A gas-phase reaction cell for modern Atom Probe systems

In this work, we demonstrate a new system for the examination of gas interactions with surfaces via Atom Probe Tomography. This system provides the capability to examine the surface and subsurface interactions of gases with a wide range of specimens, as well as a selection of input gas types. This system has been primarily developed to aid the investigation of hydrogen interactions with metallurgical samples, to better understand the phenomenon of hydrogen embrittlement. In its current form, it is able to operate at pressures from 10^-6 to 1000 mbar (abs), can operate using a variety of gasses, and is equipped with heating and cryogenic quenching capabilities. We use this system to examine the interaction of hydrogen with Pd, as well as the interaction of water vapour and oxygen in Mg samples

Nanoscale Analysis of Frozen Water by Atom Probe Tomography Using Graphene Encapsulation and Cryo-Workflows: A Parametric Study

There has been an increasing interest in atom probe tomography (APT) to characterise hydrated and biological materials. A major benefit of APT compared to microscopy techniques more commonly used in biology is its combination of outstanding 3D spatial resolution (~0.2 nm) and mass sensitivity. APT has already been successfully used to characterise biological materials, revealing key structural information at the atomic scale, however there are many challenges inherent to the analysis of hydrated materials. New preparation protocols, often involving sample preparation and transfer at cryogenic temperature, enable APT analysis of hydrated materials and have the potential to enable 3D atomic scale characterisation of biological materials in the near-native hydrated state. In this study, APT specimens of pure water at the tips of tungsten needles were prepared at room temperature by graphene encapsulation. A parametric study was conducted where samples were transferred at either room temperature or cryo-temperature and analysed by APT by varying parameters such as the flight path and pulsing mode. The differences between the acquisition scenarios are presented along with recommendations for future studies

Atom probe tomography and correlative microscopy: Key techniques for future planetary science studies

Our Galaxy is vast and awe-inspiring. The stars, planets, and our sun capture our imagination as children. For many of us, that wonder never ceases. It continues to inspire us throughout our careers and prompts us to question the evolution of our Solar System, to question what our place is within it, and how we may maintain longevity in a relatively volatile environment. To answer these questions planetary scientists turn to the study of extraterrestrial material. They analyze meteorites, impact craters, and materials returned by sample return missions for the evidence of events that are known to induce crystallographic and/or elemental changes, or for evidence of extraterrestrial isotopic abundances that point to the age and the original source of the material. Through these studies, we can constrain timelines of events that have occurred throughout the Solar System’s extensive history. Recently, atom probe tomography (APT) has been applied to the study of these materials. APT in correlation with larger-scale analysis techniques has provided insights into isotopic ratios or nanoscale distribution of elements, enriching our knowledge, and minimizing uncertainties in the time frame of critical cosmic events. The continued use of correlative microscopy with APT for the study of planetary science, including studies of small amounts of pristine materials delivered to the Earth by exciting sample return missions, promises to provide key information into the history of our Solar System. Here, we highlight the implications of correlative microscopy with APT for the future pursuits of planetary science, we reflect on the groundbreaking research already achieved, the challenges that have been overcome to achieve these outcomes and the challenges yet to come

Analysis of water ice in nanoporous copper needles using cryo atom probe tomography

The application of atom probe tomography (APT) to frozen liquids is limited by difficulties in specimen preparation. Here, we report on the use of nanoporous Cu needles as a physical framework to hold water ice for investigation using APT. Nanoporous Cu needles are prepared by the electropolishing and dealloying of Cu-Mn matchstick precursors. Cryogenic scanning electron microscopy and focused-ion beam milling reveal a hierarchical, dendritic, highly-wettable microstructure. The atom probe mass spectrum is dominated by peaks of Cu+ and H(H2O)n+ up to n <= 3, and the reconstructed volume shows the protrusion of a Cu ligament into an ice-filled pore. The continuous Cu ligament network electrically connects the apex to the cryostage, leading to enhanced electric field at the apex and increased cooling, both of which simplify the mass spectrum compared to previous reports

Breaking the icosahedra in boron carbide

Findings of laser-assisted atom probe tomography experiments on boron carbide elucidate an approach for characterizing the atomic structure and interatomic bonding of molecules associated with extraordinary structural stability. The discovery of crystallographic planes in these boron carbide datasets substantiates that crystallinity is maintained to the point of field evaporation, and characterization of individual ionization events gives unexpected evidence of the destruction of individual icosahedra. Statistical analyses of the ions created during the field evaporation process have been used to deduce relative atomic bond strengths and show that the icosahedra in boron carbide are not as stable as anticipated. Combined with quantum mechanics simulations, this result provides insight into the structural instability and amorphization of boron carbide. The temporal, spatial, and compositional information provided by atom probe tomography makes it a unique platform for elucidating the relative stability and interactions of primary building blocks in hierarchically crystalline materials

Hydrogen trapping and embrittlement in metals – a review

Hydrogen embrittlement in metals (HE) is a serious challenge for the use of high strength materials in engineering practice and a major barrier to the use of hydrogen for global decarbonization. Here we describe the factors and variables that determine HE susceptibility and provide an overview of the latest understanding of HE mechanisms. We discuss hydrogen uptake and how it can be managed. We summarize hydrogen trapping and the techniques used for its characterization. We also review literature that argues that hydrogen trapping can be used to decrease HE susceptibility. We discuss the future research that is required to advance the understanding of HE and hydrogen trapping and to develop HE-resistant alloys

Simultaneous large optical and piezoelectric effects induced by domain reconfiguration related to ferroelectric phase transitions

Electrical switching of ferroelectric domains and subsequent domain wall motion promotes strong piezoelectric activity; however, light scatters at refractive index discontinuities such as those found at domain wall boundaries. Thus, simultaneously achieving large piezoelectric effect and high optical transmissivity is generally deemed infeasible. Here, it is demonstrated that the ferroelectric domains in perovskite Pb(In1/2Nb1/2)O3 Pb(Mg1/3Nb2/3)O3-PbTiO3 domain-engineered crystals can be manipulated by electrical field and mechanical stress to reversibly and repeatably, with small hysteresis, transform the opaque poly-domain structure into a highly transparent mono-domain state. This control of optical properties can be achieved at very low electric fields (less than 1.5 kV cm−1) and is accompanied by a large (>10000 pm V−1) piezoelectric coefficient that is superior to that of linear state-of-the-art materials by a factor of three or more. The coexistence of tunable optical transmissivity and high piezoelectricity paves the way for a new class of photonic devices

Synthesis and performance evaluation of thin film PPy-PVDF multilayer electroactive polymer actuators

Bending-type microactuators less than 1 mm in length and comprising of two polypyrrole (PPy) layers separated by polyvinylidene fluoride (PVDF) membrane have previously been fabricated and was shown to operate both in air and aqueous media. The main limiting factor to increase the bending angle and to further miniaturise these actuators was the thickness of the commercially-available PVDF membrane used (110 μm). In this study, we have synthesised a porous PVDF thin film with a thickness of 32 μm using a spin coating technique, and electrochemically deposited PPy layers on both sides of this thin film to make ultra thin film polymer actuators. The electromechanical and electrochemical properties are investigated and compared with those of the thicker actuator system using the commercially-available PVDF and under identical conditions. The thin film shows very promising performance compared to its thicker counterpart