[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

The optical properties of metal nanoparticles have long been of interest in physical chemistry, starting with Faraday's investigations of colloidal gold in the middle 1800s. More recently, new lithographic techniques as well as improvements to classical wet chemistry methods have made it possible to synthesize noble metal nanoparticles with a wide range of sizes, shapes, and dielectric environments. In this feature article, we describe recent progress in the theory of nanoparticle optical properties, particularly methods for solving Maxwell's equations for light scattering from particles of arbitrary shape in a complex environment. Included is a description of the qualitative features of dipole and quadrupole plasmon resonances for spherical particles; a discussion of analytical and numerical methods for calculating extinction and scattering cross-sections, local fields, and other optical properties for nonspherical particles; and a survey of applications to problems of recent interest involving triangula...

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The Optical Properties of Metal Nanoparticles: The Influence of Size, Shape, and Dielectric Environment

The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

Monodisperse samples of silver nanocubes were synthesized in large quantities by reducing silver nitrate with ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP). These cubes were single crystals and were characterized by a slightly truncated shape bounded by {100}, {110}, and {111} facets. The presence of PVP and its molar ratio (in terms of repeating unit) relative to silver nitrate both played important roles in determining the geometric shape and size of the product. The silver cubes could serve as sacrificial templates to generate single-crystalline nanoboxes of gold: hollow polyhedra bounded by six {100} and eight {111} facets. Controlling the size, shape, and structure of metal nanoparticles is technologically important because of the strong correlation between these parameters and optical, electrical, and catalytic properties.

http://science.sciencemag.org/content/sci/298/5601/2176.full.pdf

Shape-Controlled Synthesis of Gold and Silver Nanoparticles

We present the design for an absorbing metamaterial (MM) with near unity absorbance A(omega). Our structure consists of two MM resonators that couple separately to electric and magnetic fields so as to absorb all incident radiation within a single unit cell layer. We fabricate, characterize, and analyze a MM absorber with a slightly lower predicted A(omega) of 96%. Unlike conventional absorbers, our MM consists solely of metallic elements. The substrate can therefore be optimized for other parameters of interest. We experimentally demonstrate a peak A(omega) greater than 88% at 11.5 GHz.

Perfect metamaterial absorber.

We present the results of our ultrafast optical experiments on mixed-valence manganites La 0.7 X 0.3 MnO 3 ( X = Ca, Sr ) and the heavy-fermion compounds YbXCu 4 ( X = Ag, In ) . For the manganites, 1.5 eV pump and either optical or terahertz probe reveals a dynamic spectral weight transfer that, as a function of temperature, allows us to determine the spin–lattice relaxation time. For YbXCu4, pump–probe measurements at 1.5 eV are shown to be sensitive to the onset of coherence. These results are discussed in terms of a simple hybridization gap model for the f and s electrons.

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Femtosecond studies of mixed valence state formation in strongly correlated electron materials

This paper reports a real-time tunable metamaterial based on broadside-coupled split ring resonators (BC-SRRs). The device is composed of two layers of SRRs stacked together with an air gap spacer, forming the BC-SRR configuration. One of the layers is fixed, while the other can be driven by an electrostatic comb-drive actuator. The lateral displacement between the two layers of SRRs can be changed by the actuator, resulting in the tuning of the resonance frequencies of the BC-SRRs and the transmission spectrum of the device. The preliminary results show that the resonance frequency can be tuned up to 100GHz corresponding to an 18µm lateral displacement. Our tunable metamaterials have promising applications as THz modulators, filters and sensors.

A real-time tunable terahertz metamaterial based on broadside-coupled split ring resonators

Terahertz metamaterials for active, tunable, and dynamic devices

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Time-resolved quasiparticle dynamics of the itinerant antiferromagnet UPtGa$_{5}$

A method of analyzing physical properties of a sample includes obtaining the sample and obtaining an electromagnetic spectrum of the sample using terahertz spectroscopy. A sample complex permittivity is computed from the electromagnetic spectrum of the sample. The method further includes estimating the constituents and the constituent fractions and computing an estimated effective complex permittivity based upon a model and the constituent fractions. The method further includes comparing the computed sample complex permittivity with the estimated effective complex permittivity in order to determine the physical properties the sample.

Richard D. Averitt

Papers

Femtosecond studies of mixed valence state formation in strongly correlated electron materials

A real-time tunable terahertz metamaterial based on broadside-coupled split ring resonators

Terahertz metamaterials for active, tunable, and dynamic devices

Time-resolved quasiparticle dynamics of the itinerant antiferromagnet UPtGa$_{5}$

System and method of determining rock properties using terahertz-band dielectric measurements