= 아 래 =
1. 일 시 : 2013. 4. 2 (화), 16:00 ~
2. 장 소 : 응용공학동 1층 영상강의실
3. 연 사 : 홍영준 교수 (세종대학교 나노신소재공학과)
4. 제 목 : van der Waals epitaxy of InAs on graphene substrates electrode structures
Paradigm shift from rigid single-crystalline substrate to flexible ultrathin graphene substrates has opened the great potentials for foldable, lightweight, and transparent electronics and optoelectronics. Since the honeycomb carbon crystal lattice of graphene layers can be well compatible with many semiconductors of zinc blende, and wurtzite crystal structures, the compound semiconductor fabricated on graphene layer may provide important hybrid junctions for the device applications. Nonetheless, problems associated with chemical stability of sp2-bonded carbon atoms precluded the use as a substrate for heteroepitaxy. The obstacles of non-wettable graphene surface have been circumvented by means of van der Waals (vdW) epitaxy. We demonstrate the controlled vdW epitaxy of InAs nanowires on graphene substrates. Nearly coherent in-plane lattice matching (misfit of 0.49%) between InAs and the graphene surface plays a critical role in the epitaxial formation of vertical InAs nanowires even on single-layer graphene. Cross-sectional transmission electron microscopy analyses present that 1–2 monomolecular layer ledges or kinks facilitate heterogeneous nucleation of InAs on non-wetting graphene surfaces, forming the nuclei and promoting the subsequent nanowire growth with strong vdW interactions at the heterojunction. The critical leading factors of nucleation and growth for the vdW heteroepitaxy of vertical inorganic nanowire arrays on honeycomb carbon surface are presented in terms of lattice misfit and surface potentials. Importantly, the vdW heteroepitaxy enabled to grow InAs nanowires vertically aligned on single-layer graphene, implying that the vdW attraction is strong enough to grow vertical nanostructures with high aspect ratio. Moreover, suspended single-layer graphene was utilized for verifying the role of monoatomic layer as substrates for vdW epitaxy. We also demonstrate the controlled vdW epitaxy method for high-yield and uniform InAs nanowire arrays on graphene by utilizing substrate surface etching and patterning techniques. Our work opens a new platform for the III–arsenide/graphene hybrid junction electronics and optoelectronics.