静水压对立方钙钛矿CsSnX3(X=I, Br, Cl)光电性质的第一性原理探究

全无机无铅卤化物钙钛矿已经成为重要的新一代太阳能电池材料.采用密度泛函理论的第一性原理研究了不同静水压下CsSnX₃(X=I, Br, Cl)材料的晶体结构,电子结构和光学性能,并分析了其内在联系.结果表明施加静水压可使材料中Sn-X键长减小,使原子之间的耦合增强,带隙值减小,且随着卤族元素半径的增大,压力效应越明显;随着压力的增加,材料的吸收系数和复折射率增大,吸收光谱出现红移现象,在可见光区和近红外光区吸收增强.相比CsSnBr₃和CsSnCl₃,CsSnI₃在可见光区吸收最佳且受压力作用影响最小,更适用于钙钛矿太阳能电池材料.     

50~250 keV质子入射SiC和Si靶时的电子发射特性研究

在中国科学院近代物理研究所兰州重离子加速器国家实验室测量了能量范围为50~250 keV 的质子入射碳化硅靶和硅靶表面的电子发射产额。实验结果发现,两种半导体靶材的电子发射产额随质子入射能量变化趋势均与作用过程中电子能损随质子入射能量的变化趋势相似。通过分析电子发射的能量来源,发现实验中电子发射产额主要由动能电子发射产额贡献,势能电子发射产额可以忽略不计。两种靶材的电子发射产额均近似地正比于质子入射靶材过程中的电子能损,比例系数B随入射能量略有变化。     

Electronic structure and thermochemistry for monocarbides MC,MC+ and MC− (M=Zn,Cd, Hg): CCSD(T) and DFT works

In this work, the ab-initio coupled cluster CCSD(T) method and the B3LYP, BP91W and CAM-B3LYP functional of DFT method in conjunction with the aug-cc-pVTZ-PP basis have been applied to study the group 12 monocarbides MC, MC⁺ and MC^?. The potential energy curves (PECs) for the three electronic states ³Σ^?, ⁵Σ^? and ¹Δ of the MC and the two states ²∑^- and ⁴∑^- for the MC⁺ cations and MC^? anions have been investigated. In addition, Bond distance Re, transition energy Te, vibrational frequency ω_e, ionization energy IE, electron affinity EA, dipole moment μ, dissociation energy D₀ and heat formation ΔH°f₀/ΔH°f₂₉₈, were determined for each species. The analysis of the dissociation energy for ZnC, CdC and HgC shows the decrease in the stability of the monocarbides from Zn to Hg. For ΔH°f₀/ΔH°f₂₉₈ values of MC, which are not known experimentally or theoretically, we recommend the following CCSD(T) predictions of ZnC, CdC and HgC: 181.3/178.54, 180.65/178.4 and 175.35/174.71 kcal/mol respectively. Comparing the three functionals with the CCSD(T) results, the CAM-B3LYP functional shows excellent predictive agreement for the various properties of the group 12 monocarbides.     

异原子配位结构碳基单原子电催化剂结构与性能相关性的研究进展

单原子催化剂是一类以相互孤立的单个金属原子作为催化活性中心的、 具有高原子经济性及高活性的负载型催化剂, 被广泛应用于能源电催化领域. 近年来, 通过使用两种或两种以上原子与活性中心金属原子配位, 构建具有异原子配位结构的单原子材料, 展现了优异的电催化性能. 研究发现, 这种不对称的配位结构有效调控了中心金属原子的电子结构, 优化了催化反应的吸附和脱附能量, 提高了电催化的性能. 本文综合评述了具有异原子配位结构碳基单原子电催化剂的合成策略、 表征技术与方法, 以及在前沿能源电催化应用中的催化剂性能与结构之间的构效关系, 并展望了异原子配位结构碳基单原子电催化剂的研究前景.     

蚕丝基智能纤维及织物：潜力、现状与未来展望

纤维及织物因具有良好的柔性、透气性以及适宜的力学性能而成为人们日常生活必不可少的材料。随着柔性电子器件的快速发展,纤维及织物在其自身优势的基础上,开始被人们赋予智能化特征,使得智能纤维和织物逐渐在可穿戴领域占据一席之地。天然蚕丝具有产量大、机械性能优异和生物可降解的优势。近年来,面向智能应用的蚕丝基纤维与织物逐渐发展,被用于传感、致动、光学器件、能量收集和储能等领域。本文将首先介绍天然蚕丝的层级结构和性能,并介绍各种形貌结构的再生蚕丝材料;然后根据其在智能纤维及织物中应用领域的不同,详细阐述蚕丝基智能纤维及织物的制备方法、性能及工作机制;最后讨论进一步发展所面临的挑战与机会,并对未来前景进行展望。     

Gelation study of high processability and high reliability ternary systems based on benzoxazine, epoxy, and phenolic resins for an application as electronic packaging materials

 Fourier transform mechanical spectroscopy technique (FTMS) is utilized as a powerful tool to study the sol-gel transition of covalent bonded polymeric network. Winter and Chambon criteria resulting from the fractal-geometry characteristic of the gel networks allow the determination of the gel point with only single experiment using this technique. The gelation behaviors of low melt viscosity ternary systems of benzoxazine, epoxy, and phenolic resins are investigated and analyzed by the technique in order to study the effect of epoxy diluent on the rheological property development before and after the gel points. The gel time at 140 °C ranges from 5 min to 30 min and less than 5 min at 180 °C for all tested ternary system compositions. The gelation of the ternary mixture shows an Arrhenius-type behavior and the gel time can be well-predicted by the Arrhenius equation. Received: 23 November 1999 Accepted: 2 January 2001     

Nondestructive monitoring,kinetics and antimicrobial properties of ultrasound technology applied for surface decontamination of bacterial foodborne pathogen in pork

In this study, electronic nose (E-nose) and Hyperspectral Imaging (HSI) was employed for nondestructive monitoring of ultrasound efficiency (20KHZ) in the inactivation of Salmonella Typhimurium, and Escherichia coli in inoculated pork samples treated for 10, 20 and 30 min.Weibull, and Log-linear model fitted well (R² ≥ 0.9) for both Salmonella Typhimurium, and Escherichia coli inactivation kinetics. The study also revealed that ultrasound has antimicrobial effects on the pathogens. For qualitative analysis, unsupervised (PCA) and supervised (LDA) chemometric algorithms were applied. PCA was used for successful sample clustering and LDA approach was used to construct statistical models for the classification of ultrasound treated and untreated samples. LDA showed classification accuracies of 99.26%,99.63%,99.70%, 99.43% for E-nose - S. Typhimurium, E-nose -E. coli, HSI - S. Typhimurium and HSI -E. coli respectively. PLSR quantitative models showed robust models for S. Typhimurium- (E-nose Rp² = 0.9375, RMSEP = 0.2107 log CFU/g and RPD = 9.7240 and (HSI Rp² = 0.9687 RMSEP = 0.1985 log CFU/g and RPD = 10.3217) and E. coli -(E-nose -Rp² = 0.9531, RMSEP = 0.2057 log CFU/g and RPD = 9.9604) and (HIS- Rp² = 0.9687, RMSEP = 0.2014 log CFU/g and RPD = 10.1731).This novel study shows the overall effectiveness of applying E-nose and HSI for in-situ and nondestructive detection, discrimination and quantification of bacterial foodborne pathogens during the application of food processing technologies like ultrasound for pathogen inactivation.     

X-ray absorption and Mössbauer spectra,and microwave absorption of (Co,Mn)-doped SrFe12O19 hexaferrites

Polycrystalline SrCo_1·2Fe_10·8O₁₉ (SCFO) and SrMn_1·2Fe_10·8O₁₉ (SMFO) samples were prepared by the normal ceramic technique. Powder X-ray diffraction patterns indicated the crystallization in the M-type hexaferrite structure of the samples. X-ray absorption analyses proved Co²⁺ and Mn^3+,4+ ions existing in SCFO and SMFO, respectively. Though Fe³⁺ is dominant in both the compounds, small amounts of Fe²⁺ and Fe⁴⁺ are present in SCFO and SMFO, respectively. Mössbauer spectra analyses also confirmed the dominance of Fe³⁺ in both the samples. Additionally, Fe³⁺ ions in the 12 k, 4f₁, 4f₂, and 2a sites could be attributed to the high-spin state (S = 5/2). A large QS value for the sextet assigned to the 2b site indicated that in this case Fe³⁺ could be in the low-spin state (S = 1/2) or there was the addition of Fe²⁺ (or Fe⁴⁺) when Fe in SrFe₁₂O₁₉ was partially replaced by Co²⁺ (or Mn^3+,4+). The mixture of transition-metal ions with different oxidation states influenced the magnetic properties and microwave shielding ability. At frequencies f = 10–18 GHz, we have found SCFO showing the lowest reflection loss with RL = −11.1 dB at 13.2 GHz and the thickness t = 2.2 mm. With an absorption bandwidth of 0.7 GHz, and about 92% microwave energy being absorbed, SCFO is considered as a potential candidate for microwave shielding applications.     

Field-induced spin-polarized electronic and optical properties of armchair stanene nanoribbons

Electronic and optical properties of armchair stanene nanoribbons are studied within the $s{p}^3$ tight-binding model including spin-orbit coupling in the presence of in-plane electric field. Electric field strongly modulates energy dispersions leading to a zero-gap transition, shift in edge-states, and exhibition of spin-splitting states. Then, the complex dielectric functions in the long wavelength limit is calculated from the gradient approximation. More field-induced transition channels exhibit richer optical spectra which further reveal spin-polarized feature at low frequency. Prominent plasmons in loss spectra come from π–σ mixing orbital. The plasmon peak frequency and height are tuned by field strength. Also, the threshold plasmon frequency linearly decreases as electric field increases and it vanishes at critical field. The reflectance exhibits oscillatory behaviors and shows dip structures with sharp plasmon edge, undergoing a red-shift with increasing field. The calculated results fully show that field-modulations of electronic and optical properties strongly depend on nanoribbon's geometry.     

Electronic transport on graphene armchair-edge nanoribbons with Fermi velocity and potential barriers

The transport properties of Dirac fermions through armchair-edge graphene nanoribbons (AGNRs) with a single and double rectangular Fermi velocity $v_F$ and electrostatic potential U barriers is investigated. We employ a transfer matrix method (TMM) to compute the transmission coefficient of the full set of propagating mode which is used to obtain the conductance and Fano factor spectra for both metallic and semiconducting nanoribbons. We show that a reduced Fermi velocity within the barrier region can partially suppress the backscattering resulting from the electrostatic potential. In a double barrier structure, the emergence of high-order transmitting modes is shown to substantially reduce the Fano factor in the spectral region around U. These results indicate that the simultaneous tuning of $v_F$ and U in barrier regions can be explored to control the electronic transport in graphene-based nanoelectronics structures.