Metallic Multilayer Films Research Articles

Surface Morphology, Crystal Orientation and Scratch Properties of Au/NiCr/Ta Multi-Layered Metallic Films

The crystal orientation, surface morphology, surface roughness and scratch properties of Au/NiCr/Ta multi-layered metallic films was examined by X-ray diffraction (XRD), atomic force microscopy (AFM) and a scratch test method, respectively. It was clarified that the surface morphology and surface roughness depend on the substrate temperature. The surface roughness decreases from 4.259nm to 2.935nm when substrate temperature changed from 100°C to 180°C, and then increases when substrate temperature above 180°C. The XRD revealed that there are only Au diffraction peaks with highly textured having a Au-(111) or a mixture of Au-(111) and Au-(200) orientation. The micro-scratch test reveals that both modes can be used for conventionally critical load determination, but the friction mode can additionally reflect the changes at different metallic film layers, the critical characteristic load was not sensitive to substrate temperature.

Photonic absorption bands in the spectra of nanoporous metallic films

The light absorption spectra of multilayer nanoporous metallic films containing spherical dielectric inclusions are calculated in the framework of the self-consistent electrodynamic approach (the Korringa-Kohn-Rostoker method). It is demonstrated that the coupling between Mie plasmons in different layers of nanopores leads to the formation of strong light absorption bands over a wide range of frequencies.

Characteristics of Hf-Zr Mixed Oxide Formed by Oxidation of Multi-Layered Metal Films

of Hf and Zr during the oxidation process. We also investigated the properties of the interface located between the Hf-Zr mixed high-k oxide films and the Si substrates by using X-ray photoelectron spectroscopy (XPS) and observed spectra features that could be assigned to oxygencontaining Hf- and Zr-silicide bonds. High temperature annealing at temperatures up to 900 C steadily reduced the peak intensities, resulting in the improved electrical properties. For example, the phenomena such as stretch-out and hysteresis, which are related to the interface and/or bulk trap disappear when Hf-Zr mixed high-k oxide films are annealed at temperatures over 500 C.

Pseudomorphic quasiperiodic alkali metal monolayers on ani−Al−Pd−Mnsurface

The structure and stability of quasiperiodic alkali metal monolayers and multilayer films formed on a fivefold surface of an icosahedral AlPdMn quasicrystal have been investigated using ab initio density-functional methods. A structural model of the adsorbed monolayer has been constructed on the basis of a mapping of the potential-energy landscape of a single adatom on the fivefold surface of $i\text{\ensuremath{-}}\mathrm{Al}\text{\ensuremath{-}}\mathrm{Pd}\text{\ensuremath{-}}\mathrm{Mn}$. This model consists of a dense decoration of the P1 tiling describing the atomic arrangement on a fivefold surface of $i\text{\ensuremath{-}}\mathrm{Al}\text{\ensuremath{-}}\mathrm{Pd}\text{\ensuremath{-}}\mathrm{Mn}$. Upon relaxation under action of ab initio calculated interatomic forces, a dense Na monolayer spontaneously transforms to another ordered quasiperiodic structure. The quasiperiodic ordering can be described by a decagonal DHBS tiling of decagons (D), hexagons (H), boats (B), and pentagonal stars (S). The internal decoration of these tiles, however, reduces the overall symmetry from decagonal to pentagonal. The saturation coverage of the adsorbed monolayer is $\ensuremath{\Theta}=0.50$. K monolayers can adopt the same structure. Alkali layers with a lower coverage adopt a semiregular structure with part of the atoms forming a regular grid imposed by the strong binding of the alkali atoms to the quasiperiodically distributed charge-density minima. A stable quasiperiodic bilayer film can be formed by placing alkali atoms into the hollows of the adlayer. The coverage in the second layer is reduced to $\ensuremath{\Theta}=0.39$. Films with three of more monolayers do not form a regular quasiperiodic pattern, upon relaxation they transform to a disordered amorphous arrangement.

A combinatorial study of the corrosion and mechanical properties of Zn–Al material library fabricated by ion beam sputtering

A combinatorial method was utilized to fabricate a Zn–Al material library by ion beam sputtering. The material library was produced by manipulating the position of substrate and moving shutters to deposit multilayer metal films. As-deposited films were annealed at low temperatures to form through-thickness homogenous films. Different annealing conditions were studied and high quality alloy films could be obtained by annealing at 370 °C. Electrochemical corrosion properties of the material library were evaluated by a modified tape test. Results of the electrochemical tests show that the Zn–Al film with a composition of 72.6 wt% Al has the best anti-corrosion properties in the material library. Nanoindentation tests were conducted to investigate the mechanical behaviour. Zn–Al films containing a high content of Al possess better mechanical properties with a high hardness and elastic module.

Characteristics of high-k gate oxide prepared by oxidation of multi-layered Hf/Zr/Hf/Zr/Hf metal films

We investigated the physical and electrical properties of Hf–Zr mixed high-k oxide films obtained by the oxidation and annealing of multi-layered metal films (i.e., Hf/Zr/Hf/Zr/Hf, ∼5 nm). We demonstrated that the oxidation of multi-layered metal films results in two distinctive amorphous layers: That is, Hf–Zr mixed oxide film was formed on the top of silicate film due to inter-diffusion between Hf and Zr layer. This film shows the improved dielectric constant (k) and the raised crystallization temperature. Compared with HfO2 and ZrO2 gate dielectric, the crystallization temperature of Hf–Zr mixed oxides was raised by more than 200 °C. Using AES and XPS, we observed that Zr oxide has more fully oxidized stoichiometry than Hf oxide, irrespective of annealing temperatures. We also found that the thickness of an interfacial layer located between Hf–Zr mixed oxide and Si substrate also increases as annealing temperature increases. Especially, the thin SiOx interfacial layer starts to form if annealing temperature increases over 700 °C, deteriorating the equivalent oxide thickness.

Kirkendall porosity during thermal treatment of Mo–Cu nanomultilayers

Mo–Cu nanomultilayers were investigated as part of an effort to understand mechanisms of thermal stability in layered nanostructures. The multilayers were fabricated by magnetron sputtering with a range of layer spacings. Thermal treatment of the Mo–Cu nanomultilayers showed the formation of nanovoids along Cu–Mo layer interfaces and Mo–Mo grain boundaries. The size of the void was concurrent with the size of Cu. This was attributed to a Kirkendall type of effect caused by vacancy diffusion in metallic nanoscaled multilayered films.

Analysis of thermal behavior in multi-layer metal thin films based on hyperbolic two-step model

This work theoretically analyzes non-equilibrium thermal behavior in multi-layer metal films with the hyperbolic microscopic two-step model. It is necessary to solve the coupled energy equations or an equation containing higher-order mixed derivatives in both time and space for such problems. The difference in the relaxation times of dissimilar materials introduces the complexity and causes some mathematical difficulties at the interfaces. A numerical scheme is developed in this work and is applied to the examples in double-layer and triple-layer films with an ultrashort pulse heating. To evidence the efficiency of the present numerical scheme, the analytical solutions for the illustrated examples are presented. The effects of the thermal property ratios of dissimilar metals on heat transfer are investigated. It lends the theoretical insight to hyperbolic microscale heat transfer in multi-layer metal films. Results show the difference in the thermal properties of dissimilar materials and the hyperbolic nature of heat transfer in electron gas sufficiently affect the thermal behavior in multi-layer films at early times.

Analytical electron microscopy study of growth mechanism for smoothing of metallic multilayer thin films

We have used scanning transmission electron microscopy and electron energy-loss spectroscopy techniques to study the nature of interfacial interactions in a Ta∕CuOx stack that give rise to a smooth surface morphology, which can be utilized for seeding thin magnetic multilayer devices. Our measurements reveal that the interfacial smoothing is mainly due to the preferential reaction of Ta with O at the Ta∕CuOx interface assisted by grain boundary diffusion of oxygen which thereby acts to smooth out the surface roughness created by the large crystalline grains of Cu.

Nano-scratch experiments of Au/NiCr multi-layered films for microwave integrated circuits

Au/NiCr multi-layered metallic films used in microwave integrated circuits were deposited on Al 2O 3 substrate by magnetron sputtering. The deformation behavior of films was investigated by nano-scratch measurement technique. It was found that deformation proceeds can be divided into three stages: at the low load regime, plastic deformation is dominant; then, the plastic/total deformation ratio decreases with the increase of load; finally, as the scratch load is increased to a critical value, film failure occurs. Experimental results indicate that plastic deformation always dominates over elastic deformation before the film failure. Most interesting is that as the load increases, the elastic and plastic curves come to intersect at the point where the elastic and plastic deformations have the same amount. It indicates that the film begins to delaminate and the critical load is determined.

Giant enhancement of optical nonlinearity in multilayer metallic films

The local electric field has been derived analytically inside multilayer metallic films with weak nonlinearity, and hence the effective linear dielectric constant and third-order nonlinear susceptibility of the layered structures are calculated. As the number of layers increases, the comparison with the previous results of graded metallic films shows a gradual transition from sharp peaks to a broad continuous band. These results give further evidence of the emerging absorption band reported recently [J. P. Huang and K. W. Yu, Appl. Phys. Lett. 85, 94 (2004)]. Thus, multilayer metallic films can serve as optical materials with a giant enhancement of optical nonlinearity and a large figure of merit.

Influence of interdiffusion on the electrical conductivity of multilayered metal films

Abstract The annealing-time dependence of the electrical conductivity of multilayered single-crystal and polycrystalline metal films has been analyzed theoretically within the frame of the semi-classical approach. It is demonstrated that changes in the electrical conductivity which are caused by the diffusion annealing allow for investigating the processes of the bulk and grain-boundary diffusion, and for estimating the coefficients of the diffusion. The electrical conductivity was calculated and the numerical analysis of the diffusion-annealing time dependence was performed at various parameters.

Characteristics of high- k gate oxides prepared by oxidation of 1.4 nm multi-layered Hf/Al metal film

We investigated the physical and electrical properties of high- k gate oxide formed by oxidizing multi-layered Hf and Al metal films. We demonstrated that oxidation of multi-layered metal films results in two distinctive amorphous layers: That is, Hf- and Al-doped metal oxide films were formed on the top of silicate film. The thickness of silicate layer and therefore equivalent oxide thickness (EOT) value were dependent on the number of metal films. To reduce the EOT value, higher number of metal layers is desirable. In addition, annealing has to be done at 600 °C to obtain the minimum value of EOT. Hysteresis phenomenon usually observed in high- k oxide was not observed in this work.

Effect of the interface structure in multilayered systems on x-ray specular scattering spectra

The effect of the spatial structure of an interface in multilayer metallic films on the spectrum of x-ray specular scattering is studied. Two types of interface structural defects are considered. One type is steps resulting in a variable layer thickness, and the other is the mixing of unlike metal atoms during epitaxial growth. These defects are shown to have different effects on the specular-scattering spectra. The mixing significantly decreases the Bragg-peak height, especially the height of higher order peaks. The interface roughness results in broadening of the Bragg peaks and in the disappearance of intermediate peaks between them.

High-optical-throughput individual nanoscale aperture in a multilayered metallic film

The optical transmission of an individual subwavelength aperture in a multilayered metal film is shown to be enhanced compared with that of a homogeneous metal film. The enhancement effect is due to the light coupling to surface plasmon excitation facilitated by a film periodicity. The sensitivity of the transmission to the dielectric filling of the aperture is also shown. The latter effect can be used to switch and control the transmittance. Devices based on enhanced transmission through nanosized apertures can find applications in high-density optical and magneto-optical data storage, high-resolution microscopy, and photolithography, where nanoscale light sources with high-optical-power throughput are required, as well as in sensor applications.

Nanoporous Alumina Template with In Situ Barrier Oxide Removal, Synthesized from a Multilayer Thin Film Precursor

A nanoporous alumina template made from a multilayer metal film structure has been developed that allows for the in situ removal of the electrically insulating alumina barrier layer, exposing a Pt electrode at the pore bases. This barrier-free nanoporous system is of great use for dc electrodeposition of a wide variety of materials in the alumina pores. This work in particular describes the development of a multilayer thin film precursor consisting of a Si substrate with thin Pt and Ti and a thicker Al layer in that order. After the Al is anodized, producing the porous alumina, the resulting is selectively removed at the base of the alumina pores exposing the Pt electrode. The metals in the precursor perform different roles in the fabrication and allow the alumina template to be fabricated directly on the final substrate with no film transfer technique involved. This allows Si to be used as the substrate, which could then include electronic circuitry. Several techniques are used to analyze the resulting template.

Hardness and elastic modulus of Au/NiCr/Ta multilayers on Al 2O 3 substrate by nanoindentation continuous stiffness measurement technique

Au/NiCr/Ta soft metallic multilayered films were deposited on hard Al 2O 3 substrate by magnetron sputtering. The distribution of hardness and elastic modulus was investigated by nanoindentation continuous stiffness measurement technique. The film hardness was constant for all samples at indentation depths 1/7 ≤ h/ t ≤ 1/4, which can be considered as the true hardness. The hardness increased with increasing indentation depths at 1/4 ≤ h/ t ≤ 1. The hardness was shown to be not regular at indentation depths h/ t ≤ 1/7; this is due to the different surface roughness of films. Compared to the hardness, the measured elastic modulus was more sensitive to the substrate.

Fluxless fabrications of Sn-Au solder microbumps by a hydrogen plasma reflow technique

Solder microbumps of 0.95Sn-0.05Au were successfully fabricated on a compound semiconductor wafer by reflowing a multilayer metal film in hydrogen plasma atmosphere. The microbumps melt at as low a temperature as 220°C, which is close to the lowest eutectic temperature (217°C) in a Sn-Au system. Fluxless reflowing was achieved by using hydrogen radicals. The low-temperature fluxless fabrication of Sn-Au solder microbumps is a very useful technique for electrical connection between a compound semiconductor chip and a substrate.

Dislocation-based modeling of the mechanical behavior of epitaxial metallic multilayer thin films

A 3D dislocation cellular automaton model is employed to simulate yield and hardening in nanostructured metallic multilayer thin films during in-plane, biaxial tensile loading. The films consist of two types of alternating, single-crystalline FCC layers with (0 0 1) epitaxy, a mismatch in stress-free lattice parameter, but no elastic modulus mismatch. The simulations monitor the operation of interfacial and threading sources with lengths greater than the individual layer thickness. At larger layer thickness, strength increases with decreasing layer thickness, due to slip confinement to individual layers. At sufficiently small layer thickness, slip confinement is not possible, even during initial stages of plastic deformation. Consequently, strength is not controlled by layer thickness but rather by source length, as well as coherency stress and interfacial barrier strength. Here, strength may increase, decrease, or reach a plateau depending on how source length and barrier strength vary with layer thickness.

Preparation of nanometer thin films with intense pulsed electron beam ablation

Physical processes of films deposition and the interactions between beam and target by pseudospark electron beam deposition (PED), similar to pulse laser beam deposition (PLD) have been presented in this paper. The nanometer thin films with similar ingredients as target materials are available through the interaction of intense pulsed electron beam and target to cause rapid melting, evaporations, ablation of target materials, and then nucleation crystallization on the surface of low temperature substrate. The intense interactions between beam and target affect the mass transfer processes, deposition rate, composition and space distribution of target materials, which influence and determine the components, structure and performance of films. The surface morphology, components and microstructure of nanometer thin films prepared by PED ablation have been investigated with high resolution electron microscopy (HREM), X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Due to high power density of the electron beams (10 9 W/cm 2), the rapid ablation on the surface of solid target has been obtained. Experimental results show that, by using PED ablation preparation, a variety of multilayered films with the oxides of multiple elements and refractory metal multilayered films are promising.