Nanostrukturphysik (Nanostructure Physics)

Transcription

1 Nanostrukturphysik (Nanostructure Physics) Prof. Yong Lei & Dr. Yang Xu Fachgebiet 3D-Nanostrukturierung, Institut für Physik Contact: Office: Unterpoerlitzer Straße 38 (Heisenbergbau) (tel: 3748) Vorlesung: Wedsnesday 9:00 10:30, C 108 Übung: Friday (G), 9:00 10:30, 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).

2 Contents of Class 1 A general introduction of fundamentals of nanostructured materials Definition of nanostructures or nano-structured materials Significance of nano-structured materials Structural aspects An outline of all the 10 classes Characterization of nano-strcutures One-dimensional nanostructures Surface Nanostructures realized using UTAM

3 There s plenty of room at the bottom, the principles of physics, as far as I can see, do not speak against the possibility of manoeuvring things atom by atom... By the legendary physicist Richard Feynman in 1959 (Feynman R., Eng Sci, 1960) Progress made in past two decades has proven this statement by the amazing nature of nanomaterials, has achieved exciting technological advancement for the benefit of mankind.

4 Definition of nanostructures or nano-materials The word nanometer has been assigned to indicate the size of 10-9 meter Structures with at least one dimension within nanometer (nm) called nanostructures (Prof. H. Gleiter ) The word nano derived from a Greek word nanos, means dwarf (small) Nanostructures have received high research interest because of their peculiar and fascinating properties, as well as their unique applications superior to their counterparts - bulk materials. Nowadays, nanomaterials and nanostructures are not only one of the hottest fundamental research topics, but also gradually intrude into our daily life.

5 From: J. Henk Introduction to the Theory of Nanostructures (Lecture Notes 2006)

6 Nobel Prizes with research related to nanotechnology: 1986 Physics: G. Binnig, H. Rohrer: design of the scanning tunneling microscope (STM) SPM systems; 1996 Chemistry: R. Curl, H. Kroto, R. Smalley: discovery of fullerenes (C60, bucky balls); 2002 Chemistry: J. Fenn, K. Tanaka, K. Wüthrich: identification and structure analyses of biological macromolecules; 2003 Chemistry: P. Agre, R. MacKinnon: discoveries of channels in cell membranes Physics: A. Geim, K. Novoselov: for groundbreaking experiments regarding the two-dimensional graphene

7 Nobel Prizes with research related to nanostructures: G. Binnig (German) & H. Rohrer (Swiss) Nobel Prize 1986 Physics Designing of the scanning tunneling microscope (STM) SPM systems G. Binnig also designed AFM with other 2 scientists, and started the company Definiens in He worked as honorary professors in some universities, e.g., Uni-Muenchen.

8 Konstantin Novoselov & Andre Geim (Russian) Nobel Prize 2010 Physics for groundbreaking experiments regarding the twodimensional graphene 8

9 Prof. Andre Geim (from: en.wikipedia.org/wiki/andre_geim) obtained first tenured position in 1994, associate professor at Uni-Nijmegen, one doctoral student at Nijmegen was Novoselov. Geim said that he had an unpleasant time during his career in Netherlands. He was offered professorships at Nijmegen and Eindhoven, but turned them down as he found the Dutch academic system too hierarchical and full of politicking. "This can be pretty unpleasant at times," he says. "It's not like the British system where every staff member is an equal quantity. Geim writes in his Nobel lecture that "the situation was a bit surreal because outside the university walls I received a warmhearted welcome from everyone around In 2001 he became a professor at the University of Manchester, and was appointed director of the Manchester Centre for Mesoscience and Nanotechnology in 2002.

10 1996: Curl, Kroto, Smalley 1985 or1986: fullerenes (C60, bucky balls); 2010: Geim, Novoselov : 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

11 Graphene is a 1-atom thick sheet of sp 2 -bonded carbon atoms that are densely packed in a honeycomb crystal lattice. Graphene is easily visualized as an atomic-scale wire made of carbon atoms and their bonds. Graphite consists of many graphene sheets stacked together. (

12 Zigzag carbon nanotube

13 Armchair carbon nanotube

14 Why are nanostructures interesting? small is different: new properties of materials at nanometer scale look at quantum mechanics nanostructure + functions or properties: revolution in information technology, medicine, media...

15 Many opportunities might be realized by making new types of nanostructures (fabrication ways): 1. simply by down-sizing existing microstructures into nm range: most successful example is microelectronics, where smaller means greater performance (since the invention of integrated circuits): more components per chip, faster operation, lower cost, and less power consumption;

16 Structural aspects of nano-structured materials: Extremely large surface area (very large surface/volume ratio): when the dimensions decrease from micron level to nano level, the surface area increases by 3 orders in magnitude. This will lead to much improved and enhanced physical properties (sensing, optical, catalysis...): Cube Cubic structures divided into 8 pieces surface area 2 times(doubled) Cube Cubic structures divided into 1000 pieces surface area 10 times

17 Many opportunities might be realized by making new types of nanostructures (fabrication ways): 2. Miniaturization also represent the trend in a range of other technologies: Information storage, e.g., many efforts to fabricate magnetic and optical storage components with critical dimensions (feature size) as small as tens of nanometer device miniaturization

18 Dual-core CPU feature-size 45 nm From Intel Homepage, Public Relations

19 Electronic properties: Dimensions of a system - comparable with Bohr (exciton) radius (which is comparable to nanowire diameter): energy bands cease to overlap discrete The typical electronic properties of the nanostructures are a result of tunneling currents and coulomb blockade effects. However, owing to their wavelike nature, electrons can tunnel through between two closely adjacent nanostructures If a voltage is applied between two nanostructures, which aligns discrete energy levels, resonant tunneling occurs largely increases tunneling current

20 The physical properties of functional nanostructure are different from those of the bulk materials, especially for optical properties: Quantum confinement effect (size-reduction down to the nm-sized range) a band-gap shift adjust the optical properties of nanostructures. Quantum confinement effect: It is widely accepted that quantum confinement of electrons by the potential wells of nanometer-sized structures provides the most powerful (and versatile) means to control the electrical, optical, magnetic, and thermoelectric properties of a solid-state materials. Metallic nanostructures (especially Au and Ag) have unique optical properties surface-enhanced plasmon resonance light-scattering and Raman scattering (SERS or SRR).

21 Quantum confinement effect When the feature size of a structure (e.g., particle) is comparable with the size of Bohr (exciton) radius (about 2 50nm, usually below nm), electron becomes more confined in particle, quantum confinement effect lead to an increasing of energy band-gap. Furthermore, the valence and conductive bands break into quantized discrete energy levels. Many exceptional physical properties of nano-materials are attributed to the changes in the total energy and structure of the system. Band-gap shift due to the Quantum confinement effect: ΔEg = h2/8r2μ 1.8e2 /4πεoεR

22 Quantum confinement in semiconductor nanoparticles Optical fluorescence of CdSe nanoparticles of various sizes. The band gap emission is observed to shift through the entire visible range, from red emission for the largest particles, to blue emission for the smallest clusters. (B. O. Dabbousi, J. Phys. Chem. B, 1997, 101, 9463)

23 Global funding status in nanotechnology This course is try to overview this 21st century s leading science and technology based on fundamental and applied research during the last 2 decades Nano - World

24 Deutsches Museum Zentralbau des Deutschen Museums

25 Class 1: a general introduction of fundamentals of nanostructured materials, and definition Class 2: research at 3D-Nanostructuring Class 3: optical properties of 1D nanostructures Class 4: carbon nanotubes Class 5: graphene Class 6: 2D atomically thin nanosheets Class 7: lithium-ion batteries: Si nanostructures Class 8: solar water splitting I: fundamentals Class 9: solar water splitting II: nanostructures for water splitting Class 10: solar cells

26 Class 2: research at 3D-Nanostructuring From template to energy: Sodium-ion batteries Solar water splitting Supercapacitors

27 Class 3: optical properties of 1D nanostructures Features Quantum confinement Nanowire lasing Field emission display

28 Class 4: carbon nanotubes History Fabrication Applications

29 Class 5: graphene Introduction Brief history Characterizing graphene flakes Devices with peeled graphene Alternatives to mechanical exfoliation

30 Class 6: atomically thin nanosheets Characterization of structure Electronic structure regulation Energy device construction

31 Class 7: nanostructured Si anodes for lithium-ion batteries Principle of lithiumion batteries Opportunities and challenges of Si anodes Nanostructured Si anodes

32 Class 8: fundamentals of solar water splitting Related semiconductor physics Thermodynamic and kinetics of semiconductor-liquid interface

33 Class 9: nanostructures for solar water splitting Pros and cons Material designs and nanostrcutured architectures Cathode Electrolyte Anode

34 Class 10: nanostructures for enhancing light absorption in solar cells Semiconductor nanostructures Metal nanostructures: surface plasmons

35 Characterization of nano-strcutures An appropriate characterization will play a crucial role in determining various structures and properties of nanostructures. Three broadly approved aspects of characterization are 1. Morphology 2. Crystalline structure 3. Chemical analysis

36 SEM: Scanning Electron Microscopy; STM/AFM: Scanning Tunneling Microscopy/Atomic Force Microscopy; ATEM: Analytical Transmission Electron Microscopy X-Ray: X-ray Morphology; IP: Image Processing; LM: Lightweight Morphology; RBS: Rutherford Backscattering Spectrometry (Kelsall et al., Nanoscale science and technology. 2005)

37 ATEM: Analytical Transmission Electron Microscopy; AES: Auger Electron Spectrometer; XRD: X-ray Diffraction; RBS: Rutherford Backscattering Spectrometry; XPS: X-ray Photoelectron Spectrometer; (Kelsall et al., Nanoscale science and technology. 2005)

38 SEM: Scanning Electron Microscopy; ATEM: Analytical Transmission Electron Microscopy; AEM: Auger Electron Microscopy. XRD: X-ray Diffraction; LEED: Lowenergy electron diffraction; RBS: Rutherford Backscattering Spectrometry (Kelsall et al., Nanoscale science and technology. 2005)

39 Types of Nanostructure: Two-dimensional nanostructure: nanowalls, quantum wells... One-dimensional nanostructure: nanowires, nanotubes, nanorods, nanobelts... Zero-dimensional nanostructure: quantum dots or nanoparticles

40 Graphene is a 1-atom thick sheets of sp 2 -bonded carbon atoms that are densely packed in a honeycomb crystal lattice. Graphene is easily visualized as an atomicscale wire made of carbon atoms and their bonds. Graphite consists of many graphene sheets stacked together. (

41 Templates with large-scale (1 mm 2 ) perfect rectangular pore arrays without defect

42 Templates with large-scale (1 mm 2 ) perfect rectangular pore arrays without defect

43 Perfect regular 3D nanostructure arrays with different wire configuration

44 One dimensional nanostructures One dimensional (1D) nanostructure: nanowires, nanotubes, nanorods, nanobelts... One dimensional nanostructure refers to the systems with the lateral dimension in the range of nm. In comparison with 0D nanostructures, 1D nanostructures provides a better model system to investigate the dependence of properties (electronic transport, optical, and mechanical) on size confinement and dimension. Nanowires, in particular, plays an important role as both interconnects and active components in preparing nanoscale devices (Nano-devices).

45 One-Dimensional Nanostructures (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). (Y. Lei et al., Chemistry of Materials, 2004)

46 A schematic summary of the kinds of one dimensional nanostructures already reported: (A) nanowires and nanorods; (B) core shell structures; (C) nanotubes/hollow nanorods; (D) heterostructures; (E) nanobelts/nanoribbons; (F) nanotapes; (G) dendrites; (H) hierarchical nanostructures; (I) nanosphere assembly; (J) nanosprings. (Kolmakov et al., Annu Rev Mater Res 2004)

47 CdS replicated mask Alumina CdS nanodots Highly ordered CdS nanodot arrays, UTAMs and CdS top layer on the surface of the UTAM.

48 Surface patterns in nature Structural color function of surface patterns butterfly 1 µm peacock packing of melanin cylinders (provided by L Chi)

49 Surface patterns and structures (artificial) and their applications in diverse (micro-electronic) devices Dual-core CPU feature-size 45 nm From Intel Homepage, Public Relations

50 Surface Nano-Patterning Fabrication of surface nanostructures Memory devices with high integration density; Field emission devices; Sensors with high sensitivity; Optical devices with tunable properties What is an excellent surface nano-patterning technique? 1. Ability to prepare surface patterns within the nanosized range; 2. Well-defined surface nano-patterns; 3. Large pattern area high throughput; 4. A general process applicable; 5. Low cost. Perfect?

51 Some surface nano-patterning techniques in fabricating ordered surface nanostructures Electron-beam lithography Excellent structural controlling Low throughput High equipment costs Imprint technologies High throughput Wear Structures with low aspect ratio Self assembly Low costs High throughput Limited class of materials Low structural controlling Alternative method that combines these advantages and is applicable for a broad range of surface nanostructures? UTAM (ultra-thin alumina mask) surface nano-patterning: Template-based surface nano-fabrications

52 Porous Alumina Membranes (PAMs) Interesting and useful features: highly ordered pore arrays + large area Nanometer-sized pores High aspect ratio size controllable ( nm) Configuration diagram of the PAMs

53 Porous Alumina Membranes (PAMs) (a) (b) Regular arrays of short (a) and long Ni nanowires (b) after the removal of PAM, the diameter is about 90 nm, the length is about nm (a) and 3-4 μm (b), respectively. thus the aspect ratio of the nanowires are about 10 (a) and 40 (b), respectively.

54 UTAM surface nano-patterning technique Fabrication of Highly Ordered Nanoparticle Arrays Using Ultra-thin Alumina Mask (UTAM) Motivation Use ultra-thin ordered porous alumina as evaporation or etching masks, and transfer the regularity of the pore arrays to the nanostructure arrays on substrates.

55 Fabrication process Fabricating ultra-thin alumina masks (UTAM) on Al foils and then mounting them onto the surface of silicon wafers First alumina layer Al Si foil wafer Ultra-thin Second alumina layer mask

56

57 Fabrication of the nanodot arrays Si wafer Ultra-thin Nanoparticle alumina array mask

58 CdS replicated mask Alumina CdS nanodots Highly ordered CdS nanodot arrays, UTAMs and CdS top layer on the surface of the UTAM.

59 Class 1: a general introduction of fundamentals of nanostructured materials, and definition Class 2: research at 3D-Nanostructuring Class 3: optical properties of 1D nanostructures Class 4: carbon nanotubes Class 5: graphene Class 6: 2D atomically thin nanosheets Class 7: lithium-ion batteries: Si nanostructures Class 8: solar water splitting I: fundamentals Class 9: solar water splitting II: nanostructures for water splitting Class 10: solar cells

60 Thanks for your attention