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Fredholm integral equations of the second kind are formulated to describe the anomalous skin effect in metal films on dielectric substrates. An algorithm is developed for numerical solution of the equations based on the quadrature method. As a result of its use for processing published experimental data on the spectral ellipsometry of gold films of different thicknesses on a silicon substrate, the density, relaxation time of the conduction electrons, and dielectric constant of gold are uniquely determined. The dependence of the dielectric constant of gold films on their thickness noted in a number of experimental studies is explained by using a model of the normal Drude skin effect that does not take the excitation of space charge in the film into account when solving the inverse optical problems. The optical fields in gold films are studied for different probabilities of mirror reflection of electrons from the boundary of the films It is found that in sensors for biological solutions with a Kretschmann configuration, structures in which the probability of mirror reflection of electrons from the metallic film–liquid interface approaches unity are to be preferred. [ABSTRACT FROM AUTHOR]

Fredholm integral equations of the second kind, which describe the fields of TE and TM polarized waves in metal films with allowance for the anomalous skin effect, are formulated. The equations can be solved numerically by the quadrature method. The electric fields in gold and aluminum films deposited on a silicon substrate and the angular dependences of the polarization angles of light reflected from these films are investigated. It is found that the solution of the inverse problem of multiangle ellipsometry of metal films within the approximation of the normal skin effect is characterized by the instability of the reconstructed complex refractive index of the metal with a change in the thickness of the metal film. [ABSTRACT FROM AUTHOR]

The process of ultra-thin single crystal gold film irradiated by femtosecond laser is simulated by the combination of improved two-temperature model (TTM) and molecular dynamics (MD). The results indicate that under the non-Fourier effect, the gold film shows special melting characteristics and spalling mechanism. The phenomena of homogeneous melting and pore spalling of gold film are successfully distinguished by curing rate method and atomic density method respectively. Due to the tiny thickness of the gold film studied, the damage mechanism of the gold film irradiated by laser has also changed. [ABSTRACT FROM AUTHOR]

The effect of low-intensity near ultraviolet irradiation and subsequent thermal annealing on the surface morphology of gold and silver granular films was investigated. It was found that exposure to light does not lead to immediate changes in the extinction spectra and the microstructure of the films. However, after annealing at a temperature of about 200°C, the difference between irradiated and non-irradiated areas becomes clearly visible both visually and in the extinction spectra of the island films. For the irradiated gold film, changes in the annealing process occur much more slowly than for the non-irradiated one. For silver films, the changes after annealing vary significantly depending on whether the film is irradiated in a vacuum or in air. From the optical extinction spectra and SEM images, it can be concluded that the conditions for the annealing-induced surface diffusion of metal atoms in the irradiated area change significantly, and these changes depend on the irradiation conditions. [ABSTRACT FROM AUTHOR]

Featured Application: Possible ultra sensitive and effective solution in the fields of analytical chemistry and biosensorics. Surface-enhanced Raman spectroscopy (SERS) has been intensely studied as a possible solution in the fields of analytical chemistry and biosensorics for decades. Substantial research has been devoted to engineering signal enhanced SERS-active substrates based on semi-continuous nanostructured silver and gold films, or agglomerates of micro- and nanoparticles in solution. Herein, we demonstrate the high-amplitude spectra of myoglobin precipitated out of ultra-low concentration solutions (below 10 μg/mL) using e-beam evaporated continuous self-assembled silver films. We observe up to 105 times Raman signal amplification with purposefully designed SERS-active substrates in comparison with the control samples. SERS-active substrates are obtained by electron beam evaporation of silver thin films with well controlled nanostructured surface morphology. The characteristic dimensions of the morphology elements vary in the range from several to tens of nanometers. Using optical confocal microscopy we demonstrate that proteins form a conformation on the surface of the self-assembled silver film, which results in an effective enhancement of giant Raman scattering signal. We investigate the various SERS substrates surface morphologies by means of atomic force microscopy (AFM) in combination with deep data analysis with Gwyddion software and a number of machine learning techniques. Based on these results, we identify the most significant film surface morphology patterns and evaporation recipe parameters to obtain the highest amplitude SERS spectra. Moreover, we demonstrate the possibility of automated selection of suitable morphological parameters to obtain the high-amplitude spectra. The developed AFM data auto-analysis procedures are used for smart optimization of SERS-active substrates nanoengineering processes. [ABSTRACT FROM AUTHOR]

Abstract: Spin–orbit (SO) splitting of surface states in ultrathin Au films was examined on the basis of density-functional theory. Due to the interaction between the top and the bottom Au layers, the SO splitting in the Au (111) films with few atomic layers is usually negligible. The splitting is, however, detectable if one surface of the film is terminated by adatoms, such as Al or H atoms. Similar effect can also be achieved if an external electric field is applied perpendicular to the surface. In addition, an interesting even–odd oscillating behavior in the SO splitting can be observed in a Au/Al interlaced structure. All these can be explained by the inversion-symmetry breaking. Our work provides a deep understanding of the SO effect in ultrathin heavy-metal films, which will be helpful in future all-electric spintronics. [Copyright &y& Elsevier]

Dynamics of nanoparticle formation were observed after nanosecond laser irradiation of thin gold films. Gold films of different thickness (3, 4, 5, 6, 10, 15, 20, 25 nm) were evaporated on the silicon (110) substrate and irradiated with the pulsed nanosecond laser using different pulse energies and the number of pulses in a burst. A single Gaussian beam as well as an interference of a few laser beams were used for irradiation. Morphological changes appeared in the films only when the pulse energy was high enough to initiate the phase transition. The threshold energy density for phase transitions in the films was estimated from the thermal model of the laser beam and sample interaction. With the pulse energy just above the threshold, it was possible to observe evolution of nanoparticle formation from a plane metal film by changing the number of pulses applied, as duration of the pulse burst represented the time the liquid phase existed. The final size of nanoparticles was a function of the film thickness and was found to be weakly dependent on the pulse energy and the number of pulses. The nanoparticle size distribution width was much narrower after irradiation with periodical intensity distribution produced by 3 interfering beams compared with the single beam treatment. Moreover, the nanoparticles tended to be periodically distributed on the substrate. [ABSTRACT FROM AUTHOR]

Abstract: Phase change processes including melting, vaporization and resolidification during the multiple femtosecond laser pulses irradiations on a thin gold film are investigated numerically. A two-temperature model is coupled with the phase interface track methods to describe the temperature variation and the solid–liquid and liquid–vapor interface evolutions. The relationship between the maximum vaporization temperature and melting depth, ablation depth are analyzed and compared with that of the single pulse irradiation. It is found that for two pulses irradiation, if deeper melting depth is desirable, the second pulse should be launched as soon as the melting depth induced by the first pulse reaches to the maximum. In comparison to a single pulse irradiation resulting in the same lattice temperature, this two-pulse approach leads to a greater melting depth. For laser irradiation with more than two consecutive pulses, if the total laser fluence remains a constant, larger pulse number and longer separation times between pulses leads to a smaller melting depth. However, the melting depth is much deeper compared to that by induced by a single pulse that causes the same lattice temperature. [Copyright &y& Elsevier]