In this paper ultra clean monolayer and bilayer Chemical Vapor Deposited (CVD) graphene membranes with diameters up to 500 µm and 750 µm, respectively have been fabricated using Inverted Floating Method (IFM) followed by thermal annealing in vacuum. The yield decreases with size but we show the importance of choosing a good graphene raw material. Dynamic mechanical properties of the membranes at room temperature in different diameters are measured before and after annealing. The quality factor ranges from 200 to 2000 and shows no clear dependence on the size. The resonance frequency is inversely proportional to the diameter of the membranes. We observe a reduction of the effective intrinsic stress in the graphene, as well as of the relative error in the determination of said stress after thermal annealing. These measurements show that it is possible to produce graphene membranes with reproducible and excellent mechanical properties.

We report on the design and operation of a world-to-chip microfluidic interface and experimental setup for fluidic micro- and nano-electromechanical systems. The central component of the interface is an engineered polyether ether ketone connector that brings fluid samples from a commercial syringe pump to the chip with the help of o-rings. In addition to that, the connector serves as an on-chip vacuum chamber. To confirm the adequate operation of our interface, we use complex microfluidic devices that were previously fabricated, suspended microchannel resonators, and demonstrate a fast exchange between fluids (on the scale of 130 s from isopropyl alcohol to water), in-vacuum operation of the devices (intrinsic damping regime), and accurate temperature control of the chip at different set points.

Uncooled infrared detectors have enabled the rapid growth of thermal imaging applications. These detectors are predominantly bolometers, reading out a pixel’s temperature change due to infrared radiation as a resistance change. Another uncooled sensing method is to transduce the infrared radiation into the frequency shift of a mechanical resonator. We present here highly sensitive resonant infrared sensors, based on thermo-responsive shape memory polymers. By exploiting the phase-change polymer as transduction mechanism, our approach provides 2 orders of magnitude improvement of the temperature coefficient of frequency. Noise equivalent temperature difference of 22 mK in vacuum and 112 mK in air are obtained using f/2 optics. The noise equivalent temperature difference is further improved to 6 mK in vacuum by using high-Q silicon nitride membranes as substrates for the shape memory polymers. This high performance in air eliminates the need for vacuum packaging, paving a path towards flexible non-hermetically sealed infrared sensors.

Thermal analysis is essential for the characterization of polymers and drugs. However, the currently established methods require a large amount of sample. Here, we present pyrolytic carbon resonators as promising tools for micromechanical thermal analysis (MTA) of nanograms of polymers. Doubly clamped pre-stressed beams with a resonance frequency of 233 ± 4 kHz and a quality factor (Q factor) of 800 ± 200 were fabricated. Optimization of the electrical conductivity of the pyrolytic carbon allowed us to explore resistive heating for integrated temperature control. MTA was achieved by monitoring the resonance frequency and quality factor of the carbon resonators with and without a deposited sample as a function of temperature. To prove the potential of pyrolytic carbon resonators as thermal analysis tools, the glass transition temperature ( T g ) of semicrystalline poly(L-lactic acid) (PLLA) and the melting temperature ( T m ) of poly(caprolactone) (PCL) were determined. The results show that the T g of PLLA and T m of PCL are 61.0 ± 0.8 °C and 60.0 ± 1.0 °C, respectively, which are in excellent agreement with the values measured by differential scanning calorimetry (DSC).

Pool boiling has a high heat removal capability and is considered as one of the most effective cooling methods due to utilization of latent heat of vaporization. Surface wettability plays a key role in boiling heat transfer since it controls the contact line between liquid, gas, and solid phases. Here, surfaces with mixed wettability (biphilic) were fabricated for assessing the effect of biphilic surfaces on bubble dynamics and boiling heat transfer as well as for the determination of an optimum hydrophobic area to the total surface area (A* = A(Hydrophobic)/A(total)) to achieve the best heat transfer performance. Pool boiling experiments were conducted on biphilic surfaces with A* ranging from 0.19% to 95%. It was shown that biphilic surfaces directly affected both the critical heat flux (CHF) and boiling heat transfer. According to the experimental results, the surface with A* of 38.46% delivered the highest CHF enhancement (197 W/cm(2), and maximum boiling heat transfer enhancement of 103%) among the tested biphilic surfaces. To represent a better understanding of related heat transfer mechanisms, bubble dynamics was obtained using a high-speed camera system. Visualization results revealed that bubble formation took place sooner on biphilic surfaces with A* of higher than 38.46%, thereby triggering the generation of vapor blanket on the surfaces and CHF occurrence at lower heat fluxes. (C) 2019 Elsevier Ltd. All rights reserved.

The modern theory of charge polarization in solids is based on a generalization of Berry's phase. The possibility of the quantization of this phase arising from parallel transport in momentum space is essential to our understanding of systems with topological band structures. Although based on the concept of charge polarization, this same theory can also be used to characterize the Bloch bands of neutral bosonic systems such as photonic or phononic crystals. The theory of this quantized polarization has recently been extended from the dipole moment to higher multipole moments. In particular, a two-dimensional quantized quadrupole insulator is predicted to have gapped yet topological one-dimensional edge modes, which stabilize zero-dimensional in-gap corner states. However, such a state of matter has not previously been observed experimentally. Here we report measurements of a phononic quadrupole topological insulator. We experimentally characterize the bulk, edge and corner physics of a mechanical metamaterial (a material with tailored mechanical properties) and find the predicted gapped edge and in-gap corner states. We corroborate our findings by comparing the mechanical properties of a topologically non-trivial system to samples in other phases that are predicted by the quadrupole theory. These topological corner states are an important stepping stone to the experimental realization of topologically protected wave guides in higher dimensions, and thereby open up a new path for the design of metamaterials.

We report on the first experimental demonstration of vibrating two-dimensional nanoelectromechanical systems (2D NEMS) with on-chip piezoelectric excitation. Combining a wafer-scale aluminum nitride (AlN) thin film technology with an all-dry transfer technique for atomic layer 2D semiconductors, we fabricate and piezoelectrically excite few-atomic-layer molybdenum disulfide (MoS2) NEMS resonators in the high frequency (HF) band. Multimode resonances up to 38MHz are observed, with efficient electromechanical drive from the AlN layer off the vibrating 2D NEMS device region (to avoid compromising the movable 2D device by electrodes needed for on-chip excitation and readout). The piezoelectrically excited 2D NEMS resonators may enable remotely driven, ultrasensitive transducers. Combined with on-chip electrical readout techniques (e.g., mixing), this device platform also holds promise for future radio frequency (RF) electronics and integrated systems.

.................................................................................................................................. 2 Introduction ............................................................................................................................. 4 Fabrication: clean room ............................................................................................................ 5 Chips with channels ............................................................................................................... 5 Pattern ............................................................................................................................. 5 Process flow ...................................................................................................................... 5 Silicon nitride lids .................................................................................................................. 7 Processflow ....................................................................................................................... 7 Fabrication: laboratory .............................................................................................................. 9 Silicon nitride lids: etching ..................................................................................................... 9 First try ............................................................................................................................. 9 Second try....................................................................................................................... 10 Third try.......................................................................................................................... 11 Fourth try ........................................................................................................................ 11 Fifth try ........................................................................................................................... 12 Sixth try .......................................................................................................................... 12 Final try .......................................................................................................................... 13 Transference ...................................................................................................................... 14 Dry transference .............................................................................................................. 14 Wet transference ............................................................................................................. 15 Results .................................................................................................................................. 20 Perspectives ........................................................................................................................... 21 Conclusion ............................................................................................................................. 22 References............................................................................................................................. 23 Appendix 1: Process flow chips with channels ........................................................................... 24 Appendix 2: Process flow Silicon nitride lids .............................................................................. 26 Appendix 3: dates .................................................................................................................. 28 Chips with channels ......................................................................................................... 28 Silicon nitride lids ............................................................................................................. 29

..................................................................................................................................... 4 List of Figures and Tables.......................................................................................................... 7 Chapter 1: Introduction .......................................................................................................... 9 Background about M/NEMS Resonators................................................................... 9 Two-dimensional (2D) Materials and their potential use in NEMS ........................ 11 1.2.1 2D Materials and their properties ........................................................................ 11 1.2.2 Potential use of 2D Material for NEMS Resonators ............................................ 15 Thesis Objective and Structure ................................................................................ 16 1.3.1 Thesis Objective................................................................................................... 16 1.3.2 Thesis Structure ................................................................................................... 17 Chapter 2: Graphene based NEMS Resonators ................................................................. 18 Graphene Production Methods ................................................................................ 18 2.1.1 Mechanical Exfoliation ........................................................................................ 18 2.1.2 Epitaxial Growth on Silicon Carbide (SiC) ......................................................... 19 2.1.3 Chemical Vapour Deposition ............................................................................... 19 Properties of GNEMS Resonators ........................................................................... 20 Fabrication of GNEMS Resonators ......................................................................... 21 2.3.1 GNEM Resonators based on Exfoliated Graphene .............................................. 21 2.3.2 GNEMS Resonators based on Large Scale Synthesised Graphene ..................... 23 Actuation and Detection of GNEMS Resonators .................................................... 25 2.4.1 Optical Transduction ............................................................................................ 25 2.4.2 Electrical Transduction ........................................................................................ 25 Design Schematics and Working Principles ............................................................ 26 Chapter 3: Graphene Transfer and Device Fabrication .................................................... 29 Graphene Transfer ................................................................................................... 29 3.1.1 Overview of Graphene Transfer Methods ........................................................... 29 3.1.2 Employed Graphene Transfer Procedures ........................................................... 30

In this project, characterization of a series of previously fabricated Aluminium clamped-clamped micro beams and cantilevers by electrical measurements in order to investigate the effects of scaling down on mechanical properties of micro/nano structures is presented. The Young’s modulus that depends on the thickness of the microstructure, residual stress and surface properties as opposed to a constant Young’s modulus in macro scale theories was investigated. Due to insufficient sample space and high stresses during fabrication, a correlation was not obtained. KeywordsAluminium beams, Coupled Stress theory, Residual Stress theory, Surface Elasticity theory, Combined stress model, electrical characterization.

In this paper we describe five different transduction techniques for the motion of NEMS resonators. We describe how these techniques differ from those used for MEMS and how centrosymmetric or amorphous materials can be used to fabricate NEMS.

Fabrication of silicon based micro-channels is typically a complex process involving multiple steps such as lithography, bonding, thin film deposition, etching, surface migration etc. We present a method for the fabrication of microchannels . insired by 2D material transferring techniques, we transfer a 100 nm thick silicon nitride film on top of a silicon nitride coated chip with predefined trenches and holes to form silicon nitride microchannels and membranes.

Optical detection back-action in cantilever resonant or static detection presents a challenge when striving for state-of-the-art performance. The origin and possible routes for minimizing optical back-action have received little attention in literature. Here, we investigate the position and mode dependent optical back-action on cantilever beam resonators. A high power heating laser (100 mu W) is scanned across a silicon nitride cantilever while its effect on the first three resonance modes is detected via a low-power readout laser (1 mu W) positioned at the cantilever tip. We find that the measured effect of back-action is not only dependent on position but also the shape of the resonance mode. Relevant silicon nitride material parameters are extracted by fitting finite element (FE) simulations to the temperature-dependent frequency response of the first three modes. In a second round of simulations, using the extracted parameters, we successfully fit the FEM results with the measured mode and position dependent back-action. From the simulations, we can conclude that the observed frequency tuning is due to temperature induced changes in stress. Effects of changes in material properties and dimensions are negligible. Finally, different routes for minimizing the effect of this optical detection back-action are described, allowing further improvements of cantilever-based sensing in general.

Electrothermal actuators have many advantages compared to other actuators used in micro-electro-mechanical systems (MEMS). They are simple to design, easy to fabricate and provide large displacements at low voltages. Low voltages enable less stringent passivation requirements for operation in liquid. Despite these advantages, thermal actuation is typically limited to a few kHz bandwidth when using step inputs due to its intrinsic thermal time constant. However, the use of pre-shaped input signals offers a route for reducing the rise time of these actuators by orders of magnitude. We started with an electrothermally actuated cantilever having an initial 10-90% rise time of 85 mu s in air and 234 mu s in water for a standard open-loop step input. We experimentally characterized the linearity and frequency response of the cantilever when operated in air and water, allowing us to obtain transfer functions for the two cases. We used these transfer functions, along with functions describing desired reduced rise-time system responses, to numerically simulate the required input signals. Using these pre-shaped input signals, we improved the open-loop 10-90% rise time from 85 mu s to 3 mu s in air and from 234 mu s to 5 mu s in water, an improvement by a factor of 28 and 47, respectively. Using this simple control strategy for MEMS electrothermal actuators makes them an attractive alternative to other high speed micromechanical actuators such as piezoelectric stacks or electrostatic comb structures which are more complex to design, fabricate, or operate.

Measurement of thermal radiation through uncooled bolometers is at the heart of many industrial applications. From the development of the Honey- well silicon microstructure developed in 1982, no particular change in paradigm was recorded. The advent of 2D-materials offers a whole new promising future for bolometric measurements and thermal detection. 2D-materials have record properties extremely sensitive to external stimuli making them great candidates for boosting bolometers performance. In this work, a method to model, fabricate and characterise 2D material- based bolometers is presented. The proposed design uses a suspended 2D- material beam as thermal sensor and IR absorber. The model suggests an im- provement of the state of the art on three different aspects. Reduction of thermal losses, tunable enhancement of absorption and increased bandwidth. An inno- vative read-out technique is also suggested. Bolometers employing graphene as suspended beam were successfully fab- ricated. An optimised fabrication process is proposed and allow to consistently produce devices having optimal properties to host graphene. Electrical mea- surements on graphene beams lying on silicon dioxide showed good tunability of graphene resistance through electrostatic gating proving possible to enhance thermal radiation absorption in graphene. The results obtained offers a promis- ing outlook toward the future of 2D material-based bolometers.

We present here the fabrication of large suspended sheets of graphene for mechanical resonators. The diameter of the circular resonators varies from 1.2 μm to 26.5 μm resulting in diameter-to-thickness aspect ratios as large as 74000. The membranes were fabricated in arrays with yields of up to more than 90%. Assuming low to moderate tensile stress, <1 GPa, the mechanical resonance frequency of these structures potentially spans the range from 1 MHz to 1 GHz. The successfully fabrication of graphene membranes will allow us to first study their mechanics (resonance frequency and damping) and later explore their use for various sensing applications, including mass sensing.

The fabrication and working principle of an electrochemical gas sensor for direct gas phase detection of organic molecules is presented. The sensor is composed of two Pt electrodes where redox reactions can occur, and an ion exchange membrane to conduct H+ from an electrode to the other. As proton exchange membrane they used a spin-coated Nafion((R)) layer. An underlying SU-8 layer assures a double role of adhesion of the Nafion to the substrate and water reservoir to limit dehydration of the Nafion. The sensor is characterised for its electrochemical properties and tested for the detection of CO as model pollutant. The detection tests are performed in the form of cyclic voltammetry, and show that the sensor can detect the gas at the applied voltage corresponding to the oxidation potential of CO into CO2.