Novel pressure and displacement sensors based on carbon nanotubes

We report newly designed pressure and displacement capacitive sensors based on a flexible paper–CNT structure.The carbon nanotube（CNT） powder was deposited on a thin paper substrate and was pressed at an elevated temperature.The sheet resistance of the paper–CNT films was in the range of 2–4 kΩ/cm^2. The paper–CNT films were used to fabricate pressure and displacement sensors. The sensitivities of the pressure and the displacement sensors were found to be17.3 p F·m^2/k N and 0.93 10-3p F/μm, respectively. The experimental results were compared with the simulated data and they found good agreement with each other.

Carbon nanotube cuprous oxide composite based pressure sensors

In this paper, we present the design, the fabrication, and the experimental results of carbon nanotube （CNT） and Cu20 composite based pressure sensors. The pressed tablets of the CNT Cu20 composite are fabricated at a pressure of 353 MPa. The diameters of the multiwalled nanotubes （MWNTs） are between 10 nm and 30 nm. The sizes of the Cu20 micro particles are in the range of 3-4 μm. The average diameter and the average thickness of the pressed tablets are 10 mm and 4.0 mm, respectively. In order to make low resistance electric contacts, the two sides of the pressed tablet are covered by silver pastes. The direct current resistance of the pressure sensor decreases by 3.3 times as the pressure increases up to 37 kN/m^2. The simulation result of the resistance-pressure relationship is in good agreement with the experimental result within a variation of ±2%.

Aluminium phthalocyanine chloride thin films for temperature sensing

This study presents the fabrication and temperature sensing properties of sensors based on aluminium phthalocyanine chloride （AlPcCl） thin films. To fabricate the sensors, 50-nm-thick electrodes with 50-μ gaps between them are deposited on glass substrates. AlPcCl thin films with thickness of 50–100 nm are deposited in the gap between electrodes by thermal evaporation. The resistance of the sensors decreases with increasing thickness and the annealing at 100 ℃ results in an increase in the initial resistance of sensors up to 24%. The sensing mechanism is based on the change in resistance with temperature. For temperature varying from 25 ℃ to 80 ℃, the change in resistance is up to 60%. Simulation is carried out and results obtained coincide with experimental data with an error of ±1%.

Electrical characterization of the organic semiconductor Ag/CuPc/Au Schottky diode

This paper reports on the fabrication and investigation of a surface-type organic semiconductor copper phthalocyanine（CuPc） based diode.A thin film of CuPc of thickness 100 nm was thermally sublimed onto a glass substrate with preliminary deposited metallic electrodes to form a surface-type Ag/CuPc/Au Schottky diode.The current-voltage characteristics were measured at room temperature under dark conditions.The barrier height was calculated as 1.05 eV.The values of mobility and conductivity was found to be 1.74×10;cm;/（V·s） and 5.5×10;Ω;·cm;,respectively.At low voltages the device showed ohmic conduction and the space charge limited current conduction mechanisms were dominated at higher voltages.

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, ca- pacitance 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.

Resistive humidity sensor based on vanadium complex films

A resistive-type relative humidity （RH） sensor based on vanadium complex （VO2（3-f[）） film is reported in this study. Gold electrodes were deposited on the glass substrates in a co-planar structure. A thin film of vanadium complex was coated as a humidity-sensing material on the top of the pre-patterned electrodes. The humidity-sensing principle of the sensor was based on the conductivity change of coated sensing element upon adsorption/desorption of water vapor. The resistance of the humidity sensor measured at 1 kHz decreased linearly with increasing the humidity in the range of 35%-70% RH. The overall resistance of the sensor decreases 11 times. An equivalent circuit for the VO2（3-fl） based resistive-type humidity sensor was developed. The properties of the sensor studied in this work make it beneficial for use in the instruments for environmental monitoring of humidity.

Impedance hygrometer based on cellulose and CuPc

An investigation has been made on the properties of an impedance hygrometer fabricated using cellulose and copper phthalocyanine（Ag/cellulose/CuPc/Ag）.A 5wt%suspension of cellulose was prepared in water while the CuPc was dissolved in methanol.Cellulose film was deposited on glass substrates with preliminary deposited metallic electrodes followed by deposition of CuPc film.The resistances and capacitances of the samples were evaluated under the effect of humidity.The impedance was calculated from resistance and capacitance measurements.It was also measured during the experiment.It was observed that the capacitance of the sensor increases and resistance and impedance decrease with an increase in the relative humidity level.It was found that the impedance-humidity relationship showed more uniform changes in the interval of 31%—98%RH than the resistance-and capacitance-humidity relationships that showed visible changes in the humidity intervals of 31%-80%RH and 80%-98%RH respectively.The humidity-dependent impedance of the sample makes it attractive for use in impedance hygrometers.The impedance hygrometer may be used in instruments for the environmental monitoring of humidity.

Ag/PEPC/NiPc/ZnO/Ag thin film capacitive and resistive humidity sensors

A thin film of blended poly-N-epoxypropylcarbazole（PEPC）（25 wt.%）,nickel phthalocyanine（NiPc）（50 wt.%） and ZnO nano-powder（25 wt.%） in benzene（5 wt.%） was spin-coated on a glass substrate with silver electrodes to produce a surface-type Ag/PEPC/NiPc/ZnO/Ag capacitive and resistive sensor.Sensors with two different PEPC/NiPc/ZnO film thicknesses（330 and 400 nm） were fabricated and compared.The effects of humidity on capacitance and resistance of the Ag/PEPC/NiPc/ZnO/Ag sensors were investigated at two frequencies of the applied voltage：120 Hz and 1 kHz.It was observed that at 120 Hz under humidity of up to 95%RH the capacitance of the sensors increased by 540 times and resistance decreased by 450 times with respect to humidity conditions of 50%RH. It was found that the sensor with a thinner semiconducting film（330 nm） was more sensitive than the sensor with a thicker film（400 nm）.The sensitivity was improved when the sensor was used at a lower frequency as compared with a high frequency.It is assumed that the humidity response of the sensors is associated with absorption of water vapors and doping of water molecules in the semiconductor blend layer.This had been proven by simulation of the capacitance-humidity relationship.

Humidity sensing properties of CU_2O-PEPC nanocomposite films

A blend of copper oxide nanopowder （Cu2O）, 3 wt.%, and poly-N-epoxypropylcarbazole （PEPC）, 2 wt.%, in benzol was drop-casted on glass substrates with pre-deposited surface-type silver electrodes for the fabrication of Cu20-PEPC nanocomposite thin films. The thicknesses of the Cu20-PEPC films were in the range of 10-13 μm. The effect of humidity on the electrical properties of the nanocomposite films was investigated by measuring the capacitance and dissipation of the samples at two different frequencies of the applied voltage： 120 Hz and 1 kHz. The AC resistance of the samples was determined from the dissipation values, and the DC resistance was measured directly. The effect of ageing on the humidity sensing properties of the nanocomposite was observed. After ageing, it was observed that at 120 Hz and 1 kHz, under a humidity of up to 86% RH, the capacitance of the cell increased by 85 and 8 times, and the resistance decreased by 345 and 157 times, accordingly, with respect to 30% RH conditions. It was found that with an increase in frequency, the capacitance and resistance of the samples decreased. It is assumed that the humidity response of the cell is associated with the diffusion of water vapors and doping of the semiconductor nanocomposite by water molecules.

Synthesis of metal oxide composite nanosheets and their pressure sensing properties

This study presents the synthesis of metal oxides composite nanosheets （oxides of cobalt, zinc and iron） and their pressure sensing properties. A transducer has been fabricated to directly measure the resistance- pressure and impedance-pressure relationships of pristine nanopowder. At the initial stage, a nanopowder sample of 10 mm diameter and 1 mm height was placed in the transducer and by applying pressure of up to 8.15 kN/m^2; the DC resistance and the impedance are reduced by 44% on average. It can be explained by the densification of the samples and a decrease in porosity due to the effect of pressure. It was also observed that the DC resistance increases with time and saturated within 8 min. It is considered that this phenomenon is based on the effect of displacement currents of bound charges. The dependences of the impedance phase （8） on frequency and pressure have also been investigated.

Temperature sensor based on composite film of vanadium complex(VO_2(3-fl))and CNT

A vanadium complex （VO2（3-fl）） and CNT composite film based temperature sensor is reported in this study. Surface-type silver electrodes were deposited on the glass substrates. A thin film of VOE（3-fl） and CNT composite was coated as a temperature-sensing material on the top of the pre-patterned Ag electrodes. The temperature-sensing principle of the sensor was based on the conductivity change of the coated sensing element upon heating or cooling processes. DC and AC （100 Hz） resistances of the temperature sensor decreased quasi- linearly with increasing the temperature in the range of 25-80 ℃. The overall resistance of the sensor decreases by 1.8-2.1 and 1.9-2.0 times at DC and AC voltage, respectively. The resistance temperature coefficients of the sensor were in the range of-（0.9-1.3）% and -（1.1-1.3）% at DC and AC voltage, respectively. The properties of the sensor studied in this work, make it beneficial to be used in the instruments for environmental monitoring of temperature.

Optical transmission in thin films of vanadium compounds

Thin films of five vanadium compounds/composite： （1） VO2（3-fl） （3-fl = 3-Hydroxyflavone）, （2） VO（pbd）： （pbd = 1-Phenyl-l, 3-butadione）, （3） VO（dbm）2 （dbm = Dibenzoylmethane）, （4） VPc （Vanadyl Phthalocyanine） and （5） V2O5-PEPC （V2O5- poly-N-epoxypropylcarbazole composite）, were deposited by the dropcasting method from the solution in benzene. The transmittance-irradiance relationships were investigated and the transmission in the visible spectrum and optical images were obtained as well. It was found that the transmittance of the VO2（3-fl）, VO（pbd）2, VO（dbm）2 and VPc, was practically independent of the irradiance; whereas the transmittance of V2O5-PEPC decreased by 4% for thin and 9% for thick films with an increase of the irradiance.

CuPc based organic-inorganic hetero-junction with Au electrodes

A hetero-junction of n-silicon（n-Si） and copper phthalocyanine（CuPc） has been fabricated.The current -voltage characteristics were investigated to explain the rectification and conduction mechanism.The effect of temperature and humidity on the electrical properties of n-Si/CuPc hetero-junction has also been investigated.The characteristics of the junction have been observed to be temperature and humidity dependent,so it is suggested that this junction can be used as a temperature and humidity sensor.

Surface-type humidity sensor based on cellulose-PEPC for telemetry systems

Au/cellulose-PEPC/Au surface-type humidity sensors were fabricated by drop-casting cellulose and poly-N-epoxypropylcarbazole （PEPC） blend thin films. A blend of 2wt% of each cellulose and PEPC in benzol was used for the deposition of humidity sensing films. Blend films were deposited on glass substrates with preliminary deposited surface-type gold electrodes. Films of different thicknesses of cellulose and PEPC composite were deposited by drop-casting technique. A change in electrical resistance and capacitance of the fabricated devices was observed by increasing the relative humidity in the range of 0-95% RH. It was observed that the capacitances of the sensors increase, while their resistances decrease with increasing the relative humidity. The sensors were connected to op-amp square wave oscillators. It was observed that with increasing the relative humidity, the oscillator＇s frequencies were also increased in the range of 4.2-12.0 kHz for 65μm thick film sample, 4.1-9.0 kHz for 88μm thick film sample, and 4.2-9.0 kHz for 210μm sample. Effects of film thickness on the oscillator＇s frequency with respect to humidity were also investigated. This polymer humidity sensor controlled oscillator can be used for short-range and long-range remote systems at environmental monitoring and assessment of the humidity level.