Arun Devaraj

De-vitrification of nanoscale phase-separated amorphous thin films in the immiscible copper–niobium system

Copper and niobium are mutually immiscible in the solid state and exhibit a large positive enthalpy of mixing in the liquid state. Using vapour quenching via magnetron co-sputter deposition, far-from equilibrium amorphous Cu–Nb films have been deposited which exhibit a nanoscale phase separation. Annealing these amorphous films at low temperatures (~200u2009°C) initiates crystallization via the nucleation and growth of primary nanocrystals of a face-centred cubic Cu-rich phase separated by the amorphous matrix. Interestingly, subsequent annealing at a higher temperature (>300u2009°C) leads to the polymorphic nucleation and growth of large spherulitic grains of a body-centred cubic Nb-rich phase within the retained amorphous matrix of the partially crystallized film. This sequential two-stage crystallization process has been investigated in detail by combining transmission electron microscopy [TEM] (including high-resolution TEM) and atom probe tomography studies. These results provide new insights into the crystallization behaviour of such unusual far-from equilibrium phase-separated metallic glasses in immiscible systems.

Reduced Magnetism in Core–Shell Magnetite@MOF Composites

The magnetic susceptibility of synthesized magnetite (Fe3O4) microspheres was found to decline after the growth of a metal-organic framework (MOF) shell on the magnetite core. Detailed structural analysis of the core-shell particles using scanning electron microscopy, transmission electron microscopy, atom probe tomography, and57Fe-Mössbauer spectroscopy suggests that the distribution of MOF precursors inside the magnetic core resulted in the oxidation of the iron oxide core.

Microstructure of Multistage Annealed Nanocrystalline SmCo2Fe2B Alloy with Enhanced Magnetic Properties

The microstructure and chemistry of SmCo2Fe2B melt-spun alloy after multistage annealing was investigated using high resolution transmission electron microscopy (HRTEM) and 3D atom probe tomography. The multistage annealing resulted in an increase in both the coercivity and magnetization. The presence of Sm(Co,Fe)4B (1:4:1) and Sm2(Co,Fe)17Bx (2:17:x) magnetic phases were confirmed using both techniques. Fe2B at a scale of ∼5u2009nm was found by HRTEM precipitating within the 1:4:1 phase after the second-stage annealing. Ordering within the 2:17:x phase was directly identified both by the presence of antiphase boundaries observed by TEM and the interconnected isocomposition surface network found in 3D atom probe results in addition to radial distribution function analysis. The variations in the local chemistry after the secondary annealing were considered pivotal in improving the magnetic properties.

Investigations of Omega Precipitation in Titanium Molybdenum Alloys by Coupling 3D Atom Probe Tomography and High Resolution (S)TEM

Titanium-base alloys are used in a number of critical components in aerospace and defense, biomedical, automotive, and a range of other industries. These alloys typically exhibit complex multi-phase microstructures spanning across a range of length scales and also involving a large number of alloying additions. The ω phase is commonly observed in many commercial β or nearβ titanium alloys on quenching from the solution treatment temperature in the single beta phase field [1]. These ω precipitates typically have an embrittling effect on the alloy and are therefore considered detrimental for its mechanical properties [2]. However, since ω precipitates are highly refined (nanometer scale) and homogeneously distributed, and due to the fact that they reject β-stabilizing elements, it is possible that they can act as heterogeneous nucleation sites for the precipitation of the equilibrium α phase. This leads to a homogeneous distribution of refined α precipitates that can substantially strengthen the alloy [1,3]. Therefore, the detailed investigation of ω precipitation in the beta matrix of titanium alloys is rather important.

Effects of cooling rate on the microstructure and solute partitioning in near eutectoid Ti–Cu alloys

The effect of cooling rate on eutectoid decomposition in a near eutectoid (Ti-5.5 at.% Cu) alloy has been investigated in a systematic manner by coupling scanning electron microscopy, transmission electron microscopy and atom probe tomography studies. Thus, the competition between nucleation and growth of proeutectoid α plates from pre-existing β grain boundaries, and eutectoid decomposition (αu2009+u2009Ti2Cu) via a pearlitic mechanism has been studied as a function of cooling rate, using a Jominy-end quenched sample that was cooled from the high-temperature single β phase. When the alloy was subjected to very fast cooling (160u2009K/s), proeutectoid α plates, supersaturated in Cu, are formed along with a highly refined lamellar eutectoid product between these α plates. In contrast, intermediate (9u2009K/s) and slow (2u2009K/s) cooling results in considerably coarser proeutectoid α plates as well as lamellar eutectoid products. With the decrease in the cooling rate, there was a substantial increase in the volume fraction of the lamellar eutectoid product and the composition of all decomposition products approached their equilibrium values. Also, the slowest cooled sample (2u2009K/s) exhibited substantially rougher and irregular interfaces between the proeutectoid α and the lamellar eutectoid product, which seems to promote the cooperative growth of lamellar αu2009+u2009Ti2Cu. Irrespective of the cooling rate, nucleation of the lamellar eutectoid (αu2009+u2009Ti2Cu) product appears to only occur at the interface between the proeutectoid α plates and the β matrix.

Theoretical Model for Volume Fraction of UC, 235U Enrichment, and Effective Density of Final U 10Mo Alloy

The purpose of this document is to provide a theoretical framework for (1) estimating uranium carbide (UC) volume fraction in a final alloy of uranium with 10 weight percent molybdenum (U-10Mo) as a function of final alloy carbon concentration, and (2) estimating effective 235U enrichment in the U-10Mo matrix after accounting for loss of 235U in forming UC. This report will also serve as a theoretical baseline for effective density of as-cast low-enriched U-10Mo alloy. Therefore, this report will serve as the baseline for quality control of final alloy carbon content

Detecting the Extent of Eutectoid Transformation in U-10Mo

During eutectoid transformation of U-10Mo alloy, uniform metastable γ UMo phase is expected to transform to a mixture of α-U and γ’-U2Mo phase. The presence of transformation products in final U-10Mo fuel, especially the α phase is considered detrimental for fuel irradiation performance, so it is critical to accurately evaluate the extent of transformation in the final U-10Mo alloy. This phase transformation can cause a volume change that induces a density change in final alloy. To understand this density and volume change, we developed a theoretical model to calculate the volume expansion and resultant density change of U-10Mo alloy as a function of the extent of eutectoid transformation. Based on the theoretically calculated density change for 0 to 100% transformation, we conclude that an experimental density measurement system will be challenging to employ to reliably detect and quantify the extent of transformation. Subsequently, to assess the ability of various methods to detect the transformation in U-10Mo, we annealed U-10Mo alloy samples at 500°C for various times to achieve in low, medium, and high extent of transformation. After the heat treatment at 500°C, the samples were metallographically polished and subjected to optical microscopy and x-ray diffraction (XRD) methods. Based on ourmorexa0» assessment, optical microscopy and image processing can be used to determine the transformed area fraction, which can then be correlated with the α phase volume fraction measured by XRD analysis. XRD analysis of U-10Mo aged at 500°C detected only α phase and no γ’ was detected. To further validate the XRD results, atom probe tomography (APT) was used to understand the composition of transformed regions in U-10Mo alloys aged at 500°C for 10 hours. Based on the APT results, the lamellar transformation product was found to comprise α phase with close to 0 at% Mo and γ phase with 28–32 at% Mo, and the Mo concentration was highest at the α/γ interface.«xa0less

Level Set Method for Tip Shape Evolution Simulation for Atom Probe Tomography

Tomography Jie Bao, Zhijie Xu, Robert Colby, Suntharampillai Thevuthasan, Arun Devaraj 1 Nuclear Science Division, Pacific Northwest National Laboratory, Richland, WA, USA; 2 Computational Mathematics Division, Pacific Northwest National Laboratory, Richland, WA, USA; 3 Environmental Molecular sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, USA; 4 Qatar Energy and Environmental Research Institute, Qatar, UAE

Three-Dimensional Nanoscale Mapping of State-of-the-Art Field-Effect Transistors (FinFETs)

The semiconductor industry has seen tremendous progress over the last few decades with continuous reduction in transistor size to improve device performance. Miniaturization of devices has led to changes in the dopants and dielectric layers incorporated. As the gradual shift from two-dimensional metal-oxide semiconductor field-effect transistor to three-dimensional (3D) field-effect transistors (finFETs) occurred, it has become imperative to understand compositional variability with nanoscale spatial resolution. Compositional changes can affect device performance primarily through fluctuations in threshold voltage and channel current density. Traditional techniques such as scanning electron microscope and focused ion beam no longer provide the required resolution to probe the physical structure and chemical composition of individual fins. Hence advanced multimodal characterization approaches are required to better understand electronic devices. Herein, we report the study of 14 nm commercial finFETs using atom probe tomography (APT) and scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy (STEM-EDS). Complimentary compositional maps were obtained using both techniques with analysis of the gate dielectrics and silicon fin. APT additionally provided 3D information and allowed analysis of the distribution of low atomic number dopant elements (e.g., boron), which are elusive when using STEM-EDS.

Atomic Elemental Tomography of Heavy Element Biomaterials

Natural small “tools” of arthropods such as jaw teeth, leg claws or stings are particularly fractureresistant. Unlike calcified tissues such as bone or teeth of vertebrate, these small functional organs are not biomineralized but instead are predominantly organic with some heavy elements (e.g. Zn, Mn and Cu) [1] However, so far the distribution and binding sites of these heavy elements in these class of biomaterials are unknown. Laser-assisted Atom Probe Tomography (APT) is developing in to an efficient technique to visualize the elemental distribution in biomaterials at near atomic scale spatial resolution [2-3]. Therefor an attempt was made to utilize laser-assisted APT to analyze the elemental distribution in such heavy element biomaterials.