The poor reversibility of Zn metal anodes arising from water-induced parasitic reactions poses a ... more The poor reversibility of Zn metal anodes arising from water-induced parasitic reactions poses a significant challenge to the practical applications of aqueous zinc-ion batteries (AZIBs). Herein, a novel quasi-solid-state water-in-swelling-clay electrolyte (WiSCE) containing zinc sulfate and swelling clay bentonite (BT) is designed to enable highly reversible Zn metal anodes. AZIB full 2 cells based on the WiSCE exhibit excellent cyclic stability at various current densities, long shelf life, low self-discharge rate, and outstanding high-temperature adaptability. Particularly, the capacity of WiSCE-based AZIB full cells retains 90.47% after 200 cycles at 0.1 A/g, 96.64% after 2000 cycles at 1 A/g, and 88.29% after 5000 cycles at 3 A/g. Detailed density functional theory calculations show that strong hydrogen-bonds are formed between BT and water molecules in the WiSCE. Thus, water molecules are strongly confined by BT particularly within the interlayers, which significantly inhibits...
Considering the d electronic spin configurations of transition metals, a deep understanding of he... more Considering the d electronic spin configurations of transition metals, a deep understanding of hexacyanometallates was developed for higher redox potentials.
Covalent functionalization of transition metal dichalcogenides (TMDCs) is investigated for air-st... more Covalent functionalization of transition metal dichalcogenides (TMDCs) is investigated for air-stable chemical doping. Specifically, p-doping of WSe(2) via NOx chemisorption at 150 °C is explored, with the hole concentration tuned by reaction time. Synchrotron based soft X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) depict the formation of various WSe(2-x-y)O(x)N(y) species both on the surface and interface between layers upon chemisorption reaction. Ab initio simulations corroborate our spectroscopy results in identifying the energetically favorable complexes, and predicting WSe(2):NO at the Se vacancy sites as the predominant dopant species. A maximum hole concentration of ∼ 10(19) cm(-3) is obtained from XPS and electrical measurements, which is found to be independent of WSe(2) thickness. This degenerate doping level facilitates 5 orders of magnitude reduction in contact resistance between Pd, a common p-type contact metal, and WSe(2). More gener...
We investigate the band offsets and stability for Ni/Bi2Te3and Co/Bi2Te3interfaces by first princ... more We investigate the band offsets and stability for Ni/Bi2Te3and Co/Bi2Te3interfaces by first principles calculations. It is found that the surface termination strongly affects the band offsets. Ni and Co are found to form Ohmic contacts to Bi2Te3. The interface formation energies for Co/Bi2Te3interfaces are much lower than those of Ni/Bi2Te3interfaces. Our calculations are consistent with the experimental data.
Solid state quantum defects are promising candidates for scalable quantum information systems whi... more Solid state quantum defects are promising candidates for scalable quantum information systems which can be seamlessly integrated with the conventional semiconductor electronic devices within the 3D monolithically integrated hybrid classical-quantum devices. Diamond nitrogen-vacancy (NV) center defects are the representative examples, but the controlled positioning of an NV center within bulk diamond is an outstanding challenge. Furthermore, quantum defect properties may not be easily tuned for bulk crystalline quantum defects. In comparison, 2D semiconductors, such as transition metal dichalcogenides (TMDs), are promising solid platform to host a quantum defect with tunable properties and a possibility of position control. Here, we computationally discover a promising defect family for spin qubit realization in 2D TMDs. The defects consist of transition metal atoms substituted at chalcogen sites with desirable spin-triplet ground state, zero-field splitting in the tens of GHz, and s...
First principles design of a P2-type Fe–Mn oxide cathode for Na ion batteries with improved elect... more First principles design of a P2-type Fe–Mn oxide cathode for Na ion batteries with improved electrochemical performance and suppression of its phase transition by Cu doping. The improvements are confirmed using experimental cathode synthesis and battery test.
2D metallic materials offer a solution to the problem of poor scalability of elemental metals wit... more 2D metallic materials offer a solution to the problem of poor scalability of elemental metals within ever-downscaling device interconnects. With the absence of surface scattering, they could be used for interconnects in future integrated circuits.
Carrier mobility in amorphous semiconductors remained unpredictable due to random electronic stat... more Carrier mobility in amorphous semiconductors remained unpredictable due to random electronic states in the absence of the long-range order in a lattice structure, although amorphous semiconductors have been investigated over several decades and widely used in diverse electronic devices. In this work, we develop a method to predict mobility of disordered systems by virtue of the first-principles calculation without using any empirical parameters. Quantum transport modeling based on the nonequilibrium Green's function formalism enables us to establish a formula to connect first-principles results with amorphous-phase mobility. Finally, the developed approach is quantitatively validated by comparing the theoretical predictions with previously measured mobilities of amorphous metal oxides (SnO 2 , In 2 O 3 , and ZnO) and amorphous silicon. Localization analysis provides further physical insight into a distinct feature between the amorphous metal oxides and amorphous silicon.
In MIM devices (left), internal field is small in contrast to MIS FeFETs (right) consistent with ... more In MIM devices (left), internal field is small in contrast to MIS FeFETs (right) consistent with high MIM endurance due to electrostatic interactions between dielectric and ferroelectric layers.
The current needs to overcome our dependence on the fossil fuels have drawn a growing interest to... more The current needs to overcome our dependence on the fossil fuels have drawn a growing interest to the development of more advanced energy storage systems. Among them, rechargeable Li-ion batteries have been the focus of numerous experimental and theoretical studies. The two key properties to characterize the energy density of a Li-ion battery electrode are the specific capacity and voltage of operation. While the specific capacity theoretical limit is given by the chemical formula of the dierent compounds, the voltage depends on the morphology, relative stability and other electronic properties of the electrode material. In our study, we have focused our attention in polyoxyanion silicates as positive electrode materials. These materials incorporate transition metals (TM) in the host structures to allow the necessary electronic conductivity for the open circuit of the battery, and their voltage is mainly due to the redox activity of these TM. There is always an intrinsic [1] voltage...
We utilize real-time time-dependent density functional theory and Ehrenfest dynamics scheme to in... more We utilize real-time time-dependent density functional theory and Ehrenfest dynamics scheme to investigate excited-state nonadiabatic dynamics of ligand dissociation of cobalt tricarbonyl nitrosyl, Co(CO)3NO, which is a precursor used for cobalt growth in advanced technologies, where the precursor’s reaction is enhanced by electronic excitation. Based on the first-principles calculations, we demonstrate two dissociation pathways of the NO ligand on the precursor. Detailed electronic structures are further analyzed to provide an insight into dynamics following the electronic excitations. This study sheds light on computational demonstration and underlying mechanism of the electronic-excitation-induced dissociation, especially in molecules with complex chemical bonds such as the Co(CO)3NO.
Dislocation driven spiral and non-spiral growth in layered chalcogenides: morphology, mechanism, ... more Dislocation driven spiral and non-spiral growth in layered chalcogenides: morphology, mechanism, and mitigation Yifan Nie,† Adam T. Barton,† Rafik Addou,† Yongping Zheng,† Lee A. Walsh,† Sarah M. Eichfeld,‡ Ruoyu Yue,† Christopher Cormier,† Chenxi Zhang,† Qingxiao Wang,† Chaoping Liang,† Joshua A. Robinson,‡ Moon Kim,† William Vandenberghe,† Luigi Colombo,§ Pil-Ryung Cha,‖ Robert M. Wallace,† Christopher L. Hinkle,† and Kyeongjae Cho∗,† †Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, United States ‡Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States ¶Center for Two-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, United States §Texas Instruments Incorporated, 13121 TI Boulevard, Dallas, Texas 75243, United States ‖School of Advanced Materials, Kookmin University, Jeongneung-gil 77, S...
Substitutional doping in 2D semiconductor MoS2 was investigated by charge transition level (CTL) ... more Substitutional doping in 2D semiconductor MoS2 was investigated by charge transition level (CTL) calculations for Nitrogen group (N, P, As, Sb) and Halogen group (F, Cl, Br, I) dopants at the S site of monolayer MoS2. Both n-type and p-type dopant levels are calculated to be deep mid-gap states (~1 eV from band edges) from DFT total energy-based CTL and separate DFT + GW calculations. The deep dopant levels result from the giant renormalization of hydrogen-like defect states by reduced dielectric screening in ultrathin 2D films. Theoretical analysis based on Keldysh formulation provides a consistent impurity binding energy of ~1 eV for dielectric thin films. These findings of intrinsic deep impurity levels in 2D semiconductors MoS2 may be applicable to diverse novel emerging device applications.
A quantum confined transport based on a zinc oxide composite nanolayer that has conducting states... more A quantum confined transport based on a zinc oxide composite nanolayer that has conducting states with mobility edge quantization is proposed and was applied to develop multivalue logic transistors with stable intermediate states. A composite nanolayer with zinc oxide quantum dots embedded in amorphous zinc oxide domains generated quantized conducting states at the mobility edge, which we refer to as "mobility edge quantization". The unique quantized conducting state effectively restricted the occupied number of carriers due to its low density of states, which enable current saturation. Multi-value logic transistors were realized by applying a hybrid superlattice consisting of zinc oxide composite nanolayers and organic barriers as channels in the transistor. The superlattice channels produced multiple states due to current saturation of the quantized conducting state in the composite nanolayers. Our multi-value transistors exhibited excellent performance characteristics, stable and reliable operation with no current fluctuation, and adjustable multi-level states.
A two-dimensional (2D) heterobilayer system consisting of MoSon WSe, deposited on epitaxial graph... more A two-dimensional (2D) heterobilayer system consisting of MoSon WSe, deposited on epitaxial graphene, is studied by scanning tunneling microscopy and spectroscopy at temperatures of 5 and 80 K. A moiré pattern is observed, arising from lattice mismatch of 3.7% between the MoSand WSe. Significant energy shifts are observed in tunneling spectra observed at the maxima of the moiré corrugation, as compared with spectra obtained at corrugation minima, consistent with prior work. Furthermore, at the minima of the moiré corrugation, sharp peaks in the spectra at energies near the band edges are observed for spectra acquired at 5 K. The peaks correspond to discrete states that are confined within the moiré unit cells. Conductance mapping is employed to reveal the detailed structure of the wave functions of the states. For measurements at 80 K, the sharp peaks in the spectra are absent, and conductance maps of the band edges reveal little structure.
Controlled growth of crystalline solids is critical for device applications, and atomistic modeli... more Controlled growth of crystalline solids is critical for device applications, and atomistic modeling methods have been developed for bulk crystalline solids. Kinetic Monte Carlo (KMC) simulation method provides detailed atomic scale processes during a solid growth over realistic time scales, but its application to the growth modeling of van der Waals (vdW) heterostructures has not yet been developed. Specifically, the growth of single-layered transition metal dichalcogenides (TMDs) is currently facing tremendous challenges, and a detailed understanding based on KMC simulations would provide critical guidance to enable controlled growth of vdW heterostructures. In this work, a KMC simulation method is developed for the growth modeling on the vdW epitaxy of TMDs. The KMC method has introduced full material parameters for TMDs in bottom-up synthesis: metal and chalcogen adsorption/desorption/diffusion on substrate and grown TMD surface, TMD stacking sequence, chalcogen/metal ratio, flak...
The poor reversibility of Zn metal anodes arising from water-induced parasitic reactions poses a ... more The poor reversibility of Zn metal anodes arising from water-induced parasitic reactions poses a significant challenge to the practical applications of aqueous zinc-ion batteries (AZIBs). Herein, a novel quasi-solid-state water-in-swelling-clay electrolyte (WiSCE) containing zinc sulfate and swelling clay bentonite (BT) is designed to enable highly reversible Zn metal anodes. AZIB full 2 cells based on the WiSCE exhibit excellent cyclic stability at various current densities, long shelf life, low self-discharge rate, and outstanding high-temperature adaptability. Particularly, the capacity of WiSCE-based AZIB full cells retains 90.47% after 200 cycles at 0.1 A/g, 96.64% after 2000 cycles at 1 A/g, and 88.29% after 5000 cycles at 3 A/g. Detailed density functional theory calculations show that strong hydrogen-bonds are formed between BT and water molecules in the WiSCE. Thus, water molecules are strongly confined by BT particularly within the interlayers, which significantly inhibits...
Considering the d electronic spin configurations of transition metals, a deep understanding of he... more Considering the d electronic spin configurations of transition metals, a deep understanding of hexacyanometallates was developed for higher redox potentials.
Covalent functionalization of transition metal dichalcogenides (TMDCs) is investigated for air-st... more Covalent functionalization of transition metal dichalcogenides (TMDCs) is investigated for air-stable chemical doping. Specifically, p-doping of WSe(2) via NOx chemisorption at 150 °C is explored, with the hole concentration tuned by reaction time. Synchrotron based soft X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) depict the formation of various WSe(2-x-y)O(x)N(y) species both on the surface and interface between layers upon chemisorption reaction. Ab initio simulations corroborate our spectroscopy results in identifying the energetically favorable complexes, and predicting WSe(2):NO at the Se vacancy sites as the predominant dopant species. A maximum hole concentration of ∼ 10(19) cm(-3) is obtained from XPS and electrical measurements, which is found to be independent of WSe(2) thickness. This degenerate doping level facilitates 5 orders of magnitude reduction in contact resistance between Pd, a common p-type contact metal, and WSe(2). More gener...
We investigate the band offsets and stability for Ni/Bi2Te3and Co/Bi2Te3interfaces by first princ... more We investigate the band offsets and stability for Ni/Bi2Te3and Co/Bi2Te3interfaces by first principles calculations. It is found that the surface termination strongly affects the band offsets. Ni and Co are found to form Ohmic contacts to Bi2Te3. The interface formation energies for Co/Bi2Te3interfaces are much lower than those of Ni/Bi2Te3interfaces. Our calculations are consistent with the experimental data.
Solid state quantum defects are promising candidates for scalable quantum information systems whi... more Solid state quantum defects are promising candidates for scalable quantum information systems which can be seamlessly integrated with the conventional semiconductor electronic devices within the 3D monolithically integrated hybrid classical-quantum devices. Diamond nitrogen-vacancy (NV) center defects are the representative examples, but the controlled positioning of an NV center within bulk diamond is an outstanding challenge. Furthermore, quantum defect properties may not be easily tuned for bulk crystalline quantum defects. In comparison, 2D semiconductors, such as transition metal dichalcogenides (TMDs), are promising solid platform to host a quantum defect with tunable properties and a possibility of position control. Here, we computationally discover a promising defect family for spin qubit realization in 2D TMDs. The defects consist of transition metal atoms substituted at chalcogen sites with desirable spin-triplet ground state, zero-field splitting in the tens of GHz, and s...
First principles design of a P2-type Fe–Mn oxide cathode for Na ion batteries with improved elect... more First principles design of a P2-type Fe–Mn oxide cathode for Na ion batteries with improved electrochemical performance and suppression of its phase transition by Cu doping. The improvements are confirmed using experimental cathode synthesis and battery test.
2D metallic materials offer a solution to the problem of poor scalability of elemental metals wit... more 2D metallic materials offer a solution to the problem of poor scalability of elemental metals within ever-downscaling device interconnects. With the absence of surface scattering, they could be used for interconnects in future integrated circuits.
Carrier mobility in amorphous semiconductors remained unpredictable due to random electronic stat... more Carrier mobility in amorphous semiconductors remained unpredictable due to random electronic states in the absence of the long-range order in a lattice structure, although amorphous semiconductors have been investigated over several decades and widely used in diverse electronic devices. In this work, we develop a method to predict mobility of disordered systems by virtue of the first-principles calculation without using any empirical parameters. Quantum transport modeling based on the nonequilibrium Green's function formalism enables us to establish a formula to connect first-principles results with amorphous-phase mobility. Finally, the developed approach is quantitatively validated by comparing the theoretical predictions with previously measured mobilities of amorphous metal oxides (SnO 2 , In 2 O 3 , and ZnO) and amorphous silicon. Localization analysis provides further physical insight into a distinct feature between the amorphous metal oxides and amorphous silicon.
In MIM devices (left), internal field is small in contrast to MIS FeFETs (right) consistent with ... more In MIM devices (left), internal field is small in contrast to MIS FeFETs (right) consistent with high MIM endurance due to electrostatic interactions between dielectric and ferroelectric layers.
The current needs to overcome our dependence on the fossil fuels have drawn a growing interest to... more The current needs to overcome our dependence on the fossil fuels have drawn a growing interest to the development of more advanced energy storage systems. Among them, rechargeable Li-ion batteries have been the focus of numerous experimental and theoretical studies. The two key properties to characterize the energy density of a Li-ion battery electrode are the specific capacity and voltage of operation. While the specific capacity theoretical limit is given by the chemical formula of the dierent compounds, the voltage depends on the morphology, relative stability and other electronic properties of the electrode material. In our study, we have focused our attention in polyoxyanion silicates as positive electrode materials. These materials incorporate transition metals (TM) in the host structures to allow the necessary electronic conductivity for the open circuit of the battery, and their voltage is mainly due to the redox activity of these TM. There is always an intrinsic [1] voltage...
We utilize real-time time-dependent density functional theory and Ehrenfest dynamics scheme to in... more We utilize real-time time-dependent density functional theory and Ehrenfest dynamics scheme to investigate excited-state nonadiabatic dynamics of ligand dissociation of cobalt tricarbonyl nitrosyl, Co(CO)3NO, which is a precursor used for cobalt growth in advanced technologies, where the precursor’s reaction is enhanced by electronic excitation. Based on the first-principles calculations, we demonstrate two dissociation pathways of the NO ligand on the precursor. Detailed electronic structures are further analyzed to provide an insight into dynamics following the electronic excitations. This study sheds light on computational demonstration and underlying mechanism of the electronic-excitation-induced dissociation, especially in molecules with complex chemical bonds such as the Co(CO)3NO.
Dislocation driven spiral and non-spiral growth in layered chalcogenides: morphology, mechanism, ... more Dislocation driven spiral and non-spiral growth in layered chalcogenides: morphology, mechanism, and mitigation Yifan Nie,† Adam T. Barton,† Rafik Addou,† Yongping Zheng,† Lee A. Walsh,† Sarah M. Eichfeld,‡ Ruoyu Yue,† Christopher Cormier,† Chenxi Zhang,† Qingxiao Wang,† Chaoping Liang,† Joshua A. Robinson,‡ Moon Kim,† William Vandenberghe,† Luigi Colombo,§ Pil-Ryung Cha,‖ Robert M. Wallace,† Christopher L. Hinkle,† and Kyeongjae Cho∗,† †Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, United States ‡Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States ¶Center for Two-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, United States §Texas Instruments Incorporated, 13121 TI Boulevard, Dallas, Texas 75243, United States ‖School of Advanced Materials, Kookmin University, Jeongneung-gil 77, S...
Substitutional doping in 2D semiconductor MoS2 was investigated by charge transition level (CTL) ... more Substitutional doping in 2D semiconductor MoS2 was investigated by charge transition level (CTL) calculations for Nitrogen group (N, P, As, Sb) and Halogen group (F, Cl, Br, I) dopants at the S site of monolayer MoS2. Both n-type and p-type dopant levels are calculated to be deep mid-gap states (~1 eV from band edges) from DFT total energy-based CTL and separate DFT + GW calculations. The deep dopant levels result from the giant renormalization of hydrogen-like defect states by reduced dielectric screening in ultrathin 2D films. Theoretical analysis based on Keldysh formulation provides a consistent impurity binding energy of ~1 eV for dielectric thin films. These findings of intrinsic deep impurity levels in 2D semiconductors MoS2 may be applicable to diverse novel emerging device applications.
A quantum confined transport based on a zinc oxide composite nanolayer that has conducting states... more A quantum confined transport based on a zinc oxide composite nanolayer that has conducting states with mobility edge quantization is proposed and was applied to develop multivalue logic transistors with stable intermediate states. A composite nanolayer with zinc oxide quantum dots embedded in amorphous zinc oxide domains generated quantized conducting states at the mobility edge, which we refer to as "mobility edge quantization". The unique quantized conducting state effectively restricted the occupied number of carriers due to its low density of states, which enable current saturation. Multi-value logic transistors were realized by applying a hybrid superlattice consisting of zinc oxide composite nanolayers and organic barriers as channels in the transistor. The superlattice channels produced multiple states due to current saturation of the quantized conducting state in the composite nanolayers. Our multi-value transistors exhibited excellent performance characteristics, stable and reliable operation with no current fluctuation, and adjustable multi-level states.
A two-dimensional (2D) heterobilayer system consisting of MoSon WSe, deposited on epitaxial graph... more A two-dimensional (2D) heterobilayer system consisting of MoSon WSe, deposited on epitaxial graphene, is studied by scanning tunneling microscopy and spectroscopy at temperatures of 5 and 80 K. A moiré pattern is observed, arising from lattice mismatch of 3.7% between the MoSand WSe. Significant energy shifts are observed in tunneling spectra observed at the maxima of the moiré corrugation, as compared with spectra obtained at corrugation minima, consistent with prior work. Furthermore, at the minima of the moiré corrugation, sharp peaks in the spectra at energies near the band edges are observed for spectra acquired at 5 K. The peaks correspond to discrete states that are confined within the moiré unit cells. Conductance mapping is employed to reveal the detailed structure of the wave functions of the states. For measurements at 80 K, the sharp peaks in the spectra are absent, and conductance maps of the band edges reveal little structure.
Controlled growth of crystalline solids is critical for device applications, and atomistic modeli... more Controlled growth of crystalline solids is critical for device applications, and atomistic modeling methods have been developed for bulk crystalline solids. Kinetic Monte Carlo (KMC) simulation method provides detailed atomic scale processes during a solid growth over realistic time scales, but its application to the growth modeling of van der Waals (vdW) heterostructures has not yet been developed. Specifically, the growth of single-layered transition metal dichalcogenides (TMDs) is currently facing tremendous challenges, and a detailed understanding based on KMC simulations would provide critical guidance to enable controlled growth of vdW heterostructures. In this work, a KMC simulation method is developed for the growth modeling on the vdW epitaxy of TMDs. The KMC method has introduced full material parameters for TMDs in bottom-up synthesis: metal and chalcogen adsorption/desorption/diffusion on substrate and grown TMD surface, TMD stacking sequence, chalcogen/metal ratio, flak...
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Papers by Kyeongjae Cho