ICMCTF 2025 Session CM1-2-ThA: Spatially-resolved and in situ Characterization of Thin Films, Coating and Engineered Surfaces II

Interfaces separating bi- and multilayered thin film structures, are susceptible to premature failure due to the challenge of bridging distinct physical properties of adjacent materials. Thus, the reliability of these interfaces significantly influences the overall lifespan of such structures. Consequently, a thorough investigation of their reliability and a comprehensive understanding of the underlying failure mechanisms are essential for enhancing novel material composites and combinations.

In this study, we investigate the fracture behavior of model crystalline-amorphous interfaces, specifically focusing on Cu thin films delaminating from bulk glass substrates and nanocrystalline Cu – amorphous CuZr multilayers. Utilizing advanced characterization techniques, we aim to study the delamination behavior, interface adhesion, and fracture under static and cyclic loading of such structures using advanced experimental techniques spanning both the meso-scale and nanoscale, incorporating in situ transmission electron microscopy for a detailed exploration of these phenomena.

Complex concentrated alloys (CCAs), including medium- and high-entropy alloys, offer attractive thermomechanical properties which make them promising candidates for various technologies such as corrosion resistant or radiation tolerant structural materials. Among the various CCAs, alloys with multi-principal refractory elements (RCCA) have drawn significant attention for hydrogen (H) storage applications [1-3] due to their ability to reversibly absorb H in the form of metal hydrides. However, up to now, studies on RCCA for H storage have only focused on bulk materials, with limited attention to thin film counterparts, which could be considered as model materials enabling an easy tailor of composition, phase and microstructural features (grain size, porosity or texture), providing valuable insights on the mechanisms of hydride formation and dissolution in RCCAs.

In this work, (TiZrHf)_100-xTa_x thin films, with thickness up to 700 nm and Ta content ranging from 0 to 60 at.%, were synthesized by co-sputtering deposition. The phase composition, crystal structure, morphology and elemental composition was determined using a combination of analytical techniques (XRD, SEM/TEM, EDS), while the intrinsic stress was measured in situ during deposition by wafer curvature method. The mechanical properties of the films were assessed by nanoindentation and opto-acoustics (Brillouin light scattering and picosecond laser ultrasonics) methods. By tuning the Ta content, different phases were stabilized in these quaternary alloys, from hcp to bcc and amorphous. These structural changes are accompanied by variation in growth morphology (evolving from nanocolumns to vein-like patterns), stress reduction and a progressive softening of hardness, shear and elastic modulus with increasing Ta content. The experimental findings are discussed and compared with results obtained from atomistic models of random alloys and amorphous phases, using ab initio molecular dynamics simulations combined with machine-learned interatomic potentials, as well as relevant data from the existing literature [4].

References:
1. Marques, F., Balcerzak, M., et al., Review and outlook on high-entropy alloys for hydrogen storage. Energy Environ. Sci. 14, 5191 (2021)
2. Kong, L., Cheng, B., Wan, D., Xue, Y., A review on BCC-structured high-entropy alloys for hydrogen storage, Front. Mater. 10, 1135864 (2023)
3. Shahi, R. R., Gupta, A. K., Kumari, P., Perspectives of high entropy alloys as hydrogen storage materials, Int. J. Hydrogen Energy 48, 21412 (2023)
4. Huang, S., Li, W., Holmström, E., Vitos, L., Phase-transition assisted mechanical behavior of TiZrHfTax high-entropy alloys, Sci. Rep. 8, 12576 (2018)

Mechanical behavior of thin films deposited on polymeric substrates was investigated under in-situ controlled tensile biaxial loading conditions. The study employed synchrotron X-ray diffraction (XRD), digital image correlation (DIC) techniques, and electrical resistivity measurements. The combination of X-ray diffraction and digital image correlation provides classical stress-strain curves.

The three complementary measurement techniques allow for a comprehensive analysis of the deformation characteristics of each component of the thin film. This approach helps to identify and distinguish the various deformation regimes that arise during mechanical loading. Beyond the yield stress, distinct mechanical behaviors are observed in the stress-strain curves, which can be attributed to plasticity and fracture phenomena. These behaviors are identified as characteristic signatures of material failure modes.

Additionally, the experimental setup offers the capability to assess whether deformations are fully transmitted through the interfaces between the thin film and the substrate, providing also insight into the interaction between different layers in a multilayer coating.

The direct measurement of elastic constants for thin films is not yet a routine procedure and presents a number of significant technical and analytical challenges when compared to the analysis of bulk materials. Ab initio density functional theory calculations can provide a theoretical basis for understanding the properties of materials. However, discrepancies between model systems and real-world properties persist, primarily due to a lack of available experimental data for newly emerging material systems. Furthermore, computationally affordable models are typically constrained to defect-free single crystals, thereby excluding microstructural effects that exert a pronounced influence on the material's behavior.

This study addresses this gap by proposing a novel experimental approach to measure direction-dependent elastic constants, combining synchrotron microdiffraction and micropillar compression. The approach was tested on a polycrystalline face-centered cubic TiN thin film, where linear elastic failure prevails. An advanced in-situ testing environment has been established to enable the continuous recording of the load-displacement of the indenter, while simultaneously collecting the material's deformation response to uniform uniaxial compression. This dynamic approach permits the evaluation of the orientation-dependent elastic strain components and the macroscopic uniaxial compressive stresses, each over time, thereby enabling a differential analysis to assess the elastic and X-ray elastic constants.

The excellent agreement between experimental and ab initio data serves to corroborate the here-proposed robust method for direct elastic constant measurements, which is of crucial importance for advancements in thin film material testing.

Industries in photonics, optics, and semiconductors are increasingly challenged by particles emitted during PVD/ALD deposition processes. As device miniaturization advances, stricter requirements on defect size and particles inclusions make effective control essential to ensure product conformity.

Currently, these industries rely on preventive maintenance schedules that do not account for unexpected particle emissions or variations in machine usage. When particles appear, repeated maintenance is required due to the lack of a system to detect or locate their source. Integrating a real-time particles sensor into machines would transform this approach by enabling predictive monitoring, reducing downtime, and improving operational efficiency.

This session will deliver key insights into particle emissions during PVD deposition, explore market trends, and present business cases for the PVD/ALD market.

The challenge of green-house gas reduction pushes towards a better thermal insulation of housing. In this context, glass industry strives to decrease the infra-red radiative transfer across windows while keeping transparency. In the so-called low-E or solar control glazings, the functionality is provided by a complex stack of layers deposited by magnetron sputtering in which the active component is a ~10 nm thick Ag film encapsulated in between ZnO dielectric layers. Because of its noble character, Ag follows intrinsically a Volmer-Weber growth mode and is prone to dewetting upon thermal treatments such as windows tempering. Thus, there is tremendous need of understanding and control of its out-of-equilibrium growth process.

In this context, this presentation will illustrate the interest of combining real-time measurements (UV-vis spectroscopy^1,2; stress measurement via wafer curvature and digital image correlation³; film resistivity) with in situ photoemission spectroscopy to have a full overview on the Ag growth mechanism. Among others, the impact of sputtering deposition parameters and of gas additives on stress build-up and relaxation, on film percolation and on Ag chemistry will be discussed^4-6. The second part of the talk will show the contribution of model experiments in understanding the epitaxy at Ag/ZnO interface⁷, the reactivity⁸ and band alignment⁹ at metal/ZnO interfaces as seen by in situ hard x-ray photoemission and the various contributions to Ag film resistivity⁷.

[1] I. Gozhyk, L. Dai, Q. Hérault, R. Lazzari, and S. Grachev. J. Phys. D: Appl. Phys., 52:095202, 2018.

[2] R. Lazzari, J. Jupille, R. Cavallotti, E. Chernysheva, S. Castilla, M. Messaykeh, Q. Herault, and E. Meriggio. ACS Appl. Nano Mater., 3:12157–12168, 2020.

[3] S. Grachev, Q. Hérault, J. Wang, M. Balestrieri, H. Montigaud, R. Lazzari, and I. Gozhyk. Nanotechnology, 33:185701, 2022.

[4] Q. Hérault, I. Gozhyk, M. Balestrieri, H. Montigaud, S. Grachev, and R. Lazzari. Acta Mater., 221:117385, 2021.

[5] R. Zapata, M. Balestrieri, I. Gozhyk, H. Montigaud, and R. Lazzari. ACS Appl. Mater. Interfaces, 15:36951–36965, 2023.

[6] R. Zapata, M. Balestrieri, I. Gozhyk, H. Montigaud, and R. Lazzari. Appl. Surf. Sci., 654:159546, 2024.

[7] F. Corbella, V. Haspot, Y. Zheng, D. Guimard, H. Montigaud, and R. Lazzari. submitted, 2024.

[8] E. Chernysheva, Rensmo H. Philippe, B., O. Karis, M. Gorgoi, E. Burov, S. Grachev, M. Montigaud, and R. Lazzari. Appl. Surf. Sci., 680:161409, 2023.

[9] E. Chernysheva, W. Srour, B. Philippe, B. Baris, S. Chenot, R. F. Duarte, M. Gorgoi, H. Cruguel, H. Rensmo, H. Montigaud, J. Jupille, G. Cabailh, S. Grachev, and R. Lazzari. Phys. Rev. B, 97:235430, 2018.

Silver thin films are used in a number of applications (e.g., transparent and conductive electrodes and plasmonic devices) which require a continuous layer with thickness below a few nanometers. However, Ag films grown by magnetron sputtering have the tendency to form 3D-structures on weakly interacting substrates, what prevents their application as transparent and conductive layers. It is reported that the use of gas additives (particularly N₂ [1]) allows for obtaining a continuous layer at earlier deposition stage.

A thorough understanding of the nanoscale mechanisms of thin film formation requires real-time techniques [2]. In particular the widely used ex situ diagnostics can provide misleading information, as the structure of the thin film can evolve even under high vacuum conditions. We employ a simultaneous combination of real-time grazing incidence small-angle x-ray scattering (GISAXS), grazing incidence diffraction (GID), and substrate curvature measurements to get information about polycrystalline thin film evolution during growth. In particular, GISAXS reveals changes in nanoscale morphology, GID gives insight into the crystallinity of thin films, and substrate curvature measurements provide information about the average intrinsic stress. With our methodology we can study the interdependence between stress state, thin film structure and morphology, using the quantitative information obtained from the scattering techniques. Since the influence of the substrate curvature can be crucial for grazing incidence condition x-ray techniques, we show that in the curvature regime encountered in our experiment the effect on GISAXS is negligible.

Using the information from all three techniques, we will discuss the impact of nitrogen additive on all growth stages (from initial stages of island nucleation, growth, and coalescence, up to formation of percolated and continuous films), including the relaxation of the film during growth interruptions.

Acknowledgements: The work is performed within the frame of the ANR-DFG project IRMA (491224986).

Literature:

[1] A. Jamnig et al., ACS Appl. Nano Mater. 3, 4728-4738 (2020)

[2] B. Krause et al., ACS Appl. Mater. Interfaces 15, 11268-11280 (2023)