Nassiopoulou et al. Nanoscale Research Letters 2011, 6:597 http://www.nanoscalereslett.com/content/6/1/597 Page 5 of 8 Figure 4 SEM images of SiNWs formed on the blank Si wafer and on lithographically defined areas. Cross-sectional SEM images of SiNWs fabricated on non-patterned Si areas (a) and on 100 × 100-μm2 lithographically defined areas (b). defined 100 × 100-μm2 surface areas at a temperature of 30°C. The results are shown in Figure 5. In non-patterned areas, the SiNW length increases linearly with the etching time, in agreement with results in the literature [30]. On the other hand, on lithographically patterned areas, the etch rate is higher at the beginning of the process and becomes almost parallel to the etch rate of non-patterned areas after an etching time of approximately 60 min. The etch rate of large non-patterned areas was found to be approximately 0.4 μm/min, while for the 100 × 100-μm2 areas, it was 0.66 μm/min for an etching time from 0 to 60 min and 0.45 μm/min at higher etching times. We also investigated the temperature dependence of the Si NW length in a temperature ranging from 20°C Figure 5 A graph of the SiNW length versus the processing duration. The graph shows the evolution of the SiNW length as a function of the etching time by MACE at 30°C of non-patterned areas (black squares) and of 100 × 100-μm2 lithographically defined surface areas (red circles). It is clearly depicted that the etching rate is much higher on lithographically defined areas compared to the non-patterned ones. This mainly occurs at the beginning of the process.