Anastas S Nikolov - Academia.edu (original) (raw)

Uploads

Papers by Anastas S Nikolov

Journal of Molecular Structure

Nanomaterials, 2022

Our work presents, for the first time, a comprehensive study of the synthesis of fully metallic p... more Our work presents, for the first time, a comprehensive study of the synthesis of fully metallic platinum nanoparticles (Pt-NPs) involving the ablation process in double distilled water using a KrF excimer laser. To obtain detailed information on Pt-NP morphology and optical properties, prepared colloids were characterized using High Resolution Scanning Transmission Electron Microscopy (HR-STEM) with advanced capabilities for Energy Dispersive X-ray Analysis (EDX), UV/Vis optical spectroscopy, and Direct Analysis in Real Time—Mass Spectrometry (DART-MS). The influence of the applied laser fluence and laser repetition rate (RR) values on the characteristics of the obtained Pt-NPs and the ablation process, respectively, were also analyzed. Spherical and spherical-like nanoparticles exhibiting aggregation were produced. The Pt-NP mean size values were between 2.2 ± 1.2 nm and 4.0 ± 1.0 nm, while their interplanar distance measurements showed a face-centered cubic (FFC) Pt lattice (111),...

It is presented a method, by which it could be assessed the middle size of the monocrystal nanopa... more It is presented a method, by which it could be assessed the middle size of the monocrystal nanoparticles in oxidfree porous silicon. The surface to volume ratio of the structure is considered as a measure for the particles diameter. In order to obtain this ratio, the relative number of hydrogen and silicon atoms was independently measured via a combination of thermal effusion and gravimetry. The results were verified using nuclear scattering experiments and oxidative combustion. The type of the hydrides on the surface of the nanocrystals was investigated by means of thermal effusion and infrared spectroscopy. The size is calculated assuming a certain shape of the particles and a middle surface density of the silicon atoms. The results were compared with the available literature data. The dependence of the luminescence maximum position on the size of the particles basically confirms the theoretical predictions.

Materials Science and Engineering: B, 2019

Abstract The aim of our work was to obtain graphene-like phases (graphene oxide and reduced graph... more Abstract The aim of our work was to obtain graphene-like phases (graphene oxide and reduced graphene oxide) as fine suspensions by applying pulsed laser ablation to highly purified microcrystalline graphite targets immersed into a water medium. The fundamental wavelength, the second and the fourth harmonic wavelengths of a Nd:YAG laser system (λ = 1064 nm) were used. The morphology of the particles dispersed in water was studied by scanning electron microscopy. Their phase composition and structure were explored by SEM, Raman and XP spectroscopy, GIXRD, as well as TEM. We establish that besides of the main phases of reduced graphene oxide (rGO) with flakes of micro- to nano-sized area and graphite micro-particles, the colloids contain some graphene oxide and defected, multilayered and folded multilayered graphene. The spacing of {0 0 1} increases by about 5–

Applied Physics A, 2017

Nanostructures of noble metal were produced by pulsed laser ablation in liquid. A solid Ag target... more Nanostructures of noble metal were produced by pulsed laser ablation in liquid. A solid Ag target was immersed in double distilled water and a CuBr laser in a master oscillator—power amplifier configuration oscillating at 511 nm and emitting pulses with duration of 30 ns at a repetition rate of up to 20 kHz was employed to produce different colloids. The impact was studied of the laser pulse repetition rate and the beam scanning speed on the morphology of the nanostructures formed. Further, the optical extinction spectra of the colloids in the UV/VIS range were measured and used to make an indirect assessment of the changes in the shape and size distribution of the nanostructures. The transmission values in the near UV range were used to estimate the efficiency of the ablation process under the different experimental conditions implemented. A visualization of the nanostructures was made possible by transmission electron microscopy (TEM). The structure and phase composition of the nanoparticles were studied by high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED), while the alteration of the target surface caused by the impact of the high-repetition-rate laser illumination was investigated by X-ray photoelectron spectroscopy (XPS). The optimal conditions were determined yielding the highest efficiency in terms of amount of ablated material.

Journal of Molecular Structure, 1990

20th International Conference and School on Quantum Electronics: Laser Physics and Applications, 2019

Mixtures of micron to submicron complex carbon phases, namely, defective graphene, graphene-like ... more Mixtures of micron to submicron complex carbon phases, namely, defective graphene, graphene-like (multi-layered graphene, graphene oxide etc.), graphite flakes etc. as fine suspensions were obtained by pulsed laser ablation of highly purified microcrystalline graphite targets immersed in double distilled water. The fundamental wavelength (λ = 1064 nm) and the fourth harmonic (λFHG = 266 nm) of a Nd:YAG laser system (15 ns pulse duration, 10 Hz pulse repetition rate) were used in the fabrication process. The laser fluence value corresponding to the onset of the ablation process, the one initiating optical breakdown in water and an intermediate value were used for each of the wavelengths mentioned above. The morphology of the particles dispersed in water was studied by scanning electron microscopy (SEM). Their phase composition and structure were explored by Raman spectroscopy. It showed the presence of some traces of polymerized hydrocarbons (polystyrene, polybutadiene etc.) in addition to the main carbon phases: defected graphene, reduced graphene oxide and graphite.

Materials Science and Engineering: B

Abstract The aim of our work was to obtain graphene-like phases (graphene oxide and reduced graph... more Abstract The aim of our work was to obtain graphene-like phases (graphene oxide and reduced graphene oxide) as fine suspensions by applying pulsed laser ablation to highly purified microcrystalline graphite targets immersed into a water medium. The fundamental wavelength, the second and the fourth harmonic wavelengths of a Nd:YAG laser system (λ = 1064 nm) were used. The morphology of the particles dispersed in water was studied by scanning electron microscopy. Their phase composition and structure were explored by SEM, Raman and XP spectroscopy, GIXRD, as well as TEM. We establish that besides of the main phases of reduced graphene oxide (rGO) with flakes of micro- to nano-sized area and graphite micro-particles, the colloids contain some graphene oxide and defected, multilayered and folded multilayered graphene. The spacing of {0 0 1} increases by about 5–

Polymers

We report on a new approach toward a laser-assisted modification of biocompatible polydimethylsil... more We report on a new approach toward a laser-assisted modification of biocompatible polydimethylsiloxane (PDMS) elastomers relevant to the fabrication of stretchable multielectrode arrays (MEAs) devices for neural interfacing technologies. These applications require high-density electrode packaging to provide a high-resolution integrating system for neural stimulation and/or recording. Medical grade PDMS elastomers are highly flexible with low Young’s modulus < 1 MPa, which are similar to soft tissue (nerve, brain, muscles) among the other known biopolymers, and can easily adjust to the soft tissue curvatures. This property ensures tight contact between the electrodes and tissue and promotes intensive development of PDMS-based MEAs interfacing devices in the basic neuroscience, neural prosthetics, and hybrid bionic systems, connecting the human nervous system with electronic or robotic prostheses for restoring and treating neurological diseases. By using the UV harmonics 266 and 35...

Journal of Molecular Structure, 1990

Raman study of lead germanate vanadate single crystals has been reported for the. first time. Int... more Raman study of lead germanate vanadate single crystals has been reported for the. first time. Internal vibrations of germanate and vanadate ions have been mainly discussed. Group theory methods, polarization and frequencies of observed spectral bands and IR reflection spectra of mixed germanate-silicate crystals have been used to assign the observed lines and to make some conclusions about the ion positions in crystal structure.

Physica Status Solidi B-basic Solid State Physics, 1990

ABSTRACT A group-theoretical analysis of the vibrational spectrum of lead-germanate vanadate crys... more ABSTRACT A group-theoretical analysis of the vibrational spectrum of lead-germanate vanadate crystal is presented, extended with some remarks concerning positional disorder observed in the new X-ray study of this crystal. Raman spectra of the crystal studied are compared with the theoretical results as well as with infrared and Raman spectra of similar compounds.Es wird eine gruppentheoretische Analyse des Schwingungspektrums eines Blei-Vanadingermanat-Kristalls vorgestellt, ergänzt durch einige Anmerkungen über Positionsfehlordnungen, die bei Röntgenuntersuchungen dieses Kristalls festgestellt werden. Die Raman-Spektren des untersuchten Kristalls werden mit theoretisch gefundenen Ergebnissen, sowie mit Infrarot- und Raman-Spektren ähnlicher Verbindungen verglichen.

Journal of Molecular Structure

Nanomaterials, 2022

Our work presents, for the first time, a comprehensive study of the synthesis of fully metallic p... more Our work presents, for the first time, a comprehensive study of the synthesis of fully metallic platinum nanoparticles (Pt-NPs) involving the ablation process in double distilled water using a KrF excimer laser. To obtain detailed information on Pt-NP morphology and optical properties, prepared colloids were characterized using High Resolution Scanning Transmission Electron Microscopy (HR-STEM) with advanced capabilities for Energy Dispersive X-ray Analysis (EDX), UV/Vis optical spectroscopy, and Direct Analysis in Real Time—Mass Spectrometry (DART-MS). The influence of the applied laser fluence and laser repetition rate (RR) values on the characteristics of the obtained Pt-NPs and the ablation process, respectively, were also analyzed. Spherical and spherical-like nanoparticles exhibiting aggregation were produced. The Pt-NP mean size values were between 2.2 ± 1.2 nm and 4.0 ± 1.0 nm, while their interplanar distance measurements showed a face-centered cubic (FFC) Pt lattice (111),...

It is presented a method, by which it could be assessed the middle size of the monocrystal nanopa... more It is presented a method, by which it could be assessed the middle size of the monocrystal nanoparticles in oxidfree porous silicon. The surface to volume ratio of the structure is considered as a measure for the particles diameter. In order to obtain this ratio, the relative number of hydrogen and silicon atoms was independently measured via a combination of thermal effusion and gravimetry. The results were verified using nuclear scattering experiments and oxidative combustion. The type of the hydrides on the surface of the nanocrystals was investigated by means of thermal effusion and infrared spectroscopy. The size is calculated assuming a certain shape of the particles and a middle surface density of the silicon atoms. The results were compared with the available literature data. The dependence of the luminescence maximum position on the size of the particles basically confirms the theoretical predictions.

Materials Science and Engineering: B, 2019

Abstract The aim of our work was to obtain graphene-like phases (graphene oxide and reduced graph... more Abstract The aim of our work was to obtain graphene-like phases (graphene oxide and reduced graphene oxide) as fine suspensions by applying pulsed laser ablation to highly purified microcrystalline graphite targets immersed into a water medium. The fundamental wavelength, the second and the fourth harmonic wavelengths of a Nd:YAG laser system (λ = 1064 nm) were used. The morphology of the particles dispersed in water was studied by scanning electron microscopy. Their phase composition and structure were explored by SEM, Raman and XP spectroscopy, GIXRD, as well as TEM. We establish that besides of the main phases of reduced graphene oxide (rGO) with flakes of micro- to nano-sized area and graphite micro-particles, the colloids contain some graphene oxide and defected, multilayered and folded multilayered graphene. The spacing of {0 0 1} increases by about 5–

Applied Physics A, 2017

Nanostructures of noble metal were produced by pulsed laser ablation in liquid. A solid Ag target... more Nanostructures of noble metal were produced by pulsed laser ablation in liquid. A solid Ag target was immersed in double distilled water and a CuBr laser in a master oscillator—power amplifier configuration oscillating at 511 nm and emitting pulses with duration of 30 ns at a repetition rate of up to 20 kHz was employed to produce different colloids. The impact was studied of the laser pulse repetition rate and the beam scanning speed on the morphology of the nanostructures formed. Further, the optical extinction spectra of the colloids in the UV/VIS range were measured and used to make an indirect assessment of the changes in the shape and size distribution of the nanostructures. The transmission values in the near UV range were used to estimate the efficiency of the ablation process under the different experimental conditions implemented. A visualization of the nanostructures was made possible by transmission electron microscopy (TEM). The structure and phase composition of the nanoparticles were studied by high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED), while the alteration of the target surface caused by the impact of the high-repetition-rate laser illumination was investigated by X-ray photoelectron spectroscopy (XPS). The optimal conditions were determined yielding the highest efficiency in terms of amount of ablated material.

Journal of Molecular Structure, 1990

20th International Conference and School on Quantum Electronics: Laser Physics and Applications, 2019

Mixtures of micron to submicron complex carbon phases, namely, defective graphene, graphene-like ... more Mixtures of micron to submicron complex carbon phases, namely, defective graphene, graphene-like (multi-layered graphene, graphene oxide etc.), graphite flakes etc. as fine suspensions were obtained by pulsed laser ablation of highly purified microcrystalline graphite targets immersed in double distilled water. The fundamental wavelength (λ = 1064 nm) and the fourth harmonic (λFHG = 266 nm) of a Nd:YAG laser system (15 ns pulse duration, 10 Hz pulse repetition rate) were used in the fabrication process. The laser fluence value corresponding to the onset of the ablation process, the one initiating optical breakdown in water and an intermediate value were used for each of the wavelengths mentioned above. The morphology of the particles dispersed in water was studied by scanning electron microscopy (SEM). Their phase composition and structure were explored by Raman spectroscopy. It showed the presence of some traces of polymerized hydrocarbons (polystyrene, polybutadiene etc.) in addition to the main carbon phases: defected graphene, reduced graphene oxide and graphite.

Materials Science and Engineering: B

Abstract The aim of our work was to obtain graphene-like phases (graphene oxide and reduced graph... more Abstract The aim of our work was to obtain graphene-like phases (graphene oxide and reduced graphene oxide) as fine suspensions by applying pulsed laser ablation to highly purified microcrystalline graphite targets immersed into a water medium. The fundamental wavelength, the second and the fourth harmonic wavelengths of a Nd:YAG laser system (λ = 1064 nm) were used. The morphology of the particles dispersed in water was studied by scanning electron microscopy. Their phase composition and structure were explored by SEM, Raman and XP spectroscopy, GIXRD, as well as TEM. We establish that besides of the main phases of reduced graphene oxide (rGO) with flakes of micro- to nano-sized area and graphite micro-particles, the colloids contain some graphene oxide and defected, multilayered and folded multilayered graphene. The spacing of {0 0 1} increases by about 5–

Polymers

We report on a new approach toward a laser-assisted modification of biocompatible polydimethylsil... more We report on a new approach toward a laser-assisted modification of biocompatible polydimethylsiloxane (PDMS) elastomers relevant to the fabrication of stretchable multielectrode arrays (MEAs) devices for neural interfacing technologies. These applications require high-density electrode packaging to provide a high-resolution integrating system for neural stimulation and/or recording. Medical grade PDMS elastomers are highly flexible with low Young’s modulus < 1 MPa, which are similar to soft tissue (nerve, brain, muscles) among the other known biopolymers, and can easily adjust to the soft tissue curvatures. This property ensures tight contact between the electrodes and tissue and promotes intensive development of PDMS-based MEAs interfacing devices in the basic neuroscience, neural prosthetics, and hybrid bionic systems, connecting the human nervous system with electronic or robotic prostheses for restoring and treating neurological diseases. By using the UV harmonics 266 and 35...

Journal of Molecular Structure, 1990

Raman study of lead germanate vanadate single crystals has been reported for the. first time. Int... more Raman study of lead germanate vanadate single crystals has been reported for the. first time. Internal vibrations of germanate and vanadate ions have been mainly discussed. Group theory methods, polarization and frequencies of observed spectral bands and IR reflection spectra of mixed germanate-silicate crystals have been used to assign the observed lines and to make some conclusions about the ion positions in crystal structure.

Physica Status Solidi B-basic Solid State Physics, 1990

ABSTRACT A group-theoretical analysis of the vibrational spectrum of lead-germanate vanadate crys... more ABSTRACT A group-theoretical analysis of the vibrational spectrum of lead-germanate vanadate crystal is presented, extended with some remarks concerning positional disorder observed in the new X-ray study of this crystal. Raman spectra of the crystal studied are compared with the theoretical results as well as with infrared and Raman spectra of similar compounds.Es wird eine gruppentheoretische Analyse des Schwingungspektrums eines Blei-Vanadingermanat-Kristalls vorgestellt, ergänzt durch einige Anmerkungen über Positionsfehlordnungen, die bei Röntgenuntersuchungen dieses Kristalls festgestellt werden. Die Raman-Spektren des untersuchten Kristalls werden mit theoretisch gefundenen Ergebnissen, sowie mit Infrarot- und Raman-Spektren ähnlicher Verbindungen verglichen.