Time of flight backscattering spectrometry (ToF-BS) was successfully implemented in a helium ion microscope (HIM). Its integration introduces the ability to perform laterally resolved elemental analysis as well as elemental depth profiling on the nm scale. A lateral resolution of ≤54nm and a time resolution of Δt≤17ns(Δt/t≤5.4%) are achieved. By using the energy of the backscattered particles for contrast generation, we introduce a new imaging method to the HIM allowing direct elemental mapping as well as local spectrometry. In addition laterally resolved time of flight secondary ion mass spectrometry (ToF-SIMS) can be performed with the same setup. Time of flight is implemented by pulsing the primary ion beam. This is achieved in a cost effective and minimal invasive way that does not influence the high resolution capabilities of the microscope when operating in standard secondary electron (SE) imaging mode. This technique can thus be easily adapted to existing devices. The particular implementation of ToF-BS and ToF-SIMS techniques are described, results are presented and advantages, difficulties and limitations of this new techniques are discussed.
Unstable cathode
electrolyte interphase (CEI) formation increases degradation in high
voltage Li-ion battery materials. Few techniques couple characterization
of nano-scale CEI layers on the macroscale with
in situ
chemical characterization, and thus, information on how the underlying
microstructure affects CEI formation is lost. Here, the process of
CEI formation in a high voltage cathode material, LiCoPO
4
, has been investigated for the first time using helium ion microscopy
(HIM) and
in situ
time-of-flight (ToF) secondary
ion mass spectrometry (SIMS). The combination of HIM and Ne-ion ToF-SIMS
has been used to correlate the cycle-dependent morphology of the CEI
layer on LiCoPO
4
with a local cathode microstructure, including
position, thickness, and chemistry. HIM imaging identified partial
dissolution of the CEI layer on discharge resulting in in-homogenous
CEI coverage on larger LiCoPO
4
agglomerates. Ne-ion ToF-SIMS
characterization identified oxyfluorophosphates from HF attack by
the electrolyte and a Li-rich surface region. Variable thickness of
the CEI layer coupled with inactive Li on the surface of LiCoPO
4
electrodes contributes to severe degradation over the course
of 10 cycles. The HIM–SIMS technique has potential to further
investigate the effect of microstructures on CEI formation in cathode
materials or solid electrolyte interphase formation in anodes, thus
aiding future electrode development.
Cross-linking of a self-assembled monolayer of 1,1'-biphenyl-4-thiol by low energy electron irradiation leads to the formation of a carbon nanomembrane, which is only 1 nm thick. Here we study the perforation of these freestanding membranes by slow highly charged ion irradiation with respect to the pore formation yield. It is found that a threshold in potential energy of the highly charged ions of about 10 keV must be exceeded in order to form round pores with tunable diameters in the range of 5-15 nm. Above this energy threshold the efficiency for a single ion to form a pore increases from 70% to nearly 100% with increasing charge state. These findings are verified by two independent methods, namely the analysis of individual membranes stacked together during irradiation and the detailed analysis of exit charge state spectra utilizing an electrostatic analyzer.
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