Publications
2024 |
Loh, Leyi; Ho, Yi Wei; Xuan, Fengyuan; del Aguila, Andres Granados; Chen, Yuan; Wong, See Yoong; Zhang, Jingda; Wang, Zhe; Watanabe, Kenji; Taniguchi, Takashi; Pigram, Paul J; Bosman, Michel; Quek, Su Ying; Koperski, Maciej; Eda, Goki Nb impurity-bound excitons as quantum emitters in monolayer WS2 Journal Article NATURE COMMUNICATIONS, 15 (1), 2024. @article{ISI:001360396900001, title = {Nb impurity-bound excitons as quantum emitters in monolayer WS_{2}}, author = {Leyi Loh and Yi Wei Ho and Fengyuan Xuan and Andres Granados del Aguila and Yuan Chen and See Yoong Wong and Jingda Zhang and Zhe Wang and Kenji Watanabe and Takashi Taniguchi and Paul J Pigram and Michel Bosman and Su Ying Quek and Maciej Koperski and Goki Eda}, doi = {10.1038/s41467-024-54360-5}, times_cited = {0}, year = {2024}, date = {2024-11-20}, journal = {NATURE COMMUNICATIONS}, volume = {15}, number = {1}, publisher = {NATURE PORTFOLIO}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {Point defects in crystalline solids behave as optically addressable individual quantum systems when present in sufficiently low concentrations. In two-dimensional (2D) semiconductors, such quantum defects hold potential as versatile single photon sources. Here, we report the synthesis and optical properties of Nb-doped monolayer WS2 in the dilute limit where the average spacing between individual dopants exceeds the optical diffraction limit, allowing the emission spectrum to be studied at the single-dopant level. We show that these individual dopants exhibit common features of quantum emitters, including narrow emission lines (with linewidths <1 meV), strong spatial confinement, and photon antibunching. These emitters consistently occur within a narrow spectral range across multiple samples, distinct from common quantum emitters in van der Waals (vdW) materials that show large ensemble broadening. Analysis of the Zeeman splitting reveals that they can be attributed to bound exciton complexes comprising dark excitons and negatively charged Nb.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Point defects in crystalline solids behave as optically addressable individual quantum systems when present in sufficiently low concentrations. In two-dimensional (2D) semiconductors, such quantum defects hold potential as versatile single photon sources. Here, we report the synthesis and optical properties of Nb-doped monolayer WS2 in the dilute limit where the average spacing between individual dopants exceeds the optical diffraction limit, allowing the emission spectrum to be studied at the single-dopant level. We show that these individual dopants exhibit common features of quantum emitters, including narrow emission lines (with linewidths <1 meV), strong spatial confinement, and photon antibunching. These emitters consistently occur within a narrow spectral range across multiple samples, distinct from common quantum emitters in van der Waals (vdW) materials that show large ensemble broadening. Analysis of the Zeeman splitting reveals that they can be attributed to bound exciton complexes comprising dark excitons and negatively charged Nb. |
Erofeev, Ivan; Hartanto, Antony Winata; Khan, Muhaimin Mareum; Deng, Kerong; Kumar, Krishna; Aabdin, Zainul; Tjiu, Weng Weei; Zhang, Mingsheng; Pacco, Antoine; Philipsen, Harold; Chowdhuri, Angshuman Ray; Huynh, Han Vinh; Holsteyns, Frank; Mirsaidov, Utkur Digital Etching of Molybdenum Interconnects Using Plasma Oxidation Journal Article ADVANCED MATERIALS INTERFACES, 2024, ISSN: 2196-7350. @article{ISI:001357050400001, title = {Digital Etching of Molybdenum Interconnects Using Plasma Oxidation}, author = {Ivan Erofeev and Antony Winata Hartanto and Muhaimin Mareum Khan and Kerong Deng and Krishna Kumar and Zainul Aabdin and Weng Weei Tjiu and Mingsheng Zhang and Antoine Pacco and Harold Philipsen and Angshuman Ray Chowdhuri and Han Vinh Huynh and Frank Holsteyns and Utkur Mirsaidov}, doi = {10.1002/admi.202400558}, times_cited = {0}, issn = {2196-7350}, year = {2024}, date = {2024-11-12}, journal = {ADVANCED MATERIALS INTERFACES}, publisher = {WILEY}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {Molybdenum (Mo) has a high potential of becoming the material of choice for sub-10 nm scale metal structures in future integrated circuits (ICs). Manufacturing at this scale requires exceptional precision and consistency, so many metal processing techniques must be reconsidered. In particular, present direct wet chemical etching methods produce anisotropic etching profiles with significant surface roughness, which can be detrimental to device performance. Here, it is shown that polycrystalline Mo nanowires can be etched uniformly using a cyclic two-step "digital" method: the metal surface is first oxidized with isotropic oxygen plasma to form a layer of MoO3, which is then selectively removed using either wet chemical or dry isotropic plasma etching. These two steps are repeated in cycles until the intended metal recess is achieved. High uniformity of plasma oxidation defines the etching uniformity, and small metal recess per cycle (typically 1-2 nm) provides precise control over the etching depth. This method can replace wet etching where high etching precision is needed, enabling the reliable manufacturing of nanoscale metal interconnects.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Molybdenum (Mo) has a high potential of becoming the material of choice for sub-10 nm scale metal structures in future integrated circuits (ICs). Manufacturing at this scale requires exceptional precision and consistency, so many metal processing techniques must be reconsidered. In particular, present direct wet chemical etching methods produce anisotropic etching profiles with significant surface roughness, which can be detrimental to device performance. Here, it is shown that polycrystalline Mo nanowires can be etched uniformly using a cyclic two-step "digital" method: the metal surface is first oxidized with isotropic oxygen plasma to form a layer of MoO3, which is then selectively removed using either wet chemical or dry isotropic plasma etching. These two steps are repeated in cycles until the intended metal recess is achieved. High uniformity of plasma oxidation defines the etching uniformity, and small metal recess per cycle (typically 1-2 nm) provides precise control over the etching depth. This method can replace wet etching where high etching precision is needed, enabling the reliable manufacturing of nanoscale metal interconnects. |
Ratwani, Chirag R; Donato, Katarzyna Z; Grebenchuk, Sergey; Mija, Alice; Novoselov, Kostya S; Abdelkader, Amr M Enhanced Self-Healing in Dual Network Entangled Hydrogels by Macromolecular Architecture and Alignent of Surface Functionalized hBN Nanosheets Journal Article ADVANCED MATERIALS INTERFACES, 2024, ISSN: 2196-7350. @article{ISI:001357180100001, title = {Enhanced Self-Healing in Dual Network Entangled Hydrogels by Macromolecular Architecture and Alignent of Surface Functionalized hBN Nanosheets}, author = {Chirag R Ratwani and Katarzyna Z Donato and Sergey Grebenchuk and Alice Mija and Kostya S Novoselov and Amr M Abdelkader}, doi = {10.1002/admi.202400691}, times_cited = {0}, issn = {2196-7350}, year = {2024}, date = {2024-10-31}, journal = {ADVANCED MATERIALS INTERFACES}, publisher = {WILEY}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {Hydrogels have shown great promise as versatile biomaterials for various applications, ranging from tissue engineering to flexible electronics. Among their notable attributes, self-healing capabilities stand out as a significant advantage, facilitating autonomous repair of mechanical damage and restoration of structural integrity. In this work, a dual network macromolecular biphasic composite is designed using an anisotropic structure which facilitates unidirectional chain diffusion and imparts superior self-healing and mechanical properties. The resulting nanocomposite demonstrates significantly higher self-healing efficiency (92%) compared to traditional polyvinyl alcohol (PVA) hydrogels, while also improving the tensile strength and elastic modulus, which typically compete with each other in soft materials. This improvement is attributed to enhanced barrier properties within the matrix due to the alignment of surface-functionalized 2D hBN nanosheets along the biopolymer scaffold. The insights gained from this research can be leveraged to develop advanced self-healing materials by using 2D nanofillers as "safety barriers" to define the movement of polymeric chains.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Hydrogels have shown great promise as versatile biomaterials for various applications, ranging from tissue engineering to flexible electronics. Among their notable attributes, self-healing capabilities stand out as a significant advantage, facilitating autonomous repair of mechanical damage and restoration of structural integrity. In this work, a dual network macromolecular biphasic composite is designed using an anisotropic structure which facilitates unidirectional chain diffusion and imparts superior self-healing and mechanical properties. The resulting nanocomposite demonstrates significantly higher self-healing efficiency (92%) compared to traditional polyvinyl alcohol (PVA) hydrogels, while also improving the tensile strength and elastic modulus, which typically compete with each other in soft materials. This improvement is attributed to enhanced barrier properties within the matrix due to the alignment of surface-functionalized 2D hBN nanosheets along the biopolymer scaffold. The insights gained from this research can be leveraged to develop advanced self-healing materials by using 2D nanofillers as "safety barriers" to define the movement of polymeric chains. |
Wang, Dingguan; Haposan, Tobias; Fan, Jinwei; Arramel, ; Wee, Andrew T S Recent Progress of Imaging Chemical Bonds by Scanning Probe Microscopy: A Review Journal Article ACS NANO, 18 (45), pp. 30919-30942, 2024, ISSN: 1936-0851. @article{ISI:001345125600001, title = {Recent Progress of Imaging Chemical Bonds by Scanning Probe Microscopy: A Review}, author = {Dingguan Wang and Tobias Haposan and Jinwei Fan and Arramel and Andrew T S Wee}, doi = {10.1021/acsnano.4c10522}, times_cited = {0}, issn = {1936-0851}, year = {2024}, date = {2024-10-30}, journal = {ACS NANO}, volume = {18}, number = {45}, pages = {30919-30942}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {In the past decades, the invention of scanning probe microscopy (SPM) as the versatile surface-based characterization of organic molecules has triggered significant interest throughout multidisciplinary fields. In particular, the bond-resolved imaging acquired by SPM techniques has extended its fundamental function of not only unraveling the chemical structure but also allowing us to resolve the structure-property relationship. Here, we present a systematical review on the history of chemical bonds imaged by means of noncontact atomic force microscopy (nc-AFM) and bond-resolved scanning tunneling microscopy (BR-STM) techniques. We first summarize the advancement of real-space imaging of covalent bonds and the investigation of intermolecular noncovalent bonds. Beyond the bond imaging, we also highlight the applications of the bond-resolved SPM techniques such as on-surface synthesis, the determination of the reaction pathway, the identification of molecular configurations and unknown products, and the generation of artificial molecules created via tip manipulation. Lastly, we discuss the current status of SPM techniques and highlight several key technical challenges that must be solved in the coming years. In comparison to the existing reviews, this work invokes researchers from surface science, chemistry, condensed matter physics, and theoretical physics to uncover the bond-resolved SPM technique as an emerging tool in exploiting the molecule/surface system and their future applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In the past decades, the invention of scanning probe microscopy (SPM) as the versatile surface-based characterization of organic molecules has triggered significant interest throughout multidisciplinary fields. In particular, the bond-resolved imaging acquired by SPM techniques has extended its fundamental function of not only unraveling the chemical structure but also allowing us to resolve the structure-property relationship. Here, we present a systematical review on the history of chemical bonds imaged by means of noncontact atomic force microscopy (nc-AFM) and bond-resolved scanning tunneling microscopy (BR-STM) techniques. We first summarize the advancement of real-space imaging of covalent bonds and the investigation of intermolecular noncovalent bonds. Beyond the bond imaging, we also highlight the applications of the bond-resolved SPM techniques such as on-surface synthesis, the determination of the reaction pathway, the identification of molecular configurations and unknown products, and the generation of artificial molecules created via tip manipulation. Lastly, we discuss the current status of SPM techniques and highlight several key technical challenges that must be solved in the coming years. In comparison to the existing reviews, this work invokes researchers from surface science, chemistry, condensed matter physics, and theoretical physics to uncover the bond-resolved SPM technique as an emerging tool in exploiting the molecule/surface system and their future applications. |
Deng, Kerong; Erofeev, Ivan; Chowdhuri, Angshuman Ray; Philipsen, Harold; Aabdin, Zainul; Hartanto, Antony Winata; Tjiu, Weng Weei; Zhang, Mingsheng; Fernando, Devshan; Saidov, Khakimjon; Kumar, Krishna; Pacco, Antoine; Holsteyns, Frank; Huynh, Han Vinh; Mirsaidov, Utkur Nanoscale Wet Etching of Molybdenum Interconnects with Organic Solutions Journal Article SMALL, 2024, ISSN: 1613-6810. @article{ISI:001337998600001, title = {Nanoscale Wet Etching of Molybdenum Interconnects with Organic Solutions}, author = {Kerong Deng and Ivan Erofeev and Angshuman Ray Chowdhuri and Harold Philipsen and Zainul Aabdin and Antony Winata Hartanto and Weng Weei Tjiu and Mingsheng Zhang and Devshan Fernando and Khakimjon Saidov and Krishna Kumar and Antoine Pacco and Frank Holsteyns and Han Vinh Huynh and Utkur Mirsaidov}, doi = {10.1002/smll.202406713}, times_cited = {0}, issn = {1613-6810}, year = {2024}, date = {2024-10-22}, journal = {SMALL}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {Molybdenum (Mo) has emerged as a promising material for advanced semiconductor devices, especially in the design and fabrication of interconnects requiring sub-10 nm metal nanostructures. However, current wet etching methods for Mo using aqueous solutions struggle to achieve smooth etching profiles at such scales. To address this problem, we explore wet chemical etching of patterned Mo nanowires (NWs) using an organic solution: ceric ammonium nitrate (CAN) dissolved in acetonitrile (ACN). In this study, we demonstrate two distinct etching pathways by controlling the reaction temperature: i) digital cyclic scheme at room temperature, with a self-limiting Mo recess per cycle of approximate to 1.6 nm, and ii) direct etching at elevated temperature (60 degrees C), with a time-controlled Mo recess of approximate to 2 nm min-1. These methods not only offer a highly controllable nanoscale Mo etching but also ensure smooth and uniform etching profiles independent of the crystal grain orientation of the metal.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Molybdenum (Mo) has emerged as a promising material for advanced semiconductor devices, especially in the design and fabrication of interconnects requiring sub-10 nm metal nanostructures. However, current wet etching methods for Mo using aqueous solutions struggle to achieve smooth etching profiles at such scales. To address this problem, we explore wet chemical etching of patterned Mo nanowires (NWs) using an organic solution: ceric ammonium nitrate (CAN) dissolved in acetonitrile (ACN). In this study, we demonstrate two distinct etching pathways by controlling the reaction temperature: i) digital cyclic scheme at room temperature, with a self-limiting Mo recess per cycle of approximate to 1.6 nm, and ii) direct etching at elevated temperature (60 degrees C), with a time-controlled Mo recess of approximate to 2 nm min-1. These methods not only offer a highly controllable nanoscale Mo etching but also ensure smooth and uniform etching profiles independent of the crystal grain orientation of the metal. |
Tang, Ho-Kin; Yudhistira, Indra; Chattopadhyay, Udvas; Ulybyshev, Maksim; Sengupta, P; Assaad, F F; Adam, S Spectral functions of lattice fermions on the honeycomb lattice with Hubbard and long-range Coulomb interactions Journal Article PHYSICAL REVIEW B, 110 (15), 2024, ISSN: 2469-9950. @article{ISI:001334829900007, title = {Spectral functions of lattice fermions on the honeycomb lattice with Hubbard and long-range Coulomb interactions}, author = {Ho-Kin Tang and Indra Yudhistira and Udvas Chattopadhyay and Maksim Ulybyshev and P Sengupta and F F Assaad and S Adam}, doi = {10.1103/PhysRevB.110.155120}, times_cited = {0}, issn = {2469-9950}, year = {2024}, date = {2024-10-09}, journal = {PHYSICAL REVIEW B}, volume = {110}, number = {15}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {The absence of screening of the nonlocal Coulomb interaction in Dirac systems at charge neutrality leads to the breakdown of the Fermi liquid and divergence of the Fermi velocity. On the other hand, Mott-Hubbard physics and the concomitant formation of local moments is dominated by the local effective Hubbard interaction. Using quantum Monte Carlo methods combined with stochastic analytical continuation, we compute the single particle spectral function of fermions on the honeycomb lattice for a realistic interaction that includes both the Hubbard interaction and long-ranged Coulomb repulsion. To a first approximation, we find that the generic high-energy features, such as the formation of the upper Hubbard band near the phase transition, are primarily determined by the local effective Hubbard interaction. In the weakly interacting regime, the long-range Coulomb interaction enhances the bandwidth of quasiparticles and suppresses their lifetime. Conversely, near the phase transition, the long-range Coulomb interaction suppresses the background antiferromagnetic fluctuation, which potentially promotes the propagation of spin polarons, leading to a slight enhancement of the quasiparticle spectral weight and lifetime.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The absence of screening of the nonlocal Coulomb interaction in Dirac systems at charge neutrality leads to the breakdown of the Fermi liquid and divergence of the Fermi velocity. On the other hand, Mott-Hubbard physics and the concomitant formation of local moments is dominated by the local effective Hubbard interaction. Using quantum Monte Carlo methods combined with stochastic analytical continuation, we compute the single particle spectral function of fermions on the honeycomb lattice for a realistic interaction that includes both the Hubbard interaction and long-ranged Coulomb repulsion. To a first approximation, we find that the generic high-energy features, such as the formation of the upper Hubbard band near the phase transition, are primarily determined by the local effective Hubbard interaction. In the weakly interacting regime, the long-range Coulomb interaction enhances the bandwidth of quasiparticles and suppresses their lifetime. Conversely, near the phase transition, the long-range Coulomb interaction suppresses the background antiferromagnetic fluctuation, which potentially promotes the propagation of spin polarons, leading to a slight enhancement of the quasiparticle spectral weight and lifetime. |
Carrio, Juan A G; Echeverrigaray, Sergio G; Talluri, V S S L P; Sudhakaran, Deepa P; Gan, Hui T; Gardeno, Daniel; Friess, Karel; Neto, Antonio Castro H Performance of GO laminated membranes in H2/CO2 separation as a function of the membrane thickness Journal Article INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 90 , pp. 646-654, 2024, ISSN: 0360-3199. @article{ISI:001332104500001, title = {Performance of GO laminated membranes in H2/CO2 separation as a function of the membrane thickness}, author = {Juan A G Carrio and Sergio G Echeverrigaray and V S S L P Talluri and Deepa P Sudhakaran and Hui T Gan and Daniel Gardeno and Karel Friess and Antonio Castro H Neto}, doi = {10.1016/j.ijhydene.2024.09.435}, times_cited = {0}, issn = {0360-3199}, year = {2024}, date = {2024-10-08}, journal = {INTERNATIONAL JOURNAL OF HYDROGEN ENERGY}, volume = {90}, pages = {646-654}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND}, abstract = {Hydrogen gas (H2) is a promising energy carrier capable of replacing fossil fuels and achieving net zero emissions. However, purifying H2 for applications like fuel cells and industrial processes is challenging due to impurities affecting performance. Two-dimensional (2D) materials, particularly graphene-based membranes, are promising for H2 purification due to their unique properties. The hydrogen (H2) permeation capability of graphene-based membranes is particularly significant. This study examines the use of commercial and costeffective graphene oxide (GO) to fabricate multilayer graphene membranes, focusing on the impact of membrane thickness on H2 and CO2 separation. By using a scalable vacuum filtration method to coat porous ceramic substrates, membranes with controlled thicknesses were produced and characterised using AFM, FESEM, XRD, and gas permeation measurements. The study identified an optimal membrane thickness range (4 nm-250 nm) and the GO quantity (0.44 mu g/cm2 to 1.76 mu g/cm2) needed for effective H2/CO2 separation. This research aims to guide the development of cost-effective, mass-produced 2D-based membranes for industrial H2 purification.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Hydrogen gas (H2) is a promising energy carrier capable of replacing fossil fuels and achieving net zero emissions. However, purifying H2 for applications like fuel cells and industrial processes is challenging due to impurities affecting performance. Two-dimensional (2D) materials, particularly graphene-based membranes, are promising for H2 purification due to their unique properties. The hydrogen (H2) permeation capability of graphene-based membranes is particularly significant. This study examines the use of commercial and costeffective graphene oxide (GO) to fabricate multilayer graphene membranes, focusing on the impact of membrane thickness on H2 and CO2 separation. By using a scalable vacuum filtration method to coat porous ceramic substrates, membranes with controlled thicknesses were produced and characterised using AFM, FESEM, XRD, and gas permeation measurements. The study identified an optimal membrane thickness range (4 nm-250 nm) and the GO quantity (0.44 mu g/cm2 to 1.76 mu g/cm2) needed for effective H2/CO2 separation. This research aims to guide the development of cost-effective, mass-produced 2D-based membranes for industrial H2 purification. |
Chen, Mingyao; Liu, Huimin; He, Xu; Li, Minjuan; Tang, Chi Sin; Sun, Mengxia; Koirala, Krishna Prasad; Bowden, Mark E; Li, Yangyang; Liu, Xiongfang; Zhou, Difan; Sun, Shuo; Breese, Mark B H; Cai, Chuanbing; Wang, Le; Du, Yingge; Wee, Andrew T S; Yin, Xinmao Uncovering an Interfacial Band Resulting from Orbital Hybridization in Nickelate Heterostructures Journal Article ACS NANO, 18 (40), pp. 27707-27717, 2024, ISSN: 1936-0851. @article{ISI:001324763700001, title = {Uncovering an Interfacial Band Resulting from Orbital Hybridization in Nickelate Heterostructures}, author = {Mingyao Chen and Huimin Liu and Xu He and Minjuan Li and Chi Sin Tang and Mengxia Sun and Krishna Prasad Koirala and Mark E Bowden and Yangyang Li and Xiongfang Liu and Difan Zhou and Shuo Sun and Mark B H Breese and Chuanbing Cai and Le Wang and Yingge Du and Andrew T S Wee and Xinmao Yin}, doi = {10.1021/acsnano.4c09921}, times_cited = {0}, issn = {1936-0851}, year = {2024}, date = {2024-09-26}, journal = {ACS NANO}, volume = {18}, number = {40}, pages = {27707-27717}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {The interaction of atomic orbitals at the interface of perovskite oxide heterostructures has been investigated for its profound impact on the band structures and electronic properties, giving rise to unique electronic states and a variety of tunable functionalities. In this study, we conducted an extensive investigation of the optical and electronic properties of epitaxial NdNiO3 synthesized on a series of single-crystal substrates. Unlike nanofilms synthesized on other substrates, NdNiO3 on SrTiO3 (NNO/STO) gives rise to a unique band structure featuring an additional unoccupied band situated above the Fermi level. Our comprehensive investigation, which incorporated a wide array of experimental techniques and density functional theory calculations, revealed that the emergence of the interfacial band structure is primarily driven by orbital hybridization between the Ti 3d orbitals of the STO substrate and the O 2p orbitals of the NNO thin film. Furthermore, exciton peaks have been detected in the optical spectra of the NNO/STO film, attributable to the pronounced electron-electron (e-e) and electron-hole (e-h) interactions propagating from the STO substrate into the NNO film. These findings underscore the substantial influence of interfacial orbital hybridization on the electronic structure of oxide thin films, thereby offering key insights into tuning their interfacial properties.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The interaction of atomic orbitals at the interface of perovskite oxide heterostructures has been investigated for its profound impact on the band structures and electronic properties, giving rise to unique electronic states and a variety of tunable functionalities. In this study, we conducted an extensive investigation of the optical and electronic properties of epitaxial NdNiO3 synthesized on a series of single-crystal substrates. Unlike nanofilms synthesized on other substrates, NdNiO3 on SrTiO3 (NNO/STO) gives rise to a unique band structure featuring an additional unoccupied band situated above the Fermi level. Our comprehensive investigation, which incorporated a wide array of experimental techniques and density functional theory calculations, revealed that the emergence of the interfacial band structure is primarily driven by orbital hybridization between the Ti 3d orbitals of the STO substrate and the O 2p orbitals of the NNO thin film. Furthermore, exciton peaks have been detected in the optical spectra of the NNO/STO film, attributable to the pronounced electron-electron (e-e) and electron-hole (e-h) interactions propagating from the STO substrate into the NNO film. These findings underscore the substantial influence of interfacial orbital hybridization on the electronic structure of oxide thin films, thereby offering key insights into tuning their interfacial properties. |
Huang, Jianwei; Setty, Chandan; Deng, Liangzi; You, Jing-Yang; Liu, Hongxiong; Shao, Sen; Oh, Ji Seop; Guo, Yucheng; Zhang, Yichen; Yue, Ziqin; Yin, Jia-Xin; Hashimoto, Makoto; Lu, Donghui; Gorovikov, Sergey; Dai, Pengcheng; Denlinger, Jonathan D; Allen, J W; Hasan, Zahid M; Feng, Yuan-Ping; Birgeneau, Robert J; Shi, Youguo; Chu, Ching-Wu; Chang, Guoqing; Si, Qimiao; Yi, Ming Observation of flat bands and Dirac cones in a pyrochlore lattice superconductor Journal Article NPJ QUANTUM MATERIALS, 9 (1), 2024. @article{ISI:001316044100001, title = {Observation of flat bands and Dirac cones in a pyrochlore lattice superconductor}, author = {Jianwei Huang and Chandan Setty and Liangzi Deng and Jing-Yang You and Hongxiong Liu and Sen Shao and Ji Seop Oh and Yucheng Guo and Yichen Zhang and Ziqin Yue and Jia-Xin Yin and Makoto Hashimoto and Donghui Lu and Sergey Gorovikov and Pengcheng Dai and Jonathan D Denlinger and J W Allen and Zahid M Hasan and Yuan-Ping Feng and Robert J Birgeneau and Youguo Shi and Ching-Wu Chu and Guoqing Chang and Qimiao Si and Ming Yi}, doi = {10.1038/s41535-024-00683-x}, times_cited = {3}, year = {2024}, date = {2024-09-19}, journal = {NPJ QUANTUM MATERIALS}, volume = {9}, number = {1}, publisher = {NATURE PORTFOLIO}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {Emergent phases often appear when the electronic kinetic energy is comparable to the Coulomb interactions. One approach to seek material systems as hosts of such emergent phases is to realize localization of electronic wavefunctions due to the geometric frustration inherent in the crystal structure, resulting in flat electronic bands. Recently, such efforts have found a wide range of exotic phases in the two-dimensional kagome lattice, including magnetic order, time-reversal symmetry breaking charge order, nematicity, and superconductivity. However, the interlayer coupling of the kagome layers disrupts the destructive interference needed to completely quench the kinetic energy. Here we demonstrate that an interwoven kagome network-a pyrochlore lattice-can host a three dimensional (3D) localization of electron wavefunctions. Meanwhile, the nonsymmorphic symmetry of the pyrochlore lattice guarantees all band crossings at the Brillouin zone X point to be 3D gapless Dirac points, which was predicted theoretically but never yet observed experimentally. Through a combination of angle-resolved photoemission spectroscopy, fundamental lattice model and density functional theory calculations, we investigate the novel electronic structure of a Laves phase superconductor with a pyrochlore sublattice, CeRu2. We observe evidence of flat bands originating from the Ce 4f orbitals as well as flat bands from the 3D destructive interference of the Ru 4d orbitals. We further observe the nonsymmorphic symmetry-protected 3D gapless Dirac cone at the X point. Our work establishes the pyrochlore structure as a promising lattice platform to realize and tune novel emergent phases intertwining topology and many-body interactions.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Emergent phases often appear when the electronic kinetic energy is comparable to the Coulomb interactions. One approach to seek material systems as hosts of such emergent phases is to realize localization of electronic wavefunctions due to the geometric frustration inherent in the crystal structure, resulting in flat electronic bands. Recently, such efforts have found a wide range of exotic phases in the two-dimensional kagome lattice, including magnetic order, time-reversal symmetry breaking charge order, nematicity, and superconductivity. However, the interlayer coupling of the kagome layers disrupts the destructive interference needed to completely quench the kinetic energy. Here we demonstrate that an interwoven kagome network-a pyrochlore lattice-can host a three dimensional (3D) localization of electron wavefunctions. Meanwhile, the nonsymmorphic symmetry of the pyrochlore lattice guarantees all band crossings at the Brillouin zone X point to be 3D gapless Dirac points, which was predicted theoretically but never yet observed experimentally. Through a combination of angle-resolved photoemission spectroscopy, fundamental lattice model and density functional theory calculations, we investigate the novel electronic structure of a Laves phase superconductor with a pyrochlore sublattice, CeRu2. We observe evidence of flat bands originating from the Ce 4f orbitals as well as flat bands from the 3D destructive interference of the Ru 4d orbitals. We further observe the nonsymmorphic symmetry-protected 3D gapless Dirac cone at the X point. Our work establishes the pyrochlore structure as a promising lattice platform to realize and tune novel emergent phases intertwining topology and many-body interactions. |
Donato, Katarzyna Z; Koon, Gavin K W; Lee, Sarah J; Carvalho, Alexandra; Tan, Hui Li; Costa, Mariana C F; Tolasz, Jakub; Ecorchard, Petra; Michalowski, Pawel P; Donato, Ricardo K; Neto, Castro A H Disordered metallic carbon materials from graphene edge chemistry Journal Article MATERIALS TODAY, 79 , pp. 49-59, 2024, ISSN: 1369-7021. @article{ISI:001316339100001, title = {Disordered metallic carbon materials from graphene edge chemistry}, author = {Katarzyna Z Donato and Gavin K W Koon and Sarah J Lee and Alexandra Carvalho and Hui Li Tan and Mariana C F Costa and Jakub Tolasz and Petra Ecorchard and Pawel P Michalowski and Ricardo K Donato and Castro A H Neto}, doi = {10.1016/j.mattod.2024.07.011}, times_cited = {0}, issn = {1369-7021}, year = {2024}, date = {2024-09-12}, journal = {MATERIALS TODAY}, volume = {79}, pages = {49-59}, publisher = {ELSEVIER SCI LTD}, address = {125 London Wall, London, ENGLAND}, abstract = {The creation of three dimensional (3D) structures out of two-dimensional (2D) materials while retaining their extraordinary mechanical and transport properties after processing is one of the current great challenges in materials sciences (Ruoff, 2008; Kong et al., 2019; Lin et al., 2019). Guided by density functional theory (DFT) and molecular dynamics (MD) simulations we found a successful route for a sustainable production of 3D metallic carbon materials that are synthesized from pristine 2D graphene flakes with hydrolyzed edges. The edge hydrolysis lead to strong geometrical anisotropy and self-organization in solution before processing. After processing we obtain a 3D carbon structure where 2D graphene flakes are crosslinked by carbon chains with aromatic groups at very mild annealing temperatures (similar to 150 degrees C), eliminating the constraints for achieving the in-situ preparation of conductive carbon structures. These 3D carbon structures preserve microscopic order but are macroscopically disordered, presenting physical properties of anisotropic metallic carbon with large Young modulus (E approximate to 20 GPa), and room temperature thermal (k approximate to 180 W/mK) and electrical (sigma approximate to 300 kS/m) conductivities comparable to ordinary metals.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The creation of three dimensional (3D) structures out of two-dimensional (2D) materials while retaining their extraordinary mechanical and transport properties after processing is one of the current great challenges in materials sciences (Ruoff, 2008; Kong et al., 2019; Lin et al., 2019). Guided by density functional theory (DFT) and molecular dynamics (MD) simulations we found a successful route for a sustainable production of 3D metallic carbon materials that are synthesized from pristine 2D graphene flakes with hydrolyzed edges. The edge hydrolysis lead to strong geometrical anisotropy and self-organization in solution before processing. After processing we obtain a 3D carbon structure where 2D graphene flakes are crosslinked by carbon chains with aromatic groups at very mild annealing temperatures (similar to 150 degrees C), eliminating the constraints for achieving the in-situ preparation of conductive carbon structures. These 3D carbon structures preserve microscopic order but are macroscopically disordered, presenting physical properties of anisotropic metallic carbon with large Young modulus (E approximate to 20 GPa), and room temperature thermal (k approximate to 180 W/mK) and electrical (sigma approximate to 300 kS/m) conductivities comparable to ordinary metals. |
Afrose, Ramal; Keser, Aydin Cem; Sushkov, Oleg P; Adam, Shaffique Tunable viscous layers in Corbino geometry using density junctions Journal Article PHYSICAL REVIEW B, 110 (12), 2024, ISSN: 2469-9950. @article{ISI:001309683400002, title = {Tunable viscous layers in Corbino geometry using density junctions}, author = {Ramal Afrose and Aydin Cem Keser and Oleg P Sushkov and Shaffique Adam}, doi = {10.1103/PhysRevB.110.125409}, times_cited = {0}, issn = {2469-9950}, year = {2024}, date = {2024-09-06}, journal = {PHYSICAL REVIEW B}, volume = {110}, number = {12}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {In sufficiently clean materials where electron-electron interactions are strong compared to momentum-relaxing scattering processes, electron transport resembles the flow of a viscous fluid. We study hydrodynamic electron transport across density interfaces (n-n junctions) in a 2DEG in the Corbino geometry. From numerical simulations in COMSOL using realistic parameters, we show that we can produce tunable viscous layers at the density interface by varying the density ratio of charge carriers. We quantitatively explain this observation with simple analytic expressions together with boundary conditions at the interface. We also show signatures of these viscous layers in the magnetoresistance. Breaking down viscous and Ohmic contributions, we find that when the outer radial region of the Corbino has higher charge density compared to the inner region, the viscous layers at the interface serve to suppress the magnetoresistance produced by momentum-relaxing scattering. Conversely, the magnetoresistance is enhanced when the inner region has higher density than the outer. Our results add to the repertoire of techniques for engineering viscous electron flows, which hold a promise for applications in future electronic devices.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In sufficiently clean materials where electron-electron interactions are strong compared to momentum-relaxing scattering processes, electron transport resembles the flow of a viscous fluid. We study hydrodynamic electron transport across density interfaces (n-n junctions) in a 2DEG in the Corbino geometry. From numerical simulations in COMSOL using realistic parameters, we show that we can produce tunable viscous layers at the density interface by varying the density ratio of charge carriers. We quantitatively explain this observation with simple analytic expressions together with boundary conditions at the interface. We also show signatures of these viscous layers in the magnetoresistance. Breaking down viscous and Ohmic contributions, we find that when the outer radial region of the Corbino has higher charge density compared to the inner region, the viscous layers at the interface serve to suppress the magnetoresistance produced by momentum-relaxing scattering. Conversely, the magnetoresistance is enhanced when the inner region has higher density than the outer. Our results add to the repertoire of techniques for engineering viscous electron flows, which hold a promise for applications in future electronic devices. |
Wu, Wenjun; Sun, Shuo; Tang, Chi Sin; Wu, Jing; Ma, Yu; Zhang, Lingfeng; Cai, Chuanbing; Zhong, Jianxin; Milosevic, Milorad V; Wee, Andrew T S; Yin, Xinmao Realization of a 2D Lieb Lattice in a Metal-Inorganic Framework with Partial Flat Bands and Topological Edge States Journal Article ADVANCED MATERIALS, 36 (40), 2024, ISSN: 0935-9648. @article{ISI:001296568000001, title = {Realization of a 2D Lieb Lattice in a Metal-Inorganic Framework with Partial Flat Bands and Topological Edge States}, author = {Wenjun Wu and Shuo Sun and Chi Sin Tang and Jing Wu and Yu Ma and Lingfeng Zhang and Chuanbing Cai and Jianxin Zhong and Milorad V Milosevic and Andrew T S Wee and Xinmao Yin}, doi = {10.1002/adma.202405615}, times_cited = {0}, issn = {0935-9648}, year = {2024}, date = {2024-08-23}, journal = {ADVANCED MATERIALS}, volume = {36}, number = {40}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {Flat bands and Dirac cones in materials are the source of the exotic electronic and topological properties. The Lieb lattice is expected to host these electronic structures, arising from quantum destructive interference. Nevertheless, the experimental realization of a 2D Lieb lattice remained challenging to date due to its intrinsic structural instability. After computationally designing a Platinum-Phosphorus (Pt-P) Lieb lattice, it has successfully overcome its structural instability and synthesized on a gold substrate via molecular beam epitaxy. Low-temperature scanning tunneling microscopy and spectroscopy verify the Lieb lattice's morphology and electronic flat bands. Furthermore, topological Dirac edge states stemming from pronounced spin-orbit coupling induced by heavy Pt atoms are predicted. These findings convincingly open perspectives for creating metal-inorganic framework-based atomic lattices, offering prospects for strongly correlated phases interplayed with topology.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Flat bands and Dirac cones in materials are the source of the exotic electronic and topological properties. The Lieb lattice is expected to host these electronic structures, arising from quantum destructive interference. Nevertheless, the experimental realization of a 2D Lieb lattice remained challenging to date due to its intrinsic structural instability. After computationally designing a Platinum-Phosphorus (Pt-P) Lieb lattice, it has successfully overcome its structural instability and synthesized on a gold substrate via molecular beam epitaxy. Low-temperature scanning tunneling microscopy and spectroscopy verify the Lieb lattice's morphology and electronic flat bands. Furthermore, topological Dirac edge states stemming from pronounced spin-orbit coupling induced by heavy Pt atoms are predicted. These findings convincingly open perspectives for creating metal-inorganic framework-based atomic lattices, offering prospects for strongly correlated phases interplayed with topology. |
Song, Jingting; Qian, Zheng-Xin; Yang, Ji; Lin, Xiu-Mei; Xu, Qingchi; Li, Jian-Feng In situ/Operando Investigation for Heterogeneous Electro-Catalysts: From Model Catalysts to State-of-the-Art Catalysts Journal Article ACS ENERGY LETTERS, 9 (9), pp. 4414-4440, 2024, ISSN: 2380-8195. @article{ISI:001293296300001, title = {In situ/Operando Investigation for Heterogeneous Electro-Catalysts: From Model Catalysts to State-of-the-Art Catalysts}, author = {Jingting Song and Zheng-Xin Qian and Ji Yang and Xiu-Mei Lin and Qingchi Xu and Jian-Feng Li}, doi = {10.1021/acsenergylett.4c01488}, times_cited = {2}, issn = {2380-8195}, year = {2024}, date = {2024-08-17}, journal = {ACS ENERGY LETTERS}, volume = {9}, number = {9}, pages = {4414-4440}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Electrochemical reactions, including water splitting, oxygen reduction, hydrogen oxidation, carbon dioxide reduction, nitrogen oxide reduction, etc., are critical for sustainable energy conversion and storage. Achieving high efficiency in these reactions requires catalysts with superior activity, selectivity, and stability, often realized through nanostructured metal catalysts. However, practical challenges such as low selectivity and catalytic degradation persist. In situ and operando characterization techniques offer real-time insights into catalyst behavior under reaction conditions, enabling a deeper understanding of structure-performance relationships and, therefore, guiding the design and optimization of electro-catalysts. This review discusses the common in situ/operando techniques, highlights their applications in model catalysts, including single-atom and single-crystal catalysts, and further explores their combinational analysis to study practical complex nanocatalysts. Finally, we provide suggestions and perspectives on the development of the in situ/operando techniques to further advance the field of electrochemical catalysis.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Electrochemical reactions, including water splitting, oxygen reduction, hydrogen oxidation, carbon dioxide reduction, nitrogen oxide reduction, etc., are critical for sustainable energy conversion and storage. Achieving high efficiency in these reactions requires catalysts with superior activity, selectivity, and stability, often realized through nanostructured metal catalysts. However, practical challenges such as low selectivity and catalytic degradation persist. In situ and operando characterization techniques offer real-time insights into catalyst behavior under reaction conditions, enabling a deeper understanding of structure-performance relationships and, therefore, guiding the design and optimization of electro-catalysts. This review discusses the common in situ/operando techniques, highlights their applications in model catalysts, including single-atom and single-crystal catalysts, and further explores their combinational analysis to study practical complex nanocatalysts. Finally, we provide suggestions and perspectives on the development of the in situ/operando techniques to further advance the field of electrochemical catalysis. |
Erofeev, Ivan; Saidov, Khakimjon; Baraissov, Zhaslan; Yan, Hongwei; Maurice, Jean-Luc; Panciera, Federico; Mirsaidov, Utkur 3D Shape Reconstruction of Ge Nanowires during Vapor-Liquid-Solid Growth under Modulating Electric Field Journal Article ACS NANO, 18 (34), pp. 22855-22863, 2024, ISSN: 1936-0851. @article{ISI:001289867600001, title = {3D Shape Reconstruction of Ge Nanowires during Vapor-Liquid-Solid Growth under Modulating Electric Field}, author = {Ivan Erofeev and Khakimjon Saidov and Zhaslan Baraissov and Hongwei Yan and Jean-Luc Maurice and Federico Panciera and Utkur Mirsaidov}, doi = {10.1021/acsnano.4c00087}, times_cited = {0}, issn = {1936-0851}, year = {2024}, date = {2024-08-12}, journal = {ACS NANO}, volume = {18}, number = {34}, pages = {22855-22863}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Bottom-up growth offers precise control over the structure and geometry of semiconductor nanowires (NWs), enabling a wide range of possible shapes and seamless heterostructures for applications in nanophotonics and electronics. The most common vapor-liquid-solid (VLS) growth method features a complex interaction between the liquid metal catalyst droplet and the anisotropic structure of the crystalline NW, and the growth is mainly orchestrated by the triple-phase line (TPL). Despite the intrinsic mismatch between the droplet and the NW symmetries, its discussion has been largely avoided because of its complexity, which has led to the situation when multiple observed phenomena such as NW axial asymmetry or the oscillating truncation at the TPL still lack detailed explanation. The introduction of an electric field control of the droplet has opened even more questions, which cannot be answered without properly addressing three-dimensional (3D) structure and morphology of the NW and the droplet. This work describes the details of electric-field-controlled VLS growth of germanium (Ge) NWs using environmental transmission electron microscopy (ETEM). We perform TEM tomography of the droplet-NW system during an unperturbed growth, then track its evolution while modulating the bias potential. Using 3D finite element method (FEM) modeling and crystallographic considerations, we provide a detailed and consistent mechanism for VLS growth, which naturally explains the observed asymmetries and features of a growing NW based on its crystal structure. Our findings provide a solid framework for the fabrication of complex 3D semiconductor nanostructures with ultimate control over their morphology.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Bottom-up growth offers precise control over the structure and geometry of semiconductor nanowires (NWs), enabling a wide range of possible shapes and seamless heterostructures for applications in nanophotonics and electronics. The most common vapor-liquid-solid (VLS) growth method features a complex interaction between the liquid metal catalyst droplet and the anisotropic structure of the crystalline NW, and the growth is mainly orchestrated by the triple-phase line (TPL). Despite the intrinsic mismatch between the droplet and the NW symmetries, its discussion has been largely avoided because of its complexity, which has led to the situation when multiple observed phenomena such as NW axial asymmetry or the oscillating truncation at the TPL still lack detailed explanation. The introduction of an electric field control of the droplet has opened even more questions, which cannot be answered without properly addressing three-dimensional (3D) structure and morphology of the NW and the droplet. This work describes the details of electric-field-controlled VLS growth of germanium (Ge) NWs using environmental transmission electron microscopy (ETEM). We perform TEM tomography of the droplet-NW system during an unperturbed growth, then track its evolution while modulating the bias potential. Using 3D finite element method (FEM) modeling and crystallographic considerations, we provide a detailed and consistent mechanism for VLS growth, which naturally explains the observed asymmetries and features of a growing NW based on its crystal structure. Our findings provide a solid framework for the fabrication of complex 3D semiconductor nanostructures with ultimate control over their morphology. |
Guo, Qiangbing; Zhang, Qiuhong; Zhang, Tan; Zhou, Jun; Xiao, Shumin; Wang, Shijie; Feng, Yuan Ping; Qiu, Cheng-Wei Colossal in-plane optical anisotropy in a two-dimensional van der Waals crystal Journal Article NATURE PHOTONICS, 18 (11), 2024, ISSN: 1749-4885. @article{ISI:001288597300001, title = {Colossal in-plane optical anisotropy in a two-dimensional van der Waals crystal}, author = {Qiangbing Guo and Qiuhong Zhang and Tan Zhang and Jun Zhou and Shumin Xiao and Shijie Wang and Yuan Ping Feng and Cheng-Wei Qiu}, doi = {10.1038/s41566-024-01501-3}, times_cited = {1}, issn = {1749-4885}, year = {2024}, date = {2024-08-08}, journal = {NATURE PHOTONICS}, volume = {18}, number = {11}, publisher = {NATURE PORTFOLIO}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {Polarization, a fundamental property of light, has been widely exploited from quantum physics to high-dimensional optics. Materials with intrinsic optical anisotropy, such as dichroism and birefringence, are central to light polarization control, including the development of polarizers, waveplates, mirrors and phase-matching elements. Therefore, materials with strong optical anisotropy have been long-sought. Recently, two-dimensional van der Waals crystals show high optical anisotropy but are mostly restricted to the out-of-plane direction, which is challenging to access in optical engineering. Here we report a two-dimensional van der Waals material, NbOCl2, that exhibits sharp electronic and structural contrast between its in-plane orthogonal axes. Colossal in-plane optical anisotropy-linear dichroism (up to 99% in ultraviolet) and birefringence (0.26-0.46 within a wide visible-near-infrared transparency window)-is experimentally demonstrated. Our findings provide a powerful and easy-to-access recipe for ultracompact integrated polarization industries.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Polarization, a fundamental property of light, has been widely exploited from quantum physics to high-dimensional optics. Materials with intrinsic optical anisotropy, such as dichroism and birefringence, are central to light polarization control, including the development of polarizers, waveplates, mirrors and phase-matching elements. Therefore, materials with strong optical anisotropy have been long-sought. Recently, two-dimensional van der Waals crystals show high optical anisotropy but are mostly restricted to the out-of-plane direction, which is challenging to access in optical engineering. Here we report a two-dimensional van der Waals material, NbOCl2, that exhibits sharp electronic and structural contrast between its in-plane orthogonal axes. Colossal in-plane optical anisotropy-linear dichroism (up to 99% in ultraviolet) and birefringence (0.26-0.46 within a wide visible-near-infrared transparency window)-is experimentally demonstrated. Our findings provide a powerful and easy-to-access recipe for ultracompact integrated polarization industries. |