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Synthesis and characterization of tw...

Gao, Jian.

Synthesis and characterization of two dimensional transition metal dichalcogenides.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Synthesis and characterization of two dimensional transition metal dichalcogenides.
Author:	Gao, Jian.
Published:	Ann Arbor : ProQuest Dissertations & Theses, 2016
Description:	102 p.
Notes:	Source: Dissertation Abstracts International, Volume: 77-10(E), Section: B.
Notes:	Advisers: Nikhil Koratkar; Toh-Ming Lu.
Contained By:	Dissertation Abstracts International77-10B(E).
Subject:	Materials science.
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10123926
ISBN:	9781339820675

Synthesis and characterization of two dimensional transition metal dichalcogenides.
Gao, Jian.

Synthesis and characterization of two dimensional transition metal dichalcogenides. - Ann Arbor : ProQuest Dissertations & Theses, 2016 - 102 p.

Source: Dissertation Abstracts International, Volume: 77-10(E), Section: B.

Thesis (Ph.D.)--Rensselaer Polytechnic Institute, 2016.

Two-dimensional transition metal dichalcogenides (TMDs) are an emerging class of atomically thin semiconductors that show potential in next-generation electronics, optoelectronics, and energy storage batteries. The successful synthesis and doping of TMDs is the key to their applications. I have synthesized monolayer MoS2, WS2, and multilayer ReS2 flakes by CVD, and studied an unprecedented one-pot synthesis for transition-metal substitution doping in large-area, synthetic monolayer TMDs. Electron microscopy, optical and electronic transport characterization and ab initio calculations indicate that our doping strategy preserves the attractive qualities of TMD monolayers, including semiconducting transport and strong direct-gap luminescence. The Re doping of MoS2 greatly improve the contact quality (one of the biggest issue in TMDs) and the FET shows Ohmic contact even at low temperature (4K). These results potentially enables next-generation optoelectronic technology in the atomically-thin regime. Besides, TMDs are generally considered to be 'air-stable', however, we have found that they exhibit poor long-term stability in air in morphology, chemical states, photo-emission, and demonstrated a potential solution to this problem by encapsulation of the monolayer sheet with transparent parylene C. Synthetic TMDs tend to grow parallel to the growth substrate, however, high performance energy conversion and storage devices prefer flakes with high exposed surface area. Therefore by choosing the right precursors and appropriate tuning of the CVD growth conditions, we have grown vertical ReS2 nanosheets on various growth substrates. We show that these structural features of the vertically grown ReS2 sheets can be exploited to significantly improve their performance as electrochemical catalysts in Lithium-Sulfur (Li-S) batteries and in hydrogen evolution reactions (HER). After 300 cycles, the specific capacity of the Li-S battery with vertical-ReS2 catalyst is retained above 750 mA h g-1 with only &sim;0.063% capacity decay per cycle, much better than the baseline battery. As a HER catalyst, the vertical-ReS 2 provides very small onset over-potential (< 100 mV) and an exceptional exchange current density (&sim;67.6 microA/cm2), which is superior to most previous work with TMD catalysts.

ISBN: 9781339820675Subjects--Topical Terms:

221779
Materials science.

Synthesis and characterization of two dimensional transition metal dichalcogenides.
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520 $a Two-dimensional transition metal dichalcogenides (TMDs) are an emerging class of atomically thin semiconductors that show potential in next-generation electronics, optoelectronics, and energy storage batteries. The successful synthesis and doping of TMDs is the key to their applications. I have synthesized monolayer MoS2, WS2, and multilayer ReS2 flakes by CVD, and studied an unprecedented one-pot synthesis for transition-metal substitution doping in large-area, synthetic monolayer TMDs. Electron microscopy, optical and electronic transport characterization and ab initio calculations indicate that our doping strategy preserves the attractive qualities of TMD monolayers, including semiconducting transport and strong direct-gap luminescence. The Re doping of MoS2 greatly improve the contact quality (one of the biggest issue in TMDs) and the FET shows Ohmic contact even at low temperature (4K). These results potentially enables next-generation optoelectronic technology in the atomically-thin regime. Besides, TMDs are generally considered to be 'air-stable', however, we have found that they exhibit poor long-term stability in air in morphology, chemical states, photo-emission, and demonstrated a potential solution to this problem by encapsulation of the monolayer sheet with transparent parylene C. Synthetic TMDs tend to grow parallel to the growth substrate, however, high performance energy conversion and storage devices prefer flakes with high exposed surface area. Therefore by choosing the right precursors and appropriate tuning of the CVD growth conditions, we have grown vertical ReS2 nanosheets on various growth substrates. We show that these structural features of the vertically grown ReS2 sheets can be exploited to significantly improve their performance as electrochemical catalysts in Lithium-Sulfur (Li-S) batteries and in hydrogen evolution reactions (HER). After 300 cycles, the specific capacity of the Li-S battery with vertical-ReS2 catalyst is retained above 750 mA h g-1 with only &sim;0.063% capacity decay per cycle, much better than the baseline battery. As a HER catalyst, the vertical-ReS 2 provides very small onset over-potential (< 100 mV) and an exceptional exchange current density (&sim;67.6 microA/cm2), which is superior to most previous work with TMD catalysts.
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