Halbleiter Prof. Yong Lei Prof. Thomas Hannappel yong.lei@tu-ilmenau.de thomas.hannappel@tu-ilmenau.de http:///nanostruk/
Organic semiconductors Small-molecular materials Rubrene Pentacene Polymers PEDOT:PSS P3HT π-conjugated organic molecules
1996: Curl, Kroto, Smalley 1985 or 1986: fullerenes (C60, bucky balls); 2010: Geim, Novoselov 2005-2007: 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 http://en.wikipedia.org/wiki/carbon.
Carbon allotropes Chem. Rev. 2015, 115, 4744 4822 24.01.2018 Page 4
Carbon allotropes 24.01.2018 Page 5
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". 24.01.2018 Page 6
Discovery of fullerenes laser evaporation of graphite 24.01.2018 Page 7
Fullerenes based acceptors for heterojunction organic solar cells Functionalization 24.01.2018 Page 8
24.01.2018 Page 9 Carbon nanotubes
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, 99-102.
Graphene: The Nobel Prize in Physics 2010 Andre Geim Konstantin Novoselov for groundbreaking experiments regarding the two-dimensional material graphene 24.01.2018 Page 11
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. (http://en.wikipedia.org/wiki/graphene)
Zigzag carbon nanotube could be either semiconducting or metallic
Armchair carbon nanotube all metallic
Graphene: The Nobel Prize in Physics 2010 Highly oriented pyrolytic graphite (HOPG) Science (2004) 306, 666; Proc. Natl. Acad. Sci. (2005) 102, 10451. 24.01.2018 Page 15
Graphite to Graphene Exfoliation 24.01.2018 Page 16
D.I.Y. Graphene from graphite: top-down approach 24.01.2018 Page 17
Graphene The Mother Of All Graphites Graphene: a single layer of carbon packed in hexagonal lattice, with a carbon-carbon distance of 0.142 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, 183-191. 24.01.2018 Page 18
Synthesis of Graphene 24.01.2018 Page 19
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. 24.01.2018 Page 20
Chemical vapor deposition (CVD) of Graphene Cu or Ni foil Science 2009;324, 1312; Nature 2009, 457, 706. 24.01.2018 Page 21
24.01.2018 Page 22 Science 2009;324, 1312; Nature 2009, 457, 706.
24.01.2018 Page 23 Science 2009;324, 1312; Nature 2009, 457, 706.
CVD of Graphene foam Nature Materials 2011, 10, 424-428 24.01.2018 Page 24
Graphene foam via CVD A 170 220 mm 2 free-standing graphene foam Nature Materials 2011, 10, 424-428 24.01.2018 Page 25
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, 4844 4850 24.01.2018 Page 26
Synthesis of Graphene 250 ºC 1350 ºC Exfoliation of Graphite into Graphene ACS Nano, 2013, 7, 3598 3606 High-temperature carbonization Nature Commun. 2013, 4, 2905 24.01.2018 Page 27
Synthesis of Graphene: seconds timescale water electrolytic oxidation Nature Communications 2018, 9, 145 24.01.2018 Page 28
Synthesis of Graphene Science 2008, 319, 1229-1232 Nature 2009, 458, 877-880 24.01.2018 Page 29
PECVD Growth of Vertically Oriented Graphene Carbon sources: C2H2 or CH4 Plasma gas: H2 or Ar 24.01.2018 Page 30
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, 1316 1323 24.01.2018 Page 31
Comparison of different methods for graphene mass-production Nature, 2012, 490, 192-200 24.01.2018 Page 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. 24.01.2018 Page 33
Basic properties of Graphene Graphene's unique electronic structure enables this extraordinary material to break many records of strength, electricity and heat conduction. 24.01.2018 Page 34
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, 109. 24.01.2018 Page 35
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. 24.01.2018 Page 36
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) 24.01.2018 Page 37
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, 951-954. J. Mater. Chem., 2011, 21, 3335-3345 24.01.2018 Page 38
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, 206 213 https://phys.org/news/2017-02-platform-graphene-electronic-properties.html 24.01.2018 Page 39
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. 24.01.2018 Page 40
24.01.2018 Page 41 Applications of graphene
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 24.01.2018 Page 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 24.01.2018 Page 43
24.01.2018 Page 44 Nature Reviews, 2016, 1, 16033
24.01.2018 Page 45 Nature Reviews, 2016, 1, 16033
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). https://phys.org/news/2013-02-graphene-transistor-principle.html 24.01.2018 Page 46
Graphene for energy conversion and storage Nanoscale, 2013, 5, 10108-10126 24.01.2018 Page 47
12 new features of energy-storage devices by graphene Nature Reviews, 2016, 1, 16033 24.01.2018 Page 48
12 new features of energy-storage devices by graphene Nature Reviews, 2016, 1, 16033 24.01.2018 Page 49
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). 24.01.2018 Page 50
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, 231-237. 24.01.2018 Page 51
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PECVD Growth of Vertically Oriented Graphene Carbon sources: C2H2 or CH4 Plasma gas: H2 or Ar 24.01.2018 Page 53
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, 1637 24.01.2018 Page 54
Graphene-nanotube 3D architecture for dye-sensitized solar cells Science Advance 2015,1,1400198 Showed a power conversion efficiency of 6.8 % and out-performed the counterparts with an expensive Pt wire counter electrode by a factor of 2.5. 24.01.2018 Page 55
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. 24.01.2018 Page 56
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, 4400--4416 24.01.2018 Page 57
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, 4400--4416 24.01.2018 Page 58
Graphene in biomedical applications Drug delivery Chem. Soc. Rev., 2017, 46, 4400--4416 24.01.2018 Page 59
Graphene in biomedical applications Biosensors Chem. Soc. Rev., 2017, 46, 4400--4416 24.01.2018 Page 60
Roadmap: Graphene-based display & electronic devices Nature, 2012, 490, 192-200 24.01.2018 Page 61
Roadmap: graphene-based photonics applications 24.01.2018 Page 62
The era of carbon allotropes since 2016 Nature Materials, 2013, 9, 3077 24.01.2018 Page 63
Thank you!