Synthesis of α‐Willemite Nanoparticles by Post‐calcination of Flame‐made Zinc Oxide/Silica Composites

Composite ZnO/SiO₂ nanoparticles were made by flame spray pyrolysis (FSP). Characteristics of the product powder and its crystallization behavior on post‐calcination were evaluated. Polyhedral aggregates of nano‐sized primary particles consisting of ZnO nano‐crystals 1–3 nm in size and amorphous SiO₂ were obtained by FSP. A short residence time in the flame can result in the co‐existence of the ZnO and SiO₂ clusters without substitution or reaction hindering each other's grain growth. There was almost no change in the XRD pattern by calcination at 600 °C for 2 h, suggesting a high thermal stability of the ZnO nano‐crystals in the composite particles. A pure α‐willemite phase was obtained at 900 °C. At this calcination temperature, d_C and d_BET of the powder were 63 and 44 nm, respectively. The nano‐composite structure of the FSP‐made particles can suppress crystalline growth of ZnO during calcination to maintain a high reactivity of ZnO with SiO₂, obtaining pure α‐willemite with high specific surface area at low calcination temperatures.     

Silica-based composite and mixed-oxide nanoparticles from atmospheric pressure flame synthesis

Binary TiO₂/SiO₂ and SnO₂/SiO₂ nanoparticles have been synthesized by feeding evaporated precursor mixtures into an atmospheric pressure diffusion flame. Particles with controlled Si:Ti and Si:Sn ratios were produced at various flow rates of oxygen and the resulting powders were characterized by BET (Brunauer–Emmett–Teller) surface area analysis, XRD, TEM and Raman spectroscopy. In the Si–O–Ti system, mixed oxide composite particles exhibiting anatase segregation formed when the Si:Ti ratio exceeded 9.8:1, while at lower concentrations only mixed oxide single phase particles were found. Arrangement of the species and phases within the particles correspond to an intermediate equilibrium state at elevated temperature. This can be explained by rapid quenching of the particles in the flame and is in accordance with liquid phase solubility data of Ti in SiO₂. In contrast, only composite particles formed in the Sn–O–Si system, with SnO₂ nanoparticles predominantly found adhering to the surface of SiO₂ substrate nanoparticles. Differences in the arrangement of phases and constituents within the particles were observed at constant precursor mixture concentration and the size of the resultant segregated phase was influenced by varying the flow rate of the oxidant. The above effect is due to the variation of the residence time and quenching rate experienced by the binary oxide nanoparticles when varying the oxygen flow rate and shows the flexibility of diffusion flame aerosol reactors.     

离子注入Zn的Si(001)基片热氧化制备纳米ZnO团簇及其生长行为研究

采用离子注入技术将Zn离子注入Si（001）基片,并在大气环境下加热氧化制备了ZnO纳米团簇.利用电子探针、薄膜X射线衍射仪、原子力显微镜和透射电子显微镜,对注入和热氧化后的薄膜成分、表面形貌和微观结构进行表征,探讨了热氧化温度以及注入剂量对纳米ZnO团簇的成核过程及生长行为的影响.结果表明,Zn离子注入到Si基片表面后形成了Zn纳米团簇,热氧化过程中Zn离子向表面扩散,在表面SiO₂非晶层和Si基片多晶区的界面处形成纳米团簇.热氧化温度是影响ZnO纳米团簇结晶质量的一个重要参数.随着热氧化温度的升高,金属Zn的衍射峰强度逐渐变弱并消失,而ZnO的（101）衍射峰强度逐渐增强.当热氧化温度高于800 ℃以后,ZnO与SiO₂之间开始发生化学反应形成Zn₂SiO₄. 关键词： ZnO纳米团簇 离子注入 微观结构 形貌分析     

Flame-synthesized Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Tb<Superscript>3+</Superscript> nanocrystals as spectral converting materials

In flame spray pyrolysis (FSP), the generation of uniform nanoparticles can be quite challenging due to difficulties in controlling droplet sizes during liquid spraying and uneven flame temperature. Here, we report a method to produce relatively uniform nanocrystals of a Tb³⁺ doped Y₂O₃ phosphor. In ethanol, metal nitrate precursors were simply mixed with organic surfactants to form a homogeneous solution which was then subjected to FSP. Depending on relative concentrations of the surfactant (oleic acid) to the metal precursors (yttrium and terbium nitrates), different sizes and morphologies of Y₂O₃:Tb³⁺ particles were obtained. By adjusting the surfactant concentration, Y₂O₃:Tb³⁺ crystals as small as 20~25 nm were acquired. X-ray diffraction and transmittance electron microscopy were used to prove that as-synthesized nanoparticles were highly crystalline due to the high temperature of FSP. X-ray photoelectron spectroscopy revealed that terbium dopants were well distributed throughout Y₂O₃ particles and a small portion of carbonate impurities were remained on the surface of particles, presumably originated from incomplete combustion of the organic surfactants. Photoluminescence (PL) spectra of Y₂O₃:Tb³⁺ nanocrystals exhibited a green light emission ensuring that the terbium doping was successfully occurred. However, when post-annealing was performed on the nanocrystals, their PL was dramatically enhanced indicating that quenching centers such as carbonate impurities and surface defects may have been removed by the annealing process. Owing to the continuous processability of FSP, this current method can be a practical way to produce nanoparticles in a large quantity. The obtained Y₂O₃:Tb³⁺ nanocrystals were used to fabricate a transparent film with poly-ethylene-co-vinyl acetate (poly-EVA) polymer, which was suitable for a spectral converting layer for a solar cell.

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Graphical abstract ?

     

离子束增强沉积制备p型氧化锌薄膜及其机理研究

采用离子束增强沉积方法在Si和SiO₂/Si衬底上制备In-N共掺杂ZnO薄膜(INZO)，溅射靶是用ZnO和2 atm% In₂O₃粉体均匀混合并压制而成，在氩离子溅射ZnO靶的同时，氮、氩混合离子束垂直注入沉积的薄膜.实验结果显示INZO薄膜具有(002)的择优取向，并且为p型导电，电阻率最低为0.9Ωcm.薄膜在氮气、氧气气氛下退火，对薄膜的结构和电学特性与成膜和退火条件的关系进行了分析. 关键词： 氧化锌薄膜 p型掺杂 离子束增强沉积     

Fabrication of a solution-processed thin-film transistor using zinc oxide nanoparticles and zinc acetate

We have fabricated a solution-processed ZnO thin-film transistor without vacuum deposition. ZnO nanoparticles were prepared by the polyol method from zinc acetate, polyvinyl pyrrolidone, and diethyleneglycol. The solution-processable semiconductor ink was prepared by dispersing the synthesized ZnO in a solvent. Inverted stagger type thin-film transistors were fabricated by spin casting the ZnO ink on the heavily doped Si wafer with 200 nm thick SiO₂, followed by evaporation of Cr/Au source and drain electrodes. After the drying and heat treatment at 600 C, a relatively dense ZnO film was obtained. The film characteristics were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). In order to obtain the electrical properties of the solution-derived transistor, the on–off ratio, threshold voltage, and mobility were measured.     

Morphology of the Si-ZnO interface

For Si-ZnO heterostructures, prepared by magnetron sputtering, the interface morphology is studied by XPS and UPS. ZnO films on Si(1 1 1) surfaces (H-termination and 7 × 7) were prepared by magnetron sputtering and metal organic molecular beam epitaxy (MOMBE) and are investigated in well defined deposition steps and the interface properties were studied in situ. All samples were handled in situ under ultra high vacuum (UHV) conditions. Up to five different interface phases were detected depending on ZnO preparation. Beside a SiO_x film induced by the sputter process, ZnO and Zn₂SiO₄ phases are resolved. In addition hydrogen, appearing as ZnOH_x, is found in considerable concentrations in the films.     

Nanoscale ion-beam mixing in Au–Si and Ag–Si eutectic systems

MeV ion induced mixing in the nanoscale regime for Au and Ag nanoislands on silicon substrates has been studied. Au and Ag nanoislands are grown on silicon substrates at room temperature and irradiated with 1.5-MeV Au²⁺ ions at various fluences. Cross-sectional high-resolution transmission electron microscopy and Rutherford backscattering spectrometry (RBS) are used to study the ion-beam mixing in Au/SiO_x/Si and Ag/SiO_x/Si systems. We observe a metastable mixed phase for the Au–Si system at a fluence of 1×10¹⁴ ionscm^-2, while no mixed phase is formed for the Ag–Si system. For both Au–Si and Ag–Si systems, a part of the islands is pushed into the substrate. The mixed phase of the Au–Si system is found to be crystalline in nature. The higher eutectic temperature and lower heat of mixing of the Ag–Si system compared to the Au–Si system could be responsible for the lack of mixing and silicide formation in the Ag–Si system. PACS 61.80.Jh; 61.82.Rx; 68.37.Lp; 64.75.+g; 61.46.+w     

Transformation mechanism of n-butyl terminated Si nanoparticles embedded into Si1−xCx nanocomposites mixed with Si nanoparticles and C atoms

Bright-field transmission electron microscopy (TEM) images, high-resolution TEM (HRTEM) images, and fast-Fourier transformed electron-diffraction patterns showed that n-butyl terminated Si nanoparticles were aggregated. The formation of Si_1−xC_x nanocomposites was mixed with Si nanoparticles and C atoms embedded in a SiO₂ layer due to the diffusion of C atoms from n-butyl termination shells into aggregated Si nanoparticles. Atomic force microscopy (AFM) images showed that the Si_1−xC_x nanocomposites mixed with Si nanoparticles and C atoms existed in almost all regions of the SiO₂ layer. The formation mechanism of Si nanoparticles and the transformation mechanism of n-butyl terminated Si nanoparticles embedded into Si_1−xC_x nanocomposites mixed with Si nanoparticles and C atoms are described on the basis of the TEM, HRTEM, and AFM results. These results can help to improve the understanding of the formation mechanism of Si nanoparticles.     

Surface Sol–gel Synthesis of Ultrathin Titanium and Tantalum Oxide Films

TiO₂, Ta₂O₅, and mixed TiO₂/Ta₂O₅ ultrathin films were grown layer-by-layer using a surface sol–gel deposition technique. The technique allows one to prepare smooth films of mixed composition with ångstrom-level control of thickness. The thickness increases per adsorption/hydrolysis cycle were 4.5, 2.1, and 2.5, respectively, for TiO₂, Ta₂O₅, and mixed TiO₂/Ta₂O₅ (1.6sol;1) films. By combining X-ray diffraction and ellipsometric analysis, it was determined that the as-deposited TiO₂ films are less dense than bulk TiO₂, and do not adhere persistently to Si/SiO₂ or Au/2-mercaptoethanol substrates. These green films were annealed at 400°C to produce denser and highly adherent films. Patterning the surface by microcontact printing of siloxane polymer thin films allows one to prepare patterned sol–gel oxide thin films.     

Core/shell structured ZnO/SiO2 nanoparticles: Preparation, characterization and photocatalytic property

ZnO nanoparticles were prepared by a simple chemical synthesis route. Subsequently, SiO₂ layers were successfully coated onto the surface of ZnO nanoparticles to modify the photocatalytic activity in acidic or alkaline solutions. The obtained particles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS) and zeta potential. It was found that ultrafine core/shell structured ZnO/SiO₂ nanoparticles were successfully obtained. The photocatalytic performance of ZnO/SiO₂ core/shell structured nanoparticles in Rhodamine B aqueous solution at varied pH value were also investigated. Compared with uncoated ZnO nanoparticles, core/shell structured ZnO/SiO₂ nanoparticles with thinner SiO₂ shell possess improved stability and relatively better photocatalytic activity in acidic or alkaline solutions, which would broaden its potential application in pollutant treatment.     

CEMS characterization of Kr++ irradiated Fe-Pd bilayers

Ion beam mixing in Fe-Pd bilayers evaporated onto SiO₂ substrates has been studied using Rutherford backscattering spectrometry and Mössbauer spectroscopy. To achieve some depth selectivity in the Mössbauer measurements, a 5 nm thick⁵⁷Fe layer was evaporated at either the Pd-Fe interface or the Fe-substrate interface. A disordered FePd₃ phase is formed predominantly in the mixed region. The underlying unmixed Fe layer does not undergo any structural phase transformation.     

ZnO nanoparticle creating in a SiO2/Si structure using the Zn ion implantation with subsequent heat treatment

The distribution profiles of the dopant in the surface layer of a SiO₂/Si structure implanted with Zn and O ions are studied via Rutherford backscattering spectroscopy for He²⁺ ions using the channeling technique. The redistribution of implanted impurities in the Si surface layer during the formation process of zinc oxide (ZnO) nanoparticles is analyzed. The effect of the annealing temperature on the formation process and growth of ZnO nanoparticles is studied. The sample-surface morphology is examined via atomic force microscopy. The optical absorption and photoluminescence of the implanted layers are studied.     

Effects of electron tunneling in photophysics of quantum-sized luminescent nanosilicon

The paper deals with the processes of photoburning and dark recovery of the photoluminescence (PL) yield of a “core-shell”-type hybrid nanoparticles Si/SiO _x (npSi/SiO _x ) after exposure to laser light with a wavelength of 405 nm and power density of 0.05–1 W/cm². The PL of npSi/SiO _x occurs after excitation of nanocrystalline Si core and subsequent energy transfer to the luminescent oxygen-deficient centers (ODC) in the SiO _x shell of a nanoparticle. These photoburning effects linearly depend on the power density of the exciting laser light, and the dynamics of the photoburning of PL is significantly non-exponential: the burning rate strongly drops during the exposure. The stop of laser exposure of npSi/SiO _x is accompanied by a slow dark recovery of the quantum efficiency of PL up to its initial level. We have demonstrated the possibility of controlling the photosensibility of npSi/SiO _x through changing the electron affinity of the environment. We have also proposed a physical mechanism that explains the observed photoburning and subsequent dark recovery of npSi/SiO _x PL based on the existence of “traps” for electrons residing in the SiO _x shell, where the electrons come as a result of tunneling from the excited ODC. The limiting time for this process is the lifetime of PL of ODC ranging from 10^?5 to 10^?4 s. The drop of the burning rate during exposure is caused by a strong difference in tunneling probabilities for different pairs of “ODC-trap”. The dark back tunneling of an electron from a trap to the original ODC occurs significantly (7–10 orders of magnitude) slower than the direct tunneling due to higher energy barrier.

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Graphical abstract Dark recovery of photoluminescence efficiency of Si nanoparticles following laser burning in three surrounding media differing in electron affinity

     

Silicon nanocrystal synthesis by implantation of natural Si isotopes

Implantations of pure , , and into SiO₂ can provide significant insight into the formation of silicon nanocrystals (Si-nc) and their light emission properties. Si-nc produced with different fractions of the heavier Si isotopes have been characterized by Raman and photoluminescence spectroscopy. Weak Stokes shifts of the Si-nc phonon peaks indicate that both the implanted Si and the native Si from the SiO₂ substrate contribute to Si-nc nucleation. The Raman measurements also indicate that the Si isotopic composition of the Si-nc is similar to the Si isotopic fraction of the implanted SiO₂. The Si-nc photoluminescence (PL) spectra are shifted towards the blue with increasing Si isotope mass, an indication that the increase of the Si-nc effective mass enhances the excitonic bandgap. Measurements from samples implanted with heavy isotopes at high Si excess concentrations indicate that the Si-nc isotope fraction evolves with annealing time such that the heaviest Si isotope are more concentrated in the vicinity of the Si-nc/SiO₂ interface, which can modify the energy states involved in the radiative transitions associated with Si-nc.     

Effects of LaNiO<Subscript>3</Subscript> on the structures and properties of SrBi<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>9</Subscript> thin films

SrBi₂Ta₂O₉(SBT)/LaNiO₃(LNO)/Si and SBT/Pt/TiO₂/SiO₂/Si multilayers were fabricated by pulsed laser deposition. With Pt top electrodes, the measured remanent polarization (2P_r) of Pt/SBT/LNO/Si and Pt/SBT/Pt/TiO₂/SiO₂/Si capacitors was 6.5 C/cm² and 5.2 C/cm², respectively. Using LNO as both bottom electrodes and buffer layers, enhanced non-c-axis crystalline SBT films were induced, which resulted in a 2P_r greater than that of the Pt/SBT/Pt/TiO₂/SiO₂/Si capacitor. The hysteresis loop of the Pt/SBT/LNO/Si capacitor showed a great external-field-dependent horizontal shift. Using an electron-injection model, this dependence was addressed. The fatigue-free property of the Pt/SBT/LNO/Si capacitor was experimentally established, in that the non-volatile polarization decreased by less than 5% of the initial value after 1.44×10⁹ switching cycles . PACS 77.84.Dy; 68.65.+g     

Prepare high efficiency Mn-doped Zn2SiO4 green phosphors in air using nano-particles

In this study, nano-scale precursors of ZnO, SiO₂, and MnO₂ powders were used to prepare mixtures with the compositions of 2ZnO+SiO₂+X mol% MnO₂ (X=MnO₂/2ZnO, abbreviated as Zn₂SiO₄-X-MnO₂), where 2≤X≤5. The mixed Zn₂SiO₄-X-MnO₂ mixtures were calcined from 900 to 1300 °C in air in order to synthesize Zn₂SiO₄:Mn²⁺ green phosphors. The X-ray diffraction patterns of Zn₂SiO₄-X-MnO₂ particles indicated that ZnO was present in the 900 °C-calcined Zn₂SiO₄-X-MnO₂ phosphors, but not in particles calcined at temperatures of 1000 °C and higher. However, the unapparent secondary phase of ZnMnO₃ was found in the 1200 and 1300 °C-calcined Zn₂SiO₄-5-MnO₂ compositions. The luminescent characteristics of Zn₂SiO₄-X-Mn²⁺ phosphors were compared with that of a commercial product (Nichia Corp., Japan). The photoluminescence (PL) intensity of 1200 °C-calcined Zn₂SiO₄-4-MnO₂ phosphors was higher and the decay times of all synthesized Zn₂SiO₄-X-MnO₂ phosphors were longer than those of the commercial product.     

Homogeneous ZnO Nanoparticles by Flame Spray Pyrolysis

Zinc oxide (ZnO) nanoparticles were made by flame spray pyrolysis (FSP) of zinc acrylate–methanol–acetic acid solution. The effect of solution feed rate on particle specific surface area (SSA) and crystalline size was examined. The average primary particle diameter can be controlled from 10 to 20nm by the solution feed rate. All powders were crystalline zincite. The primary particle diameter observed by transmission electron microscopy (TEM) was in agreement with the equivalent average primary particle diameter calculated from the SSA as well as with the crystalline size calculated from the X-ray diffraction (XRD) patterns for all powders, indicating that the primary particles were rather uniform in diameter and single crystals. Increasing the solution feed rate increases the flame height, and therefore coalescence and/or surface growth was enhanced, resulting in larger primary particles. Compared with ZnO nanoparticles made by other processes, the FSP-made powder exhibits some of the smallest and most homogeneous primary particles. Furthermore, the FSP-made powder has comparable BET equivalent primary particle diameter with but higher crystallinity than sol–gel derived ZnO powders.     

Properties of Natural Rubber Vulcanizates/Nanosilica Composites Prepared Based on the Method of In-situ Generation and Coagulation

Using the characteristics of silica sol dispersing well in water and easy formation of silica gel when the silica sol is heated, by mixing a system of concentrated natural rubber latex and silica sol, the silica sol can in-situ generate SiO₂ particles when heated. After coagulation of the mixed system, natural rubber/nanosilica composites C(NR/nSiO₂) were obtained. The composites C(NR/nSiO₂) and their vulcanizates were studied using a rubber processing analyzer (RPA), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The influence of silica contents on the C(NR/nSiO₂) vulcanizates mechanical properties, cross-linking degree, Payne effect, dissipation factor (tanδ), and the particle size and dispersion of SiO₂ in NR were investigated. The results obtained were compared with the NR/SiO₂ composites based on traditional dry mixing of bale natural rubber and precipitated silica (white carbon black). The results showed that when using a sulfur curing system with a silica coupling agent (Si69) in C(NR/nSiO₂), the vulcanizate had better mechanical properties, higher wet resistance, and lower rolling resistance than those without Si69. In the composites C(NR/nSiO₂) and their vulcanizates, the SiO₂ particles’ average grain diameter was 60 nm, and the good-dispersion of the in-situ generated SiO₂ in the rubber matrix were a significant contribution to the satisfactory properties of C(NR/nSiO₂) composites and their vulcanizates.     

Efficient laser induced consolidation of nanoparticulate ZnO thin films with reduced thermal budget

Layers of ZnO nanoparticles with thicknesses of about 40 nm were prepared on Si substrates. It was shown that UV laser irradiation is suitable for consolidation and significant densification of the ZnO particle layers under ambient conditions. Both experiments and simulations show that an underlying SiO₂ particle layer has a beneficial effect in inhibiting heat transfer towards the substrate and thus enables the application of temperature-sensitive carrier substrates like polymer foils despite the extremely high melting temperature of ZnO.