Tuesday, April 8, 2014

One-Atom-Thick Layers of Molybdenum Diselenide by CVD

Azonano.com reports today on a "Novel Scalable Method for Producing One-Atom-Thick Layers of Molybdenum Diselenide" published by Rice University USA and Nanyang Technological University in Singapore. A scalable method for making one-atom-thick layers of molybdenum diselenide. The results are also reported in a press release by Rice University including downloads to released material.
  • MoS2 is a  semiconductor that is similar to graphene but has better properties
  • Can be integrated for future switchable transistors and light-emitting diodes
  • The two-dimensional molybdenum diselenide was made by chemical vapor deposition (CVD)

A TEM image that shows the individual atoms in a two-dimensional sheet of molybdenum diselenide (Azonano.com) 

“This new method will allow us to exploit the properties of molybdenum diselenide in a number of applications,” said study leader Pulickel Ajayan, chair of Rice’s Department of Materials Science and NanoEngineering. “Unlike graphene, which can now easily be made in large sheets, many interesting 2-D materials remain difficult to synthesize. Now that we have a stable, efficient way to produce 2-D molybdenum diselenide, we are planning to expand this robust procedure to other 2-D materials.”

Full store here: http://www.azonano.com/news.aspx?newsID=29848 and the publication in ACS Nano Letters below:

Band Gap Engineering and Layer-by-Layer Mapping of Selenium-Doped Molybdenum Disulfide

Yongji Gong, Zheng Liu, Andrew R. Lupini, Gang Shi, Junhao Lin, Sina Najmaei, Zhong Lin, Ana Laura Elías, Ayse Berkdemir, Ge You, Humberto Terrones, Mauricio Terrones, Robert Vajtai, Sokrates T. Pantelides, Stephen J. Pennycook, Jun Lou, Wu Zhou, and Pulickel M. Ajayan

Nano Lett., 2014, 14 (2), pp 442–449, DOI: 10.1021/nl4032296

Abstract: Ternary two-dimensional dichalcogenide alloys exhibit compositionally modulated electronic structure, and hence, control of dopant concentration within each individual layer of these compounds provides a powerful tool to efficiently modify their physical and chemical properties. The main challenge arises when quantifying and locating the dopant atoms within each layer in order to better understand and fine-tune the desired properties. Here we report the synthesis of molybdenum disulfide substitutionally doped with a broad range of selenium concentrations, resulting in over 10% optical band gap modulations in atomic layers. Chemical analysis using Z-contrast imaging provides direct maps of the dopant atom distribution in individual MoS2 layers and hence a measure of the local optical band gaps. Furthermore, in a bilayer structure, the dopant distribution is imaged layer-by-layer. This work demonstrates that each layer in the bilayer system contains similar local Se concentrations, randomly distributed, providing new insights into the growth mechanism and alloying behavior in two-dimensional dichalcogenide atomic layers. The results show that growth of uniform, ternary, two-dimensional dichalcogenide alloy films with tunable electronic properties is feasible.