Photoemission of Plasmonic Gold Nanostars in Laser-Controlled Electron Current Devices for Technical and Biomedical Applications.

The main goal of this work was to modify the previously developed blade-type planar structure using plasmonic gold nanostars in order to stimulate photofield emission and provide efficient laser control of the electron current. Localization and enhancement of the field at the tips of gold nanostars provided a significant increase in the tunneling electron current in the experimental sample (both electrical field and photofield emission). Irradiation at a wavelength in the vicinity of the plasmon resonance (red laser) provided a gain in the photoresponse value of up to 5 times compared to irradiation far from the resonance (green laser). The prospects for transition to regimes of structure irradiation by femtosecond laser pulses at the wavelength of surface plasmon resonance, which lead to an increase in the local optical field, are discussed. The kinetics of the energy density of photoinduced hot and thermalized electrons is estimated. The proposed laser-controlled matrix current source is promising for use in X-ray computed tomography systems.

Modeling of Laser-Induced Plasmon Effects in GNS-DLC-Based Material for Application in X-ray Source Array Sensors.

An important direction in the development of X-ray computed tomography sensors in systems with increased scanning speed and spatial resolution is the creation of an array of miniature current sources. In this paper, we describe a new material based on gold nanostars (GNS) embedded in nanoscale diamond-like carbon (DLC) films (thickness of 20 nm) for constructing a pixel current source with photoinduced electron emission. The effect of localized surface plasmon resonance in GNS on optical properties in the wavelength range from UV to near IR, peculiarities of localization of field and thermal sources, generation of high-energy hot electrons, and mechanisms of their transportation in vacuum are investigated. The advantages of the proposed material and the prospects for using X-ray computed tomography in the matrix source are evaluated.

Quantification of laser local hyperthermia induced by gold plasmonic nanoparticles.

This paper discusses one of the key problems of laser-induced tissue/cell hyperthermia mediated by gold nanoparticles, namely, quantifying and precise prediction of the light exposure to provide a controllable local heating impact on living organisms. The distributions of such parameters as an efficiency factor of absorption, differential and integral absorbing power of a nanoparticle, temperature increment, and Arrhenius damage integral were used to quantify nanoparticle effectiveness in the two-dimensional coordinate space "laser wavelength (λ) × radius of gold nanoparticles (R)." It was found that the fulfillment of required spatial and temporal characteristics of temperature fields in the vicinity of nanoparticle determines the optimal λ and R. As a result, the area in the space (λ × R) with a minimal criticality to alterations of the local hyperthermia may be significantly displaced from the position of the plasmonic resonance. The aspects of generalization of the proposed methodology for the analysis of local hyperthermia using nanoparticles of different shapes (nanoshells, nanorods, nanostars) and short pulse laser radiation are discussed.

Thermal energy transfer by plasmon-resonant composite nanoparticles at pulse laser irradiation.

Heating of composite plasmon-resonant nanoparticles (spherical gold nanoshells) under pulse laser illumination is considered. The numerical solution of the time-dependent heat conduction equation accounting for spatial inhomogeneities of absorbed laser radiation is performed. Important features of temperature kinetics and thermal flux inside nanoparticles are analyzed. Possible applications of the observed effects in nanotechnology and medicine are discussed.

Novel thermal effect at nanoshell heating by pulsed laser irradiation: hoop-shaped hot zone formation.

Photonic nanotechnologies have good perspectives to be widely used in biophotonics. In this study we have developed an approach for calculation of nanoparticle temperature field accounting for absorbed local intensity at pulse laser radiation of composite spherical nanoparticles (nanoshells). This approach allowed us to analyze spatial inhomogeneities of light field diffracted into a nanoshell and corresponding distribution of the absorption energy and to provide numerical solution of time-dependent heat conduction equation accounting for corresponding spatially inhomogeneous distribution of heating sources. We were able to predict the appearance of a novel thermal effect - hoop-shaped hot zone on the nanoshell surface. The observed effect has potential applications in cell biology and medicine for controlled cell optoporation and nanosurgery, as well as cancer cell killing.