B-SNAM

In scanning near-field microscopies, such as scanning tunnelling microscopy (STM), atomic force microscopy (AFM) or near-field optical microscopy (SNOM), the imaging resolution is dictated by the size of the imaging tip, as opposed to far-field techniques whose resolution is given by the diffraction limit, typically half the relevant wavelength. In the 90s, scanning-near field acoustic microscopy (SNAM) was developed following the principles of STM and AFM, in particular by use of vibrating cantilevers. The objective of SNAM was to provide acoustic images with sub-micron resolution, beyond the ultimate resolution achievable by diffraction-limited acoustic microscopes operating in the GHz range. In B-SNAM, we propose to develop and investigate a totally novel type of scanning near-field acoustic microscope, with a tip made of a resonant air bubble in water. Air bubbles in water are indeed sub-wavelength resonators, as their size is typically 200 smaller than the resonance wavelength in water. As a consequence, the approach proposed by B-SNAM has a resolution dictated by the size if the bubble, i.e. typically 100 times better than diffraction-limited acoustic microscopy operating at the same frequency. As opposed to conventional SNAM approach aimed specifically at submicron resolution, B-SNAM provides a fully scalable resolution range, through the size of the air bubble. Indeed, at the heart of the B-SNAM is the possibility to hold and manipulate air-bubbles stabilized inside 3D-printed frames of various sizes, invented at the LIPhy. The B-SNAM project has several objectives, from the understanding of the physical mechanisms involved in the imaging process to the fabrication of a low-cost, micrometer resolution acoustic microscope prototype operating at MHz frequencies. A "human scale" prototype will also be developed both for demonstrations for scientific dissemination to a wide audience, as well as for applications to the study of the properties of sedimentary deposits. B-SNAM is a transdisciplinary project that will address different research questions, from the practical resolution of instrumental challenges to the study of the physics of the interaction between a resonant bubble and its local environment.