Abstract
We report the catalyst-free growth of InAs/InxGa1−xAs coaxial nanorod heterostructures on large-area graphene layers using molecular beam epitaxy and our investigation of the chemical composition and crystal structure of these heterostructures using electron microscopy. The graphene layers used as the substrate were prepared by chemical vapor deposition and transferred onto SiO2/Si substrates. InAs nanorods and their heterostructures were grown vertically on the graphene layers; electron microscopy images revealed uniform distributions for their diameter, length and density. Cross-sectional electron microscopy images showed that InxGa1−xAs layers, having uniform composition, coated heteroepitaxially the entire surface of the InAs nanorods, without interfacial layers or structural defects. The catalyst-free growth mechanism of InAs nanorods on graphene was investigated using in situ reflection high-energy electron diffraction. Nanorods with InAs cores and InxGa1−xAs shells have been grown catalyst-free on graphene using molecular beam epitaxy by scientists in Korea. Inorganic semiconductor nanorods on graphene layers are promising for producing electronic and optoelectronic devices that are simultaneously flexible and have long lifetimes and high efficiencies. Now, researchers at Seoul National University led by Gyu-Chul Yi have realized catalyst-free molecular beam epitaxy growth of InAs/InxGa1−xAs coaxial nanorods on graphene. This is an important step as catalyst-free molecular beam epitaxy can produce ultrapure single crystals and multilayered heterostructures with precisely-controlled thickness and chemical compositions. Analysis showed that the cores and shells were clearly defined with clean interfaces and had uniform compositions and thicknesses. This demonstration opens up the path for monolithic integration of semiconductor coaxial nanorod heterostructures on two-dimensional materials. We report the catalyst-free growth of InAs/InxGa1−xAs coaxial nanorod heterostructures on large-area graphene layers using molecular beam epitaxy and our investigation of the chemical composition and crystal structure of these heterostructures using electron microscopy. Cross-sectional electron microscopy images showed that InxGa1−xAs layers, having uniform composition, coated heteroepitaxially the entire surface of the InAs nanorods, without interfacial layers or structural defects. The catalyst-free growth mechanism of InAs nanorods on graphene was investigated using in situ reflection high-energy electron diffraction.
Highlights
The use of inorganic semiconductors as an active material is desirable for flexible electronic and optoelectronic device applications,[1,2,3] due to the many potential advantages over organic semiconductors in terms of lifetime and efficiency.[4]
molecular beam epitaxy (MBE) growth of InAs/InxGa1 − xAs coaxial nanorod heterostructures on graphene layers The surface morphologies of InAs nanorods and InAs/InxGa1 − xAs coaxial nanorod heterostructures grown on Chemical vapor deposited (CVD) graphene layers were investigated using scanning electron microscopy
From the fact that the reflection high electron energy diffraction (RHEED) patterns maintained the same shape during coaxial shell-layer growth, we suggest that the InxGa1 − xAs coaxial shell layer grew epitaxially on the InAs nanorods; this was later confirmed by cross-sectional transmission electron microscopy (TEM) analysis
Summary
The use of inorganic semiconductors as an active material is desirable for flexible electronic and optoelectronic device applications,[1,2,3] due to the many potential advantages over organic semiconductors in terms of lifetime and efficiency.[4]. Direct growth of semiconductor nanorods on graphene that has high mechanical strength and flexibility was demonstrated recently, mainly using metal-organic chemical vapor deposition;[5,6,7] for example, flexible light-emitting diodes and solar cells using metal-organic chemical vapor deposition-grown GaN and InGaAs nanorods on graphene.[8,9,10,11] molecular beam epitaxy (MBE) can provide accurate control over the growth parameters for high-quality nanorod heterostructures with very clean and sharp interfaces using various in situ monitoring techniques, such as reflection high electron energy diffraction (RHEED).[12,13] Realizing the advantage of MBE growth method, Zhuang et al demonstrated In droplet-assisted growth of InAs nanorods on mechanically exfoliated graphite flakes using MBE.[14] it is important to develop catalyst-free MBE growth method of nanorods on graphene, as this growth method is known to be the best method to produce ultrapure nanorods with homogeneous composition, which are essential building blocks for future nanorod-based devices.[15] Here we demonstrate the growth of high-quality InAs/InxGa1 − xAs coaxial nanorod heterostructures on graphene layers using MBE, with a clean interface Both transmission electron microscopy (TEM) and in situ RHEED were used to investigate the structural properties and growth mechanism of the nanorod heterostructures
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