The study of lanthanide (Ln)-transition-metal (TM) heterometallic clusters which play key roles in various high-tech applications is a rapid growing field of research. Despite the achievement of ...numerous Ln-TM cluster compounds comprising one Ln atom, the synthesis of Ln-TM clusters containing multiple Ln atoms remains challenging. Here, we present the preparation and self-assembly of a series of Au-bridged heterometallic clusters containing multiple cerium (Ce) atoms via on-surface coordination. By employing different pyridine and nitrile ligands, the ordered coordination assemblies of clusters containing 2, 3 and 4 Ce atoms bridged by Au adatoms are achieved on Au(111) and Au(100), as revealed by scanning tunneling microscopy. Density functional theory calculations uncover the indispensable role of the bridging Au adatoms in constructing the multi-Ce-containing clusters by connecting the Ce atoms via unsupported Ce-Au bonds. These findings demonstrate on-surface coordination as an efficient strategy for preparation and organization of the multi-Ln-containing heterometallic clusters.
A hierarchical array of ZnO nanocones covered with ZnO nanospikes was hydrothermally fabricated and employed as the photoanode in a CdS quantum dot-sensitized solar cell (QDSSC). This QDSSC ...outperformed the QDSSC based on a simple ZnO nanocone photoanode in all the four principal photovoltaic parameters. Using the hierarchical photoanode dramatically increased the short circuit current density and also slightly raised the open circuit voltage and the fill factor. As a result, the conversion efficiency of the QDSSC based on the hierarchical photoanode was more than twice that of the QDSSC based on the simple ZnO nanocone photoanode. This improvement is attributable to both the enlarged specific area of the photoanode and the reduction in the recombination of the photoexcited electrons.
Aligned single-walled carbon nanotube arrays provide a great potential for the carbon-based nanodevices and circuit integration. Aligning single-walled carbon nanotubes with selected helicities and ...identifying their helical structures remain a daunting issue. The widely used gas-directed and surface-directed growth modes generally suffer the drawbacks of mixed and unknown helicities of the aligned single-walled carbon nanotubes. Here we develop a rational approach to anchor the single-walled carbon nanotubes on graphite surfaces, on which the orientation of each single-walled carbon nanotube sensitively depends on its helical angle and handedness. This approach can be exploited to conveniently measure both the helical angle and handedness of the single-walled carbon nanotube simultaneously at a low cost. In addition, by combining with the resonant Raman spectroscopy, the (n,m) index of anchored single-walled carbon nanotube can be further determined from the (d,θ) plot, and the assigned (n,m) values by this approach are validated by both the electronic transition energy Eii measurement and nanodevice application.
We provide a wet chemical approach for organizing randomly tangled single-walled carbon nanotubes (SWCNTs) on gold surfaces. The as-grown nanotubes were first chemically cut into short pipes and ...thiol-derivatized at the open ends. The ordered assembly of SWCNTs was made by their spontaneous chemical adsorption to gold via Au−S bonds. Tapping mode atomic force microscopy (AFM) images clearly show that the nanotubes have been organized on gold, forming a self-assembled monolayer structure with a perpendicular orientation. The adsorption kinetics of the nanotubes was very slow in comparison to conventional alkanethiols. The adsorption rate varied inversely with tube length. The nanotubes tend to form bundles as the adsorption propagates, following a “nucleation adsorption mechanism”. This work demonstrates that “giant” carbon nanotubes can be assembled on Au surfaces using wet chemistry similar to that exploited for “small” organic self-assembling species. We believe that assembled nanotube arrays will provide wide possibilities for applications.
Flexible fiber-type CdS quantum dot-sensitized solar cells (CdS FF-QDSSCs), in which all the components are assembled into a flexible plastic capillary tube, are designed and fabricated. In each ...FF-QDSSC, a Pt wire along the capillary tube axis acts as the counter electrode. A number of surrounding Ti wires coated with CdS-sensitized ZnO nanorods act as the working electrodes. This design provides the cells with good flexibility and all-direction light harvesting capability. The photovoltaic performances of the FF-QDSSCs can be effectively improved by increasing the number of the working electrodes up to six. The conversion efficiency of the cell with six working electrodes (FF-QDSSC-6) is more than five times that of the cell with only one working electrode. Furthermore, for simultaneously illuminating the cell from all the directions perpendicular to the capillary tube, an Al reflector is placed behind the cell. This measure raised the maximum power output of an FF-QDSSC-6 by 55%.
We present a theoretical study of the electronic and magnetic properties of single-walled manganese phthalocyanine (MnPc) nanotubes which can be thought of as rolled-up ribbons of the two-dimensional ...(2D) polymeric MnPc sheet. Our density functional theory calculations show that all of the MnPc nanotubes investigated here are half-metals with 100% spin polarization around the Fermi level. Following the increase of the tube diameter, the number of spin-down energy bands of MnPc nanotubes is always increased while the spin-up band gap of MnPc nanotubes approaches that of the 2D MnPc sheet in an oscillatory manner. Because the half-metallic character of MnPc nanotubes is deeply rooted in the distribution of electrons in the energy bands dominated by the Mn 3d atomic orbitals, adsorption of CO molecules on the Mn ions leads to a redistribution of electrons in the Mn 3d orbitals and thus can tune precisely the spin state and electronic transport properties of MnPc nanotubes, demonstrating promising applications of MnPc nanotubes in future molecular spintronics and single-molecule sensors.
The conductive atomic force microscope (CAFM) has been shown to be a powerful tool to study the physical and electrical properties of high-k materials on nanoscale. However, such accurate ...measurements could be altered by external factors. In this work, the main factors affecting CAFM measurements including environmental conditions, tip coating materials and the tip-sample bias are evaluated by analyzing the topographic and current maps performed on HfO
2
stacks in different conditions. It is found that environmental conditions have notable effects on the CAFM measurements due to the water meniscus formed by adsorbed water layers on the tip and sample surface in air. And the lateral resolution of the technique can be improved remarkably by measuring in a high vacuum environment. The mechanical and electrical properties of tip coating materials are found to be related to the stability of tip conductivity and the real voltage drop in the stack, hence have a key influence on the current measurement. Moreover, the tip-sample interaction can be altered by the electrostatic force induced by the applied bias, leading to variations of the topographic image of the surface with the bias voltage. Our results indicate that the impact of these factors must be taken into account when performing CAFM measurements under different conditions or comparing the results obtained in different experiments.
Based on density functional theory calculations, we predict the stability and electronic structures of single-walled indium nitride (InN) nanotubes. Compared with other group III-nitride nanotubes ...with a similar diameter, strain energies of InN nanotubes relative to their graphitic sheet are the lowest, suggesting the possibility of the formation of InN nanotubes. Considering the stability of a graphitic InN sheet, InN nanotubes are in metastable states with the stability between GaN nanotubes and AlN nanotubes. Contrary to the case of carbon nanotubes and BN nanotubes, the bond-length of both horizontal and vertical In–N bonds in InN nanotubes decreases as the tube diameter increases. InN nanotubes are all semiconductors with an almost constant band gap of about 1
eV. The existence of a direct gap in zigzag InN nanotubes and the small band gap indicate that they may have potential applications in light emitting devices and solar cells.
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