Since the first isolation of graphene in 2004, [1] 2D materials have gained growing attention because of their unique physical and physicochemical properties, [2,3] originating from their reduced dimensions, [4] strong electron confinement, [5] abundant active sites, [6] and edge polarization. [7] These features, in turn, endow 2D materials with exciting prospects for promising applications in the fields of energy storage/conversion and optoelectronics. In the early stages, the research on 2D materials was primarily focused on single or binary elemental materials. [8][9][10][11][12][13] Recently, however, 2D ternary materials have attracted increasing attention due to their multiple degrees of freedom. [14][15][16][17][18][19][20] The added freedom of stoichiometry variation in 2D ternary materials can be used to tune their physical properties and therefore may lead to promising applications. [21,22] Ternary Ga 2 In 4 S 9 is a layered material with weak van der Waals interaction and reveals n-type semiconducting behavior. [23,24] The multinary compound that reveals an unprecendented robust electronic character as well as a wide bandgap close to 2.7 eV with pronounced photosensitivity and temperature-dependent optical absorption edge opens a new paradigm for UV detection. [23] This is particularly desirable for military and civilian fields. [25] Specifically, as a kind of homobimetallic sulfide, the ternary Ga 2 In 4 S 9 is believed to possess novel electronic and optoelectronic properties compared the 2D counterparts. [26] Up to now, only work on bulk Ga 2 In 4 S 9 with a thickness of a few micrometers has been reported, in which bulk Ga 2 In 4 S 9 is obtained by chemical vapor transport. [23,27] The bulk structure actually hinders their practical application in the field of micro-nano electronic and optoelectronic devices. [28] Unfortunately, there are no reports on the synthesis of 2D ternary Ga 2 In 4 S 9 flakes with controllable stoichiometry, which may be attributed to the difficulty in selecting optimal homobimetallic precursors. Recently, the creation of atomically thin metal oxides or selenides by adopting eutectic gallium melts with tunable metal elements offers a promising approach to grow ternary semiconductors. [29][30][31][32] In this letter, we report the growth of ultrathin Ga 2 In 4 S 9 flakes by employing liquid gallium/indium (Ga/In) alloy as the reaction environment. Because of the reduced reaction temperature by using the liquid Ga/In alloy, [31] the key point of our growth 2D ternary systems provide another degree of freedom of tuning physical properties through stoichiometry variation. However, the controllable growth of 2D ternary materials remains a huge challenge that hinders their practical applications. Here, for the first time, by using a gallium/indium liquid alloy as the precursor, the synthesis of high-quality 2D ternary Ga 2 In 4 S 9 flakes of only a few atomic layers thick (≈2.4 nm for the thinnest samples) through chemical vapor deposition is realized. Their UV-light-sensing appl...
