摘要：
Two-dimensional (2D) metallic states induced by oxygen vacancies ( VOs) at oxide surfaces and interfaces provide opportunities for the development of advanced applications, but the ability to control the behavior of these states is still limited. We used angle resolved photoelectron spectroscopy combined with density-functional theory (DFT) to study the reactivity of VO-induced states at the (001) surface of anatase TiO2, where both 2D metallic and deeper lying in-gap states (IGs) are observed. The 2D and IG states exhibit remarkably different evolutions when the surface is exposed to molecular O2: while IGs are almost completely quenched, the metallic states are only weakly affected. DFT calculations indeed show that the IGs originate from surface VOs and remain localized at the surface, where they can promptly react with O2. In contrast, the metallic states originate from subsurface vacancies whose migration to the surface for recombination with O2 is kinetically hindered on anatase TiO2 (001), thus making them much less sensitive to oxygen dosing.
作者机构：
[Zhang, Deng-Yu; Xu, Zhi-Feng; Tang, Zhen-Kun] Hengyang Normal Univ, Coll Phys & Elect Engn, Hengyang 421008, Peoples R China.;[Zhang, Deng-Yu; Xu, Zhi-Feng; Tang, Zhen-Kun] Hengyang Normal Univ, Coll Chem & Mat Sci, Hengyang 421008, Peoples R China.;[Hu, Shu-Xian; Lau, Woon-Ming; Tang, Zhen-Kun; Liu, Li-Min] Beijing Computat Sci Res Ctr, Beijing 100084, Peoples R China.;[Lau, Woon-Ming] Univ Sci & Technol Beijing, Sch Math & Phys, Ctr Green Innovat, Beijing 100083, Peoples R China.
通讯机构：
[Liu, Li-Min] B;Beijing Computat Sci Res Ctr, Beijing 100084, Peoples R China.
摘要：
The suitable band structure is vital for perovskite solar cells, which greatly affect the high photoelectric conversion efficiency. Cation substitution is an effective approach to tune the electric structure, carrier concentration, and optical absorption of hybrid lead iodine perovskites. In this work, the electronic structures and optical properties of cation (Bi, Sn, and TI) doped tetragonal formamidinium lead iodine CH(NH2) 2PbI3 (FAPbI(3)) are studied by first-principles calculations. For comparison, the cation-doped tetragonal methylammonium lead iodine CH3NH3PbI3 (MAPbI(3)) are also considered. The calculated formation energies reveal that the Sn atom is easier to dope in the tetragonal MAPbI(3)/FAPbI(3) structure due to the small formation energy of about 0.3 eV. Besides, the band gap of Sn-doped MAPbI(3)/FAPbI(3) is 1.30/1.40 eV, which is considerably smaller than the un-doped tetragonal MAPbI(3)/FAPbI(3). More importantly, compare with the un-doped tetragonal MAPbI(3)/FAPbI(3), the Sn-doped MAPbI(3) and FAPbI(3) have the larger optical absorption coefficient and theoretical maximum efficiency, especially for Sndoped FAPbI(3). The lower formation energy, suitable band gap and outstanding optical absorption of the Sn-doped FAPbI(3) make it promising candidates for high-efficient perovskite cells.
期刊：
PHYSICAL CHEMISTRY CHEMICAL PHYSICS,2017年19(31):20968-20973 ISSN：1463-9076
通讯作者：
Hu, Shu-Xian;Liu, Li-Min
作者机构：
[Hu, SX; Liu, Li-Min; Hu, Shu-Xian; Zhang, Le] Beijing Computat Sci Res Ctr, Beijing 100193, Peoples R China.;[Tang, Zhen-Kun] Hengyang Normal Univ, Coll Phys & Elect Engn, Hengyang 421008, Peoples R China.;[Lau, Woon-Ming] Univ Sci & Technol Beijing, Sch Math & Phys, Ctr Green Innovat, Beijing 100083, Peoples R China.;[Yin, Wen-Jin] Hunan Univ Sci & Technol, Sch Phys & Elect Sci, Xiangtan 411201, Peoples R China.
通讯机构：
[Hu, SX; Liu, LM] B;Beijing Computat Sci Res Ctr, Beijing 100193, Peoples R China.
摘要：
Bismuth oxyhalides (BiOX, X = Cl, Br, and I) are a new family of promising photocatalysts. BiOCl and BiOBr possess large band gaps and weak absorption in visible light regions, which limit their applications. Although the band gap of BiOI is suitable to absorb most of the visible light, its redox capability is very weak. In this work, the doping and strain effects on the electronic structures and optical properties of BiOCl are explored using first principle calculations. The results show that doping in BiOCl, especially co-doping of Sb and I atoms, can obviously decrease the band gaps along with enhancing the optical absorption coefficients of pristine BiOCl because of the electronegativity difference between Sb/I atoms and Bi/Cl atoms. Meanwhile the band gap of BiOCl can be tuned under strain. This work offers potential strategies to enhance BiOCl absorption coefficients in the visible light region and its photocatalyst activity.
作者机构：
[Luo, Jun; Luo, J; Zhu, Jing; Li, Zuocheng; Yan, Xingxu] Tsinghua Univ, Key Lab Adv Mat MOE, State Key Lab New Ceram & Fine Proc, Natl Ctr Electron Microscopy Beijing,Sch Mat Sci, Beijing 100084, Peoples R China.;[Tang, Zhenkun; Liu, Li-Min] Beijing Computat Sci Res Ctr, Beijing 100094, Peoples R China.;[Tang, Zhenkun] Hengyang Normal Univ, Coll Phys & Elect Engn, Hengyang 421008, Peoples R China.;[Huo, Ziyang] Griffith Univ, Queensland Micro & Nano Ctr, Brisbane, Qld 4111, Australia.;[Luo, Jun; Li, Guoliang] Tianjin Univ Technol, Sch Mat Sci & Engn, Inst New Energy Mat & Low Carbon Technol, Ctr Electron Microscopy,TUT FEI Joint Lab, Tianjin 300384, Peoples R China.
通讯机构：
[Luo, J; Zhu, J; Luo, Jun] T;[Liu, Li-Min] B;Tsinghua Univ, Key Lab Adv Mat MOE, State Key Lab New Ceram & Fine Proc, Natl Ctr Electron Microscopy Beijing,Sch Mat Sci, Beijing 100084, Peoples R China.;Beijing Computat Sci Res Ctr, Beijing 100094, Peoples R China.;Tianjin Univ Technol, Sch Mat Sci & Engn, Inst New Energy Mat & Low Carbon Technol, Ctr Electron Microscopy,TUT FEI Joint Lab, Tianjin 300384, Peoples R China.
摘要：
Electronic properties of two-dimensional (2D) MoS2 semiconductors can be modulated by introducing specific defects. One important type of defect in 2D layered materials is known as rotational stacking fault (RSF), but the coexistence of multiple RSFs with different rotational angles was not directly observed in freestanding 2D MoS2 before. In this report, we demonstrate the coexistence of three RSFs with three different rotational angles in a freestanding bilayer MoS2 sheet as directly observed using an aberration-corrected transmission electron microscope (TEM). Our analyses show that these RSFs originate from cracks and dislocations within the bilayer MoS2. First-principles calculations indicate that RSFs with different rotational angles change the electronic structures of bilayer MoS2 and produce two new symmetries in their bandgaps and offset crystal momentums. Therefore, employing RSFs and their coexistence is a promising route in defect engineering of MoS2 to fabricate suitable devices for electronics, optoelectronics, and energy conversion.
期刊：
Journal of Physical Chemistry Letters,2016年7(22):4795-4801 ISSN：1948-7185
通讯作者：
Tse, John S.;Liu, Li-Min
作者机构：
[Tang, Zhen-Kun; Tse, JS; Liu, Li-Min; Tse, John S.] Beijing Computat Sci Res Ctr, Beijing 100084, Peoples R China.;[Tang, Zhen-Kun] Hengyang Normal Univ, Coll Phys & Elect Engn, Hengyang 421008, Peoples R China.;[Tse, John S.] Univ Saskatchewan, Dept Phys & Engn Phys, Saskatoon, SK S7N 5E2, Canada.
通讯机构：
[Tse, JS; Liu, LM] B;[Tse, John S.] U;Beijing Computat Sci Res Ctr, Beijing 100084, Peoples R China.;Univ Saskatchewan, Dept Phys & Engn Phys, Saskatoon, SK S7N 5E2, Canada.
摘要：
Liquid electrolytes play an important role in commercial lithium-ion (Li-ion) batteries as a conduit for Li-ion transfer between anodes and cathodes. It is generally believed that the Li-ions move along with the salt ions; thus, Li-ion diffusion is only affected by the viscosity and salt concentration in the liquid electrolytes based on the Stokes-Einstein equation. In this study, a novel and faster Li-ion diffusion mechanism in electrolytes containing a cyanogen group is identified from first-principles molecular dynamics (FPMD) simulations. In this mechanism, the Li-ions are first detached from the Li-salt and then diffuse along with the solvent molecules, and the Li-ion diffusion does not obey the traditional StokesEinstein equation. The ionic conductivity of the electrolyte systems with this solvent-assisted Li-ion diffusion mechanism is further enhanced through Li-ion hopping. This novel Li-ion diffusion process explains recent findings of high Li-ion conductivity in electrolytes with cyanogen groups and furnishes a new paradigm for the design of fast-charging liquid electrolyte for Li-ion batteries.
作者机构：
[Lau, Woon-Ming; Yin, Wen-Jin; Zhang, Le; Liu, Li-Min; Lau, WM; Tang, Zhen-Kun; Wen, Bo] Beijing Computat Sci Res Ctr, Beijing 100084, Peoples R China.;[Zhang, Deng-Yu; Tang, Zhen-Kun] Hengyang Normal Univ, Coll Phys & Elect Engn, Hengyang 421008, Peoples R China.;[Lau, Woon-Ming] Univ Sci & Technol Beijing, Ctr Green Innovat, Sch Math & Phys, Beijing 100083, Peoples R China.
通讯机构：
[Liu, LM; Lau, WM] B;[Lau, Woon-Ming] U;Beijing Computat Sci Res Ctr, Beijing 100084, Peoples R China.;Univ Sci & Technol Beijing, Ctr Green Innovat, Sch Math & Phys, Beijing 100083, Peoples R China.
摘要：
The electronic structures and photocatalytic properties of bismuth oxyhalide bilayers (BiOX1/BiOX2, X1 and X2 are Cl, Br, I) are studied by density functional theory. Briefly, their compositionally tunable bandgaps range from 1.85 to 3.41 eV, suitable for sun-light absorption, and all bilayers have band-alignments good for photocatalytic water-splitting. Among them, heterogeneous BiOBr/BiOI bilayer is the best as it has the smallest bandgap. More importantly, photo-excitation of BiOBr/BiOI leads to electron supply to the conduction band minimum with localized states belonging mainly to bismuth of BiOBr where the H+/H2 half-reaction of water-splitting can be sustained. Meanwhile, holes generated by such photo-excitation are mainly derived from the iodine states of BiOI in the valence band maximum; thus, the O2/H2O half-reaction of water splitting is facilitated on BiOI. Detailed band-structure analysis also indicates that this intriguing spatial separation of photo-generated electron-hole pairs and the two half-reactions of water splitting are good for a wide photo-excitation spectrum from 2–5 eV; as such, BiOBr/BiOI bilayer can be an efficient photocatalyst for water-splitting, particularly with further optimization of its optical absorptivity.
