Ivalina Avramova Avramova

Prof. Ivalina Avramova Avramova

Institute of General and Inorganic Chemistry, Sofia, Sofia-Grad, Bulgaria
orcid

Research Focus & Metrics

Academic Career Length

6Years (2021-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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22 February 2023 in Nanomaterials
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DKDimitrina Petrova Kerina
Dimitrina Petrova Kerina
BNBlagovest Napoleonov
Blagovest Napoleonov
CMChau Nguyen Hong Minh
Chau Nguyen Hong Minh
Vera MarinovaVera Marinova
Vera Marinova
YLYUPIN LAN
YUPIN LAN
DDDimitre Dimitrov
Dimitre Dimitrov
In this paper, aluminum-doped zinc oxide (ZnO:Al or AZO) thin films are grown using atomic layer deposition (ALD) and the influence of postdeposition UV–ozone and thermal annealing treatments on the films’ properties are investigated. X-ray diffraction (XRD) revealed a polycrystalline wurtzite structure with a preferable (100) orientation. The crystal size increase after the thermal annealing is observed while UV–ozone exposure led to no significant change in crystallinity. The results of the X-ray photoelectron spectroscopy (XPS) analyses show that a higher amount of oxygen vacancies exists in the ZnO:Al after UV–ozone treatment, and that the ZnO:Al, after annealing, has a lower amount of oxygen vacancies. Important and practical applications of ZnO:Al (such as transparent conductive oxide layer) were found, and its electrical and optical properties demonstrate high tunability after postdeposition treatment, particularly after UV–Ozone exposure, offers a noninvasive and easy way to lower the sheet resistance values. At the same time, UV–Ozone treatment did not cause any significant changes to the polycrystalline structure, surface morphology, or optical properties of the AZO films.

19 February 2021 in Journal of Materials Science: Materials in Electronics
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Albena PaskalevaAlbena Paskaleva
Albena Paskaleva
BBBlagoy Spasov Blagoev
Blagoy Spasov Blagoev
PTPenka Terziyska
Penka Terziyska
VMVladimir Mehandzhiev
Vladimir Mehandzhiev
PTPetyr Tzvetkov
Petyr Tzvetkov
KGKostadinka Gesheva
Kostadinka Gesheva

16 November 2023 in Materials
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Teodor Ivanov MilenovTeodor Ivanov Milenov
Teodor Ivanov Milenov
DTDimitar Trifonov
Dimitar Trifonov
DKDobromir Antonov Kalchevski
Dobromir Antonov Kalchevski
SKStefan Kolev
Stefan Kolev
IAIvalina Avramova Avramova
Ivalina Avramova Avramova
EVEvgenia Valcheva
Evgenia Valcheva
Different nano-sized phases were synthesized using chemical vapor deposition (CVD) processes. The deposition took place on {001} Si substrates at about 1150–1160 °C. The carbon source was thermally decomposed acetone (CH3)2CO in a main gas flow of argon. We performed experiments at two ((CH3)2CO + Ar)/Ar) ratios and observed that two visually distinct types of layers were deposited after a one-hour deposition process. The first layer type, which appears more inhomogeneous, has areas of SiO2 (about 5% of the surface area substrates) beside shiny bright and rough paths, and its Raman spectrum corresponds to diamond-like carbon, was deposited at a (CH3)2CO+Ar)/Ar = 1/5 ratio. The second layer type, deposited at (CH3)2CO + Ar)/Ar = a 1/0 ratio, appears homogeneous and is very dark brown or black in color and its Raman spectrum pointed to defect-rich multilayered graphene. The performed structural studies reveal the presence of diamond and diamond polytypes and seldom SiC nanocrystals, as well as some non-continuously mixed SiC and graphene-like films. The performed molecular dynamics simulations show that there is no possibility of deposition of sp3-hybridized on sp2-hybridized carbon, but there are completely realistic possibilities of deposition of sp2- on sp2- and sp3- on sp3-hybridized carbon under different scenarios.

24 May 2024 in Coatings
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PRPeter Metodiev Rafailov
Peter Metodiev Rafailov
VMVladimir Mehandzhiev
Vladimir Mehandzhiev
PSPeter Sveshtarov
Peter Sveshtarov
BBBlagoy Spasov Blagoev
Blagoy Spasov Blagoev
PTPenka Terziyska
Penka Terziyska
SLShiuan Lin
Shiuan Lin
The deposition of thin uniform dielectric layers on graphene is important for its successful integration into electronic devices. We report on the atomic layer deposition (ALD) of Al2O3 nanofilms onto graphene grown by chemical vapor deposition onto copper foil. A pretreatment with deionized water (DI H2O) for graphene functionalization was carried out, and, subsequently, trimethylaluminum and DI H2O were used as precursors for the Al2O3 deposition process. The proper temperature regime for this process was adjusted by means of the ALD temperature window for Al2O3 deposition onto a Si substrate. The obtained Al2O3/graphene heterostructures were characterized by Raman and X-ray photoelectron spectroscopy, ellipsometry and atomic force and scanning electron microscopy. Samples of these heterostructures were transferred onto glass substrates by standard methods, with the Al2O3 coating serving as a protective layer during the transfer. Raman monitoring at every stage of the sample preparation and after the transfer enabled us to characterize the influence of the Al2O3 coating on the graphene film.

5 March 2025 in Applied Sciences
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PVPaunka Vassileva
Paunka Vassileva
IUIvan Uzunov
Ivan Uzunov
TPTeodora Petrova Popova
Teodora Petrova Popova
DVDimitrinka Voykova
Dimitrinka Voykova
IAIvalina Avramova Avramova
Ivalina Avramova Avramova
DMDimitar Mehandjiev
Dimitar Mehandjiev
The objective of this research was to investigate silver adsorption on biochars prepared by the carbonization of desiliconized rice husks and cotton fabric, and to elucidate the adsorption mechanism. The biochars were characterized using various instrumental techniques, including thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and low-temperature nitrogen adsorption. The adsorption process was studied under multiple parameters affecting silver adsorption and was best described by the pseudo-second-order kinetic model. Both the Langmuir and Freundlich isotherm models provided good correlations for the adsorption of silver ions onto the biochars. Thermodynamic analysis indicated that the adsorption of Ag+ ions was spontaneous and exothermic. XPS confirmed the presence of metallic silver (Ag0) in the biochars RHB and ARHB, suggesting that a reduction process occurred during silver adsorption. Additionally, in vitro studies were conducted to evaluate the antimicrobial activity of silver-loaded activated rice husk biochar against E. coli strains.

10 May 2023 in Materials
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TVTodorka Vladkova
Todorka Vladkova
ASAnna Staneva
Anna Staneva
IAIvalina Avramova Avramova
Ivalina Avramova Avramova
IIIlianaIvanova Ivanova
IlianaIvanova Ivanova
DGDilyana Gospodinova
Dilyana Gospodinova
The deposition of low-adhesive siloxane coatings is a current trend for the non-toxic control of bacterial growth and biofilm formation. Total elimination of biofilm formation has not been reported so far. The aim of this investigation was to study the ability of a non-toxic, natural, biologically active substance, such as fucoidan, to inhibit bacterial growth on similar medical coatings. The fucoidan amount was varied, and its impact on the bioadhesion-influencing surface characteristics, as well as on bacterial cell growth, was investigated. The inclusion of up to 3–4 wt.% brown algae-derived fucoidan in the coatings increases their inhibitory effect, more significantly on the Gram-positive bacterium S. aureus than on the Gram-negative bacterium Escherichia coli. The biological activity of the studied siloxane coatings was ascribed to the formation of a low-adhesive, biologically active surface top layer consisting of siloxane oil and dispersed water-soluble fucoidan particles. This is the first report on the antibacterial activity of fucoidan-containing medical siloxane coatings. The experimental results give reason to expect that relevantly selected, natural biologically active substances can be efficient in the non-toxic control of bacterial growth on medical devices and, as a result, medical device-associated infections.