We explore theoretically the feasibility of functionalizing carbon nanostructures for hydrogen storage, focusing on the coating of C60 fullerenes with light alkaline-earth metals. Our first-principles density functional theory studies show that both Ca and Sr can bind strongly to the C60 surface, and highly prefer monolayer coating, thereby explaining existing experimental observations. The strong binding is attributed to an intriguing charge transfer mechanism involving the empty d levels of the metal elements. The charge redistribution, in turn, gives rise to electric fields surrounding the coated fullerenes, which can now function as ideal molecular hydrogen attractors. With a hydrogen uptake of >8.4 wt % on Ca32C60, Ca is superior to all the recently suggested metal coating elements.

Using first-principles calculations within density functional theory, we explore systematically the capacity of charged carbon fullerenes Cn (20

Semiconductor photocatalysts capable of broadband solar photon absorption may be nonetheless precluded from use in driving water splitting and other solar-to-fuel related reactions due to unfavorable band edge energy alignment. Using first-principles density functional theory and beyond, we calculate the electronic structure of passivated CdSe surfaces and explore the opportunity to tune band edge energies of this and related semiconductors via electrostatic dipoles associated with chemisorbed ligands. We predict substantial shifts in band edge energies originating from both the induced dipole at the ligand/CdSe interface and the intrinsic dipole of the ligand. Building on important induced dipole contributions, we further show that, by changing the size and orientation of the ligand's intrinsic dipole moment via functionalization, we can control the direction and magnitude of the shifts of CdSe electronic levels. Our calculations suggest a general strategy for enabling new active semiconductor photocatalysts with both optimal opto-electronic, and photo- and electrochemical properties.

The growth of single‐crystal III‐nitride films with a low stress and dislocation density is crucial for the semiconductor industry. In particular, AlN‐derived deep‐ultraviolet light‐emitting diodes (DUV‐LEDs) have important applications in microelectronic technologies and environmental sciences but are still limited by large lattice and thermal mismatches between the epilayer and substrate. Here, the quasi‐van der Waals epitaxial (QvdWE) growth of high‐quality AlN films on graphene/sapphire substrates is reported and their application in high‐performance DUV‐LEDs is demonstrated. Guided by density functional theory calculations, it is found that pyrrolic nitrogen in graphene introduced by a plasma treatment greatly facilitates the AlN nucleation and enables fast growth of a mirror‐smooth single‐crystal film in a very short time of ≈0.5 h (≈50% decrease compared with the conventional process), thus leading to a largely reduced cost. Additionally, graphene effectively releases the biaxial stress (0.11 GPa) and reduces the dislocation density in the epilayer. The as‐fabricated DUV‐LED shows a low turn‐on voltage, good reliability, and high output power. This study may provide a revolutionary technology for the epitaxial growth of AlN films and provide opportunities for scalable applications of graphene films.

Single-crystalline GaN-based light-emitting diodes (LEDs) with high efficiency and long lifetime are the most promising solid-state lighting source compared with conventional incandescent and fluorescent lamps. However, the lattice and thermal mismatch between GaN and sapphire substrate always induces high stress and high density of dislocations and thus degrades the performance of LEDs. Here, the growth of high-quality GaN with low stress and a low density of dislocations on graphene (Gr) buffered sapphire substrate is reported for high-brightness blue LEDs. Gr films are directly grown on sapphire substrate to avoid the tedious transfer process and GaN is grown by metal-organic chemical vapor deposition (MOCVD). The introduced Gr buffer layer greatly releases biaxial stress and reduces the density of dislocations in GaN film and In Ga N/GaN multiple quantum well structures. The as-fabricated LED devices therefore deliver much higher light output power compared to that on a bare sapphire substrate, which even outperforms the mature process derived counterpart. The GaN growth on Gr buffered sapphire only requires one-step growth, which largely shortens the MOCVD growth time. This facile strategy may pave a new way for applications of Gr films and bring several disruptive technologies for epitaxial growth of GaN film and its applications in high-brightness LEDs.

Using first-principles calculations within density functional theory, we study the relative impacts of quantum confinement and strain on the electronic structure of two II-VI semiconductor compounds with a large lattice-mismatch, CdSe and CdTe, in core/shell nanowire geometries with different core radii and shell thicknesses. For fixed CdSe core radius, we find that the electronic band gap in the core is significantly reduced with increasing CdTe shell thickness, by an amount comparable to that expected from quantum confinement, due to the development of a large and highly anisotropic strain throughout the heterostructure. A straightforward analysis allows us to separate quantitatively changes in band gap due to quantum confinement and strain. Our studies elucidate and quantify the importance of strain in determining the electronic and optical properties of core/shell nanostructures.

We report the growth of high-quality AlN films on nano-patterned sapphire substrates (NPSSs) by graphene-assisted quasi-van der Waals epitaxy, which enables rapid coalescence to shorten the growth time. Due to the presence of graphene (Gr), AlN tends to be two-dimensional laterally expanded on the NPSS, leading to the reduction of dislocation density and strain release in the AlN epitaxial layer. Using first-principles calculations, we confirm that Gr can reduce the surface migration barrier and promote the lateral migration of metal Al atoms. Furthermore, the electroluminescence results of deep ultraviolet light emitting diodes (DUV-LEDs) have exhibited greatly enhanced emission located at 280 nm by inserting the Gr interlayer. The present work may provide the potential to solve the bottleneck of high efficiency DUV-LED.

Wafer-scale highly oriented graphene harvesting a high carrier mobility and a low sheet resistance is directly grown on sapphire.