[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 describe a method for obtaining solvent free high purity C60. Purities of as great as 99.97 % have been obtained. Films grown from this high purity source material have been studied using photoluminescence spectroscopy. In addition, films have been grown with intentional addition of solvent impurities. Spectral broadening due to impurity-induced site disorder is observed in the photoluminescence spectra of these films.

Solvent Free High Purity Solid C60: Optical Properties

In this work, we demonstrate THz metamaterials exhibiting either amplitude control, via carrier injection or depletion in the active semiconductor substrate or frequency control, via photoexcitation of carriers into active semiconducting materials incorporated into the sub-wavelength metamaterial structure.

Active THz metamaterials

Food Sensors: Silk‐Based Conformal, Adhesive, Edible Food Sensors (Adv. Mater. 8/2012)

We use ultrafast terahertz transmission and emission spectroscopy to study ultrafast demagnetization in ferromagnetic iron. We show that demagnetization proceeds with a 1.7 ps/spl plusmn/0.3 ps lifetime in ferromagnetic films at room temperature.

Terahertz spectroscopy of ultrafast demagnetization in ferromagnetic iron

We present frequency tunable metamaterials at terahertz frequencies using broadside-coupled split ring resonators (BC-SRRs). Frequency tuning, arising from changes in near field coupling, is obtained by in-plane displacement between the SRR layers. For electrical excitation, the resonance frequency continuously redshifts as a function of displacement. A maximum frequency shift occurs for displacement of half a unit cell resulting in a shift of 663 GHz (51% of f 0 ). We discuss the difference in the BC-SRR response for electrical excitation in comparison to magnetic excitation in terms of hybridization arising from inductive and capacitive coupling.

Richard D. Averitt

Papers

Solvent Free High Purity Solid C60: Optical Properties

Active THz metamaterials

Food Sensors: Silk‐Based Conformal, Adhesive, Edible Food Sensors (Adv. Mater. 8/2012)

Terahertz spectroscopy of ultrafast demagnetization in ferromagnetic iron

Frequency tunable metamaterial designs using near field coupled SRR structures in the terahertz region