The Influence of Experimental Parameters and Specimen Geometry on the Mass Spectra of Copper During Pulsed-Laser Atom-Probe Tomography

2014 ◽  
Vol 20 (6) ◽  
pp. 1715-1726 ◽  
Author(s):  
R. Prakash Kolli ◽  
Frederick Meisenkothen
Keyword(s):  
Pulse Energy ◽  
Mass Spectra ◽  
Pulsed Laser ◽  
Atom Probe ◽  
Pulse Frequency ◽  
Resolving Power ◽  
Base Temperature ◽  
Mass Resolving Power ◽  
Half Angle ◽  
Tip Radius

AbstractWe have studied the influence of experimental factors and specimen geometry on the quality of the mass spectra in copper (Cu) during pulsed-laser atom-probe tomography. We have evaluated the effects of laser pulse energy, laser pulse frequency, specimen base temperature, specimen tip radius, and specimen tip shank half-angle on the effects of mass resolving power, (m/Δm), at full-width at half-maximum and at full-width at tenth-maximum, the tail size after the major mass-to-charge state (m/n) ratio peaks, and the mass spectra. Our results indicate that mass resolving power improves with decreasing pulse energy between 40 and 80 pJ and decreasing base temperature between 20 and 80 K. The mass resolving power also improves with increasing tip radius and shank half-angle. A pulse frequency of 250 kHz slightly improves the mass resolving power relative to 100 or 500 kHz. The tail size decreases with increasing pulse energy. The mass resolving power improves when the cooling time is reduced, which is influenced by the thermal diffusivity of Cu and the specimen base temperature.

On the Field Evaporation Behavior of a Model Ni-Al-Cr Superalloy Studied by Picosecond Pulsed-Laser Atom-Probe Tomography

2008 ◽  
Vol 14 (6) ◽  
pp. 571-580 ◽  
Author(s):  
Yang Zhou ◽  
Christopher Booth-Morrison ◽  
David N. Seidman
Keyword(s):  
Atom Probe Tomography ◽  
Mass Spectra ◽  
Pulsed Laser ◽  
Picosecond Laser ◽  
Atom Probe ◽  
Resolving Power ◽  
Noise Levels ◽  
Thermally Activated ◽  
Mass Resolving Power

AbstractThe effects of varying the pulse energy of a picosecond laser used in the pulsed-laser atom-probe (PLAP) tomography of an as-quenched Ni-6.5 Al-9.5 Cr at.% alloy are assessed based on the quality of the mass spectra and the compositional accuracy of the technique. Compared to pulsed-voltage atom-probe tomography, PLAP tomography improves mass resolving power, decreases noise levels, and improves compositional accuracy. Experimental evidence suggests that Ni2+, Al2+, and Cr2+ ions are formed primarily by a thermally activated evaporation process, and not by post-ionization of the ions in the 1+ charge state. An analysis of the detected noise levels reveals that for properly chosen instrument parameters, there is no significant steady-state heating of the Ni-6.5 Al-9.5 Cr at.% tips during PLAP tomography.

Advances in Pulsed-Laser Atom Probe: Instrument and Specimen Design for Optimum Performance

2007 ◽  
Vol 13 (6) ◽  
pp. 418-427 ◽  
Author(s):  
Joseph H. Bunton ◽  
Jesse D. Olson ◽  
Daniel R. Lenz ◽  
Thomas F. Kelly
Keyword(s):  
Stainless Steel ◽  
Three Dimensional ◽  
Pulsed Laser ◽  
Atom Probe ◽  
Spot Size ◽  
Laser Wavelength ◽  
Resolving Power ◽  
Laser Source ◽  
Three Dimensional Model ◽  
Tip Radius

The performance of the pulsed-laser atom probe can be limited by both instrument and specimen factors. The experiments described in this article were designed to identify these factors so as to provide direction for further instrument and specimen development. Good agreement between voltage-pulsed and laser-pulsed data is found when the effective pulse fraction is less than 0.2 for pulsed-laser mode. Under the conditions reported in this article, the thermal tails of the peaks in the mass spectra did not show any significant change when produced with either a 10-ps or a 120-fs pulsed-laser source. Mass resolving power generally improves as the laser spot size and laser wavelength are decreased and as the specimen tip radius, specimen taper angle, and thermal diffusivity of the specimen material are increased. However, it is shown that two of the materials used in this study, aluminum and stainless steel, depend on these factors differently. A one-dimensional heat flow model is explored to explain these differences. The model correctly predicts the behavior of the aluminum samples, but breaks down for the stainless steel samples when the tip radius is large. A more accurate three-dimensional model is needed to overcome these discrepancies.

A Model Ni–Al–Mo Superalloy Studied by Ultraviolet Pulsed-Laser-Assisted Local-Electrode Atom-Probe Tomography

2015 ◽  
Vol 21 (2) ◽  
pp. 480-490 ◽  
Author(s):  
Yiyou Tu ◽  
Elizaveta Y. Plotnikov ◽  
David N. Seidman
Keyword(s):  
Laser Pulse ◽  
Charge State ◽  
Pulse Energy ◽  
Atom Probe Tomography ◽  
Laser Pulse Energy ◽  
Pulsed Laser ◽  
Atom Probe ◽  
Resolving Power ◽  
Full Width ◽  
Experimental Conditions

AbstractThis study investigates the effects of the charge-state ratio of evaporated ions on the accuracy of local-electrode atom-probe (LEAP) tomographic compositional and structural analyses, which employs a picosecond ultraviolet pulsed laser. Experimental results demonstrate that the charge-state ratio is a better indicator of the best atom-probe tomography (APT) experimental conditions compared with laser pulse energy. The thermal tails in the mass spectra decrease significantly, and the mass resolving power (m/Δm) increases by 87.5 and 185.7% at full-width half-maximum and full-width tenth-maximum, respectively, as the laser pulse energy is increased from 5 to 30 pJ/pulse. The measured composition of this alloy depends on the charge-state ratio of the evaporated ions, and the most accurate composition is obtained when Ni2+/Ni+ is in the range of 0.3–20. The γ(f.c.c.)/γ'(L12) interface is quantitatively more diffuse when determined from the measured concentration profiles for higher laser pulse energies. Conclusions of the APT compositional and structural analyses utilizing the same suitable charge-state ratio are more comparable than those collected with the same laser pulse energy.

Understanding of Capping Effects on the Tip Shape Evolution and on the Atom Probe Data of Bulk LaAlO3 Using Transmission Electron Microscopy

2017 ◽  
Vol 23 (2) ◽  
pp. 329-335 ◽  
Author(s):  
Chang-Min Kwak ◽  
Young-Tae Kim ◽  
Chan-Gyung Park ◽  
Jae-Bok Seol
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Atom Probe ◽  
Resolving Power ◽  
Shape Evolution ◽  
Oxide Materials ◽  
Field Evaporation ◽  
Laser Illumination ◽  
Transmission Electron ◽  
Mass Resolving Power

AbstractTwo challenges exist in laser-assisted atom probe tomography (APT). First, a drastic decline in mass-resolving power is caused, not only by laser-induced thermal effects on the APT tips of bulk oxide materials, but also the associated asymmetric evaporation behavior; second, the field evaporation mechanisms of bulk oxide tips under laser illumination are still unclear due to the complex relations between laser pulse and oxide materials. In this study, both phenomena were investigated by depositing Ni- and Co-capping layers onto the bulk LaAlO3 tips, and using stepwise APT analysis with transmission electron microscopy (TEM) observation of the tip shapes. By employing the metallic capping, the heating at the surface of the oxide tips during APT analysis became more symmetrical, thereby enabling a high mass-resolving power in the mass spectrum. In addition, the stepwise microscopy technique visualized tip shape evolution during APT analysis, thereby accounting for evaporation sequences at the tip surface. The combination of “capping” and “stepwise APT with TEM,” is applicable to any nonconductors; it provides a direct observation of tip shape evolution, allows determination of the field evaporation strength of oxides, and facilitates understanding of the effects of ultrafast laser illumination on an oxide tip.

scholarly journals Improved Mass Resolving Power and Yield in Atom Probe Tomography

2013 ◽  
Vol 19 (S2) ◽  
pp. 994-995 ◽  
Author(s):  
D.J. Larson ◽  
T.J. Prosa ◽  
J.H. Bunton ◽  
D.P. Olson ◽  
D.F. Lawrence ◽  
...  
Keyword(s):  
Atom Probe Tomography ◽  
Atom Probe ◽  
Resolving Power ◽  
Mass Resolving Power

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

scholarly journals Single-Ion Deconvolution of Mass Peak Overlaps for Atom Probe Microscopy

2017 ◽  
Vol 23 (2) ◽  
pp. 300-306 ◽  
Author(s):  
Andrew J. London ◽  
Daniel Haley ◽  
Michael P. Moody
Keyword(s):  
Kinetic Energy ◽  
Point Cloud ◽  
Atom Probe ◽  
Resolving Power ◽  
Isotopic Abundance ◽  
Mass Peak ◽  
Peak Overlap ◽  
Mass Resolving Power ◽  
Charge Spectrum ◽  
Isotopic Abundances

AbstractDue to the intrinsic evaporation properties of the material studied, insufficient mass-resolving power and lack of knowledge of the kinetic energy of incident ions, peaks in the atom probe mass-to-charge spectrum can overlap and result in incorrect composition measurements. Contributions to these peak overlaps can be deconvoluted globally, by simply examining adjacent peaks combined with knowledge of natural isotopic abundances. However, this strategy does not account for the fact that the relative contributions to this convoluted signal can often vary significantly in different regions of the analysis volume; e.g., across interfaces and within clusters. Some progress has been made with spatially localized deconvolution in cases where the discrete microstructural regions can be easily identified within the reconstruction, but this means no further point cloud analyses are possible. Hence, we present an ion-by-ion methodology where the identity of each ion, normally obscured by peak overlap, is resolved by examining the isotopic abundance of their immediate surroundings. The resulting peak-deconvoluted data are a point cloud and can be analyzed with any existing tools. We present two detailed case studies and discussion of the limitations of this new technique.

scholarly journals MeasuringContributions to Mass Resolving Power in Atom Probe Tomography

2011 ◽  
Vol 17 (S2) ◽  
pp. 754-755 ◽  
Author(s):  
E Oltman ◽  
T Kelly ◽  
T Prosa ◽  
D Lawrence ◽  
D Larson
Keyword(s):  
Atom Probe Tomography ◽  
Atom Probe ◽  
Resolving Power ◽  
Mass Resolving Power

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Atom-Probe Tomography of Nickel-Based Superalloys with Green or Ultraviolet Lasers: A Comparative Study

2012 ◽  
Vol 18 (5) ◽  
pp. 971-981 ◽  
Author(s):  
Yaron Amouyal ◽  
David N. Seidman
Keyword(s):  
Mass Spectra ◽  
Bulk Material ◽  
Ion Beam ◽  
Laser System ◽  
Picosecond Laser ◽  
Atom Probe ◽  
Green Laser ◽  
Resolving Power ◽  
Uv Laser ◽  
Ion Milling

AbstractRecent developments in the technology of laser-pulsed local-electrode atom-probe (LEAP) tomography include a picosecond ultraviolet (UV) laser system having a 355 nm wavelength and both external and in-vacuum optics. This approach ensures focusing of the laser beam to a smaller spot diameter than has heretofore been obtained using a green (532 nm wavelength) picosecond laser. We compare the mass spectra acquired, using either green or UV laser pulsing, from nickel-based superalloy specimens prepared either electrochemically or by lifting-out from bulk material using ion-beam milling in a dual-beam focused ion beam microscope. The utilization of picosecond UV laser pulsing yields improved mass spectra, which manifests itself in higher signal-to-noise ratios and mass-resolving power (m/Δm) in comparison to green laser pulsing. We employ LEAP tomography to investigate the formation of misoriented defects in nickel-based superalloys and demonstrate that UV laser pulsing yields better accuracy in compositional quantification than does green laser pulsing. Furthermore, we show that using a green laser the quality of mass spectra collected from specimens that were lifted-out by ion milling is usually poorer than for electrochemically-sharpened specimens. Employing UV laser pulsing yields, however, improved mass spectra in comparison to green laser pulsing even for ion-milled microtips.

Local Electrode Atom Probes

1998 ◽  
Vol 4 (S2) ◽  
pp. 84-85
Author(s):  
Thomas F. Kelly ◽  
Patrick P. Camus
Keyword(s):  
Thin Film ◽  
Data Collection ◽  
Atom Probe ◽  
Atomic Scale ◽  
Specimen Geometry ◽  
Resolving Power ◽  
Charge Ratio ◽  
Atom Probes ◽  
Mass Resolving Power ◽  
Analytical Standards

The Need for Improvements. Though atom probe techniques have impressive atomic-scale analytical capabilities, there are some definite needs for improvement. The needle shape of APFIM specimens is a difficult geometry to make for many types of materials, especially technologically important thin-film materials. Even though 3DAPs collect more data than traditional APs, the analysis volumes are still small by analytical standards: typically there are fewer than 1 million atoms in an image which is about 15nm x 15nm x 50nm. The data collection rate (up to tens of atoms per second) limits the practical size of analyzed volumes to about 1 million atoms. Poor mass resolution makes it difficult to separate ions of similar mass-to-charge ratio in spectra of approximately 20% of samples. Thus, there are three principal areas where improvements are desirable: 1) specimen geometry, 2) data collection rates, and 3) mass resolving power.

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