Nanostructures: Physics on the chip

Transcription

1 Course outline Basis of nanophysics 1) Physical principles of nanostructures 2) Microscopy 3) Synthesis 4) Carbon nanostructures 5) Applications to photonics, magnetism, catalysis and energy Sources: 1) Hans-Eckhardt Shaefer Nanoscience 2) Klaus D. Sattler-Handbook of Nanophysics, Volume I_ Principles and Methods-CRC Press (2010) 3) Introduction to Nanoelectronics: V. V. Mitin, V. A. Kochelap Michael A. Stroscio

2 Nanostructures: Physics on the chip atomo molecola colorante proteina oro colloidalebatterio cellula fluorescente Tecnologia del silicio Punto quantico

3 Moore Law I. Transistors density doubles every months II. Parallel increase of the cost of installations for silicon technology 200 billions dollars in 2015.

4 MOSFET

5 Problems due to integration Short channels introduce saturation in carriers velocity. Threshold voltage cannot be reduced in order to turn the device off. Problems of tunnel effects in ultrathin oxide <2nm ( highly dielectric materials) Higher capacitance and delays

6 Further limits Heat problems. A processor dissipates like a bulb lamp of 100W Cross-talk between devices. Doping at the 1018 at/cm3 means 10-3at/nm3. Any distribution fluctuation will result in different functionality.

7 Macroscopic world µm Nanotechnology & nanoscience It is not possible to extrapolate from the bottom or from above the behavior Quantum physics pm

8 Mesoscale In the range interdisciplinarity with bioscience is huge Chemistry and biology can prepare nanotechnological systems to be studied from the physical point of view

9 Mesoscale R.P. Feynman ( nobel 1965) Complex systems at this scale will have infinite technological applications P.W. Anderson( nobel 1977) Interaction between complex systems at the such a scale is a fundamental physics discipline

10 Mesoscale What is it the science of mesoscale? Difficult to say But we know that: 1)Only few systems have been tested. 2) Real nanotech is even rarer. 3) IBM would have discovered MGR even without the nanotechnology being invented

11 2 real examples 1) Giant magnetoresistance 2) heterogeneous catalysis

12 HARD DISK Fe magnetic Cr not magnetic tipo Fe2O3 Fe3O4 (magnetite) ( hematite) NOBEL Physics Fert and Grűnberg Giant magnetic resistance Cr = [Ar] 3d54s1 Fe = Fe/Cr/Fe [Ar]3d64s2 3nm

13 Heterogeneous catalysis (the catalyst has a different phase from the reagent) Nobel Chemistry 2007 G. Ertl N2 + 3H2=2NH3 Ertl discovered that on Fe nanoparticles were some N atoms and the transformation in NH3 increased. The potential barrier for the splitting of the molecule was reduced by iron. N/ Superficie del Fe(001) In a similar way in catalytic exhausts in cars 2CO+ O2 = 2CO2 Catalysis

14 10 nanotechnology products Forbes 2005

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16 Hot topics? Main effects due to the size are: 1) 2) 3) 4) 5) 6) 7) Surface to volume ratio effects Quantum confinement Quantized conductance supersensors Brownian motion granularity Quantum forces

17 S V Surface to volume effects ~50% on the surface ~10% on the surface

18 Quantum confinement e - Photon has null moment and only vertical transitions are allowed x Photon absorption and emission λ λ =confined electron wavelength Initial and final momenta are much bigger than the photon moment and transitions are always vertical ( Si laser)

19 Meta-materials Negative refraction index Nature Nanotechnology 2, n=± εµ ( ε<0 µ <0 )

20 Quantized conductance single electron transistor - Island will block current in a quantized way I isola Va According to the Moore law a CMOS in 2014 will work with 8 electrons.

21 Thermal conductance quantization Shwab nel 1999: Thermal dissipation in a quantum-mechanical system

22 ULTRASENSORS at the quantum limit (NEMS) Displacements and forces up to the Heisenberg limit

23 Smart Dust Nanodevices distributed for pervasive control Energy independent rectification of noise

24 Nanomaterials Graphene (2D) Fluctuations are predicted to slice 1 layer solids and also melting but have been confuted mass-less electrons on such lattice

25 0 Brownian motion Example : Oxygen in H2O D= RT/N(6πηa) =18 x 10 ˉ6 cm²/sˉ¹ diffusion time for L is t= L² / D. 10nm in msec nm in 1 min 1 cm 100 anni brownian motion is the main transport process in microbiology

26 Nanoscale Forces van der Waals 0

27 Surface tension cohesion Large surface energy Contact angle <5 adhesion Contact angle > 165 small surface energy glass H2O Soap reduces surface energy Hg

28 Camecara beetle Namib desert hydrophilic Contact angle > 165 Humid air hydrophobic Contact angle <5 SuperHydrophobic surface SuperHydrophilic surface 20nm Silica particles

29 Friction GRAFITE quantized friction

30 Photonic crystals Guida d onda

31 Granularity Fluctuation affects morphology at low atom numbers

32 Thermal fluctuations An hard disk should be unstable. Oscillazioni quantistiche (entropia) Principio di fluttuazione e dissipazione σ2 ~ < N2> =NKT ρ KT KT = compressibilità isoterma

33 0 Nanoscale forces Casimir vacuum field Standing waves