▎ 摘　　要

The superior electronic properties of graphene change with number of layers, making different layered flakes suitable for different applications. Bilayer has a tunable band gap and is promising material for electronic applications. Liquid phase synthesis methods are scalable, can provide flakes with size suitable for microelectronic fabrication technologies and allow easy, defect-free transfer of flakes to the application substrate. However, these methods yield flakes with different number of layers. Here, we show a modified electrochemical exfoliation of graphite that gives a bilayer-rich graphene suspension. The method first obtains particles of stage-2 graphite intercalation compound. These particles have alternating weak and strong attraction between the two nearest neighboring layers which allowed the tuning of ultrasonic agitation intensity, such that cleavages occurred at weak attraction sites yielding primarily bilayer graphene flakes. Graphene flakes were produced only on ultrasonic cleaving and were done in DMF, a medium favorable for graphene dispersion thus avoiding aggregation of the freshly generated bilayer flakes. In principle, our method can be tuned for the liquid phase synthesis of layer-specific graphene flakes for any given number of layers. The method could therefore provide a general synthesis process for graphene required in different end-use. (C) 2018 Elsevier Ltd. All rights reserved.