Novel Devices ♦ news digest
Due to their miniature property; they are highly versatile and flexible. The uniqueness of QD material lies in the fact that its power intensity depends on the input source and size of QD.
There are several ways to confine excitons in semiconductors, resulting in different methods to produce quantum dots. In general, quantum wires, wells, and dots are grown by advanced epitaxial techniques in nanocrystals produced by chemical methods or by ion implantation, or in nanodevices created from state-of-the- art lithographic techniques.
The QD market is expected to grow from $108.41 million that it accounts for, currently, in 2013 to $3,414.54 million in 2020, at a CAGR of 71.13 percent from 2014 to 2020. Optoelectronics applications are expected to be the major market share holder with an expected revenue generation of $2,458.47 million in 2020.
Exfoliation method paves the way for photonics and electronics
The versatility of new technique for materials shows promise as a new benchmark in exfoliation chemistry of two-dimensional chalcogenides
A team of scientists from the National University of Singapore (NUS) has developed a method to chemically exfoliate molybdenum disulphide crystals, into high quality monolayer flakes, with higher yield and larger flake size than current methods.
The exfoliated chalcogenide compound flakes can be made into a printable solution, which can be applied in printable photonics and electronics.
This breakthrough, led by Loh Kian Ping, a professor who heads the Department of Chemistry at the NUS Faculty of Science, and is also a principal investigator with the Graphene Research Centre at the Faculty, has generic applicability to other two-dimensional chalcogenides. These include tungsten diselenide and titanium disulphide, and results in high yield exfoliation for all of these two-dimensional materials.
The NUS team collaborated with scientists from the Ulsan National Institute of Science and Technology in Korea, and the findings were first published online in prestigious scientific journal Nature Communications on 2nd January 2014.
Demand for high efficiency exfoliation method
Transition metal dichalcogenides, formed by a combination of chalcogens, such as sulphur or selenium, and transition metals, such as molybdenum or tungsten, have recently attracted great attention as the next generation of two-dimensional materials due to their unique electronic and optical properties, for applications in optoelectronic devices such as thin film solars, photodetectors flexible logic circuits and sensors.
However, current processes of producing printable single layer chalcogenides 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.
As most applications require clean and large-sized flakes, this pinpoints a clear need to explore new ways to make high quality single-layer transition metal dichalcogenides with high yield.
Breakthrough in production
To address the production bottleneck, the NUS team explored the metal adducts of naphthalene. They prepared naphthalenide adducts of lithium, sodium and potassium, and compared the exfoliation efficiency and quality of molybdenum disulphide generated. The processing steps are detailed below.
Schematic of pre-exfoliation, intercalation and exfoliation processes
a. Bulk molybdenum disulphide crystal was expanded by decomposition of hydrazine
b.The expanded molybdenum disulphide reacted with sodium naphthalenide to form an intercalation sample, then exfoliated into single layer sheets by immersing in water. c. Scanning electron microscopy image of single layer molybdenum disulphide on silicon dioxide d. Atomic force microscopy image of single layer molybdenum disulphide on silicon dioxide e. Bulk single crystal molybdenum disulphide
January / February 2014
www.compoundsemiconductor.net 161
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