Electron-induced fragmentation mechanisms in organic monomers and their implications for photoresist optimization for EUV lithography.

Secondary electrons generated during the Extreme Ultraviolet Lithography (EUVL) process are predominantly responsible for inducing important patterning chemistry in photoresist films. Therefore, it is crucial to understand the electron-induced fragmentation mechanisms involved in EUV-resist systems to improve their patterning performance. To facilitate this understanding, mechanistic studies were carried out on simple organic EUV-resist monomers, methyl isobutyrate (MIB) and methacrylic acid (MAA), both in the condensed and gas phases. Electron-stimulated desorption (ESD) studies on MIB in the condensed phase showed desorption peaks at around 2 and 9 eV electron energies. The gas-phase study on MIB showed that the monomer followed the dissociative ionization (DI) fragmentation pathway, under single collision conditions, which opened up at electron energies above about 11 eV. No signs of dissociative electron attachment (DEA) were detected for MIB in the gas phase under single collision conditions. However, DEA was an active process in MAA in the gas phase under single collision conditions at around 2 eV, showing that slight modifications of the molecular structures of photoresists may serve to sensitize them to certain electron-induced processes.

Model-Driven Controlled Alteration of Nanopillar Cap Architecture Reveals its Effects on Bactericidal Activity.

Nanostructured surfaces can be engineered to kill bacteria in a contact-dependent manner. The study of bacterial interactions with a nanoscale topology is thus crucial to developing antibacterial surfaces. Here, a systematic study of the effects of nanoscale topology on bactericidal activity is presented. We describe the antibacterial properties of highly ordered and uniformly arrayed cotton swab-shaped (or mushroom-shaped) nanopillars. These nanostructured surfaces show bactericidal activity against Staphylococcus aureus and Pseudomonas aeruginosa. A biophysical model of the cell envelope in contact with the surface, developed ab initio from the infinitesimal strain theory, suggests that bacterial adhesion and subsequent lysis are highly influenced by the bending rigidity of the cell envelope and the surface topography formed by the nanopillars. We used the biophysical model to analyse the influence of the nanopillar cap geometry on the bactericidal activity and made several geometrical alterations of the nanostructured surface. Measurement of the bactericidal activities of these surfaces confirms model predictions, highlights the non-trivial role of cell envelope bending rigidity, and sheds light on the effects of nanopillar cap architecture on the interactions with the bacterial envelope. More importantly, our results show that the surface nanotopology can be rationally designed to enhance the bactericidal efficiency.

Quantifying the human-robot interaction forces between a lower limb exoskeleton and healthy users.

To counter the many disadvantages of prolonged wheelchair use, patients with spinal cord injuries (SCI) are beginning to turn towards robotic exoskeletons. However, we are currently unaware of the magnitude and distribution of forces acting between the user and the exoskeleton. This is a critical issue, as SCI patients have an increased susceptibility to skin lesions and pressure ulcer development. Therefore, we developed a real-time force measuring apparatus, which was placed at the physical human-robot interface (pHRI) of a lower limb robotic exoskeleton. Experiments captured the dynamics of these interaction forces whilst the participants performed a range of typical stepping actions. Our results indicate that peak forces occurred at the anterior aspect of both the left and right legs, areas that are particularly prone to pressure ulcer development. A significant difference was also found between the average force experienced at the anterior and posterior sensors of the right thigh during the swing phase for different movement primitives. These results call for the integration of instrumented straps as standard in lower limb exoskeletons. They also highlight the potential of such straps to be used as an alternative/complementary interface for the high-level control of lower limb exoskeletons in some patient groups.

Muscular activity and physical interaction forces during lower limb exoskeleton use.

Spinal cord injury (SCI) typically manifests with a loss of sensorimotor control of the lower limbs. In order to overcome some of the disadvantages of chronic wheelchair use by such patients, robotic exoskeletons are an emerging technology that has the potential to transform the lives of patients. However, there are a number of points of contact between the robot and the user, which lead to interaction forces. In a recent study, the authors have shown that peak interaction forces are particularly prominent at the anterior aspect of the right leg. This study uses a similar experimental protocol with additional electromyography (EMG) analysis to examine whether such interaction forces are due to the muscular activity of the participant or the movement of the exoskeleton itself. Interestingly, the authors found that peak forces preceded peak EMG activity. This study did not find a significant correlation between EMG activity and force data, which would indicate that the interaction forces can largely be attributed to the movement of the exoskeleton itself. However, we also report significantly higher correlation coefficients in muscle/force pairs located at the anterior aspect of the right leg. In their previous research, the authors have shown peak interaction forces at the same locations, which suggests that muscular activity of the participant makes a more significant contribution to the interaction forces at these locations. The findings of this study are of significance for incomplete SCI patients, for whom EMG activity may provide an important input to an intuitive control schema.