[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 report THz electric and magnetic field-induced nonlinear responses in metamaterial structures. We demonstrate air breakdown in SiNx metamaterials with THz electric fields, and highly nonlinear responses in 3D silicon metamaterials with THz magnetic fields.

Electric and magnetic responses in nonlinear terahertz metamaterials

Transfer printing of negative-index metamaterials with areas of tens of square centimetres onto flexible substrates paves the way for practical, low-cost, large-area exotic optics.

Metamaterials: a stamp of quality.

We use active metamaterials as external modulators for a 2.4 THz quantum cascade laser. We present initial optical modulation results with the goal of designing an electrically-driven modulator.

External modulation of Terahertz quantum cascade lasers using metamaterials.

We present experimental results of metamaterials operating at terahertz and mm-wave frequencies Metamaterials consist of a single layer of 200 nm thick gold on a doped or undoped semiconducting substrate By optical and electronic doping of supporting semiconducting substrates we show external control of planar arrays of metamaterials, characterized with terahertz time domain spectroscopy Both methods yield meta-material / semiconductor devices which can be utilized as switches or modulators, enabling modulation of THz transmission by 50 percent Experiments are supported by simulations and results agree well Because of the universality of metamaterial response over many decades of frequency, these results have implications for other regions of the electromagnetic spectrum and will undoubtedly play a key role in future demonstrations of novel high-performance devices

Metamaterials and their THz applications

Femtosecond time-resolved optical spectroscopy is an excellent experimental alternative to conventional spectroscopic methods that probe the low energy electronic structure in strongly correlated electron systems [1]. In particular, it has been shown that carrier relaxation dynamics are very sensitive to changes in the low energy density of states (e.g. associated with the formation of a low energy gap or pseudogap) providing new insights into the low energy electronic structure in these materials. In this report we present the first studies of carrier relaxation dynamics in heavy fermion (HF) systems by means of femtosecond time-resolved optical spectroscopy. Our results show that the carrier relaxation dynamics, below the Kondo temperature (TK), are extremely sensitive to the low energy density of states (DOS) near the Fermi level to which localized f-moments contribute. Specifically, we have performed measurements of the photoinduced reflectivity ∆R/R dynamics as a function of temperature and excitation intensity on the series of HF compounds YbXCu4 (X=Ag, Cd, In) [2] in comparison to their non-magnetic counterparts LuXCu4.

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Richard D. Averitt

Papers

Electric and magnetic responses in nonlinear terahertz metamaterials

Metamaterials: a stamp of quality.

External modulation of Terahertz quantum cascade lasers using metamaterials.

Metamaterials and their THz applications

Carrier relaxation dynamics in heavy fermion compounds