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Domain structures of single layer graphene imaged with conductive probe atomic force microscopy
Kwon, Sangku,Chung, H. J.,Seo, Sunae,Park, Jeong Young John Wiley Sons, Ltd 2012 Surface and interface analysis Vol.44 No.6
<P>We report nanoscale domain boundaries on single layer graphene probed with conductive probe atomic force microscopy in ultrahigh vacuum. Graphene was prepared using the inductively coupled plasma chemical vapor deposition technique on a copper substrate. Current mapping revealed domains 50–100 nm in size on the single layer graphene. Stick slip images revealed a hexagonal structure of the graphene layer in the middle of the domain. The conductance on the domain boundary is lower than that inside the domain structure, which is associated with disorder on the boundary, while friction and adhesion measurements on the domain boundaries did not show any contrast. We found that the conductance contrast is prominent at high loads, suggesting the domain boundary plays a significant role in the charge transport properties of graphene under mechanical deformation. Copyright © 2012 John Wiley & Sons, Ltd.</P>
Enhanced Nanoscale Friction on Fluorinated Graphene
Kwon, Sangku,Ko, Jae-Hyeon,Jeon, Ki-Joon,Kim, Yong-Hyun,Park, Jeong Young American Chemical Society 2012 NANO LETTERS Vol.12 No.12
<P>Atomically thin graphene is an ideal model system for studying nanoscale friction due to its intrinsic two-dimensional (2D) anisotropy. Furthermore, modulating its tribological properties could be an important milestone for graphene-based micro- and nanomechanical devices. Here, we report unexpectedly enhanced nanoscale friction on chemically modified graphene and a relevant theoretical analysis associated with flexural phonons. Ultrahigh vacuum friction force microscopy measurements show that nanoscale friction on the graphene surface increases by a factor of 6 after fluorination of the surface, while the adhesion force is slightly reduced. Density functional theory calculations show that the out-of-plane bending stiffness of graphene increases up to 4-fold after fluorination. Thus, the less compliant F-graphene exhibits more friction. This indicates that the mechanics of tip-to-graphene nanoscale friction would be characteristically different from that of conventional solid-on-solid contact and would be dominated by the out-of-plane bending stiffness of the chemically modified graphene. We propose that damping via flexural phonons could be a main source for frictional energy dissipation in 2D systems such as graphene.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2012/nalefd.2012.12.issue-12/nl204019k/production/images/medium/nl-2011-04019k_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl204019k'>ACS Electronic Supporting Info</A></P>
Kwon, Sangku,Lee, Seon Joo,Kim, Sun Mi,Lee, Youngkeun,Song, Hyunjoon,Park, Jeong Young The Royal Society of Chemistry 2015 Nanoscale Vol.7 No.29
<P>The electrical nature of the nanoscale contact between metal nanodots and semiconductor rods has drawn significant interest because of potential applications for metal-semiconductor hybrid nanostructures in energy conversion or heterogeneous catalysis. Here, we studied the nanoscale electrical character of the Pt/CdSe junction in Pt/CdSe/Pt nanodumbbells on connected Au islands by conductive-probe atomic force microscopy under ultra-high vacuum. Current-voltage plots measured in contact mode revealed Schottky barrier heights of individual nanojunctions of 0.41 0.02 eV. The measured value of the Schottky barrier is significantly lower than that of planar thin-film diodes because of a reduction in the barrier width and enhanced tunneling probability at the interface.</P>
Superlubric Sliding of Graphene Nanoflakes on Graphene
Feng, Xiaofeng,Kwon, Sangku,Park, Jeong Young,Salmeron, Miquel American Chemical Society 2013 ACS NANO Vol.7 No.2
<P>The lubricating properties of graphite and graphene have been intensely studied by sliding a frictional force microscope tip against them to understand the origin of the observed low friction. In contrast, the relative motion of free graphene layers remains poorly understood. Here we report a study of the sliding behavior of graphene nanoflakes (GNFs) on a graphene surface. Using scanning tunneling microscopy, we found that the GNFs show facile translational and rotational motions between commensurate initial and final states at temperatures as low as 5 K. The motion is initiated by a tip-induced transition of the flakes from a commensurate to an incommensurate registry with the underlying graphene layer (the superlubric state), followed by rapid sliding until another commensurate position is reached. Counterintuitively, the average sliding distance of the flakes is larger at 5 K than at 77 K, indicating that thermal fluctuations are likely to trigger their transitions from superlubric back to commensurate ground states.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2013/ancac3.2013.7.issue-2/nn305722d/production/images/medium/nn-2012-05722d_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn305722d'>ACS Electronic Supporting Info</A></P>