J.F. Pierson

Transmittance enhancement and optical band gap widening of Cu2O thin films after air annealing

Cu2O thin films have been grown on glass substrates at room temperature by reactive magnetron sputtering. As-deposited films exhibit high electrical resistivity and low optical transmittance. To improve the film properties, post annealing treatments in air at various temperatures have been performed. Low temperature annealing (<300 °C) avoids the film oxidation into CuO and the films remain single-phased. In this temperature range, the annealing in air enhances the transmittance in the visible region due to the decrease of the defect scattering. Moreover, the optical band gap of Cu2O thin films is enlarged from 2.38 to 2.51 eV with increasing annealing temperature. The increase of optical band gap accompanying the reduction of Urbach energy indicates that the widening of optical band gap may result from the partial elimination of defect band tail after thermal annealing in air. Combining experimental results with recent reported calculations, the peak at about 1.7 eV in photoluminescence spectra is assign...

On the deactivation of the dopant and electronic structure in reactively sputtered transparent Al-doped ZnO thin films

We report on the possible origin of electrical heterogeneities in 4 at% Al-doped ZnO (AZO) reactively sputtered films. It is found through the Zn L3 and Al K edge x-ray absorption near-edge structure that a fraction of the Al dopant is deactivated by its positioning in octahedral conformation with oxygen. This fraction as well as the conductivity, optical bandgap and c-axis parameter of ZnO wurtzite are all found to depend on the sample position during deposition. The present results suggest the formation of a metastable Al2O3(ZnO)m homologous phase that degrades the electrical conductivity.

Influence of oxygen flow rate on the structural and mechanical properties of reactively magnetron sputter-deposited Zr–B–O coatings

Abstract Zr–B–O coatings were deposited on both construction steel and stainless steel substrates by magnetron sputtering of ZrB 2 targets in reactive Ar–O 2 gaseous mixtures. In this paper, the deposition rate and the structural and mechanical properties of Zr–B–O films will be investigated as a function of the inlet oxygen flow rate. We will show that two domains are available owing to the sputtering phenomena. In the former, the coating enrichment is quite proportional to the oxygen flow rate. Even for a weak oxygen enrichment, amorphization of the Zr–B–O films is observed which also decreases both their intrinsic internal stress and microhardness, thus improving the physical quality of the coatings. As the oxygen flow rate increases, the amorphous coatings, initially composed of a single-phase ZrB 2− x O x solid solution, present an increasing fraction of amorphous ZrO 2 , and then, of amorphous B 2 O 3 simultaneously with the disappearance of the metallic solid solution. Higher oxygen flow rates allow the synthesis of optically transparent amorphous oxide mixture films, the composition and mechanical properties of which become independent of the inlet oxygen flow rate.

Structural, optical and electrical properties of reactively sputtered iron oxynitride films

In this paper, the properties of iron oxynitride films prepared by magnetron sputtering of an iron target in Ar–N2–O2 reactive mixtures using constant nitrogen and argon flow rates are presented. The oxygen flow rate varied from 0 to 2 sccm. The thickness of the films deposited on silicon substrates ranged from 0.2 to 2 µm. The structure and chemical composition of these films were determined by x-ray diffraction and Rutherford backscattering spectrometry, respectively. These studies revealed the formation of a new fcc intermediate phase of iron oxynitride FeNxOy films between iron nitride (e-Fe2N) and an oxide close to Fe2O3. In addition, optical and electrical properties measurements at room temperature were investigated during this work. Refractive index and extinction coefficient were determined from spectroscopic ellipsometry. The electrical behaviour of the films evolved from a metallic one to a semiconductor one which is consistent with other investigations. In order to determine the morphology of the films, scanning electron microscopy was used.

Structure-properties relationship in reactively sputtered Ag-Cu-O films

Ag–Cu–O films were deposited on glass substrates by pulsed dc sputtering of a silver–copper target (Ag50Cu50) in reactive Ar–O2 mixtures. The film chemical composition was estimated by x-ray energy dispersive spectrometry and the structure was studied by x-ray diffraction (XRD). Optical properties (reflectance and transmittance) and room temperature electrical resistivity were evaluated using spectrophotometry and the four point probe method, respectively. Since silver atoms are less reactive versus oxygen than copper ones, the increase in the oxygen flow rate introduced into the deposition chamber induced the preferential oxidation of sputtered copper atoms. XRD analysis showed that the structure of the deposited films can be divided into three domains. At low oxygen flow rate, the films were biphased (metallic silver-based solid solution and crystalline copper-based oxide). At intermediate oxygen flow rate, the films were x-ray amorphous (grain size lower than 2 nm). At high oxygen flow rate, the films contained a crystalline silver–copper oxide phase and a crystalline unknown phase. Thanks to the absorption band of silver in the UV range, reflectance measurements were used to show the occurrence of metallic silver phase in the films. It was shown that the chemical environment of silver atoms in the x-ray amorphous region evolved from metallic to oxide when the oxygen flow rate increased. Transmittance evolution versus the oxygen flow rate were well correlated with that of the electrical resistivity. The evolution of Ag–Cu–O film properties was discussed in connection with the structure and chemical composition.

Low temperature ZrB2 remote plasma enhanced chemical vapor deposition

Abstract Deposition of zirconium diboride films on Zircaloy-4 substrates at 733 K over 20 cm is carried out by remote plasma enhanced chemical vapor deposition (RPECVD). Different post-discharge compositions (Ar–H 2 , Ar–H 2 –BCl 3 and Ar–BCl 3 ) are tested in several process configurations. Experiments performed by thermal CVD and RPECVD with Ar–H 2 post-discharge show that the deposition of ZrB 2 films on oxidized Zircaloy-4 is impossible at temperature lower than 853 K. Ar–H 2 –BCl 3 post-discharges do not give to adherent films on oxidized Zircaloy-4 at a temperature lower than 753K. It is shown that ZrB 2 thin films can be synthesized by using flowing Ar–BCl 3 microwave post-discharges. Chlorine must etch the zirconia protective layer before zirconium diboride is synthesized. Therefore, the control of thickness of this zirconia layer by a previous oxidation treatment gives homogeneous deposition. The structure of the films has been determined to be nanograins of ZrB 2 dispersed in an amorphous solid solution of boron and zirconium oxides. The origin of the boron species incorporated in the ZrB 2 films is attributed to the eching of the quartz tube by chlorine.

Characterization of Silver Oxide Films Formed by Reactive RF Sputtering at Different Substrate Temperatures

Silver oxide (A2O) films were deposited on glass and silicon substrates held at temperatures in the range 303–473 K by reactive RF magnetron sputtering of silver target. The films formed at room temperature were single phase Ag2O with polycrystalline in nature, while those deposited at 373 K were improved in the crystallinity. The films deposited at 423 K were mixed phase of Ag2O and Ag. Atomic force micrographs of the films formed at room temperature were of spherical shape grains with size of 85 nm, whereas those deposited at 473 K were with enhanced grain size of 215 nm with pyramidal shape. Electrical resistivity of the single phase films formed at room temperature was 5.2 × 10−3 Ωcm and that of mixed phase was 4.2 × 10−4 Ωcm. Optical band gap of single phase films increased from 2.05 to 2.13 eV with the increase of substrate temperature from 303 to 373 K, while in mixed phase films it was 1.92 eV.

Bacterial adhesion on biomedical surfaces covered by micrometric silver Islands

A set of Cu-Mn-O and Ag-Cu-Mn-O films were sputter-deposited onto polished Ti-6Al-4V coupons and the microbiological adherence of Staphylococcus sp. was studied in these biomedical surfaces modified by using advanced ternary and quaternary oxides, these latter incorporated micrometric silver islands. Silver is known to have a natural biocidal character and its presence in the surface of Ti-6Al-4V forming large micrometric islands. In principle, predicted to enhance the antimicrobial properties of biomedical surfaces. Microbial adhesion tests were performed using collection strains and six clinical Staphylococcus aureus and Staphylococcus epidermidis strains. The adherence study was performed using a previously published protocol by Kinnari et al. Collection strains and clinical strains showed decreased adherence to modified materials; however, only on the clinical strains were there statistically significant differences between Cu-Mn-O and Ag-Cu-Mn-O containing silver islands. Nanocrystalline silver dissolves and releases both Ag(+) and Ag(0) whereas other silver sources release only Ag+. We can conclude that nanocrystalline silver coating, confirmed by XRD, appears to alter the biological properties of the solution, particularly antimicrobial activity.

Thermochromic effect in NdNiO3−δ thin films annealed in ambient air

The synthesis of NdNiO3 perovskite structure was achieved by soft post deposition annealing of initially amorphous thin films reactively sputter deposited on silicon substrates. The physical measurements were fully consistent with the properties expected for the thermochromic NdNiO3 phase. Upon heating, the optical transmission that was correlated with the electrical properties decreased in the infrared domain showing a thermochromic effect in this optical region. The metal–insulator transition temperature was found to be −68 °C for the specimen tested and the jump in resistance at the transition was 1.4 orders of magnitude. The state-of-the-art methods that normally involve an annealing at a high oxygen pressure (200 × 105 Pa) or epitaxial stabilization were considerably improved in this work by the use of dc sputtering and the optimization of the deposition conditions. Therefore, the novel soft process proposed here opens up numerous research possibilities.

Low temperature growth mechanism of zirconium diboride films synthesised in flowing microwave Ar–BCl3 post-discharges

Abstract Zirconium diboride films are synthesised at 460°C by a flowing microwave Ar–BCl 3 post-discharge CVD process to coat Zircaloy-4 substrates. As a zirconium tetrachloride flow is of no use to synthesise these films, they are grown by a mechanism which consists of a diffusion step. To identify how this step occurs, characteristics of the films are compared with those that could be expected when three different diffusion processes are considered: boron diffusion, zirconium diffusion and BCl 3 diffusion. As the last process requires a high porosity of the film (about 50%) to occur, it cannot be referred to describe the ZrB 2 synthesis mechanism. The physico-chemical and structural characteristics of ZrB 2 films do not help to distinguish the two processes involving a diffusion step in solid state. Only a profilometric study of the film growth direction has shown that zirconium diffuses into the Zircaloy-4 substrate from the core to the solid–gas interface. This mechanism implies that zirconium tetrachloride is also synthesised at the surface of the film. The influence of this mechanism on the behaviour of the Zircaloy-4 alloying elements has also been analysed. A precise description of the tin behaviour is provided and its consequences on adhesion of ZrB 2 films are examined.