Date on Master's Thesis/Doctoral Dissertation

5-2024

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Physics and Astronomy

Degree Program

Physics, PhD

Committee Chair

Sumanasekera, Gamini

Committee Co-Chair (if applicable)

Mendes, Sergio

Committee Member

Yu, Ming

Committee Member

Jasinski, Jacek

Committee Member

Jacek Jasinsk

Author's Keywords

Angle-resolved polarized raman spectroscopy; black arsenic phosphorus; 2D alloys; magneto-optic kerr effect; analog subtraction technique; triclinic Cr2Se3

Abstract

This research work reports investigations of structural and physical properties of novel magnetic and non-magnetic 2D alloys. Three techniques were utilized in this investigation: Angle-resolved polarized Raman spectroscopy (ARPRS), Electrical &Thermoelectric power measurements, Magneto-optic Kerr effect (MOKE) spectroscopy. ARPRS and MOKE experiments were constructed during the course of this work. ARPRS was used to study the anisotropy of 2-dimensional black-arsenic phosphors (b-AsxP1-x) as a function of arsenic concentration (x). It was observed experimentally that all Raman modes of the studied samples with x=0, 0.4, 0.8 exhibit polarization dependence. More interestingly, the polarization dependence of Raman modes due to the vibrations of Arsenic and Phosphoros atoms could not be explained unless a superposition of the two in-plane vibrational modes (A2g and B2g) is considered. A comprehensive theoretical calculation by DFT was conducted and the result of the theoretical calculation agrees very well with experiment. In addition, ARP Raman measurements were performed on 2-dimensional Cr2Se3 grown on a Si/SiO2 substrate. These samples can manifest in two distinct crystal structures: Trigonal and Triclinic. Both crystal structures have been predicted theoretically. However, so far only the Trigonal crystal structure has been observed experimentally. Through ARPTS and XRD measurements, we report for the first time the observation of Cr2Se3 with triclinic crystal structure. Next, the temperature dependence of thermopower (Seebeck coefficient) and 4-probe resistance of Cr2Se3 crystals were investigated. These measurements showed a conventional nondegenerate semiconductor behavior with thermopower changing sign as the temperature was decreased. Lastly, a highly sensitive magneto-optic Kerr effect system was developed for measuring magnetic hysteresis, as well as optical and magneto-optical constants of magnetic ultrathin films and nanostructures.

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