The effect of tetrafluoromethane plasma post-treatment on the electrical property of tungsten oxide nanowires

The effects of tetrafluoromethane (CF4) plasma on the surface morphology, chemical compositions, and electrical property of tungsten oxide (W18O49) nanowires are investigated. The nanostructured tungsten oxide nanowires with average length of 250-350 nm were self-catalytically grown on Si substrate. By post-treatment with CF4 plasma for 10 min, the W18O49 nanowires on the substrate showed the highest current response. Longer CF4 plasma post-treatment time demonstrated higher etching effect which demolished the nanowires and resulted in lower conductivity of the samples. The disintegration of the W18O49 nanowires layer after CF4 plasma treatment, revealed physically by the decrease of the average thickness and chemically by the decrease of XRD peak ratio (I 23.0/I 26.0), was closely related to the overall electrical performance. The etching effect was further reveled by Raman spectra showing the evolution of O-W-O and W=O characteristics with the increased post-treatment time. Moreover, the improvement of the electrical property of W18O49 nanowires was elucidated by the exposure rate to explain the mechanism of plasma post treatment in three stages: passivation, degradation and ablation. The maximum exposure rate, corresponding to the maximum conductivity, was achieved by 10 min of CF4 plasma treatment. The time-differentiated exposure analyses confirmed the evolution of resistance of W18O49 nanowires on Si with different post-treatment time which supported the results of surface characterizations.