Field induced and surface catalyzed formation of novel ions : A pulsed-laser time-of-flight atom-probe study

Abstract

High electric field induced formation of novel ions such as H+3, AuH+2, RhHe2+, and PtHe2+2 on metal surfaces has been studied in the pulsed-laser time-of-flight atom-probe field ion microscope. From the fractional abundances, and the high resolution mass spectra and energy distributions measured for these ions, several conclusions can be drawn. Field desorption of hydrogen below the evaporation field of the substrate often results in formation of H+3 ions. This formation depends not only on the applied field strength, but surprisingly also on the material and the atomic structure of the substrate. Plenty of H+3 ions can be found from the high index planes and the lattice steps of Mo, W, and Au surfaces in the field range of 2 to 3 V/Å. Few are found from Ir and Ni surfaces, and none are found from the densely packed W(110) plane. Formation of H+3 can therefore be considered a surface catalyzed and field induced chemical reaction. Using H2–D2 mixed gases, we find little correlation between the ionic species obseved in field desorption and the chemisorption states of the gases. The field desorbed ions are formed directly from the field adsorbed state. Field adsorption occurs mostly in the diatomic molecular form. On highly protruded atomic sites of some materials, field adsorption occurs also partly in the triatomic molecular form. Field evaporation of metals in hydrogen or helium often results in the formation of metal hydride and metal helide ions. These ions are formed right at the metal surface by a polarization binding. A fraction of them dissociates in the high field region near the surface. The ‘‘dissociation zone’’ is found to be only several Å in width. From this width, the average lifetime of these complex ions in a field of 3 to 4.4 V/Å is estimated to be on the order of 5×10−13 s.

Nano- and micro-geochronology in Hadean and Archean zircons by atom-probe tomography and SIMS: New tools for old minerals

“…Hydride interferences are evaluated for several adjacent peak positions in the APT spectra and their importance is found to be highly variable according to the element and proportions involved. The intensity of hydride interferences is significantly reduced for doubly ionized species (Tsong et al 1983;Heck et al 2014) and thus for this study, we consider it unlikely that the intensity of ( 206 PbH) ++ interference on 207 Pb ++ is significant for the range of 207 Pb/ 206 Pb ratios measured (0.17 to 1.2) and the analytical precision reported (±4-17%).…”

Controlling residual hydrogen gas in mass spectra during pulsed laser atom probe tomography

“…It also does not easily field dissociate until a field strength of approximately 3.0 V/Å [ 44 , 45 ], and thus, it can be detected in the mass spectra. Furthermore, the quantity of measured ions depends on the metal surface atom’s crystallographic structure, field strength, laser pulse energy, and the specimen tip apex temperature [ 1 , 46 , 47 ]. For example, elements with a face-centered cubic (f.c.c.)…”

“…The experimental observations in this study are consistent with those in Refs. [ 1 , 46 , 47 ] that indicate the quantity of ions measured in the mass spectra is dependent on the experimental parameters. For example, approximately 223 ions are measured when the laser pulse energy is 40 pJ, and ca.…”

Quantification of solute deuterium in titanium deuteride by atom probe tomography with both laser pulsing and high-voltage pulsing: influence of the surface electric field

“…A small peak at 3 Da, more obvious at 70 pJ laser pulsing, is ascribed as mainly HD + , not H 3 + , considering the very small amount of D 3 + in the peak at 6 Da. The peak at 4 Da is considered to stem solely from D 2 + and not from H 4 + , given that no quadruple ions D 4 + occurs at peak 8 Da, and H 4 + was never reported even under much high H-partial pressures [37].…”