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After a decade of intensive research on two-dimensional (2D) materials inspired by the discovery of graphene, the field of 2D electronics has reached a stage with booming materials and device architectures. However, the efficient integration of 2D functional layers with three-dimensional (3D) systems remains a significant challenge, limiting device performance and circuit design. In this review, we investigate the experimental efforts in interfacing 2D layers with 3D materials and analyze the properties of the heterojunctions formed between them. The contact resistivity of metal on graphene and related 2D materials deserves special attention, while the Schottky junctions formed between metal/2D semiconductor or graphene/3D semiconductor call for careful reconsideration of the physical models describing the junction behavior. The combination of 2D and 3D semiconductors presents a form of p-n junctions that have just marked their debut. For each type of the heterojunctions, the potential applications are reviewed briefly.

Tellurium (Te) has a trigonal crystal lattice with inherent structural anisotropy. Te is multifunctional, e.g., semiconducting, photoconductive, thermoelectric, piezoelectric, etc., for applications in electronics, sensors, optoelectronics, and energy devices. Due to the inherent structural anisotropy, previously reported synthetic methods predominantly yield one-dimensional (1D) Te nanostructures. Much less is known about 2D Te nanostructures, their processing schemes, and their material properties. This review focuses on the synthesis and morphology control of emerging 2D tellurene and summarizes the latest developments in understanding the fundamental properties of monolayer and few-layer tellurene, as well as the recent advances in demonstrating prototypical tellurene devices. Finally, the prospects for future research and application opportunities as well as the accompanying challenges of 2D tellurene are summarized and highlighted.

High-performance MoS2 transistors scaled down to 100 nm are studied at various temperatures down to 20 K, where a highest drive current of 800 μA μm(-1) can be achieved. Extremely low electrical noise of 2.8 × 10(-10) μm(2) Hz(-1) at 10 Hz is also achieved at room temperature. Furthermore, a negative differential resistance behavior is experimentally observed and its origin of self-heating is identified using pulsed-current-voltage measurements.

ABSTRACT:We report the direct measurement of the Dirac point, the Fermi level, and the work function of graphene by performing internal photoemission measurements on a graphene/SiO 2 /Si structure with a unique optical-cavity enhanced test structure. A complete electronic band alignment at the graphene/SiO 2 /Si interfaces is accurately established. The observation of enhanced photoemission from a one-atom thick graphene layer was possible by taking advantage of the constructive optical interference in the SiO 2 cavity. The photoemission yield was found to follow the well-known linear density-of-states dispersion in the vicinity of the Dirac point. At the flat band condition, the Fermi level was extracted and found to reside 3.3 eV ± 0.05 eV below the bottom of the SiO 2 conduction band. When combined with the shift of the Fermi level from the Dirac point, we are able to ascertain the position of the Dirac point at 3.6 eV ± 0.05 eV with respect to the bottom of the SiO 2 conduction band edge, yielding a work function of 4.5 eV ± 0.05 eV which is in an excellent agreement with theory. The accurate determination of the work function of graphene is of significant importance to the engineering of graphene-based devices, and the measurement technique we have advanced in this Letter will have significant impact on numerous applications for emerging graphene-like 2-dimensional material systems. KEYWORDS: Graphene, work function, internal photoemission, band alignment, graphene−insulator−semiconductor S ince the pioneering work of Novoselov et al. in 2004, 1 graphene has attracted an immense amount of interest from many related disciplines.2,3 Fundamental knowledge of the physical properties of graphene and the physical mechanisms governing the electrical operation of graphenebased devices has grown dramatically. 4 With the recent success of large area chemical vapor deposition (CVD) growth of graphene, 5 industrial applications such as transparent electrodes, 6 field-effect transistors (FETs), 7 and quantum well devices 8 are becoming more promising. Many studies have been conducted to characterize the various physical properties of graphene, including the work function, which is one of the most important electronic parameters. Among the numerous investigations by techniques such as Kelvin probe measurements, 9−11 ab initio calculations, 9,12 and recently by capacitance−voltage measurements, 13 the values of work function scatter in a rather wide range from 4.2 to 5.0 eV. Experimentally, the work function may be found to vary depending on the type of metal contact due to interactions between the graphene and the metal, which may result in pinning of the work function.9−13 Surprisingly, there is little information on the intrinsic electronic band alignment of the graphene/oxide interface to date, despite its important role in the design, fabrication, and characterization of graphene-based devices. For example, the accurate band alignment between graphene and another material determines how effectively to turn on an...

Guest Editors Hua Zhang, Hui-Ming Cheng and Peide Ye introduce the 2D nanomaterials: beyond graphene and transition metal dichalcogenides themed issue of Chemical Society Reviews.

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Two-dimensional (2D) transition metal dichalcogenides (TMDs) have very versatile chemical, electrical and optical properties. In particular, they exhibit rich and highly tunable electronic properties, with a bandgap that spans from semi-metallic up to 2 eV depending on the crystal phase, material composition, number of layers and even external stimulus. This paper provides an overview of the electronic devices and circuits based on 2D TMDs, such as Esaki diodes, resonant tunneling diodes (RTDs), logic and RF transistors, tunneling field-effect transistors (TFETs), static random access memories (SRAMs), dynamic RAM (DRAMs), flash memory, ferroelectric memories, resistitive memories and phase-change memories. We address the basic device principles, the advantages and limitations of these 2D electronic devices, and our perspectives on future developments.