Effect of Substrate on the Chemically Prepared Graphene Sheets on Sensor

Applications

Presented by, Deepak K. Pandey, Gyan Prakash, Suprem R. Das

Department of Physcs, and Birck Nanotechnology CenterPurdue UniversityWest Lafayette, IN

Proposal PresentationPhys-570X

Outline

1. Graphene Preparation and characterization

2. Device Fabrication

            (a) Suspended Graphene-sensor

            (b) Graphene Oxide based Sensor ( Suspended and Supported)

            (c) 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

Graphene Preparation and characterizationPreparation:

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].

700nm

191.66

0.00

Å

Å

A

B

C

0.0 0.5 1.0 1.5 2.0 2.5 3.00

20

40

60

80

A

B

C

Z (

nm

)

X (nm)

Wrinkles

1

23

(a)

(b)

(c)

0.89

0.00

1.13 Å

0.0 Å

(a) (b)

6.0 Å6.0 Å

0.89

0.00

2.76 Å

0.0 Å

A B

C

(a)

[1]. Yu et al., Appl. Phys. Lett., 93, 113103 (2008)[2]. Pandey et al., ECS Transection (2009)

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.

Mixture of powdered flake graphite and NaNO3

H2SO4

Ice bath

Add KMnO4

400 nm400 nm

HOPG

OG

400 nm400 nm

HOPG

OG

[1]. Hummers et al., J. Am. Chem. Soc., 80, 1339 (1958)

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. 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.

2. 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).

3. Both types of sensors will be compared to evaluate the selective sensing properties.

4. 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)

5. 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

6. Metal nano-particles (Pt, Pd) embedded graphene sheets will be used for hydrogen sensing.

Our Proposal

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

1. Being 2D, whole volume is exposed to surface adsorbates

2. Highly conductive, so having low Johnson noise even with no charge carriers, so a few carriers cause notable change in signal

3. Can be made defect free sheet, thereby a low level of excess (1/f) noise caused by their thermal switching

4. Four-probe measurements possible over a single sheet, with low resistant ohmic contact

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

Device Fabrication

Procedure

SLG size: 10m x 10m 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

AFM linescan

Data by Y. Dan et al

(a) EBL defined Hall bar on SLG

Device Fabrication contd…

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 oneconduction regime to other

~ 7.2E10 cm-2V-1 (from Hall meas)

Geim et al., Nature Materials, 6, 183 (2007)

Device Characterization

Graphene sensors: resolutions can be ~ ppb

Graphene can be doped in conc > 1012

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

Spike-like changes in Hall Resistivity near neutrality point

Single molecule sensing

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)

Device Characterization- Mass Sensor

' 2 '1( ) .

2dc dc

el g g g g gF C V C V V

1/2 2 2 2 20

0

[ ( / ) / ] 0.57 / 2 .m f

f A E t L A T L wtm f

Sensitivity in Air: 30.25 7.1 10m

f MHzm

1. D. Garcia-Sanchez, Nano Lett, 8(5), 1399 ; 2. J. S. Bunch, Science, 315, 490 (2007)

Conclusions

Prof. Y. P. Chen and the team members of this project.

1. Graphene will be prepared using chemical segregation on Ni and by chemical functionalization of graphite

2. Supported and suspended electronic and mass sensors will be prepared on single layer graphene (SLG) and bilayer graphene (BLG).

3. Effect of substrates on graphene sensor will be studied.

4. Combined, electronic and mass sensor will be developed.

Acknowledgement

THANKS!

Noise Analysis