Halbleiter Prof. Yong Lei Prof. Thomas Hannappel

Transcription

1 Halbleiter Prof. Yong Lei Prof. Thomas Hannappel

2 Organic semiconductors Small-molecular materials Rubrene Pentacene Polymers PEDOT:PSS P3HT π-conjugated organic molecules

3 1996: Curl, Kroto, Smalley 1985 or 1986: fullerenes (C60, bucky balls); 2010: Geim, Novoselov : 2D graphene The allotropes of carbon: hardest natural substance, diamond one of the softest known substances, graphite. For carbon nanotubes CNT (by Ijima in 1991) and the equally important discovery of inorganic fullerene structures (by Tenne) Allotropes of carbon: a) diamond; b) graphite; c) lonsdaleite; d f) fullerenes (C 60, C 540, C 70 ); g) amorphous carbon; h) carbon nanotube. from

4 Carbon allotropes Chem. Rev. 2015, 115, Page 4

5 Carbon allotropes Page 5

6 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 6

7 Discovery of fullerenes laser evaporation of graphite Page 7

8 Fullerenes based acceptors for heterojunction organic solar cells Functionalization Page 8

9 Page 9 Carbon nanotubes

10 MoS 2 transistors with 1-nm gate lengths - The world's smallest transistor The gate length is considered as a defining dimension of transistor, with the choice of proper materials, there is a lot more room to shrink our electronics. Science 2016, 354,

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 Zigzag carbon nanotube could be either semiconducting or metallic

14 Armchair carbon nanotube all metallic

15 Graphene: The Nobel Prize in Physics 2010 Highly oriented pyrolytic graphite (HOPG) Science (2004) 306, 666; Proc. Natl. Acad. Sci. (2005) 102, Page 15

16 Graphite to Graphene Exfoliation Page 16

17 D.I.Y. Graphene from graphite: top-down approach Page 17

18 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 18

19 Synthesis of Graphene Page 19

20 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 20

21 Chemical vapor deposition (CVD) of Graphene Cu or Ni foil Science 2009;324, 1312; Nature 2009, 457, Page 21

22 Page 22 Science 2009;324, 1312; Nature 2009, 457, 706.

23 Page 23 Science 2009;324, 1312; Nature 2009, 457, 706.

24 CVD of Graphene foam Nature Materials 2011, 10, Page 24

25 Graphene foam via CVD A mm 2 free-standing graphene foam Nature Materials 2011, 10, Page 25

26 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 26

27 Synthesis of Graphene 250 ºC 1350 ºC Exfoliation of Graphite into Graphene ACS Nano, 2013, 7, High-temperature carbonization Nature Commun. 2013, 4, Page 27

28 Synthesis of Graphene: seconds timescale water electrolytic oxidation Nature Communications 2018, 9, Page 28

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

30 PECVD Growth of Vertically Oriented Graphene Carbon sources: C2H2 or CH4 Plasma gas: H2 or Ar Page 30

31 PECVD Growth of Vertically Oriented Graphene Butter Inductively Coupled Plasma Chemical Vapour Deposition (ICP CVD) Ni foam was pasted with butter prior to be loaded in reactor. A gas mixture of Ar and H 2 was fed into the system for growing VG. The power of RF plasma was at 1000 W and the growth lasted for 9 min. Adv. Energy Mater. 2013, 3, Page 31

32 Comparison of different methods for graphene mass-production Nature, 2012, 490, Page 32

33 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 33

34 Basic properties of Graphene Graphene's unique electronic structure enables this extraordinary material to break many records of strength, electricity and heat conduction Page 34

35 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 35

36 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 36

37 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 37

38 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 38

39 A platform to study graphene's electronic properties Device to detect graphene's electronic properties: graphene sandwiched in 2 layers of insulating BN. By tuning voltages applied on graphite and Si, the changes in conductance of graphene can be measured, which reflects its electronic properties. Nano Lett. 2017, 17, Page 39

40 Electrons of graphene represented by Dirac cone (2 cones like a sandglass), with a small point in between (Dirac Point). The differences in the electronic structures are shown as filling the sandglass by an electron liquid. Applying negative voltage on Si & graphite is equivalent to drinking, and positive voltage to filling the glass with more electron liquid. The Fermi level is the maximum level where you can find electrons Page 40

41 Page 41 Applications of graphene

42 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 42

43 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 43

44 Page 44 Nature Reviews, 2016, 1, 16033

45 Page 45 Nature Reviews, 2016, 1, 16033

46 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 46

47 Graphene for energy conversion and storage Nanoscale, 2013, 5, Page 47

48 12 new features of energy-storage devices by graphene Nature Reviews, 2016, 1, Page 48

49 12 new features of energy-storage devices by graphene Nature Reviews, 2016, 1, Page 49

50 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 50

51 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 51

52 Page 52

53 PECVD Growth of Vertically Oriented Graphene Carbon sources: C2H2 or CH4 Plasma gas: H2 or Ar Page 53

54 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 54

55 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 55

56 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 56

57 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 57

58 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 58

59 Graphene in biomedical applications Drug delivery Chem. Soc. Rev., 2017, 46, Page 59

60 Graphene in biomedical applications Biosensors Chem. Soc. Rev., 2017, 46, Page 60

61 Roadmap: Graphene-based display & electronic devices Nature, 2012, 490, Page 61

62 Roadmap: graphene-based photonics applications Page 62

63 The era of carbon allotropes since 2016 Nature Materials, 2013, 9, Page 63

64 Thank you!