Lu掺杂AlN的电子结构和光学性质的第一性原理研究

为了探索AlN在光电器件中的潜在应用,采用第一性原理计算了不同Lu掺杂浓度(以原子分数x表示)的AlN(Al_1-xLu_xN)的电子结构和光学性质。研究结果表明,Al_1-xLu_xN的超胞体积随着Lu掺杂浓度的增加而增加,而带隙则相反。Al_1-xLu_xN的静态介电常数在低能区随掺杂浓度的提高而提高,随后逐渐趋向一致。随着Lu掺杂浓度的增加,反射率和吸收系数的峰值强度降低,峰值向较低能量方向移动。Al_1-xLu_xN的能量损失光谱表现出明显的等离子体振荡特性,且峰值低于本征AlN。Al_1-xLu_xN的光电导率在低能区随能量的增加而急剧增加。     

Lu掺杂AlN的电子结构和光学性质的第一性原理研究

为了探索 AlN在光电器件中的潜在应用,采用第一性原理计算了不同 Lu掺杂浓度(以原子分数 x表示)的 AlN(Al_1-xLu_xN)的电子结构和光学性质。研究结果表明,Al_1-xLu_xN的超胞体积随着Lu掺杂浓度的增加而增加,而带隙则相反。Al_1-xLu_xN的静态介电常数在低能区随掺杂浓度的提高而提高,随后逐渐趋向一致。随着Lu掺杂浓度的增加,反射率和吸收系数的峰值强度降低,峰值向较低能量方向移动。Al_1-xLu_xN的能量损失光谱表现出明显的等离子体振荡特性,且峰值低于本征AlN。Al_1-xLu_xN的光电导率在低能区随能量的增加而急剧增加。     

19F coupling constants and chemical shifts in some dimethylamino and alkoxy derivatives of tellurium hexafluoride,cis TeF4XY

The spectra of A₂BC spin systems provided by the ¹⁹F nuclei in cis (RO) (MeO)TeF₄ and (RO) (Me₂N)TeF₄ (R = Me, Et, Pr, i-Pr) have been recorded and analysed. The geminal coupling constants ²J(F,F) range from 137–174 Hz and trends in the ¹⁹F chemical shifts permit complete assignment of the resonances. Stereospecific coupling between ¹⁹F and the protons of the N-methylamino groups is also observed.     

Investigation of opto-dielectric properties of Ti-doped Ga2O3 thin films

Several Ti-incorporated Ga-oxide (Ga₂O₃) thin films with different amounts of Ti contents have been prepared by vacuum evaporation method on glass and silicon substrates. The Ti incorporation level was measured with energy dispersion X-ray spectroscopy (EDX) method. The crystalline structure of the prepared films was determined with X-ray diffraction method. Experimental data indicate that Ti⁴⁺ ions doped in host Ga₂O₃ form solid solutions (SS) even with so large Ti% content ∼10.4% wt. All the prepared solid solutions have the known orthorhombic (ɛ-phase) phase of Ga₂O₃. The doping controls the optical and electrical properties of the host Ga₂O₃. It was found that the bandgap of the prepared undoped Ga oxide is 5.23 eV, which was decreased monotonically with increasing of Ti doping level so that it is possible to engineer the bandgap. Furthermore, the electrical measurements show that with Ti doping, it is possible to turn the high-k Ga oxide into low-k dielectric material. The optical sensitivity of the capacitance, dissipation factor, and ac-conductance of the Ga₂O₃:Ti films grown on Si was studied as a function of Ti-doping level. It was observed that the prepared Ga₂O₃:Ti film with 6–10% doping level has the highest photosensitivity among the other samples.     

氯钯共掺对Cs2TiBr6光电性能影响的第一性原理计算

全无机无铅钙钛矿Cs₂TiBr₆具有光电特性良好、带隙可调和环境友好等优点,是一种潜力巨大的光吸收材料。为改善Cs₂TiBr₆的相关性能,我们采用基于第一性原理的方法,针对Pd、Cl掺杂的Cs₂TiBr₆钙钛矿结构进行了研究。结果表明,用Pd取代Ti后产生杂质带,将原来间接带隙的Cs₂TiBr₆转变为直接带隙材料。用25.0%Pd掺杂后,晶体带隙值降低26%,掺杂后的晶体在320～415 nm近紫外光区吸收能力加强约50%,在645～900 nm的红外光区及近红外光区的光吸收能力加强约134%。在此基础上,将Cl与25.0%Pd共掺杂时,Cl掺杂不仅可以把Pd的形成能在单掺的基础上减小约9%,而且Cl的不同掺杂位置对材料的光电性能也有一定的影响。     

In Situ Growth of MnO2 Nanosheets on N‐Doped Carbon Nanotubes Derived from Polypyrrole Tubes for Supercapacitors

Nitrogen‐doped porous carbon nanotubes@MnO₂ (N‐CNTs@MnO₂) nanocomposites are prepared through the in situ growth of MnO₂ nanosheets on N‐CNTs derived from polypyrrole nanotubes (PNTs). Benefiting from the synergistic effects between N‐CNTs (high conductivity and N doping level) and MnO₂ nanosheets (high theoretical capacity), the as‐prepared N‐CNTs@MnO₂‐800 nanocomposites show a specific capacitance of 219 F g^?1 at a current density of 1.0 A g^?1, which is higher than that of pure MnO₂ nanosheets (128 F g^?1) and PNTs (42 F g^?1) in 0.5 m Na₂SO₄ solution. Meanwhile, the capacitance retention of 86.8 % (after 1000 cycles at 10 A g^?1) indicates an excellent electrochemical performance of N‐CNTs@MnO₂ prepared in this work.     

Electrochemical Fabrication and Properties of Highly Ordered Fe‐Doped TiO2 Nanotubes

Highly‐ordered Fe‐doped TiO₂ nanotubes (TiO₂nts) were fabricated by anodization of co‐sputtered Ti–Fe thin films in a glycerol electrolyte containing NH₄F. The as‐sputtered Ti–Fe thin films correspond to a solid solution of Ti and Fe according to X‐ray diffraction. The Fe‐doped TiO₂nts were studied in terms of composition, morphology and structure. The characterization included scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray diffraction, UV/Vis spectroscopy, X‐ray photoelectron spectroscopy and Mott–Schottky analysis. As a result of the Fe doping, an indirect bandgap of 3.0 eV was estimated using Tauc’s plot, and this substantial red‐shift extends its photoresponse to visible light. From the Mott–Schottky analysis, the flat‐band potential (E_fb) and the charge carrier concentration (N_D) were determined to be ?0.95 V vs Ag/AgCl and 5.0 ×10¹⁹ cm^?3 respectively for the Fe‐doped TiO₂nts, whilst for the undoped TiO₂nts, E_fb of ?0.85 V vs Ag/AgCl and N_D of 6.5×10¹⁹ cm^?3 were obtained.     

Characterization and optical properties of mechanochemically synthesized molybdenum-doped rutile nanoparticles and their electronic structure studies by density functional theory

The optical and electronic properties of molybdenum (Mo) doped rutile TiO₂ prepared by the mechanochemical method were studied both experimentally and using density functional theory (DFT). The synthesized nanoparticles were characterized by XRD, TEM, EDS-MAP, and XPS. The XRD results showed the successful incorporation of Mo in the rutile crystal lattice. High-resolution TEM images illustrated a decreasing trend in the (110) d-spacing for samples doped up to 3 at%. The shift toward higher binding energies in the XPS spectra was due to the higher oxidization tendencies of Mo⁵⁺ and Mo⁶⁺ substituted in Ti⁴⁺ sites. The optical behavior of samples was examined by UV–Vis and photoluminescence spectroscopy. The bandgap energy value of rutile was reduced from 3.0 eV to 2.4 eV by 2 at% Mo doping. The DFT calculations showed a reduction of bandgap energy value of rutile to 2.35 eV with 2 at% Mo, which is in harmony with the experimental results. The creation of energy states below the conduction band because of Mo doping was identified as the reason for reducing the bandgap energy and photoluminescence emission of rutile.     

New Insights into the Band‐Gap Narrowing of (N,P)‐Codoped TiO2 from Hybrid Density Functional Theory Calculations

The electronic properties of anatase‐TiO₂ codoped by N and P at different concentrations have been investigated via generalized Kohn–Sham theory with the Heyd–Scuseria–Ernzerhof (HSE06) hybrid functional for exchange‐correlation in the context of density functional theory. At high doping concentrations, we find that the high photocatalytic activity of (N, P)‐codoped anatase TiO₂ vis‐à‐vis the N‐monodoped case can be rationalized by a double‐hole‐mediated coupling mechanism [Yin et al., Phys. Rev. Lett. 2011, 106, 066801] via the formation of an effective N? P bond. On the other hand, Ti³⁺ and Ti⁴⁺ ions’ spin double‐exchange results in more substantial gap narrowing for larger separations between N and P atoms. At low doping concentrations, double‐hole‐coupling is dominant, regardless of the N? P distance.     

Structure and Properties of Tetracyanomanganate(II), [MnII(CN)4]2−, The First Paramagnetic Tetrahedral Cyanometalate Complex

A place in the sun for solutions of [(Ph₃P)₂N]₂[Mn(CN)₆] provides—by photochemical degradation—[Mn^II(CN)₄]²⁻ ions, the only homoleptic cyanide complex ion that is high spin (structure depicted on the right). Magnetic measurements indicate a high-spin ⁶A₁ ground state (S=5/2), and the cyanide ligands are virtually entirely σ donors, without significant binding contributions from d–π* back-bonding.     

Secondary Binding Interactions in a Synthetic Receptor for Trimethyllysine

We have systematically studied how secondary interactions with neighboring lysine (Lys) and arginine (Arg) residues influence the binding and selectivity of the synthetic receptor A₂N for trimethyllysine (Kme₃). Multiple secondary binding sites on A₂N are formed by carboxylates rigidly positioned over aromatic rings, a motif that has been shown to stabilize salt bridges. We varied the spacing between Kme_X (X=0, 3) and an ancillary Lys or Arg and measured binding by isothermal titration calorimetry (ITC). These studies revealed that both neighboring residues improve the binding of A₂N to Kme_X by approximately 1 kcal mol^?1, with little influence of the spacing. Nonetheless, the improvement in affinity caused by Arg is enthalpically driven, while for Lys it is entropically driven, suggesting different mechanisms by which the residues interact with the secondary binding site.     

Single‐crystal neutron‐diffraction study of 3.4% Zn‐doped (ND4)2[Cu(D2O)6](SO4)2 at 20 K

Doping the perdeuterated ammonium copper Tutton salt (ND₄)₂[Cu(D₂O)₆](SO₄)₂ [perdeuterated diammonium hexa­aqua­copper(II) bis­(sulfate)] with Zn leads to a change in the structure from dimorph A (low density) to dimorph B (high density). This change, which accompanies a switch in the direction of the Jahn–Teller distortion, had previously been observed to occur with substitution of Zn²⁺ at the Cu²⁺ site of between 1.3 (A) and 3.4% (B). In this study, the single‐crystal neutron‐diffraction analysis of (ND₄)₂[(Cu/Zn)(D₂O)₆](SO₄)₂ at 20 K, with 3.4% Zn doping and a deuterium substitution of 85% on the H‐atom sites, reveals that the structure is entirely of type B, with the Cu/Zn site at an inversion centre and with no evidence of disorder or unusual atomic displacement parameters that might occur near a phase transition boundary.     

Comparative computational investigation of N and F substituted polyoxoanionic compounds: The case of Li2FeSiO4 electrode material

First principles calculations are used to anticipate the electrochemistry of polyoxoanionic materials consisting of XO_{4 − y}A_y (A = F, N) groups. As an illustrative case, this work focuses on the effect of either N or F for O substitution upon the electrochemical properties of Li₂FeSiO₄. Within the Pmn2₁–Li₂FeSiO₄ structure, virtual models of Li₂Fe₂^2.5+SiO_3.5N_0.5 and Li_1.5Fe²⁺SiO_3.5F_0.5 have been analyzed. We predict that the lithium deinsertion voltage associated to the Fe^3+/Fe⁴⁺ redox couple is decreased by both substituents. The high theoretical specific capacity of Li₂FeSiO₄ (330 mAh/g) could be retained in N-substituted silicates thanks to the oxidation of N³⁻ anions, whilst Li_1.5Fe²⁺SiO_3.5F_0.5 has a lower specific capacity inherent to the F substitution. Substitution of N/F for O will respectively improve/worsen the electrode characteristics of Li₂FeSiO₄.     

Systematic Tuning and Switching of Neutral and Ionic Phases in a Donor–Acceptor Chain Compound by Doping with Less‐Active Donors and by Pressure Application

The temperature‐induced stepwise neutral–ionic (N–I) phase transition in the covalently bonded donor–acceptor chain compound [Ru₂(2,3,5,6‐F₄PhCO₂)₄DMDCNQI] ? 2(p‐xylene) (2,3,5,6‐F₄PhCO₂^?=2,3,5,6‐tetrafluorobenzoate; DMDCNQI=2,5‐dimethyl‐N,N′‐dicyanoquinodiimine) was systematically tuned over a wide temperature range using two techniques: 1) A chemical technique based on doping with a less‐active donor unit [Ru₂^II,II(F₅PhCO₂)₄] (F₅PhCO₂^?=pentafluorobenzoate), thereby providing an isostructural doped series [{Ru₂^II,II(2,3,5,6‐F₄PhCO₂)₄}_1?x{Ru₂^II,II(F₅PhCO₂)₄}_xDMDCNQI] ? 2(p‐xylene), with x=0.06, 0.10, 0.21, and 0.24; and 2) a physical technique, which was the application of hydrostatic pressure to the doped compounds. The stepwise N–I transition observed in the original compound was systematically varied in terms of the viewpoints of both transition temperature and transition features (stepwise or monotonic) dependent on the amount of dopants x. Application of pressure efficiently tuned the N–I transitions, with the oxidation phases being dramatically modified by applying only weak pressure up to 4 kbar. Even in cases that led to N–I transitions in small domains of the chains at ambient pressure, the application of pressure caused an expansion of the domains that enabled N–I transitions, finally leading to a complete change in the oxidation state of the chains, from neutral to ionic, accompanied by a change from a paramagnetic state to a ferrimagnetically ordered state.     

Unusual hydrogen bonding in L‐cysteine hydrogen fluoride

L‐Cysteine hydrogen fluoride, or bis(L‐cysteinium) difluoride–L‐cysteine–hydrogen fluoride (1/1/1), 2C₃H₈NO₂S⁺·2F⁻·C₃H₇NO₂S·HF or L‐Cys⁺(L‐Cys...L‐Cys⁺)F⁻(F⁻...H—F), provides the first example of a structure with cations of the `triglycine sulfate' type, i.e.A⁺(A...A⁺) (where A and A⁺ are the zwitterionic and cationic states of an amino acid, respectively), without a doubly charged counter‐ion. The salt crystallizes in the monoclinic system with the space group P2₁. The dimeric (L‐Cys...L‐Cys⁺) cation and the dimeric (F⁻...H—F) anion are formed via strong O—H...O or F—H...F hydrogen bonds, respectively, with very short O...O [2.4438 (19) Å] and F...F distances [2.2676 (17) Å]. The F...F distance is significantly shorter than in solid hydrogen fluoride. Additionally, there is another very short hydrogen bond, of O—H...F type, formed by a L‐cysteinium cation and a fluoride ion. The corresponding O...F distance of 2.3412 (19) Å seems to be the shortest among O—H...F and F—H...O hydrogen bonds known to date. The single‐crystal X‐ray diffraction study was complemented by IR spectroscopy. Of special interest was the spectral region of vibrations related to the above‐mentioned hydrogen bonds.     

Rational Design of a Confacial Pentaoctahedron: Anisotropic Exchange in a Linear ZnIIFeIIIFeIIIFeIIIZnII Complex

The first confacial pentaoctahedron comprised of transition metal ions namely Zn^IIFe^III_AFe^III_BFe^III_AZn^II has been synthesized by using a dinucleating nonadentate ligand. The face-sharing bridging mode enforces short Zn^II⋅⋅⋅Fe^III_A and Fe^III_A⋅⋅⋅Fe^III_B distances of 2.83 and 2.72 Å, respectively. Ab-initio CASSCF/NEVPT2 calculations provide significant negative zero-field splittings for Fe^III_A and Fe^III_B with |D_A|>|D_B| with the main component along the C₃ axis. Hence, a spin-Hamiltonian comprised of anisotropic exchange, zero-field, and Zeeman term was employed. This allowed by following the boundary conditions from the theoretical results the simulation in a theory-guided parameter determination with J^xy=+0.37, J^z=−0.32, D_A=−1.21, E_A=−0.24, D_B=−0.35, and E_B=−0.01 cm⁻¹ supported by simulations of high-field magnetic Mössbauer spectra recorded at 2 K. The weak but ferromagnetic Fe^III_AFe^III_B interaction arises from the small bridging angle of 84.8° being at the switch from anti- to ferromagnetic for the face-sharing bridging mode.     

Coupled Vacancy Pairs in Ni-Doped CoSe for Improved Electrocatalytic Hydrogen Production Through Topochemical Deintercalation

Vacancy engineering plays vital role in the design of high-performance electrocatalysts. Here, we introduced coupled cation-vacancy pairs in Ni-doped CoSe to achieve boosted hydrogen evolution reaction (HER) activity through a facile topochemical intercalation approach. Adjacent Co vacancy pairs and heteroatom Ni doping contribute together for the upshift of the Se 4p_z orbital, which induces larger overlap between the Se 4p and H 1s orbitals. As a result, the free energy of H adsorption can be lowered significantly. With an advanced HER activity of 185.7 mV at 10 mA cm⁻², this work provides new direction and guidance for the design of novel electrocatalysts.     

On the electronic structure of N2H2. A possible triplet ground state in diazines

Within the frame of closed-shell and restricted open-shell ab initio SCF calculations 1,1-dihydrodiazine H₂N=N has a triplet ground state, ³A₂. This result, though not unsuspected from simple valence theory, is critically discussed and possible chemical implications are briefly mentioned.The ab initio calculations were performed at the IBM Research Center, San Jose, California.     

Copper(II) complexes with derivatives of salen and tetrahydrosalen: a spectroscopic, electrochemical and structural study

Salen type complexes, CuL, the corresponding tetrahydrosalen type complexes, Cu[H₄]L, and N,N′-dimethylated tetrahydrosalen type complexes, Cu[H₂Me₂]L, were investigated using cyclic voltammetry, and electronic and ESR spectroscopy. In addition, the analogous copper(II) complexes with a derivative of the tetradentate ligand ‘salphen’ [salphen=H₂salphen=N,N′-disalicylidene-1,2-diaminobenzene] were studied. Solutions of CuL, Cu[H₄]L and Cu[H₂Me₂]L are air-stable at ambient temperature, except for the complex Cu(^tBu, Me)[H₄]salphen [H₂(^tBu, Me)[H₄]salphen=N,N′-bis(2-hydroxy-3-tert-butyl-5-methylbenzyl)-1,2-diaminobenzene]. Cu(^tBu, Me)[H₄]salphen interacts with dioxygen and the ligand is oxidatively dehydrogenated (–CH₂–NH–→–C=N–) to form Cu(^tBu, Me)[H₂]salphen and finally, in the presence of base, Cu(^tBu, Me)salphen. X-ray structure analysis of Cu(^tBu, Me)[H₂Me₂]salen confirms a slightly tetrahedrally distorted planar geometry of the CuN₂O₂ coordination core. The complexes were subjected to spectrophotometric titration with pyridine, to determine the equilibrium constants for adduct formation. It was found that the metal center in the complexes studied is only of weak Lewis acidity. In dichlormethane, the oxidation Cu(II)/Cu(III) is quasireversible for the CuL type complexes, but irreversible for the Cu[H₄]L and Cu[H₂Me₂]L type. A poorly defined wave was observed for the irreversible reduction Cu(II)/Cu(I) at potentials less than −1.0 V. The ESR spectra of CuL at both 77 K and room temperature reveal that very well resolved lines can be attributed to the interaction of an unpaired electron spin with the copper nuclear spin, ¹⁴N donor nuclei and to a distant interaction with two equivalent protons [A^Cu(iso)≈253 MHz, A^N(iso)≈43 MHz, A^N(iso)≈20 MHz]. These protons are attached to the carbon atoms adjacent to the ¹⁴N nuclei. In contrast to CuL, the number of lines in the spectra of the complexes Cu[H₄]L and Cu[H₂Me₂]L is greatly reduced. At room temperature, only a quintet with a considerably smaller nitrogen shf splitting constant [A^N(iso)≈27 MHz] is observed. Both factors, planarity and conjugation, are thus essential for the observation of distant hydrogen shf splitting in CuL. Due to the C=N bond hydrogenation, the coordination polyhedra of the complexes Cu[H₄]L and Cu[H₂Me₂]L is more flexible and more sensitive to ligand modification than that of CuL. The electron-withdrawing effect of the phenyl ring of the phenylenediamine bridge is reflected in a reduction of the copper hyperfine coupling constants in Cu(^tBu, Me)[H₄]salphen and Cu(^tBu, Me)[H₂Me₂]salphen complexes [A^Cu(iso)≈215 MHz].