Scanning gate microscopy on graphene: charge inhomogeneity and extrinsic doping.

We have performed scanning gate microscopy (SGM) on graphene field effect transistors (GFET) using a biased metallic nanowire coated with a dielectric layer as a contact mode tip and local top gate. Electrical transport through graphene at various back gate voltages is monitored as a function of tip voltage and tip position. Near the Dirac point, the response of graphene resistance to the tip voltage shows significant variation with tip position, and SGM imaging displays mesoscopic domains of electron-doped and hole-doped regions. Our measurements reveal substantial spatial fluctuation in the carrier density in graphene due to extrinsic local doping from sources such as metal contacts, graphene edges, structural defects and resist residues. Our scanning gate measurements also demonstrate graphene's excellent capability to sense the local electric field and charges.

[1]  Y. Ochiai,et al.  Scanning gate study of organic thin-film field-effect transistor , 2008 .

[2]  B. Alphenaar,et al.  Near room temperature self-assembly of nanostructures by reaction of gallium with metal thin films. , 2006 .

[3]  K. Novoselov,et al.  Detection of individual gas molecules adsorbed on graphene. , 2006, Nature materials.

[4]  Andre K. Geim,et al.  The rise of graphene. , 2007, Nature materials.

[5]  R. Cohn,et al.  Selective self-assembly at room temperature of individual freestanding Ag2Ga alloy nanoneedles , 2005 .

[6]  Supriyo Datta,et al.  Effect of contact induced states on minimum conductivity in graphene , 2007, 0710.2727.

[7]  SUPARNA DUTTASINHA,et al.  Graphene: Status and Prospects , 2009, Science.

[8]  N. Kybert,et al.  Intrinsic response of graphene vapor sensors. , 2008, Nano letters.

[9]  A. M. van der Zande,et al.  Photo-thermoelectric effect at a graphene interface junction. , 2009, Nano letters.

[10]  M I Katsnelson,et al.  Strong suppression of weak localization in graphene. , 2006, Physical review letters.

[11]  F. Guinea,et al.  The electronic properties of graphene , 2007, Reviews of Modern Physics.

[12]  D. Cobden,et al.  Tip-modulation scanned gate microscopy. , 2008, Nano letters.

[13]  Sergei V Kalinin,et al.  Role of single defects in electronic transport through carbon nanotube field-effect transistors. , 2002, Physical review letters.

[14]  K. Klitzing,et al.  Observation of electron–hole puddles in graphene using a scanning single-electron transistor , 2007, 0705.2180.

[15]  Michael S. Fuhrer,et al.  Charge transport and inhomogeneity near the minimum conductivity point in graphene , 2008 .

[16]  J. Gilman,et al.  Nanotechnology , 2001 .

[17]  C. N. Lau,et al.  Spatially resolved spectroscopy of monolayer graphene on SiO2 , 2008, 0812.1073.

[18]  S. Das Sarma,et al.  Ground state of graphene in the presence of random charged impurities. , 2008, Physical review letters.

[19]  C. Stampfer,et al.  Imaging localized states in graphene nanostructures , 2010, 1005.2024.

[20]  K. Novoselov,et al.  Molecular doping of graphene. , 2007, Nano letters.

[21]  E. Anderson,et al.  Scanned probe microscopy of electronic transport in carbon nanotubes. , 2000, Physical review letters.

[22]  N. Wilson,et al.  Carbon nanotube tips for atomic force microscopy. , 2009, Nature nanotechnology.

[23]  Influence of metal contacts and charge inhomogeneity on transport properties of graphene near the neutrality point , 2008, 0811.1459.

[24]  J. Brink,et al.  Doping graphene with metal contacts. , 2008, Physical review letters.

[25]  Charles M. Lieber,et al.  Resonant electron scattering by defects in single-walled carbon nanotubes. , 2001, Science.

[26]  Charles M. Lieber,et al.  Encoding Electronic Properties by Synthesis of Axial Modulation-Doped Silicon Nanowires , 2005, Science.

[27]  R. Westervelt,et al.  Imaging universal conductance fluctuations in mesoscopic graphene , 2009 .

[28]  F. Xia,et al.  Role of contacts in graphene transistors: A scanning photocurrent study , 2009 .

[29]  R. Westervelt,et al.  Imaging coherent transport in graphene (part II): probing weak localization , 2010, Nanotechnology.

[30]  D. Goldhaber-Gordon,et al.  Evidence of the role of contacts on the observed electron-hole asymmetry in graphene , 2008, 0804.2040.

[31]  Kwang S. Kim,et al.  Tuning the graphene work function by electric field effect. , 2009, Nano letters.

[32]  Andre K. Geim,et al.  Raman spectrum of graphene and graphene layers. , 2006, Physical review letters.

[33]  A. Geim,et al.  Two-dimensional gas of massless Dirac fermions in graphene , 2005, Nature.

[34]  A. H. Castro Neto,et al.  Graphene as an electronic membrane , 2007, cond-mat/0702562.

[35]  Andre K. Geim,et al.  Electric Field Effect in Atomically Thin Carbon Films , 2004, Science.

[36]  Klaus Kern,et al.  Contact and edge effects in graphene devices. , 2008, Nature nanotechnology.

[37]  P. Kim,et al.  Experimental observation of the quantum Hall effect and Berry's phase in graphene , 2005, Nature.

[38]  H. Dai,et al.  N-Doping of Graphene Through Electrothermal Reactions with Ammonia , 2009, Science.

[39]  Michael F. Crommie,et al.  Origin of spatial charge inhomogeneity in graphene , 2009, 0902.4793.

[40]  E. Williams,et al.  Charged Impurity Scattering in Graphene , 2007, 0708.2408.

[41]  G. A. C. Jones,et al.  Scanning gate microscopy of current-annealed single layer graphene , 2009, 0911.3832.

[42]  R. Rosenfeld.  Nature , 2009, Otolaryngology--head and neck surgery : official journal of American Academy of Otolaryngology-Head and Neck Surgery.

[43]  R. Westervelt,et al.  CRYOGENIC SCANNING PROBE CHARACTERIZATION OF SEMICONDUCTOR NANOSTRUCTURES , 1996 .

[44]  D. Ferry,et al.  Imaging of integer quantum Hall edge state in a quantum point contact via scanning gate microscopy , 2005 .

[45]  S. Tans,et al.  Molecular transistors: Potential modulations along carbon nanotubes , 2000, Nature.

[46]  R. M. Westervelt,et al.  Coherent branched flow in a two-dimensional electron gas , 2000, Nature.

[47]  S. Sarma,et al.  A self-consistent theory for graphene transport , 2007, Proceedings of the National Academy of Sciences.

[48]  C G Smith,et al.  Nanoanalysis of graphene layers using scanning probe techniques , 2010, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[49]  R. Westervelt,et al.  Imaging coherent transport in graphene (part I): mapping universal conductance fluctuations , 2010, Nanotechnology.