查看更多>>摘要：? 2022 Elsevier B.V.Transparent conducting materials (TCMs) provide low cost and effective solution for the modern optoelectronics. However, simultaneous high electrical conductivity and optical transparency in the near-infrared (NIR) and middle-infrared (MIR) spectral ranges remain challenging. This study proposes thin film of the semimetal calcium disilicide (CaSi2) with hR6 polymorph modification to fill this niche. Investigation of the electrical, magnetoresistance and magnetic properties shed light on its semimetal behavior. CaSi2 film grown on Si substrate demonstrates competitive electrical and optical properties from the NIR to MIR ranges compared to commonly used TCMs reaching maximum transmittance of 47% at an important telecommunication wavelength of 1550 nm in addition to the low sheet resistance of 6.6 Ω/sq, which results in high TCM figure of merit of 0.2 Ω?1. Moreover, demonstrated for the first time partial optical transparency of the CaSi2 in the visible range could significantly heighten its applicability for Si-based optoelectronics.
查看更多>>摘要：? 2022 Elsevier B.V.This study reports the synthesis (by the co-precipitation method) and characterization of the PrAsO4 polycrystals. The crystal structure has been determined using the Rietveld method. Two validation methods were used to confirm the structural model: the bond valence sum (BVS) and the charge distribution (CHARDI). A constructive description of the structure was made, starting with the connection modes of the coordination polyhedron. The electronic structure of the compound, determined by the DFT method, shows a direct band gap semiconductor material with a calculated energy of 2.21 eV. This compares favorably with the experimental band gap energy value of about 2.52 eV. The microstructural study showed grain and crystalline sizes of about 500 and 17 nm, respectively. TGA analysis was used to study the thermal stability of the compound, which showed a plateau in the 550 ? 650 °C range due to the oxidation of Pr3+ to Pr4+. This oxidation was confirmed by the emission spectra of Pr3+ obtained from the photoluminescence study. The electrical study in the 440–600 °C temperature range shows that the PrAsO4 is a bad ionic conductor with a value of about 10?8 Scm?1. The dielectric study showed a value of 1400 for the dielectric constant ε, and the dipolar polarization dominated the polarization phenomenon. About 10?6 s was obtained for the relaxation time (τr)
查看更多>>摘要：? 2022 Elsevier B.V.In this study, chlorine (Cl) treatment was carried out on p-AlGaN to enhance the performance of ultraviolet-C light emitting diodes (UVC LEDs) by modifying ITO work function and hence reducing the contact resistance of ITO/Al reflector. The Cl-treated UVC LEDs exhibit the forward voltage of 6.88 V at 20 mA, whereas the reference samples show 7.50 V. The light output power and relative wall plug efficiency (WPE) of the Cl-treated UVC LEDs are enhanced by 17.1% at 500 mW and 19.5% at 100 mA, respectively, as compared to the reference. Additionally, the Cl-treated LEDs also display reduction in both the leakage current and ideality factor. Further, the photoluminescence (PL) intensity of AlGaN micro-disks is also enhanced by the Cl-treatment. X-ray photoemission spectroscopy (XPS) results indicate the formation of Cl-ITO at the ITO/p-AlGaN interface and the passivation of the surface states of AlGaN by Cl radicals. Based on the XPS results, a possible mechanism for the improved performance of Cl-treated UVC AlGaN-based LEDs is described and discussed.
查看更多>>摘要：? 2022 Elsevier B.V.The initial intensity and afterglow duration of existing long-wavelength persistent phosphors are insufficient for practical applications. Herein, the afterglow of orange-emitting Sr3Al2O5Cl2:Eu2+, Dy3+ phosphors are enhanced by co-doping with Mg2+ using the conventional solid-state reaction. Rietveld refinement for the prepared phosphor revealed that all Eu2+ cations were placed on the Sr2+ sites, whereas Dy3+ occupancy in the lattice was improved by incorporating Mg2+. All phosphor samples with different Mg2+ concentrations emit 609-nm-centred orange luminescence caused by the 5d→4f transition of Eu2+. The photoluminescence was significantly enhanced with the increase in the Mg2+ doping due to the increased amount of divalent Eu2+ in the samples, as confirmed by the X-ray photoelectron spectroscopy investigation. Incorporating Mg2+ also enhanced the afterglow performance by creating suitable electron traps in the phosphor. The afterglow profiles were simulated by a double exponential decay model, and the results revealed that significant improvement in the afterglow lifetime was achieved for the 0.3 Mg2+-doped phosphors. Also, Mg2+ introduction resulted in a deeper trap level (～0.72 eV) and an increased trap concentration. Consequently, the Mg2+-doped exhibits brighter initial photoluminescence and longer afterglow.
查看更多>>摘要：? 2022 Elsevier B.V.Amorphous chalcogenides, particularly Ge2Sb2Te5 (GST) based alloys, are well known for their non-volatile phase-change random access memory applications (PCRAM). In this work, the phase change properties of Ge2Sb2?xAsxTe5 (x = 0, 0.5, 1.0, 2.0) thin films deposited by thermal evaporation are reported. The As substituted samples crystallize at higher temperatures compared to parent GST. During the phase change for x > 1.0, a direct transition from amorphous to the stable hexagonal structure has been observed. A distinct two-step transition in Sb rich samples and a single step transition for As rich samples are observed in R-T measurements with a high contrast in electrical resistivity. The transition is becoming sharper and sharper with increasing As substitution. A composition-dependent Metal-Insulator Transition (MIT) is also observed in these samples. Compared to GST, As substituted samples show an increase in crystallization temperature and activation energy for crystallization. For GST, the 10-year data retention temperature is 67 °C, and with complete As substitution, it increases to 169 °C, with a significant rise of 102 °C in the data retention temperature. High thermal stability, sharp transition and increased data retention of As substituted Ge-Sb-Te suggest that they are promising candidates for PCRAM applications.
查看更多>>摘要：? 2022 Elsevier B.V.The photocatalytic efficiency is greatly limited due to the narrow light response range and the low charge separation of MoS2. The 1 T @ 2 H phase MoS2 nanoflowers with controllable fabrication of defect levels were successfully prepared with excellent full-spectrum response by controlling various amounts of excesses thiourea as a sulfur source. Meanwhile, the 1 T @ 2 H MoS2-S4 sample with the optimal S defect level showed excellent photocatalytic degradation activity under UV-Vis and NIR light, with a degradation rate of 95.0% and 99.1% respectively. The EDS, EPR and UV-Vis-NIR absorption results show that the S defects has a significant effect on expanding the light absorption response range and enhancing the light absorption capacity. Compared with 1 T @ 2 H MoS2, the light absorption capacity of 1 T @ 2 H MoS2-S4 increased by 2.2 times due to the introduction of S vacancy. Ulteriorly, the introduction of 1 T phase has an excellent optimization effect on the photogenerated charge transmission path due to its own higher electron concentration and conductivity. Therefore, defect engineering and phase engineering are of great significance to the investigate of full-spectrum photocatalytic materials.
查看更多>>摘要：? 2022 Elsevier B.V.Successful formation of the absorber layer is regarded as the most important step when fabricating Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells. A high-quality CZTSSe absorber layer can enhance the parameters of thin-film solar cells. We concentrated on analyzing the CZTSSe surface, which is directly related to forming the p-n junction. We made changes to the surface of the absorber layer by controlling the Cu content via the sputtering time. When the Cu content was insufficient, secondary phases and agglomerated metallic precursors appeared on top of the CZTSSe absorber layer. We analyzed the defects and secondary phases that could adversely affect the formation of the p-n junction by using energy-dispersive X-ray spectroscopy, X-ray diffractometer, and Raman spectroscopy. We also measured and calculated the electric parameters of CZTSSe thin-film solar cells to investigate the CZTSSe/CdS interface. The performance of a CZTSSe thin-film solar cell was enhanced and stabilized by optimizing the concentration of Cu in the absorber layer. Our results indicate the importance of the Cu ratio on the surface of the CZTSSe absorber layer as it affects the p-n junction in the CZTSSe thin-film solar cell. The highest photoconversion efficiency was 9.4% when the Cu component was optimized.
查看更多>>摘要：? 2022 Elsevier B.V.A series of n-type polycrystalline SnSe0.95 - xmol% NdCl3 samples were synthesized using the melting method combined with spark plasma sintering (SPS). Doping NdCl3 significantly improves the electrical conductivity and suppresses the deterioration of the Seebeck coefficient after thermal excitation, which leads to significantly higher power factors than SnSe0.95. In addition, excessive doping of NdCl3 not only introduces a large number of point defects but also produces NdCl3 precipitates, which largely enhances the phonon scattering and significantly reduces the thermal conductivity. As a result, a maximum ZT value of 1.3 at 773 K has been obtained in SnSe0.95 - 1.5 mol% NdCl3 sample, indicating that the doping of rare earth halides can effectively enhance the thermoelectric performance of n-type SnSe0.95 by simultaneously improving the power factor and reducing the lattice thermal conductivity.
查看更多>>摘要：? 2022 Elsevier B.V.The evolution behavior of α lamellae and evolution relationship between α lamellae and β phase in TC17 alloy during isothermal heating and subsequent compression were investigated. The results show that the α/β interface of TC17 alloy is made up of stable terrace plane and movable ledge plane. The ledge plane migrates along the length direction of α lamellae during isothermal heating, which results in rapid decrease of length and slow decrease of thickness of α lamellae. During compression, the continuous dynamic recrystallization (CDRX) are the main evolution mechanism of α and β phases. The slip systems of β phase are easily activated and the slip in β phase (i.e. (110)[1?11]) will promote the slip in α phase (i.e. (0001)[112?0]) at the initial stage of compression. Thus the CDRX of β phase is preferentially initiated by more activated slip and it will promotes the CDRX of α phase, then the HABs are formed in α lamellae. Meanwhile, the β stabilized elements Cr and Mo diffuse into the α/α boundaries in a short-time deformation. The α→β phase transformation is promoted by the enrichment of Cr and Mo elements and finally the α lamellae are separated with further compression.
查看更多>>摘要：? 2022 Elsevier B.V.Magnetic Tunnel Junctions (MTJ) are employed in a range of technologies such as data storage, sensing, and so on due to their compact nature and high field sensitivity. In magnetic films and structures, ion irradiation is capable of modifying the crystal structure, phases and magnetic properties including magnetic anisotropy, which enables tunability of the sensing axis of devices such as MTJ sensors. Irradiation can also adjust the magnetic properties of specific layers without affecting the others, making it one of the most effective methods to post-process multi-layered devices. In this article we review the literature of light ion irradiation effects on MTJs and their component materials, focusing on the effects most relevant to MTJ sensors, such as magnetic anisotropy and magnetization. We first briefly review the effects of the ion-solid interaction, then discuss the causes of magnetic anisotropy, and lastly, we summarize the state of the field of ion-induced modification of magnetic properties in ferromagnetic thin films, antiferromagnetic structures, and MTJs.
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