Theory and Fundamentals

Micro and nano-mechanical components at the first glance seem to obey classical mechanics. However, many phenomena and properties in these devices are still fundamentally unclear. Two dimensional materials, for instance, can show intrinsic tensions, which could be related to manufacturing effects, but might also have a fundamental origin like Brownian fluctuations or van der Waals forces at the clamping point. Moreover, understanding the non-linearities at the nano scale is still elusive. For instance, damping of nano-membranes is high, non-linear and strongly temperature dependent for unknown reasons. Therefore, in this research theme we focus on the fundamentals and physics of micro and nano-mechanical systems (such as cantilevers, beams, and membranes) and their non-linear dynamics behaviour.

Dynamics and fluid-structure interaction in hollow microfluidic devices

The characterization of biological molecules and cells in lab-on-a-chip devices is one of several achievements reached by the Nano/Micro-Electro-Mechanical-Systems (NEMS/MEMS) community. Among diverse configurations, hollow microstructures have shown superior qualities in terms of dynamic range and damping performance with the capability of placing the liquid inside the structure. This indeed provides new opportunities for mass-based flow cytometry and inspection of biological samples. The goal of this project is to introduce a new methodology for mass sensing applications in liquid exploiting nonlinear dynamics of hollow microfluidic devices.

Nonclassical elasticity vs Molecular Dynamics

As materials scale down, the classical continuum models fail to give accurate results, thus higher-order elastic theories must be applied to account for contributions from strain gradients. The goal of the project is to determine higher-order length-scale parameters used in the non-classical theory by inspecting the correlation of results given by a semi-analytical solution and molecular dynamics simulations.

Nonlinear dynamics in Atomic Force Microscopy (AFM)

Amplitude Modulation (Tapping mode) Atomic Force Microscopy (AFM) has evolved into a useful method for nanoscale imaging of surfaces in molecular metrology and biology. This is carried out by scanning surfaces using a resonating microcantilever (probe) with a sharp nanoscale tip that periodically touches the sample and lifts off at frequencies of about 50–500 kHz. Tip-sample interactions in AFM are highly nonlinear. This project aims to identify the nonlinear parameters involved in tip-sample interaction by means of novel numerical techniques to characterize tip wear and sample properties. 

Nonlinear dynamics and modal interactions in 2D materials

Graphene-based resonators are receiving considerable attention recently due to their potential applications in NEMS devices. Thermal excitation is a promising actuation technique in such systems that allow fast characterization of multiple samples. This project focuses on the theoretical and experimental characterization of thermally actuated graphene drums by exploiting their nonlinear dynamics features.

Design and Fabrication

Fabrication methods are key prerequisites for the study of the dynamics of micro and nanosystems. Although quite some work on archetypical devices like graphene drums has been performed, the fabrication and characterization of mechanical devices from 2D materials is still in its infancy. Current device fabrication methods have low yield, show large device-to-device variations and are not compatible with high-volume manufacturing. We intend to improve these methods, both by internal device fabrication and by collaborations with leading groups and companies. The facilities at TU Delft are excellent to achieve this goal, since nano and microstructures, with proper electrode configurations, can be created in the Kavli Nanolab and the Else Kooi Lab. We have collaborations with the companies Graphenea and Applied Nanolayers that transfer their CVD graphene layers on our structures.

Micro and nano electromechanical sensors
Design optimization of graphene resonators
Development of fabrication methods for 2D sensors

Experimental Characterization

Experimental characterization of nanoscale devices is an important challenge. Since device dimensions are smaller than the optical wavelength, optical methods have their limitation. On the other hand, measurements by scanning probe techniques like AFM have the drawback of strong tip-device interactions that modify device properties and are not able to capture the dynamics of these devices at high frequencies. Therefore, the investigation of novel actuation and detection methods for MEMS and NEMS will be a key aspect of this research line.

 

Furthermore, for designing and developing the ultimate NEMS devices, reliable and efficient descriptions of their dynamic response are essential. Therefore, another mission of the group is the theoretical characterization and development of accurate numerical tools that can be used in design of NEMS devices.

Mechanical characterization of 2D nanomaterials

Although 2D NEMS devices have shown promising applications, their development is still far from being considered well-established. One of the problems is the large variability that can be seen in mechanical properties of these devices obtained by available techniques. For instance, Young’s modulus of Graphene membranes has been reported between 0.1 and 1 TPa. In this project we aim at developing new methods utilizing nonlinearities for mechanical characterization of 2D materials 

Nonlinear identification of cracks in microsystems

Propagation of micro-cracks in silicon-based devices cause malfunction in a large number of integrated circuits and microelectromechanical systems. In this study, using a combined theoretical and experimental scheme, we investigate the effect of damage on the nonlinear response of micro structures.

Mechanical characterization of micro systems in liquid

The objective of this project is designing a test set up for enabling modal testing of microsystems which have to operate in fluidic environment. Examples include submerged AFM cantilevers to facilitate the imaging of biological samples.

Applications

The research results of the other three research lines will position the group perfectly to study and develop new devices that can serve as prototypes for applications. As a consequence of their small mass and high flexibility, resonating cantilevers and nano membranes are extremely sensitive to external forces. For this reason it is the plan to study their use as mass sensors, stiffness sensors, pressure sensors, and gas sensors.

Mass and stiffness sensor for biological samples

Micro and nano resonators have been successfully applied for detection of biological organisms such as bacteria, viruses and DNA. The ongoing challenge in this project is to utilize dynamics for developing biomechanical sensors capable of rapidly assessing characteristic properties of biological samples with the aim to help in early medical diagnosis.

Ultra sensitive pressure sensors
Graphene pumps
Graphene molecular sieve osmometer