image: (a) Schematic of vapor deposition process with two heat zones. (b) SEM image of fibers formed on SiO2/Si substrate. (c) Comparison of XRD data for fibers and the source. (d) TEM image of a fiber. (e) Corresponding SAED pattern of the fiber in d. (f) Optical image of thin-film transferred onto SiO2/Si substrate. Inset: a 5 cm × 5 cm thin film on Si/SiO2 wafer. (g) Optical closed-up image of a thin film with an edge. Inset: the corresponding SEM image of the thin film sample. (h) AFM height image of the thin film with an edge on a SiO2/Si substrate, which shows that the thickness of the thin film is approximately 2.81 nm (Inset). (i) XPS spectra of a thin film on SiO2/Si (top red) and source (bottom blue), showing the absence of Br groups in the thin film. view more
Credit: ©Science China Press
This research is accomplished by Wenqian Yao (Sino-Danish Center for Education and Research, Sino-Danish College, University of Chinese Academy of Sciences, Beijing 100049, China.) and Dr. He Yang (Beijing National Laboratory for Molecular Sciences, Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Science, Beijing 100190, P. R. China) under the guidance of Prof. Yunqi Liu and Prof. Bin Wu.
It is well-known that chemical vapor deposition is a conventional synthesis method to fabricate large-scale and high-quality two-dimensional materials, such as graphene, hexagonal boron nitride, and transition-metal dichalcogenides. While, for organic films, solution-based methods, such as inkjet printing, spin coating, and drop and micro-contact printing, are commonly used.
Wenqian Yao and He Yang, together with lab director Yunqi Liu and Bin Wu, sought to determine whether insoluble molecules could also be used to prepare films with chemical vapor deposition. They chose three kinds of molecules which were homemade in Yunqi Liu’s group.
The team demonstrate a general method for growing wafer-scale continuous, uniform, and ultrathin (2–5 nm) organic films. This method is based on a copper (Cu) surface-mediated reaction and polymerization of several equivalent bromine (Br)-containing π-conjugated small molecules (C12S3Br6, C24H4O2Br2, and C24H12Br2N4), in which local surface-mediated polymerization and internal π-π interactions among organic molecules are responsible for the dimension and uniformity control of the thin films. Besides, by using different facet of underlying Cu substrates, the growth rate and morphology of thin films were found to be Cu-facet-dependent, and single-crystal Cu(111) surfaces could improve the uniformity of thin films. In addition, the number of Br groups and size of organic molecules were critical for crystallinity and thin-film formation.
It is proposed that this method can be used to fabricate heterostructures, such as organic film/graphene, paving a new way for various functional materials and device applications.
See the article:
Vapor-solid interfacial reaction and polymerization for wafer-scale uniform and ultrathin two-dimensional organic films
https://doi.org/10.1007/s40843-021-1918-x