T. Del Caño

Molecular Spectra and Molecular Organization in Thin Solid Films of Bis(Neopentylimido) Perylene

The synthesis, molecular spectra, and thin solid film properties of a perylene dye, bis(neopentylimido) perylene (BNPTCD),§ are reported. Absorption and emission molecular spectra are used to probe the structure of vacuum-evaporated thin films and Langmuir–Blodgett monolayers of BNPTCD. The experimental assignment of electronic, infrared, and Raman spectra are aided with calculated molecular structure and spectra using density functional theory (DFT) and Hartree–Fock (HF) computational methods at 6–31G level of theory. Characteristic vibrational modes and local symmetry of the planar perylene tetracarboxylic chromophore (PTCD) are used to extract molecular organization and film packing properties from spectral data collected using transmission and reflection-absorption (RAIRS) infrared spectroscopy. From the infrared spectra, using surface selection rules and polarization properties, it was extracted that the PTCD plane in BNPTCD is organized in the evaporated film with the plane head-on tilted over the substrate. After the molecular organization was identified, the effect of thermal annealing and solvent vapors on the film structure was examined. It is found that the PTCD plane turns to a flat-on orientation when the film is thermal annealed or solvent treated. The aggregation and molecular stacking in films was also inspected using the electronic absorption and fluorescence of monomers and aggregates.

Observation of persistent photoconductivity in vanadyl phthalocyanine

Persistent photoconductivity (PPC) in vanadyl phthalocyanine (VOPc) organic light-emitting diodes was investigated using photoconductive time response, photocurrent?voltage characteristics and charge extraction in linearly increasing voltage (CELIV) measurements. The experiments were performed in phase 1 (amorphous) and in phase 2 (crystalline) samples obtained by the physical vapour deposition (PVD) technique over ITO/glass electrodes with an Al covering electrode. The results indicated a photoconductivity with a long decay time in phase 1 VOPc described by a stretched exponential relaxation. The device showed a rectifying behaviour and the mobility of holes was measured by CELIV, following a dispersive model. In crystalline samples the PPC effect was not observed and the dominant mechanism of transport of holes was hopping in a Gaussian density of states.

Energy transfer between Langmuir-Blodgett monolayers of Titanylphthalocyanine and Bisneopentyl(imido)perylene

Abstract In the present work, the energy transfer between Langmuir–Blodgett (LB) monolayers of a donor molecule (the Bisneopentyl(imido)perylene) and an acceptor molecule (the Titanylphthalocyanine) has been investigated. The Langmuir–Blodgett technique has also been used to study the distance dependence of the energy transfer, using spacer layers of arachidic acid between the donor and acceptor planes. The optical properties of the LB films have been characterized using absorption and emission spectroscopy. The energy transfer has been extracted from photoluminescence measurements and illustrated with fluorescence imaging. A discussion of the different physical models and a first estimation of the critical energy transfer distance is presented.

Porous SiGe nanostructures formed by electrochemical etching of thin poly-SiGe films

We have studied the effect of the current density (J) and etching time in the formation of porous poly-SiGe (pp-SiGe) layers, with Ge fractions in the 0 to 0.55 range, by electrochemical etching. The starting material was unintentionally doped polycrystalline SiGe thin films, deposited in amorphous state by low-pressure chemical vapor deposition and subsequently crystallized. pp-Si structures were found to be homogeneous at large scale and show nanocrystalline of around 5 nm for low J values. The pp-SiGe structures show nonuniformities in their structure; the nanocrystal size is around 10 nm for low J and decreases for high J values and increasing etching times, reaching values of 2-4 nm. The composition of the pp-SiGe films, for low to moderate J values, shows a slight Ge enrichment. For high J values, in samples with x = 0.38, all the Si was etched and the composition of the porous layer is pure Ge. This effect is not so strong for samples with high Ge fractions (x = 0.55). The dominant radiative recombination mechanism is not excitonic; we associate it with recombination via defects in the crystalline structure of the porous film or states at the interface nanocrystals/native SiO 2 .

Hydrogen-free SiCN Films Obtained by Electron Cyclotron Resonance Plasma A Study of Composition, Optical, and Luminescent Properties

The Electrochemical Society, Inc. 2007. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproduced, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS). The archival version of this work was published in Journal of the Electrochemical Society Vol. 154 Issue 4 (2007): H325-H330