Highly adhesive calcium phosphate layer on UHMWPE prepared by IBAD

A study has been made on adhesive strength and chemical states of calcium phosphate layer deposited on the surface of ultra-high molecular weight polyethylene (UHMWPE) by ion beam assisted deposition (IBAD). IBAD is well known to be able to give an atomic intermixed zone at layer/substrate interface during deposition. The X-ray diffraction (XRD) results demonstrated that the main structure is amorphous calcium phosphate (ACp) in the layer. Tape test and scratch test were used to measure the adhesive strength between layer and substrate. Both results show that the adhesive strength between layer and substrate of samples prepared by IBAD is much stronger than that of contrast samples prepared by ion beam sputtering deposition (IBSD). It has been found by XPS that there are much more stable covalent bonds between layer and substrate in IBAD samples than that in IBSD samples. The results above lead us to a conclusion that besides the atomic intermixed zone at the interface, the increment of covalent bonds between layer and substrate also enhanced the adhesive strength between layer and substrate in IBAD samples.     

Trends in the spectral distribution of the absorption coefficient of complex organic molecules

General trends in formation of the observed vibrational spectra are analyzed by calculating spectral distributions of the absorption coefficient in the IR region for 45 molecules of different classes ignoring the electrooptical paramaters of particular bonds and structural groups. It is shown that for many molecules, only vibrations of peripheral X-H bonds make a prevailing contribution to the total integral absorption in a wide spectral range. The effect of increasing intensities of some bands is clearly observed for skeleton vibrations, when optical parameters of external X-H bonds are zero. V. I. Vernadski Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences, 19, Kosygin St., Moscow, 117975, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 491–496, July–August, 1998.     

Study of Diffusion Bonding of 45 Steel through the Compacted Nickel Powder Layer

The microstructure of the transition zone and powder spacer, the concentration distribution of chemical elements over the width of the diffusion-bonded joint, and microhardness of 45 steel–compacted Ni powder spacer–45 steel layered composites formed by diffusion bonding have been investigated. It has been shown that the relative spacer thickness χ < 0.06 is optimal for obtaining a high-quality joint has been formed under a compacting pressure of 500 MPa. The solid-state diffusion bonding is accompanied by sintering the nickel powder spacer and the formation of the transition zone between the spacer and steel. The transition zone consists of solid solution of nickel in the α-Fe phase and ordered solid solution of iron in nickel (FeNi₃).     

Atomistic Failure Mechanism of Single Wall Carbon Nanotubes with Small Diameters

Single wall carbon nanotubes with small diameters （〈 5.0 A） subjected to bending deformation are simulated by orthogonal tight-binding molecular dynamics approach. Based on the calculations of C-C bond stretching and breaking in the bending nanotubes, we elucidate the atomistic failure mechanisms of nanotube with small diameters. In the folding zone of bending nanotube, a large elongation of C-C bonds occurs, accounting for the superelastic behaviour. The C-C bonds parallel to the axis direction of nanotube are broken firstly due to the sustained longitudinal stretching strain, giving rising to forming one-notch or two-notch bond-breaking mode depending on nanotube chirMities. The direct bond-breaking mechanism is responsible for the brittle fracture behaviour of nanotubes with small diameters.     

Dynamics of the strength of adhesive-bond joints between polymers and steel

We have investigated the time dependences of the strength of adhesive bonds between polymers (epoxy adhesive and polyamide) and steel 45 at various temperatures. These dependences have been determined based on the rates of two opposite processes, viz., an increase in strength due to the formation of coordination bonds between polymer molecules and Fe²⁺ ions and a decrease in strength due to ruptures of adhesive or polyamide molecules under the effect of internal stresses. The values of activation energy of these processes have been determined.     

石墨烯/铝基复合材料在纳米压痕过程中位错与石墨烯相互作用机制的模拟研究

石墨烯因其优异的力学性能已成为增强金属基复合材料的理想增强体.然而,目前对石墨烯/金属基复合材料在纳米压痕过程中嵌入石墨烯与位错之间的相互作用仍不清晰.本文采用分子动力学模拟方法,对90°,45°和0°位向的石墨烯/铝基复合材料进行了纳米压痕模拟,研究了压痕加载和卸载过程中石墨烯/铝基复合材料的位错形核及演化,以获取不同位向的石墨烯与位错的相互作用机制,并分析其对塑性区的影响.研究发现,石墨烯可以有效阻碍位错运动,并且石墨烯会沿着位错滑移方向发生弹性变形.在纳米压痕过程中,位错与不同位向石墨烯之间的相互作用差异导致塑性区的变化趋势不同.研究结果表明,在石墨烯/铝基复合材料中,位向不同的石墨烯对位错阻碍强度和方式不同,且石墨烯位向为45°的复合材料的硬度高于其他模型.此外,石墨烯/铝基复合材料的位错线总长度的演化规律与石墨烯位向紧密相关.本文研究可为设计和制备高性能石墨烯/金属基复合材料提供一定的理论指导.     

氢气区熔硅单晶氢致缺陷的研究

本文应用X射线透射截面形貌技术研究了氢气区熔硅单晶中氢致缺陷与热处理温度的关系。根据早期氢致缺陷的X射线形貌图衍衬分析,指出氢沉淀周围晶格受到压缩性应变,并简单阐述了硅氢键断裂与氢致缺陷形成过程。 关键词：     

Compound Fresnel Zone Lens Conformal to Truncated Cone: Antenna Application

A millimeter wave antenna consisting of two Fresnel zone plate lenses, plane and conical, is examined numerically by use of the vector diffraction theory. The lenses are of Wood-Wiltse (double-dielectric) or Soret (half-open) type, and are designed for the frequency of 117 GHz. The lenses are made conformal to a truncated circular cone with a base diameter of 500 mm and a plateau diameter of 250 mm. Designs for two opening semi-angles, 45° and 75° each of them with a particular lens thickness are presented. For the angle of 90° the cone lens becomes a plane ring lens, which in combination with the plateau zone lens forms a plane lens of size equal to the cone base diameter. Illuminated by directive feeds set at a focal distance of 525 mm from the cone apex, the double-dielectric and half-open compound and plane lenses, form three pairs of Fresnel zone lens antennas, the co-polar and cross-polar radiation characteristics of which have been compared numerically. The double-dielectric lens antennas examined are about 5 dB superior in gain to the half-open lens antennas, which has a gain of approximately 45 dBi. Because all lenses are of equal transverse aperture, the corresponding lens antennas exhibit the same −3 dB beamwidth of about 0.33 degrees. The plane zone lens antenna is very thin and simple. Instead, the antenna comprising a 3-D compound Fresnel zone lens is thicker but can be made conformal to a specific surface shape and possesses more levels of design and optimization freedom.     

紫外光固化暗反应过程中CC双键转化率的红外光谱研究

利用红外光谱分析技术,测定了紫外光固化体系中CC双键在1 648～1 589 cm-1 特征吸收峰面积,以此研究紫外光辐照后暗反应过程中的CC双键转化率。系统地考察了光引发剂、活性稀释剂和光敏树脂等对紫外光固化暗反应的影响。研究结果表明：在45 s的紫外光辐照后,体系中40%～85%的CC双键转化是在暗反应过程中完成的,暗反应在1.75 h以后趋于平缓,但要达到95%的CC双键转化率则需要24 h以上。体系中CC双键的转化速率和最终转化率受光引发剂的种类和用量、氧阻效应以及活性稀释剂的官能度影响较大,而光敏树脂的种类及其官能度只影响转化速率,但对最终转化率影响不大。     

Electronic structure of Li3GaN2

First principles calculations, by means of the full-potential linearized augmented plane wave method within the local density approximation, were carried out for the electronic properties of Li₃GaN₂. The calculated lattice parameter is in good agreement with the measured one. The bandgap is direct at the Brillouin zone centre. The Li-N and Ga-N bonds are both ionic with a small covalent character of the latter one.     

化学键对闪锌矿型晶体能带结构的影响

本文在Slater与Koster的简化原子轨道线性组合方法的基础上,引入了化学键的参量。将布里渊区的某些特殊点的能级表示为这些参量的函数。讨论了禁带宽度与导带最小点之位置随化学组成的变化而变化的情况。得到的结果与已有事实定性符合。     

Vibration spectra and the valence force field of the LiCuVO<Subscript>4</Subscript> crystal

Polarized Raman spectra of single-crystal LiCuVO₄ containing quasi-one-dimensional cuprate chains are measured. The force constants of the valence force field are calculated for the phonon modes at the center of the Brillouin zone with an accuracy sufficient to describe the experiment. From the results, it follows that the crystal contains rigid Cu-O-V-Cu-O-V structural rings with a charge distributed along their bonds.     

Chemical bond formation during laser bonding of Teflon FEP and titanium

Teflon^® FEP (fluorinated ethylene propylene) is resistant to most chemical solvents, is heat sealable and has low moisture uptake, which make this polymer attractive as a packaging materials for electronics and implantable devices. Teflon^® FEP/Ti microjoints were fabricated by using focused infrared laser irradiation. Teflon^® FEP/Ti interfaces were studied by using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). The XPS results give evidence for the formation of Ti-F bonds in the interfacial region. The AES and SEM-EDS results show that the chemical bond formation occurs only in the actual bond area. No evidence for chemical bond formation was found in the heat affected zone surrounding the laser bonds.     

Research on identifying the order of fringe pattern traces using angular scan and zone search method

A method for automatically identifying the order of fringe pattern traces is presented. It uses the simplified Otsu algorithm for obtaining the threshold, the angular scan in the range of 45~ for searching the trace positions, and the zone search technique for identifying different traces. Experimental results show that the proposed method may reliably obtain the order of fringe pattern traces orientating from almost 45° to 90°.     

Determination of the lattice vibrations of imidazole by neutron scattering

The external molecular vibrations of deuterated imidazole have been investigated at 12 K for wave vectors along the three principal directions of the Brillouin zone by neutron scattering and by Raman scattering at the zone center. A complete symmetry assignment is obtained. The dominant role of the N-H … N hydrogen bond within the intermolecular interactions is reflected in a relatively simple manner in the shape of the dispersion curves because of the chain-like arrangement of hydrogen bonds. The experiment yields directly a stretching force constant of 0.33 mdyn Å^?1 for this bond. This value is compatible with monopole-dipole and dipole-dipole interactions as major contributions to the attractive interactions of the hydrogen bond of this length (2.86 Å). Relatively strong static monopoles and dipoles are confirmed by a $\text{CNDO}\text{2}$ calculation and are consequently incorporated into the interaction model.     

氢气氛区熔硅单晶热处理缺陷形成机理

本文用X射线衍射形貌法、红外吸收光谱法和金相腐蚀坑法,探讨了氢气氛区熔硅单晶热处理缺陷的形成机理。在生长态晶体中存在着三种Si-H键,对应的红外吸收峰波长分别为4.55微米、4.75微米和5.13微米。随着加热过程的进行,Si—H键逐渐分解而消失。5.13微米吸收峰的消失温度是450℃,4.55微米吸收峰的消失温度是600℃,4.75微米吸收峰的消失温度是700℃。晶体中的热处理缺陷是由于氢沉淀造成的,沉淀过程首先是Si—H键分解,然后是氢的扩散和聚集。沉淀过程的激活能是2.4电子伏特(56000卡/克分 关键词：     

LEED study of the stepped surface of vicinal Si (100)

Periodic stepped surfaces prepared on vicinal silicon (100) by ion bombardment and annealing have been studied by LEED. An unusual aspect of the diffraction patterns from [01&#x0304;1] zone samples was the presence of fractional order multiplets with half the splitting of the integral order doublets. An explanation is given, based on the superposition of diffraction from three distinct domain types. These differ in the orientations of their dangling bonds and the arrangements of successive terraces. The simpler patterns from [001] zone samples evidenced just two reconstruction domains. All non-integral order beams disappeared when samples were exposed to ionized hydrogen. This facilitated both the identification of certain lattice distortions, and the determination of step heights, which were found to be two atomic layers in all cases.     

Study on the softening in overlapping zone by laser-overlapping scanning surface hardening for carbon and alloyed steel

Softening in overlapping passes by laser-overlapped scanning surface hardening is a difficult problem of laser surface modification. Despite the advantage of laser quenching, softening in overlapping zone limits its practical application. In this paper, 45, 9Cr2Mo and W18Cr4V steel were hardened by laser-overlapping quenching. Softening occurred in all overlapping zones. The results of hardness testing indicated the softening width of 45 steel was the broadest and that of W18Cr4V steel was the narrowest. Different mixed microstructures composed the overlapping zone for three steels, i.e., tempered sorbite and a little tempered martensite in 45 steel, tempered martensite, tempered sorbite and a small amount of carbides in 9Cr2Mo steel, tempered martensite and a little carbide in W18Cr4V steel. The effect of activation energy of diffusion for carbon in steel and cooling rate on the decomposition of martensite have been investigated by developing a diffusion model based on the principle of carbon diffusion in martensite. The results indicated that action energy for diffusion of carbon in steel plays a main role in hindering decomposition of carbide and cooling rate has a limited action in reducing temper softening during laser-overlapping scanning.     

Experimental band structure of GaSe obtained by angular resolved photoemission

A very detailed experimental band structure of the layered compound GaSe has been obtained in all the symmetry directions of the Brillouin zone for photon energy varying between 21 and 45 eV. It is shown that in this energy range the dispersion curves E (K//) are independent of the final state and that it is also possible, assuming a free electron like conduction band, to have information along the normal to the layers.     

经ORC处理银衬底上核酸碱基的SERS研究

利用天线共振子模型对银的表面增强喇曼散射(SERS)特性进行了计算和分析.结果显示，银增强因子在近红外的1.38 eV处为最大，达140以上；近紫外3.35 eV、3.90 eV、4.30 eV位置处依次减小，分别为60、48、45；而在可见光区，银增强因子的最大值为70. 在经氧化还原过程(ORC)处理的银片上做了核酸碱基腺嘌呤、尿嘧啶的SERS谱，腺嘌呤的SERS谱虽然存在荧光的影响，但SERS效应明显.尿嘧啶的SERS谱出现4个明锐的峰值，1035 cm－1是所出现的最强的模式，该模式应是尿嘧啶在核酸中存在的SERS环呼吸模式，可作为检测尿嘧啶存在的判定依据.