Copper Phthalocyanine Thin Films Research Articles

Deposition of copper phthalocyanine films by glow discharge-induced sublimation for gas sensing applications

In this work, the deposition of copper phthalocyanine (CuPc) thin films by glow discharge-induced sublimation (GDS) is investigated. The physical properties of the deposited films are studied by FT-IR spectroscopy and nitrogen physisorption measurements. The gas/film interaction of the deposited coatings is tested by measuring their IR response and electrical conductivity in NO2- and NO-containing atmospheres.

Deposition of Copper Phthalocyanine Films by Glow-Discharge-Induced Sublimation

Copper phthalocyanine (CuPc) thin films have been deposited by a recently developed plasma-based method named glow-discharge-induced sublimation (GDS). The deposition of CuPc films has also been ob...

X-ray waveguide phenomenon in copper phthalocyanine thin film

A white X-ray beam was irradiated on a copper phthalocyanine (CuPc) thin film under grazing incidence condition, and X-rays propagated in the film due to the waveguide phenomenon were observed by an energy-dispersive detector. Energy profiles of guided X-rays showed four specific resonant modes. By comparing them with the calculated ones, a three-layer model of CuPc film was proposed.

Study of thin films of carrier-doped strontium titanate with emphasis on their interfaces with organic thin films

Fifty nanometer-thick metal-doped strontium titanate (M:STO, M = La and V) films deposited epitaxially on single crystalline STO substrates were characterized in comparison with indium tin oxide (ITO) covered glasses, to check their applicability to optically transparent anode materials for organic optoelectronic devices. M:STO, in particular V:STO, films turned out to have distinct surface flatness, needfully low electric resistivities and notably large work functions. While their optical transmittances are lower than those of ITOs at this moment, we suggest that M:STO films have a potential to take the place of ITO films. Further, we have observed energy level alignments for copper phthalocyanine thin films at the interface of V:STO.

The Influence of Molecular Structure Modification on the Photoluminescence and Optical Absorption of Thin Copper Phthalocyanine Films in the Near-IR Range

We have studied the luminescence and optical absorption of thin films of copper phthalocyanine (CuPc) with a modified molecular structure of the peripheral fragments. The coefficient of absorption in the near-IR and visible range (absorption by defects) and the photoluminescence spectra exhibit correlated changes depending on the modification of the CuPc structure.

Nondestructive characterization of surface resistance for copper(II) phthalocyanine thin films using a near-field scanning microwave microscope

We observed the surface resistance of copper(II) phthalocyanine (Cu-Pc) thin films dependence on substrate heat-treatment conditions by a nondestructive characterization method using a near-field scanning microwave microscope (NSMM) at an operating frequency f=5.2–5.3 GHz. The changes in surface resistance were investigated by NSMM by measuring the reflection coefficient S 11. The surface resistance of Cu-Pc thin films depends on the grain alignment. When the Cu-Pc thin films were annealed at 150 °C for 3 h, the films are aligned with the b-axis normal to the substrate and have a lower surface resistance.

Nondestructive characterization of various thin films using a near-field scanning millimeter-wave microscope

We demonstrate a nondestructive millimeter-wave surface imaging technique using a near-field scanning millimeter-wave microscope (NSMM) with a resonant standard waveguide probe at an operation frequency f = 30 – 39 GHz . A chemically etched metallic probe tip, was coupled to the resonant rectangular waveguide. By properly tuning the tunable resonator and the probe tip, we could improve sensitivity and spatial resolution of the NSMM. Measuring the change of the reflection coefficient S 11 in the near-field zone, sheet resistance changes of Ag, ITO, YBa 2Cu 3O y , organic copper(II) phthalocyanine (Cu–Pc) thin films, and MgO were obtained. We observed the NSMM images of Ag thin film on the glass substrate with a spatial resolution better than 2 μm.

The anisotropic dielectric function for copper phthalocyanine thin films

Abstract Copper phthalocyanine (CuPc) thin films were prepared by organic molecular beam deposition (OMBD) in high vacuum and ultra-high vacuum on passivated Si(1 1 1) using β-phase CuPc as source material. The substrates were kept at room temperature during the deposition. The IR peak positions indicate that the films consist mainly of α-phase CuPc, while the relative intensities suggest that the films are anisotropic. The anisotropic dielectric function for these CuPc layers was determined from ellipsometric spectra using uniaxial models in the range from 0.73 to 5 eV.

Epitaxial Growth of a Copper-phthalocyanine on a Transparent Conductive Substrate with an Atomically Flat Surface

A copper-phthalocyanine (CuPc) thin film was heteroepitaxially grown by the organic molecular beam epitaxy method at 200 °C on an indium−tin oxide (ITO) film with an atomically flat terraced and stepped surface. Two different epitaxial domains with a 6-fold symmetry of CuPc were grown on the ITO substrate with relationships of (100){001}CuPc || (111){112}ITO (major domain) and (100){001}CuPc || (111){110}ITO (minor domain). The orientation of the major domain was better than that of the minor domain. The difference in orientation may be understood by considering geometrical matching between the CuPc molecules and the ITO surface.

Annealing effects on the gas sensing properties of copper phthalocyanine films

Heat treatment is able to cause the structure transformation of phthalocyanine thin film either during the gas sensing operation or during the post-deposition heat treatment. The annealing effects of the two processes on the film characteristics and sensing properties of vacuum deposited copper phthalocyanine thin films were studied. The results show that the structure re-organization of CuPc film occurs during the sensing period when the sensing is operated at temperature up above 225 °C. Such structure transformation was inhibited by post-deposition annealing at 300 °C. However, the pre-annealing leads to a larger-grain and a more compact structure. As a result, the film sensitivity and response rate of sensing experiment are decreased after the heat treatment due to the reducing in the surface area. On the contrary, the recovery characteristic of the CuPc film is improved after heat treatment.

A time-domain analysis of dipolar effects in copper phthalocyanine thin films on indium–tin–oxide substrates

Transient charging in response to pulsed bias of copper phthalocyanine (CuPc) organic thin films on indium–tin–oxide (ITO) was investigated by charge transient spectroscopy (QTS) in situ under ultra-high vacuum conditions. The charge relaxation phenomena in response to a bias pulse are modelled in terms of dipolar effects, considering alternatively possible orientation of the dipoles (polarization) under an applied external electric field and capture of charge carriers in dipole-induced electron states. Assuming a Gaussian energetic distribution of the density of states (DOS) as a consequence of disorder, a simple formalism is derived to determine the width (variance) σd of the DOS from QTS data. The isothermal QTS response of single-layer Ag/CuPc/ITO samples provides evidence for dipolar effects in CuPc, an example of using the new formalism in practice. The dipole moment of the CuPc molecule proved to be too small for the assignment of the amount of transient charges to the reorientation of dipoles. The model of trapping of charge carriers at a Gaussian DOS induced by polar molecules in a non-polar solid has mediated an estimate of the fraction of polar molecules from the experimentally assessed variance σd of the Gaussian DOS. The resulting dependence of σd on the dipole moment is in striking coincidence with literature data related to other types of polar molecules in molecular glasses.

Submolecular-Resolution Studies on Metal-Phthalocyanines by Noncontact Atomic Force Microscopy

Copper phthalocyanine (CuPc) thin films deposited on Au (111) surfaces were investigated by noncontact atomic force microscopy (NC-AFM). Structures with a periodic modulation of the spacing between the molecular rows of CuPc multilayer films were found. Submolecular features of each individual molecule on a film were successfully imaged. The obtained contrast was interpreted by the chemical interactions between a tip and the spatial electron density distribution of chemically active molecular orbitals such as highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). In addition, the energy dissipation in the NC-AFM imaging of monolayer films was studied on a molecular scale. The obtained high-resolution contrast in the dissipation images was discussed in connection with the random fluctuation of molecules.

Studies of surface resistance of copper(II) phthalocyanine thin films by using a near-field scanning microwave microscope

We observed the surface resistance of copper(II) phthalocyanine (Cu–Pc) thin films dependence on substrate heating temperature by using a near-field scanning microwave microscope (NSMM). The NSMM system was coupled to a dielectric resonator with a distance regulation system at an operating frequency f=4.5–5.5 GHz. The crystal structures and surface resistance of Cu–Pc thin films due to different heating temperatures were observed by using X-ray diffraction including the 2 θ and φ-scan and the near-field scanning microwave microscope. As the temperatures increased from room temperature to 200 °C, the crystal structure of Cu–Pc thin films was transformed from monoclinic α-Phase to thermally stable monoclinic β-Phase. The changes in surface resistance of Cu–Pc thin films due to different substrate heating temperatures were investigated by NSMM by measuring the reflection coefficient S 11. The surface resistance of Cu–Pc thin films depends on the morphology and crystal alignment of these films. When the substrate temperature for deposition was 150 °C, the minimum surface resistance of Cu–Pc thin films was obtained.

Noncontact atomic force microscopy study of copper-phthalocyanines: Submolecular-scale contrasts in topography and energy dissipation

Copper-phthalocyanine (CuPc) thin films on MoS2 surfaces were investigated by noncontact atomic force microscopy (NC-AFM). Submolecular resolution was successfully obtained in both topographic and dissipation images of CuPc monolayers. For topographic contrasts, the influence of short-range chemical interactions is particularly considered while the dissipation contrasts are discussed in relation to the tip-induced molecular fluctuations. Molecularly-resolved NC-AFM image was also obtained on CuPc multilayer, which revealed the structural difference between the monolayer and multilayer surfaces. The energy dissipation measured on these surfaces showed distinctive difference reflecting the different structural stabilities in the films. Furthermore, local surface modification of CuPc monolayer was demonstrated by NC-AFM. This is a direct evidence for the existence of energy transfer from the vibrating cantilever to the molecules through dissipative tip–sample interactions.

Time-of-Flight Measurement of Lateral Carrier Mobility in Organic Thin Films

Lateral carrier transport in a copper phthalocyanine (CuPc) thin film has been investigated by the time-of-flight technique using a micro-excitation system. Drift mobility in the CuPc film has been estimated from the transient photocurrent measured for various electric field strengths. The drift mobility has been compared to the field-effect mobility of a thin-film transistor with CuPc as the channel material. The field-effect mobility was comparable to the drift mobility measured by the TOF technique.

Photoemission and theoretical investigations on NO 2 doping of copper phthalocyanine thin films

The doping effect by NO 2 molecules of copper phthalocyanine (CuPc) thin films has been studied by means of X-ray photoemission spectroscopy (XPS). The core level spectra indicate that the NO 2 molecules form a stable chemical bond with the copper central atom of the molecule, determining charge transfer effects also in the nitrogen spectra. Instead, no variation on the carbon chemical state is experimentally observed. Theoretical calculations, performed by means of Dmol 3 code, confirm that the most reactive part of the CuPc molecule is the copper atom, while the outer benzene rings are completely not affected by the NO 2 molecule adsorption. The theoretical calculations, in terms of charge transfer and effects on the core levels, agree very well with the experimental data.

Solar cells based on two organic layers

Solar cells composed of two organic layers have been prepared. Thin films of copper phthalocyanine (CuPc) and perylene tetracarboxylic (PTCD) with thicknesses of about 50 nm have been, respectively, deposited on silicon substrates using a sublimation technique. The prepared cells show an improvement of approximately 20% in their physical parameters over the cells fabricated with only one organic layer.

Orderly Growth of Copper Phthalocyanine on Highly Oriented Pyrolytic Graphite (HOPG) at High Substrate Temperatures

The growth of an ordered thin film of copper phthalocyanine (CuPc) on highly oriented pyrolytic graphite at high substrate temperatures was studied. High-resolution electron energy loss spectroscopy investigation revealed that the CuPc molecules remained lying flat on the substrate throughout the growth from monolayer to multilayer. Scanning tunneling microscopy and X-ray diffraction measurements showed the CuPc thin film assumed a dense-packed structure in the horizontal direction and a face-to-face stacking mode in the surface normal direction. The totality of the results presented a clear view of the orderly growth process of CuPc molecules.

Influence of Molecular Orientation on Electrical Conductivity in Copper Phthalocyanine Thin Films

Control the orientation of molecular stacking in copper phthalocyanine (CuPc) thin films were tried by applying an electric field during vacuum deposition. The results of the absorption spectra and X-ray diffraction suggest that the electric field changes the molecular configuration in the CuPc thin films. The vertical resistivity of the film grown under the electric field was smaller than that of film grown without electric field.

IN-PLANE RESISTANCE OF AN ULTRA THIN GOLD FILM: INFLUENCE OF A COPPER PHTHALOCYANINE OVERLAYER

We have constructed an apparatus to evaporate ultra thin films of Copper Phthalocyanine (CuPc) on ultra thin gold epitaxial film grown by MBE, which thicknesses are in the range of 30 Å. We present STM pictures of CuPc on ultra thin gold which show a columnar alignment perpendicular to the substrate and preliminary in-situ resistance measurement of the hybrid device. Using theoretical modeling on a simpler system, we calculate the electronic properties and estimate the expected changes in the quantum and temperature dependent resistance of the thin gold layer, when it is covered by a discotic overlayer.