AFM Study on Interface of HTHP As-grown Diamond Single Crystal and Metallic Film

The study for the interface of as-grown diamond and metallic film surrounding diamond is an attractive way for understanding diamond growth mechanism at high temperature and high pressure (HTHP), because it is that through the interface carbon atom groups from the molten film are transported to growing diamond surface. It is of great interest to perform atomic force microscopy (AFM) experiment; which provides a unique technique different from that of normal optical and electron microscopy studies, to observe the interface morphology. In the present paper,we report first that the morphologies obtained by AFM on the film are similar to those of corresponding diamondsurface, and they are the remaining traces after the carbon groups moving from the film to growing diamond. The fine particles and a terrace structure with homogeneous average step height are respectively found on the diamond(100) and (111) surface. Diamond growth conditions show that its growth rates and the temperature gradients inthe boundary layer of the molten film at HTHP result in the differences of surface morphologies on diamond planes,being rough on (100) plane and even on the (111) plane. The diamond growth on the (100) surface at HPHT could be considered as a process of unification of these diamond fine particles or of carbon atom groups recombination on the growing diamond crystal surface. Successive growth layer steps directly suggest the layer growth mechanism of the diamond (111) plane. The sources of the layer steps might be two-dimensional nuclei and dislocations.     

Contact Angle and Contact Mechanics of a Glass/Epoxy Interface

An attempt was made to extract the thermodynamic work of adhesion from contact angle measurements and contact mechanics in order to compare it with interfacial toughness values of a glass/epoxy interface. The three probe liquid method, in conjunction with laser goniometry, yielded a value of the work of adhesion of 93 mJ/m². This was an order of magnitude less than the value extracted from the Maugis solution for contacting spheres with surface interactions. These work of adhesion values were both lower than the 1.5 J/m² which was determined in a parallel study of interfacial fracture as a mode-mix independent component of the overall interfacial toughness. Some of the reasons for these differences are explored. This revised version was published online in August 2006 with corrections to the Cover Date.     

金刚石薄膜用钢基表面过渡层研究进展

介绍了影响钢基表面金刚石薄膜沉积的不利因素,分析和综述了近10年来在提高金刚石薄膜质量以及薄膜粘结性等方面所采用的各种中间过渡层及其研究进展.过渡层可采用沉积法制备,也可采用表面改性法制备.过渡层可以制备成单层膜结构,也可制备成多层膜结构.对于不同的基底材料应选择不同的过渡层.     

Mechanical and thermal behaviour of polyamide 6/silicon carbide nanocomposites toughened with maleated styrene–ethylene–butylene–styrene elastomer

Polyamide 6 (PA6) based nanocomposites reinforced with 1–7 wt% silicon carbide nanoparticles (SiC_p) and toughened with 20 wt% maleated styrene–ethylene–butylene–
stryrene (SEBS‐g‐MA) were fabricated by melt blending followed by injection moulding. The effects of SiC_p addition on thermal and mechanical properties of such nanocomposites were investigated. Differential scanning calorimetry tests showed that SiC_p act as effective nucleators for the crystallization of PA6 and enhance the degree of crystallinity. Mechanical measurements revealed that SiC_p addition improves the Young's modulus and yield strength of PA6/SEBS‐g‐MA 80/20 blend at the expenses of tensile ductility and impact strength. The essential work of fracture (EWF) approach under tensile mode was employed to characterize the fracture toughness of PA6/SEBS‐g‐MA/SiC_p nanocomposites. EWF results indicated that SiC_p addition reduces both the specific EWF and specific non‐essential plastic work of fracture. Thus SiC_p additions were detrimental to the fracture toughness of PA6/SEBS‐g‐MA 80/20 blends.     

Quantifying the Nanomachinery of the Nanoparticle–Biomolecule Interface

A study is presented of the nanomechanical phenomena experienced by nanoparticle‐conjugated biomolecules. A thermodynamic framework is developed to describe the binding of thrombin‐binding aptamer (TBA) to thrombin when the TBA is conjugated to nanorods. Binding results in nanorod aggregation (viz. directed self‐assembly), which is detectable by absorption spectroscopy. The analysis introduces the energy of aggregation, separating it into TBA–thrombin recognition and surface‐work contributions. Consequently, it is demonstrated that self‐assembly is driven by the interplay of surface work and thrombin‐TBA recognition. It is shown that the work at the surface is about ?10 kJ mol^?1 and results from the accumulation of in‐plane molecular forces of pN magnitude and with a lifetime of <1 s, which arises from TBA nanoscale rearrangements fuelled by thrombin‐directed nanorod aggregation. The obtained surface work can map aggregation regimes as a function of different nanoparticle surface conditions. Also, the thermodynamic treatment can be used to obtain quantitative information on surface effects impacting biomolecules on nanoparticle surfaces.     

Measurement of the Loss and Depolarization Probability of UCN on Beryllium and Diamond Like Carbon Films

Currently several institutes worldwide are working on the development of a new generation of ultracold neutron (UCN) sources. In parallel with source development, new materials for guiding and storage of UCN are developed. Currently the best results have been achieved using ⁵⁸Ni, Be, solid O₂ and low temperature Fomblin oil (LTF). All of these materials have their shortcomings like cost, toxicity or difficulty of use. A novel very promising material is diamond like carbon (DLC). Several techniques exist to coat surfaces, and industrial applications (e.g., for extremely hard surfaces) are already wide spread. Preliminary investigations using neutron reflectometry at PSI and Los Alamos yielded a critical velocity for DLC of about 7 m/s thus comparable to Beryllium. A low upper limit of depolarization probability for stored polarized UCN has been measured at the PF2 facility of the Institut Laue-Langevin (ILL) by North Carolina State University (NCSU), Los Alamos National Laboratory (LANL), and Petersburg Nuclear Physics Institute (PNPI), thus making it also a good material for storage and guidance of polarized UCN. Still missing is the loss probability per bounce. We will be able to extract this number and a more stringent value for the depolarization from our experiment thus proving the suitability of DLC as a wall material for a wide range of UCN applications.     

A “Sticky” Mucin‐Inspired DNA‐Polysaccharide Binder for Silicon and Silicon–Graphite Blended Anodes in Lithium‐Ion Batteries

New binder concepts have lately demonstrated improvements in the cycle life of high‐capacity silicon anodes. Those binder designs adopt adhesive functional groups to enhance affinity with silicon particles and 3D network conformation to secure electrode integrity. However, homogeneous distribution of silicon particles in the presence of a substantial volumetric content of carbonaceous components (i.e., conductive agent, graphite, etc.) is still difficult to achieve while the binder maintains its desired 3D network. Inspired by mucin, the amphiphilic macromolecular lubricant, secreted on the hydrophobic surface of gastrointestine to interface aqueous serous fluid, here, a renatured DNA‐alginate amphiphilic binder for silicon and silicon–graphite blended electrodes is reported. Mimicking mucin's structure comprised of a hydrophobic protein backbone and hydrophilic oligosaccharide branches, the renatured DNA‐alginate binder offers amphiphilicity from both components, along with a 3D fractal network structure. The DNA‐alginate binder facilitates homogeneous distribution of electrode components in the electrode as well as its enhanced adhesion onto a current collector, leading to improved cyclability in both silicon and silicon–graphite blended electrodes.     

Precipitation processes in a Mg–Zn–Sn alloy studied by TEM and SAXS

The microstructural evolution of a Mg–Zn–Sn alloy was studied by combining X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) in order to determine the individual phases, their size and volume fraction of the alloy. Solutionized and aged samples are analysed in detail concerning the nucleation, growth, morphology, and stability of precipitate phases. In the aged samples, firstly MgZn₂ particles with a rod-like shape form, and secondly plate-like MgSn₂ precipitates. The MgZn₂ phase shows a well-defined orientation relationship with the Mg matrix. The formation of two types of precipitates is responsible for the occurrence of two pronounced hardness maxima. The growth behaviour of the MgZn₂ phase is determined by combining TEM and SAXS measurements and the results are compared to the Lifschitz–Slyozov–Wagner (LSW) theory.     

Interface evolution in the platelet-like SiC@C and SiC@SiO<Subscript>2</Subscript> monocrystal nanocapsules

Carbon-coated SiC@C nanocapsules (NCs) with a hexagonal platelet-like morphology were fabricated by a simple direct current (DC) arc-discharge plasma method.The SiC@C NCs were monocrystalline,120-150 nm in size,and approximately 50 nm thick.The formation of the as-prepared SiC@C NCs included nucleation of truncated octahedral SiC seeds and subsequent anisotropic growth of the seeds into hexagonal nanoplatelets in a carbon-rich atmosphere.The disordered carbon layers on the SiC@C NCs were converted into SiO2 shells of SiC@SiO2 NCs by heat treatment at 650 ℃ in air,during which the shape and inherent characteristics of the crystalline SiC core were obtained.The interface evolution from carbon to SiO2 shells endowed the SiC@SiO2 NCs with enhanced photocatalytic activity due to the hydrophilic and transparent nature of the SiO2 shell,as well as to the photosensitive SiC nanocrystals.The band gap of the nanostructured SiC core was determined to be 2.70 eV.The SiC@SiO2 NCs degraded approximately 95％ of methylene blue in 160 min under visible light irradiation.     

Incorporation of amorphous and microcrystalline silicon in n–i–p solar cells

We have investigated the material properties and n–i–p solar cell quality of hot-wire deposited amorphous and microcrystalline silicon. Although it is possible to make high quality amorphous silicon solar cells, occasionally many cells show shunting behavior. Therefore, better control over the variation in cell performance is needed. We prove that this behavior is correlated with the filament age and different methods for improving the reproducibility of the cell performance are presented. Furthermore, the influence of different deposition parameters of microcrystalline silicon layers on the material and solar cell properties was studied. Although some of these microcrystalline layers are porous and oxidize in air, an initial efficiency of 4.8% is obtained for an n–i–p cell on untextured stainless steel.     

温度对金刚石刀具影响的理论模型和实验分析

为减小大型金属反射镜在金刚石车削中,刀具的热变形对加工精度的影响,研究了金刚石刀具在温度影响下的热变形规律,结合俄罗斯在热力学方面的研究成果,根据金刚石晶体和刀体的热膨胀系数和导温系数的不同,建立了刀具变形量随温度变化的理论计算模型,并采用高精度的热像仪和电感测微仪记录刀具的温度变化和变形量,发现当温度从23．4℃升高到32．1℃时,刀具变形量达到1．48μm．