Investigation of electron-induced cross-linking of self-assembled monolayers by scanning tunneling microscopy.

Ultrathin membranes with subnanometer pores enabling molecular size-selective separation were generated on surfaces via electron-induced cross-linking of self-assembled monolayers (SAMs). The evolution of p-terphenylthiol (TPT) SAMs on Au(111) surfaces into cross-linked monolayers was observed with a scanning tunneling microscope. As the irradiation dose was increased, the cross-linked regions continued to grow and a large number of subnanometer voids appeared. Their equivalent diameter is 0.5 ± 0.2 nm and the areal density is ≈1.7 × 1017 m-2. Supported by classical molecular dynamics simulations, we propose that these voids may correspond to free volumes inside a cross-linked monolayer.

A new three-step hybrid approach is a safe procedure for incisional hernia: early experiences with a single centre retrospective cohort.

PURPOSE: In this study, a three-step novel surgical technique was developed for incisional hernia, in which a laparoscopic procedure with a mini-laparotomy is combined: so-called 'three-step incisional hybrid repair'. The aim of this study was to reduce the risk of intestinal lacerations during adhesiolysis and recurrence rate by better symmetrical overlap placement of the mesh. OBJECTIVES: To evaluate first perioperative outcomes with this technique. METHODS: From 2016 to 2020, 70 patients (65.7% females) with an incisional hernia of > 2 and ≤ 10 cm underwent a elective three-step incisional hybrid repair in two non-academic hospitals performed by two surgeons specialised in abdominal wall surgery. Intra- and postoperative complications, operation time, hospitalisation time and hernia recurrence were assessed. RESULTS: Mean operation time was 100 min. Mean hernia size was 4.8 cm; 45 patients (64.3%) had a hernia of 1-5 cm, 25 patients (35.7%) of 6-10 cm. Eight patients had a grade 1 complication (11.4%), five patients a grade 2 (7.1%), two patients (2.8%) a grade 4 complication and one patient (1.4%) a grade 5 complication. Five patients had an intraoperative complication (7.0%), two enterotomies, one serosa injury, one omentum bleeding and one laceration of an epigastric vessel. Mean length of stay was 3.3 days. Four patients (5.6%) developed a hernia recurrence during a mean follow-up of 19.5 weeks. CONCLUSION: A three-step hybrid incisional hernia repair is a safe alternative for incisional hernia repair. Intraoperative complications rate was low.

Electron-induced chemistry of surface-grown coordination polymers with different linker anions.

Electron beam processing of surface-grown coordination polymers is a versatile approach to the fabrication of nanoscale surface structures. Depending on their molecular components, these materials can be converted into pure metallic particles or they can be activated to become a template for the spatially selective decomposition of suitable gaseous precursor molecules and subsequent autocatalytic growth of deposits. However, insight into the fundamental electron-induced chemistry for such processes has been scarce so far. Therefore, we investigated the electron-induced reactions of three self-assembled copper-containing materials, namely, copper(ii) oxalate, copper(ii) squarate, and copper(ii) 1,3,5-benzenetricarboxylate (HKUST-1) which were grown on the surface of self-assembled monolayers of mercaptoundecanoic acid in a layer-by-layer approach from copper(ii) acetate and various linker molecules. Changes incurred to these materials during electron irradiation were monitored by four complementary techniques. Reflection absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS) were used to identify the chemical species that are formed upon electron exposure. The temporal evolution of electron-stimulated desorption (ESD) of neutral volatile fragments was monitored to reveal the kinetics governing the decomposition of the different materials. Furthermore, the morphology was investigated by helium ion microscopy (HIM). A detailed analysis of the results for the different linker molecules provides new insights into the electron-induced chemistry of such surface-grown layers.

Rapid Water Permeation Through Carbon Nanomembranes with Sub-Nanometer Channels.

The provision of clean water is a global challenge, and membrane filtration is a key technology to address it. Conventional filtration membranes are constrained by a trade-off between permeance and selectivity. Recently, some nanostructured membranes demonstrated the ability to overcome this limitation by utilizing well-defined carbon nanoconduits that allow a coordinated passage of water molecules. The fabrication of these materials is still very challenging, but their performance inspires research toward nanofabricated membranes. This study reports on molecularly thin membranes with sub-nanometer channels that combine high water selectivity with an exceptionally high permeance. Carbon nanomembranes (CNMs) of ∼1.2 nm thickness are fabricated from terphenylthiol (TPT) monolayers. Scanning probe microscopy and transport measurements reveal that TPT CNMs consist of a dense network of sub-nanometer channels that efficiently block the passage of most gases and liquids. However, water passes through with an extremely high permeance of ∼1.1 × 10-4 mol·m-2·s-1·Pa-1, as does helium, but with a ∼ 2500 times lower flux. Assuming all channels in a TPT CNM are active in mass transport, we find a single-channel permeation of ∼66 water molecules·s-1·Pa-1. This suggests that water molecules translocate fast and cooperatively through the sub-nanometer channels, similar to carbon nanotubes and membrane proteins (aquaporins). CNMs are thus scalable two-dimensional sieves that can be utilized toward energy-efficient water purification.

Amplified cross-linking efficiency of self-assembled monolayers through targeted dissociative electron attachment for the production of carbon nanomembranes.

The determination of the negative ion yield of 2'-chloro-1,1'-biphenyl (2-Cl-BP), 2'-bromo-1,1'-biphenyl (2-Br-BP) and 2'-iodo-1,1'-biphenyl (2-I-BP) upon dissociative electron attachment (DEA) at an electron energy of 0 eV revealed cross section values that were more than ten times higher for iodide loss from 2-I-BP than for the other halogenides from the respective biphenyls (BPs). Comparison with dissociative ionization mass spectra shows that the ratio of the efficiency of electron impact ionization induced fragmentation of 2-I-BP, 2-Br-BP, and 2-Cl-BP amounts to approximately 1:0.7:0.6. Inspired by these results, self-assembled monolayers (SAMs) of the respective biphenyl-4-thiols, 2-Cl-BPT, 2-Br-BPT, 2-I-BPT as well as BPT, were grown on a Au(111) substrate and exposed to 50 eV electrons. The effect of electron irradiation was investigated by X-ray photoelectron spectroscopy (XPS), to determine whether the high relative DEA cross section for iodide loss from 2-I-BPT as compared to 2-Br-BP and 2-Cl-BP is reflected in the cross-linking efficiency of SAMs made from these materials. Such sensitization could reduce the electron dose needed for the cross-linking process and may thus lead to a significantly faster conversion of the respective SAMs into carbon nanomembranes (CNMs) without the need for an increased current density. XPS data support the notation that DEA sensitization may be used to achieve more efficient electron-induced cross-linking of SAMs, revealing more than ten times faster cross-linking of 2-I-BPT SAMs compared to those made from the other halogenated biphenyls or from native BPT at the same current density. Furthermore, the transfer of a freestanding membrane onto a TEM grid and the subsequent investigation by helium ion microscopy (HIM) verified the existence of a mechanically stable CNM created from 2-I-BPT after exposure to an electron dose as low as 1.8 mC/cm2. In contrast, SAMs made from BPT, 2-Cl-BPT and 2-Br-BPT did not form stable CNMs after a significantly higher electron dose of 9 mC/cm2.

Shear melting and high temperature embrittlement: theory and application to machining titanium.

We describe a dynamical phase transition occurring within a shear band at high temperature and under extremely high shear rates. With increasing temperature, dislocation deformation and grain boundary sliding are supplanted by amorphization in a highly localized nanoscale band, which allows for massive strain and fracture. The mechanism is similar to shear melting and leads to liquid metal embrittlement at high temperature. From simulation, we find that the necessary conditions are lack of dislocation slip systems, low thermal conduction, and temperature near the melting point. The first two are exhibited by bcc titanium alloys, and we show that the final one can be achieved experimentally by adding low-melting-point elements: specifically, we use insoluble rare earth metals (REMs). Under high shear, the REM becomes mixed with the titanium, lowering the melting point within the shear band and triggering the shear-melting transition. This in turn generates heat which remains localized in the shear band due to poor heat conduction. The material fractures along the shear band. We show how to utilize this transition in the creation of new titanium-based alloys with improved machinability.

Elastic response of graphene nanodomes.

The mechanical behavior of a periodically buckled graphene membrane has been investigated by noncontact atomic force microscopy in ultrahigh vacuum. When a graphene monolayer is grown on Ru(0001), a regular arrangement of 0.075 nm high nanodomes forming a honeycomb lattice with 3 nm periodicity forms spontaneously. This structure responds in a perfectly reversible way to relative normal displacements up to 0.12 nm. Indeed, the elasticity of the nanodomes is proven by realistic DFT calculations, with an estimated normal stiffness k∼40 N/m. Our observations extend previous results on macroscopic graphene samples and confirm that the elastic behavior of this material is maintained down to nanometer length scales, which is important for the development of new high-frequency (terahertz) electromechanical devices.

Systematic achievement of improved atomic-scale contrast via bimodal dynamic force microscopy.

Judiciously matched experiments, calculations, and theory demonstrate that a higher sensitivity to short-range interactions and, consequently, improved resolution on the atomic scale can be achieved by bimodal noncontact dynamic force microscopy. The combination of sub-Angström tip oscillation at the second flexural resonance of a commercially available silicon cantilever with the commonly used large amplitude oscillation at the fundamental resonance frequency enables this performance improvement while avoiding potentially damaging jump-to-contact instabilities.