Nanostrukturphysik (Nanostructure Physics)

Transcription

1 Nanostrukturphysik (Nanostructure Physics) Prof. Yong Lei & Dr. Yang Xu Fachgebiet 3D-Nanostrukturierung, Institut für Physik Contact: Office: Unterpoerlitzer Straße 38 (Heisenbergbau) (tel: 3748) Vorlesung: Thursday 7:00 8:30, F 3001 (Faradaybau) Übung: Friday (G), 11:00 12:30, C 110 (a) (b 1 ) (b 2 ) UTAM-prepared free-standing one-dimensional surface nanostructures on Si substrates: Ni nanowire arrays (a) and carbon nanotube arrays (b).

2 Class 1: A general introduction of fundamentals of nano-structured materials Class 2: Structures and properties of nanocrystalline materials Class 3: Graphene Class 4: 2D atomically thin nanosheets Class 5: Optical properties of 1D nanostructures and nano-generator Class 6: Carbon nanotubes Class 7: Solar water splitting I: fundamentals Class 8: Solar water splitting II: nanostructures for water splitting Class 9: Lithium-ion batteries: Si nanostructures Class 10: Sodium-ion batteries and other ion batteries, and Supercapacitors Class 11: Solar cells Class 12: Other nanostructures

3 Contents of Class 3 Graphene

4 Graphene: honeycomb carbon Introduction Brief history Mechanical exfoliation Alternatives to mechanical exfoliation Characterizing graphene flakes Devices with graphene

5 Carbon allotropes Chem. Rev. 2015, 115, Page 5

6 Carbon allotropes Page 6

7 Fullerene: The Nobel Prize in Chemistry 1996 Robert F. Curl Jr. Sir Harold W. Kroto Richard E. Smalley The Nobel Prize in Chemistry 1996 was awarded jointly to Robert F. Curl Jr., Sir Harold W. Kroto and Richard E. Smalley "for their discovery of fullerenes" Page 7

8 Discovery of fullerenes laser evaporation of graphite Page 8

9 Fullerenes based acceptors for heterojunction organic solar cells Functionalization Page 9

10 Page 10 Carbon nanotubes

11 Graphene: The Nobel Prize in Physics 2010 Andre Geim Konstantin Novoselov for groundbreaking experiments regarding the two-dimensional material graphene Page 11

12 Graphene is a 1-atom thickness sheet of sp 2 -bonded carbon atoms that are densely packed in a honeycomb crystal lattice. Graphite consists of many graphene sheets stacked together. (

13 Graphite to Graphene Exfoliation Page 13

14 Graphene: The Nobel Prize in Physics 2010 Highly oriented pyrolytic graphite (HOPG) Science (2004) 306, 666; Proc. Natl. Acad. Sci. (2005) 102, Page 14

15 D.I.Y. Graphene from graphite: top-down approach Page 15

16 Graphene The Mother Of All Graphites Graphene: a single layer of carbon packed in hexagonal lattice, with a carbon-carbon distance of nm. Graphene: a basic building block for carbon materials of all other dimensions: wrap up into 0D fullerene roll up into 1D nanotubes stacked into 3D graphite A.K. Geim & K.S. Novoselov, Nat. Mater. 2017, 6, Page 16

17 Zigzag carbon nanotube could be either semiconducting or metallic

18 Armchair carbon nanotube all metallic

19 Alternatives to mechanical exfoliation Requirements A process must produce high quality in the 2D crystal lattice to ensure high mobility The method must provide fine control over crystallite thickness so as to deliver uniform device performance Alternatives Chemical exfoliation Total organic synthesis Epitaxial growth and chemical vapor deposition

20 Synthesis of Graphene Page 20

21 Chemically derived graphene from graphite oxide Chemical modification of graphite to produce a water dispersible graphene oxide (GO) Complete exfoliation of GO upon addition of mechanical energy This is due to strength of interactions between water and oxygencontaining (epoxide and hydroxyl) functionalities introduced during oxidation. Hydrophilic property leads water to readily being inserted between sheets and disperse them as individuals. Nat. Nanotechnol. 2009, 4, 25.

22 Cross-sectional SEM image of GO stacking in a film produced by filtration. Nature 2007, 448, 457. Chemical reduction produces a film with shiny color. Science 2008, 320, 1170.

23 Chemical synthesis of Graphene: Hummers method Most widely used for producing graphene by oxidizing graphite to GO by using suitable oxidizing agents. GO is then reduced to produce graphene Page 23

24 Chemical vapor deposition (CVD) of Graphene Cu or Ni foil Science 2009;324, 1312; Nature 2009, 457, Page 24

25 Page 25 Science 2009;324, 1312; Nature 2009, 457, 706.

26 CVD of Graphene foam Nature Materials 2011, 10, Page 26

27 Graphene foam via CVD A mm 2 free-standing graphene foam Nature Materials 2011, 10, Page 27

28 CVD Growth of Graphene with Ni Nanowires Formation of graphene tubular structure: (a) Ni nanowire; (b) graphene grown on Ni nanowire template; (c) chemical removal of Ni nanowire. 2 layers 3 layers 5 layers 10 layers Nano Lett. 2010, 10, Page 28

29 Synthesis of Graphene Science 2008, 319, Nature 2009, 458, Page 29

30 Epitaxial graphene Substrate-based methods Epitaxial growth: silicon carbide (SiC) is reduced to graphene as silicon sublimes at high temperature. J. Phys. Chem. Solids 2006, 67, 2172.

31 Comparison of different methods for graphene mass-production Nature, 2012, 490, Page 31

32 Basic properties of Graphene Graphene's unique electronic structure enables this extraordinary material to break many records of strength, electricity and heat conduction. Density of graphene: 0.77 mg m -2 Almost optical transparent: absorbs only 2.3% of light intensity, independent of the wavelength in optical domain. Young s modulus of 1 Tera-Pascal and intrinsic strength of 130 Giga- Pascal, more than 100 times stronger than the strongest steel. RT electron mobility: μ = 200,000 cm 2 V 1 s 1. Very high thermal conductivity: ~ 3000 W m K 1, 10 times better than copper Page 32

33 Energy band structure of graphene The valence band (lower band) and conduction band (upper band) of graphene touch at six points (Brillouin zone corners), thus making graphene a zero-band-gap semiconductor. More details: The electronic properties of graphene, A. H. Castro Neto, F. Guinea, N. M. R. Peres, K. S. Novoselov, and A. K. Geim, Rev. Mod. Phys. 2009, 81, Page 33

34 Graphene: zero-band-gap semiconductor Because of its symmetrical structure its atoms scatter electrons in such a way that they cancel each other out, graphene has no electronic band gap, which is the key semiconductoring property controlling the operations of transistors, lasers, and other solid-state devices Page 34

35 Widely tunable bandgap in bilayer graphene Graphene lacks a band gap because of its symmetrical structure its atoms scatter electrons in such a way that they cancel each other out. The introduction of an electric field perpendicular to the layers creates an asymmetry, which generates a band gap. Though small, the gap is tunable, creating possibilities for new devices. Nature Nanotechnology 5, 32 (2009); Nature 459, 820 (2009) Page 35

36 Chemical doping for band gap tuning in graphene The band structure near the Dirac point of bilayer epitaxial graphene grown on the surface of SiC can be easily tuned by potassium doping. Science 2006, 313, J. Mater. Chem., 2011, 21, Page 36

37 Characterizing graphene flakes Optical Scanning probe microscopy: AFM and STM Raman spectroscopy Optical absorbance: 2.3% per layer Science 2008, 320, 1308.

38 Graphite: showing three carbons that eclipse a neighbor in the sheet directly below. Graphene: all six carbons are equivalent and thus visible. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 9209.

39 Intensity: ¼ and ½ of the G peak 3-5 cm -1 higher G band (near 1584 cm -1 ): E 2g vibrational mode G band (near 2700 cm -1 ): second-order two-phonon mode Intensity: 4 times of the G peak Phys. Rev. Lett. 2006, 97,

40 Page 40 Applications of graphene

41 1.Create rugged sensors 2.Sequence DNA 3.Re-imagine aircraft design 4.Detect concealed weapons 5.Build better electronics 6.Ramp up the performance of supercapacitors and batteries 7.Design new types of batteries 8.Kill E. coli bacterio 9.Print electronic devices 10.Soak up arsenic Page 41

42 11. Improve electron sources 12. Make high-performance modulators 13. Store hydrogen 14. Remove water from a mixture 15. Remove water from a mixture 16. Remove unwanted heat from electronics 17. Form transparent electrodes for displays 18. Make rare-element-free magnets 19. Store data 20. Harness energy from the Sun Page 42

43 Devices: single molecule detection Chemical sensors 2D structure: absolute maximum of the surface area to volume ratio in a layered material High sensitivity, every adsorption event is significant Either electron withdrawing or donating groups can lead to chemical gating of the material, which can be easily monitored in a resistive-type sensor setup. Nat. Mater. 2007, 6, 652.

44 Graphene transistor with new operating principle Graphene in a switching transistor: electric current can t be sufficiently interrupted (no band gap). A new operating principle performing switching operation with a small band gap is required: 2 top gates are placed on graphene (irradiated via He ion beam to introduce crystalline defects. Gate biases applied to 2 top gates, allowing carrier densities in top-gated graphene regions be effectively controlled. Its transistor polarity be electrically controlled and inverted (new) Page 44

45 Graphene for energy conversion and storage Nanoscale, 2013, 5, Page 45

46 Graphene as electrode materials for supercapacitors Graphene as electrode materials for supercapacitors: energy storage mechanism is: charges are electrochemically stored through the adsorption-desorption of electrolyte ions on the surface of graphene, socalled electric double-layer capacitors (EDLC) Page 46

47 Graphene-based supercapacitor: hummers method TEM SEM High-performance supercapacitors based on graphene for efficient energy storage under extreme environmental temperatures, a wide range of temperatures from -20 ºC to 45 ºC. Vellacheri R., Al-Haddad A., Zhao H.P., Wang W.X., Wang C.L., Lei Y.*, Nano Energy, 2014, 8, Page 47

48 Page 48

49 PECVD Growth of Vertically Oriented Graphene Carbon sources: C2H2 or CH4 Plasma gas: H2 or Ar Page 49

50 Vertically Oriented Graphene for Supercapacitors Supercapacitors have a very fast response time (sub-millisecond timescale). Supercapacitors via vertically oriented graphene could be charged and discharged in less than a millisecond, This ultrafast supercapacitor could replace the large electrolytic capacitors used in today s electronics and may someday help make electronic devices smaller and lighter. Science 2010, 329, Page 50

51 Graphene-nanotube 3D architecture for dye-sensitized solar cells Science Advance 2015,1, Showed a power conversion efficiency of 6.8 % and out-performed the counterparts with an expensive Pt wire counter electrode by a factor of Page 51

52 Graphene as electrode materials for batteries Graphene is a great substrate for LIB anode and cathode materials to create highenergy-density, fast-charging and longer-lasting batteries. Although graphite is an excellent anode in LIBs, it cannot be utilized in Na + and Al 3+ batteries because these ions are too large to effectively insert into graphite, so alternative anode materials are required, such as porous graphene composites Page 52

53 Graphene in bio-applications In addition to electronics and photonics, graphene also has great potentials in bio-applications, such as drug delivery, tissue engineering, biosensors. Graphene sheets are highly hydrophobic and tend to aggregate, exhibiting a low water dispersibility, thus are not suitable for direct bio-applications. Chem. Soc. Rev., 2017, 46, Page 53

54 Graphene in bio-applications Graphene oxide (GO) can be easily synthesized by Hummers method, offers a richer surface chemistry due to the presence of the oxide groups. Reduced graphene oxide (rgo): chemically reduced GO to remove oxygen functional groups. rgo can be considered as an intermediate structure between the graphene sheet and the highly-oxidized GO. GO and rgo can be more easily handled, especially in liquids, since they generally exhibit good water dispersibility and a very rich surface chemistry, which allows a wide range of biomedical applications. Chem. Soc. Rev., 2017, 46, Page 54

55 Graphene in biomedical applications Drug delivery Chem. Soc. Rev., 2017, 46, Page 55

56 Graphene in biomedical applications Biosensors Chem. Soc. Rev., 2017, 46, Page 56

57 Class 1: A general introduction of fundamentals of nano-structured materials Class 2: Structures and properties of nanocrystalline materials Class 3: Graphene Class 4: 2D atomically thin nanosheets Class 5: Optical properties of 1D nanostructures and nano-generator Class 6: Carbon nanotubes Class 7: Solar water splitting I: fundamentals Class 8: Solar water splitting II: nanostructures for water splitting Class 9: Lithium-ion batteries: Si nanostructures Class 10: Sodium-ion batteries and other ion batteries, and Supercapacitors Class 11: Solar cells Class 12: Other nanostructures

58 Thank you!