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1.
Nanotechnology ; 29(44): 445702, 2018 Nov 02.
Artigo em Inglês | MEDLINE | ID: mdl-30124437

RESUMO

In this work, we show that remote heteroepitaxy can be achieved when Cu thin film is grown on single crystal, monolayer graphene buffered sapphire(0001) substrate via a thermal evaporation process. X-ray diffraction and electron backscatter diffraction data show that the epitaxy process forms a prevailing Cu crystal domain, which is remotely registered in-plane to the sapphire crystal lattice below the monolayer graphene, with the (111) out-of-plane orientation. As a poor metal with zero density of states at its Fermi level, monolayer graphene cannot totally screen out the stronger charge transfer/metallic interactions between Cu and substrate atoms. The primary Cu domain thus has good crystal quality as manifested by a narrow crystal misorientation distribution. On the other hand, we show that graphene interface imperfections, such as bilayers/multilayers, wrinkles and interface contaminations, can effectively weaken the atomic interactions between Cu and sapphire. This results in a second Cu domain, which directly grows on and follows the graphene hexagonal lattice symmetry and orientation. Because of the weak van der Waals interaction between Cu and graphene, this domain has inferior crystal quality. The results are further confirmed using graphene buffered spinel(111) substrate, which indicates that this remote epitaxial behavior is not unique to the Cu/sapphire system.

2.
ACS Nano ; 12(6): 6100-6108, 2018 Jun 26.
Artigo em Inglês | MEDLINE | ID: mdl-29746775

RESUMO

Antimony (Sb) nanostructures, including islands, sheets, and thin films, of high crystallinity were epitaxially grown on single-crystalline graphene through van der Waals interactions. Two types of graphene substrates grown by chemical vapor deposition were used, the as-grown graphene on Cu(111)/ c-sapphire and the transferred graphene on SiO2/Si. On the as-grown graphene, deposition of ultrathin Sb resulted in two growth modes and associated morphologies of Sb. One was Sb islands grown in Volmer-Weber (VW) mode, and the other was Sb sheets grown in Frank-van der Merve (FM) mode. In contrast, only Sb islands grown in VW mode were found in a parallel growth experiment on the transferred graphene. The existence of Sb sheets on the as-grown graphene was attributed to the remote epitaxy between Sb and Cu underneath the graphene. In addition, Sb thin films were grown on both the as-grown and transferred graphene substrates. Both films indicated high quality, and no significant difference can be found between these two films. This work unveiled two epitaxial alignments between Sb(0001) and graphene, namely, Sb [101̅0]∥graphene [10] for Sb islands and Sb [21̅1̅0]∥graphene [10] for Sb sheets. For Sb thin films on graphene, the epitaxial alignment followed that of Sb islands, implying that Sb thin films originated from the continued growth of Sb islands. Last, Raman spectroscopy was used to probe the state of graphene under ultrathin Sb. No strain, doping, or disorder was found in the graphene postgrowth of Sb. The knowledge of the interface formation between ultrathin Sb and graphene provides a valuable foundation for future research on van der Waals heterostructures between antimonene and graphene.

3.
ACS Appl Mater Interfaces ; 9(27): 23081-23091, 2017 Jul 12.
Artigo em Inglês | MEDLINE | ID: mdl-28621924

RESUMO

The symmetry of graphene is usually determined by a low-energy electron diffraction (LEED) method when the graphene is on the conductive substrates, but LEED cannot handle graphene transferred to SiO2/Si substrates due to the charging effect. While transmission electron microscopy can generate electron diffraction on post-transferred graphene, this method is too localized. Herein, we employed an azimuthal reflection high-energy electron diffraction (RHEED) method to construct the reciprocal space mapping and determine the symmetry of wafer-size graphene both pre- and post-transfer. In this work, single-crystalline Cu(111) films were prepared on sapphire(0001) and spinel(111) substrates with sputtering. Then the graphene was epitaxially grown on single-crystalline Cu(111) films with a low pressure chemical vapor deposition. The reciprocal space mapping using azimuthal RHEED confirmed that the graphene grown on Cu(111) films was single-crystalline, no matter the form of the monolayer or multilayer structure. While the Cu(111) film grown on sapphire(0001) may occasionally consist of 60° in-plane rotational twinning, the reciprocal space mapping revealed that the in-plane orientation of graphene grown atop was not affected. The proposed method for checking the crystalline integrity of the post-transferred graphene sheets is an important step in the realization of the graphene as a platform to fabricate electronic and optoelectronic devices.

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