石墨烯吸附氨气-2009

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Adsorption of ammonia on graphene

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2009 Nanotechnology 20 245501

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IOP P UBLISHING N ANOTECHNOLOGY Nanotechnology20(2009)245501(8pp)doi:10.1088/0957-4484/20/24/245501

Adsorption of ammonia on graphene

Hugo E Romero1,Prasoon Joshi2,Awnish K Gupta1,

Humberto R Gutierrez1,Milton W Cole1,3,

Srinivas A Tadigadapa2,3,4and Peter C Eklund1,3,4

1Department of Physics,Pennsylvania State University,University Park,PA16802,USA

2Department of Electrical Engineering,Pennsylvania State University,University Park,

PA16802,USA

3Materials Research Institute,Pennsylvania State University,University Park,PA16802,USA

E-mail:sat10@ and pce3@

Received26January2009,infinal form28April2009

Published26May2009

Online at /Nano/20/245501

Abstract

We report on experimental studies of NH3adsorption/desorption on graphene surfaces.The

study employs bottom-gated graphenefield effect transistors supported on Si/SiO2substrates.

Detection of NH3occurs through the shift of the source–drain resistance maximum(‘Dirac

peak’)with the gate voltage.The observed shift of the Dirac peak toward negative gate voltages

in response to NH3exposure is consistent with a small charge transfer(f∼0.068±0.004

electrons per molecule at pristine sites)from NH3to graphene.The desorption kinetics involves

a very rapid loss of NH3from the top surface and a much slower removal from the bottom

surface at the interface with the SiO2that we identify with a Fickian diffusion process.

(Somefigures in this article are in colour only in the electronic version)

1.Introduction

Graphene is a singleflat atomic sheet of carbon with the atoms arranged in a two-dimensional(2D)honeycomb configuration.Recent progress in isolating graphene on an insulating substrate(e.g.,SiO2or SiC)now enable this exotic 2D system to be probed experimentally[1–3].It has been shown to be a promising building block for novel generation of high speed and sensitive electronic devices[4–12].Electron transport experiments on graphene have demonstrated,among other effects,unusual carrier-density-dependent conductiv-ity[1,13,14],anomalous quantum Hall effect[13–15], minimum quantum conductivity[13],and exceptionally high electron mobilities[16,17].These remarkable electronic properties stem from the unique band structure of graphene, which exhibits conduction and valence bands with near-linear dispersion that touch at the Brillouin zone corners to make a zero gap semiconductor.

Similar to earlier experiments on carbon nanotubes[18], the transport properties of graphene have been shown to be sensitive to molecules adsorbed on the surface(e.g.NH3,NO2, H2O and CO)[10,19].The details of the strength and character of the adsorption(chemi versus physisorption),and the degree of charge transfer between the analyte and graphene is still 4Authors to whom any correspondence should be addressed.under debate.Geim and co-workers were thefirst to report that a graphene Hall effect sensor device is capable of detecting individual molecules of NO2[10].Charge transfer between the graphene and NO2is thought to be important in this particular case[19,20].

Here,we report studies of the interaction of NH3with graphenefield effect transistors(FETs)supported on Si/SiO2 substrates in order to provide further insight into the nature of the molecule–graphene interaction.The SiO2is used as a gate dielectric and the heavily doped Si substrate as the bottom gate electrode.By sweeping the gate voltage,we can follow the time evolution of the peak in the drain-source resistance (known as the‘Dirac’peak)to monitor the change of the Fermi level in graphene in response to the adsorption and desorption of NH3.Presumably,this shift of the Dirac peak is dominated by charge transfer effects.The Dirac peak shift and the thermodynamic data for NH3on graphite are used to determine the effective charge transfer per NH3molecule(f) to the graphene.Our value for f will be compared to recent theoretical calculations for NH3bound to the surface[20]and to the edges[21]of graphene.

2.Experimental details

The graphene FETs studied here were supported on Si/SiO2 substrates and bottom-gated using the SiO2(300nm thermal