Shuqin Zhou

The gas sensitivity of a metal-insulator-semiconductor field-effect-transistor based on Langmuir–Blodgett films of a new asymmetrically substituted phthalocyanine

Abstract Langmuir–Blodgett (LB) films of an amino-tri- tert -butyl-phthalocyanine (AmBuPc) were fabricated as the semiconductor thin layer for a metal-insulator-semiconductor field-effect-transistor (MISFET). The gas sensitivity of the low-conducting LB films MISFET was measured in a NO 2 atmosphere at different concentration. The results showed that the gas concentration and the drain-source current of the AmBuPc gas sensor satisfy Langmuir adsorption isotherm.

Highly ordered vacuum-deposited thin films of copper phthalocyanine induced by electric field

The properties of copper-phthalocyanine (CuPc) thin films vacuum evaporated on glass substrates under different electric fields have been investigated. The resistances of the film decrease rapidly with increasing electric fields. The results of AFMs, XPS and X-ray diffraction reveal that electric fields change the chemical environment of Cu and increase the order of copper phthalocyanine molecules. A possible mechanism of this phenomenon is discussed in this paper.

The application of Langmuir-Blodgett films of a new asymmetrically substituted phthalocyanine, amino-tri-tert-butyl-phthalocyanine, in diodes and in all organic field-effect-transistors

Abstract Amino-tri- tert -butyl-phthalocyanine (AmBuPc) was used as the semiconductor thin layers in model Schottky diode and all organic field-effect transistor (OFET). The diode cell showed a rectifying effect with a rectification ratio of 60 at ±3.2 V. The ideality factors were 1.38 in the low voltage region and 3.09 in the high voltage region, respectively. The results of OFET proved that AmBuPc Langmuir–Blodgett (LB) films could be used as the semiconducting layer of OFET, and the OFET could function as a p-channel accumulation device. From the OFET electrical characteristics, the channel carrier mobility is calculated to be about 5.2×10 −6 cm 2 V −1 s −1 , which is higher than that of vacuum-deposited film OFET (7.8×10 −7 cm 2 V −1 s −1 ) utilizing the same polymer. This phenomenon can be explained as the highly ordered structure of AmBuPc molecules in the LB films. This suggests that a wide conduction channel is able to form in this all organic device, which provides a new method to simplify the fabrication process of OFET and improve their properties.

THE GAS SENSITIVITY OF LANGMUIR-BLODGETT FILMS OF A NEW ASYMMETRICALLY SUBSTITUTED PHTHALOCYANINE

Abstract Langmuir–Blodgett (LB) films of amino-tri- tert -butyl-phthalocyanine (AmBuPc) were fabricated. The gas sensitivities of the low-conducting LB films were measured in different concentrations of NO 2 atmosphere. The results showed that a good linear relationship exists between the logarithm of the resistance of AmBuPc gas sensor and the concentration of NO 2 , which could be explained in terms of the gas diffusion theory in the LB films. XPS results proved that the attack centers of NO 2 are the two pyrrole N-linked free H atoms of the Pc macro-ring. Temperature had significant influences to the recovery and cyclic properties of sensor and the conductivity of gas sensor. The values of activation energy are 0.14 and 0.43 eV, respectively, at temperatures lower and higher than 60°C in NO 2 .

Synthesis and Self‐Assembly of 2,9,16‐Tri(tert‐butyl)‐23‐(10‐mercaptodecyloxy)phthalocyanine and the Application of Its Self‐Assembled Monolayers in Organic Light‐Emitting Diodes

2,9,16-Tri(tert-butyl)-23-(10-mercaptodecyloxy)phthalocyanine (8) and its disulfide (9) have been synthesized and characterized, and their self-assembling behaviors on gold substrates have been studied. Characteristic Q-bands were observed at about 630 nm in the UV/visible spectra of the self-assembling monolayers (SAMs). They were broadened and blue-shifted relative to those observed in solution. Binding energies for S2p have the same values (161.70 eV) and are in accord with those for gold thiolates. The application of the SAMs in organic light-emitting diode was investigated. It shows that the SAM promotes the hole injection process from the anode.

Synthetic Molecular Rectifier of a Langmuir–Blodgett Film Based on a Novel Asymmetrically Substituted Dicyano-tri-tert-butylphthalocyanine

A novel asymmetrically substituted dicyano-tri-tert-butylphthalocyanine ((CN)2BuPc) with rectifying behavior has been synthesized. The morphology and conductive properties of (CN)2BuPc Langmuir–Blodgett (LB) films on mica and highly ordered pyrolytic graphite (HOPG) substrates were studied by atomic force microscopy (AFM) and scanning tunneling microscopy (STM), in air at 22 °C. The average area of each (CN)2BuPc molecule obtained from the AFM topography in situ is ca. 73.6 A2, which is in good agreement with the result of ca. 74 A2 obtained from the π–A isotherm curve of a LB film. This indicates that the molecules are standing edge-on, tilted by 38° against the surface normal of the substrate. The conductive properties for the 7-layer LB films of (CN)2BuPc were studied by STM with a tungsten tip. The asymmetric I–V curve revealed a type of rectifying behavior for a negative and a positive bias. A feature model of the intramolecular and intermolecular charge transfer is presented. It not only interprets electron transfer from electron-donor to electron-acceptor molecules via a molecular “bridge”, but also the tunneling effect through intermolecular charge transfer.

Rectifying behaviors of Langmuir–Blodgett films of an asymmetrically substituted phthalocyanine

Abstract A multilayer Langmuir–Blodgett (LB) film of an asymmetrically substituted phthalocyanine derivative (NtBuPc), deposited onto a HOPG substrate, was studied by scanning tunneling microscopy using a Pt/Ir nanotip in air at 23°C. The asymmetrical I – V curves for 3- and 7-layer LB films of NtBuPc reveal a rectifying behavior for a negative and a positive bias. This suggests that NtBuPc molecules cause the rectification and not the Schottky barrier formed at the electrode–LB interface. The rectification mechanism can be explained by a modification of the Aviram–Ratner model. The electron transfer between bilayers might be interpreted as a quantum well effect through interlayer tunneling. Such quantum tunneling between layers would accelerate charge transport between bilayers, and thus rectification of 7-layer films is better than that of three layers.

The synthesis of aminotri-tert-butyl phthalocyanine and its gas sensitivity to nitrogen dioxide

Aminotri-tert-butyl phthalocyanine (AmBuPc) is a new asymmetrical phthalocyanine, which possesses three tert-butyl groups and one amino-group. All the substituents are electron-donating ones and have a strong electron-donating ability when they interact with oxidizing gases, such as NO2. We report its synthesis and its gas sensitivity to nitrogen dioxide, and reveal the electrochemical properties of this compound.

STM studies of 1D smectic row of a novel asymmetrically substituted phthalocyanine on HOPG

A novel asymmetrically substituted dicyano-tri-tert-butyl-phthalocyanine (CN) 2 BuPc was self-physiosorbed on a highly ordered pyrolytic graphite (HOPG) substrate. The morphology of a 1D-smectic structure with two rows was obtained from the self-physiosorbed layer by STM in air at 22°C. Suggesting that the 1D-smectic structure grew up along the crystallization direction of HOPG (111) surface in an epitaxial style. The I-V characteristic was estimated and reveals an asymmetrical behavior. In the 1D-smectic structure, a phenomena with negative conductivity was observed at ac. -0.9 V, It might be explained that the sum role of the molecular separate level and tunneling process would create the physical phenomena. These studies imply an important role of interactions between molecule and substrate or molecule and molecule for some material systems in the self-physiosorbed and crystallizing process on an ordering substrate.