NiPc Film Research Articles

Effect of pressure on the electrical properties of flexible NiPc thin films fabricated by rubbing-in technology

Nickel phthalocyanine (NiPc) film was deposited onto the surface of flexible conductive glass by rubbing-in technology and used to fabricate devices based on ITO/NiPc/CNT/rubber structure. The I–V characteristics of the devices were investigated under different uniaxial pressures of 200, 280, and 480 gf/cm2, applied perpendicular to the surface of the NiPc film. Results showed that the nonlinearity coefficients of the I–V curves are in the range of 2 to 3, which was found to be decreased with the increase of the pressure. The rectification ratio of the devices was estimated to be varied from 1.5 to 3 based on the applied pressure. Concluding, the resistance of the active layers was decreased with the increase of both pressure and voltage. We believe that using the rubbing-in technology under sufficient applied pressure it is possible to utilize NiPc for the development of various electronic devices such as diodes, nonlinear resistors, and sensors.

Nickel phthalocyanine based organic photo transistor: effect of semiconductor film thickness

Organic semiconducting photo transistors have been fabricated by depositing nickel phthalocyanine (NiPc) and semitransparent thin films of aluminum in sequence by vacuum evaporation on a glass substrate having silver source and drain electrodes. The thickness of NiPc film has been varied as 100 nm, 200 nm and 300 nm. The fabricated organic photo transistors (OPTs) having metal (aluminum)-semiconductor (NiPc) Schottky junction are then characterized and the effects of light irradiation on its characteristics have been investigated. It is observed that the drain current of OPTs rises with increasing radiation intensity and the OPTs having 200 nm thick NiPc film exhibited better performance as compared to the transistors having 100 nm and 300 nm thick films of NiPc.

Studies on the electrochemical properties of nickel phtalocyanine for impedimetric detection of environment pollutants: hydroquinone and bisphenol A

A self-assembled film of nickel phtalocyanine (NiPc) has been immobilised onto gold (Au) substrate to develop a new impedimetric method for environmental pollutants detection. NiPc/Au electrode was first characterised using contact angle measurements and cyclic voltammetry to investigate the adhesion and the kinetic behaviour of the self-assembled film. Results demonstrated the interaction between Au and benzene group and at the same time showed the formation of a completely covered NiPc layer on the Au surface. In addition, the NiPc film seems to exhibit reversible redox behaviour and is found to act as an electronic conductor which allows rapid electron transfer. The electrochemical impedance spectroscopy spectra of the NiPc/Au electrode, as a function of hydroquinone (HQ) and Bisphenol A (BPA) concentration, reveal that the value of the charge transfer resistance increases with increased concentration. The electrical behaviour of the structure was studied according to an equivalent circuit by fitting the experimental spectra. Moreover, this technique demonstrates that this membrane exhibits a high sensitivity towards the toxic pollutants HQ and BPA. The differences in selectivity are clearly displayed by variations in the membrane resistance (Rm) and in the charge transfer resistance (Rtc) of the interface.

DC AND AC MEASUREMENTS ON ITO/NIPC/METAL CELLS IN HUMID ENVIRONMENT

Current density-vs-voltage characteristics and frequency dependences of impedance were analyzed for sandwich cells ITO/NiPc/Metal, where ITO is a transparent conducting double indium-tin oxide, NiPc is a thermally evaporated nickel phthalocyanine thin film, and Metal is aluminum or indium top electrode. After testing in dry air, these cells were exposed to saturated water vapors, or mixed water/ammonia vapors with different pressures. Comparative analysis of the data taken from DC and AC measurements in the dark was carried out. Contributions of the NiPc film bulk and the NiPc/Metal interfacial region to conducting properties of the cells were elucidated. Impedance of the cells in various environments was interpreted using equivalent circuits, and the time scales for relaxation processes in NiPc films were thus estimated.

The electronic structure of Ni-phthalocyanine/metal interfaces studied by X-ray and ultraviolet photoelectron spectroscopy

Nickel phthalocyanine (NiPc) thin films were grown stepwise on polycrystalline gold and silver substrates and the formed interfaces were characterized by X-ray and ultraviolet photoelectron spectroscopies (XPS, UPS). The variation of the XPS core level binding energy with NiPc film thickness yields information about band bending and interface dipoles. The valence band structure of the NiPc thin films was determined by UPS and exhibits four main features at binding energies 1.50 eV, 3.80 eV, 6.60 eV and 8.85 eV, respectively. The NiPc highest occupied molecular orbital (HOMO) cut-off was measured at ∼1.00 eV from the analyzer Fermi level and from the measured work function change of the growing NiPc film a final work function value for NiPc was estimated at 3.90 ± 0.10 eV. The main C1s peak of the NiPc film (∼5.0 nm) consists of two components at 284.8 eV (C–C bonds), 286.2 eV (C–N bonds) reflecting photoemission from multiple carbon sites within the molecule and a satellite at 287.9 eV, whereas the Ni2p and N1s peaks appear at ∼855.9 eV and ∼399.3 eV, respectively and are due to Ni–N bonds. The energy level diagrams of the NiPc/Au and NiPc/Ag interfaces were determined from a combination of the XPS and UPS results, yielding a hole injection barrier of 0.90 ± 0.10 eV for both substrates.

A study of the Ni-phthalocyanine/gold interface using x-ray and ultraviolet photoelectron spectroscopies

Nickel phthalocyanine (NiPc) thin films (∼25 m thick) were grown stepwise on a polycrystalline Au substrate and the interface was characterized by x-ray and ultraviolet photoelectron spectroscopies (XPS, UPS). The C 1s peak of the bulk (∼5 nm) NiPc film was resolved into three components reflecting photoemission from multiple sites within the molecule. The peak at 284.8 eV corresponds to C-C bonds, the one at 286.2 eV to C-N bonds, while the last one at 287.9 eV is satellite of the main peak. The Ni 2p and N 1s peaks appear at ∼855.9 eV and ∼399.3 eV respectively and are due to Ni-N bonds. The NiPc highest occupied molecular orbital (HOMO) cut-off position was determined from the valence band spectrum of the bulk organic film, and was found at ∼1.00 eV from the analyser Fermi level. The work function of the Au foil and the bulk NiPc film were found to be 5.20 ± 0.05 eV and 4.20 ± 0.05 eV respectively. The combination of UPS and XPS results led to the determination of the energy level diagram of the NiPc/Au interface.

Surface morphology and gas sensing characteristics of nickel phthalocyanine thin films

The effect of surface morphology on the sensor current of a chemiresistor-type NO sensor based on the vacuum-deposited nickel phthalocyanine (NiPc) thin films is investigated in this work. We found that the surface morphology of the NiPc film depends on both the substrate temperature during deposition and the post-deposition annealing. Three types of films are obtained, i.e. the short-whisker α-NiPc, the long-whisker α-NiPc and the columnar β-NiPc. Upon exposure to 60 ppm NO gas, the sensor current is found to be the largest for the short-whisker α-NiPc film, slightly smaller for the long-whisker α-NiPc film, and three orders of magnitude smaller for the columnar β-NiPc film. The effect of morphology on the sensor current is explained by the difference in the number of adsorption sites and in the conductive path. An adsorption–desorption model is also used to interpret the response characteristics of the NiPc films.

Influence of oxygen doping on the electrical and photovoltaic properties of Schottky type solar cells based on α-nickel phthalocyanine

Single layer thin film cells were fabricated by successive thermal sublimation of gold, nickel phthalocyanine and lead under high vacuum conditions (10 −4 Pa). Structural properties of NiPc film were studied using X-ray diffraction measurements. Charge carrier transport mechanisms were identified from the dark current density–voltage ( J– V) characteristics. A rectifying junction was found to exist at the NiPc/Pb interface. The potential barrier height was evaluated under high vacuum and upon exposure of the cells to dry air for different periods of time. Density of acceptors was calculated for O 2 doped cells utilising the small a.c. signal capacitance-voltage technique. A photovoltaic effect was observed upon illumination of the sample with white light. Various photovoltaic parameters were determined from the J– V characteristics of the cells as a function of incident light intensity and exposure time to dry air. Although the initial power conversion efficiency (under vacuum) was low the cells show promising photovoltaic characteristics upon doping with O 2.

Raman polarization study of the film orientation of liquid crystalline NiPc

In this work, we determine, using Raman spectroscopy, the orientation of molecules relative to the substrate surface in films of octa(13,17-dioxanonacosane-15-sulfanyl)-substituted nickel(II) phthalocyanine, showing a liquid crystalline phase at room temperature. It was stated that the phthalocyanine molecules in the film are disordered relative to z-axis and rotated around x and y-axis on fixed α and β angles, respectively. We study the dependence of film orientation on temperature in the range from 0 to 30°C. The α angle is decreased from 30 to 10° with increasing temperature, whereas, the β angle is held constant (65°). The phase transition from liquid crystalline to isotropic phase in the NiPc film is observed at approximately 10°C.

Study of the Structural Change Due to Heat‐Treatment in High Resistivity Electroless NiPC Film

Structural changes caused by heat‐treatment of newly developed electroless NiPC films were investigated. The NiPC films containing a few atom percent of carbon, which exhibit an exceptionally high resistivity (ρ) and an excellent temperature coefficient of resistance value were prepared by using diethylenetriamine and β‐alanine as complexing agents. The ρ value of this film decreased upon heat‐treatment. The differential scanning calorimetry measurements showed that the NiPC films exhibit peaks which are distinct from the peaks of the conventional NiP film. The X‐ray diffraction results indicated that these peaks could be associated with structural changes. In fact, observed crystallization temperatures of the NiPC films were higher than that of the NiP film. Gas components desorbed from the NiPC films during annealing were identified. It is evident that the NiPC films contain various organic elements and water. Transmission electron microscope bright‐field images for the NiPC films reveal unique bean‐like features. The bean‐like features are retained even after crystallization and presumably affect the resistivity. The high resistivity is associated with organic elements incorporated in the film as well as the bean‐like features.

Thermal Stability of High Resistivity NiP Thin Film Resistor Formed by Means of an Electroless Deposition.

In this study, we check the relatively lower thermal annealing effect on the NiPC film as comparing the usual NiP amorphous film