Abstract:Pure carbon clusters
have received considerable attention for a
long time. However, fundamental questions, such as what the smallest
stable carbon cluster dication is, remain unclear. We investigated
the stability and fragmentation behavior of C
n
2+
(
n
= 2–4) dications using
state-of-the-art atom probe tomography. These small doubly charged
carbon cluster ions were produced by laser-pulsed field evaporation
from a tungsten carbide field emitter. … Show more
“…For instance, dissociative events producing neutral fragments have been detected in SiO2 [27], GaN [29] and Fe3O4 [26]. No such tracks are observed on the correlation histogram in this study, which is similar to the case of carbon clusters [40]. However, in a theoretical study of the ZnO 2+ dissociation pathways by Zanuttini et.…”
Section: Possibility Of Neutral Generation During Cluster Dissociationsupporting
confidence: 54%
“…Faint evidence of another similar track, i.e., As 8 2+ → As 4 + + As 4 + , was also observed experimentally. As outlined by Blum et.al [39] and Peng et.al [25], [40], the fact that we can see them originates from the Coulomb repulsion between the fragments as this alters their respective trajectories and TOF, thereby allowing us to detect such dissociation events on the ion-correlation histogram despite the fact that the fragments possess identical m/n ratios. Since the spatial separation distance of the fragments at the detector is determined by the orientation of the parent ion with respect to the electric field during dissociation [39], depending on the dissociation angle and the detector capabilities (dead-time and dead-zone), a non-negligible possibility for As loss due to ion pile-up cannot be ruled out.…”
With the objective of applying Laser-Assisted Atom Probe Tomography to compositional analysis within nanoscale InGaAs devices, experimental conditions that may provide an accurate composition estimate were sought by extensively studying an InGaAs blanket film.Overall, the determined Arsenic concentration was found to exhibit an electric field dependent deficiency, which was more pronounced at low field conditions, whereas, the determined group III site-fraction remained more or less independent of analysis conditions and in close agreement with the nominal value. In this study, we investigate and discuss the mechanisms that could potentially contribute to As underestimation. Given the field dependence observed, the phenomena occurring between low and high field conditions are compared. At low field, the tendency of As to field evaporate in significant amounts as multiply charged cluster ions (Asn i+ with n as large as 9 and i=1,2,3) is shown to be a significant source of compositional inaccuracy. These clusters may lead to peak overlap in the mass spectrum (e.g. the peak at 150 Da may represent As4 2+ or As2 + or both), thereby creating an uncertainty in the quantification. Emitted clusters may also dissociate with the likelihood of neutral generation and multi-hit losses being non-negligible. Experimental studies and density functional theory calculations are presented to characterize cluster stability and its contribution to measurement uncertainty. Under high field conditions, although fewer clusters are detected and the composition appears more accurate, the emergence of two additional mechanisms, i.e., multi-hits and DC evaporation, may degrade the data quality. The challenges in evaluating the impact of all these loss mechanisms are examined in detail. Finally, we show that for InGaAs under UV illumination, due to the lasertip interaction, the resulting asymmetric electric field distribution across the apex introduces local concentration variations.
“…For instance, dissociative events producing neutral fragments have been detected in SiO2 [27], GaN [29] and Fe3O4 [26]. No such tracks are observed on the correlation histogram in this study, which is similar to the case of carbon clusters [40]. However, in a theoretical study of the ZnO 2+ dissociation pathways by Zanuttini et.…”
Section: Possibility Of Neutral Generation During Cluster Dissociationsupporting
confidence: 54%
“…Faint evidence of another similar track, i.e., As 8 2+ → As 4 + + As 4 + , was also observed experimentally. As outlined by Blum et.al [39] and Peng et.al [25], [40], the fact that we can see them originates from the Coulomb repulsion between the fragments as this alters their respective trajectories and TOF, thereby allowing us to detect such dissociation events on the ion-correlation histogram despite the fact that the fragments possess identical m/n ratios. Since the spatial separation distance of the fragments at the detector is determined by the orientation of the parent ion with respect to the electric field during dissociation [39], depending on the dissociation angle and the detector capabilities (dead-time and dead-zone), a non-negligible possibility for As loss due to ion pile-up cannot be ruled out.…”
With the objective of applying Laser-Assisted Atom Probe Tomography to compositional analysis within nanoscale InGaAs devices, experimental conditions that may provide an accurate composition estimate were sought by extensively studying an InGaAs blanket film.Overall, the determined Arsenic concentration was found to exhibit an electric field dependent deficiency, which was more pronounced at low field conditions, whereas, the determined group III site-fraction remained more or less independent of analysis conditions and in close agreement with the nominal value. In this study, we investigate and discuss the mechanisms that could potentially contribute to As underestimation. Given the field dependence observed, the phenomena occurring between low and high field conditions are compared. At low field, the tendency of As to field evaporate in significant amounts as multiply charged cluster ions (Asn i+ with n as large as 9 and i=1,2,3) is shown to be a significant source of compositional inaccuracy. These clusters may lead to peak overlap in the mass spectrum (e.g. the peak at 150 Da may represent As4 2+ or As2 + or both), thereby creating an uncertainty in the quantification. Emitted clusters may also dissociate with the likelihood of neutral generation and multi-hit losses being non-negligible. Experimental studies and density functional theory calculations are presented to characterize cluster stability and its contribution to measurement uncertainty. Under high field conditions, although fewer clusters are detected and the composition appears more accurate, the emergence of two additional mechanisms, i.e., multi-hits and DC evaporation, may degrade the data quality. The challenges in evaluating the impact of all these loss mechanisms are examined in detail. Finally, we show that for InGaAs under UV illumination, due to the lasertip interaction, the resulting asymmetric electric field distribution across the apex introduces local concentration variations.
“…It is worth noting that carbon can be notoriously difficult to quantify by APT partly because of overlaps between atomic and molecular ions, but also its tendency to be detected as part of multiple hits and lost because of pile-up at the detector (Sha et al, 1992; Thuvander et al, 2011; Peng et al, 2018). Carbon-containing molecular ions can also dissociate, with an exchange of kinetic energy that can lead to additional trajectory aberrations that will tend to further broaden the peak in the composition profile (Peng et al, 2019 b ). Fig.…”
Section: Compositional Width Of An Interfacementioning
Interfaces play critical roles in materials and are usually both structurally and compositionally complex microstructural features. The precise characterization of their nature in three-dimensions at the atomic scale is one of the grand challenges for microscopy and microanalysis, as this information is crucial to establish structure–property relationships. Atom probe tomography is well suited to analyzing the chemistry of interfaces at the nanoscale. However, optimizing such microanalysis of interfaces requires great care in the implementation across all aspects of the technique from specimen preparation to data analysis and ultimately the interpretation of this information. This article provides critical perspectives on key aspects pertaining to spatial resolution limits and the issues with the compositional analysis that can limit the quantification of interface measurements. Here, we use the example of grain boundaries in steels; however, the results are applicable for the characterization of grain boundaries and transformation interfaces in a very wide range of industrially relevant engineering materials.
“…In particular, species loss has been observed for anions in covalently or ionically bonded materials, such as oxides, nitrides, carbides or hydrides. Species loss of anions is probably due to their complex field evaporation behavior (Gault et al 2016;Zanuttini et al 2017;Peng et al 2019;Chang et al 2019). Cations seem to be less strongly affected by species specific losses, probably because of their electronic affinity.…”
We used atom probe tomography to complement electron microscopy for the investigation of spinodal decomposition in alkali feldspar. To this end, gem-quality alkali feldspar of intermediate composition with a mole fraction of a K = 0.43 of the K end-member was prepared from Madagascar orthoclase by ion-exchange with (NaK)Cl molten salt. During subsequent annealing at 550 • C and close to ambient pressure the ion-exchanged orthoclase unmixed producing a coherent lamellar intergrowth of Na-rich and K-rich lamellae. The chemical separation was completed, and equilibrium Na-K partitioning between the different lamellae was attained within four days, which was followed by microstructural coarsening. After annealing for 4 days, the wavelength of the lamellar microstructure was ≈ 17 nm and it increased to ≈ 30 nm after annealing for 16 days. The observed equilibrium compositions of the Na-rich and K-rich lamellae are in reasonable agreement with an earlier experimental determination of the coherent solvus. The excess energy associated with compositional gradients at the lamellar interfaces was quantified from the initial wavelength of the lamellar microstructure and the lamellar compositions as obtained from atom probe tomography using the Cahn-Hilliard theory. The capability of atom probe tomography to deliver quantitative chemical compositions at nm resolution opens new perspectives for studying the early stages of exsolution. In particular, it helps to shed light on the phase relations in nm scaled coherent intergrowth.
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