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Topic Review
Structural and Physiochemical Characteristics of Chitosan
Chitosan is a fibrous compound derived from chitin, which is the second most abundant natural polysaccharide and is produced by crustaceans, including crabs, shrimps, and lobsters. Chitosan has all of the important medicinal properties, including biocompatibility, biodegradability, and hydrophilicity, and it is relatively nontoxic and cationic in nature. 
  • 460
  • 04 May 2023
Topic Review
Gallium Nitride Epitaxy
Gallium nitride (GaN) is a wide-bandgap semiconductor material with excellent electrical and optical properties, making it a promising candidate for various electronic and optoelectronic devices. In particular, the unique characteristics of GaN make it a popular choice for high-power and high-frequency applications, such as power electronics, RF amplifiers, and light-emitting diodes (LEDs).
  • 701
  • 25 Apr 2023
Topic Review
Thin Films of Sn Perovskites
Compared to Pb-based perovskites solar cells (PSCs), tin-based perovskite solar cells (TPSCs) exhibit a much lower power conversion energy (PCE), mainly due to the poor film quality, correlated degradation, and detrimental effects. Perovskite films are often fabricated from solutions due to ease of fabrication. In order to create a high-performance tin-based PSC, it is imperative to form dense, compact, well-crystalline perovskite films. Many ways have been proposed to resolve the instabilities of tin-based perovskites. The first step to enhance the stability of the device is to gain a deeper understanding of the degradation mechanisms. Earlier, the researchers briefly pointed out the effects of moisture, oxygen, illumination, ion migration, and chemical reactions which are the most common causes of degradation in perovskite halides.
  • 285
  • 20 Apr 2023
Topic Review
Multicore Fiber Interferometric Sensors
Due to the specificity of fiber structure, i.e., multiple cores integrated into only one fiber cladding, multicore fiber (MCF) interferometric sensors exhibit many desirable characteristics compared with traditional fiber interferometric sensors based on single-core fibers, such as structural and functional diversity, high integration, space-division multiplexing capacity, etc. Thanks to the unique advantages, e.g., simple fabrication, compact size, and good robustness, MCF interferometric sensors have been developed to measure various physical and chemical parameters such as temperature, strain, curvature, refractive index, vibration, flow, torsion, etc., among which the extraordinary vector-bending sensing has also been extensively studied by making use of the differential responses between different cores of MCFs.
  • 323
  • 14 Apr 2023
Topic Review
Short Wavelength Energy-Efficient High-Speed Vertical-Cavity Surface-Emitting Lasers
Vertical-cavity surface-emitting lasers (VCSELs) were becoming the dominating optical sources for data communication in such centers for all distances and wavelengths. VCSELs are of low production cost, can be tested on-wafer, and enable low energy consumption. 850 nm multi-mode VCSELs are widely used for the optical links inside data centers and supercomputers, together with multi-mode fibers. Long-wavelength single-mode VCSELs (1310 nm or 1550 nm) based on InP extend the transmission distance and enable wavelength division multiplexing (WDM) technologies.
  • 411
  • 13 Apr 2023
Topic Review Peer Reviewed
Wavefunction Collapse Broadens Molecular Spectrum
Spectral lines in the optical spectra of atoms, molecules, and other quantum systems are characterized by a range of frequencies ω or a range of wavelengths λ=2πc/ω, where c is the speed of light. Such a frequency or wavelength range is called the width of the spectral lines (linewidth). It is influenced by many specific factors. Thermal motion of the molecules results in broadening of the lines as a result of the Doppler effect (thermal broadening) and by their collisions (pressure broadening). The electric fields of neighboring molecules lead to Stark broadening. The linewidth to be considered here is the so-called parametric broadening (PB) of spectral lines in the optical spectrum. PB can be considered the fundamental type of broadening of the electronic vibrational–rotational (rovibronic) transitions in a molecule, which is the direct manifestation of the basic concept of the collapse of a wavefunction that is postulated by the Copenhagen interpretation of quantum mechanics. Thus, that concept appears to be not only valid but is also useful for predicting physically observable phenomena.
  • 850
  • 11 Apr 2023
Topic Review
Properties of MXene Products
MXenes are two-dimensional layered materials containing early transition metal carbides, nitrides, and carbonitrides. 
  • 360
  • 03 Apr 2023
Topic Review
Central High-Order Aberrations and Accommodation
High-order aberrations (HOAs) are optical defects that degrade the image quality. They change with factors such as pupil diameter, age, and accommodation. The changes in optical aberrations during accommodation are mainly due to lens shape and position changes. Primary spherical aberration (Z(4.0)) is closely related to accommodation and some studies suggested that it plays an important role in the control of accommodation. Furthermore, central and peripheral HOAs vary with refractive error and seem to influence eye growth and the onset and progression of myopia. The variations of central and peripheral HOAs during accommodation also appear to be different depending on the refractive error. Central and peripheral high-order aberrations are closely related to accommodation and influence the accuracy of the accommodative response and the progression of refractive errors, especially myopia. 
  • 474
  • 31 Mar 2023
Topic Review
Mechanism of Surface-Enhanced Raman Spectroscopy
Raman spectroscopy is an analytical technique discovered by the Indian scientist C.V. Raman. It can be applied to analyze the molecular structure based on the molecular vibration and rotation information of scattering spectra. Benefiting from the recent advancements in material science, nanotechnology and optical technology, surface-enhanced Raman scattering (SERS) was developed and widely used in bioanalysis, clinical diagnosis and biomedical research. In SERS, Raman signals of molecules can be enhanced by six to ten orders of magnitude, owing to the electromagnetic field enhancement and chemical enhancement effects generated by nanostructures. The detection limit of SERS is even as low as the single-molecule level, so SERS is regarded as an ultrasensitive technique.
  • 316
  • 21 Mar 2023
Topic Review
Long-Wavelength Vertical-Cavity Surface-Emitting Lasers
Single-mode long-wavelength (LW) vertical-cavity surface-emitting lasers (VCSELs) present an inexpensive alternative to DFB-lasers for data communication in next-generation giga data centers, where optical links with large transmission distances are required. The use of long-wavelength (1300–1550 nm) single-mode (SM) VCSELs makes it possible to reduce the modal and chromatic dispersion in an optical link and, as a result, to extend its reach. Moreover, spatial division multiplexing (SDM) transmission by multicore fibers using long-wavelength (LW or short-wavelength infrared, SWIR) VCSELs are enabling many larger-scale data center networks than presently possible. 1300 nm VCSELs are of particularly strong importance for hybrid integration with silicon photonics, providing integrated modulators and InP- and GaAs-based integrated photonic circuits.
  • 439
  • 20 Mar 2023
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