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Micro, Volume 2, Issue 1 (March 2022) – 14 articles

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Article
Clove Essential Oil–Hydroxypropyl-β-Cyclodextrin Inclusion Complexes: Preparation, Characterization and Incorporation in Biodegradable Chitosan Films
Micro 2022, 2(1), 212-224; https://0-doi-org.brum.beds.ac.uk/10.3390/micro2010014 - 16 Mar 2022
Viewed by 546
Abstract
The encapsulation of clove essential oil (CEO) in hydroxypropyl-β-cyclodextrin (HP-β-CD) and the subsequent incorporation of the inclusion complex in an elastic chitosan film in order to achieve a controlled release profile of the volatile CEO are herein presented. Freshly distilled CEO was found [...] Read more.
The encapsulation of clove essential oil (CEO) in hydroxypropyl-β-cyclodextrin (HP-β-CD) and the subsequent incorporation of the inclusion complex in an elastic chitosan film in order to achieve a controlled release profile of the volatile CEO are herein presented. Freshly distilled CEO was found to contain eugenol in concentrations higher than 70%. The kneading method was implemented for the preparation of a CEO-HP-β-CD inclusion complex, resulting in a 50% inclusion efficiency of the essential oil in particles sized 214.40 nm with ζ-potential −27.5 mV. Free CEO and CEO-HP-β-CD inclusion complex were tested for their ability to scavenge the 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical, and it was found that the CEO-HP-β-CD complex presented enhanced antioxidant activity (88%) compared to the free CEO (71%). Choline chloride-containing chitosan (CS) films were prepared, incorporating either the pure CEO or the CEO-HP-β-CD inclusion complex, and their mechanical properties were determined. The study of the release profile in different pH values demonstrated the capacity of the CS-HP-β-CD system to provide sustained release of CEO, noting its potential use in food processing as smart packaging. Full article
(This article belongs to the Section Microscale Materials Science)
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Article
Biomimetic Full-Thickness Skin-on-a-Chip Based on a Fibroblast-Derived Matrix
Micro 2022, 2(1), 191-211; https://0-doi-org.brum.beds.ac.uk/10.3390/micro2010013 - 12 Mar 2022
Cited by 1 | Viewed by 806
Abstract
Current commercially available in vitro skin models do not fully reproduce the structure and function of the native human skin, mainly due to their use of animal-derived collagen and their lack of a dynamic flow system. In this study, a full-thickness skin-on-a-chip (SoC) [...] Read more.
Current commercially available in vitro skin models do not fully reproduce the structure and function of the native human skin, mainly due to their use of animal-derived collagen and their lack of a dynamic flow system. In this study, a full-thickness skin-on-a-chip (SoC) system that reproduces key aspects of the in vivo cellular microenvironment is presented. This approach combines the production of a fibroblast-derived matrix (FDM) with the use of an inert porous scaffold for the long-term, stable cultivation of a human skin model. The culture of a dermal compartment under fluid flow results in the increased synthesis and deposition of major FDM proteins, collagen I, and fibronectin, compared to tissues cultured under static conditions. The developed SoC includes a fully differentiated epidermal compartment with increased thickness and barrier function compared to the controls. Contrary to other SoC platforms that include a collagen-based matrix, the described model presents superior stability and physiological relevance. Finally, the skin barrier function was quantitatively evaluated via in situ transepithelial electrical resistance (TEER) measurements and in situ permeation tests. The SoC model presents a significantly higher TEER and lower permeability to FITC-dextran. In the future, this innovative low-cost platform could provide a new in vitro tissue system compatible with long-term studies to study skin diseases and evaluate the safety and efficacy of novel drugs and technologies. Full article
(This article belongs to the Section Microscale Biology and Medicines)
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Communication
Stable Cu2P3I2 and Ag2P3I2 Single-Wire and Thin Film Devices for Humidity Sensing
Micro 2022, 2(1), 183-190; https://0-doi-org.brum.beds.ac.uk/10.3390/micro2010012 - 03 Mar 2022
Viewed by 888
Abstract
Cu2P3I2 wires were synthesized and converted to Ag2P3I2 via post-synthetic modification. Single-wire and thin film devices were constructed from each material and evaluated as rapidly reversible humidity sensing semiconductors. All devices exhibited a [...] Read more.
Cu2P3I2 wires were synthesized and converted to Ag2P3I2 via post-synthetic modification. Single-wire and thin film devices were constructed from each material and evaluated as rapidly reversible humidity sensing semiconductors. All devices exhibited a dramatic increase in current when exposed to a ~30.85% RH (~9745.3 ppm by moisture volume) atmosphere compared to that of dry N2. Cu2P3I2 devices exhibited greater sensitivity compared to their respective Ag2P3I2 analogs with the highest being the thin film at 2.43 × 10−8 A% RH. While all devices exhibited rapid (<5 s) reversibility, the thin film devices exhibited greater sensitivity compared to their single-wire forms. Full article
(This article belongs to the Section Microscale Materials Science)
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Article
Effect of Polyolefin Elastomers’ Characteristics and Natural Magnesium Hydroxide Content on the Properties of Halogen-Free Flame-Retardant Polyolefin Composites
Micro 2022, 2(1), 164-182; https://0-doi-org.brum.beds.ac.uk/10.3390/micro2010011 - 02 Mar 2022
Viewed by 542
Abstract
This study examines the preparation of several composites that are based on natural magnesium hydroxide (n-MDH) and various poly(ethylene-co-octene) polyolefin elastomers (POEs). Design of experiment (DoE) principles have been applied in order to optimize the mechanical, rheological, and flame-retardant properties of the final [...] Read more.
This study examines the preparation of several composites that are based on natural magnesium hydroxide (n-MDH) and various poly(ethylene-co-octene) polyolefin elastomers (POEs). Design of experiment (DoE) principles have been applied in order to optimize the mechanical, rheological, and flame-retardant properties of the final composites. DoE allows one to evaluate the influence of each variable on an experiment’s final properties. By increasing the density and crystallinity of the POE, a higher elastic modulus was obtained, which resulted in greater tensile strength and lower elongation at break. Improved flame retardant properties (as measured by the limiting oxygen index (LOI) and vertical burning tests) were obtained by increasing the amount of filler within the composite up to 65% and using a polymer with high crystallinity. More specifically, the best balance between mechanical, rheological, and flame retardant properties was provided by DoE using 63.75% n-MDH filler. The agreement between the predicted performance and the final properties of the composites has enabled the innovative use of DoE to provide reliable predictions about the final mechanical and flame retardant properties of the compounds that are used for low voltage electrical cable applications. Full article
(This article belongs to the Section Microscale Materials Science)
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Article
A Biomimetic Strategy for the Fabrication of Micro- and Nanodiamond Composite Films
Micro 2022, 2(1), 154-163; https://0-doi-org.brum.beds.ac.uk/10.3390/micro2010010 - 24 Feb 2022
Viewed by 484
Abstract
This investigation is motivated by increasing interest in diamond and composite films for applications in biomedical and electronic devices. A biomimetic strategy is based on the use of commercial bile acids, such as ursodeoxycholic acid (UDCA) and hyodeoxycholic acid (HDCA). Composite films are [...] Read more.
This investigation is motivated by increasing interest in diamond and composite films for applications in biomedical and electronic devices. A biomimetic strategy is based on the use of commercial bile acids, such as ursodeoxycholic acid (UDCA) and hyodeoxycholic acid (HDCA). Composite films are developed using UDCA and HDCA as solubilizing agents for poly(ethyl methacrylate) (PEMA) in isopropanol and as dispersing agents for micro- and nanodiamonds. In this approach, the use of traditional toxic solvents for PEMA dissolution is avoided. The ability to obtain high concentrations of high molecular mass PEMA and disperse diamond particles in such solutions is a key factor for the development of a dip-coating method. The PEMA dissolution and diamond dispersion mechanisms are discussed. The composition and microstructure of the films can be varied by variation of the diamond particle size and concentration in the suspensions. The films can be obtained as singular layers of different compositions, multilayers of similar composition, or alternating layers of different compositions. The films combine corrosion protection property and biocompatibility of PEMA with advanced functional properties of diamonds. Full article
(This article belongs to the Section Microscale Materials Science)
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Article
Biomass Waste Carbonization in Piranha Solution: A Route to Hypergolic Carbons?
Micro 2022, 2(1), 137-153; https://0-doi-org.brum.beds.ac.uk/10.3390/micro2010009 - 28 Jan 2022
Viewed by 878
Abstract
In the present work we report for the first time the carbonization of biomass waste, such as stale bread and spent coffee, in piranha solution (H2SO4-H2O2) at ambient conditions. Carbonization is fast and exothermic, resulting [...] Read more.
In the present work we report for the first time the carbonization of biomass waste, such as stale bread and spent coffee, in piranha solution (H2SO4-H2O2) at ambient conditions. Carbonization is fast and exothermic, resulting in the formation of carbon nanosheets at decent yields of 25–35%, depending on the starting material. The structure and morphology of the nanosheets were verified by X-ray diffraction, Raman, X-ray photoelectron and microscopy techniques. Interestingly, the obtained carbon spontaneously ignites upon contact with fuming nitric acid HNO3 at ambient conditions, thus offering a rare example of hypergolicity involving carbon as the solid fuel (i.e., hypergolic carbon). Based on the relatively large interlayer spacing of the as-produced carbons, a simple structural model is proposed for the observed hypergolicity, wherein HNO3 molecules fit in the gallery space of carbon, thus exposing its basal plane and defect sites to a spontaneous reaction with the strong oxidizing agent. This finding may pave the way towards new type hypergolic propellants based on carbon, the latter exclusively obtained by the carbonization of biomass waste in piranha solution. Full article
(This article belongs to the Section Microscale Materials Science)
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Article
Micro-Optical Waveguides Realization by Low-Cost Technologies
Micro 2022, 2(1), 123-136; https://0-doi-org.brum.beds.ac.uk/10.3390/micro2010008 - 27 Jan 2022
Viewed by 725
Abstract
Microscale optofluidic devices are a category of microscale devices combining fluidic and optical features. These devices typically enable in-situ fluid flow measurement for pharmaceutical, environmental or biomedical applications. In micro-optofluidic devices, in order to deliver, as close as possible, the input light to [...] Read more.
Microscale optofluidic devices are a category of microscale devices combining fluidic and optical features. These devices typically enable in-situ fluid flow measurement for pharmaceutical, environmental or biomedical applications. In micro-optofluidic devices, in order to deliver, as close as possible, the input light to the sample or a specific chip section and, collect the output signal, it is necessary to miniaturize optical components. In this paper, two low-cost technologies, 3D Printing PDMS-based and laser cutting PMMA-based (PDMS stands for Poly-dimethyl-siloxane and PMMA for Poly-methyl-methacrylate), were investigated as novel methods to realize micro-optical waveguides (μWGs) comparing their performances. An ad-hoc master-slave protocol developed to realize PDMS components by 3D Printing has been fully optimized. The manufacturing technologies proposed require simple and low-cost equipment and no strictly controlled environment. Similar results are obtained for both the micro-optical waveguides realized. Their losses, disregarding the losses caused by the fibers’ alignment and the miss-match of the geometry with the waveguide, are of the order of 20%, almost equivalent for both approaches (PDMS-μWG and PMMA-μWG). The losses are of the order of 10% when the PDMS-μWG is shielded by a copper layer, with a significant improvement of the signal acquired. The results obtained show the possibility of using the two low-cost technologies presented for the realization of micro-optical waveguides suitable to be integrated in micro-optofluidic devices and the potential of creating micro-optical paths inside micro-embedded systems. Full article
(This article belongs to the Section Microscale Engineering)
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Article
Investigations of Deformation Behavior and Microstructure of Al Tailored Ti–Mo High Temperature Shape Memory Alloys during Isothermal Holding at 393 K
Micro 2022, 2(1), 113-122; https://0-doi-org.brum.beds.ac.uk/10.3390/micro2010007 - 25 Jan 2022
Viewed by 895
Abstract
To utilize β-Ti based high temperature (HT) shape memory alloys (SMAs), a high Al concentration of 14 mol% was designed for sufficient suppressing the undesired ω-phase. HTSMA exhibits shape memory effect (SME) above 373 K, and thus the operating temperature is over 373 [...] Read more.
To utilize β-Ti based high temperature (HT) shape memory alloys (SMAs), a high Al concentration of 14 mol% was designed for sufficient suppressing the undesired ω-phase. HTSMA exhibits shape memory effect (SME) above 373 K, and thus the operating temperature is over 373 K. However, the SME and the mechanical properties of most β-Ti SMAs deteriorate after holding at elevated temperatures due to the ω-embrittlement. The Ti-4.5Mo-14Al alloy (mol%) and the Ti-6Mo-7Al alloy as a comparison, both of which possess the identical reverse martensitic transformation start temperature of 407 K, were isothermally held at 393 K for up to 360 ks, and deformation behaviors and microstructures were investigated. It was found that after the isothermal holding, the deformation behavior of the Ti-6Mo-7Al alloy altered significantly; on the other hand, that of the Ti-4.5Mo-14Al alloy remained almost intact. Transmission electron microscopy observations revealed that the isothermal ω-phase (ωiso) was successfully suppressed in the Ti-4.5Mo-14Al alloy, while the ωiso phase grew in Ti-6Mo-7Al alloy. Moreover, the isothermal α″-phase coexisted in the Ti-4.5Mo-14Al alloy. It is concluded that a high Al concentration is a crucial prerequisite in the practical β-Ti HTSMAs. The presented design could be a useful guideline for developing Ti SMAs with comparable Mo- and Al-equivalents. Full article
(This article belongs to the Section Microscale Materials Science)
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Article
Effect of Viscosity on High-Throughput Deterministic Lateral Displacement (DLD)
Micro 2022, 2(1), 100-112; https://0-doi-org.brum.beds.ac.uk/10.3390/micro2010006 - 24 Jan 2022
Cited by 1 | Viewed by 711
Abstract
Biosample analysis often requires the purification, separation, or fractionation of a biofluid prior to transport to the biosensor. Deterministic lateral displacement (DLD) is a size-based microfluidic separation technique that shows promise for biosample preparation. Recently, high-throughput DLD separation has been demonstrated with airfoil-shaped [...] Read more.
Biosample analysis often requires the purification, separation, or fractionation of a biofluid prior to transport to the biosensor. Deterministic lateral displacement (DLD) is a size-based microfluidic separation technique that shows promise for biosample preparation. Recently, high-throughput DLD separation has been demonstrated with airfoil-shaped pillars at higher flow rates, but this also changes separation dynamics as the Reynolds number (Re) increases. In this work, the particle trajectories in the airfoil DLD with two different angle-of-attacks (AoAs) were studied at a range of Re with alterations of fluid viscosity to mimic biological fluids. Previous studies have found that the critical diameter (Dc) decreases as Re climes. We demonstrated that variations of the fluid viscosity do not alter the separation dynamics if the Re is kept constant. As the associated Re of the flow increases, the Dc decreases regardless of viscosity. The negative AoA with an airfoil DLD pillar design provided the stronger Dc shift to negate pressure increases. Full article
(This article belongs to the Section Microscale Engineering)
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Article
Periodic Relief Fabrication and Reversible Phase Transitions in Amorphous Ge2Sb2Te5 Thin Films upon Multi-Pulse Femtosecond Irradiation
Micro 2022, 2(1), 88-99; https://0-doi-org.brum.beds.ac.uk/10.3390/micro2010005 - 20 Jan 2022
Cited by 2 | Viewed by 859
Abstract
Ge2Sb2Te5 based devices attract the attention of researchers due to wide opportunities in designing phase change memory. Herein, we studied a possibility to fabricate periodic micro- and nanorelief at surfaces of Ge2Sb2Te5 thin [...] Read more.
Ge2Sb2Te5 based devices attract the attention of researchers due to wide opportunities in designing phase change memory. Herein, we studied a possibility to fabricate periodic micro- and nanorelief at surfaces of Ge2Sb2Te5 thin films on silicon oxide/silicon substrates under multi-pulse femtosecond laser irradiation with the wavelength of 1250 nm. One-dimensional lattices with periods of 1250 ± 90 and 130 ± 30 nm were obtained depending on the number of acted laser pulses. Emergence of these structures can be explained by plasmon-polariton generation and laser-induced hydrodynamic instabilities, respectively. Additionally, formation of the lattices whose spatial period is close to the impacted laser wavelength can be modelled by considering the free carrier contribution under intensive photoexcitation. Raman spectroscopy revealed both crystallization and re-amorphization of the irradiated films. The obtained results show a possibility to fabricate rewritable all-dielectric data-storage devices based on Ge2Sb2Te5 with the periodic relief. Full article
(This article belongs to the Section Microscale Materials Science)
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Article
Active Textile Glove for Cooling and Personal Protection
Micro 2022, 2(1), 68-87; https://0-doi-org.brum.beds.ac.uk/10.3390/micro2010004 - 19 Jan 2022
Viewed by 617
Abstract
Conventional gloves partially insulate against heat transfer from a hot external environment. They also prevent metabolic heat generated by the human body from escaping. Thus, gloves are a source of heat buildup and heat stress in workers. Heat stress can lead to hyperthermia. [...] Read more.
Conventional gloves partially insulate against heat transfer from a hot external environment. They also prevent metabolic heat generated by the human body from escaping. Thus, gloves are a source of heat buildup and heat stress in workers. Heat stress can lead to hyperthermia. Described herein is a glove that cools using a carbon nanotube (CNT) fabric micro-liner and forced convection from a fan. A cold sink is assumed to be located in the glove to cool the convection air. This glove is called an active textile glove. CNT fabric has high thermal conductivity in the plane of the fabric, low thermal conductivity through its thickness, and a large surface area for convection cooling. Thus, the active textile glove can transfer heat from the hand to cooler air in the environment. This paper simulates the performance of a CNT-cooled glove using simple theoretical heat transfer models. Cooling was also demonstrated by testing the glove using a hot plate. Forced convection was found to provide the greatest cooling effect, with it working in synergy with the CNT fabric which aids in spreading heat. CNT fabric also acts as a shield from environmental dangers. The fabric is flame resistant, attenuates radio frequency waves, and prevents smoke particles and toxic chemicals from entering the glove. Testing illustrates the shielding properties of CNT fabric. Full article
(This article belongs to the Section Microscale Materials Science)
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Article
Buckling Electrothermal NEMS Actuators: Analytic Design for Very Slender Beams
Micro 2022, 2(1), 54-67; https://0-doi-org.brum.beds.ac.uk/10.3390/micro2010003 - 13 Jan 2022
Viewed by 753
Abstract
Analytic approximations are presented for the response of buckling-mode electrothermal actuators with very slender beams with a width-to-length ratio of W/L0.001 of the type found in nanoelectromechanical systems (NEMS). The results are found as closed-form solutions to the Euler [...] Read more.
Analytic approximations are presented for the response of buckling-mode electrothermal actuators with very slender beams with a width-to-length ratio of W/L0.001 of the type found in nanoelectromechanical systems (NEMS). The results are found as closed-form solutions to the Euler beam bending theory rather than by an iterative numerical solution or a time-consuming finite element analysis. Expressions for transverse deflections and stiffness are presented for actuators with the common raised cosine and chevron pre-buckled shapes. The approximations are valid when the effects of bending dominate over those of axial compression. A few higher-order approximations are also presented for less slender beams with 0.001W/L0.01. Full article
(This article belongs to the Section Microscale Engineering)
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Review
Ion Implantation Doping in Silicon Carbide and Gallium Nitride Electronic Devices
Micro 2022, 2(1), 23-53; https://0-doi-org.brum.beds.ac.uk/10.3390/micro2010002 - 10 Jan 2022
Cited by 2 | Viewed by 851
Abstract
Wide band gap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) are excellent materials for the next generation of high-power and high-frequency electronic devices. In fact, their wide band gap (>3 eV) and high critical electric field (>2 MV/cm) enable superior [...] Read more.
Wide band gap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) are excellent materials for the next generation of high-power and high-frequency electronic devices. In fact, their wide band gap (>3 eV) and high critical electric field (>2 MV/cm) enable superior performances to be obtained with respect to the traditional silicon devices. Hence, today, a variety of diodes and transistors based on SiC and GaN are already available in the market. For the fabrication of these electronic devices, selective doping is required to create either n-type or p-type regions with different functionalities and at different doping levels (typically in the range 1016–1020 cm−3). In this context, due to the low diffusion coefficient of the typical dopant species in SiC, and to the relatively low decomposition temperature of GaN (about 900 °C), ion implantation is the only practical way to achieve selective doping in these materials. In this paper, the main issues related to ion implantation doping technology for SiC and GaN electronic devices are briefly reviewed. In particular, some specific literature case studies are illustrated to describe the impact of the ion implantation doping conditions (annealing temperature, electrical activation and doping profiles, surface morphology, creation of interface states, etc.) on the electrical parameters of power devices. Similarities and differences in the application of ion implantation doping technology in the two materials are highlighted in this paper. Full article
(This article belongs to the Special Issue Innovative Methods for Semiconductor Doping)
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Review
Electrical and Optical Doping of Silicon by Pulsed-Laser Melting
Micro 2022, 2(1), 1-22; https://0-doi-org.brum.beds.ac.uk/10.3390/micro2010001 - 24 Dec 2021
Cited by 1 | Viewed by 746
Abstract
Over four decades ago, pulsed-laser melting, or pulsed-laser annealing as it was termed at that time, was the subject of intense study as a potential advance in silicon device processing. In particular, it was found that nanosecond laser melting of the near-surface of [...] Read more.
Over four decades ago, pulsed-laser melting, or pulsed-laser annealing as it was termed at that time, was the subject of intense study as a potential advance in silicon device processing. In particular, it was found that nanosecond laser melting of the near-surface of silicon and subsequent liquid phase epitaxy could not only very effectively remove lattice disorder following ion implantation, but could achieve dopant electrical activities exceeding equilibrium solubility limits. However, when it was realised that solid phase annealing at longer time scales could achieve similar results, interest in pulsed-laser melting waned for over two decades as a processing method for silicon devices. With the emergence of flat panel displays in the 1990s, pulsed-laser melting was found to offer an attractive solution for large area crystallisation of amorphous silicon and dopant activation. This method gave improved thin film transistors used in the panel backplane to define the pixelation of displays. For this application, ultra-rapid pulsed laser melting remains the crystallisation method of choice since the heating is confined to the silicon thin film and the underlying glass or plastic substrates are protected from thermal degradation. This article will be organised chronologically, but treatment naturally divides into the two main topics: (1) an electrical doping research focus up until around 2000, and (2) optical doping as the research focus after that time. In the first part of this article, the early pulsed-laser annealing studies for electrical doping of silicon are reviewed, followed by the more recent use of pulsed-lasers for flat panel display fabrication. In terms of the second topic of this review, optical doping of silicon for efficient infrared light detection, this process requires deep level impurities to be introduced into the silicon lattice at high concentrations to form an intermediate band within the silicon bandgap. The chalcogen elements and then transition metals were investigated from the early 2000s since they can provide the required deep levels in silicon. However, their low solid solubilities necessitated ultra-rapid pulsed-laser melting to achieve supersaturation in silicon many orders of magnitude beyond the equilibrium solid solubility. Although infrared light absorption has been demonstrated using this approach, significant challenges were encountered in attempting to achieve efficient optical doping in such cases, or hyperdoping as it has been termed. Issues that limit this approach include: lateral and surface impurity segregation during solidification from the melt, leading to defective filaments throughout the doped layer; and poor efficiency of collection of photo-induced carriers necessary for the fabrication of photodetectors. The history and current status of optical hyperdoping of silicon with deep level impurities is reviewed in the second part of this article. Full article
(This article belongs to the Special Issue Innovative Methods for Semiconductor Doping)
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