Showing papers by "Ying Dai published in 2015"
TL;DR: The established heterojunction between the interfaces of TiO2 nanoparticles and g-C3N4 nanosheets as well as introduced Ti(3+) led to the rapid electron transfer rate and improved photoinduced electron-hole pair's separation efficiency, resulting in the improved photocatalytic performance of the Ti( 3+) self-doped TiO 2/g-C 3N4 heterojunctions.
Abstract: A simple one-step calcination route was used to prepare Ti3+ self-doped TiO2/g-C3N4 heterojunctions by mixture of H2Ti3O7 and melamine. X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR) spectroscopy, and UV–Vis diffuse reflectance spectroscopy (UV–vis DRS) technologies were used to characterize the structure, crystallinity, morphology, and chemical state of the as-prepared samples. The absorption of the prepared Ti3+ self-doped TiO2/g-C3N4 heterojunctions shifted to a longer wavelength region in comparison with pristine TiO2 and g-C3N4. The photocatalytic activities of the heterojunctions were studied by degrading methylene blue under a 30 W visible-light-emitting diode irradiation source. The visible-light photocatalytic activities enhanced by the prepared Ti3+ self-doped TiO2/g-C3N4 heterojunctions were observed and proved to be better than that of pure TiO2 and ...
476 citations
TL;DR: This study reveals that the concentration of S vacancies can be controlled by varying the amount of the reducing agent NaBH4 in the synthesis, and the prepared ZnS samples exhibit photocatalytic activity for H2 production under visible-light irradiation without loading noble metal.
Abstract: Synthesis and characterization of ZnS with controlled amount of S vacancies for photocatalytic H 2 production under visible light
187 citations
TL;DR: It is predicted that methyl-functionalized bismuth, antimony, and lead bilayers are 2D topological insulators (TIs) with protected Dirac type topological helical edge states, and thus suitable QSH systems, and it is shown that the topological properties in these three systems are robust against mechanical deformation.
Abstract: One of the major obstacles to a wide application range of the quantum spin Hall (QSH) effect is the lack of suitable QSH insulators with a large bulk gap. By means of first-principles calculations including relativistic effects, we predict that methyl-functionalized bismuth, antimony, and lead bilayers (Me-Bi, Me-Sb, and Me-Pb) are 2D topological insulators (TIs) with protected Dirac type topological helical edge states, and thus suitable QSH systems. In addition to the explicitly obtained topological edge states, the nontrivial topological characteristic of these systems is confirmed by the calculated nontrivial Z2 topological invariant. The TI characteristics are intrinsic to the studied materials and are not subject to lateral quantum confinement at edges, as confirmed by explicit simulation of the corresponding nanoribbons. It is worthwhile to point out that the large nontrivial bulk gaps of 0.934 eV (Me-Bi), 0.386 eV (Me-Sb), and 0.964 eV (Me-Pb) are derived from the strong spin–orbit coupling within...
173 citations
TL;DR: The results suggest that bismuth-based MOFs could be promising candidates for the development of efficient visible-light photocatalysts.
Abstract: A visible-light-responsive bismuth-based metal-organic framework (Bi-mna) is demonstrated to show good photoelectric and photocatalytic properties. Combining experimental and theoretical results, a ligand-to-ligand charge transfer (LLCT) process is found to be responsible for the high performance, which gives rise to a longer lifetime of photogenerated charge carriers. Our results suggest that bismuth-based MOFs could be promising candidates for the development of efficient visible-light photocatalysts.
131 citations
TL;DR: In this article, a Si-based pentagonal monolayers is constructed on the basis of the okayamalite structure by means of first principles calculations, and the carrier mobilities up to 2500 cm2 V−1 s−1 are quantitatively investigated by using deformation potential theory with effective mass approximation.
Abstract: A new family of Si-based pentagonal monolayers is constructed on the basis of the okayamalite structure by means of first principles calculations. Phonon spectra and ab initio molecular dynamics simulations provide eloquent examinations for the dynamical and thermal stabilities of p-SiX (X = B, C, and N) monolayers. Electronic structures show that p-SiC and p-SiN are indirect semiconductors with band gaps of 2.35 and 4.98 eV by HSE hybrid functional, respectively. The carrier mobilities up to 2500 cm2 V−1 s−1 are quantitatively investigated by using deformation potential theory with effective mass approximation. And the band structures can be modulated monotonically under proper isotropic strains. This indicates that p-SiX can be used as field effect transistors or other electronic devices. More intriguingly, the band gap of p-SiC corresponds to the wavelength of 528 nm, showing a semiconducting character absorption in the green region of the visible spectra. Enlightened by prominent photocatalytic behavior of g-C3N4, we demonstrate that both band gap and band edges of p-SiC can meet the requirement of the reduction and oxidation levels in water splitting. The new type of Si-based nanomaterial offers an interesting alternative to diverse nanodevices and paves way for new metal-free photocatalysts.
124 citations
TL;DR: In this paper, a family of robust 2D topological insulators (TIs) with intrinsic intrinsic nontrivial band gaps ranged from 24 to 187 meV were predicted for monolayer square transition-metal dichalcogenides.
Abstract: Two-dimensional (2D) topological insulators (TIs) hold promise for applications in spintronics based on the fact that the propagation direction of an edge electronic state of a 2D TI is locked to its spin orientation. Here, using first-principles calculations, we predict a family of robust 2D TIs in monolayer square transition-metal dichalcogenides $M{X}_{2}\phantom{\rule{0.28em}{0ex}}(M=\mathrm{Mo},\phantom{\rule{0.28em}{0ex}}\mathrm{W};\phantom{\rule{0.28em}{0ex}}X=\mathrm{S},\phantom{\rule{0.28em}{0ex}}\mathrm{Se},\phantom{\rule{0.28em}{0ex}}\mathrm{Te})$, which show sizeable intrinsic nontrivial band gaps ranged from 24 to 187 meV, thus ensuring the quantum spin Hall (QSH) effect at room temperature. Different from the most known 2D TIs with comparable band gaps, these sizeable energy gaps arise from the strong spin-orbit interaction related to $d$ electrons of the Mo/W atoms. A pair of topologically protected helical edge states emerges at the edge of these systems with a Dirac-type dispersion within the bulk band gap. The topologically nontrivial natures are confirmed by the nontrivial ${\mathrm{Z}}_{2}$-type topological invariant. More interestingly, with applied strain, a topological quantum phase transition between a QSH phase and a trivial insulating/metallic phase can be realized, and the corresponding topological phase diagram is well established.
120 citations
TL;DR: The photophysical properties of Bi-BTC are investigated which shows high activity of O2 production in photocatalysis and a novel 3D framework consisting of trimesic acid and DMF which contains two helix chains which assemble regularly.
Abstract: A bismuth based metal-organic framework ([Bi(BTC)(DMF)]·DMF (CH3OH)2, Bi-BTC) with a novel topology structure is synthesized by a solvothermal method. Bi-BTC crystalizes in the P21/n space group, exhibits a novel 3D framework consisting of trimesic acid (H3BTC) linked with {Bi2O14} units and contains two helix chains which assemble regularly. In addition, we investigated the photophysical properties of Bi-BTC which shows high activity of O2 production in photocatalysis.
79 citations
TL;DR: In this article, a prototype V 2 O 5 nanowire microyarns-based gas sensor with high response and selectivity for ethanol was developed, which is very similar to drawing a thread from a silk cocoon.
Abstract: In this paper, a prototype V 2 O 5 nanowire microyarns-based gas sensor with high response and selectivity for ethanol was developed. The V 2 O 5 nanowire yarns were directly spun from ultralong V 2 O 5 nanowires viscous solution. This process is very similar to drawing a thread from a silk cocoon. The microyarns wound around alumina tubes like a spiral were tested for gas sensing toward ethanol, methanol, ammonia and toluene gases. It was found that the microyarns exhibit good response and selectivity to ethanol. The response of the yarns reaches the maximum value of 9.09 to 1000 ppm ethanol at 330 °C, which is around 3.5 times higher than that of the randomly ultralong nanowires. In contrast, only very little response was observed for methanol, ammonia and toluene, which indicated that V 2 O 5 nanowire microyarns would be a potential candidate for practical gas detector.
74 citations
TL;DR: The results show that an isolated GeCH3 layer has no dynamic instability, and is a QSH insulator under reasonable strain, which has a large enough band gap and metallic edge states characterized by nontrivial topology.
Abstract: Quantum spin Hall (QSH) insulators exhibit a bulk insulting gap and metallic edge states characterized by nontrivial topology. We investigated the electronic structure of an isolated layer of methyl substituted germanane GeCH3 by density functional calculations (DFT), and its dynamic stability by phonon dispersion calculations. Our results show that an isolated GeCH3 layer has no dynamic instability, and is a QSH insulator under reasonable strain. This QSH insulator has a large enough band gap (up to 108 meV) at 12% strain. The advantageous features of this QSH insulator for practical room-temperature applications are discussed.
68 citations
TL;DR: The physical insights pave the way for the good performance of MoS2/TM2CO2 in next-generation electronic devices and photocatalysts.
Abstract: Two-dimensional (2D) transition metal compound (TMC) monolayers, as well as their van der Waals heterostructures with unique properties, are fundamentally and technologically intriguing. Here, heterostructures consisting of a MoS2 monolayer and TM2CO2 (TM?=?Ti, Zr or Hf) monolayers are systematically researched by means of the density functional theory (DFT). Different from semiconductor/metal contacts, MoS2 and TM2CO2 monolayers are all semiconductors with band gaps ranging from 0.25?1.67 eV. According to rigorous screening of stacking patterns, MoS2/Zr2CO2 is shown to be an indirect type-II semiconductor with the maximum valence and minimum conduction bands spatially separated on opposite monolayers. Simultaneously, the interface charges transfer from Zr2CO2 to MoS2 results in a built-in field that separates the electrons and holes efficiently. Also, the smaller effective masses of electrons and the holes of band edges indicate the higher carrier mobility. Moreover, strain regulation can make the hetero-bilayer?s character a semiconductor?semimetal?metal transition. The physical insights pave the way for the good performance of MoS2/TM2CO2 in next-generation electronic devices and photocatalysts.
66 citations
15 Mar 2015
TL;DR: It is a synergetic effect that enables the composites to harvest light and promote charge separation, which eventually leads to the enhancement of the photocatalytic efficiencies.
Abstract: The C3N4/BiOIO3 composites with heterostructures have been fabricated by simply depositing BiOIO3 on the surface of C3N4 at hydrothermal conditions, using bismuth nitrate and potassium iodate as precursors. C3N4 is an excellent organic semiconductor, which can be excited by visible light. BiOIO3 is a layered bismuth-based compound that has an internal polar field. Coupling C3N4 with BiOIO3 can combine the advantages of the two compounds and obtain better photocatalytic properties. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Fourier transformation infrared spectra have been carried out to confirm the structures and morphologies of as-prepared products. The absorption properties have been characterized by diffuse reflectance spectra and the photocatalytic activities have been evaluated by photodegradation of methyl orange, Rhodamine B and 2,4-dichlorophenol. Compared with C3N4, all C3N4/BiOIO3 composites exhibit better visible-light-driven photocatalytic properties. It is a synergetic effect that enables the composites to harvest light and promote charge separation, which eventually leads to the enhancement of the photocatalytic efficiencies. Under UV-vis light irradiation, C3N4/BiOIO3 composites also exhibit better activities, and the charge transfer process is similar to a redox mediator-free Z-scheme system.
TL;DR: In this article, the electronic structures and photocatalytic properties of Ag2ZnSn(S1−xSex)4 (x = 0, 1) were investigated by the combination of GGA+U and hybrid functional methods.
Abstract: The silver-based quaternary chalcogenides have potential applications in solar cell absorbers and photocatalytic water splitting to produce hydrogen. In the present work, the electronic structures and photocatalytic properties of Ag2ZnSn(S1–xSex)4 (x = 0–1) were investigated by the combination of GGA+U and hybrid functional methods. The results indicate that Ag2ZnSnS4 (x = 0) and Ag2ZnSnSe4 (x = 1) have a dispersive conduction band and small electron effective masses, which are beneficial to the photogenerated carrier separation. The hole effective masses are remarkably direction dependent, and that along the [100] and [010] directions are sensitive to strain, which indicates easy modulation of photocatalytic properties. In addition, the band gaps of the Ag2ZnSn(S1–xSex)4 solid solution can be tuned continuously by controlling the x component, which indicates the easy manipulation of light response range. The transfer abilities of charge carriers can also be improved with increasing Se incorporation. In a...
TL;DR: In this article, a simple solvothermal process was used to synthesize BiOBr-PVP hybrid, and the adsorption and photocatalytic properties were investigated.
TL;DR: In this paper, the authors verified that electrons and holes can be distributed on the opposite constituent of the heterostructures, forming a type-II band alignment and enabling physical separation of excitons.
Abstract: On the basis of density functional electronic calculations, heterostructures of single-layer GaS and GaSe were found to exhibit novel physical properties due to their specific interfacing effects and versatile structural features. We verified that electrons and holes can be distributed on the opposite constituent of the heterostructures, forming a type-II band alignment and enabling physical separation of excitons, which is highly desirable in applications such as solar energy conversion. We found the Rashba effects in the two-dimensional GaS/GaSe heterostructures due to the breaking of inversion symmetry and the intrinsic polarization, which reveals new possibility in applications in spintronic and electronic nanodevices. In addition, we confirmed that the electronic properties of GaS/GaSe van der Waals heterostructures can be continuously tuned by external strain.
TL;DR: In this paper, self-doped TiO2 nanoparticles were synthesized by hydrothermal treatment of a gel precursor obtained using TiH2 as the Ti source and H2O2 as oxidant.
TL;DR: In this paper, a series of new IATIsos in saturated Group III-Bi bilayers are predicted, which preserve extraordinary large bulk band gaps, which are well above room temperature, allowing for viable applications in room-temperature spintronic devices.
Abstract: The search for inversion-asymmetric topological insulators (IATIs) persists as an effect for realizing new topological phenomena. However, so far only a few IATIs have been discovered and there is no IATI exhibiting a large band gap exceeding 0.6 eV. Using first-principles calculations, we predict a series of new IATIs in saturated Group III-Bi bilayers. We show that all these IATIs preserve extraordinary large bulk band gaps, which are well above room temperature, allowing for viable applications in room-temperature spintronic devices. More importantly, most of these systems display large bulk band gaps that far exceed 0.6 eV and, part of them even are up to \ensuremath{\sim}1 eV, which are larger than any IATIs ever reported. The nontrivial topological situation in these systems is confirmed by the identified band inversion of the band structures, ${Z}_{2}$ topological invariants, and an explicit demonstration of the topological edge states. Owning to their asymmetric structures, remarkable Rashba spin splitting is produced in both the valence and conduction bands of these systems. These predictions strongly revive these new systems as excellent candidates for IATI-based novel applications.
TL;DR: The present work can provide a key guideline for the creation of highly efficient noble-metal-free plasmonic photocatalysts and have a much wider impact in infrared bioimaging and spectroscopy where infrared LSPR is essential.
Abstract: The unique capacity of localized surface plasmon resonance (LSPR) offers a new opportunity to overcome the limited efficiency of semiconductor photocatalyst. Here we unravel that LSPR, which usually occurs in noble metal nanoparticles, can be realized by hydrogen doping in noble-metal-free semiconductor using TiO2 as a model photocatalyst. Moreover, its LSPR is located in infrared region, which supplements that of noble metal whose LSPR is generally in the visible region, making it possible to extend the light response of photocatalyst to infrared region. The near field enhancement is shown to be comparable with that of noble-metal nanoparticles, indicating that highly enhanced light absorption rate can be expected. The present work can provide a key guideline for the creation of highly efficient noble-metal-free plasmonic photocatalysts and have a much wider impact in infrared bioimaging and spectroscopy where infrared LSPR is essential.
Journal Article•
TL;DR: In this article, a series of new IATIsos in saturated Group III-Bi bilayers are predicted and shown to preserve extraordinary large bulk band gaps, which are well above room temperature, allowing for viable applications in room-temperature spintronic devices.
Abstract: The search for inversion-asymmetric topological insulators (IATIs) persists as an effect for realizing new topological phenomena. However, so far only a few IATIs have been discovered and there is no IATI exhibiting a large band gap exceeding 0.6 eV. Using first-principles calculations, we predict a series of new IATIs in saturated Group III-Bi bilayers. We show that all these IATIs preserve extraordinary large bulk band gaps, which are well above room temperature, allowing for viable applications in room-temperature spintronic devices. More importantly, most of these systems display large bulk band gaps that far exceed 0.6 eV and, part of them even are up to ∼1 eV, which are larger than any IATIs ever reported. The nontrivial topological situation in these systems is confirmed by the identified band inversion of the band structures, Z2 topological invariants, and an explicit demonstration of the topological edge states. Owning to their asymmetric structures, remarkable Rashba spin splitting is produced in both the valence and conduction bands of these systems. These predictions strongly revive these new systems as excellent candidates for IATI-based novel applications. © 2015 American Physical Society.
TL;DR: In this article, a new family of 2D topological insulators (TIs) comprising g-TlA (A = N, P, As, and Sb) monolayers constructed by Tl and group-V elements is predicted by first-principles calculations and molecular-dynamics (MD) simulations.
Abstract: A new family of two-dimensional (2D) topological insulators (TIs) comprising g-TlA (A = N, P, As, and Sb) monolayers constructed by Tl and group-V elements is predicted by first-principles calculations and molecular-dynamics (MD) simulations. The geometric stability, band inversion, nontrivial edge states, and electric polarity are investigated to predict the large-gap quantum spin Hall insulator and Rashba-Dresselhaus effects. The MD results reveal that the g-TlA monolayers remain stable even at room temperature. The g-TlA (A = As, Sb) monolayers become TIs under the influence of strong spin-orbit couplings with large bulk bandgaps of 131 and 268 meV, respectively. A single band inversion is observed in each g-TlA (A = As, Sb) monolayer, indicating a nontrivial topological nature. Furthermore, the topological edge states are described by introducing a sufficiently wide zigzag-nanoribbon. A Dirac point in the middle of the bulk gap connects the valence- and conduction-band edges. The Fermi velocity near the Dirac point with a linear band dispersion is ~0.51 × 106 m/s, which is comparable to that of many other 2D nanomaterials. More importantly, owing to the broken inversion symmetry normal to the plane of the g-TlA films, a promising Rashba-Dresselhaus effect with the parameter up to 0.85 eV·A is observed in the g-TlA (A = As, Sb) monolayers. Our findings regarding 2D topological g-TlA monolayers with room-temperature bandgaps, intriguing topological edge states, and a promising Rashba-Dresselhaus effect are of fundamental value and suggest potential applications in nanoelectronic devices.
TL;DR: In this paper, a uniformly dispersed sulfur doped BiOCl was prepared via a one-pot solvothermal method, which displays higher photocatalytic activity towards oxygen evolution from water compared to pure BiOCL.
Abstract: Uniformly dispersed sulfur doped BiOCl was prepared via a one-pot solvothermal method, which displays higher photocatalytic activity towards oxygen evolution from water compared to pure BiOCl. This is associated with the impurity states above the valence band induced by S doping, which is beneficial for the separation of photo-generated electron–hole pairs.
TL;DR: In this paper, a series of structures constructed by hexagonal boron nitride (h-BN) and zigzag graphene monolayers based on first-principles calculations are analyzed.
Abstract: Very recently, the lateral heterojunctions of hexagonal boron nitride (h-BN)/graphene were experimentally realized for the time. To study the related properties of such heterojunctions with the purpose of searching for new avenues to realize controllable and tunable 2D electric devices, in the present work we perform a systematic theoretical investigation on a series of structures constructed by zigzag h-BN and zigzag graphene monolayers based on first-principles calculations. Our results demonstrate that the electronic structures as well as the magnetic properties of the hybridized monolayers can be modified efficiently. Furthermore, the character transition from insulator to metal can also be realized by the proposed approaches of adjusting the numbers or the ratios of the zigzag h-BN and zigzag graphene. Interestingly, the investigation of the strain dependence of the electronic properties in the selected structure reveals that the external strain applied along the Y-axis plays a decisive role in the bandgap engineering. Moreover, the calculated effective masses give a reasonable physical representation of the carrier transport properties. Our results show that the mobility direction of the charge carriers is parallel to the interface. These predictions provide new potential strategies for tuning electronic properties and will allow new device functionalities, such as in-plane transistors, diodes and spintronic devices, to be integrated within a single thin layer.
TL;DR: In-plane TMD heterostructures with the ultimate thickness limit for semiconductor heterostructure will definitely spark a surge in research activity.
Abstract: Electronic structures of in-plane two-dimensional transition-metal dichalcogenide (TMD) heterostructures have been studied on the basis of the first-principles density functional calculations. In contrast to vertically stacked TMD heterostructures, true type-II band alignment could be established in in-plane TMD heterostructures due to their coherent lattice and strong electronic coupling, and thus leads to the efficient separation of electrons and holes. In in-plane TMD heterostructures interfaced along the zigzag direction, electronic reconstruction causes band bending in constituent TMDs, unveiling the great potential in achieving high efficiency of water splitting and constructing Schottky barrier solar cells. In addition, type-I alignment could also be demonstrated in in-plane TMD heterostructures, enriching the photoluminescence features of TMD materials. In-plane TMD heterostructures with the ultimate thickness limit for semiconductor heterostructures will definitely spark a surge in research activity.
TL;DR: In this article, the photocatalytic activity of Bi2SiO5 and Bi2S3/Bi2SO5 heterojunctions was investigated under visible light and UV-vis light irradiation.
Abstract: In order to improve the photocatalytic activity of Bi2SiO5 under visible light irradiation, Bi2S3/Bi2SiO5 heterojunctions were synthesized through a facile in situ ion exchange method. Thioacetamide (TAA) is regarded as the appropriate sulfur source. The as-prepared samples of Bi2SiO5 and Bi2S3/Bi2SiO5 were systematically characterized by XRD, SEM-EDS, TEM, XPS, PL, UV-vis DRS and BET techniques. The photocatalytic activities of the samples were evaluated by degrading rhodamine B (RhB) under visible light and UV-vis light irradiation, respectively. Bi2S3/Bi2SiO5 heterojunctions show enhanced photocatalytic activities under visible light irradiation. Further investigation reveals that ion exchange reaction time plays an important role in the photocatalytic efficiency. The mechanism of the enhanced photocatalytic activity was proposed.
TL;DR: It is shown that the n-type doping in TiO2 can significantly decrease the ability of F-adsorption in switching the relative stability of the two surfaces, which provides new insights into the physical and chemical properties about both pure and F-ADSorbed surfaces ofTiO2.
Abstract: The stability of both the pure and fluorine (F)-adsorbed surface of TiO2 is examined on the basis of density functional calculations. For pure surfaces, both the beneficial local geometric structures and local potential strengthen the Ti-O binding in (101), rendering it the most stable surface. For F-adsorbed surfaces, F-adsorption significantly weakens the Ti-O bonds in (101) but strengthens them in (001), so that (001) becomes more stable than (101) for the F-adsorbed surfaces. On the basis of this observation, we further show that the n-type doping in TiO2 can significantly decrease the ability of F-adsorption in switching the relative stability of the two surfaces. The present work not only provides new insights into the physical and chemical properties about both pure and F-adsorbed surfaces of TiO2 and conclusively explains related experimental results but also suggests viable ways to prepare TiO2 samples with a high percentage of (001).
TL;DR: It is demonstrated that electron-hole pairs can be spatially separated, and the carrier mobility would be benefited from the absorbed γ-graphyne in the BDHs, and a new strategy for fabricating unprecedented 2D nanomaterials with exciting properties is proposed.
Abstract: Vertical and lateral heterostructures with atomically clean and sharp interfaces have opened up new realms in materials science, device physics and engineering. Herein, inspired by recent experiments, the unprecedented bidirectional heterostructures (BDHs) of γ-graphyne@MoSe2/WSe2 as well as γ-graphyne@MoSe2 and γ-graphyne@WSe2 are proposed and examined on the basis of first-principles calculations. Our results reveal that a novel wrinkled γ-graphyne with narrowed energy gap and strong binding strength is achieved on the planar and smooth substrate in γ-graphyne@MoSe2/WSe2. The direct-indirect band gap crossover is also found in terms of interlayer coupling. Furthermore, we demonstrate that electron–hole pairs can be spatially separated, and the carrier mobility would be benefited from the absorbed γ-graphyne in the BDHs. These results provide not only new insights into the physical and chemical properties of the vertical and bidirectional heterostructures, but also a new strategy for fabricating unpreced...
TL;DR: In this article, the formation energies and electronic structures of defects contained in Ta3N5 are studied by first principles density functional theory in detail, and it is shown that substitution of O for three-coordinated N possesses a low formation energy and introduces a shallow donor under both Nrich and N-poor conditions, making a major contribution to the n-type conductivity.
Abstract: Ta3N5 is a good candidate for an oxygen evolution photocatalyst or a photoanode for a Z-scheme device due to its n-type feature. In the present work, the formation energies and electronic structures of defects contained in Ta3N5 are studied by first principles density functional theory in detail. Our results show that the substitution of O for three-coordinated N in Ta3N5 possesses a low formation energy and introduces a shallow donor under both N-rich and N-poor conditions, making a major contribution to the n-type conductivity. By investigation of the optical transition levels, we show that the four-coordinated N vacancy in Ta3N5 is responsible for the observed 720 nm sub-band gap optical absorption. In addition, for alkali metal doped Ta3N5, our results reveal that the interstitial doping can lead to enhanced conductivity and reduced band gap, and the doping of Na and K in Ta3N5 are expected to produce higher photocatalytic activity compared to Rb and Cs. These results are useful to understand the recent experimental observations and provide guidance to engineer Ta3N5 with improved photocatalytic efficiency.
TL;DR: Interestingly, two-dimensional quantum wells of in-plane TMD can enrich the photoluminescence properties of TMD materials and demonstrates the possibility to achieve topological insulator state and valleytronics in TMD quantum wells.
Abstract: In-plane transition-metal dichalcogenides (TMDs) quantum wells have been studied on the basis of first-principles density functional calculations to reveal how to control the electronic structures and the properties. In collection of quantum confinement, strain and intrinsic electric field, TMD quantum wells offer a diverse of exciting new physics. The band gap can be continuously reduced ascribed to the potential drop over the embedded TMD and the strain substantially affects the band gap nature. The true type-II alignment forms due to the coherent lattice and strong interface coupling suggesting the effective separation and collection of excitons. Interestingly, two-dimensional quantum wells of in-plane TMD can enrich the photoluminescence properties of TMD materials. The intrinsic electric polarization enhances the spin-orbital coupling and demonstrates the possibility to achieve topological insulator state and valleytronics in TMD quantum wells. In-plane TMD quantum wells have opened up new possibilities of applications in next-generation devices at nanoscale.
TL;DR: In this paper, the effects of various Ti/Zn molar ratios and preparation processes on the structural, morphological, optical, photocurrent and photocatalytic properties of the resulting samples were investigated systematically.
TL;DR: In this paper, the structure, morphologies, and light absorption properties of Ag9(SiO4)2NO3 were investigated, and an internal electric field can be formed inside the material, which can facilitate the photogenerated charge separation during the photocatalytic process.
Abstract: Ag9(SiO4)2NO3 was prepared by a reactive flux method. The structures, morphologies, and light absorption properties were investigated. Owing to the polar crystal structure, an internal electric field can be formed inside the material, which can facilitate the photogenerated charge separation during the photocatalytic process. Based on both the wide light absorption spectra and high charge separation efficiency originated from the polarized internal electric field, Ag9(SiO4)2NO3 exhibit higher efficiency over Ag3PO4 during the degradation of organic dyes under visible light irradiation, which is expected to be a potential material for solar energy harvest and conversion.
TL;DR: It is found that Ir(111) preserves the 2D character of silicene but significantly distorts its structure from the trigonal one expected for an isolated silicen, but exhibits a hidden linear-dispersive band, which is related to the linear- Dispersive conduction band of an isolatedsilicene.
Abstract: The structure of silicene/Ir(111) was examined on the basis of density functional theory. We have found that Ir(111) preserves the 2D character of silicene but significantly distorts its structure from the trigonal one expected for an isolated silicene. The electronic structure of silicene is strongly hybridized with that of Ir(111) so that silicene on Ir(111) loses its linear band dispersion around the Fermi level, giving rise to a metallic band structure; however, silicene/Ir(111) exhibits a hidden linear-dispersive band, which is related to the linear-dispersive conduction band of an isolated silicene.