Graphene Micro Devices - University of Minnesota 17_1... · Properties of Graphene Graphene: Mother of all graphitic forms. Graphene is a 2D building material : It can be wrapped

Graphene Micro Devices

Tianhong Cui

ME8254

Outline

Properties of graphene

Graphene synthesis methods

Applications of graphene

Conclusion

Outline




Conclusion

Properties of Graphene

Graphene: Motherof all graphiticforms.Graphene is a 2Dbuilding material :It can be wrappedup into 0DFullerene, rolledinto 1D nanotubesor stacked into 3Dgraphite.

Graphene, one-atom-thick planar sheet of sp2-bonded carbonatoms densely packed in a honeycomb crystal lattice, is thethinnest known material in the universe.


Single layer graphene was firstobserved by Geim and others atManchester University in 2004.

A few layer flake of grphene on SiO2.“Electric Field Effect in Atomically ThinCarbon Films”K. S. Novoselov, et al. Science, 2004.

The discovery of graphene led to an explosion of interest, in part because two-dimensionalcrystals were thought to be thermodynamically unstable at finite temperatures.

In 2007, Geim’s group derived the firstfreely suspended graphene sheets. Beforethat, graphenes were all integral part oflarger three-dimensional structures.

TEM image of suspended graphene membrane.“The structure of suspended graphene sheets”.Jannik C. Meyer, et al, Nature, 2007.


The isolation of single-layer graphene firstyielded access to a large amount ofinteresting Physics. The most exploredaspect of graphene physics is its electronicproperties:1. Electrons propagating through thehoneycomb lattice completely lose theireffective mass.2. Its electrons can cover submicrometerdistances without scattering.3. Quantum effects in graphene are robustand can survive even at room temperature.4. Ambipolar field effect. Carriers can beturned continuously between holes andelecctrons by supplying the requisite gatebias.

Quantum update

Ambipolar field effect: conduction and valencebands meet at the Dirac point. Under gate bias,the Fermi level moves above or below theDirac point to introduce a significant number offree electrons or holes. (“Honeycomb Carbon:A Review of Graphene” Matthew J. Allen, et al,Chem. Rev. 2010.)


Main Physical Properties of graphene:1. High carrier mobility;2. Low 1/f noise;3. High thermal conductivity;4. High Young’s modulus;5. Band gap: 0.

material Young’smodulus(

Pa)

Thermalconductivity(W/m-K)

Carriermobility(cm3/Vs)

Graphene 1.06T 3,000 200,000

Carbonnanotube

1T 3,000 100,000

Silicon 165G 148 1,400

Comparison of graphene and other materials

Noise density spectrum for SWNT andreduced graphene oxide devices.(“Reduced graphene oxide molecularsensors”, Jeremy T. Robinson, et al,Nano Letters, 2008.)


Raman spectroscopy is apowerful tool for the studyof graphene. The majorfeatures of the Ramanspectra of graphite andgraphene are the G band at∼1584 cm-1 and the G′band at ∼2700 cm-1. The Gband is due to the E2g

vibrational mode, and theG′ band is a second-ordertwo-phonon mode.

In bulk graphite, the G′ band is comprised oftwo components. For single layer graphene, theG′ band is a single sharp peak at the lower shift,with intensity roughly 4 times that of the Gpeak.

“fingerprint” of graphene

Outline




Conclusion

Graphene Synthesis Methods

1. Mechanical cleaving of graphite

Schematic of graphene-on-demand by cut-and-choose transfer-printing.(“Graphene TransistorsFabricated via Transfer-Printing In Device Active-Areas on Large Wafer”Xiaogan Liang, et al,Princeton University,Nano letters, 2007)

Graphene is stacked layers of many graphene sheets, bonded together by week van derWaals force. Thus, it is possible to produce graphene from a graphite by mechanicalexfoliation. This is how graphene was first discovered by Geim’s group in 2004.Despite tremendous progress with alternatives, mechanical exfoliation still producesthe highest quality graphene flakes available.


Xiaogan Liang, et al,used electrostatic forceto peel of graphene.(“Electrostatic ForceAssisted Exfoliation ofPrepatterned Few-Layer Graphenes intoDevice Sites”Xiaogan Liang, et al,Berkeley, Nano letters,2009 )

Li Song et al fromRice University usegold layer which issputtered on graphiteto peel of graphene.(“Transfer Printing ofGraphene Using GoldFilm”Li Song, et al, RiceUniversity, Acsnano,2009.)


2. Chemical vapor depositon/ epitaxial growth

Prakash’s group, for the first time,experimentally demonstrated that planer fewlayer graphenes (PFLGs) can be synthesized bysimple thermal CVD method. Ni substrate waschosen.

TEM image of thePFLG film on Nisubstrates. (“Planernano-graphenes fromcamphor by CVD”Prakash R. Somani, etal, Chemical PhysicsLetters, 2006.)

Graphene was also synthesized onCu foil by CVD.

Graphene on Cu foil. (“Large-AreaSynthesis of High-Quality and UniformGraphene Films on Copper Foils”Xuesong Li, et al, Science, 2009.)


Kim et al, show growth of graphene on Ni film. The film thickness wasoptimized for best quality of graphene. High cooling rate is important tominimize the number of layers. Graphene was later transferred on to PDMS.

Schematic flowchart of Synthesisof patterned graphene films onthin nickel layers, and transfergraphene onto PDMS.“Large-scale pattern growth ofgraphene films for stretchabletransparent electrodes”Keun Soo Kim, et al, Nature,2009.


The largest graphene film so far was fabricated by lijima’s group. Thegraphene films was grown by chemical vapour deposition onto flexiblecopper substrates. The graphene is 30 inch in size.

Graphene-based touch-screenpanel connected to a computerwith control software

A transparent ultralarge-area graphene filmtransferred on a 35-inch PET sheet.

“Roll-to-roll production of 30-inch graphene films for transparent electrodes”Sukang Bae, et al, Nature Nanotechnology, 2010.


3. Chemical exfoliation

Nature graphite is subjected to oxidation which makes it more easily to dividedinto layers, followed by purification processes (reduction), The product, however,is not fully reduced and found to have some amount of oxygen functional groupsand defaults.

Schematic of the exfoliated graphitereintercalated with sulphuric acidmolecules (teal spheres) betweenthe layers(a), and TBA (bluespheres) insertion into theintercalated graphite(b).“Highly conducting graphene sheetsand Langmuir–Blodgett films”XIAOLIN LI, et al, StanfordUniversity, Nature nanotechnology,2008.


4. CNTs methods

Dmitry V. Kosynkin et alfrom Rice Universitydeveloped a simple solution-based oxidative process forproducing a nearly 100%yield of nanoribbonstructures by lengthwisecutting and unravelling ofmultiwalled carbon nanotube.(MWCNT) side walls.(“Longitudinal unzipping ofcarbon nanotubes to formgraphene nanoribbons”Dmitry V. Kosynkin, et al, RiceUniversity, Nature, 2009.)


Hongjie Dai’s group developed a easy way to fabricate graphenenanoribbons. MWNTs were first partly embedded in a polymer film.Graphene nanoribbons were produced by plasma etching of MWNTs,

“Narrow graphenenanoribbons fromcarbon nanotubes”Liying Jiao, et al,Stanford University,Nature, 2009.


1. Mechanical cleaving of graphite.Best quality so farLabor intense; not suitable for large area growth.

2. Chemical exfoliation.Easy to separated into individual sheetsHas many defects and oxygen functional groups.

3. Chemical vapor deposition and epitaxial growthThe ability to grow large area;Electronic properties are changed by the disorderintroduced by substrate; high temperature is needed, and insome situation high vacuum is also needed.

4. CNTs methodsEasy to fabricate graphene ribbons which has non-zero bandgap and is suitable for electronic device.Not suitable for large area growth.

Comparison of different methods

Outline




Conclusion

Applications of Graphene

1. Graphene based transistor

High carrier mobility means graphenebased transistor can be operated atvery high frequency. Y.-M. Lin et alfrom IBM present field-effecttransistors fabricated on a 2 inchgraphene wafer with a cutofffrequency as high as 100 GHz.(“100-GHz Transistors from Wafer-Scale Epitaxial Graphene”Y.-M. Lin, et al, Science, 2010.)

High carrier mobility, low noise, and ambipolarity make graphene agood candidate for electronic devices.


Hongjie Dai’s group developed a chemicalroute to produce graphene nanoribbons(GNR) with width below 10 nanometers.And used them to fabricate graphene fieldeffect transistors with on-off ratios of about107 at room temperature.(“Chemically Derived, UltrasmoothGraphene Nanoribbon Semiconductors”Xiaolin Li, et al, Stanford University,Science, 2008.)

The drawback of graphene being a transistor is zero band gap. Thus manygroups focus on how to generate band gap in graphene in order to increaseon-off ratio of graphene based transistor. One effective method is usinggraphene ribbon.


Yuanbo Zhang et al from U.C.Berkeley fabricated a dual-gate bi-layer graphenetransistor which band gap can reach 250 meV.(“Direct observation of a widely tunable band gap in bilayer graphene” YuanboZhang, et al, Berkeley, Nature, 2009.)

Another method of generating band gap is bi-layer graphene with double gate.Gate voltage can not only generate but also control the band gap.


J. Scott Bunch et al from Cornell Universityfabricated the first graphene-based resonator.( “Electromechanical Resonators from Graphenesheets” J. Scott Bunch, et al. Science, 2007.)

The enormous stiffness and low density of graphene make it an idealmaterial for nanoelectromechanical applications

2. Graphene based electromechanical device


“Performance of monolayer graphene nanomechanical resonatorswith electrical readout”Changyao Chen, et al, Nature nanotechnology, 2009.

James Hone’s group fabricated a graphene resonator withelectrical readout. The quality factor reached10000 at 5 K. Themass sensitivity of the best sample was 2 zg.


Kaveh M. Milaninia et al from M.I.T. demonstrated an electromechanical switchcomprising two graphene films; each deposited using ambient pressure chemicalvapor deposition. The top film is pulled into electrical contact with the bottom filmby application of approximately 5 V between the layers. Contact is broken bymechanical restoring forces after bias is removed.

“All graphene electromechanical switch fabricated by chemical vapor deposition”Kaveh M. Milaninia et al, Applied Physics Letters, 2009.


3. Graphene based gas/bio sensor

“Detection of individual gas molecules adsorbed on graphene”F. SCHEDIN, et al, Nature Materials, 2007.

Graphene has the maximum surface to volume ratio, and very low noise,which make it a good choice for gas/bio sensor.Geim’s group from Manchester University fabricated the first graphene basedgas sensor, which can detect individual molecules of NO2 and NH3.


“Reduced graphene oxide molecularsensors”, Jeremy T. Robinson, et al, NanoLetters, 2008.

Jeremy T. Robinson et al fabricated aReduced Graphene Oxide gas sensor,which shows10-100 fold reduction in 1/fnoise over SWNT-based sensors.

Jesse D. Fowler et al from USLA developeda chemical sensors from chemicallyconverted graphene. The resistance of the p-type material decreases upon exposure toelectron withdrawers (e.g., NO2) andincreases upon exposure to electron donors(e.g., NH3).

“Practical Chemical Sensors fromChemically Derived Graphene”Jesse D. Fowler, et al, Acsnano, 2009


There are few questions about the limits of sensitivity for graphenebased gas/bio sensors. The real drawback so far is a lack of selectivity.

Nihar Mohanty et al developed the first graphene biological device. They demonstratedthe interfacing of chemically modified graphene with biological systems to build anovel live-bacterial-hybrid device and a DNA-hybridization device with excellentsensitivity.

“Graphene-Based Single-Bacterium Resolution Biodevice and DNA Transistor:Interfacing Graphene Derivatives with Nanoscale and Microscale Biocomponents”Nihar Mohanty et al, Nano Letters, 2008.

Outline




Conclusion

Conclusions

Graphene has attracted great interest amongphysicists, chemists and engineers sincesingle-layer flakes were first isolated in 2004,because graphene possesses a combination ofspecial properties which happen to answerseveral limitations of currently knownmaterials and systems. Organic and materialschemists are busily working on new syntheticroutes to high-quality single layers, whileengineers are designing novel devices toexploit graphene’s extraordinary properties. Itis easy to believe that the future for grapheneis nothing but bright.

Documents

Graphene Micro Devices - University of Minnesota 17_1... · Properties of Graphene Graphene: Mother of all graphitic forms. Graphene is a 2D building material : It can be wrapped