Dehzangi et al. Nanoscale Research Letters 2012, 7:381 http://www.nanoscalereslett.com/content/7/1/381 Page 3 of 9 Figure 2 Schematic presentation of LAO process on SOI sample surface. etching which, accordingly, the accuracy and precaution are important. To remove the undesired Si area, KOH was used as an etchant. The KOH concentration also affects the quality of the etched surface. Referring to the previous reports in KOH wet etching [33-37], we used a 30 wt.% KOH solution, saturated with isopropyl alcohol (IPA) at 63°C to remove all the non-protected silicon areas. IPA was used in this work as initiator to improve the cleaning process providing smooth surface. IPA reduces the etch rate, hence improving the surface roughness and making the etching process more controllable. The best optimized condition was the solution of 30 wt.% KOH with 10 vol.% IPA for wet etching at 63°C, immersing time for 20 s, and stirring at 600 rpm. The stirring of the solution is to en- sure the uniformity of the etching process. The final structure was obtained by removing the oxide layer using HF acid (Figure 3b,d). In fact, several models have been proposed for the silicon anisotropic etching mechanism in aqueous KOH, which we have chosen as the method by considering of the crystallographic planes for a cubic crystal. In a cubic crystal, the (110) plane is normal to the diagonal of a surface plane, and the (111) plane is normal to a volume diagonal. For the atoms located on the (100) plane, they have two dangling bonds and two bonds remaining in the crystal. Like in our case, when a (100) plane is exposed by the etching solution, OH− can attach to the dangling bonds and loosen the other bonds, so they can break easily. The KOH etching of (100)-oriented silicon provides V-shaped grooves [33]. In Figure 4, the high magnification transmission elec- tron microscopy (TEM) micrograph of the etch depth for nanowire profile is shown for another sample. The adjacent gate is not shown in the picture. The SOI with 90 nm thickness of the Si layer makes the whole struc- ture, after etching with the thickness of 90 nm. Both SG and DG structures have 100 nm for the channel width, 200 nm for the channel length, and 4 μm for the dis- tance between the source and the drain. The gap be- tween the gate and the channel for both structures were 100 nm (Figure 3). The electrical connections were pro- vided by two pads considered as source and drain with the gate work function of 5.12 eV. The Si thickness of the whole structure including the channel, gate pad(s), source and drain contacts were 90 nm with the same p- type doping concentration (1015). Figure 3 AFM and SEM images of DG (a,b) and SG (c,d) JLTs after LAO and etching process.