ZnO-TiO_2核壳纳米线结构及其热稳定性研究

采用热还原法和原子层沉积技术制备了ZnO-TiO_2核壳纳米线,研究沉积厚度、沉积温度及退火对于ZnO-TiO_2核壳纳米线晶化和结构的影响。利用X射线衍射(XRD)、扫描电子显微镜(SEM)、高分辨率透射电镜(HRTEM)等手段对退火前后核壳纳米线进行表征。结果表明:沉积厚度和温度的增加有利于TiO_2壳层发生非晶向晶化的转变;500℃退火提高了TiO_2的结晶性,但可能会使细核壳纳米线(ZnO纳米线直径80 nm)产生波浪形变形,使150℃沉积的非晶TiO_2壳层形成凸出晶粒,并导致其界面处ZnO缺失。     

Decoration of In2O3 nanowires with BaTiO3 nanoparticles for enhancement of magnetic properties

We have fabricated the composite nanowires consisting of In₂O₃ core and BaTiO₃ shell, via a two-step method. The BaTiO₃ shell has been deposited on core In₂O₃ core nanowires by means of pulsed laser deposition technique. X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy were employed to analyze the structure and morphology of the products. While SEM confirmed that the products maintained the one dimensional morphology, the shell layer corresponded to the nanoparticles of the hexagonal BaTiO₃ phase. With bare In₂O₃ nanowires exhibiting weak ferromagnetism, the ferromagnetic behavior was enhanced by decorating the In₂O₃ nanowires with BaTiO₃ nanoparticles. The shell coating enhanced the ferromagnetic behavior at both 5 and 300 K, in terms of the increase of coercive field, remanent magnetization, and saturation magnetization values in the hysteresis curves. We suggested that the generation of BaTiO₃ nanoparticles and oxygen vacancies during the high-temperature shell coating process played a role in enhancing the ferromagnetic properties of the nanowires.     

Generation of Zn2SiO4 Nanocrystallites in a Shell of ZnO/SiOx Core-Shell Nanowires to Change Photoluminescence Properties

This study addresses the annealing effects of ZnO/SiO_x core-shell nanowire optical properties, in terms of Zn₂SiO₄ crystallite generation. At 700 °C, the integrated PL intensity of deep-level emission was increased by annealing. With regard to UV emission, free exciton (FX) peak intensity was reduced and the ratio of FX to non-FX peak intensities increased as annealing temperature was increased. These annealing induced changes, including the enhancement of deep-level emission and suppression of FX emission, are mainly related to the generation of Zn₂SiO₄ crystallites. Transmission electron microscopy revealed that Zn₂SiO₄ crystallites were formed inside the SiO_x shell layer.     

SnO2@TiO2核-壳纳米线的制备及其光催化性能研究

本文通过固-液-气(VLS)生长机制,利用化学气相沉积法(CVD)制备SnO₂纳米线。利用原子层沉积(ALD)以钛酸四异丙酯为前驱体在SnO₂纳米线表面沉积不同厚度的TiO₂壳层,形成SnO₂@TiO₂核-壳纳米线结构。通过中间Al₂O₃插层,分别制备出金红石和锐钛矿两种不同晶型的TiO₂,从而制备出两种不同复合结构的SnO₂@TiO₂核-壳纳米线。实验研究该复合结构中TiO₂的厚度与晶型对紫外光下光催化降解甲基橙溶液活性的影响。     

TiO2/SiOx core-shell nanowires generated by heating the multilayered substrates

By heating Au/TiN/Si substrates, we fabricated TiO₂/SiO_x core-shell nanowires. By changing the thickness of predeposited Au layers, we demonstrated that the thickness of the Au layer needs to be optimized to obtain nanowires. High-resolution transmission electron microscopy image, X-ray diffraction spectrum, and selected area electron diffraction pattern coincidentally revealed that the resultant core nanowires had a tetragonal rutile structure of TiO₂, and the shell was comprised of amorphous SiO_x. The dominant growth mechanism was a base-growth mode, in which Au played a catalytic role, resulting in morphological changes with variation of the Au layer thickness. The TiO₂/SiO_x core-shell nanowires exhibited a broad photoluminescence emission band, which comprised four peaks centered at 1.54, 2.34, 2.67, and 2.99 eV, respectively. We expected that the 1.54 eV- and 2.34 eV-centered peaks arised from the TiO₂ core, whereas the 2.67 eV- and 2.34 eV-peaks were ascribed to both the TiO₂ core and the SiO_x shell.     

Characteristics of SiOx-cored composite nanowires with Pd shell layers

This paper describes the fabrication of Pd-coated SiO_x nanowires via a simple approach and reports the effects of subsequent thermal annealing. While the as-synthesized Pd-coated SiO_x nanowires exhibited smooth one-dimensional (1D) nanostructures, the thermal annealing induced a rough surface. X-ray diffraction, selected area electron diffraction, and lattice-resolved transmission electron microscopy coincidentally revealed that the assynthesized Pd-coated SiO_x nanowires were comprised of a cubic Pd phase, whereas annealing generated a tetragonal PdO phase. Micro-Raman spectroscopy measurements showed the presence of 630 cm⁻¹-peak, which can be assigned to the B_1g mode of single crystal PdO, whether samples had been annealed or not. Although both Pd and PdO phases did not exhibit PL emission, the PL intensity of core SiO_x nanowires has been significantly reduced by the Pd-coating, presumably due to the covering effect.     

Defect evolution of nanocrystalline SnO2 thin films induced by pulsed delivery during in situ annealing

The microstructural defects of nanocrystalline SnO₂ thin films prepared by pulsed laser deposition have been investigated using transmission electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy. Defects inside nanocrystalline SnO₂ thin films could be significantly reduced by in situ annealing SnO₂ thin films at 300 °C for 2 h. High-resolution transmission electron microscopy showed that the stacking faults and twins were annihilated upon in situ annealing. In particular, the inside of the SnO₂ nanoparticles demonstrated perfect lattices free of defects after in situ annealing. Raman spectra also confirmed that the in situ annealed specimen was almost defect-free. By using in situ annealing, defect-free nanocrystalline SnO₂ thin films can be prepared in a simple and practical way, which holds the promise for applications as transparent electrodes and solid-state gas sensors.     

均匀自支撑的二氧化钒纳米线的水热合成及相变特性研究

二氧化钒(VO₂)在接近室温时发生由半导体态向金属态的Mott相变,在智能窗和红外自适应伪装技术领域具有一定的应用前景。本文采用一种新颖的水热法制备均匀自支撑的VO₂纳米线。合成的纳米线的直径为150±30 nm,长度达到几十微米。通过X射线衍射、X射线光电子能谱、高分辨透射电镜和选取电子衍射等手段验证了高纯单斜相VO₂纳米线的成功制备。而且,VO₂纳米线的可逆相变性能采用差示量热扫描、变温XRD和变温Raman光谱进行了探究。结果表明：VO₂纳米线升温相变点为65.2 °C,磁滞回线宽度窄至6.5 °C,具有良好的可逆相变性。这些为VO₂纳米线的金属-半导体相变研究提供基础。     

High-temperature oxidation of Permalloy in air

Hematite (α-Fe₂O₃) nanowires were observed through directly annealing Ni₈₁Fe₁₉ foils at 600 °C for 120 min in atmosphere. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used to characterise the nanowires. The results indicate that the growing mechanism includes iron segregation to the surface combined with an internal stress induced by the oxidation process.     

Effect of SnO2 intermediate layer on performance of Ti/SnO2/MnO2 electrode during electrolytic-manganese process

SnO₂ intermediate layers were coated on the titanium (Ti) substrate by thermal decomposition. Scanning electron microscope (SEM) and X-ray diffraction (XRD) results show that uniform SnO₂ intermediate layers with rutile crystal structure were successfully achieved. According to the results of linear sweep voltammetry (LSV), oxygen evolution potential (OEP) of the Ti/SnO₂/MnO₂ electrodes decreases with increasing SnO₂ content, indicating that the electro-catalytic oxidation activity of the electrode increases. Accelerated service life tests results demonstrate that SnO₂ intermediate layer can improve the service life of the Ti/SnO₂/MnO₂ electrode. As the content of SnO₂ intermediate layer increases, the cell voltage and the energy consumption decrease apparently.     

Enhanced NO2 sensing characteristics of Pd-functionalized networked In2O3 nanowires

In this work, we fabricated Pd-functionalized networked In₂O₃ nanowires. For the Pd-functionalization, In₂O₃-Pd core-shell nanowires were synthesized by depositing Pd layers using a sputtering method on bare In₂O₃ nanowires. The continuous Pd shell layers were transformed into islands of cubic Pd/PdO phase by thermal heating. We compared the NO₂ sensing characteristics of the sensors fabricated from Pd-functionalized and bare In₂O₃ nanowires, respectively. The results demonstrated that Pd functionalization greatly improves sensitivity and response time in In₂O₃ nanowire-based gas sensors. The improvement of sensing properties is likely caused by not only the enhanced adsorption or dissociation of NO₂, but also the associated spillover effects, which are both caused by the Pd-functionalization.     

Heterojunction semiconductor SnO2/SrNb2O6 with an enhanced photocatalytic activity: The significance of chemically bonded interface

Heterojunction photocatalysts SnO₂/SrNb₂O₆ were synthesized by a milling–annealing technique. The powders were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) method, transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and UV–vis diffuse reflection spectroscopy (DRS). Their UV-induced photocatalytic activities were evaluated by the degradation of methyl orange and methylene blue. The results generally show that the binary semiconductors SnO₂/SrNb₂O₆, with matching band potentials, exhibit better photocatalytic properties than the single phase SrNb₂O₆ or SnO₂. The effective electron–hole separation both at the chemically bonded interface and in the two semiconductors is believed to be mainly responsible for the increased photocatalytic performance of composites. The formation of chemically bonded interfaces between SnO₂ and SrNb₂O₆ particles makes the interparticle charge transfer more spatially available and smoother, which is significant to enhance the photocatalytic activity.     

Annealing time dependent structural,morphological, optical and electrical properties of RF sputtered p-type transparent conducting SnO2/Al/SnO2 thin films

Transparent p-type conducting SnO₂/Al/SnO₂ multilayer films were fabricated on quartz substrates by radio frequency (RF) sputtering using SnO₂ and Al targets. The deposited films were annealed at a fix temperature of 500 °C for different time durations (1–8 h). The effect of annealing time on the structural, morphological, optical and electrical performances of SnO₂/Al/SnO₂ multilayer films was studied. X-ray diffraction (XRD) results show that all the p-type conducting films possess polycrystalline SnO₂ with tetragonal rutile structure. Hall-effect results indicate that 500 °C for 1 h is the optimum annealing condition for p-type SnO₂/Al/SnO₂ multilayer films, resulting in a hole concentration of 1.14×10¹⁸ cm^–3 and a low resistivity of 1.38 Ω·cm, respectively. The optical transmittance of the p-type SnO₂/Al/SnO₂ multilayer films is above 80% within annealing time range of 1–8 h, showing maximum for the films annealed for 1 h.     

P-type transparent conducting SnO2:Zn film derived from thermal diffusion of Zn/SnO2/Zn multilayer thin films

Highly transparent, p-type conducting SnO₂:Zn thin films are prepared from the thermal diffusion of a sandwich structure of Zn/SnO₂/Zn multilayer thin films deposited on quartz glass substrate by direct current (DC) and radio frequency (RF) magnetron sputtering using Zn and SnO₂ targets. The deposited films were annealed at various temperatures for thermal diffusion. The effect of annealing temperature and time on the structural, electrical and optical performances of SnO₂:Zn films was studied. XRD results show that all p-type conducting films possessed polycrystalline SnO₂ with tetragonal rutile structure. Hall effect results indicate that the treatment at 400 °C for 6 h was the optimum annealing parameters for p-type SnO₂:Zn films which have relatively high hole concentration and low resistivity of 2.389 × 10¹⁷ cm^− 3 and 7.436 Ω cm, respectively. The average transmission of the p-type SnO₂:Zn films was above 80% in the visible light range.     

Structural,electrical and optical properties of p-type transparent conducting SnO2:Al film derived from thermal diffusion of Al/SnO2/Al multilayer thin films

Highly transparent, p-type conducting SnO₂:Al films derived from thermal diffusion of a sandwich structure Al/SnO₂/Al multilayer thin films deposited on quartz substrate have been prepared by direct current and radio-frequency magnetron sputtering using Al and SnO₂ targets. The deposited films were annealed at various temperatures for different durations. The effect of thermal diffusing temperature and time on the structural, electrical and optical performances of SnO₂:Al films has been studied. X-ray diffraction results show that all p-type conducting films possessed polycrystalline SnO₂ with tetragonal rutile structure. Hall-effect results indicate that 450 °C for 4 h were the optimum annealing parameters for p-type SnO₂:Al films, resulting in a relatively high hole concentration of 7.2 × 10¹⁸ cm^?3 and a low resistivity of 0.81 Ω cm. The transmission of the p-type SnO₂:Al films was above 80%.     

Preparation and electrocatalytic property of Au-Pt/SnO<Subscript>2</Subscript>/GC composite electrode

Au-Pt/SnO₂/GC composite electrode was prepared by self-assembling Au-Pt nanoparticles on SnO₂ film, which was deposited on actived glassy carbon (GC). Atomic force microscopy (AFM) and scanning electron microscopy (SEM) images revealed that dense and uniform Au-Pt particles with 25-nm diameter were dispersed on SnO₂ film. X-ray photoelectron spectroscopy (XPS) results proved that there was an interaction between Au-Pt nanoparticles and SnO₂ support. Electrochemical experiments showed that Au-Pt/SnO₂/GC composite electrode had a good electrocatalytic activity to the oxidation of methanol.     

Tailoring microstructure and mechanical properties of aluminum matrix composites reinforced with novel Al/CuFe multi-layered core-shell particles

Aluminum matrix composites (AMCs), reinforced with novel pre-synthesized Al/CuFe multi-layered core- shell particles, were fabricated by different consolidation techniques to investigate their effect on microstructure and mechanical properties. To synthesize multi-layered Al/CuFe core-shell particles, Cu and Fe layers were deposited on Al powder particles by galvanic replacement and electroless plating method, respectively. The core-shell powder and sintered compacts were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDX), pycnometer, microhardness and compression tests. The results revealed that a higher extent of interfacial reactions, due to the transformation of the deposited layer into intermetallic phases in spark plasma sintered composite, resulted in high relative density (99.26%), microhardness (165 HV_0.3) and strength (572 MPa). Further, the presence of un-transformed Cu in the shell structure of hot-pressed composite resulted in the highest fracture strain (20.4%). The obtained results provide stronger implications for tailoring the microstructure of AMCs through selecting appropriate sintering paths to control mechanical properties.     

Synthesis and electrochemical properties of SnO2-CuO nanocomposite powders

1 Introduction Since YOSHIO et al[1] announced the commercia- lization of tin oxide as negative electrodes of 1ithium-ion batteries, the tin oxide anode has attracted much attention due to its high specific capacity, which is about twice that of graphite…     

Effects of Co content on the Cu diffusion barrier property of electroless NiCoP film

The characteristics of electroless NiCoP films were investigated as a function of Co content. Sheet resistance of a multi-stacked film of SiO₂/Ta/Cu/NiP dramatically increased after annealing at 500 °C, but as more Co was co-plated in NiCoP film, the change in sheet resistance of the stacked film of SiO₂/Ta/Cu/NiCoP at 500 °C became smaller. A CoP/Cu film showed no change in resistance value after annealing, which indicates the CoP film is the most effective Cu diffusion barrier. X-ray diffraction analysis showed that an as-plated NiP film of amorphous structure is easily crystallized by thermal annealing over 300 °C, while CoP showed an insignificant change in crystal structure by thermal annealing up to 500 °C. This result reveals that the CoP film is capable of preventing the diffusion of Cu at 500 °C due to the thermal stability of CoP film.     

Thermal CVD synthesis and photoluminescence of SiC/SiO2 core–shell structure nanoparticles

SiC/SiO₂ core–shell nanoparticles were firstly successfully synthesized by using a novel route of thermal CVD and thermal annealing process. The properties of the nanoparticles were characterized by scanning electron microscope, Transmission electron microscope, and X-ray diffraction. A possible growth mechanism was proposed for the nanoparticles according to the characterization results. The photoluminescence spectrum of the untreated nanoparticles revealed broad visible luminescence emission band. After the annealing treatment, the nanoparticles showed good blue emission, indicating potential applications in blue-light optoelectronic devices.