Understanding Intrinsic Stress Evolution in Polycrystalline Thin Films that Grow by the Volmer-Weber Method PDF Download

Author: Ashok Rajamani
Publisher:
ISBN:
Category : Polycrystals
Languages : en
Pages : 304

View

Book Description

Author: Juan S. Tello
Publisher:
ISBN: 9780549677369
Category : Mechanical engineering
Languages : en
Pages : 160

View

Book Description
Stress evolution in polycrystalline thin solid films that grow by the Volmer Weber mechanism is studied numerically by means of an adaptive finite element model. The model tracks the shape of an array of islands as they grow and coalesce into a continuous film, changing shape as a result of a deposition flux, as well as surface and grain boundary diffusion. Stress is generated in the film as a result of forces exerted between neighboring islands as they meet to form a grain boundary. The internal stresses in the islands and the diffusive changes on their surfaces and grain boundaries are computed using a coupled finite element scheme. Interactions between neighboring islands are modeled using a cohesive zone law. The model predicts stress-thickness vs thickness behavior that is in excellent agreement with experiments. Specifically, it exhibits a three-stage growth process consisting of a stress-free pre-coalescence stage, a rapid tensile rise at coalescence, and an eventual transition to a steady-state. The steady state stress may be tensile or compressive, depending on the deposition rate, the grain size, and the properties of the film. Detailed parametric studies are conducted to establish the influence of material properties and growth conditions on the stress history, and the results are compared with experimental observations and previous models dating back to 1976. One of the limitations of the model is its inability to accurately capture atomistic behavior near the triple junction region. In light of this, a framework for coupling models of physical problems involving diffusion in a continuum region with one treated using a discrete formulation is presented. This methodology could potentially be used to couple the continuum description of stresses in thin films presented here with say, a Kinetic Monte Carlo simulation of the atomistics in and around the triple junction.

Author: Hang Yu (Ph. D.)
Publisher:
ISBN:
Category :
Languages : en
Pages : 222

View

Book Description
Growth of polycrystalline films involves poorly understood kinetic processes that occur far from equilibrium and lead to complex co-evolution of the surface, microstructure and intrinsic stress of the films. Here we present a comprehensive study consisting of in situ stress measurements, microstructure characterization, and analytical modeling for various polycrystalline systems. We find that in systems of high atomic mobility, the stress change after polycrystalline film growth can be attributed to a fast reversible surface process and a slow irreversible bulk process. The fast process is weakly dependent on temperature and is associated with changes in the shape of grain surfaces. The slow process is strongly dependent on temperature and is mostly associated with grain growth in the bulk of the film. We also discovered a turnaround phenomenon in which, under conditions of intermediate atomic mobility, the stress evolves from a tensile toward a compressive state, and then turns around to evolve toward a tensile state. This stress turnaround phenomenon is strongly dependent on the substrate temperature and deposition rate, and can be attributed to an increase of the grain size during film deposition. Grain growth during deposition not only leads to a tensile component of the intrinsic stress, but also changes the grain size dependence of the compressive component. The compressive component results from incorporation of excess adatoms in grain boundaries, and the magnitude of the compressive stress is controlled by a competition between adatom incorporation in 2D islands and incorporation at grain boundaries. We also investigated the effect of the angle of incidence of the flux of depositing atoms on stress and structure evolution during polycrystalline film growth. We find that as the angle of incidence increases, the coalescence thickness increases and the stress becomes less compressive or more tensile. We attribute these phenomena to the enhanced surface roughness, the shadowing effect, the steering effect and the presence of Ehrlich-Schwoebel barriers during oblique angle deposition. All these effects lead to suppression of the adatom-grain boundary incorporation process. Based on this thesis work, intrinsic stresses in polycrystalline films can be categorized into three types: Type I, the intermediate type and Type II. These behaviors are observed in systems of low, intermediate and high atomic mobility, respectively. Compressive stresses develop in Type II behavior and tensile stresses develop in Type I behavior. The transition of the stress behavior from Type I, to the intermediate type and to Type II is continuous and can be achieved by adjusting deposition conditions. Whether the post-coalescence stress is tensile, or compressive, or evolving from compressive to tensile depends on the homologous temperature, the deposition rate and the angle of the incidence of the flux of depositing atoms.

Author:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 906

View

Book Description

Author: Steven Craig Seel
Publisher:
ISBN:
Category :
Languages : en
Pages : 588

View

Book Description
(Cont.) Using the contact-angle-dependent FEM calculations of island-coalescence stress, simulations closely matched the stress-thickness measurements of Al, by assuming perfect island-substrate traction, and of Ag, by assuming partial island-substrate sliding, over the range of thicknesses prior to film continuity. The compressive stress evolution during deposition of continuous films and the stress behavior during interrupts of film growth was modeled in terms of a non-equilibrium surface morphology that develops during deposition. For the resulting non-equilibrium grain shapes, the in-plane compressive stress resulting from excess surface stress was calculated using FEM. Model predictions are consistent with observed decreasing compressive stress-thickness with increasing film thickness observed experimentally for Cu and a-Ge, as well as the reversible tensile rise behavior observed during growth interrupts of Cu.

Author: Joanna R. Groza
Publisher: CRC Press
ISBN: 1420004824
Category : Technology & Engineering
Languages : en
Pages : 840

View

Book Description
The field of materials science and engineering is rapidly evolving into a science of its own. While traditional literature in this area often concentrates primarily on property and structure, the Materials Processing Handbook provides a much needed examination from the materials processing perspective. This unique focus reflects the changing comple

Author: Rafael Alvarez
Publisher: MDPI
ISBN: 3036503943
Category : Science
Languages : en
Pages : 178

View

Book Description
This Special Issue deals with the synthesis of nanostructured surfaces and thin films by means of physical vapor deposition techniques such as pulsed laser deposition, magnetron sputtering, HiPIMS, or e-beam evaporation, among others. The nanostructuration of the surface modifies the way a material interacts with the environment, changing its optical, mechanical, electrical, tribological, or chemical properties. This can be applied in the development of photovoltaic cells, tribological coatings, optofluidic sensors, or biotechnology to name a few. This issue includes research presenting novel or improved applications of nanostructured thin films, such as photovoltaic solar cells, thin-film transistors, antibacterial coatings or chemical and biological sensors, while also studying the nanostructuration mechanisms, from a fundamental point of view, that produce rods, columns, helixes or hexagonal grids at the nanoscale.

Author: Mykola Nechyporuk
Publisher: Springer Nature
ISBN: 3030942597
Category : Technology & Engineering
Languages : en
Pages : 1078

View

Book Description
The International Scientific and Technical Conference “Integrated Computer Technologies in Mechanical Engineering” – Synergetic Engineering (ICTM) was established by National Aerospace University “Kharkiv Aviation Institute”. The Conference ICTM’2021 was held in Kharkiv, Ukraine, during October 28–29, 2021. During this conference, technical exchanges between the research community were carried out in the forms of keynote speeches, panel discussions, as well as special session. In addition, participants were treated to a series of receptions, which forge collaborations among fellow researchers. ICTM’2021 received 203 papers submissions from different countries. Target Groups ICTM was formed to bring together outstanding researchers and practitioners in the field of information technology in the design and manufacture of engines; creation of rocket space systems, aerospace engineering from all over the world to share their experience and expertise.

Author: Mahmood Aliofkhazraei
Publisher: Elsevier
ISBN: 044463245X
Category : Science
Languages : en
Pages : 500

View

Book Description
Handbook of Modern Coating Technologies: Advanced Characterization Methods reviews advanced characterization methods of modern coating technologies. The topics in this volume consist of scanning vibrating electrode technique, spectroscopic ellipsometry, advances in X-ray diffraction, neutron reflectivity, micro- and nanoprobes, fluorescence technique, stress measurement methods in thin films, micropotentiometry, and localized corrosion studies.

Author: Thomas Michely
Publisher: Springer Science & Business Media
ISBN: 3642186726
Category : Technology & Engineering
Languages : en
Pages : 327

View

Book Description
Crystal growth far from thermodynamic equilibrium is nothing but homoepitaxy - thin film growth on a crystalline substrate of the same material. Because of the absence of misfit effects, homoepitaxy is an ideal playground to study growth kinetics in its pure form. Despite its conceptual simplicity, homoepitaxy gives rise to a wide range of patterns. This book explains the formation of such patterns in terms of elementary atomic processes, using the well-studied Pt/Pt(111) system as a reference point and a large number of Scanning Tunneling Microscopy images for visualization. Topics include surface diffusion, nucleation theory, island shapes, mound formation and coarsening, and layer-by-layer growth. A separate chapter is dedicated to describing the main experimental and theoretical methods.