Copper Phthalocyanine Thin Films Research Articles

Structural and Surface Morphology Analysis of Copper Phthalocyanine Thin Film Prepared by Pulsed Laser Deposition and Thermal Evaporation Techniques

In the present paper, Copper Phthalocyanine (CuPc) thin films were deposited on glass and silicon substrate by thermal evaporation and pulsed laser deposition (PLD) methods. CuPc thin films prepared at different annealing temperatures (298, 323, 348, 373, 423 K) respectively. The structure and surface morphology of CuPc in powder and thin films forms prepared by two methods were studied using Energy dispersive X-ray (EDX), X-ray florescence (XRF), X-ray diffraction (XRD), Atomic force microscope (AFM), and Scanning electron microscope (SEM). It showed that there was a change and enhancement in the crystallinity and surface morphology due to change in the annealing temperature (Ta). The purpose of our work is to find the optimal temperature for which the film produces best structural properties for CuPc thin film to produce organic field effect transistor. Analysis of X-ray diffraction patterns of CuPc in powder form showed that it had an α-poly-crystalline phase with monoclinic structure, with preferentially oriented (100) plane transform to β-single crystalline morestable structure at different annealing temperatures.

Facile electrochemical growth of nanostructured copper phthalocyanine thin film via simultaneous anodic oxidation of copper and dilithium phthalocyanine for photoelectrochemical hydrogen evolution

We present a novel electrochemical approach to grow copper phthalocyanine (CuPc) thin-film photoelectrodes through anodic oxidation of copper and dilithium phthalocyanine (Li2Pc). This circumvents the challenges associated with the electrochemical processing of unsubstituted CuPc from solution. The potentiostatic co-electrooxidation reaction at the heterogeneous interface favors the growth of CuPc thin film. The surface morphology of thin film exhibits nanorod-like features. UV-Vis, grazing angle Fourier transform infrared (FTIR), and grazing angle X-ray diffraction patterns reveal that the nanocrystalline phase corresponds only to α-CuPc and no admixture of other polymorphs. Photocurrent measurement shows a stable photoresponse in neutral medium. The photoelectrochemical hydrogen evolution on p-type CuPc coated copper photocathode shows an enhanced activity over bare copper and indium tin oxide (ITO) electrodeposited with CuPc and monolithium phthalocyanine radical (LiPc) thin films.

Study of Optical and Electrical Properties of Bismuth-Doped Copper Phthalocyanine Thin Films Grown by Thermal Co-Evaporation

Bismuth-doped copper phthalocyanine (Bi-doped CuPc) thin films were grown by organic-source thermal co-evaporation under five different deposition rates. Morphological, optical and chemical properties of the doped-films were characterized by atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), UV-Visible spectroscopy and X-ray photoelectron spectroscopy (XPS). Furthermore, electrical properties of ITO/Bi-doped-CuPc/Al devices i.e. carrier mobility and carrier concentration were characterized by current-voltage and capacitance-voltage measurements. Morphology of the doped films shows strong dependence on preparation conditions, as clearly observed by features of film surface i.e surface grain size and roughness. Optical absorption spectra of all doping conditions provide regular three dominant α-phase peaks at 339, 620 and 695 nm corresponding to absorption from B-band and Q-band, respectively. Electrical properties exhibit the enhancement of the film conductivity due to increase of both carrier mobility and carrier concentration with higher Bi-doping level. Moreover, photoelectron analysis reveals chemical information of the metal dopant in the host material.

High switching speed copper phthalocyanine thin film transistors with cut-off frequency up to 25 kHz

The characteristics of high frequency and high speed are demonstrated in vertical structure organic thin film transistors (VOTFTs) fabricated by DC magnetron sputtering and vacuum evaporation. The saturated current–voltage characteristics can be determined by drain-source negative bias voltage. Responsive frequency of the device is as high as 20 kHz when rectangular wave dynamic signal is applied to the gate-source electrode, and switch characteristic time reaches the microsecond. The unsaturated current–voltage characteristics are observed when the drain-source bias voltage is positive. In the condition of VDS = 3 V and VGS = 0 V, the drain-source current IDS is 2.986 × 10−5 A, and the current density is 1.194 mA/cm2. Cut-off frequency fc is 25 kHz when a small sine wave dynamic signal is applied to the gate-source electrode. The volt-ampere characteristic of VOTFTs transfers from linear to nonlinear with increasing of drain-source bias voltage.

Near room temperature ferromagnetism of copper phthalocyanine thin films

We reported near room temperature ferromagnetism of α-CuPc films without and with light Ni-doping. Two samples were characterized by X-ray photoelectron spectroscopy (XPS) to confirm the absence of other ferromagnetic impurities. The α-CuPc film exhibited ferromagnetic hysteresis with saturation magnetization of ∼6.77emu/cm3 and coercivity of ∼96Oe at 280K, while that of the Ni-doped α-CuPc film are ∼0.69emu/cm3 and ∼113Oe, respectively. Through the density functional theory (DFT) calculations, the origin of the ferromagnetism arise from Cu 3d states and N 2s2p electronic spin polarization, as well as p-d exchange coupling interactions, and spin-unbalanced electronic structure of C 2p induced by the π–π interactions.

Crystal-Domain Orientation and Boundary in Highly Ordered Organic Semiconductor Thin Film

Conduction of electric charges is often done in polycrystalline materials. Unavoidably, the crystallite size, orientation, and domain boundaries (DBs) affect the transport of the charge carriers. It is particularly so for organic semiconductors known to be highly anisotropic and strongly dependent on DBs. Understanding those effects will have a strong impact on improving the performance of organic electronic and optoelectronic devices. Herein, we report our investigation on the crystal-domain orientation and boundary on the charge transport of operating device with copper phthalocyanine (CuPc) thin films grown on p-sexiphenyl (p-6P) by Kelvin probe force microscopy. In CuPc intradomains, the voltage drop increases as the angle increases between the domain orientation and the source-drain electric field. In DBs, the potential wells and steep voltage drops were observed. The increase of the DBs width and the angle between the orientations of neighboring domains results in the raise of voltage drop across th...

Effects of Heat Annealing on the Gas Sensing Properties of Spin Coated Unsubstituted Copper Phthalocyanine Films

Unsubstituted copper phthalocyanine (CuPc) thin films on glass substrate were prepared using spin coating technique. The effects of heat annealing of CuPc films on the NO2 gas sensing properties were studied. The results showed that the films annealed at 150°C have highest sensitivity, highest response rate and lower response time. Sensitivity and response rate were decreased and response time was increased after annealing with temperature 200°C and above. The duration over which the films were annealed changes the gas sensing properties. Highest sensitivity, highest response rate, lower response time and highest recovery rate were observed for 2 hour (150°C) annealed films. Longer annealing time causes the decrease of sensitivity, response rate and recovery rate and increase of response time however improves recovery ratio. The heat treatment limited to the temperature of 150°C for 2 hours duration improves the sensing properties of the films. Hence heat annealed unsubstituted CuPc spin coated films can be used as nitrogen dioxide gas sensor.

Effect of thermal annealing on the structural and optical properties of spin coated copper phthalocyanine thin films

Low cost sol–gel spin coating was used to deposit copper phthalocyanine (CuPc) thin films on both fused quartz and glass substrate. The prepared films were studied before and after thermal annealing at 350 °C for 1 h in air. X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) were used to study the structural properties. From the structural characterization results, the films transformed from the metastable α-phase to the stable β-phase. Refractive index, absorption coefficient, and lattice dielectric constant were evaluated before and after annealing for the first time for spin coated CuPc thin films using spectrophotometric measurements in the spectral range 200–2500 nm. The values of the direct optical band gap of the as deposited film at 1.52 eV and 2.85 eV were redshifted to 1.4 eV and 2.42 eV for the annealed film. This shift is significant for near infrared photonics. The third order non-linear susceptibility was presented at lower photon energy for the CuPc films showing higher value for the annealed film.

Influence of Substrate Temperature on the Optoelectronic Properties of CuPc Thin Film

The copper phthalocyanine thin films were deposited on quartz and Si/SiO2 substrates at different substrate temperatures. The morphologies, structures and optical properties of CuPc films were characterized by scanning electron microscopy, X-ray diffra ction and UV-Visible spectroscopy. The polymorph of alpha–CuPc was observed in films deposited at temperature ranging from 20°C to 145°C. The transmission and absorption spectra of CuPc films deposited at different temperatures are presented.

Copper phthalocyanine thin films on Cu(111): Sub-monolayer to multi-layer

Abstract Scanning tunneling microscopy (STM) has been used to observe the growth mode and crystal structure of sub-monolayer (ML) to multilayer thin films of copper phthalocyanine (CuPc) molecules on the Cu(111) surface at room temperature (RT). At sub-ML coverage the molecules are mobile on the surface. At approximately one ML coverage the molecules become sterically confined and lying flat on the Cu substrate form an ordered, multi-domained, 2D oblique lattice. As coverage is increased beyond 1 ML the molecule–substrate interaction diminishes in strength while the intermolecular interaction begins to dominate, causing the layer separation to increase, and the crystal domain size and lattice constants to shrink as the crystal structure begins to more closely resemble the bulk α-phase CuPc molecular solid. This trend continues for the layer-by-layer growth of 3 complete ML, eventually giving way to the emergence of large 3D islands at a coverage equivalent to 4 ML.

Experimental study and analytical modeling of the channel length influence on the electrical characteristics of small-molecule thin-film transistors

Bottom-contact p-type small-molecule copper phthalocyanine (CuPc) thin film transistors (TFTs) with different channel lengths have been fabricated by thermal evaporation. The influence of the channel length on the current–voltage characteristics of the fabricated transistors were investigated in the linear and saturation regimes. The devices exhibit excellent p-type operation characteristics. Results show that devices with smaller channel length (L=2.5μm and 5μm) present the best electrical performance, in terms of drain current value, field effect mobility and subthreshold slope. Saturation field-effect mobilities of 1.7×10−3cm2V−1s−1 and 1×10−3cm2V−1s−1 were obtained for TFTs with channel lengths of L=2.5μm and L=5μm, respectively. Transmission line method was used to study the dependence of the contact resistance with the channel length. Contact resistance becomes dominant with respect to the channel resistance only in the case of short channel devices (L=2.5μm and 5μm). It was also found that the field effect mobility is extremely dependent on the channel length dimension. Finally, an analytical model has been developed to reproduce the dependence of the transfer characteristics with the channel length and the obtained data are in good agreement with the experimental results for all fabricated devices.

Molecular orientation of copper phthalocyanine thin films on different monolayers of fullerene on SiO2 or highly oriented pyrolytic graphite

The interface electronic structures of copper phthalocyanine (CuPc) have been studied using ultraviolet photoemission spectroscopy as different monolayers of C60 were inserted between CuPc and a SiO2 or highly ordered pyrolytic graphite (HOPG) substrate. The results show that CuPc has standing up configuration with one monolayer of C60 insertion on SiO2 while lying down on HOPG, indicating that the insertion layer propagates the CuPc-substrate interaction. Meanwhile, CuPc on more than one monolayers of C60 on different substrates show that the substrate orientation effect quickly vanished. Our study elucidates intriguing molecular interactions that manipulate molecular orientation and donor-acceptor energy level alignment.

Spin coated unsubstituted copper phthalocyanine thin films for nitrogen dioxide sensors

Copper phthalocyanine ( CuPc ) is synthesized chemically and used for making CuPc thin films using spin coating technique. Films were prepared from trifluroacetic acid (TFA) and chlorobenzene mixed solution on the glass substrate. Spin coated films of unsubstituted CuPc films were heat annealed at 150°C for 2 h duration and were used to study NO 2 gas sensing characteristics. α-phase of CuPc is noted by UV-visible absorption spectra. IR spectra of undoped CuPc films and doped CuPc films with NO 2 revealed that, doping of nitrogen dioxide modifies and deletes some of the bands. The effect of NO 2 at various concentrations from 50 ppm to 500 ppm in atmospheric air at room temperature on the electrical conductivity of CuPc films was studied. Sensitivity, response time and repeatability of the CuPc sensor were discussed in this paper.

Structural and Optical Properties of Vacuum Coated and Annealed Copper Phthalocyanine (CUPC) Thin Films

Heat treatment is able to cause the structural transformation of phthalocyanine thin film during the post-deposition heat treatment. The annealing effects of the process on the film characteristics of vacuum deposited copper phthalocyanine thin films were studied. However, the pre-annealing leads to a larger-grain and a more compact structure. Structure transformation was inhibited by post-deposition annealing at 300oC. Thin films of CuPc were deposited using vacuum evaporation technique method onto glass substrates. The films were annealed at 4 different temperatures (323, 333, 343 and 353K) in air at different intervals of time. Optical studies were done and the results are discussed. The optical band gap for the film as obtained from the graph for all the thin films are tabulated and analyzed. X ray diffraction studies on the deposited film showed crystallinity with a major peak for CuPc.

Controllable growth of copper-phthalocyanine thin film on rough graphene substrate

Film growth behavior of copper-phthalocyanine (CuPc) on rough graphene (RG) and smooth graphene (SG) substrates was investigated experimentally. Both the RG and the SG are single layer graphene on metal substrates. The RG samples were prepared on copper foils and show rough surfaces; whereas, the SG samples prepared on Ni(111) substrates are characterized with much smoother surfaces. While CuPc molecules deposited on the two graphene substrates show similar molecular alignment, morphologies of the deposited films show considerable differences. On the SG substrate, CuPc molecules form two-dimensional islands with large size and sharp edges. While on the RG substrate, CuPc nucleates into particle-like grains without regular shapes. The high density of topographical defects on the RG substrate is believed to be a primary factor which leads to the formation of the smaller grains. The variation of thin film structures of CuPc with respect to the substrate temperature was also studied. Films with good crystallinity can still be obtained on the RG substrates when the substrate temperature is 80 °C or higher.

Excitation of optical modes supported by strong absorption in organic thin films at attenuated total reflection geometry

Reflection dips observed at attenuated total reflection (ATR) geometry for metal thin films are interpreted from excitations of surface plasmon polaritons. We have presented that the absorption induced by enhanced electric fields in a metal film is an origin of this phenomenon (Wakamatsu et al (2007 J. Opt. Soc. Am. B 24 2307)). This viewpoint provides that ATR dips can be generated not only in metals but in other materials. Here, the absorption spectra of copper phthalocyanine (CuPc) thin films were observed at ATR geometry without a metal layer. Only from p-polarized ATR measurements was a strong absorption dip observed in the short wavelength region of the CuPc absorption bands. Kramers–Kronig analyses for the transmittance spectra of a CuPc thin film revealed that the refractive index of the film lowers around the spectral position of the p-polarized ATR dip. Transfer matrix analyses indicated that the lowered refractive index of CuPc induces the enhancement of evanescent fields in the film. These results demonstrate that the ATR dip generation is attributable to the absorption derived from enhanced evanescent fields in the CuPc film.

Quantitative correlation between air induced changes of electronic parameters and morphological features of copper phthalocyanine thin film surfaces

In this work, utilizing fine-resolved photoemission yield spectroscopy (PYS) method, the set of electronic parameters of the space charge layer of 16 nm-copper phthalocyanine (CuPc) thin films deposited on n-type Si(111) substrate covered with modified SiO2 was determined after long term air exposure. The PYS investigation revealed that work function and surface band bending increased upon gas adsorption by 0.64 eV and 0.32 eV respectively for organic layer and surface dipole effect appeared as the shift in electron affinity of 0.32 eV. Obtained results were compared with photoemission data received for corresponding CuPc films on different types of silicon Si(111) substrate. Collected parameters were correlated with the morphological features of the CuPc's surfaces measured applying atomic force microscopy (AFM) ability. Results of compiled PYS and AFM studies indicated particular electronic tendency for oxidation processes for certain shapes of phthalocyanine crystallites. It may suggest that by manipulation of the initial films' morphology it would be possible to control the air stability of the CuPc-based electronic devices and their vulnerability to degradation processes.

Solution-processed copper phthalocyanine–gold nanoparticle hybrid nanocomposite thin films

Copper phthalocyanine (CuPc) thin film and gold nanoparticles (Au NPs) of size ~20nm were deposited on conducting indium tin oxide coated glass substrates. Thin films were ~500nm thick having crystalline nature determined by surface profilometer and X-ray diffraction technique. The concentration of Au NPs in the films was varied whereas the concentration of CuPc was constant. It was observed that surface morphology varied with Au NP concentration increase in the films accompanied by changes in the optical spectra over 300-1000nm range and increase in the electrical conduction but no changes in the Fourier transform infra-red spectra. Such nanocomposite films would be useful in the fabrication of organic solar cells.

Enhancing charge transport in copper phthalocyanine thin film by elevating pressure of deposition chamber

Copper phthalocyanine (CuPc)-based thin film transistors were fabricated using CuPc films grown under different deposition pressure (Pdep) (ranging from 1.8×10−4Pa to 1.0×10−1Pa). The transistor performance highly depended on Pdep. A field-effect mobility of 2.1×10−2cm2/(Vs) was achieved under 1.0×10−1Pa. Detailed investigations revealed that Pdep modulates the molecular packing and orientation of the organic films grown on a SiO2/Si substrate and influences the charge transport. Furthermore, from a device physics point of view, contact resistance of the fabricated transistors decreased when Pdep increased, which was beneficial in reducing energy consumption.

Molecular arrangement investigation of copper phthalocyanine grown on hydrogen passivated Si(111) surfaces

Abstract Chemical, electronic and structural properties of ultra thin films of copper phthalocyanine (CuPc) grown on hydrogen passivated silicon (1 1 1) surfaces were investigated in situ by X-ray photoelectron spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), X-ray photoelectron diffraction (XPD) and electron diffraction (LEED). The early stages of copper phthalocyanine adsorption (1–2) were characterized by the saturation of surface defects and by a flat lying disposition on the surface. Upon further CuPc coverage, the passivation of Si surfaces resulted in the molecule taking a standing position in films. The molecular packing deduced from these studies appears very close to the one in the bulk α phase of CuPc. The work function of the films was found to be decreasing during the growth and was correlated with the molecular orientation.