future prediction of wireless technology using nano devices

Optical Properties of Nanoscale Optical Properties of Nanoscale Materials Materials David G. Stroud David G. Stroud , , Department of Physics Department of Physics , , Ohio State University Columbus OH 43210 Ohio State University Columbus OH 43210 Work supported by NSF Grant DMR01-04987 and NSF DMR04-12295 Work supported by NSF Grant DMR01-04987 and NSF DMR04-12295 and by the Ohio Supercomputer Center and by the Ohio Supercomputer Center OUTLINE OUTLINE Introduction: Linear Optical Properties and Surface Plasmons Introduction: Linear Optical Properties and Surface Plasmons Liquid-Crystal Coated Nanoparticles Liquid-Crystal Coated Nanoparticles Surface Plasmons in Nanoparticle Chains Surface Plasmons in Nanoparticle Chains Composites of Gold Nanoparticles and DNA Composites of Gold Nanoparticles and DNA Conclusions Conclusions “ “ Labors of the Months” (Norwich, England, ca. 1480). Labors of the Months” (Norwich, England, ca. 1480). (The ruby color is probably due to embedded (The ruby color is probably due to embedded gold nanoparticles.) gold nanoparticles.) The Lycurgus Cup (glass; British The Lycurgus Cup (glass; British Museum; 4 Museum; 4 th th century A. D.) century A. D.) When illuminated from outside, it appears green. However, when Illuminated from within the cup, it glows red. Red color is due to very small amounts of gold powder (about 40 parts per million) Lycurgus Cup illuminated from Lycurgus Cup illuminated from within within When illuminated from within, the Lycurgus cup glows red. The red color is due to tiny gold particles embedded in the glass, which have an absorption peak at around 520 nm What is the origin of the color? What is the origin of the color? Answer: ``surface plasmons’’ Answer: ``surface plasmons’’  An SP is a natural oscillation of the electron gas An SP is a natural oscillation of the electron gas inside a inside a gold gold nanosphere nanosphere . .  SP frequency depends on the SP frequency depends on the dielectric dielectric function function of the gold, and the of the gold, and the shape shape of the nanoparticle. of the nanoparticle. electron sphere Ionic background Electron cloud oscillates with frequency of SP; ions provide restoring force. (not to scale) Sphere in an applied electric field Sphere in an applied electric field Surface plasmon is excited when a long- Surface plasmon is excited when a long- wavelength electromagnetic wave is incident on a wavelength electromagnetic wave is incident on a metallic sphere. metallic sphere. Metallic sphere EM wave Incident electric field is E_0exp(-i w t) Calculation of SP Frequency Calculation of SP Frequency 0 0 0 2 3 EE in in εε ε + = = 0 E 2 2 1 ω ω ε p in −= 0 0 21 ε ω ω + = applied electric field; = Drude dielectric function Surface plasmon frequency is therefore: = 0 ε host dielectric function (This assumes particle is small compared to wavelength.) Extinction coefficient, dilute suspension of Au Extinction coefficient, dilute suspension of Au particles in acqueous solution particles in acqueous solution Crosses: experiment [Elghanian et al, Science 277, 1078 (1997); Storhoff et al, JACS 120, 1959 (1998). Dashed and full curves: calculated with and without quantum size corrections [Park and Stroud, PRB 68, 224201 (2003)]. Control of Surface Plasmons Using Control of Surface Plasmons Using Nematic Liquid Crystals Nematic Liquid Crystals  A nematic liquid crystal (NLC) is a liquid made up of rod-like A nematic liquid crystal (NLC) is a liquid made up of rod-like molecules, which can be oriented by an applied dc electric field. molecules, which can be oriented by an applied dc electric field.  The axis of the NLC is known as the director. The axis of the NLC is known as the director.  The dielectric tensor of the NLC is anisotropic, with different The dielectric tensor of the NLC is anisotropic, with different components parallel and perpendicular to the director. components parallel and perpendicular to the director. Schematic of experimental configuration Experiment to show electric field control of surface plasmon frequency of gold nanoparticles, using nematic liquid crystals [J. Muller et al, Appl. Phys. Lett. 81, 171 (2002).] [...]... energy flow around corners, etc Nanoparticle chain d a Surface plasmons can propagate along a periodic chain of metallic nanoparticles (above) Photon STM Image of a Chain of Au nanoparticles [from Krenn et al, PRL 82, 2590 (1999)] Individual particles: 100x100x40 nm, separated by 100 nm and deposited on an ITO substrate Sphere at end of waveguide is excited using the tip of near-field scanning optical... comparison of unlinked and aggregated Au nanoparticles Absorptance of unlinked and aggregated Au nanoparticles, as measured by Storhoff et al [J Am Chem Soc 120, 1959 (1998)] Description of Previous Slide    Source: R Jin et al, J Am Chem Soc 125, 1643 (2003) Top two pictures show (a) samples under transmitted light before and after being exposed to the target (b) UV and visible extinction coefficients of. .. detected using fluorescent nanospheres Calculation of SP modes in nanoparticle chain  In the dipole approximation, there are three SP modes on each sphere, two polarized perpendicular to chain, and one polarized parallel The propagating waves are linear combinations of these modes on different spheres  In our calculation, we include all multipoles, not just dipoles Then there are a infinite number of. .. (Experimental splitting at zero applied field closest to “melon” morphology Maximum splitting in expt: 30 meV; in melon config, 22 mev) Propagating Waves of Surface Plasmons in Chains of Nanoparticles     A chain of closely spaced metallic nanoparticles allows WAVES of surface plasmons to propagate down the chain The waves can be either transverse (T) or longitudinal (L) modes, and can have group velocities... volumes, each of which carry dipole moment Dipole moment due to local electric field from all the other dipoles Calculate total cross-section, using multipole-scattering approach Can be used for anisotropic, and absorbing, scatterers Connect polarizability of small volume to dielectric function, using Clausius-Mossotti approximation Calculated surface plasmon frequency as a function of metal particle... 2003a]         Place Au nanoparticles on a simple cubic (SC) lattice Each Au particle has N single DNA strands, of which N/z point towards each of z nearest neighbors (z = 6 for SC) Two-state model for reaction converting two single strands into a double strand: S+S = D Probability of double-strand forming is p(T), determined by chemical equilibrium constant of reaction Probability that no...Measured deviation of surface plasmon resonance energy from mean value, vs angular position of polarization analyzer From Muller et al, Appl Phys Lett 81, 171 (2002) Maximum splitting: 30 mev (expt) Pictures (b) and © from D.R.Nelson, Nano Lett (2002) Plausible configurations of liquid crystal coating: (a) “uniform” (director always in same direction);... dispersion relations s(k) for L and T modes in a chain of nanoparticles, plotted vs k for (a-f) a/d=0.25,0.33,0.4,0.45, 0.49,0.5 (spheres touching) a=sphere radius, d=distance between sphere centers Open symbols: point dipole approx The symbol s = (1 − ε m / ε s ) −1 [Park and Stroud, PRB69, 125418 (2004)] Melting and Optical Properties of Gold/DNA Nanocomposites Linker DNA At high T, single Au particles... dehybridization of DNA duplexes, using T-dependent bond-breaking probability used for percolation model Repeat this aggregation/dehybridization process many times Result is a fractal cluster with a T-dependent fractal dimension Appropriate when aggregation process is non-equilibrium Once aggregation process is complete, calculate optical properties versus T, using DDA Discrete Dipole Approximation Melting of Au/DNA... particles on a cubic lattice (a): all bonds present; (b) 50% of bonds present; (c) 20% of bonds present (d) Low temperature cluster formed by reaction-limited cluster-cluster aggregation (RLCA) Extinction coefficient, dilute suspension Extinction coefficient per unit vol of Au,dilute suspension Crosses: experiment [Elghanian et al, Science (1997); Storhoff et al, JACS (1998) Dashed and full curves: calculated . metallic nanoparticles (above) chain of metallic nanoparticles (above) a d Photon STM Image of a Chain of Photon STM Image of a Chain of Au nanoparticles. detected using fluorescent nanospheres. detected using fluorescent nanospheres. Calculation of SP modes in Calculation of SP modes in nanoparticle chain nanoparticle