Stefan Kolev Kolev

Bulgarian Academy of Sciences | BAS · Emil Djakov Institute of Electronics

The chemical interactions of two types of graphite and two types of carbon black (CB) with acetone, toluene, and phenol were studied in order to evaluate the influence of chemical treatment on the structure and morphology of the carbon phases. The experimental treatment of carbon phases was carried out at room temperature for 1 hour. The chemical a...

The interactions between Na+ or Mg2+ ions with different parts of single-stranded RNA molecules, namely, the oxygen atoms from the phosphate groups or the guanine base, in water solution have been studied using first-principles molecular dynamics. Sodium ions were found to be much more mobile than Mg2+ ions and readily underwent transitions between...

Thin films of TiO 2 doped with carbon were deposited on 15×25×1 mm ³ glass substrates by r.f. magnetron co-sputtering of TiO 2 target and carbon plates on their erosion zone in Ar + air atmosphere (0.5 Pa and 0.6 Pa, respectively). Two different process parameters were varied in different experiments: the total area of the carbon plates (84 mm ² ,...

The cover image is based on the Research Article Aluminized Enhanced Blast Explosive Based on Polysiloxane Binder by Stefan K. Kolev and Tsvetomir T. Tsonev https://doi.org/10.1002/prep.202100195.

The mesopores formation in zeolite crystals has long been considered to occur through the stochastic hydrolysis and removal of framework atoms. Here, we investigate the NH4F etching of representative small, medium, and large pore zeolites and show that the zeolite dissolution behavior, therefore the mesopore formation probability, is dominated by z...

Thin films of TiO2 doped with carbon were deposited on 15×25×1 mm 3 glass substrates by r.f. magnetron co-sputtering of TiO2 target and carbon plates on their erosion zone in Ar + air atmosphere (0.5 Pa and 0.6 Pa, respectively). Two different process parameters were varied in different experiments: the total area of the carbon plates (84 mm 2 , 56...

Drastic measures are taken in order to improve the properties of enhanced blast explosives. First, a binder with high reactivity as reducing agent is selected. The binder, platinum cure silicone, generates pyrophoric decomposition products in situ during the detonation. Arising problems with curing inhibition of the polymer are solved, as nanosized...

In the present work, the surface chemistry of reduced graphene oxide, modified with hydrocarbon, hydroxyl, aldehyde and carboxyl groups is studied by means of computational chemistry. The simulations by ab-initio molecular dynamics show that the reactions depend on the proximity of chemical groups and possibilities for H-atom transfer and gas evolu...

Drastic measures are taken in order to improve the properties of enhanced blast explosives. First, a binder with high reactivity as reducing agent is selected. The binder, platinum cure silicone, generates pyrophoric decomposition products in situ during the detonation. Silicon dioxide, the result of binder pyrolysis, plays the role of a catalyst f...

We modified single- and few-layer nano-sized graphene films deposited by pulsed laser deposition (PLD) on ∼300-nm-thick SiO 2 /Si substrates. The samples were irradiated by a UV C lamp (wavelength of 254 nm) for 15 and 30 minutes in air atmosphere. The light was directed almost parallel (about 2 - 2.5 arcdeg declination angle) to the films’ surface...

The aim of this work was to obtain graphene-like phases (defected graphene, graphene oxide and reduced graphene oxide) as fine suspensions by applying pulsed laser ablation (PLA) of micro-crystalline graphite suspension in water medium. The fundamental (λ = 1064 nm), second (λ = 532 nm), third (λ = 355 nm) and fourth harmonics (λ = 266 nm) of a Nd:...

The study aims to explore the effect of low fluence UV-C radiation on the structural quality of thin carbon films. We have modified single to few-layered nano-sized graphene-like films deposited by pulsed laser deposition (PLD) on ∼300 nm SiO2/Si substrates and additionally different hydrogenated amorphous carbon a-C:H, tetrahedral amorphous carbon...

The electric activities of cortical pyramidal neurons are supported by structurally stable, morphologically complex axo-dendritic trees. Anatomical differences between axons and dendrites in regard to their length or caliber reflect the underlying functional specializations, for input or output of neural information, respectively. For a proper asse...

The electric activities of cortical pyramidal neurons are supported by structurally stable, morphologically complex axo-dendritic trees. Anatomical differences between axons and dendrites in regard to their length or caliber reflect the underlying functional specializations, for input or output of neural information, respectively. For a proper asse...

We modified by UV C light single to few-layered nano-sized graphene films deposited by pulsed laser deposition (PLD) on ~300-nm SiO 2 /Si substrates. The samples were irradiated by UV C lamps (wavelength of 254 nm) for 15, 30, 60 and 90 minutes in air. The influence of the modification was evaluated by following the changes in the X-ray photoelectr...

We modified carbon black (CB) with a large surface area (ENSACO 350 GRANULAR) by acetone and further thermal treatment. The pristine and the modified CB were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD) and Raman spectroscopy. The acetone treatment increases the content...

In the present article, graphene complexes with out-of-plane organic substances triphenylmethyl radical, anion and cation are studied. Comparison is made with the similar closed-shell molecule (cyclohexa-2,5-dien-1-ylidenemethylene)dibenzene. The nearest contact in the complexes is realized between a hydrogen atom of the organic molecule and a carb...

The initial stages of deposition of graphene-like thin films have been studied by X-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectroscopy and ellipsometry. The deposition process has been performed by sublimation of amorphous carbon on 330 nm SiO2/ (001) Si substrates with surface area of 15× 15 mm². The sublimation proce...

The modification of Cabot Corporation SPHERON 5000 carbon black by thermal treatment has been studied by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy. The thermal annealing was performed at temperatures ranging from 500°C to 1150°C for 3 hours in an air-atmosphere. XPS established that th...

Pulsed laser deposition (PLD) of thin carbon films on SiO 2 /Si substrates was performed and the resulting films were examined by X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), Raman spectroscopy and ellipsometry. The deposition process was accomplished by laser ablation with Nd:YAG laser (third harmonic λ = 355 nm, pulse...

A recipe on how to engineer a band gap in the energy spectrum for the carriers in graphene is conveyed. It is supported by a series of numerical simulations inspired by an analytical result based on the opening of a band gap in periodically corrugated graphene, e.g. the buffer layer grown on SiC at high temperatures.

Phone (Stefan Kolev): +359 878 633801 https://www.linkedin.com/in/stefan-kolev-34070848/ ABSTRACT Solid state fuel-air EBX and TBX (enhanced blast and thermobaric explosives) have very promising features. They can combine superior air blast impulse with metal fragmentation and acceleration effects, thus enabling to create ordnance with improved eff...

Alkaline and alkaline earth ions, namely Na+, K+, Mg2+ and Ca2+, are critical for the stability, proper folding and functioning of RNA. Moreover, those metal ions help to facilitate macromolecular interactions as well as the formation of supramolecular structures (e.g. the ribosome and the ribozymes). Therefore, identifying the interactions between...

We present results on the deposition and characterization of defected graphene by the chemical vapor deposition (CVD) method. The source of carbon/carbon-containing radicals is thermally decomposed acetone (C2H6CO) in Ar main gas flow. The deposition takes place on (001) Si substrates at about 1150-11600C. We established by Raman spectroscopy the p...

The study of graphene is important because it is a promising material for a variety of applications in the electronic industry. In the present work, the properties of а 2D periodic graphene sheet are studied with the use of ab initio molecular dynamics. DFT in the generalized gradient approximation is used in order to carry out the dynamical simula...

We synthesized undoped as well as up to 6 at.% nitrogen (N) doped thin amorphous carbon (α-C) films by plasma- enhanced chemical vapor deposition (PECVD) method. The source of carbon/carbon containing radicals was benzene (C6H6) in Ar gas- mixture. The obtained thin films were studied by optical microscopy, X-ray powder diffraction, UV-VIS- NIR Spe...

High-energy irradiation of protic solvents can transiently introduce excess electrons that are implicated in a diverse range of reductive processes. Here we report the evolution of electron solvation in water and in alcohols following photodetachment from aqueous hydroxide or the corresponding alkoxides studied by two- and three-pulse femtosecond s...

Solid state fuel-air (enhanced blast or thermobaric) explosives have very promising features. They can combine superior air blast impulse with metal fragmentation and metal acceleration effects, thus enabling to create ordnance with improved effectiveness and combined modes of action on the targets. Despite the efforts for practical application, ho...

The interactions between sodium or magnesium ions and phosphate groups of the RNA backbone represented as dinucleotide fragment in water solution have been studied using ab initio Born - Oppenheimer molecular dynamics. All systems have been simulated at 300 K and 320 K. Sodium ions have higher mobility than the magnesium ions and readily change the...

Various hydrogen-bonded complexes of methanol with different proton accepting and proton donating molecules containing Cl, F, NH(2), OH, OR, and COOH functional groups have been modeled using DFT with hybrid B3LYP and M05-2X functionals. The latter functional was found to provide more accurate estimates of the structural and thermodynamic parameter...