Leron Vandsburger

Experimental Review of Graphene

This review examines the properties of graphene from an experimental perspective. The intent is to review the most important experimental results at a level of detail appropriate for new graduate students who are interested in a general overview of the fascinating properties of graphene. While some introductory theoretical concepts are provided, including a discussion of the electronic band structure and phonon dispersion, the main emphasis is on describing relevant experiments and important results as well as some of the novel applications of graphene. In particular, this review covers graphene synthesis and characterization, field-effect behavior, electronic transport properties, magnetotransport, integer and fractional quantum Hall effects, mechanical properties, transistors, optoelectronics, graphene-based sensors, and biosensors. This approach attempts to highlight both the means by which the current understanding of graphene has come about and some tools for future contributions.

Modification of hardwood samples in the flowing afterglow of N2–O2 dielectric barrier discharges open to ambient air

Abstract The effect of O2 addition in the gas feed of an open-to-air N2–O2 dielectric barrier discharge (DBD) on the surface modification of sugar maple hardwood samples is reported. After treatment by N2–O2 plasma, an increase of the contact angle with water and a decrease of the contact angle with diiodomethane was observed. X-ray photoelectron spectroscopy and Fourier-transform infra-red analyses further reveal a decrease of the O/C as well as increase of the C=O peak and surface aromaticity. When O2 is added to the nominally pure N2 DBD, the discharge transits from a homogeneous regime to a filamentary regime with increased dissipated power and neutral gas temperature. As a result, surface modification by N2–O2 plasmas becomes similar to those occurring under a low-temperature heat treatment of wood surfaces. In such conditions, a mechanism involving the thermally-activated deacetylation and depolymerisation of hemicelluloses and cross-linking between lignin and furfural and hydroxylmethylfurfural, leading to the increase of wood hydrophobicity is proposed.

Degradation of carbon nanotubes by electron bombardment in radio-frequency glow discharge afterglows

A capacitively coupled radio-frequency afterglow is used to isolate the role of electron bombardment in the degradation process of muti-walled carbon nanotubes (MWNTs). MWNTs grown on a metal substrate act as a nanostructured anode that accelerate and focus electron bombardment, facilitated by the field enhancement effect. Tip-localized MWNT degradation has been observed in scanning electron microscope images showing the progression of the MWNT degradation process. This finding is confirmed by Raman spectra. GC-MS measurements indicate that the major products of MWNT degradation are short unsaturated hydrocarbons, identified as both propyne and 1,3-butadiyne vapours. This finding is corroborated by time-resolved optical emission spectroscopy during plasma oxidation of the degradation products. Analysis of the kinetics of plasma oxidation confirm that MWNT degradation produces species consistent with thermal evaporation, such as short carbon chains, C3?C4, but not monatomic or diatomic species, C1 and C2.

Adsorption dynamics of plasma-generated N atoms on graphene films

Graphene is leading the charge in the drive to develop the next generation of electronics and optoelectronics. The applications for which it is ideally suited as a 2D conductor have been complemented by further domains where it can function as a semiconductor or a magnetic metamaterial. These, however, depend on the availability of versatile post-growth processing techniques that can adapt it for implementation in technologies where band gap or magnetic response are necessary. The n-type doping of graphene by nitrogen atoms has been addressed as a means either for increasing electron density in graphene films or for inducing a band gap by direct incorporation or carbon replacement.

Anhydrous Oxidation of Multiwall Carbon Nanotubes in Argon-Water Direct Current Glow Discharges

A multiwalled carbon nanotube (MWNT) covered stainless steel mesh was used as the cathode of a low-pressure dc glow discharge sustained in a 1:1 mixture of Ar:H2O at 3 torr. The negative glow produced a visible reddish emission. Optical emission spectroscopy of this region revealed a strong emission from the Hα line (656.28 nm) that was not observed in bare stainless steel mesh control tests. The finding strongly indicated anhydrous oxidation of MWNTs, by O radicals. An image taken of the cathode in operation is presented, along with a diagram of the electrode setup showing how the image was taken and an illustration of the structures in the negative glow.