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Topic Review
Unified Atomic Mass Unit
The unified atomic mass unit or dalton (symbol: u, or Da) is a standard unit of mass that quantifies mass on an atomic or molecular scale (atomic mass). One unified atomic mass unit is approximately the mass of one nucleon (either a single proton or neutron) and is numerically equivalent to 1 g/mol. It is defined as one twelfth of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest, and has a value of 1.660539040(20)×10−27 kg, or approximately 1.66 yoctograms. The CIPM has categorised it as a non-SI unit accepted for use with the SI, and whose value in SI units must be obtained experimentally. The amu without the "unified" prefix is technically an obsolete unit based on oxygen, which was replaced in 1961. However, many sources still use the term amu but now define it in the same way as u (i.e., based on carbon-12). In this sense, most uses of the terms atomic mass units and amu, today, actually refer to unified atomic mass unit. For standardization, a specific atomic nucleus (carbon-12 vs. oxygen-16) had to be chosen because the average mass of a nucleon depends on the count of the nucleons in the atomic nucleus due to mass defect. This is also why the mass of a proton or neutron by itself is more than (and not equal to) 1 u. The atomic mass unit is not the unit of mass in the atomic units system, which is rather the electron rest mass (me).
  • 7.3K
  • 21 Oct 2022
Topic Review
Ultrasensitive Magnetic Field Sensors
One of the cutting-edge topics today is the use of magnetic field sensors for applications such as magnetocardiography, magnetotomography, magnetomyography, magnetoneurography, or their application in point-of-care devices. Types of magnetic field sensors include direct current superconducting quantum interference devices, search coil, fluxgate, magnetoelectric, giant magneto-impedance, anisotropic/giant/tunneling magnetoresistance, optically pumped, cavity optomechanical, Hall effect, magnetoelastic, spin wave interferometry, and those based on the behavior of nitrogen-vacancy centers in the atomic lattice of diamond. Current developments of magnetometry in biological diagnostics are revised in review paper DOI: 10.3390/s20061569.
  • 2.3K
  • 11 Jun 2021
Topic Review
Types of Liquid Crystal Biosensors
Interactions between liquid crystal molecules and target analytes open up various biosensing applications for quick screening and point-of-care applications. There exist different kinds of biosensors, such as electrochemical, wearable, amperometric, potentiometric, optical, impedimetric and thermometric. Liquid crystal (LC) biosensors belong to the type of optical biosensors, which employ its anisotropy and sensitivity to external stimuli. As it is known, LCs are highly sensitive to environment changes, e.g., temperature, electric fields and surface interactions. The inherent property of LCs to respond to external stimuli gives LC biosensors a high potential to contribute to the new biosensing era. 
  • 176
  • 02 Jan 2024
Topic Review
Tunneling Quantum Dynamics in Ammonia
Ammonia is a well-known example of a two-state system and must be described in quantum-mechanical terms. In this article, we will explain the tunneling phenomenon that occurs in ammonia molecules from the perspective of trajectory-based quantum dynamics, rather than the usual quantum probability perspective.
  • 678
  • 03 Aug 2021
Topic Review
Tunneling and Blocking Oxides on Memory Cells
Flash memory is an electronic, non-volatile information storage device that can be electrically erased and reprogrammed. Ideally, the information stored in such a device should be preserved for long when the power is switched off. There are two flash memories designs at present: floating gate and charge trapping. Both of them work by storage of electrical charges in the space above the channel of the MOSFET. The charge storage volume of the flash cell, either poly-Si floating gate or charge trapping dielectric/dielectric stack is confined between blocking and tunnel oxides for electrical insulation from the gate electrode and Si substrate. Blocking and tunnelling oxides are important parts of the flash memory cells, as they affect retention, endurance and program/erase speed performance.
  • 463
  • 20 Oct 2023
Topic Review
Triboelectric Nanogenerators Based on 2D Materials
The development and production of nanogenerators provide a promising solution to address the energy crisis. Triboelectric nanogenerators, in particular, have attracted significant attention due to their portability, stability, high energy conversion efficiency, and compatibility with a wide range of materials. Triboelectric nanogenerators (TENGs) have many potential applications in various fields, such as artificial intelligence (AI) and the Internet of Things (IoT). Additionally, by virtue of their remarkable physical and chemical properties, two-dimensional (2D) materials, such as graphene, transition metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN), MXenes, and layered double hydroxides (LDHs), have played a crucial role in the advancement of TENGs. 
  • 358
  • 23 May 2023
Topic Review
Triboelectric Nanogenerator for Sports Applications
Progress in science and technology drives the continuous innovation of energy collection and utilization. In the field of sports, the information collection and analysis based on Internet of things have attracted particular attention. On this basis, it is considered that the stability of devices, the universality of materials, and the scientificity of application of the TENG in the future need to be improved. There is a direction for further upgrading energy collection technology to promote the high-quality development of human mechanical energy sensing in the field of sports.
  • 471
  • 06 Sep 2022
Topic Review
Transparent Solar Windows
Many modern glass and window products are based on metal-dielectric coatings, which can control properties such as thermal emissivity, heat gain, colour, and transparency. These can also enable solar energy harvesting through PV integration, if the glazing structure is purpose-designed, to include luminescent materials and special microstructures. Recently, significant progress has been demonstrated in building integrated transparent solar windows, which are expected to add momentum towards the development of smart cities. These window systems are, at present in 2019, the only type of transparent and clear construction materials capable of providing significant energy savings in buildings, simultaneously with renewable energy generation.
  • 2.8K
  • 11 Feb 2021
Topic Review
Traditional Chinese Timekeeping
The traditional Chinese time systems refers to the time standards for divisions of the day used in China until the introduction of the Shixian calendar in 1628 at the beginning of the Qing dynasty.
  • 385
  • 30 Oct 2022
Topic Review
Ti/Al/X/Au Au-Contained Ohmic Contact Technique
AlGaN/GaN high electron mobility transistors (HEMTs) are regarded as promising candidates for a 5G communication system, which demands higher frequency and power. Source/drain ohmic contact is one of the key fabrication processes crucial to the device performance. Firstly, Aucontained metal stacks combined with RTA high-temperature ohmic contact schemes were presented and analyzed, including process conditions and contact formation mechanisms. Considering the issues with the Au-contained technique, the overview of a sequence of Au-free schemes is given and comprehensively discussed. In addition, in order to solve various problems caused by hightemperature conditions, novel annealing techniques including microwave annealing (MWA) and laser annealing (LA) were proposed to form Au-free low-temperature ohmic contact to AlGaN/GaN HEMT. The most popular metallization schemes of ohmic contact in AlGaN/GaN HEMT is Ti/Al/X/Au, where X can be Ni, Mo, Pt, Ta, Ir, etc.
  • 1.3K
  • 28 Jun 2022
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