Synthesis, two-dimensional assembly, and surface pressure-induced coalescence of ultranarrow PbS nanowires

Ultranarrow (1.8 nm) PbS nanowires are synthesized in a single step, under benchtop conditions at relatively low temperature (90 degrees C). The nanowires exhibit a nearly perfect crystal lattice, high width uniformity, and tight side-by-side registry. Two-dimensional (2D) assembly over large areas (>15 microm2) is achieved using the Langmuir Blodgett method. The wire width can be readily controlled in the range 1.8-10 nm by a surface pressure-induced coalescence reaction, as monitored by transmission electron microscopy and Raman spectroscopy. The fluorescence of the 2D assembly shows strong polarization dependence along the long axis of the wires, making the system potentially suitable for orientation-sensitive devices.     

Polymer assisted preferential growth of PbS and PbS:Mn nanorods: structural and optical properties

We report here the structural and optical properties of PbS and PbS:Mn nanorods (diameter 30–80 nm) grown in a polymer (polypyrrole) matrix. X-ray diffraction data of nanorods clearly reveals preferential growth of PbS nanorods with a strong lattice distortion from a bulk cubic to tetragonal one. The strain introduced lattice distortion is inherent to the growth process and strongly depends on polymer concentration. The polymer concentration is found to play an important role in controlling the structural properties. The effect of Mn²⁺ incorporation into PbS lattice shows no appreciable change in the structural properties. Optical absorption behaviors in such PbS and PbS:Mn nanorods are also reported. The absorption peak energy shows blue-shift with increase in Mn²⁺ concentration to some critical value beyond which red-shift is observed.     

Nonlinear optical properties of the PbS nanorods synthesized via surfactant-assisted hydrolysis

PbS nanorods were synthesized by surfactant-assisted homogenous hydrolysis. The products were characterized by UV–vis spectrophotometer, X-ray powder diffraction (XRD) and transmission electron microscope (TEM). PbS nanorods were measured by the Z-scan technique to investigate the third-order nonlinear optical (NLO) properties. The result of the NLO measurements shows that the PbS nanorods have the third-order nonlinear optical properties of both NLO absorption and NLO refraction with self-focusing effects. The nonlinear absorption coefficient and refractive index of the PbS nanorods are 2.16 × 10^− 9 m/W and 3.52 × 10^− 16 m²/W respectively.     

Immunity of electronic and transport properties of phosphorene nanoribbons to edge defects

We present an extensive study of the electronic properties and carrier transport in phosphorene nanoribbons (PNRs) with edge defects by using rigorous atomistic quantum transport simulations. This study reports on the size- and defect-dependent scaling laws governing the transport gap, and the mean free path and carrier mobility in the PNRs of interest for future nanoelectronics applications. Our results indicate that PNRs with armchair edges (aPNRs) are more immune to defects than zig-zag PNRs (zPNRs), while both PNR types exhibit superior immunity to defects relative to graphene nanoribbons (GNRs). An investigation of the mean free path demonstrated that even in the case of a low defect density the transport in PNRs is diffusive, and the carrier mobility remains a meaningful transport parameter even in ultra-small PNRs. We found that the electron–hole mobility asymmetry (present in large-area phosphorene) is retained only in zPNRs for W > 4 nm, while in other cases the asymmetry is smoothed out by edge defect scattering. Furthermore, we showed that aPNRs outperform both zPNRs and GNRs in terms of carrier mobility, and that PNRs generally offer a superior mobility-bandgap trade-off, relative to GNRs and monolayer MoS₂. This work identifies PNRs as a promising material for the extremely scaled transistor channels in future post-silicon electronic technology, and presents a persuasive argument for experimental work on nanostructured phosphorene.

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化学还原法合成硫化铅纳米棒及其表征

硫化铅纳米材料具有特殊的光电性能。许多方法用于合成各种形貌的硫化铅纳米材料。主要介绍以硝酸铅、四氢呋喃、硫粉和硼氢化钾为原料，通过化学还原方法来合成硫化铅纳米棒。在合成过程中，硝酸铅、四氢呋喃、硫粉和硼氢化钾的混合物在无水的条件下进行磁力搅拌，半导体硫化铅纳米棒即形成。硫化铅纳米棒分别通过x射线粉末衍射、透射电镜、紫外，可见光，近红外光分光光度仪和荧光分光光度仪进行表征。在透射电镜图中，硫化铅纳米棒的直径和长度分别为500hm和11μm。由于量子限域效应，分散在丙酮中的硫化铅纳米棒的紫外，可见光，近红外光吸收峰在1731nm，比硫化铅块体有明显的蓝移。通过532nm的绿色激光激发，硫化铅纳米棒在1516nm处发出荧光。     

Synthesis and characterization of ultra small PbS nanorods in sucrose ester microemulsion

In the present study, we report for the first time the synthesis of ultra small PbS nanorods in a non-ionic sugar based water-in-oil (w/o) microemulsion system using food grade sucrose ester as surfactant. PbS was formed by mixing lead nitrate and thioacetamide in the water core of the microemulsion system. The as-prepared PbS nanorods were characterized by X-ray diffractometry (XRD), uv–visible absorption spectroscopy (UV–VIS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The diameter of the PbS nanorods were found to be extremely small, which is in the range of 2.64 nm to 2.91 nm depending on reaction aging time. Spherical PbS nanoparticles were formed after 12 h and PbS nanorods were formed after more than 1 day of reaction aging time.     

Size and shape-tuned overgrowth on Au nanorods regulated by polyallylamine

Au nanorods prepared by a photochemical method were used as seeds for the overgrowth of thin shell of gold by using a mild reducing agent, ascorbic acid at ambient conditions. The overgrowth rate along different crystal facets of the starting gold nanorods was regulated by the addition of polyallylamine. The shape of the resulting gold nanorods was different from the naturally overgrown Au nanorods without any additives.     

扩散诱导的锌间隙相关施主缺陷对ZnO纳米棒结构及光电特性的影响

采用射频磁控溅射技术和水浴法在SiO2单晶衬底上生长了Zn纳米颗粒/ZnO纳米棒复合材料(Zn/ZnO)。后期热处理促使Zn/ZnO界面之间发生元素相互扩散,直接向ZnO纳米棒中引入额外锌杂质,从而获得了富锌的ZnO纳米棒材料。借助扫描电子显微镜、X射线衍射仪、霍尔测试仪、分光光度计和拉曼光谱仪研究了富锌ZnO纳米棒的形貌、结构以及光电特性。结果表明,所有ZnO纳米棒均呈整齐的六角纤锌矿结构,相比ZnO纳米棒,富锌纳米棒具有相对较差的结晶质量,较好的导电性,较低的透射率和较窄的禁带宽度。拉曼光谱研究表明,通过扩散法向ZnO纳米棒引入的锌间隙相关施主缺陷,是其拉曼光谱中出现异常的275 cm^-1振动模的来源,也是导致富锌ZnO纳米棒微结构以及光电特性显著变化的主要原因。     

Grain boundary segregation of impurities and point defects in ionocovalent materials: The case of NiO bicrystals

Point defects and impurities may interact with an extended defect: surface, dislocation, grain boundary, etc…. Such an interaction leads, at thermodynamic equilibrium, to a species concentration in extended defects different from the bulk's, together with electrical charge phenomena; such concentrations, in the proximity of these interfaces, vary in turn, to screen the core charge; a redistribution of these entities can then be observed showing concentration profiles, thereby indicating a segregation phenomena.The aim of our work falls in with that framework and consists firstly in studying the segregation and potential of three impurities, namely, Aluminium, Cobalt and Cerium in NiO bicrystal grain boundaries, for two given orientations, F(12¯2)/[011] and F(310)/[001].The problem is tackled in the case of diluted solutions as well as real ones; for the latter, the use of Debye–Hückel theory enables us to calculate the activity coefficients of the given species whose values have a significant effect upon the variations of the impurities intergranular concentration curves.     

Interaction of point defects with impurities in the Si-SiO2 system and its influence on the properties of the interface

The results of investigations of the point defect generation, redistribution and interaction with impurities in the Si-SiO₂ system during the process of its formation by means of electron paramagnetic resonance (EPR) and nucleus magnetic resonance (NMR) techniques are presented. The type and density of the point defects that are generated in the Si surface layer during thermal oxidation depend on the oxidation condition: temperature, cooling rate, oxidation time, and impurity content. The interaction between the point defects with extended defects and impurities affects the properties of the Si-SiO₂ interface. The influence of the point defects may be diminished and the interface properties improved by an appropriate choice of the oxidation conditions. The difference between the interface properties of n- and p-type wafers may be connected with the different position of the Fermi level at the interface and different point defects density in the volume near the interface.     

Effects of annealing on the photoluminescence of ZnSe nanorods coated with Au

Au-functionalized ZnSe nanorods were synthesized by the thermal evaporation of ZnSe powder followed by Au sputter-deposition and thermal annealing. Photoluminescence (PL) showed that the intensity of near-band edge (NBE) emission of ZnSe nanorods was enhanced remarkably by Au-coating and annealing in a H₂ atmosphere. The intensity ratio of NBE emission to the deep level emission, I_NBE/I_DL of Au-coated ZnSe nanorods after annealing in a H₂ atmosphere was ∼68 times higher than that of the pristine (unannealed, uncoated) ZnSe nanorods. The increase in I_NBE/I_DL might be due to a combination of carrier transfer from the defect level to the Fermi level of Au nanoparticles, surface plasmon resonance in Au nanoparticles and hydrogen passivated deep level defects.     

Autostresses induced by point defects in sintering phenomena: effect on mass transport and sintering stress

States of anelastic strain can be associated with excess concentrations of point defects, as generated by mass transport in a sintering compact. Correspondingly, states of mechanical long-range self-equilibrated stresses (autostresses) can be produced. The relationships between anelastic strain and autostresses have been derived for a two-particle model. A generalized relation between chemical potentials and autostresses, including surface stresses, is provided, which allows derivation of local thermodynamic driving forces for mass transport. The concept of equivalent external sintering stress, assumed to be the driving force for the global densification process, is shown to correspond, approximately, to the material- and history dependent normal autostress component acting on the neck cross-sections. Predictions made from the model provide a new interpretation of experimental observations of the effect of gaseous phases, such as H₂O and CO₂, on the sintering of MgO and CaO powders.     

Ligand effects on electronic and optoelectronic properties of two-dimensional PbS necking percolative superlattices

The inter-nanocrystal (NC) distance,necking degree,ordering level,and NC surface ligands all affect the electronic and optoelectronic properties of NC solids.Herein,we introduce a unique PbS structure of necking percolative superlattices to exclude the morphological factors and study the effect of ligands on the NC properties.X-ray photoelectron spectroscopy data indicate that 1,2-ethanedithiol (EDT),oxalic acid,mercaptopropionic acid,and NH4SCN (SCN)ligands were attached to the surface of NCs by substrate-supported ligand exchange.Field-effect transistors were tested and photodetector measurements were performed to compare these NC solids.An SCN-treated film had the highest mobility and responsivity under high-power intensity irradiation owing to its high carrier density,whereas an EDT-treated film had the lowest mobility,photocurrent,and dark current.These findings introduce new avenues for choosing suitable ligands for NC applications.     

Preparation and photoluminescence properties of reverse type-I ZnO/PbS core/shell nanorods

ZnO/PbS one-dimensional core/shell nanorods have been fabricated by a two-step growth method. Photoluminescence properties of these samples with different shell thickness are studied in detail. The result reveals that the photoluminescence intensity of the ZnO/PbS core/shell nanorods changes with the increase of thickness of PbS shell. When the shell is very thin, the increase in photoluminescence intensity is attributed to the modification of surface defect state. When the shell becomes thicker, the formation of a reverse type-I band alignment between the core and shell is ascribed to be the factor resulting in the decrease in intensity of the photoluminescence properties.     

Formation of rectangularly shaped Pd/Au bimetallic nanorods: evidence for competing growth of the Pd shell between the 110 and 100 side facets of Au nanorods

In this letter, we report the competing growth of a Pd shell on the {110} and {100} facets of Au nanorods (Au NRs). This results in the disappearance of unstable {110} facets and the formation of rectangularly shaped Pd/Au bimetallic nanorods that show only four stable {100} side surfaces. The energy minimization to a more stable morphology is believed to be the driving force for the formation of the rectangular shape of the Pd shell.     

Plasmonic detection of mercury via amalgam formation on surface-immobilized single Au nanorods

Abstract

Au nanorods were used as plasmonic transducers for investigation of mercury detection through a mechanism of amalgam formation at the nanorod surfaces. Marked scattering color transitions and associated blue shifts of the surface plasmon resonance peak wavelengths (λ_max) were measured in individual nanorods by darkfield microscopy upon chemical reduction of Hg(II). Such changes were related to compositional changes occurring as a result of Hg–Au amalgam formation as well as morphological changes in the nanorods’ aspect ratios. The plot of λ_max shifts vs. Hg(II) concentration showed a linear response in the 10–100 nM concentration range. The sensitivity of the system was ascribed to the narrow width of single nanorod scattering spectra, which allowed accurate determination of peak shifts. The system displayed good selectivity as the optical response obtained for mercury was one order of magnitude higher than the response obtained with competitor ions. Analysis of mercury content in river and tap water were also performed and highlighted both the potential and limitation of the developed method for real sensing applications.     

Effect of impurities on SIMS

Results showing the effect of implantation of various species into copper on the secondary Cu⁺ ion signal are presented. Preliminary analysis indicates that both a physical change in the sample induced by the implantation and a chemical effect due to the presence of the implant species are responsible for the observed changes.     

Surfactant-induced defects and photoluminescence of Co doped SnO2 nanorods

The microstructure and defect evolution of Co-doped SnO2 nanostructures have been mediated by the surfactant via a hydrothermal method. The microstructure is characterized by X-ray diffraction and Raman spectra in detail. It is found that the density of structural defects considerably increases with the increase of the surfactant amount used in the preparation process. Meanwhile, the orange emission enhances dramatically. The growth process and defect evolution have been investigated by the following time-dependent experiments. Due to the existence of hollow scrolls in the growth, the mesocrystal lamellar attachment and the rolling process are proposed for the possible growth mechanism. In the synthetic process, surfactant cations, which are incorporated into the network of the self-assembled structure, strongly interact with tin hydroxyl anions. After removing the surfactants by calcination, the vacancies create in the corresponding locations, which promote the orange emission. Our finding opens a new way to control SnO2 defects and strength the optical emission.