In-situ Engineering of Graphene with Electrons

Transcription

1 Wright State University CORE Scholar Special Session 5: Carbon and Oxide Based Nanostructured Materials (2012) Special Session In-situ Engineering of Graphene with Electrons Mark Ruemmeli Follow this and additional works at: Part of the Physics Commons Repository Citation Ruemmeli, M. (2012). In-situ Engineering of Graphene with Electrons.. This Presentation is brought to you for free and open access by the Special Session 5 at CORE Scholar. It has been accepted for inclusion in Special Session 5: Carbon and Oxide Based Nanostructured Materials (2012) by an authorized administrator of CORE Scholar. For more information, please contact corescholar@ library-corescholar@wright.edu.

2 In situ Engineering of Graphene with Electrons DSL 2012 Istanbul

3 Introduction/Motivation The Goal: Develop Low voltage TEM (LV TEM) in situ engineering and chemistry Ho w do (carbon) materials behave under these conditions? Ho w far can we use electrons to engineer nanostructures? Electrical currents Electron beams

4 Electrical currents through graphene High bias regime (2 3 V) Joul e heating ~ 2000 C Contamination removed [sublimation,current reduces] Cracking [usually at centre from edges, current reduces] Atom lattice ~ 30 ev Atom vacancy ~ 7 ev

5 Electrical currents through graphene Crack propogation at high bias

6 Electrical currents through graphene Layer by layer sublimation Crack propogation folds around edges

7 Electrical currents through graphene Layer by layer sublimation

8 Electrical currents through graphene Fusing of two overlapping graphene layers Overlap region heals out (high temperatures)

9 Electrical currents through graphene Seamles s bilayer constriction fabrication Breakdown current density, J BR, increases with constriction width reduction scattering at optical phonons surpressed at small constrictions? More adsorbates on larger widths (unlikely)?

10 Electrical currents through graphene constrictions

11 Electrical currents through graphene constrictions

12 Electrical currents through graphene constrictions Constrictions are seamless bi layer graphene structures Anisotropi c lattice expansion observed. Anisotropy due to strain Expansion increases with decreasing width Lattice expansion greatest in constriction [Expansion between 1.5% and 5%!]

13 Electrical currents through graphene constrictions Har d to explain the anomously large expansion Joule heating: Extrapolated estimates from literature yield temperatures between 4000 K and 5500 K doe s not make sense! Assuming 4000 K (upper limit) estimates for the thermal conductivity is ~200 W/m.K doe s not make sense! Effects of strain limited ( < 30% change in thermal conductivity) Assuming 2800 W/m.K (published bi layer value) then T = 630 K. Does not makes sense either! Is impact ionisation relevant?! incoming electron excites bonding electron to antiboniding state

14 Fabricating graphene with electrical on graphene graphitisation graphene on graphene Probably a thermally driven process Sublimation appears limited Th e technique can heal holes/vacancies

15 Fabricating graphene with electrical currents M D simulations indicate thermally driven crystallisation (1800 K) va n der Waals interactions aid planar graphene formation

16 Fabricating graphene with electron beams amorphous Carbon graphitized Carbon Electron beam (80 kv) Carbon onions Reference C C

17 Fabricating graphene with electron beams Irradiation region Plana r graphene formation

18 Fabricating graphene with electron deposition irradiation h BN h BN h BN + Graphite irradiation va n der Waals forces drive planar graphitisation

19 Destruction of graphene with electron beams Scanning TEM mode (focussed beam) A t 80 kv planar graphene is stable (as expected and shown in TEM mode) Edg e sputtering observed due to reduced knock.on damage threshold

20 Destruction of graphene with electron beams smal patches or corner from larger patches erode underlying graphene Larg patches sublime (re) depstion is also observed

21 Destruction of graphene with electron beams Knock on damage X Secondary Knock damage X energy transfered to a lighter atom, e.g. H. The accelerated atoms knock out C. Unlikely steps taken to prevent this, e.g. Beam shower, and damage would be more likely where is present O or H etching X (see above arguments) Only remaining option is: HEAT

22 Destruction of graphene with electron beams Understanding graphene etching: Estimat e for a homogenous film yields a temperature rise of 1 K to 2 K Estimate for 100 atom cluster yields heat dissipation yields a temperature rise of 10 9 K M D simulations suggest an explosive process. Knock on damage leads to hole formation

23 Destruction of graphene with electron beams Understanding graphene etching: Estimat e for a homogenous film yields a temperature rise of 1 K to 2 K Estimate for 100 atom cluster yields heat dissipation yields a temperature rise of 10 9 K M D simulations suggest an explosive process. Knock on damage leads to hole formation

24 Destruction of graphene with electron beams Electrical currents in graphene can be used to: clean graphene structure graphene heal graphene fabricate graphene Electron beams irradiation on graphene can be used to: clean graphene structure graphene fabricate graphene etch graphene

25 Acknowledgements The DSL 2012 Organizers At the IFW: The molecular nanostructures group Bernd Büchner Martin Knupfer Bernd Rellinghaus Financial support: European Union (ECEMP) Freestate of Saxony At the TUD: Gianaurelio Cuniberti Stanislav Avdoshenko (Perdue) At Delft University: Lieven M K Vandersypen Amelia Barreiro (Columbia) At Radboud University: Makhail I Katsnelson THANK YOU