Search

Conventional metal oxide semiconductor (MOS) gas sensors have been investigated for decades to protect our life and property. However, the traditional devices can hardly fulfill the requirements of our fast developing mobile society, because the high operating temperatures greatly limit their applications in battery-loaded portable systems that can only drive devices with low power consumption. As ammonia is gaining importance in the production and storage of hydrogen, there is an increasing demand for energy-efficient ammonia detectors. Hence, in this work, a Schottky diode resulting from the contact between zinc oxide nanorods and gold is designed to detect gaseous ammonia at room temperature with a power consumption of 625 μW. The Schottky diode gas sensors benefit from the change of barrier height in different gases as well as the catalytic effect of gold nanoparticles. This diode structure, fabricated without expensive interdigitated electrodes and displaying excellent performance at room temperature, provides a novel method to equip mobile devices with MOS gas sensors.

We have used a ferroelectric BaTiO3 substrate with a hematite (α-Fe2O3) nanostructured surface to form a heterogeneous BaTiO3/α-Fe2O3 photocatalyst. In this study we show that varying the mass ratio of α-Fe2O3 on BaTiO3 has a significant influence on photoinduced decolorization of rhodamine B under simulated sunlight. The highest photocatalytic activity was obtained for BaTiO3–Fe2O3-0.001M, with the lowest mass ratio of α-Fe2O3 in our study. This catalyst exhibited a 2-fold increase in performance compared to pure BaTiO3 and a 5-fold increase when compared to the higher-surface-area pure α-Fe2O3. The increases in performance become more marked upon scaling for the lower surface area of the heterostructured catalyst. Performance enhancement is associated with improved charge-carrier separation at the interface between the ferroelectric surface, which exhibits ferroelectric polarization, and the hematite. Increasing the mass ratio of hematite increases the thickness of this layer, lowers the number of tripl...

ZnO is an interesting material for photoactive and optoelectronic devices because of the wide range of available nanostructures and advantageous semiconducting properties. However, a significant drawback of ZnO is the low stability in high or low pH solutions. This has limited the development of ZnO core-shell materials for use in Z-scheme systems or photovoltaics, where any secondary phase is produced using chemical solution processing at low or high pH. Here, we show a simple process to produce an organic capping layer of 3-aminopropyltriethoxysilane that can successfully stabilize nanostructured ZnO for processing below pH 1. We demonstrate that this process can be used to produce a ZnO-BiFeO3 (BFO) core-shell structure by a sol-gel process. Using a range of physical and analytical techniques, we show that BFO is highly crystalline and produces a conformal coating with a thickness of 2.5 nm. X-ray photoelectron spectroscopy and X-ray diffraction confirm the phase and expected chemical composition of BFO. Finally we are able to demonstrate that diodes produced using the ZnO-BFO core-shell structure have improved performance with a rectification ratio at ±3 V of 2800 because of the reduction in reverse current typically associated with surface recombination on ZnO. Our process opens a route to producing a range of hitherto prohibited ZnO core-shell structures that may have applications ranging from photovoltaic devices to core-shell photocatalysts.

Lithium-substituted 0.95[0.94(Bi0.5Na(0.5–x)Lix)TiO3–0.06BaTiO3]–0.05CaTiO3 materials include the polar rhombohedral R3c and the weakly polar tetragonal P4bm phases. On increasing lithium content, the (R3c/P4bm) phase ratio decreased, while the rhombohedral and tetragonal lattice distortions remained the same. The temperature corresponding to the shoulder in the dielectric permittivity shows no clear shift with respect to lithium substitution because of the rhombohedral distortion remaining constant. Electrical poling produced an increase of the rhombohedral phase fraction together with a rise of the rhombohedral and tetragonal distortion. This confirmed the occurrence of a phase transition from the weakly polar to the polar phase during electrical poling. Four peaks found in the current–electric field (I–E) loops are related to reversible electric field induced transitions. By studying the temperature dependence of the current peaks in the I–E loops, it was found that the minimum temperature where these electric field induced transitions take place decreases with increasing lithium substitution.

BaTiO3 is used as a target catalyst to probe the influence of ferroelectricity on the decolorization of a typical dye molecule—Rhodamine B—under simulated solar light. We show that there is a 3-fold increase in the decolorization rate using BaTiO3 with a high tetragonal content compared to predominantly cubic material. This is ascribed to the ferroelectricity of the tetragonal phase. The influence of ferroelectricity ensures a tightly bound layer of dye molecule and also acts to separate the photoexcited carriers due to the internal space charge layer. Both of these features act to enhance the catalytic performance. When nanostructured Ag is photochemically deposited on the surface of the BaTiO3, we find a further increase in the reaction rate that gives complete decolorization of the dye in around 45 min.

Photocatalytic decolorization of acid black 1 (a.k.a. amido black 10B) and rhodamine b was investigated over powders of lithium niobate or lithium niobate doped with iron to form n-type material doped or p-type magnesium doped lithium niobate. In all cases, photostimulation was performed using simulated solar illumination. The rate of decolorization of the dye solutions was found to be fastest over p-type material than with the undoped powder, with the n-type proving least effective. The change in rate was attributed to changes in the majority carrier, associated with the dopant altering the ratio of reactive species (holes and electrons). We also show that the surface depolarization field associated with a ferroelectric material alters the surface chemistry by changing the Stern and inner Helmholtz plane due to the interaction of catalyst surface charge and the polar nature of solvated species. The spatial separation of REDOX reactions in ferroelectric powders positively influences the proportion of reac...

In this work, we have investigated the photochemical reaction with a variety of metal salts on a polarizable semiconductor, lead zirconate titanate (PZT 30/70 [111]). The exact position of the band edges can influence properties such as the width of the space-charge region and barriers for charge injection, which play an important role in devices built with such materials such as FeRAM and MLC. Observations show that there can be metal deposition on positive domains or photodecomposition on negative domains. The exact reaction was found to be dependent on the reduction potential of the cation and whether a nitrate or chloride salt was used. We show that for certain cations such as Fe2+, with a reduction potential near the edge of the conduction band of the PZT, either reduction or photodecomposition can happen. This effect can be explained because of the presence of an uncertainty in the location of the band edges at the surface of the PZT. The exact position of these edges is determined by the Femi level...

The photochemical growth of silver nanoparticles on the negative domains of lead zirconate titanate thin films is reported. A sample of highly [100] orientated lead zirconate titanate, with a ratio of 30:70, that was 65-70 nm thick grown on Pt-coated MgO was poled by use of piezoresponse force microscopy to produce defined regions of surface positive and negative polarization. A comparison between the growth of silver nanoparticles on the surface of the lead zirconate titanate when illuminated with two sources of super band gap UV is given. In both cases the wavelength of illumination leads to growth on the positive domains but only illumination with a Honle H lamp, with a high photon output over 250-200 nm, caused significant growth of silver nanoparticles on the negative domain. The deposition on the negative domain is explained in terms of changed band bending due to the excitation of electrons into the conduction band, the rate of decay to the ground state, and dimensions of the ferroelectric film. The rate of deposition of silver nanoparticles on the negative domains is approximately half that on the positive domains.

Atomic polarization in ferroelectric compounds is manipulated to control local electronic structure and influence chemical reactivity. Ferroelectric domains are patterned with electron beams or with probe tips, and electron exchange reactions occur preferentially on positive or negative domains. Using photo reduction from aqueous solution, metal nanoparticles are produced in predefined locations on an oxide substrate. Subsequently, organic molecules are reacted selectively to the particles. The process can be repeated to develop complex structures consisting of nanosized elements of semiconductors, metals, or functional organic molecules.