Sverre Myhra

Structure and crystal chemistry of Ti3SiC2

Carbide-derived layered Ti3SiC2 has an unusual combination of electrical, thermal and mechanical properties. The structure of Ti3SiC2 has been refined from Rietveld analysis of neutron diffraction patterns. The c-axis stacking sequence includes double layers of distorted edge-sharing CTi6 octahedra, reminiscent of the TiC structure. The double layers are separated by square-planar Si sheets. Bond lengths and angles were measured to greater accuracy than in previous studies. The refined structure is used in conjunction with data from X-ray photoelectron spectroscopy (XPS) to hypothesize that the origin of the observed high electrical conductivity is with the Ti–C blocks. The XPS analysis shows that both Ti and C species are exceptionally well screened, even in comparison with other carbides. Also, surface-specific compositional analysis by XPS shows that freshly prepared fracture faces exhibit relatively high Ti abundance while the Si abundance is low, in comparison with expected bulk stoichiometry.

A gecko skin micro/nano structure - A low adhesion, superhydrophobic, anti-wetting, self-cleaning, biocompatible, antibacterial surface.

Geckos, and specifically their feet, have attracted significant attention in recent times with the focus centred around their remarkable adhesional properties. Little attention however has been dedicated to the other remaining regions of the lizard body. In this paper we present preliminary investigations into a number of notable interfacial properties of the gecko skin focusing on solid and aqueous interactions. We show that the skin of the box-patterned gecko (Lucasium sp.) consists of dome shaped scales arranged in a hexagonal patterning. The scales comprise of spinules (hairs), from several hundred nanometres to several microns in length, with a sub-micron spacing and a small radius of curvature typically from 10 to 20 nm. This micro and nano structure of the skin exhibited ultralow adhesion with contaminating particles. The topography also provides a superhydrophobic, anti-wetting barrier which can self clean by the action of low velocity rolling or impacting droplets of various size ranges from microns to several millimetres. Water droplets which are sufficiently small (10-100 μm) can easily access valleys between the scales for efficient self-cleaning and due to their dimensions can self-propel off the surface enhancing their mobility and cleaning effect. In addition, we demonstrate that the gecko skin has an antibacterial action where Gram-negative bacteria (Porphyromonas gingivalis) are killed when exposed to the surface however eukaryotic cell compatibility (with human stem cells) is demonstrated. The multifunctional features of the gecko skin provide a potential natural template for man-made applications where specific control of liquid, solid and biological contacts is required.

Putative Functions and Functional Efficiency of Ordered Cuticular Nanoarrays on Insect Wings

The putative functions and functional efficiencies of periodic nanostructures on the surface of cicada wings have been investigated by atomic force microscopy (AFM) used as a tool for imaging, manipulation, and probing of adhesion. The structures consist of hexagonal close-packed protrusions with a lateral spacing of approximately 200 nm and may have multiple functionalities. Not only do the structures confer survival value by virtue of camouflage, but they may also serve as antiwetting and self-cleaning surfaces and thus be resistant to contamination. These effects have been demonstrated by exposure to white light, liquid droplets, and AFM adhesion measurements. The dependence of optical reflectivity and surface adhesion on surface topography has been demonstrated using AFM as a nanomachining tool as well as an imaging and force-sensing probe. The intact arrays display exceptionally low adhesion for particles in the size range 20 nm-40 microm. The particles can be removed from the array by forces in the range 2-20 nN; conversely, forces in the range 25-230 nN are required to remove identical particles from a flat hydrophilic surface (i.e., polished Si). Measurements of contact angles for several liquids and particle adhesion studies show that the wing represents a low-surface-energy membrane with antiwetting properties. The inference is that a combination of chemistry and structure constitutes a natural technology for conferring resistance to contamination.

Ultra-low friction for a layered carbide-derived ceramic, , investigated by lateral force microscopy (LFM)

The carbide-derived ceramic has a layered structure with double TiC-like blocks separated by planes of Si in six-fold coordination. It also has an unusual combination of electrical, thermal and mechanical properties. The polycrystalline ceramic exhibits a preferred plane of easy cleavage. Fracture/cleavage faces have been investigated by lateral and atomic force microscopy, scanning electron microscopy and other techniques. The results show that the ceramic is an exceptional solid lubricant. Freshly prepared (by fracture, abrasion or scraping) cleavage faces exhibit coefficients of friction at or below the limit of resolution, about , which are comparable to the lowest values measured for the best solid lubricants ( and graphite). Exposure to air leads to slight degradation, but values below were obtained after exposures of several months. Analysis of other faces leads to outcomes in the range 0.1-0.3, which are consistent with the outcome of macroscopic analysis. The favourable mechanical and electrical properties, in combination with ultra-low solid friction, may have important technical implications.

Nanographene oxide-based radioimmunoconstructs for in vivo targeting and SPECT imaging of HER2-positive tumors

Nanographene oxide (NGO) is a novel nano-wall material that tracks to tumors in vivo, and which, as a consequence of its large surface area, has the capacity to carry a large payload. This study explores the use of anti-HER2 antibody (trastuzumab)-conjugated NGO, radiolabeled with (111)In-benzyl-diethylenetriaminepentaacetic acid (BnDTPA) via ππ-stacking, for functional imaging. In two HER2-overexpressing murine models of human breast cancer, high tumor-to-muscle ratio was achieved, resulting in clear visualization of tumor using single-photon emission computed tomography (SPECT). In the BALB/neuT model and in BALB/c nu/nu mice bearing 231/H2N xenografts, tumor accumulation amounted to 12.7 ± 0.67 and 15.0 ± 3.7% of the injected dose/g (%ID/g) of tumor tissue at 72 h, with tumor-to-muscle ratios of 35:1 and 7:1, respectively. Radiolabeled NGO-trastuzumab conjugates demonstrated superior pharmacokinetics compared to radiolabeled trastuzumab without NGO, with more rapid clearance from the circulation. The use of NGO as a scaffold to build radiolabeled nano-immunoconstructs holds promise for molecular imaging of tumors.

Imaging and Force-Distance Analysis of Human Fibroblasts In Vitro by Atomic Force Microscopy

The structure of human fibroblasts have been characterised in vitro by atomic force microscopy (AFM) operated in the imaging or in the force versus distance (F-d) modes. The choice of cell substrate is important to ensure good adhesion. Of greater significance in the context of AFM analysis, is the observation that the substrate affects the imaging conditions for in vitro analysis of live cells. For instance, very rarely will glass coverslips lead to acceptable outcomes (i.e., resolved cytoskeletal structure). Activated tissue culture dishes, on the other hand, promote conditions that routinely result in good quality images. Those conditions are then unaffected by adoption of relatively high force loadings (more than 10 nN), large fields of view (100 x 100 microm2) and high scan speeds (up to ca. 200 microm/sec), all of which exceed values recommended in the literature. Plasma membranes are fragile in the context of AFM analysis (F-d analysis gives an equivalent Youngs Modulus of ca. 5 kPa). However, the present work suggests that fragility per se need not be a problem, rather it is the adhesive interactions with the tip, which under some circumstances may exceed 20 nN, that are the source of poor imaging conditions. The present results, being supported by a qualitative model, suggest that the activated substrate acts as a preferential scavenger of cellular debris thus preventing the tip from biofouling, and will therefore promote low adhesion between tip and membrane. Good imaging conditions provide non-destructive in vitro information about cytoskeletal structure and dynamics, as shown in two examples concerned with cytochalasin treatment and with the MTT assay.

Transmission electron microscopy and high-resolution transmission electron microscopy studies of the early stages in the degradation of yba2cu3o7-δ superconductor in water vapour

Abstract The initial stages of water vapour attack of the high-temperature superconductor YBa2Cu3O7-δ have been studied by transmission electron microscopy (TEM). The planar defects both of thickness 0·2 nm and of thickness 0·4 nm reported previously have been observed. The defects are sometimes associated with preexisting sites of strain in the material, but such strain is certainly not required for their nucleation, since often they occur in initially perfect material. A model for the thinner defect has been developed, which fits well with the TEM observations, as well as with bond valence calculations and previous work on the degradation of YBa2Cu3O7-δ by water. The implications of the model for that degradation process are discussed.

Lateral force microscopy — a quantitative approach

Abstract The requirements for placing lateral force microscopy (LFM) on a quantitative basis are considered, with a view to enhancing the prospects for application in nanotribology. Methods for determining the critical parameters of the LFM system are reviewed and discussed (e.g. tip shape, detector sensitivity, normal and lateral spring constants of the force-sensing/loading lever, effective normal and lateral forces, and influence of topography). The emphasis is on exploitation of the capabilities inherent in the AFM/LFM system so as to obtain the relevant parameters and variables in situ during the conduct of an experiment.

Calibration of AFM cantilever spring constants

In this paper we present two simple, reliable and readily applicable methods for calibrating cantilevers and measuring the thickness of thin gold films. The spring constant calibration requires knowledge of the Youngs modulus, density of the cantilever and resonant frequency. The thickness of thin gold layers was determined by measuring changes in the resonant frequency and Q-factor of beam shaped AFM cantilevers before and after coating. The techniques for measuring the spring constant and thin film thickness provide accuracy on the order of 10-15%.

Polystyrene spheres on mica substrates: AFM calibration, tip parameters and scan artefacts

Atomic force microscopy (AFM), in various versions, has had major impact as a surface structural and spectroscopic tool since its invention in 1986. At its present state of development, however, the interpretation of AFM images is limited by the current state of methodologies for calibration over the wide dynamic range of magnification. Also, the parameters of individual tips, as well as the generic characteristics of different kinds of tips, affect both the quality of the images and their interpretation. Finally, the very nature of the tip‐to‐surface interaction will generate artefacts, in addition to those associated with tip shape, which need to be fully understood by the practitioners of force microscopy. This project seeks to address and shed light on some of these issues.