GRAPHENE: A PARADIGM SHIFT AND THE ADVENT OF 2D MATERIALS RAJARSHI ROY POSTDOCTORAL RESEARCHER, RG PLASMA TECHNOLOGIES CEITEC, MASARYK UNIVERSITY Funded by European Regional Development Fund-Project "MSCAfellow2@MUNI" (No. CZ.02.2.69/0.0/0.0/18_070/0009846) SUMMARY OF DISCUSSIONS • FUNDAMENTAL PROPERTIES • SYNTHESIS STRATEGIES • BASIC CHARACTERIZATIONS • SOME APPLICATIONS • CONCLUSIONS RAJARSHI ROY 3 FUNDAMENTAL PROPERTIES PREMISE Rajarshi Roy 4 A. GEIM, K. NOVOSELOV UNIVERSITY OF MANCHESTER, UK NOBEL PRIZE IN PHYSICS (2010) FOR GROUNDBREAKING EXPERIMENTS WITH 2D MATERIAL CALLED GRAPHENEALLOTROPES OF CARBON IN DIFFERENT DIMENSIONS WHY IS GRAPHENE IS IMPORTANT AND WORTHY OF NOBEL PRIZE? Landau and Peierls argued that strictly two-dimensional (2D) crystals were thermodynamically unstable and could not exist. Band Theory of Graphite, P. R. Wallace, PRL, 1947. K.S. Novoselov et al., SCIENCE, 2004. RAJARSHI ROY 5 GRAPHENE IS A ONE-ATOM THICK LAYER OF GRAPHITE WHERE THE CARBON ATOMS ARE ARRANGED IN A ‘HONEYCOMB’ LATTICE ‘HONEYCOMB’ LATTICE HEXAGONAL, Sp2 J. C. Mayer et al. NATURE 446, 60 ,2007 BAND STRUCTURE OF GRAPHENE RAJARSHI ROY 6 x E(k2D) kx ky ⊥  kvE F   Band structure of graphene (Wallace 1947) Zero effective mass particles moving with a constant speed vF = c/300 kx' ky' E empty filled RAJARSHI ROY 7 Effective mass (m*) ~ [dE2/dk2]-1 Most semiconductors, 0.1 m0 < m* < 1 me Graphene, m* < 0.01 m0 (depending on number of carriers) Therefore, expect VERY high mobility in graphene both holes and electrons can be carriers The velocity of an electron at the Fermi level (vF) is inversely related to m* 106 m/s ~ c/300 ~ VFRelativistic Realm: Follows Dirac Equation from relativistic QM and correlation to quantum electrodynamics Electron mobility ~ 200000 cm2⋅V−1⋅s−1 ; Resistivity ~10−6 Ω⋅cm (at room temperature) A. Geim, SCIENCE 384, 1530, 2009. EXOTIC PROPERTIES OF GRAPHENE RAJARSHI ROY 8 SLG ON 285 nm Si/SiO2 FQHE AMBIPOLAR ELECTRIC FIELD EFFECT PSEUDOMAGNETIC FIELD QUANTIZATION KLEIN TUNELLING K.S. Novoselov et al., SCIENCE, 2004. Katnelson et al., NAT. PHYS., 2006 Levy et al., SCIENCE, 2010 METALLICITY AND TRANSPARENCY IN GRAPHENE RAJARSHI ROY 9 • Opacity of suspended graphene (1) is defined solely by the fine structure constant, a = e2/ℏc ≈ 1/137 (where c is the speed of light), the parameter that describes coupling between light and relativistic electrons • Despite being only one atom thick, graphene is found to absorb a significant (pa = 2.3%) fraction of incident white light, a consequence of graphene’s unique electronic structure. Nair et al., SCIENCE, 2008 OVERVIEW RAJARSHI ROY 10 Bleu et al., FRONTIERS IN CHEMISTRY, 2018 RAJARSHI ROY 11 SYNTHESIS STRATEGIES RAJARSHI ROY 12 MICROMECHANICAL CLEAVAGE OF HOPG (SCOTCH TAPE METHOD) Yi et al., J. MATER. CHEM. A, 2015. CHEMICAL VAPOUR DEPOSITION (CVD) RAJARSHI ROY, 13 (Cu, Ni, Ga, Pt) GROWTH LP PRESSURE CVD ATMOSPHERIC PRESSURE CVD • SINGLE CRYSTAL DOMAIN • THICKNESS CONTROL • MORE TIME TO GROWTH IN LARGE AREA • POLYCRYSTALLINE • THICKNESS CONTROL NOT POSSIBLE • LESS TIME TO GROWTH IN LARGE AREA • SUBSTRATE QUALITY IS IMPORTANT ECS J. Solid State Sci. Technol. 2017 CVD on SiC RAJARSHI ROY 14 YANG ET AL., APPL. SURF. SCI., 2018. RAJARSHI ROY 15 ATMOSPHERIC PRESSURE CVD LOW PRESSURE CVD (1mbar) GAO ET AL. NATURE COMMUN., 2011 ZHANG ET AL., NAT. COMMUN. 2016 TRANSFER MECHANISM RAJARSHI ROY 16 STANDARD WET TRANSFER STAMPING METHOD Bleu et al., FRONTIERS IN CHEMISTRY, 2018 RAJARSHI ROY 17 BUBBLE TRANSFER GAO ET AL. NATURE COMMUN., 2011 CHEMICAL METHODS RAJARSHI ROY 18 Parvez et al. SYNTHETIC METALS, 2015 MERITS AND DEMERITS RAJARSHI ROY 19 Micromechanical Exfoliation • Low Yield • Adhesive residue • However can expect very clean samples if processed correctly CVD • Can be obtained as thin films for large area device applications. For example: solar cells, sensors, photodiode • Precise layer thickness could be manipulated • Careful Transfer to substrate is essential otherwise there could be presence many defects • Added doping and residues of PL tend to stick to the surface and effects graphene’s performance Chemical Methods • Very high yield which are essential for composite preparation in mechanical and energy related applications • Can be obtained in solution or powder form • Ease of handling • Some of the species may not be graphene at all but rather derivative of graphene like RGO which is a semiconductor • Presence of multilayers and more defects are present in many cases BASIC CHARACTERISATIONS RAJARSHI ROY 20 RAJARSHI ROY 21 OPTICAL MICROSCOPY ATOMIC FORCE MICROSCOPY HRTEM 1 Cooper et al.,ISRN Condensed Matter Physics, 2012 2 WITEC, gmbh, Germany RAMAN RAJARSHI ROY 22 1 Ferrari et al. Nat. Nanotech. 8, 235, 2013 2 Ferrari et al. PRL 97, 187401 (2006). 3 Dresselhaus et al. Nano Lett. (2010). ROADBLOCK RAJARSHI ROY 23 • GRAPHENE WITH ZERO BANDGAP IS ENTICING FOR EXOTIC PHYSICS BUT NOT FOR ELECTRONICS • ULTRA HIGH MOBILITY IN GRAPHENE TRANSISTORS CANT BE USED AS THEY DON’T SWITCH OFF [DEADLOCK] • ON-OFF RATIO ~106-1010 IS NEEDED IN MOSFET • BANDGAP CAN BE OPENED IN GRAPHENE BY FUNCTIONALIZATION OR DOPING FUNCTIONZATION DOPING C B V B SOME APPLICATIONS RAJARSHI ROY 24 TRANSPARENT FLEXIBLE CONDUCTORS SENSORS DRUG DELIVERY INK FOR PAINT, COATINGS RAJARSHI ROY 25 SOLAR CELL Li-ION BATTERY CATALYSIS RAJARSHI ROY 26 OPTICAL DETECTORS TEXTILE CONCLUSIONS RAJARSHI ROY 27 • FIRST SUCH DISCOVERY OF NEW 2D MATERIALS • EXPLORATION INTO EXOTIC PHENOMENOLOGICAL ASPECTS AND MERGER OF NEW CONCEPTS BETWEEN CONDENSED MATTER AND HIGH ENERGY PHYSICS WITH VALIDATION • DISCOVERY OF NEW TYPES OF 2D MATERIALS (hBN, TMDC-WS2,MoS2, BOROPHENE, GERMANENE, PHOPHORENE, STANENE ETC.) • DISCOVERY OF NEW TYPES OF QUASIPARTICLES AND NEW BRANCES OF QUANTUM PHYSICS (VALLEYTRONICS) • NEW WAY OF DESIGNING MATERIALS: vdW HETEROSTRUCTURES (hBN-GRAPHENE,MoS2-WS2) AND CONCEPT OF WONDER MATERIALS BEING ESTABLISHED WITH WIDE ARRAY OF APPLICATIONS THANK YOU