调制掺杂ZnSe/BeTe Ⅱ型量子阱结构中的内秉电场和新型带电激子

报道了调制掺杂的ZnSe/BeTe/ZnSe Ⅱ型量子阱(type-Ⅱ QW)在低温(2—5 K)条件下的光致发光(PL),光致发光激发(PLE)和磁性光致发光(magneto-PL)光谱的实验结果.　观察到非掺杂样品的PL有两个很强的主发光峰而掺杂样品只有一个的奇异发光.　PL直线偏振度和PLE的测量结果都表明了这些空间间接型跃迁PL是来自两个异质结界面的贡献,非掺杂样品的两个主发光峰的分离则是起因于QW结构中的内秉电场(built-in electric field).在平行于QW生长方向的强磁场中, 关键词： 光致发光 二维电子气 带电激子 Ⅱ型量子阱     

Isotopic fingerprint of electron-phonon coupling in high-Tc cuprates

Angle-resolved photoemission spectroscopy with low-energy tunable photons along the nodal direction of oxygen isotope substituted Bi(2)Sr(2)CaCu(2)O(8+delta) reveals a distinct oxygen isotope shift near the electron-boson coupling "kink" in the electronic dispersion. The magnitude (a few meV) and direction of the kink shift are as expected due to the measured isotopic shift of phonon frequency, and are also in agreement with theoretical expectations. This demonstrates the participation of the phonons as dominant players, as well as pinpointing the most relevant of the phonon branches.     

Electronic processes in NO dimerization on Ag and Cu clusters: DFT and MRMP2 studies

Experimentally observed NO dimerization on Cu and Ag surfaces is surprising because binding energy of NO dimer is very small in gas phase. MRMP2, MP2 to MP4, CCSD(T), and DFT studies of NO dimerization on Ag₂ and Cu₂ clusters disclosed that the CCSD(T) method could be applied to this reaction on Ag₂ and Cu₂ unlike NO dimerization in gas phase which exhibits significantly large nondynamical electron correlation effect. Charge-transfer (CT) from Ag₂ and Cu₂ to NO moieties plays important role in N N bond formation between two NO molecules. This CT considerably decreases nondynamical correlation effect. Also, the DFT method could be applied to this NO dimerization, if appropriate DFT functional is used; all pure functionals examined here and most of the hybrid functionals underestimated the activation barrier (E_a), while only ωB97X provided E_a similar to CCSD(T)-calculated value. NO dimerization on similar Cu₂ and Cu₅ needs moderately larger E_a than those on Ag₂ and Ag₅, because frontier orbital participating in the CT exists at lower energy in Cu₂ and Cu₅ than in Ag₂ and Ag₅. The E_a decreases in the order Ag₂ >> Ag₃₈ > Ag₇ ∼ Ag₅ and the reaction energy (ΔE) is positive (endothermic) in Ag₂ but significantly negative in Ag₃₈, Ag₇, and Ag₅, indicating that various Ag clusters could be effective for NO dimerization except for Ag₂. The decreasing order of E_a and increasing order of exothermicity are attributed to increasing order of the frontier orbital energy of Ag₂ < Ag₃₈ < Ag₇ ∼ Ag₅. © 2018 Wiley Periodicals, Inc.     

Dioxacyclophanes as a Scaffold for Silicon-based Circularly Polarized Luminescent Materials

Planar chiral dioxacyclophanes were designed and synthesized as a key scaffold for materials with circularly polarized luminescence (CPL). Representative planar chiral 1,12-dioxa[12](1,4)naphthaleneophane-derived organosilane compounds (?)-(R)-1, (+)-(R)-2, and (?)-(R)-3 were prepared by (+)-sparteine-mediated aryl metalation and an electrophilic reaction with chlorosilanes. The absolute configurations of the planar chirality were determined in the R form by single-crystal X-ray analysis. Optically active compound (+)-(R)-2 exhibited blue fluorescence and a CPL signal with a dissymmetry factor (g_lum value) of 0.001 in solution. The electronic structure was corroborated by DFT and TD-DFT calculations rationalizing the observed spectroscopic properties.     

Effect of clay surface on aldehyde-diol equilibrium

The effect of clay surface on the equilibrium between aldehyde and diol was examined by using 4-formyl-1-methylpyridin-1-ium chloride (MPy⁺) as a substrate. MPy⁺ exists as diol (DHMPy⁺) and aldehyde (FMPy⁺) in water and acetonitrile, respectively. It was turned out that FMPy⁺ was clearly observed in the presence of clay nanosheet even in water. This indicates that clay nanosheet surface acts as unique chemical reaction field, affecting the potential energy surface between FMPy⁺ and DHMPy⁺.     

Texture change of ice on anomalously preserved methane clathrate hydrate

We used a confocal scanning microscope to observe growth and texture change of ice due to the dissociation of methane gas clathrate hydrate (CH(4) hydrate). The experiments were done under CH(4) gas atmospheric pressure and isothermal conditions between 170 and 268 K. Above 193 K, the dissociation of CH(4) hydrate resulted in many small ice particles that covered the hydrate surface. These ice particles had roughly the same shape and density between 193 and 210 K. In contrast, above 230 K the ice particles developed into a sheet of ice that covered the hydrate surface. Moreover, the measured release of CH(4) gas decreased when the sheet of ice formed at the surface of the hydrate. These findings can explain the anomalous preservation behavior of CH(4) hydrate; that is, the known increase of storage stability of CH(4) hydrate above 240 K is likely related to the formation of the ice that we observed in the experiments.     

Thermoanalytical Study of Baryte Decrepitation

The decrepitation results of mineral baryte BaSO₄ (Rudňany, Slovakia) of various quality obtained by completed Acoustic Emission (AE)-TG-DTA measurements are presented in this paper. The overall effect of decrepitation ability of major component BaSO₄ is not hindered by accompanying mineral siderite FeCO₃. This fact confirms decrepitation study of pure minerals by the thermovacuum impulse method, too. This revised version was published online in August 2006 with corrections to the Cover Date.     

Efficient calculations of coulombic interactions in biomolecular simulations with periodic boundary conditions

To make improved treatments of electrostatic interactions in biomacromolecular simulations, two possibilities are considered. The first is the famous particle–particle and particle–mesh (PPPM) method developed by Hockney and Eastwood, and the second is a new one developed here in their spirit but by the use of the multipole expansion technique suggested by Ladd. It is then numerically found that the new PPPM method gives more accurate results for a two-particle system at small separation of particles. Preliminary numerical examination of the various computational methods for a single configuration of a model BPTI–water system containing about 24,000 particles indicates that both of the PPPM methods give far more accurate values with reasonable computational cost than do the conventional truncation methods. It is concluded the two PPPM methods are nearly comparable in overall performance for the many-particle systems, although the first method has the drawback that the accuracy in the total electrostatic energy is not high for configurations of charged particles randomly generated. © 1993 John Wiley & Sons, Inc.