Crystallographic orientation errors in mechanical exfoliation

We evaluate the effect of mechanical exfoliation of van der Waals materials on crystallographic orientations of the resulting flakes. Flakes originating from a single crystal of graphite, whose orientation is confirmed using STM, are studied using facet orientations and electron back-scatter diffraction (EBSD). While facets exhibit a wide distribution of angles after a single round of exfoliation ([Formula: see text]), EBSD shows that the true crystallographic orientations are more narrowly distributed ([Formula: see text]), and facets have an approximately [Formula: see text] error from the true orientation. Furthermore, we find that the majority of graphite fractures are along armchair lines, and that the cleavage process results in an increase of the zigzag lines portion. Our results place values on the rotation caused by a single round of the exfoliation process, and suggest that when a 1-2 degree precision is necessary, the orientation of a flake can be gauged by the orientation of the macroscopic single crystal from which it was exfoliated.

Paradoxical Long-Timespan Opening of the Hole in Self-Supported Water Films of Nanometer Thickness

The opening of holes in self-supported thin (nanoscaled) water films has been investigated in situ with the environmental scanning electron microscope. The opening of a hole occurs within a two-stage process. In the first stage, the rim surrounding a hole is formed, resembling the process that is observed under the puncturing of soap bubbles. In the second stage, the exponential growth of the hole is observed, with a characteristic time of a dozen seconds. We explain the exponential kinetics of hole growth by the balance between inertia (gravity) and viscous dissipation. The kinetics of opening a microscaled hole is governed by the processes taking place in the nanothick bulk of the self-supported liquid film. Nanoparticles provide markers for the visualization of the processes occurring in self-supported thin nanoscale liquid films.

Revisiting the fine structure of the triple line

The fine structure of the triple line for water droplets deposited on porous polymer substrates was investigated. Substrates were obtained with the breath-figures self-assembly. Water droplets demonstrated the pronounced Cassie-Baxter wetting regime. The triple line was imaged with environmental scanning electron microscopy. The roughness of a triple line was characterized with its averaged root-mean-square (rms) width w(L), and its scaling experimental dependence upon the length L of the triple line w(L) is proportional to L(ζ) was analyzed. The values of exponents in the range of 0.60-063 were established. The deduced values of ζ evidence the local nature of the triple-line elasticity and support the idea that the elastic potential of the triple line includes only even powers of the displacement.

Dynamic study of nanodroplet nucleation and growth on self-supported nanothick liquid films

The dynamics of water condensation on self-supported thin films was studied at the nanoscale using transmitted electrons in an environmental scanning electron microscope. The initial stages of nucleation and growth over nanothick water films have been investigated. Irregularities at the water-film boundaries constituted nucleation sites for asymmetric dropwise and filmwise condensation. Nanodroplet growth was associated with center of mass movement, and the dynamic growth power law dependence was explored for the nanoscale.

Perovskites in the comb roof base of hornets: Their possible function

On the ceiling of the Oriental hornet comb cell, there are mineral granules of polycrystalline material known to belong to the group of perovskites. In a comb cell intended to house a worker hornet, the roof base usually carries one or several such perovskite granules containing titanium (Ti), whereas in the roof base of a cell housing a developing queen, there are usually several granules containing a high percentage of silicon (Si), aluminum (Al), calcium (Ca), and iron (Fe), but very little if any Ti. In worker comb cells, Ti usually appears as ilmenite (FeTiO3). Besides documenting the above-mentioned facts, this report discusses possible reasons for the appearance of ilmenite crystals in worker cells only and not in queen cells.

Accumulation of heavy metals in epidermal glands of the waterlily (Nymphaeaceae)

This study investigates the anatomical aspects of heavy-metal accumulation in the waterlily (Nymphaea 'Aurora', Nymphaeaceae). Epidermal glands were identified by light microscopy on the abaxial side of the leaf laminae and on the epidermis of the rhizome; glandular trichomes were observed in the petiole epidermis. Glands were not observed in the roots. Accumulation of heavy metals in these glands was monitored using a scanning electron microscope equipped for energy-dispersive spectroscopy. Further experiments showed maximal cadmium and calcium accumulation in the mature leaf lamina in daylight, and this accumulation was inhibited by the herbicide 3-(3',4'-dichlorophenyl)-1,1-dimethylurea. These results suggest that, in Nymphaea, heavy metals are accumulated primarily in association with glands found in plant organs that have direct contact with water or mud. Deposition and storage of heavy metals by these glands may represent a stage in the sequestration and detoxification of the metals. Our results raise the possibility of utilizing waterlilies for the removal of heavy metals from polluted environments.

Scanning electron microscopy and X-ray diffraction studies in the analysis of medical materials: Gore-Tex versus braided polyester tape for repair of the incompetent cervix

Cathodoluminescence in the scanning electron microscope and roentgenogram diffraction studies were applied to the analysis of two different medical materials used in cervical cerclage, the treatment of cervical incompetence. Braided polyester tape or Gore-Tex was used as suture material and was analyzed both before and after use in cerclage of the cervix. Results of SEM and X-ray diffraction studies showed distinct differences between the two materials, with the Gore-Tex demonstrating a superior morphological integrity and a decreased likelihood of phagocyte adhesion. These results correlated well with the clinical observations, which also showed Gore-Tex to be a superior medical material.

Expanded polytetrafluoroethylene patch versus braided polyester tape for the repair of incompetent cervix

BACKGROUND

This study was done to evaluate pregnant patients with cervical incompetence using an expanded polytetrafluoroethylene (ePTFE) patch versus the commonly used braided polyester tape, comparing the rate of local tissue reaction or onset of contractions, or both.

STUDY DESIGN

This study was a prospective clinical trial on 20 patients divided into two groups. Patients having tissue reactions or contractions were identified and each material was analyzed using a new approach by means of scanning electron microscopy (SEM) and roentgenogram diffraction studies.

RESULTS

In the group of pregnant patients sutured with polyester tape there were four failures because of infection and contractions. There were no direct or indirect complications encountered in the ePTFE group. Bacteriologic evaluations of the failures revealed Escherichia coli, Gardnerella vaginalis, Bacteroides species, and Trichomonas vaginalis in various combinations, in addition to crystal structure degradation and layers of phagocytes.

CONCLUSIONS

Our results provide a rationale for understanding the differences in morphologic integrity and the superiority of the ePTFE patch over the polyester tape using a new analytic approach of SEM and roentgenographic diffraction studies. Because of the small number of patients and because the procedure was performed in a select patient population, we recommend that further trials be undertaken with a larger number of patients in more advanced gestational age and in patients presenting with emergent cervical incompetence.