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Conductance and Geometry of Pyridine-Linked Single-Molecule Junctions
Kamenetska, M.,Quek, Su Ying,Whalley, A. C.,Steigerwald, M. L.,Choi, H. J.,Louie, Steven G.,Nuckolls, C.,Hybertsen, M. S.,Neaton, J. B.,Venkataraman, L. American Chemical Society 2010 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.132 No.19
<P>We have measured the conductance and characterized molecule−electrode binding geometries of four pyridine-terminated molecules by elongating and then compressing gold point contacts in a solution of molecules. We have found that all pyridine-terminated molecules exhibit bistable conductance signatures, signifying that the nature of the pyridine−gold bond allows two distinct conductance states that are accessed as the gold−molecule−gold junction is elongated. We have identified the low-conductance state as corresponding to a molecule fully stretched out between the gold electrodes, where the distance between contacts correlates with the length of the molecule; the high-conductance state is due to a molecule bound at an angle. For all molecules, we have found that the distribution of junction elongations in the low-conductance state is the same, while in the high-conductance state, the most likely elongation length increases linearly with molecule length. The results of first-principles conductance calculations for the four molecules in the low-conductance geometry agree well with the experimental results and show that the dominant conducting channel in the conjugated pyridine-linked molecules is through the π* orbital.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2010/jacsat.2010.132.issue-19/ja1015348/production/images/medium/ja-2010-015348_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja1015348'>ACS Electronic Supporting Info</A></P>
Edge Structures for Nanoscale Graphene Islands on Co(0001) Surfaces
Prezzi, Deborah,Eom, Daejin,Rim, Kwang T.,Zhou, Hui,Lefenfeld, Michael,Xiao, Shengxiong,Nuckolls, Colin,Heinz, Tony F.,Flynn, George W.,Hybertsen, Mark S. American Chemical Society 2014 ACS NANO Vol.8 No.6
<P>Low-temperature scanning tunneling microscopy measurements and first-principles calculations are employed to characterize edge structures observed for graphene nanoislands grown on the Co(0001) surface. Images of these nanostructures reveal straight well-ordered edges with zigzag orientation, which are characterized by a distinct peak at low bias in tunneling spectra. Density functional theory based calculations are used to discriminate between candidate edge structures. Several zigzag-oriented edge structures have lower formation energy than armchair-oriented edges. Of these, the lowest formation energy configurations are a zigzag and a Klein edge structure, each with the final carbon atom over the hollow site in the Co(0001) surface. In the absence of hydrogen, the interaction with the Co(0001) substrate plays a key role in stabilizing these edge structures and determines their local conformation and electronic properties. The calculated electronic properties for the low-energy edge structures are consistent with the measured scanning tunneling images.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-6/nn500583a/production/images/medium/nn-2014-00583a_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn500583a'>ACS Electronic Supporting Info</A></P>
Kang, Seok Ju,Kim, Bumjung,Kim, Keun Soo,Zhao, Yue,Chen, Zheyuan,Lee, Gwan Hyoung,Hone, James,Kim, Philip,Nuckolls, Colin WILEY‐VCH Verlag 2011 Advanced Materials Vol.23 No.31
<P><B>Pattern array of CVD‐grown single layer graphene (SLG)</B> is demonstrated by using micro‐patterned PDMS stamp. These ultrathin SLG electrodes can use as the source and drain for organic field effect transistors. The devices have high hole mobilities exceeding 10 cm<SUP>2</SUP>/Vs, high on‐off current ratios larger than 10<SUP>7</SUP> and a low threshold voltage for switching. </P>
Atomically thin p–n junctions with van der Waals heterointerfaces
Lee, Chul-Ho,Lee, Gwan-Hyoung,van der Zande, Arend M.,Chen, Wenchao,Li, Yilei,Han, Minyong,Cui, Xu,Arefe, Ghidewon,Nuckolls, Colin,Heinz, Tony F.,Guo, Jing,Hone, James,Kim, Philip Nature Publishing Group, a division of Macmillan P 2014 Nature nanotechnology Vol.9 No.9
Semiconductor p–n junctions are essential building blocks for electronic and optoelectronic devices. In conventional p–n junctions, regions depleted of free charge carriers form on either side of the junction, generating built-in potentials associated with uncompensated dopant atoms. Carrier transport across the junction occurs by diffusion and drift processes influenced by the spatial extent of this depletion region. With the advent of atomically thin van der Waals materials and their heterostructures, it is now possible to realize a p–n junction at the ultimate thickness limit. Van der Waals junctions composed of p- and n-type semiconductors—each just one unit cell thick—are predicted to exhibit completely different charge transport characteristics than bulk heterojunctions. Here, we report the characterization of the electronic and optoelectronic properties of atomically thin p–n heterojunctions fabricated using van der Waals assembly of transition-metal dichalcogenides. We observe gate-tunable diode-like current rectification and a photovoltaic response across the p–n interface. We find that the tunnelling-assisted interlayer recombination of the majority carriers is responsible for the tunability of the electronic and optoelectronic processes. Sandwiching an atomic p–n junction between graphene layers enhances the collection of the photoexcited carriers. The atomically scaled van der Waals p–n heterostructures presented here constitute the ultimate functional unit for nanoscale electronic and optoelectronic devices.
Lee, Gwan-Hyoung,Yu, Young-Jun,Cui, Xu,Petrone, Nicholas,Lee, Chul-Ho,Choi, Min Sup,Lee, Dae-Yeong,Lee, Changgu,Yoo, Won Jong,Watanabe, Kenji,Taniguchi, Takashi,Nuckolls, Colin,Kim, Philip,Hone, James American Chemical Society 2013 ACS NANO Vol.7 No.9
<P>Atomically thin forms of layered materials, such as conducting graphene, insulating hexagonal boron nitride (hBN), and semiconducting molybdenum disulfide (MoS<SUB>2</SUB>), have generated great interests recently due to the possibility of combining diverse atomic layers by mechanical “stacking” to create novel materials and devices. In this work, we demonstrate field-effect transistors (FETs) with MoS<SUB>2</SUB> channels, hBN dielectric, and graphene gate electrodes. These devices show field-effect mobilities of up to 45 cm<SUP>2</SUP>/Vs and operating gate voltage below 10 V, with greatly reduced hysteresis. Taking advantage of the mechanical strength and flexibility of these materials, we demonstrate integration onto a polymer substrate to create flexible and transparent FETs that show unchanged performance up to 1.5% strain. These heterostructure devices consisting of ultrathin two-dimensional (2D) materials open up a new route toward high-performance flexible and transparent electronics.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2013/ancac3.2013.7.issue-9/nn402954e/production/images/medium/nn-2013-02954e_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn402954e'>ACS Electronic Supporting Info</A></P>