Laser-driven metal exchange and preparation of metal phthalocyanine

Two types of laser-driven dry processes for the preparation of metal phthalocyanine are reported. In the first one, laser-driven metal exchange, the excimer laser beam was focused on a copper target, and ablated copper atoms were injected onto a thin film of dilithium phthalocyanine (Li₂Pc). The central metal atoms of Li₂Pc were partially exchanged by copper atoms, and the blue thin film of copper phthalocyanine (CuPc) was obtained after removal of the residual Li₂Pc by the hydrochloric acid treatment. In the second one, direct synthesis using the component organic molecule, CuPc was prepared by the implantation of laser-ablated copper atoms onto a thin film of 1,3-diiminoisoindoline (D I I I).     

Hydrogen Sensors Based on AlGaN/AlN/GaN Schottky Diodes

Pt/AlGaN/AlN/GaN Schottky diodes are fabricated and characterized for hydrogen sensing. The Pt Schottky contact and the Ti/Al/Ni/Au ohmic contact are formed by evaporation. Both the forward and reverse currents of the device increase greatly when exposed to hydrogen gas. A shift of 0.3 V at 300 K is obtained at a fixed forward current after switching from N2 to 10%H2＋N2. The sensor responses under different concentrations from 50ppm H2 to 10%H2＋N2 at 373K are investigated. Time dependences of the device forward current at 0.5 V forward bias in N2 and air atmosphere at 300 and 373K are compared. Oxygen in air azcelerates the desorption of the hydrogen and the recovery of the sensor. Finally, the decrease of the Schottky barrier height and sensitivity Of the sensor are calculated.     

Improvement of Field Emission Characteristics of Copper Nitride Films with Increasing Copper Content

A copper nitride （Cu3N） thin film is deposited on a Si substrate by the reactive magnetron sputtering method. The XPS measurements of the composite film indicate that the Cu content in the film is increased to 80.82 at. % and the value of the Cu/N ratio to 4.2：1 by introducing 4% 112 into the reactive gas. X-ray diffraction measurements show that the film is composed of Cu3N crystallites with an anti-ReO3 structure. The effects of the increase of copper content on the field emission characteristics of the Cu3N thin film are investigated. Significant improvement in emission current density and emission repeatability could be attributed to the geometric field enhancement, caused by numerous surface nanotips, and the decrease of resistivity of the film.     

A highly sensitive and selective hydrogen gas sensor from thick oriented films of MoS2

A new process is developed to fabricate a highly sensitive and selective hydrogen sensor by depositing a partially crystalline and highly oriented film of MoS₂ from its single layer suspension on an alumina substrate. When these films are promoted with some catalysts selected from Pt-group metals (Pt, Pd, Ru or any combination of these metals) they exhibit a high sensitivity and selectivity to hydrogen gas. Unlike other metal oxide sensors which are sensitive to many reducing and oxidizing gases and operate at a temperature of 350 °C or higher; this sensor is highly selective to hydrogen gas and its operating temperature is from 25 to 150°C. The lower operating temperature enhances safety when dealing with hydrogen gas. The sensor response to hydrogen at 120 °C is linear in concentration from 30 to 10⁴ ppm with a 10 to 30 second response time and a 45 to 90 second recovery time. Above 10⁴ ppm the sensor is still linear but the slope of conductance versus hydrogen concentration changes.     

Temperature dependence of NO2 sensitivity of YSZ-based mixed potential type sensor attached with NiO sensing electrode

A mixed potential type yttria-stabilized zirconia-based sensor using NiO sensing electrode and Pt reference electrode was fabricated, and its NO₂ sensing characteristics were examined at various operating temperatures in the range of 700–950 °C. It was observed that the sensitivity to NO₂ strongly depends on the operating temperature of the sensor; the sensitivity decreases with increasing operating temperature, while the response/recovery rates increase. To rationalize this temperature dependence of NO₂ response, polarization curves and complex impedances of the sensor were measured in the base gas and in the sample gas (400 ppm NO₂?+?base gas) at various operating temperatures. It turned out that the operating temperature had a strong influence on the rate of anodic reaction of oxygen; the increased rate of anodic reaction leads to lower NO₂ sensitivity and quicker response/recovery at higher operating temperature.     

The enhancement of dark d.c. conductivity by gas adsorption on thin films of macrocyclic copper complexes

The dark d.c. conductance of thin films of copper complexes of phthalocyanine (α-form), hemiporphyrazine and dihydrodibenzo [b, i] [1, 4, 8, 11] tetra-azacyclotetradecine has been studied in vacuo and in the presence of an extensive range of gases. Only those gases which can be classed as electron acceptors increased the conductance, with NO₂/N₂O₄ (“NOX”) being particularly effective. Spectroscopic evidence is provided to show that the NOX-copper phthalocyanine interaction generates the organic radical cation and NO^-₂, and that substantial quantities of gas are accumulated within the thin film. A new class of extrinsic organic semiconductor is described.     

The light-enhanced NO2 sensing properties of porous silicon gas sensors at room temperature

The NO2 gas sensing behavior of porous silicon（PS） is studied at room temperature with and without ultraviolet（UV） light radiation.The PS layer is fabricated by electrochemical etching in an HF-based solution on a p ＋-type silicon substrate.Then,Pt electrodes are deposited on the surface of the PS to obtain the PS gas sensor.The NO2 sensing properties of the PS with different porosities are investigated under UV light radiation at room temperature.The measurement results show that the PS gas sensor has a much higher response sensitivity and faster response-recovery characteristics than NO2 under the illumination.The sensitivity of the PS sample with the largest porosity to 1 ppm NO2 is 9.9 with UV light radiation,while it is 2.4 without UV light radiation.We find that the ability to absorb UV light is enhanced with the increase in porosity.The PS sample with the highest porosity has a larger change than the other samples.Therefore,the effect of UV radiation on the NO2 sensing properties of PS is closely related to the porosity.     

Fiber-Optic Chemical Sensor for Detection of NO2 Using Poly (3-Octylthiophene)

Abstract

A fiber-optic chemical sensor (FOCS) for detection of nitrogen dioxide (NO ₂ ) molecules is reported. The FOCS presents an optropode structure because of the transmission properties of the sensitive material. The NO ₂ FOCS is activated by using the semiconductor polymer: regioregular head-to-tail poly(3-octylthiophene-2,5-diyl). The operation wavelength of the sensor is 543.5 nm such that a simple LED and detector can be used for the design of this device. The sensor response decreases after each exposure, demonstrating the reduction in sensitivity as well as irreversibility lower than 5%. However, its properties such as rapid response, high selectivity, high sensitivity (0.43 ± 0.01 muW/ppm), hygroscopic properties, and its operation at room temperature make this kind of FOCS a good alternative for NO ₂ toxic gas detection.     

Graphene-based nitrogen dioxide gas sensors

In this study, we demonstrated that graphene could selectively absorb/desorb NO_x molecules at room temperature. Chemical doping with NO₂ molecules changed the conductivity of the graphene layers, which was quantified by monitoring the current–voltage characteristics at various NO₂ gas concentrations. The adsorption rate was found to be more rapid than the desorption rate, which can be attributed to the reaction occurred on the surface of the graphene layer. The sensitivity was 9% when an ambient of 100 ppm NO₂ was used. Graphene-based gas sensors showed fast response, good reversibility, selectivity and high sensitivity. Optimization of the sensor design and integration with UV-LEDs and Silicon microelectronics will open the door for the development of nano-sized gas sensors that are extremely sensitive.     

固体电解质ZrO2薄膜气敏光学特性的研究

本文采用溶胶凝胶法制备了ZrO₂薄膜,并研究它在乙醇蒸汽和氨蒸汽中的透射光谱,发现当掺入适量的稳定剂后,其光学特性显著增大,光学透过率随乙醇蒸汽和氨蒸汽的浓度增大而单调上升,敏感波段扩展至整个可见光区域.其气敏光学特性的灵敏度、单调性、可重复性表明了该材料是一种有实用价值的气敏光纤传感器新材料.本文亦讨论了ZrO₂薄膜的气敏光学机理.     

Ferroelectric Properties of Bi3.25La0.75Ti3O12 Thin Films Crystallized inDifferent N2/O2 Ambients

Bi3.25La0.75 Ti3O12 （BLT） ferroelectric thin films are deposited by sol-gel method and annealed for crystallizaion in total l eccm N2/02 mixed gas with various ratio at 750℃ for 30rain. The effect of crystallization ambient on the structural and ferroelectric properties of the BLT films is studied. The growth direction and grain size of BLT film are revealed to affect ferroeleetric properties. Alter the BLT film is annealed in 20%O2, the largest P~ value is obtained, which is ascribed to an increase of random orientation and large grain size. The fatigue property is improved with the concentration of oxygen in the ambient increasing, which is ascribed to annealing in the ambient with high concentrated oxygen adequately decreasing the defects related to lack of oxygen.     

NO<Subscript>2</Subscript>-sensing properties of La<Subscript>0.65</Subscript>Sr<Subscript>0.35</Subscript>MnO<Subscript>3</Subscript> synthesized by self-propagating combustion

Ultrafine-structure La_0.65Sr_0.35MnO₃ (LSM) powders synthesized by self-propagating combustion method have been used to fabricate sensing electrodes (SEs) for NO₂ mixed-potential sensors based on yttria-stabilized zirconia (YSZ). This type of sensor was found to provide better NO₂ sensitivity at 500 °C than sensors with LSM powders synthesized by traditional solid-state methods. The response values of the sensor have good linear relationship (sensitivity 36.6 mV/decade and linear fit 0.99) with the logarithm of NO₂ concentration varying from 30 to 500 ppm. The influence of sintering temperature (1000, 1100, 1200, and 1300 °C) on sensor response was also examined and was found to have a significant effect on the morphology of LSM-SEs. Moreover, in the presence of NO, CO₂, CO, and NO₂, the sensor exhibited good NO₂ selectivity.     

Fiber-Optic Ammonia Sensors Utilizing Rectangular-Cladding Eccentric-Core Fiber

A new fiber-optic ammonia sensor utilizing rectangular-cladding eccentric-core fiber and a sensitive film containing an indicator dye is demonstrated. The sensitive film is a SiO₂-GeO₂ gel film including an indicator dye of bromocresol purple or bromocresol green, which is dip-coated by a sol-gel technique. The attenuation of this sensor changes depending on the concentration of ammonia at the wavelength range of 500–700 nm. This sensor can detect several ppm of gaseous ammonia. Various factors determining the sensitivity to detect the ammonia gas and time response of the sensor are also studied.     

Influence of CuO catalyst in the nanoscale range on SnO2 surface for H2S gas sensing applications

The dispersal of CuO catalyst on the surface of the semiconducting SnO₂ film is found to be of vital importance for improving the sensitivity and the response speed of a SnO₂ gas sensor for H₂S gas detection. Ultra-thin CuO islands (8 nm thin and 0.6 mm diameter) prepared by evaporating Cu through a mesh and subsequent oxidation yield a fast response speed and recovery. Ultimately nanoparticles of Cu (average size = 15 nm) prepared by a chemical technique using a reverse micelle method involving the reduction of Cu(NO₃)₂ by NaBH₄ exhibited significant improvement in the gas sensing characteristics of SnO₂ films. A fast response speed of ∼14 s and a recovery time of ∼60 s for trace level ∼20 ppm H₂S gas detection have been recorded. The sensor operating temperature (130° C) is low and the sensitivity (S = 2.06 × 10³) is high. It is found that the spreading over of CuO catalyst in the nanoscale range on the surface of SnO₂ allows effective removal of excess adsorbed oxygen from the uncovered SnO₂ surface due to spill over of hydrogen dissociated from the H₂S-CuO interaction.     

Preparation of WO3 nanoparticles and application to NO2 sensor

WO₃ nanoparticles were prepared by evaporating tungsten filament under a low pressure of oxygen gas, namely, by a gas evaporation method. The crystal structure, morphology, and NO₂ gas sensing properties of WO₃ nanoparticles deposited under various oxygen pressures and annealed at different temperatures were investigated. The particles obtained were identified as monoclinic WO₃. The particle size increased with increasing oxygen pressure and with increasing annealing temperature. The sensitivity increased with decreasing particle size, irrespective of the oxygen pressure during deposition and annealing temperature. The highest sensitivity of 4700 to NO₂ at 1 ppm observed in this study was measured at a relatively low operating temperature of 50 °C; this sensitivity was observed for a sensor made of particles as small as 36 nm.     

Sensors for the nitrogen oxides, NO2, NO and N2O, based on In2O3 and WO3 nanowires

Sensing characteristics of ZnO, In₂O₃ and WO₃ nanowires have been investigated for the three nitrogen oxides, NO₂, NO and N₂O. In₂O₃ nanowires of ∼20 nm diameter prepared by using porous alumina membranes are found to have a sensitivity (defined as the ratio of the sensor resistance in the gas concerned to that in air) of about 60 for 10 ppm of all the three gases at a relatively low temperature of 150 °C. The response and recovery times are around 20 s. The sensitivity of these In₂O₃ nanowires is around 40 for 0.1 ppm of NO₂ and N₂O at 150 °C. WO₃ nanowires of 5–15 nm diameter, prepared by the solvothermal process show a sensitivity of 20–25 for 10 ppm of the three nitrogen oxides at 250 °C. The response and recovery times are 10 s and 60 s, respectively. The sensitivity is around 10 for 0.1 ppm of NO₂ at 250 °C. The sensitivity of In₂O₃ and WO₃ nanowires is not affected by humidity even up to 90% relative humidity. The study also reveals that the sensing mechanism for the three nitrogen oxides have a commonality in that the desorption of oxygen is a crucial step in all the cases. PACS 07.07.Df; 85.35.-p; 82.35.Np     

Mixed-potential-type NOx sensor based on YSZ and zinc oxide sensing electrode

Electrochemical sensors using tubular yttria-stabilized zirconia (YSZ) and oxide sensing electrode (SE) were fabricated and examined for NO_x detection at high temperatures. The mixed-potential-type NO_x sensor using ZnO-SE gave the highest sensitivity to NO_x among other single-type oxides tested as SEs in the temperature range of 600–700 °C. The response of the ZnO-attached device was a linear for the logarithm of NO₂ (NO) concentrations from 40 to 450 ppm. The sensing mechanism of the sensor was discussed on the basis of the gas adsorption-desorption behavior, the catalytic activity data, and electrochemical behavior for oxides examined.     

Facile synthesis of nanostructured CuO for low temperature NO2 sensing

Detection of environmental pollutant and health hazardous, nitrogen dioxide (NO₂) is reported using nanostructured CuO particulates (NPs). Powder X-ray diffraction and field emission scanning electron microscopy were used to probe crystalline phase and morphological details, respectively. Small crystallites of ∼10–12 nm and a strain of 4% were found in the leafy structure of CuO. Raman studies further supported the presence of nanosized CuO phase. This is the first instance of utilizing CuO NPs to detect 5 ppm of NO₂ even at a low operating temperature of 50 °C. The highest sensitivity for NO₂ was observed at 150 °C, for the first time, in CuO NPs. A low activation energy of 0.18 eV was found for sensing process. The CuO NPs sensor responded to NO₂ within a few seconds and recovered totally under a minute. The kinetics of the NO₂ gas adsorption on the CuO film surface was described following the Elovich model.     

Effect of solution concentration on physicochemical and gas sensing properties of sprayed WO3 thin films

Sub-stoichiometric tungsten trioxide (WO₃) thin films are deposited onto the glass substrates by spray pyrolysis technique using ammonium metatungstate. Effect of solution concentration on structural, morphological, optical, electrical and NO₂ sensing properties of WO₃ thin films is studied. Films are polycrystalline with monoclinic crystal structure and sub-stoichiometric as observed form the XRD and XPS studies, respectively. The SEM and AFM images show micro grained structure and surface roughness increases with increase in solution concentration. The PL studies revealed that the majority of the defects are the oxygen vacancies. From XPS and PL studies it is observed that, oxygen vacancies decrease with increase in solution concentration. The dielectric constant of the films as a function of frequency is in concurrence with resistivity measurements. Films show reproducible and reversible gas response at various operating temperatures and gas concentrations. Highest sensor response (38%) towards 200 ppm NO₂ concentration is observed for the film with 15 mM solution concentration at moderate operating temperature (200 °C). Pd sensitization enhanced gas response to 68% and improved kinetics of the sensor. Films are highly selective towards NO₂ as compared with the various gases such as SO₂, LPG, NH₃ and H₂S.     

Red and Near-Infrared Electroluminescences from Metal-Free Phthalocyanine

Organic light emitting diodes are fabricated based on metal-free phthalocyanine (H₂Pc) doped into tris-(8-hydroxyquinoline) aluminium (Alq₃). The device structure is ITO/NPB (30nm)/Alq₃: H₂Pc(30nm)/BCP(20nm)/Alq₃(20 nm)/Al. In the light-emitting layers, H₂Pc concentrations are varied from 0wt% to 100wt%. The emissions around 708nm and 800nm appear at low concentrations, while the emissions around 910nm and 930nm appear at high concentrations. The emissions around 708nm and 800nm are from H₂Pc monomers. The emissions around 910nm and 930nm are from H₂Pc aggregates. The dominant mechanism in the doped devices is direct chargetrapping.