Search

The effect of high-energy electron irradiation on poly(vinylidene fluoride-trifluoroethylene) 80/20 mol % copolymers has been studied in a broad dose ranging from 0 to 120 Mrad. It was found that the copolymers transformed from a normal ferroelectric to a relaxor ferroelectric phase (RFE) at high electron doses. For copolymers irradiated at the dose above 90 Mrad, they exhibited typical dielectric behavior of RFE, e.g., whose dielectric constant peaks show strong frequency dispersion. X-ray diffraction patterns showed that the irradiation induced a coexistence of the polar and nonpolar phase in the crystalline regions, leading to nanosized coherent regions in the irradiated copolymer films. Differential scanning calorimetery and polarization hysteresis loops also revealed the reduction in the crystallinity and stability of the ferroelectric state, reflecting significant changes in the ferroelectric-to-paraelectric phase transition due to the effect of high-energy electron irradiation.

(Ba0.6Sr0.4)92.5%K7.5%TiO3 (BSKT) thin films doped by Mn from 0 to 6 mol % were fabricated by the sol-gel method on a Pt/TiO2/SiO2/Si substrate. The structure and surface morphology of Mn-doped BSKT thin films were investigated as a function of Mn concentration by x-ray diffraction and scanning electron microscopy. The dielectric measurements were conducted on metal-insulator-metal capacitors at the frequency from 100 Hz to 1 MHz at room temperature. It was found that the Mn concentration in Mn doped BSKT thin films has a strong influence on material properties including surface morphology and dielectric and tunable properties. Increasing Mn content leads to simultaneous decreasing of surface roughness, dielectric constant, and tunability of Mn doped BSKT films. However the dielectric loss of Mn doped BSKT decreases first and then increases with the increase in Mn dopant. The effects of Mn doping on the microstructure and dielectric and tunable properties of Mn doped BSKT thin films were analyzed. (Ba0.6S...

Bi1−xCexFeO3 (x=0, 0.05, 0.1, 0.15, and 0.20) (BCFO) thin films were deposited on Pt/TiN/Si3N4/Si and fluorine-doped SnO2 glass substrates by sol-gel technique, respectively. The effect of Ce doping on the microstructure, electrical and magnetic properties of BCFO films was studied. Compared to counterparts of BiFeO3 (BFO) film, the fitted Bi 4f7/2, Bi 4f5/2, Fe 2p3/2, Fe 2p1/2, and O 1s peaks for Bi0.8Ce0.2FeO3 film shift toward higher binding energy regions by amounts of 0.33, 0.29, 0.43, 0.58, and 0.49 eV, respectively. Raman redshifts of 2–4 cm−1 and shorter phonon lifetimes for the Bi0.8Ce0.2FeO3 film might be related to anharmonic interactions among Bi–O, Ce–O, (Bi, Ce)–O, and Fe–O bonds in the distorted oxygen octahedron. Compared to the pure counterparts, the dielectric and ferroelectric properties of the Bi0.8Ce0.2FeO3 film are improved due to the decreased oxygen vacancies by the stabilized oxygen octahedron. Current density values for the BFO and Bi0.8Ce0.2FeO3 film capacitors are 9.89×10−4 and...

To strengthen the adhesion of platinum layer to counterelectrodes of dye sensitized solar cells, titanium thin film has been utilized as adhesion layer between platinum and substrate [Wei et al., Appl. Phys. Lett. 90, 153122 (2007)]. In our study, platinum/titanium bilayer counterelectrodes were fabricated by magnetron sputtering. The structural, electrical, and electrochemical properties of the bilayer counterelectrode were studied by varying the thickness of both platinum and titanium layers. The influence of both electrochemical active surface and crystallite size on charge transfer resistance of the bilayer counterelectrode was explored. From these evaluations, it was found that the as-prepared titanium layer was almost amorphous, and intermetallic phase was formed between platinum and titanium layers. As expected, sheet resistance of the electrode decreased with the increase in deposition time of both platinum and titanium layers. Metal titanium was found to be inert in the catalyzing reduction in tr...

Bulk acoustic wave induced mixing in microfluidic systems has been studied by using a pair of small size ultrasonic transducers integrated into a prototype polydimethylsiloxane device. The acoustic properties of the integrated ultrasonic transducers were evaluated, demonstrating the generation of bulk acoustic wave in the mixing chamber when a low ac voltage is applied. Then, the mixing efficiency of the device was studied by using two stream laminar flows and taking into account the particular geometry of the mixing chamber. Because of the limited power consumption, the system should be compatible with the requirements of a number of applications in both analytical chemistry and biology.

c-axis oriented polycrystalline ZnO:Al (AZO) films were deposited at different substrate temperature (Ts) and oxygen ambient (PO2) by pulsed laser deposition. It is found that with the increase in Ts and PO2, the 2θ position of AZO (0002) shifts to higher angle, which can be attributed to the different amounts and species of defects in AZO films. Furthermore, the full width at half maximum of 2θ and (0002) rocking curve indicate the different crystalline qualities for AZO films grown at different conditions. At the same time, the carrier concentration decreases with the increase in Ts and PO2 for most of the samples; however, the Hall mobility usually attains its maximum at proper Ts and PO2. Moreover the transport of electrons may be governed by different mechanisms for AZO films grown at different conditions. The AZO transmission spectra show that the ultraviolet absorption edge and infrared transparency limit shift toward longer wavelength with the increase in Ts and PO2, which are due to the changes o...

P-poly(9, 9-diethylfluorene)/n-silicon nanowire (SiNW) heterojunctions were prepared by spin coating p-type conductive organic polymer on as-prepared n-SiNWs, which were fabricated by electroless metal deposition method. This hybrid nanowire p-n heterojunction shows good rectifying behavior with turn-on voltage of about 1V at room temperature. Temperature-dependent current-voltage properties in the range of 253–413K were investigated and they follow the standard p-n heterojunction electron transport mechanism. The hybrid nanowire heterojunction shows good photovoltaic properties and good sensitivity toward visible light, and a responsivity of 3.23mA∕W under a reverse bias of 10V was obtained. These results present potential applications in the future nanoelectronic and photonic devices based on organic and inorganic p-n heterojunction arrays.

To evaluate the influence of thickness on structural, electrical, and optical properties of ZnO:Al (AZO) films, a set of polycrystalline AZO samples with different thicknesses were deposited by pulsed laser deposition. X-ray diffraction measurement shows that the crystal quality of AZO films was improved with the increase of film thickness. Film surface morphology reveals that a transition of growth mode from vertical growth to lateral growth exists when the films become thicker. The resistivity decrease of AZO films with increase of film thickness owes to the change of carrier concentration for 80% regardless of film thickness in the visible region. The photoluminescence spectra of AZO films can be fitted well by seven emissions, and the emi...

The varistor-capacitor property of CaCu3Ti4O12 ceramics has been characterized by a combination of ac impedance spectroscopy and dc measurement. The results demonstrate that the non-Ohmic property and ultrahigh dielectric constant of CaCu3Ti4O12 ceramics are associated with the grain-boundary behavior. The I‐V and C‐V characteristics of grain-boundary regions in CaCu3Ti4O12 ceramics are explained on the basis of a back-to-back potential barrier model. We suggest that the origin of the potential barrier is related to Cu ions segregated to grain boundaries.

Ba0.6Sr0.4TiO3 (BST) thin films doped by K (BSTK) from 1to20mol% were fabricated by sol-gel method on a Pt∕TiO2∕SiO2∕Si substrate. Thermal evolutionary process of the Ba0.6Sr0.4TiO3 and (Ba0.6Sr0.4)0.95K0.05TiO3 dry gel was carried out by thermogravimetry and differential thermal analysis system. The structure and surface morphology of BST thin films were investigated as functions of K concentration by x-ray diffraction and atomic force microscopy. The dielectric measurements were conducted on metal-insulator-metal capacitors at the frequency from 100Hzto1MHz. The K concentration in BST thin films has a strong influence on the material properties including surface morphology and dielectric and tunable properties. The grain size, surface root-mean-square roughness, dielectric constant, dissipation factor, and tunability all increased with increasing K content up to 7.5mol% and then decreased with increasing K content from 7.5to20mol% in the BSTK thin films at 1MHz. The effects of K doping on the microstruc...