Subcategory: Physics (not Nanoscience)
Room: Exhibit Hall A
Marisa Romanelli - Boston College
Co-Author(s): Prof. Vanessa Sih, University of Michigan; Spencer Batalden, University of Michigan
The field of spintronics envisions a future in which information can be encoded in the spins of electrons, creating a new generation of spin-based electronic devices that could revolutionize technology. However, before this future can become a reality, much still has to be understood about the behavior of spins in materials. One promising material for spintronics experiments is tungsten diselenide (WSe2), as previous measurements of optically excited spin polarization in WSe2 show that it has a long spin lifetime of 60 to 80 ns. However, time-resolved measurements only tell part of the story of spin polarization in WSe2; as the samples used to obtain this data are inhomogeneous, the behavior of the spins may also vary with position. Spatially-resolved measurements are therefore necessary to fully understand spin polarization in this material. Taking these measurements is in and of itself a challenge, since the piezoelectric stages used to move the sample often move inconsistently between different measurements. For this reason, I worked to find the parameters that made the stages’ motion the most repeatable, in order to make it possible to take consistent spatial scans of WSe2. Specifically, I measured how the distance moved by the stages per step of the piezoelectric motors varied with applied AC voltage. I repeated these measurements three times for each voltage tested and found the percent error in the distance traveled to get a value for the repeatability of the motion. Measurements were also taken at four different temperatures: 10 K, 30 K, 50 K, and room temperature. As a result, I was able to determine the voltages that made the stages? behavior the most repeatable at each temperature, and the corresponding distance traveled per step. As expected, the distance traveled increased with both temperature and voltage. More surprisingly, it also depended on the direction of the motion; the X stage moved faster than the Y stage, most likely because it is stacked on top of the Y stage, and forward motion was consistently faster than backward. Future work could use this information about the stages’ behavior to take repeatable spatially-resolved scans of spin polarization in WSe2 or other materials. The consistency of the stages’ motion could also be further improved by testing how it varies with the frequency of the applied voltage.  Song, Xinlin et al. ?Long-Lived Hole Spin/Valley Polarization Probed by Kerr Rotation in Monolayer WSe2.? Nano Lett. 2016 16 8 5010-5014.
Funder Acknowledgement(s): This project was supported by an NSF grant to Prof. Myron Campbell at the University of Michigan.
Faculty Advisor: Prof. Vanessa Sih, University of Michigan, firstname.lastname@example.org
Role: I was responsible for optimizing the repeatability of the motion of the piezoelectric stages that would be used to take spatially-resolved measurements.