When scanning tunneling microscopy gets the wrong adsorption site: H on Rh(100)

Scanning tunneling microscopy (STM) is widely used to image surface structures at the atomic level. However, when adsorbates are highly mobile, STM images may not accurately reflect their true positions. Prior research has shown that STM can be affected by interactions between the tip and the sample, potentially altering the observed configuration. In the case of hydrogen on Rh(100), STM images have been interpreted as showing H atoms in all bridge sites. This interpretation has not been validated by other methods. No prior work had resolved whether the observed protrusions correspond to actual H positions or tip-induced effects. That uncertainty drove the need for complementary techniques. Quantitative low-energy electron diffraction and temperature programmed desorption offer independent assessments of surface coverage and site occupancy. These methods provide a more objective measure of adsorption sites than STM alone.

This study aimed to clarify the discrepancy between STM imaging and actual H adsorption sites on Rh(100). The goal was to determine whether the observed protrusions in STM images truly represent H atoms in bridge sites or are artifacts caused by the imaging process. The researchers focused on understanding how the STM tip might influence the observed configuration. They sought to validate the STM findings using alternative experimental approaches. The motivation was to prevent misinterpretation of STM data in systems with mobile adsorbates. The study aimed to establish the importance of cross-checking STM results with other methods. The researchers also wanted to investigate the role of tip-sample interactions in STM imaging. This work contributes to improving the accuracy of surface characterization techniques.

The study combined scanning tunneling microscopy (STM) with quantitative low-energy electron diffraction (LEED) and temperature programmed desorption (TPD) to analyze H adsorption on Rh(100). STM was used to image the surface at low tunneling resistance. LEED provided structural information about the H coverage and site occupancy. TPD was employed to measure desorption temperatures and quantify H coverage. Density functional theory (DFT) calculations were performed to model the interaction between H atoms and the STM tip. The calculations aimed to explain how the tip could influence the observed H positions. The researchers compared the results from all three methods to identify discrepancies. This multi-technique approach allowed a comprehensive analysis of H adsorption behavior.

STM images suggested H atoms in all bridge sites of Rh(100), but LEED and TPD revealed a much lower H coverage. Most H atoms were found in fourfold hollow sites rather than bridge sites. DFT calculations showed that the STM tip attracts mobile H atoms into bridge sites during imaging. This tip-induced effect explains the discrepancy between STM and other methods. The study found that the STM result is not representative of the true adsorption configuration. The H atoms are highly mobile and can be manipulated by the tip during imaging. This finding highlights the limitations of STM in systems with mobile adsorbates. The results emphasize the need for complementary techniques to validate STM observations.

The study demonstrates that STM images of highly mobile adsorbates can be misleading due to tip-sample interactions. The observed protrusions in STM images of H on Rh(100) do not correspond to actual H positions. Instead, the STM tip attracts H atoms into bridge sites during imaging. This effect is supported by DFT calculations and confirmed by LEED and TPD data. The findings suggest that STM should be used cautiously in systems with mobile adsorbates. The authors propose that additional analysis techniques are essential for accurate surface characterization. The study underlines the importance of cross-validating STM results with other methods. These conclusions align with the authors' stated implications and are directly supported by the data presented.