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Applied Physics Letters / Volume 96 / Issue 9 / ORGANIC ELECTRONICS AND PHOTONICS

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Appl. Phys. Lett. 96, 093303 (2010); http://dx.doi.org/10.1063/1.3332577 (3 pages)

Band gap states of copper phthalocyanine thin films induced by nitrogen exposure

Tomoki Sueyoshi, Haruya Kakuta, Masaki Ono, Kazuyuki Sakamoto, Satoshi Kera, and Nobuo Ueno

Graduate School of Advanced Integration Science, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

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(Received 21 Nov 2009; accepted 4 Feb 2010; published online 3 Mar 2010)

The impact of 1 atm N2 gas exposure on the electronic states of copper phthalocyanine thin films was investigated using ultrahigh-sensitivity ultraviolet photoelectron spectroscopy. The highest occupied molecular orbital band of the film showed a drastic reversible change in the bandwidth and band shape as well as in the energy position upon repeated cycles of N2 exposure and subsequent annealing. Furthermore, two types of gap-state densities with Gaussian and exponential distributions appeared after the exposure and disappeared due to the annealing. These changes are ascribed to a weak disorder in the molecular packing structure induced by N2 diffusion into the film.

© 2010 American Institute of Physics

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KEYWORDS and PACS

Keywords

annealing, copper, diffusion, energy gap, exponential distribution, Gaussian distribution, molecular electronic states, organic compounds, organic semiconductors, organic-inorganic hybrid materials, semiconductor thin films, ultraviolet photoelectron spectra

PACS

  • 71.20.Rv

    Polymers and organic compounds

  • 79.60.-i

    Photoemission and photoelectron spectra

  • 82.80.Pv

    Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

  • 81.40.Gh

    Other heat and thermomechanical treatments

  • 02.50.Ng

    Distribution theory and Monte Carlo studies

  • 66.30.-h

    Diffusion in solids

ARTICLE DATA

Digital Object Identifier
http://dx.doi.org/10.1063/1.3332577

PUBLICATION DATA

Publisher

$abstract.society.value is a Member of CrossRef American Institute of Physics

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Figures (click on thumbnails to view enlargements)

FIG.1
He Iα UPS spectra of CuPc(7 nm)/Au at 300 K for as-grown (○), annealed (thick curve) and 1 atm N2 exposed (thin curve) film for valence bands and secondary cutoff (left panel) and HOMO (right panel) regions. (a) Comparison of as-grown and preannealed film at 343 K for 12 h (before 1 atm N2 exposure). (b) Comparison of preannealed (before 1 atm N2 exposure) and 1 atm N2 exposed film at 300 K for 19 h.

FIG.1 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.2
He Iα UPS spectra (300 K) of HOMO and band gap region of CuPc(7 nm)/Au on log intensity scale for (a) annealed film at 343 K for 12 h before 1 atm N2 exposure, (b) 1 atm N2 exposed film at 300 K for 19 h, and (c) annealed film at 343 K for 15 h after (b). Panel A: Raw UPS spectra (dots) with convoluted curves (black curves) with two Gaussian functions for HOMO (see panel B), photoelectrons from Au substrate and constant background. Panel B: UPS spectra after subtraction of substrate photoelectrons and constant background after intensity normalization of substrate signal at EFS (see Ref. 8 for normalization method). Photoelectron intensity from substrate is very small in spectra (b). Convoluted HOMO spectra with two Gaussian functions (parabolas in each spectrum) are also shown by black curves.

FIG.2 Download High Resolution Image (.zip file) | Export Figure to PowerPoint

FIG.3
Variations in (a) full width at half maximum of HOMO and (b) ionization potential of HOMO peak (IPpeak) and vacuum level (VL) of CuPc(7 nm)/Au after each treatment. Treatment no. 1 corresponds to as-grown film on 300-K substrate; no. 2, no. 4, no. 6, and no. 8 to annealed film at 343 K for 12, 15, 34, and 21 h, respectively; no. 3, no. 5, and no. 7 to 1 atm N2 exposed film at 300 K for 19 h. (c) Schematic energy diagram of CuPc(7 nm)/Au before and after 1 atm N2 exposure, with energies after treatments of no. 4 and no. 5. EB positions of HOMO peak (peak) and shoulder (s) [second Gaussian component, see Fig. 2 (panel B)] are indicated in (c).

FIG.3 Download High Resolution Image (.zip file) | Export Figure to PowerPoint



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