Advancements in nanoscale engineering of oxide interfaces and heterostructures have led to discoveries of emergent phenomena and new artificial materials. Combining the strengths of reactive molecular-beam epitaxy and pulsed-laser deposition, we show that atomic layer-by-layer laser molecular-beam epitaxy (ALL-Laser MBE) significantly advances the state of the art in constructing oxide materials with atomic layer precision. Using Sr1+xTi1-xO3 as example, we demonstrate the effectiveness of the technique in producing oxide films with stoichiometric and crystalline perfection. With the growth of La5Ni4O13, a Ruddlesden-Popper phase with n = 4 that has never been reported in the literature, we demonstrate that ALL-Laser MBE allows us to push the equilibrium thermodynamic boundary further. By growing LaAl1+yO3 films of different stoichiometry on TiO2-terminated SrTiO3 substrate at high oxygen pressure, we show that the behavior of the two-dimensional electron gas at the LaAlO3/SrTiO3interface can be quantitatively explained by the electronic reconstruction mechanism. In LaNiO3 films on LaAlO3 substrate with LaAlO3 buffer layer, we observed the metal insulator transition in 1.5 unit cells, which is driven by oxygen vacancies in addition to epitaxial strain and reduced dimensionality.
As Interim Chair of Temple University’s Physics Department, May 20, 2015 was a normal day for me filled with work on my class, research, promotion of colleagues, and a university task force I was chairing. I had given a public lecture for “Pint of Science,” a science festival, at an Irish pub before picking up my wife at the airport, who was returning from an overseas conference trip. My elder daughter had come home a day earlier from college for a few days. We made a plan to visit a restaurant to try their famous Korean fried chicken. All of this was suddenly and forever changed a few hours later when I was awoken by the urgent pounding on my door. I was arrested by armed FBI agents and indicted by the U.S. government for sharing protected U.S. company technology with China. The indictment was dismissed in September after it had become clear that I did not share the protected technology with China. My case has raised serious concerns about international collaborations in science and technology, civil rights, and the long-term national security and economic future of the United States.