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
