基于多尺度模拟研究Ni/Cu薄膜压痕塑性的原子机制

基于准连续介质多尺度模拟方法研究了Ni/Cu双层薄膜初始压痕塑性的原子机制,结果主要包括:(1)当Ni晶体层厚度小于10nm时,随着Ni晶体层厚度的减少,薄膜弹性极限所对应的临界接触力逐渐降低,即Ni/Cu薄膜随Ni晶体层厚度减小而变软;(2)压头下方晶格Shockley分位错的开动、界面位错的分解、以及界面位错与晶格位错的相互作用是Ni/Cu薄膜初始塑性的微观原子机制,(3)根据模拟结果观察和位错弹性理论计算,承载初始塑性的界面位错数目变少是Ni/Cu薄膜软化的主要原子机制.本文研究结果能够为异质界面力学行为研究提供有益参考.     

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.     

Interface dislocation structures at the onset of coherency loss in nanoscale Ni–Cu bilayer films

We have performed a transmission electron microscopy study, using weak beam imaging, of the interface dislocation arrays that form initially at the (001) Ni–Cu interface during coherency loss. Interface dislocations were absent in the 2.5?nm Ni/100?nm Cu bilayers, but were present in the 3.0?nm Ni samples, indicating that the critical Ni film thickness for coherency loss is between 2.5 and 3?nm. The key features of the interface dislocation structure at the onset of coherency loss are: (i) the majority of interface dislocations are 60° dislocations, presumably formed by glide of threading dislocations in the coherently stressed Ni layer, and have Burgers vector in the {111} glide plane; (ii) the interface contained approximately 5% Lomer edge dislocations, with Burgers vector in the {001} interface plane, and an occasional Shockley partial dislocation and (iii) isolated segments of interface dislocations terminating at the surface are regularly observed. Possible mechanisms that lead to these dislocation configurations at the interface are discussed. This experimental study shows that near the critical thickness, accumulation of interface dislocations occurs in a somewhat stochastic fashion with favourable regions where coherency is first lost.     

GaN基紫光LED的高反射率p型欧姆接触

研究用于GaN基大功率倒装焊(Flip-chip)紫光LED(UV-LED)的高反射率p型欧姆接触的电学和光学性能。用磁控溅射的方法在GaN基LED外延片表面沉积了不同厚度Ag,Al,Au和Pd四种金属,测量了样品的反射率和透射率。结合同步辐射高强度X射线衍射和AFM对金属薄膜的晶体结构进行分析,并对表面形貌进行了观测,对由金属薄膜构成的多层膜结构及其对光反射率的作用机理进行了研究。测量结果表明,在入射光波长为400nm时,Ni/Au/Ag和Ni/Au/Al电极的反射率比Ni/Au的反射率提高了三倍。同时与p-GaN有良好的欧姆接触特性。     

低接触电阻率Ni/Ag/Ti/Au反射镜电极的研究

研究了Ag的厚度、退火时间、沉积温度对于Ni/Ag/Ti/Au电极的反射率及与p-GaN欧姆接触性能的影响. 利用分光光度计测量反射率, 采用圆形传输线模型计算比接触电阻率. 结果表明: 随着Ag厚度的增加, Ni/Ag/Ti/Au电极的反射率逐渐增大; 在氧气氛围中, 随着退火时间从1 min增至10 min, 300 ℃退火时, 比接触电阻率持续下降, 而对于400-600 ℃退火, 比接触电阻率先减小后增大; 在300和400 ℃氧气中进行1-10 min 的退火后, Ni/Ag/Ti/Au的反射率变化较小, 退火温度高于400 ℃时, 随着退火时间的增加, 反射率急剧下降; 在400 ℃氧气中3 min退火后, 比接触电阻率可以达到3.6×10^-3 Ω·cm². 此外, 适当提高沉积温度可以增加Ni/Ag/Ti/Au的反射率并降低比接触电阻率, 沉积温度为120 ℃条件下的Ni/Ag/Ti/Au电极在450 nm处反射率达到90.1%, 比接触电阻率为6.4×10^-3 Ω·cm². 综合考虑电学和光学性能, 在沉积温度为120 ℃下蒸镀Ni/Ag/Ti/Au (1/200/100/100 nm)并在400 ℃氧气中进行3 min退火可以得到较优化的电极. 利用此电极制作的垂直结构发光二极管在350 mA电流下的工作电压为2.95 V, 输出光功率为387.1 mW, 电光转换效率达到37.5%.     

Effect of interface structure on deformation behavior of crystalline Cu/amorphous CuZr sandwich structures

The effect of interface types (namely, sharp interface and graded interface) and its thickness on the deformation behavior of crystalline/amorphous/crystalline sandwich structures (CACSSs) under tensile loading are studied using molecular dynamics simulation. Compared with the CACSSs with sharp interface, the CACSSs with gradient interface consistently exhibit good plasticity when the interface thickness is larger than 6 nm, due to the coupling effects among crystalline layer, amorphous layer and crystalline–amorphous interface. With the increase of interface thickness, the plastic deformation mechanism of CACSSs with gradient interface changes from the local plastic deformation in amorphous layer to the homogeneous plastic deformation.     

Synthesis of NiAu alloy and core–shell nanoparticles in water-in-oil microemulsions

NiAu alloy nanoparticles with various Ni/Au molar ratios were synthesized by the hydrazine reduction of nickel chloride and hydrogen tetrachloroaurate in the microemulsion system. They had a face-centered cubic structure and a mean diameter of 6–13 nm, decreasing with increasing Au content. As Au nanoparticles did, they showed a characteristic absorption peak at about 520 nm but the intensity decreased with increasing Ni content. Also, they were nearly superparamagnetic, although the magnetization decreased significantly with increasing Au content. Under an external magnetic field, they could be self-organized into the parallel lines. In addition, the core–shell nanoparticles, Ni₃Au₁@Au, were prepared by the Au coating on the surface of Ni₃Au₁ alloy nanoparticles. By increasing the hydrogen tetrachloroaurate concentration for Au coating, the thickness of Au shells could be raised and led to an enhanced and red-shifted surface plasmon absorption.     

Soft X-ray photoelectron spectroscopic investigation of Au-deposited amorphous In–Ga–Zn–O thin-film surface

Thin Au layers (0.04 nm, 0.06 nm, 0.08 nm, 0.21 nm) were deposited on an amorphous In–Ga–Zn–O (a-IGZO) thin-film surface by thermal evaporation in an ultrahigh vacuum. The chemical-state changes of the Au layer and the a-IGZO surface were investigated by measuring the Au 4f, O 1s, In 3d, Ga 3d and Zn 3d peaks as well as the valence bands by soft X-ray photoelectron spectroscopy. Upon initial deposition, an oxidized Au component formed, whereas a metallic Au component was dominant. At the later deposition stages, the metallic Au component dominated the spectral features. When the Au thickness was thicker than 0.08 nm, a split Au 5d feature was apparent. And as the Au thickness continued to increase, In 3d showed a strong lower-binding-energy (lower-BE) component; the Ga 3d and Zn 3d also showed lower-BE components, but of much reduced intensities relative to In 3d. These results seem to imply that compared with other elements, Au atoms prefer to occupy oxygen vacancies and strongly interact with In atoms.     

High-Temperature Characteristics of Ti/Al/Ni/Au Ohmic Contacts to n-GaN

We present the high-temperature characteristics of Ti/Al/Ni/Au（15 nm/220 nm/40 nm/50 nm） multiplayer contacts to n-type GaN （Nd = 3.7 × 10^17 cm^-3, Nd = 3.0 × 10^18 cm^-3）. The contact resistivity increases with the measurement temperature. Furthermore, the increasing tendency is related to doping concentration. The higher the doped, the slower the contact resistivity with decreasing measurement temperature. Ti/Al/Ni/Au ohmic contact to heavy doping n-GaN takes on better high temperature reliability. According to the analyses of XRD and AES for the n-GaN/Ti/Al/Ni/Au, the Au atoms permeate through the Ni layer which is not thick enough into the AI layer even the Ti layer.     

Effect of Au interlayer thickness on the structural,electrical, and optical properties of GZO/Au/GZO multilayers

We report on the structural, electrical, and optical properties of Ga-doped ZnO/Au/Ga-doped ZnO (GZO/Au/GZO) multilayers as a function of Au interlayer thickness. Aggregated Au islands formed a continuous film as the thickness of the Au interlayer increased from 3 to 12 nm. Consequently, the sheet resistance, resistivity, and optical transmittance decreased with increasing Au interlayer thickness compared to a GZO single layer. However, a relatively high peak transmittance and a high figure of merit were obtained for an Au interlayer thickness of 9 nm. These results showed that the characteristics of GZO/Au/GZO multilayers could be improved by inserting an Au interlayer of optimized thickness. In addition, it indicated that the GZO/Au/GZO multilayer is the most promising candidates for indium free transparent conducting oxides (TCOs).     

Dislocation motion in anisotropic multilayer materials

Line integral forms for the elastic field of dislocations in anisotropic, multilayer materials are developed and utilized in Parametric Dislocation Dynamics (PDD) computer simulations. Developed equations account for interface image forces on dislocations as a result of elastic modulus mismatch between adjacent layers. The method is applied to study dislocation motion in multilayer thin films. The operation of dislocation sources, dislocation pileups, confined layer slip (CLS), and the loss of layer confinement are demonstrated for a duplex Cu/Ni system. The strength of a thin film of alternating nanolayers is shown to increase with decreasing layer thickness, and that the maximum strength is determined by the Koehler barrier in the absence of coherency strains. For alternating Cu/Ni nanolayers, the dependence of the strength on the duplex layer thickness is found to be consistent with experimental results, down to a layer thickness of ≈10nm.     

Gap plasmon modes resolved by ultraflat nanogap and linear polarization in terrace-stepped hexagonal boron nitride spacer sandwiched by Ag nanowire and metal substrates

We investigate the nanogap and polarization-resolved excitation of gap plasmon modes using terrace-stepped hexagonal boron nitride (hBN) sandwiched between Ag nanowires and Au substrates for a metal–insulator–metal gap structure. The gap plasmon modes in the proposed hybrid structure are dominantly excited by a P-polarized incident light, which is supported by full-wave numerical simulations. Plasmon mode evolution for various hBN spacer thicknesses ranging from 5 to 90 nm shows that optical signals acquired via unpolarized dark-field mapping spectroscopy are primarily due to the optical scattering of the P-polarized incident light. Moreover, this plasmonic mode changes significantly from gap plasmon mode to Fabry–Perot-type resonance in a hBN thickness of 50–90 nm. Our analysis reveals that the proposed hybrid structure based on Ag nanowires and stepped hBN provides a well-defined gap thickness and is a robust platform for analyzing gap plasmon modes.     

Au电极厚度对MgZnO紫外探测器性能的影响

利用分子束外延设备(MBE)制备了MgZnO薄膜.X射线衍射谱、紫外-可见透射光谱和X射线能谱表明薄膜具有单一六角相结构,吸收边为340 nm,Zn/Mg组分比为62:38.采用掩膜方法使用离子溅射设备,在MgZnO薄膜上制备了Au电极,并实现了Au-MgZnO-Au结构的紫外探测器.通过改变溅射时间,得到具有不同Au电极厚度的MgZnO紫外探测器.研究结果表明:随着Au电极厚度的增加,导电性先缓慢增加,再迅速增加,最后缓慢增加并趋于饱和;而Au电极的透光率则随厚度的增加呈线性下降.此外,随着Au电极厚度的增加,器件光响应度先逐渐增大,在Au电极厚度为28 nm时达到峰值,之后逐渐减小.     

Dumbbell to Core–Shell Structure Transformation of Ni–Au Nanoparticle Driven by External Stimuli

Conversion of CO₂ gas to CO fuels is one of the most promising solutions for the increasing threat of global warming and energy crisis. The efficient catalyst Ni–Au dumbbell converting CO₂ into CO at elevated temperatures has high CO product selectivity; however, the accompanied atomic diffusion and subsequent surface reconstruction affect the catalytic efficiency of chemical reaction. Atomic scale characterization of structural evolution of the catalyst, which is essential to correlate the functional mechanism to active catalyst surfaces, is yet to be studied. Here, in situ transmission electron microscopy experiments and atomistic simulations are performed to characterize the structural evolution of Ni–Au dumbbell nanoparticles under two different external stimuli. In the condition of high temperature and vacuum, the Ni–Au nanostructure reveals a clear shape reconstruction from the initial dumbbell to core–shell‐like, which is induced by capillary force to minimize free surface energy of the system. The shape transformation involves two stages of processes, initial fast Au diffusion followed by slow source‐controlled diffusion. At ambient temperature, the combination of CO₂ and electron flux surprisingly induces analogous structural transformation of Ni–Au nanostructure, where the associated chemical reaction and CO absorption stimulate the Au migration on Ni surface. Such surface reconstruction can be widely present in catalytic reactions in different environmental conditions, and the results herein demonstrate the detailed processes of Ni–Au structure evolution, which provide important insights for understanding the catalyst performance.     

197Au Mössbauer study of Au/Ni artificial multilayers

¹⁹⁷Au Mössbauer measurements have been performed at 16 K on the Au/Ni artificial multilayers having three different thickness of the layers those are 10Å Au/10Å Ni, 30Å Au/30Å Ni and 53Å Au/53Å Ni on a 250Å pure Au buffer layer. Mössbauer spectra obtained can be decomposed into mainly two components. One is an unperturbed component having an identical isomer shift value to the bulk Au metal. The other is the component perturbed strongly by the Ni layer indicating a broad contribution at positive velocity side and its intensity depends on the thickness of the Au layer. The spectrum from 10Å Au/10Å Ni multilayer is an entirely perturbed one and its area ratio to the component rising from pure Au buffer layer indicates the large Debye-Waller-factor suggesting the supermodulus effect in this multilayer.     

Structure and peculiarities of nanodeformation in Ti–Zr–Ni quasi-crystals

Ti–Zr–Ni samples with a substantial predominance of icosahedral quasicrystalline phase were produced by the melt-spinning technique. Their structure and mechanical properties were studied by X-ray diffraction and nanoindentation methods. The quasicrystalline phase was found to have a primitive lattice with the quasicrystallinity parameter a _q = 0.5200–0.5210?nm. Quasicrystalline deformation behaviour under nanoindentation versus phase composition and structure is discussed in comparison with single crystal W–12?wt%?Ta. The estimated elastic modulus E of the quasicrystalline phase shows no correlation with the element composition. The nanohardness was shown to increase with increasing quasicrystalline-phase perfection. Load–displacement curves of Ti–Zr–Ni quasicrystals (QCs) show stepwise character with alternation of elastic and plastic sections. Such non-uniform plastic flow in QCs might be caused by the localization of plastic deformation in shear bands. The non-uniformity of the plastic deformation increases with the increasing quasicrystalline phase perfection.     

Microwave absorption properties of the Ni nanofibers fabricated by electrospinning

Ni nanofibers with an average diameter of about 100 nm were synthesized by a simple and cost-effective electrospinning technology. The nanofibers have a polycrystalline structure and each nanofiber is composed of fine particles. The complex permittivity and permeability properties of Ni nanofibers composite have been measured in the frequency range of 1–15 GHz. The double-resonance behavior of microwave magnetic permeability is observed. Natural resonance peak happens at 4.0 GHz with the contribution of shape anisotropy. The second resonance peak around 12.5 GHz originates from exchange resonance effect. The permeability spectra were fitted with the Landau–Lifshitz–Gibert equation. The minimum reflection loss of the Ni nanofibers composite reaches ?35.4 dB at 1.3 GHz with a matching thickness of 8.4 mm, which shows promising application of the Ni nanofibers composites in microwave absorber.     

基于MoO_3/Au/MoO_3透明电极的有机太阳能电池

以透明导电薄膜Mo O3/Au/Mo O3代替铟锡氧化物(ITO)作为有机太阳能电池(OSCs)的阳极,研究了一系列结构为Mo O3/Au/Mo O3的透明电极和Mo O3(y nm)/Au(x nm)/Mo O3(y nm)/Cu Pc(25 nm)/C60(40nm)/BCP(8 nm)/Al(100 nm)的有机太阳能电池。研究表明,Mo O3/Au/Mo O3电极的光电特性可通过改变各层薄膜厚度加以调控,在Mo O3薄膜厚度为40 nm、Au薄膜厚度为10 nm时性能最优,且以该薄膜为电极的有机太阳能电池器件的性能接近于电极为ITO的有机太阳能电池器件。     

Experimental characterization of bi-directional terahertz emission from gold-coated nanogratings

The THz radiation emission of Au-coated nanogratings (fused silica substrate, 30?nm Au layer thickness, 500?nm grating constant) upon fs laser irradiation (785?nm, 150?fs, 1?kHz,???1?mJ/pulse) is observed in both directions along the laser beam axis (forward and backward) and for both, illumination of the Au/air or the Au/silica interface. THz radiation along the laser beam propagation is emitted in a narrow solid angle of about 15°?fwhm independent on the laser pulse fluence, the angle of incidence and the nanograting profile. The bar width and groove depth of the nanograting as well as the angle of laser beam incidence strongly affect the THz radiation yield. The energy of single THz light pulses is measured absolutely (2?fJ in the 0.3?C0.38?THz range) using a highly sensitive and fast superconducting transition edge sensor. The bi-directional emission of THz radiation is in agreement with the model assumption of surface plasmon polaritons propagating simultaneously on both Au layer interfaces (Au/air and Au/silica).     

Simulation on effect of metal/graphene hybrid transparent electrode on characteristics of GaN light emitting diodes

In order to decrease the Schottky barrier height and sheet resistance between graphene(Gr) and the p-GaN layers in GaN-based light-emitting diodes(LEDs), some transparent thin films with good conductivity and large work function are essential to insert into Gr and p-GaN layers. In this work, the ultra-thin films of four metals(silver(Ag), golden(Au), nickel(Ni), platinum(Pt)) are explored to introduce as a bridge layer into Gr and p-GaN, respectively. The effect of a different combination of Gr/metal transparent conductive layers(TCLs) on the electrical, optical, and thermal characteristics of LED was investigated by the finite element methods. It is found that both the TCLs transmittance and the surface temperature of the LED chip reduces with the increase of the metal thickness, and the transmittance decreases to about 80% with the metal thickness increasing to 2 nm. The surface temperature distribution, operation voltage, and optical output power of the LED chips with different metal/Gr combination were calculated and analyzed. Based on the electrical, optical, and thermal performance of LEDs, it is found that 1.5-nm Ag or Ni or Pt, but 1-nm Au combined with 3 layered(L) Gr is the optimal Gr/metal hybrid transparent and current spreading electrode for ultra-violet(UV) or near-UV LEDs.