PHYS-E0424 Nanophysics Lecture 5: Fullerenes, Carbon Nanotubes and Graphene

Transcription

1 PHYS-E0424 Nanophysics Lecture 5: Fullerenes, Carbon Nanotubes and Graphene PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 1

2 SEM/TEM Recently I was operating SEM for a first time for GaAs nanowires classification lab work. An interesting thing that I observed was, that at +300x magnification resolution decreased. The image was blurring and moving, due to a travelling beam. What is the nature of this effect? Can it be a visualization of Brownian motion? And what are the limits that can be resolved with SEM? As TEM operates at voltages of 100kV and higher, how can we overcome heating and charging of a specimen? It is a common thing, that a sample image is darkening because of surface charging in electron microscopy. How this charge can be removed from the specimen after? Igor Prozheev - At very high magnification the image might blur because of sample drift/motion or charging. - Heating depends on electron beam current rather than voltage - Surface charging leads to blurring. A conducting layer needs to be added to avoid this PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 2

3 Sample Quality TEM vs. STM How much does sample quality limit TEM resolution (compared to other factors)? How does sample quality limit the other imaging methods (STM, for example)? Are some methods affected more by poor sample quality than others? Jesper Ilves PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 3

4 Sample Quality TEM vs. STM - TEM images atom columns - TEM specimen nm thick PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 4

5 Sample Quality TEM vs. STM - STM images atoms at surface PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 5

6 Seminar By Michael Kosterlitz Welcome to the seminar "Topological excitations in two dimensions held by J. Michael Kosterlitz, Nobel Prize in Physics 2016 winner / 16:00-18:00 Lecture hall D, Otakaari 1, 02150, Espoo, FI Program - Welcome by Kay Brandner, Postdoctoral Researcher - Tuula Teeri, President of Aalto University - Professor J. Michael Kosterlitz s lecture on "Topological excitations in two dimensions" - President s reception Seminar is open for Aalto staff and students. Registration here. PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 6

7 Visit to Murata - 31 October (instead of lecture) - Sign-up sheet PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 7

8 Nanophysics Topics - Short presentation on nanophysics topic (12 minutes + 3 minutes discussion) - 28/11 or 5/12 - Essay on a nanophysics topic (submission deadline: ) - Essay is based on literature review - Contains. Introduction, description of physics, state-of-the-art, outlook, summary, list of references PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 8

9 Blue light-emitting diodes PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 9

10 Magnetic nanoparticles (applications) PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 10

11 Quantum computation PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 11

12 DNA origami PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 12

13 Brain-inspired computing Cognitive computing Use of memristors to mimic synaptic functions PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 13

14 Graphene (applications) PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 14

15 In-situ TEM techniques PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 15

16 Single-electron devices PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 16

17 Carbon nanotubes PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 17

18 Molecular self-assembly PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 18

19 Three-dimensional imaging Three-dimensional imaging is a technique that combines many scans (from computed tomography, MRI or ultrasonography) computationally. PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 19

20 Multiferroic materials PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 20

21 Nanosphere lithography PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 21

22 Biomimetic materials PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 22

23 Atomic layer deposition PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 23

24 Self-organization of semiconductor quantum dots PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 24

25 Organic electronics PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 25

26 Topological insulators PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 26

27 Skyrmions PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 27

28 Spin Hall effect (magnetic switching) PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 28

29 Suggested Topics - Blue light-emitting diodes - Magnetic nanoparticles (applications) - Quantum computation - DNA origami - Brain-inspired computing - Graphene (applications) - In-situ TEM techniques - Single-electron devices - Carbon nanotubes - Molecular self-assembly - Three-dimensional imaging - Multiferroic materials - Nanosphere lithography - Biomimetic materials - Atomic layer deposition - Self-organization of semiconductor quantum dots - Organic electronics - Topological insulators - Skyrmions - Spin Hall effect (magnetic switching) PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 29

30 Selected Topics 28 November - Self-organization of semiconductor quantum dots - Jesper - Nanosphere lithography - Topi - Atomic layer deposition - Paavo - 2D materials - Syed - Spark discharge generation of single wall CNT - Saeed - Multiferroic materials - Timm - Topological insulators - Jashasvi - Skyrmions - Tuomas 5 December - Single-electron devices - Esin - Magnetic nanoparticles (applications) - Igor - Blue light-emitting diodes - Joonas - Organic electronics - Clemens - Brain-inspired computing - Zhennan - Optical logic - Timo PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 30

31 PHYS-E0424 Nanophysics Lecture 5: Fullerenes, Carbon Nanotubes and Graphene PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 31

32 Carbon Structures diamond (3D) graphite (2D) carbon nanotube (1D) C 60 (0D) PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 32

33 Diamond - Diamond crystal structure consists of two interpenetrating face centred cubic Bravais lattices of carbon atoms - sp 3 hybridization - Strong bond between carbon atoms (bond length = 1.54 Å) - Transparent - Isolator with 5.5 ev band gap PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 33

34 Graphite - Graphite crystal structure consists of hexagonal planes - sp 2 hybridization - Strong C-C bond in the plane (bond length = 1.42 Å) - Weak binding between hexagonal planes (distance = 3.35 Å) - Used for writing and lubrication - Semimetal with electron transport in the lattice plane PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 34

35 The Discovery of Fullerenes : Kroto, Heath, O Brien, Curl, Smalley - Nd:YAG (neodymium-doped yttrium aluminium garnet) laser evaporation of graphite + time-of-flight mass spectrometry cluster integration cup P He = 760 Torr P He = 10 Torr Kroto et al., Nature 318 (1985) 162 PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 35

36 Fullerene Nanostructures C 20 (I h ) C 24 (C 3d ) C 26 (D 3h ) C 28 (T d ) C 30 (C 2v ) C 32 (D 3h ) C 34 (C 3v ) C 36 (D 6h ) C 38 (D 3h ) C 40 (T d ) C 42 (D 3 ) C 44 (D 3h ) C 46 (C s ) C 48 (D 6d ) C 50 (D 3 ) C 60 (I h ) C 70 (I h ) C 180 C 240 C 320 C 500 C 720 PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 36

37 Carbon Nanostructures - C 60 and other carbon nanostructure resemble architecture by Buckminster Fuller - These structures are now referred to as buckyballs or more generally fullerenes Montreal biosphere by Buckminster Fuller (1967) PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 37

38 Carbon Nanotubes - Carbon nanotubes consist of one or several rolled-up graphene sheets - Discovered in Fundamental research on carbon nanotubes - Model system for physicists Possible applications: - Nanoprobes - Molecular electronics - Gas storage - Mechanical properties - Electron field emitters - Transparent conducting films PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 38

39 The Discovery - In 1991 Iijima et al. discovered the formation of cylindrical objects during the fabrication of C 60 - The cylindrical objects contained different numbers of graphene sheets and had a diameter of a few nanometer Iijima et al., Nature 354, 56 (1991) Scanning electrode microscopy (SEM) images PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 39

40 Structure of CNTs roll-up vector c = na 1 + ma 2 a 1 zigzag (n, 0) a 2 c (7, 3) one example of chiral tube armchair (n, n) PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 40

41 Structure of CNTs Armchair (5,5) Zig-zag (9,0) Chiral (10,5) PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 41

42 Electronic Properties of Single-Wall CNTs Armchair (n=m): metallic Zig-zag (n,0): Chiral (n,m): metallic if (n-m)=3i semiconducting if (n-m) 3i PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 42

43 STM on Single-Wall CNTs (14,-3) SWNT semiconducting Band gap is a function of tube diameter PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 43

44 CNT Diameter and Band Gap Carbon nanotube diameter (d): acc d 3 n m mn n m mn a CC = nm (C-C bond length) Carbon nanotube band gap (E gap ): E gap 2y0a d CC y 0 = C-C bonding energy (2.7 ev) PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 44

45 CNT Density of States acc d 3 n m mn n m mn PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 45

46 Graphene Graphite Graphene Layered poorly conducting semimetal PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 46

47 Graphene - Fabrication Exfoliation (Scotch tape method): - For a long time it was assumed that planar graphene did not exist in the free state due to an instability towards the formation of curved structures such as fullerenes and nanotubes (Landau and Peierls theory) - In 2004 Novoselov and Keim used mechanical exfoliation of graphene sheets from highly oriented pyrolytic graphite (commonly referred to as the Scotchtape method) and identified graphene by an optical microscopy method - Since this discovery the number of experimental studies on graphene has exploded (these studies mostly focus on the electronic properties of graphene) K.S. Novoselov et al., Science 306, 666 (2004) PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 47

48 Graphene The Discovery PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 48

49 Graphene - Fabrication Epitaxial growth on SiC: - High temperature annealing (> 1100 C) - Area depends on size of wafer - Thickness and electrical properties highly influenced by surface termination - Bonding to substrate influences band gap carrier mobility etc J. Kedzierski et al., IEEE Trans. Elec. Dev. 55, 2078 (2008) PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 49

50 Graphene - Fabrication Epitaxial growth on metal substrates: - CVD growth on e.g. Ni, Cu, Ir - Difficult to control layer thickness over large areas (this problem is circumvented by the growth on copper, as growth is automatically stopped after a single graphene layer) - Bonding to substrate influences band gap, carrier mobility etc - Transfer to other substrate has been demonstrated Graphene grown on Ni and transferred onto a Si wafer PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 50

51 Graphene - Carbon has 4 electron in the outer s-p shell - sp 2 hybridisation forms strong covalent bonds - p z ( ) orbital determine conduction properties of graphene PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 51

52 Band Structure of Graphene - Zero band gap two-dimensional semiconductor - Conduction and valance band meet at single points in momentum space - Linear dispersion of conduction and valance bands - Electron-hole symmetry PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 52

53 Graphene Electronic Structure Conventional 2D electron system Graphene PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 53

54 Graphene Electronic Structure - Charge carriers in graphene have zero rest mass (Dirac fermions) - Relativistic behaviour of charge carriers is not described by the Schrödinger equation but by Dirac s relativistic equation E k v de dk c / m/s Angle-resolved photoemission spectroscopy A. Bostwick et al., Nature Physics 3, 36 (2007) PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 54

55 Band Gap Engineering - Substrate can influence the electronic structure of graphene - Graphene on SiC exhibits a band gap - Band gap depends on number of graphene sheets - Band gap engineering important for applications such as transistors S.Y. Zhoe et al., Nature Materials 6, 770 (2007) PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 55

56 Band Structure of 2D Systems in B Field - The energy of electrons in strong magnetic fields is quantized into Landau levels because of cyclotron motion - Energy separation between Landau levels is given by cyclotron energy: - Number of states in Landau level is: - Landau quantization is directly responsible for oscillations in electronic properties of materials as a function of applied magnetic field. PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 56

57 Electronic Oscillations Quantum effects in electronic transport: Shubnikov De Haas effect Quantum Hall effect Note: Effect of Landau quantization is only observed when the mean thermal energy is smaller than the Landau energy quantization (kt < ħ c ) PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 57

58 Shubnikov De Haas Effect - Resistance oscillation parallel to current path ( xx ) - With increasing magnetic field, the Landau levels move to higher energy. When an energy level passes through the Fermi energy, it depopulates and the electrons become free to flow as current. PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 58

59 Quantum Hall Effect - Resistance oscillation perpendicular to current path ( xy ) - In classical Hall effect the Hall resistance is given by - When Landau levels from the bottom up to the i-th level are filled, then: PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 59

60 Quantization Effects in Graphene - Anomalous quantum Hall effect in graphene xy 4 e 2 N 0.5 h - Shift of 0.5 is due to a quantized level at zero energy, which is shared by electrons and holes K.S. Novoselov et al., Nature 438, 197 (2005) PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 60

61 Quantization Effects in Graphene - Anomalous quantum Hall effect in graphene xy 4 e 2 N 0.5 h - Shift of 0.5 is due to a quantized level at zero energy, which is shared by electrons and holes K.S. Novoselov et al., Nature 438, 197 (2005) PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 61

62 Spin Transport in Graphene - Non-local spin-valve geometry used to probe spin transport and spin precession in graphene - Spin relaxation length of about 2 m at room temperature N. Tombros et al., Nature 448, 571 (2007) PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 62

63 This Week s Articles PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 63

64 Next Lectures 24/10 No lecture 31/10 Visit to Murata 7/11 Nanoelectronics PHYS-E0424 Nanophysics Lecture 5: Carbon Nanostructures Sebastiaan van Dijken 64