AFM探针

Synchronized Modulation Kelvin Probe Force Microscopy for Surface Photovoltage Studies in Optoelectronic Systems

Kelvin Probe Force Microscopy (KPFM) has become an essential atomic force microscopy (AFM) technique for investigating surface potentials and charge distributions in electronic and optoelectronic materials. However, conventional KPFM measurements can be affected by thermal drift, probe degradation, and environmental changes during data acquisition, making the accurate characterization of dynamic systems particularly challenging. In this article, Zeinab Eftekhari, Ariane Ufer, Ursula Wurstbauer, and Rebecca Saive introduce synchronized modulation Kelvin probe force microscopy (SM-KPFM), an advanced in-operando approach designed to overcome these limitations.

The authors developed SM-KPFM by synchronizing external stimulus modulation, such as illumination or electrical bias, with the AFM scan direction. In synchronized illumination KPFM, the sample remains unilluminated during the trace scan and illuminated during the retrace scan, enabling direct comparison of surface potential states within the same raster image. This strategy minimizes measurement artifacts arising from drift, thermal effects, and AFM probe degradation while providing highly reproducible surface photovoltage measurements.

The technique was demonstrated on a silicon photodiode and a molybdenum disulfide (MoS₂) bilayer deposited on a gold substrate. By capturing illuminated and non-illuminated contact potential difference (CPD) measurements along identical scan paths, SM-KPFM produced accurate, drift-free surface photovoltage maps and provided improved insight into nanoscale photovoltaic behavior and charge separation processes in optoelectronic materials.

Kelvin Probe Force Microscopy measurements were performed in sideband mode using a NanoWorld ARROW-EFM AFM probe. The Pt/Ir-coated AFM probe, featuring a resonance frequency of 68 kHz and a spring constant of 2.8 N/m, enabled highly sensitive surface potential mapping with excellent electrical conductivity and measurement stability. The synchronization approach required only triggering the illumination source using the AFM scan direction signal, making the technique readily applicable to existing KPFM workflows without complex hardware modifications.

This work demonstrates how combining an innovative synchronized measurement strategy with a NanoWorld ARROW-EFM AFM probe significantly improves the reliability of operando Kelvin Probe Force Microscopy. The methodology opens new opportunities for investigating nanoscale electronic and optoelectronic devices, photovoltaic materials, and other functional nanostructures where precise surface potential mapping is essential.

figure 3. — KPFM measurements of a MoS₂ flake on gold electrodes under dark and illuminated conditions. (a) Topography and (b) optical image of the MoS₂ flake on the gold electrodes, where the black box shows the scanned area under AFM/KPFM. The topography image was post-processed to have the substrate and gold contact surfaces on the same level such that the thin flake becomes visible. (c, d) CPD maps acquired in separate scans under dark (c) and illuminated (d) conditions using conventional KPFM (red box). (e) SPV map derived from the sequential scans. (f) Trace (dark) and (g) retrace (illuminated) CPD maps obtained using SM- KPFM (blue box). (h) SPV map (retraced minus trace).

Full citation:
Eftekhari, Z.; Ufer, A.; Wurstbauer, U.; Saive, R.
Synchronized modulation Kelvin probe force microscopy for surface photovoltage studies in optoelectronic systems.
MRS Communications 16 (2026), 180–186.
https://doi.org/10.1557/s43579-025-00899-3

Microfibrillated Cellulose Films from Agri-Food Wastes and Plant Residues for Food Packaging Applications – A Comparative Investigation

Sustainable alternatives to conventional plastic packaging are receiving increasing attention as industries seek circular economy solutions and renewable material sources. In this article, Tommaso Bellesia, Daniele Carullo, Andrea Fachin, Maral Soltanzadeh, Masoud Ghaani, Giorgio Innocenzo Ascrizzi, Laura Piazza, and Stefano Farris investigate the potential of microfibrillated cellulose (MFC) obtained from agri-food waste streams and plant residues as high-performance materials for food packaging applications.
The authors produced MFC dispersions from giant cane, Posidonia oceanica seagrass, and coffee silverskin using high-pressure homogenization and compared the resulting films with a commercially available cellulose-based packaging material. An extensive characterization of the dispersions and films was performed, including rheological, mechanical, optical, barrier, surface, and morphological analyses.
In this article, atomic force microscopy (AFM) confirmed the successful production of microfibrillated cellulose structures with average fibril diameters below 100 nm. The resulting films demonstrated excellent oxygen barrier performance, high stiffness, strong tensile properties, and effective UV-shielding capabilities. Among the investigated materials, films produced from coffee silverskin exhibited particularly promising performance, highlighting the potential of converting agricultural by-products into value-added packaging materials.
To investigate film surface topography, AFM measurements were performed in contact resonance amplitude imaging mode using a NanoWorld Arrow-FMR AFM probe. The AFM probe features a rectangular cantilever with a triangular free end and a tetrahedral tip with a typical radius of curvature of approximately 10 nm. With a spring constant of 2.8 N/m and a resonance frequency of 75 kHz, the Arrow-FMR AFM probe enabled detailed nanoscale characterization of film morphology and surface roughness.
The study demonstrates how AFM analysis using a NanoWorld AFM probe contributes to understanding the relationship between cellulose microstructure and the functional performance of sustainable packaging materials. The results further support the development of renewable, high-performance cellulosic thin films derived from waste biomass sources.

Figure 1Fig. 1. AFM height image of MFC from PO-derived cellulose.

Full citation:
Bellesia, T.; Carullo, D.; Fachin, A.; Soltanzadeh, M.; Ghaani, M.; Ascrizzi, G. I.; Piazza, L.; Farris, S.
Microfibrillated cellulose films from agri-food wastes and plant residues for food packaging applications – A comparative investigation.
Food Packaging and Shelf Life 2026, 54, 101728.
https://doi.org/10.1016/j.fpsl.2026.101728

Attribution 4.0 International
https://creativecommons.org/licenses/by/4.0/

Does the Hfq Protein Contribute to RNA Cargo Translocation into Bacterial Outer Membrane Vesicles?

Gram-negative bacteria release outer membrane vesicles (OMVs) that play a central role in host–pathogen interactions by transporting biomolecules, including proteins and nucleic acids. In this article, Marisela Velez and Véronique Arluison investigate the role of the RNA chaperone Hfq in mediating the interaction of small regulatory RNAs (sRNAs) with bacterial membranes.

In this article, it is shown that RNA binding to the inner membrane of Escherichia coli occurs in an Hfq-dependent manner. The study further demonstrates that membrane composition is a key factor in this process, with cardiolipin-rich lipid domains significantly enhancing RNA–membrane interactions. These findings provide new insight into the mechanism of RNA translocation from the cytoplasm to the periplasm, supporting its subsequent incorporation into OMVs.

Atomic force microscopy (AFM) was used to verify the formation and integrity of supported lipid bilayers and to monitor peptide–membrane interactions. Imaging was performed in tapping mode using a NanoWorld Pyrex-Nitride PNP-DB AFM probe with a resonance frequency of 15 kHz and a spring constant of 0.48 N/m. Measurements were carried out in liquid environment, enabling high-resolution characterization of biologically relevant membrane structures.

This work highlights the importance of AFM-based analysis for studying lipid–protein interactions and provides new understanding of RNA transport mechanisms in bacterial systems.

Figure 1
E. coli lipid bilayer incubated in the absence (A) or presence (B) of Hfq-CTR. Panel (A) shows the E. coli lipids bilayer. The height profile under the line shown on the upper image indicates that the domains are 0.8 nm higher than the rest of the membrane. The lower panel shows a three-dimensional representation of a small region. Panel (B) shows the E. coli lipid bilayer incubated in the presence of Hfq-CTR. The peptide accumulated on top of some of the domains, generating 1 nm high regions in some of them, as shown on the height profile. The arrows point the regions where the change in height occurs.

Full citation:
Velez, M.; Arluison, V.
Does the Hfq Protein Contribute to RNA Cargo Translocation into Bacterial Outer Membrane Vesicles?
Pathogens 2025, 14(4), 399.
https://doi.org/10.3390/pathogens14040399

License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/)