ICMCTF 2025 Session PP5-TuM: Microfabrication Techniques with Lasers and Plasmas

2D materials have been the focus of intense research in the last decade due to their unique physical properties. This presentation will highlight our recent progress on the large-area synthesis of two-dimensional transition metal chalcogenides for nanoelectronics using advanced plasma-enhanced atomic layer deposition cycle schemes. First, I will show how we can use advanced cycle schemes to deposit wafer-scale polycrystalline MoS₂ thin films at very low temperatures down to 100 °C. We have identified the critical role of hydrogen during the plasma step in controlling the composition and properties of molybdenum sulfide films. By increasing the H₂/H₂S ratio or adding an extra hydrogen plasma step to our ALD process, we can deposit pure polycrystalline MoS2 films at temperatures as low as 100 °C. To the best of our knowledge, this represents the lowest temperature for crystalline MoS₂ films prepared by any chemical gas-phase method.[1]

The most dominant methods for preparing MoS₂ via ALD is to alternately expose a substrate to a metalorganic precursor and a hydrogen sulfide (H₂S) or a plasma containing H₂S. H₂S is a corrosive, toxic, and flammable gas that is heavier than air, which makes it hazardous and expensive to store, install, and transport. Alternative sulfur precursors in the solid or liquid phase would be beneficial in terms of cost and safety and would require the installation of no additional hardware for most ALD reactors. In the second half of this contribution, the widely researched ALD process using bis(tert-butylimido)bis(dimethylamino)molybdenum(IV) ((^tBuN)₂(NMe₂)₂Mo) and H₂S plasma is compared to a novel ALD process using (^tBuN)₂(NMe₂)₂Mo, hydrogen plasma, and di-tert-butyl disulfide (TBDS), which is an inexpensive, liquid-phase sulfur precursor.

New methods to monitor plasma processes in microelectronics industry, such as deposition, etching, and surface modification, require fine control of plasma parameters, basic plasma-surface interactions, and structural/chemical resolution. These challenges can be solved by implementing nanocalorimeter devices, which usually consist of a 100 nm-thin self-sustained silicon nitride membrane with lithographically defined metallic structure as a resistive temperature sensor and heater. The lateral sizes of the sensor can range from micrometer to millimeter scales. The small size/thermal mass, functionalization versatility, and low wafer-scale fabrication cost of nanocalorimeters, enable their facile integration into any reactor chamber to meet specific plasma process requirements. Here, we report on pilot tests of NIST-microfabricated nanocalorimeters aimed to detect reactive radicals generated by hydrogen cold plasma at typical conditions for semiconductor manufacturing (75 W RF, 10-30 Pa). The setup consists of a parallel arrangement of one gold-coated active sensor and a second alumina-coated reference sensor. Au layer serves as a catalyst with known hydrogen recombination coefficient. Hence, the difference in heat of recombination reactions is detected comparatively by activated and reference nanocalorimeters. The inert, reference sensor enables discrimination against the incoming UV-vis radiation, and fluxes of ions and electrons, which constitute the major parasitic signals. The setup was successfully tested, and parameters such as sensitivity in radical detection (5×10²⁰ m^-2s^-1) and in radical density (10¹⁸ m^-3), and response time (sub-100 ms), are discussed within the framework of standard plasma diagnostic techniques. In conclusion, fast-scanning nanocalorimetry constitutes a promising platform for plasma process monitoring, whose flexibility enables its possible integration into other optical or electrical metrologies.

Nowadays, the reduction of complications following breast implant surgery together with the enhancement of implant integration and performance through the modulation of the foreign body response (FBR) still represents a fundamental challenge. Therefore, influencing FBR by tailoring the material’s physical characteristics can provide a significant outcome in implantology. While polydimethylsiloxane (PDMS) patterning on 2D substrates is a relatively established and available procedure, micropatterning multiscaled bioactive interfaces on a controlled large area has been more challenging. Therefore, in the present work, novel PDMS-based shell interfaces featuring honeycomb-like wells microtextures were designed and their effectiveness towards creating a pro-healing environment was investigated. The microtextures were achieved through replication on a large-scale using moulds obtained by an innovative laser-based 3D fabrication assisted by a grayscale masks process. By comparison to the smooth substrate, the honeycomb topography altered the fibroblasts’ behaviour in terms of adhesion and morphology and reduced the macrophages’ inflammatory response. Additionally, the microstructured surface hindered the macrophage fusion process, and decreased the retention of Gram-positive and Gram-negative microbial strains. Overall, our study presents a novel approach for an attenuated in vitro FBR to silicone through the development of honeycomb like topography of prosthetic interfaces.

Magnetron sputter deposition of metal atoms onto vacuum compatible liquids allows producing colloidal solutions of small metal nanoparticles (NPs) without any additional reducing or stabilizing reagents [1]. This presentation aims at presenting the results during which the process parameters were varied to study how the properties of the as-formed metal NPs are impacted. Parameters such as pressure, sputter power, and sputtering regime, e.g., DC or HiPIMS, were varied as well as the characteristics of the host liquid chemistry and viscosity. To monitor in space and time the behaviour of the NPs inside the liquid, in situ UV-Vis absorption spectrophotometry was implemented [2]. The temperature of the liquid was measured as well.

Our data show that the formation of a cloud of particles underneath the oil surface is usually observed while films form in the case of high viscosity liquids [3]. The effect of sputtering time and power, argon pressure, type of sputtering plasma (dcMS vs HiPIMS) were also studied taking castor oil, a vegetable liquid, as substrate. In this case, few - nm - in - diameter Au-NPs have a higher stability in the oil than Ag-NPs but secondary growth processes take place. Interestingly, HiPIMS promotes the formation of NPs larger than those obtained in dcMS mode [4]. Most recent experiments highllight the possibility of elaborating hydrogel / nanoparticle composites in a two step process by choosing an appropriate polymerizable host liquid [5]. Preliminary measures confirm that the as-obtained Ag-NPs / hydrogel composite can be used to detect mercury cations in aqueous solutions through color change.

Our data highlight that sputtering onto liquid allows for the synthesis of a few nm in diameter NPs but the plasma and liquid parameters matter. Ultimately, by chooseing carefully the liquid host, it is possible to elaborate polymer / NP functional composites.

[1] A. Sergievskaya, A. Chauvin, S. Konstantinidis. Beilstein J. Nanotechnol. 13 (2022) 10–53.

[2] S. Konstantinidis, F.- E. Bol, G. Savorianakis, P. Umek, P., A. Sergievskaya, Instr. Sci. Technol. 52(2), 125–137. https://doi.org/10.1080/10739149.2023.2223627

[3] A. Sergievskaya, R. Absyl, A. Chauvin, K. Yusenko, J. Veselý, T. Godfroid, S. Konstantinidis, Phys. Chem. Chem. Phys. 25 (2023), 2803–2809.

[4] A. Sergievskaya, A. O’Reilly, H. Alem, J. De Winter, D. Cornil, J. Cornil, S. Konstantinidis, Front. Nanotechnol. 3 (2021) 57.

[5] V. Jauquet, Master Thesis, University of Mons (June 2023).

This research introduces an innovative approach for the rapid and efficient deposition of silver and gold using atmospheric pressure plasma jets (APPJs) to produce Surface-Enhanced Raman Spectroscopy (SERS) substrates and conductive tracks. Central to this method is the utilisation of plasma, which enables precise and uniform deposition of zerovalent metallic nanoparticles on a variety of substrates, including glass, ceramics, and metallic objects.

The APPJ technique takes advantage of the unique properties of non-thermal plasma, facilitating the reduction of metal ions to zerovalent metals in a single step. The highly energised electrons in the plasma allow intricate redox chemistry to occur. The flexibility of the APPJ method extends to a wide range of materials, including silver, gold, and binary metal mixtures. Furthermore, by mounting an APPJ on a 5-axis manifold enables metallic deposition on topologically complex surfaces, which has significant applications in analytical chemistry and materials science.

SERS substrates can be produced using an APPJ by depositing silver or gold directly onto topologically complex, multi-material surfaces without the need for post-plasma treatment. The APPJ prints metallic islands with diameters of 150 ± 25 µm and heights of approximately 370 nm, spaced 500 µm apart, forming the fundamental structure of the SERS substrates. With a production time of only 5 seconds per SERS substrate, our method offers a significantly faster alternative compared to other manufacturing techniques.

Our APPJ SERS substrates have undergone rigorous testing with various analytes, demonstrating performance on par with commercially available products. The substrates exhibit an impressive detection limit of 154 ppb when tested with 4-mercaptobenzoic acid.

Plasma-prepared substrates show significant gains with respect to the economical use of materials and the rapidity of the synthesis of the substrates. We showcase using the atmospheric pressure plasma jet method for synthesis and deposition as an integral part of an analytical device. This approach presents a key advantage for academic and industrial applications.

In our ALPS Institute, laser technology and thin-film deposition are combined with the objective to unlock novel functionalities in nanofabrication. As a first example, by leveraging precise and partial laser ablation within multilayer systems, we achieve high-resolution decorative effects with nanometric precision. Laser structuring on thin-film materials enables tuning of material properties, as seen on carbon allotropes. Additionally, laser processing can be employed to generate nanoparticles by ablating a target, which can then be embedded in coatings to form nanocomposites with enhanced mechanical, optical, or catalytic properties. This presentation will explore a few specific applications and case studies that highlight the advantages of integrating laser processing with thin-film technologies.