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Yakimova, Rositsa
Alternative names
Publications (10 of 399) Show all publications
Shi, Y., Zakharov, A. A., Ivanov, I. G., Yazdi, G. R., Jokubavicius, V., Syväjärvi, M., . . . Sun, J. (2018). Elimination of step bunching in the growth of large-area monolayer and multilayer graphene on off-axis 3CSiC (111). Carbon, 140, 533-542
Open this publication in new window or tab >>Elimination of step bunching in the growth of large-area monolayer and multilayer graphene on off-axis 3CSiC (111)
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2018 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 140, p. 533-542Article in journal (Refereed) Published
Abstract [en]

Multilayer graphene has exhibited distinct electronic properties such as the tunable bandgap for optoelectronic applications. Among all graphene growth techniques, thermal decomposition of SiC is regarded as a promising method for production of device-quality graphene. However, it is still very challenging to grow uniform graphene over a large-area, especially multilayer graphene. One of the main obstacles is the occurrence of step bunching on the SiC surface, which significantly influences the formation process and the uniformity of the multilayer graphene. In this work, we have systematically studied the growth of monolayer and multilayer graphene on off-axis 3CSiC(111). Taking advantage of the synergistic effect of periodic SiC step edges as graphene nucleation sites and the unique thermal decomposition energy of 3CSiC steps, we demonstrate that the step bunching can be fully eliminated during graphene growth and large-area monolayer, bilayer, and four-layer graphene can be controllably obtained on high-quality off-axis 3CSiC(111) surface. The low energy electron microscopy results demonstrate that a uniform four-layer graphene has been grown over areas of tens of square micrometers, which opens the possibility to tune the bandgap for optoelectronic devices. Furthermore, a model for graphene growth along with the step bunching elimination is proposed.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-151054 (URN)10.1016/j.carbon.2018.08.042 (DOI)000450120200057 ()
Note

Funding agencies: Swedish Research Council (Vetenskapsradet) [621-2014-5461, 621-2014-5825]; Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) [2016-00559]; Swedish Foundation for International Cooperation in Research and Higher 

Available from: 2018-09-12 Created: 2018-09-12 Last updated: 2018-12-13
Nachawaty, A., Yang, M., Nanot, S., Kazazis, D., Yakimova, R., Escoffier, W. & Jouault, B. (2018). Large nonlocality in macroscopic Hall bars made of epitaxial graphene. Physical Review B, 98(4), Article ID 045403.
Open this publication in new window or tab >>Large nonlocality in macroscopic Hall bars made of epitaxial graphene
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 4, article id 045403Article in journal (Refereed) Published
Abstract [en]

We report on nonlocal transport in large-scale epitaxial graphene on silicon carbide under an applied external magnetic field. The nonlocality is related to the emergence of the quantum Hall regime and persists up to the millimeter scale. The nonlocal resistance reaches values comparable to the local (Hall and longitudinal) resistances. At moderate magnetic fields, it is almost independent on the in-plane component of the magnetic field, which suggests that spin currents are not at play. The nonlocality cannot be explained by thermoelectric effects without assuming extraordinary large Nernst and Ettingshausen coefficients. A model based on counterpropagating edge states backscattered by the bulk reproduces quite well the experimental data.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-149682 (URN)10.1103/PhysRevB.98.045403 (DOI)000437110900005 ()
Note

Funding Agencies|French Agence Nationale de la Recherche [ANR-16-CE09-0016]; grant NEXT [ANR-10-LABX-0037]

Available from: 2018-07-25 Created: 2018-07-25 Last updated: 2018-08-14
Shtepliuk, I. I., Vagin, M., Ivanov, I. G., Iakimov, T., Yazdi, G. & Yakimova, R. (2018). Lead (Pb) interfacing with epitaxial graphene. Physical Chemistry, Chemical Physics - PCCP, 20(25), 17105-17116
Open this publication in new window or tab >>Lead (Pb) interfacing with epitaxial graphene
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2018 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 25, p. 17105-17116Article in journal (Refereed) Published
Abstract [en]

Here, we report the electrochemical deposition of lead (Pb) as a model metal on epitaxial graphene fabricated on silicon carbide (Gr/SiC). The kinetics of electrodeposition and morphological characteristics of the deposits were evaluated by complementary electrochemical, physical and computational methods. The use of Gr/SiC as an electrode allowed the tracking of lead-associated redox conversions. The analysis of current transients passed during the deposition revealed an instantaneous nucleation mechanism controlled by convergent mass transport on the nuclei locally randomly distributed on epitaxial graphene. This key observation of the deposit topology was confirmed by low values of the experimentally-estimated apparent diffusion coefficient, Raman spectroscopy and scanning electron microscopy (SEM) studies. First principles calculations showed that the nucleation of Pb clusters on the graphene surface leads to weakening of the interaction strength of the metal-graphene complex, and only spatially separated Pb adatoms adsorbed on bridge and/or edge-plane sites can affect the vibrational properties of graphene. We expect that the lead adatoms can merge in large metallic clusters only at defect sites that reinforce the metal-graphene interactions. Our findings provide valuable insights into both heavy metal ion electrochemical analysis and metal electroplating on graphene interfaces that are important for designing effective detectors of toxic heavy metals.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-149854 (URN)10.1039/c8cp01814f (DOI)000436571800024 ()29896595 (PubMedID)
Note

Funding Agencies|VR grant [621-2014-5805]; SSF [SSF GMT14-0077, SSF RMA15-0024]; Angpanneforeningens Forskningsstiftelse [16-541]

Available from: 2018-08-02 Created: 2018-08-02 Last updated: 2018-08-20
Jokubavicius, V., Syväjärvi, M. & Yakimova, R. (2018). Silicon Carbide Surface Cleaning and Etching. In: Konstantinos Zekentes and Konstantin Vasilevskiy (Ed.), Advancing Silicon Carbide Electronics Technology I: (pp. 1-26). Materials Research Forum LLC
Open this publication in new window or tab >>Silicon Carbide Surface Cleaning and Etching
2018 (English)In: Advancing Silicon Carbide Electronics Technology I / [ed] Konstantinos Zekentes and Konstantin Vasilevskiy, Materials Research Forum LLC , 2018, p. 1-26Chapter in book (Refereed)
Abstract [en]

Silicon carbide (SiC) surface cleaning and etching (wet, electrochemical, thermal) are important technological processes in preparation of SiC wafers for crystal growth, defect analysis or device processing. While removal of organic, particulate and metallic contaminants by chemical cleaning is a routine process in research and industrial production, the etching which, in addition to structural defects analysis, can also be used to modify wafer surface structure, is very interesting for development of innovative device concepts. In this book chapter we review SiC chemical cleaning and etching procedures and present perspectives of SiC etching for new device development.

Place, publisher, year, edition, pages
Materials Research Forum LLC, 2018
Series
Materials Research Foundations, ISSN 2471-8890, E-ISSN 2471-8904 ; 37
Keywords
Silicon Carbide, Chemical Cleaning, Wet Etching, Electrochemical Etching, Porous SiC
Identifiers
urn:nbn:se:liu:diva-151048 (URN)10.21741/9781945291852-1 (DOI)9781945291845 (ISBN)9781945291852 (ISBN)
Available from: 2018-09-11 Created: 2018-09-11 Last updated: 2018-09-24Bibliographically approved
Shavanova, K., Bakakina, Y., Burkova, I., Shtepliuk, I., Viter, R., Ubelis, A., . . . Khranovskyy, V. (2016). Application of 2D Non-Graphene Materials and 2D Oxide Nanostructures for Biosensing Technology. Sensors, 16(2)
Open this publication in new window or tab >>Application of 2D Non-Graphene Materials and 2D Oxide Nanostructures for Biosensing Technology
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2016 (English)In: Sensors, ISSN 1424-8220, E-ISSN 1424-8220, Vol. 16, no 2Article, review/survey (Refereed) Published
Abstract [en]

The discovery of graphene and its unique properties has inspired researchers to try to invent other two-dimensional (2D) materials. After considerable research effort, a distinct "beyond graphene" domain has been established, comprising the library of non-graphene 2D materials. It is significant that some 2D non-graphene materials possess solid advantages over their predecessor, such as having a direct band gap, and therefore are highly promising for a number of applications. These applications are not limited to nano- and opto-electronics, but have a strong potential in biosensing technologies, as one example. However, since most of the 2D non-graphene materials have been newly discovered, most of the research efforts are concentrated on material synthesis and the investigation of the properties of the material. Applications of 2D non-graphene materials are still at the embryonic stage, and the integration of 2D non-graphene materials into devices is scarcely reported. However, in recent years, numerous reports have blossomed about 2D material-based biosensors, evidencing the growing potential of 2D non-graphene materials for biosensing applications. This review highlights the recent progress in research on the potential of using 2D non-graphene materials and similar oxide nanostructures for different types of biosensors (optical and electrochemical). A wide range of biological targets, such as glucose, dopamine, cortisol, DNA, IgG, bisphenol, ascorbic acid, cytochrome and estradiol, has been reported to be successfully detected by biosensors with transducers made of 2D non-graphene materials.

Place, publisher, year, edition, pages
MDPI AG, 2016
Keywords
transition metal dichalcogenides; transducers; beyond graphene; biosensors; two-dimensional materials; two-dimensional oxides; transition metal oxides
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-126850 (URN)10.3390/s16020223 (DOI)000371787800102 ()26861346 (PubMedID)
Note

Funding Agencies|EC FP-7 International Research Staff Exchange Scheme (IRSES) Grant [318520]; Linkoping Linnaeus Initiative for Novel Functional Materials (LiLi-NFM); European Union [604391]; Swedish Research Council (VR) Marie Sklodowska Curie International Career Grant [2015-00679]

Available from: 2016-04-05 Created: 2016-04-05 Last updated: 2017-11-30
Beshkova, M., Hultman, L. & Yakimova, R. (2016). Device applications of epitaxial graphene on silicon carbide. Vacuum, 128, 186-197
Open this publication in new window or tab >>Device applications of epitaxial graphene on silicon carbide
2016 (English)In: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 128, p. 186-197Article, review/survey (Refereed) Published
Abstract [en]

Graphene has become an extremely hot topic due to its intriguing material properties allowing for ground-breaking fundamental research and applications. It is one of the fastest developing materials during the last several years. This progress is also driven by the diversity of fabrication methods for graphene of different specific properties, size, quantity and cost. Graphene grown on SiC is of particular interest due to the possibility to avoid transferring of free standing graphene to a desired substrate while having a large area SiC (semi-insulating or conducting) substrate ready for device processing. Here, we present a review of the major current explorations of graphene on SiC in electronic devices, such as field effect transistors (FET), radio frequency (RF) transistors, integrated circuits (IC), and sensors. The successful role of graphene in the metrology sector is also addressed. Typical examples of graphene on SiC implementations are illustrated and the drawbacks and promises are critically analyzed. (C) 2016 Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2016
Keywords
Graphene FET; RF-transistors; IC; Graphene sensors; Detectors; Quantum Hall resistance
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-129150 (URN)10.1016/j.vacuum.2016.03.027 (DOI)000376052500026 ()
Note

Funding Agencies|European Union [604391]; Swedish Research Council [VR 621-2014-5805]; LiU Linnaeus Grant

Available from: 2016-06-13 Created: 2016-06-13 Last updated: 2017-11-28
Shtepliuk, I., Khranovskyy, V. & Yakimova, R. (2016). Effect of c-axis inclination angle on the properties of ZnO/Zn1-xCdxO/ZnO quantum wells. Thin Solid Films, 603, 139-148
Open this publication in new window or tab >>Effect of c-axis inclination angle on the properties of ZnO/Zn1-xCdxO/ZnO quantum wells
2016 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 603, p. 139-148Article in journal (Refereed) Published
Abstract [en]

The development of optoelectronic devices based on highly-promising Zn1 - xCdxO semiconductor system demands deep understanding of the properties of the Zn1 - xCdxO-based quantum wells (QWs). In this regard, we carried out a numerical study of the polarization-related effects in polar, semi-polar and non-polar ZnO/ Zn1 - xCd xO/ZnO QWs with different parameters of the quantum well structure. The effects of well width, barrier thickness, cadmium content in the active layer and c-axis inclination angle on the distribution of the electron and hole wave function and transition energy were investigated using the 6 x 6 k center dot p Hamiltonian and one-dimensional self-consistent solutions of nonlinear Schrodinger-Poisson equations with consideration of spatially varying dielectric constant and effective mass. The strong sensitivity of the internal electric field, transition energy and overlap integral to cadmium content and well thickness in the angle range from 0 to 40 degrees was revealed. An unexpected change of the internal electric fields sign was observed at the angles ranging from 70 to 90 degrees. We also found a difference in the electronic properties between (0001)-, (11 (2) over bar2)-and (10 (1) over bar0)-oriented QWs.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2016
Keywords
Inclination angle; Quantum well; Polarization; ZnCdO alloy; Transition energy
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-127431 (URN)10.1016/j.tsf.2016.02.007 (DOI)000372794900022 ()
Note

Funding Agencies|Swedish Institute scholarship

Available from: 2016-05-01 Created: 2016-04-26 Last updated: 2017-11-30
Yazdi, G., Iakimov, T. & Yakimova, R. (2016). Epitaxial Graphene on SiC: A Review of Growth and Characterization. Crystals, 6(5), Article ID 53.
Open this publication in new window or tab >>Epitaxial Graphene on SiC: A Review of Growth and Characterization
2016 (English)In: Crystals, ISSN 2073-4352, Vol. 6, no 5, article id 53Article, review/survey (Refereed) Published
Abstract [en]

This review is devoted to one of the most promising two-dimensional (2D) materials, graphene. Graphene can be prepared by different methods and the one discussed here is fabricated by the thermal decomposition of SiC. The aim of the paper is to overview the fabrication aspects, growth mechanisms, and structural and electronic properties of graphene on SiC and the means of their assessment. Starting from historical aspects, it is shown that the most optimal conditions resulting in a large area of one ML graphene comprise high temperature and argon ambience, which allow better controllability and reproducibility of the graphene quality. Elemental intercalation as a means to overcome the problem of substrate influence on graphene carrier mobility has been described. The most common characterization techniques used are low-energy electron microscopy (LEEM), angle-resolved photoelectron spectroscopy (ARPES), Raman spectroscopy, atomic force microscopy (AFM) in different modes, Hall measurements, etc. The main results point to the applicability of graphene on SiC in quantum metrology, and the understanding of new physics and growth phenomena of 2D materials and devices.

Place, publisher, year, edition, pages
MDPI AG, 2016
Keywords
graphene; epitaxial; SiC; sublimation
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-129674 (URN)10.3390/cryst6050053 (DOI)000377262000006 ()
Note

Funding Agencies|European Union Seventh Framework Program [604391]; Swedish Research Council [VR 621-2014-5805]; SSF; KAW funding

Available from: 2016-06-27 Created: 2016-06-23 Last updated: 2017-11-28
Alexander-Webber, J. A., Huang, J., Maude, D. K., Janssen, T. J., Tzalenchuk, A., Antonov, V., . . . Nicholas, R. J. (2016). Giant quantum Hall plateaus generated by charge transfer in epitaxial graphene. Scientific Reports, 6(30296)
Open this publication in new window or tab >>Giant quantum Hall plateaus generated by charge transfer in epitaxial graphene
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2016 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, no 30296Article in journal (Refereed) Published
Abstract [en]

Epitaxial graphene has proven itself to be the best candidate for quantum electrical resistance standards due to its wide quantum Hall plateaus with exceptionally high breakdown currents. However one key underlying mechanism, a magnetic field dependent charge transfer process, is yet to be fully understood. Here we report measurements of the quantum Hall effect in epitaxial graphene showing the widest quantum Hall plateau observed to date extending over 50 T, attributed to an almost linear increase in carrier density with magnetic field. This behaviour is strong evidence for field dependent charge transfer from charge reservoirs with exceptionally high densities of states in close proximity to the graphene. Using a realistic framework of broadened Landau levels we model the densities of donor states and predict the field dependence of charge transfer in excellent agreement with experimental results, thus providing a guide towards engineering epitaxial graphene for applications such as quantum metrology.

Place, publisher, year, edition, pages
Nature Publishing Group, 2016
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-130834 (URN)10.1038/srep30296 (DOI)000380203800001 ()27456765 (PubMedID)
External cooperation:
Note

Funding Agencies|UK EPSRC; Graphene Flagship [CNECT-ICT-604391]; EMRP project GraphOhm; AFRL grant [FA9550-15-C-0067]; LNCMI-CNRS; International Collaborative Energy Technology R&D Program of the Korean Institute of Energy Technology Evaluation and Planning (KETEP); Ministry of Trade, Industry & Energy, Republic of Korea [20148520011250]

Available from: 2016-08-26 Created: 2016-08-26 Last updated: 2017-11-21Bibliographically approved
Jokubavicius, V., Sun, J., Liu, X., Yazdi, G., Ivanov, I. G., Yakimova, R. & Syväjärvi, M. (2016). Growth optimization and applicability of thick on-axis SiC layers using sublimation epitaxy in vacuum. Journal of Crystal Growth, 448, 51-57
Open this publication in new window or tab >>Growth optimization and applicability of thick on-axis SiC layers using sublimation epitaxy in vacuum
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2016 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 448, p. 51-57Article in journal (Refereed) Published
Abstract [en]

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 1018 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.

Keywords
Mass transfer;Substrates;Single crystal growth;Semiconducting materials
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-128610 (URN)10.1016/j.jcrysgro.2016.05.017 (DOI)
Available from: 2016-05-25 Created: 2016-05-25 Last updated: 2017-11-30
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