Tunable Work Function of Graphene by Nickel-Assisted In-situ Boron Doping for Direct Synthesis on Insulators
Chien-Kuang Lee2*, Wen-Chun Yen2, Yi-Chen Hsieh2, Henry Medina2, Yu-Lun Chueh2
1材料所, 清華大學, 新竹市, Taiwan
2material and science engineering department, National Tsing Hua university, Hsinchu, Taiwan
* presenting author:李建廣, email:ilaf0836@hotmail.com
Doping of graphene provides an efficient way to spread out the band-gap and alter the work function necessary to improve the performance in applications such as organic and optical electronics. Many different methods have been proposed to achieve graphene doping for both n-type and p-type doping such as electro-bias, strain or by absorption of chemical species. Only few works have sought to increase the work function using spin coating of chemical species to be used as anode material in photovoltaics. Nevertheless, most of chemical dopants produce uncontrollable doping and are linked with graphene only by physical adsorption, having low thermal, air and vacuum stability and could be easily removed from the graphene surface. The incorporation of other atomic elements different from carbon into graphene hexagonal lattice by strong chemical bonding, provides a way to resolve the stability problem on doped graphene devices. Most of the synthesis effort has been focused on n-type doping graphene lowering the work function, while no efforts have been attained to achieve substitutional p-doping of graphene for a precise tuning with increased work function. Here, we present an effective method using a vapor-assisted CVD process to synthesize graphene while inducing substitutional Boron doping at the same time. The Boron atoms replace carbon sites forming strong bonds in the graphene hexagonal lattice. The surface doping concentration can reach 3.24 at % and the sheet carrier concentration can be tuned up to 1013/cm2. Moreover, by using Ni vapor assisted method the b-doped graphene can be at once deposited on insulating substrates avoiding the wrinkles, scratches and polymer related contaminants inherent to the commonly used polymer transfer process. Opposite from the physical adsorption doping; our substitutional boron doping can be precisely controlled achieving different work function, changing from 20 to 180 meV analyzed by Kelvin probe force microscopy by adjusting the graphene deposition rate. Our approach gives graphene a step forward for its use in applications such as photovoltaics, optical and organic electronics that requires a precise control of the work function for device performance enhancement.

Keywords: graphene, boron-doping, tunable work function, insulator