Andrew Wee
Degree: PhD
Position: Professor
Affiliation: NUS – Department of Physics
Research Type: Experiment
Office: S13 03-12
Email: phyweets@nus.edu.sg
Contact: (65) 6516 6362
Website: http://www.physics.nus.edu.sg/~phyweets/
Research Interests
Scanning tunneling microscopy (STM) and synchrotron radiation studies of the molecule-substrate interface, graphene and 2D materials, and related device studies
CA2DM Publications:
2023 |
Hu, Junxiong; Han, Yulei; Chi, Xiao; Omar, Ganesh Ji; Ezzi, Mohammed Mohammed Esmail Al; Gou, Jian; Yu, Xiaojiang; Andrivo, Rusydi; Watanabe, Kenji; Taniguchi, Takashi; Wee, Andrew Thye Shen; Qiao, Zhenhua; Ariando, A Tunable Spin-Polarized States in Graphene on a Ferrimagnetic Oxide Insulator Journal Article ADVANCED MATERIALS, 36 (8), 2023, ISSN: 0935-9648. @article{ISI:001113825300001, title = {Tunable Spin-Polarized States in Graphene on a Ferrimagnetic Oxide Insulator}, author = {Junxiong Hu and Yulei Han and Xiao Chi and Ganesh Ji Omar and Mohammed Mohammed Esmail Al Ezzi and Jian Gou and Xiaojiang Yu and Rusydi Andrivo and Kenji Watanabe and Takashi Taniguchi and Andrew Thye Shen Wee and Zhenhua Qiao and A Ariando}, doi = {10.1002/adma.202305763}, times_cited = {0}, issn = {0935-9648}, year = {2023}, date = {2023-12-06}, journal = {ADVANCED MATERIALS}, volume = {36}, number = {8}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {Spin-polarized two-dimensional (2D) materials with large and tunable spin-splitting energy promise the field of 2D spintronics. While graphene has been a canonical 2D material, its spin properties and tunability are limited. Here, this work demonstrates the emergence of robust spin-polarization in graphene with large and tunable spin-splitting energy of up to 132 meV at zero applied magnetic fields. The spin polarization is induced through a magnetic exchange interaction between graphene and the underlying ferrimagnetic oxide insulating layer, Tm3Fe5O12, as confirmed by its X-ray magnetic circular dichroism (XMCD). The spin-splitting energies are directly measured and visualized by the shift in their Landau-fan diagram mapped by analyzing the measured Shubnikov-de-Haas (SdH) oscillations as a function of applied electric fields, showing consistent fit with the first-principles and machine learning calculations. Further, the observed spin-splitting energies can be tuned over a broad range between 98 and 166 meV by field cooling. The methods and results are applicable to other 2D (magnetic) materials and heterostructures, and offer great potential for developing next-generation spin logic and memory devices.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Spin-polarized two-dimensional (2D) materials with large and tunable spin-splitting energy promise the field of 2D spintronics. While graphene has been a canonical 2D material, its spin properties and tunability are limited. Here, this work demonstrates the emergence of robust spin-polarization in graphene with large and tunable spin-splitting energy of up to 132 meV at zero applied magnetic fields. The spin polarization is induced through a magnetic exchange interaction between graphene and the underlying ferrimagnetic oxide insulating layer, Tm3Fe5O12, as confirmed by its X-ray magnetic circular dichroism (XMCD). The spin-splitting energies are directly measured and visualized by the shift in their Landau-fan diagram mapped by analyzing the measured Shubnikov-de-Haas (SdH) oscillations as a function of applied electric fields, showing consistent fit with the first-principles and machine learning calculations. Further, the observed spin-splitting energies can be tuned over a broad range between 98 and 166 meV by field cooling. The methods and results are applicable to other 2D (magnetic) materials and heterostructures, and offer great potential for developing next-generation spin logic and memory devices. |
Zhang, Wen; Fu, Qiang; Li, Jiahui; Lian, Beilei; Xia, Yuze; Zhou, Liguo; Wee, Andrew Thye Shen; Wong, Ping Kwan Johnny Probing van der Waals magnetic surface and interface via circularly polarized X-rays Journal Article APPLIED PHYSICS REVIEWS, 10 (4), 2023, ISSN: 1931-9401. @article{ISI:001111315300002, title = {Probing van der Waals magnetic surface and interface via circularly polarized X-rays}, author = {Wen Zhang and Qiang Fu and Jiahui Li and Beilei Lian and Yuze Xia and Liguo Zhou and Andrew Thye Shen Wee and Ping Kwan Johnny Wong}, doi = {10.1063/5.0164400}, times_cited = {0}, issn = {1931-9401}, year = {2023}, date = {2023-12-01}, journal = {APPLIED PHYSICS REVIEWS}, volume = {10}, number = {4}, publisher = {AIP Publishing}, address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA}, abstract = {Advances in research of magnetic two-dimensional van der Waals (2D vdW) materials have opened up new opportunities in miniaturization of spintronic devices at the atomically thin limit. One major research thrust, which is the subject of this review, is that the magnetism of 2D vdW materials and their derived hetero-interface may be significantly affected by the local atomic geometry and environment. As a result, there is a pressing need for powerful advanced technique to characterize magnetic vdW surface and interface. Circularly polarized X-rays from synchrotron radiation light sources are key to this endeavor, as they can probe the microscopic magnetism of a specific element, for their atomic sensitivity, element-specificity, core-level excitation as well as capability of separation for the spin and orbit moments. We review a series of representative experimental achievements, exploiting circularly polarized X-rays, in (1) 2D vdW magnet, (2) magnetic metal/vdW interface, (3) molecule/vdW interface as well as (4) vdW/2D interface. On the basis of the review, advantages of probing magnetic vdW surface and interface by circularly polarized X-rays are presented, and challenges and opportunities are also discussed.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Advances in research of magnetic two-dimensional van der Waals (2D vdW) materials have opened up new opportunities in miniaturization of spintronic devices at the atomically thin limit. One major research thrust, which is the subject of this review, is that the magnetism of 2D vdW materials and their derived hetero-interface may be significantly affected by the local atomic geometry and environment. As a result, there is a pressing need for powerful advanced technique to characterize magnetic vdW surface and interface. Circularly polarized X-rays from synchrotron radiation light sources are key to this endeavor, as they can probe the microscopic magnetism of a specific element, for their atomic sensitivity, element-specificity, core-level excitation as well as capability of separation for the spin and orbit moments. We review a series of representative experimental achievements, exploiting circularly polarized X-rays, in (1) 2D vdW magnet, (2) magnetic metal/vdW interface, (3) molecule/vdW interface as well as (4) vdW/2D interface. On the basis of the review, advantages of probing magnetic vdW surface and interface by circularly polarized X-rays are presented, and challenges and opportunities are also discussed. |
Hu, Junxiong; Tan, Junyou; Ezzi, Mohammed Al M; Chattopadhyay, Udvas; Gou, Jian; Zheng, Yuntian; Wang, Zihao; Chen, Jiayu; Thottathil, Reshmi; Luo, Jiangbo; Watanabe, Kenji; Taniguchi, Takashi; Wee, Andrew Thye Shen; Adam, Shaffique; Ariando, A Controlled alignment of supermoire lattice in double-aligned graphene heterostructures Journal Article NATURE COMMUNICATIONS, 14 (1), 2023. @article{ISI:001029450400007, title = {Controlled alignment of supermoire lattice in double-aligned graphene heterostructures}, author = {Junxiong Hu and Junyou Tan and Mohammed Al M Ezzi and Udvas Chattopadhyay and Jian Gou and Yuntian Zheng and Zihao Wang and Jiayu Chen and Reshmi Thottathil and Jiangbo Luo and Kenji Watanabe and Takashi Taniguchi and Andrew Thye Shen Wee and Shaffique Adam and A Ariando}, doi = {10.1038/s41467-023-39893-5}, times_cited = {0}, year = {2023}, date = {2023-07-12}, journal = {NATURE COMMUNICATIONS}, volume = {14}, number = {1}, publisher = {NATURE PORTFOLIO}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {The supermoire lattice, built by stacking two moire patterns, provides a platform for creating flat mini-bands and studying electron correlations. An ultimate challenge in assembling a graphene supermoire lattice is in the deterministic control of its rotational alignment, which is made highly aleatory due to the random nature of the edge chirality and crystal symmetry. Employing the so-called "golden rule of three", here we present an experimental strategy to overcome this challenge and realize the controlled alignment of double-aligned hBN/graphene/hBN supermoire lattice, where the twist angles between graphene and top/bottom hBN are both close to zero. Remarkably, we find that the crystallographic edge of neighboring graphite can be used to better guide the stacking alignment, as demonstrated by the controlled production of 20 moire samples with an accuracy better than similar to 0.2 degrees. Finally, we extend our technique to low-angle twisted bilayer graphene and ABC-stacked trilayer graphene, providing a strategy for flat-band engineering in these moirematerials.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The supermoire lattice, built by stacking two moire patterns, provides a platform for creating flat mini-bands and studying electron correlations. An ultimate challenge in assembling a graphene supermoire lattice is in the deterministic control of its rotational alignment, which is made highly aleatory due to the random nature of the edge chirality and crystal symmetry. Employing the so-called "golden rule of three", here we present an experimental strategy to overcome this challenge and realize the controlled alignment of double-aligned hBN/graphene/hBN supermoire lattice, where the twist angles between graphene and top/bottom hBN are both close to zero. Remarkably, we find that the crystallographic edge of neighboring graphite can be used to better guide the stacking alignment, as demonstrated by the controlled production of 20 moire samples with an accuracy better than similar to 0.2 degrees. Finally, we extend our technique to low-angle twisted bilayer graphene and ABC-stacked trilayer graphene, providing a strategy for flat-band engineering in these moirematerials. |
Gou, Jian; Bai, Hua; Zhang, Xuanlin; Huang, Yu Li; Duan, Sisheng; Ariando, A; Yang, Shengyuan A; Chen, Lan; Lu, Yunhao; Wee, Andrew Thye Shen Two-dimensional ferroelectricity in a single-element bismuth monolayer Journal Article NATURE, 617 (7959), pp. 67-+, 2023, ISSN: 0028-0836. @article{ISI:000990835100012, title = {Two-dimensional ferroelectricity in a single-element bismuth monolayer}, author = {Jian Gou and Hua Bai and Xuanlin Zhang and Yu Li Huang and Sisheng Duan and A Ariando and Shengyuan A Yang and Lan Chen and Yunhao Lu and Andrew Thye Shen Wee}, doi = {10.1038/s41586-023-05848-5}, times_cited = {0}, issn = {0028-0836}, year = {2023}, date = {2023-04-05}, journal = {NATURE}, volume = {617}, number = {7959}, pages = {67-+}, publisher = {NATURE PORTFOLIO}, address = {HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY}, abstract = {Ferroelectric materials are fascinating for their non-volatile switchable electric polarizations induced by the spontaneous inversion-symmetry breaking. However, in all of the conventional ferroelectric compounds, at least two constituent ions are required to support the polarization switching(1,2). Here, we report the observation of a single-element ferroelectric state in a black phosphorus-like bismuth layer(3), in which the ordered charge transfer and the regular atom distortion between sublattices happen simultaneously. Instead of a homogenous orbital configuration that ordinarily occurs in elementary substances, we found the Bi atoms in a black phosphorous-like Bi monolayer maintain a weak and anisotropic sp orbital hybridization, giving rise to the inversion-symmetry-broken buckled structure accompanied with charge redistribution in the unit cell. As a result, the in-plane electric polarization emerges in the Bi monolayer. Using the in-plane electric field produced by scanning probe microscopy, ferroelectric switching is further visualized experimentally. Owing to the conjugative locking between the charge transfer and atom displacement, we also observe the anomalous electric potential profile at the 180 degrees tail-to-tail domain wall induced by competition between the electronic structure and electric polarization. This emergent single-element ferroelectricity broadens the mechanism of ferroelectrics and may enrich the applications of ferroelectronics in the future.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Ferroelectric materials are fascinating for their non-volatile switchable electric polarizations induced by the spontaneous inversion-symmetry breaking. However, in all of the conventional ferroelectric compounds, at least two constituent ions are required to support the polarization switching(1,2). Here, we report the observation of a single-element ferroelectric state in a black phosphorus-like bismuth layer(3), in which the ordered charge transfer and the regular atom distortion between sublattices happen simultaneously. Instead of a homogenous orbital configuration that ordinarily occurs in elementary substances, we found the Bi atoms in a black phosphorous-like Bi monolayer maintain a weak and anisotropic sp orbital hybridization, giving rise to the inversion-symmetry-broken buckled structure accompanied with charge redistribution in the unit cell. As a result, the in-plane electric polarization emerges in the Bi monolayer. Using the in-plane electric field produced by scanning probe microscopy, ferroelectric switching is further visualized experimentally. Owing to the conjugative locking between the charge transfer and atom displacement, we also observe the anomalous electric potential profile at the 180 degrees tail-to-tail domain wall induced by competition between the electronic structure and electric polarization. This emergent single-element ferroelectricity broadens the mechanism of ferroelectrics and may enrich the applications of ferroelectronics in the future. |
2022 |
Mahyuddin, Muhammad Haris; Arramel, ; Diguna, Lina Jaya; Agusta, Mohammad Kemal; Mulyani, Irma; Onggo, Djulia; Shiddiq, Muhandis; Tang, Chi Sin; Yin, Xinmao; Diao, Caozheng; Birowosuto, Muhammad Danang; Wee, Andrew Thye Shen; Rusydi, Andrivo Tailoring the Optical and Electronic Properties of 2D Hybrid Dion-Jacobson Copper Chloride Perovskites Journal Article JOURNAL OF PHYSICAL CHEMISTRY C, 126 (50), pp. 21297-21307, 2022, ISSN: 1932-7447. @article{ISI:000895662800001, title = {Tailoring the Optical and Electronic Properties of 2D Hybrid Dion-Jacobson Copper Chloride Perovskites}, author = {Muhammad Haris Mahyuddin and Arramel and Lina Jaya Diguna and Mohammad Kemal Agusta and Irma Mulyani and Djulia Onggo and Muhandis Shiddiq and Chi Sin Tang and Xinmao Yin and Caozheng Diao and Muhammad Danang Birowosuto and Andrew Thye Shen Wee and Andrivo Rusydi}, doi = {10.1021/acs.jpcc.2c06050}, times_cited = {2}, issn = {1932-7447}, year = {2022}, date = {2022-12-09}, journal = {JOURNAL OF PHYSICAL CHEMISTRY C}, volume = {126}, number = {50}, pages = {21297-21307}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {The upsurge of low-dimensional Dion-Jacobson (DJ) phase perovskites has brought significant interest in view of their appealing stability against harsh environmental conditions as well as their promising performance in optoelectronic applications. Few reports to date have concentrated on the fundamental relationship of fine-tuning the control of diamine-based perovskite single crystals toward their electronic properties and optical behaviors. Here, we demonstrate that cationic control is proposed to regulate the role of hydrogen bonding of organic ligands with the edge-sharing [CuCl6](4-) octahedral layers, leading to strong differences in the material excitonic profile and tunability of their electronic properties. Interestingly, we observe a significant reduction of photoluminescence intensity upon controlling the Cu2+/Cu+ proportion in this hybrid system. According to the photoemission measurements, variation in the oxidation states of Cu cations plays a crucial role in stabilizing the diammonium-based perovskite geometric structure. Interestingly, we find that the electronic signatures of the singlet spin-state and high-energy region transition are not influenced by the thermal effect, as probed by temperature-dependent X-ray absorption spectroscopy (XAS) at elevated temperature. Density functional calculations suggest that such an electronic difference originates from the hydrogen bonding reduction that altered the magnitude of the octahedral distortion within the DJ layered structure. As a result, the +3NHC4H9NH3+ conformation produces a non-negligible interaction toward tuning the optical and electronic properties of DJ copper-based perovskites.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The upsurge of low-dimensional Dion-Jacobson (DJ) phase perovskites has brought significant interest in view of their appealing stability against harsh environmental conditions as well as their promising performance in optoelectronic applications. Few reports to date have concentrated on the fundamental relationship of fine-tuning the control of diamine-based perovskite single crystals toward their electronic properties and optical behaviors. Here, we demonstrate that cationic control is proposed to regulate the role of hydrogen bonding of organic ligands with the edge-sharing [CuCl6](4-) octahedral layers, leading to strong differences in the material excitonic profile and tunability of their electronic properties. Interestingly, we observe a significant reduction of photoluminescence intensity upon controlling the Cu2+/Cu+ proportion in this hybrid system. According to the photoemission measurements, variation in the oxidation states of Cu cations plays a crucial role in stabilizing the diammonium-based perovskite geometric structure. Interestingly, we find that the electronic signatures of the singlet spin-state and high-energy region transition are not influenced by the thermal effect, as probed by temperature-dependent X-ray absorption spectroscopy (XAS) at elevated temperature. Density functional calculations suggest that such an electronic difference originates from the hydrogen bonding reduction that altered the magnitude of the octahedral distortion within the DJ layered structure. As a result, the +3NHC4H9NH3+ conformation produces a non-negligible interaction toward tuning the optical and electronic properties of DJ copper-based perovskites. |
Maulida, Pramitha Yuniar Diah; Wang, Dingguan; Maddalena, Francesco; Tang, Chi Sin; Yin, Xinmao; Diao, Caozheng; Mulyani, Irma; Onggo, Djulia; Noviyanto, Alfian; Birowosuto, Muhammad Danang; Arramel, ; Wee, Andrew Thye Shen; Rusydi, Andrivo Unraveling Correlated Electronic States in Layered Manganese- Based Perovskites Journal Article JOURNAL OF PHYSICAL CHEMISTRY C , 126 (37), pp. 15801-15808, 2022, ISSN: 1932-7447. @article{ISI:000859975300001, title = {Unraveling Correlated Electronic States in Layered Manganese- Based Perovskites }, author = {Pramitha Yuniar Diah Maulida and Dingguan Wang and Francesco Maddalena and Chi Sin Tang and Xinmao Yin and Caozheng Diao and Irma Mulyani and Djulia Onggo and Alfian Noviyanto and Muhammad Danang Birowosuto and Arramel and Andrew Thye Shen Wee and Andrivo Rusydi}, doi = {10.1021/acs.jpcc.2c04739}, times_cited = {0}, issn = {1932-7447}, year = {2022}, date = {2022-09-22}, journal = {JOURNAL OF PHYSICAL CHEMISTRY C }, volume = {126}, number = {37}, pages = {15801-15808}, publisher = {AMER CHEMICAL SOC }, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA }, abstract = {The tunable control in the inorganic octahedral framework of hybrid perovskites offers potential applications in photovoltaics, solid-state lighting, and radiation detection. However, the implication of the structure and optoelectronic properties pose challenges due to competition between organic??? inorganic coupling and intraoctahedral interactions. In this study, we combine X-ray absorption spectroscopy (XAS) and Raman analysis to interpret the angular-dependent behavior and anharmonicity of manganese-based single-crystal perovskites differing by a single methylene unit. The XAS spectra of manganese-based single-crystal perovskites with 2-phenethylamine (PEA) compared to 3-phenyl-1-propylamine (PPA) as organic cations unambiguously demonstrated a 180?? intensity shift as a function of the incoming photon, suggesting a pronounced structural ligand variation. The out-of-plane polarization is found to be more prominent in L2-edge than in L3. In addition, an accompanying shoulder peak around 643 eV was attributed to the electron excitation from Mn 2p to 3d orbitals to form d5L states. A decrease in terms of field strength is prominently observed that infers a low crystal field splitting energy. Raman analysis of the two hybrid perovskites displays a notable difference in the respective translational modes at 84 and 87 cm???1, which signifies the amplified anharmonicity due to extended chain length. Based on this phenomenological approach, a longer chain promotes a rather unique octahedral deformation than anharmonicity shift that is crucially important to decoupling the nature of the active units. This effort sheds some light to implement the orientational ordering toward an efficient charge transport of hybrid perovskite semiconductors. }, keywords = {}, pubstate = {published}, tppubtype = {article} } The tunable control in the inorganic octahedral framework of hybrid perovskites offers potential applications in photovoltaics, solid-state lighting, and radiation detection. However, the implication of the structure and optoelectronic properties pose challenges due to competition between organic??? inorganic coupling and intraoctahedral interactions. In this study, we combine X-ray absorption spectroscopy (XAS) and Raman analysis to interpret the angular-dependent behavior and anharmonicity of manganese-based single-crystal perovskites differing by a single methylene unit. The XAS spectra of manganese-based single-crystal perovskites with 2-phenethylamine (PEA) compared to 3-phenyl-1-propylamine (PPA) as organic cations unambiguously demonstrated a 180?? intensity shift as a function of the incoming photon, suggesting a pronounced structural ligand variation. The out-of-plane polarization is found to be more prominent in L2-edge than in L3. In addition, an accompanying shoulder peak around 643 eV was attributed to the electron excitation from Mn 2p to 3d orbitals to form d5L states. A decrease in terms of field strength is prominently observed that infers a low crystal field splitting energy. Raman analysis of the two hybrid perovskites displays a notable difference in the respective translational modes at 84 and 87 cm???1, which signifies the amplified anharmonicity due to extended chain length. Based on this phenomenological approach, a longer chain promotes a rather unique octahedral deformation than anharmonicity shift that is crucially important to decoupling the nature of the active units. This effort sheds some light to implement the orientational ordering toward an efficient charge transport of hybrid perovskite semiconductors. |
Maulida, Pramitha Yuniar Diah; Wang, Dingguan; Maddalena, Francesco; Tang, Chi Sin; Yin, Xinmao; Diao, Caozheng; Mulyani, Irma; Onggo, Djulia; Noviyanto, Alfian; Birowosuto, Muhammad Danang; Arramel, ; Wee, Andrew Thye Shen; Rusydi, Andrivo Unraveling Correlated Electronic States in Layered Manganese- Based Perovskites Journal Article JOURNAL OF PHYSICAL CHEMISTRY C, 126 (37), pp. 15801-15808, 2022, ISSN: 1932-7447. @article{ISI:000859802500001, title = {Unraveling Correlated Electronic States in Layered Manganese- Based Perovskites}, author = {Pramitha Yuniar Diah Maulida and Dingguan Wang and Francesco Maddalena and Chi Sin Tang and Xinmao Yin and Caozheng Diao and Irma Mulyani and Djulia Onggo and Alfian Noviyanto and Muhammad Danang Birowosuto and Arramel and Andrew Thye Shen Wee and Andrivo Rusydi}, doi = {10.1021/acs.jpcc.2c04739}, times_cited = {0}, issn = {1932-7447}, year = {2022}, date = {2022-09-13}, journal = {JOURNAL OF PHYSICAL CHEMISTRY C}, volume = {126}, number = {37}, pages = {15801-15808}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {The tunable control in the inorganic octahedral framework of hybrid perovskites offers potential applications in photovoltaics, solid-state lighting, and radiation detection. However, the implication of the structure and optoelectronic properties pose challenges due to competition between organic??? inorganic coupling and intraoctahedral interactions. In this study, we combine X-ray absorption spectroscopy (XAS) and Raman analysis to interpret the angular-dependent behavior and anharmonicity of manganese-based single-crystal perovskites differing by a single methylene unit. The XAS spectra of manganese-based single-crystal perovskites with 2-phenethylamine (PEA) compared to 3-phenyl-1-propylamine (PPA) as organic cations unambiguously demonstrated a 180?? intensity shift as a function of the incoming photon, suggesting a pronounced structural ligand variation. The out-of-plane polarization is found to be more prominent in L2-edge than in L3. In addition, an accompanying shoulder peak around 643 eV was attributed to the electron excitation from Mn 2p to 3d orbitals to form d5L states. A decrease in terms of field strength is prominently observed that infers a low crystal field splitting energy. Raman analysis of the two hybrid perovskites displays a notable difference in the respective translational modes at 84 and 87 cm???1, which signifies the amplified anharmonicity due to extended chain length. Based on this phenomenological approach, a longer chain promotes a rather unique octahedral deformation than anharmonicity shift that is crucially important to decoupling the nature of the active units. This effort sheds some light to implement the orientational ordering toward an efficient charge transport of hybrid perovskite semiconductors.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The tunable control in the inorganic octahedral framework of hybrid perovskites offers potential applications in photovoltaics, solid-state lighting, and radiation detection. However, the implication of the structure and optoelectronic properties pose challenges due to competition between organic??? inorganic coupling and intraoctahedral interactions. In this study, we combine X-ray absorption spectroscopy (XAS) and Raman analysis to interpret the angular-dependent behavior and anharmonicity of manganese-based single-crystal perovskites differing by a single methylene unit. The XAS spectra of manganese-based single-crystal perovskites with 2-phenethylamine (PEA) compared to 3-phenyl-1-propylamine (PPA) as organic cations unambiguously demonstrated a 180?? intensity shift as a function of the incoming photon, suggesting a pronounced structural ligand variation. The out-of-plane polarization is found to be more prominent in L2-edge than in L3. In addition, an accompanying shoulder peak around 643 eV was attributed to the electron excitation from Mn 2p to 3d orbitals to form d5L states. A decrease in terms of field strength is prominently observed that infers a low crystal field splitting energy. Raman analysis of the two hybrid perovskites displays a notable difference in the respective translational modes at 84 and 87 cm???1, which signifies the amplified anharmonicity due to extended chain length. Based on this phenomenological approach, a longer chain promotes a rather unique octahedral deformation than anharmonicity shift that is crucially important to decoupling the nature of the active units. This effort sheds some light to implement the orientational ordering toward an efficient charge transport of hybrid perovskite semiconductors. |
Hu, Junxiong; Luo, Jiangbo; Zheng, Yuntian; Chen, Jiayu; Omar, Ganesh Ji; Wee, Andrew Thye Shen; Ariando, A Magnetic proximity effect at the interface of two-dimensional materials and magnetic oxide insulators Journal Article JOURNAL OF ALLOYS AND COMPOUNDS, 911 , 2022, ISSN: 0925-8388. @article{ISI:000797655000001, title = {Magnetic proximity effect at the interface of two-dimensional materials and magnetic oxide insulators}, author = {Junxiong Hu and Jiangbo Luo and Yuntian Zheng and Jiayu Chen and Ganesh Ji Omar and Andrew Thye Shen Wee and A Ariando}, doi = {10.1016/j.jallcom.2022.164830}, times_cited = {6}, issn = {0925-8388}, year = {2022}, date = {2022-04-18}, journal = {JOURNAL OF ALLOYS AND COMPOUNDS}, volume = {911}, publisher = {ELSEVIER SCIENCE SA}, address = {PO BOX 564, 1001 LAUSANNE, SWITZERLAND}, abstract = {Two-dimensional (2D) materials can serve as a platform for developing novel spintronic devices and circuits for low-power electronics. In particular, inducing magnetism and injecting spins in graphene have promised the emerging field of graphene spintronics. This review focuses on magnetic proximity effects at the interface of 2D materials and magnetic oxide insulators. We highlight unique spin-related phenomena arising from magnetic exchange interaction and spin-orbital coupling in 2D materials coupled with magnetic oxides. We also describe the fabrication of multifunctional hybrid devices based on spin transport. We conclude with a perspective of the field and highlight challenges for the design and fabrication of 2D spintronic devices and their potential applications in information storage and logic devices.(c) 2022 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Two-dimensional (2D) materials can serve as a platform for developing novel spintronic devices and circuits for low-power electronics. In particular, inducing magnetism and injecting spins in graphene have promised the emerging field of graphene spintronics. This review focuses on magnetic proximity effects at the interface of 2D materials and magnetic oxide insulators. We highlight unique spin-related phenomena arising from magnetic exchange interaction and spin-orbital coupling in 2D materials coupled with magnetic oxides. We also describe the fabrication of multifunctional hybrid devices based on spin transport. We conclude with a perspective of the field and highlight challenges for the design and fabrication of 2D spintronic devices and their potential applications in information storage and logic devices.(c) 2022 Elsevier B.V. All rights reserved. |
Sahdan, Muhammad Fauzi; Arramel, ; Xiaodai, Sharon Lim; Wang, Hong; Birowosuto, Muhammad Danang; Haur, Sow Chorng; Ang, Kah-Wee; Wee, Andrew Thye Shen Metal-insulator transition switching in VOx-VSe2 heterojunctions Journal Article PHYSICAL REVIEW MATERIALS, 6 (1), 2022, ISSN: 2475-9953. @article{ISI:000747807700002, title = {Metal-insulator transition switching in VO_{\textit{x}}-VSe_{2} heterojunctions}, author = {Muhammad Fauzi Sahdan and Arramel and Sharon Lim Xiaodai and Hong Wang and Muhammad Danang Birowosuto and Sow Chorng Haur and Kah-Wee Ang and Andrew Thye Shen Wee}, doi = {10.1103/PhysRevMaterials.6.014003}, times_cited = {0}, issn = {2475-9953}, year = {2022}, date = {2022-01-19}, journal = {PHYSICAL REVIEW MATERIALS}, volume = {6}, number = {1}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {First-order metal-insulator transition (MIT) observed in strongly correlated systems such as vanadium dioxide (VO2) holds potential in electronics, energy, to optical applications. Starting from a vanadium diselenide (VSe2) bulk crystal, we demonstrated a direct surface conversion from VSe2 to VO2 via laser exposure in ambient condition. The process generates defects, and the heat from the laser promotes oxidation forming VOx. Raman spectra at room temperature suggest the resulting oxide formed is monoclinic (M1) VO2. Above the transition temperature (T-C), all the phonon modes are damped indicating formation of the rutile phase (metallic). Photoluminescence (PL) intensity enhancement and peak shifts observed at T-C suggest correlation to the band structure transformation. In addition, we observed electrically induced MIT in our lateral VSe2-VOx heterojunction device.}, keywords = {}, pubstate = {published}, tppubtype = {article} } First-order metal-insulator transition (MIT) observed in strongly correlated systems such as vanadium dioxide (VO2) holds potential in electronics, energy, to optical applications. Starting from a vanadium diselenide (VSe2) bulk crystal, we demonstrated a direct surface conversion from VSe2 to VO2 via laser exposure in ambient condition. The process generates defects, and the heat from the laser promotes oxidation forming VOx. Raman spectra at room temperature suggest the resulting oxide formed is monoclinic (M1) VO2. Above the transition temperature (T-C), all the phonon modes are damped indicating formation of the rutile phase (metallic). Photoluminescence (PL) intensity enhancement and peak shifts observed at T-C suggest correlation to the band structure transformation. In addition, we observed electrically induced MIT in our lateral VSe2-VOx heterojunction device. |
Arramel, ; Maddalena, Francesco; Mahyuddin, Muhammad Haris; Yin, Xinmao; Tang, Chi Sin; Agusta, Mohammad Kemal; Sahdan, Muhammad Fauzi; Diao, Caozheng; Dang, Cuong; Birowosuto, Muhammad Danang; Wee, Andrew Thye Shen; Rusydi, Andrivo Temperature-induced orbital polarizations and tunable charge dynamics in layered double perovskite thin films Journal Article MATERIALS TODAY ENERGY, 24 , 2022, ISSN: 2468-6069. @article{ISI:000820237900002, title = {Temperature-induced orbital polarizations and tunable charge dynamics in layered double perovskite thin films}, author = {Arramel and Francesco Maddalena and Muhammad Haris Mahyuddin and Xinmao Yin and Chi Sin Tang and Mohammad Kemal Agusta and Muhammad Fauzi Sahdan and Caozheng Diao and Cuong Dang and Muhammad Danang Birowosuto and Andrew Thye Shen Wee and Andrivo Rusydi}, doi = {10.1016/j.mtener.2021.100921}, times_cited = {0}, issn = {2468-6069}, year = {2022}, date = {2022-01-10}, journal = {MATERIALS TODAY ENERGY}, volume = {24}, publisher = {ELSEVIER SCI LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND}, abstract = {The realization of lead-free all-inorganic perovskites in emergent materials requires an in-depth understanding of strongly correlated systems toward optoelectronics or spintronics applications. Herein, we report the electronic and optical variation of the < 111 >-oriented layered double perovskites (LDP) family with the formula of (Cs4MBi2Br12)-Bi-II thin films (where MII: Cu, Mn, Pb, or Sr). The element and shell-specific orbital polarization based on soft X-ray linear dichroism spectroscopy probes the Cs M-4,M-5- and Mn L-2,L-3-edges of Cs4MnBi2Br12 thin films as a function of temperature. A strong reversal orbital polarization at the respective edges at 150 K indicates a thermally induced orbital-selective rearrangement at low temperature. In addition, the valence band analysis indicates different orbital admixtures of Br 4p and M-II d states, corroborated by the density functional theory calculations. In terms of the transient charge dynamics, we observe the photoluminescence peak maxima position trend line is shifted toward a longer wavelength. In addition, the longest average lifetime is recorded for Cs4CuBi2Br12 at 27.40 +/- 1 mu s. As the LDP structural integrity is lead-free, therefore, these all-inorganic perovskites hold promising potentials as sustainable and green materials for photophysics applications. (c) 2021 Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The realization of lead-free all-inorganic perovskites in emergent materials requires an in-depth understanding of strongly correlated systems toward optoelectronics or spintronics applications. Herein, we report the electronic and optical variation of the < 111 >-oriented layered double perovskites (LDP) family with the formula of (Cs4MBi2Br12)-Bi-II thin films (where MII: Cu, Mn, Pb, or Sr). The element and shell-specific orbital polarization based on soft X-ray linear dichroism spectroscopy probes the Cs M-4,M-5- and Mn L-2,L-3-edges of Cs4MnBi2Br12 thin films as a function of temperature. A strong reversal orbital polarization at the respective edges at 150 K indicates a thermally induced orbital-selective rearrangement at low temperature. In addition, the valence band analysis indicates different orbital admixtures of Br 4p and M-II d states, corroborated by the density functional theory calculations. In terms of the transient charge dynamics, we observe the photoluminescence peak maxima position trend line is shifted toward a longer wavelength. In addition, the longest average lifetime is recorded for Cs4CuBi2Br12 at 27.40 +/- 1 mu s. As the LDP structural integrity is lead-free, therefore, these all-inorganic perovskites hold promising potentials as sustainable and green materials for photophysics applications. (c) 2021 Elsevier Ltd. All rights reserved. |
2021 |
Zhang, Wen; Wong, Ping Kwan Johnny; Jiang, Sheng; Chen, Qian; Huang, Wei; Wee, Andrew Thye Shen Integrating spin-based technologies with atomically controlled van der Waals interfaces Journal Article MATERIALS TODAY, 51 , pp. 350-364, 2021, ISSN: 1369-7021. @article{ISI:000733421200002, title = {Integrating spin-based technologies with atomically controlled van der Waals interfaces}, author = {Wen Zhang and Ping Kwan Johnny Wong and Sheng Jiang and Qian Chen and Wei Huang and Andrew Thye Shen Wee}, doi = {10.1016/j.mattod.2021.09.015}, times_cited = {7}, issn = {1369-7021}, year = {2021}, date = {2021-12-15}, journal = {MATERIALS TODAY}, volume = {51}, pages = {350-364}, publisher = {ELSEVIER SCI LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND}, abstract = {As the feature sizes of electronic devices continue to shrink, new technologies-in particular spintronics and derived interfacial architectures-become increasingly pivotal. In this context, two-dimensional van der Waals materials and their interfaces are particularly attractive, relying on their ultimate atomic thicknesses and exceptional spin-related properties. This review provides a critical evaluation on the state-of-the-art of van der Waals interfaces and projected technological applications in spintronics, highlights major challenges and a viable solution-an all-in-situ growth and characterization strategy, and finally identifies several emerging spin-based technologies that might significantly benefit from the versatile van der Waals interfaces enabled by the strategy.}, keywords = {}, pubstate = {published}, tppubtype = {article} } As the feature sizes of electronic devices continue to shrink, new technologies-in particular spintronics and derived interfacial architectures-become increasingly pivotal. In this context, two-dimensional van der Waals materials and their interfaces are particularly attractive, relying on their ultimate atomic thicknesses and exceptional spin-related properties. This review provides a critical evaluation on the state-of-the-art of van der Waals interfaces and projected technological applications in spintronics, highlights major challenges and a viable solution-an all-in-situ growth and characterization strategy, and finally identifies several emerging spin-based technologies that might significantly benefit from the versatile van der Waals interfaces enabled by the strategy. |
Xu, Wenshuo; Ke, Yuxuan; Wang, Zhuo; Zhang, Wenjing; Wee, Andrew Thye Shen The metallic nature of two-dimensional transition-metal dichalcogenides and MXenes Journal Article SURFACE SCIENCE REPORTS, 76 (4), 2021, ISSN: 0167-5729. @article{ISI:000724478600001, title = {The metallic nature of two-dimensional transition-metal dichalcogenides and MXenes}, author = {Wenshuo Xu and Yuxuan Ke and Zhuo Wang and Wenjing Zhang and Andrew Thye Shen Wee}, doi = {10.1016/j.surfrep.2021.100542}, times_cited = {0}, issn = {0167-5729}, year = {2021}, date = {2021-11-29}, journal = {SURFACE SCIENCE REPORTS}, volume = {76}, number = {4}, publisher = {ELSEVIER}, address = {RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS}, abstract = {Metallic two-dimensional (2D) materials such as transition-metal dichalcogenides (TMDCs) and MXenes exhibit intriguing properties, including superconductivity, magnetism and electrocatalysis. Studies on the correlation between their nanoscale structures and properties can facilitate the development of photodetectors, supercapacitors, nanocatalysts, etc., but this topic has not been reviewed systematically. Here, we provide a comprehensive overview on the key factors that dictate the structures and properties of these 2D metals. We examine their phase transitions induced by structural or electronic modifications based on microscopic imaging, spectral characterization, and electrical measurements. From the perspective of surface and interface engineering, we elucidate the influences of lattice defects, dopants, and intercalated species between adjacent layers. Moreover, heterostructures involving highly conductive 2D component(s) are discussed, which may enable the observation of fascinating phenomena and/or synergistic effects due to the interlayer interactions. Finally, we provide insights into opportunities for new applications, e.g., radio-frequency antennas and electromagnetic interference shields. Feasible routes are also proposed to overcome the current challenges. (c) 2021 Elsevier B.V. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Metallic two-dimensional (2D) materials such as transition-metal dichalcogenides (TMDCs) and MXenes exhibit intriguing properties, including superconductivity, magnetism and electrocatalysis. Studies on the correlation between their nanoscale structures and properties can facilitate the development of photodetectors, supercapacitors, nanocatalysts, etc., but this topic has not been reviewed systematically. Here, we provide a comprehensive overview on the key factors that dictate the structures and properties of these 2D metals. We examine their phase transitions induced by structural or electronic modifications based on microscopic imaging, spectral characterization, and electrical measurements. From the perspective of surface and interface engineering, we elucidate the influences of lattice defects, dopants, and intercalated species between adjacent layers. Moreover, heterostructures involving highly conductive 2D component(s) are discussed, which may enable the observation of fascinating phenomena and/or synergistic effects due to the interlayer interactions. Finally, we provide insights into opportunities for new applications, e.g., radio-frequency antennas and electromagnetic interference shields. Feasible routes are also proposed to overcome the current challenges. (c) 2021 Elsevier B.V. All rights reserved. |
Cao, Lulu; Guo, Qingjie; Liang, Jian; Kou, Zhaoxia; Zhou, Xiaochao; Huang, Zhaocong; Zhai, Ya; Du, Jun; You, Biao; Zhao, Huihui; Li, Qi; Zhang, Wen; Wee, Andrew Thye Shen; Wong, Ping Kwan Johnny; Yu, Xiaojiang Preparation of sputtered Fe3O4 thin film Journal Article JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 32 (18), pp. 23645-23653, 2021, ISSN: 0957-4522. @article{ISI:000689522900004, title = {Preparation of sputtered Fe_{3}O_{4} thin film}, author = {Lulu Cao and Qingjie Guo and Jian Liang and Zhaoxia Kou and Xiaochao Zhou and Zhaocong Huang and Ya Zhai and Jun Du and Biao You and Huihui Zhao and Qi Li and Wen Zhang and Andrew Thye Shen Wee and Ping Kwan Johnny Wong and Xiaojiang Yu}, doi = {10.1007/s10854-021-06858-7}, times_cited = {0}, issn = {0957-4522}, year = {2021}, date = {2021-08-26}, journal = {JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS}, volume = {32}, number = {18}, pages = {23645-23653}, publisher = {SPRINGER}, address = {VAN GODEWIJCKSTRAAT 30, 3311 GZ DORDRECHT, NETHERLANDS}, abstract = {Fe3O4, as a half-metallic ferrimagnetic material, is believed to be one of the most promising materials in spin transport for spintronics. However, fabricating stoichiometric Fe3O4 film is still challenging because the oxidation is hard to control for various preparing methods. In this paper, series of Fe3O4 thin films on Si (100) substrates are grown by sputtering from a Fe3O4 target without oxygen atmosphere at different growth temperature and then extra heat treatment in high vacuum. By combining X-ray diffractometer (XRD), Raman spectrum, X-ray photoelectron spectroscopy and X-ray magnetic circular dichroism, VSM analysis, we see that the structure and magnetic moment of Fe3O4 film are not only related with growth temperature during sputtering, but also refer to the temperature of post-heat treatments. When the growth temperature is lower than 300 degrees C, the film does not show any XRD diffraction peaks. When the growth temperature increases from 300 to 500 degrees C, the film shows the (111) texture of Fe3O4 film clearly. However, the other XRD diffraction peaks are observed after post-heat treatment. The saturation magnetization increases with growth temperature and the largest saturation magnetization is 473 emu/cm(3) for growth temperature of 450 degrees C and extra heat treatment, which is close to bulk Fe3O4. Our results suggest that a selectable method can be used to fabricate high magnetic moment of Fe3O4 thin film.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Fe3O4, as a half-metallic ferrimagnetic material, is believed to be one of the most promising materials in spin transport for spintronics. However, fabricating stoichiometric Fe3O4 film is still challenging because the oxidation is hard to control for various preparing methods. In this paper, series of Fe3O4 thin films on Si (100) substrates are grown by sputtering from a Fe3O4 target without oxygen atmosphere at different growth temperature and then extra heat treatment in high vacuum. By combining X-ray diffractometer (XRD), Raman spectrum, X-ray photoelectron spectroscopy and X-ray magnetic circular dichroism, VSM analysis, we see that the structure and magnetic moment of Fe3O4 film are not only related with growth temperature during sputtering, but also refer to the temperature of post-heat treatments. When the growth temperature is lower than 300 degrees C, the film does not show any XRD diffraction peaks. When the growth temperature increases from 300 to 500 degrees C, the film shows the (111) texture of Fe3O4 film clearly. However, the other XRD diffraction peaks are observed after post-heat treatment. The saturation magnetization increases with growth temperature and the largest saturation magnetization is 473 emu/cm(3) for growth temperature of 450 degrees C and extra heat treatment, which is close to bulk Fe3O4. Our results suggest that a selectable method can be used to fabricate high magnetic moment of Fe3O4 thin film. |
Zhu, Rui; Gao, Zhibin; Liang, Qijie; Hu, Junxiong; Wang, Jian-Sheng; Qiu, Cheng-Wei; Wee, Andrew Thye Shen Observation of Anisotropic Magnetoresistance in Layered Nonmagnetic Semiconducting PdSe2 Journal Article ACS APPLIED MATERIALS & INTERFACES, 13 (31), pp. 37527-37534, 2021, ISSN: 1944-8244. @article{ISI:000685245800085, title = {Observation of Anisotropic Magnetoresistance in Layered Nonmagnetic Semiconducting PdSe_{2}}, author = {Rui Zhu and Zhibin Gao and Qijie Liang and Junxiong Hu and Jian-Sheng Wang and Cheng-Wei Qiu and Andrew Thye Shen Wee}, doi = {10.1021/acsami.1c10500}, times_cited = {0}, issn = {1944-8244}, year = {2021}, date = {2021-08-01}, journal = {ACS APPLIED MATERIALS & INTERFACES}, volume = {13}, number = {31}, pages = {37527-37534}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Anisotropy in crystals usually has remarkable consequences in two-dimensional (2D) materials, for example, black phosphorus, PdSe2, and SnS, arising from different lattice periodicities along different crystallographic directions. Electrical anisotropy has been successfully demonstrated in 2D materials, but anisotropic magnetoresistance in 2D materials is rarely studied. Herein, we report anisotropic magnetoresistance in layered non-magnetic semiconducting PdSe2 flakes. Anisotropic magnetoresistance along the two crystalline axes under a perpendicular magnetic field is demonstrated, and the magnetoresistance along the a-axis is apparently different from the magnetoresistance along the b-axis. The magnetoresistance can also be flexibly tuned by applying a gate voltage, leveraging the semiconductor properties of PdSe2. The computed anisotropic electronic density of states and electronic mobility with ab initio density functional calculations support the anisotropic and measured magnetoresistance. Our findings advance the understanding of magnetoresistance in anisotropic transition-metal dichalcogenides and pave the way for potential applications in anisotropic spintronic devices.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Anisotropy in crystals usually has remarkable consequences in two-dimensional (2D) materials, for example, black phosphorus, PdSe2, and SnS, arising from different lattice periodicities along different crystallographic directions. Electrical anisotropy has been successfully demonstrated in 2D materials, but anisotropic magnetoresistance in 2D materials is rarely studied. Herein, we report anisotropic magnetoresistance in layered non-magnetic semiconducting PdSe2 flakes. Anisotropic magnetoresistance along the two crystalline axes under a perpendicular magnetic field is demonstrated, and the magnetoresistance along the a-axis is apparently different from the magnetoresistance along the b-axis. The magnetoresistance can also be flexibly tuned by applying a gate voltage, leveraging the semiconductor properties of PdSe2. The computed anisotropic electronic density of states and electronic mobility with ab initio density functional calculations support the anisotropic and measured magnetoresistance. Our findings advance the understanding of magnetoresistance in anisotropic transition-metal dichalcogenides and pave the way for potential applications in anisotropic spintronic devices. |
Arramel, Arramel; Fauzi, Angga Dito; Yin, Xinmao; Tang, Chi Sin; Mahyuddin, Muhammad Haris; Sahdan, Muhammad Fauzi; Aminah, Mimin; Onggo, Djulia; Shukri, Ganes; Diao, Caozheng; Wang, Hong; Birowosuto, Muhammad Danang; Wee, Andrew Thye Shen; Rusydi, Andrivo Ligand size effects in two-dimensional hybrid copper halide perovskites crystals Journal Article COMMUNICATIONS MATERIALS , 2 (1), 2021. @article{ISI:000671667600001, title = {Ligand size effects in two-dimensional hybrid copper halide perovskites crystals }, author = {Arramel Arramel and Angga Dito Fauzi and Xinmao Yin and Chi Sin Tang and Muhammad Haris Mahyuddin and Muhammad Fauzi Sahdan and Mimin Aminah and Djulia Onggo and Ganes Shukri and Caozheng Diao and Hong Wang and Muhammad Danang Birowosuto and Andrew Thye Shen Wee and Andrivo Rusydi}, doi = {10.1038/s43246-021-00175-6}, times_cited = {10}, year = {2021}, date = {2021-07-01}, journal = {COMMUNICATIONS MATERIALS }, volume = {2}, number = {1}, publisher = {SPRINGERNATURE }, address = {CAMPUS, 4 CRINAN ST, LONDON, N1 9XW, ENGLAND }, abstract = {Intensive effort to tailor photophysics of lead-free perovskites is appealing in recent years. However, their combined electronic and optical property elucidations remain elusive. Here, we report spectroscopic observations of the coexistence Zhang-Rice singlet state and exotic electronic transitions in two-dimensional copper-based perovskites. Herein, several perovskites with different alkylammonium spacers are investigated to unravel their correlated electronic systems and optical responses. Namely, methylammonium, ethylammonium, phenylmethylammonium and phenethylammonium. Using temperature dependent high-resolution X-ray absorption spectroscopy, we observe distinct electronic features highlighting the impact of short spacer chains compared to long-conjugated ligands, demonstrating a pronounced 3d(9) and 3d(9)L signature linewidth variation. Corroborated by density functional theory calculations, the transient dynamics evolution of copper-based hybrid perovskites is influenced by the strong interplay of electron-phonon interactions and geometric constrictions. This finding sheds light on tuning the electronic and optical properties of hybrid perovskites towards efficient photoactive-based devices. Hybrid organic-inorganic perovskites are known to display unique optical properties. Here, electronic transitions in 2D copper-based hybrid perovskites are studied experimentally and theoretically, revealing how ligand size can be used to tune electronic and optical behavior. }, keywords = {}, pubstate = {published}, tppubtype = {article} } Intensive effort to tailor photophysics of lead-free perovskites is appealing in recent years. However, their combined electronic and optical property elucidations remain elusive. Here, we report spectroscopic observations of the coexistence Zhang-Rice singlet state and exotic electronic transitions in two-dimensional copper-based perovskites. Herein, several perovskites with different alkylammonium spacers are investigated to unravel their correlated electronic systems and optical responses. Namely, methylammonium, ethylammonium, phenylmethylammonium and phenethylammonium. Using temperature dependent high-resolution X-ray absorption spectroscopy, we observe distinct electronic features highlighting the impact of short spacer chains compared to long-conjugated ligands, demonstrating a pronounced 3d(9) and 3d(9)L signature linewidth variation. Corroborated by density functional theory calculations, the transient dynamics evolution of copper-based hybrid perovskites is influenced by the strong interplay of electron-phonon interactions and geometric constrictions. This finding sheds light on tuning the electronic and optical properties of hybrid perovskites towards efficient photoactive-based devices. Hybrid organic-inorganic perovskites are known to display unique optical properties. Here, electronic transitions in 2D copper-based hybrid perovskites are studied experimentally and theoretically, revealing how ligand size can be used to tune electronic and optical behavior. |