Wang Jiang-Long

Laser-induced voltage effects in Ca 3 Co 4 O 9 thin films on tilted LaAlO 3 (001) substrates grown by chemical solution deposition

Laser-induced voltage effects in c-axis oriented Ca3Co4O9 thin films have been studied with samples fabricated on 10° tilted LaAlO3 (001) substrates by a simple chemical solution deposition method. An open-circuit voltage with a rise time of about 10 ns and full width at half maximum of about 28 ns is detected when the film surface is irradiated by a 308-nm laser pulse with a duration of 25 ns. Besides, open-circuit voltage signals are also observed when the film surface is irradiated separately by the laser pulses of 532 nm and 1064 nm. The results indicate that Ca3Co4O9 thin films have a great potential application in the wide range photodetctor from the ultraviolet to near infrared regions.

Effect of microstructure on the thermoelectric properties of CSD-grown Bi2Sr2Co2Oy thin films

Three Bi2Sr2Co2Oy thin films with different microstructures have been prepared by chemical solution deposition on LaAlO3(001) through varying the annealing temperature. With the decrease in the annealing temperature, both the size and c-axis alignment degree of grains in the film decrease as well, leading to an increase in the film resistivity. In addition, the decrease in the annealing temperature also results in a slight increase in the Seebeck coefficient due to the enhanced energy filtering effect of the small-grain film. The nanostructured Bi2Sr2Co2Oy film with an average grain size of about 100 nm shows a power factor comparable to that of films with larger grains. Since the thermal conductivity of the nanostructured films can be depressed due to the enhanced phonon scattering by grain boundary, a higher figure of merit is expected in Bi2Sr2Co2Oy thin film with grains in nanometer size.

High temperature thermoelectric properties of highly c-axis oriented Bi2Sr2Co2Oy thin films fabricated by pulsed laser deposition

High-temperature thermoelectric transport property measurements have been performed on the highly c-axis oriented Bi2Sr2Co2Oy thin films prepared by pulsed laser deposition on LaAlO3 (001). Both the electric resistivity ρ and the seebeck coefficient S of the film exhibit an increasing trend with the temperature from 300 K–1000 K and reach up to 4.8 mΩ cm and 202 μV/K at 980 K, resulting in a power factor of 0.85 mW/mK which are comparable to those of the single crystalline samples. A small polaron hopping conduction can be responsible for the conduction mechanism of the film at high temperature. The results demonstrate that the Bi2Sr2Co2Oy thin film has potential application in high temperature thin film thermoelectric devices.

The Enhancement of Laser-Induced Transverse Voltage in Tilted Bi2Sr2Co2Oy Thin Films with a Graphite Light Absorption Layer

Laser-induced transverse voltage effect is investigated in c-axis tilted Bi2Sr2Co2Oy thin films coated with a graphite layer by using three different laser sources with wavelength ranging from ultraviolet to near-infrared. Due to the transverse thermoelectric effect, voltage signals are detected when the film surface is irradiated by these three lasers and the voltage sensitivity is enhanced as a result of the increasing light absorption at the graphite layer. This work demonstrates that the graphite can be used as an effective absorption layer for fabrication of light detectors based on the photo-thermo-electric conversion.

Temperature-dependent rectifying and photovoltaic characteristics of an oxygen-deficient Bi2Sr2Co2Oy/Si heterojunction

A Bi2Sr2Co2Oy/Si heterojunction is obtained by growing a layer of p-type oxygen-deficient Bi2Sr2Co2Oy film on a commercial n-type silicon wafer by pulsed laser deposition. Its rectifying and photovoltaic properties are studied in a wide temperature range from 20 K to 300 K. The transport mechanism under the forward bias can be attributed to a trap-filled space-charge-limited current conduction mechanism. Under the irradiation of a 532-nm continuous wave laser, a clear photovoltaic effect is observed and the magnitude of photovoltage increases as the temperature decreases. The results demonstrate the potential application of a Bi2Sr2Co2Oy-based heterojunction in the photoelectronic devices.

High temperature thermoelectric performanceof Sr doped CdO polycrystalline bulks

In this paper, Cd 1 - x Sr x O polycrystalline bulks were synthesized via conventional solid state reaction method and the effect of Sr doping on the high temperature thermoelectric performance of CdO were investigated. XRD results revealed all samples were pure CdO and the lattice parameters increased with Sr content, demonstrating that all doped Sr entered the CdO lattice. The dopant Sr inhibited the grain growth of CdO polycrystals, gave rise to the reduction of grain size as well as increase of grain boundaries. Due to the large difference on electrical affinities of CdO and SrO, the introduction of SrO into CdO polycrystals resulted in decreased carrier concentration, which further led to the increment of both electrical resistivity and Seebeck coefficient. Experimental data on thermal properties verified that doping of Sr was an effective way to reduce the thermal conductivity of CdO. Attributing to the increased electrical resistivity, the electrical thermal conductivity decreased significantly with increasing Sr content. On the other hand, the long-wavelength phonon scattering was greatly enhanced by increased grain boundaries, resulted in suppressed phonon thermal conductivity. Meanwhile, the size and mass differences on Sr and Cd atoms led to strong strain field fluctuation scattering and mass fluctuation scattering, which drastically reduced the phonon thermal conductivity. Benefiting from the decreased electrical and phonon thermal conductivities, the total thermal conductivity experienced a remarkable reduction, from 3.52 W m -1 K -1 for the pristine CdO to 1.71 W m -1 K -1 for the Cd 0.95 Sr 0.05 O at 1000 K, lower than most oxide thermoelectric materials. Originating from the reduced thermal conductivity, the thermoelectric performances of all doped samples were promoted, the Cd 0.97 Sr 0.03 O sample reached the highest ZT value of 0.40 at 1000 K despite of the low power factor, which was 25% higher compared to pure CdO, and was comparable to the best reported n type oxide thermoelectric materials.