Chapter 2 Properties on the Nanoscale NANO 101 Introduction to Nanotechnology 1.
Post on 05-Jan-2016
Chapter 2Properties on the NanoscaleNANO 101Introduction to Nanotechnology1Why Miniaturize?Properties start to change as size decreases!2Talking about inorganic bulk materials like metals or semiconductors2Particles are small High surface-to-volume ratioReact differentlyAct differently (new properties)Interact with light differentlyAre on the scale of small biological structures
Quantum Mechanics meet Classical Mechanics
Interesting new structuresWhy Nano is Interesting33(mostly surface!)How Much Surface Area?4
1,000 1 mm cubes, 2/3 of an index card 1 x 10^21 1nm cubes, larger than a football field! http://www.nano.gov/nanotech-101/specialSurface energy increases with surface areaLarge surface energy = instabilityDriven to grow to reduce surface energySurface Area and Energy
C. Nutzenadel et al., Eur. Phys. J. D. 8, 245 (2000).5 diameter (nm) Surface atoms (%)Surface energy = Extra energy at surface compared to bulk
Physical Structure Physical PropertyWhat are the structural differences on the nanoscale?High percentage surface atomsLarge surface energySpatial confinementReduced imperfectionsWhat properties are affected?What properties can we tune?6Spatial confinement -> of an electron orbitalReduced defects due to self purificationMelting PointsLower melting point for nanostructures Surface Plasmon Resonance16
Optical PropertiesLocalized Surface Plasmon Resonancesea of electrons excited
17Bulk plasmons oscillations of electronsSurface occur at interface of metal and dielectric
Optical PropertiesLocalized Surface Plasmon Resonancesea of electrons excited 18
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr200908sf5.htmlBulk plasmons oscillations of electronsSurface occur at interface of metal and dielectric
Optical Properties: Quantum DotsBand gap decreases as particle size increasesEMetal Insulator Semiconductor 50 nm QD 10 nm QD19SummaryProperties that change on the nanoscale:Melting pointMechanical properitesElectrical propertiesOptical propertiesWhy?Nanostructures are mostly surfaceNanostructres may be smaller than electron orbitals and light wavelengths
20Scaling LawsModel how properties change as things get miniaturized(minimize theoretical calculations)
How do we measure size?
Characteristic dimension: D
Surface area2121Using Scale LawsAn elephant has D ~ 1 m. What is its S/V ratio?
A flea has D ~ 1 mm.What is its S/V ratio?
22Deriving Scale LawsYou are told strength is proportional to D2
and that weight is proportional to D3
Write the expression for strength to weight ratio.23Practice with Scaling LawsHow many times greater is the strength to weight ratio of a nanotube (D = 10 nm) than the leg of a flea (D = 100 m)? the leg of an elephant (D = 2 m)?24