Silicon Telluride Nanocrystals: Tunable Broadband Photoresponse

University Of California-Davis, Davis CA

Investigators

Abstract

With the support of the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Professor Kristie Koski of the University of California, Davis is studying a new silicon-based semiconductor nanomaterial, colloidal silicon telluride (Si2Te3). Si2Te3 nanoparticles offer a cheap, controllable photodetector material that is less-toxic than many current alternatives. More importantly, their optical properties are tunable, meaning that the color of light produced or absorbed by the nanoparticles can be adjusted over a wide range including both infrared and visible light. This is done by controlling the size, shape, chemical doping, and intercalation (placing atoms or ions in between the few-atom-thick layers of Si2Te3). This work will address fundamental questions of how to best create and control this unique material and why the properties of this material, especially the capability for intercalation, are so different for nanoparticles than they are for bulk-scale material. Colloidal silicon telluride stands out as a unique nanoparticle and will join the library of nanocrystal systems with promising nanoscale properties offering many applications in future technologies. This work will train undergraduate and graduate students for careers in science and engineering. Given the simplicity of growth, silicon telluride synthesis will be developed as an undergraduate laboratory experiment. With the support of the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Professor Kristie Koski of the University of California, Davis is studying synthetic control of size, shape, hyper-branching, and surface functionalization of colloidal, luminescent silicon telluride (Si2Te3) nanoparticles. Nanoscale synthesis and control will be achieved by combining new synthetic pathways with systematic studies to enable a complete understanding of the nucleation and growth of this unique material, thereby producing control of the properties that are most critical for application: dimensionality and optically active electronic states. Hypothesis-driven strategies for control of morphology, hyper-branching, size, shape, and ligand-chemistry will be developed. Photoluminescence in Si2Te3 originates from deep defect trap states which are affected by size, shape, morphology, doping, surface-functionalization, and intercalant guests, where competing trap state energy is easily shifted with measurable photoresponse. Tunability of full spectrum optical properties of colloidal Si2Te3 nanoparticles using ionic (Li+, Mn+) and atomic intercalation will be established. This work will try to understand why colloidal nanoparticles uptake more intercalant guests at faster rates despite having bulkier ligands and surface charge that should affect initial stages of intercalation—addressing outstanding questions about intercalation at the nanoscale using in situ single-nanoparticle optical photoluminescence. Si2Te3 is the perfect testbed for such a study. It is easy to make, layered, and it has an easy-to-measure optical photoresponse (from 600 nm to the infrared) that is highly sensitive to morphology, doping, and intercalation. Chemically tunable photoresponse in silicon telluride nanoparticles will be demonstrated offering potential for future tunable IR photodetection. Undergraduate and graduate students will be trained for technical careers in science and engineering. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.