# Investigation of the optical properties of Ag by means of thin semi-transparent films

TL;DR: In this paper, the optical constants of thin Ag films are determined from measurements of both their transmittance and reflectance, in terms of intra and interband transitions, in relation with the film crystallographic structure.

Abstract: The optical constants of thin Ag films are determined from measurements of both their transmittance and reflectance. The complex dielectric constant is discussed in terms of intra and interband transitions, in relation with the film crystallographic structure. The optical mass of the conduction electrons is found to be very low, 0·87; their optical relaxation time to depend strongly on the film structure and to be smaller than their electrical relaxation time. The absorption due to interband transitions is considered. A supplementary absorption band related to film imperfections is observed in some cases. Plasma oscillations are also studied in relation with the film quality.

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TL;DR: In this article, the pump-probe signals near the plasmon resonance of the nanoparticles reveal the importance of electron-electron scattering during several hundreds of femtoseconds.

Abstract: We studied the dynamics of electrons in copper and silver nanoparticles embedded in a transparent matrix, using the technique of pump–probe femtosecond spectroscopy. Comparative measurements are made in thin films of the same metals. In the case of the nanoparticles, the electron dynamics is strongly influenced by the surface at the boundary of the metal and the surrounding dielectric matrix. A detailed study of the pump–probe signals near the plasmon resonance of the nanoparticles reveals the importance of electron–electron scattering during several hundreds of femtoseconds. The influence of these scattering processes on the real and imaginary parts of the metal dielectric function is compared in the nanoparticles and thin films. In addition, the non-thermal component of the electrons and the heat transfer to the surrounding dielectric are measured. The results are analyzed with a model of effective medium, where the metal dielectric function is described in the random phase approximation, including the surface effects in a phenomenological way.

310 citations

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TL;DR: The ideal spectral properties are treated, an illustrative experimental example of how well this goal can be realized is given, and a corresponding theoretical curve is shown indicating to what extent the measured results can be theoretically understood.

Abstract: Matter continuously exchanges energy with its surroundings. This exchange can be dominated by radiation, conduction, or convection. In this brief review we discuss how proper design of radiative surface properties can be used for heating and cooling purposes. The desired properties can be understood once it is realized that solar and terrestrial radiation take place in different wavelength ranges and that only part of the solar spectrum is useful for vision and for photosynthesis in plants. These facts allow the possibility of tailoring the spectral absorptance, emittance, reflectance, and transmittance of a surface to meet different demands in different wavelength intervals, i.e., to take advantage of spectral selectivity. One example is the selective surface for efficient photothermal conversion of solar energy, which has high absorptance over the solar spectrum but low emittance for the longer wavelengths relevant to thermal reradiation. Below we discuss the pertinent spectral radiative properties of our ambience. These data are then used as background to the subsequent sections treating four examples of spectrally selective surfaces. The first example is the previously mentioned selective surface for converting solar radiation to useful heat. The second example considers surfaces capable of reaching low temperatures by benefiting from the spectral emittance of the clear night sky. The third example concerns two related types of transparent heat mirror. The fourth example, finally, treats radiative cooling of green leaves; this part is included since it gives a nice example of how nature solves a difficult problem in an elegant and efficient way. This example hence provides an interesting background to the other cruder types of artificial selective surfaces. Throughout our discussion we treat the ideal spectral properties, give an illustrative experimental example of how well this goal can be realized, and—where this is possible—show a corresponding theoretical curve indicating to what extent the measured results can be theoretically understood.

264 citations

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TL;DR: In this article, the surface plasmons in silver films with narrow straight grooves were visualized in unprecedented detail by means of near-field optical techniques, and their values were determined semiquantitatively.

Abstract: Excitation and propagation of surface plasmons in silver films structured with narrow straight grooves were visualized in unprecedented detail by means of near-field optical techniques. Reflectivity, transmissivity, and scattering loss of the grooves are demonstrated. Their values are determined semiquantitatively. The surface plasmon attenuation are found to be dominated by material and surface/interface imperfections.

148 citations

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TL;DR: In this paper, the dispersion of surface plasmons at an air-metal interface has been studied experimentally using the method of attenuated total reflection, and it was shown that surface plasmon interactions must be characterized by a complete response-function surface rather than by a single dispersion curve.

Abstract: The dispersion of surface plasmons at an air-metal interface has been studied experimentally using the method of attenuated total reflection. In the vicinity of the surface plasmon energy the dispersion curve was found to bend back toward the light line instead of increasing asymptotically to the surface plasmon energy at infinite momentum. We conclude that surface plasmon interactions must be characterized by a complete response-function surface rather than by a single dispersion curve.

125 citations

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TL;DR: In this paper, the authors demonstrate how to obtain the ultimate lateral resolution in surface plasmon microscopy (SPM) (diffraction limited by the objective) by determining the optimal depth values for wavelengths ranging from 531 to 676 nm.

Abstract: In this article we demonstrate how to obtain the ultimate lateral resolution in surface plasmon microscopy (SPM) (diffraction limited by the objective). Surface plasmon decay lengths are determined theoretically and experimentally, for wavelengths ranging from 531 to 676 nm, and are in good agreement. Using these values we can determine for each particular situation which wavelength should be used to obtain an optimal lateral resolution, i.e., where the plasmon decay length does not limit the resolution anymore. However, there is a trade‐off between thickness resolution and lateral resolution in SPM. Because of the non‐optimal thickness resolution, we use several techniques to enhance the image acquisition and processing. Without these techniques the use of short wavelengths results in images where the contrast has vanished almost completely. In an example given, a 2.5 nm SiO2 layer on a gold layer is imaged with a lateral resolution of 2 μm, and local reflectance curves are measured to determine the laye...

124 citations

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General Electric

^{1}TL;DR: In this paper, experimental data for the optical constants of Ag and Cu extending to 25 eV are discussed in terms of three fundamental physical processes: (1) free-electron effects, (2) interband transitions, and (3) collective oscillations.

Abstract: Experimental data for the optical constants of Ag and Cu extending to 25 eV are discussed in terms of three fundamental physical processes: (1) free-electron effects, (2) interband transitions, and (3) collective oscillations. Dispersion theory is used to obtain an accurate estimate of the average optical mass characterizing the free-electron behavior over the entire energy range below the onset of interband transitions. The values are ${m}_{a}=1.03\ifmmode\pm\else\textpm\fi{}0.06$ for Ag and 1.42\ifmmode\pm\else\textpm\fi{}0.05 for Cu. The interband transitions to 11 eV are identified tentatively using Segall's band calculations. Plasma resonances involving both the conduction band and $d$ electrons are identified and described physically.

931 citations

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403 citations

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TL;DR: In this paper, the real and imaginary parts of the dielectric constant of Au were accurately determined in the 0.5-6-eV range from measurements of the reflectance and transmittance of thin semitransparent films.

Abstract: Both the real and imaginary parts of the dielectric constant of Au were accurately determined in the 0.5-6-eV range from measurements of the reflectance and transmittance of thin semitransparent films. The results obtained on well-crystallized films were in general agreement with previous data on bulk samples. They allowed a thorough analysis of the absorption spectrum of Au in terms of intra- and interband transitions. Deviations from the Drude theory were observed, and the values of the optical mass and relaxation time of the conduction electrons are discussed. The absorption edge was investigated very accurately. Further information on the absorption processes was also obtained by studying films with different crystallographic structures. In particular, the supplementary absorption often observed in Au below the absorption edge was shown to be due to impurities.

321 citations

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TL;DR: The reflection-transmission method for determining the optical constants of a film on a substrate has been examined and a computer program for the solution of the equation system has been written.

Abstract: The reflection–transmission method for determining the optical constants of a film on a substrate has been examined and a computer program for the solution of the equation system has been written. A new method involving only transmittance data in a limited wavelength region has been worked out and has been found to give accurate results. The computer program for this method gives directly n and k curves from the transmission curve.

192 citations

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TL;DR: In this article, a mathematical method of determining the complex index n − ik of an absorbing thin film of known thickness from measured values of the normal incidence reflectance Rex and transmittance Tex is described.

Abstract: We describe a mathematical method of determining the complex index n — ik of an absorbing thin film of known thickness from measured values of the normal incidence reflectance Rex. and transmittance Tex. Special attention is paid to the following points; a) In general, we find several values of n — ik corresponding to the measured .Rex and Tex; b) As this method consists in successive approximations, the obtained solution depends on the choice of the starting values of n — ik. Some numerical examples are given in order to illustrate the characteristics of the method.

132 citations