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Iakimov, Tihomir
Publications (10 of 27) Show all publications
Zakharov, A., Vinogradov, N. A., Aprojanz, J., Nguyen, T. T., Tegenkamp, C., Struzzi, C., . . . Jokubavicius, V. (2019). Wafer Scale Growth and Characterization of Edge Specific Graphene Nanoribbons for Nanoelectronics. ACS Applied Nano Materials, 2(1), 156-162
Open this publication in new window or tab >>Wafer Scale Growth and Characterization of Edge Specific Graphene Nanoribbons for Nanoelectronics
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2019 (English)In: ACS Applied Nano Materials, ISSN 2574-0970, Vol. 2, no 1, p. 156-162Article in journal (Refereed) Published
Abstract [en]

One of the ways to use graphene in field effect transistors is to introduce a band gap by quantum confinement effect. That is why narrow graphene nanoribbons (GNRs) with width less than 50 nm are considered to be essential components in future graphene electronics. The growth of graphene on sidewalls of SiC(0001) mesa structures using scalable photolithography was shown to produce high quality GNRs with excellent transport properties. Such epitaxial graphene nanoribbons are very important in fundamental science but if GNRs are supposed to be used in advanced nanoelectronics, high quality thin (<50 nm) nanoribbons should be produced on a large (wafer) scale. Here we present a technique for scalable template growth of high quality GNRs on Si-face of SiC(0001) and provide detailed structural information along with transport properties. For the first time we succeeded now to avoid SiC-facet instabilities in order to grow high quality GNRs along both [11̅00] and [112̅0] crystallographic directions on the same substrate. The quality of the grown nanoribbons was confirmed by comprehensive characterization with atomic resolution STM, dark field LEEM, and transport measurements. This approach generates an entirely new platform for both fundamental and application driven research of quasi one-dimensional carbon based magnetism and spintronics.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-160224 (URN)10.1021/acsanm.8b01780 (DOI)000464491500018 ()
Available from: 2019-09-11 Created: 2019-09-11 Last updated: 2019-09-17Bibliographically approved
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
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
Pallon, J., Syväjärvi, M., Wang, Q., Yakimova, R., Iakimov, T., Elfman, M., . . . Ros, L. (2016). Ion beam evaluation of silicon carbide membrane structures intended for particle detectors. Paper presented at 22nd International Conference on Ion Beam Analysis (IBA). Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 371, 132-136
Open this publication in new window or tab >>Ion beam evaluation of silicon carbide membrane structures intended for particle detectors
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2016 (English)In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 371, p. 132-136Article in journal (Refereed) Published
Abstract [en]

Thin ion transmission detectors can be used as a part of a telescope detector for mass and energy identification but also as a pre-cell detector in a microbeam system for studies of biological effects from single ion hits on individual living cells. We investigated a structure of graphene on silicon carbide (SiC) with the purpose to explore a thin transmission detector with a very low noise level and having mechanical strength to act as a vacuum window. In order to reach very deep cavities in the SiC wafers for the preparation of the membrane in the detector, we have studied the Inductive Coupled Plasma technique to etch deep circular cavities in 325 mu m prototype samples. By a special high temperature process the outermost layers of the etched SiC wafers were converted into a highly conductive graphitic layer. The produced cavities were characterized by electron microscopy, optical microscopy and proton energy loss measurements. The average membrane thickness was found to be less than 40 mu m, however, with a slightly curved profile. Small spots representing much thinner membrane were also observed and might have an origin in crystal defects or impurities. Proton energy loss measurement (also called Scanning Transmission Ion Microscopy, STIM) is a well suited technique for this thickness range. This work presents the first steps of fabricating a membrane structure of SiC and graphene which may be an attractive approach as a detector due to the combined properties of SiC and graphene in a monolithic materials structure. (C) 2015 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2016
Keywords
Transmission detector; Graphene; ICP; Nuclear microprobe
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-127570 (URN)10.1016/j.nimb.2015.10.045 (DOI)000373412000025 ()
Conference
22nd International Conference on Ion Beam Analysis (IBA)
Available from: 2016-05-04 Created: 2016-05-03 Last updated: 2017-11-30
Karlsson, M., Wang, Q., Zhao, Y., Zhao, W., Toprak, M. S., Iakimov, T., . . . Ivanov, I. G. (2015). Wafer-scale epitaxial graphene on SiC for sensing applications. In: Benjamin J. Eggleton, Stefano Palomba (Ed.), Micro+Nano Materials, Devices, and Systems: . Paper presented at Micro+Nano Materials, Devices, and Systems, Sydney, Australia, 6–9 December 2015 (pp. 96685T-1-96685T-7). SPIE - International Society for Optical Engineering, 9668
Open this publication in new window or tab >>Wafer-scale epitaxial graphene on SiC for sensing applications
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2015 (English)In: Micro+Nano Materials, Devices, and Systems / [ed] Benjamin J. Eggleton, Stefano Palomba, SPIE - International Society for Optical Engineering, 2015, Vol. 9668, p. 96685T-1-96685T-7Conference paper, Published paper (Refereed)
Abstract [en]

The epitaxial graphene-on-silicon carbide (SiC-G) has advantages of high quality and large area coverage owing to a natural interface between graphene and SiC substrate with dimension up to 100 mm. It enables cost effective and reliable solutions for bridging the graphene-based sensors/devices from lab to industrial applications and commercialization. In this work, the structural, optical and electrical properties of wafer-scale graphene grown on 2’’ 4H semi-insulating (SI) SiC utilizing sublimation process were systemically investigated with focus on evaluation of the graphene’s uniformity across the wafer. As proof of concept, two types of glucose sensors based on SiC-G/Nafion/Glucose-oxidase (GOx) and SiC-G/Nafion/Chitosan/GOx were fabricated and their electrochemical properties were characterized by cyclic voltammetry (CV) measurements. In addition, a few similar glucose sensors based on graphene by chemical synthesis using modified Hummer’s method were also fabricated for comparison. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2015
Series
SPIE - International Society for Optical Engineering. Proceedings, ISSN 0277-786X ; 9668
Keywords
Graphene, SiC, wafer-scale, sensors
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-123956 (URN)10.1117/12.2202440 (DOI)000370723500076 ()9781628418903 (ISBN)
Conference
Micro+Nano Materials, Devices, and Systems, Sydney, Australia, 6–9 December 2015
Available from: 2016-01-15 Created: 2016-01-15 Last updated: 2016-03-21Bibliographically approved
Hens, P., Zakharov, A. A., Iakimov, T., Syväjärvi, M. & Yakimova, R. (2014). Large area buffer-free graphene on non-polar (001) cubic silicon carbide. Carbon, 80, 823-829
Open this publication in new window or tab >>Large area buffer-free graphene on non-polar (001) cubic silicon carbide
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2014 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 80, p. 823-829Article in journal (Refereed) Published
Abstract [en]

Graphene is, due to its extraordinary properties, a promising material for future electronic applications. A common process for the production of large area epitaxial graphene is a high temperature annealing process of atomically flat surfaces from hexagonal silicon carbide. This procedure is very promising but has the drawback of the formation of a buffer layer consisting of a graphene-like sheet, which is covalently bound to the substrate. This buffer layer degenerates the properties of the graphene above and needs to be avoided. We are presenting the combination of a high temperature process for the graphene production with a newly developed substrate of (0 0 1)-oriented cubic silicon carbide. This combination is a promising candidate to be able to supply large area homogenous epitaxial graphene on silicon carbide without a buffer layer. We are presenting the new substrate and first samples of epitaxial graphene on them. Results are shown using low energy electron microscopy and diffraction, photoelectron angular distribution and X-ray photoemission spectroscopy. All these measurements indicate the successful growth of a buffer free few layer graphene on a cubic silicon carbide surface. On our large area samples also the epitaxial relationship between the cubic substrate and the hexagonal graphene could be clarified.

Place, publisher, year, edition, pages
Elsevier, 2014
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-112605 (URN)10.1016/j.carbon.2014.09.041 (DOI)000344132400088 ()
Available from: 2014-12-10 Created: 2014-12-05 Last updated: 2017-12-05
Ivanov, I. G., Ul Hassan, J., Iakimov, T., Zakharov, A. A., Yakimova, R. & Janzén, E. (2014). Layer-number determination in graphene on SiC by reflectance mapping. Carbon, 77, 492-500
Open this publication in new window or tab >>Layer-number determination in graphene on SiC by reflectance mapping
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2014 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 77, p. 492-500Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier, 2014
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-110689 (URN)10.1016/j.carbon.2014.05.054 (DOI)000340689400054 ()
Note

Funding Agencies|GRAPHIC-RF project within the EuroGRAPHENE program of the European Science Foundation (ESF); EPIGRAT project within the EuroGRAPHENE program of the European Science Foundation (ESF)

Available from: 2014-09-24 Created: 2014-09-19 Last updated: 2017-12-05
Yakimova, R., Iakimov, T., Yazdi, G., Bouhafs, C., Eriksson, J., Zakharov, A., . . . Darakchieva, V. (2014). Morphological and electronic properties of epitaxial graphene on SiC. Physica. B, Condensed matter, 439, 54-59
Open this publication in new window or tab >>Morphological and electronic properties of epitaxial graphene on SiC
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2014 (English)In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 439, p. 54-59Article in journal (Refereed) Published
Abstract [en]

We report on the structural and electronic properties of graphene grown on SiC by high-temperature sublimation. We have studied thickness uniformity of graphene grown on 4H-SiC (0 0 0 1), 6H-SiC (0 0 0 1), and 3C-SiC (1 1 1) substrates and investigated in detail graphene surface morphology and electronic properties. Differences in the thickness uniformity of the graphene layers on different SiC polytypes is related mainly to the minimization of the terrace surface energy during the step bunching process. It is also shown that a lower substrate surface roughness results in more uniform step bunching and consequently better quality of the grown graphene. We have compared the three SiC polytypes with a clear conclusion in favor of 3C-SiC. Localized lateral variations in the Fermi energy of graphene are mapped by scanning Kelvin probe microscopy It is found that the overall single-layer graphene coverage depends strongly on the surface terrace width, where a more homogeneous coverage is favored by wider terraces, It is observed that the step distance is a dominating, factor in determining the unintentional doping of graphene from the SiC substrate. Microfocal spectroscopic ellipsometry mapping of the electronic properties and thickness of epitaxial graphene on 3C-SiC (1 1 1) is also reported. Growth of one monolayer graphene is demonstrated on both Si- and C-polarity of the 3C-SiC substrates and it is shown that large area homogeneous single monolayer graphene can be achieved on the Si-face substrates. Correlations between the number of graphene monolayers on one hand and the main transition associated with an exciton enhanced van Hove singularity at similar to 4.5 eV and the free-charge carrier scattering time, on the other are established It is shown that the interface structure on the Si- and C-polarity of the 3C-SiC (1 1 1) differs and has a determining role for the thickness and electronic properties homogeneity of the epitaxial graphene.

Place, publisher, year, edition, pages
Elsevier, 2014
Keywords
Epitaxial graphene; Sublimation of SiC; Electronic properties; Step-bunching; Spectroscopic ellipsometry mapping
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-105565 (URN)10.1016/j.physb.2013.12.048 (DOI)000331620700012 ()
Available from: 2014-03-31 Created: 2014-03-27 Last updated: 2017-12-05
Yakimova, R., Yazdi, G., Iakimov, T., Eriksson, J. & Darakchieva, V. (2013). Challenges of Graphene Growth on Silicon Carbide. ECS Transactions, 53(1), 9-16
Open this publication in new window or tab >>Challenges of Graphene Growth on Silicon Carbide
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2013 (English)In: ECS Transactions, Vol. 53, no 1, p. 9-16Article in journal (Refereed) Published
Abstract [en]

One of the main challenges in the fabrication of device quality graphene is the achievement of large area monolayer graphene that is processing compatible. Here, the impact of the substrate properties on the thickness uniformity and electronic characteristics for epitaxial graphene on SiC produced by high temperature sublimation has been evidenced and discussed. Several powerful techniques have been used to collect data, among them large scale ellipsometry mapping has been demonstrated for the first time. The study is covering all three SiC polytype, e.g. 4H-, 6H- and 3C-SiC in order to reveal eventual peculiarities that have to be controlled during graphene growth. The advantage of the cubic polytype is unambiguously demonstrated.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-118762 (URN)10.1149/05301.0009ecst (DOI)
Available from: 2015-06-03 Created: 2015-06-03 Last updated: 2015-06-18
Yazdi, G., Vasiliauskas, R., Iakimov, T., Zakharov, A., Syväjärvi, M. & Yakimova, R. (2013). Growth of large area monolayer graphene on 3C-SiC and a comparison with other SiC polytypes. Carbon, 57, 477-484
Open this publication in new window or tab >>Growth of large area monolayer graphene on 3C-SiC and a comparison with other SiC polytypes
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2013 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 57, p. 477-484Article in journal (Refereed) Published
Abstract [en]

Epitaxial graphene growth was performed on the Si-terminated face of 4H-, 6H-, and 3C-SiC substrates by silicon sublimation from SiC in argon atmosphere at a temperature of 2000 degrees C. Graphene surface morphology, thickness and band structure have been assessed by using atomic force microscopy, low-energy electron microscopy, and angle-resolved photoemission spectroscopy, respectively. Differences in the morphology of the graphene layers on different SiC polytypes is related mainly to the minimization of the terrace surface energy during the step bunching process. The uniformity of silicon sublimation is a decisive factor for obtaining large area homogenous graphene. It is also shown that a lower substrate surface roughness results in more uniform step bunching with a lower distribution of step heights and consequently better quality of the grown graphene. Large homogeneous areas of graphene monolayers (over 50 x 50 mu m(2)) have been grown on 3C-SiC (1 1 1) substrates. The comparison with the other polytypes suggests a similarity in the surface behaviour of 3C- and 6H-SiC.

Place, publisher, year, edition, pages
Elsevier, 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-94597 (URN)10.1016/j.carbon.2013.02.022 (DOI)000319030000055 ()
Note

Funding Agencies|FP7 EU project Concept Graphene and the Swedish Research Council (VR)|2011-44472010-3511 Grafic ESF|

Available from: 2013-06-27 Created: 2013-06-27 Last updated: 2017-12-06
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