We have determined the optical constants in the energy range 0.1-6 eV for bulk Cu, Ag, and Au using Kramers-Kronig analysis of previously unpublished reflectance data. The results are compared to those commonly used from the literature. 2 Studies of the optical properties of the transition metals culminated in 1981 in a two volume set of figures and tables [1, 2]. These volumes have gone out of print but the data were abridged and published in the Handbook of Chemistry and Physics [3]. The originals have also been scanned and are available on one of the authors' websites [4]. Other authors also compiled data sets, including the well known volumes by Palik [5] which included the transition metal data. To our knowledge, there have been no more recent experimental studies, such work having gone out of vogue as investigations of the band structure through photon spectroscopies have yielded to photoemission and related spectroscopies that probe E(k) with exquisite precision. The optical constants of the noble metals Cu, Ag, and Au are important to those who use the data for such studies as photonics, plasmonics and nanoparticle arrays [6]. While the optical constants in Ref. 2 have stood the tests of time for Au, those for Cu and Ag were taken from tabulations by Hagemann, Gudat, and Kunz (HGK) [7, 8] who in turn relied on the results by Johnson and Christy (JC) [9]. To provide a critical reassessment of the optical properties of Cu and Ag, we returned to some largely unpublished absorptivity measurements by Weaver et al. While the reflectance results were shown in Ref. 2, the authors were interested at that time in structure in the dielectric constants and those structures were well described by JC [9] (see the comparison figures in Ref. 2). Here, we are interested in the magnitudes of  and N, the complex dielectric constant and complex index of refraction, and we performed Kramers-Kronig analyses to compare with prior results in the 0.1-6 eV range. Extensive comparisons that extend to 30 eV are available from the Weaver website [4]. The samples were mechanically polished single crystals that were chemically cleaned to remove work damage, as described previously [1, 2]. The measured quantity was the absorptivity, A = 1-R where R is the reflectivity. In the infrared, R is nearly 100%, and a measurement of A rather than R provides inherently greater accuracy. For Ag, to extend the spectral range for the KK analyses, we used the results from Leveque, Olson, and Lynch to 30 eV [10] For Cu, we tied our results to those of JC [9] and then HGK to 30 eV. Standard power law extrapolations of the form R = RoE-3.5 were used to 1000 eV.

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Silver nanocrystals have been grown on Xe buffer layers at 50 K. These 3D nanocrystals are delivered to Si(111)-͑7 3 7͒ surfaces when the Xe layer is desorbed, but the density observed on the surface depends strongly on the buffer layer thickness. This dependence reflects an unusual desorption-assisted coalescence process. The results suggest that buffer-layer-assisted growth can be used to prepare nanocrystals of different sizes for a wide variety of materials and substrates. [S0031-9007(98)05945-6]

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The absorptivity or reflectivity of polycrystalline samples of Ti, Zr, and Hf was measured from 0.15 to ∼30 eV. The data were Kramers-Kronig analyzed to determine the dielectric functions. Between ∼0.2 and ∼7 eV, each metal showed five structures in the absorptivity and ε2. These were interpreted as interband transitions within the d bands. The ε2 spectra had minima near 7 eV similar to that observed in the bcc transition metals. Additional structures at higher energy could be related to transitions involving highlying bands and the core levels. The electron-energy-loss functions were calculated and discussed in terms of volume and surface plasmons. These metals, like the other transition metals studied, exhibited two volume and two surface plasmons. The absorptivity or reflectivity of polycrystalline samples of Ti, Zr, and Hf was measured from 0.15 to -30 eV. The data were Kramers-Kronig analyzed to determine the dielectric functions. Between -0.2 and -7 eV, each metal showed five structures in the absorptivity and c,. These were interpreted as interband transitions within the d bands. The e2 spectra had minima near 7 eV similar to that observed in the bcc transition metals. Additional structures at higher energy could be related to transitions involving highlying bands and the core levels. The electron-energy-loss functions were calculated and discussed in terms of volume and surface plasmons. These metals, like the other transition metals studied, exhibited two volume and two surface plasmons. Keywords

Physical vapor deposition of Au onto Xe multilayers on amorphous carbon at 20 K produces three-dimensional nanoclusters. Warming to room temperature desorbs the Xe and imparts limited mobility to the clusters. Coalescence occurs when two clusters come in contact, and the extent of coalescence depends on the buffer layer thickness. Using transmission electron microscopy images, we determined the spatial distribution of clusters as a function of Xe thickness and applied the scaling concepts of cluster-cluster aggregation to better understand processes associated with growth. Analysis shows a coverage dependent fractal dimension that extends from D $ 1:42 to 1.72 for initial fractional surface coverages of q 0 $ 0:04-0.21, consistent with Monte Carlo simulations of two-dimensional diffusion-limited cluster aggregation (DLCA). Both the total number of clusters per unit area and the weighted average cluster size show a power law dependence on the Xe layer thickness, where the buffer layer thickness plays the role of time in DLCA modeling. These relationships will facilitate the design of nanostructure arrays generated by desorption-assisted coalescence.