Patterning and characterization of graphene nano-ribbon by electron beam induced etching

Sébastien Linas 1
1 CEMES-GNS - Groupe NanoSciences
CEMES - Centre d'élaboration de matériaux et d'études structurales
Abstract : Graphene is one of the most promising candidates to build fu ture electronic devices. Its pecu liar electronic properties derive from its atomic structure and are character ized by a two-dimensional electron gas at macroscopic scale and molecular states at the nanometer scale. This thesis work aims at patterning graphene monolayer over this entire range of length scales to produce arbitrarily shaped graphene nanoribbons (GNR) continuously connected to graphene pads. The three main objec- tives consist in (i) producing, contacting and patterning graphene monolayer down to features size of about 10 nm for a ribbon length of several hundreds of nanometers, (ii) inte grating all steps while minimizing contamination to ultimately reach UHV-compatible samples and (iii) etching GNRs while preserving the high crystallinity of graphene and minimizing its amorphization. The first part will focus on the characterization of the gr aphene monolayer itself by ambient AFM topography and Raman spectroscopy. We show that these techniques suffer from a poor reproducibility of the height measurement and a limited sensitivity to low defect density. However, the source of AFM instabilities is identified as the presence of a water meniscus. Stable operating conditions are found and yield reproducible hei ght measurements. In order to enhance the Raman signal of defects in graphene, we investigate the in tensity evolution near crys talline gold nanorods placed close to graphene edges. The second part describes in detail how GNR can be etched directly in graphene using a low energy (1-20 keV) electron beam in the presence of water vapor. We show that electron beam induced etching (EBIE) can produce < 20 nm-wide GNRs with length of hundreds of nanometers or micrometer-long trenches to isolate the GNR form the graphene sheet. A particu- lar attention is paid to the characteriza tion of the structural quality of the GNR e dges. A spherical aberration corrected TEM analysis demonstrates that the graphene lattice is intact at less than 2 nm from the EBIE-cut edges. The last part is dedicated to the application of our promising EBIE method to the fabrication of contacted GNR electronic field-effect devices. We show that graphene devices supporte d on silica are significantly am orphized by backscattered elec- trons. A new design of devices made of locally suspended graphene is proposed and makes it possible to produce GNRs (typically 30x200 nm) connected to el ectrodes on a back-gated substrate. This work opens the way to electrical transport measurements of GNR and, beyond, GNR-based complex structures and constitutes the first step towards an integrated atomic technology of molecular graphene devices.
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Sébastien Linas. Patterning and characterization of graphene nano-ribbon by electron beam induced etching. Materials Science [cond-mat.mtrl-sci]. Université Paul Sabatier - Toulouse III, 2012. English. ⟨NNT : 2012TOU30323⟩. ⟨tel-01025043⟩

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