In this paper, the energetics of the formation of pyramidal epitaxial islands with different contact angles are investigated. Two approximations are considered: without and with the formation energy of additional edges taken into account. The possibility of energetically favorable change in island shape during growth is deduced for the first time. Methods for estimating the surface energy of the facets and the specific energy of formation of new edges at a known contact angle are proposed. The existence of an equilibrium value of the contact angle is demonstrated, at which the free energy reaches a minimum for given energetic, elastic, and morphological parameters of the system, thereby corresponding to the experimentally observed geometric shape of the island. The presented model can be applied to various epitaxial systems with different values of mismatch and energy parameters.
For dye-sensitized solar cells (DSSCs) to be commercialized, a highly active electrocatalyst with long stability and that is reasonably priced must be developed as a substitute for platinum (Pt). In this work, CdSe quantum dots (QDs) core–shell structures on multi-walled carbon nanotubes (MWCNTs) were used as the counter electrode (CE) for DSSCs, which were synthesized using a straightforward sol–gel process. The morphological analysis of the synthesized sample was performed using FESEM and TEM methods, which confirmed the successful incorporation of CdSe core–shell nanodots into the MWCNTs. The spectroscopic tools, such as Raman, FTIR, UV–Vis, and UV-DRS, further deduced the covering of CdSe QDs over MWCNTs to form nanohybrid structures. The electrochemical performance of MWCNT@CdSe CE was revealed superior properties and electrocatalytic activities as compared to MWCNTs CE for triiodide reduction. The MWCNT@CdSe CE achieved a power conversion efficiency of 4.1 %, significantly outperforming MWCNTs CE (2.8 %). This noticeable proficiency is related to the synergistic effects between CdSe QDs and MWCNTs, which enhance electron transfer to active sites, prevent agglomeration, and increase the availability of active sites. Consequently, the MWCNT@CdSe QDs emerges as an auspicious product for high-performance DSSCs.
SnO2 nanowires have attracted considerable interest because of their electrical and chemical properties, which are relevant to gas sensing and optoelectronic devices. In this work, Ti2SnC MAX phase was used as a precursor to develop a simple route for preparing SnO2 nanowires through high-temperature oxidation in air. The results indicate that the oxidation process is initiated by the temperature-dependent decomposition of Ti2SnC, with an onset temperature of approximately 500–600 ℃, followed by the release and subsequent oxidation of A-site Sn. Meanwhile, continuous decomposition of the layered Ti2SnC structure provided a persistent Sn source near the nanowire root. The local structural environment of the decomposing matrix may further influence the migration and distribution of Sn-containing species and contribute to one-dimensional growth. This work provides a simple strategy for preparing SnO2 nanowires and offers mechanistic insights into the behavior of A-site elements in MAX phases during high-temperature oxidation and their role in regulating one-dimensional oxide growth.
The structural quality of reactive rf magnetron sputtered AlN thin films is often limited by insufficient nitrogen incorporation, oxygen-related interfacial bonding, and the requirement for post-deposition annealing at ultra-high-temperatures. In this work, a systematic three-stage experimental approach was employed to investigate the combined influence of sapphire nitridation, reactive plasma chemistry, and post deposition annealing on the structural, chemical, morphological, and electrical properties of AlN thin films. In the first stage, AlN films were grown on two sets of samples- ‘With Nitridation’ and ‘Without Nitridation’ c-plane sapphire substrates under different argon /nitrogen- gas (N2) plasma concentrations. Treatment of sapphire substrates at 1000°C in N2 atmosphere modified the surface, as evidenced by reduced –OH related FTIR absorption, nitrogen detection by XPS, and improved surface wettability. Increasing the N2 fraction progressively in plasma, modified the AlN (002) diffraction intensity, altered the Al-N/Al-O bonding ratio, strengthened Raman response, and reduced surface roughness from 2.28 to 0.51 nm for ‘Without Nitridation’ sample and from 0.92 to 0.24 nm for nitridated substrates. Based on these results, selected sapphire ‘With Nitridation’ samples were subsequently annealed at 1100°C and 1200°C in N2 ambient. Post-deposition annealing resulted in narrowing of rocking-curve full width at half maximum from 0.82° to 0.40° for the sample grown with 40% N2 contribution in plasma and from 0.32° to 0.18° for the 70% N2 contributing plasma, indicating improved crystallographic ordering. The N2-70 sample when annealed at 1200°C exhibited the lowest leakage current (3.5 × 10-9 A at ± 20 V) and highest breakdown field (18 MV.cm−1). These results demonstrate that the combined strategy of sapphire nitridation, optimized N2 −rich plasma engineering, and post-deposition annealing at 1200°C provides an effective route for improving the quality of sputtered AlN thin films while substantially reducing the thermal budget compared to conventional ultra-high-temperature annealing approaches.
To achieve precise control over the growth interface of large-sized 4H-SiC single crystals, this study proposes an improved design incorporating a double-ring heater at the top of the crucible. A numerical model was established to investigate in depth the effects of key dimensional parameters of the double-ring top heater on the thermal field, crystal growth interface morphology, thermal stress, and dislocation density. The results show that when Dm/Dc = 0.56 and the ring spacing is 27 mm, the radial temperature gradient of the seed crystal decreases to −0.03 °C/cm with a slightly concave growth interface. Under these conditions, the thermal stress within the crystal is relatively low, and the dislocation density is the lowest among all dimensional configurations. On this basis, reducing the power of the double top heaters by 150 W causes the radial temperature gradient of the seed crystal to shift from negative to positive, reaching 0.06 °C/cm, and the growth interface to transform into an ideal, nearly flat, and slightly convex morphology. The interface morphology of the 8-inch SiC single crystal prepared in actual growth experiments is highly consistent with the simulation, validating the effectiveness of this scheme in enabling low-defect fabrication of large-sized 4H-SiC single crystals.
X-ray crystallography is an indispensable technique for high-resolution protein structure determination, although protein crystallization remains a significant bottleneck. Optical trapping-induced crystallization (OTIC), which utilizes a tightly focused laser beam to locally concentrate protein molecules via optical forces, has emerged as a promising strategy for promoting nucleation in supersaturated solutions. However, the potential effects of laser irradiation and solvent environments on the resulting protein structures have not been fully elucidated. In this study, we performed lysozyme crystallization under 1064-nm laser irradiation in both H2O and D2O solutions and conducted X-ray structure analysis to clarify the influence of optical forces and solvent-specific thermal effects, with the aim of evaluating the suitability of the resulting protein crystals for high-resolution structural biology. The results suggest that optical trapping induces local molecular accumulation at the focal spot, thereby promoting nucleation in both solvents. Notably, crystal formation was achieved even in H2O, despite its higher laser absorption and localized heating compared to D2O. X-ray diffraction analysis revealed that lysozyme crystals grown via OTIC in both solvents exhibited comparable quality to those grown under spontaneous conditions. The average crystal structures of all obtained crystals remained essentially identical, confirming that laser irradiation induces neither detectable conformational changes nor structural damage to the lysozyme protein within the crystal lattice. These results demonstrate that OTIC enables protein crystallization in physiologically relevant aqueous media without perturbing the molecular structure, supporting its potential as a noninvasive technique to overcome crystallization challenges in structural biology.
Mullite whiskers have received much attention in the last decade due to their outstanding-high temperature thermal stability, high mechanical strength and good thermal shock resistance. Conventionally preparing methods of mullite whiskers require fluorinated catalysts and long isothermal durations in the high temperature electric furnace are energy-intensive, time-consuming and environmentally unfriendly. In this study, an environmentally friendly ultrafast fabrication technique without catalysts was reported. Mullite whiskers were rapidly fabricated through direct Joule heating of graphite paper with water-absorbed mullite polycrystalline fibers as raw materials. The influence of water absorption and the temperature on the growth of whiskers were investigated. A H2O-assisted solid–liquid-solid growth mechanism of mullite whiskers by the hydrothermal catalysis reaction at high temperature was proposed. Compared with traditional preparation techniques of mullite whiskers with fluoride catalysts, the preparation of mullite whiskers by hydrothermal catalysis reaction and Joule heating is a novel, environmental and energy-saving method for the rapid preparation of whiskers. This study could also provide a new approach for the synthesis of analogous oxide whiskers
Two-dimensional Fe3GeTe2 (FGT) is a metallic van der Waals ferromagnet with strong perpendicular magnetic anisotropy and significant potential for spintronic applications. Here, epitaxial FGT thin films were grown on GaAs(111) with nominal Fe:Ge flux ratios from 3:1 to 5:1. A preferentially c-axis-oriented FGT phase remained dominant up to 4:1, whereas a secondary FeTe phase emerged at 4.5:1 and became pronounced at 5:1, indicating that excessive Fe promotes competing phase formation rather than stabilizing Fe-rich FGT. The representative FGT4 film exhibited homogeneous elemental distribution and well-defined out-of-plane crystalline alignment. All films showed predominantly metallic transport and ferromagnetic ordering, with transition temperatures of approximately 170–210 K. FGT4 also displayed clear magnetic hysteresis and a pronounced anomalous Hall response at low temperatures, both of which weakened and nearly vanished around 200 K. These results reveal a strong correlation between Fe:Ge flux ratio, phase evolution, electrical transport, and magnetic behavior.
N-polar GaN/Al0.9Ga0.1N/AlN heterostructures were fabricated using metal–organic vapor phase epitaxy to investigate the effect of the F-value of the carrier gas defined by the H2/(H2 + N2) ratio on GaN channel performance. Five samples were prepared with varying F-values during GaN growth, and their structural and electrical properties were systematically evaluated. The results showed that GaN growth did not occur at an F-value of 0. The lowest sheet resistance and highest carrier mobility were obtained at an F-value of 0.46, and further increase in F-value beyond this point led to a decrease in both the growth rate and carrier mobility and an increase in sheet resistance. Surface roughness remained consistently low across all samples, indicating successful growth of laterally continuous GaN layers, while impurity incorporation may have contributed to the differences in electrical properties. Temperature-dependent mobility measurement and secondary ion mass spectrometry result suggested that lower impurity concentrations were achieved at the optimal F-value.
