Jiangong Cheng

Ferroelectricity in sol-gel derived Ba0.8Sr0.2TiO3 thin films using a highly diluted precursor solution

Barium strontium titanate films with good ferroelectricity have been obtained by a developed sol-gel processing, using a highly dilute spin-on solution. X-ray diffraction and scanning electron microscopy investigations show that large grains with the size of 100–200 nm in the films are formed from highly dilute spin-on solutions with layer-by-layer homoepitaxy. Polarization-electric field and dielectric constant-temperature (er−T) measurements reveal that the ferroelectricity becomes more evident as the grain size increases. The measurements for quality Ba0.8Sr0.2TiO3 ferroelectric films derived from a 0.05 M solution have shown a remnant polarization of 3.5 μC/cm2, a coercive field of 86 kV/cm, and two distinctive phase transitions.

Pyroelectric properties in sol–gel derived barium strontium titanate thin films using a highly diluted precursor solution

The pyroelectric coefficient and pyroelectric infrared response in the sol–gel derived Ba0.8Sr0.2TiO3 thin films have been studied for possible infrared detector applications. The measured pyroelectric coefficient is larger than 3.1×10−4 C/m2 K at temperatures ranging from 10 to 26 °C and reaches the maximum value of 4.1×10−4 C/m2 K at 16 °C. The infrared detectivity of 4.6×106 cm Hz1/2 W−1 has been obtained at 19 °C and 10 Hz in the Ba0.8Sr0.2TiO3 films deposited on thick (500 μm) platinum coated silicon substrates. The better infrared response can be expected by the improvement in the thermal isolation of pyroelectric element and the electrode materials.

High performance aniline vapor detection based on multi-branched fluorescent triphenylamine-benzothiadiazole derivatives: branch effect and aggregation control of the sensing performance

A series of benzothiadiazole-pyridine branched triphenylamine derivatives TPA1BP, TPA2BP and TPA3BP have been designed and synthesized to sense aniline vapor with distinguished sensitivity, selectivity and repeatability via photoinduced electron transfer (PET). Suitable energy levels ensure the high selectivity to aniline for all three sensory materials. However, the aggregations of the three materials in the film state on a quartz substrate increase along with the branches, which highly deteriorate the sensing performance for less efficient fluorescence, lower contact area and inferior vapor penetration. The oriented ZnO nanorod array is introduced as the substrate to eliminate the aggregation and enhance the sensing performance, because of its high surface-to-volume ratio and 3D structure. Therefore, the cooperative effect that the sensing performance of TPAnBP increases with the number of branches could be observed; fluorescence intensities of the films on the nano-substrate are 34%, 45% and 54% quenched for TPA1BP, TPA2BP and TPA3BP, respectively, after exposure to 300 ppm aniline vapor for less than 5 s. Moreover, the fluorescences of all three sensory materials are almost 100% recovered by eluting with fresh air for 20 s and could be reused immediately. The detection limits are predicted to be 1 ppm for TPA1BP, 100 ppb for TPA2BP and 1 ppb for TPA3BP according to the fitted plot, demonstrating a significant cooperative effect of the molecular branches.

Pyroelectric Ba0.8Sr0.2TiO3 thin films derived from a 0.05 M solution precursor by sol–gel processing

Tetragonal Ba0.8Sr0.2TiO3 thin films with large columnar grains 100–200 nm in diameter have been prepared on Pt/Ti/SiO2/Si substrates using a 0.05 M solution precursor by sol–gel processing. The ferroelectric phase transition in the prepared Ba0.8Sr0.2TiO3 thin films is broadened, and suppressed to 40 °C with a maximum dielectric constant of er (100 kHz)=680. The observed low dissipation factor tan δ=2.6% and high pyroelectric coefficient p=4.586×10−4 C/m2 K at 33 °C render the prepared Ba0.8Sr0.2TiO3 thin films promising for uncooled infrared detector and thermal imaging applications.

Low-temperature crystallized pyrochlore bismuth zinc niobate thin films by excimer laser annealing

The crystallization temperature of Bi1.5Zn0.5Nb1.5O6.5 (BZN) films was reduced by a combination of conventional heating and irradiation with a pulsed KrF excimer laser. Both the energy density and substrate temperature affect the properties of laser-annealed BZN films. It was found that the crystallinity and dielectric properties improved after a postannealing at 400°C for 2h in an oxygen atmosphere. BZN films crystallized with an energy density of 27mJ∕cm2 at a substrate temperature of 400°C with postannealing showed dielectric properties comparable to those of rapid thermal annealed BZN films. Laser crystallization at substrate temperatures ⩽400°C makes integration with polymeric substrates possible.

Conjugated polymer-titania nanoparticle hybrid films: random lasing action and ultrasensitive detection of explosive vapors.

We have first demonstrated that a random laser action generated by a hybrid film composed of a semiconducting organic polymer (SOP) and TiO(2) nanoparticles can be used to detect 2,4,6-trinitrotoluene (TNT) vapors. The hybrid film was fabricated by spin-casting SOP solution dispersed with nanosized TiO(2) particles on quartz glass. The SOP in the hybrid film functioned as both the gain medium and the sensory transducer. A random lasing action was observed with a certain pump power when the size (diameter of 50 nm) and concentration (8.9 x 10(12)/cm(3)) of TiO(2) nanoparticles were optimized. Measurements of fluorescence quenching behavior of the hybrid film in TNT vapor atmosphere (10 ppb) showed that attenuated lasing in optically pumped hybrid film displayed a sensitivity to vapors of explosives more than 20 times higher than was observed from spontaneous emission. This phenomenon has been explained with the four-level laser model. Since the sensory transducer used in the hybrid polymer/nanoparticles system could be replaced by other functional materials, the concept developed could be extended to more general domains of chemical or environment detection.

Sensitivity gains in chemosensing by optical and structural modulation of ordered assembly arrays of ZnO nanorods.

Nanomaterials and -structures have attracted much attention owing to their applications to ultrasensitive nanodevices. In this work, ordered assembly arrays of ZnO nanorods have been hydrothermally fabricated and used as optical substrates of fluorescence sensors for toxic vapors. The unique fastigiate nanorod assembly combines merits of single fibers and clusters, possessing identical orientation, large surface-to-volume ratio, evanescent transmission, and evanescent coupling. As coated on the assembly arrays, different sensing materials all generated amplified spontaneous emission (ASE) action such that the fluorescence intensity of the narrowed spectrum was 52.4-fold enhanced. Results of sensing experiments indicate that sensors based on the assembly arrays displayed 100% elevated normalized quenching rate and several times longer full-load time compared with reference sensors. This work provides a facile method to fabricate secondary structures of 1D rigid material and presents a new way to design highly sensitive optic sensors. Furthermore, evanescent excitation caused ASE action of fluorescent organics, and the correlative sensitivity gain is of interest in both theoretical research and the applications field.

Dependence of texture development on thickness of single-annealed-layer in sol–gel derived PZT thin films

Abstract PbZr0.5Ti0.5O3 thin films have been prepared on Pt (111)/Ti/SiO2/Si substrates by a modified sol–gel technique. The PZT films were annealed layer by layer using a rapid thermal annealing (RTA) method during the spin-coating process. A novel route was used to obtain PZT films with different single-annealed-layer in thickness from the same precursor solution. It is found that the degree of (111) orientation of the films increases with the reduction thickness of single-annealed-layer. As the thickness of single-annealed-layer drops to 40 nm, the film shows a high degree of (111) preferred orientation. The decrease of single-annealed-layer thickness also leads to the increase of the remanent polarization and the dielectric constant.

Concise and Efficient Fluorescent Probe via an Intromolecular Charge Transfer for the Chemical Warfare Agent Mimic Diethylchlorophosphate Vapor Detection

Sarin, used as chemical warfare agents (CWAs) for terrorist attacks, can induce a number of virulent effects. Therefore, countermeasures which could realize robust and convenient detection of sarin are in exigent need. A concise charge-transfer colorimetric and fluorescent probe (4-(6-(tert-butyl)pyridine-2-yl)-N,N-diphenylaniline, TBPY-TPA) that could be capable of real-time and on-site monitoring of DCP vapor was reported in this contribution. Upon contact with DCP, the emission band red-shifted from 410 to 522 nm upon exposure to DCP vapor. And the quenching rate of TBPY-TPA reached up to 98% within 25 s. Chemical substances such as acetic acid (HAc), dimethyl methylphosphonate (DMMP), pinacolyl methylphosphonate (PAMP), and triethyl phosphate (TEP) do not interfere with the detection. A detection limit for DCP down to 2.6 ppb level is remarkably achieved which is below the Immediately Dangerous to Life or Health concentration. NMR data suggested that a transformation of the pyridine group into pyridinium salt via a cascade reaction is responsible for the sensing process which induced the dramatic fluorescent red shift. All of these data suggest TBPY-TPA is a promising fluorescent sensor for a rapid, simple, and low-cost method for DCP detection, which could be easy to prepare as a portable chemosensor kit for its practical application in real-time and on-site monitoring.

A BODIPY dye as a reactive chromophoric/fluorogenic probe for selective and quick detection of vapors of secondary amines

A new reaction based fluorescence turn-off strategy for detection of secondary amines was developed. The probe shows fast response and high selectivity to secondary amines in solution/film at sub-ppm levels through chromogenic and fluorescent dual-mode signal changes.