S. Valkov

Dr. S. Valkov

Institute of Electronics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee blvd., 1784 Sofia, Bulgaria
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Research Focus & Metrics

Academic Career Length

11Years (2016-Present)

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

Representative Publications

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10 September 2020 in Metals
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S. ValkovS. Valkov
S. Valkov
Maria OrmanovaMaria Ormanova
Maria Ormanova
Petеr PetrovPetеr Petrov
Petеr Petrov
During the last decades, electron-beam treatment technologies (EBTT) have been widely used for surface modification of metals and alloys. The EBT methods are known as accurate and efficient. They have many advantages in comparison with the conventional techniques, such as very short technological process time, uniform distribution of the energy of the electron beam, which allows a precise control of the beam parameters and formed structure and properties of the materials, etc. Moreover, electron-beam treatment technologies are a part of the additive techniques, which are known as modern methods for manufacturing of new materials with unique functional properties. Currently, modern trends in the surface treatment of metals and alloys are based on the combination of electron-beam technologies with other methods, such as thin film deposition, plasma nitriding, etc. This approach results in a significant improvement in the surface properties of the materials which opens new potential applications and can involve them into new industrial fields. This paper aims to summarize the topics related to the manufacturing and surface treatment of metals and alloys by means of electron-beam technologies. Based on a literature review, the development and growth of EBT are considered in details. The benefits of these technologies—as well as their combination with other methods—are extensively discussed.

1 August 2018 in Vacuum
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PPP. Petrov
P. Petrov
DDD. Dechev
D. Dechev
NIN. Ivanov
N. Ivanov
THT. Hikov
T. Hikov
S. ValkovS. Valkov
S. Valkov
AAA. Andreeva
A. Andreeva

1 December 2016 in Applied Surface Science
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Journal Article
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S. ValkovS. Valkov
S. Valkov
PPP. Petrov
P. Petrov
Rumyana LazarovaRumyana Lazarova
Rumyana Lazarova
RBR. Bezdushnyi
R. Bezdushnyi
DDD. Dechev
D. Dechev

13 August 2019 in Coatings
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S. ValkovS. Valkov
S. Valkov
SPStoyan Parshorov
Stoyan Parshorov
AAAndreana Andreeva
Andreana Andreeva
RBRuslan Bezdushnyi
Ruslan Bezdushnyi
Maria NikolovaMaria Nikolova
Maria Nikolova
Petеr PetrovPetеr Petrov
Petеr Petrov
This study examines the effect of electron beam treatment (EBT) of Co–Cr substrate on the film growth mechanism, mechanical properties, and surface topography of TiN/TiO2 coatings deposited by reactive magnetron sputtering. The obtained results and processes that occurred during the deposition are discussed in the context of crystallographic principles, and special attention is paid to the crystallographic orientation and growth mechanism studied by X-ray diffraction (XRD). The mechanical properties were investigated by means of nanoindentation and wear tests. The surface topography was evaluated using atomic force microscopy (AFM). The results obtained in the present study showed that polycrystalline TiN and anatase TiO2 phases were present in all cases. Electron beam treatment of Co–Cr substrate tended to form a reorientation of the microvolumes from (111) to (200) of TiN, leading to a change in the growth mechanism from three-dimensional (Volmer–Weber) to layer-by-layer (Frank–van der Merwe). It was found that the electron beam treatment process did not significantly affect the thickness of the coatings and the deposition rate. The treatment process led to an increase in surface roughness. The higher surface roughness after the EBT process should be appropriate to support cell growth and adhesion on the surface of the deposited bilayer coating. It was demonstrated that EBT of the substrate caused a decrease in hardness of the deposited coatings from 10 to 5 GPa. The observed decrease in hardness was attributed to the change in the preferred crystallographic orientation and film growth mechanism. The hardness of the bilayer coating after the application of EBT of the Co–Cr substrate was much closer to that of human bones, which means that severe stress shielding effect could not be expected. The evaluated coefficient of friction (COF) exhibited significantly lower values in the case of EBT of the substrate compared to the untreated Co–Cr material.

1 January 2020 in Materials Today: Proceedings
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Journal Article
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Maria NikolovaMaria Nikolova
Maria Nikolova
VNVeselina Nikolova
Veselina Nikolova
VIVeronika L. Ivanova
Veronika L. Ivanova
S. ValkovS. Valkov
S. Valkov
PPPeter Petrov
Peter Petrov
Margarita D. ApostolovaMargarita D. Apostolova
Margarita D. Apostolova

9 August 2024 in Sensors
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DDDimitar Dichev
Dimitar Dichev
DDDimitar Diakov
Dimitar Diakov
DDDimitar I. Diakov
Dimitar I. Diakov
S. ValkovS. Valkov
S. Valkov
Maria OrmanovaMaria Ormanova
Maria Ormanova
OKOleksandr Kupriyanov
Oleksandr Kupriyanov
This paper presents a new method for correction of dynamic errors occurring when measuring flat surfaces in the presence of mechanical effects. Mechanical effects cause inertial forces and moments that affect the moving components of measuring instruments, thereby causing dynamic errors. The study proposes a mathematical model, on the basis of which algorithms for correction of dynamic errors can be developed. The basic concept of the model is based on determining the optimal estimate in the current coordinate point on the basis of the theoretical model of the measured surface and the information from the measurement that contains errors caused by internal and external factors. Based on this model, an algorithm for real-time data processing has been developed. The algorithm works in “predictor-corrector” mode at each step of which the best estimate is obtained. The estimate is based on minimizing the variance of a random component in which the main values are formed from the accumulated statistical data of the error of the model and the measurement error. This paper presents the results of experimental studies, carried out with simulations of mechanical effects in four modes. The results confirm the high efficiency of the algorithm for high-accuracy measurement of flat surfaces in the presence of mechanical effects.