[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.

Higher Order Plasmon Resonances of Gold Nanoshells

The relationship between structure and mechanical properties of sputter-deposited boron carbide films was investigated. Changes in the structure induced by annealing were characterized in terms of chemical composition, chemical bonding and concentrations of defects and of trapped impurities. The creation of new intericosahedral chains for higher annealing temperatures was revealed by infrared and Raman measurements, and the intensity of the infrared band at 1500 cm{sup -1} was found to be related with the hardness. The content of trapped Ar atoms and of open-volume defects are insensitive to relatively high annealing temperatures and do not influence the recovery of the hardness. Our results suggest annealing as a pathway to enhance the mechanical properties of boron carbide films.

Experimental Evidence of the Role of Intericosahedral Chains in the Hardness of Boron Carbide Films Deposited by Sputtering

We experimentally study the excitonic Fano resonance in $\text{GaAs}/{\text{Al}}_{0.3}{\text{Ga}}_{0.7}\text{As}$ multiple quantum wells under an external electric field. The resonance results from exciton transitions via localized states and continuum minibands of Wannier-Stark states. In photoreflectance spectra the line shape displays anomalous behavior as a function of increasing field. Our theoretical analysis reveals that this effect, which is absent for the conventional Fano resonance, arises from the field dependence of the nonuniform density of continuum states.

Effect of nonuniform continuum density of states on a Fano resonance in semiconductor quantum wells

The lattice damage and the chemical bonding in H implanted Si substrates with different doping levels were analyzed with Rutherford backscattering spectroscopy (RBS) in channeling mode and Infrared Spectroscopy (IR), respectively. We observed that the damage of room temperature implanted Si consisted of Si–H complexes and irradiation induced interstitial/vacancy pairs, and that the lattice damage decreased in the presence of pre-implanted boron. This reduction in lattice damage was most pronounced when B was not activated, regardless of Si substrate type.

Relationship between damage evolution and Si–H complexes formation in hydrogen implanted Si

We present recent work utilizing terahertz field enhancement in metamaterial structures to drive carrier generation in semiconductors. We implement this as a novel platform to detect terahertz radiation.

Richard D. Averitt

Papers

Higher Order Plasmon Resonances of Gold Nanoshells

Experimental Evidence of the Role of Intericosahedral Chains in the Hardness of Boron Carbide Films Deposited by Sputtering

Effect of nonuniform continuum density of states on a Fano resonance in semiconductor quantum wells

Relationship between damage evolution and Si–H complexes formation in hydrogen implanted Si

Metamaterial-enhanced nonlinear responses in semiconductors as a THz detection platform