Synthesis of ultrathin two-dimensional nanosheets and van der Waals heterostructures from non-layered γ-CuI

Abstract

Two-dimensional (2D) nanosheets have attracted considerable recent interest for their atomically thin geometry and unique thickness-dependent electronic properties. The 2D nanosheets studied to date are generally limited to intrinsically layered materials, in which the covalently bonded atomic layers are held together by weak van der Waals forces and can be readily exfoliated to single or few-atom thick nanosheets. To prepare 2D nanosheets from non-layered materials can greatly expand the scope of 2D materials, but is much less straightforward. Here, we report the successful synthesis of ultrathin nanosheets from nonlayered γ-CuI on SiO 2 /Si substrate using a facile physical vapor deposition process. The resulting γ-CuI nanosheets display a triangular and hexagonal geometry with the lateral dimension up to 5 μm and thickness down to 1 nm. Raman spectroscopy, X-ray diffraction, and transmission electron microscopy studies demonstrate the resulting nanosheets retain single-crystalline γ-CuI phase. Additionally, we further show the γ-CuI nanosheets can be readily grown on other 2D materials (e.g., 2D-WSe 2 , 2D-WS 2) to form van der Waals heterostructures (vdWHs). Optical microscopy images and Raman intensity mappings confirm the formation of γ-CuI/WS 2 and γ-CuI/WSe 2 vertical heterostructures. The electrical transport studies show that γ-CuI nanosheets exhibit a low resistivity of~0.3 Ω cm and γ-CuI/WS 2 vertical heterostructures display a p-n diode behavior with distinct current rectification. The synthesis of γ-CuI nanosheets and heterostructures open a pathway to ultrathin nanosheets and van der Waals heterostructures from non-layered materials and could open up exciting opportunities in electronics and optoelectronics.

Optoelectronic and photonic devices based on transition metal dichalcogenides

“…The heterostructure consisting of GQDs, physical vapor deposition (PVD) grown monolayer (ML) WSe 2 and n-type Si can reach a responsivity of ∼700 mA W −1 at a short response time of 0.2 ms. The technique is scalable due to PVD-grown large area ML WSe 2 as opposed to the mechanical exfoliation technique adopted in a majority of PD studies [91,92]. Figure 4(b) illustrates the (i) schematic, (ii) photoresponse and (iii) transport mechanism of a nitrogendoped (N-)GQD/ML WSe 2 heterostructure FET [93].…”

Solution-processed two-dimensional materials for next-generation photovoltaics

“…In addition, their chemical reactivity can be used to create in situ interface engineering for the design/realization of novel concepts of charge extraction. 109,214 Example of 2D nonlayered materials are oxides/hydroxides (e.g., a-FeOOH, 215 CoOOH, 215 TiO 2 , 215 g-Ga 2 O 3 , 216 Fe 2 O 3 , 217 Co 3 O 4 , 217 Mn 2 O 3 , 217 and mixed oxides such as ZnMn 2 O 4 (ZMO), 217 ZnCo 2 O 4 , 217 NiCo 2 O 4 , 217 and CoFe 2 O 4 217 ), sulfides (e.g., Ga 2 S 3 , 218 ZnS, 215 NiS, 215 FeS 2 , 219 and CuFeS 2 220 ), selenides (e.g., In 2 Se 3 221 and ZnSe 222 ), tellurides (e.g., ZnTe), 223 Ni-B oxide, 224 g-CuBr, 225 CuI, 226 InI, 227 PbS, 215 carbonates (e.g., CaCo 3 , ZnCO 3 , MnCO 3 , FeCO 3 , and PbCO 3 ), 215 as well as elemental Ge, 228 Bi, 229,230 Te, 231 and Se. 232 In this list, In 2 S 3 is a direct-bandgap semiconductor in both monolayer and few-layer forms, 221 leading to a significantly different behavior compared to group-6 TMDs.…”

Optoelectronic properties of the CuI, AgI and Janus Cu2BrI, and Ag2BrI monolayers by many-body perturbation theory

“…The bulk γ-phase of CuI is known for a high thermopower coefficient and substantial optoeletric properties [17]. Very recently, ultrathin nanosheets of γ-phase CuI has been synthesized on SiO 2 /Si substrate using a facile physical vapor deposition process [18]. It was also shown that the CuI nanosheets can be synthesized on the 2D substrates like WS 2 and WSe 2 .…”