Surface and volume superconductivity of Pb embedded in nanopores

The heat capacity of lead embedded in glass nanopores (7 nm in diameter) and bulk lead was studied in the temperature range 2–40 K without a magnetic field and in magnetic fields of 1–8 T. The properties of lead nanoparticles and bulk lead were compared. The results obtained allowed us to separate the surface superconductivity from the volume superconductivity. The temperature dependence of the heat capacity of lead nanoparticles was shown to exhibit two superconducting transitions above and below the transition temperature for bulk lead (T _c = 7.2 K), which are associated with the surface and volume superconductivity. The upper critical fields H _c3 for the surface superconductivity and H _c2 for the volume superconductivity were determined. It turned out that these fields for Pb nanoparticles are two orders of magnitude higher than those for bulk lead. The “superconductor-normal metal” phase diagrams were constructed for lead nanoparticles. The study established an increase in the density of low-frequency excitations in Pb nanocrystals as compared to bulk Pb and a difference in the electronic heat capacity of Pb nanoparticles as compared to bulk Pb.     

铅纳米微粒用作油性润滑的摩擦学性能研究

在石蜡油 聚乙二醇的混合溶剂中 ,通过液相分散法成功地制备出了铅纳米微粒 .其中 ,石蜡油是反应介质 ,聚乙二醇是抗氧化剂 .同时 ,对铅纳米微粒的形貌和结构进行了透射电镜 (TEM)和X光衍射 (XRD)表征 .结果表明 ,铅纳米微粒呈球形 ,平均粒径为 70nm ,具有与本体铅相同的晶体结构 .另外 ,在四球试验机上表征了铅纳米微粒作为润滑油添加剂的摩擦学性能 .摩擦试验表明 ,铅纳米微粒具有良好的减摩抗磨性能 ,并能够显著改善基础油的承载能力 .磨斑表面分析表明 ,铅纳米微粒的抗磨减摩机制不是形成金属沉积膜 ,可能是在摩擦接触面形成滑动 轴承系     

Inverse oxide/metal catalysts: A versatile approach for activity tests and mechanistic studies

There is a general desire to improve the configuration of industrial catalysts to take advantage of the intrinsic properties of metal oxides. In recent years, a series of studies has been published examining the growth of oxide nanoparticles on metal substrates. These studies have revealed structures for the supported oxide which are different from those found in bulk phases. In addition, the oxide ? metal interactions can alter the electronic states of the oxide producing new chemical properties. On an inverse oxide/metal catalyst, the reactants can interact with defect sites of the oxide nanoparticles, metal sites, and the metal–oxide interface. In these systems, one can couple the special reactivity of the oxide nanoparticles to the reactivity of the metal to obtain high catalytic activity. Furthermore, an oxide/metal system is also an attractive model for fundamental studies. It can be used to investigate the role of the oxide in a catalytic process, and how the stability of different reaction intermediates depends on the nature of the oxide.     

Enhancement of silicon solar cell performances due to light trapping by colloidal metal nanoparticles

Photovoltaics is the most promising technology for the future of green energy production. To fully realize the potential use of photovoltaic technology, low manufacturing cost and high working photoconversion efficiency must be obtained. Light trapping by metal nanoparticles is an attractive strategy in thin film as well as in bulk silicon solar cells aimed to confine light within the active layer to promote the photon absorption and therefore achieving higher efficiency. In this paper, we tested the deposition of silver and gold nanoparticles on bulk silicon solar cells by colloidal technique in order to enhance their photovoltaic conversion efficiency by means of Plasmonic Light Scattering by metal nanoparticles. The feasible Plasmonic Light Scattering related enhancement was examined using spectral response and I–V measurements. Relative increases of the total delivered power under simulated solar irradiation were observed for cells both with and without antireflection coating using silver and gold nanoparticles.     

金属纳米颗粒LSPR光纤生物传感DDA方法研究

研究了金属纳米颗粒的局部表面等离子体共振(LSPR)行为,并讨论了其在光纤生物传感领域的应用.采用离散偶极近似(DDA)的方法,从理论上分析了金属纳米颗粒的尺寸、形状对其传感灵敏度的影响.计算结果显示,金属纳米颗粒的等离子共振吸收峰同时受到颗粒尺寸和形状的影响,但形状对其传感灵敏度的影响最为明显,计算结果与实验数据能较好地吻合.     

Effect of Fe/Pb molar ratio on the structure,magnetic and dielectric properties of PbFe12O19 nanoparticles

In this paper, lead hexaferrite (PbFe₁₂O₁₉) nanoparticles were synthesized by sol-gel method. In order to prepare PbFe₁₂O₁₉ nanoparticles, the metal nitrates with Fe/Pb?=?8, 10, 11, 12, 14 ratios and citric acid were used. The structure, morphology, magnetic, and dielectric properties of PbFe₁₂O₁₉ nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), vibrating sample magnetometer (VSM) and LCR meter. XRD results revealed that the samples with Fe/Pb?≤?10 and Fe/Pb?>?10 have single-phase hexaferrite and hematite (α- Fe₂O₃) structures, respectively. As a result, the sample with Fe/Pb?=?10 is single-phase and shows the highest values of the saturation magnetization and remanence magnetization. We found that the values of dielectric constant (ε′) and dielectric loss (ε″) increase with an increase in the Fe/Pb molar ratio from 8 to 12 and then decreases with an increase of Fe/Pb molar ratio to 14. The variation of ac conductivity (σ_ac) with frequency ranging from 1?kHz to 200?kHz showed that electrical conductivity in these ferrites is mainly due to the electron hopping mechanism.     

Novel NdCo<Subscript>5</Subscript> nanoflakes and nanoparticles produced by surfactant-assisted high-energy ball milling

High-energy ball milling has been shown to be a promising method for the fabrication of rare earth—transition metal nanopowders. In this work, NdCo₅ nanoflakes and nanoparticles have been produced by a two-stage high-energy ball milling (HEBM), by first using wet HEBM to prepare precursor nanocrystalline powders followed by surfactant-assisted HEBM. NdCo₅ flakes have a thickness below 150 nm and an aspect ratio as high as 10²–10³; the nanoparticles have an average size of 7 nm. Both the nanoparticles and nano-flakes exhibited high coercivities at low temperatures, with values at 50 K of 3 and 3.7 kOe, respectively. The high values of coercivity can be attributed to the large surface anisotropy of nanoparticles that leads to an effective uniaxial-type of behavior in contrast to the planar anisotropy of the bulk samples. Angle-dependent magnetization measurements at different temperatures were used to determine the spin reorientation transitions in the nanopowders and nanoparticles. The nanoparticles showed spin reorientation temperatures, T _SR1 = 276 and T _SR2 = 237 K which are lower when compared with the values of 290 and 245 K, respectively for bulk.     

用可调探测深度电子能量损失谱与俄歇电子能谱研究Pb/Ni(001)界面

本工作用可调探测深度电子能量损失谱(ELS)与俄歇电子能谱(AES)研究Pb在Ni(001)表面的生长过程。发现Pb是一层一层地在表面生长的,即按Franck-van der Merwe(F-M)模式生长。当Pb的覆盖度大于1单层(ML)时,Pb的6s能带对应的电子能量损失峰开始出现,当Pb的覆盖度为3ML时,Pb的体等离激元的损失峰已相当明显。在Pb的蒸镀过程及随后的整个退火过程中,Pb的体等离激元峰,6s能带峰和Ni的3p能带峰的峰位与峰宽均保持与纯金属相同的值,也没有出现新的体等离激元峰。由此说明P     

Molecular dynamics study of bimetallic Fe–Cu Janus nanoparticles formation by electrical explosion of wires

Bimetallic nanoparticles comprised of two elements which are immiscible in the bulk present a unique combination of physical–chemical properties that strongly depend on the atomic arrangement within the particle. In this study, molecular dynamics (MD) simulations of bimetallic Fe–Cu nanoparticles formation by high-velocity collision of individual metal nanoparticles (IMNPs) were performed. Physically these conditions model fast electrical explosion of two metal wires (Fe and Cu). By varying the size, temperature and velocity of colliding IMNPs, the conditions under which phase-segregated Janus nanoparticles are formed were determined. The model predictions showed good agreement with the experimental results. The present work is a step forward to understanding the formation mechanisms of bimetallic nanoparticles with different chemical configurations.     

基于水溶液中金属元素检测的超声波雾化辅助SIBS技术研究

为了建立一套高灵敏和低成本的液体样品金属元素检测分析方法,设计制造了一套超声波雾化辅助电火花击穿光谱(UN-SIBS)的实验系统。利用超声波雾化装置将液体样品转化为密集小液滴组成的气溶胶,并使用高压放电线圈和铜电极击穿气溶胶样品诱导等离子体,通过采集分析光谱信号实现对样品金属成分的分析。实验研究了该方法的发射光谱谱线特性,对等离子体的电子温度和密度等物理特性参数进行了计算分析。针对含有不同浓度重金属铅(Pb)元素的样品,在较大的浓度范围内绘制了Pb元素261.37 nm处的原子峰强度随质量浓度变化的曲线。实验结果显示,UN-LIBS方法对Pb元素检测限不高于2.07 ppt,优于同类方法所报道的检测限。同时,与金属活性相对较低的钙(Ca)元素SIBS检测结果进行了比较,分析了UN-SIBS方法的相关机理。     

含硫磷酸钙纳米颗粒的制备及对铅离子的高效选择性去除

用一种简易共沉淀法制备了非晶含硫磷酸钙（SCP）材料,实现硫原子原位引入磷酸钙纳米颗粒中,并研究了其对Pb（II）的吸附特性和机理。与羟基磷灰石相比,SCP对Pb（II）的去除性能显著增强,在10 min内能快速将20 ppm的Pb（II）溶液降低至饮用水标准下。由Langmuir吸附等温线模型计算可知,SCP对Pb（II）的最大饱和吸附量高达1720.57 mg/g,这个数值远远超过以往所报道的绝大部分吸附剂材料。在竞争离子Ni（II）,Co（II）,Zn（II）和Cd（II）共存的条件下,SCP还表现出对Pb（II）的选择性去除。研究表明,SCP对Pb（II）超高的去除效率和优异的亲和力归因于其可通过溶解沉淀和离子交换反应在其表面形成棒状的羟基磷酸铅晶体,以及形成沉淀物硫化铅。SCP以其对Pb（II）快速、高效和优异选择性成为在实际铅污染治理中的理想材料.     

Instantaneous integration of magnetite nanoparticles on graphene oxide assisted by ultrasound for efficient heavy metal ion retrieval

We fabricated a magnetite nanoparticle-graphene oxide (GO) hybrid via a non-chemical and one-step process assisted by ultrasound in an aqueous solution where the nanoparticle attached to the hydrophobic region on graphite oxide (multi-layered GO) which, at the same time, was exfoliated. Unlike chemical methods such as precipitation, oxygen-containing functional groups on GO have not been consumed or reduced during the hybridization, leading that this hybrid exhibited good water solubility and high adsorption capacity for heavy metal ions such as Pb(II) and Au(III). After the adsorption, the hybrid was instantly collected using a magnet. This method can be useful for hybridizing various nanoparticles with GO.     

新型螯合磁性纳米Fe_3O_4的制备及其性能研究

采用共沉淀法制备了磁性四氧化三铁(Fe3O4)纳米粒子,并通过硅烷偶联剂对其表面进行改性,进一步在其表面偶联修饰氨基硫脲,制备了螯合磁性纳米Fe3O4粒子。利用广角X射线衍射仪(WAXD)、红外光谱仪(FTIR)、分光光度计等对磁性纳米粒子的结构和性能进行了表征。结果表明,纳米Fe3O4为反尖晶石结构,通过偶联修饰可以实现氨基硫脲在纳米粒子表面的化学改性。螯合磁性纳米粒子具有良好的分散性和磁响应性,且对多种金属离子(Pb2+、Hg2+、Zn2+、Cd2+)具有良好的螯合效果。     

Thermalization time of noble metal nanoparticles: effects of the electron density profile

The lack of d-electron screening in the s-electron spill-out region at the surface of Ag nanoparticles increases the electron-electron interaction in this region compared to the bulk. Therefore when comparing the electron-electron interaction contribution to the thermalization time of nanoparticles of varying radius, smaller particles thermalize faster due to the increased surface to bulk ratio. One aspect which has not been addressed is the effect of the spatial distribution of charge at the surface of the nanoparticle. In this work it is shown that the size dependence of the thermalization time is very sensitive to the surface density profile. The electron thermalization time of conduction electrons in noble metal nanoparticles as a function of the radius is calculated. The sensitivity of the scattering rate to the spatial distribution of charge at the surface of the nanostructure is analyzed using several model surface profiles. The change in surface charge distribution via charging or coating of the nanospheres is shown to be a tool for control and probing of the ultra-fast electron-electron dynamics in metallic nanoparticles.     

合成聚丙酰胺-硫属半导体复合纳米材料的新技术

在水溶液体系中采用同步聚合－水解技术制备聚丙烯酰胺－半导体纳米复合材料，该ＳＰＨ技术是基于丙烯胺单体的聚合和ＭＳ纳米粒子的形成同步发生，使生成的半导体纳米粒子可均匀分散在聚丙烯酰胺基质中，该技术还为制备其它有机聚合物－金属硫化物纳米复合物提供了一种新途径。     

光谱二阶差分Gabor展开法土壤铜铅污染鉴别

土壤是人类生存环境的重要载体,因此,土壤重金属污染问题一直备受关注。随着遥感技术的发展,高光谱遥感在土壤重金属研究中取得了大量的成果,但是,基本上是根据土壤中有机质、铁、粘土矿物等的光谱吸收特征和反演土壤中重金属含量,而不能够区分土壤重金属污染光谱之间的微弱差异。通过盆栽土壤不同浓度铜(Cu)、铅(Pb)污染实验得到不同浓度Cu和Pb污染下盆栽土壤光谱曲线、土壤含水率和有机质含量,提出了一种光谱二阶差分Gabor展开方法探测不同浓度Cu和Pb污染下土壤光谱曲线之间的微弱差异。以二阶差分为基础,首先将土壤光谱转换为稀疏光谱,然后结合土壤稀疏光谱与Gabor展开理论,在频率域中检测不同浓度土壤重金属污染光谱之间的微弱差异,因此,摆脱了单纯通过土壤光谱反射率信息反演土壤重金属含量的研究,而是对土壤重金属污染光谱信息进行时频分析,最终达到检测土壤重金属污染瞬时光谱存在的目的。结果表明：受Cu和Pb污染的盆栽土壤光谱二阶差分Gabor展开系数尺度及等高线分布有较大的差异,Cu污染的盆栽土壤光谱二阶差分Gabor展开系数尺度分布存在两个较高的峰值,且等高线在第1 800~3 600项之间稀疏分布,Pb污染的盆栽土壤光谱二阶差分Gabor展开系数尺度分布存在一个较高的峰值,且等高线在第3 200~3 600项之间密集分布;二阶差分Gabor展开法检测的土壤Cu和Pb污染结果与土壤Cu和Pb含量、土壤含水率、土壤有机质是密切相关的,由于土壤Cu和Pb含量、有机质含量、含水率的不同,土壤Cu和Pb污染二阶差分Gabor展开光谱尺度分布而不同。根据相关性分析结果,分别将土壤Cu和Pb污染划分为三组：Cu(50)~Cu(300),Cu(400)~Cu(800),Cu(1 000)以上;Pb(50)以下,Pb(100)~Pb(300),Pb(400)~Pb(1 200)。     

Chalcogenide-based thin film sensors prepared by pulsed laser deposition technique

One advantage of the pulsed laser deposition (PLD) method is the stoichiometric transfer of multi-component target material to a given substrate. This advantage of the PLD determined the choice to prepare chalco-genide-based thin films with an off-axis geometry PLD. Ag-As-S and Cu-Ag-As-Se-Tetargets were used to deposit thin films on Si substrates for an application as a heavy metal sensing device. The films were characterized by means of Rutherford backscattering spectrometry (RBS), transmission electron microscopy (TEM), and electrochemical measurements. The same stoichiometry of the films and the targets was confirmed by RBS measurements. We observed a good long-term stability of more than 60 days and a nearly Nernstian sensitivity towards Pb and Cu, which is comparable to bulk sensors.     

Structure of cobalt nanoparticles as studied by X-ray absorption spectroscopy

Ab initio modeling is used to analyze the specific near-edge features of the X-ray absorption K spectra of ∼3-nm cobalt nanoparticles. It is established that the observed differences between the spectra of the nanoparticles and those of bulk cobalt samples are due to contribution from atoms of the nanoparticles’ surface layer, the local environment of which is considerably different from that of atoms in the bulk of the nanoparticle. It is also established that the local environment of cobalt atoms in the nanoparticle bulk corresponds to the FCC structure of bulk metal, and the fraction of such atoms is found to be 65 ± 5%.     

Theoretical study and pathways for nanoparticle capture during solidification of metal melt

Nanocomposites can provide exciting physical, chemical, and mechanical properties for numerous applications. The solidification processing method has great potential for economical fabrication of bulk nanocomposites, especially for those with crystalline materials as the matrix, such as metal matrix nanocomposites (MMNCs). However, it is extremely difficult to effectively capture nanoparticles (less than 100 nm) into the solidification fronts during solidification. It is thus very important to initiate a theoretical study to examine the physics that governs the interactions between nanoparticles and the solidification front, and to provide enabling pathways for effective nanoparticle capture during solidification. The aim of this paper is to establish a theoretical framework for the fundamental understanding of nanoparticle capture during solidification of metal melt in order to obtain bulk MMNCs. A thermodynamically favorable condition is set as the starting point for further theoretical analysis of the three-party model system, namely a nanoparticle-metal-melt-solidification front. Three key interaction potentials, the interfacial energy at short range (0.2-0.4 nm), the van der Waals potential (especially at a longer range beyond 0.4 nm and up to ～10 nm) and the Brownian potential, were studied. Three possible pathways for nanoparticle capture were thus devised: viscous capture, Brownian capture and spontaneous capture. Spontaneous capture is proposed as the most favorable for nanoparticle capture during solidification of metal melt. The theoretical model of nanoparticle capture from this study will serve as a powerful tool for future experimental studies to realize exciting functionalities offered by bulk MMNCs.     

Preparation of triethylamine stabilized silver nanoparticles for low-temperature sintering

In this article, silver nanoparticles were synthesized by chemical reduction from silver nitrate using triethylamine as the protecting and reducing agents simultaneously. The average size of the silver nanoparticles was about 2.10–4.65 nm, which allowed low-temperature sintering of the metal. X-ray diffraction (XRD), thermogravimetric analysis (TGA), and energy dispersive spectrometric (EDS) analysis results indicate that silver nitrate has been converted to silver nanoparticles completely. Using a 20 wt% silver nanoparticles suspension with thermal treatment at 150 °C, silver films with a resistivity of 8.09 × 10⁻⁵ Ω cm have been produced, which is close to the resistivity of bulk silver.