Photon stimulated desorption of hydrogen from diamond surfaces via core-level excitations: fundamental processes and applications to surface studies

Hoffman, A.; Laikhtman, A.

doi:10.1088/0953-8984/18/30/s08

Cited by 16 publications

(19 citation statements)

References 51 publications

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“…This effect was hinted at in an experiment involving the photon-stimulated desorption of H + and H − ions from hydrogen-terminated diamond surfaces. 75 The experimental results suggested that H − ions were released via an indirect mechanism involving secondary electrons as an intermediary versus H + ions which were produced via a direct mechanism related to the core excitation, both consistent with the eFF simulation results.…”

Section: B Auger Relaxation In Core-ionized Diamondoidssupporting

confidence: 81%

The dynamics of highly excited electronic systems: Applications of the electron force field

Goddard

2009

The Journal of Chemical Physics

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Highly excited heterogeneous complex materials are essential elements of important processes, ranging from inertial confinement fusion to semiconductor device fabrication. Understanding the dynamics of these systems has been challenging because of the difficulty in extracting mechanistic information from either experiment or theory. We describe here the electron force field ͑eFF͒ approximation to quantum mechanics which provides a practical approach to simulating the dynamics of such systems. eFF includes all the normal electrostatic interactions between electrons and nuclei and the normal quantum mechanical description of kinetic energy for the electrons, but contains two severe approximations: first, the individual electrons are represented as floating Gaussian wave packets whose position and size respond instantaneously to various forces during the dynamics; and second, these wave packets are combined into a many-body wave function as a Hartree product without explicit antisymmetrization. The Pauli principle is accounted for by adding an extra spin-dependent term to the Hamiltonian. These approximations are a logical extension of existing approaches to simulate the dynamics of fermions, which we review. In this paper, we discuss the details of the equations of motion and potentials that form eFF, and evaluate the ability of eFF to describe ground-state systems containing covalent, ionic, multicenter, and/or metallic bonds. We also summarize two eFF calculations previously reported on electronically excited systems: ͑1͒ the thermodynamics of hydrogen compressed up to ten times liquid density and heated up to 200 000 K; and ͑2͒ the dynamics of Auger fragmentation in a diamond nanoparticle, where hundreds of electron volts of excitation energy are dissipated over tens of femtoseconds. These cases represent the first steps toward using eFF to model highly excited electronic processes in complex materials.

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Section: B Auger Relaxation In Core-ionized Diamondoidssupporting

confidence: 81%

The dynamics of highly excited electronic systems: Applications of the electron force field

Goddard

2009

The Journal of Chemical Physics

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“…We find that, in the direct Auger process, nonionized but excited electrons play a key role in causing carbon-hydrogen and carbon-carbon bonds to break. In addition, we discover with eFF a previously unknown minor pathway for proton desorption involving electron impact ionization, which may explain the doubly peaked kinetic energy distribution for ejected protons observed experimentally (14).…”

Section: Discussionmentioning

confidence: 60%

“…Experimentally, it has been observed that protons produced via photon-stimulated desorption (PSD) on hydrogenated diamond are emitted with a doubly peaked kinetic energy distribution (14). We interpret these two classes of protons as originating from direct Auger versus secondary impact pathways, with direct Auger protons ejected more slowly because of the presence of electrons that linger in the bond over the core hole lifetime.…”

Section: Resultsmentioning

confidence: 92%

“…4 shows the fragmentation over time of CH bonds in coreionized adamantane, tracking the lengths of the bonds and the charges associated with the protons. This analysis, performed over 410 trajectories, can be compared with a recent experiment (14), where a hydrogenated diamond surface was exposed to photons with energies near the core level, causing protons and hydride ions to be desorbed (the detector was insensitive to neutral species). The proton ion signal was predominantly a step function relative to the incident electron energy, suggesting that protons were emitted via a direct Auger mechanism.…”

Section: Resultsmentioning

confidence: 99%

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Mechanisms of Auger-induced chemistry derived from wave packet dynamics

Goddard

2009

Proc. Natl. Acad. Sci. U.S.A.

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To understand how core ionization and subsequent Auger decay lead to bond breaking in large systems, we simulate the wave packet dynamics of electrons in the hydrogenated diamond nanoparticle C 197 H 112 . We find that surface core ionizations cause emission of carbon fragments and protons through a direct Auger mechanism, whereas deeper core ionizations cause hydrides to be emitted from the surface via remote heating, consistent with results from photon-stimulated desorption experiments [Hoffman A, Laikhtman A, (2006) J Phys Condens Mater 18:S1517-S1546]. This demonstrates that it is feasible to study the chemistry of highly excited large-scale systems using simulation and analysis tools comparable in simplicity to those used for classical molecular dynamics.electron force field | fermionic molecular dynamics | floating Gaussian orbitals G reat uncertainties remain concerning how highly excited states (∼100 eV) induced by energetic photons, electrons, ions, or plasmas induce chemical processes at surfaces (1), particularly in large covalent systems (2) relevant to semiconductor fabrication (3). To determine the electron dynamics and atomic mechanisms involved in large-scale highly excited processes, we have developed the electron force field (eFF), a molecular dynamics model that includes electrons. We previously used eFF to compute the thermodynamic properties of warm dense hydrogen, and found excellent agreement with high-level theory, as well as both static compression and dynamic shock experiments (4).We report now the application of eFF to study Auger processes in a hydrogenated diamond nanoparticle C 197 H 112 (Fig. 1A). In the Auger process, ionization of a core electron leads to the collapse of a valence electron into the core hole, together with the ejection of another valence electron, all over several femtoseconds (5). During and after this time, secondary processes occur, causing protons, hydrides, and other species to desorb from hydrogen-terminated surfaces (1). We study the coupled electron-nuclear dynamics of both the primary Auger and accompanying secondary processes, ionizing core electrons both at the diamondoid surface and at different depths below the surface. In this way, we determine how the distance over which an Auger excitation relaxes and propagates affects the energies of electrons and composition of atomic species desorbed from the surface.In eFF, all electrons, valence and core, are modeled as spherical Gaussian wave packets:while nuclei are modeled as classical charged particles moving in the mean field of the electrons. The positions x i and sizes s i of the electrons are continuously variable, giving them the flexibility to participate in covalent, ionic, multicenter, and even metallic bonding; p x,i and p s,i are the corresponding conjugate momenta. This description is well-suited for representing highly excited systems, where electron density maxima and spreads may be distorted from equilibrium positions and values.Substituting the above expression into the time-dependent Schr...

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“…This could be due to the decrease in the CÀ H functionalization of the surface. [23] The Fe 2p XAS spectra for the SWCNT samples are shown in Figure 4B. In the L 3 -edge, the observed peak at lower energy arises from metallic Fe, whereas the higher peak comes from oxidized Fe.…”

Section: X-ray Absorption Spectroscopymentioning

confidence: 99%

Effect of Electrochemical Oxidation on Physicochemical Properties of Fe‐Containing Single‐Walled Carbon Nanotubes

et al. 2020

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Metal catalysts are necessary for fabricating carbon nanotubes, but are often considered impurities in the end products, and arduous steps are used to remove catalyst residues from the nanotube structure. However, as metals can be electrocatalytic, instead of removing them we can utilize their role in detection of analgesics. Herein, we study the physicochemical properties of Fe-containing single-walled carbon nanotubes (SWCNTs), and the effect of simple oxidative pretreatment on them. We show that a gentle anodic pretreatment i) increased the amount of oxidized Fe nanoparticles, most likely exhibiting phases Fe 3 O 4 and Fe 2 O 3 and ii) effectively removed disordered carbonaceous material from SWCNT bundles surfaces. Pretreatment had only a marginal effect on sensitivity towards analgesics. However, interestingly, selectivity of Fe-SWCNTs towards paracetamol and morphine could be modified with pretreatment. Through this kind of in-depth investigation, we can, to a certain extent, correlate various material properties of SWCNTs with the observed electrochemical performance. This approach allows us to evaluate what factors in SWCNTs truly affect the electrochemical detection of biomolecules.

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Photon stimulated desorption of hydrogen from diamond surfaces via core-level excitations: fundamental processes and applications to surface studies

Cited by 16 publications

References 51 publications

The dynamics of highly excited electronic systems: Applications of the electron force field

The dynamics of highly excited electronic systems: Applications of the electron force field

Mechanisms of Auger-induced chemistry derived from wave packet dynamics

Effect of Electrochemical Oxidation on Physicochemical Properties of Fe‐Containing Single‐Walled Carbon Nanotubes

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