| 1. |
- Cattelan, Mattia, et al.
(author)
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Anodization study of epitaxial graphene : insights on the oxygen evolution reaction of graphitic materials
- 2019
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In: Nanotechnology. - : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 30:28
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Journal article (peer-reviewed)abstract
- The photoemission electron microscopy and x-ray photoemission spectroscopy were utilized for the study of anodized epitaxial graphene (EG) on silicon carbide as a fundamental aspect of the oxygen evolution reaction on graphitic materials. The high-resolution analysis of surface morphology and composition quantified the material transformation during the anodization. We investigated the surface with lateral resolution amp;lt;150 nm, revealing significant transformations on the EG and the role of multilayer edges in increasing the film capacitance.
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| 2. |
- Giannazzo, F., et al.
(author)
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Probing the uniformity of hydrogen intercalation in quasi-free-standing epitaxial graphene on SiC by micro-Raman mapping and conductive atomic force microscopy
- 2019
-
In: Nanotechnology. - : IOP PUBLISHING LTD. - 0957-4484 .- 1361-6528. ; 30:28
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Journal article (peer-reviewed)abstract
- In this paper, micro-Raman mapping and conductive atomic force microscopy (C-AFM) were jointly applied to investigate the structural and electrical homogeneity of quasi-free-standing monolayer graphene (QFMLG), obtained by high temperature decomposition of 4H-SiC(0001) followed by hydrogen intercalation at 900 degrees C. Strain and doping maps, obtained by Raman data, showed the presence of sub-micron patches with reduced hole density correlated to regions with higher compressive strain, probably associated with a locally reduced hydrogen intercalation. Nanoscale resolution electrical maps by C-AFM also revealed the presence of patches with enhanced current injection through the QFMLG/SiC interface, indicating a locally reduced Schottky barrier height (Phi(B)). The Phi(B) values evaluated from local I-V curves by the thermionic emission model were in good agreement with the values calculated for the QFMLG/SiC interface using the Schottky-Mott rule and the graphene holes density from Raman maps. The demonstrated approach revealed a useful and non-invasive method to probe the structural and electrical homogeneity of QFMLG for future nano-electronics applications.
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| 3. |
- Khranovskyy, Volodymyr, et al.
(author)
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Light emission enhancement from ZnO nanostructured films grown on Gr/SiC substrates
- 2016
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In: Carbon. - : Pergamon Press. - 0008-6223 .- 1873-3891. ; 99, s. 295-301
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Journal article (peer-reviewed)abstract
- We report on the application of a single layer graphene substrates for the growth of polycrystalline ZnO films with advanced light emission properties. Unusually high ultraviolet (UV) and visible (VIS) photoluminesce was observed from the ZnO/Gr/SiC structures in comparison to identical samples without graphene. The photoluminescence intensity depends non-monotonically on the films thickness, reaching its maximum for 150 nm thick films. The phenomena observed is explained as due to the dual graphene role: i) the dangling bond free substrate, providing growth of relaxed thin ZnO layers ii) a back reflector active mirror of the Fabry-Perot cavity that is formed. The reported results demonstrate the potential of two-dimensional carbon materials integration with light emitting wide band gap semiconductors and can be of practical importance for the design of future optoelectronic devices.
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| 4. |
- Santangelo, Francesca, et al.
(author)
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Real-time sensing of lead with epitaxial graphene-integrated microfluidic devices
- 2019
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In: Sensors and actuators. B, Chemical. - : ELSEVIER SCIENCE SA. - 0925-4005 .- 1873-3077. ; 288, s. 425-431
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Journal article (peer-reviewed)abstract
- Since even low concentrations of toxic heavy metals can seriously damage human health, it is important to develop simple, sensitive and accurate methods for their detection. Graphene, which is extremely sensitive to foreign species, is a key element in the development of a sensing platform where low concentrations of analyte have to be detected. This work discusses the proof of concept of a sensing platform for liquid-phase detection of heavy metals (e.g. Pb) based on epitaxial graphene sensors grown on Si-face 4H-SiC substrate (EG/SiC). The sensing platform developed includes a microfluidic chip incorporating all the features needed to connect and execute the Lab-on-chip (LOC) functions using 3D printing fast prototyping technology. Herein, we present the response of EG to concentrations of Pb2+ solutions ranging from 125 nM to 500 mu M, showing good stability and reproducibility over time and an enhancement of its conductivity with a Langmuir correlation between signal and Pb2+ concentration. Density functional theory (DFT) calculations are performed and clearly explain the conductivity changes and the sensing mechanism in agreement with the experimental results reported, confirming the strong sensitivity of the sensor to the lowest concentrations of the analyte. Furthermore, from the calibration curve of the system, a limit of detection (LoD) of 95 nM was extrapolated.
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| 5. |
- Shtepliuk, Ivan, et al.
(author)
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Clustering and Morphology Evolution of Gold on Nanostructured Surfaces of Silicon Carbide: Implications for Catalysis and Sensing
- 2021
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In: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 4:2, s. 1282-1293
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Journal article (peer-reviewed)abstract
- A fundamental understanding of the behavior of gold (Au) nanostructures deposited on functional surfaces is imperative to discover and leverage interface-related phenomena that can boost the efficiency of existing electronic devices in sensorics, catalysis, and spintronics. In the present work, Au layers with nominal thickness of 2 nm were sputter-deposited on graphenized SiC substrates represented by buffer layer (BuL)/4H-SiC and monolayer epitaxial graphene (MLG)/4H-SiC. Morphometric analysis by means of scanning electron microscopy shows that Au on BuL self-assembles in nearly round-shaped plasmonically active islands, while on MLG, a fractal growth of considerably larger and ramified islands is observed. To correlate the experimentally established differences in surface morphology on the two types of graphenized substrates with energetics and kinetics of Au nanostructure growth, the deposit-substrate interaction strength was studied using density functional theory (DFT) calculations, molecular dynamics simulations, and optical measurements. The theoretical considerations involve participation of Au clusters with different sizes and energetics at the initial stages of the metal nanostructure formation. The results indicate that gold exhibits a considerably stronger interaction with BuL than with MLG, which can be considered as a key aspect for explaining the experimentally observed morphological differences. From the statistical analysis of Raman spectra, indications of Au intercalation of MLG are discussed. The current research shows that, due to its unique surface chemistry, buffer layer has peculiar affinity to gold when compared to other atomically flat surfaces, which is beneficial for boosting high-performance catalytic and sensing technologies based on low-dimensional materials.
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| 6. |
- Shtepliuk, Ivan, et al.
(author)
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Electrochemical performance of gold-decorated graphene electrodes integrated with SiC
- 2023
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In: Microelectronic Engineering. - : Elsevier BV. - 0167-9317 .- 1873-5568. ; 278
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Journal article (peer-reviewed)abstract
- Here we investigate the interface properties of gold (Au) decorated graphenized surfaces of 4H-SiC intended for electrochemical electrodes. These are fabricated using a two-step process: discontinuous Au layers with a nominal thickness of 2 nm are sputter-deposited onto 4H-SiC substrates with different graphenization extent—zero-layer graphene (ZLG) and monolayer epitaxial graphene) —followed by thermal annealing. By performing combined morphometric analysis, Raman mapping analysis, conductive atomic force microscopy, and electrochemical impedance spectroscopy measurements, we shed light on the relationship between physical processes (Au intercalation, particle re-shaping, and de-wetting) caused by thermal annealing and the intrinsic properties of graphenized SiC (vertical electron transport, charge-transfer properties, vibrational properties, and catalytic activity). We find that the impedance spectra of all considered structures exhibit two semicircles in the high and low frequency regions, which may be attributed to the graphene/ZLG/SiC (or Au/graphene/ZLG/SiC) and SiC/ZLG/graphene/electrolyte (or SiC/ZLG//Au/electrolyte) interfaces, respectively. An equivalent circuit model is proposed to estimate the interface carrier transfer parameters. This work provides an in-depth comprehension of the way by which the Au/2D carbon/SiC interaction strength influences the interface properties of heterostructures, which can be helpful for developing high performance catalytic and sensing devices.
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| 7. |
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| 8. |
- Shtepliuk, Ivan, et al.
(author)
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Exploring the Interface Landscape of Noble Metals on Epitaxial Graphene
- 2021
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In: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 218:17
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Journal article (peer-reviewed)abstract
- 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.
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| 9. |
- Shtepliuk, Ivan I., 1987-, et al.
(author)
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Lead (Pb) interfacing with epitaxial graphene
- 2018
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 20:25, s. 17105-17116
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Journal article (peer-reviewed)abstract
- 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.
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| 10. |
- Shtepliuk, Ivan, et al.
(author)
-
Interplay between thin silver films and epitaxial graphene
- 2020
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In: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 381
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Journal article (peer-reviewed)abstract
- Thin Ag films, with nominal thickness in the range 2 to 30 nm, are deposited using direct current magnetron sputtering and film morphology is studied by means of plan-view scanning electron microscopy. We find that for 2 mn nominal thickness the film surface consists of isolated circular nanoscale islands, which become interconnected as further material is deposited, leading to a continuous film at a nominal thickness of 30 nm. Our experimental findings are discussed in the context of the density functional theory results, which show that van der Waals forces dominate the interaction between Ag and epitaxial graphene. We also performed micro-Raman analysis and we find that the G and 2D modes of epitaxial graphene exhibit a red-shift upon Ag-layer deposition; which is interpreted as a result of charge transfer at the Ag/graphene interface. Moreover, we observed a pronounced enhancement of the G peak amplitude and area irrespective of the film nominal thickness and morphology, which we attribute to a combination of the charge transfer and plasmonic resonance effects. Our observations provide a critical information on the interaction between Ag and epitaxial graphene, which can be useful to design electronic and sensing devices based on Ag-epitaxial graphene hybrids.
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