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Fundamental Aspects of Energy Dissipation in Friction
Park, Jeong Young,Salmeron, Miquel American Chemical Society 2014 Chemical reviews Vol.114 No.1
<P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/chreay/2014/chreay.2014.114.issue-1/cr200431y/production/images/medium/cr-2011-00431y_0031.gif'></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>
Lee, Hyunsoo,Lee, Han-Bo-Ram,Kwon, Sangku,Salmeron, Miquel,Park, Jeong Young American Chemical Society 2015 ACS NANO Vol.9 No.4
<P>We report on the physical and chemical properties of atomic steps on the surface of highly oriented pyrolytic graphite (HOPG) investigated using atomic force microscopy. Two types of step edges are identified: internal (formed during crystal growth) and external (formed by mechanical cleavage of bulk HOPG). The external steps exhibit higher friction than the internal steps due to the broken bonds of the exposed edge C atoms, while carbon atoms in the internal steps are not exposed. The reactivity of the atomic steps is manifested in a variety of ways, including the preferential attachment of Pt nanoparticles deposited on HOPG when using atomic layer deposition and KOH clusters formed during drop casting from aqueous solutions. These phenomena imply that only external atomic steps can be used for selective electrodeposition for nanoscale electronic devices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-4/nn506755p/production/images/medium/nn-2014-06755p_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn506755p'>ACS Electronic Supporting Info</A></P>
Solvation and Reaction of Ammonia in Molecularly Thin Water Films
Lechner, Barbara A. J.,Kim, Youngsoon,Feibelman, Peter J.,Henkelman, Graeme,Kang, Heon,Salmeron, Miquel American Chemical Society 2015 The Journal of Physical Chemistry Part C Vol.119 No.40
<P>Determining the interaction and solvation structure of molecules with solvents near a surface is of fundamental importance for understanding electro- and photochemical processes. Here we used scanning tunneling microscopy (STM) to investigate the adsorption and solvation structure of ammonia on water monolayers on Pt(111). We found that at low coverage NH<SUB>3</SUB> binds preferentially to H<SUB>2</SUB>O molecules that are slightly elevated from the surface and weakly bound to the metal. Density functional theory (DFT) calculations showed that as the NH<SUB>3</SUB> molecule descends onto the water adlayer a high-lying water molecule reorients with zero energy barrier to expose a dangling OH ligand to H-bond NH<SUB>3</SUB>. We also found that NH<SUB>3</SUB> prefers to bind to the metal substrate when water only partially covers the surface, indicating that NH<SUB>3</SUB> is more strongly attracted to the metal than to H<SUB>2</SUB>O. In addition to this solvation interaction, a proton transfer reaction occurs as revealed by reflection–absorption infrared spectroscopy (RAIRS), leading to the formation of ammonium ions (NH<SUB>4</SUB><SUP>+</SUP>) in addition to molecularly adsorbed NH<SUB>3</SUB>.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2015/jpccck.2015.119.issue-40/acs.jpcc.5b07525/production/images/medium/jp-2015-07525v_0007.gif'></P>
Charge density wave order in 1D mirror twin boundaries of single-layer MoSe<sub>2</sub>
Barja, Sara,Wickenburg, Sebastian,Liu, Zhen-Fei,Zhang, Yi,Ryu, Hyejin,Ugeda, Miguel ,M.,Hussain, Zahid,Shen, Zhi-Xun,Mo, Sung-Kwan,Wong, Ed,Salmeron, Miquel ,B.,Wang, Feng,Crommie, Michael F. NATURE PUBLISHING GROUP 2016 NATURE PHYSICS Vol.12 No.8
We provide direct evidence for the existence of isolated, one-dimensional charge density waves at mirror twin boundaries (MTBs) of single-layer semiconducting MoSe<SUB>2</SUB>. Such MTBs have been previously observed by transmission electron microscopy and have been predicted to be metallic in MoSe<SUB>2</SUB> and MoS<SUB>2</SUB>. Our low-temperature scanning tunnelling microscopy/spectroscopy measurements revealed a substantial bandgap of 100 meV opening at the Fermi energy in the otherwise metallic one-dimensional structures. We found a periodic modulation in the density of states along the MTB, with a wavelength of approximately three lattice constants. In addition to mapping the energy-dependent density of states, we determined the atomic structure and bonding of the MTB through simultaneous high-resolution non-contact atomic force microscopy. Density functional theory calculations based on the observed structure reproduced both the gap opening and the spatially resolved density of states.