A. Lafosse

Reactivity induced at 25 K by low-energy electron irradiation of condensed NH3-CH3COOD (1:1 mixture!

Chemical reactivity is observed following electron irradiation of a binary mixture of ammonia (NH(3)) and acetic acid (CH(3)COOD) at 25 K, without any subsequent thermal activation, as evidenced by vibrational high resolution electron energy loss spectroscopy (HREELS). Analysis of the HREEL spectra and comparison with infrared and Raman data of different molecules are compatible with glycine formation in its zwitterionic form. The onset for electron induced reaction is found to be at about approximately 13 eV. The mechanisms may involve NH radicals interaction with CH(3)COOD molecules. Then glycine formation does not imply any displacement of reactants, so that it involves only NH(3) and CH(3)COOD neighboring molecules.

Chemistry induced by low-energy electrons in condensed multilayers of ammonia and carbon dioxide.

We have investigated by means of HREEL spectroscopy electron induced reactivity in a binary CO2 : NH3 ice mixture. It was shown that the interaction of low energy electrons (9-20 eV) with such mixtures induces the synthesis of neutral carbamic acid NH2COOH and that flashing the sample at 140 K induces the formation of ammonium carbamate. The products have been assigned by FTIR spectroscopy of a CO2 : NH3 mixture heated from 10 K to 240 K. A mechanism involving dissociation of NH3 molecules into NH2* and H* radicals is proposed to explain the product formation.

Reactions in condensed formic acid (HCOOH) induced by low energy (<20 eV) electrons

The interaction of low energy (< 20 eV) electrons with a five monolayer (ML) film of formic acid (HCOOH) deposited on a cryogenically cooled monocrystalline Au substrate is studied by electron stimulated desorption (ESD) of negatively charged fragment ions. A comparison with results from gas phase experiments demonstrates the strong effect of the environment for negative ion formation via dissociative electron attachment (DEA). From condensed phase formic acid (FA) a strong H desorption signal from a resonant feature peaking at 9 eV is observed. In the gas phase, the dominant reaction is neutral hydrogen abstraction generating HCOO- within a low energy resonance, peaking at 1.25 eV. ESD studies on the isotopomers HCOOD and DCOOH indicate effective H/D exchange in the precursor ion at 9 eV prior to dissociation. The evolution of the desorption signals in the course of electron irradiation and the features in the thermal desorption spectra (TDS) of the electron irradiated film suggest the formation of CO2 at electron energies above 8 eV.

Electron Processing at 50 eV of Terphenylthiol Self-Assembled Monolayers: Contributions of Primary and Secondary Electrons.

Aromatic self-assembled monolayers (SAMs) can serve as platforms for development of supramolecular assemblies driven by surface templates. For many applications, electron processing is used to locally reinforce the layer. To achieve better control of the irradiation step, chemical transformations induced by electron impact at 50 eV of terphenylthiol SAMs are studied, with these SAMs serving as model aromatic SAMs. High-resolution electron energy loss spectroscopy (HREELS) and electron-stimulated desorption (ESD) of neutral fragment measurements are combined to investigate electron-induced chemical transformation of the layer. The decrease of the CH stretching HREELS signature is mainly attributed to dehydrogenation, without a noticeable hybridization change of the hydrogenated carbon centers. Its evolution as a function of the irradiation dose gives an estimate of the effective hydrogen content loss cross-section, σ = 2.7-4.7 × 10(-17) cm(2). Electron impact ionization is the major primary mechanism involved, with the impact electronic excitation contributing only marginally. Therefore, special attention is given to the contribution of the low-energy secondary electrons to the induced chemistry. The effective cross-section related to dissociative secondary electron attachment at 6 eV is estimated to be 1 order of magnitude smaller. The 1 eV electrons do not induce significant chemical modification for a 2.5 mC cm(-2) dose, excluding their contribution.

Response under low-energy electron irradiation of a thin film of a potential copper precursor for focused electron beam induced deposition (FEBID)

Background: Focused electron beam induced deposition (FEBID) allows for the deposition of free standing material within nanometre sizes. The improvement of the technique needs a combination of new precursors and optimized irradiation strategies to achieve a controlled fragmentation of the precursor for leaving deposited material of desired composition. Here a new class of copper precursors is studied following an approach that probes some surface processes involved in the fragmentation of precursors. We use complexes of copper(II) with amines and perfluorinated carboxylate ligands that are solid and stable under ambient conditions. They are directly deposited on the surface for studying the fragmentation with surface science tools. Results: Infrared spectroscopy and high-resolution electron energy loss spectroscopy (HREELS) are combined to show that the precursor is able to spontaneously lose amine ligands under vacuum. This loss can be enhanced by mild heating. The combination of mass spectrometry and low-energy electron irradiation (0–15 eV) shows that full amine ligands can be released upon irradiation, and that fragmentation of the perfluorinated ligands is induced by electrons of energy as low as 1.5 eV. Finally, the cross section for this process is estimated from the temporal evolution in the experiments on electron-stimulated desorption (ESD). Conclusion: The release of full ligands under high vacuum and by electron irradiation, and the cross section measured here for ligands fragmentation allow one to envisage the use of the two precursors for FEBID studies.

Amino Acid Formation by Electron Irradiation

The origin of amino acid formation in the early years is still not well known. Munoz Caro and collaborators showed the generation of amino acid by UV irradiation of a mixture of organic molecules reproducing the interstellar media. Although the photochemistry is one of the mechanism which would be active in the early years, it is also important to study other mechanisms such as the electrochemistry or electron induced chemistry which would act as well as a tool for the amino acid formation. The aim of this work is to demonstrate the amino acid formation by low energy electron irradiation of condensed organic molecules. In particular, our purpose is the formation of glycine by low energy electron irradiation of a film composed of a mixture of condensed NH3 and CH3COOD. Prior to the study of amino acid formation it is important to know about the effect of the interaction between electrons and organic molecules, so the first step in this work is the study of the electron irradiation of NH3 and CH3COOD films ...

Discharging, enhancement, and control of electron emission of hydrogen free diamond film surfaces by subband gap light illumination

We report on the surface charge elimination, enhancement, and control of secondary electron emission from hydrogen free polycrystalline diamond film surfaces subjected to continuous low energy electron irradiation. Hydrogen free diamond surfaces severely charge under electron irradiation by nonresonance charge trapping in surface π bonds associated with surface reconstruction. Concurrent electron irradiation and illumination of the diamond surface with subband gap photons enhance the secondary electron emission yield and discharge the surface accumulated charge. These effects are suggested to be associated to direct photoexcitation of trapped charge in midgap surface states which result in neutralization and unpinning of the surface bands.