Graphene, a single monolayer of graphite, has recently attracted considerable interest owing to its novel magneto-transport properties, high carrier mobility and ballistic transport up to room temperature. It has the potential for technological applications as a successor of silicon in the post Moore's law era, as a single-molecule gas sensor, in spintronics, in quantum computing or as a terahertz oscillator. For such applications, uniform ordered growth of graphene on an insulating substrate is necessary. The growth of graphene on insulating silicon carbide (SiC) surfaces by high-temperature annealing in vacuum was previously proposed to open a route for large-scale production of graphene-based devices. However, vacuum decomposition of SiC yields graphene layers with small grains (30-200 nm; refs 14-16). Here, we show that the ex situ graphitization of Si-terminated SiC(0001) in an argon atmosphere of about 1 bar produces monolayer graphene films with much larger domain sizes than previously attainable. Raman spectroscopy and Hall measurements confirm the improved quality of the films thus obtained. High electronic mobilities were found, which reach mu=2,000 cm (2) V(-1) s(-1) at T=27 K. The new growth process introduced here establishes a method for the synthesis of graphene films on a technologically viable basis.

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Towards wafer-size graphene layers by atmospheric pressure graphitization of silicon carbide

International Technology Roadmap for Semiconductors 2003の要求清浄度について － シリコンウエハ表面と雰囲気環境に要求される清浄度, 分析方法の現状について －

From diagnosis of life-threatening diseases to detection of biological agents in warfare or terrorist attacks, biosensors are becoming a critical part of modern life. Many recent biosensors have incorporated carbon nanotubes as sensing elements, while a growing body of work has begun to do the same with the emergent nanomaterial graphene, which is effectively an unrolled nanotube. With this widespread use of carbon nanomaterials in biosensors, it is timely to assess how this trend is contributing to the science and applications of biosensors. This Review explores these issues by presenting the latest advances in electrochemical, electrical, and optical biosensors that use carbon nanotubes and graphene, and critically compares the performance of the two carbon allotropes in this application. Ultimately, carbon nanomaterials, although still to meet key challenges in fabrication and handling, have a bright future as biosensors.

Carbon Nanomaterials in Biosensors: Should You Use Nanotubes or Graphene?

We report variation of the work function for single and bilayer graphene devices measured by scanning Kelvin probe microscopy (SKPM). By use of the electric field effect, the work function of graphene can be adjusted as the gate voltage tunes the Fermi level across the charge neutrality point. Upon biasing the device, the surface potential map obtained by SKPM provides a reliable way to measure the contact resistance of individual electrodes contacting graphene.

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Tuning the graphene work function by electric field effect.

We report variation of the work function for single and bi-layer graphene devices measured by scanning Kelvin probe microscopy (SKPM). Using the electric field effect, the work function of graphene can be adjusted as the gate voltage tunes the Fermi level across the charge neutrality point. Upon biasing the device, the surface potential map obtained by SKPM provides a reliable way to measure the contact resistance of individual electrodes contacting graphene.

Tuning the graphene work function by electric field effect

Low-energy electron microscopy (LEEM) was used to measure the reflectivity of low-energy electrons from graphitized $\mathrm{SiC}(0001)$. The reflectivity shows distinct quantized oscillations as a function of the electron energy and graphite thickness. Conduction bands in thin graphite films form discrete energy levels whose wave vectors are normal to the surface. Resonance of the incident electrons with these quantized conduction band states enhances electrons to transmit through the film into the $\mathrm{SiC}$ substrate, resulting in dips in the reflectivity. The dip positions are well explained using tight-binding and first-principles calculations. The graphite thickness distribution can be determined microscopically from LEEM reflectivity measurements.

Microscopic thickness determination of thin graphite films formed on SiC from quantized oscillation in reflectivity of low-energy electrons

We used spectroscopic photoemission and low-energy electron microscopy to investigate the electronic properties of epitaxial few-layer graphene grown on 6H-SiC(0001). Photoelectron emission microscopy (PEEM) images using secondary electrons (SEs) and $\text{C}\text{ }1s$ photoelectrons can discriminate areas with different numbers of graphene layers. The SE emission spectra indicate that the work function increases with the number of graphene layers and that unoccupied states in the few-layer graphene promote SE emission. The $\text{C}\text{ }1s$ PEEM images indicate that the $\text{C}\text{ }1s$ core level shifts to lower binding energies as the number of graphene layers increases, which is consistent with the reported thickness dependence of the Dirac point energy.

Dependence of electronic properties of epitaxial few-layer graphene on the number of layers investigated by photoelectron emission microscopy

The energetics of the atomic process of Si-oxide growth on Si(100) surfaces and at ${\mathrm{SiO}}_{2}$/Si(100) interfaces are theoretically studied by first-principles calculation. It is found that the stress induced during the growth plays a crucial role in the growth procedure itself. The preferential growth direction of the oxide nucleus on the surfaces is vertical to the substrate, whereas that at the interfaces is lateral. Moreover, Si atoms are inevitably emitted from the interface to release the stress induced during Si oxide growth.

First-Principles Study of Oxide Growth on Si(100) Surfaces and at SiO 2 /Si(100) Interfaces

A method of calculating momentum matrix elements using pseudopotentials is proposed A core-repair term is introduced in the method to eliminate errors created by the poor representation of the atomic core region by the pseudopotentials Calculating the core-repair term requires fewer computational resources especially for separable form pseudopotentials This approach is suitable for non-norm-conserving pseudopotentials as well as general norm-conserving pseudopotentials The effectiveness of the method is verified for various isolated atoms The method is also applied to calculate momentum matrix elements for planar polysilane, planar siloxene, gallium arsenide, and gallium nitride

Momentum-matrix-element calculation using pseudopotentials

The essential role that Si atoms emitted from the interface play in determining the silicon-oxidation rate is theoretically pointed out, and a universal theory for the oxide growth rate taking account of the interfacial Si-atom emission is developed. Our theory can explain the oxide growth rate for the whole range of the oxide thickness without any empirical modifications, while the rate for an oxide thickness of less than 10 nm in dry oxidation cannot be explained with the Deal-Grove theory.

https://iopscience.iop.org/article/10.1143/JJAP.38.L971/pdf

Hiroyuki Kageshima

Papers

Microscopic thickness determination of thin graphite films formed on SiC from quantized oscillation in reflectivity of low-energy electrons

Dependence of electronic properties of epitaxial few-layer graphene on the number of layers investigated by photoelectron emission microscopy

First-Principles Study of Oxide Growth on Si(100) Surfaces and at SiO 2 /Si(100) Interfaces

Momentum-matrix-element calculation using pseudopotentials

Universal Theory of Si Oxidation Rate and Importance of Interfacial Si Emission