Photoelectron spectroscopy of hybrid interfaces for light emitting diodes: Influence of the substrate work function

Applied Physics Letters

Volumn 79, Issue 19, 2001, Pages 3185-3187

  Greczynski, G ^a   Salaneck, W R ^a  

^a LINKÖPING UNIVERSITY   (Sweden)

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EID: 0001648092     PISSN: 00036951     EISSN: None     Source Type: Journal    
DOI: 10.1063/1.1416159     Document Type: Article

References (23)

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14. Since the work function of a metallic substrate is not necessarily the same as that of the corresponding overlayer vapor deposited in an UHV, we emphasize this difference in the notation used (e.g., AU vs Au). In particular, AU stands for the work function of the gold substrate cleaned in a special way, i.e., by ozone treatment, which results in φ=5.4eV. The vapor deposited layer of gold (denoted here as Au) has a work function lower by 0.3 eV, which is, on the other hand, a typical value for sputter-cleaned gold substrate.
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19. The relative separations in BE between the C(Lv) peaks from PFO films on different substrates are preserved when going from a pristine case to the 2 A metal coverage. For the thicker metal overlayers, the influence of the second factor - changes in the electrical potential - starts to be dominant.
20. Although the chemical interaction between Al atoms and PFO can also lead to the BE shifts of the C(1s) core level, it does not influence the present analysis mainly for the following reasons: (i) first of all, Al can only interact with the carbon atoms from the polymer backbone, whereas the strongest contribution to C(1s) core-level signal originates from the non-affected side-chains and (ii) the angle dependent study shows that the Al/PFO interface extends to not more than 10 A into the polymer layer, thus a number of the affected polymer sites is rather small as compared to the number of unaffected chains contributing to the signal.
21. The Al film prepared in an UHV has the work function 0.2 eV higher than the Al substrate with the native oxide layer on it (denoted here as AL).
22. The work function of the PFO/AU system is 5.2 eV instead of 5.4 eV due to the 0.2 eV mismatch of the vacuum levels at this interface (see Ref. 6).
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