DFT study on the structural and electronic properties of Pt-doped boron nitride nanotubes

First-principles calculations based on density functional theory were carried out to investigate the structural and electronic properties of Pt substitution-doped boron nitride (BN) nanotubes. The electronic and structural properties were studied for substituted Pt in the boron and the nitrogen sites of the (BN) nanotube. The band gap significantly diminishes to 2.095 eV for Pt doping at the B site while the band gap diminishes to 2.231 eV for Pt doping at the N site. The band density increases in both the valence band and the conduction band after doping. The effects of the hardness and softness group 17 (halogen elements) were calculated by density functional theory (DFT).     

Isoelectronic doping of graphdiyne with boron and nitrogen: stable configurations and band gap modification

Graphdiyne, consisting of sp- and sp(2)-hybridized carbon atoms, is a new member of carbon allotropes which has a natural band gap ~1.0 eV. Here, we report our first-principles calculations on the stable configurations and electronic structures of graphdiyne doped with boron-nitrogen (BN) units. We show that BN unit prefers to replace the sp-hybridized carbon atoms in the chain at a low doping rate, forming linear BN atomic chains between carbon hexagons. At a high doping rate, BN units replace first the carbon atoms in the hexagons and then those in the chains. A comparison study indicates that these substitution reactions may be easier to occur than those on graphene which composes purely of sp(2)-hybridized carbon atoms. With the increase of BN component, the band gap increases first gradually and then abruptly, corresponding to the transition between the two substitution motifs. The direct-band gap feature is intact in these BN-doped graphdiyne regardless the doping rate. A simple tight-binding model is proposed to interpret the origin of the band gap opening behaviors. Such wide-range band gap modification in graphdiyne may find applications in nanoscaled electronic devices and solar cells.     

Adsorption of hydrogen molecules on the platinum-doped boron nitride nanotubes

Adsorption of hydrogen molecules on platinum-doped single-walled zigzag (8,0) boron nitride (BN) nanotube is investigated using the density-functional theory. The Pt atom tends to occupy the axial bridge site of the BN tube with the highest binding energy of -0.91 eV. Upon Pt doping, several occupied and unoccupied impurity states are induced, which reduces the band gap of the pristine BN nanotube. Upon hydrogen adsorption on Pt-doped BN nanotube, the first hydrogen molecule can be chemically adsorbed on the Pt-doped BN nanotube without crossing any energy barrier, whereas the second hydrogen molecule has to overcome a small energy barrier of 0.019 eV. At least up to two hydrogen molecules can be chemically adsorbed on a single Pt atom supported by the BN nanotube, with the average adsorption energy of -0.365 eV. Upon hydrogen adsorption on a Pt-dimer-doped BN nanotube, the formation of the Pt dimer not only weakens the interaction between the Pt cluster and the BN nanotube but also reduces the average adsorption energy of hydrogen molecules. These calculation results can be useful in the assessment of metal-doped BN nanotubes as potential hydrogen storage media.     

Hybrid density functional theory band structure engineering in hematite

We present a hybrid density functional theory (DFT) study of doping effects in α-Fe(2)O(3), hematite. Standard DFT underestimates the band gap by roughly 75% and incorrectly identifies hematite as a Mott-Hubbard insulator. Hybrid DFT accurately predicts the proper structural, magnetic, and electronic properties of hematite and, unlike the DFT+U method, does not contain d-electron specific empirical parameters. We find that using a screened functional that smoothly transitions from 12% exact exchange at short ranges to standard DFT at long range accurately reproduces the experimental band gap and other material properties. We then show that the antiferromagnetic symmetry in the pure α-Fe(2)O(3) crystal is broken by all dopants and that the ligand field theory correctly predicts local magnetic moments on the dopants. We characterize the resulting band gaps for hematite doped by transition metals and the p-block post-transition metals. The specific case of Pd doping is investigated in order to correlate calculated doping energies and optical properties with experimentally observed photocatalytic behavior.     

Adsorption of transition-metal atoms on boron nitride nanotube: a density-functional study

Adsorption of transition atoms on a (8,0) zigzag single-walled boron nitride (BN) nanotube has been investigated using density-functional theory methods. Main focuses have been placed on configurations corresponding to the located minima of the adsorbates, the corresponding binding energies, and the modified electronic properties of the BN nanotubes due to the adsorbates. We have systemically studied a series of metal adsorbates including all 3d transition-metal elements (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) and two group-VIIIA transition-metal elements (Pd and Pt). We found that many transition-metal atoms can be chemically adsorbed on the outer surface of the BN nanotubes and that the adsorption process is typically exothermic. Upon adsorption, the binding energies of the Sc, Ti, Ni, Pd, and Pt atoms are relatively high (>1.0 eV), while those of V, Fe, and Co atoms are modest, ranging from 0.62 to 0.92 eV. Mn atom forms a weak bond with the BN nanotube, while Zn atom cannot be chemically adsorbed on the BN nanotube. In most cases, the adsorption of transition-metal atoms can induce certain impurity states within the band gap of the pristine BN nanotube, thereby reducing the band gap. Most metal-adsorbed BN nanotubes exhibit nonzero magnetic moments, contributed largely by the transition-metal atoms.     

Electronic Properties of Transition and Alkaline Earth Metal Doped CuS: A DFT Study

CuS is a unique semiconductor with potential in optoelectronics. Its unusual electronic structure, including a partially occupied valence band, and complex crystal structure with an S−S bond offer unique opportunities and potential applications. In this work, the use of doping to optimize the properties of CuS for various applications is investigated by density functional theory (DFT) calculations. Among the dopants studied, Ni, Zn, and Mg may be the most practical due to their lower formation energies. Doping with Fe, Ni, or Ca induces significant distortion, which may be beneficial for achieving materials with high surface areas and active states. Significantly, doping alters the conductor-like behavior of CuS, opening a band gap by increasing bond ionicity and reducing the S−S bond covalency. Thus, doping CuS can tune the plasmonic properties and transform it from a conductor to an intrinsic fluorescent semiconductor. Ni and Fe doping give the lowest band gaps (0.35 eV and 0.39 eV, respectively), while Mg doping gives the highest (0.86 eV). Doping with Mg, Ca, and Zn may enhance electron mobility and charge separation. Most dopants increase the anisotropy of electron-to-hole mass ratios, enabling device design that exploits directional-dependence for improved performance.     

Nitrogen monoxide storage and sensing applications of transition metal–doped boron nitride nanotubes: a DFT investigation

The structural properties, electronic properties, and adsorption abilities for nitrogen monoxide (NO) molecule adsorption on pristine and transition metal (TM = V, Cr, Mn, Nb, Mo, Tc, Ta, W, and Re) doping on B or N site of armchair (5,5) single-walled boron nitride nanotube (BNNT) were investigated using the density functional theory method. The binding energies of TM-doped BNNTs reveal that the Mo atom doping exhibits the strongest binding ability with BNNT. In addition, the NO molecule weakly interacts with the pristine BNNT, whereas it has a strong adsorption ability on TM-doped BNNTs. The increase in the adsorption ability of NO molecule onto the TM-doped BNNTs is due to the geometrical deformation on TM doping site and the charge transfer between TM-doped BNNTs and NO molecule. Moreover, a significant decrease in energy gap of the BNNT after TM doping is expected to be an available strategy for improving its electrical conductivity. These observations suggest that NO adsorption and sensing ability of BNNT could be greatly improved by introducing appropriate TM dopant. Therefore, TM-doped BNNTs may be a useful guidance to be storage and sensing materials for the detection of NO molecule.

     

Cu掺杂MgF2晶体的电子结构及光学特性

基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法,计算了纯的MgF2晶体和掺杂不同原子分数(2.08%,4.16%,6.24%)Cu的MgF2晶体结构、电学性质以及光学性质.结果表明:Cu的掺入导致MgF2晶体禁带宽度逐渐变窄,并且Cu掺杂使得MgF2晶体折射率和吸收峰增加,特别是在4eV附近区域出现了新吸收峰.同时也给出了引起体系性质变化的物理机制,Cu掺杂MgF2晶体在光电化学方面有着潜在的应用价值.     

Band gap engineering of bulk ZrO2 by Ti doping

It has been experimentally observed that Ti doping of bulk ZrO(2) induces a large red-shift of the optical absorption edge of the material from 5.3 to 4.0 eV [Livraghi et al., J. Phys. Chem. C, 2010, 114, 18553-18558]. In this work, density functional calculations based on the hybrid functional B3LYP show that Ti dopants in the substitutional position to Zr in the tetragonal lattice cause the formation of an empty Ti 3d band about 0.5 eV below the bottom of the conduction band. The optical transition level ε(opt)(0/-1) from the topmost valence state to the lowest empty Ti impurity state is found at 4.9 eV in a direct band gap of 5.7 eV. The calculated shift is consistent with the experimental observation. The presence of Ti(3+) species in Ti-doped ZrO(2), probed by means of electron paramagnetic resonance (EPR), is rationalized as the result of electron transfers from intrinsic defect states, such as oxygen vacancies, to substitutional Ti(4+) centers.     

Opening of Band Gap of Graphene with High Electronic Mobility by Codoping BN Pairs

Two-dimensional(2D) materials with a high density and low power consumption have become the most popular candidates for next-generation semiconductor electronic devices. As a prototype 2D material, graphene has attracted much attention owing to its stability and ultrahigh mobility. However, zero band gap of graphene leads to very low on-off ratios and thus limits its applications in electronic devices, such as transistors. Although some new 2D materials and doped graphene have nonzero band gaps, the electronic mobility is sacrificed. In this study, to open the band gap of graphene with high electronic mobility, the structure and property of BN-doped graphene were evaluated using first-principles calculations. The formation energies indicate that the six-membered BN rings doped graphene has the most favorable configuration. The band structures show that the band gaps can be opened by such type of doping. Also, the Dirac-cone-like band dispersion of graphene is mostly inhibited, ensuring high electronic mobility. Therefore, codoping BN into graphene might provide 2D materials with nonzero band gaps and high electronic mobility.     

Is the band gap of pristine TiO(2) narrowed by anion- and cation-doping of titanium dioxide in second-generation photocatalysts?

Second-generation TiO(2)-(x)D(x) photocatalysts doped with either anions (N, C, and S mostly) or cations have recently been shown to have their absorption edge red-shifted to lower energies (longer wavelengths), thus enhancing photonic efficiencies of photoassisted surface redox reactions. Some of the studies have proposed that this red-shift is caused by a narrowing of the band gap of pristine TiO(2) (e.g., anatase, E(bg) = 3.2 eV; absorption edge ca. 387 nm), while others have suggested the appearance of intragap localized states of the dopants. By contrast, a recent study by Kuznetsov and Serpone (J. Phys. Chem. B, in press) has proposed that the commonality in all these doped titanias rests with formation of oxygen vacancies and the advent of color centers (e.g., F, F(+), F(++), and Ti(3+)) that absorb the visible light radiation. This article reexamines the various claims and argues that the red-shift of the absorption edge is in fact due to formation of the color centers, and that while band gap narrowing is not an unknown occurrence in semiconductor physics it does necessitate heavy doping of the metal oxide semiconductor, thereby producing materials that may have completely different chemical compositions from that of TiO(2) with totally different band gap electronic structures.     

Synthesis and Photoluminescence of Cd-doped alpha-MnS Nanowires

Cd-doped alpha-MnS nanowires (av diam = 70 nm) were synthesized by the chemical vapor deposition of MnCl(2)/CdS powders. They all consisted of single-crystalline rock-salt MnS structures with the [111] growth direction. The X-ray diffraction pattern analysis indicates that 10% Cd doping would expand the lattice constants by 0.3%. As the content of Cd increases, the band edge emission band (2.9 eV) of photoluminescence becomes broader, and the Mn(2+) emission band (1.6 eV), which emerged at temperatures below approximately 150 K, decreases in intensity. The decay time of the 1.6 eV band decreases from 40 to 30 mus when the Cd doping is increased from 0 to 10%. In contrast to the bulk (T(N) = 150 K), the MnS nanowires were found to be paramagnetic with antiferromagnetic interactions. These distinctive magnetic properties of the nanowires have a strong correlation with their photoluminescence, which could be influenced by the nanosize effect and the Cd doping.     

A Response Surface Model to Predict and Experimentally Tune the Chemical,Magnetic and Optoelectronic Properties of Oxygen-Doped Boron Nitride**

Porous boron nitride (BN), a combination of hexagonal, turbostratic and amorphous BN, has emerged as a new platform photocatalyst. Yet, this material lacks photoactivity under visible light. Theoretical studies predict that tuning the oxygen content in oxygen-doped BN (BNO) could lower the band gap. This is yet to be verified experimentally. We present herein a systematic experimental route to simultaneously tune BNO's chemical, magnetic and optoelectronic properties using a multivariate synthesis parameter space. We report deep visible range band gaps (1.50–2.90 eV) and tuning of the oxygen (2–14 at.%) and specific paramagnetic OB₃ contents (7–294 a.u. g⁻¹). Through designing a response surface via a design of experiments (DOE) process, we have identified synthesis parameters influencing BNO's chemical, magnetic and optoelectronic properties. We also present model prediction equations relating these properties to the synthesis parameter space that we have validated experimentally. This methodology can help tailor and optimise BN materials for heterogeneous photocatalysis.     

Theoretical study of CeO2 and Ce2O3 using a screened hybrid density functional

The predicted structures and electronic properties of CeO(2) and Ce(2)O(3) have been studied using conventional and hybrid density functional theory. The lattice constant and bulk modulus for CeO(2) from local (LSDA) functionals are in good agreement with experiment, while the lattice parameter from a generalized gradient approximation (GGA) is too long. This situation is reversed for Ce(2)O(3), where the LSDA lattice constant is much too short, while the GGA result is in reasonable agreement with experiment. Significantly, the screened hybrid HSE functional gives excellent agreement with experimental lattice constants for both CeO(2) and Ce(2)O(3). All methods give insulating ground states for CeO(2) with gaps for the 4f band lying between 1.7 eV (LSDA) and 3.3 eV (HSE) and 6-8 eV for the conduction band. For Ce(2)O(3) the local and GGA functionals predict a semimetallic ground state with small (0-0.3 eV) band gap but weak ferromagnetic coupling between the Ce(+3) centers. By contrast, the HSE functional gives an insulating ground state with a band gap of 3.2 eV and antiferromagnetic coupling. Overall, the hybrid HSE functional gives a consistent picture of both the structural and electronic properties of CeO(2) and Ce(2)O(3) while treating the 4f band consistently in both oxides.     

The Electronic and Optical Properties of Au Doped Single-Layer Phosphorene

The electronic properties and optical properties of single and double Au-doped phosphorene have been comparatively investigated using the first-principles plane-wave pseudopotential method based on density functional theory. The decrease from direct band gap 0.78 eV to indirect band gap 0.22 and 0.11 eV are observed in the single and double Au-doped phosphorene, respectively. The red shifts of absorbing edge occur in both doped systems, which consequently enhance the absorbing of infrared light in phosphorene. Band gap engineering can, therefore, be used to directly tune the optical absorption of phosphorene system by substitutional Au doping.     

Aqueous synthesis of mercaptopropionic acid capped ZnSe QDs and investigation of photoluminescence properties with metal doping

An aqueous-based green route has been demonstrated for the preparation of ZnSe quantum dots (QDs) and doping of transition metals in the presence of thiol mercaptopropionic acid (MPA) as growth moderator by refluxing at 100 ​°C. The structure and morphology of synthesized ZnSe quantum dots have been investigated by using X-ray diffraction studies (XRD), Ultraviolet–Visible spectroscopy (UV–vis), Fourier Transform Infrared Spectroscopy (FTIR) and Photoluminescence (PL) Spectroscopy. XRD studies indicate the structure of the quantum dots is cubic with diameters in the range of 4–5 ​nm. Fourier Transform Infrared (FTIR) studies proves that MPA ligands were bound strongly on the ZnSe nanocrystal surface as thiolate. The band gap energy (E_g) was calculated to be 3.8 ​eV which is blue shifted from the standard value of bulk band gap (2.60–2.70eV. Photoluminescence spectra shows broad emission value ranging between 400 and 700 ​nm due to surface defects which has been reduced by doping with transition metals (Fe, Co, Ni, Cd) in aqueous medium. The effective passivation of trap luminescence is done by doping leading to increase in photoluminescence quantum yield specifically with nickel and cadmium doped ZnSe QDs.     

Electronic properties of vanadium-doped TiO2

The electronic properties of vanadium-doped rutile TiO(2) are investigated theoretically with a Hartree-Fock/DFT hybrid approach. The most common oxidation states (V(2+), V(3+), V(4+), and V(5+)) in different spin states are investigated and their relative stability is calculated. The most stable spin states are quartet, quintet, doublet, and singlet for V(2+), V(3+), V(4+), and V(5+) doping, respectively. By comparing the formation energy with respect to the parent oxides and gas-phase oxygen (ΔE), we conclude that V(4+) (ΔE=145.3 kJ mol(-1)) is the most likely oxidation state for vanadium doping with the possibility of V(5+) doping (ΔE=283.5 kJ mol(-1)). The energetic and electronic properties are converged with dopant concentrations in the range of 0.9 to 3.2%, which is within the experimentally accessible range. The investigation of electronic properties shows that V(4+) doping creates both occupied and unoccupied vanadium states in the band gap and V(5+) doping creates unoccupied states at the bottom of the conduction band. In both cases there is a significant reduction of the band gap by 0.65 to 0.75 eV compared to that of undoped rutile TiO(2).     

Rules of Boron–Nitrogen Doping in Defect Graphene Sheets: A First‐Principles Investigation of Band‐Gap Tuning and Oxygen Reduction Reaction Catalysis Capabilities

Introduction of defects and nitrogen doping are two of the most pursued methods to tailor the properties of graphene for better suitability to applications such as catalysis and energy conversion. Doping nitrogen atoms at defect sites of graphene and codoping them along with boron atoms can further increase the efficiency of such systems due to better stability of nitrogen at defect sites and stabilization provided by B?N bonding. Systematic exploration of the possible doping/codoping configurations reflecting defect regions of graphene presents a prevalent doping site for nitrogen‐rich BN clusters and they are also highly suitable for modulating (0.2–0.9 eV) the band gap of defect graphene. Such codoped systems perform significantly better than the platinum surface, undoped defect graphene, and the single nitrogen or boron atom doped defect graphene system for dioxygen adsorption. Significant stretching of the O?O bond indicates a lowering of the bond breakage barrier, which is advantageous for applications in the oxygen reduction reaction.     

Tuning the Properties of Tetracene-Based Nanoribbons by Fluorination and N-Doping

The structural stabilities and electronic properties are studied for the recently synthesized one-dimensional (1-D) tetracene-based nanoribbons with four-membered rings by using first-principles calculation. All three configurations (named as straight, zigzag, and armchair) are stable and exhibit an indirect band gap of 1.46, 0.73, and 0.32 eV, respectively. The band gaps can be effectively tuned by substituting hydrogen with fluorine atoms and by doping with nitrogen atoms. Substituting hydrogen with fluorine atoms leads to gradual decrease of the electronic band gaps of all configurations. Nitrogen doping changes the band gap from indirect to direct, displaying flexibility of tuning the band structure.     

锂离子电池LiTi0.25Fe0.75SO4F正极材料的电子结构

采用密度泛函理论平面波赝势的方法,计算了LiFeSO₄F和LiTi_0.25Fe_0.75SO₄F正极材料的电子结构。计算结果表明：当锂嵌入材料后,S、O和F的原子布居变化较小,电子主要填充在过渡金属的3d轨道,导致过渡金属被还原,成为电化学反应的活性中心。在嵌锂态中,锂和氧（氟）之间形成了离子键,而过渡金属（Ti和Fe）与氧（氟）之间则形成了共价键,S-O键的共价性最强。态密度的计算结果则表明：Ti和Fe均保持高自旋排列结构;LiFeSO₄F的两个自旋通道的带隙分别为2.88和2.29 eV,其导电性很差;Ti掺杂使体系的带隙消失,显著地提高了正极材料的导电性;LiTi_0.25Fe_0.75SO₄F系统中Ti-O和Ti-F键均比纯相中的Fe-O和Fe-F键的共价性更强,因此Ti掺杂材料具有更好的结构稳定性。