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To enhance contact resonance atomic force microscopy (CR-AFM) and harmonic AFM imaging simultaneously, we design a multifunctional cantilever. Precise tailoring of the cantilever's dynamic properties is realized by either mass-removing or mass-adding. As prototypes, focused ion beam drilling or depositing is used to fabricate the optimized structures. CR-AFM subsurface imaging on circular cavities covered by a piece of highly oriented pyrolytic graphite validates the improved CR frequency to contact stiffness sensitivity. The detectable subsurface depth and cavity radius increase accordingly by using the multifunctional cantilever. At the same time, the free resonance frequency of the second mode is tuned to an integer multiple of the fundamental one. Harmonic AFM imaging on polystyrene and low-density polystyrene mixture shows the improved harmonic amplitude contrast and signal strength on the two material phases. The multifunctional cantilever can be extended to enhance other similar AFM operation modes and it has potential applications in relevant fields such as mechanical characterization and subsurface imaging. [ABSTRACT FROM AUTHOR]

We proposed a method for measuring undercut etching based on contact resonance atomic force microscopy (CR-AFM). Suspended undercut structures were fabricated through isotropic wet etching on a patterned SiNx/Si architecture. The materials beneath the SiNx masks with circular and rectangular shapes were partially etched to form center-supported thin plates. A clear contrast was observed between the supported and suspended regions by CR-AFM amplitude imaging, enabling accurate determination of the undercut boundary and the corresponding etched length. CR-spectroscopy measurements of the undercut dimensions were also applied by acquiring the contact stiffness distribution and by further fitting with models of analyzing the plate deflection. The etching rates given by both the imaging and spectroscopy measurements were in close accordance. The theoretical measurement error induced by finite CR-frequency to stiffness sensitivity was evaluated to be around 5% under our experimental settings. This work paves the way for in situ and real-time detection of undercut etching at the nanoscale and benefits relevant micro- and nano-fabrications. [ABSTRACT FROM AUTHOR]

Improvement of contact resonance atomic force microscopy (CR-AFM) frequency sensitivity at a high contact stiffness condition and subsequent enhancement of its subsurface imaging capability were demonstrated by adding an additional mass on the cantilever backside near the free end. The influence of mass and its position on the CR-AFM performances was analytically investigated by using a simplified cantilever vibration model and further compared with finite element analysis. Theoretical results and FEA simulations showed good agreement and they could provide a general guide on the cantilever's modification by attaching a proper mass to improve the CR-AFM capability. As a prototype, a Pt micro-disc with precisely controlled size and position on the cantilever, which served as the attached mass, was deposited by utilizing focused ion beam. The improvement of frequency sensitivity was verified through CR spectroscopy and subsurface imaging on cavities having pre-determined diameters and covered with highly oriented pyrolytic graphite flakes. Compared with the original unmodified cantilever, obvious enhancement of CR-AFM subsurface nano-imaging was obtained. The mass-attached cantilever can benefit characterizing sample's mechanical properties and enhancing subsurface imaging based on tip-generated stress. [ABSTRACT FROM AUTHOR]

Water holding capacity, texture characteristics, and qualitative structural properties had been mainly focused on heat-induced gelation of myofibrillar proteins; however, the quantitative analysis to ultrastructure of the proteins and heat-induced gel was rarely reported in the previous study. The objective of this study was to investigate quantitatively the effects of different pH values and ion concentrations on the ultrastructure of myofibrillar proteins and thermal-induced gel from swine longissimus dorsi using atomic force microscopy. Protein and gel groups in different conditions were set up, respectively, for the comparative study. The proteins of the gel group were treated first by water and 0.1 M, 0.3 M, 0.6 M NaCl solutions separately at pH 5.5, 6.5, 7.5, and then heated in the water bath. However, protein group were treated without the water bath but directly dried in the air at room temperature. Image roughness Rq were used as an index for quantitative analysis. Atomic force microscopy and related offline analysis software were used to collect the height images and determine the roughness of the myofibrillar proteins and heat-induced gel, respectively. It had been indicated that pH values and ionic concentrations had shown a significant effect on the roughness of heat-induced gel and myofibrillar proteins according to the atomic force microscopy (AFM) height images. The roughness of the gel is minimal while the myofibrillar proteins were treated by 0.6 M NaCl at pH 7.5. It is suggested that roughness of AFM height images could be used as an index to determine the gelling conditions. [ABSTRACT FROM AUTHOR]

• Automatic contour-tracking based on Gaussian processes was proposed. • Adaptive inference of complex contour was realized and verified. • Significant improvement of measurement efficiency was demonstrated. A local scan method based on Gaussian processes inference was developed for efficient atomic force microscopy measurements of string-like nano-objects such as DNA molecules, nanowires, shape boundaries, and so on. Unlike conventional line-by-line raster scan, the proposed method can adaptively track the nano-objects deposited on a flat substrate through accurate prediction of the x - and y - coordinates along the objective contour. Therefore, the used time in scanning the featureless substrate is drastically eliminated. Compared with conventional raster scan, the time efficiency can be improved by almost one order of magnitude. Numerical simulations and practical experiments demonstrated that such a method has several advantages including automatic tracking, significant reduction of scan distance and improvement of measurement efficiency. [ABSTRACT FROM AUTHOR]

• A binary coding scheme of AFM cantilever was proposed to tune dynamic characteristics. • Optimizations were carried out to satisfy multi-objectives by combining genetic algorithms and finite element analysis. • Spectroscopy characterization and harmonic imaging were performed to verify the effectiveness of the proposed method. • The binary coding method can help to design cantilevers for enhanced performances in various sensing and imaging applications. Harmonic atomic force microscopy (AFM) has been widely applied to characterize local mechanical properties of the specimens under imaging. However, the harmonic amplitude is commonly quite weak owing to the fast decay at an off-resonance state for a conventional cantilever and the internal resonance between eigenfrequencies and higher harmonics can amplify the harmonic response. Therefore, specific dynamic characteristics of AFM cantilevers are frequently required. Here, we proposed a coding scheme of a cantilever where the structure is described by a two-dimensional binary matrix to tailor its dynamic characteristics. Genetic algorithms combined with finite element analysis were used to optimize the code configuration. Cantilever properties including eigenfrequencies, stiffness and quality factor can be conveniently tuned to satisfy multiple requirements. AFM cantilevers were then re-designed with the second and the third resonance frequencies being moved to integer multiples of the fundamental one for higher harmonic enhancement, yet with minor stiffness alteration. Harmonic AFM imaging on a polymer mixture demonstrated that the amplitude difference between two material phases was increased up to at least 2.7 times for the 6th harmonic and 1.6 folds for the 18th harmonic using the optimized cantilevers. The enhancement of harmonic contrast can benefit the discrimination of different materials. The proposed binary coding method has advantages such as flexible tailoring of dynamic characteristics, multiple outputs of optimal structures, and automatic optimization. Consequently, it could be a promising way to design cantilevers for enhanced performances in various dynamic AFM imaging applications and also cantilever-based sensing. [ABSTRACT FROM AUTHOR]

• Several subsurface imaging methods based on mechanical sensing were compared. • Maximum detectable buried depth was evaluated quantitatively. • Depth limit from high to low is contact resonance, bimodal and harmonic AFM. • Sensitivity to local mechanical properties was analyzed numerically. 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 SiO 2 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. [ABSTRACT FROM AUTHOR]