![]() Therefore, significant radiative exciton decay occurs that produces photoluminescence (PL) 14. Due to this modest energy difference between conduction band minimums at the M and Γ points, free carriers can be exchanged between valleys via room temperature thermal excitation 17. Specially, bilayer GaS, which has a thickness equivalent to c of the unit cell, is an indirect bandgap semiconductor with a conduction band minimum at the M point and an associated bandgap of ∼3.1 eV and a direct transition at the Γ point with only a ∼210 meV wider bandgap 17. The electronic band structure of 2D GaS is particularly interesting 4, 16, 17. ( h) Two concurrent steps of chemical vapour treatment: first, GaCl 3 layer is formed via exposure to HCl vapour and, second, sulfurization by exposure to S vapour forming GaS. ( g) Placing Ga liquid metal and removing it with soft PDMS that leaves a cracked layer of Ga oxide. ( f) Covering the exposed area of the substrate with vaporized FDTES. ![]() ( e) Lithography process for establishing the negative pattern of the photoresist. ( e, h) Schematics of the synthesis process for patterning 2D GaS via printing the skin oxide of liquid Ga. The SiO 2 substrate becomes more hydrophobic and thus resists wetting by liquid Ga. ( c, d) Functionalization of the substrate with FDTES changes the contact angle between a Ga drop and the substrate by 12.9°. The Ga atoms are green and the S atoms are blue. The GaS crystal lattice is composed of Ga–Ga and Ga–S covalent bonds that extend in two dimensions, forming a stratified crystal made of planes that are held together by van der Waals attractions. ( a) Side view of bilayer GaS, showing a unit cell c=15.492 Å made of two GaS layers. Stick-and-ball representation of GaS crystal. 2D GaS has been recently explored for applications in transistors 10, energy storage 12, optoelectronics 13, gas sensing 14 and nonlinear optics 15. A representative example of this family is gallium (II) sulfide (GaS) that has a hexagonal crystal structure with a unit cell of a= b=3.587 Å, c=15.492 Å ( c is equal to two fundamental layers of GaS Fig. This family typically exists in the monochalcogenide form of MX, where M=Ga, In and X=S, Se, Te, with further stoichiometries based on higher oxidation states also reported 10, 11. However, the temperatures used are above 550 ☌ that is incompatible with many electronic industry processes and, more negatively, the deposition process takes many hours that significantly adds to the cost and practicality.Īmong the family of 2D materials, semiconductors based on post-transition metals of group III and VI elements have been scarcely explored. So far, only one report has addressed the wafer-scale homogeneity for the deposition of MoS 2 using a metal–organic chemical vapour-based technique 9. However, large-scale, high-quality and homogeneous deposition of such 2D sheets has proven to be a major challenge. Many methods have been proposed for the synthesis of 2D materials including exfoliation of flakes from a layered bulk 2, 5 followed by depositing the obtained flakes on a desired substrate, as well as chemical vapour deposition 6, 7 and atomic layer deposition 8 techniques for directly growing 2D layers on substrates. The initial step in fabricating such devices is the formation of the 2D sheet on a chosen substrate. ![]() 2D semiconductors, the most common of which are transition metal dichalcogenides, have recently attracted significant attention, particularly in electronic and optical device fabrication 1, 3. Two-dimensional (2D) materials present many promising avenues for future technologies due to their remarkable characteristics 1, 2, 3, 4. The presented deposition and patterning method offers great commercial potential for wafer-scale processes. By controlling the surface chemistry of the substrate, we produce large area two-dimensional semiconducting GaS of unit cell thickness ( ∼1.5 nm). In the case of liquid gallium, the oxide skin attaches exclusively to a substrate and is then sulfurized via a relatively low temperature process. The layer increases the wettability of the liquid metal placed on oxygen-terminated substrates, leaving the thin oxide layer behind. In an oxygen-containing atmosphere, these metals establish an atomically thin oxide layer in a self-limiting reaction. ![]() Here we introduce a technique for depositing and patterning of wafer-scale two-dimensional metal chalcogenide compounds by transforming the native interfacial metal oxide layer of low melting point metal precursors (group III and IV) in liquid form. A variety of deposition methods for two-dimensional crystals have been demonstrated however, their wafer-scale deposition remains a challenge. ![]()
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