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Lee HY, Haidari MM, Kee EH, Choi JS, Park BH, Campbell EEB, Jhang SH. Charge Transport in UV-Oxidized Graphene and Its Dependence on the Extent of Oxidation. NANOMATERIALS (BASEL, SWITZERLAND) 2022; 12:2845. [PMID: 36014709 PMCID: PMC9415921 DOI: 10.3390/nano12162845] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/27/2022] [Revised: 08/15/2022] [Accepted: 08/15/2022] [Indexed: 06/15/2023]
Abstract
Graphene oxides with different degrees of oxidation are prepared by controlling UV irradiation on graphene, and the charge transport and the evolution of the transport gap are investigated according to the extent of oxidation. With increasing oxygenous defect density nD, a transition from ballistic to diffusive conduction occurs at nD≃1012 cm-2 and the transport gap grows in proportion to nD. Considering the potential fluctuation related to the e-h puddle, the bandgap of graphene oxide is deduced to be Eg≃30nD(1012cm-2) meV. The temperature dependence of conductivity showed metal-insulator transitions at nD≃0.3×1012 cm-2, consistent with Ioffe-Regel criterion. For graphene oxides at nD≥4.9×1012 cm-2, analysis indicated charge transport occurred via 2D variable range hopping conduction between localized sp2 domain. Our work elucidates the transport mechanism at different extents of oxidation and supports the possibility of adjusting the bandgap with oxygen content.
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Affiliation(s)
- Hwa Yong Lee
- School of Physics, Konkuk University, Seoul 05029, Korea
| | | | - Eun Hee Kee
- School of Physics, Konkuk University, Seoul 05029, Korea
| | - Jin Sik Choi
- School of Physics, Konkuk University, Seoul 05029, Korea
| | - Bae Ho Park
- School of Physics, Konkuk University, Seoul 05029, Korea
| | - Eleanor E. B. Campbell
- EaStCHEM, School of Chemistry, Edinburgh University, David Brewster Road, Edinburgh EH9 3FJ, UK
| | - Sung Ho Jhang
- School of Physics, Konkuk University, Seoul 05029, Korea
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2
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Wang Z, Cao Q, Sotthewes K, Hu Y, Shin HS, Eigler S. Interlayer electron modulation in van der Waals heterostructures assembled by stacking monolayer MoS 2 onto monolayer graphene with different electron transfer ability. NANOSCALE 2021; 13:15464-15470. [PMID: 34505854 DOI: 10.1039/d1nr03708k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Achieving tunable optoelectronic properties and clarifying interlayer interactions are key challenges in the development of 2D heterostructures. Herein, we report the feasible modulation of the optoelectronic properties of monolayer MoS2 (1L-MoS2) on three different graphene monolayers with varying ability in extracting electrons. Monolayer oxygen-functionalized graphene (1L-oxo-G, a high amount of oxygen of 60%) with a work function (WF) of 5.67 eV and its lowly oxidized reduction product, namely reduced-oxo-G (1L-r-oxo-G, a low amount of oxygen of 0.1%), with a WF of 5.85 eV serving as hole injection layers significantly enhance the photoluminescence (PL) intensity of MoS2, whereas pristine monolayer graphene (1L-G) with a work function (WF) of 5.02 eV results in PL quenching of MoS2. The enhancement in the PL intensity is due to increase of neutral exciton recombination. Furthermore, 1L-r-oxo-G/MoS2 exhibited a higher increase (5-fold) in PL than 1L-oxo-G/MoS2 (3-fold). Our research can help modulate the carrier concentration and electronic type of 1L-MoS2 and has promising applications in optoelectronic devices.
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Affiliation(s)
- Zhenping Wang
- Department of Chemistry, Low-Dimensional Carbon and 2D Materials Center, Ulsan National Institute of Science and Technology, Ulsan 44919, Republic of Korea.
| | - Qing Cao
- Institute of Chemistry and Biochemistry, Freie Universität Berlin, Takustraße 3, 14195 Berlin, Germany.
| | - Kai Sotthewes
- Physics of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
| | - Yalei Hu
- Institute of Chemistry and Biochemistry, Freie Universität Berlin, Takustraße 3, 14195 Berlin, Germany.
| | - Hyeon S Shin
- Department of Chemistry, Low-Dimensional Carbon and 2D Materials Center, Ulsan National Institute of Science and Technology, Ulsan 44919, Republic of Korea.
| | - Siegfried Eigler
- Institute of Chemistry and Biochemistry, Freie Universität Berlin, Takustraße 3, 14195 Berlin, Germany.
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Malhotra R, Han Y, Nijhuis CA, Silikas N, Castro Neto AH, Rosa V. Graphene nanocoating provides superb long-lasting corrosion protection to titanium alloy. Dent Mater 2021; 37:1553-1560. [PMID: 34420797 DOI: 10.1016/j.dental.2021.08.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2021] [Revised: 07/17/2021] [Accepted: 08/04/2021] [Indexed: 11/30/2022]
Abstract
OBJECTIVE The presence of metallic species around failed implants raises concerns about the stability of titanium alloy (Ti-6Al-4V). Graphene nanocoating on titanium alloy (GN) has promising anti-corrosion properties, but its long-term protective potential and structural stability remains unknown. The objective was to determine GN's anti-corrosion potential and stability over time. METHODS GN and uncoated titanium alloy (Control) were challenged with a highly acidic fluorinated corrosive medium (pH 2.0) for up to 240 days. The samples were periodically tested using potentiodynamic polarization curves, electrochemical impedance spectroscopy and inductively coupled plasma-atomic emission spectroscopy (elemental release). The integrity of samples was determined using Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and scanning electron microscopy. Statistical analyses were performed with one-sample t-test, paired t-test and one-way ANOVA with Tukey post-hoc test with a pre-set significance level of 5%. RESULTS There was negligible corrosion and elemental loss on GN. After 240 days of corrosion challenge, the corrosion rate and roughness increased by two and twelve times for the Control whereas remained unchanged for GN. The nanocoating presented remarkably high structural integrity and coverage area (>98%) at all time points tested. SIGNIFICANCE Graphene nanocoating protects titanium alloy from corrosion and dissolution over a long period while maintaining high structural integrity. This coating has promising potential for persistent protection of titanium and potentially other metallic alloys against corrosion.
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Affiliation(s)
- Ritika Malhotra
- Faculty of Dentistry, National University of Singapore, Singapore.
| | - Yingmei Han
- Department of Chemistry, National University of Singapore, Singapore.
| | - Christian A Nijhuis
- Department of Molecules and Materials, Faculty of Science and Technology, University of Twente, Netherlands.
| | - Nikolaos Silikas
- Dental Biomaterials, Dentistry, The University of Manchester, Manchester, United Kingdom.
| | - A H Castro Neto
- Centre for Advanced 2D Materials, National University of Singapore, Singapore.
| | - Vinicius Rosa
- Faculty of Dentistry, National University of Singapore, Singapore; Centre for Advanced 2D Materials, National University of Singapore, Singapore.
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Ramadan S, Zhang Y, Tsang DKH, Shaforost O, Xu L, Bower R, Dunlop IE, Petrov PK, Klein N. Enhancing Structural Properties and Performance of Graphene-Based Devices Using Self-Assembled HMDS Monolayers. ACS OMEGA 2021; 6:4767-4775. [PMID: 33644584 PMCID: PMC7905810 DOI: 10.1021/acsomega.0c05631] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Accepted: 01/27/2021] [Indexed: 06/12/2023]
Abstract
The performance of graphene devices is often limited by defects and impurities induced during device fabrication. Polymer residue left on the surface of graphene after photoresist processing can increase electron scattering and hinder electron transport. Furthermore, exposing graphene to plasma-based processing such as sputtering of metallization layers can increase the defect density in graphene and alter the device performance. Therefore, the preservation of the high-quality surface of graphene during thin-film deposition and device manufacturing is essential for many electronic applications. Here, we show that the use of self-assembled monolayers (SAMs) of hexamethyldisilazane (HMDS) as a buffer layer during the device fabrication of graphene can significantly reduce damage, improve the quality of graphene, and enhance device performance. The role of HMDS has been systematically investigated using surface analysis techniques and electrical measurements. The benefits of HMDS treatment include a significant reduction in defect density compared with as-treated graphene and more than a 2-fold reduction of contact resistance. This surface treatment is simple and offers a practical route for improving graphene device interfaces, which is important for the integration of graphene into functional devices such as electronics and sensor devices.
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Nishina Y, Eigler S. Chemical and electrochemical synthesis of graphene oxide - a generalized view. NANOSCALE 2020; 12:12731-12740. [PMID: 32524106 DOI: 10.1039/d0nr02164d] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Graphene oxide (GO) is a water soluble carbon material in general, suitable for applications in electronics, the environment, and biomedicine. GO is produced by oxidation of abundantly available graphite, turning black graphite into water-dispersible single layers of functionalized graphene-related materials. Therefore, oxidation gives chemicals access to the complete surface area of GO. These fundamentals have led to a rich chemistry of GO. Here, we review the progress made in controlling the synthesis of GO, introduce the current structural models used to explain the phenomena and present versatile strategies to functionalize the surface of GO. Finally, an outlook is given for future directions.
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Affiliation(s)
- Yuta Nishina
- Graduate School of Natural Science and Technology, Okayama University Tsushimanaka, Kita-ku, Okayama, 700-8530, Japan. and Research Core for Interdisciplinary Sciences, Okayama University Tsushimanaka, Kita-ku, Okayama, 700-8530, Japan
| | - Siegfried Eigler
- Institute of Chemistry and Biochemistry, Freie Universität Berlin, Takustraße 3, 14195 Berlin, Germany.
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Brülls SM, Cantatore V, Wang Z, Tam PL, Malmberg P, Stubbe J, Sarkar B, Panas I, Mårtensson J, Eigler S. Evidence for Electron Transfer between Graphene and Non-Covalently Bound π-Systems. Chemistry 2020; 26:6694-6702. [PMID: 32227533 PMCID: PMC7317416 DOI: 10.1002/chem.202000488] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Revised: 03/19/2020] [Indexed: 11/19/2022]
Abstract
Hybridizing graphene and molecules possess a high potential for developing materials for new applications. However, new methods to characterize such hybrids must be developed. Herein, the wet-chemical non-covalent functionalization of graphene with cationic π-systems is presented and the interaction between graphene and the molecules is characterized in detail. A series of tricationic benzimidazolium salts with various steric demand and counterions was synthesized, characterized and used for the fabrication of graphene hybrids. Subsequently, the doping effects were studied. The molecules are adsorbed onto graphene and studied by Raman spectroscopy, XPS as well as ToF-SIMS. The charged π-systems show a p-doping effect on the underlying graphene. Consequently, the tricationic molecules are reduced through a partial electron transfer process from graphene, a process which is accompanied by the loss of counterions. DFT calculations support this hypothesis and the strong p-doping could be confirmed in fabricated monolayer graphene/hybrid FET devices. The results are the basis to develop sensor applications, which are based on analyte/molecule interactions and effects on doping.
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Affiliation(s)
- Steffen M. Brülls
- Department of Chemistry and Chemical EngineeringChalmers University of TechnologyKemivägen 1041296GothenburgSweden
| | - Valentina Cantatore
- Department of Chemistry and Chemical EngineeringChalmers University of TechnologyKemivägen 1041296GothenburgSweden
| | - Zhenping Wang
- Institut für Chemie und BiochemieFreie Universität BerlinTakustraße 314195BerlinGermany
| | - Pui Lam Tam
- Department of Industrial and Materials ScienceChalmers University of TechnologyRännvägen 2A41296GothenburgSweden
| | - Per Malmberg
- Department of Chemistry and Chemical EngineeringChalmers University of TechnologyKemivägen 1041296GothenburgSweden
| | - Jessica Stubbe
- Institut für Chemie und BiochemieFreie Universität BerlinFabeckstraße 34/3614195BerlinGermany
| | - Biprajit Sarkar
- Institut für Chemie und BiochemieFreie Universität BerlinFabeckstraße 34/3614195BerlinGermany
- Institut für Anorganische ChemieUniversität StuttgartPfaffenwaldring 5570569StuttgartGermany
| | - Itai Panas
- Department of Chemistry and Chemical EngineeringChalmers University of TechnologyKemivägen 1041296GothenburgSweden
| | - Jerker Mårtensson
- Department of Chemistry and Chemical EngineeringChalmers University of TechnologyKemivägen 1041296GothenburgSweden
| | - Siegfried Eigler
- Institut für Chemie und BiochemieFreie Universität BerlinTakustraße 314195BerlinGermany
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Wang Z, Yao Q, Eigler S. Room-Temperature Transport Properties of Graphene with Defects Derived from Oxo-Graphene. Chemistry 2020; 26:6484-6489. [PMID: 31851390 PMCID: PMC7317977 DOI: 10.1002/chem.201905252] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2019] [Revised: 12/17/2019] [Indexed: 11/23/2022]
Abstract
In recent years, graphene oxide has been considered as a soluble precursor of graphene for electronic applications. However, the performance lags behind that of graphene due to lattice defects. Here, the relation between the density of defects in the range of 0.2 % and 1.5 % and the transport properties is quantitatively studied. Therefore, the related flakes of monolayers of graphene were prepared from oxo-functionalized graphene (oxo-G). The morphologic structure of oxo-G was imaged by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Field-effect mobility values were determined to range between 0.3 cm2 V-1 s-1 and 33.2 cm2 V-1 s-1 , which were inversely proportional to the density of defects. These results provide the first quantitative description of the density of defects and transport properties, which plays an important role for potential applications.
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Affiliation(s)
- Zhenping Wang
- Institute for Chemistry and BiochemistryFreie Universität BerlinTakustraße 314195BerlinGermany
| | - Qirong Yao
- Physics of Interfaces and NanomaterialUniversity of TwenteEnschede7500 AEThe Netherlands
| | - Siegfried Eigler
- Institute for Chemistry and BiochemistryFreie Universität BerlinTakustraße 314195BerlinGermany
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