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Atomically thin forms of layered materials, such as conducting graphene, insulating hexagonal boron nitride (hBN), and semiconducting molybdenum disulfide (MoS2), have generated great interests recently due to the possibility of combining diverse atomic layers by mechanical "stacking" to create novel materials and devices. In this work, we demonstrate field-effect transistors (FETs) with MoS2 channels, hBN dielectric, and graphene gate electrodes. These devices show field-effect mobilities of up

Pristine graphene is the strongest material ever measured. However, large-area graphene films produced by means of chemical vapor deposition (CVD) are polycrystalline and thus contain grain boundaries that can potentially weaken the material. We combined structural characterization by means of transmission electron microscopy with nanoindentation in order to study the mechanical properties of CVD-graphene films with different grain sizes. We show that the elastic stiffness of CVD-graphene is ide

The memristor, a composite word of memory and resistor, has become one of the most important electronic components for brain-inspired neuromorphic computing in recent years. This device has the ability to control resistance with multiple states by memorizing the history of previous electrical inputs, enabling it to mimic a biological synapse in the neural network of the human brain. Among many candidates for memristive materials, including metal oxides, organic materials, and low-dimensional nan

Electron tunneling through atomically flat and ultrathin hexagonal boron nitride (h-BN) on gold-coated mica was investigated using conductive atomic force microscopy. Low-bias direct tunneling was observed in mono-, bi-, and tri-layer h-BN. For all thicknesses, Fowler-Nordheim tunneling (FNT) occurred at high bias, showing an increase of breakdown voltage with thickness. Based on the FNT model, the barrier height for tunneling (3.07 eV) and dielectric strength (7.94 MV/cm) of h-BN are obtained;

Emerging two-dimensional (2D) semiconductors such as molybdenum disulfide (MoS2) have been intensively studied because of their novel properties for advanced electronics and optoelectronics. However, 2D materials are by nature sensitive to environmental influences, such as temperature, humidity, adsorbates, and trapped charges in neighboring dielectrics. Therefore, it is crucial to develop device architectures that provide both high performance and long-term stability. Here we report high perfor

Abstract Two-dimensional (2D) semiconductors hold promises for electronic and optoelectronic applications due to their outstanding electrical and optical properties. Despite a short research history, a wide range of ‘proof-of-concept’ devices based on 2D materials have been demonstrated, highlighting their impact in advanced technology. Here we review the unique properties 2D semiconducting materials and their applications in terms of electronic and optoelectronic devices. We summarize all the e

Perovskite solar cells (PSCs) based on organic monovalent cation (methylammonium or formamidinium) have shown excellent optoelectronic properties with high efficiencies above 22%, threatening the status of silicon solar cells. However, critical issues of long‐term stability have to be solved for commercialization. The severe weakness of the state‐of‐the‐art PSCs against moisture originates mainly from the hygroscopic organic cations. Here, rubidium (Rb) is suggested as a promising candidate for

The development of energy-efficient artificial synapses capable of manifoldly tuning synaptic activities can provide a significant breakthrough toward novel neuromorphic computing technology. Here, a new class of artificial synaptic architecture, a three-terminal device consisting of a vertically integrated monolithic tungsten oxide memristor, and a variable-barrier tungsten selenide/graphene Schottky diode, termed as a 'synaptic barrister,' are reported. The device can implement essential synap

Neuromorphic systems, which emulate neural functionalities of a human brain, are considered to be an attractive next-generation computing approach, with advantages of high energy efficiency and fast computing speed. After these neuromorphic systems are proposed, it is demonstrated that artificial synapses and neurons can mimic neural functions of biological synapses and neurons. However, since the neuromorphic functionalities are highly related to the surface properties of materials, bulk materi

Two-dimensional (2D) semiconductors such as transition metal dichalcogenides (TMDCs) and black phosphorous have drawn tremendous attention as an emerging optical material due to their unique and remarkable optical properties. In addition, the ability to create the atomically-controlled van der Waals (vdW) heterostructures enables realizing novel optoelectronic devices that are distinct from conventional bulk counterparts. In this short review, we first present the atomic and electronic structure

Epitaxial van der Waals (vdW) heterostructures of organic and layered materials are demonstrated to create high-performance organic electronic devices. High-quality rubrene films with large single-crystalline domains are grown on h-BN dielectric layers via vdW epitaxy. In addition, high carrier mobility comparable to free-standing single-crystal counterparts is achieved by forming interfacial electrical contacts with graphene electrodes.

2D semiconductors, including transition metal dichalcogenides (TMDs), have been widely studied recently. However, the device performance is deteriorated due to the significant contact resistance. The contact resistance of MoS₂-metal contacts decreases with the thickness of MoS₂. We obtained a Schottky barrier height as low as about 70 meV when MoS₂ is trilayer-thick. It is important to find the optimal choice of contact metal and layer thickness of MoS<sub>2</sub