W. A. de Heer

The growth and morphology of epitaxial multilayer graphene

The electronic properties of epitaxial graphene grown on SiC have shown its potential as a viable candidate for post-CMOS electronics. However, progress in this field requires a detailed understanding of both the structure and growth of epitaxial graphene. To that end, this review will focus on the current state of epitaxial graphene research as it relates to the structure of graphene grown on SiC. We pay particular attention to the similarity and differences between graphene growth on the two polar faces, (0001) and , of hexagonal SiC. Growth techniques, subsequent morphology and the structure of the graphene/SiC interface and graphene stacking order are reviewed and discussed. Where possible the relationship between film morphology and electronic properties will also be reviewed.

Nanocapillarity and Chemistry in Carbon Nanotubes

Open carbon nanotubes were filled with molten silver nitrate by capillary forces. Only those tubes with inner diameters of 4 nanometers or more were filled, suggesting a capillarity size dependence as a result of the lowering of the nanotube-salt interface energy with increasing curvature of the nanotube walls. Nanotube cavities should also be less chemically reactive than graphite and may serve as nanosize test tubes. This property has been illustrated by monitoring the decomposition of silver nitrate within nanotubes in situ in an electron microscope, which produced chains of silver nanobeads separated by high-pressure gas pockets.

Approaching the dirac point in high-mobility multilayer epitaxial graphene.

Multilayer epitaxial graphene is investigated using far infrared transmission experiments in the different limits of low magnetic fields and high temperatures. The cyclotron-resonance-like absorption is observed at low temperature in magnetic fields below 50 mT, probing the nearest vicinity of the Dirac point. The carrier mobility is found to exceed 250,000 cm2/(V x s). In the limit of high temperatures, the well-defined Landau level quantization is observed up to room temperature at magnetic fields below 1 T, a phenomenon unusual in solid state systems. A negligible increase in the width of the cyclotron resonance lines with increasing temperature indicates that no important scattering mechanism is thermally activated.

Landau level spectroscopy of ultrathin graphite layers.

Far infrared transmission experiments are performed on ultrathin epitaxial graphite samples in a magnetic field. The observed cyclotron resonance-like and electron-positron-like transitions are in excellent agreement with the expectations of a single-particle model of Dirac fermions in graphene, with an effective velocity of c=1.03 x 10(6) m/s.

First Direct Observation of a Nearly Ideal Graphene Band Structure

Angle-resolved photoemission and x-ray diffraction experiments show that multilayer epitaxial graphene grown on the SiC(0001) surface is a new form of carbon that is composed of effectively isolated graphene sheets. The unique rotational stacking of these films causes adjacent graphene layers to electronically decouple leading to a set of nearly independent linearly dispersing bands (Dirac cones) at the graphene K point. Each cone corresponds to an individual macroscale graphene sheet in a multilayer stack where AB-stacked sheets can be considered as low density faults.

Highly ordered graphene for two dimensional electronics

With expanding interest in graphene-based electronics, it is crucial that high quality graphene films be grown. Sublimation of Si from the 4H-SiC(0001) (Si-terminated) surface in ultrahigh vacuum is a demonstrated method to produce epitaxial graphene sheets on a semiconductor. In this letter the authors show that graphene grown from the SiC(0001¯) (C-terminated) surface are of higher quality than those previously grown on SiC(0001). Graphene grown on the C face can have structural domain sizes more than three times larger than those grown on the Si face while at the same time reducing SiC substrate disorder from sublimation by an order of magnitude.

Few-layer graphene on SiC, pyrolitic graphite, and graphene: A Raman scattering study

To show the similarities between exfoliated graphene and epitaxial few layer graphite (FLG) layers, we present micro-Raman scattering measurements on three different graphite-based materials: micro-structured Highly Oriented Pyrolytic Graphite (HOPG) disks with heights in the 20-2 nm range, exfoliated graphene monolayer, and FLG epitaxially grown on carbon terminated 4H-silicon carbide (4H-SiC) substrates. We show that despite the fact the FLG layers are composed of many layers, the band structure of FLG epitaxially grown on 4H-SiC substrate must be composed of simple electronic bands as witnessed by a single component, Lorentzian shaped, double resonance Raman feature.

Measuring physical and mechanical properties of individual carbon nanotubes by in situ TEM

Nanomaterials are a fundamental component of nanoscience and nanotechnology. The small size of nanostructures constrains the applications of well-established testing and measurement techniques, thus new methods and approaches must be developed for synthesis, property characterization and device fabrication. This has been the focus of our research, aiming at exploring state-of-the-art techniques for materials processing and characterization. This paper reviews our progress in using in situ transmission electron microscopy to measure the electric, mechanical and field emission properties of individual carbon nanotubes with well-defined structures. Quantum conductance was observed in defect-free nanotubes, which led to the transport of a superhigh current density at room temperature without heat dissipation. A nanobalance technique is demonstrated that can be applied to measure the mass of a tiny particle as light as 22 fg O 1f a 10 215 U: q 2000 Elsevier Science Ltd. All rights

A wide-bandgap metal-semiconductor-metal nanostructure made entirely from graphene

The electronic properties of graphene are spatially controlled from metallic to semiconducting by patterning steps into the underlying silicon carbide substrate. This bottom-up approach could be the basis for integrated graphene electronics.

Mechanical and electrostatic properties of carbon nanotubes and nanowires

Nano-scale manipulation and property measurements of individual nanowire-like structure is challenged by the small size of the structure. Scanning probe microscopy has been the dominant tool for property characterizations of nanomaterials. We have developed an alternative novel approach that allows a direct measurement of the mechanical and electrical properties of individual nanowire-like structures by in situ transmission electron microscopy (TEM). The technique is unique in a way that it can directly correlate the atomic-scale microstructure of the nanowire with its physical properties. This paper reviews our current progress in applying the technique in investigating the mechanical and electron field emission properties of carbon nanotubes and nanowires.