Characterizing silicon intercalated graphene grown epitaxially on Ir films by atomic force microscopy

An efficient method based on atomic force microscopy（AFM） has been developed to characterize silicon intercalated graphene grown on single crystalline Ir（111） thin films. By combining analyses of the phase image, force curves,and friction–force mapping, acquired by AFM, the locations and coverages of graphene and silicon oxide can be well distinguished. We can also demonstrate that silicon atoms have been successfully intercalated between graphene and the substrate. Our method gives an efficient and simple way to characterize graphene samples with interacted atoms and is very helpful for future applications of graphene-based devices in the modern microelectronic industry, where AFM is already widely used.

Interaction of two symmetric monovacancy defects in graphene

We investigate the interactions between two symmetric monovacancy defects in graphene grown on Ru(0001) after silicon intercalation by combining first-principles calculations with scanning tunneling microscopy(STM). First-principles calculations based on free-standing graphene show that the interaction is weak and no scattering pattern is observed when the two vacancies are located in the same sublattice of graphene, no matter how close they are, except that they are next to each other. For the two vacancies in different sublattices of graphene, the interaction strongly influences the scattering and new patterns' emerge, which are determined by the distance between two vacancies. Further experiments on silicon intercalated graphene epitaxially grown on Ru(0001) shows that the experiment results are consistent with the simulated STM images based on free-standing graphene, suggesting that a single layer of silicon is good enough to decouple the strong interaction between graphene and the Ru(0001) substrate.

Low-temperature growth of large-scale,single-crystalline graphene on Ir(111)

Iridium is a promising substrate for self-limiting growth of graphene. However, single-crystalline graphene can only be fabricated over 1120 K. The weak interaction between graphene and Ir makes it challenging to grow graphene with a single orientation at a relatively low temperature. Here, we report the growth of large-scale, single-crystalline graphene on Ir(111) substrate at a temperature as low as 800 K using an oxygen-etching assisted epitaxial growth method. We firstly grow polycrystalline graphene on Ir. The subsequent exposure of oxygen leads to etching of the misaligned domains.Additional growth cycle, in which the leftover aligned domain serves as a nucleation center, results in a large-scale and single-crystalline graphene layer on Ir(111). Low-energy electron diffraction, scanning tunneling microscopy, and Raman spectroscopy experiments confirm the successful growth of large-scale and single-crystalline graphene. In addition, the fabricated single-crystalline graphene is transferred onto a SiO_2/Si substrate. Transport measurements on the transferred graphene show a carrier mobility of about 3300 cm^2·V^(-1)·s^(-1). This work provides a way for the synthesis of large-scale,high-quality graphene on weak-coupled metal substrates.

Effects of graphene defects on Co cluster nucleation and intercalation

Four kinds of defects are observed in graphene grown on Ru （0001） surfaces. After cobalt deposition at room tem- perature, the cobalt nanoclusters are preferentially located at the defect position. By annealing at 530 ℃, cobalt atoms intercalate at the interface of Graphene/Ru （0001） through the defects. Further deposition and annealing increase the sizes of intercalated Co islands. This provides a method of controlling the arrangement of cobalt nanoclusters and also the den- sity and the sizes of intercalated cobalt islands, which would find potential applications in catalysis industries, magnetism storage, and magnetism control in future information technology.

Intercalation of metals and silicon at the interface of epitaxial graphene and its substrates

Intercalations of metals and silicon between epitaxial graphene and its substrates are reviewed. For metal intercala- tion, seven different metals have been successfully intercalated at the interface of graphene/Ru（O001） and form different intercalated structures. Meanwhile, graphene maintains its original high quality after the intercalation and shows features of weakened interaction with the substrate. For silicon intercalation, two systems, graphene on Ru（O001） and on Ir（l I 1）, have been investigated. In both cases, graphene preserves its high quality and regains its original superlative properties after the silicon intercalation. More importantly, we demonstrate that thicker silicon layers can be intercalated at the interface, which allows the atomic control of the distance between graphene and the metal substrates. These results show the great potential of the intercalation method as a non-damaging approach to decouple epitaxial graphene from its substrates and even form a dielectric layer for future electronic applications.

STM study of selenium adsorption on Au(111)surface

Adsorption of chalcogen atoms on metal surfaces has attracted increasing interest for both the fundamental research and industrial applications.Here,we report a systematic study of selenium(Se)adsorption on Au(111)at varies substrate temperatures by scanning tunneling microscopy.At room temperature,small Se clusters are randomly dispersed on the surface.Increasing the temperature up to 200℃,a well-ordered lattice of Se molecules consisting of 8 Se atoms in ring-like structure is formed.Further increasing the temperature to 250℃gives rise to the formation of Se monolayer with Au(111)-√3×√3 lattices superimposed with a quasi-hexagonal lattice.Desorption of Se atoms rather than the reaction between the Se atoms and the Au substrate occurs if further increasing the temperature.The ordered structures of selenium monolayers could serve as templates for self-assemblies and our findings in this work might provide insightful guild for the epitaxial growth of the two-dimensional transition metal dichalcogenides.

The influence of annealing temperature on the morphology of graphene islands

We report on temperature-programmed growth of graphene islands on Ru （0001） at annealing temperatures of 700 ℃, 800 ℃, and 900 ℃. The sizes of the islands each show a nonlinear increase with the annealing temperature. In 700 ℃ and 800 ℃annealings, the islands have nearly the same sizes and their ascending edges are embedded in the upper steps of the ruthenium substrate, which is in accordance with the etching growth mode. In 900 ℃ annealing, the islands are much larger and of lower quality, which represents the early stage of Smoluchowski ripening. A longer time annealing at 900 ℃ brings the islands to final equilibrium with an ordered moire pattern. Our work provides new details about graphene early growth stages that could facilitate the better control of such a growth to obtain graphene with ideal size and high quality.

High quality sub-monolayer,monolayer,and bilayer graphene on Ru(0001)

High quality sub-monolayer, monolayer, and bilayer graphene were grown on Ru（0001）. For the sub-monolayer graphene, the size of graphene islands with zigzag edges can be controlled by the dose of ethylene exposure. By increasing the dose of ethylene to 100 Langmuir at a high substrate temperature （800 ℃）, high quality single-crystalline monolayer graphene was synthesized on Ru（0001）. High quality bilayer graphene was formed by further increasing the dose of ethylene while reducing the cooling rate to 5 ℃/min. Raman spectroscopy revealed the vibrational states of graphene, G and 2D peaks appeared only in the bilayer graphene, which demonstrates that it behaves as the intrinsic graphene. Our present work affords methods to produce high quality sub-monolayer, monolayer, and bilayer graphene, both for basic research and applications.