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

This article provides a comprehensive review of recent (2008 and 2009) progress in gas sensors based on semiconducting metal oxide one-dimensional (1D) nanostructures. During last few years, gas sensors based on semiconducting oxide 1D nanostructures have been widely investigated. Additionally, modified or doped oxide nanowires/nanobelts have also been synthesized and used for gas sensor applications. Moreover, novel device structures such as electronic noses and low power consumption self-heated gas sensors have been invented and their gas sensing performance has also been evaluated. Finally, we also point out some challenges for future investigation and practical application.

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Gas Sensors Based on Semiconducting Metal Oxide One-Dimensional Nanostructures

The effect of Ag decoration on the gas sensing characteristics of SnO(2) nanowire (NW) networks was investigated. The Ag layers with thicknesses of 5-50 nm were uniformly coated on the surface of SnO(2) NWs via e-beam evaporation, which were converted into isolated or continuous configurations of Ag islands by heat treatment at 450 °C for 2 h. The SnO(2) NWs decorated by isolated Ag nano-islands displayed a 3.7-fold enhancement in gas response to 100 ppm C(2)H(5)OH at 450 °C compared to pristine SnO(2) NWs. In contrast, as the Ag decoration layers became continuous, the response to C(2)H(5)OH decreased significantly. The enhancement and deterioration of the C(2)H(5)OH sensing characteristics by the introduction of the Ag decoration layer were strongly governed by the morphological configurations of the Ag catalysts on SnO(2) NWs and their sensitization mechanism.

Facile Control of C2H5OH Sensing Characteristics by Decorating Discrete Ag Nanoclusters on SnO2 Nanowire Networks

This review will focus on the synthesis, arrangement, structural assembly, for current and future applications, of 1D nanomaterials (tubes, wires, rods) in 2D and 3D ordered arrangements. The ability to synthesize and arrange one dimensional nanomaterials into ordered 2D or 3D micro or macro sized structures is of utmost importance in developing new devices and applications of these materials. Micro and macro sized architectures based on such 1D nanomaterials (e.g. tubes, wires, rods) provide a platform to integrate nanostructures at a larger and thus manageable scale into high performance electronic devices like field effect transistors, as chemo- and biosensors, catalysts, or in energy material applications. Carbon based, metal oxide and metal based 1D arranged materials as well as hybrid or composite 1D materials of the latter provide a broad materials platform, offering a perspective for new entries into fascinating structures and future applications of such assembled architectures. These architectures allow bridging the gap between 1D nanostructures and the micro and macro world and are the basis for an assembly of 1D materials into higher hierarchy domains. This critical review is intended to provide an interesting starting point to view the current state of the art and show perspectives for future developments in this field. The emphasis is on selected nanomaterials and the possibilities for building three dimensional arrays starting from one dimensional building blocks. Carbon nanotubes, metal oxide nanotubes and nanowires (e.g. ZnO, TiO2, V2O5, Cu2O, NiO, Fe2O3), silicon and germanium nanowires, and group III–V or II–VI based 1D semiconductor nanostructures like GaS and GaN, pure metals as well as 1D hybrid materials and their higher organized architectures (foremost in 3D) will be focussed. These materials have been the most intensively studied within the last 5–10 years with respect to nano–micro integration aspects and their functional and application oriented properties. The critical review should be interesting for a broader scientific community (chemists, physicists, material scientists) interested in synthetic and functional material aspects of 1D materials as well as their integration into next higher organized architectures.

Assembly of one dimensional inorganic nanostructures into functional 2D and 3D architectures. Synthesis, arrangement and functionality

Described herein are a device utilizing a gate electrode material with a single work function for both the pMOS and nMOS transistors where the magnitude of the transistor threshold voltages is modified by semiconductor band engineering and article made thereby. Further described herein are methods of fabricating a device formed of complementary (pMOS and nMOS) transistors having semiconductor channel regions which have been band gap engineered to achieve a low threshold voltage.

CMOS devices with a single work function gate electrode and method of fabrication

Tin oxide (SnO2) nanowires with a tetragonal structure were synthesized by thermal evaporation of tin grains at 900 °C. The obtained nanowires were doped with palladium. The morphology, crystal structure, and H2 gas sensing properties of undoped and Pd-doped SnO2 nanowires were investigated. SnO2 nanowires were approximately 30–200 nm in diameter and several tens of micrometers in length. Gas sensors based on undoped, 0.8 wt% Pd-doped, and 2 wt% Pd-doped SnO2 nanowires were fabricated. These SnO2 nanowire gas sensors showed a reversible response to H2 gas at an operating temperature of RT—300 °C. The sensor response increased with increasing Pd concentration. The 2 wt% Pd-doped SnO2 nanowire sensor showed a response as high as 253 for 1000 ppm H2 gas at 100 °C. The results demonstrated that Pd doping improved the sensor response and lowered the operating temperature at which the sensor response was maximized.

Masayuki Mori

Papers

Microstructure and H2 gas sensing properties of undoped and Pd-doped SnO2 nanowires

Heteroepitaxial growth of InSb films on a Si(0 0 1) substrate via AlSb buffer layer

Heteroepitaxial growth of rotated InSb films on a Si(1 1 1) substrate via 2×2-In surface reconstruction

Heteroepitaxial growth of InSb on Si(001) surface via Ge buffer layers

Effect of AlSb buffer layer thickness on heteroepitaxial growth of InSb films on a Si(001) substrate