Fabrication and use of nanometer-sized electrodes in electrochemistry

Electrodes with electrochemical dimensions as small as 10 angstroms have been fabricated and used for electrochemical studies. These nanometer-scale electrodes have enabled the measurement of electron-transfer rate constants, k(het), that are two orders of magnitude faster than k(het) values accessible with any other electrochemical method.     

Atomic-scale control of friction by actuation of nanometer-sized contacts

Stiction and wear are demanding problems in nanoelectromechanical devices, because of their large surface-to-volume ratios and the inapplicability of traditional liquid lubricants. An efficient way to switch friction on and off at the atomic scale is achieved by exciting the mechanical resonances of the sliding system perpendicular to the contact plane. The resulting variations of the interaction energy reduce friction below 10 piconewtons in a finite range of excitation and load, without any noticeable wear. Without actuation, atomic stick-slip motion, which leads to dissipation, is observed in the same range. Even if the normal oscillations require energy to actuate, our technique represents a valuable way to minimize energy dissipation in nanocontacts.     

Observation of the one-dimensional diffusion of nanometer-sized dislocation loops

Dislocations are ubiquitous linear defects and are responsible for many of the properties of crystalline materials. Studies on the glide process of dislocations in bulk materials have mostly focused on the response of dislocations with macroscopic lengths to external loading or unloading. Using in situ transmission electron microscopy, we show that nanometer-sized loops with a Burgers vector of (1/2)111 in alpha-Fe can undergo one-dimensional diffusion even in the absence of stresses that are effective in driving the loops. The loop size dependence of the loop diffusivity obtained is explained by the stochastic thermal fluctuation in the numbers of double kinks.     

Isolation and structure of higher diamondoids,nanometer-sized diamond molecules

We exploited the exceptional thermal stability and diverse molecular shapes of higher diamondoids (C22 and higher polymantanes) to isolate them from petroleum. Molecules containing 4 to 11 diamond-crystal cages were isolated and crystallized, and we obtained single-crystal x-ray structures for representatives from three families. Rigidity, strength, remarkable assortments of three- dimensional shapes, including resolvable chiral forms, and multiple, readily derivatizable attachment sites make them valuable nanometer-size molecular building blocks.     

复合纳米材料对含蜡原油析蜡特性的影响

大庆原油是典型的高凝、高粘、高含蜡原油,其低温流动性较差。为了改善含蜡原油的低温流动性,在大庆原油中添加复合纳米材料,通过XRD扫描实验和POM拍照,研究了复合纳米材料对含蜡原油中石蜡的结晶形态和析蜡点的影响。进行了大庆原油空白样和大庆原油分别添加50g/tEVA、100g/t复合纳米材料样品的动态降温XRD扫描对比实验,结果表明:复合纳米材料能够有效地改善大庆原油中石蜡的结晶形态(原油中60.01%的正构烷烃的结晶形态得到改善),使晶粒尺度变小,晶面间距离增大,并降低了大庆原油的析蜡点,从而明显改善了原油的低温流动性,提高了原油低温流动的时效稳定性;复合纳米材料对原油的降凝、降粘效果明显优于传统的EVA类化学降凝剂。     

普鲁士蓝对养殖液中亚甲基蓝的光热催化降解

【目的】探究亚微米普鲁士蓝(Submicron Prussian blue,smPB)的光热转化效果对其光芬顿催化降解亚甲基蓝(Methylene blue, MB)污染物的促进作用。【方法】以亚铁氰化钠和聚乙烯亚胺为主要材料,在酸性条件下,通过水热缓慢结晶法,利用聚乙烯亚胺链上的氨基基团控制普鲁士蓝(Prussian blue, PB)的结晶过程,制备出具有光热及光芬顿催化降解能力的smPB。使用扫描电子显微镜(SEM)、紫外-可见漫反射吸收光谱(UV-Vis)、透射电子显微镜(TEM)、傅里叶红外分光光度计(FTIR)、X射线衍射仪(XRD)等测试仪器对smPB进行结构和形貌表征。利用太阳光模拟器照射的阳光测试了smPB在水溶液中的光热转化效果。在不同的催化条件下,测试了smPB的芬顿、光芬顿以及光热芬顿催化降解效率。【结果】smPB的光热转化率约为90%。太阳光模拟器以1个太阳光功率照射1 h的情况下,含有smPB 20 mg的100 mL水溶液温度上升8.8℃左右。在光热的条件下,使用20 mg的smPB对100 mL的MB溶液(ρ=20 mg/L)进行光热芬顿催化降解,在40...     

Atomic resolution imaging of adsorbates on metal surfaces in air: iodine adsorption on pt(111)

The adsorption of iodine on platinum single crystals was studied with the scanning tunneling microscope (STM) to define the limits of resolution that can be obtained while imaging in air and to set a target resolution for STM imaging of metal surfaces immersed in an electrochemical cell. Two iodine adlattice unit cells of slightly different iodine packing density were clearly imaged: ( radical7 x radical7) R19.1 degrees -I, surface coverage ?(I) = 3/7; and (3 x 3)-I, ?(I) = 4/9. The three iodine atoms in the ( radical7 x radical7) unit cell form a regular hexagonal lattice interatomic distance d(I) = 0.424 nanometer, with two atoms adsorbed in threefold hollow sites and one atom adsorbed at an atop site. The (3 x 3) unit cell showed two different packing arrangements of the four iodine atoms exit. In one of the (3 x 3) structures, the iodine atoms pack to form a hexagonal lattice, d(I) = 0.417 nanometer, with three of the iodine atoms at twofold adsorption sites and one atom at an atop site. Another packing arrangement of iodine into the (3 x 3) unit cell was imaged in which the iodine atoms are not arranged symmetrically.     

Detection of relativistic particles

It appears possible to extend the application of most of the existing detection techniques to the identification and separation of charged particles in the relativistic energy region.One can probably extend these applications, in certain limited cases, up to an energy region of several hundred billion electron volts. However, for general applications in the identification of particles in the ultrarelativistic region, the existing detectors are rather limited, and new methods and approaches are desirable. At present, detectors making use of the relativistic rise effect seem to show considerable promise.     

The oceanic microcosm of particles

Analyses of suspended particulate matter larger than 1 micrometer, filtered from thousands of liters of surface and deep waters during GEOSECS expeditions to the Atlantic and Pacific oceans, have provided new information on the nature and time scales of chemical processes associated with the particles. Trace element and radionuclide data show that particles scavenge trace elements such as Th, Pu, Fe, Pb, and Cu from the ocean column, thereby controlling their concentrations. For other elements, however, particles are a source: carbon and silicon, for example, are introduced at depths as sinking particles dissolve. Studies of both particulate concentrations by filtration of seawater and particulate fluxes by using sediment traps seem necessary to delineate the intricate nature of chemical processes in the oceans.     

Composition of saturnian stream particles

During Cassini's approach to Saturn, the Cosmic Dust Analyser (CDA) discovered streams of tiny (less than 20 nanometers) high-velocity (approximately 100 kilometers per second) dust particles escaping from the saturnian system. A fraction of these impactors originated from the outskirts of Saturn's dense A ring. The CDA time-of-flight mass spectrometer recorded 584 mass spectra from the stream particles. The particles consist predominantly of oxygen, silicon, and iron, with some evidence of water ice, ammonium, and perhaps carbon. The stream particles primarily consist of silicate materials, and this implies that the particles are impurities from the icy ring material rather than the ice particles themselves.     

Pentagonal aggregation of virus particles

Virus aggregates with a unique fivefotd axis have been observed in the electron microscope.     

Linear metal nanostructures and size effects of supported metal catalysts

Nickel metal catalysts composed of nanometer by micrometer strips have been produced with solid-state microfabrication techniques. The strips are actually the edges of nickelcatalyst thin films, which are sandwiched between separating support layers, which are also nanometers thick. These linear nanostructures constitute well-defined and well-controlled catalytic entities that reproduce the size of traditional supported metal clusters in one dimension, thus separating size from total number of atoms in the catalyst. Examination of their catalytic activity showed that they duplicate the behavior of conventional supported clusters. A specific rate maximum was observed for the hydrogenolysis of ethane at a nanoscale dimension similar to the cluster size at which the rate is maximum in the case of the supported cluster studies, whereas the hydrogenation of ethylene shows no such size dependency. The results suggest that the surface-to-volume ratio or the number of atoms in the catalytic entity cannot be the source of these size effects and that either support effects or nonequilibrium surface structures are the determining factors.     

基孔肯雅病毒样颗粒的制备

为制备高纯度、均一的基孔肯雅病毒的病毒样颗粒,将基孔肯雅病毒的结构蛋白基因序列(C-E3-E2-6K-E1)人工合成后克隆至杆状病毒-昆虫细胞表达载体中;重组质粒转化DH1OBac感受态细胞,经蓝白斑筛选和PCR鉴定,获得重组杆状病毒杆粒;重组杆状病毒杆粒转染ExpiSf9昆虫细胞,包装获得重组杆状病毒,并再次感染Ex...     

粉体棉花秸秆的应力松弛特性与模型建立

为探讨粉体棉花秸秆应力松弛特性,采集不同生长地域与环境、不同品种棉花秸秆样本22个,通过粉碎研磨使其通过孔径0.35mm筛制成试验样本,利用RGM-6010型万能材料试验机进行压缩应力松弛测试。利用Matlab软件分别对五元件广义Maxwell模型、三元件广义Maxwell模型和Peleg模型参数与试验测试数据进行拟合分析,以获取的信息量和拟合决定系数R2作为评价指标,建立粉体棉花秸秆应力松弛本构方程。试验结果表明:粉体棉花秸秆应力松弛过程呈指数规律变化并存在平衡应力;五元件广义Maxwell模型信息量大,可以精确地表征粉体棉花秸秆的应力松弛特性,拟合决定系数R2的均值达0.999,本构方程中平衡弹性模量E0均值为4.477MPa,第1应力松弛时间T1均值为4.39s,在第2应力松弛时间T2均值为48.65s;五元件广义Maxwell模型能精确完整地表征粉体棉花秸秆应力松弛特性。     

Chains of particles in shear flow

Interesting physical models of threads, rouleaux of red blood cells, and other flexible structures (including macromolecules) have been prepared with chains of spheres and discs. When suspended in a viscous liquid undergoing shear flow, the aggregates rotate as nearly rigid bodies, even though they have no tensile strength or stiffness until shear rates high enough to cause bending and then breaking are reached. By adding a second liquid phase which causes a meniscus to bridge adjacent particles, sufficient tensile strength can be provided to cause bending without breakage.     

Self-arrangement of molybdenum particles into cubes

An unusual distribution of particle sizes has been observed following the formation of molybdenum particles by argon ion sputtering. Many of the molybdenum particles produced by sputtering at the threshold pressure for particle formation in the vapor appear to be single crystalline cubes. There are two prominent peaks in the edge length distribution of the cubes, one centered at 4.8 nanometers with a halfwidth of approximately 1.3 nanometers and the other at 17.5 nanometers. The peak for the larger cubes is approximately square and has a total width of 7.0 nanometers. Evidence is presented that the larger cubes are formed by a 3 by 3 by 3 self-arrangement of the smaller cubes, which contain approximately 7000 atoms. Self-arrangement in inorganic structures is normally only observed when the building blocks are atoms, molecules, or clusters of less than 100 atoms.