Research

Definition: Raman spectroscopy is a type of vibrational spectroscopy used for characterizing materials, particularly carbon-based materials. It's especially useful for distinguishing between different electronic properties of materials.
Application: It helps differentiate between metallic and semiconducting carbon nanotubes (CNTs).

Carbon Nanotubes:
- The black curves in the spectrum correspond to purchased carbon nanotubes, consisting of a mixture of both metallic and semiconducting types.
- The red curves correspond to a solution which highlights important signals relevant to the study.
Metallic Carbon Nanotubes:
- A signal highlighted in gray boxes indicates the presence of metallic carbon nanotubes. Upon mixing with a polymer solution, these signals disappear, demonstrating that the polymer is selective for semiconducting carbon nanotubes.
Implications: The ability to selectively target semiconducting carbon nanotubes can lead to the development of innovative electronic devices.

Research Collaboration:
- Collaboration with researchers at the University of Ottawa focused on the synthesis of transistors using selectively dispersed carbon nanotubes in polymers.
Transistor Performance:
- The transistors made using these materials demonstrated improved performance compared to traditional silicon transistors. Performance improvements suggest enhanced electronic properties of the assembled devices.

Conjugated Polymers:
- The discussion centers on the fundamental chemistry of conjugated polymers and their selectivity towards either metallic or semiconducting carbon nanotubes.
Electron Density:
- Metallic carbon nanotubes are described as having a high electron density, leading to their conductive nature. In contrast, semiconducting carbon nanotubes exhibit lower electron density, making them electron poor relative to their metallic counterparts.

Polymer Composition:
- Conjugated polymers can be engineered with substituents that either withdraw or donate electron density to the polymer backbone, creating polymers that are either electron rich or electron poor.
- The core hypothesis is: “opposites attract.”
- Electron Rich Polymers: Predicted to preferentially interact with semiconducting carbon nanotubes.
- Electron Poor Polymers: Should selectively interact with metallic carbon nanotubes.

Development:
- A polymer known as polyfluorine copuridine was synthesized to test selectivity properties. The team included student researchers, James Wagner and Vera Palm, from prior years.
Methylation Reaction:
- The polymer contains a nitrogen atom that can be modified (methylated) to introduce a methyl group (–CH₃). This addition results in a positively charged nitrogen, rendering the polymer electron deficient.
Electron-deficient vs. Electron-rich Polymers:
- Comparison of unmethylated (electron-rich) and methylated (electron-poor) versions of the polymer was made to assess their interaction with carbon nanotubes.

Visual Observations:
- Unmethylated Polymer: Appeared yellow and maintained a green dispersion upon mixing with conducting carbon nanotubes, indicating successful interaction.
- Methylated Polymer: Initially yellow; however, after mixing, it produced a darker reddish dispersion, indicating different interaction behaviors with the carbon nanotubes.
Spectroscopy Analysis:
- Ultraviolet-visible (UV-Vis) near-infrared absorption spectroscopy provided quantitative data on interactions:
- Spectra for semiconducting carbon nanotubes highlight transitions distinct from those observed in spectra for metallic nanotubes, demonstrating selectivity.

The research group has focused on proving the hypothesis that electron-rich and electron-poor conjugated polymers can selectively interact with different types of carbon nanotubes, leading to significant advancements in material applications for electronic devices.