Sputtering of organic molecules by clusters, with focus on fullerenes

Energetic cluster beam bombardment of organic samples involves a number of physical and chemical effects that are interconnected in a complex manner. In this labyrinth for the scientist's mind, molecular dynamics ( MD) simulation constitutes our Ariadne's thread, because it provides the time-resolved microscopic view of the desorption process that is needed to interpret experiments. By combining molecular ion yield and energy distribution measurements with MD simulations, it is possible to explore desorption and ionization from thin organic films and polymers. Recent results show that the overall dynamics and, to a large extent, the details of the cluster-induced sputtering process are well described using a simpler coarse-grain prescription instead of a full atomistic model, allowing us to speed up computations and leap towards larger systems and higher projectile energies. In this article, we first describe some of the characteristic mechanisms of energetic cluster and especially fullerene projectile bombardment of organics. Then, open issues arising from recent experimental investigations are addressed, such as the importance of specific chemical reactions and ionization processes that are outside the scope of the model. Finally, the discussion highlights cases where the predictive nature of the simulations should be used to facilitate the work of experimentalists, such as testing the properties of new cluster projectiles. (C) 2008 Elsevier B. V. All rights reserved

Effects of Metal Nanoparticles on the Secondary Ion Yields of a Model Alkane Molecule upon Atomic and Polyatomic Projectiles in Secondary Ion Mass Spectrometry.

A model alkane molecule, triacontane, is used to assess the effects of condensed gold and silver nanoparticles on the molecular ion yields upon atomic (Ga (+) and In (+)) and polyatomic (C 60 (+) and Bi 3 (+)) ion bombardment in metal-assisted secondary ion mass spectrometry (MetA-SIMS). Molecular films spin-coated on silicon were metallized using a sputter-coater system, in order to deposit controlled quantities of gold and silver on the surface (from 0 to 15 nm equivalent thickness). The effects of gold and silver islets condensed on triacontane are also compared to the situation of thin triacontane overlayers on metallic substrates (gold and silver). The results focus primarily on the measured yields of quasi-molecular ions, such as (M - H) (+) and (2M - 2H) (+), and metal-cationized molecules, such as (M + Au) (+) and (M + Ag) (+), as a function of the quantity of metal on the surface. They confirm the absence of a simple rule to explain the secondary ion yield improvement in MetA-SIMS. The behavior is strongly dependent on the specific projectile/metal couple used for the experiment. Under atomic bombardment (Ga (+), In (+)), the characteristic ion yields an increase with the gold dose up to approximately 6 nm equivalent thickness. The yield enhancement factor between gold-metallized and pristine samples can be as large as approximately 70 (for (M - H) (+) under Ga (+) bombardment; 10 nm of Au). In contrast, with cluster projectiles such as Bi 3 (+) and C 60 (+), the presence of gold and silver leads to a dramatic molecular ion yield decrease. Cluster projectiles prove to be beneficial for triacontane overlayers spin-coated on silicon or metal substrates (Au, Ag) but not in the situation of MetA-SIMS. The fundamental difference of behavior between atomic and cluster primary ions is tentatively explained by arguments involving the different energy deposition mechanisms of these projectiles. Our results also show that Au and Ag nanoparticles do not induce the same behavior in MetA-SIMS of triacontane. The microstructures of the metallized layers are also different. While metallic substrates provide higher yields than metal islet overlayers in the case of silver, whatever the projectile used, the situation is reversed with gold

Molecular ion yield enhancement induced by gold deposition in static secondary ion mass spectrometry

Static ToF-SIMS was used to evaluate the effect of gold condensation as a sample treatment prior to analysis. The experiments were carried out with a model molecular layer (Triacontane M = 422.4 Da), upon atomic (In+) and polyatomic (Bi-3(+)) projectile bombardment. The results indicate that the effect of molecular ion yield improvement using gold metallization exists only under atomic projectile impact. While the quasi-molecular ion (M+Au)(+) signal can become two orders of magnitude larger than that of the deprotonated molecular ion from the pristine sample under In+ bombardment, it barely reaches the initial intensity of (M-H)(+) when Bi-3(+) projectiles are used. The differences observed for mono- and polyatomic primary ion bombardment might be explained by differences in near-surface energy deposition, which influences the sputtering and ionization processes. (c) 2008 Elsevier B.V. All rights reserved

Graphitic Cathodes for Aluminum Batteries with Aqueous Electrolytes

Concerns over lithium-ion battery safety and environmental impact have led to increased exploration of alternative energy storage systems. Of these, aluminum is of particular interest, being environmentally friendly, safe and easy to handle. In this work, we explore graphitic cathodes with an aqueous electrolyte (aluminum trifluoromethanesulfonate) and study their electrochemical performance. Finally, a reduced graphene cathode with tailored porosity results in an eco-friendly and inherently safe rechargeable battery with promising electrochemical performanc

Electrode–Electrolyte Interactions in an Aqueous Aluminum–Carbon Rechargeable Battery System

Being environmentally friendly, safe and easy to handle, aqueous electrolytes are of particular interest for next-generation electrochemical energy storage devices. When coupled with an abundant, recyclable and low-cost electrode material such as aluminum, the promise of a green and economically sustainable battery system has extraordinary appeal. In this work, we study the interaction of an aqueous electrolyte with an aluminum plate anode and various graphitic cathodes. Upon establishing the boundary conditions for optimal electrolyte performance, we find that a mesoporous reduced graphene oxide powder constitutes a better cathode material option than graphite flakes