Noshin Fatima

Compositional engineering of VOPcPhO-TiO2 nano-composite to reduce the absolute threshold value of humidity sensors

This research work demonstrates compositional engineering of an organic-inorganic hybrid nano-composites for modifying absolute threshold of humidity sensors. Vanadyl-2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine (VOPcPhO), an organic semiconductor, doped with Titanium-dioxide nanoparticles (TiO2 NPs) has been employed to fabricate humidity sensors. The morphology of the VOPcPhO:TiO2 nano-composite films has been analyzed by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). The sensors have been examined over a wide range of relative humidity i.e. 20-99% RH. The sensor with TiO2 (90nm) shows reduced sensitivity-threshold and improved linearity. The VOPcPhO:TiO2 (90nm) nano-composite film is comprised of uniformly distributed voids which makes the surface more favorable for adsorption of moisture content from environment. The VOPcPhO:TiO2 nano-composite based sensor demonstrates remarkable improvement in the sensing parameter when equated with VOPcPhO sensors.

Sensitivity enhancement of OD-and OD-CNT-based humidity sensors by high gravity thin film deposition technique

The humidity sensing properties of the thin films of an organic semiconductor material orange dye (OD) and its composite with CNTs deposited at high gravity conditions have been reported. Impedance, phase angle, capacitance and dissipation of the samples were measured at 1 kHz and room temperature conditions. The impedance decreases and capacitance increases with an increase in the humidity level. It was found that the sensitivity of the OD-based thin film samples deposited at high gravity condition is higher than the samples deposited at low gravity condition. The impedances and capacitance sensitivities of the of the samples deposited under high gravity condition are 6.1 times and 1.6 times higher than the films deposited under low gravity condition.

Effect of humidity on copper phthalocyanine films deposited at different gravity conditions

Purpose The paper aims to study the effects of humidity on the electrical properties of copper phthalocyanine (CuPc) thin films deposited at different gravity conditions. Design/methodology/approach Surface-type samples were fabricated on glass substrates with preliminary-deposited copper electrodes. The CuPc solution was prepared in benzene. The thin films of CuPc were deposited on these substrates at diverse gravity conditions by drop-casting and centrifugation at 1 × g and 70 × g, respectively. Impedance and capacitance of the fabricated devices were measured against the different relative humidity ranging from 32 to 98 per cent. Findings The impedance and the capacitance of the CuPc film were found to be dependent on the ambient humidity levels (32-98 per cent) and the gravity conditions (1 × g and 70 × g) opted during the fabrication process. Research limitations/implications The centrifugation technique can potentially be used in the instrumentation industry for the fabrication of humidity sensors. Practical implications The results of the investigations can potentially be used in the instrumentation and optoelectronics industry for the fabrication of humidity sensors. Originality/value CuPc films were deposited from a solution in benzene using drop-casting and centrifugation. The electrical properties of the films were found to be dependent on film fabrication conditions and ambient humidity levels. Growth-dependent electrical properties of the CuPc films can be explained by considering their structure.

Optical sensors based on the NiPc–CoPc composite films deposited by drop casting and under the action of centrifugal force

In this study, solution processed composite films of nickel phthalocyanine (NiPc) and cobalt phthalocyanine (CoPc) are deposited by drop casting and under centrifugal force. The films are deposited on surface-type inter-digitated silver electrodes on ceramic alumina substrates. The effects of illumination on the impedance and capacitance of the NiPc CoPc composite samples are investigated. The samples deposited under centrifugal force show better conductivity than the samples deposited by drop casting technique. In terms of impedance and capacitance sensitivities the samples fabricated under centrifugal force are more sensitive than the drop casting samples. The values of impedance sensitivity (Sz) are equal to (-1.83) MWΩcm2/mW and (-5.365) MWΩcm2/mW for the samples fabricated using drop casting and under centrifugal force, respectively. Similarly, the values of capacitance sensitivity (Sc) are equal to 0.083 pFΩcm2/mW and 0.185 pFΩcm2/mW for the samples fabricated by drop casting and under centrifugal force. The films deposited using the different procedures could potentially be viable for different operational modes (i.e., conductive or capacitive) of the optical sensors. Both experimental and simulated results are discussed.

Humidity effect on organic semiconductor NiPc films deposited at different gravity conditions

In this study, thin films of Nickel Phthalocyanine (NiPc) were deposited by centrifugation at high gravity (70g), and also at normal gravity (1g) conditions to fabricate humidity sensors. Ceramic alumina sheet, coated with silver electrodes, having interelectrode distance of 0.2l mm were used to assess the electrical properties of the sensors. Room temperature capacitance and impedance variations were measured as a function of relative humidity ranging from 25% ~ 95% at 1 kHz frequency. It was observed that sensors fabricated at 70g were more sensitive compared to sensors fabricated at 1g. Sensors fabricated at 70g exhibited 1.8 times decrease in their impedance and1.5 times increase in their capacitance at peak ambient humidity. SEM images showed more roughness for the films deposited at 70g compared to films deposited at 1g. It was assumed that surface irregularities might have increased active surface area of 70g sensors hence changed the electrical response. Impedance-humidity and capacitance-humidity relationships were modeled and a good agreement was observed between experimental and modeled data. Experimental data showed that NiPc films could be useful for instrumentation industry to fabricate organic humidity sensors.

Effect of humidity and temperature on organic semiconductor CuPc films deposited at different gravity conditions

In this paper effects of humidity and temperature on the electrical properties of thin films of organic semiconductor CuPc deposited from four different solutions (acetone, benzene, methanol and toluene) at different gravity conditions (1g and 70g) by centrifugation are reported. Surface-type samples were fabricated using copper thin films as electrodes deposited on glass substrates. Impedance and capacitance variations at room temperature were measured as a response of relative humidity ranging from 32%~98% at 1 kHz frequency. Similar parameters were measured at 1 kHz and fixed humidity for variable temperatures of 25~70°C. In addition, depending on the solution used during the deposition process, decrease in impedance and increase in capacitance with an increase in either humidity or temperature is also observed. Change in the properties of the CuPc films, deposited at different gravity conditions from different solutions, can be considered due to the changes in the structure and composition of the films. The results of the investigations potentially can be used for the fabrication of organic electronic devices that can be used in instrumentation and optoelectronics.