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Local transport measurements in graphene on SiO<sub>2</sub> using Kelvin probe force microscopy
Willke, P.,Mohle, C.,Sinterhauf, A.,Kotzott, T.,Yu, H.K.,Wodtke, A.,Wenderoth, M. Pergamon Press ; Elsevier Science Ltd 2016 Carbon Vol.102 No.-
<P>By using Kelvin Probe Force Microscopy with an additional applied electric field we investigate the local voltage drop in graphene on SiO2 under ambient conditions. We are able to quantify the variation of the local sheet resistance and to resolve localized voltage drops at line defects. Our data demonstrates that the resistance of line defects has been overestimated so far. Moreover, we show that wrinkles have the largest resistance, rho(Wrinkle) < 80 Omega mu m. Temperature-dependent measurements show that the local monolayer sheet resistance reflects the macroscopic increase in resistance with temperature while the defect resistance for folded wrinkles is best described by a temperature-independent model which we attribute to interlayer tunneling. (C) 2016 Elsevier Ltd. All rights reserved.</P>
Baik, Jeong Min,Zielke, Mark,Kim, Myung Hwa,Turner, Kimberly L.,Wodtke, Alec M.,Moskovits, Martin American Chemical Society 2010 ACS NANO Vol.4 No.6
<P>An electronic nose (e-nose) strategy is described based on SnO<SUB>2</SUB> nanowire arrays whose sensing properties are modified by changing their operating temperatures and by decorating some of the nanowires with metallic nanoparticles. Since the catalytic processes occurring on the metal nanoparticles depend on the identity of the metal, decorating the semiconducting nanowires with various metal nanoparticles is akin to functionalizing them with chemically specific moieties. Other than the synthesis of the nanowires, all other steps in the fabrication of the e-nose sensors were carried out using top-down microfabrication processes, paving the way to a useful strategy for making low cost, nanowire-based e-nose chips. The sensors were tested for their ability to distinguish three reducing gases (H<SUB>2</SUB>, CO, and ethylene), which they were able to do unequivocally when the data was classified using linear discriminant analysis. The discriminating ability of this e-nose design was not impacted by the lengths or diameters of the nanowires used.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2010/ancac3.2010.4.issue-6/nn100394a/production/images/medium/nn-2010-00394a_0007.gif'></P>
Yu, Hak Ki,Balasubramanian, Kannan,Kim, Kisoo,Lee, Jong-Lam,Maiti, Manisankar,Ropers, Claus,Krieg, Janina,Kern, Klaus,Wodtke, Alec M. American Chemical Society 2014 ACS NANO Vol.8 No.8
<P>We present a simple approach to improving the quality of CVD grown graphene, exploiting a Cu(111) foil catalyst. The catalyst is epitaxially grown by evaporation on a single crystal sapphire substrate, thickened by electroplating, and peeled off. The exposed surface is atomically flat, easily reduced, and exclusively of (111) orientation. Graphene grown on this catalyst under atmospheric CVD conditions and without wet chemical prereduction produces single crystal domain sizes of several hundred micrometers in samples that are many centimeters in size. The graphene produced in this way can easily be transferred to other substrates using well-established techniques. We report mobilities extracted using field-effect (as high as 29 000 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP>) and Hall bar measurement (up to 10 100 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP>).</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2014/ancac3.2014.8.issue-8/nn503476j/production/images/medium/nn-2014-03476j_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn503476j'>ACS Electronic Supporting Info</A></P>
Anemone, Gloria,Climent-Pascual, Esteban,Al Taleb, Amjad,Yu, Hak Ki,Jimé,nez-Villacorta, Felix,Prieto, Carlos,Wodtke, Alec M.,De André,s, Alicia,Farí,as, Daniel Elsevier 2018 Carbon Vol.139 No.-
<P><B>Abstract</B></P> <P>Chemical vapor deposition (CVD) is one of the best ways to scalably grow low cost, high quality graphene on metal substrates; unfortunately, it not ideal for producing graphene on dielectric substrates. Here, we demontrate production of a high quality graphene layer on Sapphire using CVD with a copper catalyst. The catalyst consists of a thin copper film grown epitaxially on <I>α</I>- <SUB> Al 2 </SUB> <SUB> O 3 </SUB> (0001). After CVD growth of Graphene, the copper can be removed by simple evaporation in the presence of a carbon source ( <SUB> C 2 </SUB> <SUB> H 4 </SUB> ). We characterized the resulting graphene layer using Raman spectroscopy, atomic force microscopy (AFM), optical transmission and helium atom scattering (HAS). The sample exhibited a reduced Raman D peak and an excellent 2D to G ratio. AFM and HAS show large graphene domains over a macroscopic region. We measured > 86 % transparency over the visible spectrum.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Directional Ostwald Ripening for Producing Aligned Arrays of Nanowires
Lee, Hye Jin,Yang, U Jeong,Kim, Kyeong Nam,Park, Soojin,Kil, Kye Hyoung,Kim, Jun Soo,Wodtke, Alec M.,Choi, Won Jun,Kim, Myung Hwa,Baik, Jeong Min American Chemical Society 2019 NANO LETTERS Vol.19 No.7
<P>The remarkable electronic and mechanical properties of nanowires have great potential for fascinating applications; however, the difficulties of assembling ordered arrays of aligned nanowires over large areas prevent their integration into many practical devices. In this paper, we show that aligned VO<SUB>2</SUB> nanowires form spontaneously after heating a thin V<SUB>2</SUB>O<SUB>5</SUB> film on a grooved SiO<SUB>2</SUB> surface. Nanowires grow after complete dewetting of the film, after which there is the formation of supercooled nanodroplets and subsequent Ostwald ripening and coalescence. We investigate the growth mechanism using molecular dynamics simulations of spherical Lennard-Jones particles, and the simulations help explain how the grooved surface produces aligned nanowires. Using this simple synthesis approach, we produce self-aligned, millimeter-long nanowire arrays with uniform metal-insulator transition properties; after their transfer to a polymer substrate, the nanowires act as a highly sensitive array of strain sensors with a very fast response time of several tens of milliseconds.</P> [FIG OMISSION]</BR>