Amount Of Si Doping Research Articles

Enhanced electrocaloric effect in a Si-doped PbZr0.95Ti0.05O3 film deposited on FTO substrate

Materials with an electrocaloric effect (ECE) have been extensively studied for their cooling applications. Most ECE films are oriented and are difficult to integrate into industrial production processes. Here, an ECE (ΔS = 4.48 J K−1 kg−1 and ΔT = 6.4 °C at ΔE = 390 kV cm−1) is obtained in an unoriented PbZr0.95Ti0.05O3 (PZT) film fabricated on an FTO substrate using an improved sol-gel method. To improve the ECE, Si-doped PZT films with 1–4 mol. % of Si are deposited. X-ray diffraction and X-ray photoelectron spectroscopy results confirm that Si was doped into the PZT lattice. The orthorhombic and tetragonal antiferroelectric phases coexist in the PZT/0.01 Si film. A large ECE (ΔS = 5.89 J K−1 kg−1 and ΔT = 8.5 °C at ΔE = 390 kV cm−1) is acquired in the PZT/0.01 Si film, which was measured by an indirect method. This work demonstrates that ECE of unoriented PZT antiferroelectric films on FTO substrates can be improved by a certain amount of Si doping.

Zinc-blende and wurtzite phase separation in catalyst-free molecular beam epitaxy vapor–liquid–solid-grown Si-doped GaAs nanowires on a Si(111) substrate induced by Si doping

The effect of Si-doping on the phase separation of wurtzite (WZ) and zinc-blende (ZB) phases in catalyst-free Si-doped GaAs nanowires (NWs) grown on a Si(111) substrate was investigated using transmission electron microscope (TEM), high-resolution X-ray diffraction (HR-XRD), low-temperature photoreflectance (PR), and photoluminescence (PL) techniques. The appearance of WZ structure with an increase in the amount of Si dopant was observed through TEM, and the results showed that the thicknesses of ZB and WZ structures were random. Furthermore, all NW samples exhibited HR-XRD diffraction peaks at the (0002) and (111) planes, which correspond to the WZ and ZB structures, respectively. Their peak intensity ratio [WZ/(WZ + ZB)] increased with the amount of Si doping. The PR modulus and PL spectra at 4 K for the sample with the middle amount of Si doping in three samples exhibited peaks at 1.43, 1.49, and 1.51 eV. The peaks at 1.51 and 1.49 eV were presumed to result from band-to-band and conduction-band-to-Si-acceptor transitions, respectively. In accordance with the prediction by a theoretical band alignment calculation of the conduction- and valence-bands discontinuities, the transition energy of 1.43 eV was due to the interband transition at the WZ-ZB interface. We also found that the 1.43 eV PR and PL peaks became dominant when the amount of Si doping increased. This indicate that this interband transition became significant when the amount of WZ phase increased, which resulted from the increased Si doping. The appearance of type-II band structures induced by Si doping was also confirmed.

GaInN-Based Tunnel Junctions in n–p–n Light Emitting Diodes

We optimized p++-GaInN/n++-GaN tunnel junctions grown on conventional light-emitting diodes, corresponding to n–p–n structures. We investigated two dependences at the tunnel junctions, the InN mole fraction dependence and a doping dependence. The lowest voltage drop at the reverse-biased tunnel junction was 0.68 V at 20 mA with a 3 nm p++-Ga0.8In0.2N (Mg: 1×1020 cm-3)/30 nm n++-GaN (Si: 4×1020 cm-3) structure. We then found that the Mg memory effect was reasonably suppressed by using the p++-GaInN instead of a p++-GaN. At the same time, the amount of Si doping in the following n++-GaN should be substantially high to overcome the Mg memory effect.

Effect of Si-Doping on Thermal Stability and Diesel Oxidation Activity of Pt Supported Porous γ-Al2O3 Monolithic Catalyst

A series of different contents of Si-stabilized aluminas with high thermal stability were synthesized by the coprecipitation method and were used as the support of Pt diesel oxidation catalysts. The physicochemical properties of SiO2–Al2O3 (SA) and the catalytic performance of Pt/SiO2–Al2O3 (Pt/SA) were characterized in detail by TG–DTA, XRD, infrared spectroscopy, N2 adsorption, NMR, CO-TPD, and the catalytic activity evaluation of CO and C3H6 oxidations as well as NO reduction in simulating diesel exhaust. The results indicate that the presence of Si can remarkably enhance the thermal stability and phase transition temperature of alumina. It was also found that the catalytic activity is virtually independent of surface area, and only appropriate amount of Si doping can improve the diesel oxidation activity, as compared to pure Pt/Al2O3 under the same conditions as a result of the better dispersion of Pt on SA–W supports. The appropriate amount of Si doped can enhance the diesel oxidation activity of Pt/Al2O3 monolithic catalyst at the same condition as the result of the better dispersion of Pt on SiO2–Al2O3 samples.

Time dependence of water‐reducing photocurrent with change of the characteristics of n‐type GaN photo‐illuminated working electrodes

AbstractNitride semiconductors are expected for the working electrodes of photoelectrochemical water splitting due to the chemical stability and band‐gap configuration. The p‐type nitrides are stable under photoelectrochemical conditions but the efficiency of light to hydrogen energy is low. The n‐type nitrides have relatively high energy‐conversion especially for the quantum efficiency, but the photoelectrochemical reaction is not stable because of the anodic photocorrosion. In this article, the relationships between the characteristics of n‐type GaN and the photocurrent stability are discussed. The amount of Si doping was clarified to relate to the stability. The suitable properties for stable photocurrent were different from those for high energy‐conversion efficiency at initial stage. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of Si Doping on the Microstructure and Photocatalytic Performance of TiO2 Hollow Microspheres

Solid precursory microspheres composed of Ti/Si species were in situ formed on the surface of a colloid carbon microsphere template derived from glucose polymerization and carbonization by a one-pot hydrothermal method using ammonium fluorotitanate,ammonium fluorosilicate,and glucose as source materials. Si-doped TiO2 hollow microspheres were then obtained after calcination and removal of the carbon microsphere template at high temperature. High-resolution transmission electron microscopy,X-ray diffraction,X-ray photoelectron spectroscopy,and N2 adsorption-desorption were used to characterize the samples. The effect of Si doping on the microstructure and photocatalytic performance of the TiO2 hollow microspheres was investigated. The results confirmed that the Si element entered into the lattice of TiO2 and formed Si–O–Ti bond,which could not only effectively suppress the phase transformation from anatase to rutile,but also restrain the rapid growth of TiO2 nanocrystallites during the calcination process. The average grain size of the nanocrystallites constituting the shell of the microspheres decreased gradually and the specific surface area and pore volume of the hollow microspheres increased progressively with the increase in the amount of Si doping. The photocatalytic activity of the Si-doped TiO2 hollow microspheres was measured under ultraviolet light using methylene blue solution as a simulated degradation model. The results demonstrated that the degradation efficiency of TiO2 hollow microspheres enhanced gradually with increasing Si doping in its mol fraction range of 0–0.5. Especially,the degradation efficiency of TiO2 hollow microspheres is 1.25 times that of P25 when the Si mol fraction is 0.5.