@article {702,
	title = {Effect of MA orientation and thickness on the bandgap in quasi-2D perovskites (PEA)$_{2}$(MA)ₙ$_{-}$$_{1}$PbₙI$_{3}$ₙ$_{+}$$_{1}$},
	journal = {J. Phys. Chem. C},
	volume = {128},
	year = {2024},
	pages = {17091},
	abstract = {Three-dimensional organic{\textendash}inorganic perovskite photovoltaic materials such as MAPbI$_{3}$ (MA is methylammonium) have rapidly advanced in their performance over the past decade, but their instability remains a problem. One of the methods to improve their stability is by reducing their dimensionality. This dimensional reduction is performed by adding a large organic cation as a spacer to separate the original bulk lattice, forming a new quasi-two-dimensional (quasi-2D) structure. In this study, we have investigated the electronic properties of the quasi-2D structures of (PEA)$_{2}$(MA)ₙ$_{-}$$_{1}$PbₙI$_{3}$ₙ$_{+}$$_{1}$ (PEA is phenylethylammonium) with various thicknesses (n) and MA orientations using first-principles calculations. Our results show that the bandgap decreased as the number of layers (n) increased for quasi-2D structures. The structures with in-plane MA orientations and mirror symmetry along the z-axis are found to be the most stable and exhibit a converging trend in the bulk bandgap when n > 6. Our calculations reveal how the orientations of the MA ions affect the electronic structure via symmetry breaking and electric dipole formation. These two factors change the electrostatic potential and band energies of the individual PbI$_{3}$ layers, which lead to enhanced band splitting and bandgap reduction. The results of this work would give some insights into the electronic structures and may provide directions for the crystal growth design of quasi-2D perovskite materials in photovoltaic applications.},
	doi = {10.1021/acs.jpcc.4c03540},
	author = {Yang-Hao Lee and Gennevieve M. Macam and Rovi Angelo B. Villaos and Liang-Ying Feng and Chia-Hsiu Hsu and Zhi-Quan Huang and Deng-Chi Wang and Hsin Lin and Feng-Chuan Chuang}
}
@article {701,
	title = {Electronic, magnetic, and topological properties of ferromagnetic 2D perovskite-type oxides},
	journal = {New J. Phys.},
	volume = {26},
	year = {2024},
	pages = {123031},
	abstract = {Two-dimensional (2D) materials within the hematene-type binary oxides and perovskites family have recently gathered huge research interest for nanoelectronic devices. However, the exploration of their fascinating topological properties remains limited. Herein, through first-principles calculations, we systematically examine the electronic, magnetic, and topological properties of substitutionally doped 2D ABO$_{3}$ (A = As, Sb, or Bi, and B = V, Nb, or Ta) perovskite structures at the B site of a B$_{2}$O$_{3}$ system. Interestingly, the atomic substitution makes the 2D ABO$_{3}$ structures dynamically stable. Our detailed calculations show the ferromagnetic (FM) and antiferromagnetic phases of these materials. The calculated Chern number (C) for the FM 2D ABO$_{3}$ (A = As, Sb, or Bi, B = Nb or Ta) suggests their topologically non-trivial phases. Furthermore, the computed nontrivial Berry curvature highlights the topological properties in AsNbO$_{3}$. These findings highlight opportunities in 2D-ABO$_{3}$ materials, for applications in spintronics.},
	doi = {10.1088/1367-2630/ad9be0},
	author = {Susaiammal Arokiasamy and Gennevieve M. Macam and Puthiya Covilakam Sreeparvathy and Rovi Angelo B. Villaos and Zhi-Quan Huang and Chia-Hsiu Hsu and Yoshinori Okada and Hsin Lin and Feng-Chuan Chuang}
}
@article {650,
	title = {Prediction of quantum spin Hall and Rashba effects in two-dimensional ilmenite oxides},
	journal = {Chinese J. Phys.},
	volume = {86},
	year = {2023},
	pages = {242},
	abstract = {Using first-principles calculations, we investigate the structural, electronic, and topological properties of two-dimensional (2D) pristine ilmenite oxides ABO$_{3}$ (A~=~Au, Ag, or Cu; and B~=~Bi, Sb, or As) and their corresponding Janus structures. Phonon dispersions reveal the dynamic stability of these compounds. Interestingly, pristine CuBiO$_{3}$ and AuBiO$_{3}$, and Janus Cu$_{0}$.$_{5}$Ag$_{0}$.$_{5}$BiO$_{3}$, Au$_{0}$.$_{5}$Cu$_{0}$.$_{5}$BiO$_{3}$, Au$_{0}$.$_{5}$Ag$_{0}$.$_{5}$BiO$_{3}$, and CuBi$_{0}$.$_{5}$As$_{0}$.$_{5}$O$_{3}$ are topological insulators, while AuBi$_{0}$.$_{5}$As$_{0}$.$_{5}$O$_{3}$, CuBi$_{0}$.$_{5}$Sb$_{0}$.$_{5}$O$_{3}$, and AuBi$_{0}$.$_{5}$Sb$_{0}$.$_{5}$O$_{3}$ are topological semimetals, as confirmed by their Z2 invariance and conducting edge states under the hybrid functional approach. Moreover, we found van Hove singularities in Au$_{0}$.$_{5}$Ag$_{0}$.$_{5}$BiO$_{3}$ and Cu$_{0}$.$_{5}$Ag$_{0}$.$_{5}$BiO$_{3}$ near the Fermi level, suggesting the coexistence of superconductivity and nontrivial topology. Finally, isotropic Rashba spin-splitting is studied in detail for Au$_{0}$.$_{5}$Ag$_{0}$.$_{5}$BiO$_{3}$. Our findings demonstrate that 2D ilmenite oxides can be a new material playground for potential spintronic applications.},
	doi = {10.1016/j.cjph.2023.09.022},
	url = {https://www.sciencedirect.com/science/article/abs/pii/S0577907323001806},
	author = {Susaiammal Arokiasamy and Gennevieve M. Macam and Rovi Angelo B. Villaos and Aniceto B. Maghirang and Zhi-Quan Huang and Chia-Hsiu Hsu and Guoqing Chang and Feng-Chuan Chuang}
}
@article {604,
	title = {Band engineering and van Hove singularity on HfX$_{2}$ thin films (X = S, Se, or Te)},
	journal = {ACS Appl. Electron. Mater.},
	volume = {3},
	year = {2021},
	pages = {1071},
	abstract = {Two-dimensional transition metal dichalcogenides (TMDs) have become well-known due to their versatile and tunable physical properties for potential applications, specifically on low-power and optical devices. Here, we explored the structural stability and electronic properties of bulk and thin-film (from 1 up to 6 layers) structures of hafnium dichalcogenides (HfX$_{2}$, X = S, Se, or Te) using first-principles calculations. Our calculations reveal that the most stable phase is 1T for both thin films and bulk. The bulk and thin-film structures of HfTe$_{2}$ are semimetallic, while those of HfS$_{2}$ and HfSe$_{2}$ are insulating. Both HfS$_{2}$ and HfSe$_{2}$ thin films exhibit a decreasing band gap with increasing thickness, while HfTe$_{2}$ thin films remain semimetallic with increasing number of layers. Moreover, van Hove singularity (vHs), due to the contribution of the pz orbital from S atoms, is observed in 3L-HfS$_{2}$ at the valence band maximum, which can be further enhanced by applying an in-plane biaxial strain, suggesting possible superconductivity. Finally, the bulk and monolayer band structures of HfTe$_{2}$, under HSE06 and GGA + U with the effective Hubbard U parameter of 4.6 eV, are in good agreement with the experimental ARPES data. Our results indeed show that HfX$_{2}$ have sensitive and tunable electronic properties through film thickness control and strain for future potential applications.},
	doi = {10.1021/acsaelm.0c00907},
	author = {Harvey N. Cruzado and John Symon C. Dizon and Gennevieve M. Macam and Rovi Angelo B. Villaos and Thi My Duyen Huynh and Liang-Ying Feng and Zhi-Quan Huang and Chia-Hsiu Hsu and Shin-Ming Huang and Hsin Lin and Feng-Chuan Chuang}
}
@article {597,
	title = {Engineering surface structure of spinel oxides via high-valent vanadium doping for remarkably enhanced electrocatalytic oxygen evolution reaction},
	journal = {ACS Appl. Mater. Interfaces},
	volume = {11},
	year = {2019},
	pages = {33012},
	abstract = {Spinel oxides (AB$_{2}$O$_{4}$) with unique crystal structures have been widely explored as promising alternative catalysts for efficient oxygen evolution reactions; however, developing novel methods to fabricate robust, cost-effective, and high-performance spinel oxide based electrocatalysts is still a great challenge. Here, utilizing a complementary experimental and theoretical approach, pentavalent vanadium doping in the spinel oxides (i.e., Co$_{3}$O$_{4}$ and NiFe$_{2}$O$_{4}$) has been thoroughly investigated to engineer their surface structures for the enhanced electrocatalytic oxygen evolution reaction. Specifically, when the optimal concentration of vanadium (ca. 7.7 at. \%) is incorporated into Co$_{3}$O$_{4}$, the required overpotential to reach a certain jGEOM and jECSA decreases dramatically for oxygen evolution reactions in alkaline media. Even after 30 h of chronopotentiometry, the required potential for V-doped Co$_{3}$O$_{4}$ just increases by 16.3 mV, being much lower than that of the undoped one. It is observed that the pentavalent vanadium doping introduces lattice distortions and defects on the surface, which in turn exposes more active sites for reactions. DFT calculations further reveal the rate-determining step changing from the step of *-O to *-OOH to the step of *-OH to *-O, while the corresponding energy barriers decrease from 1.73 to 1.57 eV accordingly after high-valent V doping. Moreover, the oxygen intermediate probing method using methanol as a probing reagent also demonstrates a stronger OH* adsorption on the surface after V doping. When vanadium doping is performed in the inverse spinel matrix of NiFe2O4, impressive performance enhancement in the oxygen evolution reaction is as well witnessed. All these results clearly illustrate that the V doping process can not only efficiently improve the electrochemical properties of spinel transition metal oxides but also provide new insights into the design of high-performance water oxidation electrocatalysts.},
	doi = {10.1021/acsami.9b10868},
	author = {Renjie Wei and Xiuming Bu and Wei Gao and Rovi Angelo B. Villaos and Gennevieve M. Macam and Zhi-Quan Huang and Changyong Lan and Feng-Chuan Chuang and Yongquan Qu and Johnny C. Ho}
}