Chao Li

Direct Observations of Nanofilament Evolution in Switching Processes in HfO2‐Based Resistive Random Access Memory by In Situ TEM Studies

Resistive switching processes in HfO2 are studied by electron holography and in situ energy-filtered imaging. The results show that oxygen vacancies are gradually generated in the oxide layer under ramped electrical bias, and finally form several conductive channels connecting the two electrodes. It also shows that the switching process occurs at the top interface of the hafnia layer.

New responsive property of poly(ε-caprolactone) as the thermal switch from superhydrophobic to superhydrophilic

A reversible switch between superhydrophobicity at low temperature and superhydrophilicity at high temperature was fabricated by coating poly(epsilon-caprolactone) on a rough substrate, which resulted from the combination of the different adaptability of the polymer chain upon crystalline/amorphous phase transition and the optimized roughness.

High power, tunable mid-infrared BaGa 4 Se 7 optical parametric oscillator pumped by a 2.1 μm Ho:YAG laser

We, for the first time, demonstrate a tunable mid-infrared BaGa4Se7-based optical parametric oscillator pumped by a acousto-optical Q-switched Ho:YAG laser at 2090.6 nm. Up to 1.55 W of average power was generated in the 3-5 μm range, corresponding to an optical-to-optical conversion efficiency of 14.4% and a slope efficiency of 19.9%. The mid-IR radiation spectra were also seriously researched at different phase-matched angles. The tunable range was 3.49-4.13 μm for the signal, and 5.19-4.34 μm for the idler.

Li2MnSnSe4：A New Quaternary Diamond‐Like Semiconductor with Nonlinear Optical Response and Antiferromagnetic Property

A new selenide with a diamond-like structure, Li2 MnSnSe4 , was synthesized for the first time by using a conventional high-temperature solid-state reaction method. Li2 MnSnSe4 crystallizes in the space group Pmn21 (no.u200531) of the orthorhombic system. Its three-dimensional framework is constructed by corner-sharing LiSe4 , MnSe4 , and SnSe4 tetrahedra. The title compound has been discovered to have both typeu2005I phase-matchable behavior and to exhibit moderate powder second-harmonic generation intensity, about 0.5u2005times that of commercial AgGaS2 in the particle size of 200-250u2005μm at a laser radiation of 2.09u2005μm. In addition, Li2 MnSnSe4 exhibits congruent melting behavior, which makes the bulk single-crystal growth by the Bridgman-Stockbarger method possible. The temperature-dependent susceptibility measurement indicates an antiferromagnetic interaction with a Néel temperature (TN ) of 8.6u2005K for this compound.

A polypyridyl Co(II) complex-based water reduction catalyst with double H2 evolution sites

A series of Co(II) complexes, Co(X-TMPA)Cl2 (X-TMPA = 1-(6-substituted-pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methane amine, X = Cl (1), Br (2), H (3), and CH3 (4)), were synthesized and fully characterized. The crystal structures of 2 and 4 show that TMPA and CH3-TMPA coordinate to the Co(II) center as tetradentate ligands, while Br-TMPA coordinates as a tridentate ligand, leaving the Br-substituted pyridyl group in the second coordination sphere. All of the complexes are efficient photocatalytic H2 evolution catalysts in CH3CN/H2O (9/1) using [Ir(ppy)2(dtbpy)]Cl (ppy = 2-phenylpyridine, dtbpy = 4,4′-di-tert-butyl-2,2′-bipyridine) as the photosensitizer (PS) and triethylamine (TEA) as the sacrificial electron donor. During 6 h irradiation, the turnover numbers (TONs) of 1 and 2 reached 20u2006000, remarkably higher than those of 3 and 4. These high photocatalytic activities may be attributed to the pendent Cl/Br-substituted pyridyl group, which serves as a proton and electron relay to facilitate proton reduction at the Co center. Interestingly and importantly, it was found that the Cl-substituted pyridyl group of 1 may catalyze H2 evolution itself by electrocatalytic proton reduction reactions, endowing 1 with double catalytic sites for proton reduction. The unique coordination mode of Cl/Br-TMPA and the double catalytic H2 evolution sites of 1 provide a new strategy to design more effective WRCs.

Li7Cd4.5Ge4Se16 and Li6.4Cd4.8Sn4Se16: Strong Nonlinear Optical Response in Quaternary Diamond-Like Selenide Networks

Two new selenides with diamond-like structures, Li7 Cd4.5 Ge4 Se16 and Li6.4 Cd4.8 Sn4 Se16 , were synthesized by using a conventional high-temperature solid-state reaction method. They crystallize in the space group Pna21 (no.u200533) of the orthorhombic system. Their three-dimensional frameworks consist of corner-sharing LiSe4 , CdSe4 , and MSe4 (M=Ge, Sn) tetrahedra. These two compounds exhibit strong powder second-harmonic generation responses that are about 1.2 and 2.5u2005times that of the benchmark AgGaS2 at a laser wavelength of λ=2.09u2005μm, and also demonstrate typeu2005I phase-matchable behavior. The optical bandgaps were determined to be 2.18 and 1.95u2005eV for Li7 Cd4.5 Ge4 Se16 and Li6.4 Cd4.8 Sn4 Se16 , respectively. Furthermore, these two materials exhibit congruent melting behavior at rather low temperatures of 985 and 1060u2005K, respectively, which makes bulk single crystal growth by using the Bridgman-Stockbarger method possible. Our study indicates that these two materials show advantages over the traditional IR NLO material CdSe and are promising for practical applications.

Syntheses of 7-dehydrocholesterol peroxides and their improved anticancer activity and selectivity over ergosterol peroxide

7-Dehydrocholesterol peroxide (5α,8α-epidioxycholest-6-ene-3β-ol, CEP) and its acetate and hemisuccinate derivatives were synthesized and isolated for the first time, which exhibit improved anticancer activity and selectivity over ergosterol peroxide (5α,8α-epidioxy-22E-ergosta-6,22-dien-3β-ol, EEP), showing potential as new chemotherapeutic agents.