Growth of silver on MgO(001) and infrared optical properties

Abstract

Silver-film growth on MgO(001) was systematically studied with infrared spectroscopy in ultra-high vacuum for different substrate temperatures from 60 K to 500 K at a similar deposition rate. In all cases the spectral development clearly indicated the formation of islands. For 300 K the coalesced islands further developed to a film that reached bulk conductivity already at about 9 nm. The conductivity of the films beyond percolation was obtained from spectral fits to the Drude model of the dielectric function. Additionally to transmittance studies, infrared reflection spectra at oblique incidence of p-polarized light were measured during Ag film growth on MgO(001) at 300 K. Interestingly, a minimum reflectance (relative to the substrate reflectance) was observed at a thickness corresponding to the percolation threshold, which is a new experimental result. The island-like film morphology was directly proved with atomic force microscopy. Pictures taken immediately after film growth proved that particle size and coalescence strongly depend not only on average film thickness but also on the substrate temperature during deposition, which is related to temperature dependent diffusion.

Infrared optical properties of chromium nanoscale films with a phase transition

“…In metalisland films before percolation, the formation of separated metal islands usually is indicated by a transmittance with negative slope vs frequency, which is explained as the red tail of particle plasmon resonances. 7,32 The interaction between particles produces a red shift of the low-frequency tail of the optical absorption. 33 For film growth via metal-island formation, percolation occurs at a certain average thickness and is not extended to a thickness range of several monolayers.…”

“…37 Measurements at various different substrate temperatures 36 gave the surprising result that the IR spectra below d crit and d crit itself only negligibly depend on temperature, clearly different to the case of islandlike growth where the critical thickness for the transition to a conducting layer is observed to decrease with decreasing temperature and strong spectral changes are observed. 7 The nearly temperature independent d crit also contradicts amorphous growth effects due to hampered diffusion at low temperatures. 38 Accordingly, another reason that is not related to diffusion properties, should exist for the transition from the discontinuous phase to the bcc polycrystalline one.…”

“…On the other hand, for metal-island films, the typical IR tail of the surface plasmon polariton excitation is observed. 7 During further metal deposition, with increasing lateral island size and decreasing island distances, this excitation shifts to lower frequencies until the percolation threshold is reached where a nearly frequency independent IR transmittance appears. 13 Concerning the IR spectral development, the growth of Cr on C͑100͒ qualitatively resembles to the system Pb on Si͑111͒7 ϫ 7, where a discontinuous phase is formed in the beginning and a transition to the ordered crystalline phase takes place at a certain thickness.…”

Surface plasmonic contribution to SEIRA and asymmetrical band

“…Simultaneously with the sign switching, the crossover of inclination of both the real part and imaginary part of a complex dielectric constants has occurred. This crossover has proved that the dielectric function of the silver thin film changed from insulator-like to metal-like with the sign switching of the real part of complex dielectric constants [37,38,39]. However, although the silver thin film is changing from an insulator-like state (positive) to a metal-like state (negative), the asymmetrical band is kept.…”

Properties of Gold Nanoantennas in the Infrared

“…[1][2][3][4][5] Effects from interband transitions on the background polarizability are included in ε the dispersion of surface plasmon polaritons. 7 This resonance corresponds to collective charge carrier oscillations (plasmons) in perpendicular direction for which the film boundaries are effective.…”