2D materials

Understanding the Link Between Photonic and Electronic Performance of 2D Semiconducting Layers

  • By Burcu Ozden
  • 20 December 2017

Susan Fullerton and her colleagues wrote a scientific report on deconvoluting the photonic and electronic response of two-dimensional (2D) materials for the case of molybdenum disulfide (MoS2). What are the main criteria which provide evidence that the material is “high quality”? Are the photonic properties or electronic performance? Susan Fullerton and her colleagues have studied the MoS2 materials and their devices to answer this question and to find the correlation between electronic and optical properties in 2D materials. In their study, they used Raman, photoluminescence (PL), time-resolved photoluminescence (TRPL), high-resolution scanning transmission electron microscopy (HR-STEM), X-ray photoelectron spectroscopy (XPS), field effect transistors (FET) fabrication electrolyte gate application methods to characterize MoS2.

From 3D to 2D and Back Again

Cory Dean
Monday, September 18, 2017 - 4:30pm to 5:30pm

Graphene, a single layer of carbon atoms arranged in a hexagonal lattice, is probably the best known, and most extensively characterized two-dimensional material.  However, this represents just one of a larger class of van der Waals materials, in which atomic monolayers can be mechanically isolated from the bulk.  By integrating these materials with one another,  an exciting new opportunity has emerged in which layered heterostuctures can be fabricated with properties beyond those of the constituent materials. In this talk I will present some of our recent efforts where...

Quantum Phases and Phase Transitions in Two-Dimensional Highly Correlated Metals at Oxide Interfaces

Ramesh Budhani
Thursday, April 20, 2017 - 4:00pm to 5:00pm

The two-dimensional diffusive metal stabilized at the interface of SrTiO3 and the Mott Insulator perovskite LaTiO3[1-2] has challenged many notions related to the formation and electronic behavior of the two-dimensional electron gas (2DEG) at the well studies LaAlO3-SrTiO3 interface. Here we discuss specifically the stability of the superconducting phase[3] at LaTiO3 – SrTiO3 interface, the nature of the superconductor – normal metal quantum phase transition (T=0 limit) driven by magnetic field, significance of the field vis-à-vis the Chandrasekhar - Clogston limit for...

Paper and Circuits, Only Atoms Thick

Jiwoong Park
Monday, April 10, 2017 - 4:30pm to 5:30pm

2D layered materials are like paper: they can be colored, stitched, stacked, and folded to form integrated devices with atomic thickness. In this talk, I will discuss how different 2D materials can be grown with distinct electrical and optical properties (coloring), how they can be connected laterally to form pattered circuits (stitching), and how their properties can be controlled by the interlayer rotation (twisting). We will then discuss how these atomically thin papers and circuits can be folded to generate active 3D systems.

2D Materials: Challenges and Opportunities for Future Electronics

Robert Wallace
Friday, November 4, 2016 - 9:30am to 10:30am

The size reduction and economics of integrated circuits, captured since the 1960’s in the form of Moore’s Law, is under serious challenge. Current industry roadmaps reveal that physical limitations include reaching aspects associated with truly atomic dimensions, and the cost of manufacturing is reaching such values that only 2 or 3 companies can afford leading edge capabilities. To address the physical limitations, 2D materials such as graphene, phosphorene, h-BN, and transition metal dichalcogenides have captured the imagination of the electronics community...

CANCELLED: Tailoring Chemical and Optical Properties of 2D Transition Metal Dichalcogenides

Talat S. Rahman
Friday, October 7, 2016 - 9:30am to 10:30am

Single-layer of molybdenum disulfide (MoS2) and other transition metal dichalcogenides (TMDC) appear to be promising materials for next generation applications (optoelectronic and catalysis), because of their low-dimensionality and intrinsic direct band-gap which typically lies in the visible spectrum. Several experimental groups have already reported novel electronic and transport properties which place these materials beyond graphene for device applications. MoS2 is also known to be a leading hydrodesulfurization catalyst. Efforts are underway to further tune...

New Nature Partner Journal: npj 2D Materials and Applications

  • By Aude Marjolin
  • 23 September 2016

npj 2D Materials and Applications is an online-only, open access journal that aims to become a top-tier interdisciplinary platform for scientists to share research on 2D materials and their applications. Part of the Nature Partner Journals series, npj 2D Materials and Applications is published in partnership with FCT NOVA, Lisbon, with the support of the European Materials Research Society (E-MRS).

In terms of policy making and impact, the journal responds to the pressing requirements of translating robust research based on this new class of materials into systems and devices that deliver sustainable solutions for a wide range of applications.


Electron-electron Interaction Physics in Two-dimensional Materials

Allan MacDonald
Monday, October 17, 2016 - 4:30pm to 6:00pm

Two-dimensional (2D) materials are interesting in part because their electron density can be varied in situ by transferring charge from nearby metallic layers, and because 2D materials can be stacked in a wide variety of configurations to achieve quite different physics properties. My talk will explain several theoretically imagined examples of electron-electron interaction physics in 2D materials, some of which have already been realized experimentally. I will briefly discuss spatially-indirect exciton condensate superfluids in transition metal dichalcogenides...

Susan Fullerton Awarded NSF Grant Funds Study to Develop a Transistor Based on 2D Crystals

  • By Aude Marjolin
  • 19 May 2016

Sussan Fullerton received a $496,272 grant from the National Science Foundation to study two-dimensional semiconductors with the goal of demonstrating a switch that requires less power than conventional silicon-based transistors. 

As electronic devices continue to become more integrated into our daily lives, more energy is required to power these devices,” said Susan Fullerton, the principle investigator of the study. “On a large scale, decreasing the power requirements of electronics would impact global energy consumption.”

Department of Physics, Carnegie Mellon University
Ph.D., California Institute of Technology

The research activities of my group deal with structural and electronic properties of semiconductor materials and devices. A major tool used in the studies is the scanning tunneling microscope, which allows one to image the atomic structure of a surface and to perform spectroscopic measurements of the electronic energy levels. Many of the studies deal with semiconductor heterostructures consisting of multiple layers of different types of material, with the goal of understanding how the structure of the device (including imperfections and defects) determines its electronic properties. Growth of semiconductor heterostructures has been performed in my laboratory using molecular beam epitaxy, for GaN in particular (a semiconductor with a relatively large band gap, used for blue light-emitting devices and for microwave transistor applications).

Most recently we have focused on the study of two-dimensional (2D) materials, including graphene and hexagonal boron nitride (h-BN). We prepare these materials by growth at high temperatures, and we characterize them using both scanning tunneling microscopy and low-energy electron microscopy. The latter permits both diffraction and imaging of the surfaces, with nm-scale resolution. Additionally, spectroscopic observation of energy levels above the vacuum level is performed, which is particularly useful for these 2D materials. Heterostructures consisting of alternating layers of graphene and h-BN are being studied, because of the unique current-voltage characteristic for tunneling in such structures.

Most Cited Publications
  1. "Tunneling spectroscopy of the Si(111)2 × 1 surface," R.M. Feenstra, Joseph A. Stroscio, A.P. Fein, Surface Science 181, 295 (1987)
  2. "Atom-selective imaging of the GaAs(110) surface," R. M. Feenstra, Joseph A. Stroscio, J. Tersoff, and A. P. Fein, Phys. Rev. Lett. 58, 1192 (1987)
  3. "Electronic Structure of the Si(111)2 × 1 Surface by Scanning-Tunneling Microscopy," Joseph A. Stroscio, R. M. Feenstra, and A. P. Fein, Phys. Rev. Lett. 57, 2579 (1986)
  4. "Tunneling spectroscopy of the GaAs(110) surface," R. M. Feenstra and Joseph A. Stroscio, J. Vac. Sci. Technol. B 5, 923 (1987)
  5. "Tunneling spectroscopy of the (110) surface of direct-gap III-V semiconductors," R. M. Feenstra, Phys. Rev. B 50, 4561 (1994)
Recent Publications
  1. "Substitutional mechanism for growth of hexagonal boron nitride on epitaxial graphene," Mende, Patrick C., Jun Li, and Randall M. Feenstra. Applied Physics Letters 113.3 (2018): 031605.
  2. "Quantum-Confined Electronic States Arising from the MoiréPattern of MoS2−WSe2 Heterobilayers," Yi Pan, Stefan Fölsch, Yifan Nie, Dacen Waters, Yu-Chuan Lin, Bhakti Jariwala, Kehao Zhang, Kyeongjae Cho, Joshua A. Robinson, and Randall M. Feenstra, Nano Lett. (2018)
  3. "One dimensional metallic edges in atomically thin WSe<sub>2</sub> induced by air exposure", Rafik Addou, Christopher M Smyth, Ji-Young Noh, Yu-Chuan Lin, Yi Pan, Sarah Eichfeld, Stefan Fölsch, Joshua A Robinson, Kyeongjae Cho, Randall M Feenstra and Robert M Wallace, 2DM-102545.R1(2018)
  4. "Magnitude of the current in 2D interlayer tunneling devices," Randall M Feenstra, Sergio C de la Barrera, Jun Li, Yifan Nie and Kyeongjae Cho, J. Phys.: Condens. Matter 30 055703 (2018)
  5. "Realizing Large-Scale, Electronic-Grade Two-Dimensional Semiconductors," Yu-Chuan Lin, Bhakti Jariwala, Brian M. Bersch, Ke Xu, Yifan Nie, Baoming Wang, Sarah M. Eichfeld, Xiaotian Zhang, Tanushree H. Choudhury, Yi Pan, Rafik Addou, Christopher M. Smyth, Jun Li, Kehao Zhang, M. Aman Haque, Stefan Fölsch, Randall M. Feenstra, Robert M. Wallace, Kyeongjae Cho, Susan K. Fullerton-Shirey, Joan M. Redwing, and Joshua A. RobinsonACS Nano January 23, 2018
  6. "Large Scale 2D/3D Hybrids based on Gallium Nitride and Transition Metal Dichalcogenides," Kehao Zhang, Bhakti Jariwala, Jun Li,  Natalie Christine Briggs, Baoming Wang, Dmitry Ruzmetov, Robert A Burke,  Jordan O. Lerach, Tony G Ivanov, Aman Haque, Randall M. Feenstra and J. Robinson,  Nanoscale (2017)