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Topic Review
Single Crystal Synthesis of 11 Iron-Based Superconductors
The 11 system in the iron-based superconducting family has become one of the most extensively studied materials in the research of high-temperature superconductivity, due to their simple structure and rich physical properties. Many exotic properties, such as multiband electronic structure, electronic nematicity, topology and antiferromagnetic order, provide strong support for the theory of high-temperature superconductivity, and have been at the forefront of condensed matter physics in the past decade. One noteworthy aspect is that a high upper critical magnetic field, large critical current density and lower toxicity give the 11 system good application prospects.
  • 192
  • 21 Jul 2023
Topic Review
Avalanche Photodiodes and Silicon Photomultipliers of Non-Planar Designs
Conventional designs of an avalanche photodiode (APD) have been based on a planar p–n junction since the 1960s. APD developments have been driven by the necessity to provide a uniform electric field over the active junction area and to prevent edge breakdown by special measures. Most modern silicon photomultipliers (SiPM) are designed as an array of Geiger-mode APD cells based on planar p–n junctions. Modern Silicon Photomultipliers (SiPM) are designed as an array of Geiger-mode APD cells based on planar p-n junctions. However, the planar design faces an inherent trade-off between photon detection efficiency and dynamic range due to loss of an active area at the cell edges. Non-planar designs of APDs and SiPMs have also been known since the development of spherical APD (1968), Metal-Resistor-Semiconductor APD (1989), and Micro-well APD (2005). Recent development of Tip Avalanche Photodiode (2020) based on the spherical p-n junction eliminates the trade-off, outperforms the planar SiPMs in the photon detection efficiency, and opens new opportunities for SiPM improvements. Moreover, the latest developments of APDs based on electric field-line crowding and charge-focusing topology with quasi-spherical p-n junctions (2019–2023) show promising functionality in linear and Geiger operating modes.
  • 557
  • 27 Jun 2023
Topic Review
Calculation of the transition temperature of superconducting elements
Using the Roeser-Huber formalism, we establish a non-trivial relation between the crystal structure and the transition temperature, Tc, to the superconducting state. By means of this relation, we can calculate Tc for practically all superconducting elements quite accurately within a small error margin. It is shown that this works well also for polymorphic elements and elements under pressure. Furthermore, the Roeser-Huber formalism implies that all calculated data fall on a common line with the slope m1 = h2/(2πkB) = 5.061 × 10−45 m2 kg K, when plotting log(Σ((2x)-2n1-1ML-1))-1 versus 1/Tc, which can be employed as a test when predicting Tc of unknown superconductors.
  • 873
  • 21 Jun 2023
Topic Review
Paramagnetic Meissner Effect (PME)
When cooling a superconductor in a magnetic field below the transition temperature, Tc, the material characteristically tries to expel the magnetic flux due to the induced shielding currents (often also called Meissner currents). When measuring the magnetic moment, m(T), in this situation a diamagnetic signal (m = negative) appears. This so-called Meissner-Ochsenfeld effect is one of the two hallmarks of superconductivity besides the zero resistance and represents the strongest proof if a material is a true superconductor. However, in the literature there are also superconducting materials which show an appearing paramagnetic (positive m) signal below Tc when measuring m(T) in small applied magnetic fields. This so-called Paramagnetic Meissner Effect (PME) or Wohlleben effect was first observed in bulk, Bi2Sr2CaCu2O8 high- Tc superconducting (HTSc) materials, and subsequently as big surprise also in conventional Nb superconductors. Since then, PME was found in many more metallic and HTSc materials, having various shapes (bulks, crystals, thin films), and various aspect ratios and compositions, including multilayers and doped materials.
  • 302
  • 20 Jun 2023
Topic Review
Magnetic Properties and Magnetocaloric Effect of Pr2Co7 Compound
The Pr2Co7 compound has interesting magnetic properties, such as a high Curie temperature TC and uniaxial magnetocrystalline anisotropy. It crystallizes in a hexagonal structure (2:7 H) of the Ce2Ni7 type and is stable at relatively low temperatures (Ta ≤ 1023 K), or it has a rhombohedral structure (2:7 R) of the Gd2Co7 type and is stable at high temperatures (Ta ≥ 1223 K). Studies of the magnetocaloric properties of the nanocrystalline Pr2Co7 compound have shown the existence of a large reversible magnetic entropy change (ΔSM) with a second-order magnetic transition. 
  • 508
  • 15 Jun 2023
Topic Review
Types of Liquid Crystals
The liquid-crystalline state of matter (mesomorphic state, or mesophase) is intermediate between the crystalline and liquid states, simultaneously showing some of the anisotropic properties of solids and the fluidity of liquids. In this state, materials demonstrate a tendency to flow like liquids and have some properties similar to solids. LCs may be divided into two main classes, named thermotropics and lyotropics. The importance of liquid crystals, alongside with their technical applications, lies in their role as carriers of life. In fact, fully ordered solids are a dead matter, and fully disordered liquids are also dead. But liquid crystals, as partially ordered soft matter systems, bear all qualities that had been necessary for the emergence of life. Practically all biological structures show some features pf liquid crystalline ordering. 
  • 512
  • 15 Jun 2023
Topic Review
Properties of MXene Products
MXenes are two-dimensional layered materials containing early transition metal carbides, nitrides, and carbonitrides. 
  • 301
  • 03 Apr 2023
Topic Review
Control and Upgradation of Indoor Air Quality
Due to increasing health and environmental issues, indoor air quality (IAQ) has garnered much research attention with regard to incorporating advanced clean air technologies. Various physicochemical air treatments have been used to monitor, control, and manage air contaminants, such as monitoring devices (gas sensors and internet of things-based systems), filtration (mechanical and electrical), adsorption, UV disinfection, UV photocatalysts, a non-thermal plasma approach, air conditioning systems, and green technologies (green plants and algae).
  • 613
  • 24 Feb 2023
Topic Review
Models of the Structure of Humic Substances
Natural organic matter, including humic substances (HS), comprises complex secondary structures with no defined covalent chemical bonds and stabilized by inter- and intra-molecular interactions, such as hydrogen bonding, Van der Waal’s forces, and pi-pi interactions. The latest view describes HS aggregates as a hydrogel-like structure comprised by a hydrophobic core of aromatic residues surrounded by polar and amphiphilic molecules akin a self-assembled soft material. A different view is based on the classification of this material as either mass or surface fractals. The former is intended as made by the clustering of macromolecules generating dendritic networks, while the latter have been modelled in terms of a solvent-impenetrable core surrounded by a layer of lyophilic material. 
  • 299
  • 22 Feb 2023
Topic Review
Nanocrystalline Magnetic Semiconductors for Spintronics
Сhallenge for spintronics is to find new ways for the control of electronic phenomena and magnetic properties of solids at nanoscale. Some promising aspects are connected with developing new materials. The research highlights the areas devoted to the creation of new functional materials for spintronics based on magnetic semiconductors and demonstrates the technical possibilities of creating various devices, in particular, a maser, a p-n junction with a colossal magnetoresistance, a spin valve, a magnetic lens, modulators, spin wave amplifier, etc. A magnetic semiconductor is a magnetic material that, in terms of specific conductivity, occupies an intermediate position between a conductor and an insulator, and has a band gap comparable to ~kBT. Most known magnetic semiconductors (SC) are either oxides or chalcogenides (sulfides, selenides and tellurides) of 3d transition metals, rare earth 4f metals or a combination. Spintronics (spin electronics) studies spin current transfer (spin-polarized transport) in condensed media, including contact structures, heterostructures, superlattices and multilayers. Much attention is paid to the mechano-physical methods of obtaining of high-density transparent nanoceramics based on magnetic semiconductors. The potential possibility of using nanoceramics as an absorber of solar energy, as well as in modulators of electromagnetic radiation, is also presented. The THz magneto-optics in magnetic semiconductors is shown to be beneficial to the intensively developing fields of spintronics – ultrafast magnetooptics and magnetophotonics in magnetic semiconductors.
  • 563
  • 20 Dec 2022
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