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 nonmeta… Show more
“…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.…”
Section: Resultssupporting
confidence: 61%
“…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.…”
Section: Dependence Of Hydrides Formation On the Surface Electric Fieldmentioning
confidence: 99%
“…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.…”
Section: Introductionmentioning
confidence: 99%
“…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.…”
We investigate the microscopic behaviour of hydrogen‐containing species formed on the surface of III‐N semiconductor samples by the residual hydrogen in the analysis chamber in laser‐assisted atom probe tomography (APT). We analysed AlGaN/GaN heterostructures containing alternate layers with a thickness of about 20 nm. The formation of H‐containing species occurs at field strengths between 22 and 26 V/nm and is independent of the analysed samples. The 3D APT reconstruction makes it possible to map the evolution of the surface behaviour of these species issued by chemical reactions. The results highlight the strong dependence of the relative abundances of hydrides on the surface field during evaporation. The relative abundances of the hydrides decrease when the surface field increases due to the evolution of the tip shape or the different evaporation behaviour of the different layers.
“…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.…”
Section: Resultssupporting
confidence: 61%
“…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.…”
Section: Dependence Of Hydrides Formation On the Surface Electric Fieldmentioning
confidence: 99%
“…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.…”
Section: Introductionmentioning
confidence: 99%
“…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.…”
We investigate the microscopic behaviour of hydrogen‐containing species formed on the surface of III‐N semiconductor samples by the residual hydrogen in the analysis chamber in laser‐assisted atom probe tomography (APT). We analysed AlGaN/GaN heterostructures containing alternate layers with a thickness of about 20 nm. The formation of H‐containing species occurs at field strengths between 22 and 26 V/nm and is independent of the analysed samples. The 3D APT reconstruction makes it possible to map the evolution of the surface behaviour of these species issued by chemical reactions. The results highlight the strong dependence of the relative abundances of hydrides on the surface field during evaporation. The relative abundances of the hydrides decrease when the surface field increases due to the evolution of the tip shape or the different evaporation behaviour of the different layers.
“…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.…”
Atom Probe Tomography (APT) analysis is being actively used to provide near-atomic-scale information on the composition of complex materials in three-dimensions. In recent years, there has been a surge of interest in the technique to investigate the distribution of hydrogen in metals. However, the presence of hydrogen in the analysis of almost all specimens from nearly all material systems has caused numerous debates as to its origins and impact on the quantitativeness of the measurement. It is often perceived that most H arises from residual gas ionization, therefore affecting primarily materials with a relatively low evaporation field. In this work, we perform systematic investigations to identify the origin of H residuals in APT experiments by combining density-functional theory (DFT) calculations and APT measurements on an alkali and a noble metal, namely Na and Pt, respectively. We report that no H residual is found in Na metal samples, but in Pt, which has a higher evaporation field, a relatively high signal of H is detected. These results contradict the hypothesis of the H signal being due to direct ionization of residual H2 without much interaction with the specimen's surface. Based on DFT, we demonstrate that alkali metals are thermodynamically less likely to be subject to H contamination under APT-operating conditions compared to transition or noble metals. These insights indicate that the detected H-signal is not only from ionization of residual gaseous H2 alone, but is strongly influenced by material-specific physical properties. The origin of H residuals is elucidated by considering different conditions encountered during APT experiments, specifically, specimen-preparation, transportation, and APT-operating conditions by taking thermodynamic and kinetic aspects into account.
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