المؤلفون: Khestanova, Ekaterina, Ivanova, Tatyana, Gillen, Roland, Elia, Alessandro D, Lacey, Oliver Nicholas Gallego, Wysocki, Lena, Gruneis, Alexander, Kravtsov, Vasily, Strupinski, Wlodek, Maultzsch, Janina, Kandyba, Viktor, Cattelan, Mattia, Barinov, Alexei, Avila, Jose, Dudin, Pavel, Senkovskiy, Boris V.

المصدر: ACS Photonics 2023

مصطلحات موضوعية: Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science

الوصف: Monolayer transition-metal dichalcogenide (TMD) semiconductors exhibit strong excitonic effects and hold promise for optical and optoelectronic applications. Yet, electron doping of TMDs leads to the conversion of neutral excitons into negative trions, which recombine predominantly non-radiatively at room temperature. As a result, the photoluminescence (PL) intensity is quenched. Here we study the optical and electronic properties of a MoS2/WSe2 heterostructure as a function of chemical doping by Cs atoms performed under ultra-high vacuum conditions. By PL measurements we identify two interlayer excitons and assign them to the momentum-indirect Q-Gamma and K-Gamma transitions. The energies of these excitons are in a very good agreement with ab initio calculations. We find that the Q-Gamma interlayer exciton is robust to the electron doping and is present at room temperature even at a high charge carrier concentration. Submicrometer angle-resolved photoemission spectroscopy (micro-ARPES) reveals charge transfer from deposited Cs adatoms to both the upper MoS2 and the lower WSe2 monolayer without changing the band alignment. This leads to a small (10 meV) energy shift of interlayer excitons. Robustness of the momentum-indirect interlayer exciton to charge doping opens up an opportunity of using TMD heterostructures in light-emitting devices that can work at room temperature at high densities of charge carriers.

الوصول الحر: http://arxiv.org/abs/2304.02513Test

المؤلفون: Whelan, Patrick R., De Fazio, Domenico, Pasternak, Iwona, Thomsen, Joachim D, Zelzer, Steffen, Mikkelsen, Martin O, Booth, Timothy J., Diekhöner, Lars, Sassi, Ugo, Johnstone, Duncan, Midgley, Paul A, Strupinski, Wlodek, Jepsen, Peter U, Ferrari, Andrea C., Bøggild, Peter

المصدر: Whelan , P R , De Fazio , D , Pasternak , I , Thomsen , J D , Zelzer , S , Mikkelsen , M O , Booth , T J , Diekhöner , L , Sassi , U , Johnstone , D , Midgley , P A , Strupinski , W , Jepsen , P U , Ferrari , A C & Bøggild , P 2024 , ' Mapping nanoscale carrier confinement in polycrystalline graphene by terahertz spectroscopy ' , Scientific Reports , vol. 14 , no. 1 , 3163 . https://doi.org/10.1038/s41598-024-51548-zTest

الوصف: Terahertz time-domain spectroscopy (THz-TDS) can be used to map spatial variations in electrical properties such as sheet conductivity, carrier density, and carrier mobility in graphene. Here, we consider wafer-scale graphene grown on germanium by chemical vapor deposition with non-uniformities and small domains due to reconstructions of the substrate during growth. The THz conductivity spectrum matches the predictions of the phenomenological Drude-Smith model for conductors with non-isotropic scattering caused by backscattering from boundaries and line defects. We compare the charge carrier mean free path determined by THz-TDS with the average defect distance assessed by Raman spectroscopy, and the grain boundary dimensions as determined by transmission electron microscopy. The results indicate that even small angle orientation variations below 5° within graphene grains influence the scattering behavior, consistent with significant backscattering contributions from grain boundaries.

وصف الملف: application/pdf

العلاقة: https://orbit.dtu.dk/en/publications/e0c5dd40-2029-4d16-a623-70a7284b23f5Test

الإتاحة: https://doi.org/10.1038/s41598-024-51548-zTest
https://orbit.dtu.dk/en/publications/e0c5dd40-2029-4d16-a623-70a7284b23f5Test
https://backend.orbit.dtu.dk/ws/files/352477707/Whelan_et_al-2024-Scientific_Reports.pdfTest

المؤلفون: Tortello, Mauro, Pasternak, Iwona, Zeranska-Chudek, Klaudia, Strupinski, Wlodek, Gonnelli, Renato S., Fina, Alberto

المصدر: ACS Appl. Nano Mater. 2019, 2, 2621-2633

مصطلحات موضوعية: Physics - Applied Physics, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science

الوصف: We performed Scanning Thermal Microscopy measurements on single layers of chemical-vapor-deposited -CVD- graphene supported by different substrates, namely SiO2, Al2O3 and PET using a double-scan technique to remove the contribution to the heat flux through the air and the cantilever. Then, by adopting a simple lumped-elements model, we developed a new method that allows determining, through a multi-step numerical analysis, the equivalent thermal properties of thermally conductive coatings of nanometric thickness. In this specific case we found that our CVD graphene is thermally equivalent, for heat injection perpendicular to the graphene planes, to a coating material of conductivity Keff=2.5+-0.3 mK and thickness teff=3.5+-0.3 nm in perfect contact with the substrate. For the SiO2 substrate, we also measured stacks made of 2 and 4 CVD monolayers and we found that the effective thermal conductivity increases with increasing number of layers and, with a technologically achievable number of layers, is expected to be comparable to that of one order of magnitude-thicker metallic thin films. This study provides a powerful method for characterizing the thermal properties of graphene in view of several thermal management applications.

الوصول الحر: http://arxiv.org/abs/1910.13774Test

المؤلفون: Hart, William S., Panchal, Vishal, Melios, Christos, Strupiński, Włodek, Kazakova, Olga, Phillips, Chris C.

مصطلحات موضوعية: Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Applied Physics, Physics - Optics

الوصف: We report observation of graphene plasmon interference fringes across a wide spectral range using a scattering scanning near-field optical microscope (s-SNOM) that employs a widely tunable bank of quantum cascade lasers. We use plasmon interference to measure the dispersion curve of graphene plasmons over more than an order of magnitude of plasmon wavelength, from $\lambda_{sp}$ ~140 to ~1700 nm, and extract the electron Fermi energy of 298$\pm$4 meV for hydrogen-intercalated single layer epitaxial graphene on SiC. Furthermore, we demonstrate the appearance of wavelength tuneable graphene plasmon reflection "hotspots" at single-layer/bi-layer interfaces. This work demonstrates the capability of wide-band nano-imaging to precisely measure the electrical properties of graphene and spatially control plasmon reflection focusing.
Comment: 14 pages and 5 figures

الوصول الحر: http://arxiv.org/abs/1805.10102Test

المؤلفون: Melios, Christos, Winters, Michael, Strupinski, Wlodek, Panchal, Vishal, Giusca, Cristina E., Jayawardena, K. D. G. Imalka, Rorsman, Niklas, Silva, S. Ravi P., Kazakova, Olga

المصدر: C. Melios et al. Nanoscale, 2017,9, 3440-3448

مصطلحات موضوعية: Condensed Matter - Materials Science

الوصف: The effects of humidity on the electronic properties of quasi-free standing one layer graphene (QFS 1LG) are investigated via simultaneous magneto-transport in the van der Pauw geometry and local work function measurements in a controlled environment. QFS 1LG on 4H-SiC(0001) is obtained by hydrogen intercalation of the interfacial layer. In this system, the carrier concentration experiences a two-fold increase in sensitivity to changes in relative humidity as compared to the as-grown epitaxial graphene. This enhanced sensitivity to water is attributed to the lowering of the hydrophobicity of QFS 1LG, which results from spontaneous polarization of 4H-SiC(0001) strongly influencing the graphene. Moreover, the superior carrier mobility of the QFS 1LG system is retained even at the highest humidity. The work function maps constructed from Kelvin probe force microscopy also revealed higher sensitivity to water for 1LG compared to 2LG in both QFS 1LG and as-grown systems. These results point to a new field of applications for QFS 1LG, i.e., as humidity sensors, and the corresponding need for metrology in calibration of graphene-based sensors and devices.
Comment: 16 pages, 4 figures

الوصول الحر: http://arxiv.org/abs/1804.09499Test

المؤلفون: Melios, Christos, Spencer, Steve, Shard, Alex, Strupinski, Wlodek, Silva, S. Ravi P., Kazakova, Olga

المصدر: C Melios et al 2016 2D Mater. 3 025023

مصطلحات موضوعية: Condensed Matter - Materials Science

الوصف: We perform local nanoscale studies of the surface and interface structure of hydrogen intercalated graphene on 4H-SiC(1000). In particular, we show that intercalation of the interfacial layer results in the formation of quasi-free standing one layer graphene (QFS 1LG) with change in the carrier type from n- to p-type, accompanied by a more than four times increase in carrier mobility. We demonstrate that surface enhanced Raman scattering (SERS) reveals the enhanced Raman signal of Si-H stretching mode, which is the direct proof of successful intercalation. Furthermore, the appearance of D, D+D' as well as C-H peaks for the quasi-free standing two layer graphene (QFS 2LG) suggests that hydrogen also penetrates in between the graphene layers to locally form C-H sp3 defects that decrease the mobility. Thus, SERS provides a quick and reliable technique to investigate the interface structure of graphene which is in general not accessible by other conventional methods. Our findings are further confirmed by Kelvin probe force microscopy and X-ray photoelectron spectroscopy.
Comment: 23 pages, 4 figures

الوصول الحر: http://arxiv.org/abs/1804.09492Test

المؤلفون: Sitek, Jakub, Czerniak-Łosiewicz, Karolina, Gertych, Arkadiusz P., Giza, Małgorzata, Dąbrowski, Paweł, Rogala, Maciej, Wilczyński, Konrad, Kaleta, Anna, Kret, Sławomir, Conran, Ben R., Wang, Xiaochen, McAleese, Clifford, Macha, Michał, Radenović, Aleksandra, Zdrojek, Mariusz, Pasternak, Iwona, Strupiński, Włodek

المساهمون: Narodowe Centrum Nauki, Graphene Flagship, Fundacja na rzecz Nauki Polskiej

المصدر: ACS Applied Materials & Interfaces ; volume 15, issue 28, page 33838-33847 ; ISSN 1944-8244 1944-8252

مصطلحات موضوعية: General Materials Science

الإتاحة: https://doi.org/10.1021/acsami.3c02892Test

المؤلفون: Vermeulen, Nathalie, Castello-Lurbe, David, Cheng, JinLuo, Pasternak, Iwona, Krajewska, Aleksandra, Ciuk, Tymoteusz, Strupinski, Wlodek, Thienpont, Hugo, Van Erps, Jurgen

المصدر: Phys. Rev. Applied 6, 044006 (2016)

مصطلحات موضوعية: Physics - Optics

الوصف: We experimentally demonstrate a negative Kerr nonlinearity for quasi-undoped graphene. Hereto, we introduce the method of chirped-pulse-pumped self-phase modulation and apply it to graphene-covered silicon waveguides at telecom wavelengths. The extracted Kerr-nonlinear index for graphene equals n2,gr = -10^(-13) m^2/W. Whereas the sign of n2,gr turns out to be negative in contrast to what has been assumed so far, its magnitude is in correspondence with that observed in earlier experiments. Graphene's negative Kerr nonlinearity strongly impacts how graphene should be exploited for enhancing the nonlinear response of photonic (integrated) devices exhibiting a positive nonlinearity. It also opens up the possibility of using graphene to annihilate unwanted nonlinear effects in such devices, to develop unexplored approaches for establishing Kerr processes, and to extend the scope of the "periodic poling" method often used for second-order nonlinearities towards third-order Kerr processes. Because of the generic nature of the chirped-pulse-pumped self-phase modulation method, it will allow fully characterizing the Kerr nonlinearity of essentially any novel (2D) material.

الوصول الحر: http://arxiv.org/abs/1611.07750Test

المؤلفون: Lupina, Grzegorz, Kitzmann, Julia, Costina, Ioan, Lukosius, Mindaugas, Wenger, Christian, Wolff, Andre, Vaziri, Sam, Ostling, Mikael, Pasternak, Iwona, Krajewska, Aleksandra, Strupinski, Wlodek, Kataria, Satender, Gahoi, Amit, Lemme, Max C., Ruhl, Guenther, Zoth, Guenther, Luxenhofer, Oliver, Mehr, Wolfgang

المصدر: ACS Nano, 9 (2015) 4776

مصطلحات موضوعية: Condensed Matter - Mesoscale and Nanoscale Physics

الوصف: Integration of graphene with Si microelectronics is very appealing by offering potentially a broad range of new functionalities. New materials to be integrated with Si platform must conform to stringent purity standards. Here, we investigate graphene layers grown on copper foils by chemical vapor deposition and transferred to silicon wafers by wet etch and electrochemical delamination methods with respect to residual sub-monolayer metallic contaminations. Regardless of the transfer method and associated cleaning scheme, time-of-flight secondary ion mass spectrometry and total reflection x-ray fluorescence measurements indicate that the graphene sheets are contaminated with residual metals (copper, iron) with a concentration exceeding 10$^{13}$ atoms/cm$^{2}$. These metal impurities appear to be partly mobile upon thermal treatment as shown by depth profiling and reduction of the minority charge carrier diffusion length in the silicon substrate. As residual metallic impurities can significantly alter electronic and electrochemical properties of graphene and can severely impede the process of integration with silicon microelectronics these results reveal that further progress in synthesis, handling, and cleaning of graphene is required on the way to its advanced electronic and optoelectronic applications.
Comment: 26 pages, including supporting information

الوصول الحر: http://arxiv.org/abs/1505.00889Test

المؤلفون: Whelan, Patrick R, De Fazio, Domenico, Pasternak, Iwona, Thomsen, Joachim D, Zelzer, Steffen, Mikkelsen, Martin O, Booth, Timothy J, Diekhöner, Lars, Sassi, Ugo, Johnstone, Duncan, Midgley, Paul A, Strupinski, Wlodek, Jepsen, Peter U, Ferrari, Andrea C, Bøggild, Peter

مصطلحات موضوعية: 51 Physical Sciences, 40 Engineering, 4018 Nanotechnology, 5104 Condensed Matter Physics

الوصف: Acknowledgements: We acknowledge funding from the Danish National Research Foundation (DNRF) Center for Nanostructured Graphene (DNRF103), the European Union Quantum Flagship and Graphene Flagship Core 2 (785219) and Core 3 (881603), European Union Horizon 2020 Research and Innovation Programme under Grant Agreement No. 824962 (car2TERA), European Union Seventh Framework Programme (FP7) under grant Agreement No. 604000 (GLADIATOR), Innovation Fund Denmark under grant agreement No. 12-131827 (DA-GATE), ERC grants Hetero2D, GIPT, EPSRC Grants EP/L016087/1, EP/K01711X/1, EP/K017144/1, EP/N010345/1, EP/V000055/1, EP/X015742/1 DSTL, EU Grant Graph-X. ; Funder: DSTL ; Terahertz time-domain spectroscopy (THz-TDS) can be used to map spatial variations in electrical properties such as sheet conductivity, carrier density, and carrier mobility in graphene. Here, we consider wafer-scale graphene grown on germanium by chemical vapor deposition with non-uniformities and small domains due to reconstructions of the substrate during growth. The THz conductivity spectrum matches the predictions of the phenomenological Drude-Smith model for conductors with non-isotropic scattering caused by backscattering from boundaries and line defects. We compare the charge carrier mean free path determined by THz-TDS with the average defect distance assessed by Raman spectroscopy, and the grain boundary dimensions as determined by transmission electron microscopy. The results indicate that even small angle orientation variations below 5° within graphene grains influence the scattering behavior, consistent with significant backscattering contributions from grain boundaries.

وصف الملف: application/pdf; text/xml

العلاقة: https://www.repository.cam.ac.uk/handle/1810/364443Test

الإتاحة: https://www.repository.cam.ac.uk/handle/1810/364443Test