Ivalina Avramova

Ivalina Avramova
Bulgarian Academy of Sciences | BAS · Institute of General and Inorganic Chemistry

PhD

About

103
Publications
15,196
Reads
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1,087
Citations
Citations since 2016
59 Research Items
766 Citations
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200
Additional affiliations
February 2009 - February 2011
Bilkent University
Position
  • PostDoc Position
July 2001 - present
Bulgarian Academy of Sciences
Position
  • Professor (Associate)

Publications

Publications (103)
Article
Full-text available
The present study investigates the possibility of obtaining graphene-like phases (defected graphene, graphene oxide, and reduced graphene oxide) as fine suspensions by applying a novel pulsed laser ablation (PLA) approach in flow mode. Two types of suspensions of microcrystalline graphite in aqueous suspensions and two types of microcrystalline gra...
Article
The aim of the present research is to study some aspects of the carbon doping of TiO2 thin films and the influence of low temperature thermal annealing on the phase precipitation in thin films. Тhin films of heavily doped with carbon TiO2 (up to 3 at % C) were deposited on (15 × 25 × 1 mm) glass substrates by r.f. magnetron co-sputtering of TiO2 ta...
Article
Full-text available
Thin AlN films were grown using a Picosun R-200 atomic layer deposition (ALD) reactor on SiC surfaces with different crystallographic orientation: on-axis 4H-SiC (0001) and 8° off-axis 4H-SiC. TMA (trimethylaluminium) and NH3 were used as precursors while hydrogen and nitrogen plasma were applied for in-situ substrate cleaning. The substrate temper...
Article
Full-text available
Graphene films were grown by chemical vapor deposition on Cu foil. The obtained samples were characterized by Raman spectroscopy, ellipsometry, X-ray photoelectron spectroscopy and electron back-scatter diffraction. We discuss the time-dependent changes in the samples, estimate the thickness of emerging Cu2O beneath the graphene and check the orien...
Article
Full-text available
We report the synthesis of tungsten diselenide (WSe2) flakes and continuous layers using an atmospheric pressure thermally assisted conversion (TAC) method, where the tungsten (W) layers were pre-deposited by a magnetron sputtering system onto fused silica substrates. Optical microscopy (OM) and atomic force microscopy (AFM) mapping predominantly r...
Article
The aim of our work was to obtain graphene-like phases (defected graphene, graphene oxide and reduced graphene oxide) as fine suspensions by applying pulsed laser ablation (PLA) to microcrystalline graphite suspension in water medium. The fundamental (λ = 1064 nm), second (λ= 532 nm), third (λ= 355 nm) as well as the fourth harmonic (λ= 266 nm) of...
Article
Graphene is a material with great promise for several applications within electronics. However, using graphene in any such application requires its integration in a stack of thin layers of materials. The ideal structure of graphene has a fully saturated surface without any binding sites for chemisorption of growth species, making film growth on gra...
Article
Glasses with the mol % composition 20.1Na2O/23TiO2/23.1BaO/3Al2O3/7.6B2O3/17.4SiO2/5.8Fe2O3 were synthesized. During heat treatment at 550°C for 5 min to 7 h, cubic BaTiO3 crystallized. The microstructure of the glass-ceramics was studied by scanning electron microscopy. The average size of the crystalline particles varied from 190 to 790nm, depend...
Article
Full-text available
In this work, the feasibility of atomic layer deposition (ALD) to prepare transition metal (Ni-, Co- or Fe-) doped ZnO thin films have been studied. The effects of dopant on the structure, morphology and optical properties of films have been investigated by a number of various techniques: X-ray diffraction (XRD), X-ray photoelectron spectroscopy (X...
Article
Full-text available
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...
Article
Full-text available
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:...
Article
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...
Article
Full-text available
AlN thin films (∼25 nm) have been grown with a Beneq TFS-200 ALD reactor on Si (111) substrates. TMA (trimethylaluminum) and NH 3 were used as precursors. The substrate temperatures were 330°C, ALD cycles 550. In order to study the stoichiometry of AlN film the TMA and NH 3 doses (pulses) were varied from 60 to 180 ms and from 60 to 90 ms, respecti...
Article
Full-text available
The magneto-optical (MO) properties of ZnO / Ni transition metal oxide (TMO) nano-laminate structures prepared by Atomic Layer Deposition (ALD) have been investigated. The structural (XRD) and chemical composition (XPS) analysis confirm the ZnO formation and corresponding effect of Ni incorporation in the crystal lattice. The XPS identification of...
Article
Glass-ceramics with cubic BaTiO3 as a major and hexagonal BaTi1-xFexO3-δ as a second phase were prepared by crystallization at 560°C in a glass with the composition 20.1Na2O/23TiO2/23.1BaO/3Al2O3/7.6B2O3/17.4SiO2/5.8Fe2O3. X-ray photoelectron spectroscopy revealed presence of Ti⁴⁺ and Fe³⁺ ions in tetrahedral and octahedral coordination. Ba²⁺ occur...
Chapter
Glasses are synthesized in the system Na2O/BaO/TiO2/SiO2/B2O3/Al2O3 for different Na2O/Al2O3 ratios. X-ray photoelectron spectroscopy is utilized for the estimation of the valence states of titanium and the occurrence of solely Ti4+ is observed. The presence of bonds from the type Si-O-Al, Si-O-Si and Na-O-Si is detected in the glasses and it is co...
Article
We report the study of the physicochemical properties of the spinel CuCr2O4 and its photoactive effect with the hetero-system CuCr2O4/SnO2. The spinel CuCr2O4 presents a direct gap (Eg) of 1.39 eV, a stable behavior against photo-corrosion and a cathodic photocurrent which characteristic of type p conduction in conformity with the chrono-amperometr...
Article
Full-text available
Platinum diselenide (PtSe2), which belongs to the transition metals dichalcogenide (TMDCs) class of 2D materials, is characterized with a transition from semimetal to semiconductor with a thickness variation from bulk to monolayer and found in versatile applications especially in sensors and mid-infrared detectors. In this study we report the large...
Article
Full-text available
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...
Article
Full-text available
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...
Article
Full-text available
Abstract. Ni-, Co- and Fe-doped ZnO films were grown by atomic layer deposition on Si and glass substrates. The structures prepared were studied and characterized by XRD, XPS, ellipsometry and FTIR. The crystalline ZnO structure showed a strong dependence on the substrate used and the type of transition metal ion despite of the low doping levels....
Article
Full-text available
Thin AlN films were grown on Si substrates in a Beneq TFS-200 ALD reactor. The atomic layer deposition (ALD) process consisted of two half cycles – aluminum adsorption and nitridization separated by a purging step. TMA (trimethylaluminum) and NH 3 were used as precursors, and nitrogen (N 2 ), as a carrier gas. The pulse duration, purging time, depo...
Article
Full-text available
We report the deposition of ultrathin Al-doped ZnO (AZO) films by using atomic layer deposition (ALD) and results from X-ray photoelectron spectroscopy (XPS) and photoelectrical measurements. The AZO films were deposited on glass, silicon and polyethylene terephthalate (PET) substrates and their structural and photoelectrical properties were measur...
Article
Full-text available
The corrosion protective ability of the electrodeposited mixed nanocrystalline (CeO2)x(Al2O3)1-x layers has been studied in 0.1M HNO3 solution as a function of the changing ratio between CeO2, CeAlO3 and Al2O3 on the modified SS surface. It was ascertained that the mixed layer changes substantially the character of the cathodic corrosion reaction,...
Article
Gadolinium cuprate Gd2CuO4 was synthesized by nitrate route and its physical and electrochemical properties were investigated for the first time. The cuprate was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The Diffuse reflectance infrared Fourier transform (DRIFT) spectrum...
Article
Full-text available
The effect of Ag-doped aluminium oxide coatings deposited by magnetron sputtering method on the antibacterial efficiency against Gram-positive, Gram-negative bacteria and fungi has been investigated. The structure and composition of coatings were analysed by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), ph...
Conference Paper
Full-text available
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...
Conference Paper
Full-text available
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...
Article
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...
Poster
Full-text available
This poster is focused on the effect of Cu substitution on the crystal structure and photocatalytic activity of nano-spinel oxides Ni(1-x)CuxAl2O4 (x = 0.0-1.0). The as-prepared compounds were synthesized by the co-precipitation route and characterized by XRD, SEM, FTR, XPS and RDS. The catalytic activities were followed by UV-Vis spectroscopy and...
Article
Full-text available
The present work was devoted to study the catalytic activity of lanthanum and cerium oxides separately, deposited on γ-alumina in the reaction of decomposition of nitric oxide. The catalyst samples were prepared by the method of impregnation of γ-Al2O3 using solutions, containing nitrates of lanthanum and cerium. The prepared samples were calcined...
Article
Full-text available
Biofilm development, associated with the adherence of microbial cells on various solid substrates, has an adverse economic impact and is the main reason for the spreading of microbial infections. The present article reports novel findings about the anti-bioadhesion performance of four types of superhydrophobic soot coatings, deposited via combustio...
Preprint
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 SiO 2 / (001) Si substrates with surface area of 15x 15 mm 2. The sublimation pr...
Article
Full-text available
Glasses were prepared in the system (100 - x)(0.16Na2O/0.10MnO/0.74SiO2)/xFe2O3, (x = 15 and 25 in mol %) by the traditional melt-quenching technique. Some of them were subsequently crystallized at temperatures in the range from 520 to 700 °C for times from 10 min to 100 h. The valence states of Fe and Mn in selected glasses and glass-ceramics were...
Article
The present work focuses on the effect of Cu substitution on the crystal structure and photocatalytic activity of nano-spinel oxides Ni(1−x)CuxAl2O4 (x = 0.0–1.0). The synthesized compounds by co-precipitation route are characterized by X-ray diffraction, FT-IR, X-ray Photoelectron Spectroscopy, Scanning Electron Microscopy and UV–vis diffuse refle...
Article
Full-text available
Hydrolyzed plant biomass from willow, paulownia and straw was studied by using XPS and IR spectroscopy method in order to understand in depth their chemical composition and the nature of the functional groups on their surfaces. The surface concentration and the presence or absence of some functional groups and their amount on the surface of these m...
Article
Full-text available
Three different precipitating agents (NaOH, \(\hbox {NH}_{4}(\hbox {H})\hbox {CO}_{3}\) and \(\hbox {CO}(\hbox {NH}_{2})_{2}\)) have been applied for the hydrothermal synthesis of ZnO powder materials, aiming at obtaining various types of porosity and surface species on ZnO. The synthesis procedures were carried out in the presence and in the absen...
Article
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...
Article
Highly ordered TiO2 nanotube arrays (TNTA) have attracted much attention due to the excellent photocatalytic, optical and electrical properties. However, their absorption range is limited to ultraviolet (UV) spectrum only due to the wide band gap (3.2 eV). One of the strategies to overcome this problem is doping with boron and nitrogen. They are pr...
Poster
A simplified approach is applied to produce B,N-co-doped TNTA. It consists in combining the electrochemical boron doping method with subsequent annealing in N2 atmosphere. This method is environment-sparing compared with ammonia atmosphere. It is handier and less expensive than many others methods to implant nitrogen in TNTA.
Article
Full-text available
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...
Article
The method of pulsed electric current sintering (PECS) has been used to obtain dense boron carbide (B4C) and B4C-based composite materials containing tungsten boride (W2B5). To elucidate the role of the sintering additives and the mechanism of reactive densification, three types of materials have been obtained by PECS at 1850°C and 1900°C: “pure” B...
Article
The present study is devoted to the determination of the impact of the anodization of AA2024-T3 alloys in HCl, HNO3, H2SO4 or H3PO4 on the samples’ surface morphology and properties. Subsequent systematic assessments were performed by Scanning Electron Microscopy (SEM), Energy Dispersion X-Ray Spectroscopy (EDX) and X-ray Photoelectron Spectroscopy...
Article
Full-text available
In the present work, the adsorption of Ag+ ions on hydrolyzed plant biomass (willow, paulownia, wheat straw and maize stalks) was investigated. Chemical analyses were performed to establish the composition of the obtained materials. Adsorption mechanism, adsorption sites and specific surface areas of these materials were examined by BET analysis, I...
Article
Full-text available
Here we present results on the deposition of graphene and graphene-related phases by chemical vapour deposition (CVD) method. The source of carbon is thermally decomposed acetone (C2H6CO) in Ar main gas flow at different temperatures depending on the substrate used. The deposition of graphene and/or graphene related phases is carried out on commerc...
Article
A concise investigation was undertaken to determine the impact of transitional elements on the phosphate sealing of cerium oxide primer layers deposited on AA2024-T3 aircraft alloy. The cerium oxide primer layers were deposited electrochemically on preliminary treated alloy specimens under potentiostatic conditions. The subsequent phosphate sealing...
Article
Full-text available
Polyelectrolyte multilayers (PEMs) are well-defined nanoarchitectures with many potential applications, usually as biomaterial coatings. They possess excellent characteristics, such as fine tuning of thickness, stiffness, stability, morphology and topography. Hence they may exhibit special biological properties, such as mucoadhesion and local drug...
Article
The self-healing effect of electrochemically deposited CeO2-Ce2O3 films on stainless steel OC404 (SS) in 0.5 mol/L NaCl solution was studied. It was established that the corrosion potential of the steel, after covering it with CeO2-Ce2O3 layer and thermal treatment (i.e. potential of the system CeO2-Ce2O3/SSt.t.), was shifted sharply to a considera...
Article
Full-text available
Here we present results on the influence of low-energy \(\hbox {Ar}^{+}\) plasma irradiation of different duration and further annealing on highly oriented pyrolytical graphite (HOPG) layers. We used irradiation with a dose of \(10^{15}\;\hbox {Ar}^{+}/\hbox {cm}^{-2}\) intended to impact the upper 1 nm thick layer of the treated film. The influenc...
Article
Full-text available
We report on the study of deposition of carbon films on different substrates: (001) Si, (001) Si covered with 300 nm \(\hbox {SiO}_{2} (\hbox {Si/SiO}_{2})\) film as well as on (001) Si covered with \(\hbox {SiO}_{2}\) and diamond-like carbon layers (DLC) carried out by sublimation of pyrolytic carbon layers. It is established by Raman as well as b...
Article
Full-text available
The influence of copper doping (1.5 wt%) on the structural and on the photocatalytic properties of two different types of ZnO nanopowders (commercial one and ZnO activated by an original patented procedure) was studied. The crystallite size and the oxidation state of the dopant were investigated respectively by X-ray diffractometer (XRD), Electron...
Article
Full-text available
Three different ways of preparation: activation (ZA), precipitation method using two different ingredients (ZP, ZD) were used to obtain nanosize ZnO powders. The photocatalytic activity was tested in the reaction of oxidative discoloration of diazo dye solution. The ZnO nanoparticle powders were obtained and characterized by XRD, IRS, TG - DTA, XPS...
Article
Full-text available
Kinetic investigations for ozone conversion on three different series of zinc oxide catalysts, containing pure ZnO and doped with Mn or Cu one with dopant content less than 1 wt.% were carried out. The different samples were obtained from carbonate, nitrate and acetate precursors. The as prepared catalysts were characterized by AAS, XRD, IR, EPR an...
Article
Full-text available
Activated ZnO powder has been prepared by procedures involving first its dissolution in nitric acid, then simultaneous treatment by adding NH4OH and CO2 bubbling leading to precipitation as Zn(OH)CO3 (ZH) and further thermal decomposition of ZH at 400 °C. The gas evolution leads to formation of pores and increase in the specific surface area. Chemi...
Article
Full-text available
The present work is devoted to the mechanically assisted thermal synthesis of copper oxide nickel oxide mixtures obtained from copper and nickel oxalate precursors and to their catalytic properties towards oxidation of CO. DTA/DTG methods are used to show the effect of the mechanical activation on the thermal decomposition of copper and nickel oxal...
Article
The CeOx/Al2O3 thin films on stainless steel with different ceria loading were subjected to a.c. (square wave) pulses at various frequencies in the range 10− 3 to 100 kHz while recording X-ray photoelectron spectra. The resulting binding energy differences were derived from the frequency dependence of the corresponding Al2p, Ce3d and O1s peaks. At...
Article
Full-text available
Zn(1-x)NixAl2O4 (x = 0.0-1.0) spinels were prepared at 800 °C by co-precipitation method and characterized by infrared spectroscopy, X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. The specific surface area was determined by BET. SEM image showed nano sized spherical particles. XPS confirmed the valence states...
Article
Gold catalysts supported on tungstated zirconia (containing 5–20 wt% WO3) are prepared by cationic adsorption from aqueous solution of [Au(en)2]Cl3 complex. The materials are characterized by XRD, DR-UV–vis spectroscopy and XPS. The nature of the deposited gold species is studied by FT-IR spectroscopy of adsorbed CO. It is concluded that the gold p...