Effect of Substrate on the Chemically Prepared Graphene Sheets on Sensor Applications

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Effect of Substrate on the Chemically Prepared
Graphene Sheets on Sensor Applications
Proposal Presentation Phys-570X
Presented by, Deepak K. Pandey, Gyan Prakash,
Suprem R. Das
Department of Physcs, and Birck Nanotechnology
CenterPurdue UniversityWest Lafayette, IN
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Outline

• Graphene Preparation and characterization
• Device Fabrication
•             (a) Supported and suspended
  Graphene-sensor
•             (b) Body effect or contact effect or
  interface effect
• 3. Device Characterization
•             (a) Normal resistivity and Hall
  resistivity
•             (b) Study of time response
•             (c) Mass-Sensor
• 4. Conclusions

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Graphene Preparation and characterization
Preparation Preparation of graphene will be
done by method provided by Yu et al. 1. The
procedure and quality of graphene prepared by
this method is shown in figure below 2.
1. Yu et al., Appl. Phys. Lett., 93, 113103
(2008) 2. Pandey et al., ECS Transection (2009)
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Oxidized Graphene Preparation Chemical Path to
Graphene
Preparation Preparation of oxidized graphene
will be done by Hummers method 1. Hydrazine
vapors would be used for reducing the oxidized
graphene to graphene.
Substrates Substrates used would be Si/SiO2
and SiH / SiOM, OM Organic Molecules Motivatio
n To study the role of interface states in
sensing applications,
1. Hummers et al., J. Am. Chem. Soc., 80, 1339
(1958)
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Our Proposal

• Graphene being a one atom thick sheet comes in
  direct contact with substrate, thus interface
  state should play important role in sensing. We
  propose to study the effect of different
  substrates.
• We propose that suspended graphene sheet will be
  more efficient for certain (though not all) gas
  atom adsorption, as in suspended graphene, both
  the sides of the aromatic C-sheet will be exposed
  to the gas(es).
• Both types of sensors will be compared to
  evaluate the selective sensing properties.
• We propose to fabricate identical sensor devices
  using bilayer supported and suspended graphene as
  the noise level in BLG is known to be much
  smaller than that in SLG (IBM reported)
• Establishing experimentally, whether the sensing
  is due to the body dominated or it is contact
  dominated or induced by the graphene-substrate
  interfacial defects. For the first, we cover the
  contacts with some insulator to avoid molecular
  adsorption. For the second one, we cover large
  part of the graphene sheet (except the contacts)
  using PMMA or any other insulating polymer layer
• Metal nano-particles (Pt, Pd) embedded graphene
  sheets will be used for hydrogen sensing.

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Device Fabrication

• Motivation for graphene sensors Increased
  sensitivity to ultimate limit to detect even
  single dopant
• The ultimate limit of detectable S/N ratio at RT
  in graphene is due to
• Being 2D, whole volume is exposed to surface
  adsorbates
• Highly conductive, so having low Johnson noise
  even with no charge carriers, so a few carriers
  cause notable change in signal
• Can be made defect free sheet, thereby a low
  level of excess (1/f) noise caused by their
  thermal switching
• Four-probe measurements possible over a single
  sheet, with low resistant ohmic contact

(Ref Schedin et al., Nature Materials 6, 652,
2007)
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Device Fabrication

• Procedure
• SLG size 10?m x 10?m on Si/SiO2(300nm)
• Au/Ti, Au/Cr electrical contacts using EBL
• Multi-terminal Hall bar to be defined (by etching
  graphene in O2 plasma)
• Gas / Vapor detection
• NO2, NH3, H2O, CO, O2, Iodine, Ethanol, H2
• An Ar/H2 cleaning procedure (high temp cleaning
  in a reducing atmosphere sample cleaned by
  heating in flowing H2/Ar 850sccm Ar, 950sccm H2,
  400C, 1hr) for removing polymer contaminations on
  graphene surface left during lithographic
  processing. PR and other contaminants can greatly
  reduce the sensing
• Vapor response measurements

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Device Fabrication contd
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Device Characterization

• Mechanism
• Adsorb gases changes the resistivity/conductivity
  of the graphene layer making it a gas sensitive
  resistor. Desorption of adsorb gases bring
  graphene to its natural state thus recovering the
  sensor.
• Changes in the longitudinal (normal) resistance
  upon gas adsorption
• The Hall effect in graphene-based device shows
  strong sensitivity of the Hall resistivity ?xy to
  the charge carrier density (n or p), making it
  promising feature for sensor applications.

Variation in Vg can manipulate the carrier type,
the charge carrier density, and switching from
one conduction regime to other
? 7.2E10 cm-2V-1 (from Hall meas)
Geim et al., Nature Materials, 6, 183 (2007)
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Device Characterization

• Graphene sensors resolutions can be ppb
• ? Graphene can be doped in conc gt 1012

Schedin et al., Nature Materials, 6, 652 (2007)
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Single molecule sensing
Spike-like changes in Hall Resistivity near
neutrality point
?R depends on B, number of graphene layers, and
device to device, reflecting the steepness of
Hall resistivity near neutrality point
Schedin et al., Nature Materials, 6, 652 (2007)
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Device Characterization- Mass Sensor
Sensitivity in Air
1. D. Garcia-Sanchez, Nano Lett, 8(5), 1399
2. J. S. Bunch, Science, 315, 490 (2007)
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Conclusions

• Graphene will be prepared using chemical
  segregation on Ni and by chemical
  functionalization of graphite
• Supported and suspended electronic and mass
  sensors will be prepared on single layer graphene
  (SLG) and bilayer graphene (BLG).
• Effect of substrates on graphene sensor will be
  studied.
• Combined, electronic and mass sensor will be
  developed.

Acknowledgement
Prof. Y. P. Chen and the team members of this
project.
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• THANKS!

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Noise Analysis