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Intercalation is the process of inserting chemical species into the heterointerfaces of two-dimensional (2D) layered materials. While much research has focused on the intercalation of metals and small gas molecules into graphene, the intercalation of larger molecules through the basal plane of graphene remains challenging. In this work, we present a new mechanism for intercalating large molecules through monolayer graphene to form confined oxide materials at the graphene-substrate heterointerface. We investigate the intercalation of phosphorus pentoxide (P2O5) molecules directly from the vapor phase and confirm the formation of confined P2O5 at the graphene-substrate heterointerface using various techniques. Density functional theory (DFT) corroborates the experimental results and reveals the intercalation mechanism, whereby P2O5 dissociates into small fragments catalyzed by defects in the graphene that then permeates through lattice defects and reacts at the heterointerface to form P2O5. This process can also be used to form new confined metal phosphates (e.g., 2D InPO4). While the focus of this study is on P2O5 intercalation, the possibility of intercalation from predissociated molecules catalyzed by defects in graphene may exist for other types of molecules as well. This in-depth study advances our understanding of intercalation routes of large molecules via the basal plane of graphene as well as heterointerface chemical reactions leading to the formation of distinctive confined complex oxide compounds.

Achieving control over the motion of dissolved particles in liquid metals is of importance for the meticulous realization of hierarchical particle assemblies in a variety of nanofabrication processes. Brownian forces can impede the motion of such particles, impacting the degree of perfection that can be realized in assembled structures. Here, we show that light-induced Marangoni flow in liquid metals (i.e., liquid-gallium) with Laguerre-Gaussian (LGpl) lasers as heating sources is an effective approach to overcome Brownian forces on particles, giving rise to predictable assemblies with a high degree of order. We show that by carefully engineering surface tension gradients in liquid-gallium using non-Gaussian LGpl lasers, the Marangoni and convective flow that develops in the fluid drives the trajectory of randomly dispersed particles to assemble into 100 μm wide ring-shaped particle assemblies. Careful control over the parameters of the LGpl laser (i.e., laser mode, spot size, and intensity of the electric field) can tune the temperature and fluid dynamics of the liquid-gallium as well as the balance of forces on the particle. This in turn can tune the structure of the ring-shaped particle assembly with a high degree of fidelity. The use of light to control the motion of particles in liquid metals represents a tunable and rapidly reconfigurable approach to spatially design surface tension gradients in fluids for more complex assembly of particles and small-scale solutes. This work can be extended to a variety of liquid metals, complementary to what has been realized in particle assembly out of ferrofluids using magnetic fields.

The growth of thick group-III polar InGaN films beyond the critical thickness remains a challenge due to the large miscibility gap and lattice mismatch between InN and GaN leading to phase separation and inhomogeneous distribution of indium that impacts the luminescence properties across the film. The growth of N-polar InGaN can circumvent these challenges due to the increased stability of InN, thus improving film quality. However, overall luminescence from N-polar InGaN films is consistently lower than that of group-III polar InGaN films grown under identical conditions. In this study, spatially resolved cathodoluminescence (CL) measurements are used to reveal the optical properties of group-III and N-polar thick InGaN films. In the case of group-III polar films, predominant CL luminescence arises from the periphery of V-pits which are regions with a high accumulation of indium, while negligible CL luminescence is observed at the apex of the V-pit, indicative of centers for non-radiative recombination. Large differences in the CL luminescence intensity between the group-III polar and N-polar InGaN are a result of significant differences in the carrier lifetimes of the respective polarities (∼50–200 ps: N-polar, ∼500–700 ps: group-III polar InGaN). Since the decay behavior of the transient in N-polar InGaN is bi-exponential, it is suspected that oxygen impurities play a dominant role in the overall luminescence quenching in N-polar InGaN films. [ABSTRACT FROM AUTHOR]

The growth of N-polar InGaN films by metalorganic chemical vapor deposition (MOCVD) on Npolar GaN was investigated in order to understand the evolution of growth stress and the dislocation microstructure of relatively thick InGaN films (140 nm) in the absence of hexagonal hillocks and V-pits, which are typically present in III-polar InGaN. During in situ stress measurements of N-polar InGaN, growth initiates under an initial low stress state, which gradually transitions to a constant compressive incremental stress for the remainder of the film thickness. This behavior in the growth stress evolution in N-polar InGaN occurs regardless of the stress state of the GaN base layer (i.e., compression or tension), which was controlled by varying the temperature of the initial low temperature layer in a two-step temperature growth process for N-polar GaN. A blue shift in the PL peak emission of N-polar InGaN was, however, observed with increasing incremental compressive stress in the N-polar GaN base layer. These results provide insight into potential mechanisms of plastic relaxation in high crystal quality thick N-polar InGaN films grown by MOCVD. [ABSTRACT FROM AUTHOR]