Micro and Nano Engineering最新文献

Mesoporous germanium (MP-Ge) emerges as a very appealing material for many applications such as anode material for Lithium-Ion batteries due to it high specific area and large void spaces or, in optoelectronics as sacrificial layer for III-V materials growth and detachment, allowing notably several uses of a single Ge substrate. These porous nanostructures are distinguished by a large specific surface area and are prone to degradation with time due to exposure to the environment. To understand and be able to reduce this effect, we studied the chemical and morphological evolution of porous germanium layers under various ambient storage conditions for 3 months to identify the main parameters responsible for material degradation. This study demonstrates that the ambient air environment leads to the growth of native oxide, leading to major morphology changes. Scanning electrons microscope (SEM) showed the formation of clusters and the enlargement of the pores after 90 days. These structural modifications are caused by the oxidation of Ge, and more specifically by the creation of GeO₂ matrices due to the synergy of dioxygen (O₂) and humidity (H₂O_(g)). The energy brought by light can exacerbate these phenomena and thus accelerate the degradation rate of the pore morphology. Based on these experimental results, we propose efficient solutions to limit the GeO₂ proportions and the clusters' appearance, by storing them under a dry neutral atmosphere (Ar) or by adding a hydrogen halide pre-treatment (10s 1% HBr solution).

Microscale patterning on flexible substrates is important in many applications such as in wearable sensors and microfluidics-based diagnostics, therefore low-cost fabrication methods which are scalable and amenable to mass production have attracted the interest of many companies and research groups. Dry film resists (DFRs) are commercially available materials with properties compatible with their implementation on flexible substrates to cover a wide range of applications, which also offer environmental and sustainability benefits due to the low waste generation compared to the liquid resists. However, there are limited detailed reports in the literature regarding the use of DFRs for the fabrication of microfluidic channels or other micropatterns (i.e., posts) on thin and flexible substrates. Herein we present in detail the fabrication of: a) microfluidic channels of width ranging from 50 μm up to 800 μm, and depth ranging from 30 μm up to 270 μm and b) square posts 80 μm × 80 μm in size and 30 μm in height. Particularly, our method enables the fabrication of ultra-deep microchannels (depth > 250 μm), highly ordered post arrays over large area (appr. 60 cm²), as well as complex designs with hierarchical scale features (80 μm posts inside 800 μm microchannels or micro-nanotexturing inside microchannels) on ultra-thin flexible substrates. To demonstrate the versatility of the method, three different DFRs were used on ultra-thin (30 μm), flexible, single-sided copper-clad polyimide substrates. It is also demonstrated that DFRs can be effectively modified using plasma etching to tune the surface wetting properties towards applications such as pumpless capillary action, where such functionality is required.

As the world moves towards integrating new functionalities into everyday objects, the demand for diverse substrates grows, making additive manufacturing an invaluable tool. Organic electronic materials have played a major role in this transition thanks to their excellent electronic and mechanical properties, adaptability and solution processability.

The aim of this study is to compare spin coating, inkjet printing (IJP), and aerosol jet printing (AJP) for applying poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as the channel material in organic electrochemical transistors (OECTs). This work investigates the often-overlooked impact of deposition techniques on the electrical performance of OECTs. Spin coating has been analysed as a reference technique, while AJP and IJP are addressed as promising pathways towards fully printed OECTs.

The normalized transconductance and I_on/I_off ratio have been analysed as figures of merit for this study. AJP devices have shown the best performance, displaying a normalized transconductance of 885 S∙nm and an I_on/I_off ratio around 10³. The spin coated OECTs showed a slightly lower normalized transconductance (740 S∙nm) and much lower I_on/I_off ratio in the order of 10¹. Last, IJP exhibited a transconductance of 433 S∙nm and a I_on/I_off ratio in the order of 10².

This work could be beneficial for a wide range of applications, adding an additional degree of freedom to the tunability of the OECT channel properties. It also opens the discussion for more comprehensive studies on the films from a materials perspective.

A rapid and robust method to fabricate transmission diffractive optical elements in the visible wavelengths is presented. By additive manufacturing of a polymeric photo-resin using 2-photon lithography followed by encasing of the structure in another resin with similar refractive index, the height of the structure can be made much larger, thus trading-off fabrication height for refractive index difference of the two materials. After adjusting for resin shrinkage, different diffractive optical element designs including an m = 1 vortex plate, and Laguerre-Gaussian beams with azimuthal and radial indices of (1,1), (1,2), and (2,1) were demonstrated. Experimental results show intensity patterns matching that of simulations, including size and features, although some aberration was observed, possibly due to fabrication tolerance errors or beam misalignment. This technique adds to the toolkit of micro-optics fabrication methods using additive manufacturing and 3D printing, and it would be beneficial for rapid prototyping and integration with miniaturised systems.

Polyetherimide (PEI) with 3-dimensional (3D) structures is a promising material for applications in electronic devices because of its numerous attractive properties. In the applications of PEI, the low electrical conductivity is often a shortcoming. The electrical conductivity can be improved by a metallization process. Electroless plating is a common metallization process for polymeric materials; however, conventional electroless plating process scarcely provides the metallized PEI. In this work, we overcome this limitation by a supercritical carbon dioxide (scCO₂)-assisted electroless NiP plating process. This scCO₂-assisted electroless NiP plating allows metallization of PEI with 3D structures and realizes a low electrical resistance suitable for practical use in the electronic devices.

As freshwater demand is constantly increasing, water purification via membrane distillation (MD) emerges as a promising water production technology, especially when combined with the use of superhydrophobic membranes. Here, following our previous work [1] we extend our universal, environmentally friendly, plasma nanotexturing and hydrophobization technology for rendering practically any type of membrane superhydrophobic and oleophobic. Thus, we render three commercial porous membranes superhydrophobic, namely, polyvinylidene (PVDF 0.45 μm) (initially hydrophobic), polyethersulfone (PES 1.20 μm) and nylon (NY 1.20 μm) (both initially hydrophilic). We demonstrate superhydrophobic, superoleophobic (down to 40mn/m surface tension) and oleophobic properties (down to 30mN/m surface tension) for PVDF, PES and Nylon membranes thus paving the way for their use with low surface tension waste streams. Moreover, the technology presented herein not only improves existing hydrophobic membranes but may lead to elimination of the use of Teflon-like fluorinated hydrophobic membranes altogether in the future, thereby contributing to the PFAS (Per and Poly Fluoro Alkyl Substances) and Teflon-like membrane use reduction. We subsequently evaluated the performance of the treated membranes in direct contact membrane distillation (DCMD) for desalination of sea-like water (35 g/L NaCl). All membranes showed enhanced water flux with an increase of >13% compared to the pristine hydrophobic PVDF membranes for at least 2 h of continuous operation, with salt rejection exciding 99.99%.

Manufacturing of microstructures using a microfluidic device is a largely empirical effort due to the multi-physical nature of the fabrication process. As such, in moving toward autonomous manufacturing, models are desired that will predict microstructure attributes (e.g., size, porosity, and stiffness) based on known inputs, such as sheath and core fluid flow rates. Potentially more useful is the prospect of inputting desired microfiber features into a design model to extract appropriate manufacturing parameters. In this study, we demonstrate that deep neural networks (DNNs) trained with sparse datasets augmented by synthetic data can produce accurate predictive and design models to accelerate materials development. For our predictive model with known sheath and core flow rates and bath solution percentage, calculated solid microfiber dimensions are shown to be greater than 95% accurate, with porosity and Young's modulus exhibiting greater than 90% accuracy for a majority of conditions. Likewise, the design model is able to recover sheath and core flow rates with 95% accuracy when provided values for microfiber dimensions, porosity, and Young's modulus. As a result, DNN-based modeling of the microfiber fabrication process demonstrates high potential for reducing time to manufacture of microstructures with desired characteristics.

The previous decades have seen a massive increase in the research towards reproducible and optimized surface-enhanced Raman spectroscopy (SERS) substrates. While traditional colloidal synthesis methods have commonly been used for SERS substrate fabrication, they lack reproducibility hindering their usage for many applications. The need for reproducible nanostructures showing high orders of enhancement factors has brought about a shift in the methods one can use to fabricate SERS nanostructures. Lithographic techniques have thus piqued the interest of researchers as a viable option for SERS substrate fabrication. Not only do they offer high enhancement factors and reproducible nanostructures, they also provide the ability to fabricate nanostructures with many different geometries, shapes, sizes and periodicities. Some of the most established lithographic techniques include electron beam lithography, nanosphere lithography, laser interference lithography and many more. This review discusses established lithographic techniques, such as mentioned above, along with other upcoming lithographic techniques to understand the principles and the methodology behind them. A deep understanding of how various parameters can influence the nanostructure fabrication and thereby influence the SERS enhancement is developed. A detailed description of how these nanostructures can be fabricated is also provided for better insight. In addition, strengths and limitations of each method are discussed in detail. Lastly, we also discuss the applicability of SERS substrates for commercial applications comparing the performance of chemical synthesis routes and lithography for SERS substrate fabrication. This review serves as a base to understand the concept and application of SERS from a microfabrication perspective.

Generally speaking, energy harvesting is an up-to-date technology that describes the possibility of capturing small amounts of energy (thermal, solar, or mechanical) from the surroundings and storing them as electrical energy for later uses when needed. Among the energy harvesting systems, the use of piezoelectric thin films and coatings is gaining increasing interest from both the academic and industrial communities, as these systems allow for the design and development of micro- and nano-scale devices, thanks to the possibility of being micromachined and to the added functionality offered by the electromechanical coupling. These peculiarities justify their use for different applications, ranging from high energy density harvesters to high sensitivity sensors, and even low power consumption and large displacement actuators. Further, the current focus of the research on piezoelectric energy harvesting coatings is shifting from fully inorganic to hybrid organic-inorganic (i.e., composite) systems, as the latter can offer higher flexibility (i.e., lower stiffness), making them more sensitive to small vibrations and therefore suitable for these specific harvesting conditions. In this regard, photoinduced polymerization (the so-called “UV-curing”) has become a suitable and reliable technique for the manufacturing of piezoelectric composite systems, as it is a solvent-free approach that allows for transforming a liquid mixture of monomers/oligomers into a solid 3D network in a few seconds, with a very limited energy consumption and a very high conversion. Besides, as the UV-curing process is very fast, the dispersed ceramic piezoelectric phase is not prone to settle down in the liquid resin, hence ensuring its homogeneous distribution within the polymer network after curing and better piezoelectric performance. The present review aims to provide the reader with an up-to-date overview of UV-curable coatings for piezoelectric energy harvesting purposes, highlighting their potential and piezoelectric features; further, some perspectives about possible future developments will be proposed.

In this paper the characterization of the mr-EBL 6000.5, which is an epoxy resin based chemically amplified negative tone resist from micro resist technology (Germany, Berlin) for an Intra-Level Mix & Match (ILM&M) approach is presented. The ILM&M approach combined at least two exposure technologies on the same resist layer showing the advantage to resolve patterns of different dimensions with less process steps and short processing time. Since the mr-EBL 6000.5 resist is capable of being sensitive to both electron- and UV-radiation, process parameters for i-line stepper lithography and electron beam lithography (EBL) needs to be investigated to be capable for the ILM&M approach. First, a spin curve and a post exposure bake (PEB) study were applied to find suitable process parameters for both exposure technologies. Furthermore, the minimum feature sizes for both patterning technologies are investigated by using a 500 nm thick resist layer. The impact of small feature sizes near the CD-limit of the used i-line stepper (350 nm) on the resist thickness after the development was investigated in dependence of the PEB. After all parameters were examined, they were combined to be used in the ILM&M.