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The effective heat of formation (pH') concept allows heats of formation to be calculated as a function of concentration. In this work the effective heat of formation rule is used to predict first phase formation in metal-aluminum thin-film systems and to predict subsequent phase sequence for thin metal films on thick aluminum or thin aluminum on thick metal substrates. The effective concentration at the growth interface is taken to be that of the lowest temperature eutectic (liquidus) for the binary system. Although the effective heat of formation rule may predict that formation of a certain phase would lead to the largest free energy change, this phase does not necessarily form at the moving reaction interface if it has difficulty to nucleate. By excluding phases with a large number of atoms per unit cell and which thus have difficulty to nucleate, the effective heat of formation rule successfully predicts first phase aluminide formation for all 15 metal-aluminum binary systems for which experimental data could be found. It is also shown how the effective heat of formation rule can be used to predict formation and decomposition of aluminide phases in contact with each other or in contact with their component metals.

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Mega-electron-volt ion beam induced anisotropic plasmon resonance of silver nanocrystals in glass Penninkhof, J. J.; Polman, A.; Sweatlock, L. A.; Maier, S. A.; Atwater, H. A.; Vredenberg, A. M.; Kooi, B. J. 30 MeV Si ion beam irradiation of silica glass containing Ag nanocrystals causes alignment of Ag nanocrystals in arrays along the ion tracks. Optical transmission measurements show a large splitting of the surface plasmon resonance bands for polarizations longitudinal and transversal to the arrays. The splitting is in qualitative agreement with a model for near-field electromagnetic plasmon coupling within the arrays. Resonance shifts as large as 1.5 eV are observed, well into the near-infrared.

The spontaneous emission lifetime and intensity of Er implanted into SiC>2 is modified by a Si/SiC>2 planar microcavity. The cavity strongly affects the coupling of the optically excited Er 3+ to the radiative and waveguiding modes of the system, resulting in a spontaneous lifetime of 14.8 ms for a cavity offresonance with the Er 3+ versus a lifetime of 9.1 ms for an on-resonance cavity. The observed spontaneous emission lifetime changes agree well with calculated values based on a computation method which is also presented. 32.70.Fw, 32.70.Jz, 78.66.Jg There has been much recent attention regarding the use of planar microcavities to demonstrate fundamental changes in the spontaneous emission rates and spectra of emitting media. After cavity effects at radio frequencies were first proposed by Purcell [1] in 1946, other authors [2] have demonstrated that confocal resonators indeed can drastically modify the spontaneous emission lifetime of an atom within a resonator of millimeter wavelengths. This concept has been extended to short planar cavities at optical wavelengths, where experiments using flowing dye [3], dye-containing films [4], and semiconductors [5] as the active media have demonstrated significant lifetime changes. None of these experimental results in planar cavities, however, was quantitatively compared to theoretical models. Nonradiative energy loss processes, pump-dependent spectra, and the effects of selfabsorption of emitted light by the active media [6] can affect the measured lifetimes. In our experiment, we measure the spontaneous lifetime changes of the A J\V2~^ 4^1 5/2 transition of Er 3+ ions (emission wavelength -1535 nm) implanted at low concentration into a thin (half-wavelength) SiC>2 film, surrounded by highreflectivity Si/SiC>2 planar distributed Bragg reflectors. The Er 3+ ions exhibit atomic, intra-4/, electronic transitions which are effectively shielded by the outlying 5s 2 and 5/7 6 electrons, and the probed 4 713/2 -*^ 4^ 15/2 transition has a nearly 100% quantum efficiency [7]. This system is thus ideal for measuring cavity-induced lifetime changes because of the small self-absorption of the Er 3+ ions, and the narrow atomic emission spectrum. This enables us to compare, for the first time, active-media lifetimes for various thickness planar resonators with calculated values. These result from a general computation method which is also presented.The Er-doped SiC>2 active region (X/2) is -540 nm thick and is surrounded by distributed Bragg reflectors (DBRs), which are composed [8] of 4 (bottom) and 2 j pairs (top) of Si (115 nm) and SiC>2 (270 nm) quarterwave layers, e-beam deposited on a Si substrate. The calculated bottom and top mirror reflectivities (Rbot and /?top) are 99.8% and 98.5%, respectively. Implantation of 800 keV, 1 x 10 15 Er + /cm 2 into the active region was performed prior to deposition of the top DBR, in order to yield a sharp concentration profile (full width at half maximum -260 nm) just below the center plane of the active region. The Er concentration...

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Irradiation with swift heavy ions of spherical Au nanoparticles confined within a silica matrix shapes them into prolate nanorods and nanowires whose principal axes are aligned along the beam direction. In the present paper, we investigate the role that is played by the initial nanoparticle size and concentration in this so-called ion-shaping mechanism. We have produced silica films wherein Au nanoparticles with average diameters of 15, 30, and 45 nm were embedded within a single plane and have irradiated these films at 300 K at normal incidence with 18, 25, and 54 MeV Ag ions. We demonstrate the existence of both threshold and saturation fluences for the elongation effects mentioned. The values of these critical fluences depend both on the ion energy and the initial nanoparticle size. Moreover, we show that 45 nm Au particles are not deformed when irradiated with 18 MeV Ag ions, such that this value corresponds to an energy threshold for the deformation process. As far as the influence of the nanoparticle concentration on the shaping characteristics is concerned, we have found that above the critical irradiation fluence, the deformation effect becomes very sensitive to the initial concentration of the nanoparticles.

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