Electro-optical properties of CdSe nanowires

Doctoral Dissertation

Abstract

This Thesis describes the results of electro-optical experiments performed on solution grown CdSe nanowires (NWs). TEM images reveal that such NWs have diameters between 6-40 nm, are highly crystalline and exhibit large aspect ratios (>1000, length/diameter). The morphologies of these NWs range from straight to hyper-branched. Absorption cross-sections determine how efficiently a material absorbs light. In this Thesis we calculate single NW absorption cross-sections based on UV-VIS linear extinction, TEM, and inductively coupled plasma atomic emission spectroscopy experiments. Obtained numbers compare well with theoretical estimates, having order of magnitude values of 10-11 cm2 per 1 Ìåm length of a 10 nm diameter NW. Synthesized CdSe NWs are emissive and are easily detectable at the single wire level. A surprising observation from these experiments is the modulation of the NW emission intensity by applied electrical fields. Specifically, the part of the wire closest to the positive electrode exhibits up to a 10x increase in intensity. Simultaneous quenching of identical magnitude is detected on the other side of the wire. Our current working hypothesis is that mobile electrons driven by the external electrical field passivate emission quenching centers resulting in local emission enhancement. Similarly, the smaller density of electrons on the other side of the wire yields emission quenching. To confirm the existence of these mobile carriers we perform electrophoresis measurements on NWs. Observed single wire translational and rotational dynamics can be explained by mobile carriers residing on or within the NWs. A lower limit for the carrier density of NWs in oleic acid is estimated to be ~1 charge/Ìåm. Since light absorption results in both NW emission as well as the photogeneration of carriers, photoconductivity measurements are also possible. While doing such measurements, we unexpectedly discovered that randomly oriented NW networks could exhibit a significant photocurrent polarization anisotropy with values of Ì�=0.25 (Ì�®Õ=0.04) under excitation with linearly polarized light. The remarkable conclusion from this result is that polarization sensitive devices can be built from random NW networks without the need to align component wires. To explain these results a simple geometric model has also been developed.

Attributes

Attribute NameValues
URN
  • etd-07092008-145131

Author Vladimir Protasenko
Advisor Mark Alber
Contributor Dani Meisel, Committee Member
Contributor Steven Corcelli, Committee Member
Contributor Mark Alber, Committee Chair
Contributor Masaru Kuno, Committee Member
Contributor Gregory Hartland, Committee Member
Degree Level Doctoral Dissertation
Degree Discipline Chemistry and Biochemistry
Degree Name PhD
Defense Date
  • 2008-07-08

Submission Date 2008-07-09
Country
  • United States of America

Subject
  • intermittency

  • nanowires

  • emission

  • CdSe

  • blinking

Publisher
  • University of Notre Dame

Language
  • English

Record Visibility and Access Public
Content License
  • All rights reserved

Departments and Units

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