PL Maps of 2D Materials
Two-dimensional (2D) materials such as graphene are attracting increasing scientific attention and funding. Using a Klar microscope, Prof. Yi Gu’s research group at Washington State University investigated the PL emission from α- and β-phase In2Se3 layers and junctions between the two. The peak-fitting feature was utilized to detect subtle shifts in PL energy, which were due to local temperature variations from laser heating. The temperature map proved that the α/β junction has a huge Seebeck coefficient. These greatly enhanced thermoelectric properties are attributed to the Schottky energy barriers at the junction interface, which lead to hot carrier transport and shift the balance between thermally and field-driven currents.
(a) PL spectra from the α-In2Se3 layer and the junction area; (b) PL energy map of the junction device; (c) corresponding temperature map obtained from the PL energies. After Wang et al., J. Phys. Chem. Lett. 8, 2887-2894 (2017).
Additionally, MoS2 and In2Se3 heterostructures fabricated by Prof. Gu’s group were analyzed in a similar manner. MoS2 has a PL emission peak centered near 1.84 eV. Even though this peak is very weak at room temperature, the sensitivity of the Klar microscope was able to obtain a good signal. This emission is nearly completely eliminated at the junction with In2Se3 even though MoS2 is layered on top of In2Se3. The suppression of PL may be due to electron-hole separation at the interface.
Left: In2Se3 – MoS2 heterostructures formed with In2Se3 on bottom and MoS2 on top. Electrodes are placed on top of both materials. The green box shows the region mapped on the right. Right: A 38×32 µm PL map of the MoS2 emission peak area at 1.84 eV. The map is composed of approximately 19,500 spectra, collected, fitted, and plotted using KlarFit.