Operando soft X-ray spectromicroscopic measurement and the use for high-performance devices and circuits

Two-dimensional (2D) atomic layers, such as graphene and MoS2, are promising for device applications, such as a field effect transistor (FET), a laser, and even millimeter-wave/terahertz optoelectronic circuits for the future optical and wireless communications. Furthermore, the materials have their excellent electronic properties, such as the giant carrier mobility in graphene, and their ultrathinness suppresses the so-called short channel effects that have been problems in performance of conventional electronics. However, there are several issues to be resolved for the actual device applications of the 2D atomic layers. In addition to immaturities in device processing, ironically, the ultrathinness produces a demerit for device application, i.e., the sensitivity of electronic states to environments. This indicates that electronic states of these are easily modulated due to interfaces in devices. To solve the issues, operando (=in operation) soft X-ray spectromicroscopies, such as operando X-ray absorption and photoelectron nanospectroscopies, have been developed. The spectroscopies were proven to be applicable in analyzing physics in device operation mechanisms, including FETs using graphene or MoS2 as the channels. The obtained results clearly indicated that the electronic states are largely modulated at the interfaces in devices, leading to degradation of the performances, but also provided the actual solutions for improvements.