graphene-based composite sensors for energy applications

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Prepared ByCharter D. StinespringAssociate Professor

Chemical Engineering DepartmentWest Virginia University

Prepared For2014 NETL Crosscutting Research Review Meeting

May 19 – 23, 2014

Graphene-Based Composite Sensors for Energy Applications

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BackgroundGraphene As A Sensor Material

Hypothesis, Goals, & Research Issues

Overview Of Presentation

Status of Key Research AreasGraphene Synthesis & Post Synthesis Surface Modification

Nanoparticle Nucleation and Growth

Sensor Fabrication & Electrical Characterization

Test Unit & Gas Response

Summary of Key Results

Acknowledgements

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Graphene As A Sensor MaterialStructure of graphene

Basic Question: How can target specificity be achieved?

As a gas sensor material

- p orbitals normal C-monolayer

- Chemoresistive graphene gas sensors have a rapid response and high sensitivity

- Flat monolayer of sp2 bonded C-atoms

- High charge carrier mobility- Low charge carrier density- Adsorbed molecules alter carrier density

Fundamental scientific issue addressed in this research

- May include multilayer films

Top View

Edge View

Top View

Edge View

Basic Hypothesis of this Research

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Gas adsorption mediated by different types of nanoparticles attachedto independent graphene chemoresistive sensors can yield an electricalresponse pattern specific to each adspecies.

Hypothesis

Research IssuesSynthesis of graphene & graphene-nanoparticle composites

Characterization of electrical properties

Sensor fabrication & testing

Validate the hypothesis and use graphene-nanoparticle composites todevelop a high sensitivity, rapid response electronic nose capable ofoperating over a wide range of conditions including high temperatureenergy applications

Research Goals

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Acknowledgements

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SI - SiC Substrate

Source Drain

Few Layer Graphene

Nanoclusters

Roadmap - Basic Sensor Design

SI - SiC Substrate

Source Drain

Few Layer Graphene Film Graphene synthesis

Post synthesis surface modification- Control defect levels- Modify electrical properties- Provide nucleation sites for nanoparticles

Nanocomposite Sensor Platform

Nucleation & growth of nanoparticles

Sensor fab, electrical characterization, & sensor testing

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Synthesis Of G/SiC FilmsICP-RIE

Plasma Etching

Ions Radicals Electrons

PhysicalSputtering

Chemical Etching Heating

Halogenated Carbon Overlayer

ThermalAnnealing

EpitaxialGraphene

ICP-RIE Plasma Etching

Ions Radicals Electrons

PhysicalSputtering

Chemical Etching Heating

Halogenated Carbon Overlayer

ThermalAnnealing

EpitaxialGraphene

UHVAAP-RTA

Substrates6H-SiC4H-SiC

Stinespring & coworkers, J. Vac. Sci. Technol. 30 (2012) 030605-5.

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680 685 690 695Binding Energy (eV)

Inte

nsity

(Arb

.Uni

ts) 687.6 eV

685.6 eV

F 1s - S35400 W ICP100 W RIE970oC

UHVA G/SiC Films

280 282 284 286 288 290

Binding Energy (eV)

Inte

nsity

(Arb

. Uni

ts)

C 1s - S40600 W ICP300 W RIE970oC282.5 eV

283.8 eV

285.6 eV288.1 eV

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a) Graphene oxide and b) hydrazine reduced GO

Stankovich et al., Carbon 45(2007)1558-1565.

AP-RTA G/SiC Films

280 285 290 295

Inte

nsity

(Arb

. Uni

ts)

Binding Energy (eV)

S142RTA

282.5 eV

284.6 eV

286.0 eV

288.9 eV

C-O

C(O)O

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280 285 290 295

Inte

nsity

(Arb

. Uni

ts)

Binding Energy (eV)

S142RTA

282.5 eV

284.6 eV

286.0 eV

288.9 eV

280 285 290 295In

tens

ity (A

rb. U

nits

)Binding Energy (eV)

S142RTAHCl

282.5 eV

284.0 eV

285.1 eV288.6 eV

Post Synthesis Surface Modification

C-O

C(O)O C-OC(O)O

- Enhancement and narrowing of the C-C peak / reduction of Si-C- Reduction of the C-O defects / relatively no change in edge defects

- The ability to control the surface defects is useful since they influence electrical properties & are potential sites for particle nucleation

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Nanoparticle Nucleation & Growth on GrapheneNanoparticles deposited on graphene from solution

Hypothesis is that particles will nucleate and grow on surface defects

Initial studies performed using Ag and Au nanoparticles Ag forms an oxide, Au does not

Both easily detected using SEM / XPS / AFM

Simple Reaction Mechanisms AgNO3 + NaBH4 > Ag + ½ H2 + ½ B2H6 + NaNO3

Simple Reaction Sequence Sample immersed in 10mM AgNO3/H2O

25mM NaBH4/H2O & incubated 12 hours Solomon et al., J. Chem. Ed. 84 (2007) 322-322.

Solomon et al., J. Chem. Ed. 84 (2007) 322-322.

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Ag Nanoparticle Nucleation & Growth

360 365 370 375 380 385

Binding Energy (eV)

Inte

nsity

(Arb

. Uni

ts)

Ag3d5/2

Ag3d3/2

367.3 eV0.8 eV FWHM

373.3 eV0.8 eV FWHM

6.0 eV

Ag 3d - Ag-nP/G/SiC

~1.3 at %

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Au Nanoparticle Nucleation & Growth

2 µm x 2 µm AFM Image of Au np/G/SiC (S170) RMS ~ 6.0 nm 475 nm x 475 nm Image of Au np/G/SiC (S170) RMS ~ 5.8 nm 100 nm x 100 nm AFM Image of Au np/G/SiC (S170) RMS ~ 0.2 nm

0

2

4

6

8

10

0 100 200 300 400

[nm]

[nm]

Particle DimensionsDiameter: 25 nm – 150 nmHeight: 0.5 nm – 5 nm

- Attached particles are pyramidal- Suggests heterogeneous nucleation with

Volmer-Webber growth

- Ultrasonically removed particles are spheroidal- Associated with homogeneous nucleation &

deposition from solution

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- Use shadow mask #1 & oxygen plasma to remove graphene & form SiOx strips while protecting 2 mm x 2 mm graphene regions

- Use shadow mask #2 and e-beam evaporation to produce Au/Ti device patterns (TLM & sensor)

- Use wafering saw to produce 2.5 mm x 2.5 mm die for testing

- Deposit uniform G/SiC film on1 cm x 1 cm substrate

Device Fabrication

- TLM pattern - electrical properties Sensor pattern – sensor testing

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G/6H-SiC Electrical Characterization

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.020

0 1 2 3 4 5Voltage (V)

Cur

rent

(A)

S140

- Select contact array

- Analysis of I-V data using Richardson-Dushman equation yields the carrier density and Schottky barrier height

- Determine the resistance for each contact pair

Linear Fity = 0.3756x + 17.182

R2 = 0.9236

0

5

10

15

20

25

30

0 5 10 15Aspect Ratio (d/w)

Res

ista

nce

(Ohm

)

Slope = Sheet Resistance of Film (Ohm/sq)Intercept = 2*Contact Resistance (Ohm)

S140

Film Resistivity = 3.8 x 10-8 Ohm-cmContact Resistance = 8.3 Ohm

- Using standard TLM analysis, plots of resistance versus aspect ratio yield the contact resistance and film resistance

-12

-10

-8

-6

-4

-2

0

0.5 1.0 1.5 2.0

V1/4

Red

uced

Cur

rent

Carrier Density = 8.3 x 1011 cm-2

Schottky Barrier Height = 0.5 eV

- Resistance and carrier density of G/6H-SiC comparable to exfoliated graphene

- Unlike normal graphene, fluorine & oxygen defects open band gap

- Surface modified G/6H-SiC films retain Schottky behavior

- Measure I-V characteristic for each contact pair in array

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G/4H-SiC Electrical Characterization- Both UHVA and RTA G/4H-SiC have low conductivity

- Surface modified G/4H-SiC exhibits Ohmic behavior

Summary- Electrical properties of native and

surface modified G/SiC quite diverse

- Raise interesting questions concerning the underlying physics

- Electrical properties well suited for next phase of sensor development

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Sensor Platform and Test Unit

- Useful for both electrical property measurements & sensor development

- Sensor mounted on TO header with microheater and RTD for control of temperature (≤500 °C)

- Sensor platform incorporated into test unit for characterizing response to target species

16 Pin Transistor Outline Header

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Task Schedule







Acknowledgements

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Synthesis & Post Synthesis Surface ModificationGraphene synthesis processes in hand- One, two, and three layer G/SiC reproducibly and routinely produced- UHVA and RTA defect structures characterized- Continue to optimize the process

Surface modification of continued interest - Surface modification alters defect distribution- Influences the electrical properties - May be useful in controlling the areal density of nucleation sites

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- Evidence for both homogeneously and heterogeneously nucleated particles- Brief ultrasonic treatment removes weakly attached particles- Pyramidal 0.5 – 5 nm high x 25 – 150 nn diameter particles remain- Suggest Volmer-Webber nucleation and growth mode- Studies in progress to establish role of defect sites & determine growth

kinetics

Studies of Pt, TiO2, and ZnO nucleation & growth next in line

Ag & Au nanoparticles deposited using solution chemistry

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- Native & surface modified G/SiC films exhibit diverse electrical properties - Raise highly interesting physics questions for further study

Sensor fabrication process in hand- Lithography free process developed for sensor & TLM structures- Continue to optimize process

Electrical characterization and testing in progress

Key Observation: The native & modified G/SiCwell suited for the sensor development and testing efforts now in progress

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Acknowledgements

Undergrad Students- Jason Miles - Particle nucleation and growth- McKenzie Mills – Surface modification

PhD Students- Saurabh Chaudhari – Graphene synthesis & sensor fabrication- Andrew Graves – Sensor characterization

University Coal Research Program- DOE Award Number: DE-FEOO11300

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Looking Ahead – Applications EnvironmentIntegrated Gasification Combined Cycle

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Integrated Gasification Combined Cycle (IGCC)

2300 – 2700 oFVery High

1100 – 1400 oFHigh

700 – 800 oF

350 – 400 oF

AccommodatedBy RuggedizedSensor Design

WarmRequiresModifiedSensorDesign Accommodated

By Current Sensor Design

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Sensor Test Unit & Gas Response StudiesSensor test unit operational

Temperature dependent electrical characterization and gas response measurements in progress

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Post Synthesis Surface Modification

0

10

20

30

40

50

60

70

80

90

RTA HCl NaBH4 Methanol Water Acetone

C‐Si (Substrate) C‐C (Graphene) C‐OH (Defect) C=O (Defect)

- Enhancement of the C-C peak- Reduction of the C-O defects but relatively no change in edge defects

- The ability to control the surface defects is useful since they influence electrical properties & are potential sites for particle nucleation

graphene-based composite sensors for energy applications

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