Enhancing the Electrical and Optoelectronic Performance of Nanobelt Devices by Molecular Surface Functionalization

1
Enhancing the Electrical and Optoelectronic
Performance of Nanobelt Devices by Molecular
Surface Functionalization

• Nano Letters 2007
• Devesh Khanal
• NSE C203
• Spring 2007

2
Outline

• Synthesis/setup
• Enhanced electrical conductivity
• Enhanced photoconductivity
• Enhanced gas sensitivity
• Enhanced biostability
• Motivation
• Nanowires need to show improved contacts,
  increased mobility, minimized surface defects,
  increased device stability.

3
Setup
4
Setup

• Dipped nanobelts into solution with desired
  molecules.
• Verified successful coating with molecules via
  the contact angles of water droplets.

5
Electrical Conductivity

• 5-6 orders of magnitude increase in conductance
• Different functional groups show different levels
  of conductivity

6
Electrical Conductivity

• Given explanation
• Functional groups introduce mid-gap states that
  act as transition states and effectively reduce
  the Schottky barrier.
• COOH? COO-, which is a donor.

7
Enhanced Photoconductivity

• Measured electrical response from shining 365 nm
  UV light onto surface of treated and not-treated
  nanobelts.
• HOOC(CH2)10COOH sample - 57.1 enhancement
• Untreated 22
• Explanation Organic surface groups introduce
  midgap states that help excite electrons from VB
  to CB and help separate electron hole pairs.

8
Enhanced Gas Sensitivity

• Measured electrical response to the introduction
  of O2 gas.
• HOOC(CH2)10COOH current decreased by 43
• Untreated 28
• Explanation T 300C. At this T, functional
  groups are decomposed ? creates oxygen vacancies
  ? material more sensitive to oxygen gas.

9
Increased Biostability

• Treated samples more resistant to pH 7 buffer
  solution for 15 minutes.

10
Conclusions

• Surface-treated nanobelts and nanowires showed
• Enhanced electrical conductivity
• Enhanced photoconductivity
• Enhanced gas sensitivity
• Enhanced biostability
• Regardless physical explanation for observed
  phenomena it is clear that the high surface to
  volume ratio of quasi-1D materials allows
  properties and performance of the material to be
  very dependent on surface composition and quality.