Extremely-resolution imaging and quantitative characterization of subsurface nano-features are very important in numerous fields, comparable to ultra-precision atomic manufacturing [1], [2], [3], [4], built-in digital circuit inspection [5], [6], [7], [8], semiconductor nanodevice design [9], [10], [11], [12], practical materials mechanics characterization [13], [14], [15], [16], [17], and subcellular construction monitoring [18], [19], [20], [21]. These functions have attracted the curiosity of researchers and students. Subsurface nano-features are sometimes characterised by heterogeneous materials composition, mechanical properties, and adhesion [22], [23], [24], [25]. Whereas substantial progress has been made in imaging and characterizing these options in supplies comparable to microscale composites, nano-polymers, metamaterials, and doped crystals, the demand for enhanced visualization and quantification stays. Ongoing challenges embrace a greater understanding of latest practical supplies, testing superior nano-devices, exploring life science ideas, and growing drug-related strategies. These challenges proceed to drive the refinement of progressive applied sciences.
Because the creation of scanning probe microscopy (SPM), together with scanning tunneling microscopy (STM) [26] and atomic drive microscopy (AFM) [27] within the Nineteen Eighties, the demand for ultra-resolution imaging and characterization of subsurface nano-features has been rising. This demand has led to the event of varied technical methods primarily based on single-mode or multi-mode coupling, comparable to electrical, optical, thermal, magnetic, and acoustic strategies. These methods are utilized in fields comparable to atomic fabrication, biosensing, bodily property characterization, power storage, and nanometer metrology (Fig. 1). Superior ultra-resolution imaging applied sciences have notably superior analysis in two core areas: (i) static illustration, which incorporates morphology statement, part evaluation, and characterization of bodily and chemical properties; and (ii) dynamic monitoring, which covers materials stream, course of evolution, and modifications in dwelling methods.
Methods comparable to STM, scanning electron microscopy (SEM), transmission electron microscopy (TEM), AFM, and X-ray diffraction have achieved nanometer and even sub-nanometer decision. These achievements have enabled the positioning of single atoms [28], visualization and identification of biofunctionalized nanoparticles [29], quantification of electrical polarization properties of single micro organism [30], sub-molecular insights into interfacial water [31], and revelation of structured water molecules on membrane proteins [32]. The restrictions of STM primarily stem from its requirement for extremely conductive substrates, precluding direct imaging of insulating supplies comparable to biomacromolecules or amorphous phases. Moreover, the necessitated high-vacuum atmosphere imposes inherent restrictions on in situ evaluation of liquid-phase or reside specimens. SEM, in the meantime, is topic to operational constraints imposed by high-vacuum circumstances or specialised gas-injection methods, whereas its high-energy electron irradiation induces structural degradation in organic supplies, organics, and radiation-sensitive compounds. Non-conductive samples additional necessitate conductive coating to mitigate cost accumulation artifacts, which can distort floor morphology illustration. AFM overcomes a few of these limitations by enabling measurements on insulating substrates and in liquid environments, but its decision is constrained by tip-induced curvature results, parasitic interplay forces, and sensitivity to environmental fluctuations. XRD, though highly effective for crystallographic evaluation, is basically incompatible with amorphous or extremely disordered methods, single-molecule buildings, or part boundaries. As a result of its bulk-averaged nature, XRD can not spatially resolve localized microstructural heterogeneity or particular person defect properties. Notably, all these strategies inherently undergo from limitations in subsurface characterization with out auxiliary strategies comparable to cross-sectional milling or tomographic reconstruction. Whereas superior fluorescence microscopy strategies, comparable to confocal microscopy, stimulated emission depletion microscopy, and stochastic optical reconstruction microscopy, have overcome the normal optical diffraction restrict, they’ve facilitated outstanding developments in exploring most cancers cells [33], carbon nanotubes [34], bacteriorhodopsins, and clathrin-coated pits in reside cells [35], [36], [37], buried native provider diffusion in halide perovskite crystals [38], and mitochondria and synaptonemal complexes [39]. These strategies are restricted to imaging and characterizing floor and superficial subsurface options. Scanning thermal microscopy, scanning thermal noise microscopy, photon thermal microscopy, and scanning thermoelectric microscopy have demonstrated capabilities comparable to detecting metallic nanostructures in silica core–shells [40], mapping temperature distribution in working nanoscale units [41], atomic quantity evaluation on the nanoscale [42], and fast hyperspectral imaging of reside cells throughout giant fields of view and excessive cell confluency [43]. Nevertheless, these strategies typically end result within the inactivation of organic supplies and irreversible pattern injury. Subsequently, whereas acknowledging the outstanding contributions of those strategies, figuring out their inherent limitation is essential, which, in flip, drives the event of latest imaging methods.
Acoustic microscopy, which is predicated on acoustic reflection, scattering, transmission, diffraction, and interference, is favored by life science, materials science, and nanoscience because of its superior penetration, security, and nondestructive nature, particularly for reside lively supplies. Nevertheless, conventional acoustic microscopy is proscribed to micron-level decision because of constraints in array component preparation [44], the acoustic diffraction restrict, and information hyperlink building [45]. In distinction, the mixing of an acoustic scanning probe system with AFM has made notable progress over the previous three many years (Fig. 2). This hybrid system not solely allows efficient detection of floor and subsurface far-field options but additionally achieves nanometer-level decision. Notably, functions comparable to biomass and chemical processing [46], subsurface atomic construction fingerprinting [47], detection of cracks in steel–polymer trench construction [48], subsurface holes below graphite [49], and malaria parasites inside contaminated purple blood cells [50] have been efficiently demonstrated. These achievements emphasize the potential for additional integration throughout multidisciplinary fields and underscore the promise of acoustic AFM methods in advancing our understanding of complicated organic and materials methods.
This assessment goals to supply a complete and forward-looking perception of the sector into acoustic AFM, emphasizing its significance and potential to advance multidisciplinary analysis. Subsequently, the dialogue is structured round 5 key dimensions: (1) a concise assessment of main historic developments and milestones which have formed the evolution of the acoustic AFM; (2) a scientific overview of the architectural and practical improvements in acoustic AFM instrumentation, emphasizing current developments and their impression on efficiency; (3) an in-depth evaluation of imaging distinction mechanism, together with theoretical frameworks and experimental statement to elucidate key variations and insights; (4) a complete presentation of the achievements of acoustic AFM throughout divers fields, coupled with a important examination of its limitations and challenges; and (5) a potential outlook that summarizes the event prospects, rising calls for, and untapped potential of the acoustic AFM. This multifaceted strategy goals to supply a holistic perspective on the present state and future instructions of the acoustic AFM, offering a stable basis for continued innovation and interdisciplinary collaboration.
