Nanostrukturphysik Übung 2 (Class 3&4)

Transcription

1 Nanostrukturphysik Übung 2 (Class 3&4) Prof. Yong Lei & Dr. Yang Xu Fachgebiet 3D-Nanostrukturierung, Institut für Physik Contact: yong.lei@tu-ilmenau.de (3748), yang.xu@tuilmenau.de (4902) Office: Heisenbergbau V202, Unterpörlitzer straβe 38

2 1. Graphene can be synthesized by top-down and bottom-up routes. Some of them have been introduced in the class. Can you list other methods in both routes to complete the synthesis diagram?

3 Bottom-up Top-down Pros: Cons: Pros: Cons: Simple process Large area High yields High temperature High level of defects Low level of defects No high temperatur e required Reagglomeration Low yields Numerous steps Graphite as a scarce material

4 Top-down Micromechanical cleavage Electrochemical exfoliation Exfoliation of graphite intercalation compounds (GICs) Solvent-based exfoliation Exfoliation of graphite oxide Arc discharge Unzipping carbon nantubes

5 Micromechanical cleavage Scotch tape or peel off Mono-, bi- and few-layer graphene High quality because of the limited graphite processing Labor intensive

6 Electrochemical exfoliation GIC Thermal shock Further aid Dimetylformamide (DMF) and propylene carbonate: >70% few-layer graphene

7 Exfoliation from GICs Thermal expansion: intercalates decompose into gaseous species upon heating Exposure to strong acid prior to thermal expansion Exfoliation by sonication or microwave radiation Repeat intercalation-exfoliation J. Mater. Chem. 2009, 19, 3367.

8 Solvent-based exfoliation Unmodified, natural flake graphite via sonication in solvents Best solvent (percentage of monolayer graphene): N-methyl-pyrrolidone (NMP) High boiling point of the solvents: difficult removal

9 Exfoliation of graphite oxide Hummers method Graphite Graphite oxide Concentrated acid & strong oxidants Thermal shock or sonication Graphene oxide (GO) Thermal or chemical method Reduced graphene oxide (rgo) Single layer graphite oxide

10 Arc discharge H 2 : terminate dangling carbon bonds and inhibit the rolling-up and closing of graphitic sheets He and H 2 : high crystallinity

11 Unzipping carbon nanotubes graphene nanoribbons Wet chemistry: strong oxidizing agents Physical methods: irradiation, plasma etching Zigzag Armchair

12 Bottom-up Epitaxial growth on SiC Chemical vapour deposition (CVD) Growth on metals Substrate free

13 CVD on metals Metals: Fe, Ru, Co, Rh,Ir, Ni,Pd, Pt, Cu, Au, Co-Ni, Au-Ni, Ni-Mo, stainless steel Surface-catalysis: monolayer graphene Segregation methods: few-layer graphene Cockroach leg, 1050 C, 15 min, Cu ACS Nano 2011, 5, 7601.

14 CVD: substrate free Nano Lett. 2008, 8, 2012.

15 2. Graphene can be doped with other elements to modulate its physical and chemical properties. What elements can be doped in graphene? How to dope them? What applications can doped graphene be used for?

16 Doping graphene Dopants: B, N, P, O, S, F, Cl, Br, I, etc. Methods In-situ doping Post-synthesis treatment Applications Supercapacitors Batteries Fuel cells

17 In-situ doping: CVD

18 In-situ doping: CVD ACS Nano 2012, 6, 1486.

19 In-situ doping: ball milling N 2 atmosphere Sci. Rep. 2013, 3, 2260.

20 Bottom-up in-situ doping: Wurtz-tupe reductive coupling (WRC) reaction Step 1: stripping off Cl from CCl 4 Step 2: the coupling and assembly of freshly formed C=Cand C=N- into 2D hexagonal carbon clusters Step 3: the growth of N-doped graphene from the clusters Chem. Mater. 2011, 23, 1188.

21 Post-synthesis treatment: thermal annealing Energy Environ. Sci. 2012, 5, 7936.

22 Post-synthesis treatment: wet chemical methods Sci. Rep. 2012, 2, 662.

23 Application: supercapacitors B: 0.6 at% N: 3.0 at% Doping with B and N: better conductivity, stability, chemical stability, and sheetto-sheet separation. Adv. Mater. 2012, 24, 5130.

24 Application: lithium-ion batteries ACS Nano 2011, 5, 5463.

25 Application: fuel cell Direct methanol fuel cell (DMFC): S-doped graphene/pt nanowires Oxygen reduction reaction Sci. Rep. 2013, 3, Methanol oxidation reaction

26 3. What are the types of graphene nanoribbons (GNRs) and their interesting characteristics?

27 GNRs: chemically derived, ultrasmooth Chemical intercalation of graphite: expandable graphite Rapid heating at 1000 C: single- and few-layered graphene Solution-phase sonication and functionalization by PmPV: GNRs Height: nm All scale bars are 100 nm Science 2008, 319, 1229.

28 Experimental Zigzag Armchair All scale bars are 100 nm Band gap opening up: quantum confinement and edge effects Science 2008, 319, 1229.

29 GNRs: unzipping CNTs by Ar plasma etching Nature 2009, 458, 877.

30 10 nm 1 μm 100 nm

31 Zigzag GNRs: on-surface synthesis Polymerization Functionalization Cyclodehydrogenation Nature 2016, 531, 489. Au (111) surface

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