Qingcheng Liang

Performance enhancement of ZnO UV photodetectors by surface plasmons.

Surface plasmons, a unique property of metal nanoparticles, have been widely applied to enhance the performance of optical and electrical devices. In this study, a high quality zinc oxide (ZnO) thin film was grown on a quartz substrate by a radio frequency magnetron sputtering technique, and a metal-semiconductor-metal structured ultraviolet detector was prepared on the ZnO film. The responsivity of the photodetector was enhanced from 0.836 to 1.306 A/W by sputtering metal (Pt) nanoparticles on the surface of the device. In addition, the absorption of the ZnO thin film was enhanced partly in the ultraviolet band. It is revealed that Pt nanoparticles play a key role in enhancing the performance of the photodetectors, where surface plasma resonance occurs.

Origin of the responsivity characteristics of Au/ZnO/MgZnO and Au/MgZnO/ZnO structured ultraviolet photodetectors

We report on the ultraviolet photodetectors based on the MgZnO/ZnO and ZnO/MgZnO double-layer films prepared by magnetron sputtering method. The spectral response shows only one responsivity peak in the 1.0 and 1.5 h photodetectors (denoted by the deposition time of one layer of the films) and two peaks in the 0.5 h photodetectors. To our surprise, the Au/MgZnO/ZnO photodetectors have larger responsivity than that of the Au/ZnO/MgZnO ones. A physical mechanism focused on depletion width is given to explain the above results.

Di/mono-nuclear iron(I)/(II) complexes as functional models for the 2Fe2S subunit and distal Fe moiety of the active site of [FeFe] hydrogenases: protonations, molecular structures and electrochemical properties

Di/mono-nuclear iron(I)/(II) complexes containing conjugated and electron-withdrawing S-to-S linkers, [{(μ-S)(2)(C(4)N(2)H(2))}Fe(2)(CO)(6)] (1), [{(μ-S)(2)(C(4)N(2)H(2))}Fe(2)(CO)(5)(PMe(3))] (1P), and [{(μ-S)(2)(C(4)N(2)H(2))}Fe(CO)(2)(PMe(3))(2)] (2) were prepared as biomimetic models for the 2Fe2S subunit and distal Fe moiety of the active site of [FeFe] hydrogenases. The N atoms in the heterocyclic pyrazines of 1 and 2 were protonated in the presence of proton acid to generate one and two hydrides, [1(NH)](+) CF(3)SO(3)(-), [2(NH)](+) CF(3)SO(3)(-), and [2(NH)(2)](2+) (CF(3)SO(3)(-))(2), respectively. The protonation processes were evidenced by in situ IR and NMR spectroscopy. The molecular structures of the protonated species [1(NH)](+) CF(3)SO(3)(-) and [2(NH)(2)](2+) (CF(3)SO(3)(-))(2) together with their originating complexes and , and the mono-PMe(3) substituted diiron complex were identified by X-ray crystallography. The IR and single-crystal analysis data all suggested that the electron-withdrawing bridge, pyrazine, led to decreased electron density at the Fe centers of the model complexes, which was consistent with the electrochemical studies. The cyclic voltammograms indicated that complex exhibited a low primary reduction potential at -1.17 V vs. Fc-Fc(+) with a 270 mV positive shift compared with that of the benzene-1,2-dithiolate (bdt) bridged analogue [(μ-bdt)Fe(2)(CO)(6)]. Under the weak acid conditions, complexes 1 and 2 could electrochemically catalyze the proton reduction. More interestingly, the mononuclear ferrous complex 2 showed two catalytic peaks during the formation of hydrogen, confirming its potential as a catalyst for hydrogen production.

Experimental and first-principles study of ferromagnetism in Mn-doped zinc stannate nanowires

Room temperature ferromagnetism was observed in Mn-doped zinc stannate (ZTO:Mn) nanowires, which were prepared by chemical vapor transport. Structural and magnetic properties and Mn chemical states of ZTO:Mn nanowires were investigated by X-ray diffraction, superconducting quantum interference device (SQUID) magnetometry and X-ray photoelectron spectroscopy. Manganese predominantly existed as Mn2+ and substituted for Zn (Mn Zn) in ZTO:Mn. This conclusion was supported by first-principles calculations. MnZn in ZTO:Mn had a lower formation energy than that of Mn substituted for Sn (MnSn). The nearest neighbor MnZn in ZTO stabilized ferromagnetic coupling. This observation supported the experimental results. 2013 AIP Publishing LLC.

High-performance ultraviolet photodetectors based on ZnO/Au/ZnO sandwich structure

We developed sandwich ultraviolet photodetectors by a radio frequency magnetron sputtering method. As expected, the performances of the optimized ZnO/Au/ZnO sandwich photodetectors are much better than that of a metal-semiconductor-metal structure through combing high responsivity (enlarged ~60 times) and low dark current (reduced by more than two orders of magnitudes). To investigate the above phenomena, simulations of electric-field intensity distribution in the two structured photodetectors were performed using the ANSYS software. A proposed physical mechanism is used to explain the above results, which agree well with the simulations.

Responsivity enhancement of ZnO/Pt/MgZnO/SiO2 and MgZnO/Pt/ZnO/SiO2 structured ultraviolet detectors by surface plasmons in Pt nanoparticles

The structured (ZnO/Pt/MgZnO/SiO2) ultraviolet detector was fabricated and demonstrated to investigate how metallic nanoparticles localized surface plasmons contribute when the two different dielectrics surrounded simultaneously. After sandwiching the Pt nanoparticles between the double layers of MgZnO and ZnO, the extinction was increased largely. Meanwhile, by examining the dependence of MgZnO and ZnO peak responsivity enhancement ratio, we found that MgZnO was significantly larger than ZnO. The interpretation by considering is that the localized surface plasmons of energy match with MgZnO which is superior to ZnO. In order to validate this conclusion and make it more accurate, we also fabricated the MgZnO/Pt/ZnO/SiO2 structure. Our work suggests that rational integration of double-layer and metal nanoparticles is a viable approach to perceive localized surface plasmons with double-layer ultraviolet detectors, which may help to advance optoelectronic devices.

Exploring the geometrical structures of X©BnHnm [(X, m) = (B, +1), (C, +2) for n = 5; (X, m) = (Be, 0), (B, +1) for n = 6] by an electronic method

A series of singlet and triplet wheel-type clusters obtained through an electronic method, i.e., adding two and four electrons into X©BnHnm [(X, m) = (B, +1), (C, +2) for n = 5; (X, m) = (Be, 0), (B, +1) for n = 6], have been studied theoretically. With the increase of the number of electrons, the sizes of peripheral boron rings tend to decrease due to the increase of negative charges on the boron rings. The results of the kinetic stability and the electronic stability suggest that the triplet C©B5H5 and singlet Be©B6H6 are stable and may be detected experimentally. Nucleus-independent chemical shift and molecular orbital analysis reveal that some wheel-type clusters with the planar ring possess aromaticity properties that are attributed to the delocalized π electrons conforming to the Huckel rule, i.e. 4n + 2 for singlets or 4n for triplets. These findings from this work are significant for designing novel wheel-type clusters.

The employment of a hydrophilic tris(morpholino)phosphine ligand in diiron propane-1,3-dithiolate complexes for potentially water-soluble iron-only hydrogenase active-site mimics

A tris(morpholino)phosphine (TMP) ligand was introduced into the diiron dithiolate complexes in order to improve the hydro- and protophilicity of the iron-only hydrogenase active site models. Mono- and di-TMP substituted diiron complexes, (μ-pdt)[Fe(CO)3][Fe(CO)2(TMP)] (2, pdt = 1,3-propanedithiolato) and (μ-pdt) [Fe(CO)2(TMP)]2 (3), were synthesized and spectroscopically characterized. The coordination configuration of 3 was determined by single X-ray analysis. Temperature-dependent 1H and 31P NMR spectroscopy studies provided insight into the interconversion of the irondithiacyclohexane ring and the rotation of the [Fe(CO)2PR3] moieties for 2 and 3 in solution. The electrochemical properties of 2 and 3 were investigated in pure CH3CN and CH3CN–H2O mixtures in the absence and presence of acetic acid. Hydrogen production and the dependence of current on acid concentration indicated that complexes 2 and 3 exhibited electrocatalytic activities for proton reduction in both pure and H2O-containing CH3CN solutions. The current sensitivities, i.e., electrocatalytic activities, were demonstrated to be greater in CH3CN–H2O mixtures than in pure CH3CN. The most effective electrocatalytic activities of 2 and 3 were observed with 10% added water.

Investigation of the hole transport characterization and mechanisms in co-evaporated organic semiconductor mixtures

The hole transport characteristics in small molecule semiconductor mixtures of HAT-CN : NPB, HAT-CN : TAPC and HAT-CN : CBP in the ratio of 2 : 1 have been investigated by admittance spectroscopy measurements. It is found that the hole mobility (10−5–10−4 cm2 V−1 s−1) variation with electric field in HAT-CN : NPB is the same as that in HAT-CN : TAPC. The hole transport in HAT-CN : CBP is space-charge-limited current (SCLC) with exponential distribution traps, different from SCLC with free trap distributions of HAT-CN : NPB and HAT-CN : TAPC mixtures. The hole mobility in the HAT-CN : CBP mixture is obtained as 10−7–10−5 cm2 V−1 s−1, which is one or two orders of magnitude lower than those of the other two mixtures. It can be seen that the mobility exhibits strong field-dependence in low electric field region. The mobility slightly increases as the electric field increases and almost saturates in high electric field region. It is shown that the trapping effect leads to the much lower hole mobility. The hole transport mechanisms in the three mixtures have been further studied through energy level analysis and atomic force microscopy.

An artificial [FeFe]-hydrogenase mimic with organic chromophore-linked thiolate bridges for the photochemical production of hydrogen

An artificial [FeFe]-hydrogenase ([FeFe]-H2ase) mimic 3II, consisting of dual organic chromophores covalently assembled to the [Fe2S2] active site, was constructed for light-driven hydrogen evolution. The structural conformation of synthetic photocatalyst was characterized crystallographically and spectroscopically. The photo-induced intramolecular electron transfer was evidently demonstrated by the combination of electrochemical, steady-state, and transient absorption spectroscopic studies. Finally, a remarkable activity was obtained in the present photocatalytic system, indicating the covalent incorporation of photosensitizer and catalytic center as a promising strategy to construct inexpensive, easily accessible [FeFe]-H2ase model photocatalysts.