Copper Phthalocyanine Thin Films Research Articles

Post-Deposition-Annealing-Induced Alignment of Copper Phthalocyanine Thin Films under UV Irradiation and Their Electrical Properties

Copper phthalocyanine(CuPc), a widely-used semiconducting material, was deposited onto quarts substrates via a vacuum process. SEM and XRD analysis were employed to characterize the structure-controlled CuPc films. As-deposited CuPc thin films were weakly oriented according to the XRD result and were homogeneous. The conductivity of CuPc film was estimated using four-point probe measurement technique and the values of the conductivity were 8.0 × 10−8– 3.5 × 10−7Ω−1cm−1. It was observed that thermal annealing under UV irradiation could make CuPc film well-aligned since UV irradiation could participate to increase the interaction among the CuPc molecules and between the CuPc molecule and the surface of the substrate leading to closer stacking of CuPc molecules. For well-aligned CuPc thin films, the threshold voltage in I-V characteristics of the ITO/CuPc/Al device was decreased by 20%compared to as-deposited CuPc films.

Influence of self-assembly monolayers on the characteristics of copper phthalacyanine thin film transistor

Self-assembly monolayers (SAMs) of octadecyltrichlorosilane (OTS) on a silicon dioxide substrate were formed in solution, or by vacuum vapor methods, and characterized by Fourier transform infrared (FTIR) spectroscopy. We found that the OTS SAMs on SiO2 substrates greatly affect the order and connectivity of evaporated copper phthalocyanine (CuPc) thin films, as confirmed by an atomic force microscopy (AFM) and X-ray diffraction analysis. The performance of the organic CuPc thin film transistor comprising OTS SAMs interposed between a gate dielectric and an organic semiconductor layer could be effectively enhanced as a result of improvements in the quality both of the organic/dielectric interface and the evaporated CuPc thin films. The deposition of an OTS SAM leads to a mobility of 1.48×10-3 cm2/Vs, 1–2 orders higher than that of bare silicon dioxide.

Low-energy electron mean free path in thin films of copper phthalocyanine

The formation of thin organic films of copper phthalocyanine (CuPc) deposited onto the surface of gold-coated quartz crystal resonator was studied in situ under ultrahigh vacuum conditions by means of total electron-beam-induced current spectroscopy in combination with deposit thickness determination by piezocrystal microbalance technique. Variations in the fine structure of the total current spectra of CuPc layers of var-ious thicknesses in the 0–8 nm interval have been analyzed and the electron mean free path in thin CuPc films was determined as a function of the electron energy. For electron energies of 5.0, 7.2, 14.4, and 18.0 eV above the Fermi level, the mean free path is 6.4, 3.9, 2.6, and 2.3 nm.

Growth Process of Vacuum Deposited Copper Phthalocyanine Thin Films on Rubbing-Treated Substrates

Surface morphology, crystal lattice spacings and crystallite size of copper phthalocyanine (CuPc) thin films grown on rubbed surfaces were probed at different stages of growth, by means of atomic force microscopy (AFM) and X-ray diffraction (XRD). The films consisted of many slender crystallites extending along the rubbing direction, due to the α-type columnar structure along the same direction. AFM revealed that the aspect ratio of crystal domains increases as the films grow, implying a change in the ratio of crystal growth rates in the two different directions parallel to the substrates. XRD demonstrated marked differences in the two intercolumnar directions. The molecular spacing is expanded in the thickness direction at the initial stage of growth, while it remains constant throughout the growth in the lateral (c-axis) direction. The crystallite size in the thickness direction is always comparable to the film thickness, while the size in the c-axis direction shows no change.

Growth of CuPc Thin Films on Structured SiO2/Si(100) Studied by Metastable Electron Emission Microscopy and Photoelectron Emission Microscopy

A combined metastable electron emission microscopy (MEEM) and photoelectron emission microscopy (PEEM) study has been performed for copper phthalocyanine (CuPc) thin films vacuum deposited on Si(100) with a lithographic SiO2 pattern. The MEEM image of SiO2 pattern edges changed considerably upon deposition of a very small amount of CuPc on the SiO2/Si(100) substrate, whereas no such changes were observed in the PEEM images. The different contrast features in MEEM and PEEM can be the result of different surface sensitivities of these microscopy techniques. The MEEM contrast characteristic for the pattern edges after the CuPc deposition may be ascribed to the difference of the molecular orientation of CuPc which cannot be observed by PEEM.

On the correlation between morphology and electronic properties of copper phthalocyanine (CuPc) thin films

The morphology of vacuum deposited copper phthalocyanine (CuPc) thin films surface deposited on Si(111) have been studied using the contact mode Atomic Force Microscope (AFM). The influence of substrate temperature during deposition and of the post-deposition UHV annealing on surface roughness as well as on the average and maximum grain height was determined. The observed changes of surface morphology were in a good correlation with the shift of surface Fermi level position in the band gap after O 2 exposure determined in our recent photoemission studies.

Transient charging of copper phthalocyanine: model and experiment

Thin films of copper phthalocyanine (CuPc) were deposited on indium tin oxide (ITO) substrates in ultra-high vacuum. Without breaking the vacuum, Ag dots were evaporated through a shadow mask. The present contribution is aimed at comparing experimental and simulated data on feedback-charge capacitance/voltage ( C/ V) and isothermal charge deep-level transient spectroscopy (Q-DLTS) of Ag/CuPc/ITO devices kept at ambient temperature. Two types of charge relaxation of different origins in response to a bias step (pulse) Δ U were resolved: (a) dielectric relaxation within the bulk of the CuPc semi-insulating layer; (b) emission from traps of charges injected and captured at the traps during the pulse. The dielectric relaxation is characterized by a well-defined time constant τ D ≈10 −4 s and is observable for both polarities of Δ U. The onset bias for observing the emission from traps corresponds roughly to one of the forward current. A positive Δ U is to be applied to ITO (hole injecting anode) in order to fill at least a fraction of the traps. Realizing that the traps are spatially distributed, the model previously applied to C/ V of a Si:H based devices has been updated to obtain at least a qualitative picture about the spatial distribution of the density of traps N T ( x) in CuPc. N T ( x) seems to rise when approaching the CuPc/ITO interface. These states are classified as acceptor-like ones, a situation analogous to that reported earlier for poly-( p-phenylene-vinylene). Protonation of the CuPc/ITO interface is discussed as the source of the acceptor-like states.

Heteroepitaxial copper phthalocyanine on Au(0 0 1) studied by high-resolution X-ray photoelectron spectroscopy

We report the formation of heteroepitaxial copper phthalocyanine (CuPc) thin film grown on a reconstructed Au(001) surface and the high-resolution X-ray photoelectron spectroscopy study thereof. The deposition of CuPc onto the “5×20” reconstructed Au(001) surface at room temperature results in a well-ordered CuPc overlayer. The angle-resolved XPS data reveal that adsorbed CuPc is molecular and stoichiometric. The low energy electron diffraction (LEED) further shows that the overlayer is incommensurate to the substrate with its square unit mesh measured approximately 12.7 Å by 12.7 Å along 〈110〉 and 〈11̄0〉 of the substrate. From the combined XPS and LEED data, a model of one flat-lying CuPc molecule per unit cell, which is different from the structures of the well-known α- and β-polymorphs, is proposed.

Peculiar features in the electrical characteristics of CuPc based diodes

We have investigated electrical properties of copper phthalocyanine (CuPc) thin films by means of current–voltage (I–V), capacitance–voltage (C–V) and charge deep-level transient spectroscopy (Q-DLTS) measurements. CuPc films were deposited on indium tin oxide (ITO) via organic molecular beam deposition (OMBD) at room temperature followed by Ag evaporation through a shadow mask, resulting in contacts of different sizes of dots. The measurements were carried out in situ at a pressure below 8×10−10mbar. No noticeable changes of electrical characteristics have been found after storing the devices for a few days under these conditions. Diodes of 330nm CuPc sandwiched between ITO and Ag show very low reverse currents with hysteresis-like characteristics for short delay times, which are the times between two consecutive voltage steps in an I–V measurement. Especially the bias at which current passes through zero is drastically affected by the sweep voltage direction. Almost identical curves in both directions can only be achieved using an extremely long delay time of 100s. It was found that the offset voltages for delay times of 5 and 100s are −0.85 and −0.1V for up-sweep and 0.14 and 0V for down-sweep voltage directions, respectively. This effect is likely due to the presence of deep traps which require a large time constant for charging and discharging in response to a change of the external voltage. The forward current, on the other hand, is virtually not affected, increasing initially over many orders of magnitude in a narrow voltage range and then increasing at a reduced slope. This behaviour is not stable when a high external voltage is applied. Q-DLTS measurements show presence of traps with time constants exceeding 50ms at ambient temperature.

アゾベンゼン修飾界面活性剤を用いた無電解法による銅フタロシアニン薄膜生成の速度論的検討

アゾベンゼン修飾界面活性剤を用いた無電解法による銅フタロシアニン薄膜生成の速度論的検討

Structural and Transport Properties of Copper Phthalocyanine (CuPc) Thin Films

Thin films of CuPc of various thicknesses have been deposited onto clean glass substrates using thermal evaporation technique at room temperature. The structural studies, using X-ray diffractometry and IR spectral analysis, showed that the films are mainly of β- form with preferential orientation of the plane (100). The dark electrical resistivity and the thermoelectric power measurements were carried out at different temperatures in the range 300-450 K. Room temperature current density-voltage characteristics showed ohmic conduction in the lower voltage range and spacecharge-limited – conductivity (SCLC) in the relatively high voltage. The SCLC are controlled by an exponential distribution of traps above the valence band edge. The temperature dependence of current density allows the calculations of some essential parameters such as the hole mobility, the relative permittivity, the trap concentration, the characteristic temperature and the trap density

Effects of substrate temperature on copper(II) phthalocyanine thin films

We report the crystal and band gap structures of copper(II) phthalocyanine (Cu–Pc) thin films depending on the substrate heating conditions and temperatures. The phase changes of the two α- and β-phases of Cu–Pc thin films due to different heating conditions were observed by using X-ray diffractions and electronic absorption spectra. As the temperatures increased from room temperature to 300°C, the energy gap was changed from 1.8052 to 1.7844eV and the crystal structure of Cu–Pc thin films was transformed from orthorhombic α-phase to monoclinic β-phase. The orientation of grains depended on the heat-treatment conditions and the temperatures of the substrate during film deposition. The transport properties of Cu–Pc thin films with different grain orientations were studied.

Determination of the energy band gap of thin films of cadmium sulphide, copper phthalocyanine and hybrid cadmium sulphide/copper phthalocyanine from its optical studies

Cadmium sulphide (CdS) thin films are prepared onto glass substrates by chemical bath deposition technique (CBD). Thin films of copper phthalocyanine (CuPc) are also sublimed onto glass substrates in high vacuum at room temperature. Hybrid CdS/CuPc (organic–inorganic) thin films are obtained from CdS films grown on glass substrates by CBD technique and subsequently vacuum subliming CuPc onto them. These films are annealed in air at different temperatures. Optical studies are separately done on CdS, CuPc and hybrid CdS/CuPc thin films. Optical properties are studied (between 300 and 900 nm) in a UV–VIS Spectrophotometer and the absorbance recorded as a function of photon energy. The optical band gap and maximum absorption coefficient of the as-deposited and annealed samples are determined.

Structural Investigation of Copper Phthalocyanine Thin Films Using X-Ray Diffraction, Raman Scattering and Optical Absorption Measurements

Structural properties of copper phthalocyanine (CuPc) powder and its thin films coated on glass plate are investigated using X-ray diffraction, Raman scattering and optical absorption techniques. These experiments are carried out at room temperature on CuPc powder and as-coated, 320 °C and 520 °C annealed, CuPc thin films. From the X-ray diffraction (XRD), we find that the CuPc powder exists in monoclinic phase, as-coated film is in orthorhombic α-phase and the film annealed at 320 °C exists in monoclinic β-phase with different lattice parameters as compared to those of the powder phase. The XRD peaks in 520 °C annealed film do not show the presence of CuPc but indicate the presence of copper oxide (CuO) nanoclusters of approximately 15 nm size. The optical Raman phonon frequencies of CuPc powder, as-coated and 320 °C annealed CuPc films show a slight shift in the intramolecular high frequency modes. Whereas, their low frequency Raman spectra from intermolecular modes are characteristically different indicating different phases. The different characteristic behavior of the optical absorption spectra of the as-coated and 320 °C annealed CuPc films corroborate the structural changes in the annealed film.

Ion Beam Doping of Chlorinated Copper Phthalocyanine Thin Films

Ion beam implantation of energetic nickel, germanium, and tin ions was studied for the purpose of altering the properties of the film structures of chlorinated copper phthalocyanine. Changes in the surface topology, conductivity, electron absorption spectra, and current response to ammonia were shown to be due to both ion bombardment of the samples and the subsequent thermal annealing.

アゾベンゼン修飾カチオン性界面活性剤を用いた銅フタロシアニン薄膜の作製

還元により分散能が失われるアゾベンゼン修飾カチオン性界面活性剤 (AZTAB) を用いてβ型銅フタロシアニン (CuPc) の薄膜化に成功している。AZTABのHCl, CuPc分散液に卑金属を浸せきすることにより, また, ITO基板ではアルミニウムと接触させ分散液中に同時に浸せきすることによりCuPc薄膜が得られた。得られた薄膜は使用したCuPc微粒子より構成されており, 膜厚は均一であった。また, 製膜量が最大となるAZTAB濃度が存在し, その値は分散させたCuPc量に依存していた。さらに薄膜の生成条件およびCuPc粒子へのAZTABの吸着等温線より薄膜の生成機構を推定している。

Optical Properties of Copper Phthalocyanine(CuPc)Thin Films

Vacuum sublimed thin films of copper phthalocyanine were prepared at room temperature. The optical properties of thin CuPc films have been investigated in the spectral range 200-2100 nm. The refractive index n as well as the absorption index k were calculated before and after annealing. It is obvious that the refractive index showed an anomalous dispersion in the absorption region as well as normal dispersion in the transparent region. The analysis of the spectral behavior of the absorption coefficient, α in the absorption region revealed direct transitions. The analysis of α as well as the dielectric constants e1 and e2 reveals several absorption peaks at photon energies given in the text. The fundamental and the onset energy gaps could also be estimated as 2.74+0.02 and 1.64+0.02 eV respectively.

Device preparation and characteristics of CuPc transistor

Static and dynamic characteristics of an organic static induction transistor (SIT) fabricated using copper phthalocyanine (CuPc) thin films are reported. Layered structure using CuPc as active layer consists of Al (drain)/CuPc/Al (gate)/CuPc/FTO (source)/glass. Electrical characteristics obtained are excellent at low negative gate voltages.

Femtosecond Z-scan Measurement of the Third Order Nonlinear Optical Coefficient of CuPc Thin Film

The third order nonlinear refractive index and absorption coefficient of copper-phthalocyanine (CuPc) thin film were measured by Z-scan method in ultrafast time regime. By changing pulse separation, we found that the nonlinear absorption behavior is different for the different pulse repetition rate. At 4MHz, the film exhibits RSA (reverse saturable absorption), while at 800kHz and 400kHz it shows SA (saturable absorption). Also the nonlinear refractive index is found to be different at 4MHz and other repetition rates.

Static induction transistor characteristics of organic copper phthalocyanine films

Static and dynamic characteristics of an organic static induction transistor (SIT) fabricated using copper phthalocyanine (CuPc) thin films are reported. Layered structure using CuPc as active layer consists of Au(drain)/CuPc/Al (gate)/Al(discontinuous)/CuPc/Au(source)/glass. Excellent electrical characteristics are obtained at low negative gate voltages.