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We study the effects of bifunctional linker on the optical properties of ZnO nanocolumn-linker-CdSe quantum dots heterostructure. The CdSe quantum dots are anchored on the surface of ZnO nanocolumns through either aliphatic linker of 3-aminopropyl trimethoxysilane (APS) or aromatic linker of p-aminophenyl trimethoxysilane (APhS). X-ray photoelectron spectroscopy is used to confirm the bifunctional linker bound onto CdSe quantum dots and onto the ZnO nanocolumns. The TEM study reveals a CdSe quantum dot shell of about 15 nm coated on the ZnO nanocolumns. The photoluminance (PL) spectroscopy and time-resolved PL spectroscopy of ZnO nanocolumn-linker-CdSe quantum dots reflects that the photo-induced electron transfer across the interface of ZnO and CdSe through the aromatic APhS is more efficient than the aliphatic APS. This study demonstrates that through the usage of appropriate surface linker, the charge transfer rate across the interfaces of donor/acceptor (D/A) heterostructure can be improved for potential photovoltaic cell applications.

CdSe quantum dots have been encapped with aromatic ligands: α-toluenethiol, thiophenol, and p-hydroxythiophenol to enhance the photoluminescence (PL) quenching and photoelectric properties of the quantum dots. The aromatic ligand capped CdSe quantum dots are prepared through ligand exchange with trioctylphosphine oxide (TOPO) capped CdSe quantum dots. The XPS surface chemistry analysis and elemental analysis has confirmed the success of ligand exchange from TOPO to aromatic ligands. Both XRD and HRTEM-SAED studies indicate the crystalline structure of CdSe quantum dots not only remains but is also improved by the ligand exchange of TOPO with thiol molecules. Time resolved PL decay measurements indicate thiophenol and p-hydroxythiophenol ligands effectively quench the emission and have much shorter PL lifetimes than that of TOPO and that of α-toluenethiol. Thus, both thiophenol and p-hydroxythiophenol can act as an effective acceptor for photogenerated holes through aromatic π-electrons. Thiophenol also exhibits good charge transport behavior showing a 10-fold increase in short circuit current density (Isc) as compared with TOPO in the photocurrent study of fabricated photovoltaic devices.

In this study, nickel-phosphorus (Ni-P) deposits were electroplated from the nickel sulfamate bath containing phosphorous acid using a pulse current, with emphasis on the effect of current density, duty cycle, and frequency of the pulse current. Experimental results show that both the deposit phosphorus content and current efficiency were substantially enhanced by employing the pulse current, preferentially at low duty cycles. The underlying difference for the dc and pulse currents on the effect of deposit phosphorus content and current efficiency can be explained by the detailed half-reactions relevant to incorporation of phosphorus into Ni-P alloys. Less variation in surface proton, Ni 2+ and H 3 PO 3 concentration due to the diffusion recovery during the time off of a pulse current is believed to play an important role in the improvement of the plating process.