Photoluminescence of Si from Si nanocrystal-doped SiO2/Si multilayered sample

A multilayered Si nanocrystal-doped SiO₂/Si (or Si-nc:SiO₂/Si) sample structure is studied to acquire strong photoluminescence (PL) emission of Si via modulating excess Si concentration. The Si-nc:SiO₂ results from SiO thin film after thermal annealing. The total thickness of SiO layer remains 150 nm, and is partitioned equally into a number of sublayers (N = 3, 5, 10, or 30) by Si interlayers. For each N-layered sample, a maximal PL intensity of Si can be obtained via optimizing the thickness of Si interlayer (or d_Si). This maximal PL intensity varies with N, but the ratio of Si to O is nearly a constant. The brightest sample is found to be that of N = 10 and d_Si = 1 nm, whose PL intensity is ∼5 times that of N = 1 without additional Si doping, and ∼2.5 times that of Si-nc:SiO₂ prepared by co-evaporating of SiO and Si at the same optimized ratio of Si to O. Discussions are made based on PL, TEM, EDX and reflectance measurements.     

Low-temperature transport properties of individual SnO2 nanowires

Stannic oxide (SnO₂) nanowires have been prepared by Chemical vapor deposition (CVD). The low-temperature transport properties of a single SnO₂ nanowire have been studied. It is found that the transport of the electrons in the nanowires is dominated by the Efros-Shklovskii variable-range hopping (ES-VRH) process due to the enhanced Coulomb interaction in this semiconducting nanowire. The temperature dependence of the resistance follows the relation lnR∼T^−1/2. On the I-V and dI/dV curves of the nanowire a Coulomb gap-like structure at low temperatures appears.     

Raman spectroscopic and photoluminescence study of single-crystalline SnO2 nanowires

Single-crystalline SnO₂ nanowires with sizes of 4-14 nm in diameter and 100-500 nm in length were produced in a molten salt approach by using hydrothermal synthesized precursor. Structural characters of the nanowires were examined by X-ray diffraction and high-resolution electron transmission microscopy. Raman, photoluminescence and X-ray photoelectron spectra of the samples were examined under heat treatments. Three new Raman modes at 691, 514 and 358 cm⁻¹ were recorded and assigned. The former two are attributed to activation of original Raman-forbidden A_2uLO mode and the third is attributed to defects in small-sized nanowires. A strong photoluminescence is observed at about 600 nm, the temperature effects is examined and the origin of the PL process is discussed via X-ray photoelectron spectra.     

One-dimensional structures of Bi2O3 synthesized via metalorganic chemical vapor deposition process

We have demonstrated the synthesis of one-dimensional (1D) structures of bismuth oxide (Bi₂O₃) by a reaction of a trimethylbismuth (TMBi) and oxygen (O₂) mixture at 450 °C. Scanning electron microscopy showed that the product consisted of 1D materials with width or diameters less than 1 μm and lengths up to several tens of micrometers. The X-ray energy dispersive spectroscopy revealed that the materials contained elements of Bi and O. The results of X-ray diffraction and selected area electron diffraction pattern indicated that the obtained Bi₂O₃ were crystalline with monoclinic structure.     

Growth of high-density Ru- and RuO2-composite nanodots on atomic-layer-deposited Al2O3 film

Growth of Ru- and RuO₂-composite (ROC) nanodots on atomic-layer-deposited Al₂O₃ film has been studied for the first time using ion-beam sputtering followed by post-deposition annealing (PDA). X-ray photoelectron spectroscopy analyses reveal that RuO₂ and Ru co-exist before annealing, and around 10% RuO₂ is reduced to metallic Ru after PDA at 900 °C for 15 s. Scanning electron microscopy measurements show that well-defined spherical ROC nanodots are not formed till the PDA temperature is raised to 900 °C. The mean diameter of the nanodots enlarges with increasing PDA temperature whereas the nanodot density decreases, which is attributed to coalescence process between adjacent nanodots. It is further illustrated that the resulting nanodot size and density are weakly dependent on the annealing time, but are markedly influenced by the decomposition of RuO₂. In this article, the ROC nanodots with a high density of 1.6 × 10¹¹ cm⁻², a mean diameter of 20 nm with a standard deviation of 3.0 nm have been achieved for the PDA at 900 °C for 15 s, which is promising for flash memory application.     

Photo-catalytic H2 evolution over a series of Keggin-structure heteropoly blue sensitized Pt/TiO2 under visible light irradiation

We report the visible light-induced hydrogen generation over a series of Keggin-structure heteropoly blue (HPB) anions (PW₁₂O₄₀³⁻, phosphotungstic blue (PTB), GeW₁₂O₄₀⁴⁻ (GTB), SiW₁₂O₄₀⁴⁻ (STB), BW₁₂O₄₀⁵⁻ (BTB)) sensitized Pt/TiO₂ photo-catalysts. The sensitization of TiO₂ by HPB was certified using photo-electrochemical measurements and UV-vis absorption spectra. PTB showed the most pronounced sensitization effect for TiO₂ in those HPB anions and Pt/TiO₂-PTB showed the highest hydrogen generation activity. The sensitization of TiO₂ was significantly dependent on the reduction potential of HPA, which was determined by the kind of central atom in HPA.     

Helical nanostructures of SiOx synthesized through the heating of Co-coated substrates

This paper presents the use of the simple annealing technique at 1000 °C to produce the helical nanostructures of SiO_x. We have employed the Co-coated Si substrates, with Co layer and Si substrate utilized as catalyst and Si source, respectively. Beside the ordinary straight nanowires, the helical nanowires such as nanosprings and nanorings were observed. The product was an amorphous structure of SiO_x. We have discussed the possible growth mechanism. Photoluminescence spectrum of the SiO_x nanostructures showed a blue emission at 428 nm and a green emission at 534 nm, respectively.     

Surface characterization of the Zn-Ni-Al2O3 nanocomposite coating fabricated under ultrasound condition

Zn-Ni-Al₂O₃ nanocomposite coating, which was fabricated by eletrodeposition technique with the aid of ultrasound, was investigated by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and X-ray photoelectron spectroscopy (XPS). The results reveal that 7.2 wt.% nano-alumina particles uniformly dispersed in the matrix of the composite coating. The XPS analyses demonstrate that the outermost layer of Zn-Ni-Al₂O₃ coating was composed of nano-alumina and Zn(OH)₂, while the transition layer between the outermost layer and the Zn-Ni matrix consisted of nano-alumina, metallic Zn, ZnO and metallic Ni. In order to investigate the influences of ultrasonic agitation and the incorporation of nano-alumina on the composition and surface structure of Zn-Ni matrix, the comparison studies of Zn-Ni-Al₂O₃ nanocomposite coating with Zn-Ni coatings fabricated with and without ultrasound were conducted. The results indicate that ultrasonic agitation resulted in a decrease of Ni content in the Zn-Ni matrix and an increase of the thickness of surface oxide layer; while the incorporation of nano-α-Al₂O₃ increased the Ni content in the Zn-Ni matrix.     

Low-temperature preparation of F-doped TiO2 film and its photocatalytic activity under solar light

A novel and simple method for preparing F-doped anatase TiO₂ (defined as FTO) film with high photocatalytic activity was developed using titanium-n-butoxide and NH₄F as TiO₂ and fluorine precursors under mild condition, i.e. low temperature (lower than 373 K) and ambient pressure. The prepared samples were characterized by XRD, SEM, X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectrum (DRS), photoluminescence spectrum (PL) and TG-DSC analysis. The photocatalytic activity was evaluated by decomposing X-3B under artificial solar light. The results showed that the crystallinity of TiO₂ was improved by F-doping. F⁻ ions can prevent the grain growth, and the transformation of anatase to rutile phase was also inhibited. The doped fluorine atoms existed in two chemical forms, and the ones incorporated into TiO₂ lattice might take a positive role in photocatalysis. Compared with surface fluorination samples, FTO film exhibited better photocatalytic activity. The high photocatalytic activity of FTO may due to extrinsic absorption through the creation of oxygen vacancies rather than the excitation of the intrinsic absorption band of bulk TiO₂. Furthermore, the FTO can be recycled with little photocatalytic activity depression. Without any further treatment besides rinsing, after 6 recycle utilization, the photocatalytic activity of FTO film was still higher than 79%.     

Luminescence properties of Ge implanted SiO2:Ge and GeO2:Ge films

We have investigated cathodeluminescence (CL) of Ge implanted SiO₂:Ge and GeO₂:Ge films. The GeO₂ films were grown by oxidation of Ge substrate at 550 °C for 3 h in O₂ gas flow. The GeO₂ films on Ge substrate and SiO₂ films on Si substrate were implanted with Ge-negative ions. The implanted Ge atom concentrations in the films were ranging from 0.1 to 6.0 at%. To produce Ge nanoparticles the SiO₂:Ge films were thermally annealed at various temperatures of 600-900 °C for 1 h in N₂ gas flow. An XPS analysis has shown that the implanted Ge atoms were partly oxidized. CL was observed at wavelengths around 400 nm from the GeO₂ films before and after Ge⁻-implantation as well as from SiO₂:Ge films. After Ge⁻-implantation of about 0.5 at% the CL intensity has increased by about four times. However, the CL intensity from the GeO₂:Ge films was several orders of magnitude smaller than the intensity from the 800 °C-annealed SiO₂:Ge films with 0.5 at% of Ge atomic concentration. These results suggested that the luminescence was generated due to oxidation of Ge nanoparticles in the SiO₂:Ge films.     

Scalable synthesis of Sb(III)Sb(V)O4 nanorods from Sb2O5 powder via solvothermal processing

Scalable Sb(III)Sb(V)O₄ nanorods from Sb₂O₅ powder were prepared using solvothermal route. XRD and HRTEM demonstrate that the nanorods are single-crystal orthorhombic-Sb₂O₄ phase with several micrometers long and 200-300 nm diameter size. XPS result further shows that the antimony cations in the nanorods are composed of three valence and five valence antimony ions. The emission of the nanorods appears around 450 nm wavelength. The formation mechanism of the Sb(III)Sb(V)O₄ nanorods was discussed in detail.     

Patterned aluminum nanowires produced by electron beam at the surfaces of AlF3 single crystals

Cubic- and rectangular-shape single crystals of α-AlF₃ in sizes of 5-50 μm have been synthesized by a solid-vapor phase process. Using the electron beam induced decomposition of AlF₃, a method is demonstrated for fabricating patterned aluminum nanowires in AlF₃ substrate in a scanning electron microscope. By controlling the accelerating voltage, the beam current and scanning time, it is possible to fabricate metallic nanowires of different sizes. The aluminum nanowires may act as nano-interconnects for nanoelectronics. This work demonstrates a potential technique for e-beam nanofabrication.     

Large-scale synthesis of rutile SnO2 nanorods

A high yield of tin oxide (SnO₂) nanorods was obtained via annealing a nanoscale precursor in the molten salt flux and surfactant. X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction and infrared spectroscopy showed that the nanorods are composed of SnO₂ with rutile structure. The surfactant and temperature have a profound influence on the production of SnO₂ nanorods.     

Synthesis of PEO/4Hb-TaS2 layered nanocomposite

Single-phase layered nanocomposite containing 4Hb-TaS₂ and poly(ethylene oxide) [PEO] has been first synthesized by using the exfoliation-adsorption technique. It has been characterized by powder X-ray diffraction (XRD) and electrical dc resistivity measurements. As the product exhibited lattice expansions along the stacking direction, PEO was intercalated into 4Hb-TaS₂ galleries.     

Ar irradiation of Si nanocrystal-doped SiO2: Evolution of photoluminescence

We report the evolution of photoluminescence (PL) of Si nanocrystals (nc-Si) embedded in a matrix of SiO₂ during Ar⁺ ion bombardment. The integrated intensity of nc-Si PL falls down drastically before the Ar⁺ ion fluence of 10¹⁵ ions cm⁻², and then decreases slowly with the increasing ion fluence. At the meantime, the PL peak position blueshifts steadily before the fluence of 10¹⁵ ions cm⁻², and then changes in an oscillatory manner. Also it is found that the nc-Si PL of the Ar⁺-irradiated sample can be partly recovered after annealing at 800 °C in nitrogen, but can be almost totally recovered after annealing in oxygen. The results confirm that the ion irradiation-induced defects are made up of oxygen vacancies, which absorb light strongly. The oscillatory peak shift of nc-Si can be related to a size-distance distribution of nc-Si in SiO₂.     

The electric field modulation by lateral crack coated with HfO2/SiO2 high reflector

High-dielectric constant multilayer coatings are commonly used on optics to increase the laser damage resistance of optics. In this work, the three-dimensional finite-difference time-domain is improved to simulate the electric field intensity distribution in the silica–hafnia multilayer coatings on fused silica subsurface with lateral crack. Results reveal that as the substrate is defect-free, the largest intensification is at the surface layer, especially in the hafnia layer. As the lateral crack appears on the subsurface of fused silica, the intensified sites are mainly located at distorted coatings layers. Dependences of peak LIEF on crack's parameters are detailed investigated. Results show that laser intensification is more sensitive to its width, and the modulation of lateral defect with silica–hafnia multilayer is greater than nodular defect as its width larger than 5λ.     

Ferromagnetic resonance studies in Co/SiO2 multilayers

The uniaxial in-plane and out-of-plane anisotropies of [Co/SiO₂] × 10 multilayers have been studied by ferromagnetic resonance, magnetometry and transmission electron microscopy. The surface and volume anisotropy constants are in the range of values typical for multilayers with Co and transition metals of the iron group. The influence of the intermixed Co-SiO₂ region is discussed.     

Strengthening sapphire at elevated temperatures by SiO2 films

SiO₂ films have been prepared on sapphire by radio frequency magnetron reactive sputtering in order to increase the optical and mechanical properties of infrared windows and domes of sapphire at elevated temperatures. Infrared transmission and flexural strength of uncoated and coated sapphires have been investigated at different temperatures. SiO₂ films were shown to have apparent antireflective effect on sapphire substrate at room temperature. With increasing temperature, the coated sapphires have larger average transmission than the uncoated ones. The temperature was proven to only weakly affect the absorption coefficient and antireflection capability of the deposited films. It is also indicated that the flexural strengths of the c-axis sapphire samples coated with SiO₂ films are increased by 1.2 and 1.5 times than those of uncoated at 600 and 800 °C, respectively.     

Effect of surface fluorination on the photocatalytic and photo-induced hydrophilic properties of porous TiO2 films

Porous surface-fluorinated TiO₂ (F-TiO₂) films were prepared through PEG modified sol-gel method and surface fluorination. The as-prepared films were characterized with XRD, FTIR, AFM, XPS and UV-vis DRS. The effects of surface fluorination on the photocatalytic activity and hydrophilicity of porous TiO₂ film were studied by photocatalytic degradation of rhodamine B (RhB) as well as water contact angle (CA) on porous TiO₂ film. The results showed that the surface fluorination increased the adsorption of RhB on the porous TiO₂ film and enhanced the photocatalytic degradation of RhB. The concentration and pH of NaF solutions affected much the photocatalytic activity of porous TiO₂ film. Porous F-TiO₂ film prepared in 40 mM NaF solution at pH 4.0 showed the highest photocatalytic activity. Because of its porous structure, the porous F-TiO₂ film had original water CA of 22.7°, which is much smaller than that of normal F-TiO₂ film. Under UV light irradiation, the water CA of porous F-TiO₂ film decreased to 5.1° in 90 min.     

Cr-doping induced ferromagnetic behavior in antiferromagnetic EuTiO3 nanoparticles

We have synthesized a series of high quality EuTi_1−xCr_xO₃ (x = 0.0, 0.02, and 0.04) nanoparticles by simple sol-gel technique. The averaged grain size of these obtained nanoparticles displays no obvious change with Cr-doping and is about 100 nm. The structural and magnetic properties of EuTi_1−xCr_xO₃ (x = 0.0, 0.02, and 0.04) samples were detailedly investigated. It is found that the G-antiferromagnetic (G-AFM) ordering of pure EuTiO₃ can be significantly modified with slight Cr-doping, and finally the ferromagnetic behavior is enhanced for EuTi_1−xCr_xO₃ system with Cr-doping.