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Quantifying the Damage Induced by X‑ray Photoelectron Spectroscopy Depth Profiling of Organic Conjugated Polymers
journal contribution
posted on 2019-04-22, 00:00 authored by Yvonne
J. Hofstetter, Yana VaynzofX-ray photoemission
spectroscopy (XPS) depth profiling using monatomic
Ar+ ion etching sources is a common technique that allows
for the probing of the vertical compositional profiles of a wide range
of materials. In polymer-based organic photovoltaic devices, it is
commonly used to study compositional variations across the interfaces
of the organic active layer with charge extraction layers or electrodes
as well as the vertical phase separation within the bulk-heterojunction
active layer. It is generally considered that the damage induced by
the etching of organic layers is limited to the very top surface,
such that the XPS signal (acquired from the top ∼10 nm of the
layer) remains largely unaffected, allowing for a reliable measurement
of the sample composition throughout the depth profile. Herein, we
investigate a range of conjugated polymers and quantify the depth
of the damage induced by monatomic etching for Ar+ ion
energies ranging from 0.5 to 4 keV using argon gas cluster ion beam
depth profiling. The results demonstrate that even when etching with
the lowest available monatomic ion energy for as little as 3 s, the
damaged polymer material extends deeper into the bulk than the XPS
probing depth. We show that the damaged material distorts the compositional
information obtained by XPS, resulting in erroneous depth profiles.
Furthermore, we propose that only gas cluster ion beam etching sources
should be used for depth profiling of organic conjugated polymers,
as those induce significantly less damage and maintain the compositional
information throughout the entire profile.
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Keywords
ion energiesargon gas cluster ion beam depthphotovoltaic devicescharge extraction layersion etching sourcesmonatomic Armonatomic ion energysample compositionmonatomic etchingphase separationpolymer materialgas cluster ion beam etching sourcesdepth profileOrganic Conjugated Polymers X-ray photoemission spectroscopyXPS signalDamage Induceddepth profiles4 keV
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