Design and Performances of a Carbon Monoxide Sensor Using Mid-Infrared Absorption Spectroscopy Technique at 4.6 µm

Based on infrared absorption spectroscopy technique, a carbon monoxide sensor was developed using the fundamental absorption band of carbon monoxide molecule at the wavelength around 4.6 µm. The developed sensor consists of pulse-modulated wideband incandescence, open ellipsoid light-collector gas-cell, dual-channel detector, and control and signal-processing module. With the prepared standard carbon monoxide gas sample, sensing characteristics on carbon monoxide were investigated using the sensor. Experimental results reveal that the limit of detection is about 10 ppm, the relative error at the limit of detection point is less than 14%, and that is less than 7.8% within the low concentration range of 20～180 ppm. The maximum absolute errors of 50 min long-term measurement on the 0 and 14 ppm CO gas samples are about 3 and 3.17 ppm, respectively, and the standard deviations are as small as 0.18 and 1.25 ppm, respectively. Compared with the reported carbon monoxide detection systems utilizing quantum cascaded lasers and distributed feedback lasers, the proposed sensor shows potential applications in carbon monoxide detection under the circumstances of coal-mine and environmental protection, by virtue of high performance, low cost, simple optical structure, and so on.     

Mechanism of Macroscopic Motion of Oleate Helical Assemblies: Cooperative Deprotonation of Carboxyl Groups Triggered by Photoisomerization of Azobenzene Derivatives

Macroscopic and spatially ordered motions of self‐assemblies composed of oleic acid and a small amount of an azobenzene derivative, induced by azobenzene photoisomerization, was previously reported. However, the mechanism of the generation of submillimeter‐scale motions by the nanosized structural transition of azobenzene was not clarified. Herein, an underlying mechanism of the motions is proposed in which deprotonation of carboxyl groups in cooperation with azobenzene photoisomerization causes a morphological transition of the self‐assembly, which in turn results in macroscopic forceful dynamics. The photoinduced deprotonation was investigated by potentiometric pH titration and FTIR spectroscopy. The concept of hierarchical molecular interaction generating macroscale function is expected to promote the next stage of supramolecular chemistry.     

Isoregic Thienylene‐Phenylene Polymers: The Effects of Structural Variation and Application to Photovoltaic Devices

Isoregic conjugated polymers composed of thiophene and dialkoxybenzene units were designed to harvest incident light in the mid‐visible energy range (band gap of 2.1 eV). Poly(1,4‐bis(2‐thienyl)‐2,5‐diheptoxybenzene) (PBTB(OC₇H₁₅)₂) and poly(1,4‐bis(2‐thienyl)‐2,5‐didodecyloxybenzene) (PBTB(OC₁₂H₂₅)₂) have shown significant photovoltaic performance as an electron donor when used in tandem with the electron acceptor [6, 6]‐phenyl C₆₁‐butyric acid methyl ester (PCBM) in bulk hetero‐junction photovoltaic devices. Photovoltaic devices incorporating PBTB(OC₇H₁₅)₂ and PCBM have shown AM1.5 efficiencies of ～0.6% with a short circuit current density of 2.5 mA/cm², an open circuit voltage of 0.74 V, and a fill factor of 0.32. Incident Photon‐to‐Current Efficiency (IPCE) of the device was found to be ca. 16% at 410 nm. In order to examine the relationship between the molecular structure of the polymers and their electronic energy levels, and to correlate this with photovoltaic performance, optoelectronic and electrochemical results are discussed in relation to the I‐V characteristics of the devices. Additionally, a computer‐aided simulation is used to gain further insight into the effect of polymer structure on the energetic relationships in the bulk heterojunction devices.     

A Resettable Keypad Lock with Visible Readout Based on Closed Bipolar Electrochemistry and Electrochromic Poly(3‐methylthiophene) Films

A closed bipolar electrode (BPE) system was developed with electrochromic poly(3‐methylthiophene) (PMT) films electropolymerized on the ITO/rGO electrode as one pole of BPE in the reporting reservoir and the bare ITO electrode as another pole of BPE in the analyte reservoir, in which rGO represents reduced graphene oxide. Under a suitable driving voltage (V_tot), the electrochemical reduction/oxidation of electroactive probes, such as H₂O₂/glutathione (Glu), in the analyte reservoir could induce the reversible color change of PMT films in the reporting reservoir between blue and red. Based on this, a keypad lock with H₂O₂, Glu, and V_tot=?3.0 V as the three inputs and the color change of PMT films as the visible output was established. This system was easily operated and did not need to synthesize the complex compounds or DNA molecules. The security system was easy to reset and could be used repeatedly.     

Enhancing device efficiencies of solid-state near-infrared light-emitting electrochemical cells by employing a tandem device structure

Compared to near-infrared (NIR) organic light-emitting devices, solid-state NIR light-emitting electrochemical cells (LECs) could possess several superior advantages such as simple device structure, low operating voltages and balanced carrier injection. However, intrinsically lower luminescent efficiencies of NIR dyes and self-quenching of excitons in neat-film emissive layers limit device efficiencies of NIR LECs. In this work, we demonstrate a tandem device structure to enhance device efficiencies of phosphorescent sensitized fluorescent NIR LECs. The emissive layers, which are composed of a phosphorescent host and a fluorescent guest to harvest both singlet and triplet excitons of host, are connected vertically via a thin transporting layer, rendering multiplied light outputs. Output electroluminescence (EL) spectra of the tandem NIR LECs are shown to change as the thickness of emissive layer varies due to altered microcavity effect. By fitting the output EL spectra to the simulated model concerning microcavity effect, the stabilized recombination zones of the thicker tandem devices are estimated to be located away from the doped layers. Therefore, exciton quenching near doped layers mitigates and longer device lifetimes can be achieved in the thicker tandem devices. The peak external quantum efficiencies obtained in these tandem NIR LECs were up to 2.75%, which is over tripled enhancement as compare to previously reported NIR LECs based on the same NIR dye. These efficiencies are among the highest reported for NIR LECs and confirm that phosphorescent sensitized fluoresce combined with a tandem device structure would be useful for realizing highly efficient NIR LECs.     

Promising methane gas sensor synthesized by microwave-assisted Co3O4 nanoparticles

The morphology and gas sensing characteristics of Co₃O₄ nanoparticles prepared using the microwave irradiation were investigated. XRD and TEM are used to analyze the structural and the morphological properties of the prepared nanoparticles. XRD results confirmed the formation of pure phase of these nanoparticles. The gas sensor based on the synthesis Co₃O₄ nanoparticles reveals faster response and recovery time at low temperature detection toward methane gas. Specifically, for methane concentration of 1%, the response and the recovery times at 200 °C are 100 s and 50 s, respectively. Furthermore, the sensing characteristics of Co₃O₄ nanoparticles were improved by increasing the operating temperatures and gas concentrations as well. The experimental results clearly demonstrate the potential use of Co₃O₄ nanoparticles as a sensing material in the fabrication of CH₄ sensors.     

A tool for the automatic generation and analysis of regular analog layout modules

This paper describes the characteristics of a new CAD tool that enables the creation of layout libraries of selected analog modules. This Analog Modules Generator (AMG) automatically creates multiple layout versions of two commonly used analog structures: the differential pair and arrays of series-connected or stacked devices, for the subsequent generation of layout libraries. Based on the number of devices and rows defined by the user for the layout implementation, the tool validates all possible implementations, which are later saved in a database. Additionally, an extraction process can be optionally executed over all the layout views saved in the database. The AMG generates several reports with all the characteristics of the implemented layouts, including area and parasitic components, facilitating further statistical processing. We describe the features and capabilities of the proposed AMG tool, and several test cases are presented. Results show that suitable layout implementations can be achieved by layout and circuit designers in a very reduced amount of time.     

Synthesis,electrochemical and electrochromic properties of novel 2,4,6-Tri(pyridine-4-yl)pyridilium derivatives

Four star-shaped like fused heterocyclic compounds multi-electrochromic materials 2,4,6-Tri(pyridine-4-yl)pyridilium derivatives (TPPDs) were successfully synthesized and characterized by NMR, Solid IR spectra, APCI-MS, and UV–vis spectroscopy. The electrochemical properties, electrochromic behavior, electro-optical properties, and electrochromic mechanism were investigated by thermogravimetric analysis, cyclic voltammetry and UV–vis absorption spectra. Electrochromic devices based on these compounds were fabricated with an active area of 3 cm × 4 cm and their electrochromic performances were further studied. It was found the ECDs presented a stable as well as multicolor electrochromic change from colorless to blue, then violet-blue and finally black-blue between 0 V and +4.0 V. In addition, the prepared electrochromic materials had high coloration efficiency, low switching time, and nice redox stability. This type of multi-electrochromic materials would thus be promising candidates for applications in electrochromic devices.     

Catalyst‐Free GaN Nanorods Synthesized by Selective Area Growth

GaN nanorod formation on Ga‐polar GaN by continuous mode metalorganic chemical vapor deposition selective area growth (MOCVD SAG) is achieved under a relatively Ga‐rich condition. The Ga‐rich condition, provided by applying a very low V/III ratio, alters the growth rates of various planes of the defined nanostructure by increasing relative growth rate of the semi‐polar tilted m‐plane {1–101} that usually is the slowest growing plane under continuous growth conditions. This increased growth rate relative to the non‐polar m‐plane {1–100} and even the c‐plane (0001), permits the formation of GaN nanorods with nonpolar sidewalls. In addition, a new growth mode, called the NH₃‐pulsed mode, is introduced, utilizing the advantages of both the continuous mode and the lower growth rate pulsed mode to form nanorods. Finally, nanorods grown under the different growth modes are compared and discussed.