High-resolution characterization of the diffusion of light chemical elements in metallic components by scanning microwave microscopy

Submicronic-Scale Mechanochemical Characterization of Oxygen-Enriched Materials

Conventional techniques that measure the concentration of light elements in metallic materials lack high-resolution performance due to their intrinsic limitation of sensitivity. In that context, scanning microwave microscopy has the potential to significantly enhance the quantification of element distribution due to its ability to perform a tomographic investigation of the sample. Scanning microwave microscopy associates the local electromagnetic measurement and the nanoscale resolution of an atomic force microscope. This technique allows the simultaneous characterization of oxygen concentration as well as local mechanical properties by microwave phase shift and amplitude signal, respectively. The technique was calibrated by comparison with nuclear reaction analysis and nanoindentation measurement. We demonstrated the reliability of the scanning microwave technique by studying thin oxygen-enriched layers on a Ti-6Al-4V alloy. This innovative approach opens novel possibilities for the indirect quantification of light chemical element diffusion in metallic materials. This technique is applicable to the control and optimization of industrial processes.

Subsurface imaging of rigid particles buried in a polymer matrix based on atomic force microscopy mechanical sensing

Several subsurface imaging methods based on atomic force microscopy (AFM) linear nanomechanical mapping, namely contact resonance (CR), bimodal and harmonic AFMs, are investigated and compared. Their respective subsurface detection capability is estimated and evaluated on a model specimen, which is prepared by embedding SiO₂ microparticles in a PDMS elastomer. The measured CR frequency, bimodal and harmonic amplitudes are related to local mechanical properties by analyzing cantilever dynamics and further linked to subsurface depths of the particles by finite element analysis. The maximum detectable depths are obtained from the apparent particle diameters in subsurface image channels via employing a simple geometrical model. Under common experimental settings, results demonstrate that the depth limits reach up to about 812 nm, 212 nm and 127 nm for CR, bimodal and harmonic AFM modes, respectively. The depth sensitivity can be tuned and optimized by using either different cantilever eigenmodes in CR-AFM or spectroscopy analysis in bimodal and harmonic AFMs. The three imaging methods have their own suitable application situations. The comparisons can advance a further step into understanding the subsurface image contrast via AFM mechanical sensing.

Microwave Spectroscopic Detection of Human Hsp70 Protein on Annealed Gold Nanostructures on ITO Glass Strips

Conductive indium-tin oxide (ITO) and non-conductive glass substrates were successfully modified with embedded gold nanoparticles (AuNPs) formed by controlled thermal annealing at 550 °C for 8 h in a preselected oven. The authors characterized the formation of AuNPs using two microscopic techniques: scanning electron microscopy (SEM) and atomic force microscopy (AFM). The analytical performances of the nanostructured-glasses were compared regarding biosensing of Hsp70, an ATP-driven molecular chaperone. In this work, the human heat-shock protein (Hsp70), was chosen as a model biomarker of body stress disorders for microwave spectroscopic investigations. It was found that microwave screening at 4 GHz allowed for the first time the detection of 12 ng/µL/cm² of Hsp70.

Nanoscale subsurface imaging

The ability to probe structures and functional properties of complex systems at the nanoscale, both at their surface and in their volume, has drawn substantial attention in recent years. Besides detecting heterogeneities, cracks and defects below the surface, more advanced explorations of chemical or electrical properties are of great interest. In this article, we review some approaches developed to explore heterogeneities below the surface, including recent progress in the different aspects of metrology in optics, electron microscopy, and scanning probe microscopy. We discuss the principle and mechanisms of image formation associated with each technique, including data acquisition, data analysis and modeling for nanoscale structural and functional imaging. We highlight the advances based on atomic force microscopy (AFM). Our discussion first introduces methods providing structural information of the buried structures, such as position in the volume and geometry. Next we present how functional properties including conductivity, capacitance, and composition can be extracted from the modalities available to date and how they could eventually enable tomography reconstructions of systems such as overlay structures in transistors or living systems. Finally we propose a perspective regarding the outstanding challenges and needs to push the field forward.