Self-Organization of 3D Triangular GaN Nanoislands and the Shape Variation to Hexagonal

We report on the self-organization of large-scale uniform aligned three-dimensional (3D) GaN islands with distinct triangular (0001) and smooth side facets and the shape variations of the (0001) facets from triangular to hexagonal during metalorganic vapor-phase epitaxy (MOVPE) growth of GaN films on Si-rich SiNx patterned sapphire substrates. The triangular island shaping during the recrystallization processes of GaN nucleation layers (NLs) can be attributed to the enhanced diffusion and regrowth anisotropy. The island shape transition from triangular to hexagonal in the early stages of high-temperature growth of GaN epilayers is due to the gas-phase transport dominating growth mechanism and the limited diffusion length of edge adatoms compared with the increased island size

Fabrication of Apatite-Type La_9.33(SiO₄)₆O₂ Hollow Nanoshells as Energy-Saving Oxidative Catalysts

Apatite-type La9.33(SiO4)6O2 hollow nanoshells were successfully synthesized by a controlled route. These oxide-ion-conducting hollow nanoshells were used to catalyze oxidative coupling of methane, and an enhanced catalytic performance at relatively low temperature was realized. The high-activity and energy-saving features were attributed to their hollow nanostructures and oxide ion conductivity

Supplementary document for Enhanced light extraction efficiency of GaN-based green Micro-LED modulating by thickness-tunable SiO2 passivation structure - 6691538.pdf

simulation and schematic diagra

In-plane Anisotropy of Quantum Transport in Artificial Two-dimensional Au Lattices

We report an experimental observation and direct control of quantum transport in artificial two-dimensional Au lattices. Combining the advanced techniques of low-temperature deposition and newly developed double-probe scanning tunneling spectroscopy, we display a two-dimensional carrier transport and demonstrate a strong in-plane transport modulation in the two-dimensional Au lattices. In well-ordered Au lattices, we observe the carrier transport behavior manifesting as a band-like feature with an energy gap. Furthermore, controlled structural modification performed by constructing coupled “stadiums” enables a transition of system dynamics in the lattices, which in turn establishes tunable resonant transport throughout a wide energy range. Our findings open the possibility of the construction and transport engineering of artificial lattices by the geometrical arrangement of scatterers and quantum chaotic dynamics

Phase-Dependent Magnetic Proximity Modulations on Valley Polarization and Splitting

Proximate-induced magnetic interactions present a promising strategy for precise manipulation of valley degrees of freedom. Taking advantage of the splendid valleytronic platform of transition metal dichalcogenides, magnetic two-dimensional VSe2 with different phases are introduced to intervene in the spin of electrons and modulate their valleytronic properties. When constructing the heterostructures, 1T-VSe2/WX2 (X = S and Se) showcases significant improvement in the valley polarizations at room temperature, while 2H-VSe2/WX2 exhibits superior performance at low temperatures and demonstrates heightened sensitivity to the external magnetic field. Simultaneously, considerable valley splitting with a large geff factor up to −29.0 is observed in 2H-VSe2/WS2, while it is negligible in 1T-VSe2/WX2. First-principles calculations reveal a phase-dependent magnetic proximity mechanism on the valleytronic modulations, which is dominated by interfacial charge transfer in 1T-VSe2/WX2 and the proximity exchange field in 2H-VSe2/WX2 heterostructures. The effective control over valley degrees of freedom will bridge the valleytronic physics and devices, rendering enormous potential in the field of valley quantum applications

Defect Suppression in AlN Epilayer Using Hierarchical Growth Units

Growing AlN layers remains a significant challenge because it is subject to a large volume fraction of grain boundaries. In this study, the nature and formation of the AlN growth mechanism is examined by ab initio simulations and experimental demonstration. The calculated formation enthalpies of the constituent elements, including the Al/N atom, Al–N molecule, and Al–N₃ cluster, vary with growth conditions in N-rich and Al-rich environments. Using the calculation results as bases, we develop a three-step metalorganic vapor-phase epitaxy, which involves the periodic growth sequence of (i) trimethylaluminum (TMAl), (ii) ammonia (NH₃), and (iii) TMAl+NH₃ supply, bringing in hierarchical growth units to improve AlN layer compactness. A series of AlN samples were grown, and their morphological and luminescent evolutions were evaluated by atomic force microscopy and cathodoluminescence, respectively. The proposed technique is advantageous because the boundaries and defect-related luminescence derived are highly depressed, serving as a productive platform from which to further optimize the properties of AlGaN semiconductors

Chemical Potential-Manipulated Growth of Large-Area High-Quality 2D Boron Nitride Films by APCVD

The two-dimensional material, hexagonal boron nitride (h-BN), has received significant interest due to its fascinating optical and electrical properties. However, the conventional chemical vapor deposition (CVD) process for growing h-BN often results in undesirable grain boundaries and defects due to its high nucleation density. To overcome this limitation, we studied the initial growth procedure for monomer formation, adsorption, and reaction on a Cu surface. The calculation results indicated that manipulating the growth conditions can effectively control the formation of the preferential building blocks of h-BN, such as the B/N atom, BN/BN2/B2N molecules, and BN3/B3N clusters, subsequently resulting in different nucleation dynamics and growth modes. Especially, a N-rich atmosphere could significantly suppress the h-BN nucleation due to the higher formation energy of the preferential building blocks on the Cu surface. Further experimental work verified this manipulation strategy well by constructing N-rich and B-rich growth conditions, which resulted in large-scale and high-quality h-BN films with few defects and almost unresolvable grain boundaries. The results demonstrate that the chemical-potential-based manipulation strategy has promise for optimizing h-BN growth dynamics and improving its practical applications

Ga₂O₃/GaN Heterostructural Ultraviolet Photodetectors with Exciton-Dominated Ultranarrow Response

Ultraviolet photodetectors have demonstrated a wide range of applications, e.g., missile launching, tracking detection, environmental monitoring, etc. This Article presents an ultraviolet photodetector based on a Ga2O3/GaN heterostructure that is equipped with tunable multiband detectivity via bias voltage and a record ultranarrow response. Particularly, this spectral response can be tuned from ultraviolet-C to ultraviolet-A by modulating the depletion region of the photodetector via adjusting bias. Under a higher bias, a photoresponse with a full-width at half-maximum of ∼4 nm at 363 nm is achieved. This ultranarrow response reaches 2.58 × 103 A/W and an external quantum efficiency of (8.84 × 105)% under 28 V bias. The photoluminescence, photoluminescence excitation, and light-absorption measurements suggest that this ultranarrow-band detectivity can be ascribed to the field-enhanced exciton ionization process in the GaN layer. The high responsivity can be attributed to the internal gain of the photodetector originating from the relatively large valence band offset between the Ga2O3 and GaN layers. This work provides a promising approach to the development of high-performance and versatile multiband ultraviolet photodetectors with electrical tunability. It is also worth highlighting that the features of inexpensive manufacturing and easy scalability are particularly attractive for mass production

Simultaneously Regulated Highly Polarized and Long-Lived Valley Excitons in WSe₂/GaN Heterostructures

Interlayer excitons, with prolonged lifetimes and tunability, hold potential for advanced optoelectronics. Previous research on the interlayer excitons has been dominated by two-dimensional heterostructures. Here, we construct WSe2/GaN composite heterostructures, in which the doping concentration of GaN and the twist angle of bilayer WSe2 are employed as two ingredients for the manipulation of exciton behaviors and polarizations. The exciton energies in monolayer WSe2/GaN can be regulated continuously by the doping levels of the GaN substrate, and a remarkable increase in the valley polarizations is achieved. Especially in a heterostructure with 4°-twisted bilayer WSe2, a maximum polarization of 38.9% with a long lifetime is achieved for the interlayer exciton. Theoretical calculations reveal that the large polarization and long lifetime are attributed to the high exciton binding energy and large spin flipping energy during depolarization in bilayer WSe2/GaN. This work introduces a distinctive member of the interlayer exciton with a high degree of polarization and a long lifetime

The Effects of Different Core–Shell Structures on the Electrochemical Performances of Si–Ge Nanorod Arrays as Anodes for Micro-Lithium Ion Batteries

Connected and airbag isolated Si–Ge nanorod (NR) arrays in different configurations have been fabricated on wafer scale Si substrates as anodes in micro-lithium ion batteries (LIBs), and the impacts of configurations on electrochemical properties of the electrodes were investigated experimentally and theoretically. It is demonstrated that the Si inner cores can be effectively protected by the connected Ge shells and contribute to the enhanced capacity by ∼68%, derived from an activation process along with the amorphization of the crystalline lattice. The first-principles calculations further verify the smaller forces on the Si layers at the atomic level during the restricted volume expansion with the covering of Ge layers. This work provides general guidelines for designing other composites and core–shell configurations in electrodes of micro-LIBs to accomplish higher capacities and longer cycle lives