Toh Chee Tat
Degree: PhD
Position: Research Assistant Professor
Research Type: Experiment
Office: S12-M01
Email: cttoh@nus.edu.sg
CA2DM Publications:
2025 |
Shi, Lu; Zhang, Hanning; Grebenko, Artem K; Yamaletdinov, Ruslan; Rejaul, S K; Shivajirao, Ranjith; Tong, Zheng Jue; Luchkin, Sergey; Zhang, Hongji; Iakoubovskii, Konstantin V; Alekseeva, Alena A; Starkov, Andrei; Orofeo, Carlo M; Lin, Junhao; Suenaga, Kazutomo; Toh, Chee-Tat; Mahfouz, Remi; Tayeb, Talah M; Qari, Nada; Adams, Stefan; Weber, Bent; Yazyev, Oleg V; Ozyilmaz, Barbaros Monolayer Amorphous Carbon: Unlocking Disorder-Induced Lithiophilicity Journal Article ADVANCED SCIENCE, 2025. @article{ISI:001622287600001, title = {Monolayer Amorphous Carbon: Unlocking Disorder-Induced Lithiophilicity}, author = {Lu Shi and Hanning Zhang and Artem K Grebenko and Ruslan Yamaletdinov and S K Rejaul and Ranjith Shivajirao and Zheng Jue Tong and Sergey Luchkin and Hongji Zhang and Konstantin V Iakoubovskii and Alena A Alekseeva and Andrei Starkov and Carlo M Orofeo and Junhao Lin and Kazutomo Suenaga and Chee-Tat Toh and Remi Mahfouz and Talah M Tayeb and Nada Qari and Stefan Adams and Bent Weber and Oleg V Yazyev and Barbaros Ozyilmaz}, doi = {10.1002/advs.202516490}, times_cited = {0}, year = {2025}, date = {2025-11-25}, journal = {ADVANCED SCIENCE}, publisher = {WILEY}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {Dendritic lithium growth on the current collector remains a major obstacle to developing anode-less batteries, arising from inhomogeneous lithium nucleation and uneven surface lithiophilicity. Existing approaches, such as metallic or carbonaceous interlayers, often fail to stabilize lithium deposition due to mechanical degradation or spatial variations in lithium affinity. Here, we demonstrate that a monolayer amorphous carbon (MAC) film-a single-atom-thick disordered sp2 network grown directly on copper-can fundamentally alter lithium nucleation behavior. The topological disorder of MAC produces a dense distribution of electron-rich sites that uniformly strengthen lithium binding. As a result, the MAC surface exhibits a lithium contact angle of 31 +/- 5 degrees, four times lower than that of graphene and nearly three times lower than that of bare copper, leading to homogeneous wetting and deposition. Electrochemical tests reveal a reduced nucleation overpotential of 28.9 mV at 0.5 mA cm-2. Density functional theory and scanning tunneling microscopy confirm that disorder-induced localization of states near the Fermi level enhances electronegativity and forms continuous lithium-binding sites. These findings establish intrinsic structural disorder, rather than chemical doping, as an effective route to designing uniformly lithiophilic current collectors for next-generation anode-less batteries.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Dendritic lithium growth on the current collector remains a major obstacle to developing anode-less batteries, arising from inhomogeneous lithium nucleation and uneven surface lithiophilicity. Existing approaches, such as metallic or carbonaceous interlayers, often fail to stabilize lithium deposition due to mechanical degradation or spatial variations in lithium affinity. Here, we demonstrate that a monolayer amorphous carbon (MAC) film-a single-atom-thick disordered sp2 network grown directly on copper-can fundamentally alter lithium nucleation behavior. The topological disorder of MAC produces a dense distribution of electron-rich sites that uniformly strengthen lithium binding. As a result, the MAC surface exhibits a lithium contact angle of 31 +/- 5 degrees, four times lower than that of graphene and nearly three times lower than that of bare copper, leading to homogeneous wetting and deposition. Electrochemical tests reveal a reduced nucleation overpotential of 28.9 mV at 0.5 mA cm-2. Density functional theory and scanning tunneling microscopy confirm that disorder-induced localization of states near the Fermi level enhances electronegativity and forms continuous lithium-binding sites. These findings establish intrinsic structural disorder, rather than chemical doping, as an effective route to designing uniformly lithiophilic current collectors for next-generation anode-less batteries. |
Zhang, Deqiang; Yeo, Jing Ying; Zhang, Hanning; Yamaletdinov, Ruslan; Yang, Qian; Zhan, Yufeng; Martin-Fernandez, Inigo; Yazyev, Oleg V; Toh, Chee-Tat; Ozyilmaz, Barbaros Dry Transfer of CVD Graphene Film Using Adhesion Switchable Ferroelectric Polymers Journal Article ADVANCED MATERIALS, 37 (50), 2025, ISSN: 0935-9648. @article{ISI:001618079400001, title = {Dry Transfer of CVD Graphene Film Using Adhesion Switchable Ferroelectric Polymers}, author = {Deqiang Zhang and Jing Ying Yeo and Hanning Zhang and Ruslan Yamaletdinov and Qian Yang and Yufeng Zhan and Inigo Martin-Fernandez and Oleg V Yazyev and Chee-Tat Toh and Barbaros Ozyilmaz}, doi = {10.1002/adma.202510545}, times_cited = {0}, issn = {0935-9648}, year = {2025}, date = {2025-11-19}, journal = {ADVANCED MATERIALS}, volume = {37}, number = {50}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {Although chemical vapor deposition (CVD) produces meter-scale, high-quality graphene (Gr) on copper (Cu) foils, its practical integration is hampered by challenges in the transfer process. Conventional wet transfers are slow, produce chemical waste, and lack scalability, whereas existing dry transfer methods struggle with mechanical damage and residues due to strong Gr-Cu adhesion and the difficulty in precisely tuning interfacial forces. Here, a fully dry, industrially compatible transfer platform utilizing a ferroelectric poly(vinylidene-fluoride-trifluoroethylene) (P(VDF-TrFE)) film with electrostatically switchable adhesion, serving as both a mechanical support and a transfer layer, is demonstrated. Negative Corona poling of P(VDF-TrFE) induces p-type doping in graphene. Density Functional Theory calculations confirm that this simultaneously reduces Gr-Cu adhesion while increasing P(VDF-TrFE)-Gr adhesion, enabling clean, large-scale graphene delamination from Cu foils with >99% coverage. Subsequent thermal annealing above P(VDF-TrFE)'s Curie temperature (approximate to 135 degrees C) depolarizes the film, neutralizing the interfacial charge for a clean release. The versatility of this method is shown for other two-dimensional (2D) materials, including molybdenum disulfide and hexagonal boron nitride. Crucially, the process has been validated on cm-scale samples using a fully automated system with a transfer time of <5 min, highlighting a viable path toward industrial-scale production of high-quality 2D material films.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Although chemical vapor deposition (CVD) produces meter-scale, high-quality graphene (Gr) on copper (Cu) foils, its practical integration is hampered by challenges in the transfer process. Conventional wet transfers are slow, produce chemical waste, and lack scalability, whereas existing dry transfer methods struggle with mechanical damage and residues due to strong Gr-Cu adhesion and the difficulty in precisely tuning interfacial forces. Here, a fully dry, industrially compatible transfer platform utilizing a ferroelectric poly(vinylidene-fluoride-trifluoroethylene) (P(VDF-TrFE)) film with electrostatically switchable adhesion, serving as both a mechanical support and a transfer layer, is demonstrated. Negative Corona poling of P(VDF-TrFE) induces p-type doping in graphene. Density Functional Theory calculations confirm that this simultaneously reduces Gr-Cu adhesion while increasing P(VDF-TrFE)-Gr adhesion, enabling clean, large-scale graphene delamination from Cu foils with >99% coverage. Subsequent thermal annealing above P(VDF-TrFE)'s Curie temperature (approximate to 135 degrees C) depolarizes the film, neutralizing the interfacial charge for a clean release. The versatility of this method is shown for other two-dimensional (2D) materials, including molybdenum disulfide and hexagonal boron nitride. Crucially, the process has been validated on cm-scale samples using a fully automated system with a transfer time of <5 min, highlighting a viable path toward industrial-scale production of high-quality 2D material films. |
Zhang, Hongji; Grebenko, Artem K; Iakoubovskii, Konstantin V; Zhang, Hanning; Yamaletdinov, Ruslan; Makarova, Anna; Fedorov, Alexander; Rejaul, S K; Shivajirao, Ranjith; Tong, Zheng Jue; Grebenchuk, Sergey; Karadeniz, Ugur; Shi, Lu; Vyalikh, Denis V; He, Ya; Starkov, Andrei; Alekseeva, Alena A; Tee, Chuan Chu; Orofeo, Carlo Mendoza; Lin, Junhao; Suenaga, Kazutomo; Bosman, Michel; Koperski, Maciej; Weber, Bent; Novoselov, Kostya S; Yazyev, Oleg V; Toh, Chee-Tat; Ozyilmaz, Barbaros Superior Adhesion of Monolayer Amorphous Carbon to Copper Journal Article ADVANCED MATERIALS, 37 (32), 2025, ISSN: 0935-9648. @article{ISI:001498039100001, title = {Superior Adhesion of Monolayer Amorphous Carbon to Copper}, author = {Hongji Zhang and Artem K Grebenko and Konstantin V Iakoubovskii and Hanning Zhang and Ruslan Yamaletdinov and Anna Makarova and Alexander Fedorov and S K Rejaul and Ranjith Shivajirao and Zheng Jue Tong and Sergey Grebenchuk and Ugur Karadeniz and Lu Shi and Denis V Vyalikh and Ya He and Andrei Starkov and Alena A Alekseeva and Chuan Chu Tee and Carlo Mendoza Orofeo and Junhao Lin and Kazutomo Suenaga and Michel Bosman and Maciej Koperski and Bent Weber and Kostya S Novoselov and Oleg V Yazyev and Chee-Tat Toh and Barbaros Ozyilmaz}, doi = {10.1002/adma.202419112}, times_cited = {2}, issn = {0935-9648}, year = {2025}, date = {2025-05-29}, journal = {ADVANCED MATERIALS}, volume = {37}, number = {32}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {The single-atom thickness of graphene holds great potential for device scaling, but its effectiveness as a thin metal-ion diffusion barrier in microelectronics and a corrosion barrier for plasmonic devices is compromised by weak van der Waals interactions with copper (Cu), leading to delamination issues. In contrast, monolayer amorphous carbon (MAC), a recently reported single-atom-thick carbon film with a disordered sp2 hybridized structure, demonstrates superior adhesion properties. This study reveals that MAC exhibits an adhesion energy of 85 J m-2 on Cu, which is 13 times greater than that of graphene. This exceptional adhesion is attributed to the formation of covalent-like Cu & horbar;C bonds while preserving its sp2 structure, as evidenced by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Density functional theory (DFT) calculations further elucidate that the corrugated structure of MAC facilitates the hybridization of C 2pz orbitals with Cu 4s and 3dz2 orbitals, promoting strong bonding. These insights indicate that the amorphous structure of MAC significantly enhances adhesion while preserving its elemental composition, providing a pathway to improve the mechanical reliability and performance of two-dimensional (2D) materials on metal substrates in various technological applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The single-atom thickness of graphene holds great potential for device scaling, but its effectiveness as a thin metal-ion diffusion barrier in microelectronics and a corrosion barrier for plasmonic devices is compromised by weak van der Waals interactions with copper (Cu), leading to delamination issues. In contrast, monolayer amorphous carbon (MAC), a recently reported single-atom-thick carbon film with a disordered sp2 hybridized structure, demonstrates superior adhesion properties. This study reveals that MAC exhibits an adhesion energy of 85 J m-2 on Cu, which is 13 times greater than that of graphene. This exceptional adhesion is attributed to the formation of covalent-like Cu & horbar;C bonds while preserving its sp2 structure, as evidenced by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Density functional theory (DFT) calculations further elucidate that the corrugated structure of MAC facilitates the hybridization of C 2pz orbitals with Cu 4s and 3dz2 orbitals, promoting strong bonding. These insights indicate that the amorphous structure of MAC significantly enhances adhesion while preserving its elemental composition, providing a pathway to improve the mechanical reliability and performance of two-dimensional (2D) materials on metal substrates in various technological applications. |
Shin, Bongki; Ni, Bo; Toh, Chee-Tat; Steinbach, Doug; Yang, Zhenze; Sassi, Lucas M; Ai, Qing; Niu, Kangdi; Lin, Junhao; Suenaga, Kazu; Han, Yimo; Buehler, Markus J; Ozyilmaz, Barbaros; Lou, Jun Intrinsic toughening in monolayer amorphous carbon nanocomposites Journal Article MATTER, 8 (4), 2025, ISSN: 2590-2393. @article{ISI:001462473000001, title = {Intrinsic toughening in monolayer amorphous carbon nanocomposites}, author = {Bongki Shin and Bo Ni and Chee-Tat Toh and Doug Steinbach and Zhenze Yang and Lucas M Sassi and Qing Ai and Kangdi Niu and Junhao Lin and Kazu Suenaga and Yimo Han and Markus J Buehler and Barbaros Ozyilmaz and Jun Lou}, doi = {10.1016/j.matt.2025.102000}, times_cited = {8}, issn = {2590-2393}, year = {2025}, date = {2025-04-02}, journal = {MATTER}, volume = {8}, number = {4}, publisher = {CELL PRESS}, address = {50 HAMPSHIRE ST, FLOOR 5, CAMBRIDGE, MA 02139 USA}, abstract = {Two-dimensional (2D) materials have immense potential to advance flexible electronics, yet they are limited by low fracture toughness. This study addresses the intrinsic toughening of monolayer amorphous carbon (MAC), a 2D nanocomposite, to overcome this challenge. By incorporating both amorphous and nanocrystalline phases, MAC significantly enhances energy absorption during fracture propagation, as evidenced by crack blunting, deflecting, and bridging. Using in situ tensile tests under a scanning electron microscope, our results indicate an 8-fold increase in the energy release rate compared to monolayer graphene, along with improved fracture strain and crack stability. Molecular dynamics simulations demonstrate the impact of phase composition on fracture energy. Our results present a scalable toughening strategy for 2D materials, potentially broadening their applications in fields requiring robust fracture resistance.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Two-dimensional (2D) materials have immense potential to advance flexible electronics, yet they are limited by low fracture toughness. This study addresses the intrinsic toughening of monolayer amorphous carbon (MAC), a 2D nanocomposite, to overcome this challenge. By incorporating both amorphous and nanocrystalline phases, MAC significantly enhances energy absorption during fracture propagation, as evidenced by crack blunting, deflecting, and bridging. Using in situ tensile tests under a scanning electron microscope, our results indicate an 8-fold increase in the energy release rate compared to monolayer graphene, along with improved fracture strain and crack stability. Molecular dynamics simulations demonstrate the impact of phase composition on fracture energy. Our results present a scalable toughening strategy for 2D materials, potentially broadening their applications in fields requiring robust fracture resistance. |
2021 |
Toh, Chee-Tat Squashing carbon nanotubes into nanoribbons Journal Article NATURE ELECTRONICS, 4 (9), pp. 633-634, 2021, ISSN: 2520-1131. @article{ISI:000692947500002, title = {Squashing carbon nanotubes into nanoribbons}, author = {Chee-Tat Toh}, doi = {10.1038/s41928-021-00645-2}, times_cited = {6}, issn = {2520-1131}, year = {2021}, date = {2021-09-06}, journal = {NATURE ELECTRONICS}, volume = {4}, number = {9}, pages = {633-634}, publisher = {NATURE PORTFOLIO}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2020 |
Toh, Chee-Tat; Zhang, Hongji; Lin, Junhao; Mayorov, Alexander S; Wang, Yun-Peng; Orofeo, Carlo M; Ferry, Darim Badur; Andersen, Henrik; Kakenov, Nurbek; Guo, Zenglong; Abidi, Irfan Haider; Sims, Hunter; Suenaga, Kazu; Pantelides, Sokrates T; Ozyilmaz, Barbaros Synthesis and properties of free-standing monolayer amorphous carbon Journal Article 243 NATURE, 577 (7789), pp. 199-+, 2020, ISSN: 0028-0836. @article{ISI:000506682500033, title = {Synthesis and properties of free-standing monolayer amorphous carbon}, author = {Chee-Tat Toh and Hongji Zhang and Junhao Lin and Alexander S Mayorov and Yun-Peng Wang and Carlo M Orofeo and Darim Badur Ferry and Henrik Andersen and Nurbek Kakenov and Zenglong Guo and Irfan Haider Abidi and Hunter Sims and Kazu Suenaga and Sokrates T Pantelides and Barbaros Ozyilmaz}, doi = {10.1038/s41586-019-1871-2}, times_cited = {243}, issn = {0028-0836}, year = {2020}, date = {2020-01-09}, journal = {NATURE}, volume = {577}, number = {7789}, pages = {199-+}, publisher = {NATURE PORTFOLIO}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {Bulk amorphous materials have been studied extensively and are widely used, yet their atomic arrangement remains an open issue. Although they are generally believed to be Zachariasen continuous random networks(1), recent experimental evidence favours the competing crystallite model in the case of amorphous silicon(2-4). In two-dimensional materials, however, the corresponding questions remain unanswered. Here we report the synthesis, by laser-assisted chemical vapour deposition(5), of centimetre-scale, free-standing, continuous and stable monolayer amorphous carbon, topologically distinct from disordered graphene. Unlike in bulk materials, the structure of monolayer amorphous carbon can be determined by atomic-resolution imaging. Extensive characterization by Raman and X-ray spectroscopy and transmission electron microscopy reveals the complete absence of long-range periodicity and a threefold-coordinated structure with a wide distribution of bond lengths, bond angles, and five-, six-, seven- and eight-member rings. The ring distribution is not a Zachariasen continuous random network, but resembles the competing (nano)crystallite model(6). We construct a corresponding model that enables density-functional-theory calculations of the properties of monolayer amorphous carbon, in accordance with observations. Direct measurements confirm that it is insulating, with resistivity values similar to those of boron nitride grown by chemical vapour deposition. Free-standing monolayer amorphous carbon is surprisingly stable and deforms to a high breaking strength, without crack propagation from the point of fracture. The excellent physical properties of this stable, free-standing monolayer amorphous carbon could prove useful for permeation and diffusion barriers in applications such as magnetic recording devices and flexible electronics.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Bulk amorphous materials have been studied extensively and are widely used, yet their atomic arrangement remains an open issue. Although they are generally believed to be Zachariasen continuous random networks(1), recent experimental evidence favours the competing crystallite model in the case of amorphous silicon(2-4). In two-dimensional materials, however, the corresponding questions remain unanswered. Here we report the synthesis, by laser-assisted chemical vapour deposition(5), of centimetre-scale, free-standing, continuous and stable monolayer amorphous carbon, topologically distinct from disordered graphene. Unlike in bulk materials, the structure of monolayer amorphous carbon can be determined by atomic-resolution imaging. Extensive characterization by Raman and X-ray spectroscopy and transmission electron microscopy reveals the complete absence of long-range periodicity and a threefold-coordinated structure with a wide distribution of bond lengths, bond angles, and five-, six-, seven- and eight-member rings. The ring distribution is not a Zachariasen continuous random network, but resembles the competing (nano)crystallite model(6). We construct a corresponding model that enables density-functional-theory calculations of the properties of monolayer amorphous carbon, in accordance with observations. Direct measurements confirm that it is insulating, with resistivity values similar to those of boron nitride grown by chemical vapour deposition. Free-standing monolayer amorphous carbon is surprisingly stable and deforms to a high breaking strength, without crack propagation from the point of fracture. The excellent physical properties of this stable, free-standing monolayer amorphous carbon could prove useful for permeation and diffusion barriers in applications such as magnetic recording devices and flexible electronics. |
2015 |
Wu, Jing; Koon, Gavin Kok Wai; Xiang, Du; Han, Cheng; Toh, Chee Tat; Kulkarni, Eeshan S; Verzhbitskiy, Ivan; Carvalho, Alexandra; Rodin, Aleksandr S; Koenig, Steven P; Eda, Goki; Chen, Wei; Neto, Castro A H; Oezyilmaz, Barbaros Colossal Ultraviolet Photoresponsivity of Few-Layer Black Phosphorus Journal Article 227 ACS NANO, 9 (8), pp. 8070-8077, 2015, ISSN: 1936-0851. @article{ISI:000360323300035, title = {Colossal Ultraviolet Photoresponsivity of Few-Layer Black Phosphorus}, author = {Jing Wu and Gavin Kok Wai Koon and Du Xiang and Cheng Han and Chee Tat Toh and Eeshan S Kulkarni and Ivan Verzhbitskiy and Alexandra Carvalho and Aleksandr S Rodin and Steven P Koenig and Goki Eda and Wei Chen and Castro A H Neto and Barbaros Oezyilmaz}, doi = {10.1021/acsnano.5b01922}, times_cited = {227}, issn = {1936-0851}, year = {2015}, date = {2015-08-01}, journal = {ACS NANO}, volume = {9}, number = {8}, pages = {8070-8077}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Black phosphorus has an orthorhombic layered structure with a layer-dependent direct band gap from monolayer to bulk, making this material an emerging material for photodetection. Inspired by this and the recent excitement over this material, we studied the optoelectronics characteristics of high-quality, few-layer black phosphorus-based photodetectors over a wide spectrum ranging from near-ultraviolet (UV) to near-infrared (NIR). It is demonstrated for the first time that black phosphorus can be configured as an excellent UV photodetector with a specific detectivity similar to 3 x 10(13) Jones. More critically, we found that the UV photoresponsivity can be significantly enhanced to similar to 9 x 10(4) A W-1 by applying a source-drain bias (V-SD) of 3 V, which is the highest ever measured in any 2D material and 10(7) times higher than the previously reported value for black phosphorus. We attribute such a colossal UV photoresponsivity to the resonant-interband transition between two specially nested valence and conduction bands. These nested bands provide an unusually high density of states for highly efficient UV absorption due to the singularity of their nature.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Black phosphorus has an orthorhombic layered structure with a layer-dependent direct band gap from monolayer to bulk, making this material an emerging material for photodetection. Inspired by this and the recent excitement over this material, we studied the optoelectronics characteristics of high-quality, few-layer black phosphorus-based photodetectors over a wide spectrum ranging from near-ultraviolet (UV) to near-infrared (NIR). It is demonstrated for the first time that black phosphorus can be configured as an excellent UV photodetector with a specific detectivity similar to 3 x 10(13) Jones. More critically, we found that the UV photoresponsivity can be significantly enhanced to similar to 9 x 10(4) A W-1 by applying a source-drain bias (V-SD) of 3 V, which is the highest ever measured in any 2D material and 10(7) times higher than the previously reported value for black phosphorus. We attribute such a colossal UV photoresponsivity to the resonant-interband transition between two specially nested valence and conduction bands. These nested bands provide an unusually high density of states for highly efficient UV absorption due to the singularity of their nature. |
Kulkarni, Eeshan Sandeep; Heussler, Sascha Pierre; Stier, Andreas Volker; Martin-Fernandez, Inigo; Andersen, Henrik; Toh, Chee-Tat; Ozyilmaz, Barbaros Exploiting the IR Transparency of Graphene for Fast Pyroelectric Infrared Detection Journal Article 40 ADVANCED OPTICAL MATERIALS, 3 (1), pp. 34-38, 2015, ISSN: 2195-1071. @article{ISI:000348738300003, title = {Exploiting the IR Transparency of Graphene for Fast Pyroelectric Infrared Detection}, author = {Eeshan Sandeep Kulkarni and Sascha Pierre Heussler and Andreas Volker Stier and Inigo Martin-Fernandez and Henrik Andersen and Chee-Tat Toh and Barbaros Ozyilmaz}, doi = {10.1002/adom.201400374}, times_cited = {40}, issn = {2195-1071}, year = {2015}, date = {2015-01-01}, journal = {ADVANCED OPTICAL MATERIALS}, volume = {3}, number = {1}, pages = {34-38}, publisher = {WILEY-V C H VERLAG GMBH}, address = {BOSCHSTRASSE 12, D-69469 WEINHEIM, GERMANY}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2014 |
Saha, Surajit; Kahya, Orhan; Jaiswal, Manu; Srivastava, Amar; Annadi, Anil; Balakrishnan, Jayakumar; Pachoud, Alexandre; Toh, Chee-Tat; Hong, Byung-Hee; Ahn, Jong-Hyun; Venkatesan, T; Oezyilmaz, Barbaros Unconventional Transport through Graphene on SrTiO_3: A Plausible Effect of SrTiO3 Phase-Transitions Journal Article 27 SCIENTIFIC REPORTS, 4 , 2014, ISSN: 2045-2322. @article{ISI:000340741700005, title = {Unconventional Transport through Graphene on SrTiO_3: A Plausible Effect of SrTiO3 Phase-Transitions}, author = {Surajit Saha and Orhan Kahya and Manu Jaiswal and Amar Srivastava and Anil Annadi and Jayakumar Balakrishnan and Alexandre Pachoud and Chee-Tat Toh and Byung-Hee Hong and Jong-Hyun Ahn and T Venkatesan and Barbaros Oezyilmaz}, doi = {10.1038/srep06173}, times_cited = {27}, issn = {2045-2322}, year = {2014}, date = {2014-08-22}, journal = {SCIENTIFIC REPORTS}, volume = {4}, publisher = {NATURE PORTFOLIO}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {High-k dielectric oxides are supposedly ideal gate-materials for ultra-high doping in graphene and other 2D-crystals. Here, we report a temperature-dependent electronic transport study on chemical vapor deposited-graphene gated with SrTiO3 (STO) thin film substrate. At carrier densities away from charge neutrality point the temperature-dependent resistivity of our graphene samples on both STO and SiO2/Si substrates show metallic behavior with contributions from Coulomb scattering and flexural phonons attributable to the presence of characteristic quasi-periodic nano-ripple arrays. Significantly, for graphene samples on STO substrates we observe an anomalous 'slope-break' in the temperature-dependent resistivity for T = 50 to 100 K accompanied by a decrease in mobility above 30 K. Furthermore, we observe an unusual decrease in the gate-induced doping-rate at low temperatures, despite an increase in dielectric constant of the substrate. We believe that a complex mechanism is at play as a consequence of the structural phase transition of the underlying substrate showing an anomalous transport behavior in graphene on STO. The anomalies are discussed in the context of Coulomb as well as phonon scattering.}, keywords = {}, pubstate = {published}, tppubtype = {article} } High-k dielectric oxides are supposedly ideal gate-materials for ultra-high doping in graphene and other 2D-crystals. Here, we report a temperature-dependent electronic transport study on chemical vapor deposited-graphene gated with SrTiO3 (STO) thin film substrate. At carrier densities away from charge neutrality point the temperature-dependent resistivity of our graphene samples on both STO and SiO2/Si substrates show metallic behavior with contributions from Coulomb scattering and flexural phonons attributable to the presence of characteristic quasi-periodic nano-ripple arrays. Significantly, for graphene samples on STO substrates we observe an anomalous 'slope-break' in the temperature-dependent resistivity for T = 50 to 100 K accompanied by a decrease in mobility above 30 K. Furthermore, we observe an unusual decrease in the gate-induced doping-rate at low temperatures, despite an increase in dielectric constant of the substrate. We believe that a complex mechanism is at play as a consequence of the structural phase transition of the underlying substrate showing an anomalous transport behavior in graphene on STO. The anomalies are discussed in the context of Coulomb as well as phonon scattering. |
Lee, Jong Hak; Tan, Jun You; Toh, Chee-Tat; Koenig, Steven P; Fedorov, V E; Neto, Antonio Castro H; Oezyilmaz, Barbaros Nanometer Thick Elastic Graphene Engine Journal Article 36 NANO LETTERS, 14 (5), pp. 2677-2680, 2014, ISSN: 1530-6984. @article{ISI:000336074800068, title = {Nanometer Thick Elastic Graphene Engine}, author = {Jong Hak Lee and Jun You Tan and Chee-Tat Toh and Steven P Koenig and V E Fedorov and Antonio Castro H Neto and Barbaros Oezyilmaz}, doi = {10.1021/nl500568d}, times_cited = {36}, issn = {1530-6984}, year = {2014}, date = {2014-05-01}, journal = {NANO LETTERS}, volume = {14}, number = {5}, pages = {2677-2680}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Significant progress has been made in the construction and theoretical understanding of molecular motors because of their potential use. Here, we have demonstrated fabrication of a simple but powerful 1 nm thick graphene engine. The engine comprises a high elastic membrane-piston made of graphene and weakly chemisorbed ClF3 molecules as the high power volume changeable actuator, while a 532 nm LASER acts as the ignition plug. Rapid volume expansion of the ClF3 molecules leads to graphene blisters. The size of the blister is controllable by changing the ignition parameters. The estimated internal pressure per expansion cycle of the engine is about similar to 10(6) Pa. The graphene engine presented here shows exceptional reliability, showing no degradation after 10 000 cycles.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Significant progress has been made in the construction and theoretical understanding of molecular motors because of their potential use. Here, we have demonstrated fabrication of a simple but powerful 1 nm thick graphene engine. The engine comprises a high elastic membrane-piston made of graphene and weakly chemisorbed ClF3 molecules as the high power volume changeable actuator, while a 532 nm LASER acts as the ignition plug. Rapid volume expansion of the ClF3 molecules leads to graphene blisters. The size of the blister is controllable by changing the ignition parameters. The estimated internal pressure per expansion cycle of the engine is about similar to 10(6) Pa. The graphene engine presented here shows exceptional reliability, showing no degradation after 10 000 cycles. |
Kim, Keumok; Bae, Sang-Hoon; Toh, Chee Tat; Kim, Hobeom; Cho, Jeong Ho; Whang, Dongmok; Lee, Tae-Woo; Oezyilmaz, Barbaros; Ahn, Jong-Hyun Ultrathin Organic Solar Cells with Graphene Doped by Ferroelectric Polarization Journal Article 81 ACS APPLIED MATERIALS & INTERFACES, 6 (5), pp. 3299-3304, 2014, ISSN: 1944-8244. @article{ISI:000332922900032, title = {Ultrathin Organic Solar Cells with Graphene Doped by Ferroelectric Polarization}, author = {Keumok Kim and Sang-Hoon Bae and Chee Tat Toh and Hobeom Kim and Jeong Ho Cho and Dongmok Whang and Tae-Woo Lee and Barbaros Oezyilmaz and Jong-Hyun Ahn}, doi = {10.1021/am405270y}, times_cited = {81}, issn = {1944-8244}, year = {2014}, date = {2014-03-12}, journal = {ACS APPLIED MATERIALS & INTERFACES}, volume = {6}, number = {5}, pages = {3299-3304}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Graphene has been employed as transparent electrodes in organic solar cells (OSCs) because of its good physical and optical properties. However, the electrical conductivity of graphene films synthesized by chemical vapor deposition (CVD) is still inferior to that of conventional indium tin oxide (ITO) electrodes of comparable transparency, resulting in a lower performance of OSCs. Here, we report an effective method to improve the performance and long-term stability of graphene-based OSCs using electrostatically doped graphene films via a ferroelectric polymer. The sheet resistance of electrostatically doped few layer graphene films was reduced to similar to 70 Omega/sq at 87% optical transmittance. Such graphene-based OSCs exhibit an efficiency of 2.07% with a superior stability when compared to chemically doped graphene-based OSCs. Furthermore, OSCs constructed on ultrathin ferroelectric film as a substrate of only a few micrometers show extremely good mechanical flexibility and durability and can be rolled up into a cylinder with 7 mm diameter.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Graphene has been employed as transparent electrodes in organic solar cells (OSCs) because of its good physical and optical properties. However, the electrical conductivity of graphene films synthesized by chemical vapor deposition (CVD) is still inferior to that of conventional indium tin oxide (ITO) electrodes of comparable transparency, resulting in a lower performance of OSCs. Here, we report an effective method to improve the performance and long-term stability of graphene-based OSCs using electrostatically doped graphene films via a ferroelectric polymer. The sheet resistance of electrostatically doped few layer graphene films was reduced to similar to 70 Omega/sq at 87% optical transmittance. Such graphene-based OSCs exhibit an efficiency of 2.07% with a superior stability when compared to chemically doped graphene-based OSCs. Furthermore, OSCs constructed on ultrathin ferroelectric film as a substrate of only a few micrometers show extremely good mechanical flexibility and durability and can be rolled up into a cylinder with 7 mm diameter. |
Ni, Guang-Xin; Yang, Hong-Zhi; Ji, Wei; Baeck, Seung-Jae; Toh, Chee-Tat; Ahn, Jong-Hyun; Pereira, Vitor M; Oezyilmaz, Barbaros Tuning Optical Conductivity of Large-Scale CVD Graphene by Strain Engineering Journal Article 96 ADVANCED MATERIALS, 26 (7), pp. 1081-1086, 2014, ISSN: 0935-9648. @article{ISI:000331909800012, title = {Tuning Optical Conductivity of Large-Scale CVD Graphene by Strain Engineering}, author = {Guang-Xin Ni and Hong-Zhi Yang and Wei Ji and Seung-Jae Baeck and Chee-Tat Toh and Jong-Hyun Ahn and Vitor M Pereira and Barbaros Oezyilmaz}, doi = {10.1002/adma.201304156}, times_cited = {96}, issn = {0935-9648}, year = {2014}, date = {2014-02-01}, journal = {ADVANCED MATERIALS}, volume = {26}, number = {7}, pages = {1081-1086}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2013 |
Lee, Wonho; Kahya, Orhan; Toh, Chee Tat; Oezyilmaz, Barbaros; Ahn, Jong-Hyun Flexible graphene-PZT ferroelectric nonvolatile memory Journal Article 60 NANOTECHNOLOGY, 24 (47), 2013, ISSN: 0957-4484. @article{ISI:000326816600005, title = {Flexible graphene-PZT ferroelectric nonvolatile memory}, author = {Wonho Lee and Orhan Kahya and Chee Tat Toh and Barbaros Oezyilmaz and Jong-Hyun Ahn}, doi = {10.1088/0957-4484/24/47/475202}, times_cited = {60}, issn = {0957-4484}, year = {2013}, date = {2013-11-29}, journal = {NANOTECHNOLOGY}, volume = {24}, number = {47}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {We report the fabrication of a flexible graphene-based nonvolatile memory device using Pb(Zr-0.35; Ti-0.65)O-3 (PZT) as the ferroelectric material. The graphene and PZT ferroelectric layers were deposited using chemical vapor deposition and sol-gel methods, respectively. Such PZT films show a high remnant polarization (P-r) of 30 mu C cm(-2) and a coercive voltage (V-c) of 3.5 V under a voltage loop over +/- 11 V. The graphene-PZT ferroelectric nonvolatile memory on a plastic substrate displayed an on/off current ratio of 6.7, a memory window of 6 V and reliable operation. In addition, the device showed one order of magnitude lower operation voltage range than organic-based ferroelectric nonvolatile memory after removing the anti-ferroelectric behavior incorporating an electrolyte solution. The devices showed robust operation in bent states of bending radii up to 9 mm and in cycling tests of 200 times. The devices exhibited remarkable mechanical properties and were readily integrated with plastic substrates for the production of flexible circuits.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We report the fabrication of a flexible graphene-based nonvolatile memory device using Pb(Zr-0.35; Ti-0.65)O-3 (PZT) as the ferroelectric material. The graphene and PZT ferroelectric layers were deposited using chemical vapor deposition and sol-gel methods, respectively. Such PZT films show a high remnant polarization (P-r) of 30 mu C cm(-2) and a coercive voltage (V-c) of 3.5 V under a voltage loop over +/- 11 V. The graphene-PZT ferroelectric nonvolatile memory on a plastic substrate displayed an on/off current ratio of 6.7, a memory window of 6 V and reliable operation. In addition, the device showed one order of magnitude lower operation voltage range than organic-based ferroelectric nonvolatile memory after removing the anti-ferroelectric behavior incorporating an electrolyte solution. The devices showed robust operation in bent states of bending radii up to 9 mm and in cycling tests of 200 times. The devices exhibited remarkable mechanical properties and were readily integrated with plastic substrates for the production of flexible circuits. |