Micro and nanoactuators based on bistable molecular materials

Les systèmes microélectromécaniques (MEMS) sont des dispositifs de taille micrométrique capables de transformer un signal mécanique en un signal électrique et vice-versa. Ils sont aujourd'hui largement répandus dans notre vie quotidienne pour la détection, la transformation de l'énergie et l'actionnement de dispositifs grâce à leur faible dissipation énergétique, leur réponse ultra-rapide et leur grande sensibilité. Même si depuis plusieurs décennies, les progrès technologiques ont entraîné la miniaturisation des ces dispositifs, il reste nombreux challenges à surmonter dont l'un des plus importantes est l'intégration à l'échelle nanométrique d'actionneurs à base des matériaux dit " intelligents " (à ces dimensions, les matériaux habituellement utilisés perdent leurs propriétés d'actionnement). Dans ce contexte, ce travail de thèse avait pour objectif d'explorer l'utilisation des matériaux moléculaires à transition de spin pour le développement d'actionneurs électromécaniques. Dans ce but, nous avons conçu des microleviers en silicium que nous avons recouvert par différentes molécules à transition de spin soit par sublimation, soit par " spray-coating ". Les MEMS ont été caractérisés à température et pression variables en modes dynamique et statique à l'aide d'un unique dispositif expérimental. Les résultats obtenus démontrent que les molécules à transition de spin peuvent être intégrées, à l'aide de différents procédés de fabrication, dans des dispositifs MEMS et qu'il est possible de réaliser l'actionnement à l'aide d'une source d'énergie thermique (chauffage et refroidissement) et/ou lumineuse. Simultanément, cette étude a également permis d'évaluer les propriétés mécaniques des matériaux à transition de spin (module de Young, coefficient de Poisson) qui restent mal connues.Microelectromechanical systems (MEMS) are micrometric devices able to transform a mechanical signal into an electrical one and vice-versa. In the past years they have been successfully employed in different fields of our everyday life for sensing, transducing different forms of energy and for actuating purposes thanks to their low energy dissipation, fast response and high sensibility. Even if recent technological progress has allowed a considerable miniaturization of these devices, several challenges remain. In particular the integration of smart actuating materials at the nanometric scale remains arduous because in most cases they lose their actuating properties at reduced sizes. In this context, this thesis work aimed for exploring the possibility of using molecular spin crossover materials for the development of electromechanical actuators. To this aim we have conceived silicon microcantilevers, which have been coated by various spin crossover molecules using either thermal evaporation or spray-coating methods. The MEMS have been characterized at variable temperature and pressure both in dynamical and static modes using a single experimental setup. The results prove that spin crossover molecules can be successfully integrated into silicon MEMS devices using different fabrication processes and their actuation can be achieved using either a thermal energy source or light irradiation. In parallel, this work has allowed us to extract relevant mechanical properties of spin crossover materials (Young's modulus, Poisson's ratio), which have been largely unknown previously

Biomimetic Nanomembranes: An Overview

Nanomembranes are the principal building block of basically all living organisms, and without them life as we know it would not be possible. Yet in spite of their ubiquity, for a long time their artificial counterparts have mostly been overlooked in mainstream microsystem and nanosystem technologies, being a niche topic at best, instead of holding their rightful position as one of the basic structures in such systems. Synthetic biomimetic nanomembranes are essential in a vast number of seemingly disparate fields, including separation science and technology, sensing technology, environmental protection, renewable energy, process industry, life sciences and biomedicine. In this study, we review the possibilities for the synthesis of inorganic, organic and hybrid nanomembranes mimicking and in some way surpassing living structures, consider their main properties of interest, give a short overview of possible pathways for their enhancement through multifunctionalization, and summarize some of their numerous applications reported to date, with a focus on recent findings. It is our aim to stress the role of functionalized synthetic biomimetic nanomembranes within the context of modern nanoscience and nanotechnologies. We hope to highlight the importance of the topic, as well as to stress its great applicability potentials in many facets of human life

Light modulation of electric field driven semiconductor micromotors

The future micro/nanorobots require high degrees of freedom in motion control to perform complex tasks by individuals or by a swarm. It remains a great challenge to control the motions of an individual nanomachine amidst many, to switch the operation modes facilely, and it is even more difficult to actuate several components of a nanomachine coordinately for purposed actions. This high degree of versatility is essential for the future micro/nanorobots and requires investigation of innovative actuation mechanisms. In this dissertation, we report our recent finding about a new approach combining two types of stimulation to achieve such goal. The micromotors being studied are made of semiconductor silicon nanowires. Mechanical motion of the motors is driven by several types of AC electric field. Meanwhile, the electrical property of the nanowires can be locally and instantaneously modulated by visible light illumination in a reversible manner. We demonstrate that visible light is able to change the electric polarization of semiconductor nanowires under AC electric field, and reflected by the dramatic change of mechanical motions with very rich configurations. Under a rotating electric field, the rotation speed of semiconductor Si nanowires in electric fields can instantly increase, decrease, and even reverse the orientation by light illumination in the visible to infrared regime at various AC E-field frequencies. Under a linear AC electric field, instantaneous change of alignment direction and speed of semiconductor nanowires is observed under visible-light exposure. With theoretical analysis and simulation, the working principle can be attributed to the optically tuned imaginary-part (out-phase) and real-part (in-phase) electrical polarization of a semiconductor nanowire in aqueous suspension. Based on the understanding of this system, we further propose a new approach to control the semiconductor micromotor via light tunable dielectrophoresis. Localized control of collective behavior in a highly density silicon nanowire suspension is also investigated. Finally, we demonstrated how to utilize the mechanical motion at microscale for practical application of biosensing.Materials Science and Engineerin

Emerging topics in nanophononics and elastic, acoustic, and mechanical metamaterials: an overview

This broad review summarizes recent advances and “hot” research topics in nanophononics and elastic, acoustic, and mechanical metamaterials based on results presented by the authors at the EUROMECH 610 Colloquium held on April 25–27, 2022 in Benicássim, Spain. The key goal of the colloquium was to highlight important developments in these areas, particularly new results that emerged during the last two years. This work thus presents a “snapshot” of the state-of-the-art of different nanophononics- and metamaterial-related topics rather than a historical view on these subjects, in contrast to a conventional review article. The introduction of basic definitions for each topic is followed by an outline of design strategies for the media under consideration, recently developed analysis and implementation techniques, and discussions of current challenges and promising applications. This review, while not comprehensive, will be helpful especially for early-career researchers, among others, as it offers a broad view of the current state-of-the-art and highlights some unique and flourishing research in the mentioned fields, providing insight into multiple exciting research directions

Emerging topics in nanophononics and elastic, acoustic, and mechanical metamaterials:An overview

This broad review summarizes recent advances and “hot” research topics in nanophononics and elastic, acoustic, and mechanical metamaterials based on results presented by the authors at the EUROMECH 610 Colloquium held on April 25–27, 2022 in Benicássim, Spain. The key goal of the colloquium was to highlight important developments in these areas, particularly new results that emerged during the last two years. This work thus presents a “snapshot” of the state-of-the-art of different nanophononics- and metamaterial-related topics rather than a historical view on these subjects, in contrast to a conventional review article. The introduction of basic definitions for each topic is followed by an outline of design strategies for the media under consideration, recently developed analysis and implementation techniques, and discussions of current challenges and promising applications. This review, while not comprehensive, will be helpful especially for early-career researchers, among others, as it offers a broad view of the current state-of-the-art and highlights some unique and flourishing research in the mentioned fields, providing insight into multiple exciting research directions

The 2019 surface acoustic waves roadmap

Today, surface acoustic waves (SAWs) and bulk acoustic waves are already two of the very few phononic technologies of industrial relevance and can been found in a myriad of devices employing these nanoscale earthquakes on a chip. Acoustic radio frequency filters, for instance, are integral parts of wireless devices. SAWs in particular find applications in life sciences and microfluidics for sensing and mixing of tiny amounts of liquids. In addition to this continuously growing number of applications, SAWs are ideally suited to probe and control elementary excitations in condensed matter at the limit of single quantum excitations. Even collective excitations, classical or quantum are nowadays coherently interfaced by SAWs. This wide, highly diverse, interdisciplinary and continuously expanding spectrum literally unites advanced sensing and manipulation applications. Remarkably, SAW technology is inherently multiscale and spans from single atomic or nanoscopic units up even to the millimeter scale. The aim of this Roadmap is to present a snapshot of the present state of surface acoustic wave science and technology in 2019 and provide an opinion on the challenges and opportunities that the future holds from a group of renown experts, covering the interdisciplinary key areas, ranging from fundamental quantum effects to practical applications of acoustic devices in life science

The Effect of Defects and Surface Modification on Biomolecular Assembly and Transport

Nanoscale transport using the kinesin-microtubule (MT) biomolecular system has been successfully used in a wide range of nanotechnological applications including self-assembly, nanofluidic transport, and biosensing. Most of these applications use the ‘gliding motility geometry’, in which surface-adhered kinesin motors attach and propel MT filaments across the surface, a process driven by ATP hydrolysis. It has been demonstrated that active assembly facilitated by these biomolecular motors results in complex, non-equilibrium nanostructures currently unattainable through conventional self-assembly methods. In particular, MTs functionalized with biotin assemble into rings and spools upon introduction of streptavidin and/or streptavidin-coated nanoparticles. Upon closer examination of these structures using fluorescence and electron microscopy, the structures revealed a level of irregularity including kinked and coiled domains, as well as in- and out- of -plane loops. In this work, we describe the effects of large scale “defective” segments (i.e. non-biotinylated MTs) on active assembly of nanocomposite spools. We demonstrate the preferential removal of the defective portions from spools during assembly to overcome structurally induced strain in regions that lack biotin-streptavidin bonds. Additionally, we show how the level of defective MTs affect the morphology and physical properties of the resulting nanostructures.Further, we explore alternative nanostructures for controlling transport using the kinesin-MT biomolecular system. Guiding MT transport has been achieved using lithographically patterning physical and chemical features, which have been shown to limit the MT trajectories, causing MTs to escape the barriers and lead to stalling or complete loss of MTs. Here, we demonstrate reliable guiding and transport of MTs on three different chemically modified, and structurally varying surfaces using 1) self-assembled monolayers (SAMs) with varying functional groups, 2) Fetal-bovine serum (FBS) coated SAMs to generate protein patterns, and 3) silicification of the FBS coated SAMs to preserve the surface. Overall, the work presented in this dissertation provides crucial insights for future development of dynamic and adaptable hybrid nanostructures, as well as provides biocompatible patterns to modulate MT motility with the goal of advancing self-regulating, multi-functional materials

Miniaturized Dielectric Elastomer Actuator for Mechanical Stimulation of Monolayer Cell Cultures

This thesis advances the field of dielectric elastomer actuators (DEAs) through the development of device designs, fabrication processes, strain characterization technique and modelling tool. It provides the first demonstration that DEAs can be interfaced with living cells, opening the door to real-world applications in mechanobiology, an important step for the development of this emerging soft-actuator technology. It also provides a practical approach towards low voltage DEAs, demonstrating a fully-printed actuator that works below 300 V, a range compatible with commercially available CMOS circuitry, hence enabling a variety of new applications for DEA-based technologies. The mechanisms by which cells can sense and react to their mechanical environment are still partly unknown, and advances in this field will contribute to better diagnosis and treatment of serious diseases like cancer. Research heavily relies on in vitro models, and there is therefore great interests in systems capable of applying precise mechanical strain on cell cultures. This thesis overcomes the many challenges of interfacing DEAs with living cells, and presents a biocompatible device which can sustain standard cell culture protocols like sterilization, incubation, and immersion in growth medium. The device can apply from -10% to 35% uniaxial strain on a small cell population (~100 cells), located in a transparent area (0.5mm x 1.5mm) of a larger biocompatible membrane. It can be mounted on an inverted microscope, where its novel design enables real-time high-resolution optical imaging of cells during stretching. With strain rates in the excess of 700 %/s, the in vivo environment can be reproduced with unprecedented accuracy. As a demonstration of the technology, in collaboration with the Vascular and Tumor Biology Laboratory at UNIL in Switzerland, a population of lymphatic endothelial cells (LECs) was cycled from 0% to 10% strain at 1 Hz for 24 h. The results show stretch-induced alignment of cells perpendicular to strain, and confirm that the device fringing electric field has no effect on LECs morphology. This is the first demonstration that DEAs can be interfaced with living cells, and the first time they are used to observe cell mechanosensitivity. The driving voltage of DEAs is typically in the kV range, which limits their possible applications. One approach to reduce the actuation voltage is to decrease the membrane thickness, which is typically in the 20-100 microns range, as reliable fabrication becomes challenging below this thickness. This thesis presents a pad-printed 3 microns thick DEA, and demonstrates that decreasing the membrane thickness to only a few microns significantly reduces the driving voltage, while maintaining good actuation performance. A radial strain of 7.5% was achieved at only 245 V, which corresponds to a strain-to-voltage-squared ratio of 125%/kV^2, the highest reported value to date. This thesis also investigates the electrodes stiffening impact, often overlooked in the design and development DEAs. It presents an analytical model which accounts for the electrodes stiffness, and presents a strain-mapping algorithm to compares the strain uniformity of 3 microns- and 30 microns-thick DEAs. The simulation results and the strain mapping measurements identify the electrodes as an important parameter that should not be neglected in the design and optimization of thin-DEAs