Elemental Characterization of Al Nanoparticles Buried under a Cu Thin Film: TOF-SIMS vs STEM/EDX

Abstract

In this work we present a comprehensive comparison of Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) and Scanning Transmission Electron Microscope combined with Energy-Dispersive X-ray Spectroscopy (STEM/EDX), which are currently the most powerful elemental characterization techniques in the nano-and microscale. The potential and limitations of these methods are verified using a novel dedicated model sample consisting of Al nanoparticles buried under a 50 nm thick Cu thin film. The sample design based on the low concentration of nanoparticles allowed us to demonstrate the capability of TOF-SIMS to spatially resolve individual tens of nanometre large nanoparticles under Ultra-High Vacuum (UHV) as well as High Vacuum (HV) conditions. This is a remarkable achievement especially taking into account the very small quantities of the investigated Al content. Moreover, the imposed restriction on the Al nanoparticles location, i.e. only on the sample substrate, enabled us to prove that the measured Al signal represents the real distribution of Al nanoparticles and does not originate from the artefacts induced by the surface topology. The provided comparison of TOF-SIMS and STEM/EDX characteristics delivers guidelines for choosing the most optimal method for efficient characterization of nano-objects.

Mechanisms of Fluorine-Induced Separation of Mass Interference during TOF-SIMS Analysis

“…However, with the current knowledge, it is difficult to judge on whether the ultimate matrix effect would provide the same beneficial properties as presented herein. Furthermore, the proposed methodology can be potentially applied in dedicated stand-alone TOF-SIMS instruments operating under UHV (and therefore allowing for using cluster-ion beams, such as Bi 3 2+ ), assuming that the oxygen flooding (by default used for charge compensation and additionally applied for increasing positive ion yields ,, ) could be substituted with F-containing gas. Hypothetically, a similar effect could be obtained with SF 5 primary ion source, which is available in some dedicated instruments for sputtering, given that sufficient F-flux can be provided.…”

“…The time-of-flight secondary ion mass spectrometry , (TOF-SIMS) is one of the very few analysis techniques providing three-dimensional (3D) chemical information with nanometer resolution, − and therefore capable of analyzing nanoparticle-containing systems − and thin-film-based multilayers. − The detection of all, light and heavy elements is the TOF-SIMS most important advantage over scanning transmission electron microscopy combined with energy-dispersive X-ray spectroscopy (STEM/EDX) . This is particularly crucial in the case of characterization of Li (with atomic number Z = 3) distribution in novel microdevices such as Li-ion solid-state batteries. , Furthermore, not only single ions but also ionized molecules can be measured with TOF-SIMS enabling the analysis of complex biological structures such as tumors. , STEM/EDX and APT (atom probe tomography) provide chemical information from a very small volume (the typical thicknesses of TEM lamellas and APT tips are usually <100 nm), which may be not representative for the entire sample composition, for example, due to local contaminations or material segregation.…”

Detection of Au+ Ions During Fluorine Gas-Assisted Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) for the Complete Elemental Characterization of Microbatteries

“…TOF-SIMS mass spectra are very useful for element detection analysis as the signals are integrated over a relatively large volume (usually, 1−10 4 μm 2 lateral area 29 and thickness up to approximately 1 μm). However, a sufficiently high count rate has to be ensured to represent elemental distribution in 2D or 3D with nanoscale resolution.…”

“…A detailed comparison of TOF-SIMS and STEM/EDX is presented in our previous work. 29 However, despite an extremely high sensitivity, 38 the TOF-SIMS application scope can be limited in the case of insufficiently ionizing elements and/or when a material's components ionize with different polarities. The latter results from the fact that the detection of positive and negative ions requires different ion extraction voltages, which means that they cannot be measured during a single measurement.…”

Nanoprojectile Secondary Ion Mass Spectrometry for Analysis of Extracellular Vesicles

“…Secondary ion mass spectrometry (SIMS) is ideally suited for sensitive analysis of nanometer-sized objects or ultrathin layers. − Typically, nanoscale analysis with SIMS requires the use of a focused ion beam (a few 10 nm) comprised low energy (keV) atomic or polyatomic ions. − Unfortunately, impacts of atomic or polyatomic ions result in extensive fragmentation of analyte molecules, and nanoscale analysis is limited to elemental analysis, thus the investigation of biological materials requires the use of a rare isotope or elemental tag . Recently, Nolan and colleagues reported a nano-SIMS methodology where a focused ion beam probe was used to analyze a tissue section labeled with isotopically tagged Abs. , This strategy showed considerable promise but, with a spatial resolution of ∼100 nm, it may not be suitable for the analysis of single EVs.…”