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Electron dynamics in gold and gold–silver alloy nanoparticles: The influence of a nonequilibrium electron distribution and the size dependence of the electron–phonon relaxation (1999)

Link, S. ; Burda, C.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 111 (1999), S. 1255-1264

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: Electron dynamics in gold nanoparticles with an average diameter between 9 and 48 nm have been studied by femtosecond transient absorption spectroscopy. Following the plasmon bleach recovery after low power excitation indicates that a non-Fermi electron distribution thermalizes by electron–electron relaxation on a time scale of 500 fs to a Fermi distribution. This effect is only observed at low excitation power and when the electron distribution is perturbed by mixing with the intraband transitions within the conduction band (i.e., when the excitation wavelength is 630 or 800 nm). However, exciting the interband transitions at 400 nm does not allow following the early electron thermalization process. Electron thermalization with the lattice of the nanoparticle by electron–phonon interactions occurs within 1.7 ps under these conditions, independent of the excitation wavelength. In agreement with the experiments, simulations of the optical response arising from thermalized and nonthermalized electron distributions show that a non-Fermi electron distribution leads to a less intense bleach of the plasmon absorption. Furthermore, the difference between the response from the two electron distributions is greater for small temperature changes of the electron gas (low excitation powers). No size dependence of the electron thermalization dynamics is observed for gold nanoparticles with diameters between 9 and 48 nm. High-resolution transmission electron microscopy (HRTEM) reveals that these gold nanoparticles possess defect structures. The effect of this on the electron–phonon relaxation processes is discussed. 18 nm gold–silver alloy nanoparticles with a gold mole fraction of 0.8 are compared to 15 nm gold nanoparticles. While mixing silver leads to a blue-shift of the plasmon absorption in the ground-state absorption spectrum, no difference is observed in the femtosecond dynamics of the system. © 1999 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.479310

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Absence of Dislocation Motion in 3C-SiC pn Diodes under Forward Bias (2007)

Speer, Kevin M. ; Spry, David J. ; Trunek, Andrew J. ; [et al.]

s.l. ; Stafa-Zurich, Switzerland

Materials science forum Vol. 556-557 (Sept. 2007), p. 223-226

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ISSN: 1662-9752

Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: pn diodes have recently been fabricated from 3C-SiC material heteroepitaxially grownatop on-axis 4H-SiC mesa substrate arrays [1,2]. Using an optical emission microscope (OEM), wehave investigated these diodes under forward bias, particularly including defective 3C-SiC filmswith in-grown stacking faults (SFs) nucleated on 4H-SiC mesas with steps from screw dislocations.Bright linear features are observed along 〈110〉 directions in electroluminescence (EL) images.These features have been further investigated using electron channeling contrast imaging (ECCI)[3]. The general characteristics of the ECCI images—together with the bright to dark contrastreversal with variations of the excitation error—strongly suggest that the bright linear features arepartial dislocations bounding triangular SFs in the 3C-SiC films. However, unlike partialdislocations in 4H-SiC diodes whose recombination-enhanced dislocation motion serves to expandSF regions, all the partial dislocations we observed during the electrical stressing were immobileacross a wide range of current injection levels (1 to 1000 A/cm2)