Despite the enormous potential of the single-crystalline two-dimensional (2D) materials for a wide range of future innovations and applications, 2D single-crystals are still suffering in industrialization due to the lack of efficient large-area production methods. In this work, we introduce a general approach for the scalable growth of single-crystalline graphene, which is a representative 2D material, through “transplanting” uniaxially aligned graphene “seedlings” onto a larger-area catalytic growth substrate. By inducing homoepitaxial growth of graphene from the edges of the seeds arrays without additional nucleations, we obtained single-crystalline graphene with an area four times larger than the mother graphene seed substrate. Moreover, the defect-healing process eliminated the inherent defects of seeds, ensuring the reliability and crystallinity of the single-crystalline graphene for industrialization.

Despite the enormous potential of the single-crystalline two-dimensional (2D) materials for a wide range of future innovations and applications, 2D single-crystals are still suffering in industrialization due to the lack of efficient large-area production methods. In this work, we introduce a general approach for the scalable growth of single-crystalline graphene, which is a representative 2D material, through "transplanting" uniaxially aligned graphene "seedlings" onto a larger-area catalytic growth substrate. By inducing homoepitaxial growth of graphene from the edges of the seeds arrays without additional nucleations, we obtained single-crystalline graphene with an area four times larger than the mother graphene seed substrate. Moreover, the defect-healing process eliminated the inherent defects of seeds, ensuring the reliability and crystallinity of the single-crystalline graphene for industrialization.

The electrical and optical properties of semiconducting transition metal dichalcogenides (TMDs) can be tuned by controlling their composition and the number of layers they have. Among various TMDs, the monolayer WSe2 has a direct bandgap of 1.65 eV and exhibits p-type or bipolar behavior, depending on the type of contact metal. Despite these promising properties, a lack of efficient large-area production methods for high-quality, uniform WSe2 hinders its practical device applications. Various methods have been investigated for the synthesis of large-area monolayer WSe2, but the difficulty of precisely controlling solid-state TMD precursors (WO3, MoO3, Se, and S powders) is a major obstacle to the synthesis of uniform TMD layers. In this work, we outline our success in growing large-area, high-quality, monolayered WSe2 by utilizing methane (CH4) gas with precisely controlled pressure as a promoter. When compared to the catalytic growth of monolayered WSe2 without a gas-phase promoter, the catalytic growth of the monolayered WSe2 with a CH4 promoter reduced the nucleation density to 1/1000 and increased the grain size of monolayer WSe2 up to 100 μm. The significant improvement in the optical properties of the resulting WSe2 indicates that CH4 is a suitable candidate as a promoter for the synthesis of TMD materials, because it allows accurate gas control.

In article number 1900084, Ji-Yun Moon, Dongmok Whang, Hak Ki Yu, Jae-Hyun Lee, and co-workers demonstrate a clean transfer method for large scale chemical vapor deposition (CVD) graphene using MoO3 as a protective film, which can be dissolved in pure DI water, easily and completely. The authors believe that this approach provides new solutions to overcome the limitations of the conventional transfer methods for CVD graphene and pave the way for future transfer method for CMOS manufacturing processes.

Twisted bi-layer graphene (tBLG) has attracted much attention because of its unique band structure and properties. The properties of tBLG vary with small differences in the interlayer twist angle, but it is difficult to accurately adjust the interlayer twist angle of tBLG with the conventional fabrication method. In this study, we introduce a facile tBLG fabrication method that directly picks up a single-crystalline graphene layer from a growth substrate and places it on another graphene layer with a pre-designed twist angle. Using this approach, we stacked single-crystalline graphene layers with controlled twist angles and thus fabricated tBLG and twisted multi-layer graphene (tMLG). The structural, optical and electrical properties depending on the twist angle and number of layers, were investigated using transmission electron microscopy (TEM), micro–Raman spectroscopy, and gate-dependent sheet resistance measurements. The obtained results show that the pick and place approach enables the direct dry transfer of the top graphene layer on the as-grown graphene to fabricate uniform tBLG and tMLG with minimal interlayer contamination and pre-defined twist angles.

Since the first realization of graphene synthesis through the chemical vapor deposition (CVD) method in 2009, CVD-graphene is regarded as a key material in the future electronics industry, and one that requires high standard characteristics. However, because graphene itself is not a semiconductor, therefore it does not have a bandgap, a promising application is considered to integrate its use with semiconductors, rather than completely replace Si or Ge. Although numerous methods for a clean and uniform graphene transfer process are developed, graphene growth and transfer methods that are applicable to current mainstream Si-based complementary metal-oxide-semiconductor (CMOS) manufacturing processes are not yet introduced. This study implements an eco-friendly and CMOS-compatible graphene transfer process through water-soluble inorganic MoO3 film as a supporting layer. Since the monolayer graphene is grown on hydrogen-terminated semiconductor Ge surface, the MoO3 thin film coated graphene is easily delaminated from the Ge substrate. The separated graphene could be transferred to arbitrary substrate without a chemical wet etching process, and the remaining Ge substrate could be employed for about 50 times multiple reuse for the growth of graphene, without degradation of the crystallinity of the graphene.

A highly transparent and conductive, flexible electrode is developed by alternative stacking of graphene and 2D doping layers. The transparent conducting electrode (TCE), reported by Jae-Young Choi, Dongmok Whang, and co-workers in article number 17000622, has a high optical transmittance (>90% at 550 nm), a low sheet resistance (50 Ω sq−1) and excellent thermal and mechanical stability, which shows that stacking graphene with stable 2D doping layers is a promising approach for graphene-based TCEs.

Graphene, an ultrathin flexible material with high carrier mobility and transparency, is a promising candidate for flexible transparent conducting electrodes (TCEs). However, its resistance is too high for use as a TCE material by itself. Therefore, fabricating graphene with low sheet resistance and high stability is a significant challenge for practical applications of graphene TCEs. In this study, a 2D doping layer (DL) is proposed, which can stably dope graphene to develop a highly transparent graphene TCE with low sheet resistance. For this purpose, the 2D DL is prepared by immobilizing dopant molecules on transparent graphene oxide and simply stacking it with graphene enables efficient and stable charge transfer doping of the graphene. A TCE fabricated by alternately stacking the DL and graphene has a high optical transmittance of over 90% at a wavelength of 550 nm and a low sheet resistance of 50 Omega sq(-1). Furthermore, the sheet resistance shows an excellent thermal and mechanical stability with a change of only about 2% in a bending test of 20 000 cycles or at a high temperature of 220 degrees C. This result shows that stacking graphene with stable 2D DL is a promising approach for graphene-based next generation TCE.

We report the direct growth of graphene on a dielectric SiO2 surface by utilizing complementary metal oxide semiconductor compatible germane as a gas-phase catalyst. Results of Raman spectroscopy and XPS confirmed that the synthesized graphene consist of a sp2 hybridized carbon network. We were able to fabricate graphene field effect transistors without the wet etching process, and the calculated mobility was ∼160 cm2/V·s at high carrier concentration (n = 3 × 1012 cm−2). Furthermore, the crystallinity and morphology of graphene is easily controlled from single-layer graphene to graphene nanowall structures by adjusting the reaction conditions. The results of this study verify the promising catalytic graphene growth method on a non-catalytic insulating surface without metal contaminations.

Graphene growth on a copper surface via metal-catalyzed chemical vapor deposition has several advantages in terms of providing high-quality graphene with the potential for scale-up, but the product is usually inhomogeneous due to the inability to control the graphene layer growth. The non-uniform regions strongly affect the reliability of the graphene in practical electronic applications. Herein, we report a novel graphene transfer method that allows for the selective exfoliation of single-layer graphene from non-uniform graphene grown on a Cu foil. Differences in the interlayer bonding energy are exploited to mechanically separate only the top single-layer graphene and transfer this to an arbitrary substrate. The dry-transferred single-layer graphene showed electrical characteristics that were more uniform than those of graphene transferred using conventional wet-etching transfer steps.

, 286 (2014); 344 Science et al. Jae-Hyun Lee Reusable Hydrogen-Terminated Germanium Wafer-Scale Growth of Single-Crystal Monolayer Graphene on This copy is for your personal, non-commercial use only. clicking here. colleagues, clients, or customers by , you can order high-quality copies for your If you wish to distribute this article to others here. following the guidelines can be obtained by Permission to republish or repurpose articles or portions of articles ): April 22, 2014 www.sciencemag.org (this information is current as of The following resources related to this article are available online at http://www.sciencemag.org/content/344/6181/286.full.html version of this article at: including high-resolution figures, can be found in the online Updated information and services, http://www.sciencemag.org/content/suppl/2014/04/02/science.1252268.DC1.html can be found at: Supporting Online Material http://www.sciencemag.org/content/344/6181/286.full.html#ref-list-1 , 6 of which can be accessed free: cites 32 articles This article http://www.sciencemag.org/cgi/collection/mat_sci Materials Science subject collections: This article appears in the following

The uniform growth of single-crystal graphene over wafer-scale areas remains a challenge in the commercial-level manufacturability of various electronic, photonic, mechanical, and other devices based on graphene. Here, we describe wafer-scale growth of wrinkle-free single-crystal monolayer graphene on silicon wafer using a hydrogen-terminated germanium buffer layer. The anisotropic twofold symmetry of the germanium (110) surface allowed unidirectional alignment of multiple seeds, which were merged to uniform single-crystal graphene with predefined orientation. Furthermore, the weak interaction between graphene and underlying hydrogen-terminated germanium surface enabled the facile etch-free dry transfer of graphene and the recycling of the germanium substrate for continual graphene growth.