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Publications (78)
Context. X-rays emitted from pre-main-sequence stars at the center of protoplanetary disks can induce nonthermal desorption from interstellar ices populating the cold regions of the disk. This process, known as X-ray photodesorption, needs to be quantified for complex organic molecules (COMs), including acetonitrile CH 3 CN, which has been detected...
X-rays emitted from pre-main-sequence stars at the center of protoplanetary disks can induce nonthermal desorption from interstellar ices populating the cold regions. This X-ray photodesorption needs to be quantified for complex organic molecules (COMs), including acetonitrile CH3CN, which has been detected in several disks. We experimentally estim...
X-ray photodesorption yields of $^{15}$N$_2$ and $^{13}$CO are derived as a function of the incident photon energy near the N ($\sim$400 eV) and O K-edge ($\sim$500 eV) for pure $^{15}$N$_2$ ice and mixed $^{13}$CO:$^{15}$N$_2$ ices. The photodesorption spectra from the mixed ices reveal an indirect desorption mechanism for which the desorption of...
Astrophysical observations show complex organic molecules (COMs) in the gas phase of protoplanetary disks. X-rays emitted from the central young stellar object (YSO) that irradiate interstellar ices in the disk, followed by the ejection of molecules in the gas phase, are a possible route to explain the abundances observed in the cold regions. This...
Astrophysical observations show complex organic molecules (COMs) in the gas phase of protoplanetary disks. X-rays emitted from the central young stellar object (YSO) that irradiate interstellar ices in the disk, followed by the ejection of molecules in the gas phase, are a possible route to explain the abundances observed in the cold regions. This...
Astrophysical observations show complex organic molecules (COMs) in the gas phase of protoplanetary disks. X-rays emitted from the central young stellar object (YSO) that irradiate interstellar ices in the disk, followed by the ejection of molecules in the gas phase, are a possible route to explain the abundances observed in the cold regions. This...
Astrophysical observations show complex organic molecules (COMs) in the gas phase of protoplanetary disks. X-rays emitted from the central young stellar object (YSO) that irradiate interstellar ices in the disk, followed by the ejection of molecules in the gas phase, are a possible route to explain the abundances observed in the cold regions. This...
Synopsis
Low-energy (< 20 eV) electron processing of NH 3 multilayer films, systems of interest in astrochemistry, leads to significant NH 3 desorption, fragmentation, and to a complex chemistry arising from recombination and secondary processes induced by reactive products. Quantitative desorption rates of neutral species and effective cross secti...
Water molecules were used to probe the physical and chemical properties of a model hydrophilic organic organized layer. To this end, H2O adsorption on mercaptoundecanoic acid self-assembled monolayers (SAMs) was investigated at the molecular level under ultra-high vacuum by high resolution electron energy loss spectroscopy (HREELS), through the sen...
Aromatic Self-Assembled Monolayers (SAMs) are proposed as platforms for development of supramolecular assemblies driven by surface templates. For many applications, electron processing is used to locally reinforce the layer. In order to achieve a better control of the irradiation step, terphenylthiol SAMs are studied here as model aromatic SAMs to...
Low energy electron scattering on terphenylthiol (TPT, HS-(C6H4)2-C6H5) self-assembled monolayers (SAMs) deposited onto gold was investigated using high resolution electron energy loss spectroscopy (HREELS) by recording specular elastic and inelastic excitation functions. The electron elastic reflectivity could be directly compared to the sample de...
Self-assembled monolayers of p-terphenylthiol (TPT, HS-(C6H4)2-C6H5) deposited onto gold can serve as model systems for aromatic lithography resists. Such thin molecular films are suitably probed using high resolution electron energy loss spectroscopy, due to its high surface sensitivity. Extended energy loss spectra were measured at different prob...
Here, we study the metastable decay of 5 -d(TTGCTT) in the presence of 0–6 alkaline metal ions (Li + , Na + , K + , Rb +) and 0−3 alkaline earth metal ions (Mg 2+ and Ca 2+), which replace the corresponding number of protons in the oligonucleotide. We find that all ions studied here stabilize the oligonucleotide with respect to simple 3 -C–O backbo...
Aromatic self-assembled monolayers (SAMs) can be used as negative tone electron resists in functional surface lithographic fabrication. A dense and resistant molecular network is obtained under electron irradiation through the formation of a cross-linked network. The elementary processes and possible mechanisms involved were investigated through th...
Low-energy electron induced degradation of a model self-assembled monolayer (SAM) of acid terminated alkanethiol was studied under ultra-high vacuum (UHV) conditions at room and low (∼40 K) temperatures. Low-energy electron induced chemical modifications of 11-mercaptoundecanoic acid (MUA, HS-(CH2)10-COOH) SAMs deposited on gold were probed in situ...
Electron energy loss spectrum, elastic reflectivity and selected vibrational excitation functions were measured by High Resolution Electron Energy Loss Spectroscopy (HREELS) for deuterated nanocrystalline dc GD CVD diamond films. The electron elastic reflectivity is strongly enhanced at about 13 eV, as a consequence of the second absolute band gap...
The microstructure and properties of carbon-based thin films depend on the deposition process and conditions used, including pressure, gas phase composition, and substrate temperature, as well as the energy of the reactive species (atoms or ions). For instance concerning diamond films, each method results in different type of films which may differ...
Low-energy electron processing of condensed molecular films (also called ices) is an efficient method to induce functionalization of a substrate, and thereby to modify and adjust its electronic and chemical properties. This method takes advantage of a resonant mechanism specific to low-energy electrons (by opposition to photons), the dissociative e...
The ability to control and orientate chemical reactivity in the condensed phase is a major challenge of modern research. Upon interaction with condensed molecules electrons drive bond cleavage thus generating a population of very reactive species in the condensed medium. These reactive species may interact either within the volume leading to the sy...
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 produc...
Electron-induced decarboxylation in condensed films of formic acid HCOOH, partially deuterated acetic acid CH3COOD and trifluoroacetic acid CF3COOH, has been studied in the energy range 0.7–20 eV by high resolution electron energy loss spectroscopy (HREELS). The yield of carbon dioxide formation shows a peak around 1 eV irradiation energy associate...
The present work studies the high resolution electron energy loss spectra (HR-EELS) and excitation function of hydrogenated diamond films composed of diamond grains of varying size of similar to 300, similar to 20 nm and similar to 5 nm. It is reported that HR-EELS modes associated with C-C lattice phonons are comparably more intense than modes ass...
Plasma hydrogenation of polycrystalline diamond films results in a fully hydrogenated well-ordered diamond surface and etching of the amorphous phase located at grain boundaries. Vacuum annealing to 1000 degrees C followed by in-situ hydrogenation by thermal activated hydrogen of the bared diamond surface results in the formation of sp(3)-CH(x) ads...
The vibrational spectra of thin solid films of glycine deposited at temperatures between 12 and 130 K, as
well as gaseous glycine, have been measured by high-resolution electron-energy-loss (HREEL) spectroscopy. The spectra are dominated by hydrogen-bonded glycine dimers when the films are deposited at low temperatures. The HREEL spectra of films d...
The vibrational spectra of thin solid films of glycine deposited at temperatures between 12 and 130 K, as well as gaseous glycine, have been measured by high-resolution electron-energy-loss (HREEL) spectroscopy. The spectra are dominated by hydrogen-bonded glycine dimers when the films are deposited at low temperatures. The HREEL spectra of films d...
Low-energy electrons, and subexcitation energy electrons in particular, have the ability to induce efficiently chemical modifications within condensed molecular films and at substrate surfaces. By taking advantage of the Dissociative Electron Attachment (DEA) process, which leads to selective bond cleavages, the induced reactivity can be controlled...
The present work studies the incorporation of hydrogen and its bonding configuration in diamond films composed of diamond grains of varying size which were deposited by three different methods: hot filament (HF), microwave (MW), and direct current glow discharge (dc GD) chemical vapor deposition (CVD). The size of diamond grains which constitute th...
The effects of different processes of hydrogenation, thermal treatment and ion irradiation of hydrogenated polycrystalline diamond surface have been investigated by means of high resolution electron energy loss spectroscopy (HR-EELS). Analysis of the different contributions in the CH stretching, overtones and combination modes, as well as changes i...
In this paper we report on the influence of sub-band gap photon illumination on the electron emission of hydrogenated diamond surfaces subjected to continuous low energy electron irradiation. Hydrogenated diamond surface traps charge by resonance electron attachment (REA) and formation of C–H(ads)− anionic transient surface species with a maximum c...
High resolution electron energy loss spectroscopy has been used to probe hydrogenated diamond film surfaces exposed to 1 keV Ar <sup>+</sup> ions at a dose of ∼10<sup>15</sup> cm <sup>-2</sup> and thermal annealing. The defects induced on the upper atomic layers were identified with regard to the different hydrogenated species hybridization states...
The interaction between low energy electrons and condensed acetic acid has been investigated considering H− and D− ions Electron Stimulated Desorption from the three isotopic forms CD3COOD, CD3COOH and CH3COOD. For all isotopic forms the yields of desorbing H−(D−) ions are nearly identical, peaking at an incident electron energy of 9.75 eV, and no...
Chemical Science 4(2) (2007) C10 and Chemistry World 4(2)
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 dif...
The origin of amino acid formation in the early years is still not well known. Muñoz 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...
Interaction of low-energy electrons, first with hydrogenated polycrystalline diamond surfaces, second with films of acetonitrile molecules condensed on such substrates in order to induce their functionalization, has been studied using High Resolution Electron Energy Loss Spectroscopy (HREELS). The elastic and inelastic scattering of low-energy elec...
Electron stimulated desorption (ESD) of fragment anions and thermal desorption spectroscopy (TDS) is applied to study reactions in thin films of a few CF3COOH/CF3COOD monolayers following low energy electron impact (0–20 eV). In ESD, the fragment ions H−/D− and F− are observed via resonant features in the energy range 5–12 eV similar to the dissoci...
Energy-loss spectra and inelastic excitation functions of sp(m) CHx stretching and mixed bending-lattice modes have been measured by high-resolution electron energy-loss (HREEL) spectroscopy for hydrogenated and deuterated polycrystalline diamond films. The comparison between the excitation functions recorded for surface stretching modes of sp(3)-...
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...
In this work, we study the modification of hydrogenated diamond films deposited on silicon resulting from its exposure to DBr followed by an annealing above 600 K, using high resolution electron energy loss spectroscopy (HREELS). This procedure results in silicon carbide SiC formation within the diamond film, as evidenced by the observation of a lo...
In this paper we report on the photoinduced enhancement of secondary electron emission and discharging of hydrogenated and hydrogen-free diamond surfaces subjected to continuous low energy electron irradiation. Diamon surfaces subjected to electron irradiation trap charges resulting in upwards surface band bending and consequent decrease of seconda...
In this work, we show that the interaction of
low energy electrons with CH3CN molecules condensed on hydrogenated
diamond substrates induces functionalization of the diamond. The process
is discussed in terms of electron dissociation mechanisms of acetonitrile
molecules and interaction of the subsequent fragments with the substrate. At
2eV inc...
Elastic and inelastic scattering of low energy electrons by hydrogenated and deuterated polycrystalline diamond surfaces was studied by high resolution electron energy loss spectroscopy (HREELS). Energy loss spectra extending up to 800 meV and elastic/inelastic excitation functions, intensity variations of the elastic peak/energy-loss peaks as a fu...
We reinvestigate inelastic electron scattering mechanisms involved in vibrational excitation of bending and stretching modes of 1H/Si(100)-(2 x 1) surfaces by means of high resolution electron energy loss spectroscopy (HREELS) in the specular geometry. We have obtained energy loss spectra, reflectivity curve, normalized and absolute energy dependen...
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 e...
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 diff...
The interaction between low energy electrons and condensed acetic acid has been investigated considering H À and D À ions Electron Stimulated Desorption from the three isotopic forms CD 3 COOD, CD 3 COOH and CH 3 COOD. For all isotopic forms the yields of desorbing H À (D À) ions are nearly identical, peaking at an incident electron energy of $9.75...
The influence of incident electron current on surface charging and electron emission of hydrogenated diamond films subjected to low energy electron irradiation was investigated. For incident electron energies Ei in the 5–20 eV range, it was found that for sufficiently low incident currents (<∼8 nA) the secondary electron emission (SEE) decays in in...
In this work we study changes in the chemical state of hydrogenated and bare diamond film surfaces after their exposure to water (a mixture of D2O and H2O) vapor. For this purpose X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS) measurements were performed. From XPS showing the O (1s) binding ene...
We report on an high resolution electron energy loss study of electron
surface reflectivity and excitation of the C H stretch mode of
hydrogenated polycrystalline diamond films at low energy. Their specular
energy dependences demonstrate that (i) the reflectivity is dominated by
the conduction band structure. In particular the second absolute band...
Dissociative photoionization of H2 induced by VUV linearly polarized synchrotron radiation P has been studied using the (VH+,Ve,P) vector correlation method. The ion–electron kinetic energy correlation diagrams obtained for the three photon excitation energies hν = 20, 28.5 and 32.5 eV enable us to identify and select the dominant dissociative phot...
In this work we correlate between O− electron stimulated desorption (ESD) from hydrogenated and bare polycrystalline diamond films exposed to thermally activated oxygen for incident electron energies in the 4–23 eV range and vibrational electron energy losses. By utilizing the previously established mechanism of low energy ESD of O− from diamond su...
In this paper we demonstrate that the vector correlation approach for the study of dissociative photoionization (DPI) of linear molecules enables us to achieve a complete description of molecular photoionization by performing a single experiment using only one state of circularly, or elliptically, polarized light. This is illustrated by the derivat...
A combined experimental and theoretical study of the polar and azimuthal dependence of the molecular frame photoelectron angular distributions (MFPADs) for inner-valence-shell photoionization of the O2 molecule into the O2+(B 2Σg−,3 2Πu,c 4Σu−) states is reported. The measured MFPADs, for each orientation of the molecular axis with respect to the l...
The reaction of CO2 to carbonate CO3delta- is studied on the O-enriched RuO2(110) surface using thermal desorption spectroscopy and high-resolution electron energy-loss spectroscopy. It is known that the epitaxially grown RuO2(110) surface exposes coordinatively unsaturated sites, so-called Ru-cus and O-bridge, and can be O-enriched by dissociative...
Abstract: The thermal dehydrogenation of NH3 was studied on Ru(11(2) over bar0) using high-resolution electron energy-loss spectroscopy and thermal desorption spectroscopy. Following NH3 exposure at 85 K, the expected three dehydrogenation steps could be separated, allowing to isolate successively NH2, NH and N on the surface. The R u(11(2) over ba...
The interaction Of CO2 with the bare RuO2(110) surface, exposing unsaturated Ru and oxygen atoms, was studied using high-resolution electron energy-loss spectroscopy (HREELS) and thermal desorption spectroscopy (TDS). At 85 K, CO2 is found to adsorb only on coordinatively unsaturated Ru-cus sites giving rise to three different species: physisorbed...
The interaction Of CO2 with the bare RuO2(110) surface, exposing unsaturated Ru and oxygen atoms, was studied using high-resolution electron energy-loss spectroscopy (HREELS) and thermal desorption spectroscopy (TDS). At 85 K, CO2 is found to adsorb only on coordinatively unsaturated Ru-cus sites giving rise to three different species: physisorbed...
Vector correlation is a powerful method for the investigation of photofragmentation of molecules or clusters. It consists of measuring in coincidence the velocity vectors of the electrons and atomic fragments emitted from the same physical event, and provides detailed information about the spectroscopy and intramolecular dynamics of excited states....
The general form of the molecular frame photoelectron angular distributions (MFPADs) for linear ground-state molecules ionized by linearly polarized light (n̂) is reported. A comparison between computed and measured MFPADs as a function of the polar and azimuthal emission angles is presented for photoionization of NO leading to the c3Π state of NO+...
The (VA+,Ve,P) vector correlation method for the study of dissociative photoionization (DPI) of a diatomic molecule AB, induced by linearly polarized synchrotron radiation (P), is presented. On the experimental side, imaging and time resolved coincidence techniques are combined to measure the VA+ and Ve velocity vectors for each DPI event. The info...
The thermal dehydrogenation of NH3 was studied on Ru(112̄0) using high-resolution electron energy-loss spectroscopy and thermal desorption spectroscopy. Following NH3 exposure at 85 K, the expected three dehydrogenation steps could be separated, allowing to isolate successively NH2, NH and N on the surface. The Ru(112̄0) surface is highly reactive...
Imaging and time resolved coincidence techniques are combined to determine ion-electron (VO+,Ve,P) velocity vector correlations in dissociative photoionization (DPI) of the O2 molecule induced by linearly polarized synchrotron radiation (P). The ion-electron kinetic energy correlations identify each DPI process by its reaction pathway, intermediate...
The dissociative ionization of O2 and N2 molecules following electron capture in He+-O2, N2 collisions has been investigated in the keV energy range with a new device which combines imaging and time-of-flight resolved coincidence techniques. The (VHe+, VHe, VO+(N)+) velocity vector correlation consists of measuring the VHe and VO+(N)+ velocities of...
Imaging and time-resolved coincidence techniques are combined to determine ion-electron (v-->(i),v-->(e)) velocity correlations in dissociative photoionization of diatomic molecules induced by synchrotron linearly polarized light P-->. The (v-->(i),v-->(e), P-->) vector correlation yields the identification of each process, together with the ( stra...
Using an alternative technique to trap keV ion beams, the kinetic-energy release after dissociative charge transfer of vibrationally cold HeH+ was measured. The results indicate that rapid radiative vibrational cooling takes place during the trapping, thus allowing a direct observation of the a 3Sigma+ metastable state of HeH+, which has been a sub...
In this paper we present mass transfer mapping in solution at the micron scale using interferometric microscopy. In its present form, the technique is sensitive to the solution refractive index component parallel to the surface of the electrode. The technique is able to detect optical path differences of the order of the picometer. We show the feas...
