Elastic Properties Of Films Research Articles

Comparative physical, antioxidant, and antimicrobial properties of films prepared by dissolving chitosan in bioactive vinegar varieties

Solvent casting following the dissolution of chitosan in aqueous acetic acid is the most widely used method for preparing chitosan films. In this study, an economical and practical way is proposed to improve the physicochemical properties of chitosan films by using vinegar varieties both as solvents and as bioactive additives to improve the properties of the films. Chitosan films were prepared by dissolving chitosan in pomegranate, grape, apple, and hawthorn vinegar. Vinegar contains bioactive phenolics and different organic acids together with acetic acid, depending on the main raw material from which it is obtained. The films' mechanical, optical properties, antioxidant and antimicrobial activities were compared with each other and with the chitosan film prepared by dissolving chitosan in acetic acid. The antioxidant and antimicrobial properties of chitosan films prepared with vinegar increased. The use of vinegar as a solvent increased the UV light barrier properties of the films. Improved antimicrobial, antioxidant, optical, and elastic properties of films prepared by dissolving chitosan in vinegar varieties are promising in applications of these films as potential and economic food packaging materials.

Laser Ultrasound Investigations of AlScN(0001) and AlScN(11-20) Thin Films Prepared by Magnetron Sputter Epitaxy on Sapphire Substrates.

The laser ultrasound (LU) technique has been used to determine dispersion curves for surface acoustic waves (SAW) propagating in AlScN/Al2O3 systems. Polar and non-polar Al0.77Sc0.23N thin films were prepared by magnetron sputter epitaxy on Al2O3 substrates and coated with a metal layer. SAW dispersion curves have been measured for various propagation directions on the surface. This is easily achieved in LU measurements since no additional surface structures need to be fabricated, which would be required if elastic properties are determined with the help of SAW resonators. Variation of the propagation direction allows for efficient use of the system’s anisotropy when extracting information on elastic properties. This helps to overcome the complexity caused by a large number of elastic constants in the film material. An analysis of the sensitivity of the SAW phase velocities (with respect to the elastic moduli and their dependence on SAW propagation direction) reveals that the non-polar AlScN films are particularly well suited for the extraction of elastic film properties. Good agreement is found between experiment and theoretical predictions, validating LU as a non-destructive and fast technique for the determination of elastic constants of piezoelectric thin films.

Interfacial Properties of \u03b2-Lactoglobulin at the Oil/Water Interface: Influence of Starch Conversion Products with Varying Dextrose Equivalents

In spray dried emulsions, frequently milk proteins are used as interfacial active components and starch conversion products are added as matrix material at high concentrations. To characterize interfacial properties at the oil/water interface by commonly applied methods, low protein, and carbohydrate concentrations from 1 to 2% are usually analyzed. The impact of a higher concentration of starch conversion products was not investigated so far. Therefore, the formation and rheological properties of β-lactoglobulin (β-LG) stabilized films at the oil/water interface were investigated via short and long-time adsorption behavior using pendant drop tensiometry as well as dilatational and interfacial shear rheology. Suitability of the applied methods to the chosen samples with higher concentrations >1–2% was verified by calculation of selected key numbers like capillary number and by detailed reviewing of the results which is summarized further on as key indicators. It is hypothesized, that the increase in concentration via presence of starch conversion products will delay interfacial stabilization as a result of increased bulk viscosity with decreasing degree of degradation (dextrose equivalent) of the starch. Furthermore, this increase in concentration leads to more stable interfacial films due to thermodynamic incompatibility effects between protein and starch conversion products which results in increases of local protein concentration. Key indicators proved a general suitability of applied methods for the evaluation of the investigated samples. Moreover, results showed an increase in interfacial film stability and elastic properties alongside a decreased interfacial tension if starch conversion products were present in a high concentration.Graphical abstract

Correlative plasma-surface model for metastable Cr-Al-N: Frenkel pair formation and influence of the stress state on the elastic properties

Correlatively employing density functional theory and experiments congregated around high power pulsed magnetron sputtering, a plasma-surface model for metastable Cr0.8Al0.2N (space group Fm3¯m) is developed. This plasma-surface model relates plasma energetics with film composition, crystal structure, mass density, stress state, and elastic properties. It is predicted that N Frenkel pairs form during Cr0.8Al0.2N growth due to high-energy ion irradiation, yielding a mass density of 5.69 g cm−3 at room temperature and Young's modulus of 358–130 GPa in the temperature range of 50–700 K for the stress-free state and about 150 GPa larger values for the compressive stress of 4 GPa. Our measurements are consistent with the quantum mechanical predictions within 5% for the mass density and 3% for Young's modulus. The hypothesis of a stress-induced Young's modulus change may at least in part explain the spread in the reported elasticity data ranging from 250 to 420 GPa.

Impurity-controlled film growth and elastic properties of CoCrCuFeNi thin films

The growth mode during physical vapor deposition of metallic thin films is very sensitive to the presence of impurity species. These impurities can originate from the residual ambient gases present in the vacuum chamber and usually impede continued crystal growth by inducing renucleation. During magnetron sputtering at intermediary base pressures (~10−4Pa), the effect of these impurities can be estimated from the ratio of the impurity flux to the metallic flux. In this study, the influence of the ambient impurity flux on the growth mode of CoCrCuFeNi High-Entropy Alloy (HEA) thin films is investigated. It is shown that the impurity-to-metal flux ratio effectively controls the texture, grain size, porosity, and elastic properties of the nanocrystalline CoCrCuFeNi thin films. A less clear (111) fiber texture is observed at higher impurity-to-metal flux ratio. With increasing impurity-to-metal flux ratio the grain size decreases while the porosity increases. The elastic constants, and Young's modulus for CoCrCuFeNi is reported to be the highest for the 〈111〉 direction. Hence, the change in film texture also affects the elastic constants and Young's modulus which tend to become lower as more grains with different orientation are observed at higher flux ratios. This study demonstrates that an exact knowledge of the impurity-to-metal flux ratio, or otherwise stated, of the base pressure and deposition rate during sputter deposition is imperative for the synthesis of HEA films with reproducible properties.

Externally applied stress sign and film elastic properties effects on brittle film fracture

Rectangular stainless steel samples with TiN film deposited on the front lateral surface were loaded in three-point bending to the maximum normal strain of 6%. Scanning electron microscopy showed that vertical cracks appeared in the tension zone when the tensile strain exceeded 1.5%, while horizontal cracks appeared in the compression zone when the compressive strain exceeded –2.9%. Film cracks in the compressive zone originate from the tensile stress imposed by the plastically deformed substrate due to the Poisson’s expansion. Taking plastic deformation and Poisson’s expansion of the substrate in compression into account, theoretical analysis of normal stress distribution along the cracked film segment in compression is presented. Substrate strain and film elastic properties affect film cracking in the compressive zone. At larger compressive strain, some transverse cracks along with buckling cause the film spallation. The presented method is useful for studying brittle film fracture with variable strain levels in a single sample.

Piezoelectric AlN Films for FPW Sensors with Improved Device Performance

Reactively sputtered piezoelectric aluminum nitride (AlN) films for flexural plate wave (FPW) electroacoustic sensors equipped with buried interdigital transducers (IDTs) for sensing in liquids were fabricated and characterized. In order to assess the crystallographic and elastic film properties, residual film stress, and piezoelectric response, comprehensive analyses were performed on AlN layers and bimorph AlN structures, including X-ray diffraction, atomic force microscopy, and nanoindentation, in combination with analysis of the piezoelectric charge coefficient d33,f. To demonstrate the applicability of the optimized AlN films to electro-acoustic devices, IDT equipped devices were fabricated and characterized by means of laser Doppler vibrometry.

Piezoelectric AlN Films for FPW Sensors with Improved Device Performance

Reactively sputtered piezoelectric aluminum nitride (AlN) films for flexural plate wave (FPW) electroacoustic sensors equipped with buried interdigital transducers (IDTs) for sensing in liquids were fabricated and characterized. In order to assess the crystallographic and elastic film properties, residual film stress, and piezoelectric response, comprehensive analyses were performed on AlN layers and bimorph AlN structures, including X-ray diffraction, atomic force microscopy, and nanoindentation, in combination with analysis of the piezoelectric charge coefficient d33,f. To demonstrate the applicability of the optimized AlN films to electro-acoustic devices, IDT equipped devices were fabricated and characterized by means of laser Doppler vibrometry.

Thin film interface stresses produced by high amplitude laser generated surface acoustic waves

Surface acoustic waves (SAWs) have been explored for nondestructive metrology of thin film elastic properties and thickness due to confinement of their energy within a shallow depth from a material surface. In this paper, we study the dynamic interfacial stresses produced by high amplitude SAWs generated by a strongly ablative source in a thin film-substrate system, with the goal of investigating the possibility of inducing thin film delamination at high loading rates. For modeling purposes, we represent the mechanical loading resulting from the pulsed laser-sample interaction in the ablative regime by an equivalent compressive surface load, and the resulting stresses and particle velocities induced by the generated SAWs are calculated using a linear finite element model. We explore the numerical model to study the dependence of the film-substrate interface tractions on the ratio of the film thickness and SAW wavelength for a soft film on a stiff substrate. Furthermore, by matching the numerical results obtained from the finite element model with experimental results, we are able to predict the dynamic interfacial stresses for a copper film on a fused silica substrate produced by SAWs excited by a high power pulsed laser line source. This study has implications for exploring SAWs in the characterization of interfacial failure in thin-film substrate systems.

Evaluating indent pile-up with metallic films on ceramic-like substrates

Abstract

Methods for determining piezoelectric properties of thin epitaxial films: Theoretical foundations

An analytical method is developed to determine piezoelectric properties of a thin film directly from measurements of bilayer deflection. As a significant extension to previous approaches, we include here the effects of bilayer bending, differential thermal expansion, and epitaxial lattice mismatch which commonly arise in practical measurements. The formulation reported here thus relaxes restrictive assumptions made in previous models thereby enabling a more direct link with experimental conditions. The model, which has been validated by comparison with finite element analysis, is shown to reduce to the well-known Lefki-Dormans result as a limiting case for thin films when bending and in-plane deformations are neglected. If the curvature of a simply supported bilayer can be measured, then the model offers a methodology for measuring the piezoelectric properties (ε33T, d31, d33), the film elastic constant s11E+s12E, and lattice mismatch strains, provided a value of the elastic constant s13E can be determined or estimated. If curvature measurements are not available but lattice mismatch strains are known, then we find that it is still possible to measure these piezoelectric and elastic film properties.

Taking into account of surface roughness for the calculation of elastic moduli of polymer films from acoustic impedance data

The surface roughness of deposits contributes to their acoustic impedance and affects the results of calculation of elastic moduli (G) of thin polymer films from acoustic impedance data. A simple approach was developed in this paper to account for roughness in form of small random corrugations with Gaussian spectrum. The theory used was developed originally for bare crystals and is based on Rayleigh diffraction method. Experimental acoustic impedance data for poly-3,4-ethylendioxythiophene (PEDOT) films deposited from ionic liquids (1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)amide, [BMP][TFSA], containing 1mM of EDOT monomer) were analyzed in terms of this new developed approach. The roughness was estimated ex situ by a laser profilometer. The contribution of roughness-corrected liquid impedance changes G values significantly. Further, the film elastic properties in two ionic liquids ([BMP][TFSA] and 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl) amide, [EMIm][TFSA]) were compared by using mean-field model.

Effects of Hydrolysed Whey Proteins on the Techno-Functional Characteristics of Whey Protein-Based Films.

Pure whey protein isolate (WPI)-based cast films are very brittle due to its strong formation of protein cross-linking of disulphide bonding, hydrogen bonding as well as hydrophobic and electrostatic interactions. However, this strong cross-linking is the reason for its final barrier performance. To overcome film brittleness of whey protein layers, plasticisers like glycerol are used. It reduces intermolecular interactions, increases the mobility of polymer chains and thus film flexibility can be achieved. The objective of this study was to investigate the influence of hydrolysed whey protein isolate (WPI) in whey protein isolate-based cast films on their techno-functional properties. Due to the fact, that the addition of glycerol is necessary but at the same time increases the free volume in the film leading to higher oxygen and water vapour permeability, the glycerol concentration was kept constant. Cast films with different ratios of hydrolysed and not hydrolysed WPI were produced. They were characterised in order to determine the influence of the lower molecular weight caused by the addition of hydrolysed WPI on the techno-functional properties. This study showed that increasing hydrolysed WPI concentrations significantly change the mechanical properties while maintaining the oxygen and water vapour permeability. The tensile and elastic film properties decreased significantly by reducing the average molecular weight whereas the yellowish coloration and the surface tension considerably increased. This study provided new data which put researchers and material developers in a position to tailor the characteristics of whey protein based films according to their intended application and further processing.

Determining the Elastic Modulus of Compliant Thin Films Supported on Substrates from Flat Punch Indentation Measurements

Instrumented indentation is a technique that can be used to measure the elastic properties of soft thin films supported on stiffer substrates, including polymer films, cellulosic sheets, and thin layers of biological materials. When measuring thin film properties using indentation, the effect of the substrate must be considered. Most existing models for determining the properties of thin films from indentation measurements were developed for metal and dielectric films bonded to semiconductor substrates and have been applied to systems with film-substrate modulus ratios between 0.1 and 10. In the present work, flat punch indentation of a thin film either bonded to or in contact with a substrate is examined using finite element modeling. A broad range of film-substrate modulus ratios from 0.0001 to 1 are investigated. As the substrate is effectively rigid compared to the film when the film-substrate modulus ratio is less than 0.0001, the results are also useful for understanding systems with lower film-substrate modulus ratios. The effects of the contact radius, film thickness, elastic properties, and friction between the film and the substrate on the measured stiffness were quantified using finite element modeling in order to understand how the elastic properties of the film can be extracted from indentation measurements. A semi-analytical model was developed to describe the finite element modeling results and facilitate the use of the results to analyze experimental measurements. The model was validated through analysis of indentation measurements of thin polyethylene sheets that were supported on substrates of various stiffness.

Biomimetics in thin film design – Wrinkling and fracture of pulsed laser deposited films in comparison to human skin

The goal of the current work is the biomimetic comparison of wrinkling effects on the nano- and micrometer scale in thin films and on the micro- and millimeter scale of human skin. Ti, Ag, Au, W, C, and TiN thin films with 10 to 500nm thickness were deposited by pulsed laser deposition (PLD) on smooth polyurethane, polycarbonate, polyamide 6, and polyimide polymer substrates. Such high energetic conditions like in PLD plasma lead to stiffening of the polymer surface layers by pseudodiffusion during the initial stages of film growth. Both the high intrinsic film stresses due to high energetic film growth and the huge difference in elastic properties of films and polymer substrates result in hierarchical and self-adapting nanowrinkling phenomena. Intrinsic stresses are a reason for the hierarchical and self-adapting wrinkling of human skin too, being mechanically treated quite similar to the coated polymers as a hard layer (stratum corneum) on a soft foundation (viable epidermis and dermis). Mechanically, the wrinkles have high impact on the elongation behavior: In the elastic region of the stress–strain curve, they are smoothing out at increasing strain.In fracturing, the wrinkles are an origin of cracking (channeling cracks) and afterwards fragmentation of both thin film and stratum corneum islands, respectively, as proofed with in-situ tensile straining experiments of the thin films in scanning electron microscopy.

초음파 현미경을 이용한 나노 박막의 접합 강도 평가

Abstract In recent years, nano-structured thin film systems are often applied in industries such as MEMS/NEMS device, optical coating, semiconductor or like this. Thin films are used for many and varied purpose to provide resistance to abrasion, erosion, corrosion, or high temperature oxidation and also to provide special magnetic or dielectric properties. Quite a number of articles to evaluate the characterization of thin film structure such as film density, film grain size, film elastic properties, and film/substrate interface condition were reported. Among them, the evaluation of film adhesive to substrate has been of great interest. In this study, we fabricated the polymeric thin film system with different adhesive conditions to evaluate the adhesive condition of the thin film. The nano-structured thin film system was fabricated by spin coating method. And then V(z) curve technique was applied to evaluate adhesive condition of the interface by measuring the surface acoustic wave(SAW) velocity by scanning acoustic microscope(SAM). Furthermore, a nano-scratch technique was applied to the systems to obtain correlations between the velocity of the SAW propagating within the system including the interface and the shear adhesive force. The results show a good correlation between the SAW velocities measured by acoustic spectroscope and the critical load measured by the nano-scratch test. Consequently, V(z) curve method showed potentials for characterizing the adhesive conditions at the interface by acoustic microscope.

Systematic Brillouin light scattering study of the elastic properties of porous silicon superlattices

Brillouin light scattering spectroscopy was used to determine elastic properties of porous silicon films and superlattices. The film elastic properties were compared with previously published results and also used as input for an effective elastic medium model (M Grimsditch and F Nizzoli 1986, Phys. Rev. B 33 5891) to predict the elastic constants of porous silicon superlattices with constituent layers comprised of thin copies of the films. Values of superlattice elastic constants c33 and c44 obtained from the model show reasonably good agreement with those determined directly from superlattice Brillouin data while constants c11 and c13 show crude agreement. This partial agreement suggests that the model holds promise as a means for accurately predicting the elastic properties of p-Si SLs. The results of this study show that it is possible to tailor porous silicon superlattices for custom applications as well as further fundamental studies.

Elastic properties of porous low-k dielectric nano-films

Low-k dielectrics have predominantly replaced silicon dioxide as the interlayer dielectric for interconnects in state of the art integrated circuits. In order to further reduce interconnect RC delays, additional reductions in k for these low-k materials are being pursued via the introduction of controlled levels of porosity. The main challenge for such dielectrics is the substantial reduction in elastic properties that accompanies the increased pore volume. We report on Brillouin light scattering measurements used to determine the elastic properties of these films at thicknesses well below 200 nm, which are pertinent to their introduction into present ultralarge scale integrated technology. The observation of longitudinal and transverse standing wave acoustic resonances and their transformation into traveling waves with finite in-plane wave vectors provides for a direct non-destructive measure of the principal elastic constants that characterize the elastic properties of these porous nano-scale films. The mode dispersion further confirms that for porosity levels of up to 25%, the reduction in the dielectric constant does not result in severe degradation in the Young’s modulus and Poisson’s ratio of the films.

High Frequency Ultrasound, a Tool for Elastic Properties Measurement of Thin Films Fabricated on Silicon

The main goal of this work is to develop an ultrasonic high frequency method for characterization of thin layers. The development of high frequency acoustic transducers for longitudinal waves and shear waves on silicon has enabeled the characterization of thin films deposited on this substrate. Three types of transducers have been achieved : (i) single crystal LiNbOSubscript text3 Y+163° for shear waves generation, and (ii) Y+36° for longitudinal waves, bonded and thinned on silicon substrate to achieve ultrasonic transducers in the frequency range 300-600 MHz ; (iii) thin films ZnO transducers were realized due to sputtering technologies working in the frequency range 1 GHz- 2.5 GHz. Using an inversion method and a network analyser which provide the scattering S11 parameter of the transducer versus the frequency we deduce the elastic properties of films deposited on the wafer surface. Thanks to these transducers the acoustic properties of thin films such as SU-8 based nanocomposites (doped with TiO2 , SrTiO3 or W nanoparticles) will be presented. In order to achieve mechanical impedance matching between silicon and water we control the mass of the embedded particles which provide a way to adjust the elastic properties of the characterized material. In another application an Indium metallic layer have been characterized in the high frequency range. We also use this method to characterize dielectric permittivity of the ZnO transducers.

Hydrodynamic interactions for the measurement of thin film elastic properties

We study the elasto-hydrodynamic (EHD) interaction of a sphere with a flat elastic surface in the prospect of measuring the elastic moduli of soft supported thin films, with non-contact dynamic surface forces or atomic force microscopy measurements. When the sphere is oscillated at a very small amplitude close to the surface, the linear force response undergoes a dynamic transition from a viscous-dominated behaviour at large distance to an elastic-dominated behaviour at short distance. In the limit of very thin or very thick supported layers, we show that the force response obeys simple scaling laws which allow to unambiguously determine the absolute elastic modulus of the layer. In the general case, we establish the very rich phase diagram of the EHD interaction and discuss its application for optimizing experimental parameters.