Ag-Organic Layered Samples for Optoelectronic Applications: Interface Width and Roughening Using a 500 eV Cs⁺ Probe in Dynamic Secondary Ion Mass Spectrometry

Abstract

The performance of organic optoelectronic devices depends a lot on interface structure and width. Dynamic secondary ion mass spectrometry (SIMS) has been widely used to investigate interfaces in classical semiconductor devices and limitations are quite well understood. For low-energy dynamic SIMS on organic optoelectronic devices, sputter-induced diffusion processes and roughness formation have only been investigated sparsely. In this work we use low-energy dynamic SIMS depth profiling on metal-organic multilayered model samples with compositions similar to organic optoelectronic devices to investigate limitations in the calculation of interface widths due to sputter-induced roughness formation. The samples consist of silver and organic compounds (e.g., tris(8-hydroxyquinolinato) aluminum (Alq(3)) and metal phthalocyanines) sequentially deposited by thermal evaporation in vacuum onto a Si substrate. They are analyzed by a 500 eV Cs(+) primary ion beam. Surface roughness at the SIMS crater bottoms is characterized by AFM as a function of crater depth. We find that the roughness in SIMS craters is limited to approximately 1.5 nm, which is much smaller than the interface width of the as-deposited interfaces. Thus, for the studied organic-inorganic interfaces, low-energy dynamic SIMS can yield accurate information about interface morphology, allowing the study of its dependence on sample preparation conditions and its implication on device properties.

Molecular depth profiling of organic photovoltaic heterojunction layers by ToF-SIMS: comparative evaluation of three sputtering beams

“…First, the initial roughness of the P3HT and P3HT:PCBM spin coated layers is signicantly larger than the one of the evaporated OLED layers in ref. 43 and this roughness should lead to an equivalent broadening of the interface widths measured in the prole. But this should be largely true for 45 Ar 1700 + bombardment too.…”

“…Indeed, depth proles obtained recently on OLED devices using a 500 eV Cs + ion source in the single beam, continuous bombardment mode indicate values of interfacial widths in the range of 2-4 nm for an initial layer roughness of $1 nm. 43 In this respect, the data obtained for the combination 500 eV Cs + /30 keV Bi 3 + raise questions, because the depth resolutions are poor and, in particular, they are consistently worse than those calculated for the Ar 1700 + depth proles. A possible explanation relates to the roughness of the bottom of the sputtered zone upon proling.…”

“…The analysis beam could also contribute to explain the differences observed between these results and those of ref. 43, where 500 eV Cs + is used for both sputtering and analysis. Beside the use of low-energy atomic ions for analysis, a tractable alternative for improved depth-resolution might be the use of large Ar n clusters for both analysis and sputtering, in an optimized conguration, i.e.…”

Silver Diffusion in Organic Optoelectronic Devices: Deposition-Related Processes versus Secondary Ion Mass Spectrometry Analysis Artifacts

“…Hence, to limit the diffusion during sputtering, the impact energy during depth profiling on the Cameca SC-Ultra instrument must not be too low. When the current results are combined with the conditions for the highest depth resolution from a previous paper, the 500 eV or 1 keV impact energies give the best results for depth profiling of organic multilayered samples for optoelectronic applications, depending on the organic layer. On Alq 3 , 500 eV and 1 keV give a similar mixing of silver into the organic layer, but the highest interface resolution is obtained when using the 500 eV impact energy.…”

Numerical investigation of depth profiling capabilities of helium and neon ions in ion microscopy

“…The very slow sputter yields combined with the important atomic mixing lead to a complete blurring out of the in-depth information. In general, the depth resolution is not as good as the 1 nm to few nm resolution obtained with below keV heavy primary ions [34] or cluster ion bombardment [35], but a good compromise between depth and lateral resolution. For few keV impact energies, depth resolution will be degraded but layers separated by 20 or 40 m can be still separated.…”