Group 14 Nanocrystals

The synthesis of Group 14 nanocrystals (NCs) with controlled size dispersity and composition is an area of considerable interest due to their size-dependent optical and electronic properties, thought to enable their use in a wide range of applications such as fluorophores for biological imaging and photovoltaics. Veinot group specializes in the synthesis of silicon (Si), silicon carbide (SiC), silicon nitride (Si3N4), germanium (Ge) and silicon germanium alloy nanomaterials. We also investigate their optical and electrical properties. A brief discussion is provided on the synthesis and properties of these materials below.

Silicon nanocrystals: Si NCs embedded in oxide matrix are made in our group via disproportion of "SiO1.5" type precursors. The most commonly used precursors are hydrogen silsesquioxane (HSQ) and sol-gel polymer derived from hydrolysis of HSiCl3 and the NCs are made as shown in the scheme below.

The particle size can be controlled by changing the reaction temperature and shown here are the transmission electron microscope (TEM) images of Si NCs.

Germanium nanostructures: 1D Ge-NWs have been used to fabricate prototype linear dipolar p-n transistors. Oriented crystalline Ge-NW arrays also exhibit steady field emission properties that may be used in cold-cathode-based electronics. Templated NW growth offers a unique alternative to the abovementioned methods. Anodic aluminum oxide (AAO) membranes are widely used as templates for 1D nanostructure formation and Ge NWs are prepared by this method as summarized below.

Silicon germanium alloy nanocrystals (SixGe1-x NCs): Achieving control over the bandgap of semiconductor NCs is an important goal for numerous emerging technologies utilizing these materials, including near-infrared (IR) biological tags and non-volatile memory devices. Compositional modifications have also drawn substantial interest for tailoring optoelectronic properties through the incorporation of isovalent elements and SixGe1-x is one such material. Veinot team makes SixGe1-x alloy nanocrystals (64 < x < 100) from mixing GeI2:PR3 adducts with hydrogen silsesquioxane (HSQ). The use of trialkylphosphine adducts allows GeI2 and HSQ to be homogeneously coprecipitated.

Silicon nitride (Si3N4) NCs: We have recently made luminescent Si3N4 NCs using a straightforward synthetic method with silica, urea and magnesium powder.