Nanomechanical resonators made of two-dimensional (2D) materials are the subject of intensive research due to their remarkable properties, allowing them to operate at high frequencies with high sensitivity. However, dissipation losses and manufacturing issues have prevented them from reaching their full potential. This thesis aims to overcome these challenges by dry-transferring 2D materials onto a MEMS and clamping them using electron beam-induced deposition. By in-plane straining the membranes using MEMS, the tensile energy is increased, thereby diluting intrinsic losses. This approach increased the Q-factor of 2D material resonators by 91% and allowed measuring forces down to sub-piconewtons, outperforming commercially available silicon-based force sensors.

Boron-doped diamond (BDD) is an attractive electrode material. When sufficiently boron-doped, diamond has metal-like conductivity and in comparison with other electrode materials has several advantages, such as lowand stable background current, reduced biofouling, broad potentialwindow, corrosion resistance and chemical stability. However, current fabrication processes rely on top-down techniques, that often require cleanrooms and expensive micro fabrication techniques. This research focuses on a low-cost bottom-up fabrication technique by using an inkjet printing process to locally increase the substrate seeding density. Thin-film BDD can then be selectively grown into electrode geometries. The BDD electrodes can be used as more robust and better performing electrodes for detectingmicropollutants in environmental monitoring or for detecting biomarkers in saliva, sweat or blood, in health monitoring. Inkjet manufacturing is an emerging production process in micro fabrication. Due to its accuracy, material efficiency, and given that it is a digital process, inkjet printing is a strong candidate for bottom-up fabrication of low-cost and customizable BDD (micro)-electronics. Two inkjet printers were used to investigate themicro fabrication technique for a BDD chip electrode. A hacked desktop Epson printer was used to demonstrate the capabilities of selective seeding using ’diamond’ ink on silicon substrates and to grow patterned thin-film intrinsic diamond. However, the printer lacks the required control to produce continuous structures with high accuracy. A second method for selective seeding was employed by using a PIXDRO LP-50 commercial research printer, which has a high resolution, motion controlled print bed. With the application of surface treatments, such as oxygen plasma, on the silicon substrate and the development of different inks, continuous films of nanocrystaline diamond with line resolution of approximately 60 μm are produced in a final chemical vapor deposition (CVD) growth step. In addition, by loading the printer with a silver ink part of the diamond film has been coated with silver, which demonstrates that a reference electrodes or electrode leads can be manufactured with the same production technique. This research demonstrates the potential for the bottom-up fabrication of chip electrodes using the inkjet printing process. Furthermore, as this process is not limited to the production of BDD electrodes, it opens the path towards bottom-up fabrication of other (boron-doped) diamond sensor devices, such as gas sensors or 2D heaters.

Dynamic Atomic Force Microscopy (dAFM) is an extremely powerful tool for exploring surface topology and nanoscale manipulation and characterization. A feature of dAFM is the existence of highly nonlinear forces between a cantilever tip and sample. One of these forces that plays a large role in operation of AFM is the van der Waals (vdW) force. This force is characterized in part by the Hamaker constant H and cantilever tip radius R. Measuring these two properties quickly and accurately can facilitate further characterization methods in dAFM. This research will focus on creating methods in which H and R can be extracted using the dynamic response of a cantilever. The vdW force was used to extract H by analyzing the softening behavior of Frequency Response Curves (FRCs). Electrostatic forces were used to extract R by applying a simplified Kelvin Probe Force Microscopy (KPFM) technique. The method to extract H was demonstrated numerically, and the method to extract R was proven experimentally and validated using a Scanning Electron Microscopy (SEM) image.

Micro and Nano-mechanical resonators are becoming increasingly ubiquitous in the areas of particle characterization and biological sensing. For biological sensing, however, the presence of a liquid environment is a pre-requisite. Hollow cantilevers, which allow fluids to be transported inside the resonator, often have high quality factors even when the channels are filled with fluids. This makes them attractive for both sensing mass and determining fluid properties in small volumes. This work aims at determining the density of fluids in picoliter volumes with high resolution using hollow cantilevers. In order to achieve this, we obtain the resonance frequencies of the vibrating microstructure linked to three different modes: the first two flexural modes and the first torsional mode. The first torsional mode is unique to our device and is enabled by the specific geometry of the hollow cantilever. Our approach involves filling the resonator channels with three different fluids in vacuum and monitoring the resonance frequencies and quality factors of the three modes. As the mode number increases, we observe that the shifts in resonance frequency and quality factor for each liquid also increase. This implies that as we approach higher mode numbers there is an improvement in the sensitivity and resolution of the density measurement technique. The quality factors for the three fluids for a specific mode are not significantly different. It is found that in order to achieve higher sensitivities and improved resolution in determining fluid properties, studying higher modes of hollow cantilevers in improved vacuum could indeed be an effective solution.

To control fluid transport, microfluidic systems often make use of pressure driven flow and pneumatically actuated valves. However these require bulky external instrumentation. An integrated fluid control mechanism would make microfluidic systems more portable, closed and automated. The aim of this project was to create a pH-responsive membrane for integrated fluid control in microfluidic systems. pH-responsiveness will allow the membrane to interact directly with analytes in a microfluidic system.
First pH-responsive materials and fluid control mechanisms to create a pH-responsive membrane were reviewed. Cross-linked polymer hydrogels with pH-dependent volumetric swelling were identified as the most suitable material for the membrane. These materials respond to changes in pH by large volumetric transitions, which creates potential for control over a wide range of flow rates. Furthermore they have an inherent interaction with water and are permeable to small molecules such as H+ ions. The material is synthesized from a liquid precursor that can be cured through photo-initiated free radical polymerization.
We tested a system for measuring the pH response of the material that consisted of a hydrogel disk that was vertically constrained inside a fluidic channel. Due to this constraint, expansion only occurred in the lateral direction and could be measured using an optical microscope. Furthermore, we developed a method for manufacturing macro-porous hydrogel membranes that gives control over pore size, shape and position. A photo-lithography approach was used to pattern the membranes and thereby create pores, using a photo-mask that was manufactured on an office printer in a very fast and low-cost process.
The resulting membranes had a thickness of 140-190 um and pore diameters of 100-400 um. The pore size was measured for environmental pH of 1.6 and 7.1, within this range the pores doubled in diameter. Furthermore the pH-responsive deformation ratio of the pores increased significantly with increasing curing time and decreasing pore diameter. The results suggest that there is a difference in material properties around the pores that develops due to a local difference in received exposure dose during curing.
The fluidic properties and pH-response of the membrane can be adjusted to suit a specific application by changing the design, the curing time or the chemical composition of the membrane. The constrained disk system can then be used to measure and compare the pH-response of different potential materials.