Some interesting properties of metals confined in time and nanometer space of different shapes

The properties of a material depend on the type of motion its electrons can execute, which depends on the space available for them (i.e., on the degree of their spatial confinement). Thus, the properties of each material are characterized by a specific length scale, usually on the nanometer dimension. If the physical size of the material is reduced below this length scale, its properties change and become sensitive to its size and shape. In this Account we describe some of the observed new chemical, optical, and thermal properties of metallic nanocrystals when their size is confined to the nanometer length scale and their dynamical processes are observed on the femto- to picosecond time scale.     

Vapor specific extents of uptake by nanometer scale charged particles

The uptake of vapor molecules by nanometer scale aerosol particles (clusters) is of fundamental importance in aerosol science; uptake is the first step of condensational growth in both the ambient as well as in condensation based particle detectors. However, uptake is not well understood at the nanometer scale. We examined the uptake of organic vapor molecules by nanometer scale sodium chloride cluster ions ((NaCl)_x(Na⁺)_z and (NaCl)_x(Cl^?)_z) using a differential mobility analyzer coupled with a time-of-flight mass spectrometer. Through monitoring cluster ion inverse mobilities as functions of solvent vapor pressure in the mobility analyzer, the extent of uptake was monitored for 1-butanol, ethanol, methyl ethyl ketone (MEK), and toluene. With butanol vapor pressures in the <300 Pa range, shifts in inverse mobility in excess of a factor of 2 were observed for nearly all examined clusters. Ethanol and MEK uptake led to shifts for positively charged cluster ions upwards of a factor of 1.5. Ethanol exposure led to similar sized shifts for negatively charged clusters ions, while MEK exposure led to negative ion inverse mobility shifts less than a factor of 1.3. Toluene was sorbed much less efficiently than the other solvents; toluene exposure led to shifts in inverse mobility below a factor of 1.2. In total, relative inverse mobility shifts, which are direct functions of the extent of vapor uptake, were found to be only weakly dependent on cluster ion size when compared to the influence of vapor molecular structure and cluster ion charge polarity. Classical (Kelvin-based) models are found inadequate to explain the observed mobility shifts, and we instead used a site-specific, Langmuir type model to describe the vapor uptake behavior by the cluster ions.

© 2017 American Association for Aerosol Research     

碳纳米管及其应用研究

碳纳米管的发现是碳团簇领域的又一重大科研成果,探讨了碳纳米管的结构、特性、活化方法,评述了这种纳米尺寸的新型碳材料在电化学器件、氢气存储、场发射装置、碳纳米管场效应晶体管、催化剂载体、碳纳米管修饰电极领域的应用价值,展望了碳纳米管的介入对全球性物理、化学及材料等学科界所带来的美好前景。     

金红石型纳米钛白粉在车辆涂料中的应用

介绍了金红石型纳米二氧化钛在丙烯酸金属烘干漆中的应用,通过将有机光稳定剂及不同比例的金红石型纳米二氧化钛加到丙烯酸金属烘干漆中,并检测其相应的性能,观察金红石型纳米二氧化钛对涂膜的耐候性、硬度、附着力、颜料沉淀以及金属闪光漆的随角异色效果的影响。     

Evidence for anchoring and partial occlusion of metallic clusters on the pore walls of MCM-41 and effect on the stability of the metallic clusters

In order to explain the high stability of the Co- and Ni-MCM-41 catalysts, the hypotheses of anchoring of small metallic clusters to cations in and partial occlusion of the metallic clusters by amorphous silica are proposed. Carbon monoxide chemisorption on model catalysts and Co-MCM-41 has given direct proof of the metal anchoring effect on the stability of metal cluster dispersion. The partial occlusion of metallic clusters, which may lead to physical confinement (inhibited migration) or chemical confinement (inhibited reaction), was monitored by CO in situ FTIR and CO methanation along with a kinetic study, which confirmed that the metallic clusters on the pore surface result in the stabilization of the catalysts against deactivation. A fine tuning of these physicochemical phenomena in the transition metal incorporated MCM-41 will make possible the design of stable catalytic systems for reactions requiring metallic active sites under severe reaction conditions.     

Study of Cu2+-poly(itaconic acid-co-acrylic acid) complex and copper-polymer nanocomposites

Summary Ultrafine copper particles with diameters in the range of nanometer scale have been prepared in a polymer matrix, using ionic aggregates in Cu²⁺-random poly(itaconic acid-co-acrylic acid) complex precursor films as “microreactors” of controllable size.The morphology and formation of metallic copper particles were studied by transmission electron microscopy and X-ray diffraction techniques. Results from the measurements indicate the copper ions were transformed into nanocrystalline by in situ chemical reduction. It was also found that the polymer chains prohibited the excessive aggregation of the metal atoms and have protective effect on the ultrafine copper particles. Received: 20 May 1998/Revised version: 4 September 1998/Accepted: 16 September 1998     

Cluster-assembled metallic glasses

A bottom-up approach to nanofabricate metallic glasses from metal clusters as building blocks is presented. Considering metallic glasses as a subclass of cluster-assembled materials, the relation between the two lively fields of metal clusters and metallic glasses is pointed out. Deposition of selected clusters or collections of them, generated by state-of-the-art cluster beam sources, could lead to the production of a well-defined amorphous material. In contrast to rapidly quenched glasses where only the composition of the glass can be controlled, in cluster-assembled glasses, one can precisely control the structural building blocks. Comparing properties of glasses with similar compositions but differing in building blocks and therefore different in structure will facilitate the study of structure–property correlation in metallic glasses. This bottom-up method provides a novel alternative path to the synthesis of glassy alloys and will contribute to improving fundamental understanding in the field of metallic glasses. It may even permit the production of glassy materials for alloys that cannot be quenched rapidly enough to circumvent crystallization. Additionally, gaining deeper insight into the parameters governing the structure–property relation in metallic glasses can have a great impact on understanding and design of other cluster-assembled materials.     

纳米片状铝粉的制备及其发展动态

纳米片状铝粉是新发展起来的新型金属颜料，它具有粒径分布窄、良好的金属光泽性、遮盖率和在涂料中分布均匀等优点而倍受人们的关注。本文阐述的物理气相沉积法(PVD法)是目前制备纳米片状铝粉的主要方法。     

纳米复合材料的制备技术及应用进展

综述了纳米复合材料的性能、特点、制备技术以及应用领域的现状,指出了纳米复合材料作为一种新型的纳米材料进行研究和开发的重要意义。     

Advances Towards Synthetic Machines at the Molecular and Nanoscale Level

The fabrication of increasingly smaller machines to the nanometer scale can be achieved by either a “top-down” or “bottom-up” approach. While the former is reaching its limits of resolution, the latter is showing promise for the assembly of molecular components, in a comparable approach to natural systems, to produce functioning ensembles in a controlled and predetermined manner. In this review we focus on recent progress in molecular systems that act as molecular machine prototypes such as switches, motors, vehicles and logic operators.     

The effect of hydrogen plasma chemical annealing on electron field emission of amorphous carbon films

Layer-by-layer deposition method, in which nanometer-thick film deposition and hydrogen plasma annealing processes were alternatively repeated, was applied to fabricate hydrogenated amorphous carbon films in our present work. It was found that the hydrogen plasma treatment changed the sp²/sp³ ratio due to chemical etching. Consequently, a stable vacuum electron emission with a low threshold field was achieved compared with that from conventionally deposited a-C films. The threshold electric field is as low as 2 V/μm. The influence of the hydrogen plasma chemical annealing on the field emission behavior was systematically investigated. The improvement of field emission characteristics can be attributed to the large field enhancement effect due to the inhomogeneous distribution of nanometer scale sp² clusters.     

Frictional behaviour of vertically aligned carbon nanotube films

Vertically aligned CNT films were grown on polycrystalline β-SiC wafers by the surface decomposition method. Their frictional behaviours were investigated by AFM at the nanometer scales. Compared with DLC film and silicon wafers, they demonstrate an extremely low friction coefficient at the nanometer scale about 0.03-0.04. The effect of the surface topography on the friction coefficient is obvious for the aligned CNT film sliding at the nanometer scale. This implies that the excellent tribological properties of the vertically aligned CNT films, combined with their small dimensions and structural perfection, might lead to significant improvement of the performance of nano-devices.     

炸药发展中的新技术

介绍了炸药科学在高能量密度化合物、金属化炸药，复合炸药，新型高分子粘结剂应用，反应性材料和纳米技术应用等方面的新技术和新进展，总结了目前炸药研究和应用中采用的一些新思路，并对我国炸药技术的发展提出了建议。     

Heat Conduction of Air in Nano Spacing

The scale effect of heat conduction of air in nano spacing (NS) is very important for nanodevices to improve their life and efficiency. By constructing a special technique, the changes of heat conduction of air were studied by means of measuring the heat conduction with heat conduction instrument in NS between the hot plate and the cooling plate. Carbon nanotubes were used to produce the nano spacing. The results show that when the spacing is small down to nanometer scale, heat conduction plays a prominent role in NS. It was found that the thickness of air is a non-linear parameter for demarcating the heat conduction of air in NS and the rate of heat conduction in unit area could be regard as a typical parameter for the heat conduction characterization at nanometer scale.     

Nanoscale electrodeposition of metals and compound semiconductors from ionic liquids

Employing ionic liquid electrolytes we succeeded to electrodeposit light and transition metals as well as compound semiconductors on metal and semiconductor substrates at room temperature with nanometer or atomic resolution. For this aim in situ scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy (STS) have been applied. In this article we present new and recent results of 2D phase formation and growth of Ga underpotential deposition (UPD) and of surface alloying of Cd on Au(1 1 1), as well as 3D overpotential deposition (OPD) of Ni nanocrystals and ZnSb semiconductor clusters. Particular attention is given to the respective nucleation and growth mechanisms of the selected examples. Aspects of technological applications are briefly discussed.     

Surface composition of Pt---Ru catalysts: effect of the support

The effect of support on the surface composition of bimetallic clusters was studied using Differential Scanning Calorimetry (DSC), and by the hydrogenolysis isomerization and cyclization of n-pentane. Pt---Ru bimetallic clusters were prepared from H₂PtCl₆·6H₂O and RuCl₃·3H₂O as metal precursors. The supports used were MgO, SiO₂ and Al₂O₃. Differences in the reduction behavior of both metals on each carrier were related to the composition of the metallic clusters. Preferential surface segregation in one of the metallic components of the Pt---Ru bimetallic clusters was identified using the reactions of n-pentane as a catalytic surface probe. To explain the support effect, a nucleation process is proposed in which the precursor reduced at the lower temperature forms nucleation centers on which the precursor reduced at the higher temperature is deposited.     

Tailored polymer-based nanorods and nanotubes by "template synthesis": From preparation to applications

Polymer nanotechnology allows manipulating materials microstructure, morphology and compositional variation on the nanometer scale. Thus, it is able to provide materials for many cutting edge applications, from photonics to medical devices to sensors. This article summarizes recent work on template-based fabrication and on the basic properties of one-dimensional polymeric nanostructures and their inherent advantages over their conventional counterparts. The chemistry and physics relevant for the design of these nanostructured materials are discussed and recent advances emphasized. In particular, highlighting the effects of nanoconfinement on material behavior and putting somewhat greater emphasis on molecular motions. Some examples of one-dimensional-based polymeric nanostructures with promising applications for example in the field of tissue engineering are also presented as well as some aspects concerning recyclability of the used templates.     

Stepwise Optimized 3D Printing of Arbitrary 3D Structures at Millimeter Scale with High Precision Surface

3D printing based on additive manufacturing has attracted widespread attention in the fields of microbiology and microelectronics due to its advantages of waste reduction, arbitrary manufacturing, and rapid prototyping in potential applications. These techniques can create structures at the centimeter scale, however, there are some limitations in terms of resolution and geometric constraints. Here, a micro–nano 3D printing protocol based on additive manufacturing to achieve the 3D structure (3DS) not only possessing millimeter scale structural dimensions but also nanometer features are proposed. A theory is verified to assist the design and fabrication of the 3DS with millimeter scale and nanometer precision. The structures are predesigned and the scanning strategy is optimized before 3D printing to improve the manufacturing efficiency and precision. A customized 3DS with a height of 2.2 mm is obtained, which is a challenge for the conventional two‐photon polymerization fabrication. Furthermore, a 1.2 mm 3DS with inside scaffold and smooth surface is efficiently achieved within 2.7 h with a nanometer surface roughness by using the proposed stepwise optimized 3D printing process. This study offers a flexible and low‐cost technology to generate highly customizable, precisely controllable 3DS for potential applications in microelectronics and microdevices.     

纳米金属氧化物吸附金属离子的研究现状

纳米材料由于具有较大的比表面积及许多未饱和的原子,对金属离子具有很强的吸附性,纳米金属氧化物由于价格低廉、容易合成,近年来,在研究其对金属离子吸附方面受到关注。对纳米金属氧化物吸附金属离子的机理、影响因素、及应用进行了综述,提出了目前纳米金属氧化物在吸附金属离子方面存在的问题以及对其发展前景进行了展望。