SSRM measures nanoscale resistance variations in conductive and semiconductive materials by applying a voltage through a conductive AFM tip in contact mode.

A conductive AFM probe is pressed into contact with the sample surface under high force, allowing it to penetrate any surface oxide or contamination and form a reliable ohmic contact. While scanning the surface in contact mode, a DC bias is applied between the probe and a backside or reference electrode on the sample.

The current that flows through this localized contact is measured with a wide-range, typically logarithmic, amplifier, enabling quantification of resistance ranging from a few ohms up to gigaohms. The dominant contribution to the measured resistance is the so-called “spreading resistance,” which depends on both the carrier concentration beneath the tip and the geometry of the tip-sample contact. As a result, SSRM provides direct spatial mapping of dopant concentration profiles and conductive layer uniformity in cross-sectional—and, in some cases, planar—semiconductor samples.

An oxide-free environment is critical for SSRM because the presence of oxide layers on the sample surface increases contact resistance and hinders accurate measurement of local electrical properties. Oxide layers act as insulating barriers that prevent reliable ohmic contact between the conductive AFM tip and the sample, leading to distorted resistance readings and reduced spatial resolution. To overcome this, measurements must be conducted under conditions that remove or prevent oxide formation and contamination, such as in vacuum or inert atmospheres, ensuring stable tip-sample contact and accurate resistance mapping.

Park Systems’ NX-Hivac provides an optimal oxide-free environment by integrating a high-vacuum chamber with advanced system controls. This setup minimizes surface oxidation and contamination during measurement, preserving surface cleanliness and enhancing measurement reliability and reproducibility.

Park Systems’ SSRM uses a logarithmic amplifier to cover a wide range of current levels without switching gain, enabling high-resolution mapping of resistive variations across multiple orders of magnitude (from semi-conducting region to insulating region). Operating in vacuum further minimizes oxidation and improves the accuracy of measurements by ensuring consistent ohmic contact.

SSRM results distinguish between a good and a bad device by comparing their height and resistance maps. In a good device, the resistance image displays uniform and well-defined contrast, indicating consistent electrical performance across the scanned area. In contrast, a bad device case, characterized by severe inhomogeneity and streak artifacts in the resistance map, often due to surface contamination, physical damage, or process defects, correlated with abnormal features in the height image.

The images demonstrates the application of SSRM, operated with the NX-Hivac, to characterize a lithium-ion battery electrode. The height image reveals the complex, particulate-rich surface morphology typical of battery electrode materials. The corresponding resistance image provides a spatially resolved measurement of local electrical resistance, clearly distinguishing between highly conductive regions and more resistive domains within the electrode composite. The use of NX-Hivac’s oxide-free, high-vacuum environment ensures high-fidelity electrical measurements, free from the artifacts caused by surface oxidation, and supports robust failure analysis and material optimization in advanced energy storage research.