Ionization Energy and Electronic Structure of Polycytidine

1
Ionization Energy and Electronic Structure of
Polycytidine

• Name John Magulick
• Level Junior
• Number of Semesters Participated 5
• Date of Submission 07/28/05
• Advisor Dr. Rudy Schlaf
• Department Electrical Engineering

2
Experiment

• Deposited aqueous solution of polycytidine (poly
  rC, 1 mg/ml) in multiple steps using electrospray
  injection

• Transferred substrate, highly ordered pyrolytic
  graphite (HOPG), between Prep. Chamber II and
  Analysis Chamber every deposition step

• Analyzed substrate over deposition via x-ray
  photoemission spectroscopy (XPS) and ultraviolet
  photoemission spectroscopy (UPS)
• Evaluation of spectra allows determination of
  electronic structure of poly rC/HOPG interface

3
Results

• Top figure shows UP spectra after noted
  deposition steps
• UP spectra is used to determine electronic
  structure by analyzing the development of HOMO
  emissions from poly rC (far right graph in top
  fig.)
• XP spectra (bottom figure) are used to analyze
  core level emissions which allows evaluation of
  the stoichiometry

4
Discussion/Conclusion

• One HOMO emission region chosen for interfacial
  analysis (right figure)
• Background is removed, low binding energy side of
  HOMO peak is fitted, hole injection barrier
  determined to be 3.5 eV (shown in bottom of right
  figure)
• Work function determined to be 4.60 eV from UP
  data
• When work function and hole injection barrier are
  added, ionization energy is determined to be 8.10
  eV

• Summary of electronic structure of the interface
  is shown in bottom figure
• Conclusion charge transfer at interface is
  impeded by large energy barriers in both
  directions