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The Ohio State University

1. McCormick, Elizabeth Joan, McCormick. Optical Properties of Two Dimensional Semiconductors.

Degree: PhD, Physics, 2018, The Ohio State University

Two dimensional materials (2D) have become a huge research focus in recent history due to the interesting properties and phenomena that occur with reduced dimensionality. Additionally, the reduced size of these materials, the plethora of different properties available in the 2D arsenal, and the ability to relatively easily combine different 2D materials makes them extremely promising for nanodevices and future computing architectures. Here, we investigate the optical properties of two different 2D semiconductors, germanane and transition metal dichalcogenides (TMDs). We focus on the band gap and band edge physics in thin film germanane, a topic that is largely unexplored. We are able to grow thin films of germanane and transfer them onto insulating substrates, a critical step for opto-electronic applications and investigations. Using a combination of optical and opto-electronic techniques including photoconductivity, absorption spectroscopy, and photoluminescence, we are able to investigate the band gap, as well as determine the existence of band tail and defect states in the gap. Having an understanding of the band gap is necessary for future electronic and opto-electronic applications, as many of the interesting properties of a semiconductor are highly dependent on the band gap. Transition metal dichalcogenides have very interesting spin/valley properties due to the large spin-orbit coupling and existence of non-equivalent valleys in their band structure. We investigate the long spin and valley lifetimes in tungsten disulphide, a member of the TMD family, using time resolved Kerr rotation (TRKR) microscopy and photoluminescence microscopy. Our unique approach provides insight into the role of dark trions in the long spin and valley lifetimes, in addition to the transfer of angular momentum to resident carriers in the material. We also find that the strong spin-orbit coupling leads to spins robust against in-plane external magnetic fields. In order to study the unique spin and valley transport in TMDs, including the valley Hall effect, we developed a spatially offset time resolved Kerr rotation microscopy system, which allows spins and valleys to be excited in one location and probed in another. Preliminary data on spin/valley diffusion in tungsten diselenide, another member of the TMD family, is presented, with a discussion of the substrate effect on diffusion in WSe2. These studies enable an unprecedented microscopic understanding of spin and valley dynamics in TMDs, a crucial component in developing future nanoscale spintronic and valleytronic applications. Advisors/Committee Members: Kawakami, Roland (Advisor).

Subjects/Keywords: Condensed Matter Physics; Optics; Physics; Transition Metal Dichalcogenides; TMD; ultra-fast optics; TRKR; time resolved Kerr rotation; imaging; germanane; 2D; spin dynamics; valley dynamics; photoluminescence, spin lifetime

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APA (6th Edition):

McCormick, Elizabeth Joan, M. (2018). Optical Properties of Two Dimensional Semiconductors. (Doctoral Dissertation). The Ohio State University. Retrieved from http://rave.ohiolink.edu/etdc/view?acc_num=osu1531907387651019

Chicago Manual of Style (16th Edition):

McCormick, Elizabeth Joan, McCormick. “Optical Properties of Two Dimensional Semiconductors.” 2018. Doctoral Dissertation, The Ohio State University. Accessed December 16, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1531907387651019.

MLA Handbook (7th Edition):

McCormick, Elizabeth Joan, McCormick. “Optical Properties of Two Dimensional Semiconductors.” 2018. Web. 16 Dec 2018.

Vancouver:

McCormick, Elizabeth Joan M. Optical Properties of Two Dimensional Semiconductors. [Internet] [Doctoral dissertation]. The Ohio State University; 2018. [cited 2018 Dec 16]. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=osu1531907387651019.

Council of Science Editors:

McCormick, Elizabeth Joan M. Optical Properties of Two Dimensional Semiconductors. [Doctoral Dissertation]. The Ohio State University; 2018. Available from: http://rave.ohiolink.edu/etdc/view?acc_num=osu1531907387651019

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