S. G. Przhibel’skiĭ

Correlation between the morphological characteristics and extinction spectra of sodium nanoparticles and modification of nanoparticles through photoatomic emission

The morphological characteristics of ensembles of metal nanoparticles on transparent dielectric substrates have been studied by the methods of hole-burning and linear absorption spectroscopy. The size and shape of particles were changed under the exposure to the optical radiation that induced photodetachment of atoms and their photostimulated diffusion over the surface of nanoparticles. The correlation between holes burned in different absorption bands is explained by the morphological features of the island film. The relaxation times of individual modes of collective plasma oscillations and the shape parameters of particles modeled by three-axial ellipsoids have been determined.

Conductivity and photoconductivity of granular silver films on a sapphire substrate

The photoelectric properties of a high-resistance silver film on sapphire, consisting of granules 15–20 nm across with the same intervals between them, have been investigated. The ohmic conductivity of the film increased with temperature. Photoconductivity is detected in the film when optical radiation with wavelengths up to the red limit of the photoelectric effect acts on it. A sign change of the photocurrent is detected in the photoconductivity spectrum when the current through the film increases under the action of radiation with wavelength less than 460 nm, whereas it decreases when the wavelength is greater than 460 nm. A conductivity and photoconductivity model is proposed that is based on doping of the dielectric substrate due to the metallic nanoparticles placed on it and the motion of electrons over traps in the substrate. The position of the bottom of the conduction band of the dielectric relative to the Fermi level for silver is calculated in terms of the model.

Optical manifestations of self-diffusion of atoms over the surfaces of silver nanoparticles

The kinetics of the extinction spectrum of a thin island silver film heated in the temperature range 473–553 K is studied experimentally. The observed variations in the inhomogeneously broadened extinction spectrum are related to two types of changes in the morphology of islands, namely, (i) coalescence and fragmentation of the islands at the initial stage and (ii) subsequent rounding of individual islands. This conclusion is supported by the data of electron microscopy of the film at different stages of its heating. The long duration of the relaxation process is explained by specific features of mass transfer over the surfaces of granulated nanoparticles.

Fluctuations of local optical anisotropy of island films

A method for the determination of the island film structure parameters by measuring fluctuations of optical characteristics of small areas of the film is proposed and implemented. The extinction fluctuations of the laser beam are measured experimentally in a focal spot, in which the polarization of radiation is modulated in time and which is movable over the film. From the optical data thus obtained, the optical absorption anisotropy of the nanometer-size islands of the film is evaluated. It is shown that this characteristic has a considerable frequency dispersion in the region of plasmon resonances of the nanoparticles.

Deferred action of illumination on the relaxation of a granular silver film when it is thermally annealed

It has been detected that UV radiation in the 300–400 nm wavelength interval affects the rate and final result of subsequent thermal annealing of a thin silver film on a sapphire substrate. Whereas the annealing of unirradiated films rapidly causes them to decay and causes the formation of individual fine particles of round shape, larger particles of irregular shape are formed when irradiated films are annealed, while the changes themselves occur significantly more slowly.

Optical methods of forming metallic nanostructures on the surface of insulating materials

This paper discusses nonthermal photoinduced phenomena on the surface of solids that make it possible to control the processes of depositing a new phase. It is proposed to use the phenomenon of photodesorption of metal atoms from the surface of transparent insulating materials to shift the threshold for condensing a metal on the surface of an insulator. It is shown that nonuniform surface illumination can be used to form metallic nanostructures whose shape is determined by the irradiance distribution on the substrate surface.

Photoelectron emission from island metallic sodium films during the excitation of localized plasmon resonances

The photoelectron emission from island sodium films is studied under the action of radiation that is resonant to the collective electron excitations in the nanoparticles forming a film. Noticeable deviations from the Fowler law and an increase in the photoelectron yield are detected. The dependences of the photoeffect efficiency from these films on their structural parameters, the polarization vector, and the angle of radiation incidence are obtained.

Breakdown of a nanoparticle partially ionized by a powerful ultrashort laser pulse

This paper presents the results of an analytical calculation and numerical modeling of the disintegration of a nanoparticle of a condensed medium partially ionized by a powerful ultrashort pulse (USP) of laser radiation. The mechanism of the process by which the nanoparticle is disintegrated by the Coulomb forces that result from the disruption of charge equilibrium in it under the action of the USP is established by comparing the results obtained by analytical and numerical methods. The kinetics of the energy spectrum of the dispersing ions is analyzed, taking into account the deceleration of the ions in the nanoparticle.

Ionization of nanoparticles by supershort moderate-intensity laser pulses

This paper presents the results of the numerical modelling of electron emission from metallic nanoparticles under the action of femtosecond laser pulses with peak intensity from tenths of a terawatt to tens of terawatts per square centimeter. The model takes into account the effects of the excitation of the valence electrons of the nanoparticle due to multiphoton absorption, described by the Keldysh model, and the increase of the ionization potential due to the generation of positive charge in the nanoparticle during electron emission. The transition from multiphoton ionization to tunnel emission as the laser-radiation intensity increases is demonstrated, and it is shown that Fowler’s model and its modification give a substantial underestimate of both the peak photoemission rate and the total emission current.

Modification of a dielectric surface when laser-induced Coulomb explosion of nanoparticles occurs

This paper presents the results of a study of the mechanisms of femtosecond laser interactions with a system of nanoparticles deposited on a solid insulating surface. Experiments showed that, depending on the intensity, various interaction regimes of the laser radiation with the nanoparticles are implemented, including partial and total separation (ablation) of the nanoparticles and local damage of the surface itself. In the regime of total and partial ablation of the nanoparticles, traces are recorded showing that ions of the material of the nanoparticles are incorporated in a thin near-surface layer of the substrate. Modelling the breakdown of nanoparticles by a femtosecond laser pulse confirms that it is possible for ions to be emitted from them, with subsequent incorporation in the substrate.