Browse through over scientific publications by CA2DM staff, students, collaborators, and partners.
2011 |
Santos, Jaime E; Peres, Nuno M R; dos Santos, Joao Lopes M B; Neto, Antonio Castro H Electronic doping of graphene by deposited transition metal atoms Journal Article PHYSICAL REVIEW B, 84 (8), 2011, ISSN: 2469-9950. @article{ISI:000294325400014, title = {Electronic doping of graphene by deposited transition metal atoms}, author = {Jaime E Santos and Nuno M R Peres and Joao M B Lopes dos Santos and Antonio H Castro Neto}, doi = {10.1103/PhysRevB.84.085430}, issn = {2469-9950}, year = {2011}, date = {2011-08-01}, journal = {PHYSICAL REVIEW B}, volume = {84}, number = {8}, abstract = {We perform a phenomenological analysis of the problem of the electronic doping of a graphene sheet by deposited transition metal atoms, which aggregate in clusters. The sample is placed in a capacitor device such that the electronic doping of graphene can be varied by the application of a gate voltage and such that transport measurements can be performed via the application of a (much smaller) voltage along the graphene sample, as reported in the work of Pi et al. [Phys. Rev. B 80, 075406 (2009)]. The analysis allows us to explain the thermodynamic properties of the device, such as the level of doping of graphene and the ionization potential of the metal clusters, in terms of the chemical interaction between graphene and the clusters. We are also able, by modeling the metallic clusters as perfectly conducting spheres, to determine the scattering potential due to these clusters on the electronic carriers of graphene and hence the contribution of these clusters to the resistivity of the sample. The model presented is able to explain the measurements performed by Pi et al. on Pt-covered graphene samples at the lowest metallic coverages measured, and we also present a theoretical argument based on the above model that explains why significant deviations from such a theory are observed at higher levels of coverage.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We perform a phenomenological analysis of the problem of the electronic doping of a graphene sheet by deposited transition metal atoms, which aggregate in clusters. The sample is placed in a capacitor device such that the electronic doping of graphene can be varied by the application of a gate voltage and such that transport measurements can be performed via the application of a (much smaller) voltage along the graphene sample, as reported in the work of Pi et al. [Phys. Rev. B 80, 075406 (2009)]. The analysis allows us to explain the thermodynamic properties of the device, such as the level of doping of graphene and the ionization potential of the metal clusters, in terms of the chemical interaction between graphene and the clusters. We are also able, by modeling the metallic clusters as perfectly conducting spheres, to determine the scattering potential due to these clusters on the electronic carriers of graphene and hence the contribution of these clusters to the resistivity of the sample. The model presented is able to explain the measurements performed by Pi et al. on Pt-covered graphene samples at the lowest metallic coverages measured, and we also present a theoretical argument based on the above model that explains why significant deviations from such a theory are observed at higher levels of coverage. |
Neto, Castro A H; Novoselov, K New directions in science and technology: two-dimensional crystals Journal Article REPORTS ON PROGRESS IN PHYSICS, 74 (8), 2011, ISSN: 0034-4885. @article{ISI:000293225900001, title = {New directions in science and technology: two-dimensional crystals}, author = {A H Castro Neto and K Novoselov}, doi = {10.1088/0034-4885/74/8/082501}, issn = {0034-4885}, year = {2011}, date = {2011-08-01}, journal = {REPORTS ON PROGRESS IN PHYSICS}, volume = {74}, number = {8}, abstract = {Graphene is possibly one of the largest and fastest growing fields in condensed matter research. However, graphene is only one example in a large class of two-dimensional crystals with unusual properties. In this paper we briefly review the properties of graphene and look at the exciting possibilities that lie ahead.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Graphene is possibly one of the largest and fastest growing fields in condensed matter research. However, graphene is only one example in a large class of two-dimensional crystals with unusual properties. In this paper we briefly review the properties of graphene and look at the exciting possibilities that lie ahead. |
de Gail, R; Goerbig, M O; Guinea, F; Montambaux, G; Neto, Castro A H Topologically protected zero modes in twisted bilayer graphene Journal Article PHYSICAL REVIEW B, 84 (4), 2011, ISSN: 1098-0121. @article{ISI:000292825100016, title = {Topologically protected zero modes in twisted bilayer graphene}, author = {R de Gail and M O Goerbig and F Guinea and G Montambaux and A H Castro Neto}, doi = {10.1103/PhysRevB.84.045436}, issn = {1098-0121}, year = {2011}, date = {2011-07-01}, journal = {PHYSICAL REVIEW B}, volume = {84}, number = {4}, abstract = {We show that a twisted graphene bilayer can reveal unusual topological properties at low energies, as a consequence of a Dirac-point splitting. These features rely on a symmetry analysis of the electron hopping between the two layers of graphene and we derive a simplified effective low-energy Hamiltonian which captures the essential topological properties of a twisted graphene bilayer. The corresponding Landau levels peculiarly reveal a degenerate zero-energy mode which cannot be lifted by strong magnetic fields.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We show that a twisted graphene bilayer can reveal unusual topological properties at low energies, as a consequence of a Dirac-point splitting. These features rely on a symmetry analysis of the electron hopping between the two layers of graphene and we derive a simplified effective low-energy Hamiltonian which captures the essential topological properties of a twisted graphene bilayer. The corresponding Landau levels peculiarly reveal a degenerate zero-energy mode which cannot be lifted by strong magnetic fields. |
Peres, N M R; dos Santos, Lopes J M B; Neto, Castro A H Coulomb drag and high-resistivity behavior in double-layer graphene Journal Article EPL, 95 (1, SI), 2011, ISSN: 0295-5075. @article{ISI:000291990600030, title = {Coulomb drag and high-resistivity behavior in double-layer graphene}, author = {N M R Peres and J M B Lopes dos Santos and A H Castro Neto}, doi = {10.1209/0295-5075/95/18001}, issn = {0295-5075}, year = {2011}, date = {2011-07-01}, journal = {EPL}, volume = {95}, number = {1, SI}, abstract = {We show that Coulomb drag in ultra-clean graphene double layers can be used for controlling the on-and-off ratio for current flow by tuning the external gate voltage. Hence, although graphene remains semi-metallic, the double-layer graphene system can be tuned from conductive to a highly resistive state. We show that our results explain previous data of Coulomb drag in double-layer graphene samples in disordered SiO2 substrates. Copyright (C) EPLA, 2011}, keywords = {}, pubstate = {published}, tppubtype = {article} } We show that Coulomb drag in ultra-clean graphene double layers can be used for controlling the on-and-off ratio for current flow by tuning the external gate voltage. Hence, although graphene remains semi-metallic, the double-layer graphene system can be tuned from conductive to a highly resistive state. We show that our results explain previous data of Coulomb drag in double-layer graphene samples in disordered SiO2 substrates. Copyright (C) EPLA, 2011 |
Nayak, Tapas R; Andersen, Henrik; Makam, Venkata S; Khaw, Clement; Bae, Sukang; Xu, Xiangfan; Ee, Pui-Lai R; Ahn, Jong-Hyun; Hong, Byung Hee; Pastorin, Giorgia; Oezyilmaz, Barbaros Graphene for Controlled and Accelerated Osteogenic Differentiation of Human Mesenchymal Stem Cells Journal Article ACS NANO, 5 (6), pp. 4670-4678, 2011, ISSN: 1936-0851. @article{ISI:000292055200049, title = {Graphene for Controlled and Accelerated Osteogenic Differentiation of Human Mesenchymal Stem Cells}, author = {Tapas R Nayak and Henrik Andersen and Venkata S Makam and Clement Khaw and Sukang Bae and Xiangfan Xu and Pui-Lai R Ee and Jong-Hyun Ahn and Byung Hee Hong and Giorgia Pastorin and Barbaros Oezyilmaz}, doi = {10.1021/nn200500h}, issn = {1936-0851}, year = {2011}, date = {2011-06-01}, journal = {ACS NANO}, volume = {5}, number = {6}, pages = {4670-4678}, abstract = {Current tissue engineering approaches combine different scaffold materials with living cells to provide biological substitutes that can repair and eventually improve tissue functions. Both natural and synthetic materials have been fabricated for transplantation of stem cells and their specific differentiation Into muscles, bones, and cartilages. One of the key objectives for bone regeneration therapy to be successful Is to direct stem cells' proliferation and to accelerate their differentiation in a controlled manner through the use of growth factors and osteogenic inducers. Here we show that graphene provides a promising biocompatible scaffold that does not hamper the proliferation of human mesenchymal stem cells (hMSCs) and accelerates their specific differentiation into bone cells. The differentiation rate Is comparable to the one achieved with common growth factors, demonstrating graphene's potential for stem cell research.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Current tissue engineering approaches combine different scaffold materials with living cells to provide biological substitutes that can repair and eventually improve tissue functions. Both natural and synthetic materials have been fabricated for transplantation of stem cells and their specific differentiation Into muscles, bones, and cartilages. One of the key objectives for bone regeneration therapy to be successful Is to direct stem cells' proliferation and to accelerate their differentiation in a controlled manner through the use of growth factors and osteogenic inducers. Here we show that graphene provides a promising biocompatible scaffold that does not hamper the proliferation of human mesenchymal stem cells (hMSCs) and accelerates their specific differentiation into bone cells. The differentiation rate Is comparable to the one achieved with common growth factors, demonstrating graphene's potential for stem cell research. |
Avsar, Ahmet; Yang, Tsung-Yeh; Bae, Sukang; Balakrishnan, Jayakumar; Volmer, Frank; Jaiswal, Manu; Yi, Zheng; Ali, Syed Rizwan; Guentherodt, Gernot; Hong, Byung Hee; Beschoten, Bernd; Oezyilmaz, Barbaros Toward Wafer Scale Fabrication of Graphene Based Spin Valve Devices Journal Article NANO LETTERS, 11 (6), pp. 2363-2368, 2011, ISSN: 1530-6984. @article{ISI:000291322600029, title = {Toward Wafer Scale Fabrication of Graphene Based Spin Valve Devices}, author = {Ahmet Avsar and Tsung-Yeh Yang and Sukang Bae and Jayakumar Balakrishnan and Frank Volmer and Manu Jaiswal and Zheng Yi and Syed Rizwan Ali and Gernot Guentherodt and Byung Hee Hong and Bernd Beschoten and Barbaros Oezyilmaz}, doi = {10.1021/nl200714q}, issn = {1530-6984}, year = {2011}, date = {2011-06-01}, journal = {NANO LETTERS}, volume = {11}, number = {6}, pages = {2363-2368}, abstract = {We demonstrate injection, transport, and detection of spins in spin valve arrays patterned in both copper based chemical vapor deposition (Cu-CVD) synthesized wafer scale single layer and bilayer graphene. We observe spin relaxation times comparable to those reported for exfoliated graphene samples demonstrating that chemical vapor deposition specific structural differences such as nanoripples do not limit spin transport in the present samples. Our observations make Cu-CVD graphene a promising material of choice for large scale spintronic applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We demonstrate injection, transport, and detection of spins in spin valve arrays patterned in both copper based chemical vapor deposition (Cu-CVD) synthesized wafer scale single layer and bilayer graphene. We observe spin relaxation times comparable to those reported for exfoliated graphene samples demonstrating that chemical vapor deposition specific structural differences such as nanoripples do not limit spin transport in the present samples. Our observations make Cu-CVD graphene a promising material of choice for large scale spintronic applications. |
Neto, Antonio Castro H Another Spin on Graphene Journal Article SCIENCE, 332 (6027), pp. 315-316, 2011, ISSN: 0036-8075. @article{ISI:000289516600033, title = {Another Spin on Graphene}, author = {Antonio H Castro Neto}, doi = {10.1126/science.1204496}, issn = {0036-8075}, year = {2011}, date = {2011-04-01}, journal = {SCIENCE}, volume = {332}, number = {6027}, pages = {315-316}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Neto, Castro A H; Novoselov, K Two-Dimensional Crystals: Beyond Graphene Journal Article MATERIALS EXPRESS, 1 (1), pp. 10-17, 2011, ISSN: 2158-5849. @article{ISI:000311866900002, title = {Two-Dimensional Crystals: Beyond Graphene}, author = {A H Castro Neto and K Novoselov}, doi = {10.1166/mex.2011.1002}, issn = {2158-5849}, year = {2011}, date = {2011-03-01}, journal = {MATERIALS EXPRESS}, volume = {1}, number = {1}, pages = {10-17}, abstract = {Human progress and development has always been marked by breakthroughs in the control of materials. Since pre-historic times, through the stone, bronze, and iron ages, humans have exploited their environment for materials that can be either used directly or can be modified for their benefit, to make their life more comfortable, productive, or to give them military advantage. One age replaces another when the material that is the basis for its sustainability runs its course and is replaced by another material which presents more qualities. Multi-tasking, speed, versatility, and flexibility are at the heart of modern technology. In recent years a new class of materials that can fulfill these needs have emerged: two-dimensional (2D) crystals. Graphene is probably the most famous example, but there are numerous other examples with amazing electronic and structural properties. In this paper we look into the possible routes for exploration of this new field that presents new venues in basic science as well as in applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Human progress and development has always been marked by breakthroughs in the control of materials. Since pre-historic times, through the stone, bronze, and iron ages, humans have exploited their environment for materials that can be either used directly or can be modified for their benefit, to make their life more comfortable, productive, or to give them military advantage. One age replaces another when the material that is the basis for its sustainability runs its course and is replaced by another material which presents more qualities. Multi-tasking, speed, versatility, and flexibility are at the heart of modern technology. In recent years a new class of materials that can fulfill these needs have emerged: two-dimensional (2D) crystals. Graphene is probably the most famous example, but there are numerous other examples with amazing electronic and structural properties. In this paper we look into the possible routes for exploration of this new field that presents new venues in basic science as well as in applications. |
2010 |
Pereira, Vitor M; Ribeiro, R M; Peres, N M R; Neto, Castro A H Optical properties of strained graphene Journal Article EPL, 92 (6), 2010, ISSN: 0295-5075. @article{ISI:000287023900021, title = {Optical properties of strained graphene}, author = {Vitor M Pereira and R M Ribeiro and N M R Peres and A H Castro Neto}, doi = {10.1209/0295-5075/92/67001}, issn = {0295-5075}, year = {2010}, date = {2010-12-01}, journal = {EPL}, volume = {92}, number = {6}, abstract = {The optical conductivity of graphene strained uniaxially is studied within the Kubo-Greenwood formalism. Focusing on inter-band absorption, we analyze and quantify the breakdown of universal transparency in the visible region of the spectrum, and analytically characterize the transparency as a function of strain and polarization. Measuring transmittance as a function of incident polarization directly reflects the magnitude and direction of strain. Moreover, direction-dependent selection rules permit the identification of the lattice orientation by monitoring the van Hove transitions. These photoelastic effects in graphene can be explored towards atomically thin, broadband optical elements. Copyright (C) EPLA, 2010}, keywords = {}, pubstate = {published}, tppubtype = {article} } The optical conductivity of graphene strained uniaxially is studied within the Kubo-Greenwood formalism. Focusing on inter-band absorption, we analyze and quantify the breakdown of universal transparency in the visible region of the spectrum, and analytically characterize the transparency as a function of strain and polarization. Measuring transmittance as a function of incident polarization directly reflects the magnitude and direction of strain. Moreover, direction-dependent selection rules permit the identification of the lattice orientation by monitoring the van Hove transitions. These photoelastic effects in graphene can be explored towards atomically thin, broadband optical elements. Copyright (C) EPLA, 2010 |
0000 |
Wang, Lin; Wang, Xiaojie; Zhang, Yishu; Li, Runlai; Ma, Teng; Leng, Kai; Chen, Zhi; Abdelwahab, Ibrahim; Loh, Kian Ping Exploring Ferroelectric Switching in alpha-In(2)Se(3)for Neuromorphic Computing Journal Article ADVANCED FUNCTIONAL MATERIALS, 0000, ISSN: 1616-301X. @article{ISI:000567403700001, title = {Exploring Ferroelectric Switching in alpha-In(2)Se(3)for Neuromorphic Computing}, author = {Lin Wang and Xiaojie Wang and Yishu Zhang and Runlai Li and Teng Ma and Kai Leng and Zhi Chen and Ibrahim Abdelwahab and Kian Ping Loh}, doi = {10.1002/adfm.202004609, Early Access Date = SEP 2020}, issn = {1616-301X}, journal = {ADVANCED FUNCTIONAL MATERIALS}, abstract = {Recently, 2D ferroelectrics have attracted extensive interest as a competitive platform for implementing future generation functional electronics, including digital memory and brain-inspired computing circuits. Fulfilling their potential requires achieving the interplay between ferroelectricity and electronic characteristics on the device operation level, which is currently lacking since most studies are focused on the verification of ferroelectricity from different 2D materials. Here, by leveraging the ferroelectricity and semiconducting properties of alpha-In2Se3, ferroelectric semiconductor field-effect transistors (FeSFETs) are fabricated and their potential as artificial synapses is demonstrated. Multiple conductance states can be induced in alpha-In2Se3-based FeSFETs by controlling the out-of-plane polarization, which enables the device to faithfully mimic biosynaptic behaviors. In comparison with charge-trapping-based three-terminal synaptic devices, the electronic synapses based on alpha-In(2)Se(3)have the advantages of good controllability, fast learning, and easy integration of gate dielectric, rendering them promising for neuromorphic computing. In addition, an abnormal resistive switching phenomenon in alpha-In(2)Se(3)is reported when operated in the in-plane ferroelectric switching mode. The findings pave the way forward for alpha-In2Se3-based FeSFETs for developing neuromorphic devices in brain-inspired intelligent systems.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Recently, 2D ferroelectrics have attracted extensive interest as a competitive platform for implementing future generation functional electronics, including digital memory and brain-inspired computing circuits. Fulfilling their potential requires achieving the interplay between ferroelectricity and electronic characteristics on the device operation level, which is currently lacking since most studies are focused on the verification of ferroelectricity from different 2D materials. Here, by leveraging the ferroelectricity and semiconducting properties of alpha-In2Se3, ferroelectric semiconductor field-effect transistors (FeSFETs) are fabricated and their potential as artificial synapses is demonstrated. Multiple conductance states can be induced in alpha-In2Se3-based FeSFETs by controlling the out-of-plane polarization, which enables the device to faithfully mimic biosynaptic behaviors. In comparison with charge-trapping-based three-terminal synaptic devices, the electronic synapses based on alpha-In(2)Se(3)have the advantages of good controllability, fast learning, and easy integration of gate dielectric, rendering them promising for neuromorphic computing. In addition, an abnormal resistive switching phenomenon in alpha-In(2)Se(3)is reported when operated in the in-plane ferroelectric switching mode. The findings pave the way forward for alpha-In2Se3-based FeSFETs for developing neuromorphic devices in brain-inspired intelligent systems. |
Liang, Qijie; Gou, Jian; Arramel, ; Zhang, Qian; Zhang, Wenjing; Wee, Andrew Thye Shen Oxygen-induced controllable p-type doping in 2D semiconductor transition metal dichalcogenides Journal Article NANO RESEARCH, 0000, ISSN: 1998-0124. @article{ISI:000567368300001, title = {Oxygen-induced controllable p-type doping in 2D semiconductor transition metal dichalcogenides}, author = {Qijie Liang and Jian Gou and Arramel and Qian Zhang and Wenjing Zhang and Andrew Thye Shen Wee}, doi = {10.1007/s12274-020-3038-8, Early Access Date = SEP 2020}, issn = {1998-0124}, journal = {NANO RESEARCH}, abstract = {Exposure to oxygen alters the physical and chemical properties of two-dimensional (2D) transition metal dichalcogenides (TMDs). In particular, oxygen in the ambient may influence the device stability of 2D TMDs over time. Engineering the doping of 2D TMDs, especially hole doping is highly desirable towards their device function. Herein, controllable oxygen-induced p-type doping in a range of hexagonal (MoTe2, WSe2, MoSe(2)and PtSe2) and pentagonal (PdSe2) 2D TMDs are demonstrated. Scanning tunneling microscopy, electrical transport and X-ray photoelectron spectroscopy are used to probe the origin of oxygen-derived hole doping. Three mechanisms are postulated that contribute to the hole doping in 2D TMDs, namely charge transfer from absorbed oxygen molecules, surface oxides, and chalcogen atom substitution. This work provides insights into the doping effects of oxygen, enabling the engineering of 2D TMDs properties for nanoelectronic applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Exposure to oxygen alters the physical and chemical properties of two-dimensional (2D) transition metal dichalcogenides (TMDs). In particular, oxygen in the ambient may influence the device stability of 2D TMDs over time. Engineering the doping of 2D TMDs, especially hole doping is highly desirable towards their device function. Herein, controllable oxygen-induced p-type doping in a range of hexagonal (MoTe2, WSe2, MoSe(2)and PtSe2) and pentagonal (PdSe2) 2D TMDs are demonstrated. Scanning tunneling microscopy, electrical transport and X-ray photoelectron spectroscopy are used to probe the origin of oxygen-derived hole doping. Three mechanisms are postulated that contribute to the hole doping in 2D TMDs, namely charge transfer from absorbed oxygen molecules, surface oxides, and chalcogen atom substitution. This work provides insights into the doping effects of oxygen, enabling the engineering of 2D TMDs properties for nanoelectronic applications. |
Loh, Leyi; Zhang, Zhepeng; Bosman, Michel; Eda, Goki Substitutional doping in 2D transition metal dichalcogenides Journal Article NANO RESEARCH, 0000, ISSN: 1998-0124. @article{ISI:000561269500002, title = {Substitutional doping in 2D transition metal dichalcogenides}, author = {Leyi Loh and Zhepeng Zhang and Michel Bosman and Goki Eda}, doi = {10.1007/s12274-020-3013-4, Early Access Date = AUG 2020}, issn = {1998-0124}, journal = {NANO RESEARCH}, abstract = {Two-dimensional (2D) van der Waals transition metal dichalcogenides (TMDs) are a new class of electronic materials offering tremendous opportunities for advanced technologies and fundamental studies. Similar to conventional semiconductors, substitutional doping is key to tailoring their electronic properties and enabling their device applications. Here, we review recent progress in doping methods and understanding of doping effects in group 6 TMDs (MX2}, keywords = {}, pubstate = {published}, tppubtype = {article} } Two-dimensional (2D) van der Waals transition metal dichalcogenides (TMDs) are a new class of electronic materials offering tremendous opportunities for advanced technologies and fundamental studies. Similar to conventional semiconductors, substitutional doping is key to tailoring their electronic properties and enabling their device applications. Here, we review recent progress in doping methods and understanding of doping effects in group 6 TMDs (MX2 |
Lian, Xu; Ma, Zhirui; Zhang, Zhonghan; Yang, Jinlin; Sun, Shuo; Gu, Chengding; Liu, Yuan; Ding, Honghe; Hu, Jun; Cao, Xu; Zhu, Junfa; Li, Shuzhou; Chen, Wei An in-situ spectroscopy investigation of alkali metal interaction mechanism with the imide functional group Journal Article NANO RESEARCH, 0000, ISSN: 1998-0124. @article{ISI:000559369900001, title = {An in-situ spectroscopy investigation of alkali metal interaction mechanism with the imide functional group}, author = {Xu Lian and Zhirui Ma and Zhonghan Zhang and Jinlin Yang and Shuo Sun and Chengding Gu and Yuan Liu and Honghe Ding and Jun Hu and Xu Cao and Junfa Zhu and Shuzhou Li and Wei Chen}, doi = {10.1007/s12274-020-2991-6, Early Access Date = AUG 2020}, issn = {1998-0124}, journal = {NANO RESEARCH}, abstract = {Organic anode materials have attracted considerable interest owing to their high tunability by adopting various active functional groups. However, the interaction mechanisms between the alkali metals and the active functional groups in host materials have been rarely studied systematically. Here, a widely used organic semiconductor of perylene-3,4,9,10-tetracarboxylic diimide (PTCDI) was selected as a model system to investigate how alkali metals interact with imide functional groups and induce changes in chemical and electronic structures of PTCDI. The interaction at the alkali/PTCDI interface was probed byin-situX-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), synchrotron-based near edge X-ray absorption fine structure (NEXAFS), and corroborated by density functional theory (DFT) calculations. Our results indicate that the alkali metal replaces the hydrogen atoms in the imide group and interact with the imide nitrogen of PTCDI. Electron transfer induced gap states and downward band-bending like effects are identified on the alkali-deposited PTCDI surface. It was found that Na shows a stronger electron transfer effect than Li. Such a model study of alkali insertion/intercalation in PTCDI gives insights for the exploration of the potential host materials for alkali storage applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Organic anode materials have attracted considerable interest owing to their high tunability by adopting various active functional groups. However, the interaction mechanisms between the alkali metals and the active functional groups in host materials have been rarely studied systematically. Here, a widely used organic semiconductor of perylene-3,4,9,10-tetracarboxylic diimide (PTCDI) was selected as a model system to investigate how alkali metals interact with imide functional groups and induce changes in chemical and electronic structures of PTCDI. The interaction at the alkali/PTCDI interface was probed byin-situX-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), synchrotron-based near edge X-ray absorption fine structure (NEXAFS), and corroborated by density functional theory (DFT) calculations. Our results indicate that the alkali metal replaces the hydrogen atoms in the imide group and interact with the imide nitrogen of PTCDI. Electron transfer induced gap states and downward band-bending like effects are identified on the alkali-deposited PTCDI surface. It was found that Na shows a stronger electron transfer effect than Li. Such a model study of alkali insertion/intercalation in PTCDI gives insights for the exploration of the potential host materials for alkali storage applications. |
Hu, Junxiong; Gou, Jian; Yang, Ming; Omar, Ganesh Ji; Tan, Junyou; Zeng, Shengwei; Liu, Yanpeng; Han, Kun; Lim, Zhishiuh; Huang, Zhen; Wee, Andrew Thye Shen; Ariando, Ariando Room-Temperature Colossal Magnetoresistance in Terraced Single-Layer Graphene Journal Article ADVANCED MATERIALS, 0000, ISSN: 0935-9648. @article{ISI:000554474600001, title = {Room-Temperature Colossal Magnetoresistance in Terraced Single-Layer Graphene}, author = {Junxiong Hu and Jian Gou and Ming Yang and Ganesh Ji Omar and Junyou Tan and Shengwei Zeng and Yanpeng Liu and Kun Han and Zhishiuh Lim and Zhen Huang and Andrew Thye Shen Wee and Ariando Ariando}, doi = {10.1002/adma.202002201, Early Access Date = AUG 2020}, issn = {0935-9648}, journal = {ADVANCED MATERIALS}, abstract = {Disorder-induced magnetoresistance (MR) effect is quadratic at low perpendicular magnetic fields and linear at high fields. This effect is technologically appealing, especially in 2D materials such as graphene, since it offers potential applications in magnetic sensors with nanoscale spatial resolution. However, it is a great challenge to realize a graphene magnetic sensor based on this effect because of the difficulty in controlling the spatial distribution of disorder and enhancing the MR sensitivity in the single-layer regime. Here, a room-temperature colossal MR of up to 5000% at 9 T is reported in terraced single-layer graphene. By laminating single-layer graphene on a terraced substrate, such as TiO2-terminated SrTiO3, a universal one order of magnitude enhancement in the MR compared to conventional single-layer graphene devices is demonstrated. Strikingly, a colossal MR of >1000% is also achieved in the terraced graphene even at a high carrier density of approximate to 10(12)cm(-2). Systematic studies of the MR of single-layer graphene on various oxide- and non-oxide-based terraced surfaces demonstrate that the terraced structure is the dominant factor driving the MR enhancement. The results open a new route for tailoring the physical property of 2D materials by engineering the strain through a terraced substrate.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Disorder-induced magnetoresistance (MR) effect is quadratic at low perpendicular magnetic fields and linear at high fields. This effect is technologically appealing, especially in 2D materials such as graphene, since it offers potential applications in magnetic sensors with nanoscale spatial resolution. However, it is a great challenge to realize a graphene magnetic sensor based on this effect because of the difficulty in controlling the spatial distribution of disorder and enhancing the MR sensitivity in the single-layer regime. Here, a room-temperature colossal MR of up to 5000% at 9 T is reported in terraced single-layer graphene. By laminating single-layer graphene on a terraced substrate, such as TiO2-terminated SrTiO3, a universal one order of magnitude enhancement in the MR compared to conventional single-layer graphene devices is demonstrated. Strikingly, a colossal MR of >1000% is also achieved in the terraced graphene even at a high carrier density of approximate to 10(12)cm(-2). Systematic studies of the MR of single-layer graphene on various oxide- and non-oxide-based terraced surfaces demonstrate that the terraced structure is the dominant factor driving the MR enhancement. The results open a new route for tailoring the physical property of 2D materials by engineering the strain through a terraced substrate. |
Liang, Shiheng; Shi, Shuyuan; Hsu, Chuang-Han; Cai, Kaiming; Wang, Yi; He, Pan; Wu, Yang; Pereira, Vitor M; Yang, Hyunsoo Spin-Orbit Torque Magnetization Switching in MoTe2/Permalloy Heterostructures Journal Article ADVANCED MATERIALS, 0000, ISSN: 0935-9648. @article{ISI:000554472200001, title = {Spin-Orbit Torque Magnetization Switching in MoTe2/Permalloy Heterostructures}, author = {Shiheng Liang and Shuyuan Shi and Chuang-Han Hsu and Kaiming Cai and Yi Wang and Pan He and Yang Wu and Vitor M Pereira and Hyunsoo Yang}, doi = {10.1002/adma.202002799, Early Access Date = AUG 2020}, issn = {0935-9648}, journal = {ADVANCED MATERIALS}, abstract = {The ability to switch magnetic elements by spin-orbit-induced torques has recently attracted much attention for a path toward high-performance, nonvolatile memories with low power consumption. Realizing efficient spin-orbit-based switching requires the harnessing of both new materials and novel physics to obtain high charge-to-spin conversion efficiencies, thus making the choice of spin source crucial. Here, the observation of spin-orbit torque switching in bilayers consisting of a semimetallic film of 1T `-MoTe(2)adjacent to permalloy is reported. Deterministic switching is achieved without external magnetic fields at room temperature, and the switching occurs with currents one order of magnitude smaller than those typical in devices using the best-performing heavy metals. The thickness-dependence can be understood if the interfacial spin-orbit contribution is considered in addition to the bulk spin Hall effect. Further threefold reduction in the switching current is demonstrated with resort to dumbbell-shaped magnetic elements. These findings foretell exciting prospects of using MoTe(2)for low-power semimetal-material-based spin devices.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The ability to switch magnetic elements by spin-orbit-induced torques has recently attracted much attention for a path toward high-performance, nonvolatile memories with low power consumption. Realizing efficient spin-orbit-based switching requires the harnessing of both new materials and novel physics to obtain high charge-to-spin conversion efficiencies, thus making the choice of spin source crucial. Here, the observation of spin-orbit torque switching in bilayers consisting of a semimetallic film of 1T `-MoTe(2)adjacent to permalloy is reported. Deterministic switching is achieved without external magnetic fields at room temperature, and the switching occurs with currents one order of magnitude smaller than those typical in devices using the best-performing heavy metals. The thickness-dependence can be understood if the interfacial spin-orbit contribution is considered in addition to the bulk spin Hall effect. Further threefold reduction in the switching current is demonstrated with resort to dumbbell-shaped magnetic elements. These findings foretell exciting prospects of using MoTe(2)for low-power semimetal-material-based spin devices. |
Xiong, Ting; Zhang, Yaoxin; Lee, Wee Siang Vincent; Xue, Junmin Defect Engineering in Manganese-Based Oxides for Aqueous Rechargeable Zinc-Ion Batteries: A Review Journal Article ADVANCED ENERGY MATERIALS, 0000, ISSN: 1614-6832. @article{ISI:000553341000001, title = {Defect Engineering in Manganese-Based Oxides for Aqueous Rechargeable Zinc-Ion Batteries: A Review}, author = {Ting Xiong and Yaoxin Zhang and Wee Siang Vincent Lee and Junmin Xue}, doi = {10.1002/aenm.202001769, Early Access Date = JUL 2020}, issn = {1614-6832}, journal = {ADVANCED ENERGY MATERIALS}, abstract = {The development of advanced cathode materials for aqueous the zinc ion battery (ZIB) represents a crucial step toward building future large-scale green energy conversion and storage systems. Recently, significant progress has been achieved in the development of manganese-based oxides for ZIB via defect engineering, whereby the intrinsic capacity and energy density have been enhanced. In this review, an overview of the recent progress in the defect engineering of manganese-based oxides for aqueous ZIBs is summarized in the following order: 1) the structures and properties of the commonly used manganese-based oxides, 2) the classification of the various types of defect engineering commonly reported, 3) the various strategies used to create defects in materials, and 4) the effects of the various types of defect engineering on the electrochemical performance of manganese-based oxides. Finally, a perspective on the defect engineering of manganese-based oxides is proposed to further enhance their electrochemical performance as a ZIB cathode.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The development of advanced cathode materials for aqueous the zinc ion battery (ZIB) represents a crucial step toward building future large-scale green energy conversion and storage systems. Recently, significant progress has been achieved in the development of manganese-based oxides for ZIB via defect engineering, whereby the intrinsic capacity and energy density have been enhanced. In this review, an overview of the recent progress in the defect engineering of manganese-based oxides for aqueous ZIBs is summarized in the following order: 1) the structures and properties of the commonly used manganese-based oxides, 2) the classification of the various types of defect engineering commonly reported, 3) the various strategies used to create defects in materials, and 4) the effects of the various types of defect engineering on the electrochemical performance of manganese-based oxides. Finally, a perspective on the defect engineering of manganese-based oxides is proposed to further enhance their electrochemical performance as a ZIB cathode. |
Feng, Xuewei; Li, Yida; Wang, Lin; Chen, Shuai; Yu, Zhi Gen; Tan, Wee Chong; Macadam, Nasiruddin; Hu, Guohua; Huang, Li; Chen, Li; Gong, Xiao; Chi, Dongzhi; Hasan, Tawfique; Thean, Aaron Voon-Yew; Zhang, Yong-Wei; Ang, Koh-Wee A Fully Printed Flexible MoS2 Memristive Artificial Synapse with Femtojoule Switching Energy Journal Article ADVANCED ELECTRONIC MATERIALS, 0000, ISSN: 2199-160X. @article{ISI:000486813700001, title = {A Fully Printed Flexible MoS2 Memristive Artificial Synapse with Femtojoule Switching Energy}, author = {Xuewei Feng and Yida Li and Lin Wang and Shuai Chen and Zhi Gen Yu and Wee Chong Tan and Nasiruddin Macadam and Guohua Hu and Li Huang and Li Chen and Xiao Gong and Dongzhi Chi and Tawfique Hasan and Aaron Voon-Yew Thean and Yong-Wei Zhang and Koh-Wee Ang}, doi = {10.1002/aelm.201900740, Early Access Date = SEP 2019}, issn = {2199-160X}, journal = {ADVANCED ELECTRONIC MATERIALS}, abstract = {Realization of memristors capable of storing and processing data on flexible substrates is a key enabling technology toward ``system-on-plastics''. Recent advancements in printing techniques show enormous potential to overcome the major challenges of the current manufacturing processes that require high temperature and planar topography, which may radically change the system integration approach on flexible substrates. However, fully printed memristors are yet to be successfully demonstrated due to the lack of a robust printable switching medium and a reliable printing process. An aerosol-jet-printed Ag/MoS2/Ag memristor is realized in a cross-bar structure by developing a scalable and low temperature printing technique utilizing a functional molybdenum disulfide (MoS2) ink platform. The fully printed devices exhibit an ultra-low switching voltage (0.18 V), a high switching ratio (10(7)), a wide range of tuneable resistance states (10-10(10) omega) for multi-bit data storage, and a low standby power consumption of 1 fW and a switching energy of 4.5 fJ per transition set. Moreover, the MoS2 memristor exhibits both volatile and non-volatile resistive switching behavior by controlling the current compliance levels, which efficiently mimic the short-term and long-term plasticity of biological synapses, demonstrating its potential to enable energy-efficient artificial neuromorphic computing.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Realization of memristors capable of storing and processing data on flexible substrates is a key enabling technology toward ``system-on-plastics''. Recent advancements in printing techniques show enormous potential to overcome the major challenges of the current manufacturing processes that require high temperature and planar topography, which may radically change the system integration approach on flexible substrates. However, fully printed memristors are yet to be successfully demonstrated due to the lack of a robust printable switching medium and a reliable printing process. An aerosol-jet-printed Ag/MoS2/Ag memristor is realized in a cross-bar structure by developing a scalable and low temperature printing technique utilizing a functional molybdenum disulfide (MoS2) ink platform. The fully printed devices exhibit an ultra-low switching voltage (0.18 V), a high switching ratio (10(7)), a wide range of tuneable resistance states (10-10(10) omega) for multi-bit data storage, and a low standby power consumption of 1 fW and a switching energy of 4.5 fJ per transition set. Moreover, the MoS2 memristor exhibits both volatile and non-volatile resistive switching behavior by controlling the current compliance levels, which efficiently mimic the short-term and long-term plasticity of biological synapses, demonstrating its potential to enable energy-efficient artificial neuromorphic computing. |