Material Properties Of Thin Films Research Articles

Finite element analysis of TiN coated thin film

Finite element analysis (FEA) is one of the most widely used techniques in predicting the material behavior under loading conditions in various applications e.g., thin film coating. Thin film coating offers superior mechanical characteristics such as hardness, resistance to wear, etc. In this study, the finite element analysis method is used along with the Johnson Cook Plasticity Model to obtain the deformation behavior and stress distribution of TiN-coated thin film sample. Material properties of TiN thin film coating obtained through nanoindentation are the inputs for the material model. Berkovich indenter is modelled to simulate the results. Elastoplastic analysis is done under different strain conditions as per the Johnson Cook Plasticity Model. FEA model results obtained are compared with the reported results. There is a close match between the values of material model 6 and experiment 1 which suggests that FEA is a prominent tool in predicting the nanoindentation results.

Effects of gamma radiation on structural, optical, and electrical properties of SnO2 thin films

Gamma irradiation at specific doses controls the material properties of thin films because of its high-ionization energy and high penetrating power. In the present work, the effects of gamma irradiation (γ-rays) on the structural, morphological, electrical, and optical properties of pulsed laser-deposited SnO2 thin films were examined. These films were exposed to γ-rays for doses of 0, 75, 100, 125, and 200 kGy. X-ray diffraction analysis reveals that the films are polycrystalline with a crystallite size of 49.27 nm and it increases with the gamma doses. While the dislocation density and the microstrain decrease, the band gap reduces from 3.8 eV to 3.4 eV with the increase in doses. Raman spectra show the presence of defects caused by gamma irradiation and the photo luminance spectra demonstrate a decrease in the peak intensities for thin films. The blue emission at 437 nm, is associated with oxygen-related defects produced during the phase formation. The Hall measurements confirm that these films are of n-type semiconductors. The I–V characteristics show a rise in conductivity linearly up to 125 kGy and a reduction at 200 kGy due to oxygen vacancies created at the higher gamma doses. The electrical conductivity of all the films increases as a function of temperature, and gamma doses as evident from the rectification behavior. This study infers that gamma rays can modify the material properties hence these films are useful as an electrode for sensing and radiation detection.

Impact of monolayer engineering on ferroelectricity of sub-5 nm Hf0.5Zr0.5O2 thin films

The sub-5 nm Hf0.5Zr0.5O2 (HZO) thin films have been studied for years; however, they still suffer from challenges including poor ferroelectricity, wake-up effect, and the need for high-temperature annealing. In this paper, the concept and the method of “monolayer engineering” by atomic layer deposition (ALD) are proposed and implemented, which leads to dramatic improvements in the crystallinity and ferroelectricity of the HZO thin film with a thickness of only ∼4 nm at a low annealing temperature of only 370 °C. By substituting one ZrO2 for one HfO2 atomic layer, a high ferroelectric remnant polarization (Pr) ∼15 μC/cm2 is achieved in the HZO thin film. Moreover, the pronounced ferroelectric characteristics are demonstrated in the pristine state, indicating the nearly wake-up-free property of the HZO layer. This study manifests that the monolayer engineering by ALD enables atomic tailoring to enhance the material and physical properties of nanoscale thin films.

Atomic layer engineering on resistive switching in sub-4 nm AlN resistive random access memory devices

This study demonstrates the precise tailoring of material properties of nanoscale thin films and electrical properties of AlN RRAM devices by atomic layer annealing.

Dimensionless Analysis to Determine Elastoplastic Properties of Thin Films by Indentation

By assuming the elastoplastic properties of thin-film materials, a reverse analysis method is proposed by deriving a dimensionless function for the indentation process. The substrate effect is taken into account by assuming a perfect interface between thin-film and substrate materials. In order to obtain the applied load–penetration depth (P-h) curves, the indentation process is numerically modeled as an axisymmetric problem with a rigid-body Berkovich indenter on the semi-infinite substrate when performing finite element (FE) simulations. As a typical soft film/hard substrate problem, the elastic substrate is assumed and the power–law model is used to describe the constitutive properties of thin-film materials. Varying elastic modulus (10–50 GPa), yield strength (60–300 MPa), and hardening exponent (0.1–0.5) characterize different elastoplastic mechanical properties of thin-film materials with film thickness of 10–30 μm. Owing to the good trending P-h curves with the maximum indentation depth up to the 2/3 film thickness for different elastoplastic thin-film materials, a dimensionless function is derived and validated based on the predictions by reliable FE simulations. The proposed dimensionless function elegantly elucidates the essential relationship between the elastoplastic mechanical properties of the thin-film material and indentation responses (e.g., loading and unloading variables). The elastoplastic constitutive curves predicted by the proposed reverse method are confirmed to be in good agreement with the stress-strain curves of materials by FE simulations with the randomly selected elastoplastic mechanical properties and film thicknesses. This study provides a theoretical guidance to understand the explicit relationship between elastoplastic mechanical properties of the thin-film material and indentation responses.

Effect of vanadium precursor on dip-coated vanadium oxide thin films

The effect of chemical substances is reported on the structure, surface morphology, and material properties of vanadium oxide thin films. The study of the chemical substances concentrated on the effects of initial materials (e.g., NH4VO3, NaVO3, VO2, vanadyl acetylacetonate, ammonium decavanadate) and various additives (e.g., acids, chelate ligand, reduction reagent, and tensides). The syntheses are based on sol-gel chemistry. The important aim of the sol-gel technique was to optimize the chemical conditions such as catalyst and solvent for the preparation of perfect V5+-containing layers. The other aim was to check the controllability of the V4+/V5+ ratios. The control was performed in the air by using a reducing agent and in a nitrogen atmosphere. The atomic and bond structures were investigated by 51V MAS NMR, IR, and UV spectroscopies. The supramolecular structures were determined by SEM, EDX, and GIXRD techniques.Graphical abstract

Effect of different substrates on material properties of cubic GaN thin films grown by LP-MOCVD method

The III-nitride cubic phase are promising materials in photovoltaics and other optoelectronic devices due to their favorable material properties. This research work presents the growth of cubic gallium nitride (c-GaN) thin films on two different substrate gallium phosphide (GaP) and gallium arsenide (GaAs) substrates using the low-pressure metal–organic chemical vapor deposition (LP-MOCVD) technique. The growth conditions are modified for each substrate to obtain c-GaN epitaxial films with good crystalline quality. Stress values for c-GaN epitaxial layers 0.62 GPa and 1.24 GPa were calculated using X-ray diffraction measurements for c-GaN grown on GaP and GaAs substrates, respectively. The stress state calculated by XRD proved that in both cases, c-GaN on GaP and on GaAs substrates, they was compressed layers. Raman measurements showed two peaks for c-GaN at 555 cm−1 (TO) and 745 cm−1 (LO) modes for c-GaN grown on GaP. For GaAs, only observed 555 cm−1 (TO) mode. It obtained the formation of c-GaN epitaxial films on both substrates. The surface morphology and the quality of the films depend on the type of substrates, compact layers with better crystalline quality are observed in the samples grown in GaP than GaAs substrate. Band gap (Eg) of GaN was obtained with approximate values of 380 nm for c-GaN of both substrates, which is where the Eg of c-GaN is found.

Bi-Substituted Ferrite Garnet Type Magneto-Optic Materials Studied at ESRI Nano-Fabrication Laboratories, ECU, Australia

Since 2007, at the Electron Science Research Institute (ESRI) nano-fabrication laboratories, Edith Cowan University, Australia, we have devoted research efforts to the synthesis and characterization of bismuth-containing ferrite-garnet-type thin-film magneto-optic (MO) materials of different compositions. We report on the growth and characteristics of radio frequency (RF) magnetron sputtered bismuth-substituted iron-garnet thin films. We study the process parameters associated with the RF magnetron sputter deposition technique and investigate the results of optimizing process parameters. To achieve the best MO properties, we employ a few unique techniques, such as co-sputtered nanocomposite films and all-garnet multilayer structures, as well as the application of oxygen plasma treatment to amorphous garnet layers immediately following the deposition process. We demonstrated a remarkable enhancement in the MO properties of Bi-containing ferrite-type garnet thin-film materials, including record-high MO figures of merit and improved conventional and unconventional hysteresis loops of Faraday rotation. Previously unpublished research results on the forward-looking applications of magnetic garnet coatings applied to microparticles of advanced luminescent materials are reported. In the context of developing the next-generation ultra-fast optoelectronic devices, such as light intensity switches and modulators, high-speed flat panel displays, and high-sensitivity sensors, it is important to consider the desirable optical, magnetic, and magneto-optic properties that are found in highly bismuth-substituted iron garnet thin-film materials of various composition types.

Ge/Al and Ge/Si3N4/Al Core/Shell Quantum Dot Lattices in Alumina: Boosting the Spectral Response by Tensile Strain.

We investigated the production conditions and optoelectrical properties of thin film material consisting of regularly ordered core/shell Ge/Al and Ge/Si3N4/Al quantum dots (QDs) in an alumina matrix. The materials were produced by self–assembled growth achieved by means of multilayer magnetron sputtering deposition. We demonstrated the successful fabrication of well-ordered 3D lattices of Ge/Al and Ge/Si3N4/Al core/shell quantum dots with a body-centred tetragonal arrangement within the Al2O3 matrix. The addition of shells to the Ge core enables a strong tuning of the optical and electrical properties of the material. An Al shell induces a bandgap shift toward smaller energies, and, in addition, it prevents Ge oxidation. The addition of a thin Si3N4 shell induces huge changes in the material spectral response, i.e., in the number of extracted excitons produced by a single photon. It increases both the absolute value and the width of the spectral response. For the best sample, we achieved an enhancement of over 250% of the produced number of excitons in the measured energy range. The observed changes are, as it seems, the consequence of the large tensile strain in Ge QDs which is induced by the Si3N4 shell addition and which is measured to be about 3% for the most strained QDs. The tensile strain causes activation of the direct bandgap of germanium, which has a very strong effect on the spectral response of the material.

Hemocompatibile Thin Films Assessed under Blood Flow Shear Forces.

The aim of this study was to minimize the risk of life-threatening thromboembolism in the ventricle through the use of a new biomimetic heart valve based on metal–polymer composites. Finite volume element simulations of blood adhesion to the material were carried out, encompassing radial flow and the cone and plane test together with determination of the effect of boundary conditions. Both tilt-disc and bicuspid valves do not have optimized blood flow due to their design based on rigid valve materials (leaflet made of pyrolytic carbon). The main objective was the development of materials with specific properties dedicated to contact with blood. Materials were evaluated by dynamic tests using blood, concentrates, and whole human blood. Hemostability tests under hydrodynamic conditions were related to the mechanical properties of thin-film materials obtained from tribological tests. The quality of the coatings was high enough to avoid damage to the coating even as they were exposed up to maximum loading. Analysis towards blood concentrates of the hydrogenated carbon sample and the nitrogen-doped hydrogenated carbon sample revealed that the interaction of the coating with erythrocytes was the strongest. Hemocompatibility evaluation under hydrodynamic conditions confirmed very good properties of the developed coatings.

Identification of Mechanical Properties of Thin-Film Elastoplastic Materials by Machine Learning

Identification of Mechanical Properties of Thin-Film Elastoplastic Materials by Machine Learning

Effects of working pressure on the material and defect properties of Sb2S3 thin-film solar cells achieved by the VTD method.

Antimony sulfide (Sb2S3), an emerging material for photovoltaic devices, has drawn growing research interest due to its inexpensive and high-throughput device production. In this study, the material and defect properties of Sb2S3 thin films prepared by the vapor transport deposition (VTD) method at different working pressures were studied. Solar cells based on a structure of glass/ITO/CdS/Sb2S3/Au were fabricated. The working pressure showed a significant effect on the device's performance. The current density versus voltage measurement and scanning electron microscopy analysis outcome were utilized to investigate the photovoltaic and microstructural properties in the samples. The compositional analysis by energy dispersive X-ray spectroscopy measurement confirmed the Sb/S ratio as 2:2.8 for the thin films. The identification and characterization of the defects present in Sb2S3 thin films were performed via admittance measurements. Compared to the defect density, the defect energy level was found to inherit a more important role in the device's performance. The best solar cell performance with better crystal quality, lower defect density, and longer capture lifetime was achieved under the substrate working pressure of 2 Pa. The highest efficiency was found to be 0.86% with Voc=0.55V, Jsc=5.07mA/cm2.

Evaluation of thin film material properties using a deep nanoindentation and ANN

Due to the substrate effect, there are several difficulties to evaluate the material properties of thin films via nanoindentation. In this study, an inverse analysis method based on an artificial neural network (ANN) is proposed to obtain free-volume-model (FVM) parameters of thin film metallic glass (TFMG) via nanoindentation. Unlike conventional nanoindentation procedures for thin films, a deeper indentation depth (≈ 30% of film thickness) is adopted to accurately identify the film properties even with significant substrate deformations. Both sphero-conical and Berkovich tips are employed to ensure unique solutions. A complex mapping function of inverse analysis is replaced by establishing ANN between nanoindentation (features) and material (targets) parameters. The established ANN model is trained with the database generated via systematic finite element analyses (FEA). The trained ANN model is experimentally validated by estimating the material properties of Zr55Cu30Ag15 TFMG deposited on two different substrates (Si and soda lime glass). The maximum difference of plastic indentation energy between experiments and FEA values using the estimated film material properties was within 3%.

Atomistic kinetic Monte Carlo simulation on atomic layer deposition of TiN thin film

The atomic layer deposition (ALD) process of TiN thin films is widely used in microelectronics, but the detailed growth mechanism is still elusive at the atomistic level. In the present computational study, we carry out kinetic Monte Carlo (kMC) simulations on the ALD process using TiCl4 and NH3 precursors. Based on the on-lattice model, we sort out key reactions relevant for the ALD process such as adsorption/desorption of precursors, generation of surface Cl atoms, and evolution of free HCl and Cl2 molecules. The reaction energies considering local environments are calculated at the level of density functional theory (DFT) while the activation barriers are linearly fitted to sampled cases among distinct reaction families. The resulting kMC model produces the temperature-dependent growth rates and the amounts of Cl residues in reasonable agreement with experiments. The detailed growth pathway is discussed based on the simulation results, which underscores the critical role of surface Cl atoms in the ALD process by generating HCl gas molecules. By revealing the atomistic mechanisms in the TiN-ALD process, the present work would help optimize material properties of TiN thin films.

Subpicosecond Optical Stress Generation in Multiferroic BiFeO3.

Optical excitation leads to ultrafast stress generation in the prototypical multiferroic BiFeO3. The time scales of stress generation are set by the dynamics of the population of excited electronic states and the coupling of the electronic configuration to the structure. X-ray free-electron laser diffraction reveals high-wavevector subpicosecond-time scale stress generation following ultraviolet excitation of a BiFeO3 thin film. Stress generation includes a fast component with a 1/e rise time with an upper limit of 300 fs and longer-rise time components extending to 1.5 ps. The contributions of the fast and delayed components vary as a function of optical fluence, with a reduced a fast-component contribution at high fluence. The results provide insight into stress-generation mechanisms linked to the population of excited electrons and point to new directions in the application of nanoscale multiferroics and related ferroic complex oxides. The fast component of the stress indicates that structural parameters and properties of ferroelectric thin film materials can be optically modulated with 3 dB bandwidths of at least 0.5 THz.

Assessment of the Functional Properties of Thin-Film Materials for Coating Cardiac Pacemaker Electrodes

Assessment of the Functional Properties of Thin-Film Materials for Coating Cardiac Pacemaker Electrodes

Effect of low energy nitrogen ion irradiation on MoO3 films

In the present work, Molybdenum trioxide (MoO3) thin films were deposited by the electrophoretic deposition (EPD) method. Low energy ion irradiation was used to alter the materials properties of MoO3 films. Ion irradiation was carried out at a constant ion fluence of 2.16 x 1016 ions/cm2 for energies varying from 10 keV to 40 keV. The X-ray diffraction (XRD) and Raman spectroscopy revealed the orthorhombic α-MoO3 phase. The optical band gap was observed to change from 3.73 eV to 3.08 eV in a controlled manner due to ion irradiation. Morphology of nanobelt-like structures was seen at the highest energy of ion irradiated films. Atomic force microscopy (AFM) revealed a decrease in the surface roughness with an increase in irradiated ion energy. All results are in corroboration with each other and comprehend the process of tailoring the material properties of MoO3 thin film due to low energy ion irradiation. These tailored properties could be useful for electronic or optical device applications.

Structural and electronic properties of HfO2 films on Si through H2O2 wet oxidation with improved thermal stability

The thermal stability and material properties of HfO2 thin films on Si substrates with and without H2O2 wet chemical oxidation were investigated. The HfO2 samples were deposited through plasma‐enhanced atomic layer deposition and subjected to thermal annealing. They were then examined using X‐ray diffraction, transmission electron microscopy, X‐ray photoelectron spectroscopy, reflection electron energy loss spectroscopy, and conductive atomic force microscopy. For the Si substrate without H2O2 wet chemical oxidation, a native oxide (~1.8 nm) was formed on the substrate before HfO2 deposition. After the annealing process at 600°C, the band gap (Eg) of the HfO2 films increased from 6.0 to 6.2 eV due to the diffusion of Si into HfO2. Furthermore, the conduction and valence band offsets (ΔEc and ΔEv, respectively) between HfO2 and Si changed from 1.02 to 1.42 and 3.86 to 3.66 eV, respectively. After the H2O2 wet oxidation of the Si substrate, a 1.5‐nm chemical oxide was formed instead of a native oxide. The band offset and Eg values of HfO2 were similar before and after 600°C annealing (ΔEv = 3.86 eV, ΔEc = 1.02 eV, and Eg = 6.0 eV), implying the high thermal stability of the HfO2 films. Accordingly, wet oxidation not only prevents diffusion from chemical oxide but also markedly improves the oxide leakage current, which is useful for developing highly efficient and thermally stable HfO2 gate oxides in Si‐based integrated circuit devices.

Scotch-tape surface wrinkling based thin-film material properties extraction

This paper presents a new simple method to measure thin film material properties using scotch-tape surface wrinkling. Thin metal films have been deposited on polymer substrates by e-beam evaporation. After patterned by photolithography and wet etching, long and narrow thin metal layers have been transferred by peel-off onto the scotch tape. The effect of velocity of scotch tape peel-off on the metal film transfer from polymer substrates to the scotch tape has been investigated. After metal transfer, metal film wrinkling patterns have been established on the scotch tape due to mechanical properties mismatch between the two materials. The wrinkling patterns have been characterized in term of amplitude and wavelength and they are compared with finite element method buckling simulation results for material properties extraction. By consequence, elastic moduli of 300 nm thick gold film and a multilayer of 30 nm Ti on 300 nm Au have been found 147 GPa and 885 GPa based on the measured wavelength of the wrinkling films.

Scotch-Tape Surface Wrinkling Based Thin-Film Material Properties Extraction

Abstract This paper presents a new simple method to measure thin film material properties using scotch-tape surface wrinkling. Metal thin films have been deposited on polymer substrates by e-beam evaporation. After patterned by photolithography and wet etching, long and narrow thin metal layers have been transferred by peel-off onto the scotch tape. The effect of velocity of scotch tape peel-off on the metal thin film transfer from polymer substrates to the scotch tape has been investigated. After transfer, metal thin film wrinkling patterns have been established on the scotch tape due to mechanical properties mismatch between the two materials. The wrinkling patterns have been characterized in term of amplitude and wavelength and they are compared with FEM (Finite Element Method) buckling simulation results for material properties extraction. By consequence, elastic moduli of 300 nm-thick gold film and a multilayer of 30 nm Ti on 300 nm Au have been found 147 GPa and 885 GPa based on the measured wavelength of the wrinkling films.