WorldCat Identities

Ivanov, Ivan

Works: 52 works in 72 publications in 3 languages and 421 library holdings
Roles: Author, Editor, Collector, Other
Publication Timeline
Most widely held works by Ivan Ivanov
Fluid mechanics of surfactant and polymer solutions by V. M Starov( Book )

7 editions published between 2004 and 2014 in English and held by 198 WorldCat member libraries worldwide

Colloidal systems and dispersions are of great importance in oil recovery, waist water treatment, coating, food and beverage industry, pharmaceutical industry, medicine, environmental protection etc. Colloidal systems and dispersions are always multi-component and multiphase systems. In these systems at least one dimension is in a range of colloidal forces action: colloidal dispersions/emulsions are examples of three dimensional colloidal systems, while thin liquid films are examples of one dimensional colloidal systems. The contribution presented in this issue deals with flow, distribution and redistribution, coating and deposition of surfactant and polymer molecules in colloidal systems. The book presents reviews of recent advances and trends by well-know scientists and engineers in this area
Immune interferon : properties and clinical applications by R. G Tsanev( Book )

9 editions published between 2001 and 2002 in English and held by 148 WorldCat member libraries worldwide

This volume summarizes and analyzes the numerous scientific papers and reviews covering selected aspects of the structure, biological activities and clinical effects of immune interferon, also known as interferon-gamma (IFN-gamma)
Methodical development of a parallel kinematic positioning system based on monolithic structures with flexure hinges by Ivan Ivanov( )

2 editions published in 2016 in English and held by 18 WorldCat member libraries worldwide

Marin kielen sanaston kehitys 1900-luvulla by Ivan Ivanov( Book )

4 editions published in 1998 in Finnish and held by 6 WorldCat member libraries worldwide

In-situ terahertz optical Hall effect measurements of ambient effects on free charge carrier properties of epitaxial graphene by Sean Knight( )

2 editions published in 2017 in English and held by 3 WorldCat member libraries worldwide

Unraveling the doping-related charge carrier scattering mechanisms in two-dimensional materials such as graphene is vital for limiting parasitic electrical conductivity losses in future electronic applications. While electric field doping is well understood, assessment of mobility and density as a function of chemical doping remained a challenge thus far. In this work, we investigate the effects of cyclically exposing epitaxial graphene to controlled inert gases and ambient humidity conditions, while measuring the Lorentz force-induced birefringence in graphene at Terahertz frequencies in magnetic fields. This technique, previously identified as the optical analogue of the electrical Hall effect, permits here measurement of charge carrier type, density, and mobility in epitaxial graphene on silicon-face silicon carbide. We observe a distinct, nearly linear relationship between mobility and electron charge density, similar to field-effect induced changes measured in electrical Hall bar devices previously. The observed doping process is completely reversible and independent of the type of inert gas exposure
Varnenski Archeologičeski Muzej pătevoditel = Varna Archaeological Museum : guide by Archeologičeski Muzej (Warna)( Book )

2 editions published in 2006 in Bulgarian and held by 2 WorldCat member libraries worldwide

A comparative study of high-quality C-face and Si-face 3C-SiC(1 1 1) grown on off-oriented 4H-SiC substrates by Yuchen Shi( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

We present a comparative study of the C-face and Si-face of 3C-SiC(111) grown on off-oriented 4H-SiC substrates by the sublimation epitaxy. By the lateral enlargement method, we demonstrate that the high-quality bulk-like C-face 3C-SiC with thickness of ~1 mm can be grown over a large single domain without double positioning boundaries (DPBs), which are known to have a strongly negative impact on the electronic properties of the material. Moreover, the C-face sample exhibits a smoother surface with one unit cell height steps while the surface of the Si-face sample exhibits steps twice as high as on the C-face due to step-bunching. High-resolution XRD and low temperature photoluminescence measurements show that C-face 3C-SiC can reach the same high crystalline quality as the Si-face 3C-SiC. Furthermore, cross-section studies of the C- and Si-face 3C-SiC demonstrate that in both cases an initial homoepitaxial 4H-SiC layer followed by a polytype transition layer are formed prior to the formation and lateral expansion of 3C-SiC layer. However, the transition layer in the C-face sample is extending along the step-flow direction less than that on the Si-face sample, giving rise to a more fairly consistent crystalline quality 3C-SiC epilayer over the whole sample compared to the Si-face 3C-SiC where more defects appeared on the surface at the edge. This facilitates the lateral enlargement of 3C-SiC growth on hexagonal SiC substrates
Layer-number determination in graphene on SiC by reflectance mapping by Ivan Ivanov( )

1 edition published in 2014 in English and held by 1 WorldCat member library worldwide

We report a simple, handy and affordable optical approach for precise number-of-layers determination of graphene on SiC based on monitoring the power of the laser beam reflected from the sample (reflectance mapping) in a slightly modified micro-Raman setup. Reflectance mapping is compatible with simultaneous Raman mapping. We find experimentally that the reflectance of graphene on SiC normalized to the reflectivity of bare substrate (the contrast) increases linearly with similar to 1.7% per layer for up to 12 layers, in agreement with theory The wavelength dependence of the contrast in the visible is investigated using the concept of ideal fermions and compared with existing experimental data for the optical constants of graphene. We argue also that the observed contrast is insensitive to the doping condition of the sample, as well as to the type of sample (graphene on C- or Si-face of 4H or 6H SiC, hydrogen-intercalated graphene). The possibility to extend the precise layer counting to similar to 50 layers makes reflectivity mapping superior to low-energy electron microscopy (limited to similar to 10 layers) in quantitative evaluation of graphene on the C-face of SiC. The method is applicable for graphene on other insulating or semiconducting substrates
Considerably long carrier lifetimes in high-quality 3C-SiC(111) by Xuefei( )

1 edition published in 2012 in English and held by 1 WorldCat member library worldwide

As a challenge and consequence due to its metastable nature, cubic silicon carbide (3C-SiC) has only shown inferior material quality compared with the established hexagonal polytypes. We report on growth of 3C-SiC(111) having a state of the art semiconductor quality in the SiC polytype family. The x-ray diffraction and low temperature photoluminescence measurements show that the cubic structure can indeed reach a very high crystal quality. As an ultimate device property, this material demonstrates a measured carrier lifetime of 8.2 mu s which is comparable with the best carrier lifetime in 4 H-SiC layers. In a 760-mu m thick layer, we show that the interface recombination can be neglected since almost all excess carriers recombines before reaching the interface while the surface recombination significantly reduces the carrier lifetime. In fact, a comparison of experimental lifetimes with numerical simulations indicates that the real bulk lifetime in such high quality 3C-SiC is in the range of 10-15 mu s
Calibration on wide-ranging aluminum doping concentrations by photoluminescence in high-quality uncompensated p-type 4H-SiC by Satoshi Asada( )

1 edition published in 2017 in English and held by 1 WorldCat member library worldwide

Previous work has shown that the concentration of shallow dopants in a semiconductor can be estimated from the photoluminescence (PL) spectrum by comparing the intensity of the bound-to-the- dopant exciton emission to that of the free exciton. In this work, we study the low-temperature PL of high-quality uncompensated Al-doped p-type 4H-SiC and propose algorithms for determining the Al-doping concentration using the ratio of the Al-bound to free-exciton emission. We use three different cryogenic temperatures (2, 41, and 79 K) in order to cover the Al-doping range from mid 10(14) cm( -3) up to 10(18) cm( -3). The Al-bound exciton no-phonon lines and the strongest free-exciton replica are used as a measure of the bound-and free-exciton emissions at a given temperature, and clear linear relationships are obtained between their ratio and the Al-concentration at 2, 41, and 79 K. Since nitrogen is a common unintentional donor dopant in SiC, we also discuss the criteria allowing one to determine from the PL spectra whether a sample can be considered as uncompensated or not. Thus, the low-temperature PL provides a convenient non-destructive tool for the evaluation of the Al concentration in 4H-SiC, which probes the concentration locally and, therefore, can also be used for mapping the doping homogeneity. Published by AIP Publishing
CVD growth and properties of on-axis vanadium doped semi-insulating 4H-SiC epilayers by Robin Karhu( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

Highly resistive homoepitaxial layers of 4H-SiC have been grown on the Si-face of nominally on-axis, n-type substrates using chemical vapor deposition. Vanadium tetrachloride has been used as the V-dopant which is responsible for the high resistivity of the epilayers. 100% 4H-polytype was reproduced in the epilayers using the optimized on-axis growth process. The upper limit of vanadium tetrachloride flow rate was also established to achieve high resistivity epilayers free of 3C polytype inclusion. A resistivity of more than 1 x 10(5) Omega cm has been achieved in epilayers with a very low concentration of V (1 x 10(15) cm( -3)). Owing to the low concentration of V, superior epilayer structural quality was achieved compared to V-doped and standard high purity semi-insulating bulk grown material of similar resistivity. Epitaxial layers with varying vanadium tetrachloride flow have also been grown to study the influence of V concentration on the polytype stability, structural quality, and optical and electrical properties of epilayers. A clear correspondence has been observed in the flow-rates of vanadium tetrachloride, the atomic concentration of V, and electrical, optical, and structural properties of epilayers. Published under license by AIP Publishing
Growth optimization and applicability of thick on-axis SiC layers using sublimation epitaxy in vacuum by Valdas Jokubavicius( )

1 edition published in 2016 in English and held by 1 WorldCat member library worldwide

We demonstrate growth of thick SiC layers (100-200 µm) on nominally on-axis hexagonal substrates using sublimation epitaxy in vacuum (10 −5 mbar) at temperatures varying from 1700 to 1975 °C with growth rates up to 270 µm/h and 70 µm/h for 6H- and 4H-SiC, respectively. The stability of hexagonal polytypes are related to process growth parameters and temperature profile which can be engineered using different thermal insulation materials and adjustment of the induction coil position with respect to the graphite crucible. We show that there exists a range of growth rates for which single-hexagonal polytype free of foreign polytype inclusions can be maintained. Further on, foreign polytypes like 3C-SiC can be stabilized by moving out of the process window. The applicability of on-axis growth is demonstrated by growing a 200 µm thick homoepitaxial 6H-SiC layer co-doped with nitrogen and boron in a range of 10 18 cm −3 at a growth rate of about 270 µm/h. Such layers are of interest as a near UV to visible light converters in a monolithic white light emitting diode concept, where subsequent nitride-stack growth benefits from the on-axis orientation of the SiC layer
Understanding Graphene Response to Neutral and Charged Lead Species: Theory and Experiment by Ivan Shtepliuk( )

1 edition published in 2018 in English and held by 1 WorldCat member library worldwide

Deep understanding of binding of toxic Lead (Pb) species on the surface of two-dimensional materials is a required prerequisite for the development of next-generation sensors that can provide fast and real-time detection of critically low concentrations. Here we report atomistic insights into the Lead behavior on epitaxial graphene (Gr) on silicon carbide substrates by thorough complementary study of voltammetry, electrical characterization, Raman spectroscopy, and Density Functional Theory (DFT). It is verified that the epitaxial graphene exhibits quasi-reversible anode reactions in aqueous solutions, providing a well-defined redox peak for Pb species and good linearity over a concentration range from 1 nM to 1 mu M. The conductometric approach offers another way to investigate Lead adsorption, which is based on the formations of stable charge-transfer complexes affecting the p-type conductivity of epitaxial graphene. Our results suggest the adsorption ability of the epitaxial graphene towards divalent Lead ions is concentration-dependent and tends to saturate at higher concentrations. To elucidate the mechanisms responsible for Pb adsorption, we performed DFT calculations and estimated the solvent-mediated interaction between Lead species in different oxidative forms and graphene. Our results provide central information regarding the energetics and structure of Pb-graphene interacting complexes that underlay the adsorption mechanisms of neutral and divalent Lead species. Such a holistic understanding favors design and synthesis of new sensitive materials for water quality monitoring
Resolving mobility anisotropy in quasi-free-standing epitaxial graphene by terahertz optical Hall effect by Nerijus Armakavicius( )

1 edition published in 2021 in English and held by 1 WorldCat member library worldwide

In this work, we demonstrate the application of terahertz-optical Hall effect (THz-OHE) to determine directionally dependent free charge carrier properties of ambient-doped monolayer and quasi-freestanding-bilayer epitaxial graphene on 4H-SiC(0001). Directionally independent free hole mobility parameters are found for the monolayer graphene. In contrast, anisotropic hole mobility parameters with a lower mobility in direction perpendicular to the SiC surface steps and higher along the steps in quasifree-standing-bilayer graphene are determined for the first time. A combination of THz-OHE, nanoscale microscopy and optical spectroscopy techniques are used to investigate the origin of the anisotropy. Different defect densities and different number of graphene layers on the step edges and terraces are ruled out as possible causes. Scattering mechanisms related to doping variations at the step edges and terraces as a result of different interaction with the substrate and environment are discussed and also excluded. It is suggested that the step edges introduce intrinsic scattering in quasi-free-standing-bilayer graphene, that is manifested as a result of the higher ratio between mean free path and average terrace width parameters. The suggested scenario allows to reconcile existing differences in the literature regarding the anisotropic electrical transport in epitaxial graphene. (C) 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license
Exploring the Interface Landscape of Noble Metals on Epitaxial Graphene by Ivan Shtepliuk( )

1 edition published in 2021 in English and held by 1 WorldCat member library worldwide

Understanding the interaction between noble metals (NMs) and epitaxial graphene is essential for the design and fabrication of novel devices. Within this framework, a combined experimental and theoretical investigation of the effect of vapor-deposited NM (silver [Ag] and gold [Au]) nanostructures on the vibrational and electronic properties of monolayer epitaxial graphene (MLG) on 4H-SiC is presented. Large sets of Raman scattering data are analyzed using supervised classification and statistical methods. This analysis enables identification of the specific Raman fingerprints of Au- and Ag-decorated MLG originating from different dispersion interactions and charge transfer at the metal nanostructure/MLG interface. It is found that Raman scattering spectra of Au-decorated MLG feature a set of allowed phonon modes similar to those in pristine MLG, whereas the stronger Ag physisorption triggers an activation of defect-related phonon modes and electron doping of MLG. A principal component analysis (PCA) and linear discriminant analysis (LDA) are leveraged to highlight the features in phonon dispersion of MLG that emanate from the NM deposition process and to robustly classify large-scale Raman spectra of metal-decorated graphene. The present results can be advantageous for designing highly selective sensor arrays on MLG patches decorated with different metals
Excitation properties of the divacancy in 4H-SiC by Björn Magnusson( )

1 edition published in 2018 in English and held by 1 WorldCat member library worldwide

We investigate the quenching of the photoluminescence (PL) from the divacancy defect in 4H-SiC consisting of a nearest-neighbor silicon and carbon vacancies. The quenching occurs only when the PL is excited below certain photon energies (thresholds), which differ for the four different inequivalent divacancy configurations in 4H-SiC. An accurate theoretical ab initio calculation for the charge-transfer levels of the divacancy shows very good agreement between the position of the (0/- ) level with respect to the conduction band for each divacancy configuration and the corresponding experimentally observed threshold, allowing us to associate the PL decay with conversion of the divacancy from neutral to negative charge state due to capture of electrons photoionized from other defects (traps) by the excitation. Electron paramagnetic resonance measurements are conducted in the dark and under excitation similar to that used in the PL experiments and shed light on the possible origin of traps in the different samples. A simple model built on this concept agrees well with the experimentally observed decay curves
Spin-relaxation times exceeding seconds for color centers with strong spin-orbit coupling in SiC by Carmem M Gilardoni( )

1 edition published in 2020 in English and held by 1 WorldCat member library worldwide

Spin-active color centers in solids show good performance for quantum technologies. Several transition-metal defects in SiC offer compatibility with telecom and semiconductor industries. However, whether their strong spin-orbit coupling degrades their spin lifetimes is not clear. We show that a combination of a crystal-field with axial symmetry and spin-orbit coupling leads to a suppression of spin-lattice and spin-spin interactions, resulting in remarkably slow spin relaxation. Our optical measurements on an ensemble of Mo impurities in SiC show a spin lifetime T-1 of 2.4 s at 2 K
Bioelectrocatalysis on Anodized Epitaxial Graphene and Conventional Graphitic Interfaces by Mikhail Vagin( )

1 edition published in 2019 in English and held by 1 WorldCat member library worldwide

Graphitic materials exhibit significant anisotropy due to the difference in conductivity in a single layer and between adjacent layers. This anisotropy is manifested on epitaxial graphene (EG), which can be manipulated on the nanoscale in order to provide tailor-made properties. Insertion of defects into the EG lattice was utilized here for controllable surface modification with a model biocatalyst and the properties were quantified by both electrochemical and optical methods. A comparative evaluation of the electrode reaction kinetics on the enzyme-modified 2D material vs conventional carbon electrode materials revealed a significant enhancement of mediated bioelectrocatalysis at the nanoscale
Charge state control of the silicon vacancy and divacancy in silicon carbide by Nguyen T Son( )

1 edition published in 2021 in English and held by 1 WorldCat member library worldwide

Color centers in silicon carbide (SiC), such as the negative silicon vacancy (V-Si(-)) and neutral divacancy (VSiVC0), have recently been shown to be promising quantum bits (qubits) for a variety of applications in quantum communications and sensing. Considerable effort has been spent on improving the performance of these optical spin qubits, and the instability of their charge state is an important issue to be solved. Using electron paramagnetic resonance to monitor the charge state of dominant intrinsic defects in n-type, high-purity semi-insulating and p-type 4H-SiC, we reveal carrier compensation processes and the windows of the Fermi level that allow us to obtain stable V-Si(-) and VSiVC0 in equilibrium. We show that stable V-Si(-) and VSiVC0 ensembles can be obtained in n-type (p-type) via controlling the concentration of the Si vacancy (the C vacancy and the C antisite-vacancy pairs). The charge-state control of single V-Si(-) and VSiVC0 emitters is expected to be possible in pure p-type layers by controlling the concentration of the C vacancy. In ultrapure materials, optical repumping is required for charge state control of single emitters
Probing the uniformity of silver-doped epitaxial graphene by micro-Raman mapping by 8th South African Conference on Photonic Materials (SACPM)( )

1 edition published in 2020 in English and held by 1 WorldCat member library worldwide

We present a Raman spectroscopy study on epitaxial graphene decorated with thin Ag films (2-15 nm), which are deposited using magnetron sputtering. We find that the presence of Ag on the graphene surface induces doping, the uniformity and efficiency of which is determined by Ag nominal thickness. Deposition of Ag films with thicknesses up to 5 nm favors the effective electron transfer from Ag to epitaxial graphene. A significant redshift and broadening of the 2D peak are observed with increasing the Ag-layer thickness above 5 nm, which is indicative of large strain and doping fluctuations. We also observe a non-trivial linear growth of 2D/G peak intensity ratio with increasing D/G ratio for all Ag-decorated samples, which is explained by increase of peak amplitude due to surface enhanced Raman scattering and charged impurity-induced screening caused by the presence of Ag on the graphene surface
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Audience level: 0.70 (from 0.66 for In-situ te ... to 0.97 for In-situ te ...)

Fluid mechanics of surfactant and polymer solutions
Immune interferon : properties and clinical applications
Alternative Names
Ivanov, Ivan Gueorguiev