Strain and Isotopic Effects in WSe2

Watch recording above or on YouTube
Date: Tuesday, December 11, 2018
Speaker: Dr. Michael T. Pettes
Description: Control over disorder arising from nonequilibrium of atomic positions and distributions of mass offers a promising route to design nanomaterial properties for integration into a wide range of existing and future applications. I will discuss our recently developed method to create highly-spatially localized and well-separated emission sites in a continuous film of nominally bilayer WSe2 using an ultra-sharp dielectric tip array where we have measured a second order photon correlation parameter to be below 0.3. I will also discuss our very recent discovery of the isotope effect in bilayer 186W80Se2, which is the first report of isotope engineering in a transition metal dichalcogenide (TMD) two-dimensional material. These discoveries have general implications to defect engineering, and hence impact varied and promising technological areas from energy conversion to quantum communication.

Measuring and Understanding Optical Spectra of Layered Materials Systems

Watch recording above or on YouTube
Date: Tuesday, November 13, 2018
Speaker: Dr. Shengxi Huang
Description: Two-dimensional (2D) layered materials have gained increasing attention due to their unique and extraordinary electronic and photonic properties. It is critical to gain a clear understanding of the fundamental light-matter interactions in 2D materials, which govern many of the key material properties and are critical for device applications. This talk introduces new discoveries and pioneer works of 2D layered materials utilizing optical spectroscopic techniques, in particular Raman spectroscopy, as well as their novel applications in sensing. The methodologies presented here also provide a framework for the study of new layered materials systems.

Bulk Single Crystal Growth of Novel Quantum Materials

Watch recording above or on YouTube
Date: Tuesday, October 9, 2018
Speaker: Dr. Zhiqiang Mao, Professor of Physics, Penn State University​
Description: Bulk single crystal growth not only plays vital roles in technological advancement, but also is critical to the discoveries of novel quantum materials, such as topological materials. There are many methods for single crystal growth, including solid state growth, melt growth, solution growth and vapor phase growth. In this presentation, I will first introduce several crystal growth techniques related to the melt and solution growth methods. Then I will discuss general strategies for growing single crystal of novel quantum materials as well as crystal growth mechanisms.

The ReaxFF Method and Its Applications to Atomistic-scale Simulations of 2D-materials Growth and Interface Chemistry

Watch recording above or on YouTube
Date: Tuesday, September 25, 2018
Speaker: Dr. Adri van Duin, Professor of Mechanical Engineering and Chemical Engineering; Kenneth Kuan-Yuo Kuo Early Career Professor; Director of the Materials Computation Center
Description: The ReaxFF method (see Senftle et al. Nature Computational Materials 2016, 2, 15011 for a recent review) provides a highly transferable, computationally inexpensive method for simulating complex chemical reactions. This seminar will describe the concepts of the ReaxFF method and will provide an overview of its recent applications to 2D-materials - in particular focusing on recently published work on 2D-material interface chemistry (Yilmaz et al. Defect Creation on Two Dimensional MoS2 Structures by using Graphene Layer and Potato Stamp Concept - A ReaxFF molecular dynamics study. Journal of Physical Chemistry 2018, 122, 11911-11917 and Overbury et al. (2018) Complexity of Intercalation in an Active Layered Material: Destabilization of Urea by Titanium Carbide MXene. Journal of the American Chemical Society 2018, published online DOI: 10.1021/jacs.8b05913).

Techniques and Methods of Hall Measurements

Watch recording above or on YouTube
Date: Tuesday, May 29, 2018
Speaker: Dr. Jeffrey Lindemuth, Senior Scientist, Lake Shore Cryotronics, Inc.
Description: Hall measurements have been the mainstay of electrical transport measurements for many decades. This presentation is a tutorial on how to prepare samples, confirm the quality of the contacts to the sample, choosing the proper protocol for the hall measurement. Several applications of hall measurement, including variable field multi-carrier analysis, anomalous Hall effect, and variable temperature hall measurements will be discussed.

2D Chalcogenide Epitaxy by Gas Source Chemical Vapor Deposition

Watch recording above or on YouTube
Date: Tuesday, April 24, 2018
Speaker: Tanushree H. Choudhury
Description: Gas source CVD provides a means for obtaining large area, uniform transition metal dichalcogenide monolayer and few-layer films. In addition to choice of substrate, manipulating the growth conditions is crucial in achieving epitaxy. In this talk, I will highlight our efforts at growth of epitaxial WSe2, MoS2 and WS2 using a cold-wall gas source CVD system.

Frontiers in MBE Growth of TMDs and Topological Insulators

Watch recording above or on YouTube
Date: Tuesday, March 27, 2018
Speaker: Anthony Richardella
Description: Molecular beam epitaxy (MBE) is well known for its atomic level control of high quality crystal growth. We discuss the challenges and progress of using MBE for 2D chalcogenides focusing on the thermodynamics and defects in these materials and highlighting our recent work with magnetically doped topological insulators.

Modeling 2D Growth Outcomes

Watch recording above or on YouTube
Date: Tuesday, January 30, 2018
Speaker: Yuanxi Wang
Description: Synthesis of 2D chalcogenides usually involves complex reaction kinetics and multiple growth parameters leading to many outcomes in terms of morphology, grain size, doping level, and layer thickness. In this talk I will describe cases where growth outcomes can be modeled and predicted by theory and modeling, with focus on grain control.