Combining STEM and PiFM for Complementary Nanoscale Sample Analysis

Introduction

Scanning Transmission Electron Microscopy (STEM) is a premier imaging and analytical technique that combines the high spatial resolution of transmission electron microscopy with the precision of a focused electron probe. In STEM, a highly focused electron beam – often smaller than a single atom – is rastered across an ultrathin sample. Multiple detectors collect signals from transmitted and scattered electrons, as well as characteristic X-rays, enabling the acquisition of structural, elemental, and compositional information at sub-nanometer resolution.

This capability to image individual atomic columns, generate detailed elemental maps, and perform correlative nanoscale analyses has established STEM as a cornerstone tool in materials science, semiconductor research, and nanotechnology.

Despite its strengths, STEM has inherent limitations. The intense electron beam can damage sensitive samples, such as biological or soft materials, potentially altering surface morphology and limiting subsequent analyses. Moreover, STEM primarily provides elemental rather than molecular information, restricting its ability to fully characterize chemical composition.

Molecular Vista’s Photo-Induced Force Microscopy (PiFM) complements STEM by offering non-destructive chemical analysis with nanoscale resolution. PiFM uses a precisely tuned infrared (IR) laser to excite molecular vibrations in a defined region of the sample surface, while a sensitive atomic force microscope (AFM) probe measures the resulting photo-induced force along with its standard topography data. By operating in non-contact mode and leveraging the second mechanical resonance, PiFM minimizes tip-sample interactions, preserving sample integrity for follow-up analyses, including STEM. Additionally, the tip-enhanced field generated by the IR laser enables high-precision chemical characterization, many times with higher spatial resolution than the topographical image.

By combining STEM and PiFM, researchers can obtain a more complete understanding of sample structure, composition, and chemistry. The combination of STEM’s unparalleled structural and elemental imaging with PiFM’s molecular insight provides a powerful platform for comprehensive nanoscale analysis. For effective nanoscale correlative studies across different instruments, identifying the same region of measurement may be difficult. For STEM and PiFM, the use of the TEM grid provides the natural fiducial features to navigate to the same locations without any uncertainty.