Periodic Reporting for period 4 - ENIGMA (EXPLORING NONLINEAR DYNAMICS IN GRAPHENE NANOMECHANICAL SYSTEMS)
Periodo di rendicontazione: 2023-05-01 al 2023-10-31
Nanomechanical systems are being adopted in billions of products that address a wide range of sensor and actuator applications in modern technology. The discovery of graphene and the ability to fabricate atomically thin membranes revolutionised the field of nanotechnology and made it possible to make miniaturised resonators that are extremely sensitive to electrical signals and forces. But, soon after its discovery, it was realised that reaching the holy grail in sensing with graphene is associated with severe constraints over its linear dynamic range, since signatures of nonlinearities already emerge at amplitudes that are only a few nanometers. This nonlinear behavior that is considered as a nuisance in the design of graphene nanomechanical systems brings with itself a new unexplored field in nonlinear dynamics, where dynamics of single atom thick membranes is entangled with complex phenomena almost non-existent in other mechanical systems. These unique sources of complexity not only affect dynamics but also make mechanical characterization of these novel materials very challenging.
The goal of the ERC starting grant ENIGMA was to provide full understanding of nonlinearities in graphene nanomechancial systems in order to avoid them when unwanted while utilising them efficiently when desirable. To realize this vision, ENIGMA focused on the development of (1) novel numerical and experimental methods that capture nonlinearities and provide insight on their influence on the mechanics of atomically thin membranes; (2) novel methodologies that use nonlinearities for mechanical characterisation of such membranes.
This project contributed to the development of atomically thin resonators with applications in nanomechanical sensing and time keeping that are of paramount importance to micro and nanotechnology.
The goal of the ERC starting grant ENIGMA was to provide full understanding of nonlinearities in graphene nanomechancial systems in order to avoid them when unwanted while utilising them efficiently when desirable. To realize this vision, ENIGMA focused on the development of (1) novel numerical and experimental methods that capture nonlinearities and provide insight on their influence on the mechanics of atomically thin membranes; (2) novel methodologies that use nonlinearities for mechanical characterisation of such membranes.
This project contributed to the development of atomically thin resonators with applications in nanomechanical sensing and time keeping that are of paramount importance to micro and nanotechnology.
The development of the nonlinear dynamic methodology for graphene nanomechanical systems was associated with 4 intertwined research themes, that included R1. Geometric and material nonlinearities; R2. Opto-thermal effects and thermal fluctuations; R3. Nonlinear dissipation processes; R4. Nanoscale forces. All the research themes associated with ENIGMA were tackled with success during the course of the project.
In research theme R1, new nonlinear models were developed and successfully implemented on experimental data for estimating the Young’s modulus of graphene membranes and for probing highly anisotropic properties of 2D As2S3 layers. Moreover, molecular dynamic simulations were performed to support experimental findings on the interrelation between phonons and thermal bath in nanostructures and how such relation affect's Young's modulus at the nanoscale. In addition, modal order reduction techniques were developed from full scale finite element simulations as well as molecular dynamics to underpin the complex nonlinear phenomena that are observed in the experiments
In research theme R2, new methodologies and numerical models were built to study the high frequency stochastic switching of nonlinear graphene resonators as the means to boost weak signals. Moreover, reduced-order models were built to capture the complex nonlinear dynamics that atomically thin membranes exhibit when driven opto-thermally. Furthermore, the influence of temperature on the dynamics of graphene-antiferromagnetic membranes were investigated and the influence of transition temperature on nonlinear dynamic behavior of such 2D membranes was discussed
Research theme R3 was closely linked with R2 and mainly focused on understanding the dissipation processes of atomically thin membranes. Our preliminary works related to this theme was quite successful and led to a numerical model and experimental procedure that shed light on the role of mode coupling on the nonlinear dissipation processes of graphene nanomechancial systems. As a continuation of this topic , we showed how mode coupling and nonlinear dissipation could be used to engineer frequency combs with graphene resonators. In addition, the low-quality factor of graphene based nanomechancial resonators in vacuum, made us also look into other dissipation pathways. One interesting route was found to be eddy current damping which was successfully probed in diamagnetically levitating graphite plates, and later suppressed by making composite levitating structures comprising graphite particles dispersed in a polymer matrix.
Finally, related to research theme R4 an interferometry set-up was built and was successfully utilized for probing nanoscale forces of graphene nanomechanical systems. Here, we focused on measuring the forces that are generated by gas molecules passing through nanopores in graphene, and also developed a protocol for measuring the nanomotion of graphene in real-time through a nonlinear optical field. Our first estimates showed that the later can even be used for measuring tiny forces that are generated by micro-organisms. In this framework, new collaborations were initiated with biophysicist, and breakthrough experiments were performed that led to measurement of the nanoscale vibrations of single bacteria. It was found that this nanoscale motion diminishes if the bacteria are dead and persists as long as the bacteria are kept alive, thus providing new means for screening the effectiveness of antibiotics and fighting the global problem of antibiotic resistance. As a continuation of the work, it was also shown that by engineering microwells, bacterial cells can be trapped in the laser spot, and laser intensity fluctuations can be used to determine if bacteria are resistant to antibiotics or not. These advancements led to a large media coverage globally, crystalized in an ERC PoC grant, and built the foundation of the spin-off company SoundCell, that plans to offer fast antibiotic susceptibility testing using graphene drums
In research theme R1, new nonlinear models were developed and successfully implemented on experimental data for estimating the Young’s modulus of graphene membranes and for probing highly anisotropic properties of 2D As2S3 layers. Moreover, molecular dynamic simulations were performed to support experimental findings on the interrelation between phonons and thermal bath in nanostructures and how such relation affect's Young's modulus at the nanoscale. In addition, modal order reduction techniques were developed from full scale finite element simulations as well as molecular dynamics to underpin the complex nonlinear phenomena that are observed in the experiments
In research theme R2, new methodologies and numerical models were built to study the high frequency stochastic switching of nonlinear graphene resonators as the means to boost weak signals. Moreover, reduced-order models were built to capture the complex nonlinear dynamics that atomically thin membranes exhibit when driven opto-thermally. Furthermore, the influence of temperature on the dynamics of graphene-antiferromagnetic membranes were investigated and the influence of transition temperature on nonlinear dynamic behavior of such 2D membranes was discussed
Research theme R3 was closely linked with R2 and mainly focused on understanding the dissipation processes of atomically thin membranes. Our preliminary works related to this theme was quite successful and led to a numerical model and experimental procedure that shed light on the role of mode coupling on the nonlinear dissipation processes of graphene nanomechancial systems. As a continuation of this topic , we showed how mode coupling and nonlinear dissipation could be used to engineer frequency combs with graphene resonators. In addition, the low-quality factor of graphene based nanomechancial resonators in vacuum, made us also look into other dissipation pathways. One interesting route was found to be eddy current damping which was successfully probed in diamagnetically levitating graphite plates, and later suppressed by making composite levitating structures comprising graphite particles dispersed in a polymer matrix.
Finally, related to research theme R4 an interferometry set-up was built and was successfully utilized for probing nanoscale forces of graphene nanomechanical systems. Here, we focused on measuring the forces that are generated by gas molecules passing through nanopores in graphene, and also developed a protocol for measuring the nanomotion of graphene in real-time through a nonlinear optical field. Our first estimates showed that the later can even be used for measuring tiny forces that are generated by micro-organisms. In this framework, new collaborations were initiated with biophysicist, and breakthrough experiments were performed that led to measurement of the nanoscale vibrations of single bacteria. It was found that this nanoscale motion diminishes if the bacteria are dead and persists as long as the bacteria are kept alive, thus providing new means for screening the effectiveness of antibiotics and fighting the global problem of antibiotic resistance. As a continuation of the work, it was also shown that by engineering microwells, bacterial cells can be trapped in the laser spot, and laser intensity fluctuations can be used to determine if bacteria are resistant to antibiotics or not. These advancements led to a large media coverage globally, crystalized in an ERC PoC grant, and built the foundation of the spin-off company SoundCell, that plans to offer fast antibiotic susceptibility testing using graphene drums
The activities of the project went beyond the state of the art. This included (i) Methods and models that were successfully used for capturing nonlinear response of graphene membranes leading to multiple publications in Nano Letters and ACS Nano; (ii) Methods for clarifying the role of mode coupling on dissipation and its engineering for frequency comb generation, which led to publications in Nature Communications and Nano Letters; (iii) numerical simulations and theoretical models based on (1) thermal dynamics of the lattice in nanostructures to support experimental findings on the interrelation of elasticity and thermal bath that was published in physical review letters, as well as (2) finite element and molecular dynamics simulations that capture the complex nonlinear phenomena of graphene nanomechanical systems which were published in Physical Review Applied and Journal of Applied Physics; (iv) New experimental procedure for measuring the tiny forces that are exerted on graphene in fluid, from gas sensing (published in nature communications and nonlinear dynamics) to biosensing (published in nature nanotechnology and iScience)