Currently, the stability of field-effect devices based on emerging technologies is one of the most demanding research issues in terms of performance. Since solution-processed electronic devices are attracting much attention to enable low-cost flexible electronics, the reported studies of stability, seems to be conceived with arbitrary conditions. In this work, the effects of the frequency dependence of transparent dielectric based on Spin-on Glass (SOG) under electrical stress is presented. The SOG thin films were cured at 200°C in air ambient. The capacitance-voltage and capacitance-frequency characteristics were measured in Metal-Oxide-Semiconductor (MOS) capacitors using the SOG thin film. In addition, electrical stress is applied to the MOS capacitors at different voltage values and during a long period of time. The results show, depending of the bias stress applied, a reversible interface charge contribution and an irreversible charge induced by interface states probably generated by the degradation of the film.

Since its invention, atomic force microscopy (AFM) has enhanced our understanding of physical and biological systems at sub-micrometer scales. As the performance of AFM depends greatly on the properties of the cantilevers, many works have been done to improving cantilevers by means of modifying their geometries via lithography [1] and ion-beam milling [2,3] that primarily involved opening areas on the cantilever’s face, resulting in high resonant frequency, low spring constant, and low hydrodynamic damping. Similar improvements were achieved using a hollow beam cantilever with nanoscale wall thickness [4]. In fact, the combination of these two approaches (in-plane opening and hollow beam) can result in unique metamaterial structures with tunable properties [5], but it has not been explored for AFM application.

In this work, we explore the hollow AFM cantilevers with in-plane modifications. We accomplished this by (1) taking a commercial solid silicon cantilever, (2) making a different number of holes on the face using pulsed laser micromachining, and (3) coating them with alumina using atomic layer deposition and etching the internal silicon that results in a hollow probe with holes. We present the effects of these modifications on the cantilever’s resonant frequency, quality factor, and spring constant in air. This work provides an insight into strategies for tuning cantilever’s properties for both flexural and torsional modes.

References:

[1] Nilsen, M.; Port, F.; Roos, M.; Gottschalk, K.-E.; Strehle, S. Journal of Micromechanics and Microengineering 2019, 29, (2), 025014.

[2] Bull, M. S.; Sullan, R. M. A.; Li, H.; Perkins, T. T. ACS Nano 2014, 8, (5), 4984-4995.

[3] Hodges, A. R.; Bussmann, K. M.; Hoh, J. H. Review of Scientific Instruments 2001, 72, (10), 3880-3883.

[4] Cha, W.; Nicaise, S.; Lilley, D.; Lin, C.; Bargatin, I. Solid-State Sensors, Actuators and Microsystems Workshop, Hilton Head Island, South Carolina, 2018; Transducer Research Foundation: Hilton Head Island, South Carolina, pp 232-233.

[5] Lin, C.; Nicaise, S. M.; Lilley, D. E.; Cortes, J.; Jiao, P.; Singh, J.; Azadi, M.; Lopez, G. G.; Metzler, M.; Purohit, P. K.; Bargatin, I. Nature Communications 2018, 9, (1), 4442.

[5] C. Lin, S. M. Nicaise, D. E. Lilley, J. Cortes, P. Jiao, J. Singh, et al., "Nanocardboard as a nanoscale analog of hollow sandwich plates," Nature Communications, vol. 9, p. 4442, 2018/10/25 2018.

Wearable electronics are changing healthcare and increasing possibilities for human-machine interfaces. Soft electronics, directly mounted on the skin, can monitor long-term heart rate trends or direct smart prosthetics' motion. However, these capabilities are only as good as the signal quality obtained. These wearable devices are worn in the real world, often suffering from motion artifacts not previously found when measured in a stationary setting such as a clinic or laboratory. Motion artifacts can mimic many biosignals by having a similar amplitude and frequency range, making them hard to filter out. A significant source of motion artifacts is from relative motion between the sensor and the signal source. Given human tissue's elastic nature, most body-mounted sensors undergo more relative motion than on a comparable rigid machine.

Here, this work introduces a comprehensive study of materials, methods, and optimized designs that can significantly reduce motion artifacts via strain isolation, increased adhesion, and enhanced breathability for long-term recordings. Skin strain is another source of motion artifacts that can disturb electrodes' contact impedance and temporarily change the biopotential within the skin. We present a prototype electrocardiogram (ECG) device that uses a strain isolating layer to reduce skin strain at the electrode. This strategic integration of soft and hard materials reduces motion artifacts by stabilizing the electrode, while allowing freedom of movement elsewhere to maintain gentle contact with the skin. These solutions are demonstrated for long-term ECG collection but have application for any skin-mounted wearable device.

Nowadays, lipases are one of the most widely used enzymes, especially in catalysis, mostly due to their high activity in mild conditions and wide specificity. Therefore, the highest possible catalytic activity, which can be achieved through purification, is becoming more and more important. Since most of the purification techniques are time consuming, aqueous two-phase protein extraction is often investigated as a promising alternative. Additionally, this kind of extraction can be carried out in microextractors which provides not only a continuous processing of raw materials, but also significantly higher efficiencies due to high surface-to-volume ratio of microchannels. Extraction with deep eutectic solvents (DESs) fulfils all green chemistry principles, because DESs are biodegradable, non-toxic, and recyclable. In this research, the aqueous two-phase system based on natural DES for continuous protein extraction in a microextractor was investigated. The impact of salt concentration on extraction efficiency was investigated in batch experiments with six different previously characterized DESs. After determination of optimal two-phase system features, the process was transferred in a microextractor. In addition, the selected DES was tested for recyclability while the developed extraction method was verified using raw lipase produced by Thermomyces lanuginosus solid-state cultivation on hull-less pumpkin oil pomace. The highest protein extraction efficiency achieved in a batch reactor was 94.70 % for 30 min, while in a microextractor extraction efficiency obtained was 98.50 % for 30 s. Obviously the extraction process was significantly intensified by continuous microextraction. Additionally, DES used in a microextraction experiments was efficiently reused in several extraction cycles.

Since plastics industrial production, features such as cost, convenience, safety, and the low cost came up as significant benefits. Further to the benefits added the aesthetic qualities, the mechanical strength and the capability to mix with other materials such as fibres. All these contributed to the rapid expansion of plastics (polystyrene and nylon) in multiple applications and various purposes, such as biomedical materials, packaging, transport, industry, and agriculture. On the other hand, global warming is now one of the most concerning issues for all cultures worldwide [1]. It is considered that replacing some of the conventional materials in various applications such as wound dressings with biodegradable starch-based films is a step forward in addressing the environmental issues [2]. Due to mechanical debriding of tissues, traditional dressings like gauges are counterproductive and end up causing painful wound trauma during dressing procedures. The development of transparent wound dressing films enables a moist healing environment with enhanced bacterial impermeability [3].

The performance of polyvinyl alcohol/starch/citric acid (PVA/St/CA) based composite film for wound dressing applications is addressed in this work. Literature recorded fixed composition of PVA (2.5 w/w%), starch (2.5 w/w%), and glycerol (2 w/w%) during 70-80^oC casting temperature were implemented. Different citric acid concentrations (0.5 to 2g) were investigated during the development of composite film solution casting [4]. Prepared samples have been characterized by swelling index [5], solubility dependent biodegradability [6], tensile strength (TS) [7]. The film also exhibits enhanced combinations of the water vapour transmission rate and antibacterial efficiency against the bacterial flora (various bacteria existent in the air). As an extra benefit, such materials are easily degraded in water for up to seven days with a minute footprint. A potential candidate for wound dressing applications has been inferred from the biodegradable PVA/St/CA films with all these useful features.

References:

1. Jeong, H., et al., Novel Eco‐Friendly Starch Paper for Use in Flexible, Transparent, and Disposable Organic Electronics. Advanced Functional Materials, 2018. 28(3): p. 1704433.
2. Kamoun, E.A., E.-R.S. Kenawy, and X. Chen, A review on polymeric hydrogel membranes for wound dressing applications: PVA-based hydrogel dressings. Journal of advanced research, 2017. 8(3): p. 217-233.
3. Das, A., et al., Optimality of poly-vinyl alcohol/starch/glycerol/citric acid in wound dressing applicable composite films. International Journal of Biological Macromolecules, 2020.
4. Yoon, S.D., S.H. Chough, and H.R. Park, Properties of starch‐based blend films using citric acid as additive. II. Journal of Applied Polymer Science, 2006. 100(3): p. 2554-2560.
5. Das, A., R. Uppaluri, and C. Das, Compositional synergy of poly-vinyl alcohol, starch, glycerol and citric acid concentrations during wound dressing films fabrication. International Journal of Biological Macromolecules, 2020. 146: p. 70-79.
6. Boonsuk, P., et al., Modified cassava starch/poly (vinyl alcohol) blend films plasticized by glycerol: Structure and properties. Journal of Applied Polymer Science, 2020. 137(26): p. 48848.
7. Hassan, A., et al., Development of anti-bacterial PVA/starch based hydrogel membrane for wound dressing. Journal of Polymers and the Environment, 2018. 26(1): p. 235-243.

Antireflective (AR) coatings have been around for more than a century, with the simplest form dating back to Lord Rayleigh’s 1886 tarnished glass. Different approaches to obtaining AR coatings exploit index-matching, interference or absorbing phenomena. In 2002, a novel superblack surface was developed by Brown et al. at the National Physical Laboratory in UK, and soon gained significant interest among both academia and industry.¹ Since then, scientists have been competing in a race to produce the blackest material. Although extremely valuable, existing solutions usually require complicated fabrication procedures and post-application treatments.

Structural colors are ubiquitous in nature, so an interesting approach for developing AR coatings is biomimicry. Moth-eye structures are well-known for their AR properties, and they have been successfully replicated using micro- and nanofabrication methods and employed as AR coatings.^2,3 Interestingly, recent studies from Harvard highlight two types of microstructures that lead to superblack coloring in nature, i.e. barbule microstructures on birds of paradise,⁴ and cuticular bumps on peacock spiders.⁵ These publications provide detailed information on the shape of such natural superblack microstructures and the mechanisms behind the observed superblack effect. Although replication of such structures should prove extremely valuable, it has not yet been demonstrated.

In this paper, we present the fabrication and characterization of AR microarrays inspired by the peacock spiders’ superblack structures encountered in nature. Fabrication is done by super-resolution 3D printing using two-photon polymerization of an acrylic resin. The optical properties of microstructure arrays with different shape design parameters are then characterized using a homemade reflectance / transmittance setup which allows wavelength-dependent investigations in the ultraviolet, visible and near-infrared range. The influence of the shape design parameters on the optical properties of the microarrays is then discussed through experimental measurements, as well as simulations.

1. R.J.C. Brown, P.J. Brewer, M.J.T. Milton, The physical and chemical properties of electroless nickel-phosphorus alloys and low reflectance nickel-phosphorus black surfaces, J. Mater. Chem. 12 (2002) 2749–2754.
2. M. R. Lotz, C.R. Petersen, C. Markos, O. Bang, M.H. Jakobsen, R. Taboryski, Direct nanoimprinting of moth-eye structures in chalcogenide glass for broadband antireflection in the mid-infrared, Optica. 5 (2018) 557
3. M. Lotz, J. Needham, M.H. Jakobsen, R. Taboryski, Nanoimprinting reflow modified moth-eye structures in chalcogenide glass for enhanced broadband antireflection in the mid-infrared, Opt. Lett. 44 (2019) 4383.
4. D. E. McCoy, T. Feo, T.A. Harvey, R.O. Prum, Structural absorption by barbule microstructures of super black bird of paradise feathers, Nat. Commun. 9 (2018) 1–8.
5. D. E. McCoy, V.E. McCoy, N.K. Mandsberg, A. V. Shneidman, J. Aizenberg, R.O. Prum, D. Haig, Structurally assisted super black in colourful peacock spiders, Proc. R. Soc. B Biol. Sci. 286 (2019) 20190589.

Artificial Neural Network (ANN) and Data analysis are powerful tools used for supporting decision-making. They have been employed in diverse fields and one of them is nanotechnology; for example, in predicting particles size. Liposomes are nanoparticles used in different biomedical applications that can be produced in Dean Forces-based Periodic Disturbance Micromixers (PDM). In this work, ANN and data analysis techniques are used to build a liposome size prediction model by using the most relevant variables in a PDM, i.e. Flow Rate Radio (FRR) and Total Flow Rate (TFR). The ANN was designed in MATLAB and fed data from 60 experiments, which were 70% training, 15% validation and 15% testing. For data analysis, regression analysis was used. The model was evaluated, it showed 98.147% of regression number for training and 97.247% in total data comparing with 78.89% regression number obtained by data analysis. These results demonstrate that liposomes size can be better predicted by ANN with just FRR and TFR as inputs, compared with data analysis techniques when the temperature, solvents, and concentrations are kept constants.

Micromachining thechnology has been widely applied in the microelectronic equipment, aerospace, precision instrument and medical equipment. With the increasingly fierce competition in the global market, manufacturing companies pay more and more attention to technological innovation and the knowledge that promotes the realization of technological innovation. At present, most of the machining process innovation activities are highly dependent on the personal knowledge accumulation in the previous projects for a long time. The randomness and technical difficulty of existing innovation methods (e.g., brainstorming and trial-and-error) are high, and the success rate of innovation is low. Although traditional TRIZ (Theory of Inventive Problem Solving) theory provides a systematic theory and method tool for designers to discover and solve problems creatively in product innovation design, it can not be directly used to guide process innovation design due to its lack of specific parameters and corresponding principles for process innovation. In recent years, the Computer-Aided Process Innovation (CAPI) provides designers with an effective way to obtain process innovation inspiration and improve innovation efficiency. This paper proposes a structured procedure for solving machining process innovation problems, including formal description of process problems, ideas acquisition of problem solving, iterative solving of process problems, detailed design and verification of innovative solutions. Furtherly, the CAPI method and structured innovation procedure are used to systematically and innovatively solve the process problems in the micro-turbine machining.

The realization of electronic devices on flexible substrates (flexible electronics) has an important role in large area technological innovation. Semiconductor oxides are an option to implement low processing temperatures on these materials. In this work, flexible metal-insulator-semiconductor (MIS) capacitors were fabricated using zinc oxide (ZnO) and indium-doped zinc oxide (IZO) as semiconductor materials, spin-on glass (SOG) as insulator and indium doped tin oxide (ITO) as contact, deposited by solution techniques at 200 °C on PET substrates. The films were characterized by FTIR spectroscopy and four-points probe. The resistivity of the IZO films decreases with increasing doping. However, the resistivity of the film increases with the 6 wt.% doping concentration. Through FT-IR spectroscopy an irregular behavior was observed when the ZnO films are doped with In 6 wt. %. It was found that at this concentration the film has a lower amount of C-O, COO- and O-H bonds with respect to the rest of the doped and undoped films. These groups can behave as charge traps, limiting the charge transport on the semiconductor thin films. Also, an unusual displacement of the Zn-O and COO- bonds is observed, probably due to an inductive effect. This effect could imply the existence of a permanent dipole which increases the electron density due to the occupied antibonding states. The reduction of organic residuals is corroborated with the hysteresis behavior through the fabrication and characterization of MIS capacitors.

The metal-oxide semiconductor technology has attracted much attention because it is currently used in novel applications such as flexible displays, biosensing, memories or RF tags. However, the main bottleneck for commercialization of these devices is the understanding of the Density of States (DOS) within the gap of the metal-oxide semiconductors, which is the key for the development of analytical models to enable the circuits design. Moreover, determining the DOS in semiconductors is a complex work because this requires to know the contributions of the main interfaces in electronic devices such as capacitors and field-effect transistors. In this study, the modeling of the DOS through the fitting of the electrical characteristics in field-effect devices is presented. The transfer and output characteristics are fitted in Zinc Oxide thin-film transistors (ZnO TFTs), along with the capacitance - voltage curves in Metal-Insulator-Semiconductor (MIS) capacitors using ZnO as active layer. The ZnO semiconductor devices were fabricated by Ultrasonic Spray Pyrolysis at high frequency on polyethylene terephthalate plastic substrates. We propose an accurate estimation of the DOS through the calculation of equivalent DOS in similar field-effect devices of same dielectric-semiconductor interface, since this interface plays an important role to induce the channel in TFTs and to form the accumulation and depletion regions in MIS capacitors. The results show the agreement between the experimental data and the calculated electrical characteristics of the ZnO field-effect devices. Different aspects were considered and discussed to model the interfaces such as additional contributions from fixed oxide charge, interface charge density and contact resistance.