Copper Phthalocyanine Films Research Articles

The density of states in thin film copper phthalocyanine measured by Kelvin probe force microscopy

The density of states (DOS) is an important factor in understanding charge transport in organic semiconductors. We use Kelvin probe force microscopy to find the DOS in thin films of copper phthalocyanine (CuPC). We find an exponential DOS with a characteristic energy of 0.11 eV over a 0.5 eV range of the highest occupied molecular orbital of CuPC. We also find that the technique is limited by charge trapping and hysteresis at low DOSs, and nonuniform potential profiles within the CuPC film at high DOSs.

Optical and infrared spectroscopic studies of chemical sensing by copper phthalocyanine thin films

Abstract Thin films of copper phthalocyanine have been deposited on KBr and glass substrates by thermal evaporation method and characterized by the X-ray diffraction and optical absorption techniques. The observed X-ray pattern suggests the presence of α crystalline phase of copper phthalocyanine in the as-deposited thin films. Infrared spectra of thin films on the KBr pallet before and after exposure to the vapours of ammonia and methanol have been recorded in the wavenumber region of 400–1650 cm −1 . The observed infrared bands also confirm the α crystalline phase. On exposure, change in the intensity of some bands is observed. A new band at 1385 cm −1 , forbidden under ideal D 4h point group symmetry, is also observed in the spectra of exposed thin films. These changes in the spectra are interpreted in terms of the lowering of molecular symmetry from D 4h to C 4v . Axial ligation of the vapour molecules on fifth coordination site of the metal ion is responsible for lowering of the molecular symmetry.

Investigation of gas-sensing properties of copper phthalocyanine films

In this work, the sensor response of thin films of octasubstituted copper phthalocyanine derivative (CuPcR 8) with bulky substituents on R = –N(SO 2C 6H 5–CH 3)CH 2(CH 2) 8CH 3 to the vapour of benzene, chloroform, ethanol and butanol were investigated by surface plasmon resonance technique. The application and some advantages of total internal reflection ellipsometry method for determination of the organic vapours are also demonstrated.

Investigation of structural features of hexadecafluorinated copper and zinc phthalocyanine films

The structural features of hexadecafluorinated copper and zinc phthalocyanine (MPcF16) films (M = Cu, Zn) obtained by vacuum thermal deposition are investigated. The dependence of structural features of these films on the film thickness is studied by means of optical and Raman spectroscopy. It is shown that an increase in the thickness of MPcF16 films, as well as film annealing under vacuum conditions at a temperature of 220°C, leads to the formation of the phase whose crystalline structure differs from that of the 20-to 50-nm-thick initial films.

Schottky diode solar cells on electrodeposited copper phthalocyanine films

Schottky diode solar cells were fabricated on electrodeposited films of copper phthalocyanine (CuPc). The aluminum contact was deposited by two methods, viz. thermal evaporation and electron beam evaporation; the materials and electro-optical characteristics of these devices were compared. We achieved the highest ever reported open-circuit voltage of 1.19 V with the electrodeposited CuPc films. This is in contrast to an open-circuit voltage of 0.907 V reported in Schottky diode cells with evaporated CuPc films. β-Phase dominance in electrodeposited CuPc films was thought to be a major factor in enhanced performance. Effects of varying the CuPc thickness on the device performance were investigated.

Molecular structure and growth morphologies of pentacene/fluorinated copper-phthalocyanine heterostructures

By combining in-situ X-ray diffraction and atomic force microscopy, we investigate the structure and morphology of organic heterostructures formed by deposition of pentacene onto fluorinated copper-phthalocyanine (F 16CuPc) films grown with two different molecular orientations. Well ordered pentacene films grow upon deposition on top of standing-up F 16CuPc molecules ( s-structure) and finally form homogeneous films. When pentacene is deposited on lying-down F 16CuPc ( l-structure), laterally small and high crystallites form. The pentacene preserves the same thin-film structure and excellent alignment along the surface normal in either case, with mosaicities of only 0.015 ± 0.001°. We demonstrate in this work how thin organic buffer layers can be employed to tailor the growth of ordered organic heterostructures.

Electronic Properties and Orbital-Filling Mechanism in Rb-Intercalated Copper Phthalocyanine

The evolution of the electronic properties of a thin film of copper phthalocyanine deposited on Al(100) and progressively intercalated with rubidium atoms was followed by photoemission and X-ray absorption spectroscopies. Electron donation from the Rb atoms to the C32H16N8Cu molecules results in the lifting of the degeneracy in the eg ligand-derived molecular orbital and the lowering of the molecular symmetry. For Rb∼2C32H16N8Cu, spectral evidence indicates that both donated electrons reside in the first split-off eg-derived level, thus creating an electronic inequivalence between the C atoms in the benzene rings. For higher Rb concentrations, a reduction of the Cu oxidation state is observed, together with a new Cu-derived state in valence-band photoemission spectra, testifying to the filling of the b1g orbital. Thus, even though b1g is the lowest unoccupied orbital of the neutral molecule, in the film, the Cu-derived b1g-derived states are occupied only after a partial filling of the eg-derived band has taken place. Despite the fact that the eg-derived spectral weight becomes larger as the rubidium content in the RbxC32H16N8Cu compound increases, no spectral density was observed at the Fermi level, showing that the film remains insulating for all of the investigated stoichiometries.

Optimal film thickness for exciton diffusion length measurement by photocurrent response in organic heterostructures

Exciton diffusion in organic materials is crucial for designing and optimizing organic photovoltaic devices. This paper addresses the important complication of the choice of film thickness affecting measurement accuracy in the method of measuring exciton diffusion length from thickness-dependent photocurrent response in organic bilayer heterostructures. Based on the photocurrent model integrated with optical interference effect, the correlation between the exciton diffusion length and the optimal thickness of organic layer is analytically solved. It shows that the intrinsic nonlinearity of the correlation causes prominent uncertainty of estimated diffusion length. Two approaches were proposed to improve the measurement accuracy: (1) the thickness effect of each layer in this heterostructure on photocurrent response is asymmetric so that certain thickness combination can be chosen to reduce the uncertainty; (2) on account of the limited accuracy of the optimal thickness determined by photocurrent spectra, estimated diffusion length should be verified by spectrum fitting. Taking these improvements into account, the exciton diffusion length in copper phthalocyanine film is determined as 20 ± 5 nm from curve fitting by this method.

Low-Energy Electron-Induced Processes in Fluorinated Copper Phthalocyanine Films Observed by F- Desorption: Why So Little Damage?

As an indication of damage induced by hot electrons in an organic electronic material, the desorption of F- ions from a thin perfluorinated copper phthalocyanide film on SiO2 under low-energy (0-25 eV) electron impact has been recorded mass spectrometrically. Yields and damage cross sections are very low. No strong features due to negative ion resonances are found in the electron energy dependence of the desorption yield; rather the yield function rises from a threshold at about 5-6 eV continuously (with some weak structure) throughout the measured range. We discuss these findings in terms of the electronic structure of the film, as well as parameters influencing the relevant bond breaking process. We emphasize the strong influence of energy redistribution, which quenches normally long-lived negative ion resonances and selects localized and strongly repulsive excitations, as often observed in electronically induced bond breaking at surfaces. The improved understanding should be helpful in the selection of low-damage materials for organic semiconductor devices and for selection of operation parameters.

Laser desorption from the surface of copper phthalocyanine films on silicon and cadmium sulfide

We have studied laser desorption mass spectra of copper phthalocyanine (CuPc) films deposited in vacuum onto single crystal silicon and cadmium sulfide substrates. The desorption was induced by 10-ns pulses of neodymium laser radiation (quantum energy, 2.34 eV) with an energy density E varied from 0.1 to 40 mJ/cm2. It is established that laser radiation produces fragmentation of CuPc molecules and desorption of the fragments. The main fragments observed in the mass spectra are identified. The intensity of the main desorbed species has been studied as a function of the laser pulse energy density. The components of CdS substrates penetrate into the volume of deposited CuPc films in the form of Cd atoms and S2 molecules.

Copper phthalocyanine films deposited by liquid–liquid interface recrystallization technique (LLIRCT)

The simple recrystallization process is innovatively used to obtain the nanoparticles of copper phthalocyanine by a simple method. Liquid-liquid interface recrystallization technique (LLIRCT) has been employed successfully to produce small sized copper phthalocyanine nanoparticles with diameter between 3-5 nm. The TEM-SAED studies revealed the formation of 3-5 nm sized with beta-phase dominated mixture of alpha and beta copper phthalocyanine nanoparticles. The XRD, SEM, and the UV-vis studies were further carried out to confirm the formation of copper phthalocyanine thin films. The cyclic voltametry (CV) studies conclude that redox reaction is totally reversible one electron transfer process. The process is attributed to Cu(II)/Cu(I) redox reaction.

Formation of sharp metal-organic semiconductor interfaces: Ag and Sn on CuPc

A detailed investigation of the chemistry and electronic structure during the formation of the interfaces between thin films of the archetypal organic molecular semiconductor copper phthalocyanine (CuPc) and Ag or Sn deposited on it was performed using photoemission and near-edge X-ray absorption spectroscopies with synchrotron light. Our study demonstrates the formation of sharp, abrupt interfaces, a behavior which is of particular importance for applications in organic devices. Moreover, for Ag on CuPc we demonstrate that this interface is free from any reaction, whereas there is slight interface reaction for Sn/CuPc.

The absorption band at 1.128 eV of copper phthalocyanine films

We deposited copper phthalocyanine (CuPc) films on (100) silicon wafers by means of a vacuum evaporation method and investigated the absorption characteristics by means of photoacoustic (PA) spectroscopy. It was verified that we excluded the PA signal originated in the silicon substrate with the chopping frequency of 200 Hz when the thickness of the CuPc film was 4.4 μm. We then detected an absorption band at 1.128 eV (1.1 μm). This band is possibly related to the charge transfer between Cu atoms and adsorbed oxygen molecules.

Plasma Deposited Porphyrin/Phthalocyanine Films as Promising Optical Gas Sensing Materials

Abstract5,10,15,20 meso-tetraphenyl porphyrin (H2TPP) and copper phthalocyanine (CuPc) films have been deposited by means of a recently developed plasma based technique named glow discharge induced sublimation (GDS). The two macrocycles have been deposited by vacuum evaporation (VE) and H2TPP by spin coating (SPIN) as well for comparison. The physical properties of the films have been characterized by means of scanning electron microscopy (SEM) and nitrogen physisorption measurements. SEM images and physisorption isotherms highlight both the much higher surface roughness and specific surface area of GDS samples with respect to the VE and SPIN ones. Optical sensing measurements, performed in differently concentrated ethyl alcohol atmospheres, highlight that GDS samples yield much higher response intensities than SPIN and VE films, short response times and complete recovery.

Copper Phthalocyanine Thin-film Transistor with a Polycarbonate Gate Dielectric Layer

We have investigated copper phthalocyanine (CuPc) thin-film transistors (TFTs) at different substrate temperatures. X-Ray diffraction (XRD) and UV/Vis spectrometer were used to study the orientations and optical transmission spectrum of the copper phthalocyanine film which was adopted as the semiconductor layer of organic thin-film transistor. A circuit diagram was constructed to study the output characteristics of CuPc TFT with a polycarbonate (PC) gate dielectric layer. The mobility of CuPc TFT at a substrate temperature of 90°C was 1.25×10-4 cm2/Vs. The On/Off ratio was also improved when the substrate temperature increases. Threshold voltages were -17 V at a substrate temperature of 70°C and -30 V at 90°C.

Intermolecular and interlayer interactions in copper phthalocyanine films as measured with microspot photoemission spectroscopy

The authors have applied photoemission microspectroscopy to copper phthalocyanine films grown on a graphite surface with a lateral resolution of 0.3μm and an energy resolution of 30meV. The photoemission peak due to the highest occupied molecular orbital was found to be at binding energies of 1.13, 1.23, 1.38, and 1.5eV, depending on film thickness. From the thickness and light-polarization dependence, the peaks were assigned to originate from isolated molecules, the first layer, the second layer, and multilayer, respectively. They demonstrate the capability of photoemission microspectroscopy to resolve electronic states modified by fine differences of molecular environments.

Thickness-Dependent Structural Transitions in Fluorinated Copper-phthalocyanine (F16CuPc) Films

The detailed structure of F16CuPc films on SiO2 has been determined by means of in situ grazing incidence X-ray diffraction from the first monolayer to thicker films. In contrast to films of the homologous H16CuPc molecule, the F16CuPc films exhibit the same structure independently from the deposition temperature. The films show a thickness-dependent polymorphism manifested in the in-plane crystal structure, which implies large differences in the molecular tilt within the cofacial stacking of the molecules.

Effects of Heat Treatments on the Properties of Copper Phthalocyanine Films Deposited by Glow-Discharge-Induced Sublimation

Copper phthalocyanine films have been deposited by glow-discharge-induced sublimation. The films have undergone postdeposition heat treatments in air at 250 and 290 °C for different times, ranging from 30 min to 14 h. The properties of as-deposited and heated films have been investigated by different techniques in order to determine the effects of heat treatments on the film properties. Fourier transform infrared analysis and UV−visible optical absorption analysis point out a gradual evolution of the film structure from a mixture of α and β polymorphs to the only β polymorph in the sample heated at 290 °C for 14 h. A pronounced decrease of carbon and nitrogen atomic percentages against an oxygen increase in the heated films are shown by ion beam analyses (Rutherford backscattering spectrometry and nuclear reaction analysis) and X-ray photoelectron spectroscopy (XPS). X-ray absorption spectroscopy and XPS indicate that part of the copper phthalocyanine molecules decompose during heat treatments and the formation of copper oxide takes place. The replacement of copper phthalocyanine by copper oxide in the heated films accounts for the change of their surface electrical conductance and of their electrical response to NO2.

Molecular dynamics method in studies of molecular film growth processes

This review is an attempt to analyze some of the experimental problems arising in the course of growth of orientated molecular films using metal monophthalocyanine (MPc) films as an example and to demonstrate the possibilities of molecular dynamics simulation of these processes for solving experimental problems. Examples of theoretical simulation of adsorption processes are given; formation of a molecular monolayer is considered for copper phthalocyanine films as an example.

Electronic structure in thin film organic semiconductors studied using soft X-ray emission and resonant inelastic X-ray scattering

The electronic structure of thin films of the organic semiconductors copper and vanadyl (VO) phthalocyanine (Pc) has been measured using resonant soft X-ray emission spectroscopy and resonant inelastic X-ray scattering. For Cu–Pc we report the observation of two discrete states near E F. This differs from published photoemission results, but is in excellent agreement with density functional calculations. For VO–Pc, the vanadyl species is shown to be highly localized. Both dipole forbidden V 3d to V 3d*, and O 2p to V 3d* charge transfer transitions are observed, and explained in a local molecular orbital model.