Graphene quantum dots (GQDs) have received much attention due to their novel phenomena of charge transport and light absorption/emission. The optical transitions are known to be available up to ~6 eV in GQDs, especially useful for ultraviolet (UV) photodetectors (PDs). Thus, the demonstration of photodetection gain with GQDs would be the basis for a plenty of applications not only as a single-function device in detecting optical signals but also a key component in the optoelectronic integrated circuits. Here, we firstly report high-efficient photocurrent (PC) behaviors of PDs consisting of multiple-layer GQDs sandwiched between graphene sheets. High detectivity (>10¹¹ cm Hz^1/2/W) and responsivity (0.2 ~ 0.5 A/W) are achieved in the broad spectral range from UV to near infrared. The observed unique PD characteristics prove to be dominated by the tunneling of charge carriers through the energy states in GQDs, based on bias-dependent variations of the band profiles, resulting in novel dark current and PC behaviors.

We report substantially enhanced photoluminescence (PL) from hybrid structures of graphene/ZnO films at a band gap energy of ZnO ($\sim 3.3\mathrm{eV}/376\mathrm{nm}$). Despite the well-known constant optical conductivity of graphene in the visible-frequency regime, its abnormally strong absorption in the violet-frequency region has recently been reported. In this Letter, we demonstrate that the resonant excitation of graphene plasmon is responsible for such absorption and eventually contributes to enhanced photoemission from structures of graphene/ZnO films when the corrugation of the ZnO surface modulates photons emitted from ZnO to fulfill the dispersion relation of graphene plasmon. These arguments are strongly supported by PL enhancements depending on the spacer thickness, measurement temperature, and annealing temperature, and the micro-PL mapping images obtained from separate graphene layers on ZnO films.

Two-dimensional (2D) Janus transition metal dichalcogenides (TMDCs) are highly attractive as an emerging class of 2D materials, but only a few methods are available for fabricating them. These methods rely on the initial growth of 2D TMDCs in one process, followed by an additional plasma or high-temperature (T) process. To overcome these drawbacks, we employ the new approach of NaCl-assisted single-process chemical vapor deposition, which consists of three steps that proceed only by altering the temperature in situ. In the first step, MoS₂ is deposited onto a SiO₂/Si substrate with the Mo and S atoms activated in different temperature zones. In the second step, S vacancies are formed in the upper layer of the grown MoS₂ by annealing. In the third step, the vacancies are filled with activated Se atoms. Throughout the steps, NaCl lowers the melting point of the constituent atoms, while the T in each zone is properly controlled. The growth mechanism is clarified by a separate annealing experiment that does not involve a supply of activated atoms. These results highlight a simple and cost-effective approach for growing Janus MoSSe, which is more useful for fundamental studies and device applications.

Synchrotron-radiation x-ray photoelectron spectroscopy (XPS) has been used to analyze size-dependent Si $2p$ core-level spectra of Si nanocrystals (NCs) embedded in $\mathrm{Si}{\mathrm{O}}_2$ . The ${\mathrm{Si}}^0$ and suboxide XPS peaks of Si NCs shift to higher binding energies with decreasing NC size, which is based on the resolved spectra fitted by using Gaussian-Lorentzian lines for the Si oxidation states. It is also found that the shell region around Si NC bordered by $\mathrm{Si}{\mathrm{O}}_2$ consists of the three Si suboxide states, ${\mathrm{Si}}^{1+}$ , ${\mathrm{Si}}^{2+}$ , and ${\mathrm{Si}}^{3+}$ , whose densities are also strongly dependent on NC size. These results suggest that the analysis of the Si $2p$ core-level shift by XPS is useful for characterizing the size effect of Si NC at the Si $\mathrm{N}\mathrm{C}∕\mathrm{Si}{\mathrm{O}}_2$ interfaces.