Molecular dynamics study of plastic deformation mechanism in Cu/Ag multilayers

The plastic deformation mechanism of Cu/Ag multilayers is investigated by molecular dynamics(MD) simulation in a nanoindentation process. The result shows that due to the interface barrier, the dislocations pile-up at the interface and then the plastic deformation of the Ag matrix occurs due to the nucleation and emission of dislocations from the interface and the dislocation propagation through the interface. In addition, it is found that the incipient plastic deformation of Cu/Ag multilayers is postponed, compared with that of bulk single-crystal Cu. The plastic deformation of Cu/Ag multilayers is affected by the lattice mismatch more than by the difference in stacking fault energy(SFE) between Cu and Ag. The dislocation pile-up at the interface is determined by the obstruction of the mismatch dislocation network and the attraction of the image force. Furthermore, this work provides a basis for further understanding and tailoring metal multilayers with good mechanical properties, which may facilitate the design and development of multilayer materials with low cost production strategies.     

Microstructure,indentation and work hardening of Cu/Ag multilayers

Instrumented indentation and tensile tests were performed on free standing Cu/Ag multilayer thin films with layer thicknesses in the range 0.85–900?nm. The effect of layer thickness can be described by a Hall–Petch relationship. The work-hardening rate in the tensile test depends on layer thickness, which indicates that the interfaces create storage sites for dislocations and follows an inverse power law.     

Temperature‐dependent thermal properties of Ru/C multilayers

Multilayers made of Ru/C are the most promising candidates when working in the energy region 8–20 keV. The stability of its thermal properties, including thermal expansion and thermal conduction, needs to be considered for monochromator or focusing components. Ru/C multilayers with periodic thicknesses of 3, 4 and 5 nm were investigated in situ by grazing‐incidence X‐ray reflectometry and diffuse scattering in order to study their thermal expansion characteristics as a function of annealing temperature up to 400°C. The thermal conductivity of multilayers with the same structure was also measured by the transient hot‐wire method and compared with bulk values.     

磁控溅射制备的W,WSi2,Si单层膜和W/Si,WSi2/Si多层膜应力

采用直流磁控溅射技术制备了厚度约100 nm的W,WSi2,Si单层膜和周期约为20 nm,Si膜层厚度与周期的比值为0.5的W/Si,WSi2/Si周期多层膜.利用台阶仪对镀膜前后基底表面的面形进行了测试,计算并比较了不同膜系的应力值.结果表明:W单层膜表现出较大的压应力,而W/Si周期膜则表现为张应力.WSi2单层...     

Finite-element analysis of the mechanical behavior of Au/Cu and Cu/Au multilayers on silicon substrate under nanoindentation

Finite-element analysis of the nanoindentation into Au/Cu and Cu/Au multilayers was performed to deduce their mechanical characteristics from nanoindentation response. Different bilayer thicknesses, numbers, and sequences were studied using the load–displacement curve, hardness, indentation, and the residual surface profile as well as the von Mises equivalent stress. The characteristics of the multilayers were found to be dispersed between the Au and Cu. Nevertheless, if the indentation depth is smaller than the uppermost individual layer thickness of the multilayers, the intrinsic properties can be obtained. Using the von Mises equivalent stress as a failure criterion, the results showed that thinner multilayers would induce a greater potential of shear banding deformation. PACS 61.43.Bn; 62.20.-x; 68.03.Hj; 68.05.Cf; 68.08.De     

CoFe/TiZr多层膜材料界面结构与性能的极化中子反射研究

利用极化中子反射技术较系统地研究了CoFe/TiZr复合多层膜材料界面结构，结果表明.1)从多层膜超镜传输特性角度考虑，等厚对层不如非等厚对层膜结构好.2)等厚对层的最佳退火温度约250℃，非等厚对层退火温度低于250℃影响不明显，等厚和非等厚对层经350℃退火后膜层变化严重.3)从布拉格峰位变化看，随着退火温度的升高，等厚对层膜的厚度先变小后变大；非等厚对层与之相反.     

CoFe/TiZr多层膜材料界面结构与性能的极化中子反射研究

利用极化中子反射技术较系统地研究了CoFe/TiZr复合多层膜材料界面结构,结果表明.1)从多层膜超镜传输特性角度考虑,等厚对层不如非等厚对层膜结构好.2)等厚对层的最佳退火温度约250℃,非等厚对层退火温度低于250℃影响不明显,等厚和非等厚对层经350℃退火后膜层变化严重.3)从布拉格峰位变化看,随着退火温度的升高,等厚对层膜的厚度先变小后变大;非等厚对层与之相反. 关键词： CoFe/TiZr多层膜 退火影响 膜层结构 极化中子反射     

Thermodynamic instability of Ag/Au and Cu/Pd metal superlattices

We show how the formation energies of A_pB_q superlattices with arbitrary periods p and q and layer orientation Ĝ can be predicted via a 'cluster expansion' technique, given the formation energies of short period structures from first-principles calculations. We predict both bulk and epitaxial energies as well as the energies of the fully intermixed (alloyed) superlattices. Applications to Ag/Au and Cu/Pd superlattices illustrate our method, as well as a global classification scheme for superlattice stability.     

Fluence-dependent radiation damage in helium (He) ion-irradiated Cu/V multilayers

We have explored the capacity of Cu/V interfaces to absorb helium ion radiation-induced defects spanning a peak damage range of 0.6–18 displacements per atom (dpa). The study provides evidence of alleviated nucleation of He bubbles in the multilayer films from Cu/V 50?nm to Cu/V 2.5 nm. Layer interfaces are retained in all irradiated specimens. Peak bubble density increases monotonically with fluence, and is lower in multilayers with smaller individual layer thickness. Radiation hardening decreases with decreasing layer thickness and appears to reach saturation upon peak radiation damage of 6?dpa. Size- and fluence-dependent radiation damage in multilayers is discussed.     

Mo/Si multilayers used for the EUV normal incidence solar telescope

This paper first reviews an EUV normal incidence solar telescope that we have developed in our lab. The telescope is composed of four EUV telescopes and the operation wavelengths are 13.0 nm, 17.1 nm, 19.5 nm, and 30.4 nm. These four wavelengths, fundamental to the research of the solar activity and the atmosphere dynamics, are always chosen by the EUV normal incidence solar telescope. In the EUV region, almost all materials have strong absorption, so optics used in this region must be coated by the multila...     

Microstructures and strengthening mechanisms of Cu/Ni/W nanolayered composites

Cu/Ni/W nanolayered composites with individual layer thickness ranging from 5?nm to 300?nm were prepared by a magnetron sputtering system. Microstructures and strength of the nanolayered composites were investigated by using the nanoindentation method combined with theoretical analysis. Microstructure characterization revealed that the Cu/Ni/W composite consists of a typical Cu/Ni coherent interface and Cu/W and Ni/W incoherent interfaces. Cu/Ni/W composites have an ultrahigh strength and a large strengthening ability compared with bi-constituent Cu–X (X?=?Ni, W, Au, Ag, Cr, Nb, etc.) nanolayered composites. Summarizing the present results and those reported in the literature, we systematically analyze the origin of the ultrahigh strength and its length scale dependence by taking into account the constituent layer properties, layer scales and heterogeneous layer/layer interface characteristics, including lattice and modulus mismatch as well as interface structure.     

Thickness‐dependent structural characteristics for a sputtering‐deposited chromium monolayer and Cr/C and Cr/Sc multilayers

The interior structure, morphology and ligand surrounding of a sputtering‐deposited chromium monolayer and Cr/C and Cr/Sc multilayers are determined by various hard X‐ray techniques in order to reveal the growth characteristics of Cr‐based thin films. A Cr monolayer presents a three‐stage growth mode with sudden changes occurring at a layer thickness of ～2 nm and beyond 6 nm. Cr‐based multilayers are proven to have denser structures due to interfacial diffusion and layer growth mode. Cr/C and Cr/Sc multilayers have different interfacial widths resulting from asymmetry, degree of crystallinity and thermal stability. Cr/Sc multilayers present similar ligand surroundings to Cr foil, whereas Cr/C multilayers are similar to Cr monolayers. The aim of this study is to help understand the structural evolution regulation versus layer thickness and to improve the deposition technology of Cr‐based thin films, in particular for obtaining stable Cr‐based multilayers with ultra‐short periods.     

Anisotropy of the optical and magneto-optical response of Au/Co/Au/Cu multilayers grown on vicinal Si (111) surfaces

The optical and magneto-optical second harmonic reflectivity response of Au/Co/Au/Cu multilayers grown on vicinal Si (111) substrates has been studied. These azimuthal optical non-linear experiments check the uniaxial character of the crystallinity of the Au buffer layer and the magnetic behavior of the ultrathin Co films in the metallic multilayer. They clearly show the strong dependence of the growth parameters and the misorientation of the vicinal surface on the SHG reflectivity signals. This uniaxial behavior is also correlated to linear MOKE experiments on the magnetic anisotropy with an easy magnetization axis parallel to the step edges. Received: 16 October 2001 / Published online: 29 May 2002     

Orientation-dependent deformation mechanisms of bcc niobium nanoparticles

Nanoparticles usually exhibit pronounced anisotropic properties, and a close insight into the atomic-scale deformation mechanisms is of great interest. In present study, atomic simulations are conducted to analyse the compression of bcc nanoparticles, and orientation-dependent features are addressed. It is revealed that surface morphology under indenter predominantly governs the initial elastic response. The loading curve follows the flat punch contact model in [1 1 0] compression, while it obeys the Hertzian contact model in [1 1 1] and [0 0 1] compressions. In plastic deformation regime, full dislocation gliding is dominated in [1 1 0] compression, while deformation twinning is prominent in [1 1 1] compression, and these two mechanisms coexist in [0 0 1] compression. Such deformation mechanisms are distinct from those in bulk crystals under nanoindentation and nanopillars under compression, and the major differences are also illuminated. Our results provide an atomic perspective on the mechanical behaviours of bcc nanoparticles and are helpful for the design of nanoparticle-based components and systems.     

CoFeB/Pt多层膜的垂直磁各向异性研究

具有垂直磁各向异性的磁性纳米结构是自旋转移力矩器件的重要研究内容, 本文采用反常霍尔效应系统地研究了磁控溅射法制备的[CoFeB/Pt]_n多层膜的垂直磁各向异性. 当CoFeB的厚度小于0.6 nm时, 可以在[CoFeB/Pt]_n多层膜中观察到清晰的垂直磁各向异性, 其垂直磁各向异性强烈依赖于CoFeB和Pt层厚度及多层膜周期数. 当多层膜周期数n ≥ 5时, 出现零剩磁现象. 另外, [CoFeB/Pt]_n多层膜的矫顽力均小于2 kA·m^-1, 有望作为垂直自由层的重要侯选材料应用于垂直磁纳米结构中.     

Nucleation and growth of bubbles in He ion-implanted V/Ag multilayers

Microstructures of He ion-implanted pure Ag, pure V and polycrystalline V/Ag multilayers with individual layer thickness ranging from 1?nm to 50?nm were investigated by transmission electron microscopy (TEM). The bubbles in the Ag layer were faceted and larger than the non-faceted bubbles in the V layer under the same implantation conditions for both pure metals and multilayers. The substantially higher single defects surviving the spike phase and lower mobility of trapped He in bcc than those in fcc could account for this difference. For multilayers, the bubbles nucleate at interfaces but grow preferentially in Ag layers due to high mobility of trapped He in fcc Ag. In addition, the He concentration above which bubbles can be detected in defocused TEM images increases with decreasing layer thickness, from 0 for pure Ag to 4–5 at. % for 1?nm V/1?nm Ag multilayers. In contrast, the bubble size decreases with decreasing layer thickness, from approximately 4?nm in diameter in pure Ag to 1?nm in the 1?nm V/1?nm Ag multilayers. Elongated bubbles confined in the Ag layer by the V–Ag interfaces were observed in 1?nm multilayers. These observations show that bubble nucleation and growth can be suppressed to high He concentrations in nanoscale composites with interfaces that have high He solubility.     

Anomalous mechanical characteristics of Au/Cu nanocomposite processed by Cu electroplating

An Au/Cu nanocomposite is produced by electroplating Cu on a nanoporous Au, and its mechanical characteristics are investigated by hardness tests. The Au/Cu nanocomposite showed a lower hardness and a lower elastic modulus than the nanoporous Au. Furthermore, annealing caused the nanocomposite to harden twice. Large lattice strains in the Au lattice for the nanocomposite were observed by high-resolution transmission electron microscopy. Also, first-principle calculations showed that lattice strains induce the decreased elastic modulus. Therefore, both the inverse mixing behaviour and the hardening via annealing are suggested to be related to the large lattice strains.     

磁控溅射制备极紫外高反射率多层膜应力研究

为制备硼边附近6.7 nm波长的极紫外高反射率多层膜反射镜,研究了Mo2C/B4C,Mo/B4C周期多层膜,重点解决薄膜应力难题。采用直流磁控溅射技术制备了膜层厚度为30 nm的Mo,Mo2C,B4C单层膜,周期厚度为3.5 nm,30对的Mo2C/B4周期多层膜。利用台阶仪测试了镀膜前后基底面形,计算并比较了不同薄膜样品的应力值。结果表明Mo2C/B4C多层膜压应力要远小于Mo/B4C多层膜,且成膜质量与Mo/B4C相当。因此Mo2C/B4C是应用于6.7 nm反射镜较好的多层膜材料组合。C,Mo/B4C