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  New horizons in research funding: Developing junior academics and enhancing research support for humanities and social sciences

  Reorganization of RGC Subject Panels

  Liquid-based Photovoltaic/Thermal Cogeneration for Real Building Application

  Development and Study of Hybrid Photovoltaic Cells

  Interfaces between Fullerenes and Semiconductor Nanowires: Nanofabrication and Photoinduced Charge Separation

  Vagus Nerve Stimulation Therapy: 
A New Tool for Suppressing Visceral Pain

  On the Architecture of Synapses

  Unlocking the Causes of Stroke in Asia: The Importance of Intracranial Atherosclerosis

  Area of Excellence in Information Technology

  RGC Collaborative Research Fund – Layman Summaries of Projects Funded in 2010/11 Exercise

The topic:
Semiconductor nanowires have diameters of about 10 billionths of a meter, or ten thousand times smaller than a human hair. Owing to their thinness, such nanowires are expected to have special optical and electronic properties. For example, they can efficiently transport electrons with a specific energy from one place to another, a property useful for solar cell applications. Fullerenes, on the other hand, are carbon cage molecules, among which C60, the Buckminsterfullerene, has the most symmetrical soccer ball structure. These fullerene molecules have so far turned out to be the most efficient electron acceptors in organic polymer solar cells. One of the stumbling blocks in developing this type of solar cells is the difficulty in controlling the morphology of the mixture of polymers and fullerenes. To solve this problem, a hybrid structure of inorganic nanowires and fullerenes has been proposed in this project. The goal was to create inorganic nanowires coated with fullerene molecules and study their photoelectric properties.

Methodology used:
The first step was to develop various bottomup chemical methods including direct solution reactions, electrochemical reactions, and insitu interfacial reactions to synthesize inorganic nanowires. Then fullerenes were attached to the surfaces of the nanowires using different strategies including fullerene polymerization, chemical functionalization, and ligand-binding. Finally photoelectrochemistry measurements were conducted to uncover the properties of photoinduced charge separation, transport and collection.

Research findings:
The successful development of a unique copper(I)-assisted fullerene-polymerization method for preparing novel cuprous oxide-fullerene[60] core-shell nanowires was the highlight of this project. Nanoparticles were also studied for comparisons. For this work, we started from a Cu2O nanowire array obtained using our in-situ growth method. The fullerene coating was based on a reaction of C60 and ethyl isocyanoacetate to form polymerized fulleropyrolines, catalyzed by and thus seamlessly coated on the Cu2O nanomaterials. Such a Cu(I)- assisted C60-polymerization process combines the new solution chemistry and surface chemistry of C60. Interestingly, when Cu2O nanocubes were used as a core for coating fullerenes, the Cu2O cores in the composite nanocubes could be removed by acidic etching, yielding monodispersed C60 nanoboxes.




In addition, we have surface-functionalized ZnO Nanotetrapods, a type of branched nanowires, with uniform monolayers of C60 molecules functionalized with carboxylate groups. We have achieved chemical conjugation of fullerenes to CdSe nanocrystals using dithiocarbamate ligands by exchanging TOPO ligands on the CdSe nanocrystals with C60-bound dithiocarbamate ligands. This technique can be easily adapted to the fullerene functionalization of CdSe nanowires. 

Encouragingly, the above composite nanomaterials have shown enhanced photoinduced charge separation, transport and collection. For example, we have demonstrated the enhanced photocurrent of the Cu2O@C60 nanoribbons arrayed on Cu foil compared with that of the Cu2O nanoribbons. Similarly, photoelectrochemistry of a film cast from the (C60)8-CdSe conjugate revealed a significantly enhanced photocurrent compared with the film of CdSe-TOPO nanocrystals as well as that of C60 alone, suggesting that our conjugation strategy is viable for solar cell applications.

Implications to the related area or to the society: 
This project has created nanocomposites containing semiconductor nanostructures and fullerenes; the former are electron donors and the latter are electron acceptors. The synthesis methods developed in this project can be extended to the synthesis of other composite nanomaterials. Combining electron donors and acceptors at the nanoscale is an important endeavor to effectively harvest solar energy, which is of huge interest globally. The proof-of-concept for designing the materials basis for the nanoscale charge separation has been demonstrated. To utilize the photoinduced charge separation in real device applications, we have already started to implement the nanostructures as photoanodes for excitonic solar cells.

Prof Shihe YANG
Department of Chemistry
The Hong Kong University of Science and Technology