Walter Mahler

Degenerate four-wave mixing of CdS/polymer composite

Abstract We report degenerate four-wave mixing study of 50 A CdS particles embedded in a thin polymer film. The CdS band-gap is blue-shifted compared to the bulk value (quantum size effect). Photoluminescence spectra show that three particles contain intrinsic defects, most likely due to sulfur vacancies. Preliminary results show that both the four-wave mixing signal and the transmission saturate at moderate power (a few MW/cm 2 ). These results are qualitatively consistent with the three-level saturable absorber model.

Cyanocarbons—Their History From Conducting to Magnetic Organic Charge Transfer Salts

Abstract A generation ago scientists at Du Ponts Central Research and Development Department sought to prepare, understand, and exploit organic molecules lacking aliphatic hydrogens and possessing a large cyano group to carbon ratio. Like many other ambitious quests the anticipated goal (of commercializing a new family of polymers) was not realized. Nonetheless, the discoveries made during this pursuit have made a permanent mark on the evolution of science. Most notably, the discovery of tetracyanoethylene (TCNE), and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ), and the remarkable stability of their radical anions led to an unusual series of charge transfer salts. Many of the TCNQ electron-transfer salts exhibit high, metal-like, dc electrical conductivity. These initial observations led to the evolutionary development of conducting polymers and the realization of molecular based ferromagnets.

EXAFS ANALYSIS OF SIZE-CONSTRAINED SEMICONDUCTING MATERIALS

Semiconducting materials such as CdSe, CdS, PbS and GaP are included in crystalline zeolite Y and mordenite and structurally flexible ethylene-methacrylic acid copolymer solid matrices. EXAFS analysis reveals formation of species with dimensions of molecular size up to ca. 13 A in the crystalline hosts, while the polymer matrices allow agglomeration of larger semiconducting particles. Zeolite anchored structures are distinctively different to small particles with bulk crystal structure as usually found in colloidal systems.

Guest-Host Molecular Ensembles for Nonlinear Optics

Abstract This paper discusses structural strategies for assembling bulk materials for nonlinear optics. In part one, we review a strategy, based on the concepts of guest-host inclusion complexation. We incorporate molecules into crystalline environments in which molecular dipoles are assembled into materials for second harmonic generation by polar alignment of the dipoles. In part two, we review the fabrication and properties of optical quality materials for third order nonlinear optics based on nanoscale particles of semiconductors included in polymer media.

13.2: Electrochemical Deposition of Carbon Nanotube Films and Applications in Field Emission Display Devices

An electrochemical deposition (ECD) process for the formation of carbon nanotube (CNT) thin films on ITO coated glass is described. This simple and scalable process takes advantage of a highly stable aqueous dispersion of ribonucleic acids (RNA) wrapped CNTs reported previously. Thin films showing dense coverage of nanotubes can be prepared in a few minutes by the application of a few volts between a conductive substrate and a stainless steel counter electrode with both immersed in the RNA-CNT aqueous dispersion. Patterned deposit with feature size of microns can be readily obtained by masking the conductive layer on the substrate. Since ECD is an additive process with efficient use of CNTs, it provides a cost effective alternative to photoimagable deposition. Unlike electrophoretic deposition, the ECD process is an aqueous, low voltage, and field independent process. Fringing field issues which can affect deposition uniformity on patterned surfaces are therefore avoided. for electron field emission applications such as display or backlight, ECD films can be sintered and surface treated to obtain highly emissive surfaces with low threshold voltage and high uniformity emission. The field emission performance of diode and triode devices prepared with ECD is discussed.