High‐Temperature Stable Zirconia Particles Doped with Yttrium,Lanthanum, and Gadolinium

Zirconia microspheres synthesized by a wet‐chemical sol–gel process are promising building blocks for various photonic applications considered for heat management and energy systems, including highly efficient reflective thermal barrier coatings and absorbers/emitters used in thermophotovoltaic systems. As previously shown, pure zirconia microparticles deteriorate at working temperatures of ≥1000 °C. While the addition of yttrium as a dopant has been shown to improve their phase stability, pronounced grain growth at temperatures of ≥1000 °C compromises the photonic structure of the assembled microspheres. Here, a new approach for the fabrication of highly stable ceramic microparticles by doping with lanthanum, gadolinium, and a combination of those with yttrium is introduced. The morphological changes of the particles are monitored by scanning electron microscopy, ex situ X‐ray diffraction (XRD), and in situ high‐energy XRD as a function of dopant concentration up to 1500 °C. While the addition of lanthanum or gadolinium has a strong grain growth attenuating effect, it alone is insufficient to avoid a destructive tetragonal‐to‐monoclinic phase transformation occurring after heating to >850 °C. However, combining lanthanum or gadolinium with yttrium leads to particles with both efficient phase stabilization and attenuated grain growth. Thus, ceramic microspheres are yielded that remain extremely stable after heating to 1200 °C.     

阵列波导光栅中心波长温度稳定性的研究

阵列波导光栅中心波长的温度不稳定性成为限制其应用的主要原因。为了设计温度不敏感阵列波导光栅,结合弹性多层板热应力理论和应力集中效应给出掩埋波导芯层应力的解析解,利用等效折射率法计算阵列波导的有效折射率及其温度系数,考虑波导材料折射率和波导长度随温度的变化得到了硅基二氧化硅阵列波导光栅中心波长的温度系数。并研究了贴有应力板的阵列波导光栅中心波长的温度特性,结果表明在芯片底部贴有0.37 mm厚的铝板时,TE模和TM模中心波长的温度系数分别是5.9 pm/℃和8.0 pm/℃,下降到传统阵列波导光栅中心波长温度系数的一半。     

High‐stability organic red‐light photodetector for narrowband applications

Red‐light photodetectors without filters are in urgent need for narrowband applications such as full‐color imaging and multi‐output visible light communication (VLC). However, their development is hindered by the lack of small‐band‐gap and narrowband response materials. Without wavelength filters, a new type of photodetector with a simple single‐layer architecture is developed, based on a stable small‐band‐gap squarylium dye and characterized by a detectivity peak at 680 nm and full width at half maximum of 80 nm. The device, which exhibits high stability in air and humid conditions, shows a significantly low dark current of ∼2 nA·cm⁻² at −2 V and high specific detectivity of 3.2 × 10¹² Jones. The response current ratio of the device to red, green, and blue lights with a luminous flux amplitude ratio of 3:6:1 (standard ratio for white light) is 100:12:1.1. These properties indicate that the squarylium dye red‐light photodetectors are promising for VLC and other narrowband optoelectronic applications.

     

Graphene‐Based Phosphorus‐Doped Carbon as Anode Material for High‐Performance Sodium‐Ion Batteries

Graphene‐based phosphorus‐doped carbon (GPC) is prepared through a facile and scalable thermal annealing method by triphenylphosphine and graphite oxide as precursor. The P atoms are successfully doped into few layer graphene with two forms of P–O and P–C bands. The GPC used as anode material for Na‐ion batteries delivers a high charge capacity 284.8 mAh g^?1 at a current density of 50 mA g^?1 after 60 cycles. Superior cycling performance is also shown at high charge?discharge rate: a stable charge capacity 145.6 mAh g^?1 can be achieved at the current density of 500 mA g^?1 after 600 cycles. The result demonstrates that the GPC electrode exhibits good electrochemical performance (higher reversible charge capacity, super rate capability, and long‐term cycling stability). The excellent electrochemical performance originated from the large interlayer distance, large amount of defects, vacancies, and active site caused by P atoms doping. The relationship of P atoms doping amount with the Na storage properties is also discussed. This superior sodium storage performance of GPC makes it as a promising alternative anode material for sodium‐ion batteries.     

High‐temperature thermoelectric properties of Cu2In4Te7

Cu₂Ga₄Te₇ has recently been reported to have a relatively high thermoelectric (TE) figure of merit (ZT). However, the TE properties of Cu₂In₄Te₇, which has the same defect zinc‐blende structure as Cu₂Ga₄Te₇, have been hardly investigated. Here, we demonstrate that Cu₂In₄Te₇ has relatively high ZT values that are similar to those of Cu₂Ga₄Te₇. High‐density polycrystalline bulk samples of Cu₂In₄Te₇ were prepared and their electrical resistivity (?), Seebeck coefficient (S), and thermal conductivity (κ) were measured. Cu₂In₄Te₇ has a maximum ZT of 0.3 at 700 K, with ?, S, and κ values of 62.1 × 10^–5 Ω m, 394 μV K^–1, and 0.61 W m^–1 K^–1, respectively. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

High‐Pressure Evaporation‐Based Nanoporous Black Sn for Enhanced Performance of Lithium‐Ion Battery Anodes

Increasing the surface area to improve chemical activity is an unending task from conventional catalysis to recently emerging electrochemical energy conversion and storage. Here, a simple, vacuum‐deposition‐based method to form nanoporous structures of metals is reported. By utilizing thermal evaporation at a high pressure, fractal‐like nanoporous structures of Sn with porosity exceeding 98% are synthesized. The obtained nanostructure consists of nanoparticle aggregates, and the morphology can be controlled by adjusting the working pressure. The formation of the nanoporous structure is explained by homogeneous nucleation and diffusion‐limited aggregation, where nanoparticles produced by the repeated collisions of evaporated atoms adhere to the substrate without diffusion, forming porous aggregates. Due to the easy oxidation of Sn, the constituent nanoparticles are covered with amorphous SnO_x and crystalline SnO phases. When the nanoporous Sn/SnO_x aggregates are applied to a lithium‐ion battery anode through direct deposition on a Cu foil current collector without binders or conducting additives, the nanoporous Sn/SnO_x anode shows greatly enhanced cyclability and exceptional rate performance compared to those of a dense Sn thin film anode. The approach investigated in this work is expected to provide a new platform to other fields that require highly porous structures.     

The electrochemical reduction of CO2 on a copper electrode in 1‐n‐butyl‐3‐methyl imidazolium tetrafluoroborate (BMI.BF4) monitored by surface‐enhanced Raman scattering (SERS)

The electrochemical conversion of CO₂ into value‐added products using room temperature ionic liquids as solvent/electrolyte has been proposed as an alternative to minimize the environmental effects of CO₂ emissions. A key issue in the design of electrochemical systems for the reduction of CO₂ is the in situ identification of intermediate surface species as well as reaction products. Copper electrodes, besides being used as cathodes in the electrochemical reduction of CO₂, present surface‐enhanced Raman scattering (SERS) when properly activated. In this sense, the electrochemical reduction of CO₂ over a copper electrode in the room temperature ionic liquids 1‐n‐butyl‐3‐methyl imidazolium tetrafluoroborate (BMI.BF₄) was investigated by cyclic voltammetry and by in situ SERS. The cyclic voltammetries have shown that the presence of CO₂ on the BMI.BF₄ anticipates the reduction of BMI⁺ to the corresponding carbene. Fourier‐transform‐SERS spectra excited at 1064 nm and SERS spectra excited at 632.8 nm have shown vibrational signals from adsorbed CO. These SERS results indicated that CO adsorbs on the copper surface at two different surface sites. The observation of a 2275 cm⁻¹ vibration in the SERS spectra also confirmed the presence of chemically adsorbed CO₂. Other products of CO₂ reduction in BMI.BF₄, besides CO, were identified, including BMI carbene and the BMI‐CO₂ adduct. The SERS results also suggest that the presence of a thin film of Cu₂O on the copper surface anticipates the reduction of CO₂ to CO, an important component of syngas. Copyright © 2016 John Wiley & Sons, Ltd.     

MoO2@MoS2 Nanoarchitectures for High‐Loading Advanced Lithium‐Ion Battery Anodes

The capacity loading per unit area is of importance as specific capacity while evaluating the lithium‐ion battery anode. However, the low conductivity of several advanced anode materials (such as molybdenum sulfide, MoS₂) prohibits the wide application of materials. Nanostructural engineering becomes a key to overcome the obstacles. A one‐step in situ conversion reaction is employed to synthesize molybdenum oxide (MoO₂)–MoS₂ core–shell nanoarchitectures (MoO₂@MoS₂) by partially sulfiding MoO₂ into MoS₂ using sulfur. The MoO₂@MoS₂ displays a 3D architecture constructed by hundreds of MoS₂ ultrathin sheets with several layers arranged and fixed to an MoO₂ particle vertically with the size in the range of 200–500 nm. MoO₂ acts as the molybdenum source for the synthesis of MoS₂, as well as the conductive substrate. The designed 3D architectures with empty space between MoS₂ layers can prevent the damage originated from volume change of MoS₂ undergoing charge/discharge process. The lithium storage capacities of the MoO₂@MoS₂ 3D architectures are higher and the stability has been significantly improved compared to pure MoS₂. 4 mAh cm^?2 capacity loading of MoO₂@MoS₂ has been achieved with a specific capacity of more than 1000 mAh g^?1.     

热稳定空穴传输材料的合成及其电致发光器件

合成了两种NPB的新衍生物:N,N’-二(1-萘基)-N,N’-二(4-甲基苯基)-1,1’-联苯-4,4’二胺(NTB)和N,N’-二(1-萘基)-N,N’-二(4-叔丁基苯基)-1,1’-联苯-4,4’二胺(NBB)。DSC测得其玻璃态转变温度分别为108℃和129℃,表现出好的热稳定性。紫外光电子能谱测得其电离势均为5.2eV。NTB和NBB固体光致发光光谱的最大发射波长分别位于455nm和460nm。分别以NPB、NTB、NBB作为空穴传输层材料(HTM)制作了结构相同的有机电致发光器件,3种器件发光光谱相同,均为Alq₃的绿色发光,器件的起亮电压分别为11,9,8V,在15V工作电压时的亮度分别为1000,1300,1200cd/m²,初步研究了器件的发光特性和稳定性。     

Long‐Term Colloidal and Chemical Stability in Aqueous Media of NaYF4‐Type Upconversion Nanoparticles Modified by Ligand‐Exchange

Surface capping is an essential component of nanoparticles as it provides access to their outstanding properties in the real world. Upconversion nanoparticles are predominantly interesting for use in biological environments, due to their excellent optical properties such as the conversion of near‐infrared excitation light into emissions in the visible or UV range of the spectrum, high photostability, and the absence of any intermittence. One of the most efficient upconversion nanoparticles, consisting of lanthanide doped NaYF₄, suffers from limited stability in aqueous media. This study investigates a set of five types of surface coatings, ranging from small ligands to polymers of different charge and different coordinating groups, on monodisperse 28 ± 0.9 nm sized NaYF₄(Yb,Er) nanoparticles modified by a two‐step ligand exchange mediated by NOBF₄. Information on the long‐term chemical and colloidal stability for highly diluted aqueous dispersions of these particles is acquired by transmission electron microscopy, dynamic light scattering, and luminescence spectroscopy. The findings are of importance for the development of probes and labels based on upconversion nanoparticles for biological applications.     

In‐situ Raman spectroscopy study of Ru/TiO2 catalyst in the selective methanation of CO

Raman spectroscopic technique has been used to characterize a Ru/TiO₂ catalyst and to follow in situ their structural changes during the CO selective methanation reaction (S‐MET). For a better comprehension of the catalytic mechanism, the in‐situ Raman study of the catalysts activation (reduction) process, the isolated CO and CO₂ methanation reactions and the effect of the composition of the reactive stream (H₂O and CO₂ presence) have been carried out. Raman spectroscopy evidences that the catalyst is composed by islands of TiO₂–RuO₂ solid solutions, constituting Ru–TiO₂ interphases in the form of Ru_xTi_{1 − x}O₂ rutile type solid solutions. The activation procedure with H₂ at 300 °C promotes the reduction of the RuO₂–TiO₂ islands generating Ru^o–Ti³⁺ centers. The spectroscopic changes are in agreement with the strong increase in chemical reactivity as increasing the carbonaceous intermediates observed. The selective methanation of CO proceeds after their adsorption on these Ru^o–Ti³⁺ active centers and subsequent C―O dissociation throughout the formation of CH_x/C_nH_x/C_nH_xO/CH_x―CO species. These intermediates are transformed into CH₄ by a combination of hydrogenation reactions. The formation of carbonaceous species during the methanation of CO and CO₂ suggests that the CO presence is required to promote the CO₂ methanation. Similar carbonaceous species are detected when the selective CO methanation is carried out with water in the stream. However, the activation of the catalysts occurs at much lower temperatures, and the carbon oxidation is favored by the oxidative effect of water. Copyright © 2015 John Wiley & Sons, Ltd.     

Rotational and Vibrational Temperature Measurements in a High‐Pressure Cylindrical Dielectric Barrier Discharge (C‐DBD)

The rotational (T_R) and vibrational (T_v) temperatures of N₂ molecules were measured in a high‐pressure cylindrical dielectric barrier discharge (C‐DBD) source in Ne with trace amounts (0.02 %) of N₂ and dry air excited by radio‐frequency (rf) power. Both T_R and T_v of the N₂ molecules in the C ³Π_u state were determined from an emission spectroscopic analysis the 2^nd positive system (C ³Π_u → B³Π_g). Gas temperatures were inferred from the measured rotational temperatures. As a function of pressure, the rotational temperature is essentially constant at about 360 K in the range from 200 Torr to 600 Torr (at 30W rf power) and increases slightly with increasing rf power at constant pressure. As one would expect, vibrational temperature measurements revealed significantly higher temperatures. The vibrational temperature decreases with pressure from 3030 K at 200 Torr to 2270 K at 600 Torr (at 30 W rf power). As a function of rf power, the vibrational temperature increases from 2520 K at 20 W to 2940 K at 60 W (at 400 Torr). Both T_R and T_v also show a dependence on the excitation frequency at the two frequencies that we studied, 400 kHz and 13.56 MHz. Adding trace amounts of air instead of N₂ to the Ne in the discharge resulted in higher T_R and T_v values and in a different pressure dependence of the rotational and vibrational temperatures. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and decay of a two‐dimensional oxide quasicrystal: High‐temperature in situ microscopy

The recently discovered two‐dimensional oxide quasicrystal (OQC) derived from BaTiO₃ on Pt(111) is the first material in which a spontaneous formation of an aperiodic structure at the interface to a periodic support has been observed. Herein, we report in situ low‐energy electron microscopy (LEEM) studies on the fundamental processes involved in the OQC growth. The OQC formation proceeds in two steps via of an amorphous two‐dimensional wetting layer. At 1170 K the long‐range aperiodic order of the OQC develops. Annealing in O₂ induces the reverse process, the conversion of the OQC into BaTiO₃ islands and bare Pt(111), which has been monitored by in situ LEEM. A quantitative analysis of the temporal decay of the OQC shows that oxygen adsorption on bare Pt patches is the rate limiting step of this dewetting process.