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R. W. Christy

Bio: R. W. Christy is an academic researcher from Dartmouth College. The author has contributed to research in topics: Optical conductivity & Plasmon. The author has an hindex of 5, co-authored 5 publications receiving 17393 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the optical constants for the noble metals (copper, silver, and gold) from reflection and transmission measurements on vacuum-evaporated thin films at room temperature, in the spectral range 0.5-6.5 eV.
Abstract: The optical constants $n$ and $k$ were obtained for the noble metals (copper, silver, and gold) from reflection and transmission measurements on vacuum-evaporated thin films at room temperature, in the spectral range 0.5-6.5 eV. The film-thickness range was 185-500 \AA{}. Three optical measurements were inverted to obtain the film thickness $d$ as well as $n$ and $k$. The estimated error in $d$ was \ifmmode\pm\else\textpm\fi{} 2 \AA{}, and that in $n$, $k$ was less than 0.02 over most of the spectral range. The results in the film-thickness range 250-500 \AA{} were independent of thickness, and were unchanged after vacuum annealing or aging in air. The free-electron optical effective masses and relaxation times derived from the results in the near infrared agree satisfactorily with previous values. The interband contribution to the imaginary part of the dielectric constant was obtained by subtracting the free-electron contribution. Some recent theoretical calculations are compared with the results for copper and gold. In addition, some other recent experiments are critically compared with our results.

17,509 citations

Journal ArticleDOI
TL;DR: In this article, the optical constants of transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, Pd) were determined from reflection and transmission measurements on vacuum-evaporated polycrystalline thin films at room temperature, in the spectral range 0.5-6.5 eV.
Abstract: The optical constants $n$ and $k$ were determined for some transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, Pd) from reflection and transmission measurements on vacuum-evaporated polycrystalline thin films at room temperature, in the spectral range 0.5-6.5 eV. Three optical measurements were inverted to determine the film thickness $d$ as well as $n$ and $k$. The estimated error in $d$ was \ifmmode\pm\else\textpm\fi{}2 \AA{} and that in $n$, $k$ was less than \ifmmode\pm\else\textpm\fi{}2% over most of the spectral range. Transmission measurements were made on films in the thickness range 200-500 \AA{}. Many transition metals oxidize rapidly in the air and so measurements on those samples were performed in a nitrogen atmosphere. A detailed analysis of the effect of oxidation on the measured quantities indicates that it is small. The effects on the optical constants of the film thickness and the evaporation rate are discussed. Some recent theoretical calculations of the interband optical conductivity are compared with the results for V, Cr, and Ni. In addition, some other recent experiments are compared with our results.

1,399 citations

Journal ArticleDOI
TL;DR: In this paper, the optical constants for copper and nickel were determined from reflection and transmission measurements on vacuum-evaporated thin films, in the spectral range 0.5-6.5 eV and at temperatures of 78, 293, and 423 K.
Abstract: The optical constants were determined for copper and nickel from reflection and transmission measurements on vacuum-evaporated thin films, in the spectral range 0.5-6.5 eV and at temperatures of 78, 293, and 423 K. The imaginary part of the dielectric constant was nearly independent of temperature for nickel, but for copper it increased with temperature in the intraband region below 2 eV and decreased above 4 eV in the interband region. Interpretation of the increase below 2 eV according to the Drude free-electron expression suggests a temperature and frequency dependence of the relaxation time, which is not completely explained. The thermal behavior in the interband region can be largely understood, however, if the zero-temperature theory of Williams, Janak, and Moruzzi is modified by including a Debye-Waller factor in transitions between nearly-free-electron-like bands.

112 citations

Journal ArticleDOI
TL;DR: In this article, the frequency and temperature dependence of the intraband optical conductivity of the noble metals Cu, Ag and Au is measured and contributions of electron-electron scattering are assessed.
Abstract: The frequency and temperature dependence of the intraband optical conductivity of the noble metals Cu, Ag and Au is measured and contributions of electron-electron scattering are assessed. Optical measurements were performed at temperatures of 77, 295 and 425 K to obtain values of the Drude electron scattering rate with a linear dependence on temperature which may be attributed to electron-phonon scattering, and a quadratic dependence on photon energy, which is suggestive of electron-electron scattering but is a factor of two to three times greater than would be expected. Comparison of the optical data with dc electrical and thermal resistivity data which also show behavior attributed to electron-electron scattering reveals discrepancies of up to an order of magnitude. Other possible mechanisms for the frequency dependence, including absorptance, electron-surface plasmon interactions, a two-carrier model, and a structure dependence are considered, and it is concluded that the frequency dependence in the Drude scattering rates of the noble metals is not yet quantitatively understood

96 citations

Journal ArticleDOI
TL;DR: The optical constants for the bcc transition metals of the V and Cr groups from reflection and transmission measurements in the spectral range 0.5-6.5 eV were determined in this article.
Abstract: The optical constants $n$ and $k$ were determined for the bcc transition metals of the V and Cr groups from reflection and transmission measurements in the spectral range 0.5-6.5 eV. The optical measurements were made at room temperature on polycrystalline thin films, vacuum evaporated rapidly onto high-temperature (700-1000\ifmmode^\circ\else\textdegree\fi{}C) fused-quartz substrates. The films were found to be well crystallized, and the reflectance of opaque films agreed with previous bulk values. For the thin-film results to be representative of bulk crystals, high substrate temperature was essential for the Cr group, and rapid evaporation rate for the V group. The values for Cr are a significant improvement over earlier results of Johnson and Christy, but those for V are only a slight improvement. Some recent calculations of the interband optical-conductivity agree reasonably well with our results for V, Cr, Nb, and Mo. Direct transitions between $d$ bands seem to account for the optical structure.

53 citations


Cited by
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Book
15 May 2007
TL;DR: In this paper, the authors discuss the role of surface plasmon polaritons at metal/insulator interfaces and their application in the propagation of surfaceplasmon waveguides.
Abstract: Fundamentals of Plasmonics.- Electromagnetics of Metals.- Surface Plasmon Polaritons at Metal / Insulator Interfaces.- Excitation of Surface Plasmon Polaritons at Planar Interfaces.- Imaging Surface Plasmon Polariton Propagation.- Localized Surface Plasmons.- Electromagnetic Surface Modes at Low Frequencies.- Applications.- Plasmon Waveguides.- Transmission of Radiation Through Apertures and Films.- Enhancement of Emissive Processes and Nonlinearities.- Spectroscopy and Sensing.- Metamaterials and Imaging with Surface Plasmon Polaritons.- Concluding Remarks.

7,238 citations

Journal ArticleDOI
TL;DR: The surface-enhanced Raman scattering (SERS) effect was first discovered by Fleischmann, Van Duyne, Creighton, and Creighton as discussed by the authors, who showed that molecules adsorbed on specially prepared silver surfaces produce a Raman spectrum that is at times a millionfold more intense than expected.
Abstract: In 1978 it was discovered, largely through the work of Fleischmann, Van Duyne, Creighton, and their coworkers that molecules adsorbed on specially prepared silver surfaces produce a Raman spectrum that is at times a millionfold more intense than expected. This effect was dubbed surface-enhanced Raman scattering (SERS). Since then the effect has been demonstrated with many molecules and with a number of metals, including Cu, Ag, Au, Li, Na, K, In, Pt, and Rh. In addition, related phenomena such as surface-enhanced second-harmonic generation, four-wave mixing, absorption, and fluorescence have been observed. Although not all fine points of the enhancement mechanism have been clarified, the majority view is that the largest contributor to the intensity amplification results from the electric field enhancement that occurs in the vicinity of small, interacting metal particles that are illuminated with light resonant or near resonant with the localized surface-plasmon frequency of the metal structure. Small in this context is gauged in relation to the wavelength of light. The special preparations required to produce the effect, which include among other techniques electrochemical oxidation-reduction cycling, deposition of metal on very cold substrates, and the generation of metal-island films and colloids, is now understood to be necessary as a means of producing surfaces with appropriate electromagnetic resonances that may couple to electromagnetic fields either by generating rough films (as in the case of the former two examples) or by placing small metal particles in close proximity to one another (as in the case of the latter two). For molecules chemisorbed on SERS-active surface there exists a "chemical enhancement" in addition to the electromagnetic effect. Although difficult to measure accurately, the magnitude of this effect rarely exceeds a factor of 10 and is best thought to arise from the modification of the Raman polarizability tensor of the adsorbate resulting from the formation of a complex between the adsorbate and the metal. Rather than an enhancement mechanism, the chemical effect is more logically to be regarded as a change in the nature and identity of the adsorbate.

5,005 citations

Journal ArticleDOI
TL;DR: While nanorods with a higher aspect ratio along with a smaller effective radius are the best photoabsorbing nanoparticles, the highest scattering contrast for imaging applications is obtained from nanorod of high aspect ratio with a larger effective radius.
Abstract: The selection of nanoparticles for achieving efficient contrast for biological and cell imaging applications, as well as for photothermal therapeutic applications, is based on the optical properties of the nanoparticles. We use Mie theory and discrete dipole approximation method to calculate absorption and scattering efficiencies and optical resonance wavelengths for three commonly used classes of nanoparticles: gold nanospheres, silica−gold nanoshells, and gold nanorods. The calculated spectra clearly reflect the well-known dependence of nanoparticle optical properties viz. the resonance wavelength, the extinction cross-section, and the ratio of scattering to absorption, on the nanoparticle dimensions. A systematic quantitative study of the various trends is presented. By increasing the size of gold nanospheres from 20 to 80 nm, the magnitude of extinction as well as the relative contribution of scattering to the extinction rapidly increases. Gold nanospheres in the size range commonly employed (∼40 nm)...

4,065 citations

Book
01 Jan 2006
TL;DR: In this paper, the authors proposed a method for propagating and focusing of optical fields in a nano-optics environment using near-field optical probes and probe-sample distance control.
Abstract: 1. Introduction 2. Theoretical foundations 3. Propagation and focusing of optical fields 4. Spatial resolution and position accuracy 5. Nanoscale optical microscopy 6. Near-field optical probes 7. Probe-sample distance control 8. Light emission and optical interaction in nanoscale environments 9. Quantum emitters 10. Dipole emission near planar interfaces 11. Photonic crystals and resonators 12. Surface plasmons 13. Forces in confined fields 14. Fluctuation-induced phenomena 15. Theoretical methods in nano-optics Appendices Index.

3,772 citations

Journal ArticleDOI
22 Apr 2005-Science
TL;DR: This work demonstrated sub–diffraction-limited imaging with 60-nanometer half-pitch resolution, or one-sixth of the illumination wavelength, using silver as a natural optical superlens and showed that arbitrary nanostructures can be imaged with good fidelity.
Abstract: Recent theory has predicted a superlens that is capable of producing sub–diffraction-limited images. This superlens would allow the recovery of evanescent waves in an image via the excitation of surface plasmons. Using silver as a natural optical superlens, we demonstrated sub–diffraction-limited imaging with 60-nanometer half-pitch resolution, or one-sixth of the illumination wavelength. By proper design of the working wavelength and the thickness of silver that allows access to a broad spectrum of subwavelength features, we also showed that arbitrary nanostructures can be imaged with good fidelity. The optical superlens promises exciting avenues to nanoscale optical imaging and ultrasmall optoelectronic devices.

3,753 citations