Strain In Thin Films Research Articles

CMR effect exalted by substrate-induced strains in thin films of charge ordered manganites

Strained thin films of Nd 0.5Ca 0.5MnO 3 (NCMO) have been synthesized by the pulsed-laser deposition on (1 0 0)-(SrTiO 3) (STO). These films of different thicknesses have been extensively studied with numerous techniques of investigation in order to understand the relationship between structure and transport properties in manganite thin films. This study allowed us to highlight the effects of substrate-induced strains on these materials. We observed a huge decrease of the melting magnetic field. This melting field of 5 T for thin films is much lower than the one (24 T) necessary to induce the metallic phase in the bulk sample. Films undergo two phenomena: firstly, a deformation of the cell by the substrate-induced strains and secondly a structural quenching which freezes the film's structure.

Proximity effect of vanadium on strain and spin-density waves in thin Cr films

Spin-density wave state in thin Cr films is known to be under the influence of proximity effects from neighboring layers. In the present paper, we report on a combined neutron and X-ray scattering study of proximity effects in Cr/V films where the boundary conditions are due to V–Cr hybridization at interfaces. We provide evidence that the V/Cr interface has a strong and long-range influence on the global properties of the strain and spin-density waves in thin Cr films.

Effect of substrate-induced strain on the structural, electrical, and optical properties of polycrystalline ZnO thin films

The effect of substrate-induced strain in polycrystalline ZnO thin films on different substrate, e.g., GaN epilayer, sapphire (0001), quartz glass, Si(111)∕SiO2, and glass deposited by sol-gel process, has been investigated by x-ray diffraction, scanning electron microscope, electrical resistivity, and photoluminescence measurements. A strong dependence of orientation, crystallite size, and electrical resistivity upon the substrate-induced strain along the c axis has been found. The results of structural and morphological studies indicate that relatively larger tensile strain exists in ZnO deposited on sapphire and glass, while a smaller compressive strain appears in film deposited on GaN and the strain is relaxed in larger crystallite size. The electrical resistivity of the films increases exponentially with increasing strain. The excitonic peak positions are found to shift slightly towards lower energy side with increasing strain. The analysis shows that GaN being a closely lattice-matched substrate produces ZnO films of better crystallinity with a lower resistivity.

Optical band gap tuning and study of strain in CdS thin films

In this work we have taken advantage of the control of strains at the CdS films–substrate interfaces to obtain films with tunable energy band gap. We found that on decreasing the amount of strain at the layer–substrate interface, the energy band gap of the films also decreases. Thus, we could obtain CdS films with energy band gap between 2.26 and 2.5eV. The CdS films were deposited on glass slide substrates by the chemical bath deposition method using an ammonia-free cadmium–sodium citrate system. The amount of strain at the CdS–glass substrate interface was controlled by the amount of cadmium ions in the chemical deposition process. The higher the concentration of cadmium ions, the higher the amount of strain at the layer–substrate interfaces. The properties of the CdS films were determined by X-ray diffraction and optical transmission spectroscopy measurements.

Strain-related structural and vibrational properties of thin epitaxialAlNlayers

The effect of film thickness on the strain and structural properties of thin epitaxial AIN films has been investigated by high resolution x-ray diffraction techniques and transmission electron micr ...

Correlation between dielectric properties and strain in Pb 0.5 Sr 0.5TiO 3 thin films prepared by using the sol–gel method

Pb 0.5Sr 0.5TiO 3 (PST) thin films were fabricated by the alkoxide-based sol–gel process using spin-coating method on Pt/Ti/SiO 2/Si substrate. The PST films annealed from 500 °C to 650 °C for 1 h show a perovskite phase and dense microstructure with a smooth surface. The grain size and dielectric constant of PST films increase with the increase in annealing temperature, which reduces the SiO 2 equivalent thickness of the PST film. The crystallinity or internal strain in the PST thin films analyzed from the diffraction-peak widths correlates well with the decrease in the dielectric losses. The dielectric constants and dielectric loss (%) of the PST films annealed at 650 °C ( t eq=0.89 nm) were 549 and 0.21%, respectively.

An experimental technique for the strain measurement of small structures using pattern recognition

For an accurate measurement of the material behavior of small structures, an optical experimental technique is proposed. The test method uses a dual field of view microscope and the pattern matching algorithm. The dual field of view microscope can separately magnify the images of two adjacent regions to enhance the measurement resolution. The magnified views of the dual field of view microscope are captured by CCD cameras and the relative deformation is measured by tracing patterns in the images. A pattern matching and tracing algorithm was adapted to measure the movement of region of interests (ROI) in real time. Using the movement information of the patterns, the strain of a specimen can be obtained. This technique is non-contact as well as easy to apply to a specimen. It can be also applied in various types of specimens without any specimen preparation. Using this experimental technique, the deformation of solder joints in electronic packaging and the strain of the nickel thin film are successfully measured.

Elastic-strain tensor and inhomogeneous strain in thin films by X-ray diffraction

Elastic residual and inhomogeneous defect-related strains are very important parameters when considering thin-film and microelectronics device properties and operation. In regard to the residual strain/stress modeling, we describe a novel approach to model diffraction line shifts caused by elastic residual or applied stresses in textured polycrystals. The model yields the complete texture-weighted strain and stress tensors as a function of crystallite orientations, the so-called weighted strain orientation distribution function. In the second part, we present an extension to the phenomenological thermodynamic theory for ferroelectrics. It includes the contribution of both residual-elastic lattice-misfit strain and inhomogeneous strain caused by lattice defects. The model yields correction terms for dielectric and ferroelectric quantities in terms of both elastic misfit strain and defect-related strain that was successfully applied to the pristine, W and Mn 1% doped Ba 0.6Sr 0.4TiO 3 epitaxial thin films grown on the LaAlO 3 substrate.

Anisotropic in-plane strains and dielectric properties in (Pb,Sr)TiO3 thin films on NdGaO3 substrates

Anisotropic in-plane strain can be induced in (Pb,Sr)TiO3 (PST) thin film by using orthorhombic NdGaO3 (110) as a substrate. High-resolution x-ray diffraction was used to measure the strain of the PST thin film. A rocking curve with full width at half maximum of ∼0.04° illustrated that the film had nearly perfect single-crystalline quality. Reciprocal space maps around the (001), (103), and (013) reflections of the PST film revealed anisotropic in-plane strain of 485 ppm along [100] and 26 ppm along [010], respectively. Coplanar capacitance measurements also showed systematic changes in the dielectric constant and tunability due to strain; about a 15% difference in tunability at surface field of 50 kV/cm and a 20% difference in the zero-field dielectric constant were observed along [100] and [010], respectively.

Correlation of charge transport to intrinsic strain in silicon oxynitride and Si-rich silicon nitride thin films

Poole–Frenkel emission in Si-rich nitride and silicon oxynitride thin films is studied in conjunction with compositional aspects of their elastic properties. For Si-rich nitrides varying in composition from SiN1.33 to SiN0.54, the Poole–Frenkel trap depth (ΦB) decreases from 1.08 to 0.52 eV as the intrinsic film strain (εi) decreases from 0.0036 to −0.0016. For oxynitrides varying in composition from SiN1.33 to SiO1.49N0.35, ΦB increases from 1.08 to 1.53 eV as εi decreases from 0.0036 to 0.0006. In both material systems, a direct correlation is observed between ΦB and εi. Compositionally induced strain relief as a mechanism for regulating ΦB is discussed.

Domain Engineering of Epitaxial PbTiO3 Thin Films by the Control of Misfit Strain

Ferroelectric domain structures and their evolution in the epitaxial PbTiO3 thin films are greatly affected by the misfit strain and its relaxation during epitaxial film deposition on single crystalline MgO(001) substrates with epitaxial Pt electrode interlayer. The misfit strain could be controlled by varying the underlying interlayer thickness. As the thickness of Pt electrode decreases from 120 nm to 12 nm, the effective lattice constant of Pt electrode increases due to the suppressed generation of misfit dislocations at the Pt(001)/MgO(001) interface. Consequently, the compressive misfit strain in PbTiO3 thin films decreases due to the decreased lattice mismatch with Pt electrode, which enhances the formation of 90° domains. Equilibrium domain structures in the epitaxial thin films are also analyzed by the finite element simulation and found to be consistent with the experimental observation. The results manifest that the domain structure and evolution of the epitaxial PbTiO3 thin films could be engineered by the control of misfit strain.

Solid-like dynamics in ultrathin films of polymeric liquids

In this letter, we demonstrate that, at mesoscales, nonferroelectric liquid films of poly(dimethyl siloxane) exhibit significant electrostriction not present in the corresponding bulk state. Remarkably, the observed electrostrictive effect has a response time <20 μs in contrast to >5 ms recorded in conventional bulk (ferroelectric) polymers. The emergence of this fast electrostrictive strain in thin films is explained in terms of the amalgamation of two contrasting dynamic features—the influence of a highly mobile, viscous layer (at the air/film interface) on the less-mobile, but fast responding, solid-like layer at the film/substrate interface. The effect is observed for thickness below 200 nm.

Generalized infrared ellipsometry study of thin epitaxial AlN layers with complex strain behavior

The effect of film thickness on the strain and structural properties of thin epitaxial AlN films has been investigated, and a sub-layer model of the degree of strain and related defects for all films is suggested. The vibrational properties of the films have been studied by generalized infrared spectroscopic ellipsometry. The proposed sub-layer model has been successfully applied to the analysis of the ellipsometry data trough model calculations of the infrared dielectric function.

Strain and stress calculation in bulk magnetostrictive materials and thin films

In this paper, we examine some of the inconsistencies present in the solutions obtained by previous authors for the problem of finding the strains, stresses and energy densities observed in isotropic elastic magnetostrictive materials that are subjected to an arbitrary uniaxial stress, or that are in the form of thin films deposited on non-magnetic substrates. The origin of the inconsistencies is identified and more general and self-consistent solutions using an energy method based on minimization of the Gibbs free energy of the specimens are proposed. The proposed method can be used to solve problems that involve three-dimensional states of stress and can include thermal, piezoelectric, hygroscopic or other types of expansional strains. The advantages over the methods currently used are illustrated by solving a problem in which a film–substrate cantilever is subjected to the action of a point load applied at its free end. Expressions are derived to accurately calculate the strains, stresses and deflections of such a beam, regardless of the relative thickness of the film compared to the substrate. Additionally, the results are used to derive the conditions that define film–substrate cantilevers that show maximum deflection, as required in the case of sensors, or that exert maximum force, as required in the case of actuators.

736 トランジスタ絶縁膜残留歪に及ぼす微細化の影響

736 トランジスタ絶縁膜残留歪に及ぼす微細化の影響

Pyroelectric Properties of Ferroelectric Thin Films: Effect of Internal Stresses

ABSTRACTA thermodynamic model is employed to analyze the effect of internal stresses on the pyroelectric response of ferroelectric thin films. The pyroelectric coefficient as a function of the misfit strain is calculated for (001) Ba0.6Sr0.4TiO3 epitaxial thin films by taking into account formation of misfit dislocations that relieve epitaxial stresses during deposition. It is shown that the pyroelectric response is highly dependent on the misfit strain in epitaxial thin films. Enhanced pyroelectric coefficient can be achieved by adjusting the misfit strain via substrate selection and film thickness especially in the vicinity of the ferroelectric to paraelectric phase transformation.

An elastic–plastic shear lag model for fracture of layered coatings

We present a phenomenological model describing cracking under uniaxial tensile strain of a brittle thin film on a deformable substrate with an elastic–plastic interface layer. The model yields an analytical solution predicting average crack density and average crack opening as a function of applied strain and material parameters. The model has been applied to experimental data for cracks in thin SiO x films on PET substrates.

Solutions and Discussions of thin film Undergoing the Nonlinear Peeling

ABSTRACTBased on the bending model, three double-parameter criteria characterizing thin film peeling process are introduced and analyzed in detail. Three double-parameter criteria include: (1) the interfacial fracture toughness and the separation strength, (2) the interfacial fracture toughness and the interfacial crack tip slope angle of thin film, and (3) the interfacial fracture toughness and the critical von Mises effective strain of thin film at crack tip. Based on the three double-parameter criteria, the thin film nonlinear peeling problems are solved analytically for each case. The results show that the solutions of thin film nonlinear peeling based on the bending model are very sensitive to the model parameter selections. Through analyses and comparisons for different solutions, a connection between solutions based on the bending models and based on the two-dimensional elastic-plastic finite element analysis is obtained.

패턴 인식을 통한 미소 구조물의 변형 측정 기법 개발

For an accurate measurement of the material behavior of small structures, a new optical experimental technique is proposed to measure the deformation. The test method uses the dual microscope that can measure the relative deformation of two adjacent regions. The magnified view is captured by CCD cameras and the relative deformation can be measured by the pattern matching and tracing method. Using this experimental technique, the deformation of solder joints in electronic packaging and the strain of the nickel thin film are measured.

Epitaxial strain and superconductivity in La2-xSrxCuO4 thin films.

The report that T(c) was doubled in underdoped La2-xSrxCuO4 films under compressive epitaxial strain has stirred great interest. We show that such films are extremely sensitive to oxygen intake, even at very low temperature, with startling consequences including colossal lattice expansion and a crossover from semiconductor to metallic behavior. We can bring T(c) up to 40 K in La2CuO4 films on SrTiO3 substrates-without any Sr doping and under tensile strain. On LaSrAlO4 substrates, we reached T(c)=51.5 K, the highest so far in La2-xSrxCuO4.