Gas-induced electrical conductivity changes in metal phthalocyanines

Bimetallic Two-Dimensional Metal-Organic Frameworks for the Chemiresistive Detection of Carbon Monoxide

This paper describes the demonstration of a series of heterobimetallic, isoreticular 2D conductive metal-organic frameworks (MOFs) with metallophthalocyanine (MPc, M=Co and Ni) units interconnected by Cu nodes towards low-power chemiresistive sensing of ppm levels of carbon monoxide (CO). Devices achieve a sub-part-per-million (ppm) limit of detection (LOD) of 0.53 ppm toward CO at a low driving voltage of 0.1 V. MPc-based Cu-linked MOFs can continuously detect CO at 50 ppm, the permissible exposure limit required by the Occupational Safety and Health Administration (OSHA), for multiple exposures, and realize CO detection in air and in humid environment. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), density functional theory (DFT) calculations, and comparison experiments suggest the contribution of Cu nodes to CO binding and the essential role of MPc units in tuning and amplifying the sensing response.

Solution-Processed Chloroaluminum Phthalocyanine (ClAlPc) Ammonia Gas Sensor with Vertical Organic Porous Diodes

In this research work, the gas sensing properties of halogenated chloroaluminum phthalocyanine (ClAlPc) thin films were studied at room temperature. We fabricated an air-stable ClAlPc gas sensor based on a vertical organic diode (VOD) with a porous top electrode by the solution process method. The surface morphology of the solution-processed ClAlPc thin film was examined by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The proposed ClAlPc-based VOD sensor can detect ammonia (NH3) gas at the ppb level (100~1000 ppb) at room temperature. Additionally, the ClAlPc sensor was highly selective towards NH3 gas compared to other interfering gases (NO2, ACE, NO, H2S, and CO). In addition, the device lifetime was tested by storing the device at ambient conditions. The effect of relative humidity (RH) on the ClAlPc NH3 gas sensor was also explored. The aim of this study is to extend these findings on halogenated phthalocyanine-based materials to practical electronic nose applications in the future.

New Emerging One Dimensional Nanostructure Materials for Gas Sensing Application: A Mini Review

Background:

Nanomaterials have numerous potential applications in many areas such as electronics, optoelectronics, catalysis and composite materials. Particularly, one dimensional (1D) nanomaterials such as nanobelts, nanorods, and nanotubes can be used as either functional materials or building blocks for hierarchical nanostructures. 1D nanostructure plays a very important role in sensor technology.

Objective:

In the current review, our efforts are directed toward recent review on the use of 1D nanostructure materials which are used in the literature for developing high-performance gas sensors with fast response, quick recovery time and low detection limit. This mini review also focuses on the methods of synthesis of 1D nanostructural sensor array, sensing mechanisms and its application in sensing of different types of toxic gases which are fatal for human mankind. Particular emphasis is given to the relation between the nanostructure and sensor properties in an attempt to address structure-property correlations. Finally, some future research perspectives and new challenges that the field of 1D nanostructure sensors will have to address are also discussed.

Sensing alcohol vapours with novel unsymmetrically substituted metallophthalocyanines

Unsymmetrically substituted phthalocyanines were synthesized by the well-known statistical condensation method using two differently substituted precursors, 4-tert-butylphthalonitrile and 4-(4-pyrrol-1-yl)phenoxyphthalonitrile.

Fully Integrated Organic Nanocrystal Diode as High Performance Room Temperature NO2 Sensor

Organic diodes consisting of molecular nano-pyramid structures sandwiched between metal and strained nano-membrane electrodes are created. The robust and smooth contacts provided by self-curled metal layers render the molecular nano-pyramids efficent channels for detecting nitrogen dioxide airflow.

Fabrication of Gas Sensors Based on Soluble Phthalocyanines

Gas sensors based on 2,9,16,23-tetra(2,6-dimethylphenoxy)metallophthalocyanine (TDMP- MPc ) films on interlocking silver electrodes were fabricated by solvent casting from chloroform solutions containing 2,9,16,23-tetra(2,6-dimethylphenoxy)copper, cobalt or nickel phthalocyanine ( TDMP - CuPc , TDMP - CoPc or TDMP - NiPc ). The sensitivity of the gas sensors to the presence of NO 2 and the depletion of O 2 was investigated. It was confirmed that the gas sensors based on TDMP - CuPc and TDMP - CoPc films could detect 1 ppm NO 2 at room temperature and that the current responses to the presence of NO 2 and the depletion of O 2 were considerably quick. These results indicate that adsorption and desorption of NO 2 and O 2 on the surfaces of TDMP - MPc films are easily achieved at room temperature.

Synthesis of a Substituted Phthalocyaninato-polysiloxane and its Langmuir-Blodgett Films

Tetrakis-4-(2,4-di-tert-amylphenoxy)phthalocyaninato-polysiloxane was synthesized. Its molecular structure was confirmed by elemental analysis, IR and UV-vis spectra. The gas-sensitive properties of its Langmuir–Blodgett films exposed to NH 3, I 2 and NO 2 in air were measured. The results showed that the detection sensitivity on exposure to NH3 in air can reach 0.1 ppm, while it can reach 100 ppm on exposure to NO 2 and I 2 in air.

Electrical transduction in phthalocyanine-based gas sensors: from classical chemiresistors to new functional structures

Phthalocyanines are organic-based materials which have attracted a lot of research in recent times. In the field of sensors, they present interesting and valuable potentialities as sensing elements for real gas sensor applications. In the present article, and taking some of our experiments as representative examples, we review the different ways of transduction applied to such applications. Some of the new tendencies and transducers for gas sensing based on phthalocyanine derivatives are also reported. Among them, electrical transduction (resistors, field-effect transistors, diodes, etc.) has been, historically, the most commonly exploited way for the detection and/or quantification of gas pollutants, vapors and aromas, according to the conducting behavior of phthalocyanines. We will focus precisely on these systems.

Ammonia adsorption on iron phthalocyanine on Au(111): influence on adsorbate-substrate coupling and molecular spin

The adsorption of ammonia on Au(111)-supported monolayers of iron phthalocyanine has been investigated by x-ray photoelectron spectroscopy, x-ray absorption spectroscopy, and density functional theory calculations. The ammonia-induced changes of the x-ray photoemission lines show that a dative bond is formed between ammonia and the iron center of the phthalocyanine molecules, and that the local spin on the iron atom is quenched. This is confirmed by density functional theory, which also shows that the bond between the iron center of the metalorganic complex and the Au(111) substrate is weakened upon adsorption of ammonia. The experimental results further show that additional adsorption sites exist for ammonia on the iron phthalocyanine monolayer.

Influence of Substrate on In-Plane Electrical Conduction of CuPc Nano-Crystals

We have investigated the conductivity variation of copper phthalocyanine nano-crystals deposited on SiO2 and mica. The density of surface hydroxyl group on SiO2 was estimated to be more than 10 times larger than that on mica by X-ray photoelectron spectroscopy. The grown crystals on both substrates were categorized to be a-axis orientation of α–form. Conductance-distance (G-d) measurements for various crystalline grains having different heights have been carried out with current imaging using atomic force microscope. The obtained conductivity vs. crystal height plot indicates that lower height crystals have higher conductivities on both surfaces. Besides, the lower height crystals on SiO2 have higher conductivity than those on mica. These results suggest that the electrons in the bottommost molecular layer are transferred to the electrophilic functional groups on the substrate surface. Such a phenomenon at organic semiconductor/insulator interface is reported for the first time.

In2O3 nanowire mat devices as high performance NO2 gas sensors

A high sensitive and reliable In2O3 nanowire mat devices are fabricated. Detection of NO2 gas down to ppb levels was achieved. This represents orders-of-magnitude improvement over previously reported metal oxide film or nanowire/nanobelt sensors. Furthermore, this simple device shows certain selectivity to NO2 with other common chemicals such as NH3, O2, CO and H2 around.

Inductively coupled surface acoustic wave device for sensor application

We present a new type of surface acoustic wave device for sensor applications where the need for bonding wires is eliminated. Instead the device is coupled inductively to the RF circuitry. The impedance of such devices and the necessary matching have been investigated both theoretically and experimentally. The devices have repeatedly been operated at temperatures up to 400 degrees C and have shown a good temperature resistance. In order to test the suitability of the new concept for sensor applications, several devices with an operating frequency of 363 MHz were coated with copper phthalocyanine for the detection of NO(2). From these measurements we derive a detection limit of these devices below 1 ppb for NO(2).