Selection of metal oxide charge transport layers for colloidal quantum dot LEDs.

We investigate the effect of the electronic energy level positioning, conductivity, and morphology of metal oxide charge transport layers on the performance of light emitting devices (LEDs) that consist of a colloidally synthesized quantum dot (QD) luminescent film embedded between electron and hole injecting ceramic layers. We demonstrate that understanding of these material properties and their effect on charging processes in QDs enables the systematic design of higher efficiency QD-LEDs and excitation of QDs with different emission colors using the same device structure.

Vibrational spectroscopy reveals electrostatic and electrochemical doping in organic thin film transistors gated with a polymer electrolyte dielectric.

We apply attenuated total internal reflection Fourier transform infrared (ATR-FTIR) spectroscopy to directly probe active layers in organic thin film transistors (OTFTs). The OTFT studied uses the n-type organic semiconductor N-N'-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8) and a polymer electrolyte gate dielectric made from poly(ethylene oxide) and LiClO4. FTIR spectroscopy of the device shows signatures of anionic PTCDI-C8 species and broad polaron bands when the organic semiconductor layer is doped under positive gate bias (VG). There are two distinctive doping regions: a reversible and electrostatic doping region for VG 2 V. On the basis of intensity loss of vibrational peaks attributed to neutral PTCDI-C8, we obtain a charge carrier density of 2.9 x 10(14)/cm2 at VG=2 V; this charge injection density corresponds to the conversion of slightly more than one monolayer of PTCDI-C8 molecules into anions. At higher gate bias voltage, electrochemical doping involving the intercalation of Li+ into the organic semiconductor film can convert all PTCDI-C8 molecules in a 30-nm film into anionic species. For comparison, when a conventional gate dielectric (polystyrene) is used, the maximum charge carrier density achievable at VG=200 V is approximately 4.5 x 10(13)/cm2, which corresponds to the conversion of 18% of a monolayer of PTCDI-C8 molecules into anions.

Antidepressant treatment of pathologic laughing or crying in elderly stroke patients.

Pathologic laughing or crying (PLC), a complication of many neurologic disorders, involves behavior that is either inappropriate to the context or to the patient's subjective feeling state. It is due to a dysregulation of the motoric components of emotional experience. PLC is distinct from, but often associated with, major depression. The relatively few reports on treatment of PLC are primarily with tricyclic antidepressants. We report the effective treatment of PLC due to stroke in three patients with nortriptyline or fluoxetine. The cases also illustrate the broad spectrum of depressive symptoms (from none to a major depression) seen in patients with PLC. We discuss treatment implications and directions for future research.