Suspended (Free standing graphene), Graphene Membranes

 

2009

Self-Assembled Free-Standing Graphite Oxide Membrane

Chengmeng Chen, Quan-Hong Yang, Yonggang Yang, Wei Lv, Yuefang Wen, Peng-Xiang Hou, Maozhang Wang, and Hui-Ming Cheng

Nano Letters 2009 9 (9)

As a one-atom-thick two-dimensional crystal, graphene has been considered a basic building block for all sp2 carbons including fullerene, carbon nanotubes, and graphite. Since Geim et al. peeled a few graphene sheets from highly crystalline graphite by a ‘scotch tape’ method in 2004, some unique electronic properties of this conceptual matter, such as chiral quantum Hall effects and charge-carriers independent conductivity, have been found, which indicate potential applications in quantum devices, nanocomposites with various matrixes, and ultrathin membrane materials.

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Free-Standing Epitaxial Graphene

Shriram Shivaraman, Robert A. Barton, Xun Yu, Jonathan Alden, Lihong Herman, MVS Chandrasekhar, Jiwoong Park, Paul L. McEuen, Jeevak M. Parpia, Harold G. Craighead, Michael G. Spencer

Nano Letters 2009 9 (9)

We report on a method to produce free-standing graphene sheets from epitaxial graphene on silicon carbide (SiC) substrate. Doubly clamped nanomechanical resonators with lengths up to 20 ?m were patterned using this technique and their resonant motion was actuated and detected optically. Resonance frequencies of the order of tens of megahertz were measured for most devices, indicating that the resonators are much stiffer than expected for beams under no tension. Raman spectroscopy suggests that the graphene is not chemically modified during the release of the devices, demonstrating that the technique is a robust means of fabricating large-area suspended graphene structures.

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2008

Imaging and dynamics of light atoms and molecules on graphene

 

Nature 454, 319-322 (17 July 2008)

 

Jannik C. Meyer, C. O. Girit, M. F. Crommie & A. Zettl

 

Observing the individual building blocks of matter is one of the primary goals of microscopy. The invention of the scanning tunnelling microscope revolutionized experimental surface science in that atomic-scale features on a solid-state surface could finally be readily imaged. However, scanning tunnelling microscopy has limited applicability due to restrictions in, for example, sample conductivity, cleanliness, and data acquisition rate. An older microscopy technique, that of transmission electron microscopy (TEM) has benefited tremendously in recent years from subtle instrumentation advances, and individual heavy (high-atomic-number) atoms can now be detected by TEM even when embedded within a semiconductor material. But detecting an individual low-atomic-number atom, for example carbon or even hydrogen, is still extremely challenging, if not impossible, via conventional TEM owing to the very low contrast of light elements. Here we demonstrate a means to observe, by conventional TEM, even the smallest atoms and molecules: on a clean single-layer graphene membrane, adsorbates such as atomic hydrogen and carbon can be seen as if they were suspended in free space. We directly image such individual adatoms, along with carbon chains and vacancies, and investigate their dynamics in real time. These techniques open a way to reveal dynamics of more complex chemical reactions or identify the atomic-scale structure of unknown adsorbates. In addition, the study of atomic-scale defects in graphene may provide insights for nanoelectronic applications of this interesting material..

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2007

The structure of suspended graphene sheets

 

Nature Vol 446, 1 March 2007

 

Jannik C. Meyer, A. K. Geim, M. I. Katsnelson, K. S. Novoselov, T. J. Booth & S. Roth

 

The recent discovery of graphene has sparked much interest, thus far focused on the peculiar electronic structure of this material, in which charge carriers mimic massless relativistic particles. However, the physical structure of graphene—a single layer of carbon atoms densely packed in a honeycomb crystal lattice—is also puzzling. On the one hand, graphene appears to be a strictly two-dimensional material, exhibiting such a high crystal quality that electrons can travel submicrometre distances without scattering. On the other hand, perfect two-dimensional crystals cannot exist in the free state, according to both theory and experiment9. This incompatibility can be avoided by arguing that all the graphene structures studied so far were an integral part of larger three-dimensional structures, either supported by a bulk substrate or embedded in a three-dimensional matrix.

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