Surface Microscopy of Atomic and Molecular Hydrogen from Field-Evaporating Semiconductors

Abstract

We report on the microscopic behavior of residual hydrogen on nanometric field emitters. By using homogeneous or heterostructured semiconductor specimens analyzed in a laser-assisted atom probe, it is possible to study how the relative abundances of the ionic species H+, H2 +, and H3 + depend on the microscopic electric field, estimated through post-ionization statistics. In the case of Ga-containing semiconductors, the relative abundances of H+, H2 +, and H3 + follow a common trend, independent of the nonmetallic component of the matrix. The dependence of the total H flux on the electric field exhibits a more complex behavior, which depends also on the spatial direction of the variation of the field (in-depth or on-surface). The analysis of multiple detection events provides further insights into surface chemistry. Noticeably, H+–H3 + ion pairs are both correlated in number and separated by very small distances on the detector space, suggesting a possible reaction 2H2 → H3 ++H++2e– taking place on the field emitter surface.

Field‐dependent abundances of hydride molecular ions in atom probe tomography of III‐N semiconductors

“…Parasitic species such as hydrogen ions H + , H 2 + and H 3 + were identified at 1, 2 and 3 Da as seen in previous studies by Rigutti et al 23 . These ions can be either hydrogen contained in the material or residual hydrogen present in the APT analysis chamber.…”

“…Several parameters can influence the evolution of the field at the surface of the material, the structure of the sample, the crystallographic orientation and the area imaged, which increases during the analysis with a constant detection rate. 23 The 2D maps shown in the Figure 3A were obtained using the same process described in Section 3.2 for mapping the CSR(Ga) and Al sites fraction. They show from left to right the charge state ratio of Ga (repeated here for clarity) and the relative abundances of N 2 + species and its relative hydrides (N 2 H + , N 2 H 2 + and N 2 H 4 + ), respectively.…”

“…In a previous study, some of the authors of this article targeted the abundances of the hydrogen molecules H + ; H 2+ , H 3 + and their dependence on the electric field. 23 In this work, we study the formation of molecular ions containing both constituent atoms of semiconductor systems and hydrogen atoms from the surrounding environment. These problems are not only interesting for APT metrology, but may also be related to catalysis at the nanoscale.…”

“…However, the interaction of parasitic hydrogen with the specimen surface under high electric field can also be studied as an independent phenomenon. In a previous study, some of the authors of this article targeted the abundances of the hydrogen molecules H + ; H 2+ , H 3 + and their dependence on the electric field 23 . In this work, we study the formation of molecular ions containing both constituent atoms of semiconductor systems and hydrogen atoms from the surrounding environment.…”

Origins of the hydrogen signal in atom probe tomography: case studies of alkali and noble metals

“…This was studied in detail by Tsong and co-workers in the 1980s [11] who introduced low pressures of H 2 inside of the vacuum chamber of the atom probe. Using more modern instrument setups, similar observations have been reported for metals [12], semiconductors [13,14] and insulators [15] with a signal originating either from residual gases from the chamber or H 2 from the specimen itself. The H-related peaks can be minimized by reducing the hydrogen content by heat treatment in vacuum [9], or by modifying the surface of the specimen by oxidation of the deposition of H-barrier thin films (e.g.…”