Vanadyl Phthalocyanine Films Research Articles

Photo-thermally Induced Phase Transition in Vanadyl Phthalocyanine Thin Film

Abstract A vanadyl phthalocyanine (VOPc) film (Phase I) on a mica substrate was prepared and photoinduced phase transition of VOPc was tried. Changes in absorption spectra show that Phase I structure is converted to Phase II structure by the irradiation with He-Ne laser. The surface structural changes of VOPc were also observed by using atomic force microscopy (AFM). Experimental results suggest that the phase transition was induced by photo-thermal processes.

Formation and Third-Order Nonlinear Optical Properties of Triclinic Metallophthalocyanine Films

Oxomolybdenum phthalocyanine (MoOPc) and tin phthalocyanine (SnPc), which both have a pyramidal molecular shape, were deposited onto sapphire by organic molecular beam deposition. The crystalline phase of these films was determined to be triclinic by X-ray diffraction and absorption spectra with reference to previously formed titanylphthalocyanine (TiOPc) and vanadylphthalocyanine (VOPc) films. Values for the third-order nonlinear optical susceptibility χ(3) of the triclinic MoOPc and SnPc films were slightly smaller than those of TiOPc and VOPc but still much larger than those of planar metallophthalocyanines such as copper phthalocyanine and zinc phthalocyanine. Molecular shape is an important factor determining the nonlinear optical properties of metallophthalocyanines.

Structure and spectroscopic characterization of polycrystalline vanadyl phthalocyanine (VOPc) films fabricated by vacuum deposition

The polycrystalline VOPc films in phases I, II, and a less-crystallized α-form have been fabricated on an indium-tin-oxide-glass substrate. Room-temperature and low-temperature visible absorption spectroscopy. Fourier-transform infrared spectra, and X-ray diffraction patterns have been used to characterize and analyze the packing structures and interactions of VOPc molecules. Bethe splitting. broadening, and redshift of the Q absorption band have been observed in the three packing structures. Thermochromism was found in phase II and the less-crystallized α-form, but not in phase I, from the temperature dependence of the absorption spectra. The liquid nitrogen was found to be effective in the crystallization of VOPc molecules.

Fast Gas Sensing with Metal-Phthalocynaine Films in MIS Structures

The NH3gas sensing characteristics of vanadyl-phthalocyanine (VOPc) films in metal-insulator-semiconductor (MIS) hetero structures were investigated. The MIS device showed a rectification behavior and an increase in conductivity at the presence of NH3 gas. The response was very fast and reversible. The conductivity change observed for the MIS sensors was found to be originating from the change of the barrier height between the junctions.

Third-order nonlinear optical properties of vanadylphthalocyanine derivative films with additional rings

We formed thin films of vanadylphthalocyanine (VOPc), vanadyldibenzophthalocyanine (VODBPc), and vanadylnaphthalocyanine (VONc) on sapphire substrates and measured their third-harmonic generation (THG) at 1.6 and 1.9 μm. The χ (3) values of amorphous and crystalline films were in the order VOPc>VODBPc>VONc. The third-order hyperpolarizabilities estimated at 1.6 μm from the χ (3) values of amorphous films were also in the same order.

Photoprocesses in Langmuir–Blodgett vanadylphthalocyanine films

Photoprocesses in Langmuir–Blodgett vanadylphthalocyanine films

Electric quadrupole second-harmonic generation spectra in epitaxial vanadyl and titanyl phthalocyanine films grown by molecular-beam epitaxy

For epitaxial vanadyl and titanyl phthalocyanine films with Laue symmetry 4/mmm, second-harmonic generation (SHG) spectra due to only electric quadrupole and electric quadrupole coupling mechanisms were obtained under a suitable geometry, while the contributions of electric dipole, magnetic dipole, and magnetic dipole coupling mechanisms were eliminated. In addition to a resonant peak previously reported, two peaks were observed at higher energies. An oriented gas model analysis showed that in-plane components of molecular hyperquadrupole polarizabilities cause the resonances. On the basis of the molecular electronic structure calculated by the density functional theory, the resonant processes are attributed to electric quadrupole transitions at SH frequencies.

Thermal desorption measurement of ultrathin epitaxial organic films by optical spectroscopy

Thermal desorption of epitaxial films of vanadyl phthalocyanine (VOPc:C 32N 8H 16VO) and squaric acid (SQ:C 4O 4H 2) was measured by using temperature programmed optical absorption spectroscopy. The activation energies for the desorption and pre-exponential factors were determined by measuring the amount of the molecules remaining in the film. Change in the molecular arrangement of VOPc during the desorption was detected from the spectra. The effects of hydrogen bonding and antiferroelectric transition of SQ are discussed.

Polarized optical absorption spectra of orientation aligned vanadyl phthalocyanine films

Optical absorption spectra (400∼900 nm) of vanadyl phthalocyanine (VOPc) films deposited on perylenetetracarboxylic dianhydride (PTCDA) films formed on mica (VOPc/PTCDA/mica) depended on orientation of polarization plane of incident light. This means that orientations of VOPc and PTCDA molecules in VOPc/PTCDA/mica align. Since the absorption spectrum of the VOPc film with thickness 100 nm in the VOPc/PTCDA/mica formed at 60 °C corresponded to that of I-TiOPc, structure of the VOPc film was supposed to be close to I-TiOPc. Without the PTCDA film, orientation aligned II-VOPc film was formed on mica kept at 100 °C. © 1997 Elsevier Science S.A. All rights reserved.

FT-Raman Spectroscopy of Thin Films of Titanyl Phthalocyanine and Vanadyl Phthalocyanine

Thin solid films of titanyl phthalocyanine (TiOPc) and vanadyl phthalocyanine (VOPc) have been vacuum evaporated onto glass substrates held at various temperatures in the range from -30 to 240°C. FT-Raman spectra have been collected using an Nd:YAG laser emitting at 1064.1 nm, a Michelson interferometer and an InGaAs detector. The characteristic vibrational wavenumbers have been assigned in the observed Raman spectra of TiOPc and VOPc molecules. Titanyl phthalocyanine and vanadyl phthalocyanine exist in a number of polymorphic forms which have characteristic x-ray diffraction patterns. Polymorphs can also be distinguished on the basis of the FT-Raman spectra. Titanyl phthalocyanine was present in an amorphous form from −30°C to room temperature. As the temperature was increased, type II TiOPc was produced. Vanadyl phthalocyanine displayed a similar behaviour. At room temperature the VOPc was amorphous, but with increasing temperature it crystallized in the type II polymorph. At 240°C the VOPc film existed in a highly preferred (010) orientation.

FTRaman Spectroscopy of Thin Films of Titanyl Phthalocyanine and Vanadyl Phthalocyanine

FTRaman Spectroscopy of Thin Films of Titanyl Phthalocyanine and Vanadyl Phthalocyanine

Charge carrier trapping states in thin evaporated and Langmuir-Blodgett organic films

Thermally modulated space-charge-limited current (TM-SCLC) and conventional SCLC methods have been used to determine the energy parameters of the local charge trapping states for three heterocyclic organic compounds in two different structural states — as thin vacuum-evaporated layers and Langmuir-Blodgett (LB) multilayer films. The TM-SCLC method provides higher resolution and accuracy of trap depth (Et) determination with error not greater than ± 0.02 eV. In sandwich-type samples Me/organic layer/Me of metal-free phthalocyanine (α-H2Pc), five sets of hole trapping states are determined in the energy range from 0.55 to 0.07 eV; for dimethylamino-benzylidene indandione-1,3 (DMABI) samples also, five sets of trapping states are detected in the 0.5–0.28 eV range; however, for indandione pyridinium betaine-1,3 (IPB) samples, only a very shallow set of traps at Et ≈︂ kT emerged. In the case of evaporated layers the conductivity activation energy (Ea) dependence on voltage energy (U), Ea = Ea(U), decreases in a step-like manner, every step giving the trap depth Et of the corresponding set of trapping states. In the case of LB multilayers of vanadyl phthalocyanine (VOPc) and IPB films the Ea = Ea(U) dependences are of complex, oscillatory-type character, possibly caused by a spatially non-uniform trap distribution in the bulk of the sample.

Enhancement of the third-order nonlinear optical susceptibility in epitaxial vanadyl-phthalocyanine films grown on KBr

We determined the magnitude of the third-order nonlinear optical susceptibilities χ(3)(−3ω; ω, ω, ω) of vanadyl-phthalocyanine (VOPc) films grown on KBr and fused silica substrates, using the third harmonic generation method at a wavelength of 1200 nm. The χ(3) value of the film grown epitaxially on KBr was 2.87×10−10 esu, which was greater by a factor of about 7.7 than that of a polycrystalline film grown on fused silica. The enhancement of χ(3) in the epitaxial phase is associated with the optimized orientation of the two-dimensional π-electron system in the condensed phase.

Thick single crystalline vanadyl phthalocyanine film epitaxially grown on KBr crystal by molecular beam epitaxy

Structural analyses are reported of ∼ 5 μm thick VOPc films grown on a KBr(001) surface by the MBE technique. The crystal is monoclinic with lattice parameters a = 14.2 A ̊ , b = 13.1 A ̊ , c = 12.7 A ̊ and β = 103.2°. The orientation of the unit cell is influenced by the crystal lattice of the substrate even in this thickness range: The projections of the a- and b-axes of VOPc onto the (001) plane of KBr coincide with the [110] directions of KBr. Four kinds of crystal orientations were observed in pole figure measurements.

Characterization of Organic Epitaxial Films by Atomic Force Microscopy

Abstract The initial stage of the epitaxial growth of vanadyl-phthalocyanine (VOPc) films on alkali halides (AH) and MoS2 was studied by atomic force microscopy. Each grain grew epitaxially on the surface with its crystal axis parallel to that expected from the molecular arrangements determined by reflection high energy electron diffraction. The growth mode of the VOPc films on AH was the Volmer- Weber type. Although the height of the grains increased with the deposition time, the grains hardly enlarged in the lateral direction. The shape of grains was affected even by steps with atomic height on AH. On the other hand, the nuclei grew rapidly in the lateral direction on MoS2. The diffusion length of VOPc on MoS2 was estimated to be six times as long as that on KBr at room temperature. Large domains with flat surfaces were observed on a MoS2 surface when the substrate temperature was kept at 100°C during film growth.

Electronic Structure of Vanadyl Phthalocyanine. Investigations of Thin Film Samples by Electron Energy‐Loss Spectroscopy

AbstractThe energy‐loss function Im (−ε−1) of a thin polycrystalline vanadyl phthalocyanine film is determined in the range from 1 to 37 eV from energy‐loss experiments with 50 keV electrons. The electronic structure of the film investigated is analyzed by computing the complex dielectric function ε(E), optical constants (n(E) + ik(E), R(E), α(E)), and neff(E) using the Kramers‐Kronig analysis of the energy‐loss function. The spectrum of valence electron excitations is primarily interpreted in terms of π−π* and σ−σ* transitions of individual molecules and in terms of the collective excitation of the valence electron ensembles (σ + π plasmon).

Spectral dependence of the anisotropy of χ (3) of epitaxially grown vanadyl phthalocyanine film

A study on the spectral dependence of the anisotropy of χ (3) of epitaxially grown vanadyl phthalocyanine has been performed using the technique of third-harmonic generation. It is found that the variation in the anisotropy of χ (3) is a result of the dispersion of the complex ratio 3χ 1221/χ 1111. There is a sharp two-photon resonance in the χ (3) spectrum which is 1.88 eV above the ground state. Enhancement of χ (3) is achieved in the unidirectionally oriented vanadyl phthalocyanine film by one order of magnitude.

Optical recording performance of thin films of phthalocyanine compounds

As organic dyes with excellent thermal and light stability, phthalocyanine compounds have been investigated as write-once read-many optical recording materials. By selecting different substituents and metallic ions, the absorption bands of thin film of phthalocyanine compounds were matched with the wavelengths of semiconductor lasers. It was found that the absorption regions of vacuum sublimated thin films of vanadyl phthalocyanine (VOPc), tetra-pentyloxy phthalocyanine vanadyl (TPPcVO) and tetra-nonyloxy phthalocyanine vanadyl (TNPcVO) were between 580 and 850 nm. In the near-IR region, the absorbance and reflectivity of thin films of VOPc were greater than 50% and 20% respectively. The static optical recording test of the VOPc thin film showed that the write power was less than 10 mW with the write pulse width of 200 ns using an He-Ne laser as light source. The dynamic optical recording test of VOPc as a write-once read-many recording material on a 5.25 in optical disk indicated that the carrier-to-noise ratio (CNR) was greater than 45 dB.

Influence of structural order on absorption spectra of langmuir-blodgett films of vanadyl phthalocyanine

Influence of structural order on absorption spectra of langmuir-blodgett films of vanadyl phthalocyanine

χ(3) components of single-crystalline vanadyl phthalocyanine film

Single-crystalline vanadyl phthalocyanine film has been grown by the molecular-beam epitaxy technique. The χ(3) components, χ111 and χ1111, have been determined by third-harmonic generation using a fundamental Nd:YAG laser source. The relation, χ1221∼0.8χ1111, reveals that the nondiagonal component significantly contributes to the nonlinear optical response, which originates in two-dimensional π-electron system of this molecule.