bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparative analysis of platelets adhesion to the surface of Ta-based ceramic coatings deposited by magnetron sputtering
Authors: Zykova A , Safonov V , Yakovin S , Dudin S , Melnikova G , Petrovskaya A , Tolstaya T , Kuznetsova T , Chizhik S A , Donkov N 
Published: June 2020

Abstract
The adhesion of platelets to the surface of implants and stents depends on the material’s properties, such as surface roughness, topography and wettability. The present study analyzes the composition and surface properties of nanostructured Ta, Ta2O5 and TaON coatings and their correlation with the adhesion of platelets. The surface morphology and topography were observed by atomic force microscopy and electron scanning microscopy; while the elemental distribution and chemical composition were analyzed by energy dispersive X-ray spectroscopy. The coated surfaces’ advancing contact angles were evaluated by tensiometric measurements. The surface free energy (SFE) was calculated by the Owens, Wendt, Rabel and Kaeble method. The results of in vitro tests demonstrated that the deposition of Ta-based coatings leads to a decrease in the platelets adhesion and agglomeration ability.
Effect of copper and silver doping on the antibacterial properties of magnetron-sputtered aluminium oxide coatings
Authors: Donkov N , Zykova A , Safonov V , Dudin S , Yakovin S , Kussovski V , Avramov L 
Published: June 2020

Abstract
Ag- and Cu- doped aluminium oxide coatings were deposited by magnetron sputtering and their structure and composition were analyzed by means of scanning electron microscopy (SEM) and photoelectron spectroscopy (XPS). The coatings’ antimicrobial properties and efficiency against representative bacterial strains of Gram-positive, Gramnegative bacteria and fungi were analyzed by in vitro tests. The results of the study suggest that Ag and Cu doped aluminium oxide coatings possess a combined bactericidal effect and demonstrate a promising potential for various medical applications.
Improvement of the photoinduced birefringence in PAZO azopolymer doped with ZnO via electrospray deposition
Authors: Mateev G , Marinov G , Nedelchev L , Nazarova D , Stoykova E , Babeva T 
Published: June 2020

Abstract
We present a study of the birefringence photoinduced in thin nanocomposite films of an azopolymer (PAZO) doped with different concentrations of nanoparticles (NPs) of ZnO with spherical shape and size in the range 40 – 100 nm. The nanocomposite thin films were prepared by electrospray deposition of ZnO over a thin azopolymer film with a thickness below 200 nm. The different NPs concentrations were obtained through different electrospray deposition times varied from 0 to 10 minutes. Birefringence was induced by a He-Cd laser at a wavelength of 442 nm and measured by a probe diode pumped solid state (DPSS) laser at 635 nm. The birefringence dependence on the ZnO NP deposition time reached its maximum for a deposition time of 90 s.
Formation and characterization of Al-Hf alloys by selective electron-beam surface alloying
Authors: Valkov S , Petrov P 
Published: June 2020

Abstract
We report electron-beam surface alloying of Al substrates with Hf. The Al substrates were covered by a Hf coating with a thickness of 2 μm; the samples were alloyed by means of a scanning electron beam with circular geometry of the beam deflection. The phase composition of the obtained specimens was studied by X-ray diffraction (XRD); their microstructure and chemical composition were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), respectively. The results showed that the phase composition did not depend on the speed of sample motion. However, their microstructure was significantly finer and more homogeneous in the case of the lower speed of motion V
1 = 0.5 cm/s in comparison with the higher speed V
2 = 1 cm/s.
Comparative measurements of solar UV irradiation at the high-mountain stations of BEO-Moussala (BG) and NAO-Rozhen (BG)
Authors: Tyutyundzhiev N , Angelov Ch , Lovchinov K , Nitchev Hr , Arsov T , Mutafov A 
Published: June 2020

Abstract
Damaging UV radiation is an important object of investigation related to its impact on biological species. Data acquired at high-altitude stations reveal dangerous events of incident UV radiation reaching the Earth surface. Continuous multi-UV spectral measurements by open-source equipment could further deepen the knowledge of solar light propagation and the events of radiation transfer and atmospheric absorption processes. This report describes recent results on high-resolution UVA, UVB, UVC measurements of solar UV radiation at the mountain stations in Bulgaria.
Antibacterial silver nanolayers for coatings on surgical and microsurgical instruments
Authors: Koev K , Donkov N , Naidenski H , Nikov R , Kusovski V , Nurgaliev T , Avramov L 
Published: June 2020

Abstract
In this paper, we describe the antibacterial action of Ag-doped Al2O3 nanolayers deposited by RF reactive magnetron sputtering on stainless-steel surgical and microsurgical instruments. Synthesizing Ag/Al2O3 protective coatings is necessary for suppressing the infections caused by pathogenic microorganisms following the application of surgical instruments. We further conducted microbiological studies on the action of the nanocomposite Ag/Al2O3 layers against Gram-positive and Gram-negative bacteria (Staphylococcus aureus and Escherichia coli). The microbiological studies conducted proved the antibacterial effect of the nanocomposite Ag/Al2O3 layers, the strongest effect against Escherichia coli and Staphylococcus aureus being observed after 48 hours of exposure. Also, the Ag/Al2O3 nanolayers showed no cytotoxic effect. Our experimental findings suggest a very promising application of such antibacterial Ag/Al2O3 nanolayers regarding the reduction of infections when stainless-steel surgical and microsurgical instruments are used.
Dielectric and magnetic properties of Sr3Co2Fe24O41 thin hexaferrite samples in the microwave range
Authors: Dankov P , Kolev S , Koutzarova T 
Published: June 2020

Abstract
We present studies on the changes of the dielectric properties of 0.7 – 1.2-mm thick-layers of Sr3Co2Fe24O41 Z-type hexaferrite in the frequency range 5 – 40 GHz; to the best of our knowledge, for the first time we used a combination of two methods – a resonance method, which yields infomation on the dielectric and magnetic anisotropies of the samples, and a broadband transmission-line method – covered coplanar and microstrip lines. We measured an increase of the dielectric constant and dielectric loss tangent above 20 GHz and a measurable anisotropy of the permittivity and permeability. The changes in the two parameters were also investigated (a magneto-electric effect was observed) in an external dc magnetic field in directions parallel and perpendicular to the sample at room temperature. The investigations presented are complex and intricate and should be considered as a first step in the characterization of thick Sr3Co2Fe24O41 Z-type hexaferrite slabs above 3 GHz up to the mm-wave range.
Dilute nitride InGaAsN and GaAsSbN layers grown by liquid-phase epitaxy for photovoltaic applications
Authors: Donchev V , Milanova M , Georgiev S , Kostov K L , Kirilov K 
Published: June 2020

Abstract
Dilute nitride InGaAsN and GaAsSbN layers are grown by low-temperature liquid-phase epitaxy (LPE) on GaAs substrates and characterized in view of application in solar cells. The composition of the layers is determined by energy-dispersive X-ray spectroscopy. X-ray photoelectron spectroscopy measurements confirm the Sb content and provide information about the chemical bonding of the N atoms. The band gap values at room temperature assessed from surface photo-voltage and photoluminescence measurements are in good agreement. The experimental results show that the layers exhibit reproducible properties, including a good optical quality and a photosensitivity red limit extended in comparison to GaAs down to about 1.33 – 1.37 eV for InGaAsN and 1.19 – 1.23 eV for GaAsSbN layers. The results obtained highlight the capacity of the LPE for growing dilute nitride layers with good optical quality for photovoltaic applications.
Hybrid Ag/ZnO nanostructures for SERS detection of ammonium nitrate
Authors: Koleva M E , Nedyalkov N N , Nikov Ru G , Nikov Ro G , Nuzhdin V I , Valeev V F , Rogov A M , Stepanov A L 
Published: June 2020

Abstract
Ag/ZnO composite nanostructures are produced by combined laser and ion implantation techniques. The ZnO layers are grown on SiO2 (001) and Al2O3 (r-cut) substrates by pulsed laser deposition (PLD) in vacuum and in oxygen ambient using a third-harmonic Nd:YAG laser. The ion implantation allows the introduction of Ag nanoparticles (NPs) in the surface of the ZnO matrix. These NPs are incorporated into the ZnO matrices to fabricate metal-semiconductor nanocomposites with the aim of manipulating their functionalities, exploiting the characteristics of both the matrix and the metal NPs. The composite samples are modified by laser annealing at 355 nm and 532 nm. The changes are investigated in the plasmon resonance absorption of the nanostructures before and after the annealing. The influence is explored of the different substrates used and the deposition conditions of ZnO growth on the properties of Ag/ZnO. The nanostructures obtained are efficient as SERS substrates for detection of ammonium nitrate under laser excitation at 633 nm. The SERS enhancement is attributed to the synergistic interactions between the plasmonic coupling among the surface embedded AgNPs and the enhanced charge transfer properties of the ZnO.
Light irradiation effect on the gas response of pure and noble-metal-doped ZnO sensors
Authors: Atanasova G , Dilova T , Dikovska A Og , Nedyalkov N N 
Published: June 2020

Abstract
Highly porous pure and noble metal (Ag, PdAg and Pd) doped ZnO nanostructures were fabricated by pulsed laser deposition (PLD) in air at atmospheric pressure (in open air). This technology leads to the formation of nanostructures composed of nanoparticles or nanoaggregates. The as-deposited nanostructures possess a large surface-to-volume ratio, which makes them suitable for gas-sensor applications. In this work, we demonstrated the response of pure ZnO and of Ag-ZnO, Pd-ZnO and PdAg-ZnO sensor elements to NH3, CO, ethanol, and acetone exposure under UV light irradiation. The effect was studied of simultaneous UV and red or green light irradiation on the sensor element’s response, selectivity, and response and recovery time. It was found that irradiation by UV and red light has the effect of improving the Ag-ZnO sensor’s response to CO exposure and suppressing its response to NH3, ethanol and acetone. The same behavior was exhibited by the pure ZnO sensor element irradiated simultaneously by UV and green light.
Comparison of ALD-grown thin ZnO films with various thicknesses for NO2 sensing
Authors: Boyadjiev S I , Georgieva V , Szilágyi I M , Vergov L , Georgieva B , Paskaleva A 
Published: June 2020

Abstract
Thin zinc oxide (ZnO) films of various thicknesses were characterized and compared in terms of their suitability to gas sensor applications. Applying atomic layer deposition (ALD), very thin ZnO films were deposited on quartz resonators, and their gas sensing properties were studied using a quartz crystal microbalance (QCM). The ZnO thin films were prepared using diethyl zinc and water as precursors. The crystal structure of the films was studied by X-ray diffraction (XRD), and their surface was observed by scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX) used to study the films’ composition. Films of thickness of ~10 – 80 nm were deposited on quartz resonators with Au electrodes and the QCM method was used to build highly sensitive gas sensors. These were tested for sensitivity to various concentrations of NO2. Although some of the films were very thin, they were sensitive to NO2 already at room temperature and could register reliably as low concentrations as 50 ppm, while the sorption was fully reversible and the sensors could be fully recovered. With the technology presented, manufacturing of QCM gas sensors is simple, fast and cost-effective, and suitable for application in energy-effective portable equipment for real-time monitoring of NO2 in the automotive industry or environmental protection.
Cryostat for cooling samples in the study of low-temperature structural and magnetic phase transitions by neutron diffraction
Authors: Popov E P , Chernikov A N , Beskrovnyi A I , Waliszewski J , Mirzayev M N 
Published: June 2020

Abstract
A vertical cryostat was developed built around a Sumitomo RDK-101D cold head. The cryostat is intended for investigating the structure and phase transformations of different materials via neutron diffraction experiments on samples under high vacuum of up to 10−5 mbar. A working temperature of the sample close to 2 K was reached. The drift diameter of the head is 54 mm, making it possible to cool samples with a height of 55 mm and 15 mm in diameter. Test measurements were conducted and illustrative spectra were recorded on the example of a sample of HoFeO3. The cryostat was designed and manufactured at the Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research.
Femtosecond laser modification of the optical properties of glass containing noble-metal nanoparticles
Authors: Nikov Ro , Nedyalkov N , Koleva M , Stankova N , Iordanova E , Yankov G , Aleksandrov L , Iordanova R 
Published: June 2020

Abstract
The paper presents results on femtosecond laser irradiation-induced modification of the optical properties of a composite material – gold nanoparticles embedded into a borosilicate glass host. The process is initiated by laser pulses delivered by a Ti:sapphire laser system with pulse duration of 35 fs. The glass samples are prepared by melt quenching with gold added as hydrogen tetrachloroaurate (III) hydrate to the initial composition. Post-fabrication annealing leads to a homogeneous formation of nanoparticles in the glass; varying the annealing parameters results in producing nanoparticles with different sizes and shapes. The laser irradiation of the samples induces significant modification of the optical spectra of the glass through changes of the nanoparticles characteristics. The effects are studied of the laser fluence, laser wavelength and laser pulses number. The heat diffusion equation is applied to estimate the temperature evolution and explain the modifications observed. The results demonstrate this technique’s efficiency in modifying the nanoparticles properties with a high 3D spatial resolution, which can be useful in fabrication of integrated optical systems.
Ultra-fast laser surface texturing of β-tricalcium phosphate (β-TCP) ceramics for bone-tissue engineering applications
Authors: Daskalova A , Lasgorceix M , Bliznakova I , Angelova L , Hocquet S , Leriche A , Trifonov A , Buchvarov I 
Published: June 2020

Abstract
β-tricalcium phosphate (β-TCP) has provoked particular attention as graft for bone regeneration applications due to its excellent biocompatibility and biodegradability. In this work, we investigated the interaction of femtosecond laser radiation with β-TCP pellets by varying the output laser parameters in order to estimate their influence on the surface roughness and on the morphological and topographical properties of the substrate before and after laser treatment. Femtosecond laser micro-processing for pulse duration of τ = 30 fs and 130 fs was performed by varying the number of laser pulses N = 1 – 100, at λ = 800 nm and a variable repetition rate. The microstructural changes induced were characterized by confocal microscopy. Comparing the experimental results, we concluded that the femtosecond laser method can be applied for biomaterials surface functionalization with a high-level of precision.
Preliminary results on non-linear effects in Au-ion-doped glass materials irradiated by femtosecond laser pulses
Authors: Yankov G , Iordanova E , Nedyalkov N , Zamfirescu M 
Published: June 2020

Abstract
Our research was motivated by the specific properties of noble-metal nanoparticles and their wide applications. The resonance frequency for noble-metal nanostructures is in the near-UV and visible spectral ranges, where most of the commercially-available lasers oscillate. This makes these materials attractive candidates for studying their properties in view of efficient applications. We investigated filaments formation in Au-ion-doped glass materials, transparent in the visible range, during irradiation by femtosecond laser pulses. Second harmonic generation in the media was observed as well. This proved the formation of polycrystalline structures inside the media after femtosecond laser radiation. Further, self-phase modulation and continuum were observed. Thus, the nonlinearity of the media is higher than that of glass not doped with noble-metal particles. The nonlinear effects in the samples were investigated in terms of the laser beam parameters. The laser energy applied was between 10 – 40 μJ. The wavelengths used were in the range 240 – 2600 nm, as generated by an optical parametric amplifier system (TOPAS). The regenerative Ti:Sapphire amplified laser system emits at a central wavelength of 800 nm with a pulse duration of 35 fs and 1-kHz repetition rate.
Measurement and control of the substrate temperature in vertical graphene nanosheets deposition
Authors: Vachkov V , Kiss’ovski Zh 
Published: June 2020

Abstract
The characteristics of the microwave surface-wave plasma discharge at atmospheric pressure and the control of the gas mixture (Ar/H2/CH4) in the deposition chamber, together with the temperature of the metallic substrate, are important parameters in the processes of deposition of vertical graphene nanosheets. Since obtaining carbon nanostructures necessitates regulating the substrate temperature in the range 550 – 980 °C, we developed an electronic system based on an Arduino Uno microcontroller. It was designed to automatically measure and control the temperature of the substrate heater with the capability of varying smoothly the temperature by a PID-regulator. The measurements were carried out by a K-type thermocouple, whose hot end was placed at the point of measuring the temperature. The resulting thermoelectric voltage was amplified by a MAX 31855 amplifier, followed by processing by the microcontroller and subsequent determination of the temperature. This system offers the possibility of controlling accurately the temperature as required by the regime of deposition.
Effect of the inert/reactive gases ratio and bias voltage on the tribological properties of VN coatings
Authors: Rabadzhiyska S , Ormanova M , Ivanov N , Petrov P 
Published: June 2020

Abstract
Vanadium nitride (VN) thin films were deposited on 304L high-speed stainless steel (HSS) specimens using a DC reactive magnetron sputtering system. The experiments were carried out with a varying ratio of reactive/inert gases of 1.7, 2.3 and 3 and a negative substrate bias of –30 V, –40 V and –50 V. Grazing incidence X-ray diffraction was used to characterize the structure of the layers produced. The coatings’ roughness and tribological behavior was evaluated.
Modification of carbon black by thermal treatment in air atmosphere
Authors: Milenov T , Avramova I , Avdeev G , Mladenoff J , Pishinkov D , Genkov K , Zyapkov A , Russev S , Nikolov A , Stankova N , Velikova R , Kolev S , Valcheva E 
Published: June 2020

Abstract
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 of oxygen-containing radicals in CB. The thermal annealing was performed at temperatures ranging from 250 °C to 1080 °C for three hours in air atmosphere. The powder XRD patterns revealed that the broad complex peak centered at about 2θ = 24.7 – 24.8°, which arises from graphitic-ordered sp2-hybridized carbon, shifts to its usual position at 2θ = 26.2° as the annealing temperature is increased. We concluded that the above results pointed to a relative decrease in the number of 3D graphitic nano-crystals and an increase in the predominantly 2D ones. The Raman studies confirmed the above conclusions.
Structural study of thick hexaferrite films
Authors: Koutzarova T , Georgieva B , Kolev S , Ghelev Ch , Krezhov K , Kovacheva D , Vertruyen B , Closset R , Tran L-M , Zaleski A 
Published: June 2020

Abstract
We present details of the microstructural properties of Y- (Ba2Mg2Fe12O22, Ba0.5Sr1.5Zn2Fe12O22, Ba0.5Sr1.5Zn2Al0.08Fe11.92O22) and Z-type (Sr3Co2Fe24O41) hexaferrite thick films deposited by screen printing and drop casting on unpolished polycrystalline Al2O3 substrates. The hexaferrites thick films obtained by drop casting exhibited considerable roughness and porousness compared with those obtained by screen printing. We found that the powders’ morphology significantly affects the microstructure of the thick films formed by screen printing. The microstructural analysis of the thick films shows that their microstructure differs from that of the powders. Further, during the annealing process the grains in the thick films grow and form hexagonal particles, the latter having the largest size, best shape and being best observed in the case of the Ba2Mg2Fe12O22 film.
Introduction to KAON2019 – Experiments –
Authors: Yamanaka T 
Published: June 2020

Abstract
The KAON2019 is the 11th conference in the series which started in 1988. Many kaon experiments have evolved during these years. In this talk, challenges and developments of the experiments for Re(ϵ
′/ϵ) and rare

K
→
π
ν

ν
¯

decays are reviewed.
CP violation in beauty and charm at LHCb
Authors: Romero Lamas M 
Published: June 2020

Abstract
Precision measurements of CP violating observables in the decays of b and c hadrons are powerful probes to search for physics beyond the Standard Model. The most recent results on CP violation in the decay, mixing and interference of both b and c hadrons obtained by the LHCb Collaboration with Run I and years 2015-2016 of Run II are presented, including the first observation of CP violation in the charm system. In particular world best constraints and world first measurements are provided for CKM elements, unitarity angles and charm parameters. Prospects for future sensitivities are also discussed.
K → ππ decay, ε
′ and the RBC-UKQCD kaon physics program
Authors: Christ N H 
Published: June 2020

Abstract
An overview of the kaon physics program of the RBC and UKQCD collaborations will be presented with a focus on the lattice calculation of K → ππ decay and the direct CP violation parameter ε
′. We will describe substantial improvements to our earlier 2015 K → ππ calculation, including the use of three independent ππ interpolating operators and the results we obtain for I = 0 ππ scattering for energies at and below the kaon mass. While the new result for ϵ
′ is not yet complete, the enhanced statistics and improved analysis that underlies our expanded calculation will be presented.
Latest Results on Lattice Calculation Concerning K → π
ℓ
+
ℓ
− Decays
Authors: Boyle P , Jüttner A , HÓgáin F Ó , Portelli A 
Published: June 2020

Abstract
The K → π
ℓ
+
ℓ
− decay is a flavor changing neutral current process which is forbidden at tree level in the Standard Model. This suppression causes the decay to be sensitive to potential New Physics. The decay channels are dominated by long-distance contributions, which require non-perturbative methods of investigation. Previous lattice calculations by the RBC and UKQCD collaborations, at unphysical kaon/pion masses, have successfully extracted the matrix elements needed to describe the form factor of the decays. A new lattice calculation, on a gauge configuration with m

π
≈ 140 MeV and m

K
≈ 500 MeV, is underway and will be discussed here.