*3.1.2.1. Half-unit-cell thickness of alpha-Fe2O3 semiconductor nanosheets*

Recently, Wei's group successfully synthesized free-standing half-unit-cell α-Fe2O3 nanosheets using CuO nanoplate as the template [30]. The layered iron hydroxide nanosheets are first prepared on CuO template surface by the mutually promoted slow interfacial reactions of Fe2+ hydrolysis and CuO-etching process at a low temperature of 25°C for a whole day, which

**Figure 6.** (a) Schematic of synthesis strategy of α-Fe2O3 nanosheets. (b) TEM image of the α-Fe2O3 nanosheets. The in‐ sets show the HRTEM image and the Tyndall effect of the α-Fe2O3 nanosheets. (c) AFM image and (d) XRD pattern of the α-Fe2O3 nanosheets [30]. (e–g) TEM images of the assembled ultrathin ZrS2 nanodiscs obtained by rotating TEM holder under different angle. (h) HRTEM side-view image of multiply stacked 1.6-nm-thick ZrS2 nanodiscs [33].

is beneficial for the synthesis of ultrathin nanosheets. When CuO template is etched out, a heat treatment is carried out for the dehydrogenation of Fe hydroxide nanosheets, which leads to the formation of the stable and free-standing α-Fe2O3 nanosheets.

AFM and TEM image provide direct evidence for successful exfoliation of the sample. As shown in **Figure 6b**, **c**, the lateral size of α-Fe2O3 nanosheets is up to about 1 μm, and thickness is about 0.55–0.59 nm. The XRD pattern of the α-Fe2O3 shown in **Figure 6d** exhibits only a broad and weak diffraction peak corresponding to the (110) orientation plane of α-Fe2O3. It is interesting to note that ultrathin α-Fe2O3 nanosheet shows an intrinsic ferromagnetism of 0.6 μB/atom at 100 K and remains ferromagnetism at room temperature.
