Jolanta A. Blach

Surface characterization of human hair by atomic force microscopy in the imaging and F-d modes

Surface structure and surface mechanical properties of human hair have been characterized by atomic force microscopy in the imaging mode and by force vs. distance, F‐d, analysis. The effects of treatment by commercial conditioner/shampoo or by aqueous exposure have been investigated. The cuticular structure has been imaged at medium resolution; longitudinal striations with lateral spacings of 150–350 nm and vertical corrugations in the range 2–8 nm were observed at higher resolution. The features are similar to those observed for untreated wool fibre. Both adventitious debris/contamination and residues from cosmetic treatment can be imaged with resolution in the low‐nanometre range. Removal of the cuticular surface layer from treatment with alkali solution, and subsequent imaging, revealed a fibrous substructure. F‐d analysis of the surface is a rich source of spatially resolved mechanical and chemical information. Surface stiffness, and an equivalent Youngs Modulus, E, can be inferred from the shape of the ‘approach’ tip‐to‐surface contact curve. A value of E of ≈ 10 MPa was obtained for untreated hair. During aqueous exposure for 1 h the stiffness and modulus decreased by approximately a factor of 10. The discontinuity seen at ‘lift‐off’ during the retract half‐cycle of F‐d analysis represents a measure of tip‐to‐surface adhesion. Adhesion decreased during aqueous exposure and was below the level of detectability after 1 h. Likewise, treatment by conditioner had the effect of lowering adhesion. High resolution F‐d data revealed features that are consistent with the presence of a thin and readily compressible surface layer, probably analogous to the surface lipid layer on untreated wool fibre.

Demonstration of atomic scale stick-slip events stimulated by the force versus distance mode using atomic force microscopy

It has been shown that longitudinal deformation of the force-sensing/imposing lever can be stimulated by the conventional force versus distance (F-d), analytical mode of a scanning force microscope. Accordingly it is possible to measure simultaneously both in-plane and out-of-plane force components acting between a tip and a surface. Discrete atomic scale stick-slip events have been observed by F-d generated friction loop analysis of cleaved WTe2, Mica and HOPG single crystals, and of a Langmuir-Blodgett film. Due to the lever geometry, the lateral resolution arising from z-stage movement is better by an order of magnitude than that obtained from translation of the x-y-stage.

Nanolithography of polymer surfaces by Atomic Force Microscopy

Laterally differentiated chemistry and structure of surfaces are commonly employed in a variety of devices/components (e.g., biosensors, array devices). At present such devices are based on macroscopic technologies. Future applications of differentiated surfaces are expected to place considerable demands on down-sizing technologies, i.e. enable meso/nanoscopic manipulation. The atomic force microscope (AFM) has emerged as an ideal platform for manipulation, visualization and characterisation of surface structures on the nano-scale1-14. Controlled AFM-based tip-induced lithography on P(tBuMA) thin film polymer surfaces has been obtained, at line widths down to tens of nanometres and depths in the sub-nanometre range. Parameters giving rise to production of nano-structures can in principle be defined for different polymers (lever-induced out-of-plane loading and in-plane shear forces, linear tip speed, tip shape and chemistry, polymer surface chemistry and mechanical properties). However, those sets of parameters, and their relationship to lithographic outcomes, cannot be derived from the currently accepted models for wear between macroscopic objects in sliding contact.

UV patterned polymide surfaces: Characterization by Atomic Force Microscopy (AFM)

The bio-activity of polymer surfaces and interfaces depends on surface structure and chemistry, and on the size scale of lateral differentiation. The Atomic Force Microscope (AFM), in its various operational modes, is emerging as an important tool in sub-μm-scale characterization. As-received polyimide surfaces were masked with a TEM grid and irradiated for time periods ranging from 90 to 540 s. Topographical imaging revealed shrinkage of the irradiated regions, presumably arising from loss of species and/or densification. Tip-to-surface adhesion was measured in the Force-vs-distance (F-d) mode. Irradiation was found to cause increased adhesion, arising from increased hydrophilicity and thus greater capillary interaction. Lateral force maps showed that there was an associated increase in friction. This difference is due in part to the additional attractive interaction of the thicker layer of adsorbed moisture, and a contribution from change in surface chemistry. Irradiated surfaces were seeded with live human fibroblasts. One surface was seeded without any additional treatment, whilst another was exposed to poly-L-lysine prior to the seeding. After incubation and growth the surfaces were imaged in PBS (Phosphate Buffered Saline) solution. Growth and strong attachment was evident on both surfaces with no preference to either the irradiated or unirradiated regions.

Radiation patterning of P(tBuMA-co-MMA) thin films for biosensor applications: characterization by scanning probe microscopy

Poly-tert-butyl methacrylate-co-methyl methacrylate thin film surfaces were patterned and subjected to surface treatment by UV radiation and NaOH exposure, in order to tailor hydrophilic/hydrophobic conditions. The polymer has potential applications as elements of advanced biosensors and other bio-active devices. The topographies and surface chemistries on the micro- and meso-scales of thin films have been characterized by scanning force microscopy operated in the normal contact imaging mode as well as the lateral force and force versus distance modes.