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
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
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 1-100 nm Medical purpose: drug delivery, cancer detection, etc. Optoelectronics: Photovoltaic, light emitting diode, etc.
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
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
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
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)
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
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
8. Semiconductor Nanowires Nanowire Growth Unique Physical Properties Potential Applications
9. Photonic Crystals Light-Matter Coupling in 2D PhC PhC Defect Resonators Weak Coupling Strong Coupling
10. Coulomb Blockade/SET Single Electron Transistor Coulomb Blockade/Diamonds
11. Spins Effects in Self-assembled QDs Spin Qubits in QDs Spin Initialization (Tunneling) Spin Readout Experiment Spin-to-Charge Conversion
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.
13. Seeing things at the Nanoscale - Analytics of Nanostructures Transmission Electron Microscopy Scanning Probe Microscopy Atom Probe Tomography