Carbon-supported nanoparticles have been used widely as efficient catalysts due to their enhanced surface-to-volume ratio. To investigate their structure–property relationships, acquiring 3D elemental distribution is required. Here, carbon-supported Pt, PtMn alloy, and ordered Pt3Mn nanoparticles are synthesized and analyzed with atom probe tomography as model systems. A significant difference of Mn distribution after the heat-treatment was found. Finally, the field evaporation behavior of the carbon support was discussed and each acquired reconstruction was compared with computational results from an evaporation simulation. This paper provides a guideline for studies using atom probe tomography on the heterogeneous carbon-supported nanoparticle system that leads to insights toward a wide variety of applications.

Atomic mapping of nanomaterials, in particular nanoparticles, using atom probe tomography (APT) is of great interest, as their properties strongly depend on shape, size, and composition. However, APT analyses of nanoparticles are extremely challenging, and there is an urgent need for developing robust and universally applicable sample preparation methods. Herein, we explored a method based on pulse electrodeposition to embed Ag nanoparticles in a Ni matrix and prepare APT specimens from the resulting composite film. By systematically varying the duty cycle during pulse electrodeposition, the dispersion and number density of the nanoparticles within the matrix was significantly enhanced as compared to DC electrodeposition. Several Ag nanoparticles were analyzed with APT from such samples. Shape distortions and biased compositions were observed for the Ag nanoparticles after applying a standard data reconstruction protocol. Numerical simulations of the field evaporation process showed that such artifacts were caused by a difference in the evaporation field of Ni and Ag and a local magnification effect. We expect such detrimental effects to be mitigated by a careful selection of the matrix material, matching the evaporation field of the nanoparticles. Furthermore, we anticipate that the method presented herein can be extended to a wider range of nanomaterials.

We report on comparative atom probe tomography investigations of γ/γ′-forming Co–12Ti–4Mo–Cr alloys. Moderate additions of Cr (2 and 4 at%) reduced the γ/γ′ lattice misfit and increased the γ′ volume fraction of a Co–12Ti–4Mo alloy significantly. These microstructural changes were accompanied by changes in the elemental partitioning between γ and γ′ and site-occupancy in γ′. Spatial distribution maps revealed that Mo occupied both Co and Ti sub-lattice sites in γ′. In agreement with the experimental data, thermodynamic calculations predicted a stronger tendency for Mo to occupy the Co-sites than for Cr and an increase in Cr fraction on the Ti-sites with increasing Cr content.

We propose a new method for preparing atom probe tomography specimens from nanoparticles using a fusible bismuth–indium–tin alloy as an embedding medium. Iron nanoparticles synthesized by the sodium borohydride reduction method were chosen as a model system. The as-synthesized iron nanoparticles were embedded within the fusible alloy using focused ion beam milling and ion-milled to needle-shaped atom probe specimens under cryogenic conditions. An atom probe analysis revealed boron atoms in a detected iron nanoparticle, indicating that boron from the sodium borohydride reductant was incorporated into the nanoparticle during its synthesis.

Cemented tungsten carbide has been analyzed using laser-pulsed atom probe tomography (APT). The influence of experimental parameters, including laser pulse energy, pulse repetition rate, and specimen base temperature, on the acquired data were evaluated from different aspects, such as mass spectrum, chemical composition, noise-to-signal ratio, and multiple events. Within all the applied analysis conditions, only 1 MHz pulse repetition rate led to a strong detector saturation effect, resulting in a largely biased chemical composition. A comparative study of the laser energy settings showed that an ~12 times higher energy was required for the less focused green laser of the LEAPTM 3000X HR system to achieve a similar evaporation field as the finer spot ultraviolet laser of the LEAPTM 5000 XS system.

Atom-probe tomography is a materials characterization method ideally suited for the investigation of clustering and precipitation phenomena. To distinguish the clusters from the surrounding matrix, the maximum separation algorithm is widely employed. However, the results of the cluster analysis strongly depend on the parameters used in the algorithm and hence, a wrong choice of parameters leads to erroneous results, e.g., for the cluster number density, concentration, and size. Here, a new method to determine the optimum value of the parameter dmax is proposed, which relies only on information contained in the measured atom-probe data set. Atom-probe simulations are employed to verify the method and to determine the sensitivity of the maximum separation algorithm to other input parameters. In addition, simulations are used to assess the accuracy of cluster analysis in the presence of trajectory aberrations caused by the local magnification effect. In the case of Cu-rich precipitates (Cu concentration 40–60 at% and radius 0.25–1.0 nm) in a bcc Fe–Si–Cu matrix, it is shown that the error in concentration is below 10 at% and the error in radius is <0.15 nm for all simulated conditions, provided that the correct value for dmax, as determined with the newly proposed method, is employed.

Materials produced by selective laser melting (SLM) experience a thermal history that is markedly different from that encountered by conventionally produced materials. In particular, a very high cooling rate from the melt is combined with cyclical reheating upon deposition of subsequent layers. Using atom-probe tomography (APT), we investigated how this nonconventional thermal history influences the phase-transformation behavior of maraging steels (Fe–18Ni–9Co–3.4Mo–1.2Ti) produced by SLM. We found that despite the “intrinsic heat treatment” and the known propensity of maraging steels for rapid clustering and precipitation, the material does not show any sign of phase transformation in the as-produced state. Upon aging, three different types of precipitates, namely (Fe,Ni,Co)3(Ti,Mo), (Fe,Ni,Co)3(Mo,Ti), and (Fe,Ni,Co)7Mo6 (µ phase), were observed as well as martensite-to-austenite reversion around regions of the retained austenite. The concentration of the newly formed phases as quantified by APT closely matches thermodynamic equilibrium calculations.

Compound semiconductors belong to the most important materials for optoelectronic applications. Many of them exhibit favorable optical properties, such as a direct energy band gap (in contrast to silicon) and high-absorption coefficients over a wide spectral range. Moreover, varying the composition of the compound or substituting some of its elements often allows for controlled band gap engineering and optimization for specific applications. Because many compound semiconductors enable efficient conversion of light into electricity and vice versa, they are commonly used materials for optoelectronic devices.

We review microstructures and properties of metal matrix composites produced by severe plastic deformation of multiphase alloys. Typical processings are wire drawing, ball milling, roll bonding, equal-channel angular extrusion, and high-pressure torsion of multiphase materials. Similar phenomena occur between solids in frictional contact such as in tribology, friction stir welding, and explosive joining. The resulting compounds are characterized by very high interface and dislocation density, chemical mixing, and atomic-scale structural transitions at heterointerfaces. Upon straining, the phases form into nanoscaled filaments. This leads to enormous strengthening combined with good ductility, as in damascene steels or pearlitic wires, which are among the strongest nanostructured bulk materials available today (tensile strength above 6 GPa). Similar materials are Cu-Nb and Cu-Ag composites, which also have good electrical conductivity that qualifies them for use in high-field magnets. Beyond the engineering opportunities, there are also exciting fundamental questions. They relate to the nature of the complex dislocation, amorphization, and mechanical alloying mechanisms upon straining and their relationship to the enormous strength. Studying these mechanisms is enabled by mature atomic-scale characterization and simulation methods. A better understanding of the extreme strength in these materials also provides insight into modern alloy design based on complex solid solution phenomena.

Focused ion-beam milling has been applied to prepare needle-shaped atom probe tomography specimens from mechanically alloyed powders without the use of embedding media. The lift-out technique known from transmission electron microscopy specimen preparation was modified to cut micron-sized square cross-sectional blanks out of single powder particles. A sequence of rectangular cuts and annular milling showed the highest efficiency for sharpening the blanks to tips. First atom probe results on a Fe95Cu5 powder mechanically alloyed in a high-energy planetary ball mill for 20 h have been obtained. Concentration profiles taken from this powder sample showed that the Cu distribution is inhomogeneous on a nanoscale and that the mechanical alloying process has not been completed yet. In addition, small clusters of oxygen, stemming from the ball milling process, have been detected. Annular milling with 30 keV Ga ions and beam currents ≥50 pA was found to cause the formation of an amorphous surface layer, whereas no structural changes could be observed for beam currents ≤10 pA.