Two-dimensional (2D) materials have recently provided a new perspective on optoelectronics because of their unique layered structure and excellent physical properties. However, their potential use as optoelectric devices has been limited by the trade-off between photoresponsivity and response time. Here, based on a vertically stacked atomically thin p-n junction, we propose a gap-mode plasmon structure that simultaneously enables enhanced responsivity and rapid photodetection. The atomically thin 2D materials act as a spacer for enhancing the gap-mode plasmons, and their short transit length in the vertical direction allows fast photocarrier transport. We demonstrate a high responsivity of up to 8.67 A/W with a high operation speed that exceeds 35 MHz under a 30 nW laser power. Spectral photocurrent, absorption, and a numerical simulation are used to verify the effectiveness of the gap-mode plasmons in the device. We believe that the design strategy proposed in this study can pave the way for a platform to overcome the trade-off between responsivity and response time.

Stacking of atomically thin layers of two-dimensional materials has revealed extraordinary physical phenomena owing to van der Waals (vdW) interaction at the interface. However, most of the studies focused on the transition metal dichalcogenide (TMD)/TMD heterostructure, while the interlayer coupling of the TMD/hexagonal boron nitride (h-BN) heterostructure has not been extensively explored despite its importance. In this study, the temperature-dependent interlayer coupling is demonstrated in a heterostructure of molybdenum disulfide (MoS₂) and h-BN. The interface between MoS₂ and the insulating substrate exerts a significant spectroscopic impact on MoS₂ through substrate-induced local strain, charged impurity, and vdW interactions. Under non-resonant conditions, temperature-dependent peak shifts in Raman and photoluminescence (PL) spectra of MoS₂ reveal the evolution of interlayer coupling. Phonon frequencies and PL peak energies at different temperatures demonstrate how substrate-induced strain, impurity, and vdW interactions at the interface influence phonon vibration and excitonic transition of MoS₂. Under resonant conditions at low temperature, anomalous Raman modes appear in the MoS₂/h-BN heterostructure because of the enhanced electron-phonon coupling and vdW interactions. The anomalous Raman modes are quantitatively investigated by the deconvolution of the resonance Raman spectra and described by interlayer coupling at low temperature, in agreement with complementary indications from the temperature-dependent evolution of non-resonant Raman and PL spectra.

Graphene, a single atomic layer of sp²-hybridized carbon, has immense potential as a transparent conducting material in electronic applications owing to its superior properties, including optical transparency and high conductivity. Particularly, the tunable work function of graphene enables the integration of graphene electrodes with various electronic devices. To achieve high performance in graphene-based devices, effective charge transport between the graphene electrode and the semiconducting material needs to be optimized; this is closely related to the modulation of the Schottky barrier (SB). In this study, we investigate the tunable charge transport properties as a function of graphene doping in n-channel thin-film transistors (TFTs) in terms of the electrical characteristics and low-frequency noise (LFN) behaviors. Alkali metal carbonates tuned the work function of graphene, resulting in a dramatic decrease in the SB and an improvement of the carrier injection in n-channel TFTs. The electrical performance of the TFTs was evaluated by extraction of the field-effect mobilities and ratio of contact resistance to total resistance. Furthermore, the level of contact noise created by the barrier height fluctuation and relative contribution of channel noise and contact noise in the TFTs was investigated by LFN measurements to demonstrate the tunable charge transport. Our findings therefore provide new insights into the tunable charge transport mechanism in graphene-based devices and reveal the immense potential of graphene as electrodes in high performance flexible and transparent displays.

Flexible logic circuits and memory with ultra-low static power consumption are in great demand for battery-powered flexible electronic systems. Here, we show that a flexible nonvolatile logic-in-memory circuit enabling normally-off computing can be implemented using a poly(1, 3, 5-trivinyl-1, 3, 5-trimethyl cyclotrisiloxane) (pV3D3)-based memristor array. Although memristive logic-in-memory circuits have been previously reported, the requirements of additional components and the large variation of memristors have limited demonstrations to simple gates within a few operation cycles on rigid substrates only. Using memristor-aided logic (MAGIC) architecture requiring only memristors and pV3D3-memristor with good uniformity on a flexible substrate, for the first time, we experimentally demonstrated our implementation of MAGIC-NOT and -NOR gates during multiple cycles and even under bent conditions. Other functions, such as OR, AND, NAND, and a half adder, are also realized by combinations of NOT and NOR gates within a crossbar array. This research advances the development of novel computing architecture with zero static power consumption for battery- powered flexible electronic systems.

In the recent years, transition-metal dichalcogenides such as MoS₂ have attracted considerable attention owing to their unique structure and electronic properties. Chemical vapor deposition (CVD) is a popular method for producing MoS₂ flakes with different shapes. Here, we report an effective method for achieving a broad range of shape evolution in CVD-grown monolayer MoS₂ flakes. By controlling the S and MoO₃ temperatures, the shape of the monolayer MoS₂ flakes was varied from hexagonal to triangular via intermediate shapes such as truncated and multi-apex triangles. The shape evolution of the MoS₂ flakes can be explained by introducing the term "nominal Mo: S ratio", which refers to the amount of loaded MoO₃ and evaporated S powders. By using the nominal Mo: S ratio, we predicted the potential reaction atmosphere and effectively controlled the actual proportion of MoO_3−x with respect to S in the growth region, along with the growth temperature. From the systematic investigation of the behavior of the shape evolution, we developed a shape-evolution diagram, which can be used as a practical guide for producing CVD-grown MoS₂ flakes with desired shapes.