Alhtough he is six feet four inches tall, Princeton undergraduate Adam Bowman ’17 is still shorter than the molecular beam epitaxy (MBE) system that took him 10 months to build from scratch: a vacuum chamber with a myriad of tubes and wires poking out at all angles in the Yazdani lab.
Adam joined the Princeton Nanoscale Microscopy Lab (PNML) under the guidance of principal investigator, Ali Yazdani. Yazdani and his team of graduate students and postdoctoral researchers study condensed matter physics at the atomic scale, focusing on emergent properties of materials resulting from the underlying many-body physics of electrons. Integral to this research are state-of-the art scanning tunneling microscopy (STM) instrumentation and spectroscopic imaging devices custom-built in Jadwin Hall.
“I approached Professor Yazdani for a junior project and he proposed I design an MBE system while learning the physics behind recent results in the lab. The MBE is basically a spray-painter for atoms. It allows for controlled growth of 2D materials monolayer by monolayer, producing very clean, ordered samples for STM experiments.” Adam circled the MBE pointing out instrumentation features: high temperature heaters for evaporating metals, a liquid nitrogen jacket to absorb residual gases, a portable high vacuum suitcase for transferring samples without contamination and a turbomolecular pump with blades that spin at 35,000 rmp. “The pump is like a jet engine inside the MBE. It physically knocks air molecules out of the chamber with these blades.”
PNML experiments are based on bulk crystals which are grown externally and then cleaved in a high vacuum chamber to prepare a clean surface – but this process offers limited tunability of the material itself. The advantage of the MBE system is that researchers can precisely control and engineer sample growth while monitoring the crystal structure through the diffraction pattern produced when an electron beam is reflected off of the sample. This allows custom engineering of new 2D material systems. The power of STM lies in imaging how electronic wavefunctions vary spatially on a surface with atomic resolution. Combined with the MBE, STM becomes a powerful tool to study topological superconductors and other phenomena like the quantum Hall effect which require very clean 2D films. The MBE’s vacuum chamber attains one of the purest laboratory vacuums achievable.
“We are excited about the capability to grow flat superconducting films that we can then use to proximitize superconductivity into other layers,” Adam stated. “This happens when the paired electrons of the superconductor sort of leak into the other layer and change the physics. Studying the behavior of the films in STM as we vary temperature can help uncover the physics behind their unique behavior – even more exciting is the potential to study iron selenide at high magnetic fields or use it to proximitize superconductivity in other thin films. This could modify the electronic properties of superconductivity to realize more exotic physics.”
“Professor Yazdani gave me a lot of freedom to design and build this system independently and jump in head first – which was a little terrifying at first. But I designed my own experiment from the start and now I can focus on doing physics with it for my senior thesis,” Adam reflected. “Participating in the whole cycle of an experimental research project as an undergraduate is a unique experience that I am lucky to have had.”
Interview by Jennifer Bornkamp (December 2016)