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Electron microscopy (EM) and atomic force microscopy (AFM) techniques have long been used to characterize collagen fibril ordering and alignment in connective tissues. These techniques, however, are unable to map collagen fibril polarity, i.e., the polar orientation that is directed from the amine to the carboxyl termini. Using a voltage modulated AFM-based technique called piezoresponse force microscopy (PFM), we show it is possible to visualize both the alignment of collagen fibrils within a tissue and the polar orientation of the fibrils with minimal sample preparation. We demonstrate the technique on rat tail tendon and porcine eye tissues in ambient conditions. In each sample, fibrils are arranged into domains whereby neighboring domains exhibit opposite polarizations, which in some cases extend to the individual fibrillar level. Uniform polarity has not been observed in any of the tissues studied. Evidence of anti-parallel ordering of the amine to carboxyl polarity in bundles of fibrils or in individual fibrils is found in all tissues, which has relevance for understanding mechanical and biofunctional properties and the formation of connective tissues. The technique can be applied to any biological material containing piezoelectric biopolymers or polysaccharides.

The functional role of collagen piezoelectricity has been under debate since the discovery of piezoelectricity in bone in 1957. The possibility that piezoelectricity plays a role in bone remodeling has generated interest in the investigation of this effect in relevant physiological conditions; however, there are conflicting reports as to whether collagen is piezoelectric in a humid environment. In macroscale measurements, the piezoelectricity in hydrated tendon has been shown to be insignificant compared to dehydrated tendon, whereas, at the nanoscale, the piezoelectric effect has been observed in both dry and wet bone using piezoresponse force microscopy (PFM). In this work, the electromechanical properties of type I collagen from a rat tail tendon have been investigated at the nanoscale as a function of humidity using lateral PFM (LPFM) for the first time. The relative humidity (RH) was varied from 10% to 70%, allowing the piezoelectric behavior to be studied dry, humid, as well as in the hydrated range for collagen in physiological bone (12% moisture content, corresponding to 40–50% RH). The results show that collagen piezoresponse can be measured across the humidity range studied, suggesting that piezoelectricity remains a property of collagen at a biologically relevant humidity. [ABSTRACT FROM AUTHOR]

Atomic force microscopy (AFM) has been utilized for nanomechanical machining of various materials including polymers, metals, and semiconductors. Despite being important candidate materials for a wide range of applications including data storage and actuators, ferroelectric materials have rarely been machined via AFM. AFM-based machining of ferroelectric nanostructures offers advantages over established techniques, such as bottom-up approaches and focused ion beam milling, in select cases where low damage and low-cost modification of already-fabricated thin films are required. Through a systematic investigation of a broad range of AFM parameters, we demonstrate that AFM-based machining provides a low-cost option to rapidly modify local regions of the film, as well as fabricate a range of different nanostructures, including a nanocapacitor array with individually addressable ferroelectric elements. [ABSTRACT FROM AUTHOR]

In this paper, the atomic-scale structure fabrication on Si (100) substrate using atomic force microscopy (AFM) with the aid of electrochemical and mechanical processes in a humid environment and under ambient conditions is studied. The local oxidation patterns are formed using platinum-coated tips with the aid of bias applied to the tip-substrate junction, and direct removal has been achieved using single crystal diamond tips, enabling the structure fabrication at the atomic and close-to-atomic scale. The depth and height of the etched trenches reached about 1 nm, which provides an approach for the fabrication of atomic-scale electrodes for molecular device development. Furthermore, material removal close to about three silicon atoms (~3.2 Å) has been achieved. This is important in molecular device fabrication. A detailed comparison among the nanopatterns and the material removal over bare and hydrofluoric acid (HF) treated silicon substrates is provided. This comparison is useful for the application of fabricating atomic-scale electrodes needed for the molecular electronic components. A deep understanding of atomic-scale material removal can be pushed to fabricate a single atomic protrusion by removing the neighbouring atoms so that the molecule can be attached to a single atom, thereby the AFM tip and Si substrate could act as the electrodes and the molecule between them as the channel, providing basic transistor actions in a molecular transistor design. In this paper, platinum-coated and single-crystal diamond tips are used to explain the oxide formations and direct material removal, respectively. [ABSTRACT FROM AUTHOR]

Many natural surfaces, including the wings of cicada insects, have shown to display bactericidal properties as a result of surface topography. Moreover, the size and distribution of the surface features (on the nano- and microscale) are known to influence the efficacy of the surface at inhibiting bacterial cell growth. While these types of natural surfaces illustrate the effect of structure on the bactericidal activity, a deeper understanding can be achieved by creating surfaces of different feature sizes. This is essential in order to understand the effects of changes of surface topography on bacteria-surface interactions. To this end, we have performed a series of replica molding processes of the wings of the Megapomponia Intermedia cicada to prepare wing replicas in polyethylene glycol (PEG), which possess the topographical features of the wing surface, with a minimum loss of feature resolution. Atomic force microscopy characterization of these patterned surfaces in both air and aqueous environments shows that by controlling the swelling characteristics of the PEG, we can control the ultimate swollen dimensions of the nanopillar structures on the surface of PEG. As a result, by using a single wing with an average nanopillar height of 220 nm, different patterned PEG samples with nanopillar heights ranging from 180 to 307 nm were produced. [ABSTRACT FROM AUTHOR]

The ferroelectric polarization switching behavior at the 24° (100) tilt grain boundary (GB) in an epitaxial multiferroic BiFeO3 bicrystal film is studied using piezoresponse force microscopy (PFM). The PFM amplitudes across positively and negatively poled GB regions suggest the presence of a frozen polarization component at the interface. The switching experiments demonstrate that the GB attracts the domain wall and acts as a pinning center. The PFM results are compared with conductive atomic force microscopy and spectroscopy, which suggest domain wall pinning at the GB can be partially attributed to increased conductance at the GB. [ABSTRACT FROM AUTHOR]

Piezoelectric properties of PbTiO3 in 1/3PbTiO3-2/3CoFe2O4 transverse epitaxial nanostructures on differently oriented SrTiO3 were analyzed using conventional and switching-spectroscopy piezoelectric force microscopy. The results confirmed that the individual PbTiO3 nanocolumns in the CoFe2O4 matrix exhibit a detectable piezoelectric response regardless of substrate orientation. For the {100} and {110} orientations, a bias of ±10 V produced ferroelectric domain switching; however, no switching was observed for the {111} films. Small values of piezoelectric constants dzz(100)≈11 pm/V, dzz(110)≈5 pm/V, and dzz(111)≈3 pm/V are attributed to the weak intrinsic response of the nano-PbTiO3 under strong mechanical and depolarizing-field constraints in the composite films. [ABSTRACT FROM AUTHOR]

Atomic force microscopy (AFM) is widely used in liquid environments, where true atomic resolution at the solid–liquid interface can now be routinely achieved. It is generally expected that AFM operation in more viscous environments results in an increased noise contribution from the thermal motion of the cantilever, thereby reducing the signal-to-noise ratio (SNR). Thus, viscous fluids such as ionic and organic liquids have been generally avoided for high-resolution AFM studies despite their relevance to, e.g. energy applications. Here, we investigate the thermal noise limitations of dynamic AFM operation in both low and high viscosity environments theoretically, deriving expressions for the amplitude, phase and frequency noise resulting from the thermal motion of the cantilever, thereby defining the performance limits of amplitude modulation, phase modulation and frequency modulation AFM. We show that the assumption of a reduced SNR in viscous environments is not inherent to the technique and demonstrate that SNR values comparable to ultra-high vacuum systems can be obtained in high viscosity environments under certain conditions. Finally, we have obtained true atomic resolution images of highly ordered pyrolytic graphite and mica surfaces, thus revealing the potential of high-resolution imaging in high viscosity environments. [ABSTRACT FROM AUTHOR]

This study aimed to examine how microscopic morphological developments, such as lactose crystallisation, swelling of particles and changes in surface roughness, occur as a function of moisture sorption in skimmed-milk (SMP), milk protein concentrate (MPC) and whey protein isolate (WPI) powders. Atomic force microscopy (AFM) has the potential to identify high-resolution, microstructural changes in high-protein, milk powder particles. A sample preparation technique was developed, which allowed a single-layer of uniformly distributed powder particles to be applied to a mica surface for subsequent AFM analysis. An amplitude modulation (AM)-AFM technique was used, and analysis showed that equilibration of powders under conditions of increasing relative humidity (RH) causes changes in topography and increased surface roughness. In SMP, significant surface changes were observed due to the development of lactose crystallisation and eventual stacking of crystal layers with increased moisture sorption. MPC, however, showed characteristic 'dimples and folds', which may have been due to shrinkage and compaction of surfaces. With higher moisture content, the number of surface-folds and height-ranges increased, with MPC powders, held at 85% RH appearing highly jagged. The surfaces of WPI powders were smooth but were characterised by the presence of broken powder fragments. Such fragments were absent in SMP and MPC powders, suggesting that WPI powders were the most friable. WPI powders appeared not to change as a function of moisture sorption. AM-AFM was used to provide high-resolution, three-dimensional images of HPMP particles at nano- and micrometre length scales. [Display omitted] • Topographical images of dairy powder particles were examined by AM-AFM. • Skimmed milk powder showed significant microstructural changes due to lactose crystallisation. • Milk protein concentrate powder surfaces had surface folds, which increased in height with RH. • Whey protein isolate particles were smooth, with a weak mechanical structure. • A technique was developed to provide a monolayer of particles for AFM analysis. [ABSTRACT FROM AUTHOR]