Low-energy electron scattering cross section for the production of CO within solid films of carbon dioxide

Efficient electron-induced removal of oxalate ions and formation of copper nanoparticles from copper(II) oxalate precursor layers

Copper(II) oxalate grown on carboxy-terminated self-assembled monolayers (SAM) using a step-by-step approach was used as precursor for the electron-induced synthesis of surface-supported copper nanoparticles. The precursor material was deposited by dipping the surfaces alternately in ethanolic solutions of copper(II) acetate and oxalic acid with intermediate thorough rinsing steps. The deposition of copper(II) oxalate and the efficient electron-induced removal of the oxalate ions was monitored by reflection absorption infrared spectroscopy (RAIRS). Helium ion microscopy (HIM) reveals the formation of spherical nanoparticles with well-defined size and X-ray photoelectron spectroscopy (XPS) confirms their metallic nature. Continued irradiation after depletion of oxalate does not lead to further particle growth giving evidence that nanoparticle formation is primarily controlled by the available amount of precursor.

O(-) from amorphous and crystalline CO2 ices

O(-) desorbed from amorphous and crystalline films of CO2 at 18 K under low energy electron impact is studied using time of flight mass spectrometry. The nature of the CO2 film is characterized by Fourier transform infrared spectrometry as a function of film thickness. It is found that the desorption rate from amorphous films is considerably larger than that from crystalline films. The desorption signal from the 4 eV resonance is found to be the dominant one as compared to that from the higher energy resonances, notably the one at 8 eV observed in the gas phase. This is explained in terms of the large enhancement in the dissociative electron attachment cross section for the 4 eV resonance in the condensed phase reported earlier using the charge trapping method.

Absolute cross section for low-energy-electron damage to condensed macromolecules: a case study of DNA

Cross sections (CSs) for the interaction of low-energy electrons (LEE) with condensed macromolecules are essential parameters for accurate modeling of radiation-induced molecular decomposition and chemical synthesis. Electron irradiation of dry nanometer-scale macromolecular solid films has often been employed to measure CSs and other quantitative parameters for LEE interactions. Since such films have thicknesses comparable with electron thermalization distances, energy deposition varies throughout the film. Moreover, charge accumulation occurring inside the films shields a proportion of the macromolecules from electron irradiation. Such effects complicate the quantitative comparison of the CSs obtained in films of different thicknesses and limit the applicability of such measurements. Here, we develop a simple mathematical model, termed the molecular survival model, that employs a CS for a particular damage process together with an attenuation length related to the total CS, to investigate how a measured CS might be expected to vary with experimental conditions. As a case study, we measure the absolute CS for the formation of DNA strand breaks (SBs) by electron irradiation at 10 and 100 eV of lyophilized plasmid DNA films with thicknesses between 10 and 30 nm. The measurements are shown to depend strongly on the thickness and charging condition of the nanometer-scale films. Such behaviors are in accord with the model and support its validity. Via this analysis, the CS obtained for SB damage is nearly independent of film thickness and charging effects. In principle, this model can be adapted to provide absolute CSs for electron-induced damage or reactions occurring in other molecular solids across a wider range of experimental conditions.

Electron photoemission from charged films: Absolute cross section for trapping 0–5eV electrons in condensed CO2

The electron trapping or attachment cross section of carbon dioxide (CO2) condensed as thin films on a spacer of Ar is obtained using a simple model for electron trapping in a molecular film and then charge releasing from the same film by photon absorption. The measurements are presented for different electron exposures and impact energies, film thicknesses, and probing photon energies. The cross section for trapping an electron of incident energy between 0 and 5 eV reveals three different attachment processes characterized by a maximum at about 0.75 eV, a structured feature around 2.25 eV, and a shoulder around 3.75 eV. From the measurement of their dependence with the probing photon energy, the two lowest processes produce traps having a vertical electron binding energy of approximately 3.5 eV, whereas the highest one yields a slightly higher value of approximately 3.7 eV. The 0.75 eV maximum corresponds to the formation of vibrational Feshbach resonances in (CO2)n- anion clusters. The 2.25 eV feature is attributed to the formation of a vibrationally excited 2Piu anion in (CO2)n- clusters, followed by fast decay into its vibrational ground state without undergoing autodetachment. Finally, 3.75 eV shoulder is assigned to the well-known dissociative electron attachment process from 2Piu anion state producing the O- anion in the gas phase and the (CO2)nO- anions in clusters.

Damage induced by low-energy electrons in solid films of tetrahydrofuran

We report on the low-energy electron-induced production of aldehydes within thin solid films of tetrahydrofuran (THF) condensed on a solid Kr substrate. The aldehyde fragments, which remain trapped within the bulk of the THF film, are detected in situ via their 3,1(n-->pi*) and 3(pi-->pi*) electronic transitions and vibrational excitations in the ground state using high-resolution electron-energy-loss spectroscopy. The production of aldehyde is studied as a function of the electron exposure, film thickness, and incident electron energy between 1 and 18.5 eV. The aldehyde production is calibrated in terms of an electron scattering cross section, which is found to be typically 6-7 x 10(-17) cm(2) between 11 and 19 eV. Its energy dependence is characterized by a small feature around 3 eV, a strong rise from 6 eV up to a maximum at 12.5 eV, followed by two structures centered around 15 and 18 eV. The aldehyde production is discussed in terms of the formation of electron resonances or transient anion states, which may lead to the fragmentation of the molecule and explain the structures seen in the energy dependence of the measured cross section.