Search Results (51)

Heavy rare earth elements (HREEs) are widely used in permanent magnets, phosphors, catalysts, and advanced electronic devices because of their unique optical, electrical, and magnetic properties. However, their efficient separation remains a major challenge in hydrometallurgy because neighboring rare earths have highly similar ionic radii and chemical behavior. In this work, a silane-grafted aminophosphonate resin, D152-AMPA, was used to systematically investigate the adsorption behavior, adjacent-pair separation, impurity effects, and dynamic column performance of a mixed rare-earth system under different pH conditions. In the presence of Al, Fe, Ca, and Mg, the Er/Ho separation factor increased from 1.031 at pH 2 to 2.298 at pH 4, indicating that the partitioning advantage of Er over Ho was retained and further strengthened despite the presence of impurities. During elution, the purities of the Er-rich and Ho-rich fractions reached 92.79% and 94.34%, with cumulative recoveries of 88.32% and 83.05%, respectively. XPS and FT-IR analyses further indicated that Lu(III) adsorption mainly involved the oxygen donor sites of the aminophosphonate groups. These results demonstrate that D152-AMPA is capable of selective adsorption and dynamic fractionated separation in mixed and impurity-containing rare-earth systems, providing an experimental basis for greener separation and enrichment of complex rare-earth solutions. Full article

Hydrogen is frequently incorporated in alkaline-earth oxides during crystal growth or post-deposition annealing. For MgO, several studies in the past showed that interstitial monatomic hydrogen can also favourably bind with oxygen vacancies to form stable substitutional defect complexes (substitutional hydrogen or U-defect centers). The present study reports first-principles density-functional calculations of the formation energies of both interstitial and substitutional forms of the hydrogen impurity in MgO. Determination of the site-resolved densities of electronic states allowed for a detailed identification of the nature of the impurity-induced levels, both in the valence-energy region and inside the band gap of the host. The stability and diffusion mechanisms of both hydrogen defects was also studied with the aid of nudged elastic-band (NEB) calculations. Interstitial hydrogen was found to be an amphoteric defect with the lower formation energy for any realistic environment conditions (temperature and oxygen partial pressure). The NEB calculations showed that it is a fast-diffusing species when it is thermodynamically stable as a positively-charged state (bare proton). In contrast, the hydrogen-vacancy complex is a shallow donor, extremely stable against dissociation and virtually immobile as an isolated defect. Its formation is found to be favoured for a range of mid-gap Fermi-level positions where positively-charged interstitial hydrogen and neutral oxygen vacancies (F centers) are both thermodynamically stable low-energy defects. The present findings are consistent with the established consensus on the electrical activity of hydrogen in MgO as well as with experimental observations reporting the remarkable thermal stability of substitutional hydrogen defects and their ability to act as electron traps. Full article

To investigate the in situ irradiation effects of gallium nitride at varying temperatures, we combined ion beam-induced luminescence spectroscopy with variable-temperature irradiation using a home-built IBIL system and a GIC4117 2 × 1.7 MV tandem accelerator. Unlike previous static studies—limited to post-irradiation or single-temperature luminescence—we in situ tracked dynamic luminescence changes throughout irradiation, directly capturing the real-time responses of luminescent centers to coupled temperature-dose variations—a rare capability in prior work. To clarify how irradiation and temperature affect the luminescent centers of GaN, we integrated density functional theory (DFT) calculations with literature analysis, then resolved the yellow luminescence band into three emission centers via Gaussian deconvolution: 1.78 eV associated with C/O impurities, 1.94 eV linked to VGa, and 2.2 eV corresponding to CN defects. Using a single-exponential decay model, we further quantified the temperature- and dose-dependent decay rates of these centers under dual-variable temperature and dose conditions. Experimental results show that low-temperature irradiation such as at 100 K suppresses the migration and recombination of V_Ga/C_N point defects, significantly enhancing the radiation tolerance of the 1.94 eV and 2.2 eV emission centers; meanwhile, it reduces non-radiative recombination center density, stabilizing free excitons and donor-bound excitons, thereby improving near-band-edge emission center resistance. Notably, the 1.94 eV emission center linked to gallium vacancies exhibits superior cryogenic radiation tolerance due to slower defect migration and more stable free exciton/donor-bound exciton states. Collectively, these findings reveal a synergistic regulation mechanism of temperature and radiation fluence on defect stability, addressing a key gap in static studies, providing a basis for understanding degradation mechanisms of gallium nitride-based devices under actual operating conditions (coexisting temperature fluctuations and continuous radiation), and offering theoretical/experimental support for optimizing radiation-hardened gallium nitride devices for extreme environments such as space or nuclear applications. Full article

Rice husk is a lignocellulosic biomass rich in silica, which, when disposed of inappropriately, represents an environmental hazard. This study investigated the application of deep eutectic solvents (DES) as a green and efficient approach to the rice husk fractionation, combining the selective dissolution of lignin and sugars with the purification of the silica-rich inorganic fraction. Six different DES were produced from choline chloride or betaine with different hydrogen bond donors and characterized for water content and pH. The DES based on carboxylic acids was more acidic, which favored the cleavage of ester and glycosidic bonds in the biomass. The TGA, XRF, SEM, and XRD analyses revealed that the lactic acid-based DES promoted better removal of lignin and mineral impurities, resulting in a purer silica with an amorphous morphology. The 110 °C condition was the most effective in preserving the thermal integrity of the organic (sugars and lignin) and inorganic (silica-rich ash) fractions. The results highlight the potential of DES as selective, sustainable, and tunable solvents for the valorization of agricultural waste, achieving biosilica with SiO₂ purity exceeding 80% and lignin removal above 70%, reinforcing the potential of DES as sustainable solvents for agricultural waste valorization. Full article

This study presents a comprehensive numerical investigation of excitonic states in GaAs quantum wells embedded in ${\mathrm{Al}}_x$${\mathrm{Ga}}_{1-x}$As barriers, incorporating the effects of donor and acceptor impurities, external electric and magnetic fields, and varying well widths. The electron and hole wavefunctions are computed by directly solving the Schrödinger equation using the finite element method in cylindrical coordinates, without assuming trial forms. To evaluate the exciton binding energy, the implementation and comparison of two independent approaches were performed: a numerical integration method based on elliptic function corrections, and a novel finite element electrostatic formulation using COMSOL Multiphysics v5.6. The latter computes the Coulomb interaction by solving Poisson’s equation with the hole charge distribution and integrating the resulting potential over the electron density. Both methods agree within 1% and capture the spatial and field-induced modifications in excitonic properties. The results show that quantum confinement enhances binding in narrow wells, while donor impurities and electric fields reduce binding via spatial separation of carriers. Magnetic fields counteract this effect by providing radial confinement. The FEM-based electrostatic method demonstrates high spatial accuracy, computational efficiency, and flexibility for complex heterostructures, making it a promising tool for exciton modeling in low-dimensional systems. Full article

Novel wide-bandgap ZnO, BeO, and ZnBeO materials have recently gained considerable interest due to their stellar optoelectronic properties. These semiconductors are being used in developing high-resolution, flexible, transparent nanoelectronics/photonics and achieving high-power radio frequency modules for sensors/biosensors, photodetectors/solar cells, and resistive random-access memory applications. Despite earlier evidence of attaining p-type wz ZnO with N doping, the problem persists in achieving reproducible p-type conductivity. This issue is linked to charging compensation by intrinsic donors and/or background impurities. In ZnO: Al (Li), the vibrational features by infrared and Raman spectroscopy have been ascribed to the presence of isolated ${\mathrm{A}\mathrm{l}}_{\mathrm{Z}\mathrm{n}}{(\mathrm{L}\mathrm{i}}_{\mathrm{Z}\mathrm{n}})$ defects, nearest-neighbor (NN) ${[\mathrm{A}\mathrm{l}}_{\mathrm{Z}\mathrm{n}}{-\mathrm{N}}_{\mathrm{O}}$] pairs, and second NN ${[\mathrm{A}\mathrm{l}}_{\mathrm{Z}\mathrm{n}}{-\mathrm{O}-\mathrm{L}\mathrm{i}}_{\mathrm{Z}\mathrm{n}};{\mathrm{V}}_{\mathrm{Z}\mathrm{n}}-\mathrm{O}{-\mathrm{L}\mathrm{i}}_{\mathrm{Z}\mathrm{n}}]$ complexes. However, no firm identification has been established. By integrating accurate perturbation models in a realistic Green’s function method, we have meticulously simulated the impurity vibrational modes of ${\mathrm{A}\mathrm{l}}_{\mathrm{Z}\mathrm{n}}$${(\mathrm{L}\mathrm{i}}_{\mathrm{Z}\mathrm{n}})$ and their bonding to form complexes with dopants as well as intrinsic defects. We strongly feel that these phonon features in doped ZnO will encourage spectroscopists to perform similar measurements to check our theoretical conjectures. Full article

This study develops a high-performance polypropylene (PP) substrate platform by optimizing micro/macrostructures and introduces an efficient catalyst. Key findings include: (1) microstructural analysis identifies ash content impurities (>20 ppm) as triggers for partial discharge-induced insulation failure. PP molecular weights (10⁵–10⁶) with narrower distributions enhance mechanical strength, while functional groups (-CH₂/-CH₃) show no structural variations across samples. (2) Macroscopically, mixed α-β crystal interfaces increase insulation failure risks, necessitating single-crystalline structures. Higher temperatures reduce dielectric constants but increase losses, requiring environmental consideration. Crystallinity positively correlates with DC breakdown strength (443.31 kV/mm at 54.13% crystallinity). (3) Among three endo-donor catalysts, the internal electron donor 3-based catalyst achieved optimal die-test activity (47.7 kg PP/g cat·h). With 20 mL triethylamine, the catalyst reduced PP ash content by 42.1%, narrowed molecular weight distribution by 31.6%, and increased crystallinity by 8.74%. These results establish microstructure–property relationships for PP capacitors and provide technical guidelines for performance enhancement. The work addresses current limitations in PP evaluation methods and offers a practical strategy for manufacturing high-insulation PP materials through structural control and catalytic optimization. Full article

Education plays an essential role in ensuring the social sustainability of blood donation. As altruism may be insufficient to support donor engagement, this study assesses the effectiveness of incentives on ensuring the social sustainability of blood donation. A self-administered questionnaire was used to collect data from 319 medical students about socio-demographic variables, donation frequency, altruism dimensions (impure, self-regarding, reluctant, egalitarian warm glow, and kinship), the perceived importance of monetary (travel compensation, meal vouchers) and non-monetary incentives (free blood screening, paid leave, refreshments, recognition gifts), and willingness to donate during a blood donation social marketing campaign in November 2021 and November 2022. Data were analyzed in SPSS 20 using chi-square, ANOVA tests, and multiple regression models. The key findings indicate no significant associations between donor categories and incentives, but meal vouchers, free medical testing, refreshments, and recognition gifts were linked to self-regarding altruism. Additionally, neither incentives, altruism dimensions, nor their interaction predicted willingness to donate blood. These findings highlight the need for education-driven approaches to ensure a long-term commitment of blood donors, by integrating educational, sustainable curricular or extracurricular activities. Integrating blood donation awareness into formal education may cultivate a culture of civic responsibility, expanding the donor pool and strengthening the social sustainability of blood donation. Full article

Using the effective mass approximation and the finite difference method, we examined the linear, non-linear, and total optical absorption coefficients (OAC), as well as the relative refractive index coefficients (RIC) variations for an off-center shallow donor impurity in a 2D-curved electronic nanostructure subjected to external electric and magnetic fields. Our results reveal that the peak positions of the OAC and RIC are susceptible to the geometrical angles, the impurity position, and the strength of the applied electric and magnetic fields. In particular, the positions of the OAC and RIC peaks can be shifted towards blue or red by adjusting the geometric angle. In addition, the amplitudes of these peaks are influenced by the application of external fields and by the position of the impurity. This knowledge is essential for understanding and optimizing the optical characteristics of 2D-Curved nanostructure for advanced optoelectronic applications. Full article

A novel double-impurity doping process for silicon (Si) surfaces was developed, utilizing nanosecond-laser melting of an 11 nm thick gold (Au) top film and a Si wafer substrate in a laser plasma-activated liquid nitrogen (LN) environment. Scanning electron microscopy revealed a fluence- and exposure-independent surface micro-spike topography, while energy-dispersive X-ray spectroscopy identified minor Au (~0.05 at. %) and major N (~1–2 at. %) dopants localized within a 0.5 μm thick surface layer and the slight surface post-oxidation of the micro-relief (oxygen (O), ~1.5–2.5 at. %). X-ray photoelectron spectroscopy was used to identify the bound surface (SiN_x) and bulk doping chemical states of the introduced nitrogen (~10 at. %) and the metallic (<0.01 at. %) and cluster (<0.1 at. %) forms of the gold dopant, and it was used to evaluate their depth distributions, which were strongly affected by the competition between gold dopants due to their marginal local concentrations and the other more abundant dopants (N, O). In this study, 532 nm Raman microspectroscopy indicated a slight reduction in the crystalline order revealed in the second-order Si phonon band; the tensile stresses or nanoscale dimensions of the resolidified Si nano-crystallites envisioned by the main Si optical–phonon peak; a negligible a-Si abundance; and a low-wavenumber peak of the Si₃N₄ structure. In contrast, Fourier transform infrared (FT-IR) reflectance and transmittance studies exhibited only broad structureless absorption bands in the range of 600–5500 cm⁻¹ related to dopant absorption and light trapping in the surface micro-relief. The room-temperature electrical characteristics of the laser double-doped Si layer—a high carrier mobility of 1050 cm²/Vs and background carrier sheet concentration of ~2 × 10¹⁰ cm⁻² (bulk concentration ~10¹⁴–10¹⁵ cm⁻³)—are superior to previously reported parameters of similar nitrogen-implanted/annealed Si samples. This novel facile double-element laser-doping procedure paves the way to local maskless on-demand introductions of multiple intra-gap intermediate donor and acceptor bands in Si, providing related multi-wavelength IR photoconductivity for optoelectronic applications. Full article

Objective: Bone augmentation has become a significant practice in various areas of bone regeneration dentistry. This systematic review analyzes the research focused on evaluating bone substitute materials for the presence of contaminants. Methods: In June 2024, an extensive electronic search was conducted using renowned databases such as PubMed, Web of Science, and Scopus. Specific keywords employed in the search included ((bone AND (substitute) AND (remnants OR (purity)) OR ((graft AND tooth) AND (remnants OR purity)) OR ((graft AND dentin) AND (remnants OR purity)). The search adhered to the PRISMA protocol and the PICO framework. The review concentrated on the origin of bone substitute materials, the processing methods used for these materials, techniques for assessing purity, and types of contamination identified. A total of 594 articles were identified of which 22 met the criteria and were incorporated into the review. Results: Investigations into allogeneic and xenogeneic bone substitute materials have revealed that, despite manufacturers’ assurances of purity, some materials still contain contaminants. Sample analyses demonstrated the presence of donor cellular remains, cellular debris, intertrabecular fat, connective tissue, and collagen. Similarly, synthetically produced bone substitute materials (alloplastic materials) contained various impurities, such as polyvinyl alcohol (PVA), CaO phases, calcium-deficient HAp phases, oily substances containing carbon and silicone, cellulose derivatives, alpha-tricalcium phosphate (α-TCP), and heavy metals. Conclusions: Bone-derived and bone-like graft materials can contain various organic and inorganic impurities. Full article

To achieve n-type doping in diamond, extensive investigations employing first principles have been conducted on various models of phosphorus doping and boron–phosphorus co-doping. The primary focus of this study is to comprehensively analyze the formation energy, band structure, density of states, and ionization energy of these structures. It is observed that within a diamond structure solely composed of phosphorus atoms, the formation energy of an individual carbon atom is excessively high. However, the P-V complex substitutes 2 of the 216 carbon atoms, leading to the transformation of diamond from an insulator to a p-type semiconductor. Upon examining the P-B co-doped structure, it is revealed that the doped impurities exhibit a tendency to form more stable cluster configurations. As the separation between the individually doped atoms and the cluster impurity structure increases, the overall stability of the structure diminishes, consequently resulting in an elevation of the ionization energy. Examination of the electronic density of states indicates that the contribution of B atoms to the impurity level is negligible in the case of P-B doping. Full article

This paper focuses on the research and development of high-purity germanium (HPGe) crystals for detector fabrication, specifically targeting applications in rare-event physics searches. The primary objective was to produce large-scale germanium crystals weighing >1 kg with a controlled diameter of ∼10 cm and an impurity range of approximately ${10}^{10}$/cm${ }^3$. Ensuring structural integrity and excellent crystalline quality requires a thorough assessment of dislocation density, a critical aspect of the crystal development process. Dislocation density measurements play a crucial role in maximizing the sensitivity of HPGe detectors, and our findings confirmed that the dislocation density fell within acceptable ranges for detector fabrication. Additionally, this paper examines the segregation coefficient of various contaminants during the crystal development process. Comprehensive analysis of impurity segregation is essential for reducing contaminant quantities in the crystal lattice and customizing purification processes. This, in turn, minimizes undesired background noise, enhancing signal-to-noise ratios for rare-event physics searches and overall detector performance. The investigation included the segregation coefficients of three major acceptors and one donor in crystals grown at the University of South Dakota, providing valuable insights for optimizing crystal purity and detector efficiency. Full article

In a previous investigation, the authors proposed nitrogen as a possible candidate for exploiting the donor spin in silicon quantum devices. This system is characterized by a ground state deeper than the other group V impurities in silicon, offering less stringent requirements on the device temperature necessary to access the unionized state. The nitrogen donor is slightly displaced from the substitutional site, and upon heating, the system undergoes a motional transition. In the present article, we show the results from our investigation on the spin–relaxation times in ^natSi and ²⁸Si substrates and discuss the motional effects on relaxation. The stretched exponential relaxation observed is interpreted as a distribution of spin–lattice relaxation times, whose origin is also discussed. This information greatly contributes to the assessment of a nitrogen-doped silicon system as a potential candidate for quantum devices working at temperatures higher than those required for other group V donors in silicon. Full article

GaOOH, having a bandgap of 4.7–4.9 eV, can be regarded as one of several ultrawide-bandgap (UWBG) semiconductors, although it has so far mainly been used as a precursor material of Ga₂O₃. To examine the possibility of valence control and application in electronics, impurity levels in GaOOH are investigated using the first-principles density-functional theory calculation. The density values of the states of a supercell including an impurity atom are calculated. According to the results, among the group 14 elements, Si is expected to introduce a shallow donor level, i.e., a free electron is introduced. On the other hand, Ge and Sn introduce a localized state about 0.7 eV below the conduction band edge, and thus cannot act as an effective donor. While Mg and Ca can introduce a free hole and act as a shallow acceptor, Zn and Cd introduce acceptor levels away from the valence band. The transition metal elements (Fe, Co, Ni, Cu) are also considered, but none of them are expected to act as a shallow dopant. Thus, the results suggest that the carrier concentration can be controlled if Si is used for n-type doping, and Mg and Ca for p-type doping. Since GaOOH can be easily deposited using various chemical techniques at low temperatures, GaOOH will potentially be useful for transparent electronic devices. Full article