The compelling demand for higher performance and lower power consumption in electronic systems is the main driving force of the electronics industry's quest for devices and/or architectures based on new materials. Here, we provide a review of electronic devices based on two-dimensional materials, outlining their potential as a technological option beyond scaled complementary metal-oxide-semiconductor switches. We focus on the performance limits and advantages of these materials and associated technologies, when exploited for both digital and analog applications, focusing on the main figures of merit needed to meet industry requirements. We also discuss the use of two-dimensional materials as an enabling factor for flexible electronics and provide our perspectives on future developments.

Electronics based on two-dimensional materials

The effects of temperature and frequency on the dielectric properties, electromagnetic interference shielding and microwave-absorption of short carbon fiber/silica composites

The broadband and tunable high-performance microwave absorption properties of an ultralight and highly compressible graphene foam (GF) are investigated. Simply via physical compression, the microwave absorption performance can be tuned. The qualified bandwidth coverage of 93.8% (60.5 GHz/64.5 GHz) is achieved for the GF under 90% compressive strain (1.0 mm thickness). This mainly because of the 3D conductive network.

Broadband and Tunable High‐Performance Microwave Absorption of an Ultralight and Highly Compressible Graphene Foam

Using a simple hydrothermal procedure, cobalt oxide (Co3O4) nanowires were in situ synthesized on three-dimensional (3D) graphene foam grown by chemical vapor deposition. The structure and morphology of the resulting 3D graphene/Co3O4 composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The 3D graphene/Co3O4 composite was used as the monolithic free-standing electrode for supercapacitor application and for enzymeless electrochemical detection of glucose. We demonstrate that it is capable of delivering high specific capacitance of ∼1100 F g–1 at a current density of 10 A g–1 with excellent cycling stability, and it can detect glucose with a ultrahigh sensitivity of 3.39 mA mM–1 cm–2 and a remarkable lower detection limit of <25 nM (S/N = 8.5).

3D Graphene–Cobalt Oxide Electrode for High-Performance Supercapacitor and Enzymeless Glucose Detection

The synthesis of CoNi@SiO2 @TiO2 core-shell and CoNi@Air@TiO2 yolk-shell microspheres is reported for the first time. Owing to the magnetic-dielectric synergistic effect, the obtained CoNi@SiO2 @TiO2 microspheres exhibit outstanding microwave absorption performance with a maximum reflection loss of -58.2 dB and wide bandwidth of 8.1 GHz (8.0-16.1 GHz, < -10 dB).

CoNi@SiO2@TiO2 and CoNi@Air@TiO2 Microspheres with Strong Wideband Microwave Absorption

CNT/crystalline Fe nanocomposites (see Figure) have excellent microwave-absorption characteristics. This absorption property is shown to result from the confinement of crystalline Fe in carbon nanoshells, deriving mainly from magnetic rather than electric effects-the complex permittivity and permeability depend both on the shape and phase of the CNT/Fe nanocapsulates.

Microwave Absorption Enhancement and Complex Permittivity and Permeability of Fe Encapsulated within Carbon Nanotubes

We have fabricated ballistic n-type carbon nanotube (CNT)-based field-effect transistors (FETs) by contacting semiconducting single wall CNTs using Sc. Together with the demonstrated ballistic p-ty...

Doping-Free Fabrication of Carbon Nanotube Based Ballistic CMOS Devices and Circuits

A metal-semiconductor-metal (M-S-M) model for quantitative analysis of current–voltage (I–V) characteristics of semiconducting nanowires is described and applied to fit experimental I–V curves of Bi2S3 nanowire transistors. The I–V characteristics of semiconducting nanowires are found to depend sensitively on the contacts, in particular on the Schottky barrier height and contact area, and the M-S-M model is shown to be able to reproduce all experimentally observed I–V characteristics using only few fitting variables. A procedure for decoupling contact effects from that of the intrinsic parameters of the semiconducting nanowires, such as conductivity, carrier mobility and doping concentration is proposed, demonstrated using experimental I–V curves obtained from Bi2S3 nanowires and compared with the field-effect based method.

Quantitative Analysis of Current–Voltage Characteristics of Semiconducting Nanowires: Decoupling of Contact Effects

Electrical transport measurements were conducted on semiconducting nanowires and three distinct current-voltage (I-V) characteristics were observed, i.e., almost symmetric, almost rectifying, and almost linear. These I-V characteristics were modeled by treating the transport in the nanowire as in a metal-semiconductor-metal structure involving two Schottky barriers and a resistor in between these barriers, and the transport is shown to be dominated by the reverse-biased Schottky barrier under low bias and by the semiconducting nanowire at large bias. In contrast to the conventional Schottky diode, the reverse current in the nano-Schottky barrier structure is not negligible and the current is largely tunneling rather than thermionic. Experimental I-V curves are reproduced very well using our model, and a method for extracting nanowire resistance, electron density, and mobility is proposed and applied to ZnO, CdS, and Bi2S3 nanowires.

Current-voltage characteristics and parameter retrieval of semiconducting nanowires

We demonstrate a graphene-based electro-absorption modulator achieving extraordinary control of terahertz reflectance. By concentrating the electric field intensity in an active layer of graphene, an extraordinary modulation depth of 64% is achieved while simultaneously exhibiting low insertion loss (∼2 dB), which is remarkable since the active region of the device is atomically thin. This modulator performance, among the best reported to date, indicates the enormous potential of graphene for terahertz reconfigurable optoelectronic devices.

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Xuelei Liang

Papers

Microwave Absorption Enhancement and Complex Permittivity and Permeability of Fe Encapsulated within Carbon Nanotubes

Doping-Free Fabrication of Carbon Nanotube Based Ballistic CMOS Devices and Circuits

Quantitative Analysis of Current–Voltage Characteristics of Semiconducting Nanowires: Decoupling of Contact Effects

Current-voltage characteristics and parameter retrieval of semiconducting nanowires

Extraordinary control of terahertz beam reflectance in graphene electro-absorption modulators.