–gel process. The starting solution was prepared by mixing indium chloride dissolved in acetylacetone and tin chloride dissolved in ethanol. 0–20% by weight Sn-doped indium oxide (ITO) films were prepared by heat-treatment at above 400°C. The electrical, optical and structural properties of ITO thin films were investigated. The thickness of ITO film was measured by ellipsometer. The electrical resistivity was measured by using four-point probe method. The ITO thin films containing 10 wt.% Sn showed the minimum resistivity of ρ=1.5×10−3 Ω-cm. The spectral transmittance of ITO thin films was measured in the wavelength range from 275 to 900 nm by a UV-vis spectrometer. The film has high transmittance above 80% and has an absorption edge at 300 nm. X-Ray diffraction measurements employing CuKα radiation were performed to determine the crystallinity of the ITO films which showed that the ITO films were polycrystalline with a cubic bixbyite structure. XRD results show that a single phase is detected for In-Sn oxide and X-ray photoelectron spectroscopy (XPS) results show that a single valence state and chemical bonding state is observed for In and Sn in In-Sn oxides. Therefore, we can say that Sn is incorporated into the In2O3 structure substitutionally.

Preparation and properties of transparent conductive aluminum-doped zinc oxide thin films by sol–gel process

Highly conductive and transparent aluminum-doped zinc oxide thin films have been prepared from the solution of zinc acetate and aluminum nitrate in ethanol by the sol–gel process. The effect of changing the aluminum-to-zinc ratio from 0 to 5 at.u200a% and annealing temperature from 0u200a°C to 700u200a°C in air has been investigated. The resistivities of thin films were measured as a function of annealing temperature and also as a function of aluminum dopant concentration in the solution. As-deposited films have high resistivity and high optical transmission. Annealing of the as-deposited films in air leads to a substantial reduction in resistivity. The films have a minimum value of resistivity of 1.5×10−4 Ωu200acm for 0.8 at.u200a% aluminum-doped zinc oxide and a maximum transmission of about 91% when deposited on glass substrates. X-ray diffraction measurements employing Cu Kα radiation were performed to determine the crystallinity of the ZnO:Al films which showed that the films were polycrystalline with a hexagonal struct...

Investigation of annealing effects on sol–gel deposited indium tin oxide thin films in different atmospheres

Abstract Indium tin oxide (ITO) thin films have been deposited onto silicon and quartz glass substrates and also on titanium dioxide and tantalum oxide coated substrates by a sol–gel process, followed by annealing in air, oxygen and nitrogen. The effect of annealing in the temperature range of 400–700 °C on the electrical, optical and structural properties of ITO thin films has been studied. The starting solution was prepared by mixing indium chloride dissolved in acetylacetone and tin chloride dissolved in ethanol. Indium oxide (0–20 at.% Sn-doped) (ITO) films were prepared. X-ray diffraction measurements were performed to determine the crystallinity of the ITO films which showed that they were polycrystalline with a cubic bixbyite structure. Films with a thickness of 250 nm had an optical transparency up to 89% in the wavelength range of the visible spectrum, regardless of annealing atmospheres. The ITO thin films containing 10 at.% Sn showed minimum resistivity of 8.0×10−4 Ωxa0cm when annealed at 500 °C in nitrogen. The resistivity of ITO films deposited on titanium dioxide and tantalum oxide film had a minimum value of 9.5×10−4 and 9.0×10−4 Ωxa0cm, respectively, when annealed at 500 °C; higher than that deposited on glass. The conductance vs. thickness relationship for ITO shows that, when it is deposited on top of titanium or tantalum oxide, there is an interdiffusion layer of approximately 40 nm thickness. These combinations of transparent conductive ITO thin films and titanium dioxide or tantalum oxide insulating layers may be useful for thin film electroluminescent devices.

Vibrational properties of carbon nitride films by Raman spectroscopy

The Raman spectrum of amorphous carbon nitride films deposited by Penning-type opposed target DC reactive sputtering has been studied to observe the effect of nitrogen concentration on the film bonding structure. Previous FTIR studies have shown that if nitrogen is present at levels >25 at.%, the excess above this occurs in an IR invisible bonding structure. The results presented here identify a heretofore unseen Raman peak which occurs between the commonly found G and D bands of carbon nitride films. This peak becomes visible at a nitrogen content of ∼25 at.% and thereafter increases with nitrogen content. XPS results have also shown that the peak due to nitrogen-nitrogen bonding increases in a similar manner. We therefore identify this new Raman peak as being due to nitrogen–nitrogen bonding. As the nitrogen content in the film increases, an overall shifting of the G and D bands to higher wave numbers occurs due to a change in sp2 domain size and overlapping of sp2-type bonding of CC and C N stretching bands. After annealing, the nitrogen–nitrogen peak decreases due to the breaking of the bonds and outdiffusion of nitrogen. The valence band XPS spectrum shows the interlinked carbon backbone nature of the carbon nitride solid and thus can be used as a fingerprint of the structural nature of this solid, which is significantly different from diamond-like and graphitic features.

Electroluminescent zinc sulphide devices produced by sol-gel processing

Abstract Zinc sulphide thin film electroluminescent devices doped with Mn or Tb have been produced on p-type Si substrates using a process in which doped zinc oxide films are deposited by a sol-gel drain coating method from a solution of zinc acetate containing a manganese or terbium dopant. The films are then converted to ZnS by heating them in an atmosphere containing hydrogen sulphide which replaces the oxygyn with sulphur. The composition, crystalline structure and optical properties of films have shown that complete conversion from the oxide to the sulphide takes place. The luminescent characteristics of the devices so produced have been measured as a function of the doping concentrations, film thickness, insulator thickness and driving voltage and frequency. It has been found that yellow or green luminescence can be obtained using Mn or Tb doping respectively.

Effect of surface treatment on the adhesion of DLC film on 316L stainless steel

Abstract Stainless steel type 316L is a material widely used for medical implant purposes, for example, for artificial hips. To improve their wear resistance and biocompatibility, these implants are coated with various materials, in particular diamond-like carbon (DLC). It is known that numerous parameters have an influence on coating adhesion including stress in the film, contamination and chemical bonding between the film and the substrate, and the physical properties and roughness of the substrate. DLC films have been deposited on to substrates of 316L stainless steel using a saddle field neutral beam deposition system with acetylene as the process gas. The adhesion of the films has been measured as a function of the duration of in situ etching by a neutral argon beam on DLC films with thickness ∼0.4 μm. It was measured using pull-off and Rockwell C tests. Argon pre-etching for 15 min is recommended to guarantee an optimal adhesion. The relationship between etching time and film adhesion, structure and stress was investigated. It was found that the adhesion was maximised with an etching period of 15 min and that the etching process also influenced the film structure in terms of the sp2/sp3 bonding ratio and stress. The nature of the surface oxide after etching was investigated by Fourier transform infrared spectroscopy and it was found that the adhesion is correlated with a change in the structure and thickness of the native oxide layer on the surface of the steel, being greatest when the surface oxide was nickel-rich.

Characterization of transparent conductive ITO thin films deposited on titanium dioxide film by a sol–gel process

Abstract Indium tin oxide (ITO) thin films have been deposited on titanium dioxide film by a sol–gel process. The starting solution was prepared by mixing indium chloride dissolved in acetylacetone and tin chloride dissolved in ethanol. ITO thin films containing 0–20% Sn by weight were successfully prepared by heat treatment at above 400°C. The resistivity of ITO films has been minimised by optimising the tin doping concentration in the solution. The electrical, optical and structural properties of ITO thin films were investigated. The thickness of ITO films was measured by ellipsometer. The electrical resistivity was measured by using the four-point probe method. The ITO thin films containing 10 wt.% Sn showed a minimum resistivity of ρ=9.5×10−4 Ω cm. The spectral transmittance of ITO thin films was measured in the wavelength range 200–900 nm by a UV-vis spectrometer. Films with a thickness of 250 nm have a high transmittance of 90% at 900 nm. X-Ray diffraction measurements employing CuKα radiation were performed to determine the crystallinity of the ITO films, which showed that they were polycrystalline with a cubic bixbyite structure.

Bonding structure in carbon nitride films: variation with nitrogen content and annealing temperature

Abstract The variation in the bonding structure in carbon nitride films measured by IR spectroscopy was recently described. It was shown that as nitrogen content increased, an increasing proportion of the nitrogen is incorporated with IR-invisible bonding, postulated to be nitrogen—nitrogen bonding. In this paper X-ray photoelectron spectroscopy (XPS) measurements have confirmed the presence of N–N bonding in high nitrogen content films. Annealing studies have shown that the elimination of C≡N bonding as seen from IR absorption measurements is reflected in changes in the XPS behaviour. The components of the XPS C(1s) and N(1s) peaks have been identified by comparing with Fourier transform infra red (FTIR) and Raman characteristics of the films.

Electrical properties of reactively sputtered CNx films

Carbon nitride (CN x ) films have been deposited with an opposed-target Penning-type sputtering source. The DC resistivity of films with different nitrogen content has been investigated using the four-point probe method and van der Pauw structures. The resistivity of nitrogen-containing films is considerably higher than nitrogen-free films. From temperature-dependent resistivity measurements, the activation energy was found to increase with nitrogen content and from optical absorption measurements, the optical band gap was calculated as 0.4 eV for pure carbon films and small gaps ( ∼ 0.1 eV) were found for nitrogen containing films. The resistivity and the refractive index of the films was found to correlate with the C≡N bond density.