Confinement of excited states in two-dimensional, in-plane, quantum heterostructures.

Two-dimensional (2D) semiconductors are promising candidates for optoelectronic application and quantum information processes due to their inherent out-of-plane 2D confinement. In addition, they offer the possibility of achieving low-dimensional in-plane exciton confinement, similar to zero-dimensional quantum dots, with intriguing optical and electronic properties via strain or composition engineering. However, realizing such laterally confined 2D monolayers and systematically controlling size-dependent optical properties remain significant challenges.

Step engineering for nucleation and domain orientation control in WSe epitaxy on c-plane sapphire.

Epitaxial growth of two-dimensional transition metal dichalcogenides on sapphire has emerged as a promising route to wafer-scale single-crystal films. Steps on the sapphire act as sites for transition metal dichalcogenide nucleation and can impart a preferred domain orientation, resulting in a substantial reduction in mirror twins. Here we demonstrate control of both the nucleation site and unidirectional growth direction of WSe on c-plane sapphire by metal-organic chemical vapour deposition.

Role of Bilayer Graphene Microstructure on the Nucleation of WSe Overlayers.

Over the past few years, graphene grown by chemical vapor deposition (CVD) has gained prominence as a template to grow transition metal dichalcogenide (TMD) overlayers. The resulting two-dimensional (2D) TMD/graphene vertical heterostructures are attractive for optoelectronic and energy applications. However, the effects of the microstructural heterogeneities of graphene grown by CVD on the growth of the TMD overlayers are relatively unknown.

Substrate Modification during Chemical Vapor Deposition of hBN on Sapphire.

A comparison of hexagonal boron nitride (hBN) layers grown by chemical vapor deposition on -plane (0001) versus -plane (112̅0) sapphire (α-AlO) substrate is reported. The high deposition temperature (>1200 °C) and hydrogen ambient used for hBN deposition on sapphire substantially alters the -plane sapphire surface chemistry and leaves the top layer(s) oxygen deficient. The resulting surface morphology due to H etching of -plane sapphire is inhomogeneous with increased surface roughness which causes non-uniform residual stress in the deposited hBN film.

Influence of the Underlying Substrate on the Physical Vapor Deposition of Zn-Phthalocyanine on Graphene.

Graphene shows great promise not only as a highly conductive flexible and transparent electrode for fabricating novel device architectures but also as an ideal synthesis platform for studying fundamental growth mechanisms of various materials. In particular, directly depositing metal phthalocyanines (MPc's) on graphene is viewed as a compelling approach to improve the performance of organic photovoltaics and light-emitting diodes. In this work, we systematically investigate the ZnPc physical vapor deposition (PVD) on graphene either as-grown on Cu or as-transferred on various substrates including Si(100), C-plane sapphire, SiO/Si, and h-BN.

Role of the Cu substrate in the growth of ultra-flat crack-free highly-crystalline single-layer graphene.

Producing ultra-flat crack-free single-layer high-quality graphene over large areas has remained the key challenge to fully exploit graphene's potential into next-generation technological applications. In this regard, we show that epitaxial Cu(111) film represents the most promising catalyst for the chemical vapor deposition (CVD) of graphene with superior planarity and physical integrity. We first compare the most widely used Cu catalysts (foils, polycrystalline films and epitaxial films) in order to benchmark the roughness of the Cu surface which serves as a template for graphene growth.