The microstructure of aluminium thin films on amorphous SiO2

The microstructure of aluminium thin films deposited onto amorphous SiO₂ by tungsten filament evaporation was studied by transmission and scanning electron microscopy and grazing-incidence X-ray diffraction. The early stages of film growth were characterized by an island or connected-network structure and a random grain orientation. The thickness at which complete coverage occurred ranged from 15 nm at 295 K to 100 nm at 625 K, and above this thickness a 〈111〉 fibre texture became apparent.The grain size distribution of films 1 μm thick was log-normal and the average grain size ranged from 500 nm for deposition at 295 K to 4 μm for deposition at 675 K. “Growth hillocks” were observed on the surface of films deposited at 295 K but were absent when higher substrate temperatures were used. Annealing caused grain growth and the formation of “annealing hillocks” which were of different structure from the growth hillocks.Examination of a small number of electron-beam-deposited aluminium films showed these to have similar microstructures to the filament-evaporated films, whereas sputter-deposited films were characterized by a smaller grain size and random orientation.     

Delocalizing strain in a thin metal film on a polymer substrate

Under tension, a freestanding thin metal film usually ruptures at a smaller strain than its bulk counterpart. Often this apparent brittleness does not result from cleavage, but from strain localization, such as necking. By volume conservation, necking causes local elongation. This elongation is much smaller than the film length, and adds little to the overall strain. The film ruptures when the overall strain just exceeds the necking initiation strain, ε_N, which for a weakly hardening film is not far beyond its elastic limit. Now consider a weakly hardening metal film on a steeply hardening polymer substrate. If the metal film is fully bonded to the polymer substrate, the substrate suppresses large local elongation in the film, so that the metal film may deform uniformly far beyond ε_N. If the metal film debonds from the substrate, however, the film becomes freestanding and ruptures at a smaller strain than the fully bonded film; the polymer substrate remains intact. We study strain delocalization in the metal film on the polymer substrate by analyzing incipient and large-amplitude nonuniform deformation, as well as debond-assisted necking. The theoretical considerations call for further experiments to clarify the rupture behavior of the metal-on-polymer laminates.     

Experimental study on buckle evolution of thin inorganic layers on a polymer substrate

In this paper the behavior of a 250 nm and a 350 nm thick Indium tin oxide (ITO) layers deposited on a 200 μm thick high temperature aromatic polyester substrate (Arylite™) and spin coated with a 3 μm silica-acrylate hybrid coating (Hard Coat) is discussed. In-situ optical microscopy of the layered structures under uniaxial compressive strain was used to determine the buckle delamination rate at different applied strains. The effect of applied uniaxial compressive strain and layer thickness on the evolution of buckle width and height was investigated. The biaxial-residual stress, uniaxial compressive stress, poor adhesion at the interface and Poisson’s ratio are believed to be responsible for the formation of telephone-cord buckling.     

Adhesion, microstructure and composition of thermally evaporated aluminium thin layers on polyethylene terephthalate films

Industrial polyethylene terephthalate (PET) films have been metallized by aluminium evaporation in two different sets of experimental conditions. In the first set, aluminium layers of 100 nm thickness were deposited at a constant deposition rate (10 Å s⁻¹) for different residual pressures varying from 1 Pa to 10⁻⁴ Pa and, in the second set, the residual pressure was kept constant (2.6 × 10⁻³ Pa), while the deposition rate was varied from 5 Å s⁻¹ to 40 Å s⁻¹.

The adherence between the aluminium layers and the PET film was measured by means of scratch and peel tests. The critical load and the peel strength exhibit a maximum at about 10⁻² Pa when the deposition rate is kept constant.

The microstructure of the aluminium layers, mainly the mean grain size, was studied by transmission electron microscopy (TEM), while secondary ion mass spectrometry (SIMS) depth profiles through the aluminium layers were performed in order to provide the chemical information, mainly aluminium layer oxidation. Concerning the TEM results, the grain size increases when the residual pressure is decreased and also when the deposition rate is increased. The SIMS depth profiles show different levels for aluminium oxidation at the surface, in the bulk of the layers and at the interface, all increasing for high residual gas pressure and for low deposition rates.

From these results, it appears that the oxygen content at the Al---PET interface plays a critical role in the microstructure owing to its influence on the nucleation and on the growth of the aluminium layers. It also influences the adhesion between aluminium and PET for which an optimum oxygen amount seems to be required.     

Modeling of multiple cracking and decohesion of a thin film on a polymer substrate

Thin brittle films on polymer substrates are finding increasing use as gas barriers for example in the medical and food packaging industries and also for the next generation of ultra-light displays based on flexible polymer substrates. In order to determine the durability of the barrier under thermal and mechanical loads, test procedures and corresponding data reduction methods are needed to feed the analysis models. One of the tests frequently employed for this kind of multi-layer material systems is the fragmentation test, whose designation comes from the progressively denser pattern of parallel cracks developing when the specimen is loaded under uniaxial tension. From the crack-density versus strain data obtained, a critical strain for crack growth and an assessment of the adhesion of the coating to substrate can be obtained. However, no accepted data reduction methods exist to extract material properties from the test or inversely, successfully predict the crack density as a function of a set of material properties without fitting parameters. In an earlier paper, the authors presented a finite element based analysis methodology to determine the fracture toughness of both the coating and the interface from the fragmentation data. In the simulations, the plastic constitutive behavior of the substrate and the debonding of the coating from the substrate were explicitly included, the latter by use of a cohesive zone model. In this paper an extension of this methodology is presented that enables crack-density evolution with strain to be predicted. The results presented comprise comparisons with experiments to validate the methodology and the influence of (i) coating toughness, (ii) interface toughness and (iii) coating thickness on crack density versus strain.     

The effect of moisture on buckle delamination of thin inorganic layers on a polymer substrate

Moisture-induced buckle delamination of thin inorganic layers on a polymer substrate was studied. Moisture has been found to have a significant effect on the failure mode. Experimentally, an increase in the buckle width, height and the total buckle delamination length with time and humidity was observed. Moreover, a transition from straight to telephone-cord buckle pattern was taken place in a humid environment. Applying only a uniaxial compressive strain on the thin layers did not result in the transition from straight to telephone-cord. For a compliant substrate the transition from straight to telephone-cord buckle occurred at significantly higher ratio of residual strain over critical buckling strain than for a rigid substrate. A simple model for buckling was applied. Using the energy release rate, the interfacial toughness was investigated as a function of relative humidity.     

Structure and microstructure of EB-PVD yttria thin films grown on Si (111) substrate

Structure and microstructure of yttria thin films grown by electron beam physical vapour deposition on a stationary Si (111) substrate at room temperature (RT), 500° and 700 °C, were investigated by the grazing-incidence X-ray diffraction and scanning electron microscopy, respectively. X-ray photoelectron spectroscopy provided information on the surface contamination from the atmosphere and the Y oxidation state. A strong effect of the deposition temperature and the vapour flux incidence angle was found. The film deposited at RT is polycrystalline with very fine grains of the body-centered cubic (bcc) crystallographic symmetry. An increase of deposition temperature results in a rapid growth of bcc grains with an improved crystalline structure. Moreover, the based-centered monoclinic phase appears for the deposition temperature of 700 °C. Preferred grain orientation (texture) with two main components, (400) and (622), was observed in the films deposited at 500 °C whereas no texture was found for 700 °C. The microstructure exhibits the columnar feather-like structure of different degrees of perfection which can be explained by the shadowing effects caused by an oblique vapour flux incidence angle. Surface morphology of the films is governed by a combination of the triangular and four-sided (square) columns. All films were found to be dense with a little porosity between the columns.     

Thermal loading of a thin layer with circular debonding over a substrate

By using techniques appropriate to mixed boundary value problems, this study addresses the determination of stress intensity factors for a circular interface debonding between a thin layer and a substrate subjected to nearly uniform temperature change. The solution method involves three-dimensional equilibrium equations of thermo-elasticity under axisymmetry conditions. The stress intensity factors are obtained by solving the resulting pair of coupled singular integral equations numerically. This revised version was published online in August 2006 with corrections to the Cover Date.     

Investigation of LiNbO3 thin films grown on Si substrate using magnetron sputter

A RF magnetron sputter system was used to deposit lithium niobate (LiNbO₃) thin films on (1 1 1)-oriented Si substrates. An optimal sputtering condition with RF power of 100 W, Ar/O₂ ratio of 1 and substrate temperature of 575 °C was investigated. The smallest surface roughness of 6.0 nm for the deposited LiNbO₃ was measured using atomic force microscopy. The crystallinity was examined by low angle X-ray diffractometer. Using the SOPRA GES5 spectroscopic ellipsometer, the associated refractive index and extinction coefficient as a function of wavelength were measured. High optical performance with crystallinity structure of the deposited LiNbO₃ thin films was demonstrated.     

Investigation of electrical transport characteristics of nanoscale stacks fabricated on thin graphite layer

We investigated the electrical transport characteristics of nanoscale stacks of thin graphite layer fabricated using focused ion beam (FIB) three dimensional (3D) etching. By varying the stack height, we fabricated nanostacks with the dimensions of W = 1 μm, L = 1 μm, H = 100 nm and W = 1 μm, L = 1 μm, H = 200 nm. The nanostack contains lot of elementary junctions between the graphene layers with interlayer distance of 0.34 nm (along c-axis). We observed a typical semiconducting characteristic until 50 K and a metallic behavior below 50 K for all the fabricated nanostacks, which was well agreed with an identical c-axis characteristics of graphite. From I-V characteristics, we found an ohmic-like characteristic at 300 K for both low and high current biasing; however at low temperature, this behavior was turned into nonlinear characteristics when it was highly biased. The temperature dependent differential conductance measurements for the fabricated stacks were carried out and found that at 300 K, the stack showed larger conductance rather than at any other lower temperatures. However, the stack with 100 nm height showed larger conduction values of 36.3 mS and 16.95 mS for 300 K and 20 K respectively, which are comparatively smaller values of stack with 200 nm height. We also studied conductance fluctuations of nanostacks experimentally and the fluctuations are appearing on increasingly fine when the temperature goes down; however the amplitude of fluctuation is suppressed at low temperature.     

Investigation on the microstructure,phase formation and properties of aluminium alloy coatings by stud spraying

Journal of Materials Science: Materials in Electronics - This study aims to investigate a novel spraying technology. The spraying technology is named stud spraying since it has been developed by...     

Atomic layer deposition of platinum thin films on anodic aluminium oxide templates as surface-enhanced Raman scattering substrates

Platinum thin films are deposited on anodic aluminium oxide (AAO) templates by atomic layer deposition (ALD). The highly ordered island-like platinum nanostructures formed on the AAO template produce a high Raman scattering signal because of the periodical hexagonal arrangement. As an illustration, dramatic enhancement is achieved using Rhodamine 6G (R6G) as a molecular probe.Field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) show that the gap between the island-like structures is below 10 nm. Owing to activation by the incident laser beam, the localized electromagnetic field on the platinum island surface can be dramatically enhanced by the sub-10 nm regime subsequently amplifying the Raman signal. Finite-difference time-domain (FDTD) calculation matches the experimental phenomena suggesting that the excellent surface-enhanced Raman scattering (SERS) characteristics of the platinum structure arise from the high density and abundance of hot spots. Because the platinum film is inert in air, the SERS enhancing substrate can be used reliably in many trace chemical and biological detection applications.     

Effect of film thickness on properties of aluminum doped zinc oxide thin films deposition on polymer substrate

A series of aluminum doped zinc oxide thin films with different thickness (25–150 nm) were deposited on indium tin oxide coated polyethylene terephthalate substrates by radio frequency magnetron sputtering method at room temperature. The structural, optical and electrical properties of the films were investigated by X-ray Diffractometer, UV–Vis spectrometer and Hall Effect Measurement System. All the obtained films were polycrystalline with a hexagonal structure and a preferred orientation along [002] direction with the c-axis perpendicular to the substrate surface. The optical energy band gap (E_g) values of the films were found to be in the range from 3.36 to 3.26 eV, and their average optical transmissions were about 75 % in the visible region. The films had excellent electrical properties with the resistivities in the range from 2.78 × 10^?5 to 2.03 × 10^?4 Ω cm, carrier densities more than 3.35 × 10²¹ cm^?3 and Hall mobilities between 5.77 and 11.13 cm²/V s.     

Conformal coating of thin polymer electrolyte layer on nanostructured electrode materials for three-dimensional battery applications

Various three-dimensional (3D) battery architectures have been proposed to address effective power delivery in micro/nanoscale devices and for increasing the stored energy per electrode footprint area. One step toward obtaining 3D configurations in batteries is the formation of core-shell nanowires that combines electrode and electrolyte materials. One of the major challenges however in creating such architectures has been the coating of conformal thin nanolayers of polymer electrolytes around nanostructured electrodes. Here we show conformal coatings of 25-30 nm poly(methyl methacralate) electrolyte layers around individual Ni-Sn nanowires used as anodes for Li ion battery. This configuration shows high discharge capacity and excellent capacity retention even at high rates over extended cycling, allowing for scalable increase in areal capacity with electrode thickness. Our results demonstrate conformal nanoscale anode-electrolyte architectures for an efficient Li ion battery system.     

Influences of roll-to-roll process and polymer substrate anisotropies on the tensile failure of thin oxide films

The influence of internal stress anisotropy resulting from anisotropic loading in a roll-to-roll (R2R) process, and polymer substrate anisotropy on the crack onset strain (COS) of thin oxide coatings was analyzed. Experimental data obtained for R2R processed films were compared with data obtained using an isotropic sheet-to-sheet (S2S) process with the same anisotropic substrate. In the R2R case the COS was found to increase by 20% between the transverse direction and the machine direction. In the S2S case the COS was found to be independent of orientation, except at a 45° in-plane orientation with respect to the machine direction, where it was 15% higher. The internal stress in the machine direction could not be determined, presumably due to deposition-induced curvature changes of the polymer substrate, and was therefore fitted to the COS data. Fracture mechanics analysis and finite element modeling of the experimental data showed that the influence of substrate anisotropy was marginal, and that it was the process-induced internal strain in the coating which controlled the COS.     

Stress and structural studies of ZnO thin films on polymer substrate under different RF powered conditions

The ZnO films are deposited on flexible substrate Teflon by radio frequency (RF) magnetron sputtering. The structure and residual stress of the films are revealed by XRD analysis. We find that the increase of RF power results in the change in the nature of stress and the difference of the grain size in the ZnO films on Teflon substrate. This indicates the possibility of the stress relaxation by increasing the RF power. Considering the (002) orientation and the mechanical stress, we suggest that the ZnO film deposited at RF power of 200 W for 1 h is optimal.     

A thin subsurface layer of a polymer film studied by atomic force microscopy

A thin subsurface layer of a PMMA based resist film was studied in an atomic force microscope (AFM). An analysis of the AFM image allowed a modified subsurface layer thickness to be estimated, in which the polymer density is greater than that in the bulk of the film.     

Effects of annealing process on microstructure and electrical properties of cold-drawn thin layer copper cladding steel wire

The microstructure, mechanical and electrical properties of cold-drawn thin layer copper cladding steel (CCS) wires annealed after different processes were studied by optical microscopy, electron omnipotent material experiment machine, micro hardness machine, SEM and electrical resistivity measurement system. The results indicated that the recovery and recrystallization of steel-core happened in the temperature range 550–750 °C for the holding period of 120 min. When the annealing temperature was higher than 750 °C, grains begun to grow and grain sizes increased gradually with increasing the annealing temperature. The tensile strength and micro hardness were declined with increasing annealing temperature and holding time. The distance of Cu–Fe atoms interfacial diffusion of thin layer CCS wires ranged from 4 µm of cold-drawn wire to 7.5 µm of annealed wire at 850 °C for 120 min. The higher the annealing temperature become, the larger the distance of Cu–Fe atoms interfacial diffusion is. When the annealing temperature was lower than 650 °C, the resistivity was slightly less than 71 × 10^?3 Ω mm² m^?1 which was the resistivity of cold-drawn wire. When the annealing temperature was higher than 650 °C, the resistivity increased with increasing the annealing temperature. Meanwhile, the variation of electrical property of thin layer CCS wires was analyzed and discussed based on microstructure and interfacial diffusion.