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.
- "Tunneling spectroscopy of the Si(111)2 × 1 surface," R.M. Feenstra, Joseph A. Stroscio, A.P. Fein, Surface Science 181, 295 (1987)
- "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)
- "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)
- "Tunneling spectroscopy of the GaAs(110) surface," R. M. Feenstra and Joseph A. Stroscio, J. Vac. Sci. Technol. B 5, 923 (1987)
- "Tunneling spectroscopy of the (110) surface of direct-gap III-V semiconductors," R. M. Feenstra, Phys. Rev. B 50, 4561 (1994)
- "WSe 2 homojunctions and quantum dots created by patterned hydrogenation of epitaxial graphene substrates." Pan, Yi, Stefan Fölsch, Yu-Chuan Lin, Bhakti Jariwala, Joshua A. Robinson, Yifan Nie, K. J. Cho, and Randall M. Feenstra. 2D Materials (2018).
- "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.
- "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)
- "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)
- "Quantum-Confined Electronic States Arising from the Moiré Pattern of MoS2–WSe2 Heterobilayers." Pan, Yi, Stefan Fölsch, Yifan Nie, Dacen Waters, Yu-Chuan Lin, Bhakti Jariwala, Kehao Zhang, Kyeongjae Cho, Joshua A. Robinson, and Randall M. Feenstra. Nano letters 18, no. 3 (2018): 1849-1855.