Is NANO all around? Gerhard Abstreiter

Transcription

1 Is NANO all around? Gerhard Abstreiter WaiterSchottkyInstitut, Technische Universitat MOnchen, Germany WednesdaY,4 May- 11:05 a.m. Nowadays theprefix nano- is attached to nearly everythingandthis enormous hype that has arisen overthepasttwodecades givestheimpressionthatnano is all around and everywhere. Indeed most ofthepropertiesofsolidsaswell asbiological systems depend criticallyonthearrangement ofatoms andmoleculesonthenanometrescale. Nanotechnology ontheotherhand is aimingat controll ing matter onthenanometre sca leand making use ofthealtered properties of nanostructures fornovel applications. Mostofthe newfunctionalitiesare eitherdueto thelarge surface-to-volume ratioof nanometre objects (chemistry aspects) ormake use ofquantum mechanical effects (physics aspects). After a general introduction to thefield of nano-science Iwill discuss somespecific examples ofthe materials control andthephysics ofsemiconductor quantum- andnanostructures.

2 WSI Is NANO all around? - Introduction to Nano Sciences Gerhard Abstreiter Walter Schottky Institut und Physik Department Institute for Advanced Study Technische Universität München, Garching 25th Anniversary Symposium of EPL, BAdW, May 4, 2011

3 Research Campus Garching

4 Center for Nanotechnology and Nanomaterials ZNN

5 What is the meaning of NANO? Google: hits > NANO is Mega-in the word nanos is ancient Greek and means dwarf nano is used as prefix, examples: nanogramm, nanosecond, nanometer the one billionth (10-9 ) part of a unit 1 nanometer = 10-9 m = 0, meter 1 m 10 0 m 100 µm 10-4 m 100 nm 10-7 m 1 nm 10-9 m 0.1 nm m people, dwarf hair transistor molecules atoms

6 About 50 years nanoscience Richard Feynman: There is plenty of room at the bottom 1959, APS Caltech "When we get to the very, very small world [ ] we have a lot of new things that would happen that represent completely new opportunities for design. Atoms on a small scale behave like nothing on a large scale, for they satisfy the laws of quantum mechanics. So, as we go down and fiddle around with the atoms down there, we are working with different laws, and we can expect to do different things. We can manufacture in different ways." "Furthermore, a point that is most important is that it would have an enormous number of technical applications." Demokrit, 2500 years ago: The variety of nature is the combination of different atoms (atomos: undividable)

7 Nanotechnology, next industrial revolution? Source: Norman Poire (Merrill Lynch)

8 once again the length scale ~10 8 ~ Å 1 nm m

9 Our world is built from less than 100 different atoms (chemical elements)!!!!

10 Many (nearly all) properties of our macroscopic world are determined by the spatial arrangement of atoms on an atomic (nanometer) scale a few examples: manyfold of living systems inorganic and technical world First summary: yes, NANO is all around!

11 nanotechnology development of microtechnology towards nanotechnology (nanoelectronics, nanomechanics,..) (mainly top-down technology) construction of nanometer-sized systems from atoms and molecules ( bottom-up technology, selforganisation) controlled changes of materials properties of nanometer-sized systems construction of functional nanosystems or nanomachines from atoms and molecules it is expected that nanotechnology will lead to many new applications for information, communication, environment, energy, health, security,

12 Nanoscience and nanotechnology - an interdisciplinary research area Physics Materials Engineering Biophysics Chemistry Nanoworld Medicine Biochemistry Biology

13 Richard Feynman: There is plenty of room at the bottom 1959, APS Caltech "The problems of chemistry and biology can be greatly helped if our ability to see what we are doing, and to do things on an atomic level, is ultimately developed - a development which I think cannot be avoided." "The principles of physics, as far as I can see, do not speak against the possibility of maneuvering things atom by atom. It is not an attempt to violate any laws; it is something, in principle, that can be done; but in practice, it has not been done because we are too big."

14 top-down Nano-Tools Electron beam lithography Focused ion beam techniques Scanning probe techniques Nanoimprint Epitaxy Self-assembly Self-organisation Biologically inspired tools bottom-up

15 Heinrich Rohrer Gerd Binnig Physics Nobelprize 1986 Scanning Tunneling Microscope (STM) G. Binnig + H. Rohrer, Rev. Mod. Phys. 71 (1999) S324

16 Positioning of atoms on a surface at will Don Eigler, IBM

17 2 examples 48 Fe atoms on Cu (111) 25 CO molecules on Ni Don Eigler, IBM Peter Feulner, TUM Information density: bits per cm 2 > Enzyklopädia Britannica on a thumb nail

18 A proton in a trap Willi Auwärter, Physik Department, TU München

19 electron beam - microscopy lithography Ernst Ruska Physics Nobelprize 1986

20 e_line - Raith Specs: Resolution SEM: 1.0 nm@30kv, 3 nm@1kv, Schottky Field emitter Options: SEM lithography system laser interferometer stage fixed-beam moving stage

21 Nanometer scale devices Nanoelectronics, Nanomechanics, Nanophotonics,.

22 Crystal structure Semiconductor Nanosystems Electronic band structure valence bands: occupied with electrons conduction bands: empty

23 roadmap for future semiconductor electronics

24 Layered structures with atomic precision: Epitaxy (molecular beam epitaxy (MBE))

25 Principle of MBE: semiconductor wafer (Si, GaAs, InP, ) ultrahigh vacuum

26 Si In As Growth of Si doped GaAs Ga Al GaAs Substrat

27 As Ga

28 Selected examples of MBE grown nanostructures AlGaAs GaAs 10nm Elektronenstrahlmikroskopie 100nm

29 Semiconductors and light: III-V heterostructures Light emitting diodes Semiconductor lasers M.C. Amman et al; WSI

30 Semiconductor nanowires In the past 10 years many groups started growing nanowires, mainly using Au or other metals as catalysts Goal: novel devices for optoelectronics, nanophotonics nanoelectronics, quantum electronics bio/chemical sensing energy conversion and storage

31 Nanowires or whiskers an old story

32 Vapor Liquid Solid (VLS) growth mechanism Nucleation of nanowires with Au nanoparticles: Gold gathers and preferentially decomposes precursor molecules It forms a liquid alloy with the precursors There is a preferential precipitation underneath the droplet, forming the nanowire

33 MBE grown Arsenide based nanowires materials: Ga, As, Al, In, Si, C Instead of Au, we use Ga to gather As 4 molecules that solidify as GaAs underneath the droplets

34 ...adding functionality to nanowires InGaAs / GaAs axial heterostructures and quantum dots fabrication via diameter modulated structures > photon -, electron -, spin Qubits Coaxial or radial heterostructures, thanks to the control of axial versus radial growth: > waveguiding, ultra-low threshold nanowire lasers, p n High mobility 2d or 1d-electron channels in the GaAs core by remote doping of the shell structure > high electron mobility nanowire transistors, thermoelectric devices, Coaxial or radial p-n junctions > 3 rd generation solar cells, LEDs,..

35 c) (110) (10 1) B A (011) AlAs/GaAs MQWs GaAs Core [1 11] GaAs S1 GaAs S2

36 Position- and size-controlled growth on Si (111) single side polished Si (111) (n- or p-type) using thermally grown 20-nm SiO 2 mask hole structures ( nm diameter, nm pitch) by e-beam lithography RIE and lift off and chemical etching Hertenberger et al., J. Appl. Phys. 108, (2010)

37 Epitaxy of lattice mismatched systems

38 Strain relaxation

39 Self-assembled quantum dots Nanostructures formed during lattice mismatched epitaxy (e.g. GaInAs on GaAs) EPITAXIAL LAYER (e.g. InAs) Energy SUBSTRATE (GaAs) Fully encapsulated In(Ga)As islands on 2D wetting layer Island formation Time Typical dimensions ~25 x 5nm InAs GaAs GaAs GaAs GaAs

40 Quantum dot as a controllable quantum system Absorption of a single photon generates one electron in the conduction band and one hole in the valence band: an exciton InAs GaAs

41 ... energies become discrete due to quantisation of motion in all three spatial directions > artificial atom (x,y,z) s p z e S z 1 2 CB X SINGLE EXCITON hh J z 3 2 cgs e X 1 1h X 1e 1h VB

42 single quantum mechanical system: basis for Quantum-Information-Technology Qubit: two-lwevel system > superposition of two quantum mechanical states

43 Single quantum dot photodiode as a quantum mechanical two-level system the photocurrent oscillates in a deterministic way important step towards quantum information technology photocurrent is deterministic for -pulse excitation > electron turnstile Intensity (number of photons per pulse) A. Zrenner et al., Nature 2002 Rabi Oscillations

44 Control of electron spin via polarization of light + e- h+ e

45 Control of photons photonic crystals and microcavities single photon source > important for quantum cryptography weak and strong coupling > solid state based QED Cavity mode V Emitter

46 Nanotechnology opens many possibilties Nano and information-/communication technology Nano and energy Nano and health Nano and environment Nano and security Nano and but: Nanotechnology cannot solve all our problems!

47 Acknowledgements WSI Quantum dots Jonathan J. Finley Vase Jovanov Florian Klotz Dominic Heiss Martin Brandt Emily Clark Kai Müller Hubert Krenner Max Bichler....and many external collaborators Nanowires Gregor Koblmüller, Dance Spirkoska, Ilaria Zardo, Simon Hertenberger, Daniel Rudolph, Stefan Funk Sarah Yazji Martin Soini Anna Fontcuberta i Morral, Carlo Colombo, Martin Heiss Matthias Heigoldt..

48 WSI NANO is all around, but it is not everything! Thank you for your attention