CuPc Films Research Articles

The molecular orientation in copper phthalocyanine thin films deposited on metal film surfaces

The molecular orientation in copper phthalocyanine (CuPc) films deposited on metal films of Au, Ag, Cu and Cr has been studied by reflection-absorption infrared spectroscopy and X-ray diffraction. The molecular planes of CuPc in the ultra-thin films (corresponding to several tens of monolayers) deposited on Au, Ag and Cu films were found to be nearly parallel to the metal film surfaces. Further deposition (up to 100 nm) on such thin films produces a molecular orientation with the molecular planes inclined away from the metal film surfaces. This corresponds to a crystal structure of the α phase with a standing b axis configuration. However, the molecular planes of the CuPc deposited on Cr films are rather perpendicular to the Cr film surfaces. These CuPc films are in the α phase with a parallel b axis configuration.

Detection of low hydrogen concentrations by a Cu-Pc sensor

A hydrogen sensor based on copper phthalocyanine (Cu-Pc) with palladium admixture was prepared. The sensor material is obtained by mixing palladium acetate and Cu-Pc (1:8) and adding semiconductor-grade acetone. The doped Cu-Pc was printed on interdigitated Pt electrodes supported by an Al 2O 3 substrated. The detection limit of the sensor is well below 1 ppm H 2 at an operating temperature of 95 °C; the response and recovery times are about 1 min, depending on the temperature and gas concentration. An H 2 concentration of 30 ppm leads to a conductance decrease of 44% compared with the clean air value. Changes in relative humidity between 0 and 100% lead to conductance changes of less than 6%; admixture of 48 ppm CO increases the conductance by only 5%. The increase in the sensor conductance on admixture of NO 2 is comparable to vacuum-evaporated Cu-Pc thin film sensors. From the direction of resistance changes on admixture of NO 2, it is obvious that Cu-Pc with Pd admixture remains a p-type conductor. The response mechanism of the sensory may be explained by a spillover of atomic hydrogen from Pd clusters onto the Pc film and subsequent reaction with adsorbed oxygen.

Optical and recording properties of copper phthalocyanine films

Vacuum-sublimed films of copper phthalocyanine (CuPc) were prepared. The absorption spectrum and optical constants of the film were studied. It was found that there is a comparatively large absorption region at wavelength of 550 – 750 nm. A static optical recording test on a CuPc film on a glass substrate indicated that low power HeNe laser irradiation could initiate a relatively large reflectivity change. It has been observed that the introduction of a metallic reflective layer on the recording layer will raise the writing threshold energy and the maximum reflectivity contrast.

Formation and characterization of epitaxial phthalocyanine and perylene monolayers and bilayers on Cu(100): Low-energy electron diffraction and thermal desorption mass spectrometry studies

Ordered monolayer and multilayer thin films of copper phthalocyanine (CuPc) and perylene dicarboxylic dianhydride (PTCDA) have been grown on Cu(100) single crystals. CuPc grows in a commensurate square lattice configuration, with two equivalent domains consisting of closest packed, flat lying Pc rings, rotated at ±21.8° from the principle Cu(100) axes. The dimensions of these square lattices (b1=b2=13.7 Å) are comparable to those observed using other substrates which interact weakly with the Pc overlayer (layered metal dichalocogenides, cleavage faces of single-crystal salts). PTCDA grows in a commensurate rectangular lattice (5√2×4√2)-R=45°, whose dimensions (b1=14.5 Å, b2=18.1 Å) are significantly different than those seen on weakly interacting substrates. Low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy, and thermal desorption mass spectroscopy (TDMS) data for the adsorption of this molecule strongly suggest that the first monolayer is dissociatively adsorbed to the Cu(100) surface. Growth of ordered layers of PTCDA has also been carried out on a Cu(100) surface modified with 1–2 ML (monolayers) of an ordered CuPc film. LEED and TDMS data indicate the formation of a new commensurate rectangular unit cell (b1=13.7 Å, b2=20.5 Å) for these PTCDA/CuPc/Cu(100) overlayers, which suggest that the CuPc layer controls the architecture of the subsequent PTCDA layers. The formation of a wide range of highly ordered organic heterojunctions appears to be possible, starting with a strongly adsorbed first layer, on surfaces such as single-crystal metals.

Interaction of NO 2 with copper phthalocyanine thin films I: Characterization of the copper phthalocyanine films

Thin films of copper phthalocyanine (CuPc) have been deposited by vacuum evaporation on glass or alumina substrates maintained at different temperatures. The morphology and the crystallinity of as-deposited films and of heat-treated and/or NO 2-treated films have been studied by electron microscopy and X-ray diffraction. The crystallinity of the films increases with substrate temperature during deposition: films deposited at room temperature or below are rather amorphous, whereas films deposited at 80°C or 200°C exhibit a highly uniaxial order of their crystallites; this order is altered by heat treatment or NO 2 doping. Scanning electron microscopy shows that the morphology of the film surface also depends on deposition temperature and that heat treatments induce the growth of whiskers from the surface. The structural changes are also observed through the temperatures of maximum conductivity of the CuPc films doped with NO 2. The sensitivity of CuPc to NO 2 could be applied to gas sensing.

Variable angle spectroscopic ellipsometry studies of oriented phthalocyanine films. II. Copper phthalocyanine

Recent studies obtaining the anisotropic complex dielectric spectra of oriented metal-free phthalocyanine (H2Pc) films with variable angle spectroscopic ellipsometry (VASE) have been extended to similarly oriented copper phthalocyanine (CuPc) thin films. The CuPc films were vacuum vapor deposited onto sputter deposited copper substrates. Two classes of anisotropically oriented films with thicknesses on the order of 1000 Å were produced with the molecular stacking b-axis in either a ‘‘standing’’ or surface-parallel configuration by controlling the substrate temperature. Reflection absorption infrared spectroscopy and x-ray diffraction were used to verify the different orientations. VASE data were acquired over a 4000–8000 Å wavelength range in 100 Å steps, and 45°–79° incidence angle range in 2° steps. Three-dimensional plots of the ellipsometric parameters, Δ and Ψ, versus wavelength and incidence angle have different characteristic shapes for the two classes of oriented films, similar to H2Pc, leading to significant differences in the optical constant spectral solutions obtained with an isotropic film model. Knowing the high degree of uniaxial ordering in the two film classes, approximate solutions to the parallel and perpendicular optical constants taken with respect to the crystalline b axis can be extracted from the isotropic solutions using a two-dimensional Bruggeman effective medium approximation.

InP EFFECTS ON CuPc LB FILM AND THE PHASE CHANGE

Interaction between the rough surface of InP and LB thin film of CuPc have been studied, and the reversible structure phase transition are found at room temperature and liquid nitrogen temperature, respectively.

Interaction of electron-accepting vapours with phthalocyanine and related compounds: a novel calorimetric study

Heats of interaction of nitrogen dioxide with thin films of copper and lead phthalocyanine (CuPc and PbPc) and tetraazadibenzo[14]annulene (TADA) have been studied using a novel interferometric fibre-optic microcalorimeter. For CuPc the heat is consistent with weak chemisorption on a film composed of microcrystals of dimensions smaller than the film thickness of 700 Å. Comparison of simultaneous studies of the rates of heat evolution and electrical conductivity change for CuPc films at ambient temperature following exposure to NO 2 shows that the conductivity change is substantially slower than the initial adsorption process. PbPc and TADA films react with NO 2 (3 mbar) undergoing oxidative ring cleavage with partial nitration, with release of heats in excess of 800 kJ mol −1 in some cases, although these reactions do not always occur immediately following exposure to the gas. These results are discussed in the context of the use of such materials as semiconducting gas-sensing films.

Interaction of electron accepting vapours with phthalocyanines and related compounds — A novel calorimetric study

An interferometric fibre-optic calorimeter capable of measuring heats of interaction between electron acceptor dopants and thin films of a wide range of materials with μJ sensitivity has been developed and used to measure heats of interaction of NO 2 (typically at a pressure of 3.5 mbar) with copper and lead phthalocyanine (Cupc and Pbpc) films. For Cupc these heats are consistent with weak chemisorption, which occurs significantly faster than the associated increase in electrical conductivity. For Pbpc oxidative ring cleavage with partial nitration occurs, with heat release typically in excess of 800 kJ mol −1, after variable time intervals.

High field electronic conduction processes in copper phthalocyanine thin films using lead and gold electrode combinations

The electrical properties of copper phthalocyanine (CuPc) thin films have been studied using lead and gold electrode combinations. Samples with two gold electrodes showed ohmic conduction and space-charge-limited conductivity, in agreement with previous work. Samples having one electrode of each metal showed three separate regions of space-charge-limited conductivity under forward bias (gold positive), but with considerably lower current density when the non-substrate (top) electrode was lead. Diode behaviour was also observed in samples where the lead electrode was on the substrate (bottom) side of the CuPc film. Under reverse bias the injecting lead electrode was found to act as a blocking contact with barrier height approximately 1 eV. The barrier widths were approximately 40 nm and 100 nm when the lead electrode was on the bottom and top sides respectively of the CuPc films. At higher voltage levels the Poole-Frenkel effect was observed when lead was the top electrode. Sample rectification ratios were also dependent on the electrode positions, having a value of several hundred with lead as the bottom electrode and considerably lower values as the top electrode. In the latter case the rectification ratio increased by a factor of about 10 on annealing and exposure to air. The results are consistent with the establishment of a barrier region when the non-substrate side of the CuPc films is in contact with a lead electrode.

Copper Phthalocyanine Layer as an Organic Semiconductor Sensor of NO2in Air

Abstract The applicability of copper phthalocyanine (CuPc) as an organic semiconductor gas sensor for the detection of high concentrations of NO2 in air is the aim of this study. Thin films of CuPc were deposited by sublimation. Measurements were carried out to determine the effect of NO2 on the conductivity of a CuPc film. A detection method for NO2 in air is proposed.

Characterization of copper phthalocyanine Langmuir-Blodgett films

Asymetrically substituted copper phthalocyanine (as-CuPc) Langmuir-Blodgett (LB) films are prepared on metal-coated quartz substrates and the electronic behaviour of sandwich structures of metal/CuPc LB film/metal are studied under normal laboratory ambients. The results show that CuPc films are very stable and reproducible. D.c. measurements produce ohmicI(V) characteristics while the a.c. conductance shows a power-law dependence on the frequency.

Complex impedance measurements of capacitor structures on silicon with copper phthalocyanine dielectric

Measurements were made of the capacitance and the conductance of several capacitor structures with a copper phthalocyanine (CuPc) dielectric at different voltages and in the frequency range of 102–106 Hz. A thermally evaporated CuPc film about 1300 Å thick was fabricated in a parallel-plate capacitor between gold and aluminum electrodes (Al‖CuPc‖Au). Two distributions of relaxation times are observed in this frequency range. At low frequencies voltage-dependent polarization (possibly interfacial polarization) appears to be the dominant mechanism of current conduction. At high frequencies a relatively voltage-independent hopping within and/or between molecules appears to be dominant. The CuPc remains polarized for a long time. Measurements were also made of the capacitance-voltage (C-V) characteristic of a Al‖CuPc‖SiO2‖Si capacitor at 104, 105, and 106 Hz for different scanning rates. The basic features of the device’s C-V characteristics are discussed.

Formation of Copper Phthalocyanine Thin Films by Electrolysis of Surfactants with Ferrocenyl Moiety

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Enhanced infrared ATR spectra of surface layers of polymers using metal films

Enhanced infrared ATR spectra were measured for Langmuir films of CuPc deposited on PE and PVdC overlaid on PET, by using thin metal (Ni or Ag) films. The apparent intensity ratios for the bands ascribed to the upper layer were much larger than for those of the lower layer. The ratio depended on the nature as well as the mass thickness of the metal films. The mechanism of the enhancement was discussed in terms of SPP and multiple reflection effects.

Metal phthalocyanine polymer film formation by the double source evaporation of tetracyanobenzene and metal

By the double source evaporation of tetracyanobenzene (TCB) and copper under 10 −4∼10 −3 Torr argon atmosphere and subsequent heat treatment, we can make poly copper phthalocyanine (poly CuPc) thin films. Exclusion of oxygen from the vacuum chamber is one of the most important problem for the success of the poly CuPc film formation by this method.

Enhanced infrared atr spectra of surface layers using metal films

Enhanced infrared ATR spectra were measured for PVdC (polyvinylidene chloride latex) overlaid on PET (polyethylene terephthalate) and Langmuir films of CuPc (cupric phthalocyanine) deposited on PE (polyethylene), by using thin metal (Ni or Ag) films. The apparent intensity ratios for the bands ascribed to the upper layer were much larger than for those of the lower layer. Morphologies of the metal films were observed by TEM. The mechanism of the enhancement was discussed in terms of SPP and multiple reflection effects. Application of this technique to surface studies was also discussed.

An Organic Semiconductor as Gas Detector

Abstract The objective was to investigate the application of copper phthalocyanine (CuPc) films to the detection of air-borne NH3. The phenomenon of gas adsorption on the available surface area of an organic semiconductor was studied. Repeatable results can be obtained relatively quickly provided that a certain state of the semiconductor (which may be adopted as a reference system) will be re-established prior to each measurement of air-borne NH3. The development of an appropriate method for the regeneration of the CuPc film following completion of the detection procedure is described. A linear relation between minimum current intensity and partial pressure (concentration) of NH3 in the gas sample is obtained. The method proposed in this study for the measurement of atmospheric NH3 has analytical potential.

Surface-enhanced Raman scattering from copper phthalocyanine thin films

We have measured the Raman scattering from copper phthalocyanine (CuPc) thin films deposited onto surfaces of Si, glass and evaporated Ag films. A systematic measurement of the Raman intensity was performed by varying the thicknesses of CuPc and Ag films. The CuPc films deposited onto glass substrates show the normal Raman scattering and its intensity is measurable even for the films as thin as a few tens of Å. These facts allowed us to determine purely experimentally the enhancement factors, especially for the films on Ag surfaces. A relatively small enhancement of ≈ 20 is found for thick CuPc films ( ≈ 800 Å) deposited onto thick Ag films ( ≈ 400 Å). Furthermore, a large enhancement of ≈ 10 4 is found for approximately one monolayer coverage of CuPc on Ag-island films ( ≈ 50 Å). From a comparison between experiments and calculations, we show that the small enhancement of ≈ 20 is caused by the interference of multiply reflected light waves in the CuPc film. With the aid of transmission measurements, we also show that the excitation of surface plasmon polaritons in Ag-island particles is responsible for the large enhancement of ~ 10 4. Our data on the coverage dependence of the intensity for the CuPc-coated Ag-island films disagree with features generally reported. We give a possible interpretation to our data.

Photovoltage and stability of an n-type silicon semiconductor coated with metal or metal-free phthalocyanine thin films in aqueous redox solutions

An n-type silicon (n-Si) semiconductor coated with an evaporated thin film of metal phthalocyanine (MPc) or metal-free phthalocyanine (H/sub 2/Pc) worked as a fairly stable photoanode in aqueous redox solutions. The photovoltage observed for a photocell, (n-Si/CuPc/Fe/sup 3 +//Fe/sup 2 +/ aqueous solution (pH 4.2) /Pt), was 0.50 V, only slightly less than that for a p-n junction Si photocell (approx. 0.6 V). The action spectrum was similar to that of a bare n-Si electrode, except for a depression caused by photoabsorption by the CuPc film in the red region. The above wet photocell has current-voltage characteristics better than those for a solid photocell, (n-Si/CuPc/Pd).