Creating improved inkjet-printable materials for electronics and photonics
January 10, 2014
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National University of Singapore
(NUS) scientists have developed a new method for creating a chemical
solution of molybdenum disulfide for use in printable optoelectronic
devices such as thin film solar cells, flexible logic circuits,
photodetectors, and sensors.
Inkjet-printing molybdenum disulfide thin film at the end of an optical fiber (credit: TUS)
Molybdenum disulfide, combined with gold atoms, is being studied for development of ultrafast, ultrathin logic devices, as noted previously on KurzweilAI.
The process:
1. Chemically exfoliate (peel off) molybdenum disulfide crystals into high-quality single-layer flakes (the new method achieves higher yield and larger flake size than current methods).
2. Convert the flakes into an inkjet-printable solution (the good dispersion and high viscosity of the flakes make them highly suitable for inkjet printing).
3. Print wafer-size films
Current processes of producing printable single-layer chalcogenides (such as molybdenum disulfide) take a long time and the yield is poor. The flakes produced are of submicron sizes, which make it challenging to isolate a single sheet for making electronic devices.
The NUS team prepared naphthalenide combinations of lithium, sodium and potassium, and compared the exfoliation efficiency and quality of molybdenum disulfide generated.
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The NUS team collaborated with scientists from the Ulsan National Institute of Science and Technology in Korea.
Schematic
of (a) pre-exfoliation (peeling), (b) intercalation (merging layers)
and exfoliation processes. (c) Photograph of bulk single-crystal MoS2
(d) photograph of pre-exfoliated MoS2 (e) photograph of
sodium-exfoliated single-layer MoS2 dispersion in water. (credit: NUS)
Abstract of Nature Communications paper
Transition-metal dichalcogenides like molybdenum disulphide have attracted great interest as two-dimensional materials beyond graphene due to their unique electronic and optical properties. Solution-phase processes can be a viable method for producing printable single-layer chalcogenides. Molybdenum disulphide can be exfoliated into monolayer flakes using organolithium reduction chemistry; unfortunately, the method is hampered by low yield, submicron flake size and long lithiation time. Here we report a high-yield exfoliation process using lithium, potassium and sodium naphthalenide where an intermediate ternary LixMXn crystalline phase (X=selenium, sulphur, and so on) is produced. Using a two-step expansion and intercalation method, we produce high-quality single-layer molybdenum disulphide sheets with unprecedentedly large flake size, that is up to 400 μm2. Single-layer dichalcogenide inks prepared by this method may be directly inkjet-printed on a wide range of substrates.
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