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

SIZE-DEPENDENT PHONON-ASSISTED ANTI-STOKES PHOTOLUMINESCENCE IN NANOCRYSTALS OF ORGANOMETAL PEROVSKITES

Anti-Stokes photoluminescence (ASPL), which is an up-conversion phonon-assisted process of the radiative recombination of photoexcited charge carriers, was investigated in methylammonium lead bromide (MALB) perovskite nanocrystals (NCs) with mean sizes that varied from about 6 to 120 nm. The structure properties of the MALB NCs were investigated by means of the scanning and transmission electron microscopy, X-ray diffraction and Raman spectroscopy. ASPL spectra of MALB NCs were measured under near-resonant laser excitation with a photon energy of 2.33 eV and they were compared with the results of the photoluminescence (PL) measurements under nonresonant excitation at 3.06 eV to reveal a contribution of phonon-assisted processes in ASPL. MALB NCs with a mean size of about 6 nm were found to demonstrate the most efficient ASPL, which is explained by an enhanced contribution of the phonon absorption process during the photoexcitation of small NCs. The obtained results can be useful for the application of nanocrystalline organometal perovskites in optoelectronic and all-optical solid-state cooling devices

Influence of low-temperature plasma on green algae culture

Influence of low-temperature plasma, which was formed in a high-resource arc-discharge plasma jet in an argon-air mixture, was studied for a community of green algae as Chlorella vulgaris Beyerinck [Beijerinck] and Stichococcus bacillaris Nägeli. It was found that the plasma treatment for 10 minutes led to partial cell death. At the same time, the species of C. vulgaris were less sensitive to the plasma treatment than the species of S. bacillaris. After plasma exposure, the predominant growth of the latter culture was observed in comparison with the control samples. This effect can be explained by an activation of biochemical processes in the algae due to the interaction with radicals in the low-temperature plasma. The results obtained indicate the selectivity of the low-temperature plasma effect on green algae community

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

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

Application of cold plasma to control the microbiota composition on the surface of potato tubers

A study of the effect of low-temperature plasma on potato tubers was carried out. A comparative assessment of changes in the rate of germination, the size of shoots and the mass of shoots was carried out. Changes in the number of bacteria and fungi on the surface of tubers were analysed for different durations of exposure. It was found that growth characteristics did not change. The number of bacteria on the surface of tubers was significantly reduced due to the exposure to low-temperature plasma

SURFACE-ENHANCED RAMAN SCATTERING FROM DYE MOLECULES IN SILICON NANOWIRE STRUCTURES DECORATED BY GOLD NANOPARTICLES

Silicon nanowires (SiNWs) prepared by metal-assisted chemical etching of crystalline silicon wafers followed by deposition of plasmonic gold (Au) nanoparticles (NPs) were explored as templates for surface-enhanced Raman scattering (SERS) from probe molecules of Methylene blue and Rhodamine B. The filling factor by pores (porosity) of SiNW arrays was found to control the SERS efficiency, and the maximal enhancement was observed for the samples with porosity of 55%, which corresponded to dense arrays of SiNWs. The obtained results are discussed in terms of the electromagnetic enhancement of SERS related to the localized surface plasmon resonances in Au-NPs on SiNW’s surfaces accompanied with light scattering in the SiNW arrays. The observed SERS effect combined with the high stability of Au-NPs, scalability, and relatively simple preparation method are promising for the application of SiNW:Au-NP hybrid nanostructures as templates in molecular sensorics