arXiv subjects

Jonathan Houard

Publications and source records attributed to Jonathan Houard.

5 recordsLinked to original sources

arXiv2025

Exploring mechanisms leading to composition errors in monazite (CePO4) analysed with atom probe tomography

Monazite (CePO4) is widely used in U-Th-Pb geochronology due to its reliable age determinations, although isotopic disturbances often require nanoscale investigation to better understand the mechanisms at play. Atom Probe Tomography (APT) offers unique capabilities for nanoscale chemical analysis and 3D atomic reconstruction but presents challenges for insulating materials such as CePO4, particularly due to oxygen loss during field evaporation. This study investigates the effects of laser wavelength, energy, metallic coatings and detection device on mass spectrum optimization and compositional accuracy in synthetic CePO4 samples. Results show that shorter laser wavelengths (260 nm) enhance peak resolution, particularly when combined with advanced reflectron configurations, as demonstrated with the LEAP 6000 XR. Chromium coatings further improve thermal dissipation and reduce noise levels. However, compositional measurements reveal systematic underestimation of oxygen and overestimation of P and Ce, likely influenced by preferential low-field element evaporation. These findings highlight the need to carefully tune experimental parameters to mitigate quantification biases and enhance the reliability of APT analyses for geological materials.

cond-mat.mtrl-sci↗

arXiv2025

Role of defects in atom probe analysis of sol-gel silica

Silicon dioxide is a suitable material to encapsulate proteins at room temperature so that they can be analysed at the atomic level using laser-assisted atom probe tomography (La-APT). To achieve this goal, in this study we show that UV and deep UV lasers can achieve a high success rate in La-APT of silica in terms of chemical resolution and three-dimensional image volume, with both lasers providing comparable results. Since the La-APT analyses are driven by photon absorption, in order to understand the mechanisms behind the enhanced absorption of UV light, we performed density functional theory calculations to model the electronic and optical properties of amorphous silica matrices generated using a Monte Carlo approach to structural optimisation. In particular, we have investigated the role of various defects introduced during sample preparation, such as substitutional and interstitial carbon, sodium and gallium ions, and hydrogen. Our results show that the presence of defects increases the absorption of silica in the UV and deep-UV range and thus improves the La-APT capabilities of the material. However, due to the low density of free charge carriers resulting from the absorption of laser energy by defects, deviations from the nominal chemical composition and suboptimal chemical resolution may occur, potentially limiting the optimal acquisition of APT mass spectra.

cond-mat.mtrl-sci↗

arXiv2024

Evaporation of cations from non-conductive nano-samples using single-cycle THz pulses: an experimental and theoretical study

This study investigates the emission of cations from silica samples by single-cycle THz pulses, focusing on the influence of pulse polarity. Negative THz pulses were found to efficiently trigger the evaporation of cations from nanoneedles in amorphous silica samples compared to positive pulses. Conversely, this dependence on pulse polarity could not be found in samples with metallic behaviour such as LaB$_6$ and when multi-cycle pulses in different frequency ranges such as ultraviolet (UV) are used. First-principles simulations focus on silica under THz laser irradiation and show critical fields for ion evaporation of hydroxyl groups from Si(OH)$_4$, which serves as a model precursor molecule for the amorphous solid matrix. To explain our experimental results, we propose a simplified theoretical model that determines the role of the polarity of the THz pulse by taking into account the differences in electron mobility between silica and semi-metallic samples. The study explores the nonlinear microscopic mechanisms of atomic evaporation under external static and THz laser fields and clarifies the dynamics of THz-enhanced APT and related applications.

cond-mat.mtrl-sci↗

arXiv2021

Development of an energy-sensitive detector for the Atom Probe Tomography

A position-energy-sensitive detector has been developed for APT instruments in order to deal with some mass peak overlap issues encountered in APT experiments. Through this new type of detector, quantitative and qualitative improvements could be considered for critical materials introducing mass peak overlaps, such as nitrogen and silicon in TiSiN systems, or titanium and carbon in cemented carbide materials. This new detector is based on a thin carbon foil positioned on the front panel of a conventional MCP-DLD detector. According to several studies, it has been demonstrated that the impact of ions on thin carbon foils has the effect of generating a number of transmitted and reflected secondary electrons that mainly depends on both the kinetic energy and the mass of incident particles. Despite the fact that this phenomenon is well known and has been widely discussed for decades, no studies have been performed to date for using it as a mean to discriminate particles energy. Therefore, this study introduces the first experiments on a potential new generation of APT detectors that would be able to resolve mass peak overlaps through the energy-sensitivity of thin carbon foils.

physics.ins-det↗

arXiv2020

A Photonic Atom Probe coupling 3D Atomic Scale Analysis with in situ Photoluminescence Spectroscopy

Laser enhanced field evaporation of surface atoms in Laser-assisted Atom Probe Tomography (La-APT) can simultaneously excite phtotoluminescence in semiconductor or insulating specimens. An atom probe equipped with appropriate focalization and collection optics has been coupled with an in-situ micro-Photoluminescence (μPL) bench that can be operated during APT analysis. The Photonic Atom Probe instrument we have developped operates at frequencies up to 500 kHz and is controlled by 150 fs laser pulses tunable in energy in a large spectral range (spanning from deep UV to near IR). Micro-PL spectroscopy is performed using a 320 mm focal length spectrometer equipped with a CCD camera for time-integrated and with a streak camera for time-resolved acquisitions. An exemple of application of this instrument on a multi-quantum well oxide heterostructure sample illustrates the potential of this new generation of tomographic atom probe.

physics.app-ph↗