Dayong Jiang

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.

Ultraviolet Photodetector Based on a MgZnO Film Grown by Radio-Frequency Magnetron Sputtering

The metal-semiconductor-metal ultraviolet (UV) photodetector was fabricated on the Mg(0.47)Zn(0.53)O layer grown by radio-frequency magnetron cosputtering. The photodetector shows the peak response at 290 nm with a cutoff wavelength at 312 nm. It exhibits a very low dark current of about 3 pA at 5 V bias, and the UV-visible rejection ratio (R = 290 nm/R = 400 nm) is more than 4 orders of magnitude. The transient response for the detector was measured, and it was found that the rise time is 10 ns and the fall time is 30 ns. The reason for the short response time is related to the Schottky structure.

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.

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.

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.

Planar wheel-type M©BnHn2−/−/0 clusters (M = Cr, Mn and Fe for dianion, anion and neutral, respectively; n = 6 and 7)

We adopted a new “electronic” strategy that is adding two electrons into the dz2 orbital of the central M atom to form a lone pair, which is in contrast to the Hoffmann’s “electronic” strategy that is delocalizing the lone pair on the center atom, to turn the bowl-type MBnHn0/+ (M = Cr and Mn; n = 6 and 7) clusters into planar wheel-type M©BnHn2−/− clusters. Their isoelectronic neutral clusters, Fe©B6H6 and Fe©B7H7, also possess planar wheel-type structures. The large binding energy, vertical ionization potential, and vertical electron affinity indicate that the planar wheel-type M©BnHn2−/− clusters are chemically stable. This study may open up a new area in coordination chemistry for planar hexa- and hepta-coordinate transition metal and we expect further experimental explorations of synthesis and potential applications.