Conductive Behavior and Morphology of Axially Modified Gallium Phthalocyanine Thin Films onto Indium Tin Oxide Substrates

Semiconductor molecular films based on a gallium phthalocyanine chloride (GaPcCl) and a bidentate amine were prepared by using vacuum thermal evaporation and electrochemical techniques in order to investigate the preferred conduction paths within the films. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) were employed to characterize the morphology of the films. The conductivity measurements were performed with two different methods in order to investigate preferential conduction directions. The film transverse conductivity was obtained by using scanning tunneling spectroscopy (STS) and the in-plane film conductivity was measured with a four-point probe system. From spectroscopy measurements, the tunneling conductance (dI/dV) was also obtained. From these results, it was found that the conductive nature of the films was strongly influenced by the deposition technique which in turn defined the morphological characteristics of the film. The evaporated method showed better conductivity response and provided semiconductor characteristics in the film transverse direction with an in-plane ohmic response. Finally, contact angle measurements were performed and showed hydrophobic characteristics in all cases.

Synthesis and Evaluation of the Semiconductor Behavior in Vanadium Indanone Derivatives Thin Films

In this work, we propose a method to synthesize vanadium (IV) 2-benzyli-dene-1-indanone derivatives, used to prepare film structures by thermal evaporation. The complexes possess high melting point allowing the using of vacuum deposition methods. All the samples were grown at room temperature (25℃) and low deposition rates (0.4 Å/s). The surface morphology and structure of the deposited films were studied by scanning electron microscopy (SEM) and spectroscopy dispersive energy (EDS). Optical absorption studies of the complex films were performed in the 200 - 1100 nm wavelength range. The Tauc band gap (Eg) of the thin films was determined from the (αhν)1/2 vs. hν plots for indirect transitions. The vanadium (IV) complex films show optical activation energies in the range of organic semiconductors. Multilayer nylon 11/vanadium indanone devices were fabricated using ITO and silver electrodes. The d.c. electrical properties of the device were also investigated. It was found that the temperature-dependent electric current in the structure showed a semiconductor behavior. At lower voltages below 7 V, the current density in the forward direction was found to obey an ohmic I-V relationship;for higher voltages above 7 V, the conduction was dominated by a space-charge-limited (SCLC) mechanism. The electrical activation energies (Ea) of the complexes were in the 2.17 - 2.31 eV range.

Effect of Organic Dopants in Dimetallophthalocyanine Thin Films: Application to Optoelectronic Devices

Semiconductor films of organic, doped dimetallophthalocyanine M2Pcs (M = Li, Na) on different substrates were prepared by synthesis and vacuum evaporation. Tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) were used as dopants and the structure and morphology of the semiconductor films were studied using IR spectroscopy, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS). The absorption spectra recorded in the ultraviolet-visible region for the deposited films showed the Q and Soret bands related to the electronic π-π* transitions in M2Pc molecules. Optical characterization of the films indicates electronic transitions characteristic of amorphous thin films with optical bandgaps between 1.2 and 2.4 eV. Finally, glass/ITO/doped M2Pc/Ag thin-film devices were produced and their electrical behavior was evaluated by using the four-tip collinear method. The devices manufactured from Na2Pc have a small rectifying effect, regardless of the organic dopant used, while the device manufactured from Li2Pc-TCNQ presents ohmic-like behavior at low voltages, with an insulating threshold around 19 V. Parameters such as the hole mobility (μ), the concentration of thermally-generated holes (p0), the concentration of traps per unit of energy (P0) and the total trap concentration (Nt(e)) were also determined for the Li2Pc-TTF device.

Morphological and Optical Properties of Dimetallo-Phthalocyanine-Complex Thin Films

In this work, the synthesis of semiconducting molecular materials formed from metallo-phthalocyanines (MPcs) and bidentate amines is reported. Powder and thin-film samples of the synthesized materials, deposited by vacuum thermal evaporation, show the same intra-molecular bonds in IR-spectroscopy studies. The morphology of the deposited films was studied using scanning electron microscopy and atomic force microscopy. The optical parameters have been investigated using spectrophotometric measurements of transmittance in the wavelength range 200 - 1100 nm. The absorption spectra in the UV-Vis region for the deposited samples showed two bands, namely the Q and Soret bands. The optical band gap values of the thin films were calculated from the absorption coefficient α in the absorption region and were found to be around 1.4 - 1.6 eV. The dependence of the Tauc and Cody optical gaps on the thickness of the film was also determined.