Rapid Flame Synthesis of Atomically Thin MoO₃ down to Monolayer Thickness for Effective Hole Doping of WSe₂

Abstract

Two-dimensional (2D) molybdenum trioxide (MoO) with mono- or few-layer thickness can potentially advance many applications, ranging from optoelectronics, catalysis, sensors, and batteries to electrochromic devices. Such ultrathin MoO sheets can also be integrated with other 2D materials (e.g., as dopants) to realize new or improved electronic devices. However, there is lack of a rapid and scalable method to controllably grow mono- or few-layer MoO. Here, we report the first demonstration of using a rapid (<2 min) flame synthesis method to deposit mono- and few-layer MoO sheets (several microns in lateral dimension) on a wide variety of layered materials, including mica, MoS, graphene, and WSe, based on van der Waals epitaxy. The flame-grown ultrathin MoO sheet functions as an efficient hole doping layer for WSe, enabling WSe to reach the lowest sheet and contact resistance reported to date among all the p-type 2D materials (∼6.5 kΩ/□ and ∼0.8 kΩ·μm, respectively). These results demonstrate that flame synthesis is a rapid and scalable pathway to growing atomically thin 2D metal oxides, opening up new opportunities for advancing 2D electronics.

Engineering Field Effect Transistors with 2D Semiconducting Channels: Status and Prospects

“…This effect has been extensively investigated in devices with metal–MoS 2 contacts, but seems to be potentially less pronounced in other TMDs—because the forming energy of chalcogen vacancies (e.g., S, Se) in other TMDs (i.e., MoSe 2 , WS 2 ) is larger than that of sulfur vacancies in MoS 2 , which may reduce the number of vacancies in such TMDs compared to MoS 2 . Doping the metal/channel interface with substoichiometric oxides (MoO x , TiO x , and AlO x ) and/or NO 2 can efficiently lower the Schottky barrier, due to the suppression of Fermi level pinning at the interface of 2D materials and metal electrodes. Another option is to insert a buffer layer between the metal and the 2D channel, such as graphene or a thin insulating dielectric layer (such as 2 nm MgO, 1 nm TiO 2 , or 1–2 layer 2D insulating h‐BN), to form a tunneling buffer layer resulting in a metal–insulator–semiconductor (MIS) structure, which has shown a remarkable reduction of the Schottky barrier with small tunneling resistance.…”

HfSe 2 and ZrSe 2 : Two-dimensional semiconductors with native high-κ oxides

“…However, this interfacial engineering perpetuates a long-standing flaw in high-κ integration on silicon, wherein several angstroms of native SiO x are grown as a buffer, deteriorating the series capacitance of the combined dielectric gate stack ( 4 , 5 ). In addition, for Mo- and W-based dichalcogenides, this approach is nonideal because MoO 3 and WO 3 , respectively, are not good insulators and may even act as dopants ( 15 , 17 , 18 ).…”

Effect of Adventitious Carbon on Pit Formation of Monolayer MoS2

“…SO x leaves and MoO x moves, forming pits on MoS 2 monolayers. MoO x is difficult to observe in TEM due to its sensitivity to the electron beam [32] but the formation of MoO x was confirmed by SEM, Auger electron spectroscopy (AES), and XPS analysis of ex situ thermal oxidation of MoS 2 monolayers ( Figure S14, Supporting Information).…”