Off-resonance Photosensitization of a Photorefractive Polymer Composite Using PbS Nanocrystals

The photosensitization of photorefractive polymeric composites for operation at 633 nm is accomplished through the inclusion of narrow band gap semiconductor nanocrystals composed of PbS. Unlike previous studies involving photosensitization of photorefractive polymer composites with inorganic nanocrystals, we employ an off-resonance approach where the first excitonic transition associated with the PbS nanocrystals lies at ~1220 nm and not the wavelength of operation. Using this methodology, internal diffraction efficiencies exceeding 82%, two-beam-coupling gain coefficients of 211 cm-1, and response times of 34 ms have been observed, representing some of the best figures of merit reported for this class of materials. These data demonstrate the ability of semiconductor nanocrystals to compete effectively with traditional organic photosensitizers. in addition to superior performance, this approach also offers an inexpensive and easy means by which to photosensitize composite materials. the photoconductive characteristics of the composites used for this study will also be considered

Charge Carrier Mobility in an Organic-inorganic Hybrid Nanocomposite

A study was performed on charge carrier mobility in a system comprising of cadmium sulfide nanoparticles (QCdS) dispersed in poly(N-vinylcarbazole). The time-of-flight technique was used to measure the mobility of holes. It was found that hole mobility depended strongly on the temperature and electric field showing Poole-Frenkel-like activated hopping transport

Evaluating the Solid Electrolyte Interphase Formed on Silicon Electrodes: A Comparison of: Ex Situ X-Ray Photoelectron Spectroscopy and in Situ Neutron Reflectometry

This work details the in situ characterization of the interface between a silicon electrode and an electrolyte using a linear fluorinated solvent molecule, 0.1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in deuterated dimethyl perfluoroglutarate (d6-PF5M2) (1.87 x 10-2 mS cm-1). The solid electrolyte interphase (SEI) composition and thickness determined via in situ neutron reflectometry (NR) and ex situ X-ray photoelectron spectroscopy (XPS) were compared. The data show that SEI expansion and contraction (breathing) during electrochemical cycling were observed via both techniques; however, ex situ XPS suggests that the SEI thickness increases during Si lithiation and decreases during delithiation, while in situ NR suggests the opposite. The most likely cause of this discrepancy is the selective removal of SEI components (top 20 nm of the SEI) during the electrode rinse process, which is required to remove the electrolyte residue prior to ex situ analysis, demonstrating the necessity of performing SEI characterization in situ

New Frontiers of Photonics: Nanophotonics and Biophotonics

Photonics which has been called by many as the dominant technology for the 21st century is a rapidly evolving field, adding new dimensions in this area of research. In our laboratory, we have recently focused on two new areas: Nanophotonics and Biophotonics. Nanophotonics deals with optical science and technology at the nanoscale level. Biophotonics involves the use of optical methods for imaging and detection at cellular and tissue levels as well as for optically guided and activated therapy. Here we present an overview of our effort in these areas