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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.

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&ndash, 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.

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.

In this work, we investigate the spectral and polarization characteristics of a vacuum photosensor with a nanoscale molybdenum blade as a sensing element. The results of theoretical and experimental studies of the optical fields in the sensor and the photocurrent produced by laser beam irradiation in the range of wavelengths from the visible to the near infrared are presented. The existence of a photo-response far beyond the red threshold of the classical photoelectric effect is ensured by the localization of an external strong electrostatic field. Features of the field interaction of radiation with a molybdenum blade cause the registered spectral non-monotonicity of the photocurrent value, which corresponds to the results of theoretical studies. The ballistic transport of electrons in a vacuum is characterized by a high speed. Achieved results made the photosensor based on nanoscale molybdenum blade promising in the development of ultrafast vacuum micro and nanoelectronic devices.

In this work, we describe the technology and design of planar multilayer structure. It is used as a sensitive element of the vacuum photosensor. Metal and dielectric layers are of nanoscale thickness. It is shown that the use of a thin molybdenum blade in the structure ensures the localization of the electrostatic field and increases the photosensitivity of the vacuum sensor. Submicron inter-electrode gaps provide a short transit time of the electron beam caused by the action of a light pulse. The ballistic transport of electrons in a vacuum is characterized by a high speed.

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.

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.

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.

Issues pertaining to the effective solution of problems related to the creation of durable low-voltage field emission cathodes with developed working surface and high density of emission current are considered. Results of practical implementation of the concept of multielectrode field emission planar nanostructures based on diamond-like carbon are presented. High average current density (0.1–0.3 A cm–2) is ensured by the formation of a controlled zone of electrostatic field localization at the planar-edge structure. The working life of cathode samples reaches 700–3000 h due to several positive factors, such as the stabilizing properties of a diamond-like carbon film, protection of the emitter from ion bombardment, use of a system of ballast resistors, and low-voltage operation of submicron interelectrode gaps.

A mathematical model for the calculation of the optical and thermal properties of an ensemble of gold nanostars with different tip lengths L = 10 to 20 nm in an aqueous environment is proposed. The heating of a nanoparticle ensemble under irradiation by a laser pulse of a nanosecond duration: resonant λ = 808 nm and nonresonant λ = 1064 nm is studied. A significant blue shift of surface plasmon resonance during the formation of a vapor bubble around the nanoparticle was detected and described. Based on the analysis of the kinetics of nanoparticle heating under the action of a laser pulse before and after the formation of a vapor bubble, a theoretical description of the experimentally observed threshold nature of particle photomodification is given. It was found that the laser intensity Im necessary to achieve the melting temperature Tm (photomodification threshold) tends to increase with decreasing nanostar tip length and for an individual nanostar differs by an order of magnitude. However, up to 45% of the nanoparticles are heated to the melting temperature Tm by a single pulse with an intensity only 2.5 times higher than the minimum value of Im. At a wavelength of 1064 nm, Im is ∼6 times higher than at a wavelength of 808 nm.

A phenomenological model of tunneling of electrons into vacuum from a composite nanostructure - a dielectric film of diamond-like carbon on a molybdenum base - is constructed. Three mechanisms of field emission from the metal-dielectric-vacuum structure are taken into account, assuming continuity of the injection-drift-emission current density. A qualitative correspondence of the character of calculated current characteristics to the result of an experimental study is obtained.

The results of investigations of physical processes in a multi-electrode planar three-level structure with field emission are presented. It is determined how the topology of elements affects the quality of electronic transport to an anode. A solution has been found that provides a fundamental reduction in the current trapping by control electrodes. The efficiency is confirmed by the results of tests of the manufactured vacuum device, the current transmission at the level of 80-98% is ensured in the entire range of variation of the gate potential.

The tunneling photo effect has been studied in a microdiode with an electrostatic field localized at an emitter based on a nanosized DLC structure. It is established the photocurrent, when the carbon nanoemitter is exposed by laser and tunable low-coherent radiation in the spectral range from UV to near IR with photons of low energy (below work function). A linear dependence of the photocurrent on the level of optical power in the range of micro- and milliwatt power is established. The effect of saturation of the current-voltage characteristics of the tunnel photocurrent associated with a finite concentration of non-equilibrium photoelectrons is observed. The observed spectral Watt-Amper characteristics can be adequately interpreted using a modified Fowler–Nordheim equation for non-equilibrium photoelectrons.

A model for calculating the electrostatic field in the system "probe of a tunnel microscope - a nanostructure based on a DLC film" was developed. A finite-element modeling of the localization of the field was carried out, taking into account the morphological and topological features of the nanostructure. The obtained results and their interpretation contribute to the development of the concepts to the model of tunnel electric transport processes. The possibility for effective usage of the tunneling microscopy methods in the development of new nanophotonic devices is shown.

The paper provides a justification and a comparative analysis of the scaling directions of the developed and investigated planar triode field emission cathode unit with the aim of increasing the maximum field current density up to 0.75 A-cm -2 without sacrificing durability. The design features of the vacuum device with a planar structure provided low-voltage control - at 150 V in the mode of long-term durability and not more than 250 V in the mode of the maximum permissible emission current.

We have developed a numerical model describing the optical and thermal behavior of optical tissue phantoms upon laser irradiation. According to our previous studies, the phantoms can be used as substitute of real skin from the optical, as well as thermal point of view. However, the thermal parameters are not entirely similar to those of real tissues thus there is a need to develop mathematical model, describing the thermal and optical response of such materials. This will facilitate the correction factors, which would be invaluable in translation between measurements on skin phantom to real tissues, and gave a good representation of a real case application. Here, we present the model dependent on the data of our optical phantoms fabricated and measured in our previous preliminary study. The ambiguity between the modeling and the thermal measurements depend on lack of accurate knowledge of material's thermal properties and some exact parameters of the laser beam. Those parameters were varied in the simulation, to provide an overview of possible parameters' ranges and the magnitude of thermal response.

Multiple factors and their impact on the stability of DLC field emission structures are discussed in the present work. Planar multi-electrode structures, in which the formation of zones of localization the electrostatic field of a certain topology performed, are examined. Estimates carried out demonstrated the existence of an effective solution for creating reliable and durable vacuum devices for electronics and photonics. Conclusions are confirmed by the results of experimental studies. Samples of devices showed an average current density of field emission 0.30-0.35 A/cm 2 .

The phenomenon of electron tunnel photoemission from the DLC film structure is discussed. Planar multi-electrode structure provides formation of zones of localization the electrostatic field of a certain topology. Under the influence of a strong electrostatic field, both equilibrium and nonequilibrium (photoexcited or "hot") electrons tunnel into the vacuum from the zone of concentration of electrostatic field. The results of experimental studies and theoretical simulations of the process show the saturation of photoemission current component with an increase in operating voltage. This fact makes it possible to realize the high-speed control of the spectral sensitivity of the photosensor. This is fundamentally important for applications in the modern electronic and photonic devices.

The results of theoretical and experimental study of the criticality of the process of forming nanosized α-carbon blades for autoemission structures with ionic protection are given. It is shown that this technology provides reliable control of the process. A weak dependence of the field strength in the tip area of emitter from the length of the blade visor was found, which promotes a good reproducibility of its parameters.

New approaches to the problems of criticality of field emission with respect to the construction and technological factors are analyzed, and examples of their practical application are considered. These approaches provide practical applications of carbon nanotubes and carbonaceous planar-edge field-emission structures in extreme electronics areas.

Reasons for limits on application of field-emission structures in high-power microwave vacuum tubes are studied on the basis of the performed analysis and the methods for their overcoming are discussed. Prospects for application of planar end field-emission structures (PEFESs) as a long-lived current source in high-power vacuum microwave amplifiers are substantiated. The results of design of the proposed electronoptical system with cathode matrices consisting of PEFES cells, which forms electron flows with a power over 100 kW in the contiuous-wave operating conditions, are presented.

The work is devoted to presenting the results of theoretical and experimental studies of the characteristics of a planar tetrode with field emission of diamond-like carbon film. Model representations of a field emission stimulation mechanism through existing in the film diamond-like carbon nanoclusters of two phases — diamond and graphite — have been developed. It is assumed that the presence of electrical conductive and dielectric nanoclusters makes film permeable under the applied external electrostatic field, provides field localization on nanoscale inhomogeneities and initiates a low-threshold field emission. The hypothesis is discussed that the structure arises ability to limit to some degree the emission current due to emergence and growth of space charge. The experimental tests of the described micro vacuum tetrode in the long pulse mode (quasi-static mode, pulse duration of 320 μs, pulse repetition frequency of 312.5 Hz) showed stable operation of device during the 8700 hours. If the initial average emission current density was 100 mA/cm2, then observed its reduction by 60% during the first 3700 hours and by 10% the next 5000 hours.

In this paper we consider the laser irradiation of the ensemble of absorbing nanoparticles localized in macroscopically-sized area of the tissue sample. The simple formula for estimation of distribution of the local temperature is presented.

The results of the practical implementation of the concept of field-emission current source with high average current density of 0.1-0.3 A-cm-2 are shown. The durability of cathode samples at a level of 6000 hours is achieved under conditions of technical vacuum. A phenomenological model is suggested that describes the tunneling of both equilibrium and nonequilibrium electrons in a vacuum from the zone of concentration of electrostatic field. Conditions are discussed as the resulting increase in the emission current due to the connection mechanism of the photoelectric effect is thermodynamically favorable, that is not accompanied by an undesirable increase in the temperature of the local emission zone. It is shown that to ensure stability and durability of the cathode is also important to limit the concentration of equilibrium carriers using composite structures «DLC film on Mo substrate." This helps to reduce the criticality of the CVC. A possible alternative is to use a restrictive resistance in the cathode. However, this increases the heat losses and thus decreases assembly efficiency. The results of experimental studies of the structure showing the saturation of photoemission current component with an increase in operating voltage. This fact suggests the existence of an effective mechanism for control of emission at constant operating voltage. This is fundamentally important for the stabilization of field emission cathode, providing a reliability and durability. The single-photon processes and the small thickness DLC films (15-20 nm) provide high-speed process of control.

Gold nanoparticles (AuNPs) of different size and shape are widely used as photosensitizers for cancer diagnostics and plasmonic photothermal (PPT)/photodynamic (PDT) therapy, as nanocarriers for drug delivery and laser-mediated pathogen killing, even the underlying mechanisms of treatment effects remain poorly understood. There is a need in analyzing and improving the ways to increase accumulation of AuNP in tumors and other crucial steps in interaction of AuNPs with laser light and tissues. In this review, we summarize our recent theoretical, experimental, and pre-clinical results on light activated interaction of AuNPs with tissues and cells. Specifically, we discuss a combined PPT/PDT treatment of tumors and killing of pathogen bacteria with gold-based nanocomposites and atomic clusters, cell optoporation, and theoretical simulations of nanoparticle-mediated laser heating of tissues and cells.

Results of experimental and theoretical investigation of vacuum cathodoluminescent (VCL) light sources with field-electron emission from carbon-containing structures are presented. Comparative analysis of the distribution of current on the light-emitting anode surface in VCL sources of various designs has been performed. The influence of pulsed regime parameters on the VCL source brightness and efficiency has been evaluated. Promising directions in the development of VCL light sources based on planar-edge type field-emission structures are discussed.

Specific features of various methods used to increase the field-emission current of carbon-containing structures, which are intended to control the localization of electrostatic field on a micro-, nano-, and mesoscales, are considered. An original field-emission heterostructure is proposed in which the activation of the emitting layer of carbon nanotubes is ensured by incorporated dielectric inclusions. The mechanism of the electrostatic field localization in systems of this type is described. The efficiency of using mesoscale dielectric inclusions to develop technology for reliable, long-lived field electron emitters with increased current emissivity is justified.

Methods for solving analytically and numerically the problem of multiscale modelling of the laser hyperthermia processes in a medium with nanoparticles are developed with regard to composite spherical nanoparticles (nanoshells). The features of the laser radiation field localisation on nanoscale inhomogeneities are investigated. Issues related to the control of the tissue hyperthermia processes by choosing the parameters of spatiotemporal localisation of the laser beam and of the absorbing nanoparticles are discussed.

The results of modeling and development of planar multielectrode current sources based on nanoscale carbon structures with the low-threshold field emission are described. Mechanism of low-threshold field emission can be explained by the model, which describes the efficiency of tunneling of electrons from the carbon film into vacuum due to the existence of nanoscale clusters of two phases of DLC - diamond and graphite. Results of the structures tests indicating an average level of achieving the emission current density of 0.2–0.3 A/cm2 are shown. In recalculation on the thickness and perimeter of the emitting area of carbon film, this corresponds to a current density of 700–1000 kA/cm2. Achieved parameters of the described structure make it promising for use in the development of numerous electronic devices with intensive electron beams.

The major goal of this study is theoretical analysis and optimization of local laser heating of a medium doped by plasmon-resonant nanoparticles that modeling nanoparticle labeled tissue. We were focused on the development of methods for precise description of optical and thermal processes accounting for their spatio-temporal localization. The results of numerical simulation show that an approach based on using the Arrhenius damage integral provides a more reasonable choice of the size of nanoparticles and exposure modes to provide precise control of hyperthermia with minimal energy consumption.

A mathematical model of electron-optical processes has been developed and studied. The results of this analysis show that the ion current to a microscopic point emitter can be significantly reduced in planar edge field emission (PEFE) structures. The mechanism of this decrease is related to a special configuration of the electric field in the cathode-gate-anode system, which features a slope of the equipotential lines in the near-cathode region. The advantage of PEFE structures over the traditional systems based on Spindt cathodes is characterized by a decrease in the ion-current-related thermal load by more than five orders of magnitude. This decrease ensures high durability of the PEFE structures, which has been confirmed in experiment.

The work is devoted to the development of a new direction in creating of broadband photo sensors which distinctive feature is the possibility of dynamic adjustment of operating frequency range. The author’s results of study of red threshold control of classic photoelectric effect were the basis for the work implementation. This effect was predicted theoretically and observed experimentally during irradiation of nanoscale carbon structure of planar-edge type by stream of low-energy photons. The variation of the accelerating voltage within a small range allows you to change photoelectric threshold for carbon in a wide range - from UV to IR. This is the consequence of the localization of electrostatic field at tip of the blade planar structure and of changes in the conditions of non-equilibrium electrons tunneling from the boundary surface of the cathode into the vacuum. The generation of nonequilibrium electrons in the carbon film thickness of 20 nm has a high speed which provides high performance of photodetector. The features of the use of nanoscale carbon structure photocurrent registration as in the prethreshold regime, and in the mode of field emission existence are discussed. The results of simulation and experimental examination of photosensor samples are given. It is shown that the observed effect is a single-photon tunneling. This in combination with the possibility of highspeed dynamic tuning determines the good perspectives for creation of new devices working in the mode of select multiple operating spectral bands for the signal recording. The architecture of such devices is expected to be significantly simpler than the conventional ones, based on the use of tunable filters.

A mathematical model and numerical simulation of nonstationary temperature field within tissues and cells locally heated under pulse laser irradiation mediated by plasmonic nanoparticles are presented. The essential temperature alterations during laser pulse and time interval between pulses was found. Temperature spatial-temporal profile depends on a number of parameters including optical and thermophysical properties of cell membrane and nanoparticles, laser wavelength, energy, pulse duration and repetition rate. On the basis of introduced parameters a quantitative evaluation of thermal effects was done. The possibilities of usage of these parameters to study their correlation with irreversible photothermal effects, including a change in the permeability of cell membrane during optoporation, are discussed.

The results achieved in improving the reliability and durability of cathodes based on field-induced electron emission of nano-scaled carbon structures are discussed. The features of the construction of two types of emitters: using carbon nanotubes (CNTs) and carbon-based planar-edge structures (CPES) — are described. The effective density of field emission current of 1.4 A·cm−2- and longevity of the emitter at least 2000 hours were achieved experimentally. Promising directions in the development of microwave devices for communications and radar systems in the frequency range up to terahertz based on field emission structures are discussed.

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.

Paper presents and discusses the features of laser-induced thermal dynamics of the gold nanoshells, which is associated with their relatively large size and layered structure. Unlike bulk nanoparticles the existence of a novel thermal phenomenon - hoop-shaped narrow hot zone on the nanoshell surface - is found. It is caused by spatial-temporal inhomogeneities of light field diffracted by a nanoshell and corresponding absorption of laser radiation. The numerical solution of time-dependent heat conduction equation accounting for corresponding spatially inhomogeneous distribution of heating sources is presented.

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.

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.

Absence of satisfactory criteria for discrete model parameters choice during computer modeling of thermal processes of laser-biotissue interaction may be the premier sign for accuracy of numerical results obtained. The approach realizing the new concept of direct automatical adaptive grid construction is suggested. The intellectual program provides high calculation accuracy and is simple in practical usage so that a physician receives the ability to prescribe treatment without any assistance of a specialist in mathematical modeling. The real possibility of controlling of the hyperthermia processes exists: the changes of hyperthermia region volume, of its depth and of the temperature levels are possible by means of changing of free convection boundary conditions on the tissue outer surface, of the power, the radius and the shape of laser beam.

The physical processes of the skin hyperthermia accompanying the tissue irradiation by visible laser light is discussed. The numerical model based on the program complex SFEMA takes into account the physical heterogeneity and the absorption power density distribution, which was obtained by the Monte Carlo method. The temperature distribution to boundary condition and laser beam radius was researched. The possibility to obtain the needed temperature distribution was shown.

The absence of satisfactory criteria for discrete model parameters choice during computer modeling of thermal processes of laser-biotissue interaction may be the premier sign for the accuracy of the numerical results obtained. The approach realizing the new concept of direct automatical adaptive grid construction is suggested. The intellectual program provides high calculation accuracy and is simple in practical usage so that a physician receives the ability to prescribe treatment without any assistance of a specialist in mathematical modeling.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The Monte Carlo method of statistical simulations was used to evaluate the effects of anisotropic scattering and refractive index mismatch at the boundaries of the medium on light and temperature distribution in the multilayered biotissues during laser irradiation. The influence of optical parameters of multilayered tissue on its stationary thermal response was examined by using an adaptive version of finite element solution of the heat conduction equation. Calculations were performed for two models of human skin and adjacent tissues for visible (five layer model) and UV (three layer model) ranges of wavelengths. The topic of this paper is especially pertinent to laser percutaneous irradiation of blood and laser PUVA therapy.