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

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 Center Purdue University West Lafayette, IN. Outline.

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

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  1. 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

  2. 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

  3. 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)

  4. 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 Si:H / Si:OM, OM : Organic Molecules Motivation: To study the role of interface states in sensing applications, [1]. Hummers et al., J. Am. Chem. Soc., 80, 1339 (1958)

  5. 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.

  6. 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)

  7. 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

  8. Device Fabrication contd…

  9. Device Characterization Mechanism: Adsorbgases changes the resistivity/conductivity of the graphene layer making it a gas sensitive resistor. Desorptionof 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)

  10. Device Characterization • Graphene sensors: resolutions can be ~ ppb •  Graphene can be doped in conc > 1012 Schedin et al., Nature Materials, 6, 652 (2007)

  11. 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)

  12. Device Characterization- Mass Sensor Sensitivity in Air: 1. D. Garcia-Sanchez, Nano Lett, 8(5), 1399 ; 2. J. S. Bunch, Science, 315, 490 (2007)

  13. 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.

  14. THANKS!

  15. Noise Analysis

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