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Review of Solid State Physics
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
Although the presence of impurities generally affects the electronic performance of a semiconductor material, the effect can vary widely. For instance, some impurities may introduce scattering centers that can affect the free carrier mobility, but may not be electrically active, i.e., they do not introduce free charge carriers to the conduction or valence bands. For example, boron impurities in GaAs, in high concentrations, can affect the mobility of the charge carriers, but they are electrically inactive. As a result, pyrolitic BN is often used as the crucible for GaAs bulk crystal growth. By contrast carbon, sources of which are present in practically all steps of the GaAs materials preparation and crystal growth, is an electrically active shallow acceptor and behaves as a p-type dopant. Hence, carbon affects mobility and electrical conductivity.
Carbon Nanotube Products from the Floating Catalyst Method
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2019
The CNT fibers spun from the floating catalyst method often possess many iron catalyst particles or carbonaceous impurities which lower their performance (Tran et al. 2016b, 2017). These impurities can be removed by purification treatments. Most catalyst particles in the CNT assemblies are encapsulated in graphitic carbon cages that restrict the direct removal of the impurities by acid washing. Therefore, gas-phase oxidation using oxygen or air can be used to crack open these carbon layers to enable their efficient leaching by acids (Figure 9.13) (Tran et al. 2017). Additionally, the direct-spun CNT fibers can be purified by immersing the fibers in concentrated acid for a specific time (Liu et al. 2016b, Tran et al. 2016b). The acidization time should be optimum for the purification effect to be dominant on the CNT structural modification, leading to the removal of the amorphous carbon despite the negligible reduction in the amount of iron catalyst impurities (Tran et al. 2016b). Long acidization time is not favorable due to possible damage of the CNT structure (Tran et al. 2016b).
Validation of Chromatographic Methods
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
Starting from the definition of the purpose and scope of the method, a suggested process for validating analytical methods (Shabir, 2003) is shown in Figure 31.1. In general terms, the purpose of method validation is to prove that the analytical method is appropriate for its intended use. Typically, analytical methods are grouped according to the following general types of tests.Identification tests: Identification tests provide data on the identity of a compound in a sample. For example, a chromatographic method or spectroscopic detection method used for an identification test would compare the sample with a known reference standard.Analytical methods for determination of impurities including quantitative assays and limit tests: Impurity tests provide data on the purity characteristics of a sample. Sometimes, impurity testing may require more than one HPLC method to give an accurate description of the purity of a sample. Depending on whether the purpose of the method is to provide an actual numeric value (quantitative test) or provide assurance that an impurity is less than a specified amount (limit test), the requirements for method validation vary.Analytical methods for quantitation of major components: This type of test provides data on the exact quantity of the major compound present in a sample. This value may be used to calculate the potency or purity of the final drug product.
Novel synthesis of cauliflower-like nanostructured ZnFe2O4 high-performance electrode for supercapattery applications
Published in International Journal of Green Energy, 2023
Nidhi Tiwari, S.L. Kadam, R.S. Ingole, R.K. Kamat, Shrinivas Kulkarni
Undoubtedly, specific energy (E) and specific power (P) are the most important indicators to value the practicability of power sources including SCs. The relationship between E and P of the ZnFe2O4 is shown in the Ragone plot (Figure 4, (e)). The maximum specific power is obtained as 306.25 W kg−1 and the maximum specific energy is obtained as 8.72 Wh kg−1. The value for Columbic efficiency is estimated to be 80%. The poor Columbic efficiency of the electrode may be due to the presence of impurities, which can have a significant impact on the electrochemical performance of a material. Impurities can introduce defects or alter the surface chemistry of the material, affecting its ability to store or charge transfer (Liu et al. 2019). It should be recorded that the results obtained from the GCD profile indicate that the cauliflower-like ZnFe2O4 nanostructured electrode material has great potential for supercapattery devices.
Ground and two low-lying excited states binding energy in (Al,Ga)N/AlN double quantum wells: temperature and electric field effects
Published in Philosophical Magazine, 2022
Walid Belaid, Haddou El Ghazi, Mohamed A. Basyooni, Izeddine Zorkani, Anouar Jorio
As a result, understanding the impurity states in semiconductors is critical, as the incorporation of impurities can drastically alter the performance of optoelectronic devices. The application of an external electric field along the crystal growth direction enables the carrier distribution to polarise and the quantum energy state to shift, Dalgic and co-workers [1] have investigated the electric field effect on the non-hydrogenic binding energy of shallow donor impurity in a square and cylindrical GaAs/(Ga, Al)As QWW. In a similar context, Aktas and co-workers [2,3] have investigated the shallow donor impurity binding energy () under applied electric and magnetic fields in a coaxial GaAs/(Ga,Al)As QWW. Authors have calculated the versus the impurity position and barrier width for several values of magnetic and electric fields. Such effects can induce significantly alters in the energy spectrum of carriers, which can be a useful tool to modulate the output of optoelectronic devices. The temperature effect is to modify the dielectric constant, the masses of carriers, the stability of exciton the energy levels, and the potential barrier [4]. The temperature effect has been investigated by Elabsy [5] and Nithiananthi and Jayakumar [6] in a quantum well, and R. Khordad [7] in a V-groove quantum wire, and M. Hu [8] in a cylindrical GaInAs/GaAs quantum dot.
Impurity related optical properties in tuned quantum dot/ring systems
Published in Philosophical Magazine, 2019
Suvajit Pal, Manas Ghosh, C. A. Duque
Impurities in semiconductors can affect the electrical, optical, and transport properties. Understanding the nature of impurity states in semiconductor structures is, therefore, a crucial problem. Shallow hydrogenic donors enhance the conductivity of a semiconductor by several orders of magnitude. The introduction of hydrogenic impurity in the confined systems is a useful model for understanding the optoelectronic properties of these heterostructures. In order to understand how a hydrogenic donor impurity affects the spectrum of a single electron in low-dimensional semiconductor structures, many researchers focused their attention on energy quantised states of the charge carriers [55–62]. The confinement of quasiparticles in QDs leads to magnification of the oscillator strength of electron-impurity excitations in presence of hydrogenic donor impurity. It allows tunability of resonance frequency of optical transition energy influenced by confinement strength and presence of impurity. The study of the impurity states in semiconductor nanostructures was initiated by the pioneering work of Bastard [63]. In spite of growing interest in impurity doping in nanocrystallites, most of the theoretical works carried out on shallow donors in spherical QD employed variational approaches [64]. Additionally, a computational scheme yielding exact (numerical) wave functions and energies of a spherical nanocrystallite, with a shallow donor-impurity located anywhere inside, is presented by Movilla and Planelles [65].