SIMS Material Characterization: Achieving Atomic Depth Resolution for Small Particles

In the Nature Research Custom Media webcast, "Secondary Ion Mass Spectrometry Characterization of MAX and MXene Samples: Achieving Atomic Depth Resolution for Small Particles," Dr. Pawel P. Michalowski, Research Group Leader at the Institute of Microelectronics and Photonics, Lukasiewicz Research Network, discusses using Dynamic SIMS at extremely low impact energy to achieve atomic depth resolution for small particle measurements.

Dr. Michalowski presents results from the material characterization and outlines the steps to optimize the procedure, highlighting the process's intricacies. Published in Nature Nanotechnology 17, the effort was the work of cooperation of two research groups, Lukasiewicz – IMiF in Warsaw and Drexel University in Philadelphia.

Dr. Michalowski begins his presentation by discussing the measurement procedure for nanomaterials. The technique involves bombarding a sample with a primary ion beam, causing phenomena such as collision cascades and sputtering and resulting in the formation of secondary ions that can be analyzed for composition.

The interpretation of the results can be challenging due to preferential sputtering and mixing of features, which can lead to artifacts or misinterpretation of real features.

He then explains the principles of secondary ion mass spectrometry (SIMS), including the mixing effect and the ability to obtain elemental composition but limited chemical state information. He demonstrates how Dynamic SIMS can create depth profiles and lateral analysis of samples using position-sensitive detectors, providing fully free dimensional images of the sample.

Using SIMS for Characterizing 2D Materials

The SIMS experiments were performed on a CAMECA SC Ultra Dynamic SIMS, which Dr. Michalowski explains features "two very important innovations" that differentiate it from other SIMS instruments. The first is the application of EXLIE (extreme low-impact energy technology), enabling the application of RF Plasma for the oxygen column down to 60 eV and floating voltage for the cesium column down to 90 eV. The result is a dramatic reduction of the mixing effect. The second innovation is the form of the beam shape, unlike the typical Gaussian-shaped beam — it is instead projected on a pair of square stencils, producing a working spot on the sample that is rectangular and very, very homogeneous. This eliminates the problem of the blurring of the signals. These innovations, he notes, are significant to working with these materials.

Dr. Michalowski further highlights the limitations of standard measurement procedures in analyzing 2D materials, as they prioritize total ion signal over specific ion signal. He then introduces dedicated measurement procedures that prioritize specific ion signals for improved analysis of 2D materials.

He explains that the approach to measuring the samples uses sputtering, which involves bombarding the sample with high-energy ions. The first results, however, showed no atomic depth resolution. From there, Dr. Michalowski describes in detail during the webcast how the group proceeds, including optimizing SIMS for atomic-scale analysis, improving ion beam analysis for material characterization, measuring the oxygen concentration in the materials using ion beams, and using various additional advanced techniques, such as determining the oxygen content in carbon nanostructures using XPS.

The process continues until, as the authors write in Nature, "We pushed the limits of SIMS analysis to achieve atomic-depth resolution for single micrometre-sized layered MAX and MXene particles with lateral dimensions on the order of 10–30 μm."?

While more work still needs to be done, among the results, the authors write in Nature, is "the demonstration of the existence of oxycarbide MXenes offers an opportunity for developing a new subfamily of MXenes (oxycarbides and eventually oxynitrides and oxycarbonitrides), and presents an additional parameter (oxygen content) that can be used for controlling the properties of MXenes. This finding is expected to quickly stimulate computational works predicting the properties of oxycarbide MXenes and experimental studies aiming at determining the effects of oxygen content on the properties of various MXenes."

Throughout the webcast, Dr. Michalowski illustrates the group's various techniques and the role of CAMECA SC Ultra Dynamic SIMS in overcoming a series of challenges in nanostructure analysis and achieving a positive outcome. In the end, the Nature authors concluded, "Overall, our results showcase the unique capability of the SIMS technique to probe the compositions of layered materials with monoatomic layer precision. The method is certainly applicable to many other materials."

For in-depth details and discussion, view the entire webcast at "Secondary Ion Mass Spectrometry Characterization of MAX and MXene Samples: Achieving Atomic Depth Resolution for Small Particles."

About Dr. Pawel P. Michalowski

Dr. Pawel P. Michalowski is the Characterization of Materials and Devices Research Group Leader at ?ukasiewicz Research Network - Institute of Microelectronics and Photonics. With more than 15 years of experience in Secondary Ion Mass Spectrometry (SIMS), Dr. Michalowski specializes in the analysis of ultra-thin and 2D materials and measurements of full device structures. Currently, he is using a CAMECA SC Ultra tool with a depth resolution below 1nm. He has been the leader of the Research Group since 2020.