Analyte chemisorption and sensing on n- and p-channel copper phthalocyanine thin-film transistors (original) (raw)
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Gas Sensing Mechanism in Chemiresistive Cobalt and Metal-Free Phthalocyanine Thin Films
Journal of the American Chemical Society, 2007
The gas sensing behaviors of cobalt phthalocyanine (CoPc) and metal-free phthalocyanine (H2-Pc) thin films were investigated with respect to analyte basicity. Chemiresistive sensors were fabricated by deposition of 50 nm thick films on interdigitated gold electrodes via organic molecular beam epitaxy (OMBE). Time-dependent current responses of the films were measured at constant voltage during exposure to analyte vapor doses. The analytes spanned a range of electron donor and hydrogen-bonding strengths. It was found that, when the analyte exceeded a critical base strength, the device responses for CoPc correlated with Lewis basicity, and device responses for H 2Pc correlated with hydrogen-bond basicity. This suggests that the analyte-phthalocyanine interaction is dominated by binding to the central cavity of the phthalocyanine with analyte coordination strength governing CoPc sensor responses and analyte hydrogenbonding ability governing H2Pc sensor responses. The interactions between the phthalocyanine films and analytes were found to follow first-order kinetics. The influence of O2 on the film response was found to significantly affect sensor response and recovery. The increase of resistance generally observed for analyte binding can be attributed to hole destruction in the semiconductor film by oxygen displacement, as well as hole trapping by electron donor ligands.
The Journal of Physical Chemistry B, 2006
The electrical properties of 50 nm thick metallophthalocyanine films, prepared by organic molecular beam epitaxy (OMBE) on interdigitated electrodes, were studied with DC current-voltage measurements and impedance spectroscopy. The transition from Ohmic behavior at low voltages to space-charge-limited conductivity (SCLC) at higher voltages depends on the metal electrode (Pt, Pd, and Au), but does not correlate with the work function of the electrode. Impedance spectroscopy studies show the coexistence of low-and high-frequency traps in the thin film devices, and the contribution of low-frequency traps associated with Ohmic behavior diminishes at higher bias. Although device resistances are strongly influenced by the electrode material, and vary by a factor of over 300, the relative chemical sensor responses on exposure to dimethyl methylphosphonate (DMMP), methanol, water, or toluene vapors are similar for CoPc on Pt, Pd, and Au electrodes when these devices are operated in the SCLC regime at room temperature. When the devices are operated at voltages where the low-frequency interfacial traps are filled, the sensor response to analyte becomes uniform and reliable regardless of the specific interfacial electrode contact.
Fabrication and Characterization of Copper Phthalocyanine- Based Field Effect Transistors
Proceedings of the 5th International Conference on Chemical Investigation and Utilization of Natural Resource (ICCIUNR-2021), 2021
Future generations of electronic products will be enabled by flexible electronic circuits, displays, and sensors based on organic active materials, which could eventually reach the mainstream electronics industry. One of such devices is the organic field-effect transistor (OFET), which are three-terminal devices that are comprised of a gate, source, and drain electrode. In this study, we fabricated a bottom-gate bottom-contact OFET device using copper phthalocyanine (CuPc) as a semiconducting layer. CuPc is a commercially available metal complex, a known p-type semiconducting material. Au/Ti electrode is sputtered on Al gated silicon substrate with thermally grown SiO2 dielectric layer. CuPc films were then deposited over the substrate with patterned electrodes by physical vapor deposition at a rate of 0.35 nm/s, recorded by a quartz crystal microbalance at room temperature under a background pressure of 1.21x10-3 Pa. A thin layer of organic material was also deposited on glass slides and the optical properties of films with different thicknesses were determined by UV-Vis spectrometry and the optical band-gap energy was determined to be 1.64±0.01 eV. The thermal annealing effect on thin-film crystallization morphology was studied with atomic force microscopy (AFM) and contact angle measurement.
Effect of electrode geometry on gas sensitivity of lead phthalocyanine thin films
Sensors and Actuators B: Chemical, 1992
The effect of electrode geometry on the gas sensitivity of lead phthalocyanine (PbPc) thin films has been studied. The material PbPc has been chosen for this study because it has a high sensitivity ( -ppm) to oxidizing gases and may be suitable for use in a commercial solid-state chemical sensor. PbPc films of varying thickness (up to 1.5 pm) are vacuum sublimed across ultrathin (0.1 pm) coplanar pairs of gold electrodes lying on a sapphire substrate. The change of the electrical conductance of these devices in atmospheric nitrogen dioxide (NO,) is measured, over a range of electrode separations for several film thicknesses and temperatures, by a computer-controlled automated system. The temperatures are chosen around 160 "C, at which a peak sensitivity of PbPc to nitrogen dioxide has been observed. The transient and steady-state responses of these devices are analysed in terms of diffusion-rate limited and reaction-rate limited models modified from previous work on thick porous metal oxide semiconducting films. Experimental results show that the response time of the device at temperatures from 130 to 190 "C is insensitive to both the electrode separation and film thickness. Furthermore, the response time, typically 120 s, decreases with increasing nitrogen dioxide concentration (l-9 ppm). These observations are consistent with the reaction-rate limited rather than the diffusion-rate limited mode1 of mass transport in thin PbPc films. The activation energy of the PbPc films is determined from the temperature dependence of the device conductance, and found to be (0.15 + 0.1) eV; as expected, it is independent of electrode separation and film thickness. The film conductance in air increases with increasing reciprocal electrode separation, but does not follow the linear relationship predicted from the model. Furthermore, the steady-state response (defined as the fractional change in conductance) of the PbPc films to atmospheric nitrogen dioxide shows a gradual but systematic increase with electrode separation, whereas the model predicts a constant value. The deviation of the experimental results from theory suggests the presence of considerable film inhomogeneity. The nature of this deviation is consistent with a film in which both the electrical conductivity and density of adsorption sites are considerably lower near the substrate surface than elsewhere. This observed heterogeneity in the gas sensitivity of thin sublimed PbPc films makes it more difficult to characterize their behaviour and may reduce their commercial viability as chemical sensors. 092%4005/92/%5.00
Sensors and Actuators B: Chemical, 2010
The electrochemical incorporation of CuPc in conducting polypyrrole was done in presence of cationic surfactant CTAB in order to utilize the resultant material for sensing purposes. The sensor film produced by this process on ITO shows unique flake type structure of CuPc, and they were used for the sensing of a nerve gas simulant dimethyl methyl phosphonate (DMMP), and other vapors like methanol, ethanol, benzene, toluene and hexane. The sensor-I (PPy/NaClO 4) and sensor-II (PPy/CuPc/CTAB/NaClO 4) are characterized by FTIR, SEM and EDX. SEM image shows the presence of embedded flake type structure of CuPc in the PPy and this was confirmed by EDX and FTIR analysis. The sensor-II is unaffected by the interfering vapors like ethanol, benzene, toluene and hexane even at higher concentration, which makes it more suitable for DMMP sensing in presence of them.
Gas sensing behavior of metal-phthalocyanines: Effects of electronic structure on sensitivity
Chemical Physics, 2018
Cu-phthalocyanine (CuPc) and five of its metal variants (M = Mg, Mn, Co, Ni, and Zn) have been studied by density functional theory (DFT) methods for sensing five volatile organic compoundsisoprene, acetone, ammonia, methanol, and methane. Having performed experimental validation of the methods, interaction energies, binding configurations, changes in charge distributions and energy levels after interaction, and interaction barriers were studied to account for the sensitivity trend across the analytes for CuPc, while also providing supporting data from experiments carried out herein. It is also demonstrated that relatively simple calculations of interaction barrier can result in quick screening of metal-Pc variants for an analyte without any extensive experimental or computational efforts. Present literature lacks such detailed studies for these materials and analytes. Thus, this work would consolidate the understanding of sensing phenomena at the electronic structure level that could be useful for emerging technologies in gas sensing.
Electron Charge Transport in Non-Peripherally Substituted Copper Phthalocyanine
ECS Journal of Solid State Science and Technology, 2020
Bottom-gate, bottom-contact organic thin film transistors (OTFTs) were fabricated using solvent soluble copper-1,4,8,11,15,18,22,25-octakis(hexyl)phthalocyanine as the active semiconductor layer. The compound was deposited as 70 nm thick spin-coated films onto gold source-drain electrodes supported on octadecyltrichlorosilane treated 250 nm thick SiO2 gate insulator. The analysis of experimental results showed the n-type field effect behaviour. Devices annealed at 100 oC under vacuum were found to exhibit the field-effect mobility of 0.0989 cm2 V−1 s−1, with an on/off current modulation ratio of ∼106, a reduced threshold voltage of 0.7 V and a sub-threshold swing of 2.12 V decade−1. The variations in surface morphology of the devices are found reflected considerably in the electrical measurements. The device contact resistance was found to be decreased as the gate bias increased and also with the annealing.
Halogen sensing using thin films of crosswise-substituted phthalocyanines
Sensors and Actuators B: Chemical, 2001
Organic compound phthalocyanines (Pcs) are able to act as chemically sensitive ®lms because of the various physical effects induced in them by interaction with a large number of gases. Speci®cally, they are used as thin ®lm semiconducting gas sensors for the detection of halogens such as chlorine (Cl 2) and nitrogendioxide (NO 2) as well as organic vapors. In a systematic test of different materials, crosswise-substituted with two alkylsulfanyl and two amino groups phthalocyanine ®lms were investigated as sensitive materials for the detection of halogens. The sensing properties of these ®lms were investigated by measuring both dc and ac conductivity changes as a function of the gas concentration (0.05±0.15 ppm) at different temperatures (5±758C). The electrical properties of the ®lms were determined by means of dc and ac conductivity measurements under vacuum and without vacuum. The results show that the conductivity curve goes through a maximum at a certain temperature, T max , depending on the molecular structure of the phthalocyanine ®lms. The gas sensing measurements show that the sensors are highly sensitive to very low concentration of Br 2 and Cl 2 gases. The sensor signals are nearly reversible and reproducible even at room temperature. The crosswise substituted phthalocyanine thin ®lms have good selectivity.
Journal of Materials Research, 2004
Thin films of the perfluorinated phthalocyanines F16PcVO and F16PcCu were grown on insulator substrates by physical vapor deposition under high vacuum conditions to study their growth and electrical properties, analyzing them as possible candidates for n-type channel materials in organic field effect transistors. As insulator substrates, mica, amorphous SiO2, poly(styrene), poly(vinylchloride), poly(vinylcarbazole), poly(methylmetacrylate) and poly(vinylidenefluoride) were chosen, offering chemically different interactions with the molecules, degrees of order, and tribological characteristics. Optical absorption spectroscopy was used to analyze the alignment of the molecules relative to the substrates and the electronic coupling to adjacent molecules in the films. Electrical conduction measurements served to analyze the electronic coupling of the molecules parallel to the insulating substrates and to discuss the growth mode of films. Atomic force microscopy and scanning electron mic...