Aleksandra Baeva

Ms. Aleksandra Baeva


Research Focus & Metrics

Academic Career Length

4Years (2023-Present)

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

Representative Publications

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22 September 2023 in Materials
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Journal Article
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ADAnna Og Dikovska
Anna Og Dikovska
GAGenoveva Atanasova
Genoveva Atanasova
TDTina Dilova
Tina Dilova
ABAleksandra Baeva
Aleksandra Baeva
GAGeorgi Avdeev
Georgi Avdeev
NNNikolay Nedyalkov
Nikolay Nedyalkov
In this work, we present the fabrication of thin films/nanostructures of metals and metal oxides using picosecond laser ablation. Two sets of experiments were performed: the depositions were carried out in vacuum and in air at atmospheric pressure. The subjects of investigation were the noble metals Au and Pt and the metal oxides ZnO and TiO2. We studied and compared the phase composition, microstructure, morphology, and physicochemical state of the as-deposited samples’ surfaces in vacuum and in air. It was found that picosecond laser ablation performed in vacuum led to the fabrication of thin films with embedded and differently sized nanoparticles. The implementation of the same process in air at atmospheric pressure resulted in the fabrication of porous nanostructures composed of nanoparticles. The ablation of pure Pt metal in air led to the production of nanoparticles with an oxide shell. In addition, more defects were formed on the metal oxide surface when the samples were deposited in vacuum. Furthermore, the laser ablation process of pure Au metal in a picosecond regime in vacuum and in air was theoretically investigated using molecular dynamics simulation.

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Journal Article
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MGMargarita Gabrovska
Margarita Gabrovska
Dimitrinka NikolovaDimitrinka Nikolova
Dimitrinka Nikolova
Vojkan D RadonjićVojkan D Radonjić
Vojkan D Radonjić
DKDaniela Bogdanova Karashanova
Daniela Bogdanova Karashanova
ABAleksandra Baeva
Aleksandra Baeva
JKJugoslav Krstic
Jugoslav Krstic
Inspired by our finding that metallic Ni particles could be uniformly distributed on a reduced CeO2 surface and stabilized on Ce3+ sites, we suppose a possible improvement in the activity and selectivity of the MgNi/SiO2 vegetable oil hydrogenation catalyst by increasing the surface metal Ni availability via modification by ceria. The proposed approach involved the addition of a CeO2 modifier to the SiO2 carrier and as a catalyst component. Evaluation of the structure, reducibility, and surface and electronic states of the CeO2-doped MgNi/SiO2 catalyst was performed by means of the Powder X-ray diffraction (PXRD), Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS) combined with High-resolution transmission electron microscopy (HRTEM), Temperature-programmed reduction with hydrogen (H2-TPR), and H2-chemisortion techniques. So far, no studies related to this approach of designing Ni/SiO2 catalysts for the partial hydrogenation of vegetable oil have been reported. The added ceria impact was elucidated by comparing fatty acid compositions obtained by the catalysts at an iodine value of 80. In summary, tuning the hydrogenation performance of Ni-based catalysts can be achieved by structural reconstruction using 1 wt.% CeO2. The introduction mode changed the selectivity towards C18:1-cis and C18:0 fatty acids by applying ceria as a carrier modifier, while hydrogenation activity was improved upon ceria operation as the catalyst dopant.

25 November 2024 in Materials
Verified
Journal Article
Open access
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TDTina Dilova
Tina Dilova
ADAnna Og Dikovska
Anna Og Dikovska
ABAleksandra Baeva
Aleksandra Baeva
GAGenoveva Atanasova
Genoveva Atanasova
GAGeorgi Avdeev
Georgi Avdeev
NNNikolay Nedyalkov
Nikolay Nedyalkov
In this work, atmospheric pulsed laser deposition was used to prepare photosensitive elements. This technology is a practical and relatively inexpensive way of obtaining highly porous nanostructures composed of nanoparticles or nanoaggregates characterized by a large surface-to-volume ratio. Samples were produced via laser nanosecond or picosecond laser ablation of pure ZnO or mixed ZnO-TiO2 targets on quartz substrates with pre-deposited gold electrodes. The structure, morphology, optical, and electrical properties of the nanostructures obtained were studied regarding the sample composition and laser ablation regime applied. The ablation of a mixed ZnO-TiO2 target led to the fabrication of composite samples consisting of ZnO and Zn2TiO4 nanoparticles. The electrical properties of pure and composite samples were studied under exposure to UV light irradiation. It was found that the photosensitive properties of the samples depended on the ablation regime applied. The dark current measured for the nanosecond-deposited samples was a few nA, which was an order of magnitude larger compared to the picosecond-deposited samples. The value of the photogenerated current of the nanosecond-deposited samples was 103-times higher than that of the picosecond-deposited samples. This is due to the lower absorption of the picosecond-deposited samples, as well as to the presence of defect-related radiative recombination in the picosecond-deposited samples, which limits the photocurrent rise. The estimated rise and decay times were longer for the composite samples independently of the deposition regime applied.