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Selda Sonuşen Faculty of Engineering and Natural Sciences, Sabancı University, lstanbul 34956, Turkey

Munir Dede NanoMagnetics Instruments Ltd., Ankara 06800, Turkey

Yigit Uysallı, Ekin Özgönül, and Ahmet Oral Department of Physics, Middle East Technical University, Ankara 06800, Turkey (Received 11 May 2015; accepted 27 October 2015)

Few layer graphene is attractive due to its extraordinary electronic and optical properties, which are strongly influenced by the orientation between the layers called as stacking sequence. It is challenging to synthesize high quality large size single or multi layer graphene crystals on the metal catalyst using chemical vapor deposition technique. The present work is about synthesis of few layer graphene grains on platinum foil using ambient pressure chemical together vapor deposition technique. The main focus is how the different grains coalesced and maintain the stacking sequence. Different characterization techniques are used to analyze the grains when they are in the process of merging to make a bigger grain. Scanning electron microscopy clearly shows different stacking sequences and merging of different nucleation sites of different grains. Interestingly, different stacking sequences are observed during the process of coalescence of grains. Raman spectroscopy gives accurate information about the number of layers and their stacking sequence. We observed Bernal AB and twisted layer stacking in the grains when they were combining together to grow into a bigger size. The full width at half maximum (FWHM) value of 2D Raman peaks appeared in the range of 52–69 cm 1 which shows an increase from the value of single layer graphene (30.18 cm 1) and identifies Bernal stacking in grains. For twisted stacking FWHM values lie in the range of 19–32 cm 1. Shumaila Karamat obtained her Ph.D. from Nanyang Technological University (Singapore) in 2011 where she worked in the area of dilute magnetic semiconductors. She then joined the group of Ahmet Oral under Marie-Curie cofunded postdoctoral fellowship at the Middle East Technical University (Ankara, Turkey). Since 2013, she is working as an experienced researcher and her work is focused on the fabrication of Scanning Hall Probe using graphene.

Shumaila Karamat

I. INTRODUCTION

Graphene, which consists of one atom thick sp2-bonded graphite, received the attention of different disciplines of physics because of its marvelous properties.1–4 To fully utilize the graphene in industry, fabrication of high quality Contributing Editor: Mauricio Terrones a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.350 46

J. Mater. Res., Vol. 31, No. 1, Jan 14, 2016

graphene is essential. The exfoliated single-layer graphene exhibit carrier mobility of ;10,000 cm2/V s when transferred on Si wafer and 200,000 cm2/V s in its suspended form but the area coverage and number of layers are not well controlled. The most promising method to grow large area graphene on metal catalysts is chemical vapor deposition (CVD).5