# Performance evaluation of deep-ultraviolet laser-assisted Invizo 6000 and near-ultraviolet laser-assisted LEAP 5000 for a range of material systems

Chang-Gi Lee, Byeong-Gyu Chae, I-Jun Ro, Kyuseon Jang, Nak-Kyoon Kim, Jae-Pyoung Ahn, Eric Woods, Jaemin Ahn, Seong Yong Park, Baptiste Gault, et al.

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Chang-Gi Lee, Byeong-Gyu Chae, I-Jun Ro, Kyuseon Jang, Nak-Kyoon Kim, et al.. Performance evaluation of deep-ultraviolet laser-assisted Invizo 6000 and near-ultraviolet laser-assisted LEAP 5000 for a range of material systems. Ultramicroscopy, 2026, 281, pp.114296. 10.1016/j.ultramic.2025.114296. hal-05526534

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Performance evaluation of deep-ultraviolet laser-assisted Invizo 6000 and
near-ultraviolet laser-assisted LEAP 5000 for a range of material system

Chang-Gi Lee§, Byeong-Gyu Chae§, I-Jun Ro, Kyuseon Jang, Nak-Kyoon Kim, Jae-Pyoung Ahn, Eric Woods, Jaemin Ahn, Seong Yong Park, Baptiste Gault, and Se-Ho Kim*

C.-G. Lee, I.-J. Ro,
Department of Materials Science & Engineering, Korea University, Seoul, 02841 Republic of
Korea

B.-G. Chae, J. Ahn, S. Y. Park,
Analytical Engineering Group, Material Research Center, Samsung Advanced Institute of
Technology, Samsung Electronics Co., Ltd., Suwon, 16678 Republic of Korea

N.-K. Kim, J-P. Ahn
Advanced Analysis and Data Center, Korea Institute of Science and Technology (KIST),
02792, Seoul, Republic of Korea

E. Woods
Max Planck Institute for Sustainable Materials (formerly Max-Planck-Institut für
Eisenforschung GmbH), Max-Planck-Straße 1, 40237 Düsseldorf, Germany

K. Jang
Department of Materials Science & Engineering, Korea Advanced Institute of Science and
Technology, Daejeon, 34141, Republic of Korea

B. Gault
Max Planck Institute for Sustainable Materials (formerly Max-Planck-Institut für
Eisenforschung GmbH), Max-Planck-Straße 1, 40237 Düsseldorf, Germany
Department of Materials, Imperial College London, London, SW7 2AZ, United Kingdom

S.-H. Kim*
Department of Materials Science & Engineering, Korea University, Seoul, 02841 Republic of
Korea
Max Planck Institute for Sustainable Materials (formerly Max-Planck-Institut für
Eisenforschung GmbH), Max-Planck-Straße 1, 40237 Düsseldorf, Germany
Email: sehonetkr@korea.ac.kr

**Keywords:** atom probe tomography, normal ultraviolet, deep-ultraviolet, in-situ coating,
metals, oxides
Abstract

Atom probe tomography (APT) enables near-atomic-scale, three-dimensional elemental mapping through controlled field evaporation of surface atoms, triggered by the combined application of a DC voltage with either voltage or laser pulses. As selected laser wavelengths in atom probes transitioned from near-infrared (1050–1064 nm) toward shorter wavelengths, such as green (532 nm) and near-ultraviolet (NUV 355 nm), the quality of data improved and the range of analyzable materials expanded significantly. Recently, a new commercial atom probe (Invizo 6000) employing a deep ultraviolet (DUV) laser wavelength of 257.5 nm has been introduced. Invizo 6000 incorporates several new design elements, such as dual laser beam, einzel lens, and flat counter electrode. However, despite these substantial design modifications, systematic studies comparing its performance with conventional local electrode atom probe (LEAP) systems across different classes of materials remain scarce. In this study, various materials, including metals and oxides, were examined using commercial LEAP 5000 and Invizo 6000. The quality of the data obtained from both instruments was systematically evaluated using four key metrics: background levels, detection events, ion detection histograms, and mass-resolving power. Additionally, applying a thin coating to the prepared APT specimens was found to enhance data quality.

Graphical abstract

<figure><img src="image_2.png" /></figure>
# 1. Introduction

The development of innovative materials has been significantly advanced by improvements in microscopy techniques, providing a deeper physicochemical understanding at the atomic level. Atomic-resolution microscopy is thus indispensable for uncovering structure-property and chemistry-property relationships, facilitating the discovery and engineering of novel materials.

Atom probe tomography (APT) is a sophisticated analytical technique capable of producing three-dimensional chemical or elemental characterizations with sub-nanometer spatial resolution. In APT, the application of a DC voltage combined with voltage or laser pulses to a needle-shaped specimen, typically having an apex diameter below 100 nm, triggers field evaporation of individual ions. These ions then travel across a known distance toward a position-sensitive two-dimensional detector, where their time-of-flight allows precise determination of their mass-to-charge ratio.[1–6] Originally, APT relied solely on voltage pulsing, limiting analyses predominantly to conductive materials. The advent of laser pulsing expanded its application scope to non-conductive materials such as glasses,[7] oxides,[8,9] frozen liquids,[10–12] and Li-ion battery electrodes.[13–16]

Commercial APT systems have transitioned through different laser wavelengths, starting from infrared (1050–1064 nm),[17,18] progressing to green (532 nm),[19,20] and subsequently ultraviolet (355 nm).[21–23] Pulsed-laser APT primarily induces thermally driven field evaporation; however, it introduces a heat-affected zone at the specimen apex, causing unwanted surface diffusion, reduced spatial resolution, and asymmetric specimen shape evolution.[17,24,25] Minimizing the heat-affected volume is crucial for enhancing mass-resolving power (MRP), optimizing detection events, and reducing background levels in the mass spectrum. A larger heated volume increases the temperature near the apex, causing
undesirable prolonged field evaporation of atoms, degraded MRP, and increased multiple events and background noise in the mass spectrum.[4,24,26,27]

Reducing laser spot diameter has proven effective in mitigating these adverse effects by creating a thermal gradient at the specimen apex, enhancing heat dissipation, reducing thermal relaxation time, and thus improving mass spectral and spatial resolutions.[17] This advancement led to the commercialization of local electrode atom probe (LEAP) systems, initially employing green lasers in the LEAP 3000,[2,19] followed by near-ultraviolet lasers in the LEAP 4000 [28] and LEAP 5000 systems.[19,20] Most recently, deep ultraviolet (DUV, 266 nm) laser systems have been integrated into newer APT systems such as the Invizo 6000 and LEAP 6000,[22,29] as shorter wavelengths potentially enhance data quality and yield.[30] However, shorter wavelengths may also alter evaporation mechanisms, such as triggering photoionization, requiring further systematic investigation across different materials.[31–33]

The efficiency of laser-material interactions strongly depends on material absorption coefficients and reflectivity. Upon irradiation, free electrons absorb photon energy, transferring it to the lattice via phonon collisions, thus raising the local temperature. Additionally, electron ballistic motion following energy absorption can further enlarge the heat-affected volume.[30] Nevertheless, questions remain regarding the efficiency of this process when the laser wavelength falls below the absorption limit of the material, making this interaction mechanism complex and material-dependent.[26,34]

Particularly, the recently developed Invizo 6000 is equipped with a DUV laser, which can potentially overcome the absorption limit, making it essential to investigate the laser-induced uncertainties. In addition, Invizo 6000 also incorporates fundamentally new optical and
electrostatic configurations. For example, unlike conventional LEAP, using a reflectron, Invizo 6000 is equipped with an einzel lens to enhance MRP by increasing the time of flight.[35,36] Furthermore, the traditional local electrode, which applies a localized electric field to improve yield, has been replaced with a flat counter electrode in Invizo 6000. These design modifications substantially alter the electrostatic environment and ion trajectories, thereby influencing the resulting data quality. Accordingly, the results obtained from Invizo 6000 must be interpreted in light of these differences. Although recent literature reported differences between Invizo 6000 and LEAP systems through the analysis of Al, Ni, and Zr alloys,[21] comprehensive comparisons across various material systems remain scarce.

In the present study, we evaluate the data quality of a DUV-laser equipped Invizo 6000 (hereafter Invizo) compared to a NUV-equipped LEAP (hereafter LEAP) using various materials, including metals (Al, Fe) and complex oxides (FeO, $LiNi_{0.8}Co_{0.1}Mn_{0.1}O_2$ (NCM811), and $LiCoO_2$ (LCO)). Additionally, the influence of caping layers applied via *in situ* coating within a focused-ion beam (FIB) is investigated. Data quality from both LEAP and Invizo is estimated using four metrics: background levels, detection events, ion detection histograms, and MRP, with the charge-state ratio (CSR) used as a tracer for consistent electrostatic field conditions across datasets and systems.[37] This research focuses explicitly on material-specific outcomes, highlighting complexities associated with APT measurements due to varying material properties and instrumental conditions.

# 2. Materials and Methods

## 2.1. Materials

The primary materials used in this study were metals (Al 99.9% and low-carbon Fe steel 98.0%), and oxides ((100)-orientated single-crystal FeO 99.9%, $LiCoO_2$ (LCO), and
LiNi<sub>0.8</sub>Co<sub>0.1</sub>Mn<sub>0.1</sub>O<sub>2</sub> (NCM811)). Chromium metal (99.99%) for specimen coating was purchased from commercial sources.

## 2.2. Specimen fabrication

Specimens were fabricated into needle shapes using a Thermo Scientific Helios 5 HX dual-beam FIB/SEM instrument. The samples were prepared using either the “toblerone” or standard TEM-lamella lift-out methods, and then mounted on a sharpened wire or pre-sharpened Si microtips with a composite (e.g., Pt/C).[38,39] This composite was deposited by injecting a gaseous precursor on the FIB/SEM system using a gas injection system.[40,41] The mounted samples were sharpened to a final radius of less than 100 nm by annular milling with a 30-kV Ga-ion beam. In this protocol, a circle was used, in which both the inner diameter and ion-beam current were progressively reduced until the final tip radius was obtained. The sharpened specimens were cleaned with a low-current 5-kV ion beam to reduce residual Ga-ion-induced beam damage and implantation.

## 2.3. NUV-laser-assisted LEAP 5000 and DUV-laser-assisted Invizo 6000 analysis

Atom probe tomography measurements were conducted using CAMECA LEAP 5000XR and 5000XS (Madison, WI, USA) for NUV-laser and Invizo 6000 (Madison, WI, USA) for DUV-laser. Detailed measurement parameters and conditions are listed in Table 2. The constant detection rate mode was used for all APT experiments. To maintain a nearly constant flux between two systems, a higher detection rate was intentionally set in the Invizo system, although the difference in flux remained. In addition, all Invizo experiments were conducted using the dual-DUV lasers to clearly demonstrate characteristic features of Invizo system such as a compressed ion detection histogram. All acquired APT data were reconstructed using the CAMECA Atom Probe Suite (AP Suite, version 6.3), following previously described standard
protocols.[42] Consistent with Meisenkothen et al,[43] MRP is sensitive to both FOV and the applied voltage. For the performance comparison between the Invizo and LEAP systems, the entire field of view was chosen to enable a comprehensive comparison between the systems, and a comparably similar voltage range was selected. Based on the reference,[43] the applied voltage difference was selected within 2.5 kV in order to ensure that the MRP difference resulting from the voltage difference remained within 10%. (Table S1). The background was determined as approximately the median value within the voltage range. To calculate the CSR, an identical ranging width at the same mass-to-charge ratio and the most abundant peak among isotopes was used. In addition, the error in the CSR value of each material was estimated by calculating the CSR across several ROIs within the 3D reconstruction map. Table 1 summarizes the samples and equipment models employed in this study.

<table><caption>**Table 1.** Samples and equipment models.</caption><thead><tr><th rowspan="2">Materials</th><th colspan="3">Metal</th><th colspan="3">Oxide</th></tr><tr><th>Al</th><th>Fe</th><th>FeO</th><th>LiNi<sub>0.8</sub>Co<sub>0.1</sub>Mn<sub>0.1</sub>O<sub>2</sub></th></tr></thead><tbody><tr><th>Equipment</th><td>Invizo 6000</td><td>LEAP 5000XS</td><td>Invizo 6000</td><td>LEAP 5000XR</td><td>Invizo 6000</td><td>LEAP 5000XS</td></tr><tr><th>Wavelength</th><td>DUV</td><td>NUV</td><td>DUV</td><td>NUV</td><td>DUV</td><td>NUV</td></tr></tbody></table>

<table><thead><tr><th rowspan="2">Materials</th><th colspan="4">LiCoO<sub>2</sub></th></tr><tr><th>Not Coated</th><th>Not Coated</th><th>Not Coated</th><th>Coated by Cr</th></tr></thead><tbody><tr><th>Equipment</th><td>Invizo 6000</td><td>LEAP 5000XR</td><td>Invizo 6000</td><td>Invizo 6000</td></tr><tr><th>Wavelength</th><td>DUV</td><td>NUV</td><td>DUV</td><td>DUV</td></tr></tbody></table>

## 2.4. Data Analysis

Datasets containing the same number of ions were selected for each material (Figure S1) and evaluated using the following metrics: (1) detection events, (2) MRP, (3) ion histogram uniformity, and (4) background levels. Each parameter affects the quality of the APT data as described below:
(1) Multiple events, dissociated ions, or neutrals during the field-evaporation trajectory result in ambiguous spatial resolutions, hindering accurate reconstruction and causing inaccuracies in the composition analysis owing to the loss of ions.

(2) The MRP is related to the chemical resolution; that is, the higher the resolution, the higher the sensitivity and spectral resolution. A low MRP is attributed to the presence of thermal tails in the mass peaks, which lead to a loss of elemental information because the elemental peaks may become indistinguishable below these tails.

(3) Uniformity in the detector histogram is crucial for accurate reconstruction of the 3D atomic structure of an APT specimen. Irregularities originating from sources other than the sample can lead to inaccuracies in the spatial resolution.

(4) The background level determines the chemical sensitivity of the measurements. Background noise can be caused by vacuum conditions, hydrogen dissociation in the analysis vacuum chamber, changes in the electric-field strength, and delayed evaporation.[44] The ions evaporated during the pulses exhibit a high kinetic energy and are identified in the mass spectrum. However, the atoms on the specimen surface can also evaporate in-between the applied pulse durations, if the field strength is sufficiently high. The kinetic energy of these atoms may not be sufficient to trigger the MCP detector, and such atoms are identified as background noise events.

In this study, vacuum pressure did not significantly contribute to background noise, as all measurements were conducted under ultra-high vacuum (UHV) conditions at pressure below $10^{-9}$ mbar. Under these extremely low pressures, hydrogen is typically the predominant residual gas in metal vacuum chambers. Residual gas molecules adsorbed onto the specimen tip can undergo field ionization due to the strong local electric field at the specimen's apex. The resulting ions accelerate toward the detector, potentially triggering DC evaporation and generating additional signals on the microchannel plate (MCP). However, previous analyses
based on classical gas kinetics combined with electric-field enhancement have indicated that achieving even monolayer coverage of hydrogen molecules on a typical APT specimen would require approx. 10⁴ years under UHV conditions.[45] Consequently, we assumed that residual gas ionization under the experimental conditions influenced only the local electric-field strength without significantly contributing to background noise.[46]

### 3. Results and Discussion

Table 2 details the experimental conditions for each specimen, enabling a comparative analysis between NUV-assisted LEAP and DUV-assisted Invizo systems under various experimental setups. Ideally, experimental parameters such as detection rate, laser pulse energy, pulse frequency, and specimen base temperature should remain constant for the direct comparison. However, even under identical parameters, variation in tip radius, shank angle, and the relative position of the specimen with respect to the local electrode (in LEAP 5000) or flat counter electrode (in Invizo 6000) can cause an unavoidable local electric field distribution.[47,48] Therefore, not only for experimental parameters, but also the CSR-derived field condition, which reflects the combined influence of these experimental parameters, was considered (Table S2). [49,50]

<table><caption>**Table 2.** The experimental conditions of each specimen</caption><thead><tr><th rowspan="3">Materials</th><th colspan="4">Metal</th><th colspan="4">Oxide</th></tr><tr><th colspan="2">Al</th><th colspan="2">Fe</th><th colspan="2">FeO</th><th colspan="2">LiNi<sub>0.8</sub>Co<sub>0.1</sub>Mn<sub>0.1</sub>O<sub>2</sub></th></tr><tr><th>Invizo 6000</th><th>LEAP 5000XS</th><th>Invizo 6000</th><th>LEAP 5000XR</th><th>Invizo 6000</th><th>LEAP 5000XS</th><th>Invizo 6000</th><th>LEAP 5000XS</th></tr></thead><tbody><tr><td>Equipment</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Temperature (K)</td><td>50</td><td>60</td><td>50</td><td>60</td><td>30</td><td>50</td><td>50</td><td>50</td></tr><tr><td>Pulse rate (kHz)</td><td>200</td><td>100</td><td>200</td><td>200</td><td>200</td><td>200</td><td>200</td><td>100</td></tr><tr><td>Pulse energy (pJ)</td><td>400</td><td>20</td><td>100</td><td>40</td><td>20</td><td>40</td><td>1</td><td>5</td></tr><tr><td>Detection rate (%)</td><td>2</td><td>1</td><td>2</td><td>1</td><td>5</td><td>1</td><td>2</td><td>1</td></tr><tr><td>Background</td><td>4</td><td>12</td><td>15</td><td>3</td><td>6</td><td>7</td><td>300</td><td>10</td></tr></tbody></table>
<table><thead><tr><th>(ppm/ns)</th><th></th><th></th><th></th><th></th><th></th><th></th><th></th><th></th></tr></thead><tbody><tr><td>Ion flux<br>(%/µm²)</td><td>130-132</td><td>168-190</td><td>35-54</td><td>65-73</td><td>75-77</td><td>36-38</td><td>50-74</td><td>158-164</td></tr><tr><td>Pressure<br>(Torr)</td><td>5.7 x10<sup>-11</sup></td><td>2.4 x10<sup>-11</sup></td><td>7.0 x10<sup>-11</sup></td><td>1.1 x10<sup>-10</sup></td><td>5.8 x10<sup>-11</sup></td><td>1.7 x10<sup>-11</sup></td><td>7.5 x10<sup>-11</sup></td><td>8.6 x10<sup>-11</sup></td></tr></tbody></table>

<table><caption>**Table 3.** The detection event for Al, Fe, FeO, NCM811, and LCO using Invizo and LEAP. The detection event for uncoated LCO and Cr-coated using Invizo.</caption><thead><tr><th rowspan="2">Materials</th><th colspan="4">LiCoO<sub>2</sub></th></tr><tr><th>Not Coated</th><th>Not Coated</th><th>Not Coated</th><th>Coated by Cr</th></tr></thead><tbody><tr><td>Equipment</td><td>Invizo 6000</td><td>LEAP 5000XR</td><td>Invizo 6000</td><td>Invizo 6000</td></tr><tr><td>Temperature (K)</td><td>50</td><td>60</td><td>50</td><td>50</td></tr><tr><td>Pulse rate (kHz)</td><td>200</td><td>125</td><td>200</td><td>200</td></tr><tr><td>Pulse energy (pJ)</td><td>10</td><td>5</td><td>10</td><td>10</td></tr><tr><td>Detection rate (%)</td><td>1</td><td>0.5</td><td>1</td><td>1</td></tr><tr><td>Background (ppm/ns)</td><td>130</td><td>6</td><td>130</td><td>18</td></tr><tr><td>Ion flux (%/µm²)</td><td>70-105</td><td>200-420</td><td>40-130</td><td>22-30</td></tr><tr><td>Pressure (Torr)</td><td>1.0 x10<sup>-11</sup></td><td>6.5 x10<sup>-11</sup></td><td>1.9 x10<sup>-11</sup></td><td>2.1 x10<sup>-11</sup></td></tr></tbody></table>

<table><thead><tr><th rowspan="2">Detection event</th><th colspan="2">Al</th><th colspan="2">Fe</th><th colspan="2">FeO</th><th colspan="2">NCM811</th></tr><tr><th>Invizo 6000</th><th>LEAP 5000XS</th><th>Invizo 6000</th><th>LEAP 5000XR</th><th>Invizo 6000</th><th>LEAP 5000XS</th><th>Invizo 6000</th><th>LEAP 5000XS</th></tr></thead><tbody><tr><td>Single</td><td>95.0%</td><td>90.9%</td><td>90.7%</td><td>95.3%</td><td>53.4%</td><td>50.7%</td><td>47.9%</td><td>61.4%</td></tr><tr><td>Multiple</td><td>3.80%</td><td>8.17%</td><td>8.41%</td><td>3.59%</td><td>44.4%</td><td>48.9%</td><td>51.1%</td><td>37.8%</td></tr><tr><td>Partial</td><td>1.17%</td><td>0.98%</td><td>0.91%</td><td>1.08%</td><td>1.92%</td><td>0.46%</td><td>0.97%</td><td>0.81%</td></tr></tbody></table>

<table><thead><tr><th rowspan="2">Detection event</th><th colspan="4">LiCoO<sub>2</sub> (LCO)</th></tr><tr><th>Not coated</th><th>Not coated</th><th>Not coated</th><th>Coated by Cr</th></tr></thead><tbody><tr><td>Equipment</td><td>Invizo 6000</td><td>LEAP 5000XR</td><td>Invizo 6000</td><td>Invizo 6000</td></tr><tr><td>Single</td><td>55.0%</td><td>70.4%</td><td>56.2%</td><td>77.7%</td></tr><tr><td>Multiple</td><td>43.9%</td><td>28.3%</td><td>42.8%</td><td>21.5%</td></tr><tr><td>Partial</td><td>1.10%</td><td>1.31%</td><td>1.02%</td><td>0.80%</td></tr></tbody></table>

To assess the data quality of the DUV- and NUV-laser-assisted APT, we conducted a comparative analysis of datasets from a wide variety of materials, including metals (Al, Fe) and oxides (FeO, NCM811, LCO). Evaluations of the 3D atom maps in Figures 1a and 1b suggest that both Invizo and LEAP are feasible to produce datasets, demonstrating that all materials can be measured using both systems.
<figure><img src="image_3.png" /><figcaption>**Figure 1.** 3D reconstruction maps of metals (Al, Fe), oxides (FeO, $LiNi_{0.8}Co_{0.1}Mn_{0.1}O_2$) measured with (a) NUV-laser assisted LEAP and (b) DUV-laser assisted Invizo. The selected ROI is 10 × 10 × 10 nm³.</figcaption></figure>

**3.1. Metals (Al and Fe)**

Figure 2a shows the APT mass spectrum of Al, which is considered a “low evaporation field” metal having dominant ion $Al^+$ with evaporation field 19 V nm⁻¹.[51] The CSR for Al, as defined the ion counts ratio $Al^{2+}/Al^+$, was used to calculate a Invizo-to-LEAP metric (Invizo/LEAP) (e.g., Al CSR (Invizo) / Al CSR (LEAP)), which was 0.23, implying that a higher electric-field strength was used in the LEAP measurement.

The LEAP dataset exhibited a higher background (approx. 12 ppm ns⁻¹) compared to the Invizo dataset (approx. 4 ppm ns⁻¹), as shown in Table 2 and Figure 2a. This could originate from differences in electric-field strength, since higher fields typically elevate background levels by inducing continuous (non-pulsed) field evaporation.[52] Alternatively, lower evaporation-field metals generally exhibit higher background levels due to weaker laser absorption. Studies by Kim et al. reported continuous DC evaporation in low-evaporation-field materials such as BiInSn, Ga, and GaIn alloys,[53,54] attributed to poor laser absorption.
The absorption coefficient determines the increase in temperature of the APT specimen tip under laser illumination through thermal activation.[55,56] Al is also considered a low-evaporation-field metal and relatively lower absorption rate (0.08 for NUV and 0.09 for DUV wavelength), indicating a 12.5% increase in absorption rate in DUV compared to NUV.[57,58] Therefore, it exhibited a reduced background under DUV, possibly due to the improved absorption at the shorter wavelength.[59].

The MRP was calculated by dividing the mass of each element at a peak (m) by the width of the peak (Δm) at half maximum (i.e. m/Δm). Figure 2c shows the MRP values at 13.5 Da (Al²⁺) and 27 Da (Al⁺) for Invizo as 495 and 1075, respectively, whereas LEAP shows values of 435 and 700, respectively. The single-event rates were 90.9% for the LEAP and 95.0% for the Invizo (Table 3). The ion detection histogram for the Invizo shows a concentrated density of ions at the center, whereas the LEAP shows a uniform histogram across the detector, as shown in Figure 2d. Tegg et al.,[21] similarly observed that the ion detection histogram of Al sample on Invizo showed a high-density region around the center. This histogram pattern could be attributed to a higher pulse energy at Invizo, leading to the faceting of the specimen or inherent system of Invizo 6000 as mentioned above.[60] For Al, the DUV exhibited better results in terms of background, MRP, and detection events, whereas the NUV showed more homogeneous ion detection histogram.
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<figure><img src="image_11.png" /><figcaption>**Figure 2.** Mass spectra (a) Al and (b) Fe obtained using Invizo and LEAP. The bin size is 0.1 Da and the extracted ions for Al and Fe are 2 million ions and 10 million ions, respectively. The enlarged mass spectra around Al⁺ and Al²⁺ ion for (c) Al, and around Fe⁺ and Fe²⁺ ion for (d) Fe. The mass resolving power of the Invizo and LEAP is represented for an indicated peak on each sample. Ion detection histograms of (e) Al and (f) Fe obtained using Invizo (top) and LEAP (bottom).</figcaption></figure>

For a “moderate evaporation field” element, low-carbon steel (< 0.03 at.% C) with dominant ion Fe²⁺ having an evaporation field 33 V nm⁻¹,[61] was selected, and a different trend was observed. The Invizo/LEAP ratio calculated from the Fe⁺/Fe²⁺ values was 0.09, indicating that a stronger electric field was applied to the LEAP. Despite this, the 15 ppm ns⁻¹ background of the Invizo was significantly higher than the 3 ppm ns⁻¹ background of the LEAP, as shown in Table 2 and Figure 2b. For Fe, LEAP showed higher single-detection event rates of 95.3% than 90.7% for Invizo, as shown in Table 3. Figure 2e shows that the MRP values for Invizo at 28 (Fe²⁺) and 56 (Fe⁺) Da are 1144 and 574, respectively, whereas for LEAP, the values at the same Da are 1231 and 1004, respectively. Figure 2f shows that the ion detection histogram for the Invizo is more concentrated at the center than that for the LEAP, which displays an asymmetric pattern affected by trajectory aberrations from the reflectron in the HR series.[36] These differences could be attributed to the combined
influence of multiple factors, including laser wavelength, optical alignment, and the distinct ion-optical design, rather than wavelength alone. Overall, LEAP delivered superior results for Fe across background, MRP, detection events, and showed more histogram uniformity metrics.

Multiple experimental factors complicate attributing observed differences to LEAP and Invizo systems. Despite the advanced dual DUV-laser system and decelerating lens in the Invizo 6000, designed to optimize data acquisition and yield, especially for non-conductors requiring uniform heat deposition, the observed data suggest limited overall advantages of Invizo over LEAP. Thus, selection between these instrument systems should consider the specific analytical requirements and characteristics of the material under investigation.

## 3.2. Oxides (FeO and $LiNi_{0.8}Co_{0.1}Mn_{0.1}O_2$)

FeO was measured using both LEAP and Invizo, revealing an Invizo/LEAP ratio of 1.61, calculated from the CSR, defined as the $Fe^+/Fe^{2+}$ ratio, demonstrating that a higher electric field was observed in the measurement by Invizo. The background level in the Invizo (7 ppm ns⁻¹) was similar to that in the LEAP (6 ppm ns⁻¹) in Table 2 and Figure 3a. Also, in Table 3, the single-detection event rate for the Invizo was 53.4%, whereas that for the LEAP was 50.7%. A higher electric field generally increases not only the background but also the multiplicity, which is attributed to the greater possibility of correlative evaporation near neighboring atoms at higher electric fields and unwanted field evaporation at non-pulsing by a high DC voltage. However, the Invizo manifested a background similar to that of the LEAP and a better single detection event, albeit with a high electric field. This similar background could be due to the higher base temperature of LEAP than Invizo. [62] In addition, the mesh between the specimen and detector in Invizo may be attributed to a decrease in multiple events by filtering out the daughter ions that dissociated from the field-evaporated
molecule.[36]

Invizo also demonstrates an outstanding performance in terms of mass resolution. The MRP values for the Invizo at 28 ($Fe^{2+}$) and 56 ($Fe^{+}$) Da were 634 and 672, respectively, whereas those for the LEAP were 610 and 225, respectively (Figure 3c). This indicates that Invizo achieves sharper and more distinct peaks, which is crucial for the accurate identification and quantification of different ion species. The peak at 56 Da ($Fe^{+}$) in LEAP exhibits a severe thermal tail, which is often present in laser-pulsed APT data for nonconductive materials. These tails are generally attributed to thermal bulk heating and slow cooling mechanisms, resulting in time-delayed thermal desorption of surface ions.[56,63] The superior peak resolution in Invizo can be explained by a smaller heat-affected zone (<2 µm), which minimizes peak broadening and overlapping, thereby enhancing the overall resolution of the mass spectrum.[17,64,65] Another possible explanation is that the dual-beam system of the Invizo reduces the localized laser absorption in one direction, thereby suppressing the time shift caused by delayed heat transfer.

Figure 3d depicts the ion detection histogram; interestingly, the Invizo exhibits a hollow core with a dense outer layer, unlike the LEAP. A local increase in the electric field corresponding to a region of higher curvature (i.e., in the vicinity of the poles and zone lines) induces local magnification, leading to a region of low density that appears dark in the detector map. The sample used was a (100)-grown single-crystal wüstite ($FeO$), and we expected a low-density region at the (100) pole. However, the zones of low-density regions are abnormally large, and the field of view is progressively compressed compared to other oxide zones in previous reports.[66,67] This is likely due to trajectory aberrations caused by the field lens, resulting in local inhomogeneities not from the sample, but from the instrument itself.
<figure><img src="image_12.png" /><figcaption>**Figure 3.** Mass spectra of (a) FeO and (b) NCM811 obtained using Invizo and LEAP. The bin size is 0.1 Da and the extracted ions for FeO and NCM811 are 10 million ions and 3 million ions, respectively. The enlarged mass spectra around Fe⁺ and Fe²⁺ ion for (c) FeO, and around Li⁺ and Ni²⁺ ion for (e) NCM811. The mass resolving power of the Invizo and LEAP is represented for indicated peak on each sample. Ion detection histograms of (d) FeO and (f) NCM811 obtained using Invizo (top) and LEAP (bottom).</figcaption></figure>

The analysis of Li-ion battery materials using APT presents significant challenges owing to the *in situ* delithiation process (i.e. electromigration) by intense electric field during APT measurement and the large evaporation-field difference between Li and transition-metal oxides such as LCO and NCM811.[14,68,69] Despite those challenges, the battery cathode has been analyzed by optimizing the analysis conditions such as the temperature, pulse rate etc.[14,70] The Invizo/LEAP ratio calculated from the selected CSR Ni²⁺/Ni⁺ for NCM811 was 0.92, indicating that a higher electric field was applied to the LEAP measurement. Despite the higher electric field for LEAP and higher MRP value for Invizo in Figure 3e, the background level (10 ppm ns⁻¹) in the LEAP for NCM811 was considerably lower than the background (300 ppm ns⁻¹) in the Invizo as shown in Table 2 and Figure 3b. This could be attributed to the higher pulse rate in Invizo than LEAP, which may lead to thermal evaporation out of the pulse, and thereby increase the background.[10] Moreover, the single-
detection event rate for Invizo was 55.02% compared to 70.4% for LEAP in Table 3,
suggesting a higher single detection event of LEAP. Invizo results for the NCM811 show an
ion detection histogram (Figure 3f) with ions concentrated at the center and formed in an odd
triangular shape. This feature is also observed in several other specimens (Figure S3),
indicating a potential issue with ion distribution. Overall, while the Invizo demonstrates a
better MRP and irregular ion detection histogram, the LEAP performs better in terms of
background, detection events.

The background, detection events, ion detection histograms, and MRP for each material were
examined to compare the data quality between the Invizo and LEAP. In general, the
differences between the Invizo and LEAP depend on materials. For MRP, DUV typically
provides better performance. However, the Invizo detection histograms consistently showed a
centered appearance, suggesting a potential distortion or uneven field distribution.

**3.3. Application of In Situ Coating Methods**

Figure 4 presents the APT analysis of the LCO using both Invizo and LEAP. The CSR
calculated by the Co⁺/Co²⁺ ratio was of 0.58, suggesting a stronger electric field in LEAP.
However, the background (130 ppm ns⁻¹) in Invizo was substantially higher than in LEAP (6
ppm ns⁻¹) as indicated in Table 2 and Figure 4c. The MRP values of Invizo at 7 Da (Li⁺), 16
Da (O⁺), and 29.5 Da (Co²⁺) were obtained to 171, 523, and 278 in Figure 4a, while the MRP
values of LEAP were 1154, 1030, and 437, respectively, signifying higher MRP value of
Invizo. As shown in Table 3, the single detection events for LEAP and Invizo were 70.4% and
55.0%. The ion detection histogram acquired by Invizo in Figure 4b exhibits a triangular
shape and inhomogeneous event. Overall, similar to the NCM811 result, Invizo illustrates an
inhomogeneous ion detection histogram and superior MRP performance compared to LEAP,
but inferior outcomes in terms of single detection event. To mitigate these limitations of
Invizo analysis, an *in situ* coating experiment was subsequently conducted.

<figure><img src="image_13.png" /><figcaption>**Figure 4.** (a) Enlarged mass spectra of LCO at 7 Da, 16 Da, and 29.5 Da obtained using Invizo and LEAP. The mass resolving power of the DUV and NUV lasers is represented for indicated peak on each sample. Ion detection histograms of (b) LCO obtained using Invizo (top) and LEAP (bottom). (c) Mass spectra of LCO until 120 Da. The bin size is 0.1 Da, and the extracted ions are 2 million ions.</figcaption></figure>

The LCO samples were coated *in situ* using the focused-ion beam (FIB) method by following
the protocols described by Woods et al., Singh et al., and Johansen et al. [44,71,72] Briefly, a
small Cr lamella was mounted on the *in situ* micromanipulator, a half-circle was cut, and Cr
was back-sputtered using a Ga-ion beam onto the final sharpened specimen using a low ion-
beam current and time. Both Cr-coated and uncoated LCO samples were analyzed using
Invizo (Figure 5), and the scanning electron microscopy (SEM) image in Figure 5a shows that the coated sample was blunter than the uncoated sample after *in situ* Cr coating. *In situ* Cr coating helps protect the region of interest (ROI) and improves the measurement quality by stabilizing the material and reducing preferential evaporation.[44] Additionally, it may alter the charge density distribution under electric fields, making nonconductive materials measurable for NUV-APT. By providing a uniform and protective layer directly on the specimen, the coating stabilized the material and reduced background noise, thus enhancing the data quality and yield.[73,74] Furthermore, this coating improves the mass resolution and expands the effective field of view, allowing the visualization of the entire original specimen, including the surface oxide layers.[44,71,75]

<figure><img src="image_14.png" /><figcaption>**Figure 5.** SEM images and mass spectra. (a) SEM images captured before and after coating Cr on the LCO specimen. The white scale bar implies 250 nm. (b) Ion histograms of uncoated and coated LCO. (c) Mass spectra uncoated and coated LCO obtained using Invizo. The bin size is 0.1 Da and the extracted ions are 9 million ions. The inset figures (i) and (ii) are 3D reconstruction maps of LCO and Cr-coated LCO where Cr coating surface was expressed by 11.4 at.% Cr iso-compositional surface. The black scale bar implies 50 nm.</figcaption></figure>
The CSR ratio of the uncoated specimen to the coated specimen, calculated from the Co⁺/Co²⁺ counts, was 0.80, indicating that the coated samples experienced stronger electrical fields than the uncoated samples. As shown in Table 2 and Figure 5c, the background level of the coated samples (18 ppm nm⁻¹) was significantly lower than that of the uncoated samples (130 ppm nm⁻¹), despite the higher electric field applied to the coated specimens. The MRP value of coated specimen at 29.5 Da (Co²⁺) and 59 Da (Co⁺) is 680 and 785, while the MRP value of uncoated specimen shows 497 and 626, respectively, indicating the enhanced MRP value of coated sample. Moreover, the coated LCO shows higher single detection event (77.7%) than uncoated LCO (56.2%). This improvement in background noise, single detection event and MRP is likely related to thermal dissipation from the sample, as previous studies have reported that thin metal coatings (applied *ex situ* and *in situ*) can improve thermal conductivity of specimens.[74,76] At this point, we cannot fully explain why the triangular shape pattern appeared in the ion detection histogram of the uncoated specimen (Figure 5b), reducing the resolution of the measurement in Invizo. After coating, the ion detection histogram for the coated LCO samples showed suppressed abnormal triangular contour maps and low-density fluctuations at the center of the detector.

In summary, the data quality of analyzed materials using LEAP and Invizo was thoroughly assessed using four metrics (background, MRP, detection events, and ion detection histograms). The results for the background and detection events between LEAP and Invizo across different material types, such as metals and oxides do not show a distinctive trend in the performance. However, Invizo appears to have better MRP than LEAP across most metals and oxides. Possible explanations for the improved MRP with Invizo are DUV's shorter wavelength, which results in a smaller heat zone and easier thermal dissipation, and the Invizo 6000's deceleration lenses for prolonged time-of-flight.
The ion detection histograms of Invizo on the detector for all samples displayed severely distorted and compressed images, which was likely due to Invizo's newly implemented decelerating lens. When field-evaporated ions pass through the counter electrode toward the detector, a series of decelerating lenses could change the trajectory of these ions. Another possible reason for the concentrated histogram may be the dual-beam source of Invizo 6000. The laser absorption mechanism from dual-beam becomes quite complex due to various effects such as interference caused by interaction between both pulses.[30,77] This complexity contributes to the distortion of the ion detection histogram but it should be investigated further. That concentrated map could cause composition inaccuracy and lowers the spatial resolution since the position-sensitive detector cannot distinguish multiple ions nearly simultaneously impacting close spatial proximity on the MCP.[36,78] Furthermore, Artifacts in the 3D reconstruction atom map underestimate the atom distribution due to the high image compression factor.[21,35] Therefore, appropriate reconstruction methods tailored to Invizo are required to avoid such distortions, and instrumental factors must be carefully considered when interpreting such comparative data.

When bare and *in situ* Cr-coated LCO were measured using Invizo, there was a significant improvement in the background and detection events for the coated LCO compared to the uncoated LCO. This suggests that the introduction of the coating process can enhance data quality in DUV-APT systems. In particular, Cr *in situ* coating has emerged as a promising candidate for improving APT measurements, providing a strategy not only to enhance the data quality of both systems but also to reduce the variability between Invizo and LEAP results.
## 4. Conclusion

Invizo 6000 and LEAP 5000 equipped with DUV- and NUV-laser sources were compared across different types of materials (metals and oxides). In addition, the results of the *in situ* Cr coating are demonstrated in the Invizo 6000. Overall, the yields and mass resolution from Invizo were better, but no distinct improvement in data quality was observed considering the severely distorted ion histogram map. This discrepancy may be attributed to the differences in the laser wavelength, dual-illumination laser optics scheme, and decelerating lenses. Therefore, a reassessment of the application of laser sources is necessary to improve data quality. Furthermore, applying a coating to the specimen could be an effective method for stabilizing APT specimens from the beam, improving data quality, and narrowing the gap between the two laser sources. These results provide valuable insights for future studies.

## Acknowledgments

We thank Uwe Tezins, Christian Broß and Andreas Sturm for their support to the FIB and APT facilities at MPIE. S.-H.K. acknowledge supports from KIAT-MOTIE (P0023676, HRD Program for Industrial Innovation), KEIT-MOTIE (RS-2024-00431836, Technology Innovation Program) and National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (National R&D Program, RS-2024-00450561). B.G. acknowledge financial support from the ERC-CoG-SHINE-771602.

## Conflict of interest

The authors declare that they have no competing interest.
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