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The unique mechanical and electrical properties of graphene make it an exciting material for nanoelectromechanical systems (NEMS). NEMS resonators with graphene springs facilitate studies of graphene's fundamental material characteristics and thus enable innovative device concepts for applications such as sensors. Here, we demonstrate resonant transducers with ribbon-springs made of double-layer graphene and proof masses made of silicon and study their nonlinear mechanics at resonance both in air and in vacuum by laser Doppler vibrometry. Surprisingly, we observe spring-stiffening and spring-softening at resonance, depending on the graphene spring designs. The measured quality factors of the resonators in a vacuum are between 150 and 350. These results pave the way for a class of ultraminiaturized nanomechanical sensors such as accelerometers by contributing to the understanding of the dynamics of transducers based on graphene ribbons with an attached proof mass., QC 20240201

Measuring vibrations is essential to ensuring building structural safety and machine stability. Predictive maintenance is a central internet of things (IoT) application within the new industrial revolution, where sustainability and performance increase over time are going to be paramount. To reduce the footprint and cost of vibration sensors while improving their performance, new sensor concepts are needed. Here, double-layer graphene membranes are utilized with a suspended silicon proof demonstrating their operation as resonant vibration sensors that show outstanding performance for a given footprint and proof mass. The unveiled sensing effect is based on resonant transduction and has important implications for experimental studies involving thin nano and micro mechanical resonators that are excited by an external shaker., QC 20230227

Atomic force microscopy (AFM) indentation experiments are commonly used to study the mechanical properties of graphene, such as Young's modulus and strength. However, applied AFM indentation forces on suspended graphene beams or ribbons are typically limited to several tens of nanonewtons due to the extreme thinness of graphene and their sensitivity to damage caused by the AFM tip indentation. Herein, graphene ribbons with a Si mass attached to their center position are employed, allowing us to introduce an unprecedented, wide range of AFM indentation forces (0–6800 nN) to graphene ribbons before the graphene ribbons are ruptured. It is found that the Young's modulus of double-layer graphene ribbons decreases as the applied AFM indentation force is larger than ≈3000 nN, which indicates that the stiffness of double-layer graphene ribbons remains constant before exposing them to AFM indentation forces larger than ≈3000 nN., QC 20220930

Graphene has exciting potential in nanoelectromechanical system (NEMS) applications due to its unique mechanical and electrical properties as well as its ultimate thinness. In this paper, we discuss the potential of using suspended graphene structures in NEMS sensors and provide an overview of our previous research results on piezoresistive graphene NEMS sensors, including pressure sensors and accelerometers., Part of proceedings: ISBN 978-0-7381-2429-2, QC 20230117

Acceleration measurements are fundamental in applications such as consumer electronics, navigation, automotive safety and Internet of things (IoT). In comparison with capacitive or piezoresistive MEMS accelerometers, resonant graphene accelerometers have the potential to be smaller. If demonstrated, they could be a step forward in miniaturization and could enable emerging applications. In this paper. accelerations are measured with a NEMS resonant accelerometer based on graphene. The devices are made of a suspended proof mass attached by graphene ribbons [1-3]. For device evaluation, they are attached to a shaker to produce accelerations. Using a Laser Doppler Vibrometer, the changes in the resonant frequency of the devices caused by the acceleration arc quantified. The results show a linear dependence between the shifts in resonance of the devices and input accelerations at 160 Hz., Part of proceedings: ISBN 978-1-6654-1912-3, QC 20230117

Grain boundaries in two-dimensional (2D) material layers have an impact on their electrical, optoelectronic, and mechanical properties. Therefore, the availability of simple large-area characterization approaches that can directly visualize grains and grain boundaries in 2D materials such as molybdenum disulfide (MoS2) is critical. Previous approaches for visualizing grains and grain boundaries in MoS2 are typically based on atomic resolution microscopy or optical imaging techniques (i.e., Raman spectroscopy or photoluminescence), which are complex or limited to the characterization of small, micrometer-sized areas. Here, we show a simple approach for an efficient large-area visualization of the grain boundaries in continuous chemical vapor-deposited films and domains of MoS2 that are grown on a silicon dioxide (SiO2) substrate. In our approach, the MoS2 layer on a SiO2/Si substrate is exposed to vapor hydrofluoric acid (VHF), resulting in the differential etching of SiO2 at the MoS2 grain boundaries and SiO2 underneath the MoS2 grains as a result of VHF diffusing through the defects in the MoS2 layer at the grain boundaries. The location of the grain boundaries can be seen by the resulting SiO2 pattern using optical microscopy, scanning electron microscopy, or Raman spectroscopy. This method allows for a simple and rapid evaluation of grain sizes in 2D material films over large areas, thereby potentially facilitating the optimization of synthesis processes and advancing applications of 2D materials in science and technology., QC 20201022

The unique properties and atomic thickness of two-dimensional (2D) materials enable smaller and better nanoelectromechanical sensors with novel functionalities. During the last decade, many studies have successfully shown the feasibility of using suspended membranes of 2D materials in pressure sensors, microphones, accelerometers, and mass and gas sensors. In this review, we explain the different sensing concepts and give an overview of the relevant material properties, fabrication routes, and device operation principles. Finally, we discuss sensor readout and integration methods and provide comparisons against the state of the art to show both the challenges and promises of 2D material-based nanoelectromechanical sensing., Dynamics of Micro and Nano Systems, QN/van der Zant Lab, QN/Steeneken Lab

Graphene is an atomically thin material that features unique electrical and mechanical properties, which makes it an extremely promising material for future nanoelectromechanical systems (NEMS). Recently, basic NEMS accelerometer functionality has been demonstrated by utilizing piezoresistive graphene ribbons with suspended silicon proof masses. However, the proposed graphene ribbons have limitations regarding mechanical robustness, manufacturing yield, and the maximum measurement current that can be applied across the ribbons. Here, we report on suspended graphene membranes that are fully clamped at their circumference and have attached silicon proof masses. We demonstrate their utility as piezoresistive NEMS accelerometers, and they are found to be more robust, have longer life span and higher manufacturing yield, can withstand higher measurement currents, and are able to suspend larger silicon proof masses, as compared to the previous graphene ribbon devices. These findings are an important step toward bringing ultraminiaturized piezoresistive graphene NEMS closer toward deployment in emerging applications such as in wearable electronics, biomedical implants, and internet of things (IoT) devices., QC 20191011. QC 20191111

Nanoelectromechanical system (NEMS) sensors and actuators could be of use in the development of next-generation mobile, wearable and implantable devices. However, these NEMS devices require transducers that are ultra-small, sensitive and can be fabricated at low cost. Here, we show that suspended double-layer graphene ribbons with attached silicon proof masses can be used as combined spring–mass and piezoresistive transducers. The transducers, which are created using processes that are compatible with large-scale semiconductor manufacturing technologies, can yield NEMS accelerometers that occupy at least two orders of magnitude smaller die area than conventional state-of-the-art silicon accelerometers. With our devices, we also extract the Young’s modulus values of double-layer graphene and show that the graphene ribbons have significant built-in stresses., QC 20191004

The electrical contact resistance at metal-graphene interfaces can significantly degrade the properties of graphene devices and is currently hindering the full exploitation of graphene's potential. Therefore, the influence of environmental factors, such as humidity, on the metal-graphene contact resistance is of interest for all graphene devices that operate without hermetic packaging. We experimentally studied the influence of humidity on bottom-contacted chemical-vapor-deposited (CVD) graphene-gold contacts, by extracting the contact resistance from transmission line model (TLM) test structures. Our results indicate that the contact resistance is not significantly affected by changes in relative humidity (RH). This behavior is in contrast to the measured humidity sensitivity (0.059 +/- 0.011 %/% RH) of graphene's sheet resistance. In addition, we employ density functional theory (DFT) simulations to support our experimental observations. Our DFT simulation results demonstrate that the electronic structure of the graphene sheet on top of silica is much more sensitive to adsorbed water molecules than the charge density at the interface between gold and graphene. Thus, we predict no degradation of device performance by alterations in contact resistance when such contacts are exposed to humidity. This knowledge underlines that bottom-contacting of graphene is a viable approach for a variety of graphene devices and the back end of the line integration on top of conventional integrated circuits.

The shape and density of grain boundary defects in graphene strongly influence its electrical, mechanical, and chemical properties. However, it is difficult and elaborate to gain information about the large-area distribution of grain boundary defects in graphene. An approach is presented that allows fast visualization of the large-area distribution of grain boundary–based line defects in chemical vapor deposition graphene after transferring graphene from the original copper substrate to a silicon dioxide surface. The approach is based on exposing graphene to vapor hydrofluoric acid (VHF), causing partial etching of the silicon dioxide underneath the graphene as VHF diffuses through graphene defects. The defects can then be identified using optical microscopy, scanning electron microscopy, or Raman spectroscopy. The methodology enables simple evaluation of the grain sizes in polycrystalline graphene and can therefore be a valuable procedure for optimizing graphene synthesis processes., QC 20180604, European Research Council through the Starting Grants M&M’s (277879), Swedish Research Council (GEMS, 2015-05112), European Research Council through the Starting Grants InteGraDe (307311), China Scholarship Council, German Federal Ministry for Education and Research (NanoGraM, BMBF, 03XP0006C), German Research Foundation (DFG; LE 2440/1-2), German Research Council (DFG) through the Priority Program SPP 1459 Graphene

This thesis presents a novel approach to integrate chemical vapor deposition (CVD) graphene into silicon micro- and nanoelectromechanical systems (MEMS/NEMS) to fabricate different graphene based MEMS/NEMS structures and explore mechanical properties of graphene as well as their applications such as acceleration sensing, humidity sensing and CO2 sensing. The thesis also presents a novel method of characterization of CVD graphene grain boundary based defects. The first section of this thesis presents a robust, scalable, flexible route to integrate double-layer graphene membranes to a silicon substrate so that large silicon masses are suspended by graphene membranes. In the second section, doubly-clamped suspended graphene beams with attached silicon masses are fabricated and used as model systems for studying the mechanical properties of graphene and transducer elements for NEMS resonators and extremely small accelerometers, occupying die areas that are at least two orders of magnitude smaller than the die areas occupied by the most compact state-of-the-art silicon accelerometers. An averaged Young’s modulus of double-layer graphene of ~0.22 TPa and non-negligible built-in stresses of the order of 200-400 MPa in the suspended graphene beams are extracted, using analytical and FEA models. In addition, fully clamped suspended graphene membranes with attached proof masses are also realized, which are used for acceleration sensing. In the third section, CO2 sensing of single-layer graphene and the cross-sensitivity between CO2 and humidity are shown. The cross-sensitivity of CO2 is negligible at typical CO2 concentrations present in air. The properties of double-layer graphene when exposed to humidity and CO2 have been characterized, with similarly fast response and recovery behaviour but weak resistance responses, compared to single layer graphene. In the fourth section, a fast and simple method for large-area visualization of grain boundaries in CVD graphene tr, QC 20180726

Graphene has a number of remarkable properties which make it well suited for both transistor devices as well as for sensor devices such as humidity sensors. Previously, the humidity sensing properties of monolayer graphene on SiO2 substrates were examined - showing rapid response and recovery over a large humidity range. Further, the devices were fabricated in a CMOS compatible process which can be incorporated back end of the line (BEOL). We now present a way to selectively passivate graphene to suppress this humidity sensing effect. In this work, we experimentally and theoretically demonstrate effective passivation of graphene to humidity sensing - allowing for future integration with other passivated graphene devices on the same chip.