Electromechanical Imaging of Biological Systems with Sub-10 nm Resolution

Electromechanical imaging of tooth dentin and enamel has been performed with sub-10 nm resolution using piezoresponse force microscopy. Characteristic piezoelectric domain size and local protein fiber ordering in dentin have been determined. The shape of a single collagen fibril in enamel is visualized in real space and local hysteresis loops are measured. Because of the ubiquitous presence of piezoelectricity in biological systems, this approach is expected to find broad application in high-resolution studies of a wide range of biomaterials.Comment: 12 pages, 4 figures, submitted for publication in Appl. Phys. Let

Atomic Step Organization in Homoepitaxial Growth on GaAs(111)B Substrates

When homoepitaxial growth is performed on exactly oriented (singular) (111) GaAs substrates, while maintaining the √19 x √19 surface reconstruction, the originally flat surface spontaneously evolves vicinal (111) facets that are tilted approximately 2.5° toward the \u3c 211 \u3e azimuthal directions. These facets form pyramid-like structures where the distance between adjacent peaks can be varied from as little as 1 μm to tens of μm. When these surfaces are observed with atomic force microscopy (AFM), we find that they are extremely smooth with the observed tilt resulting from atomic steps which are spaced at approximately 7.5 nm. We have also studied growth on vicinal GaAs(111) substrates. Our results are interpreted as indicating that the 2.5° vicinal (111) surface has a minimum free energy for the √19 x √19 reconstruction (i.e., that 10 nm spacing of \u3c 011 \u3e steps is thermodynamically preferred). Exactly oriented (111) facets are only observed when their facet width is less than a couple of micrometers implying a minimum nucleation size. This is a surprising result since conventional wisdom argues the surfaces with low Miller indexes are preferred. A possible explanation is an anisotropy in the surface in the two degenerate phases of √19 x √19 reconstruction which are rotated ±23° from the unreconstructed surface

Electroless deposition of Fe-Ni alloys from acidic and alkaline solutions using hypophosphite as a reducing agent

The deposition of Fe–Ni alloys from acidic and alkaline solutions, using hypophosphite as a reducing agent, is studied in this work. The experimental results confirm the autocatalytic nature of this process. The composition of alloys is practically independent of the temperature deposition. Fe–Ni alloys produced from acidic solutions contained less than 1% Fe. The amount of Fe in Fe–Ni alloys produced from alkaline solutions was estimated to be about 15 %. The deposition of Fe–Ni alloys was significantly faster in the alkaline than in the acidic solutions, due to more pronounced hydrolysis of Fe(II) and Ni(II) ions under the alkaline conditions. The Fe–Ni alloys produced from both acidic and alkaline solutions contain phosphorus and as such have amorphous structure. © 2019 Serbian Chemical Society. All rights reserved

Critical Point Mounting of Kinetoplast DNA for Atomic Force Microscopy

Atomic force microscope (AFM) images of intact kinetoplast DNA were obtained from samples prepared utilizing critical point drying. These images are compared with AFM images obtained using conventional methods for DNA deposition. Although the images obtained on chemically pretreated mica show more details than on unmodified mica, images obtained with critical point drying were superior. Kinetoplast networks with expected sizes and structures were routinely observed with critical point drying. The resolution of individual strands of DNA was greatly improved, and image artifacts associated with air dried samples were eliminated. Samples prepared using mildly sonicated kinetoplast DNA show isolated minicircles