Seminars in Nanosystems - I

Transcription

1 Seminars in Nanosystems - I Winter Semester 2011/2012 Dr. Emanuela Margapoti Emanuela.Margapoti@wsi.tum.de Dr. Gregor Koblmüller Gregor.Koblmueller@wsi.tum.de Seminar Room at ZNN 1 floor

2 Topics of the seminars 1. Colloidal nanoparticles: applications 2. Quantum dots 3. Nanoscale fabrication by non-conventional approaches 4. Plasmonic nanostructures 5. Spin crossover molecules 6. Graphene and C-based structures 7. Beyond graphene: Ultrathin MoSi2 8. Semiconductor nanowires 9. Photonic Crystals 10. Coulomb Blockade/SET 11. Spin effects in self-assembled quantum dots 12. Current Limits in Top-down Nanofabrication 13. High spatially resolved Analytics for Nanostructures

3 1. Colloidal Nanoparticles: applications Nanoparticles - Metal (Au, Ag) plasmonic - Carbon NPs (C60) PV - Semiconductor (CdSe) QDs - Silicate NPs (Si, SiO2) optics, biomedical, - photonic band-gap Nanorods Monopod, tripods, tetrapod Based on metal (Au, Ag) Plasmonic properties Based on semiconductor solid state lighting, QLED display, nano-bio applications Longitudinal and transvers surface plasmon resonance Longitudinal Tuned from IR to visible by varying the size Multifunctional nanoparticles Combination of semiconductor fluorescent QDs with plasmonic materials - Quench problems overcame Photo courtesy of Wei-Shun Chang nanotechnology implementation with size ranging from nm Medical purpose: drug delivery, cancer detection, etc. Optoelectronics: Photovoltaic, light emitting diode, etc.

4 Prof. A. Geim & Dr K. Novoselov - University of Manchester 2. Quantum Dots Molecular beam epitaxy Electrostatic QDs QDs: Application in optoelectronics PV when blended (e.g. Conducting polymers) Stranski-Krastanow (S-K) Transition low power lasers QLED-quantum dots display Chemical synthesis λ scales with the dot size Götz Veser at Pittsburgh University QDs: Application in medicine Colloidal QDs agents for medical imaging

5 J. Chen et al. ACS nano3, 173 (2009) J. Huang et al. Nat. Mat. 4, 896 (2005) 3. Nanoscale fabrication by non-conventional approaches One of the key challenges in nanotechnology is to control a self-assembling system to create a specific structure soft condensed matter has weaker bonds: 1) van der Waals interactions 2) electrostatic (charge-charge, dipole-dipole) 3) H-bonds Dewetting mechanisms lithography free method solvent water Bonds easily brocken Soft-materials are easily deformable Examples of soft condensed matter: Gels Foams Biological macromolecules Complex fluids (e.g. polymers) Liquid crystals Colloidal nanocrystals polymer

6 Surface Plasmons (SPs): EM waves formed at the interface btw a metal and a dielectric material 4. Plasmonic nanostructures z d d 250 nm d m 20 nm E z The coupling of excitonic and plasmonic properties leads to Energy transfer (FRET) Enhanced absorption Enhanced PL emission Wavelength shift Applications: Photovoltaic Light emitting diode Biosensor

7 5. Spin crossover molecules Spin-Crossover inorganic electronic switch (Fe II (3d 6 ), Fe III (3d 5 ) and Co II (3d 7 )) Conditions to be fulfilled: e.g. Fe II : outer electronic configuration 3d 6 (the electrons can occupy all the lower t 2g level (low-spin) or both t 2g and e g levels (high-spin)). Spin state transition from diamagnetic (S=0) in the LS state to paramagnetic (S=2) in the HS state Spin state and magnetic moment controlled by: Temperature Pressure Electromagnetic radiation Observations: Structural changes Colours changes Magnetic moment changes Thermal hysteresis (MEMORY)

8 6. Graphene and C-based structures graphene one-atom-thick layer of crystalline carbon Eg=0 0D 1D 3D Dirac Point the energy dispersion of the carriers and their density-of-states vanish linearly extraordinary electrical transport unusual physical properties - Ambipolar electrical field effect - Nonlinear optics - Photonic crystal based graphene - Graphene oxide open a optical window - Quantum Hall effects fulleren-c60 nanotube graphite

9 7. Beyond Graphene: Ultrathin MoS 2 for 2D Electronics MoS 2 : A new Direct-Gap Semiconductor Strong Light Emission, Transistor Potentials from Monolayer MoS 2

10 8. Semiconductor Nanowires Nanowire Growth Unique Physical Properties Potential Applications

11 9. Photonic Crystals Light-Matter Coupling in 2D PhC PhC Defect Resonators Weak Coupling Strong Coupling

12 10. Coulomb Blockade/SET Single Electron Transistor Coulomb Blockade/Diamonds

13 11. Spins Effects in Self-assembled QDs Spin Qubits in QDs Spin Initialization (Tunneling) Spin Readout Experiment Spin-to-Charge Conversion

14 12. Current Limits in Top-down Nanofabrication Conventional Photo-Lithography Non-Photon based Lithography Advanced Lithography E-Beam Lithography X-ray Lithography Focused Ion Beam Writing Nanoimprinting, etc.

15 13. Seeing things at the Nanoscale - Analytics of Nanostructures Transmission Electron Microscopy Scanning Probe Microscopy Atom Probe Tomography