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Byline: Ozgur. Yalcinbayir, Gamze. Gunduz, Meral. Yildiz, Mehmet. Baykara This study aims to describe a new technique of indirect cyclopexy in the treatment of cyclodialysis. Cases who had cyclodialysis for [...]

Using atomic force microscopy experiments and molecular dynamics simulations of gold nanoislands on graphite, we investigate why ultralow friction commonly associated with structural lubricity can be observed even under ambient conditions. Measurements conducted within a few days after sample synthesis reveal previously undiscovered phenomena in structurally lubric systems: rejuvenation, a drop in kinetic friction of an order of magnitude shortly after the onset of sliding; aging, a significant increase in kinetic friction forces after a rest period of 30 min or more; and switches, spontaneous jumps between distinct friction branches. These three effects are drastically suppressed a few weeks later. Imaging of a contamination layer and simulations provide a consistent picture of how single- and double-layer contamination underneath the gold nanoislands as well as contamination surrounding the nanoislands affect structural lubricity without leading to its breakdown.

We report a comparative study involving the formation of self-assembled molecular films by two types of alkanethiols (1-octadecanethiol and 1-dodecanethiol) on graphene grown via chemical vapor deposition, for heavy metal sensing applications. Scanning tunneling microscopy measurements confirm that the alkanethiol molecules can form localized, ordered molecular films on single-layer graphene despite the presence of structural and chemical irregularities. To test and compare the sensory characteristics associated with graphene functionalized by 1-octadecanethiol and 1-dodecanethiol, graphene-based field effect transistors are fabricated via photolithography on silicon dioxide substrates. Devices based on graphene functionalized with 1-octadecanethiol are successfully employed to demonstrate the detection of mercury and lead ions at the 10 ppm level via Dirac point shifts, with a notable difference in response associated with the use of different heavy metal ions. On the other hand, devices based on graphene functionalized with 1-dodecanethiol exhibit p-type character, before and/or after exposure to heavy metal ions, complicating their use in heavy metal sensing in a straightforward fashion via Dirac point shifts.

A comprehensive analysis of contrast formation mechanisms in scanning tunneling microscopy (STM) experiments on a metal oxide surface is presented with the oxygen-induced (2√2×√2)R45° missing row reconstruction of the Cu(100) surface as a model system. Density functional theory and electronic transport calculations were combined to simulate the STM imaging behavior of pure and oxygen-contaminated metal tips with structurally and chemically different apexes while systematically varying bias voltage and tip–sample distance. The resulting multiparameter database of computed images was used to conduct an extensive comparison with experimental data. Excellent agreement was attained for a large number of cases, suggesting that the assumed model tips reproduce most of the commonly encountered contrast-determining effects. Specifically, we find that depending on the bias voltage polarity, copper-terminated tips allow selective imaging of two structurally distinct surface Cu sites, while oxygen-terminated tips show complex contrasts with pronounced asymmetry and tip–sample distance dependence. Considering the structural and chemical stability of the tips reveals that the copper-terminated apexes tend to react with surface oxygen at small tip–sample distances. In contrast, oxygen-terminated tips are considerably more stable, allowing exclusive surface oxygen imaging at small tip–sample distances. Our results provide a conclusive understanding of fundamental STM imaging mechanisms, thereby providing guidelines for experimentalists to achieve chemically selective imaging by properly selecting imaging parameters.