Nanostrukturphysik (Nanostructure Physics) Prof. Yong Lei & Dr. Yang Xu Fachgebiet 3D-Nanostrukturierung, Institut für Physik Contact: yong.lei@tu-ilmenau.de; yang.xu@tu-ilmenau.de Office: Unterpoerlitzer Straße 38 (Heisenbergbau) (tel: 3748) http:///3dnanostrukturierung/ 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).
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
Contents of Class 3 Graphene
Graphene: honeycomb carbon Introduction Brief history Mechanical exfoliation Alternatives to mechanical exfoliation Characterizing graphene flakes Devices with graphene
Carbon allotropes Chem. Rev. 2015, 115, 4744 4822 04.05.2018 Page 5
Carbon allotropes 04.05.2018 Page 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". 04.05.2018 Page 7
Discovery of fullerenes laser evaporation of graphite 04.05.2018 Page 8
Fullerenes based acceptors for heterojunction organic solar cells Functionalization 04.05.2018 Page 9
04.05.2018 Page 10 Carbon nanotubes
Graphene: The Nobel Prize in Physics 2010 Andre Geim Konstantin Novoselov for groundbreaking experiments regarding the two-dimensional material graphene 04.05.2018 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)
Graphite to Graphene Exfoliation 04.05.2018 Page 13
Graphene: The Nobel Prize in Physics 2010 Highly oriented pyrolytic graphite (HOPG) Science (2004) 306, 666; Proc. Natl. Acad. Sci. (2005) 102, 10451. 04.05.2018 Page 14
D.I.Y. Graphene from graphite: top-down approach 04.05.2018 Page 15
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. 04.05.2018 Page 16
Zigzag carbon nanotube could be either semiconducting or metallic
Armchair carbon nanotube all metallic
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
Synthesis of Graphene 04.05.2018 Page 20
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.
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.
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. 04.05.2018 Page 23
Chemical vapor deposition (CVD) of Graphene Cu or Ni foil Science 2009;324, 1312; Nature 2009, 457, 706. 04.05.2018 Page 24
04.05.2018 Page 25 Science 2009;324, 1312; Nature 2009, 457, 706.
CVD of Graphene foam Nature Materials 2011, 10, 424-428 04.05.2018 Page 26
Graphene foam via CVD A 170 220 mm 2 free-standing graphene foam Nature Materials 2011, 10, 424-428 04.05.2018 Page 27
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 04.05.2018 Page 28
Synthesis of Graphene Science 2008, 319, 1229-1232 Nature 2009, 458, 877-880 04.05.2018 Page 29
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.
Comparison of different methods for graphene mass-production Nature, 2012, 490, 192-200 04.05.2018 Page 31
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. 04.05.2018 Page 32
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. 04.05.2018 Page 33
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. 04.05.2018 Page 34
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) 04.05.2018 Page 35
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 04.05.2018 Page 36
Characterizing graphene flakes Optical Scanning probe microscopy: AFM and STM Raman spectroscopy Optical absorbance: 2.3% per layer Science 2008, 320, 1308.
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.
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, 187401.
04.05.2018 Page 40 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 04.05.2018 Page 41
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 04.05.2018 Page 42
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.
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 04.05.2018 Page 44
Graphene for energy conversion and storage Nanoscale, 2013, 5, 10108-10126 04.05.2018 Page 45
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). 04.05.2018 Page 46
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. 04.05.2018 Page 47
04.05.2018 Page 48
PECVD Growth of Vertically Oriented Graphene Carbon sources: C2H2 or CH4 Plasma gas: H2 or Ar 04.05.2018 Page 49
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 04.05.2018 Page 50
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. 04.05.2018 Page 51
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. 04.05.2018 Page 52
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 04.05.2018 Page 53
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 04.05.2018 Page 54
Graphene in biomedical applications Drug delivery Chem. Soc. Rev., 2017, 46, 4400--4416 04.05.2018 Page 55
Graphene in biomedical applications Biosensors Chem. Soc. Rev., 2017, 46, 4400--4416 04.05.2018 Page 56
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
Thank you!