Synthesis and Characterization of Zn1-xmnxse and Bi2se3 Nanowires and Nanoribbons

Open Access
Author:
Andre, Kalissa Lauren
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
September 25, 2012
Committee Members:
  • Suzanne E Mohney, Thesis Advisor
Keywords:
  • nanowire
  • thermal evaporation
  • diluted magnetic semiconductor
  • topological insulator
  • Bi2Se3
  • ZnMnSe
  • ordering
Abstract:
One-dimensional nanoscale semiconductors combined with the extra degree of freedom provided by electron spin show great promise for use in novel spintronic devices. Diluted magnetic semiconductor and topological insulator nanowires and nanoribbons manipulate the inherent spin of electrons, introducing new and interesting properties to the material, but the synthesis of these materials must be studied before they can be reliably produced. This study reports on the successful vapor-liquid-solid growth of Bi2Se3 nanowires and nanoribbons through thermal evaporation. The growth parameters were adjusted to increase the nanostructure yield during growth and preliminary transmission electron microscopy (TEM) characterization was performed. The Bi2Se3 nanowires and nanoribbons were found to have a wide range of diameters and widths, from 150 nm to 750 nm. The nanostructures did not have a common growth direction, but some of the structure studied had a growth direction in the (0001) plane. A growth direction in the (0001) plane is desired for thermoelectric and topological insulator applications as the electrical conductivity and thermoelectric fi gure of merit for Bi2Se3 is highest parallel to the (0001) planes. Zn1-xMnxSe nanowires and nanoribbons grown through thermal evaporation were characterized using TEM. Both straight and tapered nanowires were found. The straight nanowires varied in Mn fraction, with 0.1 < x < 0.28, but were consistent within individual nanowires. The tapered nanowires increased in Mn fraction within individual nanowires, from a high Mn fraction at the wider base of the wire to a low Mn fraction at the thinner tip of the wire. The tapering and systematic change in Mn fraction along the wire was attributed to a Mn-rich thin film deposition during nanowire growth. Superdi raction spots in the nanoribbons were attributed to atomic ordering of Mn on the Zn sublattice. It was determined that the atomic ordering only occurred when there was a Mn fraction of x > 0.1. Nanoribbons without atomic ordering were found for Mn fractions of 0.05 < x < 0.2. This thesis is the first time atomic ordering has been reported in nanoribbons.