Graphene nanoribbons (GNRs), quasi-one-dimensional graphene strips, have shown great potential for nanoscale electronics, optoelectronics, and photonics. Atomically precise GNRs can be "bottom-up" synthesized by surface-assisted assembly of molecular building blocks under ultra-high-vacuum conditions. However, large-scale and efficient synthesis of such GNRs at low cost remains a significant challenge. Here we report an efficient "bottom-up" chemical vapor deposition (CVD) process for inexpensive and high-throughput growth of structurally defined GNRs with varying structures under ambient-pressure conditions. The high quality of our CVD-grown GNRs is validated by a combination of different spectroscopic and microscopic characterizations. Facile, large-area transfer of GNRs onto insulating substrates and subsequent device fabrication demonstrate their promising potential as semiconducting materials, exhibiting high current on/off ratios up to 6000 in field-effect transistor devices. This value is 3 orders of magnitude higher than values reported so far for other thin-film transistors of structurally defined GNRs. Notably, on-surface mass spectrometry analyses of polymer precursors provide unprecedented evidence for the chemical structures of the resulting GNRs, especially the heteroatom doping and heterojunctions. These results pave the way toward the scalable and controllable growth of GNRs for future applications.

wafer-scale, with good crystallinity and with contamination levels compatible with large-scale back-end-of-line (BEOL) integration. At present, chemical vapor deposition (CVD) on catalytic copper (Cu) substrates is widely recognized as the most promising route to obtain scalable monolayer graphene for electronic and optoelectronic applications. [1][2][3][4] However, significant hurdles are limiting the actual integration of CVD graphene grown on Cu for most applications. In the first instance, the unavoidable transfer process over wafer-scale is rather cumbersome and introduces contamination, unintentional doping, and mechanical stress, [5][6][7] which adversely impact the physical integrity and electrical performance [8] of the graphene layer. The significant challenge involved in carrying out this seemingly straightforward task is reflected by the vast literature on large-scale transfer processes. Second, metallic contamination levels in transferred CVD graphene grown on Cu are typically well-above the specifications requested for BEOL integration. [6] Clearly, asThe adoption of graphene in electronics, optoelectronics, and photonics is hindered by the difficulty in obtaining high-quality material on technologically relevant substrates, over wafer-scale sizes, and with metal contamination levels compatible with industrial requirements. To date, the direct growth of graphene on insulating substrates has proved to be challenging, usually requiring metal-catalysts or yielding defective graphene. In this work, a metal-free approach implemented in commercially available reactors to obtain high-quality monolayer graphene on c-plane sapphire substrates via chemical vapor deposition is demonstrated. Low energy electron diffraction, low energy electron microscopy, and scanning tunneling microscopy measurements identify the Al-rich reconstruction9° of sapphire to be crucial for obtaining epitaxial graphene. Raman spectroscopy and electrical transport measurements reveal high-quality graphene with mobilities consistently above 2000 cm 2 V −1 s −1 . The process is scaled up to 4 and 6 in. wafers sizes and metal contamination levels are retrieved to be within the limits for back-end-ofline integration. The growth process introduced here establishes a method for the synthesis of wafer-scale graphene films on a technologically viable basis.

Graphene nanoribbons (GNRs) are a novel and intriguing class of materials in the field of nanoelectronics, since their properties, solely defined by their width and edge type, are controllable with high precision directly from synthesis. Here we study the correlation between the GNR structure and the corresponding device electrical properties. We investigated a series of field effect devices consisting of a film of armchair GNRs with different structures (namely width and/or length) as the transistor channel, contacted with narrowly spaced graphene sheets as the source-drain electrodes. By analyzing several tens of junctions for each individual GNR type, we observe that the values of the output current display a width-dependent behavior, indicating electronic bandgaps in good agreement with the predicted theoretical values. These results provide insights into the link between the ribbon structure and the device properties, which are fundamental for the development of GNR-based electronics.