Growth Temperature Research Articles

(Invited) Scalable 2-Step Fabrication of Core-Shell GaN Micropillars

Group III-Nitride three-dimensional structures have gained substantial interest for application in optoelectronic, energy, and sensor devices with non-planar geometries [1-4]. The benefits of 3D structures, such as GaN-based nano-/micro-rods, compared to planar films include large surface area, high structural quality, non-polar-surface utilization, small footprint, mechanical flexibility, and enhanced light absorption/extraction efficiency. To advance the technology of non-planar III-Nitride semiconductors, it is necessary to optimize and scale up the fabrication of such structures with controlled geometries and desired electronic and optical properties. Here, we report the fabrication of wafer-scale periodic arrays of vertically aligned GaN core-shell micropillars using a combination of top-down etch and epitaxial overgrowth.The two-step process consists of inductively coupled plasma (ICP) etching of lithographically patterned GaN-on-Si substrate to produce an array of micropillars followed by selective growth of GaN shells over these pillars using Hydride Vapor Phase Epitaxy (HVPE). The most significant aspect of the study is the demonstration of the sidewall facet control in the shells, ranging from truncated hexagonal pyramids with the (1-101) semi-polar sidewalls to hexagonal prisms with the (1-100) non-polar sidewalls, by employing a post-ICP wet chemical etch and by tuning the HVPE growth temperature. Optimization of both ICP etching and epitaxial overgrowth reduced dislocation density in the GaN shells, thus enhancing the transport and optical characteristics of these device platforms. Photo- and cathodoluminescence showed a substantial reduction of parasitic yellow luminescence as well as strain-relaxation in the core-shell structures, supported by Raman scattering, electron-backscatter-diffraction (EBSD), and X-ray-diffraction measurements. Transmission electron microscopy revealed improved crystal quality with reduced dislocation density in the epitaxially grown shells. This work demonstrates the feasibility of selective epitaxy on micro/nano-engineered 3D templates for realizing high-quality GaN-on-Si devices such as LEDs and p-i-n photodetectors.

Graphene-skinned alumina fiber fabricated through metalloid-catalytic graphene CVD growth on nonmetallic substrate and its mass production

Graphene growth on widely used dielectrics/insulators via chemical vapor deposition (CVD) is a strategy toward transfer-free applications of CVD graphene for the realization of advanced composite materials. Here, we develop graphene-skinned alumina fibers/fabrics (GAFs/GAFFs) through graphene CVD growth on commercial alumina fibers/fabrics (AFs/AFFs). We reveal a vapor-surface-solid growth model on a non-metallic substrate, which is distinct from the well-established vapor-solid model on conventional non-catalytic non-metallic substrates, but bears a closer resemblance to that observed on catalytic metallic substrates. The metalloid-catalytic growth of graphene on AFs/AFFs resulted in reduced growth temperature (~200 °C lower) and accelerated growth rate (~3.4 times faster) compared to that obtained on a representative non-metallic counterpart, quartz fiber. The fabricated GAFF features a wide-range tunable electrical conductivity (1-15000 Ω sq−1), high tensile strength (>1.5 GPa), lightweight, flexibility, and a hierarchical macrostructure. These attributes are inherited from both graphene and AFF, making GAFF promising for various applications including electrical heating and electromagnetic interference shielding. Beyond laboratory level preparation, the stable mass production of large-scale GAFF has been achieved through a home-made roll-to-roll system with capacity of 468-93600 m2/year depending on product specifications, providing foundations for the subsequent industrialization of this material, enabling its widespread adoption in various industries.

Intrinsic Out-Of-Plane and In-Plane Ferroelectricity in 2D AgCrS2 with High Curie Temperature.

2D ferroelectric materials have attracted extensive research interest due to potential applications in nonvolatile memory, nanoelectronics and optoelectronics. However, the available 2D ferroelectric materials are scarce and most of them are limited by the uncontrollable preparation. Herein, a novel 2D ferroelectric material AgCrS2 is reported that are controllably synthesized in large-scale via salt-assist chemical vapor deposition growth. By tuning the growth temperature from 800 to 900°C, the thickness of AgCrS2 nanosheets can be precisely modulated from 2.1 to 40nm. Structural and nonlinear optical characterizations demonstrate that AgCrS2 nanosheet crystallizes in a non-centrosymmetric structure with high crystallinity and remarkable air stability. As a result, AgCrS2 of various thicknesses display robust ferroelectric polarization in both in-plane (IP) and out-of-plane (OOP)directions with strong intercorrelation and high ferroelectric phase transition temperature (682 K). Theoretical calculations suggest that the ferroelectricity in AgCrS2 originates from the displacement of Ag atoms in AgS4 tetrahedrons, which changes the dipole moment alignment. Moreover, ferroelectric switching is demonstrated in both lateral and vertical AgCrS2 devices, which exhibit exotic nonvolatile memory behavior with distinct high and low resistance states. This study expands the scope of 2D ferroelectric materials and facilitates the ferroelectric-based nonvolatile memory applications.

Photosynthetic capacity in middle-aged larch and spruce acclimates independently to experimental warming and elevated CO2.

Photosynthetic acclimation to both warming and elevated CO2 of boreal trees remains a key uncertainty in modelling the response of photosynthesis to future climates. We investigated the impact of increased growth temperature and elevated CO2 on photosynthetic capacity (Vcmax and Jmax) in mature trees of two North American boreal conifers, tamarack and black spruce. We show that Vcmax and Jmax at a standard temperature of 25°C did not change with warming, while Vcmax and Jmax at their thermal optima (Topt) and growth temperature (Tg) increased. Moreover, Vcmax and Jmax at either 25°C, Topt or Tg decreased with elevated CO2. The Jmax/Vcmax ratio decreased with warming when assessed at both Topt and Tg but did not significantly vary at 25°C. The Jmax/Vcmax increased with elevated CO2 at either reference temperature. We found no significant interaction between warming and elevated CO2 on all traits. If this lack of interaction between warming and elevated CO2 on the Vcmax, Jmax and Jmax/Vcmax ratio is a general trend, it would have significant implications for improving photosynthesis representation in vegetation models. However, future research is required to investigate the widespread nature of this response in a larger number of species and biomes.

Correlation between photoluminescence and radiative defects in silicon oxycarbide films due to the growth temperature effect

In this work, the effect of growth temperature (678–988 °C) on silicon oxycarbide (SiCxOy) samples obtained by hot filament chemical vapor deposition (HFCVD) is reported. The samples were deposited on silicon (Si) n-type (100) and quartz substrates for optical and structural studies. At a lower temperature (678 °C), silicon oxycarbide powders were formed on Si substrates due to the homogeneous reaction occurring in the gas phase. However, for temperatures between 804 and 988 °C, silicon oxycarbide films were formed on Si substrates. By changing the temperature from 678 to 988 °C, both carbon (C) concentration (21.2–17.7 wt.%) and the relative percentage of Si–C bond density (%RtSi-C = 11.34–3.47 %) decreased, as demonstrated by EDS and FTIR measurements, respectively. On the other hand, the content of relative Si–O–Si bonds located around 1060 cm−1 remained dominant in all cases, resulting in SiCxOy films with an amorphous SiOx-type structure. These films exhibited strong photoluminescence (PL) centered in the blue region (∼3 eV), where Si–NOVS radiative centers were preferentially responsible for PL emission. At a lower temperature (678 °C), the PL intensity decreased. The determination of optical bandgap energy (Eopt) using Tauc Plots coincided with the emission due to luminescent centers (∼3 and ∼2.7 eV) observed in PL, indicating that the radiative transitions were due to defects. The AFM measurements showed an increase in roughness from 5.01 to 16.20 nm as the growth temperature decreased, as expected according to SEM measurements.

Intraspecific variation in photosynthetic thermal acclimation in Fagus crenata seedlings from two populations growing at different elevations in northern Japan.

Plants can acclimate their photosynthesis to growth temperature, but the contribution of local adaptation to intraspecific variation in thermal acclimation of photosynthesis is not fully understood. Here, we experimentally investigated the photosynthetic thermal acclimation in Fagus crenata Blume seedlings from two populations growing at different elevations and temperature regimes (low- and high-elevation sites) in northern Japan. We acclimated seedlings for 14 to 23days at daytime temperatures of either 22°C (control) or 27°C (warm treatment) and obtained photosynthetic temperature-response curves in the range of 19 to 32°C. The optimum temperature of photosynthesis (Topt) was ~0.6°C higher in seedlings acclimated at 27°C than in those acclimated at 22°C, and it was significantly lower in seedlings with higher stomatal sensitivity to leaf-to-air vapor pressure deficit than in those with lower sensitivity. The effects of warm treatment, population and treatment-population interaction on Topt were not significant in the two-way analysis of variance, but the effect of treatment became significant when stomatal sensitivity to leaf-to-air vapor pressure deficit was included as a covariate in the model. Structural equation modeling indicated that seedlings with lower root biomass had lower Topt because of the high stomatal sensitivity to leaf-to-air vapor pressure deficit. Structural equation modelling also indicated that the way of shifting the Topt differed between the two populations: seedlings from a high-elevation site depended on decreasing photosynthetic rates at low temperatures for the increase in Topt but seedlings from a low-elevation site did not. We suggest that the difference in thermal acclimation of photosynthesis between the two populations may reflect adaptation to different climate regimes and that belowground traits should be considered when investigating thermal acclimation capacity, especially in seedlings.

Development of Self-Doped Monolayered 2D MoS2 for Enhanced Photoresponsivity.

Transition metal dichalcogenides (TMDs) exist in two distinct phases: the thermodynamically stable trigonal prismatic (2H) and the metastable octahedral (1T) phase. Phase engineering has emerged as a potent technique for enhancing the performance of TMDs in optoelectronics applications. Nevertheless, understanding the mechanism of phase transition in TMDs and achieving large-area synthesis of phase-controlled TMDs continue to pose significant challenges. This study presents the synthesis of large-area monolayered 2H-MoS2 and mixed-phase 1T/2H-MoS2 by controlling the growth temperature in the chemical vapor deposition (CVD) method without use of a catalyst. The field-effect transistors (FETs) devices fabricated with 1T/2H-MoS2 mixed-phase show an on/off ratio of 107. Photo response devices fabricated with 1T/2H-MoS2 mixed-phase show ≈55 times enhancement in responsivity (from 0.32 to 17.4AW-1) and 102 times increase in the detectivity (from 4.1×1010 to 2.48×1012cmHzW-1) compare to 2H-MoS2. Introducing the metallic 1T phase within the 2H phase contributes additional carriers to the material, which prevents the electron-hole recombination and thereby increases the carrier density in the 1T/2H-MoS2 mixed-phase in comparison to 2H-MoS2. This work provides insights into the self-doping effects of 1T phase in 2H MoS2, enabling the tuning of 2D TMDs properties for optoelectronic applications.

Effect of linear antenna chemical vapor deposition process parameters on the growth of nanocrystalline diamond-on-GaN films

The present work will systematically study the effect of different linear antenna microwave plasma enhanced chemical vapor deposition (LACVD) processing parameters on the optimal deposition of the diamond films. The low pressure and low temperatures of LACVD growth conditions is expected to deposit diamond films on otherwise reactive gallium nitride (GaN) surfaces, without any intermediate nitride buffer layer. First, the distances between the quartz tube and the samples put on the stage are varied (3–15 cm), which has a direct impact on the substrate temperature (415°–300 °C). Thereafter, the microwave input power was also altered (1.5–2.8 kW) to attain low substrate temperatures. It was found that 300 °C is the temperature limit, which can be attained by heating only with microwave plasma when the substrates are kept farthest (15 cm) away from the liner antenna quartz tube. An additional heater was used under the stage for rapidly achieving such minimum substrate temperature of 300 °C. Substrate heater was used for efficient growth of the diamond phase while using pulse mode frequency of microwave power input for optimization of the diamond films. The microstructure (plate-like and cauliflower-like) of the deposited nanocrystalline diamond (NCD) films and the cross-sectional images for thickness measurements was observed under the scanning electron microscope and the elemental analysis of the film surfaces was done by electron diffraction spectroscopy. Moreover, the diamond film quality and crystallinity were evaluated by Raman spectroscopy with 488 nm laser light. Diamond-on-GaN film results were compared with conventional Si substrate. Different LACVD reactor parameters like, antenna to stage distances, microwave input power in continuous wave mode, and growth temperatures have significant impacts on the grown films, both in terms of their quality and microstructure. It was found that the optimum deposition of nanocrystalline diamond film on GaN substrates without its surface etching was possible, under pulse mode (20 kHz, 45 % duty cycle) with 2 kW average input microwave power.

QTL mapping and candidate gene identification for lower temperature tolerance and growth traits using whole genome re-sequencing in Argopecten scallops

Lower temperature tolerance (LTT) and growth traits are vital to the success of overwintering scallop farming in the North China Sea. Bohai Red, a novel selected scallop strain is the main aquaculture species in this region. However, its poor LTT hinders its growth. To improve these traits, the larger Bohai Red scallop was crossed with the smaller bay scallop (A. irradians irradians) which tolerates low temperatures. The full-sib F1 hybrids and the whole-genome resequencing (WGR) method were used to construct a high-density genetic linkage map comprising 5925 single nucleotide polymorphisms (SNPs). The consensus linkage map consisted of 16 linkage groups spanning 1343.46 cM with an average distance of 0.23 cM. Based on this genetic linkage map, 42 potentially significant quantitative trait loci (QTLs) for LTT and growth were detected in eight different linkage groups (LGs) explaining 9.2–18.6% of the phenotypic variation. LG11 may regulate both LTT and growth as 20 QTLs were localized there. Eighteen candidate genes were identified, including 2 (SCARF1, SLC28A3) for LTT and 16 for the growth-related traits. To the best of our knowledge, the present work is one of the first to fine-map the LTT and growth-related QTLs in a genetic linkage map for hybrid Argopecten spp. scallops.

High-throughput functional analysis provides novel insight into type VII secretion in Staphylococcus aureus.

Successful colonization by the opportunistic pathogen Staphylococcus aureus depends on its ability to interact with other microorganisms. Staphylococcus aureus strains harbour a T7b subtype of type VII secretion system (T7SSb), a protein secretion system found in a wide variety of Bacillota, which functions in bacterial antagonism and virulence. Assessment of T7SSb activity in S. aureus has been hampered by low secretion activity under laboratory conditions and the lack of a sensitive assay to measure secretion. Here, we have utilized NanoLuc binary technology to develop a simple assay to monitor protein secretion via detection of bioluminescence. Fusion of the 11 amino acid NanoLuc fragment to the conserved substrate EsxA permits its extracellular detection upon supplementation with the large NanoLuc fragment and luciferase substrate. Following miniaturization of the assay to 384-well format, we use high-throughput analysis to demonstrate that T7SSb-dependent protein secretion differs across strains and growth temperature. We further show that the same assay can be used to monitor secretion of the surface-associated toxin substrate TspA. Using this approach, we identify three conserved accessory proteins required to mediate TspA secretion. Co-purification experiments confirm that all three proteins form a complex with TspA.

Ethylene-mediated resistance to bacterial canker in kiwifruit is suppressed by cool temperature

Ambient temperature affects the occurrence and prevalence of plant disease. Most bacterial diseases are damaging at high temperatures. However, kiwifruit bacterial canker caused by Pseudomonas syringae pv. actinidiae (Psa) has been found to be prevalent at relatively cool temperatures, and it is unclear how ambient temperature affects the development of kiwifruit bacterial canker. In this study, basal resistance to Psa was suppressed in kiwifruit at cool growth temperature (16 °C) compared with at normal temperature (24 °C). In addition, RNA sequence analysis and ethylene content assessment indicated that ethylene modulated kiwifruit resistance to Psa at normal growth temperature and that cool temperature inhibited ethylene accumulation and Psa-induced activation of the ethylene signaling pathway in kiwifruit. Virus-mediated silencing of the kiwifruit ethylene signaling gene AcEIN2 suppressed kiwifruit resistance to Psa at normal growth temperature. Exogenous application of ethylene inhibitor 1-methylcyclopropene eliminated the difference in kiwifruit resistance to Psa at 16 and 24 °C. Exogenous application of ethylene analogues ethephon induced resistance to Psa in kiwifruit. In conclusion, cool temperatures impair basal resistance to Psa by reducing the activation of ethylene biosynthesis and signaling in kiwifruit. The results provide clues for new strategies to control plant diseases in a context of global environmental change.

Magneto-optical Kerr effect of noncollinear antiferromagnetic Mn3Ir films

We present the magneto-optical Kerr effect (MOKE) of (111)-oriented antiferromagnetic L12-Mn3Ir films epitaxially grown on MgO (111) substrates. We observed that the amplitude and sign of the polar MOKE change depending on the growth temperature. The Mn3Ir films grown at 800 and 600 °C have rotation angles of 41.6 and −4.6 mdeg and ellipticity angles of −15.3 and 9.1 mdeg, respectively. Residual strains owing to heteroepitaxial growth on the order of a few tenths of a percent can play a critical role in determining the amplitude and sign of the MOKE of a noncollinear antiferromagnet, unlike ferromagnets.

Enhancing nocturnal microclimate in Tunisian greenhouses: Experimental study on integrating an innovative conic helicoidal heat exchanger with a geothermal heat pump system

Ensuring an optimal nocturnal microclimate within greenhouses is essential for successful crop cultivation. In regions like Tunisia, characterized by arid and semi-arid climates, managing temperature and humidity during the night, particularly in cold winter months, is challenging and often requires external heating sources. This study aims to investigate the use of geothermal energy as a sustainable solution for greenhouse heating, focusing on an innovative helicoidal geothermal system to maintain ideal nocturnal conditions.The primary objective of this research is to evaluate the effectiveness of the helicoidal geothermal system in achieving optimal temperature and humidity levels for plant growth during the night. Conducted at the Research and Technology Centre of Energy in Tunisia, the experimental investigation involved a new ground heat exchanger coupled with a heat pump system.The experimental setup consisted of two greenhouses: one serving as a control and the other equipped with two Conic Helicoidal Ground Heat Exchangers (CHGHE) and a Ground-Source Heat Pump (GSHP) system, which includes both underground and suspended heat exchangers. The results demonstrated that the geothermal system, operating at an optimal flow rate of 0.6 kg/s, successfully maintained the nocturnal comfort temperature required for plant growth. The coefficients of performance for the geothermal heat pump (COPhp) and the overall system (COPsys) were calculated to be 3.12 and 2.7, respectively.These findings underscore the potential of near-surface geothermal energy, utilizing a geothermal heat pump, to efficiently heat greenhouses under the climatic conditions of Tunisia. This approach not only supports sustainable agricultural practices but also offers significant energy efficiency and cost-saving benefits.

Microscopic mechanisms of nitrogen doping in silicon carbide during epitaxial growth

We report first-principles calculations that unveil elementary processes of nitrogen donor doping during epitaxial growth of silicon carbide (SiC). We find that a N2 molecule adsorbed on the terrace migrates to a particular step edge where under-coordinated Si atoms appear, or is directly adsorbed near the step edge, and then dissociated there via the step-molecule interaction. This results in the N atom being eventually incorporated at the C substitutional site of the step. The calculated energy barriers indicate that the N incorporation reactions at the step edges occur at a typically high temperature in SiC epitaxial growth.

Diversity analysis of cyanobacterial flora from the Tatapani Hot Spring of Chhattisgarh and exploration of their industrially as well as environmentally valuable properties

The present study investigates the cyanobacterial diversity of Tatapani hot spring, Chhattisgarh, India, using a polyphasic approach, their pigment system, biofuel properties and ability to bioremediate emerging pollutant triclosan. While the microscopic analyses of the natural samples reflected high cyanobacterial diversity with all morpho-forms, physicochemical studies revealed temperature being the major factor affecting the cyanobacterial distribution in the hot spring. Among the 22 collected cyanobacterial samples, 14 were grown successfully under laboratory conditions and 10 of them showed optimum growth at 45 °C. However, four strains displayed preference for lower temperature (27 °C) for optimum growth. The polyphasic characterization of 14 strains revealed that all the thermophiles belonged to the genus Mastigocladus whereas the strains Sytonema sp. TPJ-3, Calothrix sp. TPB-2, Westiellopsis sp. TPR-29 and Desikacharya sp. TPB-4 constituted the group of mesophiles. Calothrix sp. TPB-2 was identified as a novel genus (Neocalothrix thermalis) based on distinct morphology and phylogenetic position with unique ITS folding pattern. Additionally, our study disclosed the production of comparatively higher amounts of pigments and medium chain length fatty acids (C16 to C18) by the thermophilic strains, which indicated their potential to be used as feedstocks for pigments and biofuel production respectively. Although the triclosan bioremediation study reflected considerable triclosan removal efficiencies of all the strains, most impressive results were observed in case of Westiellopsis sp. TPR-29 (93.08 %) and Mastigocladus sp. TA-8 (91.92 %). Moreover, the in-silico study-based revelation of high triclosan binding ability of cyanobacterial laccase (−5.8 and − 5.4 kcal/mol) and catechol 2,3-dioxygenase (−5.9 and − 6.0 kcal/mol) suggested the probable triclosan degrading potential of Westiellopsis and Mastigocladus. Conclusively, the Tatapani hot spring represents a unique environment with the dominance of true-branched heterocytous thermophilic cyanobacteria that have enormous potential to remove triclosan and produce high amounts of pigments and medium chain length fatty acids.

The advance of El Niño phase locking from period 1982–2000 to 2001–2022

The mature phases of El Niño-Southern Oscillation (ENSO) events exhibit a distinct tendency to peak towards the end of the calendar year, a phenomenon commonly referred to as ENSO phase locking. This phase locking is a fundamental property of the ENSO. The observed characteristics of phase locking are intricately tied to the seasonality of ENSO-related Sea Surface Temperature (SST) growth rate. In this study, notable observational evidence is presented: the strength of phase locking of El Niño weakened, and the phase locking advanced to peak at an earlier time during the period 2001 to 2022 compared to 1982 to 2000. The advancement of El Niño Phase Locking is explored by analyzing the contributions of different oceanic feedbacks to the El Niño phenomenon. Specifically, our findings highlight the significant role of nonlinear advective dynamic heating (NDH), which is influenced by the decrease in equatorial pacific surface zonal current anomaly and the equatorial pacific surface zonal gradient of sea SST anomaly. This investigation enhances our understanding of the evolving dynamics of El Niño phase locking, shedding light on the intricate interplay of oceanic feedbacks in influencing this fundamental aspect of ENSO behavior.

Embedded high-quality ternary GaAs1−x Sb x quantum dots in GaAs nanowires by molecular-beam epitaxy

Semiconductor quantum dots are promising candidates for preparing high-performance single photon sources. A basic requirement for this application is realizing the controlled growth of high-quality semiconductor quantum dots. Here, we report the growth of embedded GaAs1−x Sb x quantum dots in GaAs nanowires by molecular-beam epitaxy. It is found that the size of the GaAs1−x Sb x quantum dot can be well-defined by the GaAs nanowire. Energy dispersive spectroscopy analyses show that the antimony content x can be up to 0.36 by tuning the growth temperature. All GaAs1−x Sb x quantum dots exhibit a pure zinc-blende phase. In addition, we have developed a new technology to grow GaAs passivation layers on the sidewalls of the GaAs1−x Sb x quantum dots. Different from the traditional growth process of the passivation layer, GaAs passivation layers can be grown simultaneously with the growth of the embedded GaAs1−x Sb x quantum dots. The spontaneous GaAs passivation layer shows a pure zinc-blende phase due to the strict epitaxial relationship between the quantum dot and the passivation layer. The successful fabrication of embedded high-quality GaAs1−x Sb x quantum dots lays the foundation for the realization of GaAs1−x Sb x -based single photon sources.

Enhancing growth rate in homoepitaxial growth of β-Ga2O3 with flat surface via hydrochloric acid addition in mist CVD

Gallium oxide (Ga2O3) is a wide-bandgap oxide semiconductor, with a bandgap of ∼4.9 eV, making it a promising material for power device applications. This study focuses on the effect of hydrochloric acid addition on the growth rate in homoepitaxial growth of β-Ga2O3 using a mist chemical vapor deposition method. For homoepitaxial growth on a (001) β-Ga2O3 substrate, we introduced different concentrations of HCl into the source solution to assess its impact on the growth rate, crystal structures, and surface morphologies of the films. At a growth temperature of 900 °C, HCl addition linearly increased film thickness, enhancing the growth rate by 4.8 times with 9.09 vol. % HCl. No peaks associated with other phases were exhibited by each sample, indicating pure homoepitaxial growth. When comparing samples with similar film thicknesses, the root-mean-square (rms) roughness was enhanced by 1/7 with an increase in the HCl concentration. However, at 800 °C, an increasing solution concentration caused pronounced step bunching and elevated rms roughness, in contrast with the minimal effect observed at 900 °C. In experiments with hydrochloric acid addition at 900 °C, we observed a striped morphology, which maintained consistent rms roughness despite higher temperature.

The Growth of V5S8 Single Crystals by Chemical Vapour Transport

Single crystals of the d-electron antiferromagnetic metal V5S8 can be prepared by chemical vapour transport with gaseous iodine as a transport agent. We present the outcomes of an endeavour to synthesise high-purity single crystals of V5S8 with reduced crystalline disorder, important to the formation of novel quantum orders. We report results on the residual resistivity ratio of the single crystals as growth parameters are varied including growth temperature, temperature gradient and pre-growth processing of the initial apparatus and reagents. We demonstrate that single crystals of at least a few mm in size can be successfully grown at relatively low temperatures in the range 550–600 °C. The optimisation of this method may imply a better crystallographic organisation, reducing sulphur vacancies and increasing vanadium positional order. The resulting longer electron mean free paths may enhance the probability of finding exotic quantum states of matter at low temperatures. The results presented here may also be of relevance to the development of vanadium sulphide-based energy storage and spintronic devices.

Realization of N-polarity GaN films on graphene/SiC substrates by interfacial atomic manipulation

Growth of N-polarity GaN on a two-dimensional (2D) material is of significance for the development of high-performance nitride devices such as red light-emitting diodes. However, the realization of N-polarity GaN on a 2D material is a challenge. In this work, we successfully achieve N-polarity GaN on graphene/SiC substrates through interfacial atomic manipulation. Our results show that the growth conditions of the AlN buffer play an important role in the lattice polarity of nitride film grown on 2D graphene. A low growth temperature of AlN buffer leads to a metal-polarity nitride film, while a high growth temperature of it leads to a mix-polarity nitride film. The underlying mechanism is revealed by first-principles calculations. Under the guidance of the calculations results, the preflow of trimethylaluminum source is introduced prior to the high-temperature AlN buffer growth to manipulate the interfacial atoms between the AlN buffer and graphene/SiC. With this method, we successfully realize the fabrication of N-polarity GaN on graphene/SiC by metalorganic chemical vapor deposition. This work provides a new route for the development of high-performance N-polarity nitride devices on graphene/SiC substrates.