Papageorgiou et al. Nanoscale Research Letters 2011, 6:311 http://www.nanoscalereslett.com/content/6/1/311 Page 4 of 5 Figure 4 XRD of In2O3 NWs obtained after nitridation at 500 and 600°C for different times as described in Table 1. 600°C. This is likely due to the formation of an InN shell around the In2O3, which prevents the diffusion of N into the In2O3 core. However, H2 appears to promote the conversion of In2O3into InN [14]. In addition, the two-step process lead to the effective conversion of In2O3 NWs to InN using just NH3. In this case, the temperature was ramped at 10°C/min up to 500°C and held constant over a period of 1 h, after which the temperature was ramped again slowly to 700°C in order to promote the nitridation. Recall that the In2O3 NWs were eliminated during a single-step nitridation process at 700°C using a fast ramp rate of 30°C/min. However, it should be noted that the NWs Figure 5 XRD of In2O3 NWs obtained after nitridation at 500°C under various flows of NH3 and H2 as described in Table 1. The curve at the bottom corresponds to the two-step temperature nitridation process. treated by this two-step temperature nitridation pro- cess were bent probably due to the fact that the crystal structure changes from bcc to the hexagonal wurtzite structure, and there is a non-uniform strain distribu- tion between the core and shell. The effect of the post- growth nitridations on the PL of the In2O3 NWs is shown in Figure 3. In the case of the nitridation using just NH3 for 3 h at 500°C, one may observe that there is no substantial change in the shape of the PL of the In2O3 NWs except from the fact that the PL intensity has been reduced. However, the nitridation of the In2O3 NWs using NH3 and H2 leads to a clear suppression of the peak at 550 nm, which is attributed to oxygen consis- tent with previous investigations on Ga2O3 [4]. The peak around 400 nm maybe attributed to In vacancies [15], but not O2 as commonly suggested [11-13]. How- ever, further work is required to clarify the origin of the PL peak around 400 nm. Conclusions Straight In2O3 NWs with diameters of 50 nm, lengths ≥2 μm and a bcc crystal structure have been grown on Au/Si(001) via the wet oxidation of In at 850°C. These exhibited two broad peaks in the PL, centred around 400 and 550 nm. The post-growth nitridation of In2O3 NWs was found to be effective by using NH3 and H2 at 500 and 600°C or a two-step temperature, nitridation process at 500 and 700°C. This lead to a suppression of the PL peak around 550 nm related to O2 consistent with previous investigations on Ga2O3. In contrast, sin- gle-step temperature, nitridations using just NH3, car- ried out with fast ramp rates above 600°C lead to the complete elimination of the In2O3 NWs, while they were not effective at 500 and 600°C. Abbreviations APCVD: atmospheric pressure chemical vapour deposition; bcc: body centred cubic; DI: de-ionised; MO: metal-oxide; NWs: nanowires; NWSCs: nanowires solar cells; PL: photoluminescence; QT: quartz tube; RT: room temperature; SEM: scanning electron microscope; VLS: vapour-liquid-solid; XRD: X-ray diffraction. Acknowledgements This work was supported by the Research Promotion Foundation of Cyprus under grant BE0308/03. Author details 1Department of Physics, Research Centre of Ultrafast Science, University of Cyprus, P.O. Box 20537, Nicosia, 1678, Cyprus. 2Nanostructured Materials and Devices Laboratory, Department of Mechanical Engineering, Materials Science Group, School of Engineering, University of Cyprus, P.O. Box 20537, Nicosia, 1678, Cyprus. Authors’ contributions section MZ and PP carried out the growth, scanning electron microscopy and x-ray diffraction measurements. AO carried optical characterization. All authors read and approved the final manuscript.