Nobelova nagrada za fiziko 2010 Različni materiali na osnovi ogljika

Grafen -­‐ Nobelova nagrada za fiziko 2010 Različni materiali na osnovi ogljika so postali osnovni gradniki nanoznanos>, in sicer že od prvih odkri>j fulerenov leta 1985 naprej, nanocevk leta 1991 in do najnovejšega odkritja grafena v letu 2004. Grafen je dvodimenzionalna šestkotna mreža ogljikovih atomov in sodi med najmočnejše materiale, pri čemer je upogljiv kot guma in ima električno prevodnost višjo kot silicij. Zaradi dvodimenzionalne strukture in posebne oblike energijskih pasov ima več nenavadnih lastnos>. Na primer: prepustnost za svetlobo je neodvisna od valovne dolžine, ima neobičajno strukturo odziva kvantnega Hallovega pojava, elektrone je težko uje> v kvantne pike zaradi Kleinovega tuneliranje. 1) 
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Nobelove nagrade na podobnih področjih 1985 – 2010 Zgodovina grafena Izdelava Lastnos> (splošno) Lastnos>, posebej zanimive za fizike: a)  Struktura elektronskih pasov b)  Efek>vni model c)  Kvan>zirana prevodnost d)  Landauovi nivoji in kvantni Hallov pojav e)  Kleinovo tuneliranje 6) Povzetek Graphene
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A Two dimensional crystal •  In the 1930s, Landau and Peierls (and Mermin, later)showed thermodynamics prevented 2-­‐d crystals in free state. •  Mel>ng temperature of thin films decreases rapidly with temperature -­‐> monolayers generally unstable. •  In 2004, experimental discovery of graphene-­‐ high quality 2-­‐d crystals •  Possibly, 3-­‐d rippling stabilizes crystal Representa>on of rippling in graphene. Red arrows are ~800nm long. h`p://www.nature.com/nmat/journal/v6/n11/fig_tab/nmat2011_F1.html#figure-­‐>tle
How to make graphene •  Strangely cheap and easy. •  Either draw with a piece of graphite, or repeatedly peel with Scotch tape •  Place samples on specific thickness of Silicon wafer. The wrong thickness of silicon leaves graphene invisible. •  Graphene visible through feeble interference effect. Different thicknesses are different colors. Samples of graphene a)  Graphite films visualized through atomic force microscopy. b)  Transmission electron microscopy image c) Scanning electron microscope image of graphene. A. K. Geim & K. S. Novoselov. The rise of graphene. Nature Materials Vol 6 183-­‐191 (March 2007) Fabrica>on Cr/Au graphene Si02 E-­‐beam lithography 90 s buffered oxide etch Si Bolo>n, K.I. et al. Ultrahigh electron mobility in suspended graphene. Solid State Communica/ons 146, 351-­‐355 (2008). A representa-on of a diamond -p with a two nanometer radius inden-ng into a single atomic sheet of graphene History of Graphene •  Wallace in 1947 –  Created 2D structure to help in the understanding of 3D Graphite •  Single layers of graphite grown epitaxially on metallic substrates in the 1970s –  Tightly bound to substrate, distorted proper>es •  Term “graphene” coined in 1987 •  2004, Geim and Novoselov mechanically exfoliated sheets of graphene from graphite –  Transferred to charge neutral silicon substrate –  First successful electrical proper>es measured Geim, A. K. & MacDonald, A. H. (2007). "Graphene: Exploring carbon flatland". Physics Today. NN TBM fit to low energy Firng the parameters to the low energy spectrum: Dispersion: Edge states
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Quan>zed conducance Quan>zed conducance Δx
Quan>zed conducance (13kΩ)-1
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Quan>zed conducance (13kΩ)-1
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Quan>zed conducance (13kΩ)-1
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Quan>zed conducance (13kΩ)-1
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Simple deriva-on of ordinary Landau levels (Da`a textbook) 
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Simple deriva-on of Landau levels in graphene (adapted from A. A. Kozhevnikov, Novosibirsk State University) Phys. Rev. B 74, 155415 (2006) Landau levels of graphene honeycomb larce in a magne>c field low field Hofstadter-­‐Rammal bu:erfly 5 3 5 3 1 1 -­‐1 -­‐1 -­‐3 -­‐3 -­‐5 -­‐5 72 (Greiner …) Field-­‐Effect Transistors (FETs) •  Zero bandgap,large-­‐area single or few-­‐layers of graphene as FETs are used in this paper •  Internal fields are shown in this paper to produce an ultrafast photocurrent response in graphene h`p://rocky.digikey.com/weblib/ST
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thumb/14/2/10/graph1.jpg Xia, F. et al. Photocurrent imaging and efficient photon detec>on in a graphene transistor. Nano Le`. 9, 1039–1044 (2009). Applica>ons of Photonic applica>ons • 
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High-­‐speed op>cal communica>ons Interconnects Terahertz detec>on Imaging Remote sensing Surveillance Spectroscopy h`p://www.delen.polito.it/var/ h`p://
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images/surveillance1.jpg Geim, A. K. & Novoselov, K. S. The rise of graphene. Nature Mater. 6, 183–191 (2007). Graphene’s photonic abili>es •  Ability to absorb ~ 2% of incident light over a broad wavelength •  Mul>ple graphene layer absorb addi>vely •  The absorp>on range of a system can be tuned by changing the Fermi energy using an external gate field h`p://www.nanotech-­‐now.com/images/
NANOIDENTPhotodetectorFunc>on300.jpg Wang, F. et al. Gate-­‐variable op>cal transi>on in graphene. Science 320, 206–209 (2008). Povzetek … Graphene Mechanical Proper>es •  Breaking strength 200 >mes greater than steel •  Youngs modulus of ~ 1 tPa •  Incredible rigidity lends themselves to nanoscale pressure sensors –  Nanoscopic graphene flakes bend with increasing pressure which alters their electrical conduc>vity which can be related to the pressure  
Thermal proper>es exceed those of diamond  
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Excellent conductor of heat Phonon dominated although it can be shown that at certain condi>ons the electrical por>on is significant h`p://www.kinectrics.com/images/
CableSpan.JPG John Sco` Bunch. Mechanical and Electrical Proper>es of Graphene. Cornell University 2008. Graphene Electrical Proper>es • 
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Anomalous Quantum Hall Effect –  Quan>za>on of the Hall effect Dirac fermions –  Carriers have zero effec>ve mass Room temperature electron mobility of 15,000 cm2/V*s –  Theore>cally higher conduc>vity at room temp than silver, but unknown forces are limi>ng –  Possible op>cal phonon sca`ering from a`ached substrate  
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Both P and N-­‐type transistors have been created Recent announcement by IBM that graphene transistor was operated at a terahertz frequency Tunable band gap from 0 to 0.25 eV Excellent conduc>vity makes graphene ideal for electrical leads in sensors/capacitors or use in touch screens because of its mechanical strength Graphene ribbons have tunable electrical conduc>vity depending on the shape h`p://www.atwille`.com/
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lightningbolt_closeup.jpg Charlier, J.-­‐C., Blase, X., & Roche, S. Electronic and transport proper>es of nanotubes. Rev. Mod. Phys. A Closer Look at Graphene •  2D hexagonal carbon crystal larce –  Infinite boundaries –  Actual 2D structure is debatable •  Graphene sandwich •  Thermal effects •  Naturally occurring –  Mul>layer in graphite –  Nanospecs in soot from exhaust •  Currently one of the most researched materials h`p://www.nanotechnow.com/images/Art_Gallery/ASgraphene.jpg –  Unique physical and electrical proper>es –  Wide array of poten>al uses Ziegler, K., Robust transport proper>es in graphene. Phys. Rev. Le:. Fabrica>on Cr/Au graphene Si02 E-­‐beam lithography 90 s buffered oxide etch Si Bolo>n, K.I. et al. Ultrahigh electron mobility in suspended graphene. Solid State Communica/ons 146, 351-­‐355 (2008). Proper>es: charge carriers •  Samples are excellent-­‐ graphene is ambipolar: charge carrier concentra>on con>nuously tunable from electrons to holes in high concentra>ons A. K. Geim & K. S. Novoselov. The rise of graphene. Nature Materials Vol 6 183-­‐191 (March 2007) Andre K. Geim and K.S. Novoselov, “The rise of graphene.” cond-mat/0702595
What is nanoelectronics? 100
•  RF applica>ons –  Non-­‐linear I-­‐V -­‐> rec>fica>on –  Mixing up to 50 GHz demonstrated (so far) •  Nanotube radio! Chris Rutherglen, Irvine, California 101
•  NEMS 102
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Graphene single sheet Single-­‐walled CN of (m,n) type y ma1 + na2 a1 300 x a2