The Nature of Metastable AA' Graphite: Low Dimensional Nano- and Single-Crystalline Forms.

Jae-Kap Lee,Yong-Il Kim,Dong Ju Moon,Wooyoung Lee,K P S S Hembram,Sang-Gil Lee,Jin-Gyu Kim,Jeon-Kook Lee,Yeseul Park,Phillip John,Bong-Ki Min

doi:10.1038/srep39624

Abstract

Over the history of carbon, it is generally acknowledged that Bernal AB stacking of the sp2 carbon layers is the unique crystalline form of graphite. The universal graphite structure is synthesized at 2,600~3,000 °C and exhibits a micro-polycrystalline feature. In this paper, we provide evidence for a metastable form of graphite with an AA’ structure. The non-Bernal AA’ allotrope of graphite is synthesized by the thermal- and plasma-treatment of graphene nanopowders at ~1,500 °C. The formation of AA’ bilayer graphene nuclei facilitates the preferred texture growth and results in single-crystal AA’ graphite in the form of nanoribbons (1D) or microplates (2D) of a few nm in thickness. Kinetically controlled AA’ graphite exhibits unique nano- and single-crystalline feature and shows quasi-linear behavior near the K-point of the electronic band structure resulting in anomalous optical and acoustic phonon behavior.

Highlights

The structure of graphitic materials including bilayer graphene has been assumed to adopt Bernal AB stacking of graphene planes[1]
In this paper we present the synthesis of AA’ graphite with two different techniques, (i) thermal-treatment of graphene nanopowders (GNPs), and (ii) plasma seeded growth[10], where GNPs serve as nuclei
HRTEM images, before (Fig. 1a) and after thermal-treatment (Fig. 1b,c) indicate that GNPs crystallize into graphite in nanoribbon shapes during thermal-treatment

Summary

Introduction

The structure of graphitic materials including bilayer graphene has been assumed to adopt Bernal AB stacking of graphene planes[1]. We have shown that AA’ stacking of graphene planes (where each graphene plane is shifted by 1/2 hexagon from zigzag AA stacking or by 1/4 hexagon from armchair AB stacking) exists, and may be the structure of multi-wall carbon nanotubes (MWNTs) (i.e., helically grown AA’ graphite)[9,10] This AA’ stacking has possibly been interpreted previously as disordered turbostratic structure[11,12,13,14,15] due to the unique X-ray diffraction (XRD) pattern, lacking several peaks for AB graphite (but revealing two peaks at 2θ= 42.4° and 2θ= 77.6°) and further supported by an interlayer spacing of ~3.44 Å9–15. We reveal growth kinetics and analytical features as well as electronic and vibrational properties for an AA’ metastable form of graphite

Methods

Results

Conclusion