Papageorgiou et al. Nanoscale Research Letters 2011, 6:311 http://www.nanoscalereslett.com/content/6/1/311 quartz tube (QT). Another quartz boat with ≈5 ml of de-ionised (DI) H2O was positioned at the inlet of the tube. After loading the boats at room temperature (RT), Ar (99.999%) was introduced at a flow rate of 500 stan- dard cubic centimetres per minute (sccm) for 10 min. Following this, the temperature was ramped to 850°C under a flow of 50 sccm Ar using a ramp rate of 30°C/ min. Upon reaching the growth temperature (TG), the flow of Ar was maintained at 50 sccm for 30 min in order to grow the In2O3 NWs after which the reactor was allowed to cool down in a flow of 50 sccm of Ar for at least 30 min. The sample was always removed only when the temperature was lower than 100°C. The nitridation of the In2O3 NWs was carried out in a new 1” QT without any solid precursors. After loading each sample with In2O3 NWs from the downstream side, a flow of 500 sccm Ar was introduced for 10 min after which the temperature was ramped to the nitrida- tion temperature (TN) under a flow of NH3 that varied between 125 and 250 sccm using a ramp rate of 30°C/ min. Upon reaching TN, the same flow of NH3 was maintained for various times between 1 and 6 h after which the reactor was allowed to cool down to RT under the same flow of NH3. A list of the different tem- peratures, nitridation times and NH3 gas flows used for the nitridation of the In2O3 NWs are shown in Table 1. Similarly nitridation was carried out using NH3 and H2. In this case, the temperature was ramped to 500°C under a flow of NH3 and H2 whose relative flows varied using a ramp rate of 30°C/min. Upon reaching TN, the same flow of NH3 and H2 was maintained for 1 h. The total flow of NH3 and H2 was kept constant at 200 sccm and a list of the different flows of H2 is listed in Table 1. Finally, we carried out a two-step tempera- ture process. In this case, the temperature was ramped to 500°C under 125 sccm of NH3 using a ramp rate of 10°C/min. Upon reaching TN, the same flow of NH3 was maintained for 1 h. Then, the temperature was ramped to 700°C and the same flow of NH3 was maintained for Table 1 Summary of post-growth nitridation conditions for the conversion of In2O3 NWs to InN (I) TN (°C) (II) t (h) (III) %H2 CVD797 500°C CVD850 500°C, 3 h CVD855 10 CVD788 600°C CVD853 500°C, 6 h CVD856 20 CVD790 800°C CVD795 600°C, 1 h CVD857 40 CVD791 900°C CVD849 600°C, 2 h CVD859 80 CVD848 600°C, 3 h Initially a flow of 500 sccm of Ar was introduced into the reactor after which the temperature was ramped to TN at 30°C/min under a flow of (I) 250 sccm of NH3, (II) 125 scmms of NH3 and (III) under different flows of NH3 and H2, but keeping the total flow constant at 200 sccm. Upon reaching TN, the same flows were maintained for 1 h at various temperatures (I), different nitridation times at 500 and 600°C (II) and for 1 h at 500°C (III). Page 2 of 5 30 min after which the reactor was allowed to cool down to RT. The morphology of the as grown In2O3 NWs and those treated with NH3 were examined with a TESCAN scanning electron microscope (SEM), while their crystal structure and phase purity were investigated using a SHIMADZU, X-ray diffraction (XRD-6000), with Cu-Ka source, by performing a scan of θ - 2θ in the range between 10° and 80°. Finally, PL measurements were carried using above bandgap (approx. 3.75 eV [6]) exci- tation at 267 nm. The pulse excitation was the second harmonic of a beam from an optical parametric ampli- fier pumped with a mode-locked TiSapphire laser. The pulses were 100 fs FWHM at a repetition rate of 250 kHz. The energy per pulse incident on the samples was 40 pJ over a spot of 2 mm in diameter. Results and discussion Previously, we obtained In2O3 NWs by dry oxidation at 700°C [7]. A high yield of In2O3 NWs with an average diameter of ≈100 nm and lengths of ≈1 μm was obtained on Si(111) and quartz. However, these In2O3 NWs were slightly tapered; their diameters were larger and lengths were shorter compared to the In2O3 NWs obtained here by wet oxidation. Moreover, the distribu- tion of the In2O3 NWs obtained by wet oxidation was far superior and much more uniform compared to those obtained by dry oxidation. A typical image of In2O3 NWs that were obtained at TG = 850°C by wet oxidation is shown in Figure 1. It should be pointed out that a high yield and uniform distribution of In2O3 NWs extending over 1 cm2 was obtained when the distance between the In and the Au/n+Si (001) was ≥15 mm, which led to a light blue-like deposit. The In2O3 NWs Figure 1 Typical SEM image of In2O3 NWs obtained on 1.1 nm Au/Si(001).