Highlights

Growth of Anisotropic Silver Nanoplates on Semiconductor Substrates

Scientific Achievement

Deposition of metal nanostructures with controlled shapes on semiconductor substrates represents a sustained research direction because the unique optical and electronic properties associated with the metal/semiconductor hybrids can improve their efficiency to harvest solar energy to enable their applications in photovoltaic cells, photoelectrochemical splitting of water, photocatalysis, etc.  Up to date, the common strategy for generating metal nanostructures on semiconductor substrates includes synthesis of metal nanostructures in solutions and post-deposition (and/or assembly) of the as-synthesized nanostructures on desired substrates.  However, the two-step strategy complicates the fabrication process and the surfactants used in the solution-phase synthesis adversely affect the performance of metal nanostructures in most applications.  We have begun to develop simple, effective approaches to direct grow metal nanostructures with well-defined shapes in the absence of any additive.  Preliminary results show that high-quality silver nanoplates with tunable surface morphologies (rough versus smooth) and sizes (50 nm – 1 mm) and thicknesses (20 nm – 200 nm) can be grown on semiconductor wafers (e.g., gallium arsenide, silicon) in ambient environment at room temperature.  The as-grown silver nanoplates are characterized with pure composition. 

Systematical studies show that the synthetic approach involves galvanic reaction between metal salts (e.g., silver nitrate for silver) and semiconductor substrates.  The growth of anisotropic nanoplates includes two steps: i) forming metal nuclei with multiple parallel twin structures through fast reduction of metal ions with surface electrons of the semiconductor substrates; and ii) growing the metal nuclei into nanoplates through reduction of metal ions by hole injection process.  The well separated nucleation and growth enables the anisotropic growth of metal nanoplates on semiconductor substrates.

Significance

This synthetic approach provides a strategy to produce nanostructured metal/semiconductor composites with varying components.  The resulting materials represent a class of novel materials in photonics, photocatalysis, and optoelectronics due to strong coupling between the unique optical and electronic properties of metal nanostructures and semiconductors.  Continuous studies on these materials will lead to development of new photovoltaic devices with efficient conversion of solar energy.  This work has been published in Small 3, 1964-1975 (2007), and the cover of that issue used an image from our paper.

Performers

Y. Sun, G. Wiederrecht (Argonne-CNM)