ICMCTF 2026 Session MB2-3-ThM: Thin Films for Emerging Electronic and Quantum Photonic Devices III

Control of energetic interactions at the surface of the growing thin films allows one to selectively adjust their micro- and nanostructure. This is particularly important when synthesizing optical films by vapor-based techniques such as reactive sputtering (including HiPIMS), evaporation (including Glancing Angle Deposition), Plasma-Enhanced Chemical Vapor Deposition, Atomic Layer Deposition, Ion Beam Assisted Chemical Vapor Deposition, and Gas Agglomeration Cluster formation. As a result, this has become increasingly attractive for judicious fabrication of nanostructured optical filters with controlled film porosity, crystallinity, anisotropy, plasmonic effects, thermo-mechanical properties and other features of both passive as well as active (dynamic – e.g., electrochromic or thermochromic) coating materials with new functionalities.

This presentation will illustrate the progress and new opportunities in structurally controlled passive and active optical coating systems using a holistic approach from design to fabrication and device performance. This will specifically be highlighted by our work on high-performance low-emissivity and smart windows for energy saving in the building sector, energy control in micro/nanosatellites, hybrid (organic-inorganic) coatings and switchable electrochromic systems for ophthalmic lenses including novel transparent flexible electrodes, plasmonic optical filters for gas sensing, and other advanced optical coating devices.

References:

1. M. Crouan, B. Baloukas, O. Zabeida, J.E. Klemberg-Sapieha, L. Martinu, "Antireflective-to-mirror-like all-solid-state electrochromic devices", Optical Materials 168 (2025) 117464.

2. Z. Krtous, O. Polonskyi, P. Pleskunov, M. Cieslar, B. Baloukas, L. Martinu, J. Kousal, "Sensing of Organic Vapors with Plasmonic Distributed Bragg Reflectors", ACS Appl. Mater. Interfaces 17 (18) (2025) 27126–27135.

3. M.-A. Dionne, B. Baloukas, O. Zabeida, J. Klemberg-Sapieha, L. Martinu, "Fabrication and Performance of Randomly Patterned Tri-Layer Flexible and Transparent Electrodes", Optical Materials 166 (2025) 117200.

4. P. Rumsby, B. Baloukas, O. Zabeida, and L. Martinu, "Enhanced Durability and Antireflective Performance of Ag-Based Transparent Conductors Achieved via Controlled N-Doping", ACS Applied Materials & Interfaces 16 (2024) 24039–24051.

5. A. Shelemin, Z. Krtous, B Baloukas, O. Zabeida, J.E. Klemberg-Sapieha, L. Martinu," Fabrication of Plasmonic Indium Tin Oxide Nanoparticles by Means of a Gas Aggregation Cluster Source", ACS Omega 8 (2023) 6052−6058.

Nowadays, flexible magnetoelectric (ME) heterostructures comprising lead-free piezoelectric are of considerable interest for commercializing wearable electronic devices such as energy harvesters, nonvolatile memory, implantable medical diagnostics, and sensors. Here, we fabricate a highly flexible, cost-effective, nanostructured magnetic field sensor comprising an AlN/Ni-Mn-In ME heterostructure over Ni foils. The functionality of the AlN/Ni-Mn-In/Ni heterostructure has been investigated by measuring the magnetodielectric MD (%) and magnetoelectric coupling (α_ME) coefficient with Ni-Mn-In thickness, anisotropy, and flexibility. The thickness ratio of piezoelectric AlN (∼400 nm) and magnetostrictive Ni-Mn-In (∼385 nm) layers has been optimized to achieve the high performance of the magnetic sensor. The encapsulation of the Ni-Mn-In layer drastically enhances the performance of the fabricated heterostructure. The highest MD ∼ 2.95% and α_ME∼ 3.2 V/cm·Oe have been recorded with an equal thickness ratio of AlN and Ni-Mn-In layers. It could be ascribed to the large magnetostrictive strain transferred to the AlN piezoelectric layer, which enhances the induced ME voltage. Moreover, the nonzero value of α_ME at zero bias magnetic field has been observed and related to the piezomagnetic coefficient (q) grading in the Ni-Mn-In(+q)/Ni(−q) ferromagnetic system, which enhances the strength of magnetoelectric coupling. The fabricated device has easily detected the ultralow magnetic field of up to or less than ∼1 μT. In addition, the anisotropic functionality of the device has been explained by measuring the magnetodielectric and magnetoelectric characteristics in parallel and perpendicular dc bias fields. Further the surface acoustic wave (SAW) delay line-based piezo resonator has been fabricated over highly flexible AlN/Ni-Mn-In/Kapton for flexible MEMS application. The fabricated device resonates at ~1.40 GHz. The effect of the external magnetic field on the resonance frequency (f_R) of the device has been investigated and tunability (∆fR/fR) ~9% was observed. The device displays high sensitivity of ~0.94 Hz/nT at room temperature.

Keywords:Ferromagnetic shape memory alloys, flexible magnetic sensor, lead-free piezoelectric, magnetostrictive effect, surface acoustic waves (SAW).

Wurtzite AlN-based ternary nitride alloys are a promising platform to realize functional materials, particularly ferroelectrics and optical emitters, that can smoothly integrate with conventional microelectronics. Here, we explore substitution of multiple elements into AlN forming quaternary nitride alloys as a strategy for enabling new multifunctional materials. Through a computationally-guided approach, we successfully predict the phase diagram of these pseudo-ternary heterostructural AlN–ScN–GdN alloys as a function of effective temperature and experimentally grow Al_1−x−ySc_xGd_yN thin films via combinatorial sputter synthesis for the first time. We find that for x + y ≲ 0.35, Al_1−x−ySc_xGd_yN crystallizes into a wurtzite structure which is consistent with the calculated phase diagram. Further, we computationally probe whether co-substitution induces cooperative effects on these alloys’ piezoelectric and ferroelectric properties, finding that it is beneficial for reducing the polarization switching barrier. We also calculate that Al_1−x−ySc_xGd_yN thin films should display ferroelectric switching that could be realized experimentally in the future. This is supported by our experimental measurements of a high optical band gap, enhanced piezoelectric coefficient, and a change in the calculated polarization switching mechanism. Overall, our work sets the foundation toward quaternary wurtzite-nitride-based multifunctional materials, including piezoelectrics, ferroelectrics, and possibly multiferroics.

The metal-insulator transition (MIT) in vanadium dioxide (VO₂) thin films is a topic of great interest for applications in smart windows, memristors, and neuromorphic computing applications. VO₂ thin films are accompanied by substantial changes in the electronic and optical properties across the MIT, and these changes can be induced by external stimuli such as voltage, strain, or temperature. While several studies have shown that flexible and freestanding VO₂ films can be achieved, complex pre- or post-growth processing is required. In this work, we show that direct sputter deposition of VO₂ on flexible Kapton substrates results in a straightforward methodology to achieve flexible MIT films. A pre-deposited Al₂O₃ layer on Kapton enhances film adhesion, and the resulting flexible VO₂ films show up to 4 decades of change in resistance across the MIT. Temperature and substrate-induced strain during growth affect substantially the quality of the films. The resulting VO₂ flexible devices show ultra-low power consumption for resistive switching, up to two orders of magnitude lower than in samples grown on traditional substrates. We also demonstrate that the VO₂ MIT characteristics can be governed by mechanical deformation, resulting in a novel method to induce resistive switching and decrease power consumption. This study reveals a straightforward approach for direct growth of high-quality flexible VO₂ films exhibiting robust MIT, with promising applications in tactile sensors and electromechanical devices.

Funding Acknowledgment: This material is based upon work supported by the Air Force Office of Scientific Research under award number FA9550-22-1-0135.

The emerging hydrogen industry is stimulating efforts in developing new materials for various purposes, including the quest for efficient, sustainable, and low-power hydrogen detectors. Many such devices rely on metal oxide semiconductor materials, which are easily integrable into devices and relatively cheap but suffer from some challenges, such as low sensitivity and selectivity.

This study explores the possibility of exploiting a Glancing Angle (GLAD) sputter deposition of Cu-doped TiO₂ and WO_x films, targeting the enhancement of active surface area and, therefore, sensor sensitivity improvements.

Cu-doped TiO₂ and WO₃ films were deposited using conventional reactive DC magnetron sputtering, employing circular titanium and tungsten targets in a mixture of argon and oxygen. Cu-doping was achieved by using a composite target.Films were post-annealed prior to sensing characterization. The Glancing Angle Deposition (GLAD) technique was employed to induce a characteristic columnar nanostructure, thereby increasing the films' porosity and so leading to a desired increase in active surface area. Multiple parameters were tuned to enhance the sensing response, including the angle of deposition (80°, 85°, 88°), thickness (50–300 nm), and reactive sputtering parameters.

Synthesized films were thoroughly analyzed by SEM and XRD. Sensing response measurements revealed an interesting fact: that neither the surface roughness nor the surface area improves the response to the sensing gas monotonically. In the presented paper, we discuss the geometrical reasons as well as the synthesis parameters that influence the sensing characteristic. The comparison of the two materials, WO₃ and TiO₂, is also given.

Nanoparticle based structures are of significance for emerging technologies from antimicrobial coatings to catalysts. Sputtering based fabrication routes are particularly promising whenever high purity and monodisperse particles are required. This work establishes quantitative synthesis‐structure relations for Cu‐nanoparticles (diameter < 10 nm), synthesized through magnetron sputtering inert gas condensation and high‐power impulse hollow cathode sputtering. The two deposition methods are compared in terms of nanoparticle deposition rate, morphology and size distribution. While magnetron sputtering inert gas condensation with quadrupole mass spectrometry offers excellent control of the size distribution of single crystalline particles, high‐power impulse hollow cathode sputtering enables deposition of polycrystalline nanoparticles at higher deposition rates with more efficient target utilization. Consequently, porous, randomly assembled nanoparticle‐based films of up to 1.5 µm thickness have been fabricated. Stabilization of these structures via atomic layer deposition (Al₂O₃, thickness up to 20 nm) is demonstrated through electron microscopy and nanoscratching, linking nanoscale structure to macroscale mechanical performance. While encapsulation at 120°C does not change the Cu microstructure, the scratch resistance of the film improves with increasing encapsulation layer thickness. These findings provide a direct pathway from fundamental surface engineering to thick and robust functional nanoparticle‐based films for future bio‐medical and energy applications.

References:

1. D. Gutnik, D. Casari, L. Pethö, M. Burtscher, A. Hofer-Roblyek, C. Mitterer, B. Putz⁺, "From Copper Nanoparticles to Alumina Encapsulated Porous Layers with Enhanced Mechanical Stability", Advanced Materials Interfaces, 2026

In general, properties of thin films are dependent on their crystal orientation, and the most common approach to control the crystal orientation of thin films is to utilize epitaxial growth on single-crystalline substrates. Although a variety of materials have been synthesized on single-crystalline substrates using chemical and physical vapor deposition (CVD, PVD), epitaxial growth methods allow us to grow materials into only one fixed orientation predetermined by the substrate orientation, and typically with limited tunability in terms of area or orientation.

In this talk, we report area-selective, orientation-tunable crystallization processes of amorphous Si utilizing atomic imprint crystallization (AIC), where an amorphous Si layer is crystallized by solid phase epitaxy from an external single-crystal Si template. Using a flat template, the top surface of an amorphous Si is crystallized following the crystal orientation of the template wafer up to 5 mm diameter, indicating that the crystallization of the amorphous Si can be initiated by an external template wafer. Using micro-patterned single-crystalline Si templates, limited areas (~50 µm diameter) of an amorphous Si film, where the film surface and patterned template surface are in contact, are crystallized via SPE to create an array of crystallographically aligned dots embedded in amorphous matrix. Combining the AIC from the top surface and conventional SPE from the substrate, we developed new crystallization processes to fabricate unique microstructures such as a twisted interface with a tunable twist angle and an array of crystalline dots embedded in single-crystalline matrix with tunable in-plane rotation angle. The results demonstrate the area-selective, orientation-tunable crystallization process enabled by AIC, controlling crystallographic properties of thin films, which can open up new materials design capabilities for variety of applications in materials science including but not limited to electronics and quantum device applications.

The talk highlights automated experimental tools enabling synthesis and characterization of hundreds of samples per day. This approach, where experimentation is much faster than simulation has the potential to flip the traditional ‘order of operations’ for materials discovery where experiment feeds model during initial iterations.One high-throughput format relies on scanning lasers with broad ranges of power, scan rates, and focal positions to induce physical and chemical transformations within materials. Laser heating parameters may be set to approximate quasi-equilibrium heating as in a furnace, or induce extreme heating and cooling rates, thereby broadening the range of accessible compositions and crystal structures dictated by kinetics of both chemical reactions and crystallization. Deposition tools may also be used to create a broad range of compositions on the sample surface. Once a combinatorial sample with a desired range compositions and laser illumination conditions is processed, it can be manually or autonomously subjected to the combination of high-throughput characterization tools required for evaluation of the properties specified by the user. Autonomous systems enable users to specify a desired property and the system iterates processing and characterization data to ‘make decisions’ about optimization of conditions to realize the user-specified input.For example, an automated Raman spectroscopy system enables rapid collection of key data points (grain size, defect density, thickness, etc.) for technologically important optical, electronic, and energy materials.Some specific case studies include fundamental kinetics studies showing migration-limited crystallization kinetics amorphous materials can be directly observed.Pre-cursor materials for downstream processing can be converted directly into reaction intermediates with the appropriate non-equilibrium laser energy input to reduce process activation energy and process temperature required for high-quality materials. For photocatalysis materials rapid, non-equilibrium process conditions were identified demonstrating optimized performance with mixtures of phases.

Recently, thin films of elemental tellurium (Te) have gained increasing attention due to their intrinsically anisotropic crystal structure and morphology-dependent semiconducting properties. Molecular beam epitaxy (MBE) is an established technique for producing chemically pure, wafer-scale Te films with high morphological precision. However, post-processing of Te films for device fabrication typically relies on masked lithographic techniques, which can inadvertently degrade film quality and electrical performance. While selective-area growth approaches have been explored to mitigate these effects, mask-based methods introduce additional pre-processing complexity and crystallographic constraints. An in situ selective-area growth technique offers a pathway to reduce fabrication complexity while preserving intrinsic film properties.

Here, we demonstrate an in situ process for selective-area growth of Te thin films on muscovite mica (MuM) dielectric substrates using an electron beam generated by a reflection high-energy electron diffraction (RHEED) gun integrated within an MBE system. Spatially selective growth is achieved without physical masking, resulting in millimeter-scale lateral patterning of nanometer-thick Te films, confirmed by optical characterization. Directional control of film growth is realized through azimuthal alignment of the substrate relative to the incident electron beam. The resulting feature dimensions are found to depend strongly on electron beam voltage, exposure duration, and substrate temperature. This approach demonstrates controllable Te film shape and thickness during growth, highlighting new opportunities for direct-write epitaxial patterning within MBE systems.

Dynamic random access memory (DRAM) devices have continuously increased their integration density through aggressive device scaling and have progressively evolved toward three-dimensional (3D) architectures to overcome the limitations of planar designs. Among various approaches, 3D DRAM structures employing highly stacked Si channels and SiGe sacrificial layers are regarded as promising candidates for cell designs beyond the 4F² node. In such vertically stacked channel architectures, the selective removal of SiGe sacrificial layers from epitaxial Si/SiGe multilayers represents a critical process requirement.

In this study, the selective etching behavior of boron-doped SiGe epitaxial layers—introduced to compensate for strain arising from lattice mismatch between Si and SiGe—was systematically examined as a function of boron concentration. Dopant-dependent variations in etching behavior were observed in both blanket films and Si/SiGe multi-stack structures. To gain insight into the underlying mechanisms, the chemical bonding states of etched SiGe surfaces were analyzed using X-ray photoelectron spectroscopy (XPS), with a focus on dopant-induced modifications of oxide-related surface chemistry. The results reveal that boron incorporation significantly alters the etching response of SiGe layers through changes in surface oxide chemistry, leading to distinct dopant-dependent trends. These findings provide fundamental insight into dopant-mediated surface reactions during selective etching and offer useful considerations for process optimization in vertically stacked semiconductor device fabrication.

Acknowledgment

This work was supported by the Technology Innovation Programs (RS-2024-00434624 & RS-2025-02306457) and the K-CHIPS program (25065-15FC) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea).