Strain In Thin Films Research Articles

Depth dependent lattice disorder and strain in Mn-implanted and post-annealed InAs thin films

The lattice order degree and the strain in as-grown, Mn-implanted and post-implanted annealed InAs thin films were investigated with depth resolution by means of Rutherford backscattering spectrometry in channeling conditions (RBS/C). Three main crystallographic axes were analyzed for both In and As sublattices. The behaviour of the induced defects was evaluated in two regions with different native defects: the interface and the surface. The results show that Mn implantation and post-implantation annealing are anisotropic processes, affecting in a different way the In and As sublattices. The mechanisms influencing the enhancement and deterioration of the crystal quality during the implantation are discussed in relation to the as-grown defects and the segregation of the elements.

Large field-induced strains in a lead-free piezoelectric material

Piezoelectric materials exhibit a mechanical response to electrical inputs, as well as an electrical response to mechanical inputs, which makes them useful in sensors and actuators. Lead-based piezoelectrics demonstrate a large mechanical response, but they also pose a health risk. The ferroelectric BiFeO(3) is an attractive alternative because it is lead-free, and because strain can stabilize BiFeO(3) phases with a structure that resembles a morphotropic phase boundary. Here we report a reversible electric-field-induced strain of over 5% in BiFeO(3) films, together with a characterization of the origins of this effect. In situ transmission electron microscopy coupled with nanoscale electrical and mechanical probing shows that large strains result from moving the boundaries between tetragonal- and rhombohedral-like phases, which changes the phase stability of the mixture. These results demonstrate the potential of BiFeO(3) as a substitute for lead-based materials in future piezoelectric applications.

Measurement of applied strains in thin films deposited onto polymer by synchrotron X-ray diffraction

The objective of the present work is to study the elastic behaviour of composites exhibiting strong mechanical contrast components, namely, nanostructured metallic thin films deposited onto polymeric substrates. The stiff film/compliant substrate composites are submitted to complex stress fields during elaboration or applications and the use of a biaxial tensile device allows us mimicking the stress field of in-service thin films. The mechanical characterization of such structures and the relationship with the micro structure still require for further understanding both from fundamental and technological point of view. In such a way, the strain measurements at the macroscopic level have to be correlated with those at the microscopic level. In the present study, the applied strains were measured in situ both by X-ray diffraction (at the microscopic scale) and by digital image correlation (at the macroscopic scale). We used the biaxial testing machine dedicated to the DiffAbs beam line at the French synchrotron SOLEIL, which allows for controlling equi- or non-equi-biaxial loading on thin films supported by polymeric substrates. The metallic thin films were produced via Physical Vapour Deposition onto the centre of a cross-shaped polyimide substrate (Kapton®). The film-substrate composites were then deformed in the DiffAbs X-ray goniometer. Grain interaction models are very simple in the case of perfect local elastic isotropic materials such as tungsten. Such a material allows for directly comparing micro-strains (X-ray elastic strains) to macro-strains (DIC strains). The first results concerning W/Cu thin films deformed in situ with this biaxial testing machine are presented.

Electrical Resistivity Improvement by Precipitation and Strain in Al-Cu Thin Films

This work deals with Al-Cu thin films, deposited onto glass substrates by RF (13.56MHz) magnetron sputtering, and annealed at 773K. The film thickness was approximately the same 3-4µm. They are characterized with respect to microstructure, grain size, microstrain, dislocation density and resistivity versus copper content. Al (Cu) deposits containing 1.8, 7.21, 86.17 and 92.5at%Cu have been investigated. The use of X-ray diffraction analysis and transmission electron microscopy lead to the characterization of different structural features of films deposited at room temperature (< 400K) and after annealing (773K). The resistivity of the films was measured using the four-point probe method. The microstrain profile obtained from XRD thanks to the Williamson-Hall method shows an increase with increasing copper content.

Phonon Raman scattering of perovskite LaNiO3 thin films

We report an investigation of perovskite-type LaNiO3 thin films by Raman scattering in both various scattering configurations and as a function of temperature. The room-temperature Raman spectra and the associated phonon mode assignment provide reference data for phonon calculations and for the use of Raman scattering for structural investigations of LaNiO3, namely, the effect of strain in thin films or heterostructures. The temperature-dependent Raman spectra from 80 to 900 K are characterized by the softening of the rotational A1g mode, which suggests a decreasing rhombohedral distortion toward the ideal cubic structure with increasing temperature.

Effect of strain on the magnetic anisotropy in the epitaxial magnetic thin films

A phenomenological thermodynamic theory of magnetic thin films epitaxially grown on cubic substrates is developed by considering the thermodynamic potential, which corresponds to the actual mechanical boundary conditions. For clamped magnetic thin films with two-dimension strains, the study reveals that the magnitudes of remanent magnetization M r and coercive field H c are dependent on the strain induced by the lattice mismatch. The tensile strain can significantly enhance the out-of-plane magnetization with a larger coercivity, while the compressive strain makes correspondingly thin films exhibit an opposite in-plane magnetic anisotropy. Our analysis provides a profound understanding of magnetic anisotropy mechanism and the relationship with lattice strain in the epitaxial magnetic thin film.

Dislocation dynamics simulations of dislocation interactions and stresses in thin films

The dislocation interactions that stop threading dislocations (threads) during relaxation at increasing applied strains in single-crystal thin films are investigated using large-scale three-dimensional dislocation dynamics simulations. Threads were observed to stop via interactions with both threads and misfit dislocations (misfits). Both types of interactions were shown to depend on stress inhomogeneity. Low-stress regions enabled threads to stop in weak thread–misfit interactions even at high average film stresses. Threads were also concentrated in low-stress regions, which facilitated their interaction with other threads. Threads accumulated in thread–thread interactions, and stopped only temporarily in thread–misfit interactions. The mean free path for dislocation motion is shown to be accurately predicted from details of the inhomogeneous stress state arising from the applied strain and the misfit structure. These behaviors are analyzed to present a more complete picture of film strength, strain hardening and relaxation.

Effects of substrate temperatures on the crystallizations and microstructures of electron beam evaporation YSZ thin films

Yttria-stabilized zirconia (YSZ) thin films were grown on Si(1 0 0) substrate using electron beam (E-beam) evaporation by changing the substrate temperature from room temperature (RT) to 250 °C. Effects of different substrate temperatures on the crystalline structure, the lattice constant, the grain growth, and the strain of YSZ thin films and the thickness of interfacial SiO x layer between Si wafer and YSZ thin films were developed. Even depositing at room temperature, X-ray diffraction (XRD) analyses showed that the reflection peaks of (1 1 1), (2 0 0), (2 2 0), and (3 1 1) planes were formed. The relative reflection intensities of (1 1 1), (2 0 0), (2 2 0), and (3 1 1) planes were changed as the different substrate temperatures were used. The strains of YSZ thin films increased with increasing substrate temperature and reached a minimum value at 200 °C. The amorphous interlayer formed between Si wafer and YSZ thin films and the images of lattice mismatch were also analyzed by using high resolution transmission electron microscopy (HRTEM).

Effects of substrate-induced strain on transport properties ofLaMnO3+δandCaMnO3thin films using ferroelectric poling and converse piezoelectric effect

We have investigated the effects of the strain induced by ferroelectric poling (or the converse piezoelectric effect) on the transport properties of ${\text{LaMnO}}_{3+\ensuremath{\delta}}$ and ${\text{CaMnO}}_{3}$ thin films grown on ferroelectric $0.67\text{Pb}({\text{Mg}}_{1/3}{\text{Nb}}_{2/3}){\text{O}}_{3}\text{\ensuremath{-}}0.33{\text{PbTiO}}_{3}$ single-crystal substrates. The ferroelectric poling of the substrate gives rise to a reduction in the in-plane tensile strain of the ${\text{LaMnO}}_{3+\ensuremath{\delta}}$ film, which results in a significant decrease in the resistance and increase in the insulator-to-metal transition temperature ${T}_{P}$ of the film. The ferroelectric poling also leads to opposite effects on the magnetoresistance (MR) below and above ${T}_{P}$, namely, MR is reduced for $Tl{T}_{P}$ while MR is enhanced for $Tg{T}_{P}$. These strain effects are explained in terms of coexisting phases whose volume fractions are modified as a result of the reduction in the Jahn-Teller (JT) distortion due to ferroelectric poling. An investigation of the effects of the strain induced by the converse piezoelectric effect on the resistance of the ${\text{LaMnO}}_{3+\ensuremath{\delta}}$ and ${\text{CaMnO}}_{3}$ films shows that the resistance-strain coefficients $(\ensuremath{\Delta}R/R)/(\ensuremath{\Delta}{c}_{film}/{c}_{film})$ of the ${\text{LaMnO}}_{3+\ensuremath{\delta}}$ film is much larger than those of the ${\text{CaMnO}}_{3}$ film. This result may imply that the strain-induced modification of the electronic bandwidth alone cannot account for the large $(\ensuremath{\Delta}R/R)/(\ensuremath{\Delta}{c}_{film}/{c}_{film})$ observed in the ${\text{LaMnO}}_{3+\ensuremath{\delta}}$ film, and highlights that the strong coupling of charge carriers to JT distortion is crucial for understanding the effects of the substrate-induced strain in manganite thin films.

Modification of magnetic properties through the control of growth orientation and epitaxial strain in SrRuO3 thin films

We studied the correlation between the magnetic properties and the structural modifications in SrRuO3 thin films. Previous results on the control of growth orientation in SrRuO3 thin film have been rather limited. For example, only orthorhombic a-axis growth could be obtained for SrRuO3 film on SrTiO3 (110) substrates. Here we were able to obtain various SrRuO3 films with (100)o, (010)o, and (111)o growth orientations, as well as with different amount of strain on SrTiO3 (110) substrates by using (Ca,Sr)SnO3 and CaHfO3 buffer layers. The magnetic properties were found to change systematically with the structural distortion of the SrRuO3 thin films.

CaO buffer layer for the growth of ZnO thin film

We report the effect of CaO buffer layers on the structural properties of sputter-grown ZnO thin films. X-ray diffraction patterns indicated that enhanced crystallinity and alleviated compressive strain in the ZnO thin film were achieved by inserting a very thin CaO buffer layer between ZnO and the sapphire substrate. The interface was investigated by high-resolution transmission electron microscopy, and the result showed that the growth of CaO on the sapphire substrate follows the Stranski–Kristanov mode. The mechanism for the control of crystallinity and strain in the ZnO thin film was discussed, and was found to be strongly related to the growth mode of the CaO buffer layer.

스퍼터링법으로 증착된 산화아연 박막의 구조적 성질에 대한 산화마그네슘 완충층의 효과 연구

The effect of MgO buffer layer on the structural properties of sputter-grown ZnO thin film was investigated. Sapphire (0001) and Si (100) substrate were used for the growth and MgO buffer layer was inserted between ZnO thin film and the substrate. X-ray diffraction pattern indicated that enhanced crystallinity in the ZnO thin film grown was achieved by inserting very thin MgO buffer layer, regardless of the substrate type. The strain in the ZnO thin film could also be controlled by the insertion of the MgO buffer layer, and tendency of the strain was strongly dependent on the substrate type.

Influence of Substrate Bias on the Structural and Dielectric Properties of Magnetron-Sputtered BaxSr1-xTiO3 Thin Films

The application of a substrate bias during rf magnetron sputtering alters the crystalline structure, grain morphology, lattice strain and composition of BaxSr1-xTiO3 thin films. As a result, the dielectric properties of Pt/BaxSr1-xTiO3/Pt parallel-plate capacitors change significantly. With increasing substrate bias we observe a clear shift of the ferroelectric to paraelectric phase transition towards higher temperature, an increase of the dielectric permittivity and tunability at room temperature, and a deterioration of the dielectric loss. To a large extent these changes correlate to a gradual increase of the tensile in-plane film strain with substrate bias and an abrupt change in film composition.

Tunable lattice strain in vertically aligned nanocomposite (BiFeO3)x:(Sm2O3)1−x thin films

Unique epitaxial two-phase vertically aligned nanocomposite (VAN) (BiFeO3)x:(Sm2O3)1−x thin films were deposited on SrTiO3(001) substrates by pulsed laser deposition. The VAN thin films exhibit a highly ordered vertical columnar structure with high epitaxial quality. We demonstrate that the strains of the two phases in both out-of-plane and in-plane directions can be tuned by the deposition parameters during growth, e.g., deposition frequency and film composition of the nanocomposite. The strain tunability is found to be directly related to the systematic variation in the column widths in the nanocomposite. The dielectric property measurement shows that increasing vertical strain control will lead to a systematic dielectric loss reduction in the VAN thin films. This study suggests a promising avenue in achieving tunable strain in functional oxide thin films by using VAN structures.

Easy calibration method of vision system for in-situ measurement of strain of thin films

An easy calibration method was presented for in-situ measurement of displacement in the order of nanometer during micro-tensile test for thin films by using CCD camera as a sensing device. The calibration of the sensing camera in the system is a central element part to measure displacement in the order of nanometer using images taken with the camera. This was accomplished by modeling the optical projection through the camera lens and relative locations between the object and camera in 3D space. A set of known 3D points on a plane where the film is located on is projected to an image plane as input data. These points, known as a calibration points, are then used to estimate the projection parameters of the camera. In the measurement system of the micro-scale by CCD camera, the calibration data acquisition and one-to-one matching steps between the image and 3D planes need precise data extraction procedures and repetitive user's operation to calibrate the measuring devices. The lack of the robust image feature extraction and easy matching prevent the practical use of these methods. A data selection method was proposed to overcome these limitations and offer an easy and convenient calibration of a vision system that has the CCD camera and the 3D reference plane with calibration marks of circular type on the surface of the plane. The method minimizes the user's intervention such as the fine tuning of illumination system and provides an efficient calibration method of the vision system for in-situ axial displacement measurement of the micro-tensile materials.

Growth strains in thermally grown Al2O3 scales studied using synchrotron radiation

The strains in alumina thin films growing on high-temperature alloys at 1,000−1,100°C and during cooling have been successfully measured in-situ using a novel x-ray technique, exploiting synchrotron radiation at the Advanced Photon Source at Argonne National Laboratory. This paper summarizes results obtained from model alloys, with or without the presence of a reactive element, such as Zr, Hf, and Y, to show the importance of the dynamic nature of the stress evolution process and the effects of alloy composition on the generation and relaxation of these stresses.

Effect of stress on optical band gap of ZnO thin films with substrate temperature by spray pyrolysis

Zinc oxide (ZnO) thin films have been deposited with various substrate temperatures by spray pyrolysis method onto glass substrates. The effects of substrate temperature on the crystallization behavior and optical properties of the films have been studied. The evolution of strain and stress effects in ZnO thin films on glass substrate has been studied using X-ray diffraction. The films deposited at low substrate temperature have large compressive stress of 1.77 GPa, which relaxed to 1.47 GPa as the substrate temperature increased to 450 °C. Optical parameters such as optical transmittance, reflectance, dielectric constant, refractive index and energy band gap have been studied and discussed with respect to substrate temperature. All films exhibit a transmittance of about 85% in the visible region. It was found that the compressive stress in the films causes a decrease in the optical band gap.

Stress and strain in titanium nitride thin films

Titanium nitride (TiN) films, with thickness ranging from 0.02 µm to 1.9 µm, were grown by reactive unbalanced magnetron sputter deposition on silicon substrates. The average film stress is highly compressive in thin films and less compressive in thicker films. Two films, with thicknesses of 0.53 µm and 1.63 µm, were subjected to detailed X-ray diffraction (XRD) analysis. Sin 2 Ψ analysis was performed, both on films attached to the substrate, as well as on free-standing flakes of the film. The flakes were obtained by dissolving the substrate. Sin 2 Ψ analysis, both on the films attached to the substrate as well as on the flakes, did not yield straight lines. By combining the sin 2 Ψ measurements on films attached to the substrate with the sin 2 Ψ measurements on the flakes we were able to distinguish between a residual deformation of the lattice and the deformation due to the biaxial stress. Following this procedure the stress obtained from wafer curvature and from XRD strain measurements coincides. A residual strain parallel to the growth direction of the crystallites with the <111> direction parallel to the growth direction combined with a changeover in film texture from <001> parallel to growth direction to <111> parallel to growth direction leads us to propose a model explaining the dependence of stress on film thickness in TiN thin films.

Interface characterization of SrTiO3/Sr/Si heterostructure through X-ray reflectivity

The growth of hetero-epitaxial strontium titanate (SrTiO3) on single-crystal silicon (Si) substrate is of considerable scientific interest because of its wide range application. Unlike other hetero-epitaxial systems, there exists a fairly large lattice mismatch between SrTiO3 and Si. This leads to the possibility of strain in SrTiO3 thin film. In order to prevent the formation of amorphous SiO2 phase and interdiffusion of component atoms at the interface, an ultrathin strontium (Sr) layer is deposited on the underlying Si-substrate. The X-ray diffraction (XRD) is used for characterization of hetero-structures. In this paper, we report the characterization of SrTiO3 thin film on Si (100) substrate with Sr interlayer by a variety of X-ray measurements. Based on the data obtained from SrTiO3 thin film, the growth characteristics of the sample is objectively appreciated. The sample is prepared by laser molecular beam epitaxy (L-MBE) under optimized conditions of substrate temperature and oxygen pressure. 2θ/ω scan indicates a high crystallization quality and epitaxial grown of SrTiO3 thin film in the nanometre scale. Θ-scans have further revealed the in-plane orientation relationship between SrTiO3 and Si. The α- and c- lattice parameters of the SrTiO3 thin film are found to be 0.3898, and 0.3901 nm, respectively, which suggests a slight elastic distortion. More detailed investigations by X-ray reflectivity have therefore been carried out, in order to get better understanding to the effect of the buried heterointerface.

Vacancy Formation and Strain in Low-TemperatureCu/Cu(100)Growth

The development of compressive strain in metal thin films grown at low temperature has recently been revealed via x-ray diffraction and explained by the assumption that a large number of vacancies were incorporated into the growing films. The results of our molecular dynamics and parallel temperature-accelerated dynamics simulations suggest that the experimentally observed strain arises from an increased nanoscale surface roughness caused by the suppression of thermally activated events at low temperature combined with the effects of shadowing due to off-normal deposition.