2 research outputs found
Silver Diffusion in Organic Optoelectronic Devices: Deposition-Related Processes versus Secondary Ion Mass Spectrometry Analysis Artifacts
The
development of organic optoelectronic devices relies on controlling
interfaces during thin-film deposition and requires an accurate characterization
of the film composition at these interfaces. Dynamic secondary ion
mass spectrometry (SIMS) is widely used to investigate multilayer
thin-film structures. Routine analysis protocols are well established
for classical semiconductor samples, but for organic or mixed metallic–organic
samples the limitations of
the technique are less well established. In the current work, low-energy
dynamic SIMS is used on metal–organic multilayered model structures
similar to those in organic optoelectronic devices to study the origin
of diffusion of metal into the organic layer (e.g., irradiation-induced
diffusion during SIMS analysis or during the deposition process).
Samples contain silver and organic compounds sequentially deposited
by thermal evaporation in vacuum onto a Si substrate. They are analyzed
using a 250 eV to 1 keV Cs<sup>+</sup> primary ion beam. It is found
that the mixing of silver into the organic layer depends on the impact
energy and the conditions for sample preparation. This irradiation
effect can be minimized by a back-side depth profiling approach, which
was developed in this work. By applying this method, it is shown that
some silver is likely to diffuse into the organic layers during the
deposition process
Thermal Conductance in Cross-linked Polymers: Effects of Non-Bonding Interactions
Weak interchain interactions have
been considered to be a bottleneck
for heat transfer in polymers, while covalent bonds are believed to
give a high thermal conductivity to polymer chains. For this reason,
cross-linkers have been explored as a means to enhance polymer thermal
conductivity; however, results have been inconsistent. Some studies
show an enhancement in the thermal conductivity for polymers upon
cross-linking, while others show the opposite trend. In this work
we study the mechanisms of heat transfer in cross-linked polymers
in order to understand the reasons for these discrepancies, in particular
examining the relative contributions of covalent (referred to here
as “bonding”) and nonbonding (e.g., van der Waals and
electrostatic) interactions. Our results indicate cross-linkers enhance
thermal conductivity primarily when they are short in length and thereby
bring polymer chains closer to each other, leading to increased interchain
heat transfer by enhanced nonbonding interactions between the chains
(nonbonding interactions being highly dependent on interchain distance).
This suggests that enhanced nonbonding interactions, rather than thermal
pathways through cross-linker covalent bonds, are the primary transport
mechanism by which thermal conductivity is increased. We further illustrate
this by showing that energy from THz acoustic waves travels significantly
faster in polymers when nonbonding interactions are included versus
when only covalent interactions are present. These results help to
explain prior studies that measure differing trends in thermal conductivity
for polymers upon cross-linking with various species