News: Suppliers
19 June 2025
University of Michigan synthesizes high-quality 2D molybdenum disulfide using Veeco’s Fiji ALD system
Using the Fiji G2 plasma-enhanced atomic layer deposition (PEALD) system of epitaxial deposition and process equipment maker Veeco Instruments Inc of Plainview, NY, USA, the University of Michigan has reported the ALD of molybdenum disulfide (MoS2) using di-tert-butyl disulfide (TBDS) as a replacement for hydrogen sulfide (H2S) (Chemistry of Materials vol 37, issue 4, 11 February 2025).
H2S has been used in many sulfide ALD processes, but it is a toxic gas that requires expensive containment and abatement measures for shipping, installation and storage. In contrast, TBDS is a liquid that is significantly less hazardous and expensive than H2S.
Chemistry, Materials Science and Engineering professor Ageeth Bol and her team of students and postdoctoral students used a PEALD process to deposit high-quality two-dimensional (2D) MoS2 using an organometallic precursor and TBDS, in combination with hydrogen (H2) plasma. This research introduces a method of using TBDS liquid that is significantly less hazardous than H2S and eliminates the need for expensive safety measures associated with H2S use.
Growing interest in addressing the challenges of adopting two-dimensional materials in high-volume manufacturing has prompted a wide range of R&D activity, spurring collaboration between equipment suppliers and stakeholders. Two-dimensional materials have unique, controllable properties, including exceptional electrical conductivity, durability and optical transparency. These properties enable applications in flexible displays, sensors, energy storage, and optoelectronics.
“This development is an important step in the evolution of enabling large-scale integration of 2D transition-metal di-chalcogenides into commercial devices,” believes Ganesh Sundaram, VP of technology for ALD & MBE at Veeco. “The synthesis route undertaken by professor Bol and her group resulted in high-quality, stoichiometric molybdenum disulfide film [with limited contamination], and additionally resolves the safety and cost issues that can be associated with the use of traditional hydrogen sulfide-based processes.”
The TBDS-based PEALD process was also analyzed via mass spectrometry to determine the mechanistic roles of each reactant. Apparently, H2 plasma removes ligands from the chemisorbed Mo precursor, which allows TBDS to sulfurize the top layer, producing H2S and isobutene as byproducts. MoS2 films deposited via the TBDS-based process possessed fewer yet taller out-of-plane growths and similar crystal grain diameter (~10nm) and electrical resistivity (13.6–15.5Ω cm for 3nm-thick films) compared with films made with H2S. Thus, the TBDS-based process is a suitable and safer alternative to the H2S-based process for large-area synthesis of layered MoS2.
Veeco’s Fiji plasma-enhanced ALD system is a modular, high-vacuum thermal ALD system that supports thermal and plasma-enhanced deposition. “We’ve been pleased with the performance and capabilities of the Fiji and with our interactions with Veeco’s scientific team,” states Bol. “Indeed, we are in the process of commissioning a second Fiji system for our group, which is the third system received by the University of Michigan, to support further research activities.”
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