[en] In this paper, we studied the roughening of SiGeC surface revealed by in situ reflection high energy electron diffraction (RHEED) measurements, that happens during ultra-high vacuum chemical vapor deposition (UHV-CVD) growth under certain growth conditions. A high growth rate and a low temperature are found to be favorable for smooth surfaces. Roughening is accompanied by a dramatic decrease of the substitutional C content and, further, stacking faults develop within the epilayer. According to these observations, we proposed a model of surface roughening based on the formation of carboneous complexes on the film surface and a way to maximize substitutional C incorporation in very thin layers by using RHEED as a probe for monitoring the development of lattice defects. By this means, more than 2% of substitutional C atoms can be incorporated in 5 nm Si_1-yC_y films (assuming Vegard's law)

[en] Highlights: • Novel LiLaSiO₄:βTm³⁺,γTb³⁺ phosphors were prepared by microwave-assisted solid-phase reaction method. • LiLaSiO₄:βTm³⁺,γTb³⁺ is a blue-green color tunable phosphor. • The energy transfer mechanism in LiLaSiO₄:βTm³⁺,γTb³⁺ was demonstrated to be dipole-quadrupole interaction. • In LiLaSiO₄:βTm³⁺,γTb³⁺ phosphors, the energy transfer efficiency is 82.78% and the quantum yield is 39.8%. • LiLaSiO₄:βTm³⁺,γTb³⁺ phosphors have excellent temperature stability. In this paper, a series of color-tunable LiLaSiO₄:βTm³⁺, γTb³⁺ phosphors were quickly synthesized by microwave-assisted solid-phase reaction method. Under proper ultraviolet light excitation, Tm³⁺ ions produce ¹D₂→³F₄ energy level transition and emit blue light, and the concentration quenching point is β = 1.5%mol. The color coordinates are (0.139, 0.046), compared with commercial blue phosphors. It has a higher color purity and color saturation. The Tb³⁺ ions produce ⁵D₄→⁷F₅ energy level transition and emit green light, and the color coordinate is (0.324, 0.508). In Tm3+-Tb3+ double-doped LiLaSiO₄ phosphors, the concentration quenching point of Tb³⁺ ions is γ = 6%mol. By characterizing the fluorescence lifetime and the luminous intensity of the Tm³⁺-Tb³⁺ co-doped LiLaSiO₄ phosphor, it is verified that there is an energy transfer of Tm³⁺→Tb³⁺ in the phosphor. The energy transfer efficiency and energy transfer mechanism have been investigated in detail. From the researched luminous properties, it is found that Tm³⁺-Tb³⁺ co-doped LiLaSiO₄ phosphor is an ideal material for light-emitting diodes, luminescent materials and fluorescent display devices.

[en] GaN-based light-emitting diodes (LEDs) on Si substrates are promising to replace conventional lamps due to the advantages of energy-saving and low-cost of LEDs grown on large-size Si substrates. However, high-density dislocations and cracks of GaN epitaxial films are usually formed that limit the further development and application of GaN-based LEDs. To circumvent the issues, the step-graded AlGaN buffer layers are carefully designed to grow GaN epitaxial films on Si substrates. The mechanisms of dislocations and stresses for GaN epitaxial films controlled by step-graded AlGaN buffer layers are also investigated by analyzing dislocations evolution and stresses relaxation at the hetero-interfaces. Afterwards, 3.0 μm-thick high-quality GaN epitaxial films grown on Si substrates have been obtained, and high-quality GaN-based LED wafers are obtained accordingly with small full-width at half-maximums (FWHMs) for GaN(0002) and GaN(10–12) X-ray rocking curves of 272 and 297 arcsec, respectively. The corresponding vertical-structure LED chips reveal high-performance with a high light output power of 592 mW and a small working voltage of 2.77 V @ 456 nm, at a current of 350 mA. This work provides an effective approach for the growth of high-quality crack-free GaN epitaxial films on Si substrates for the fabrication of high-performance GaN-based devices.

[en] Self-powered photodetectors have paved the way for electronic applications in fields such as civilian communication, infrared mapping, and industrial automatic control. However, most self-powered photodetectors have faced photoresponse-speed and device-scale bottlenecks. Herein, a novel, self-powered detector with an ultrafast response speed based on a core-shell InN/In${}_2$S${}_3$ nanorod array is proposed. A wafer-scale InN/In${}_2$S${}_3$ nanorod array with good homogeneity is synthesized on Si substrates via a simple two-step method involving molecular beam epitaxy and chemical vapor deposition. The photodetector device exhibits excellent self-powered properties and a high current on/off ratio of 5 × 10${}^3$. Further analyses determined that the device have an excellent photovoltaic responsivity and detectivity of 140 mA·W${}^{-<!--\; ???\; -->1}$ and 4.0 × 10${}^{10}$ Jones, respectively (0 V). Impressively, the device exhibits an ultrafast photoresponse with a rise/fall time of 22/32 µs. The self-powered InN/In${}_2$S${}_3$ photodetector with an ultrafast response speed shows superior potential for electronic applications. The core-shell nanostructure hybrid heterojunction introduces a novel idea for wafer-scale nano-photodetectors. (© 2021 Wiley‐VCH GmbH)

[en] Highlights: • Hydrothermal treatment of biomass with H₃PO₄ produced a novel P-enriched hydrochar. • Weight yield of the P-enriched hydrochar was more than doubled with >20 wt%. • P-enriched hydrochar showed excellent ability to stabilize Pb and reduce its leaching in soils. One-step synthesis of multifunctional materials using biomass waste for environmental remediation is a current research hotspot. In this study, a novel P-enriched hydrochar was obtained by co-hydrothermal treatment of biomass (bamboo or hickory) with concentrated H₃PO₄ (biomass: H₃PO₄ = 1:4) at 200 °C for 7 h. The characteristics of the P-enriched hydrochar were determined and its effect on the stabilization of Pb in soils was investigated. Compared to pristine hydrochar, the weight yield of the P-enriched hydrochar was greater (by over 2 times). This was due to the enrichment of P (over 20% by weight), as the C, N, and H weight content was reduced. Moreover, the aromaticity, thermal stability, and surface functionality of P-enriched hydrochar were all higher than that of pristine hydrochar. Addition of the pristine hydrochar to a simulated 1300 mg·kg⁻¹ Pb-contaminated soil at 3% (w/w) resulted in a 20%–40% reduction in leached Pb only after 4 weeks, compared to the control without hydrochar amendment. However, addition of the P-enriched hydrochar to the spiked Pb-contaminated soil reduced Pb leaching by about 60% after only 1 week and about 90% after 3 weeks. Besides, using a real Pb-contaminated soil (149,000 mg·kg⁻¹ Pb), P-enriched hydrochar addition at 5% (w/w) resulted in a 100% decrease in Pb leaching in the first week and maintained leached Pb levels at −1, meeting U.S.-E.P.A. standards. Thus, P-enriched hydrochar stabilized Pb in both simulated and real Pb-contaminated soil quickly and efficiently. Hence, the potential of one-step co-hydrothermal carbonization of biomass with H₃PO₄ to produce a novel and sustainable P-enriched hydrochar with properties suitable for environmental remediation of cationic metals.