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Micro, Volume 2, Issue 4 (December 2022) – 11 articles

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20 pages, 3915 KiB  
Review
Resurgence of Electron Quantum Tunneling Sensors
by Aishwaryadev Banerjee and Carlos H. Mastrangelo
Micro 2022, 2(4), 679-698; https://doi.org/10.3390/micro2040046 - 13 Dec 2022
Cited by 1 | Viewed by 3999
Abstract
Quantum tunneling sensors are typically ultra-sensitive devices that have been specifically designed to convert a stimulus into an electronic signal using the wondrous principles of quantum mechanical tunneling. In the early 1990s, William Kaiser developed one of the first micromachined quantum tunneling sensors [...] Read more.
Quantum tunneling sensors are typically ultra-sensitive devices that have been specifically designed to convert a stimulus into an electronic signal using the wondrous principles of quantum mechanical tunneling. In the early 1990s, William Kaiser developed one of the first micromachined quantum tunneling sensors as part of his work with the NASA Jet Propulsion Laboratory. Since then, there have been scattered attempts at utilizing this phenomenon for the development of a variety of physical and chemical sensors. Although these devices demonstrate unique characteristics, such as high sensitivity, the principle of quantum tunneling often acts as a double-edged sword and is responsible for certain drawbacks of this sensor family. In this review, we briefly explain the underlying working principles of quantum tunneling and how they are used to design miniaturized quantum tunneling sensors. We then proceed to describe an overview of the various attempts at developing such sensors. Next, we discuss their current necessity and recent resurgence. Finally, we describe various advantages and shortcomings of these sensors and end this review with an insight into the potential of this technology and prospects. Full article
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9 pages, 3299 KiB  
Communication
Supramolecular Aggregation Processes on Carbon Surfaces Occurring in Bovine Serum Albumin Solutions
by Aleksei Salanov, Alexandra Serkova, Anastasia Zhirnova, Larisa Perminova and Galina Kovalenko
Micro 2022, 2(4), 670-678; https://doi.org/10.3390/micro2040045 - 9 Dec 2022
Viewed by 1165
Abstract
The processes of supramolecular aggregation occurring on carbon surfaces in aqueous solutions of bovine serum albumin (BSA) during drying were studied using modern scanning electron microscopy (SEM). The carbon materials studied were highly oriented pyrolytic graphite (HOPG) and glassy carbon (GC). Based on [...] Read more.
The processes of supramolecular aggregation occurring on carbon surfaces in aqueous solutions of bovine serum albumin (BSA) during drying were studied using modern scanning electron microscopy (SEM). The carbon materials studied were highly oriented pyrolytic graphite (HOPG) and glassy carbon (GC). Based on the analysis of SEM images and EDX-scanning element distribution maps, a possible mechanism for the formation of the observed intricate structures on the surface was proposed. The formation of fuzzy lacy structures resembling shadow replicas was explained by relatively strong hydrophobic–hydrophobic interactions of albumin molecules with carbon surfaces. Full article
(This article belongs to the Section Analysis Methods and Instruments)
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7 pages, 686 KiB  
Article
The Yield of Cherenkov and Scintillation Radiation Generated by the 2.7 MeV Electron Beam in Plate PMMA Samples
by Boris Alekseev, Viktor Tarasenko, Evgeniy Baksht, Alexaner Potylitsyn, Alexander Burachenko, Michail Shevelev, Sergey Uglov and Artem Vukolov
Micro 2022, 2(4), 663-669; https://doi.org/10.3390/micro2040044 - 25 Nov 2022
Cited by 1 | Viewed by 1643
Abstract
In this paper, we have investigated characteristics of ultraviolet and visible radiation generated by the 2.7 MeV electrons. It is shown that the Cherenkov radiation (ChR) intensity predominates over scintillations including wavelength shifting and cathodoluminescence quenching in pure poly(methylmethacrylate) (PMMA) for such electron [...] Read more.
In this paper, we have investigated characteristics of ultraviolet and visible radiation generated by the 2.7 MeV electrons. It is shown that the Cherenkov radiation (ChR) intensity predominates over scintillations including wavelength shifting and cathodoluminescence quenching in pure poly(methylmethacrylate) (PMMA) for such electron energy. To separate ChR and scintillations, we measured emission spectra and orientation dependence of the PMMA samples and compared with GEANT4 model taking into account only ChR mechanism. Full article
(This article belongs to the Section Analysis Methods and Instruments)
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14 pages, 3756 KiB  
Article
Visual Detection of Biomolecules Using Concentration Dependent Induced Aggregation of Plasmonic Gold Nanoparticles
by Monique Farrell and Aswini Pradhan
Micro 2022, 2(4), 649-662; https://doi.org/10.3390/micro2040043 - 21 Nov 2022
Viewed by 1578
Abstract
Significant advancement has occurred in the detection methods of solution-based analytes. High-pressure liquid chromatography, gas chromatography, and other systems used for analyses are quite expensive. Therefore, there is a need for new methods and for the visible detection of analytes. Here, we demonstrate [...] Read more.
Significant advancement has occurred in the detection methods of solution-based analytes. High-pressure liquid chromatography, gas chromatography, and other systems used for analyses are quite expensive. Therefore, there is a need for new methods and for the visible detection of analytes. Here, we demonstrate that 3-aminopropyl triethoxysilane (APTES) could impact the stability, optical, and morphology of gold nanoparticles (AuNps) in a colloidal solution. These impacts can be used to create a sensitive visual detection system. The strong impact of the APTES concentration on the ultraviolet–visible absorption spectra of the solutions is illustrated, which displays systematic and extensive red shifts. The presence of denatured proteins within a therapeutic drug product can induce a series of adverse effects. This report describes a fast, low cost, sensitive, and user-friendly platform where the plasmonic nanoparticles create visual biosensing of denatured proteins. Artificially heat stressed ferritin, glutathione, and insulin coupled to AuNps are exposed to ATES and upon denaturation of the protein or peptide, systematic blue or red shifts are observed in the absorbance spectra of the AuNps/biomolecules, and aminosilane solution. This serves as a proof-of-concept for a fast in-solution detection method for heat-stressed proteins or peptides. Full article
(This article belongs to the Section Microscale Materials Science)
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17 pages, 6035 KiB  
Article
Sonochemical Synthesis of Silica-Supported Iron Oxide Nanostructures and Their Application as Catalysts in Fischer–Tropsch Synthesis
by Lyufei Chen, Emily Costa, Pradheep Kileti, Rina Tannenbaum, Jake Lindberg and Devinder Mahajan
Micro 2022, 2(4), 632-648; https://doi.org/10.3390/micro2040042 - 21 Nov 2022
Cited by 3 | Viewed by 1215
Abstract
The emphasis on climate change requires processes to be more efficient to minimize CO2 emissions, and nanostructured materials as catalysts could play a crucial role due to their high surface area per unit volume. Herein, we report the synthesis of silica microspheres [...] Read more.
The emphasis on climate change requires processes to be more efficient to minimize CO2 emissions, and nanostructured materials as catalysts could play a crucial role due to their high surface area per unit volume. Herein, we report the synthesis of silica microspheres (450–600 nm) using a modified Stober process, on which iron oxide clusters were deposited by sonolysis of iron pentacarbonyl to yield a nanostructured iron material (Si-Fe). A suite of spectroscopic techniques was used to characterize the synthesized materials. The BET surface area of freshly prepared Stober silica was 8.00 m2/g, and the Si-Fe material was 24.0 m2/g. Iron is commercially used as a Fischer–Tropsch (F–T) catalyst due to its low cost. However, catalyst attrition causes catalyst loss and lower product quality. In this study, the synthesized Si-Fe materials were evaluated for F–T synthesis to address these challenges. For comparison, two commercial materials, UCI (silica-supported micron-sized iron oxide) and BASF (unsupported nanosized iron oxide), were also evaluated. All three materials were first activated by pretreatment with either CO or synthesis gas (a mixture of CO and H2) for 24 h, then evaluated for quick screening in batch mode for F–T synthesis in a Parr batch reactor at three temperatures: 493 K, 513 K, and 533 K. The F–T data at 513 K showed that the CO-pretreated Si-Fe catalyst demonstrated lower CO2 (<0.5%), lower CH4 (<0.5%), and higher (>58%) C8–C20 selectivity (mol% C) to hydrocarbons, surpassing both reference catalysts. The temperature dependence data for Si-Fe: 17.4%, 58.3%, and 54.9% at 493 K, 513 K, and 533 K, respectively, showed that the hydrocarbon yield maximized at 513 K. The surface area increased to 27.9 m2/g for the CO-reduced Si-Fe catalyst after the F–T reaction at 513 K. The morphology and structural change of catalysts, before and after the F–T runs, were imaged. Of all the catalysts evaluated, the SEM–EDS data analysis showed the least carbon deposition on the CO-treated Si-Fe catalyst after the F–T reaction at 513 K and minimized CO2, a greenhouse gas. This could pave the way for selecting nanomaterials as F–T catalysts that effectively operate at lower temperatures and produce negligible CO2 by minimizing water-gas-shift (WGS) activity. Full article
(This article belongs to the Section Microscale Materials Science)
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12 pages, 3040 KiB  
Article
Possibility of Biological Observations Using the Speckle Interferometry-Based Super-Resolution Technology
by Yasuhiko Arai
Micro 2022, 2(4), 620-631; https://doi.org/10.3390/micro2040041 - 31 Oct 2022
Viewed by 1244
Abstract
Speckle interferometry techniques based on the phase-detection method have been widely used to observe microstructures beyond the diffraction limit, and the observations of hard solid samples such as microspheres and micro-characters have been previously reported. In this study, the possibility of applying this [...] Read more.
Speckle interferometry techniques based on the phase-detection method have been widely used to observe microstructures beyond the diffraction limit, and the observations of hard solid samples such as microspheres and micro-characters have been previously reported. In this study, the possibility of applying this super-resolution technology to the observation of biological tissues is investigated using plant-cell chromosomes, which are relatively easy to handle and compatible with the diffraction limit. The results reveal that the new super-resolution technique, which is based on speckle interferometry, can be used to observe cellular tissues with complex structures that are subjected to conventional cell-fixation treatments similar to solid samples. However, the shape of the fixed-treated chromosomes is distorted and differs from that of living cells. Furthermore, when observing real living cells using current optics systems, the sample is typically observed vertically. This study indicates that these optics systems must be improved to allow horizontal placements of the samples in the culture medium. Full article
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15 pages, 4130 KiB  
Article
Microstructural Evolution of T91 in High Temperature Conditions and under Combined Effect of Stress and Temperature
by Andrea Tonti, Daniela Lega, Alessandra Antonini, Antonello Alvino, Loriana Ricciardi and Luana Campanile
Micro 2022, 2(4), 605-619; https://doi.org/10.3390/micro2040040 - 27 Oct 2022
Viewed by 1596
Abstract
ASTM A213 T91 steel is widely used in power plants and petrochemical industry for long-term service components. Due to its high resistance to creep, thermomechanical fatigue and corrosion, the use of grade 91 steel allows usual plant service parameters to be raised up [...] Read more.
ASTM A213 T91 steel is widely used in power plants and petrochemical industry for long-term service components. Due to its high resistance to creep, thermomechanical fatigue and corrosion, the use of grade 91 steel allows usual plant service parameters to be raised up to ultra-supercritical conditions (600 °C, 300 bar) so that performances are remarkably increased. The strongest factors that affect performances are the time of exposure, the temperature and the applied stress: such parameters can dramatically decrease the service life of a plant component. The improved mechanical properties of grade 91 are strictly related to its specific microstructure: a tempered martensite matrix with fine precipitates embedded in. Two typologies of secondary phases are present: M23C6 carbides (where M = Cr/Fe/Mo/Mn) and finely dispersed MX-type carbonitrides (where M = V/Nb and X = C/N). This study is focused on the microstructure evolution of grade 91 steel under creep conditions. First, three sets of laboratory-aged specimens heated in oven at 550 °C, 600 °C and 650 °C were examined; the exposure time was up to 50,000 h. Furthermore, the influence of stress on the microstructure in two sets of samples was evaluated: a first batch of specimens cut from an ex-service tube of a petrochemical plant (over 100,000 h of service at 580 °C and 19–25 bar) and a second set of samples coming from another ex-service tube under ultra-supercritical conditions (605 °C, 252 bar) in a power plant. The microstructures were characterized by optical, scanning electron and transmission electron microscopy and the results were compared to the literature. Some interesting trends were evidenced, in terms of secondary phases precipitation and coarsening, as well as martensite recovery. Furthermore, the applied stress seems to influence size and number of Laves phase particles. Full article
(This article belongs to the Special Issue State-of-the-Art Microscale and Nanoscale Researches in Italy)
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16 pages, 3815 KiB  
Article
A Method for 3D Modeling of Chemical Separation in Microfabricated Gas Chromatography Columns: Case Studies in Temperature Gradients and Stationary Phase Topologies
by Shrutika Singh, Yutao Qin and Yogesh B. Gianchandani
Micro 2022, 2(4), 589-604; https://doi.org/10.3390/micro2040039 - 9 Oct 2022
Viewed by 1553
Abstract
Conventional capillary gas chromatography (GC) columns, which have circular symmetry in cross-section and uniformity in length, are well modeled mathematically by the GC rate theory. However, even after adaptation, the theory has limited applicability to many unconventional properties in microfabricated GC columns, such [...] Read more.
Conventional capillary gas chromatography (GC) columns, which have circular symmetry in cross-section and uniformity in length, are well modeled mathematically by the GC rate theory. However, even after adaptation, the theory has limited applicability to many unconventional properties in microfabricated GC columns, such as trapezoidal cross-sections, non-uniform stationary phase, and temperature gradients. This paper reports a 3D finite-element model for the chemical separation process in microfabricated GC columns using COMSOL. The model incorporates gas flow, diffusion, partition, and temperature effects, enabling quantitative assessment of the separation performance of microfabricated GC columns with different stationary phase coating topologies and temperature gradients. To address the tremendous computational burden in such a 3D model, this paper investigates methods of providing proper meshing and dimensional scaling. For validation purposes, the implemented model was first applied to a conventional capillary GC column and showed good matches to both the analytical calculation and experimental results. Next, the model was used to assess microfabricated columns with a trapezoidal cross-section and different stationary phase coating topologies. The results showed that, for the cases under consideration, a single-side-coated column provides only a 33% lower separation resolution compared to a double-side-coated column, and a parabolic stationary phase profile provides only a 12% lower separation resolution compared to a uniform profile. The model also indicated that temperature gradients have a negligible impact on separation performance. Full article
(This article belongs to the Section Analysis Methods and Instruments)
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14 pages, 4579 KiB  
Article
Nanoindentation and Atomic Force Microscopy Derived Mechanical and Microgeometrical Properties of Tooth Root Cementum
by Evgeniy Sadyrin, Vasilina Lapitskaya, Tatyana Kuznetsova, Diana Yogina, Stanislav Maksyukov and Sergei Aizikovich
Micro 2022, 2(4), 575-588; https://doi.org/10.3390/micro2040038 - 9 Oct 2022
Viewed by 2630
Abstract
In the present research, nanoindentation, atomic-force microscopy and optical microscopy were used to study the mechanical and microgeometrical parameters of tooth tissues. A nanoindentation test unit equipped with Berkovich indenter was used to determine the values of the reduced Young’s modulus and indentation [...] Read more.
In the present research, nanoindentation, atomic-force microscopy and optical microscopy were used to study the mechanical and microgeometrical parameters of tooth tissues. A nanoindentation test unit equipped with Berkovich indenter was used to determine the values of the reduced Young’s modulus and indentation hardness and both nanoindentation and atomic force microscopy using a diamond probe on a silicon cantilever were used to study microgeometrical parameters of human tooth root cementum. Three areas of cementum were studied: the cervical region near the dentine–enamel junction, the second third of the tooth root, and the apex of the tooth root. The interpretation of the results was carried out using the Oliver–Pharr method. It was established, that the mechanical properties of cementum increase from the cervical region to the central part of the root, then decrease again towards the apex of the tooth root. On the contrary, the microgeometrical characteristics of cementum practically do not demonstrate any change in the same direction. A decrease in the roughness parameters in the direction from cellular cementum to dentine was observed. Additionally, a decrease in the reduced Young’s modulus and indentation hardness of dentine in the cervical area compared to dentine in the crown part of the tooth was found using nanoindentation. The investigation of the dentine–cementum junction with high resolution revealed the interspaced collagen fiber bridges and epithelial rests of Malassez, whose sizes were studied. The parameters of the topographic features of the cementum in the vicinity of the lacunae of cementocytes were also established. Full article
(This article belongs to the Section Microscale Biology and Medicines)
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11 pages, 3281 KiB  
Article
Identification of MEMS Geometric Uncertainties through Homogenization
by David Faraci, Valentina Zega, Alessandro Nastro and Claudia Comi
Micro 2022, 2(4), 564-574; https://doi.org/10.3390/micro2040037 - 23 Sep 2022
Cited by 1 | Viewed by 1761
Abstract
Fabrication imperfections strongly influence the functioning of Micro-Electro-Mechanical Systems (MEMS) if not taken into account during the design process. They must be indeed identified or precisely predicted to guarantee a proper compensation during the calibration phase or directly in operation. In this work, [...] Read more.
Fabrication imperfections strongly influence the functioning of Micro-Electro-Mechanical Systems (MEMS) if not taken into account during the design process. They must be indeed identified or precisely predicted to guarantee a proper compensation during the calibration phase or directly in operation. In this work, we propose an efficient approach for the identification of geometric uncertainties of MEMS, exploiting the asymptotic homogenization technique. In particular, the proposed strategy is experimentally validated on a MEMS filter, a device constituted by a complex periodic geometry, which would require high computational costs if simulated through full-order models. The complex periodic structure is replaced by an equivalent homogeneous medium, allowing a fast optimization procedure to identify imperfections by comparing a simplified analytical model with the experimental data available for the MEMS filter. The actual over-etch, obtained after the release phase, and the electrode offset of a fabricated MEMS filter are effectively identified through the proposed strategy. Full article
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15 pages, 6284 KiB  
Article
Dielectric Behaviour and Electrical Conductivity of α-BiNbO4 and β-BiNbO4 Ceramics
by S. Devesa, M. P. Graça and L. C. Costa
Micro 2022, 2(4), 549-563; https://doi.org/10.3390/micro2040036 - 21 Sep 2022
Cited by 3 | Viewed by 1660
Abstract
In this work, orthorhombic (α-BiNbO4) and triclinic bismuth niobate (β-BiNbO4) ceramics were prepared by a wet chemical route. The structure of the obtained powders was characterised by X-ray diffraction and the morphology by scanning electron microscopy. The dielectric measurements [...] Read more.
In this work, orthorhombic (α-BiNbO4) and triclinic bismuth niobate (β-BiNbO4) ceramics were prepared by a wet chemical route. The structure of the obtained powders was characterised by X-ray diffraction and the morphology by scanning electron microscopy. The dielectric measurements were performed in the radiofrequency region, at different temperatures, using the impedance spectroscopy technique. The α-BiNbO4 sample presented a temperature-dependent relaxation process, with the corresponding activation energy being calculated through the Arrhenius equation. The AC conductivity dependence on the frequency was in agreement with Jonscher’s universal power. The conduction mechanism in the α-BiNbO4 compound is governed by two processes, which can be ascribed to a hopping transport mechanism. The correlated barrier hopping model until 280 K and the non-overlapping small polaron tunnelling model above 280 K are the most suitable models to describe the conductivity of this sample. In the β-BiNbO4 compound, the motion of mobile charge carriers involves localised hopping between neighbouring sites. Full article
(This article belongs to the Section Microscale Materials Science)
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