title: Optical characterization of ultrasmall Si nanoparticles prepared through electrochemical dispersion of bulk Si.
abstract: Studying the properties and stability of silicon nanoparticles (Si-np) in aqueous environments may lead to novel applications in biological systems. In this work, we use absorption and photoluminescence (PL) spectroscopy to characterize ultrasmall Si-np prepared through anodic etching and ultrasonic fractionation of a crystalline Si wafer. Their behavior is studied over time in 2-propanol and during treatments with water, NaOH, HCl, and H(2)O(2). The observed population is divided into two types of material: bright species consisting of well-etched Si-np, approximately 1 nm in diameter, and dark species derived from partially etched or aggregated Si structures. The dark material is seen by its scattering in the 2-propanol and water solutions and is largely removed via precipitation with the NaOH or HCl treatment. The bright material includes three distinct species with their respective emissions in the UV-B, UV-A, and hard-blue regions of the spectrum. The hard-blue PL is shown to have a simple pH dependence with a pK(a) approximately 3, providing an important insight into its chemical origin and signaling for possible application of Si-np as environmental probes. Our results offer some potential for tailoring the PL properties of ultrasmall Si-np through control of their surface chemistry.
authors.affiliation: Department of Physics and Laboratory for Fluorescence Dynamics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801, USA. deckhoff@uiuc.edu
authors.forename: Dean A
authors.initials: DA
authors.lastname: Eckhoff
authors.forename: Jason D B
authors.initials: JD
authors.lastname: Sutin
authors.forename: Robert M
authors.initials: RM
authors.lastname: Clegg
authors.forename: Enrico
authors.initials: E
authors.lastname: Gratton
authors.forename: Elena V
authors.initials: EV
authors.lastname: Rogozhina
authors.forename: Paul V
authors.initials: PV
authors.lastname: Braun
mesh_terms: D000042:Absorption; D004563:Electrochemistry; D006851:Hydrochloric Acid / Q000737:chemistry; D006861:Hydrogen Peroxide / Q000737:chemistry; D006868:Hydrolysis; D049449:Luminescence; D008958:Models, Molecular; D053758:Nanoparticles / Q000737:chemistry*; D010084:Oxidation-Reduction; D010316:Particle Size; D012825:Silicon / Q000737:chemistry*; D012833:Siloxanes / Q000737:chemistry; D012972:Sodium Hydroxide / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet
chemical_list: D012833:Siloxanes; D012972:Sodium Hydroxide; D006861:Hydrogen Peroxide; D006851:Hydrochloric Acid; D012825:Silicon