Effects of oxygen gettering and target mode change in the formation process of reactively RF sputtered WOx thin films

Yamamoto, Akihisa; Abe, Yoshio; Kawamura, Midori; Sasaki, Katsutaka

doi:10.1016/s0042-207x(02)00153-7

Cited by 37 publications

(31 citation statements)

References 7 publications

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“…Consequently, oxide materials have become more interesting for tribological applications due to their expected ''oxidation stability'' and their low tribo-oxidation sensitivity [1]. There are few research works dealing with tungsten oxide with different oxygen contents focused mainly on electrical and optical properties [2]. Only recently, the structural and the mechanical properties of the W 100Àx O x , with x from 0 to 75 at%, have been studied in an author's work [3].…”

Section: Introductionmentioning

confidence: 99%

Tungsten oxide with different oxygen contents: Sliding properties

Polcar

Parreira

Cavaleiro

2007

Vacuum

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In this study, tungsten oxide coatings with 13 and 75 at% of oxygen were prepared by DC reactive magnetron sputtering from a pure W target in an Ar+O 2 atmosphere. The coating hardness (H) decreased with increasing oxygen content from 25 to 7.7 GPa. The values of H/E ratio were 0.08 and 0.07 for W 87 O 13 and W 25 O 75 , respectively.The tribological measurements were carried out on a pin-on-disc tribometer at room temperature, with a load of 5 N and steel 100Cr6, ceramic Si 3 N 4 and Al 2 O 3 balls as sliding partners. The wear track and wear debris were visualised by scanning electron microscopy and the chemical composition of the later was estimated by energy-dispersive X-ray analysis. The friction coefficient was rather high in case of the W 87 O 13 coating reaching values in the range from 0.7 to 0.75 for both counterpart materials, and slightly lower for W 25 O 75 ($0.50). The coating wear rate decreased with increasing oxygen content with the Al 2 O 3 ball, while using Si 3 N 4 ball as a counterpart showed an opposite trend. The coating with low oxygen content was more resistant to abrasive wear. r

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Section: Introductionmentioning

confidence: 99%

Tungsten oxide with different oxygen contents: Sliding properties

Polcar

Parreira

Cavaleiro

2007

Vacuum

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“…exhibit electrochromic behaviour) [1] and, more recently, due to their applications in gas sensor devices [2]. These studies were focus to the stoichiometric compound WO 3 or WO 3Àx (x = 0 -1). However, works concerning all full range of compositions between pure tungsten to tungsten trioxide (WO 3 ) are not common in the literature.…”

Section: Introductionmentioning

confidence: 99%

“…However, works concerning all full range of compositions between pure tungsten to tungsten trioxide (WO 3 ) are not common in the literature. Only recently, Yamamoto et al [3] have studied the electrical and optical properties of W -O coatings deposited by radio frequency (RF) reactive magnetron sputtering. Moreover, according Lugscheider et al [4], these coatings have good tribological properties, but their mechanical properties were not characterized yet.…”

Section: Introductionmentioning

confidence: 99%

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Synthesis, structural and mechanical characterization of sputtered tungsten oxide coatings

2006

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Tungsten oxide coatings were deposited without substrate bias by DC reactive magnetron sputtering of a tungsten target using oxygen as reactive gas. By tuning the partial pressure of oxygen ( p O 2 /p Ar ) between 0 and 4, the oxygen content of the films was changed from 0 to 75 at.%. The structure of the films (investigated by X-ray diffraction) depends on their oxygen content. For low oxygen contents, the a-W and h-W 3 O phases were observed (< 30 at.%), and with the increase of oxygen content (30 at.% < O < 67 at.%) the structure became amorphous. A transition region was obtained for oxygen content between 67 at.% and 75 at.%, and when O > 75 at.%, a nanocrystalline (WO 3 ) structure was reached.The hardness and Young's modulus were evaluated by depth sensing indentation. The decrease in hardness followed the four different ranges of chemical compositions accordingly, from å 23 GPa for pure W down to å 7 GPa for WO 3 films. A similar behaviour was observed for the Young's modulus, which ranged from 450 GPa to 150 GPa. The cohesion/adhesion of the films were investigated using a scratch-test apparatus. These coatings displayed a low adhesion (critical load, L c < 15 N) to the steel substrate because the depositions were carried out intentionally without an adhesion interfacial layer. D

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“…However, the intrinsic colours possible to be achieved in a single oxide system are very limited. For example in W-O system, besides the different tonalities of grey, only the dark blue can be obtained for slightly substochiometric WO 3 compound [2]. The pallet of colours exhibited by WO 3 coatings is due to interferometric effects.…”

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Electron microscopy characterization of W-O multilayers

Parreira¹,

Polcar²,

Pei³

et al. 2009

Microsc Microanal

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In the decorative field, besides the optical characteristics needed for achieving desired colours, the material should have suitable properties able to assure the daily use of the component without significant degradation [1]. Oxides are well known materials with a high wear and corrosion resistance which make them a preferential choice of coatings for environmental protection. However, the intrinsic colours possible to be achieved in a single oxide system are very limited. For example in W-O system, besides the different tonalities of grey, only the dark blue can be obtained for slightly substochiometric WO 3 compound [2]. The pallet of colours exhibited by WO 3 coatings is due to interferometric effects. Recently, it was shown that playing with the gradient of the chemical composition of W-O layers it was possible to tune the global colour of the coatings, which made this system an attractive candidate for decorative applications [3].In this study the microstructural characterization of W-O coatings by transmission and scanning electron microsocopies (TEM and SEM, respectively) are presented. The coatings were deposited by reactive magnetron sputtering in RGPP mode (reactive gas pulsing process) [4]. SEM micrographs show the multilayer character of the deposited coatings whatever the pulsing parameters used in the deposition were (T -period, and t ON -injection time) [5].X-ray diffraction revealed that the structure of the coatings deposited by RGPP was in agreement to the multilayer effect, i.e. the detected phases were related to the W-rich and the O-rich layers forming the stacking [5]. All the coatings exhibited a mixture of α-W, β-W 3 O and quasi-crystalline W-O (a broad peak centred at 2θ ≈ 25 º, corresponding to the more intense peaks of WO 3 ) phases attributed to the W layer, a transition layer and the compound layer, respectively [5]. Using TEM, even in high-resolution mode, only 2 layers are possible to be distinguished (Fig. 1a), and the β-W 3 O phase could hardly be observed (see Fig. 1b), although electron diffraction (insert of Fig. 1a) confirmed its existence. The W-rich layer showed a fairly crystalline structure in comparison with the featureless aspect of the nanocrystalline O-rich layer.In order to distinguish and calculate the extension of each of the layers that form the stacking, the cross section of the coatings was analysed by energy filtering images (GIF) which allows evaluating the O concentration across the film thickness. The GIF images were obtained by subtraction of two images taken before and after the O-K edge defined at 530.6 eV, i.e. at -15 eV and +15 eV, respectively. Thus, the new image was generated by the electrons with energy between 515.6 and 545.6 eV as shown in Fig. 2a. By integration of the intensities in a selected area of Fig. 2a, the oxygen distribution across the coating thickness can be accessed (Fig. 2b). In this particular case, the definition of the stacking layers, including the transition layer, can be achieved, allowing to calculate their thickness, even i...

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Effects of oxygen gettering and target mode change in the formation process of reactively RF sputtered WOx thin films

Cited by 37 publications

References 7 publications

Tungsten oxide with different oxygen contents: Sliding properties

Tungsten oxide with different oxygen contents: Sliding properties

Synthesis, structural and mechanical characterization of sputtered tungsten oxide coatings

Electron microscopy characterization of W-O multilayers

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