2D materials

 1. Graphene Nanostructures

 

Graphene, a single-atomic layer of carbon network, has been highlighted as a novel two dimensional material with their unique properties and potential applications in electronics. Due to two dimensional sp2 network of carbon in graphene, the electron shows a massless behavior which is described by the Dirac equation. This gives graphene its unique zero band gap property. However, it is possible to engender electronic band gap in graphene via fabricating graphene nanostructures such as graphene quantum dot, graphene nanoribbon and graphene nanomesh. Numerous methods to fabricate graphene nanostructures have been reported. Among the various nanostructures of graphene, graphene quantum dot is at an early developmental stage for practical fabrication. In previous research, graphene quantum dots were typically fabricated by mechanical or chemical subdividing methods from exfoliated graphene oxide or reduced graphene oxide. These methods are simple, and quantum dots obtained by this method are soluble to various solvents. However, controlling the size is a critical challenge.

 

acs_org_20121229_153249

 

In our group, block copolymer lithography is introduced for graphene nano-patterning.  Depending on polymer molecular weight and the volume fraction of each block, various morphologies can be obtained such as sphere, cylinder and lamellar. By using block copolymer lithography technique our group request is to fabricate graphene nanostructure having excellent size distribution, uniformity of size, and high resolution.

(Collaboration with Prof. Seokwoo Jeon’s group)

 

 

 2. Modulation of MoS2

 

2D 1

 

The discovery of graphene has promoted significant interest in other two-dimensional (2D) materials, especially transition metal dichalcogenides (TMDs) due to their unique electrical, optical properties. Although graphene shows a high mobility up to 106 cm2/Vs, its absence of a bandgap seriously limits its application for an active channel material in optoelectronic devices such as photodetecting and switching device applications. Alternatively, molybdenum disulfide (MoS2), one of the most widely studied semiconducting TMDs, shows a thickness-dependent energy bandgap and band structure: indirect bandgap of 1.2eV in a bulk MoS2 and direct bandgap of 1.8eV in a monolayer form. Thus MoS2 as a promising channel material has gained much attention for use in next-generation nanoelectronics.

 

2D 4

 

In our laboratory, we utilize 2D TMDs by applying various nano-technologies to enlarge applicable field of research.

 

For examples, to modify optical and electrical properties,

We introduce Thiol chemistry to get stable and tunable doping process. One the other hand, plasma doping process is developed using SiOx nanostructures fabricated by BCP.

 

2D 6

 

In our laboratory, we utilize 2D TMDs by applying various nano-technologies to enlarge applicable field of research.

To modify optical and electrical properties, we engineer the defects of MoS2 and introduce thiol chemistry. We have demonstrated the effective surface charge transfer doping via thiol based functionalization with different functional groups. One the other hand, plasma doping process is developed using Nano-scale blocking layer fabricated by BCP.

 

Plasma doping process is developed using protective nanostructures that are fabricated by PS-b-PDMS block copolymer. Local protection of few-layer thick MoS2 make enable to finely control materials’ properties and enlarge modulation range by well-established plasma process.

 

 

 

[References]

■Soonmin Yim, Dong Min Sim, Woon Ik Park, Min-Jae Choi, Jaesuk Choi, Jaebeom Jeon, Kwang Ho Kim* and Yeon Sik Jung* , “Surface-Shielding Nanostructures Derived from Self-Assembled Block Copolymers Enable Reliable Plasma Doping for Few-Layer Transition Metal Dichalcogenides”, Advanced Functional Materials, 2016.  [PDF file]

■Jinsup Lee(+), Kyungho Kim(+), Woon Ik Park, Bo-Hyun Kim, Jong Hyun Park, Tae-Heon Kim, Sungyool Bong, Chul-Hong Kim, GeeSung Chae, Myungchul Jun, Yongkee Hwang, Yeon Sik Jung*, and Seokwoo Jeon* (+ co-first) , “Uniform Graphene Quantum Dots Patterened from Self-Assembled Silica Nanodots”, Nano Letters, 2012, 12, pp 6078-6083 [PDF file]