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.

In this work, we present the potential of high vacuum-compatible timeof-flight secondary ion mass spectrometry (TOF-SIMS) detectors, which can be integrated within focused ion beam (FIB) instruments for precise and fast chemical characterization of thin films buried deep under the sample surface. This is demonstrated on complex multilayer systems composed of alternating ceramic and metallic layers with thicknesses varying from several nanometers to hundreds of nanometers. The typical problems of the TOF-SIMS technique, that is, low secondary ion signals and mass interference between ions having similar masses, were solved using a novel approach of co-injecting fluorine gas during the sample surface sputtering. In the most extreme case of the Al/Al 2 O 3 /Al/Al 2 O 3 /.../Al sample, a <10 nm thick Al 2 O 3 thin film buried under a 0.5 μm material was detected and spatially resolved using only 27 Al + signal distribution. This is an impressive achievement taking into account that Al and Al 2 O 3 layers varied only by a small amount of oxygen content. Due to its high sensitivity, fluorine gas-assisted FIB-TOF-SIMS can be used for quality control of nano-and microdevices as well as for the failure analysis of fabrication processes. Therefore, it is expected to play an important role in the development of microelectronics and thinfilm-based devices for energy applications.

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is one of very few analytical techniques allowing sample chemical structure to be characterized in three-dimensional (3D) with nanometer resolution. Due to the excellent sensitivity in the order of ppm−ppb and capability of detecting all ionized elements and molecules, TOF-SIMS finds many applications for analyzing nanoparticle-containing systems and thin films used in microdevices for new energy applications, microelectronics, and biomedicine. However, one of the main drawbacks of this technique is potential mass interference between ions having the same or similar masses, which can lead to data misinterpretation. In this work, we present that this problem can be easily solved by delivering fluorine gas to a sample surface during TOF-SIMS analysis and we propose mechanisms driving this phenomenon. Our comprehensive studies, conducted on complex thin films made of highly mass-interfering elements, show that fluorine modifies the ionization process, leading to element-specific changes of ion yields (which can vary by several orders of magnitude), and affects the efficiency of metal hydride and oxide formation. In conjunction, these two effects can efficiently induce separation of mass interference, providing more representative TOF-SIMS data with respect to the sample composition and significant enhancement of chemical image resolution. Consequently, this can improve the chemical characterization of complex multilayers in nanoscale.