V. I. Nuzhdin

Optical properties of metal nanoparticles

Recent results on the interaction of high power laser pulses with various dielectric materials containing metal nanoparticles are reviewed. The excimer laser pulse modification of silver nanoparticles synthesized by ion implantation in soda-lime silicate glasses are considered. One of features of composite samples prepared by the low energy ion implantation is the growth of metal particles with a wide size distribution in the thin depth from the irradiated substrate surface. Pulsed laser irradiation makes it possible to modify such composite layer, improving the uniformity in the size distribution of the nanoparticles. Changes induced by pulsed laser exposure suggest there are both reductions in average size of the metal nanoparticles, and some long-range dissolution of metal atoms in the matrix. Experimental data on laser modification are explained by melting of the nanoparticles in the dielectric matrix.

Optical properties of chalcogenide glasses with ion-synthesized copper nanoparticles

Substrates of chalcogenide glassy semiconductors As2S3 and Ge15.8As21S63.2 are implanted with Cu+ ions (energy 40 keV, radiation dose 1.5 × 1017 ion/cm2, fixed current density in the ion beam 1 μA/cm2). The composite layers are analyzed by measuring linear optical transmittance and recording nonlinear optical absorption using the Z-scan technique at 780 nm (probe laser radiation with 150-fs pulses; intensity of 25–100 mW). It is ascertained for the irradiated materials that (1) the linear transmission characteristic of the optical surface plasmon resonance (SPR) band, which indicates the formation of copper nanoparticles in the near-surface region, has emerged and (2) there are simultaneously saturated and two-photon nonlinear absorption types; the latter prevails as the intensity of laser irradiation is increased.

Excimer laser-assisted annealing of silicate glass with ion-synthesized silver nanoparticles

The effect of KrF excimer laser radiation on a composite layer consisting of sodium-potassium silicate glass with silver nanoparticles is studied as a function of the number of laser nanosecond pulses. The silver nanoparticles are synthesized by ion implantation. The measured optical absorption of the composite layer demonstrates that the silver nanoparticle size decreases monotonically as the number of laser pulses increases. Rutherford backscattering shows that laser annealing is accompanied by silver diffusion into the bulk of the glass and partial metal evaporation from the sample surface. The detected decrease in the silver nanoparticle size is discussed in terms of simultaneous melting of silver nanoparticles and the glass matrix due to the absorption of laser radiation.

Ion synthesis of silver nanoparticles in viscous-fluid epoxy resin

A method is described for the ion synthesis of silver nanoparticles in epoxy resin that is in a viscousfluid state (viscosity 30 Pa s) during irradiation. The viscous-fluid or glassy polymer is implanted by 30-keV silver ions at a current density of 4 μA/cm2 in the ion beam in the dose range 2.2 × 1016–7.5 × 1016 ions/cm2. The epoxy layers thus synthesized contain silver nanoparticles, which are studied by transmission electron microscopy and optical absorption spectroscopy. The use of the viscous-fluid state increases the diffusion coefficient of the implanted impurity, which stimulates the nucleation and growth of nanoparticles at low implantation doses and allows a high factor of filling of the polymer with the metal to be achieved.

Formation of a periodic diffractive structure based on poly(methyl methacrylate) with ion-implanted silver nanoparticles

We propose to form optical diffractive elements on the surface of poly(methyl methacrylate) (PMMA) by implanting the polymer with silver ions (E = 30 keV; D = 5.0 × 1014 to 1.5 × 1017 ion/cm2; I = 2 μA/cm2) through a nickel grid (mask). Ion implantation leads to the nucleation and growth of silver nanoparticles in unmasked regions of the polymer. The formation of periodic surface microstructures during local sputtering of the polymer by incident ions was monitored using an optical microscope. The diffraction efficiency of obtained gratings is demonstrated under conditions of their probing with semiconductor laser radiation in the visible spectral range.

New approach to the synthesis of porous silicon with silver nanoparticles using ion implantation technique

A new technique for the synthesis of porous silicon layers with silver nanoparticles has been proposed which is based on the high-dose low-energy implantation of crystalline silicon with metal ions. In order to demonstrate this technique, in this work we implanted a polished wafer of monocrystalline silicon Ag+-ions with an energy of 30 keV at a dose of 1.5 × 1017 ion/cm2 and a current density in the ion beam of 4 μA/cm2. Using high-resolution scanning electron and atomic force microscopy, as well as X-ray spectral microprobe analysis and Raman scattering, it is shown that an amorphous layer of a porous silicon is formed at the surface of silicon as a result of implantation with average sizes of pore holes on the order of 150–180 nm; depth of about 100 nm; and thickness of the walls of 30–60 nm, in whose structure silver nanoparticles are located with a diameter of 5–10 nm. In addition, it is shown that the formation of pores by implantation with silver ions is accompanied by sputtering the surface of silicon.

Mössbauer study of the magnetic phase composition of single-crystalline rutile (TiO2) implanted with iron ions

Depth-resolved Mössbauer measurements have been performed for four ferromagnetic samples obtained by the implantation of iron ions (enriched to ∼ 50% with 57Fe isotope) into single-crystalline rutile (TiO2) substrates with two crystallographic orientations [(100) and (001)] at different temperatures (300 and 900 K). It is established that the ferromagnetic properties of iron-implanted rutile samples at room temperature are determined by the presence of α-Fe and Fe3O4 phases. The phase composition of samples obtained by iron implantation into substrates heated to 900 K depends on the crystallographic orientation of the substrate, which is explained by a significant anisotropy of the diffusion of iron atoms in rutile.

Laser annealing induced melting of silver nanoparticles in a glass matrix

We have studied the effect of nanosecond-pulsed KrF excimer laser radiation on a composite metamaterial based on a soda-lime-silicate glass containing ion-synthesized silver nanoparticles, depending on the number of pulses. It is established that, as the number of laser pulses increases, the average size of silver nanoparticles in the ion-implanted layer monotonically decreases. In addition, the laser annealing is accompanied by the diffusion of silver inward the glass and by the partial evaporation of silver from the sample surface. The observed decrease in the size of silver nanoparticles is considered with allowance for the simultaneous melting of both the metal particles and glass matrix.

Structure and optical properties of ZnO with silver nanoparticles

Textured nanocrystalline ZnO thin films are synthesized by ion beam assisted deposition. According to X-ray diffraction data, the crystallite size is ~25 nm. Thin (~15 nm) ZnO layers containing Ag nanoparticles are formed in a thin surface region of the films by the implantation of Ag ions with an energy of 30 keV and a dose in the range (0.25–1) × 1017 ion/cm2. The structure and optical properties of the layers are studied. Histograms of the size distribution of Ag nanoparticles are obtained. The average size of the Ag nanoparticles varies from 0.5 to 1.5–2 nm depending on the Ag-ion implantation dose. The optical transmittance of the samples in the visible and ultraviolet regions increases, as the implantation dose is increased. The spectra of the absorption coefficient of the implanted films are calculated in the context of the (absorbing film)/(transparent substrate) model. It is found that the main changes in the optical-density spectra occur in the region of ~380 nm, in which the major contribution to absorption is made by Ag nanoparticles smaller than 0.75 nm in diameter. In this spectral region, absorption gradually decreases, as the Ag-ion irradiation dose is increased. This is attributed to an increase in the average size of the Ag nanoparticles. It is established that the broad surface-plasmon-resonance absorption bands typical of nanocomposite ZnO films with Ag nanoparticles synthesized by ion implantation are defined by the fact that the size of the nanoparticles formed does not exceed 1.5–2 nm.

Optical properties of ZnO and Al2O3 implanted with silver ions

ZnO and Al2O3 samples implanted with 30-keV silver ions with fluences in the interval (0.25–1.00) × 1017 ions/cm2 are studied by the method of optical photometry in the visible part of the spectrum. The optical transmission spectra of the implanted samples exhibit a selective band associated with surface plasmon resonance absorption of silver nanoparticles. The intensity of this band nonmonotonically depends on the implantation fluence. The silver ion depth distribution in the samples is calculated. It is shown that the non-monotonicity observed in experiments is due to an increase in the substrate sputtering ratio with increasing implantation fluence. It is found that vacuum thermal annealing of the implanted Al2O3 layers up to 700°C causes a considerable narrowing of the plasmon absorption bandwidth without a tangible change in its intensity. At higher annealing temperatures, the plasmon absorption band broadens and its intensity drops. Annealing of the ZnO films under such conditions causes their complete vaporization.