1Chem 172Advanced Inorganic ChemistryLecture 25/June 2ndSemiconductor Nanotechnology& Solar CellsSemiconductor NanotechnologySemiconductor Nanocrystals: Quantum Dots¾Semiconductor nanocrystals of a few nanometer diameter can exhibit size dependent optical properties due to quantum confinement.¾This unique characteristic can enable new opportunities for energy harvesting in solar cells, color luminescent material for display, and image tags for biomedicine.EQD= Eg+ C/R2EQD= hv= hc/λ= 1240/λHow small is “Nano”?Single Hair= 100 micrometers= 100,000 nanometers !1 nanometer = one billionth (10-9) meterWidth = 0.1 mmSmaller StillDNA3 nanometersHair100,000 nanometers6,000 nanometersRed blood cellNANO is Not Simply A Miniaturization PlayNot just smaller. . . . . . differentbecause it’s smallerSize-Dependent PropertiesAt the nanometer scale, properties become size-dependent.¾Chemical properties – reactivity, catalysis¾Thermal properties – melting temperature¾Mechanical properties – adhesion, capillary forces¾Optical properties – absorption and scattering of light¾Electrical properties – tunneling current¾Magnetic properties – superparamagnetic effectNanomaterials can often display characteristics that are fundamentally differentthan those of their “bulk” counterparts.
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