Micro and Nano Engineering最新文献

Metal assisted chemical etching is a promising method for fabricating high aspect ratio micro- and nanostructures in silicon. Previous results have suggested that P-type and N-type silicon etches with different degrees of anisotropy, questioning the use of P-type silicon for nanostructures. In this study, we compare processing X-ray zone plate nanostructures in N and P-type silicon through metal assisted chemical etching with a gold catalyst. Fabricated zone plates were cleaved and studied with a focus on resulting verticality, depth and porosity. Results show that for high aspect ratio nanostructures, both N and P-type silicon prove to be viable alternatives exhibiting different etch rates, but similarities regarding porosity and etch direction.

Spontaneous capillary flow in open microchannels is a phenomenon driven by surface energies. The contact angle that the liquid forms with the channel's substrate material and the cross-section of the microchannel decide whether liquid from a connected reservoir will automatically fill the channel or not. In this work we show how this behavior can be used to design a passive contact angle measurement device (CAMD) based on parabolic open microgrooves. To that end, we present a theory of open capillary flow in such microgrooves and compare the results to minimal energy surface simulations. Additionally, we discuss that the condition for capillary flow of curved microchannels is essentially equal to the condition for their straight counterparts having the same cross-section.

Lastly, we present two demonstrators of our CAMD made out of micromilled poly(methyl methacrylate). The devices consist of five open microchannels with different cross-sections which are connected to a common liquid reservoir. We show how the behavior of a liquid placed into that reservoir can be used to evaluate the contact angle between the liquid and the substrate material. A comparison to conventional contact angle goniometry shows that our approach is able to successfully estimate contact angles with an accuracy of 10° by design which can be improved by employing a greater number of microchannels. Since our devices were automatically designed and can be tuned to specific applications, this provides an easy approach to include contact angle measurement into existing lab-on-a-chip devices.

Field-effect transistors (FETs) based on MoS₂ nanotubes prepared in anodic aluminum oxide (AAO) templates have been fabricated and demonstrated in this work. MoS₂ nanotubes were prepared by the thermal decomposition of (NH₄)₂MoS₄ precursors in the AAO template. The diameter of the MoS₂ nanotubes was approximately 80 nm, which corresponded to the size of the AAO template. Schottky-type FETs were prepared with Au and Pt electrodes, and the FETs exhibited n-type behavior, with on/off ratios that exceeded 10³ at V_SD = 0.5 V.

Direct ink writing (DIW) is a promising additive manufacturing (AM) technique in the field of microsystems technology due to the potential for high detail resolution and the wide choice of materials suitable for the technique. In this study, inks of polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) as well as composite inks with reduced graphene oxide (PVDF-TrFE-rGO) were developed and adapted for continuous flow DIW. The composite PVDF-TrFE-rGO inks achieved percolation after 1.5 wt% and electrical conductivity of 2.8 S/cm at the highest loading investigate in this study (7 wt%). The inks were successfully printed with minimum nozzle diameter of 40 μm on different substrates including glass, metal and a nitrile elastomer. It was also demonstrated that the inks can be used to create a fully 3D-printed piezoelectric device with the predicted response, i.e. the fabrication technique did not deteriorate the functionality of the device. The conductive composite ink was successfully utilized as an effective electrode in the device. It was therefore demonstrated that by combining materials, such as the composite PVDF-TrFE-rGO ink and the co-polymer PVDF-TrFE with additive manufacturing techniques, the fabrication of low-cost, versatile devices can be achieved.

Integrating optically active III-V materials on silicon/insulator platforms is one potential path towards improving the energy efficiency and performance of modern computing. Here we demonstrate the applicability of direct wafer bonding combined with plasma etching to the fabrication of complex nanophotonic systems out of InP layers. We explore and optimise the plasma etching of InP, validating existing processes and developing improved ones. We explore the use of microdisk lasing as a way to evaluate fabrication fidelity, and demonstrate that we can create complex lasing systems of interest to us: coupled disk cavities and random network lasers.

Two-photon polymerization (2PP) has provided the field of cell biology with the opportunity to fabricate precisely designed microscaffolds for a wide range of studies, from mechanobiology to in vitro disease modelling. However, a multitude of commercial and in-house developed photosensitive materials employed in 2PP suffers from high auto-fluorescence in multiple regions of the spectrum. In the context of in vitro cell biological studies, this is a major problem since one of the main methods of characterization is fluorescence microscopy of immuno-stained cells. This undesired auto-fluorescence of microscaffolds affects the efficiency of such an analysis as it often overlaps with fluorescent signals of stained cells rendering them indistinguishable from the scaffolds. Here, we propose two effective solutions to suppress this auto-fluorescence and compare them to determine the superiority of one over the other: photo-bleaching with a powerful UV point source and auto-fluorescence quenching via Sudan Black B (SBB). The materials used in this study were all commercially available, namely IP-L, IP-Dip, IP-S, and IP-PDMS. Bleaching was shown to be 61.7–92.5% effective in reducing auto-fluorescence depending on the material. On the other hand, SBB was shown to be 33–95.4% effective. The worst result in presence of SBB (33%) was in combination with IP-PDMS since the adsorption of the material on IP-PDMS was not sufficient to fully quench the auto-fluorescence. However, auto-fluorescence reduction was significantly enhanced when activating the IP-PDMS structures with oxygen plasma for 30 s. Moreover, we performed a cell culture assay using a human neuroblastoma cell line (SH-SY5Y) to prove the effectiveness of both methods in immunofluorescence characterization. SBB presented a lower performance in the study especially in presence of 2PP-fabricated microchannels and microcages, within which the differentiated SH-SY5Y cells migrated and extended their axon-like processes, since the SBB obstructed the fluorescence of the stained cells. Therefore, we concluded that photo-bleaching is the optimal way of auto-fluorescence suppression. In summary, this study provides a systematic comparison to answer one of the most pressing issues in the field of 2PP applied to cell biology and paves the way to a more efficient immunofluorescence characterization of cells cultured within engineered in vitro microenvironments.

Microelectromechanical systems for biological purposes (BioMEMS) have shown huge potential for diagnostics, medical treatment or even augmenting certain body functions in humans. This is enabled by the high level of integration, manufacturing precision and high throughput of fabrication techniques in sophisticated semiconductor industries. For minimally invasive devices, mechanically compliable polymeric materials are widely used, like SU-8, polyimide and parylene C, which have good biocompatibility but are difficult to be integrated with standard fabrication processes in semiconductor industries, therefore limiting the production throughput and complexity of device architecture. In this work we present various micromachining techniques of plasma-polymerized fluorocarbon (PPFC), which is a feasible polymeric material acquirable by plasma etching systems. Due to its excellent chemical stability, PPFC is compatible with standard fabrication techniques like plasma etching, photolithography and deposition of thin metal films, which enable the functionalization of PPFC-based platforms for BioMEMS devices. The processing parameters have been discussed, and structures like high aspect ratio nanopillars and PPFC membranes are demonstrated. As a proof of concept, flexible free-standing microelectrode arrays are fabricated. Since PPFC resembles the physiochemical properties of fluorocarbon, which is recognized by USP Class VI standards, we expect PPFC-based platform to be a strong candidate for development of various BioMEMS devices, like biological implants, tissue engineering, neuroprosthetic electrodes, brain-machine interfaces, etc.

In this paper, the combination of an advanced nanopositioning technique and a tip-based system, which can be used as an atomic force microscope (AFM) and especially for field emission scanning probe lithography (FESPL) is presented. This is possible through the use of active microcantilevers that allow easy switching between measurement and write modes. The combination of nanopositioning and nanomeasuring machines and tip-based systems overcomes the usual limitations of AFM technology and makes it possible to perform high-precision surface scanning and nanofabrication on wafer sizes up to 4 in. We specifically discuss the potential of nanofabrication via FESPL in combination with the nanofabrication machine (NFM-100). Results are presented, where nanofabrication is demonstrated in form of a spiral path over a total length of 1 mm and the potential of this technique in terms of accuracy is discussed. Furthermore, ten lines were written with a pitch of 100 nm and a linewidth below 40 nm was achieved, which is in principle possible over the entire range of motion.

Here we present an alternative technological approach to paper-based microfluidics that, to the best of our knowledge, has not been reported so far. Instead of defining fluid conducting paths by cutting fluidic structures, or by printing hydrophobic substances on paper, we prepare cellulose/polymer composites that can be printed additively on, in principle, arbitrarily shaped substrates and surfaces. In this way, with respect to geometry and properties, well defined fluid conducting structures based on cellulose can be realized, that can additionally be fully embedded in an organic surface coating. Moreover, the composite can, prior to the printing step, be doped with a functional component, which facilitates the realization of printed analytical devices using just a single base material and process technology. In this sense, the proposed technology can be seen as an alternative pathway to paper-based microfluidics, that may be attractive for specific niche-applications such as, for example, bio-chemical assays embedded in the surface of everyday necessities or commodities. Especially lateral flow immunoassays, pandemic-driven needed in large quantities, may embody a future application field of the presented technology.

Worldwide, electronic waste represents the fastest-growing stream of waste. With an increasing number of connected devices, passive and eco-friendly environmental sensing solutions need to be developed. Wireless passive devices for RFID and sensing exist, however, most of them rely on non-biodegradable materials. Willing to produce entirely green radio-frequency (RF) resonators on a paper substrate, we identify potential biodegradable materials to be used as encapsulation and humidity sensing layers. Resonator encapsulation is mandatory to prevent humidity interaction with the transducer while a sensing layer above the resonator enables a good response to humidity. In this work, the radio-frequency behavior of these materials was characterized when implemented on a 3.3 GHz resonating microstrip structure made of copper on FR4 substrate. The response in resonance frequency while varying the relative humidity (RH) from 20% to 80% was monitored. Beeswax-coated resonators exhibited no change in resonance frequency when exposed to humidity and therefore provided excellent encapsulation properties. 10 μm-thick layers of psyllium, konjac and egg-albumin displayed suitable sensing behavior with suitable frequency shifts above 100 MHz from 20% to 80% RH. Konjac and psyllium showed the best compatibility when coated on the beeswax encapsulant, exhibiting reversibility and low hysteresis when exposed to humidity variations.