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Abstract: The direct imaging of individual atoms within the cellular context holds great potential for understanding the fundamental physical and chemical processes in organisms. Here, a novel approach for imaging of electrically insulated biological cells by introducing a graphene encapsulation approach to “disguise” the low‐conductivity barrier is reported. Upon successful coating using a water‐membrane‐based protocol, the electrical properties of the graphene enable voltage pulsing field evaporation for atom probe tomography (APT). Low conductive specimens prepared from both Au nanoparticles and antibiotic‐resistant bacterial cells have been tested. For the first time, a significant graphene‐enhanced APT mass resolving power is also observed confirming the improved compositional accuracy of the 3D data. The introduction of 2D materials encapsulation lays the foundation for a breakthrough direction in specimen preparation from nanomembrane and nanoscale biological architectures for subsequent 3D near‐atomic characterization. [ABSTRACT FROM AUTHOR]

We present a novel approach for analysis of low-conductivity and insulating materials with conventional pulsed-voltage atom probe tomography (APT), by incorporating an ultrathin metallic coating on focused ion beam prepared needle-shaped specimens. Finite element electrostatic simulations of coated atom probe specimens were performed, which suggest remarkable improvement in uniform voltage distribution and subsequent field evaporation of the insulated samples with a metallic coating of approximately 10 nm thickness. Using design of experiment technique, an experimental investigation was performed to study physical vapor deposition coating of needle specimens with end tip radii less than 100 nm. The final geometries of the coated APT specimens were characterized with high-resolution scanning electron microscopy and transmission electron microscopy, and an empirical model was proposed to determine the optimal coating thickness for a given specimen size. The optimal coating strategy was applied to APT specimens of resin embedded Au nanospheres. Results demonstrate that the optimal coating strategy allows unique pulsed-voltage atom probe analysis and 3D imaging of biological and insulated samples. [ABSTRACT FROM AUTHOR]

Emergence of multidrug resistant Gram-negative bacteria has caused a global health crisis and last-line class of antibiotics such as polymyxins are increasingly used. The chemical composition at the cell surface plays a key role in antibiotic resistance. Unlike imaging the cellular ultrastructure with well-developed electron microscopy, the acquisition of a high-resolution chemical map of the bacterial surface still remains a technological challenge. In this study, we developed an atom probe tomography (APT) analysis approach to acquire mass spectra in the pulsed-voltage mode and reconstructed the 3D chemical distribution of atoms and molecules in the subcellular domain at the near-atomic scale. Using focused ion beam (FIB) milling together with micromanipulation, site-specific samples were retrieved from a single cell of Acinetobacter baumannii prepared as needle-shaped tips with end radii less than 60 nm, followed by a nanoscale coating of silver in the order of 10 nm. The significantly elevated conductivity provided by the metallic coating enabled successful and routine field evaporation of the biological material, with all the benefits of pulsed-voltage APT. In parallel with conventional cryo-TEM imaging, our novel approach was applied to investigate polymyxin-susceptible and -resistant strains of A. baumannii after treatment of polymyxin B. Acquired atom probe mass spectra from the cell envelope revealed characteristic fragments of phosphocholine from the polymyxin-susceptible strain, but limited signals from this molecule were detected in the polymyxin-resistant strain. This study promises unprecedented capacity for 3D nanoscale imaging and chemical mapping of bacterial cells at the ultimate 3D spatial resolution using APT. [ABSTRACT FROM AUTHOR]

Atom probe tomography (APT) represents a significant step toward atomic resolution microscopy, analytically imaging individual atoms with highly accurate, though imperfect, chemical identity and three-dimensional (3D) positional information. Here, a technique to retrieve crystallographic information from raw APT data and restore the lattice-specific atomic configuration of the original specimen is presented. This lattice rectification technique has been applied to a pure metal, W, and then to the analysis of a multicomponent Al alloy. Significantly, the atoms are located to their true lattice sites not by an averaging, but by triangulation of each particular atom detected in the 3D atom-by-atom reconstruction. Lattice rectification of raw APT reconstruction provides unprecedented detail as to the fundamental solute hierarchy of the solid solution. Atomic clustering has been recognized as important in affecting alloy behavior, such as for the Al-1.1Cu-1.7Mg (at. %) investigated here, which exhibits a remarkable rapid hardening reaction during the early stages of aging, linked to clustering of solutes. The technique has enabled lattice-site and species-specific radial distribution functions, nearest-neighbor analyses, and short-range order parameters, and we demonstrate a characterization of solute-clustering with unmatched sensitivity and precision. [ABSTRACT FROM AUTHOR]

Atom probe tomography (APT) is a microscopy technique that provides a unique combination of information, specifically the position and elemental identity of each atom in three dimensions. Although the mass and spatial resolution is not perfect, we are still able to gain insights into materials science questions that we cannot access using other techniques. This systematic meta-analysis review summarises research in 2018 that used APT to study materials science questions in aluminium alloys. [ABSTRACT FROM AUTHOR]

Non-heat-treatable 5xxx Al alloys exhibit good corrosion resistance but can be susceptible to intergranular corrosion in service. This study applies a cyclic strengthening method to the AA5083 alloy, resulting in a significant increase in yield strength (∼300 MPa) and tensile strength (∼385 MPa) due to the formation of Mg-Al solute clusters confirmed by scanning transmission electron microscopy and atom probe tomography. After a two-month sensitization treatment at 70 °C, the clusters delay the formation of Mg-rich precipitates at grain boundaries, enhancing the resistance to sensitization. This new approach strengthens Al-Mg alloys and offers potential for manipulating the corrosion resistance and sensitization susceptibility. • Cyclic plasticity method is applied in 5xxx alloys, breaking the strength-corrosion inversion relationship. • The formation of Mg-Al solute clusters enhances the mechanical properties of the alloy. • The clusters delay sensitization and limit the formation of intergranular Mg-rich phases. [ABSTRACT FROM AUTHOR]

Three Cu-alloys (CuSn5, CuZn5, CuZn30) have been selected, to study the influence of solutes on the saturation grain size after high pressure torsion as well as the resulting mechanical properties with an emphasis on strain rate sensitivity. Compared to each other, the alloys exhibit either similar stacking fault energies or similar solid solution strengthening, allowing a separation of both parameters. The results indicate that the saturation grain size correlates with the solid solution strengthening but not with the stacking fault energy. Moreover, a reduced strain rate sensitivity with reduced grain size is observed, which is attributed to the microstructural stability. [ABSTRACT FROM AUTHOR]

Solute clusters affect the physical properties of alloys. Knowledge of the atomic structure of solute clusters is a prerequisite for material optimisation. In this study, solute clusters in a rapid-hardening Al-Cu-Mg alloy were characterised by a combination of atom probe tomography and density functional theory, making use of a hybrid data type that combines lattice rectification and data completion to directly input experimental data into atomistic simulations. The clusters input to the atomistic simulations are thus observed experimentally, reducing the number of possible configurations. Our results show that spheroidal, compact clusters are more energetically favourable and more abundant. [ABSTRACT FROM AUTHOR]

Whilst atom probe tomography (APT) is a powerful technique with the capacity to gather information containing hundreds of millions of atoms from a single specimen, the ability to effectively use this information creates significant challenges. The main technological bottleneck lies in handling the extremely large amounts of data on spatial–chemical correlations, as well as developing new quantitative computational foundations for image reconstruction that target critical and transformative problems in materials science. The power to explore materials at the atomic scale with the extraordinary level of sensitivity of detection offered by atom probe tomography has not been not fully harnessed due to the challenges of dealing with missing, sparse and often noisy data. Hence there is a profound need to couple the analytical tools to deal with the data challenges with the experimental issues associated with this instrument. In this paper we provide a summary of some key issues associated with the challenges, and solutions to extract or “mine” fundamental materials science information from that data. [ABSTRACT FROM AUTHOR]

Abstract: Progress in the reconstruction for atom probe tomography has been limited since the first implementation of the protocol proposed by Bas et al. in 1995. This approach and those subsequently developed assume that the geometric parameters used to build the three-dimensional atom map are constant over the course of an analysis. Here, we test this assumption within the analyses of low-alloyed materials. By building upon methods recently proposed to measure the tomographic reconstruction parameters, we demonstrate that this assumption can introduce significant limitations in the accuracy of the analysis. Moreover, we propose a strategy to alleviate this problem through the implementation of a new reconstruction algorithm that dynamically accommodates variations in the tomographic reconstruction parameters. [Copyright &y& Elsevier]

[Display omitted] • In-situ cryo-condensation coating technique on needle-shaped specimen and frozen hydrated cells. • Controllable surface morphologies on the needle tip including nanoscale column structures and continuous frozen shell. • Platinum-rich conductive layer on frozen hydrated bacterial cells to facilitate sectioning and imaging. We report application of nanoscale in-situ cryo-condensation coating technique on needle-shaped specimens and frozen hydrated cells. By using a cryogenic focused ion beam/ scanning electron microscopy (cryo-FIB/SEM) instrument, phase transformation of the metal–organic precursor gas has been demonstrated to occur at the cryogenically cooled metal tip of 50 nm in radius, and the properties of the deposited layer can be tuned by the control parameters. Revealed surface morphologies on the needle tip include nanoscale columns using glancing angle deposition (GLAD). With deposition performed at multiple orientations, a continuous frozen shell as thin as 40 nm can be formed. The physical mechanisms of curing by ion beam/electron beam irradiation have been further investigated with characterization tools including transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS), and the results confirm the feasibility of constructing a platinum-rich conductive layer. The proposed approach is also demonstrated by depositing a thin conductive layer on frozen hydrated bacterial cells to facilitate sectioning and high-resolution electron imaging. The proposed approach opens a novel route to nanofabrication on tip geometry as well as site-specific conductive protection to facilitate nanocharacterisation. [ABSTRACT FROM AUTHOR]

• Atom probe tomography imaging of liquid specimens has been achieved by encapsulating the target solution on the pre-sharpened tungsten tip with graphene, followed by direct freezing at the cryogenic stage inside the instrument. • High-throughput APT imaging of liquid specimens has been demonstrated for the first time by applying the proposed graphene-encapsulation method to silicon micro-tip array. Target solution can be encapsulated on multiple pre-sharpened micro-tips simultaneously, and individually analysed by APT. • Liquid specimens, including pure water and solution containing ferritins and heavy water, have been proved feasible for laser-pulsed APT by the application of graphene encapsulation method. A new method for imaging liquid specimens with atom probe tomography (APT) is proposed by introducing graphene encapsulation. By tuning the encapsulation speed and the number of encapsulations, controllable volumes of liquid can be encapsulated on a pre-sharpened specimen tip, with the end radius less than 75 nm to allow field ionization and evaporation. Encapsulation of liquid has been confirmed by using various characterization techniques, including electron microscopy and stimulated emission depletion microscopy. The graphene-encapsulated liquid specimen was then directly frozen at the cryogenic stage inside the atom probe instrument, followed by APT imaging in laser-pulsed mode. Using water as a test example, water-related ions have been identified in the acquired mass spectrum, which are spatially correlated to a reconstructed three-dimensional volume of water on top of the base specimen tip, as clearly revealed in the chemical maps. In addition, the proposed method has also been shown to produce multiple liquid specimens simultaneously on a pre-sharpened silicon micro-tip array for high-throughput APT imaging of liquid specimens. It is expected that the proposed lift-out-free method for preparing APT specimens in their hydrated state will open a new avenue for obtaining insights into various materials at atomic resolution. Overview of the proposed method of preparing liquid specimens for atom probe tomography. (a) Schematic of encapsulating liquid on a pre-sharpened tip using graphene, with controlled encapsulation speed and number of encapsulations. (b) APT imaging of the graphene-encapsulated liquid specimen in laser-pulsed mode. (c) Acquired mass-to-charge-state ratio spectrum and the reconstructed 3D chemical map of the field-evaporated liquid (water) volume on base W tip with near-atomic spatial resolution. Image, graphical abstract [ABSTRACT FROM AUTHOR]