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

Numerical modeling and analytical evaluation of light absorption by gold nanostars

In this paper, the regularity of local light absorption by gold nanostars (AuNSts) model is studied by method of numerical simulation. The mutual diffraction influence of individual geometric fragments of AuNSts is analyzed. A comparison is made with an approximate analytical approach for estimating the average bulk density of absorbed power and total absorbed power by individual geometric fragments of AuNSts. It is shown that the results of the approximate analytical estimate are in qualitative agreement with the numerical calculations of the light absorption by AuNSts

The peculiarities of localized laser heating of a tissue doped by gold nanostars

The consistent patterns for local temperature fields under laser irradiation of biological tissue doped by effectively absorbing plasmon gold nanostars are discussed. Differences in the degree of spatial localization and the kinetics of the photoinduced temperature fields under irradiation by femto-, pico- and nanosecond pulses are revealed

A Visible and Near-IR Tunnel Photosensor with a Nanoscale Metal Emitter: The Effect of Matching of Hot Electrons Localization Zones and a Strong Electrostatic Field

The results of the research and design of a novel vacuum photosensor with a planar molybdenum blade structure are presented. The advanced prototype implements the principle of an increasing penetrability of the Schottky barrier for the metal–vacuum interfaces under the action of an external strong electrostatic field. Theoretical and experimental substantiation of the photosensor performance in a wide range of wavelengths (from 430 to 680 nm and from 800 to 1064 nm) beyond the threshold of the classical photoelectric effect is given. The finite element method was applied to calculate distribution of the optical and electrostatic fields inside the photosensor structure. The sensor current-to-light response was studied using the periodic pulsed irradiation with the tunable wavelength. It was shown that the nanoscale localization zones of two types are formed near the surface of the blade tip: the zone of an increased concentration of hot electrons localized inside the molybdenum blade, and the zone with an increased strength of the external electrostatic field localized outside the blade. In general, the mutual positions of these zones may not coincide, whereas the position of the first-type localization zone significantly varies with the changes in the wavelength of the irradiating light. This causes features in the spectrum of the quantum yield of the photosensor such as expressed non-monotonic behavior and occurrence of sharp dips. The design of the photosensor that provides matching of the positions for both types of localization zones was proposed; the manufactured prototypes of the designed device were experimentally studied. In the designed photosensor, the ballistic transport of photoelectrons in the vacuum gap with a strong field provides a possibility for the creation of ultra-fast optoelectronic devices, such as modulators, detectors, and generators

Modeling of hyperthermia induced by functionalized gold nanorods bound to Staphylococcus aureus under NIR laser radiation

In this paper, a theoretical model of the formation of a local temperature field in suspensions of microorganisms with embedded plasmonic gold nanorods under irradiation by low-intensity NIR laser light was considered. The results of numerical modeling of the optical properties of plasmon nanorods used in the experiments, and the results of multiscale modeling of the parameters of local hyperthermia with various types of distribution of the concentration of plasmon nanoparticles are presented. Found that the process of concentration of nanoparticles, functionalized with human immune globulins IgA and IgG, around the cells of microorganisms with the formation of "clouds" leads to the appearance of a microscale zone of elevated temperature. This ensures a synergistic effect of a multiplicative increase in the volume of the hyperthermia zone. The results of numerical simulation provide a justification for the experimentally observed increase in the bacterium killing ability at laser hyperthermia of the cellular environment doped with functionalized nanoparticles, without a noticeable increment in the recorded average sample temperature when irradiated with a low intensity laser beam of around 100 mW/cm2

Thermal optics of ordered arrays of plasmon nanoparticles in context of SERS, cell optoporation, and pathogen destruction

Numerical modeling of spectral absorption and scattering properties of structures manufactured as the ordered arrays of plasmon nanoparticles is carried out in this work. The results of numerical 2D simulation of selective heating of an array of plasmon resonant gold nanodiscs irradiated by a CW NIR laser (810 or 1064 nm) are presented. Calculations fit well to experimental data received. We demonstrate the possibility to control the local amplification of a shining laser field in the space between nanodiscs, as well as plasmon resonance absorption of each individual nanodisc. The perspectives of application of such nanostructures for providing of precision dosed-up thermal effects in cells and biological tissues are discussed

Interaction of laser radiation and complexes of gold nanoparticles linked with proteins

The results of numerical simulation of the near-field distribution inside and in the vicinity of two types of gold nanoparticles (nanospheres and nanorods) intended for producing complexes of gold nanoparticles linked with proteins and exciting photosensitizers in the wavelength range of 532 – 770 nm are presented. Quantitative estimates of the field localisation (enhancement) are obtained depending on the type of gold nanoparticles and dimensional factors. The tendency of the red shift of the wavelength at which the maximum local field enhancement is achieved relative to the positions of the maxima of the absorption and scattering cross sections of nanoparticles and complexes is described

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

Gold/cobalt ferrite nanocomposite as a potential agent for photothermal therapy

The study encompasses an investigationof optical, photothermal and biocom-patibility properties of a composite con-sisting of golden cores surrounded bysuperparamagnetic CoFe 2 O 4 nanoparti-cles. Accompanied with the experiment,the computational modeling reveals that each adjusted magnetic nanoparticleredshifts the plasmon resonance frequency in gold and nonlinearly increases theextinction cross-section at 800 nm. The concentration dependent photothermalstudy demonstrates a temperature increase of 8.2 K and the photothermal con-version efficiency of 51% for the 100 μg/mL aqueous solution of the compositenanoparticles, when subjected to a laser power of 0.5 W at 815 nm. During anin vitro photothermal therapy, a portion of the composite nanoparticles, initiallyseeded at this concentration, remained associated with the cells after washing.These retained nanoparticles effectively heated the cell culture medium, result-ing in a 22% reduction in cell viability after 15 min of the treatment. The com-posite features a potential in multimodal magneto-plasmonic therapies