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DOE OSTI2024

Benchmarking of X‐Ray Fluorescence Microscopy with Ion Beam Implanted Samples Showing Detection Sensitivity of Hundreds of Atoms

Abstract Single impurities in insulators are now often used for quantum sensors and single photon sources, while nanoscale semiconductor doping features are being constructed for electrical contacts in quantum technology devices, implying that new methods for sensitive, non‐destructive imaging of single‐ or few‐atom structures are needed. X‐ray fluorescence (XRF) can provide nanoscale imaging with chemical specificity, and features comprising as few as 100 000 atoms have been detected without any need for specialized or destructive sample preparation. Presently, the ultimate limits of sensitivity of XRF are unknown – here, gallium dopants in silicon are investigated using a high brilliance, synchrotron source collimated to a small spot. It is demonstrated that with a single‐pixel integration time of 1 s, the sensitivity is sufficient to identify a single isolated feature of only 3000 Ga impurities (a mass of just 350 zg). With increased integration (25 s), 650 impurities can be detected. The results are quantified using a calibration sample consisting of precisely controlled numbers of implanted atoms in nanometer‐sized structures. The results show that such features can now be mapped quantitatively when calibration samples are used, and suggest that, in the near future, planned upgrades to XRF facilities might achieve single‐atom sensitivity.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Evaporation of Water Droplets Moving Through High-Temperature Gases

With the use of high-speed recording and diagnostic facilities, an experimental study has been made of the evaporation of droplets (of characteristic size R{sub m} ≈ 0.05–0.035 mm) of atomized flow of water-based suspensions with typical soil impurities (silt and clay) moving in a high-temperature (about 1100 K) gaseous medium (with the example of acetone combustion products). The relative mass concentration of soil components in the suspension was varied over the range of γ = 0–1%. A strong influence of the above impurities on the main characteristic of evaporation — the relative change in the droplet radius ΔR — has been established. The influence of the initial temperature (varied over the range of T{sub w} = 278–320 K) of the atomized suspension on the evaporation rate of the latter has been determined. It has been shown that the values of integral characteristics of the process of evaporation of suspensions with soil impurities can be much (2–3 times) higher than for water without these components.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

A Model Study of Substrate Effect on the Neutron-Scattering Spectra of Ferromagnetic Ordered Graphene

Graphene as a possible new magnetic material has stimulated research interest for application in spintronic devices. Pristine graphene does not show magnetism due to equivalence of the two sub-lattices of carbon atoms. It is predicted that impurity effects, substrate-induced gap, and defects, are expected to produce in-equivalence in two carbon sub-lattices leading to magnetism. The spins on the same sub-lattices are found to exhibit ferromagnetic order and spins of different sub-lattices are found to exhibit anti-ferromagnetic order. We consider here impurity and substrate effects as the cause of generation of magnetism in graphene. We report here a microscopic tight-binding study of frequency-dependent neutron scattering spectra for ferromagnetic ordering in the graphene systems. The tight-binding Hamiltonian consists of electron hoppings upto third nearest neighbors and substrate and impurity effects in the presence of Coulomb interaction of electrons separately at two in-equivalent A and B sub-lattices of graphene. We calculate the two-particle electron Green’s functions by using Zubarev’s Green’s function technique. The frequency-dependent scattering intensity of the system is computed numerically. The spectra displays a sharp peak at the neutron momentum transfer energy at low energies and another higher-energy peak appearing at substrate-induced gap.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

First-Principle Study on the Origin of Ferromagnetism in Non-magnetic Halide Perovskite CsCdM{sub 3} (M = Cl and Br) Doped with B, C, and N

Based on the density functional theory (DFT), we elucidate the origin of magnetization in non-magnetic cubic halide perovskite CsCdM{sub 3} (M = Cl and Br) induced by substitution of non-magnetic 2p-impurities (B, C, and N) substitution. The calculations were done within the generalized gradient approximation (GGA) and GGA plus-modified Becke and Johnson (mBJ-GGA) as the exchange correlation. The results reveal that half-metallic ferromagnetism can be obtained for C- and N-dopings with the integer magnetic moment of 3.00 and 2.00 µ{sub B} per cell. However, B substitution does not induce magnetism in both CsCdCl{sub 3} and CsCdBr{sub 3} systems. The localized magnetic moments substantially come from impurity atoms. The origin of ferromagnetism can be attributed to the p - p hybridization between 2p-impurities and its surrounding halide atoms. Our results show that doped perovskites could provide a new promising class of materials for future spintronics applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Ex Situ Spark Plasma Sintering of Short Powder-in-Tube MgB{sub 2} Tapes with Open and Closed Ends

Short powder-in-tube tapes of MgB{sub 2} in the Fe sheath were fabricated by ex situ route from a commercial powder containing some free Mg and MgO impurity phases. The final heat treatment was performed by spark plasma sintering (SPS). Tapes were with open (OT) or closed (CT) endings. Closed endings were made by folding and pressing. The MgB{sub 2} core of the OT sample has shown a higher low-field critical current density, a higher maximum pinning force, a slightly higher disorder, smaller average MgB{sub 2} crystallite size, a weak contact between Fe and MgB{sub 2} core, and more macro-flux jumps. The upper and irreversibility fields were similar for OT and CT samples. In the center of the MgB{sub 2} cores, the detected impurity phase is MgO, while at the interface with Fe, MgB{sub 4} also occurs. Impurity phases found at interface, MgO and MgB{sub 4}, are present in the center of the bulk SPSed samples. Reactions and pinning-force-related parameters are discussed with respect to Mg behavior influenced by condition of endings. It is inferred that the presence of free Mg in the raw MgB{sub 2} powder has an important contribution to observed differences, and its removal or control is recommended.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

The LLNL rabbit: determination of trace element levels in polyethylene

Rabbit facilities are systems that pneumatically transport a sample carrier (known as a rabbit) to and from a radiation source. However, trace impurities in the polyethylene (PE) rabbit may interfere with measurements of short-lived isotopes. Activated impurities with short half-lives as 28 Al interfere with the fission product γ-ray, therefore the rabbit cannot be measured immediately. Neutron activation analysis was performed on various PE samples obtained from different manufacturers and the highest quality PE was used to fabricate a high-purity PE rabbit. Here, the impurities identified in the PE study were 27 Al, 48 Ca, 37 Cl, 50 Cr, 65 Cu, 127 I, 26 Mg, 55 Mn, and 30 Si.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2018

Study of Morphology and Magnesium Purity, Formed by Vapor Phase Through Silicothermic Reduction

This article describes the influence of temperature profile on the morphology and impurity distributions of magnesium vapor condensation during silicothermic reduction of calcined dolomite. The formation of magnesium crystals was comprehensively analyzed by optical microscopy, scanning electron microscopy (SEM), and inductively coupled plasma (ICP). The results showed that the temperature changed the morphology and purity of condensation products in the condenser. When the temperature of the condenser zone was lower than 250 °C, the magnesium vapor condensation was fine and noncompacted. The crystal growth of magnesium occurred in the range of 250 °C and 380 °C. It was found that crystal magnesium became coarser and denser at higher temperatures. Based on the analysis of crystallized magnesium, the impurity distributions decreased at temperatures higher than those of the condenser. Furthermore, this indicates that the impurity contents with less than 0.04 pct were distributed randomly through the condenser.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Ultra-Shallow Doping B, Mg, Ni, Cu, Mn, Cr and Fe into SiC with Very High Surface Concentrations Based on Plasma Stimulated Room-Temperature Diffusion

Very recently, we reported a novel doping method called plasma doping without any external bias (PDWOEB) for the introduction of some impurities into Si and GaN at room temperature (RT). In this work, the RT doping of some impurities, including B, Mg, Ni, Cu, Mn, Cr and Fe, into SiC with ultra-shallow depths of tens of nanometer and very high surface concentrations, approaching or exceeding 1E20/cm{sup 3}, by using PDWOEB is reported. It has been found for the first time that the doping depths and surface concentrations of these impurities doped into SiC by the PDWOEB increase drastically with increasing doping time and the ferromagnetism of SiC due to Ni doping is demonstrated. Moreover, the approximate diffusivities of B, Mg, Ni, Cu, Mn, Cr and Fe in SiC at RT under plasma stimulation are obtained. The physical mechanism of PDWOEB is further discussed, and some unclear viewpoints are clarified.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A thermodynamic perspective on electrode poisoning in solid oxide fuel cells

A critical challenge to the commercialization of clean and high-efficiency solid oxide fuel cell (SOFC) technology is the insufficient stack lifespan caused by a variety of degradation mechanisms, which are associated with cell components and chemical feedstocks. Cell components related degradation refers to thermal/chemical/electrochemical deterioration of cell materials under operating conditions, whereas the latter regards impurities in feedstocks of oxidant (air) and reductant (fuel). This article provides a thermodynamic perspective on the understanding of the impurities-induced degradation mechanisms in SOFCs. The discussion focuses on using thermodynamic analysis to elucidate poisoning mechanisms in cathodes by impurity species such as Cr, CO 2 , H 2 O, and SO 2 and in the anode by species such as S (or H 2 S), SiO 2 , and P 2 (or PH 3 ). The author hopes the presented fundamental insights can provide a theoretical foundation for searching for better technical solutions to address the critical degradation challenges.

25 ENERGY STORAGE↗
DOE OSTI2019

Hundness versus Mottness in a three-band Hubbard–Hund model: On the origin of strong correlations in Hund metals☆

Hund metals are multi-orbital systems with moderate Coulomb interaction, U, among charges and sizeable Hund’s rule coupling, J(<U), that aligns the spins in different orbitals. They show strong correlation effects, like very low Fermi-liquid coherence scales and intriguing incoherent transport regimes, resulting in bad metallic behavior. But to what extent are these strong correlations governed by Mottness, i.e. the blocking of charge fluctuations close to a Mott insulator transition (MIT) induced by U, or by Hundness, a new route towards strong correlations induced by J? To answer this question, we study the full phase diagram of a degenerate three-band Hubbard–Hund model on a Bethe lattice at zero temperature using single-site dynamical mean-field theory and the numerical renormalization group as efficient real-frequency multi-band impurity solver. Hund metal behavior occurs in this minimal model for a filling close to n{sub d}=2, moderate U and sizeable J, the “Hund-metal regime”. In particular, strong correlations manifest themselves there by an unusually low quasiparticle weight. Generalizing previous results on this model, we show that “spin–orbital separation” (SOS) is a generic Hund’s-coupling-induced feature in the whole metallic regime of the phase diagram for 1<n{sub d}<3 and sizeable J. There orbital screening always occurs at much higher energies than spin screening below which Fermi-liquid behavior sets in. The low quasiparticle weight can then be directly explained in terms of the Hund’s-coupling-reduced Fermi-liquid scale. We carefully analyze the effect of J (Hundness), and the effect of the MIT at n{sub d}=2 and n{sub d}=3 (Mottness) on the energy scales and the nature of SOS. In the Hund-metal regime, far from any MIT, Hundness is shown to be the key player to induce strong correlations by constraining the spin rather than the charge dynamics. There, physical properties are governed by a broad incoherent energy regime of SOS where intriguing Hund metal physics occurs: large, almost unscreened spins are coupled to screened orbital degrees of freedom. With increasing proximity to an MIT correlations are further enhanced and the Fermi-liquid scale is further reduced. However, in the Hund-metal regime, this effect of Mottness is minor. In contrast, very close to the MIT at n{sub d}=2, the incoherent spin–orbital separation regime is strongly downscaled and becomes negligibly small, whereas Mottness – the localization of charges – becomes dominant in inducing strong correlations. Close to the MIT at n{sub d}=3, the SOS regime widens up because the orbital degrees of freedom get blocked by the formation of an S=(3/2) impurity spin, but its nature changes: the orbital and spin dynamics get decoupled. Our results confirm Hundness as a distinct mechanism towards strong correlations in the normal state of Hund metals, leading to various interesting implications for the nature of electronic transport.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Pozzolanic reactivity of a calcined interstratified illite/smectite (70/30) clay

Calcined clays can be potential supplementary cementitious materials if effects of heat-treatment on their structure and reactivity are understood. This work reports structural characterization of an interstratified illite/smectite clay, including a quartz impurity, upon heating using {sup 27}Al and {sup 29}Si MAS NMR spectroscopy and ICP-OES analysis. During dehydroxylation (600–900 °C) the Q{sup 3}-type SiO{sub 4} sites become disordered and octahedral AlO{sub 6} sites transform into tetrahedral sites, resulting in an amorphous material with substantial pozzolanic properties, as demonstrated by reactivity tests and hydration studies of a Portland cement–calcined clay blend. At higher temperatures (above 950 °C), inert Q{sup 4}-type phases crystallize which radically reduce the reactivity. At optimum calcination temperature (900 °C), the amorphous material contains highly dissolvable elemental species as seen from complementary ICP-OES analysis. The quartz impurity exhibits a unique variation in {sup 29}Si spin–lattice relaxation times upon heat-treatment which is ascribed to changes in the concentration of impurity ions in quartz.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Through space and through bridge channels of charge transfer at p-n nano-junctions: A DFT study

Details of charge density distribution at p-n nano interface are analyzed with density functional theory techniques using model system of dimers of doped silicon quantum dots interacting through bond and through space. Spatial distributions of transition densities between the ground and excited states suggest the character of essential electronic excitations, which have a Fӧrster, bound, unbound, or charge transfer character. A redistribution of electronic density from n-impurities to p-impurities results in a ground state polarization and creates an offset of energies of the bands localized on p-doped quantum dot and the bands localized on n-doped quantum dot. In conclusion, although impurities contribute very few orbitals to the total density, a ground state charge redistribution and polarization are both responsible for the presence of a large number of charge transfer excitations involving solely silicon orbitals.

intrinsic silicon↗
DOE OSTI2024

Impacts of point defects on shallow doping in cubic boron arsenide: A first principles study

Cubic boron arsenide (BAs) stands out as a promising material for advanced electronics, thanks to its exceptional thermal conductivity and ambipolar mobility. However, effective control of p- and n-type doping in BAs poses a significant challenge, mostly as a result of the influence of defects. In the present study, we employed density functional theory (DFT) to explore the impacts of the common point defects and impurities on p-type doping of Be B and Si As , and on n-type doping of Si B and Se As . We found that the most favorable point defects formed by C, O, and Si are C As , O B O As , Si As , C As Si B , and O B Si As , which have formation energies of less than 1.5 eV. While the O impurity detrimentally affects both p- and n-type dopings, C and Si impurities are harmful for n-type dopings, making n-type doping a potential challenge. Interestingly, the antisite defect pair A s B B As benefits both p- and n-type doping. Finally, the doping limitation analysis presented in this study can potentially pave the way for strategic development in the area of BAs-based electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Unraveling the nature of sulfide ions in hydrometallurgical recycling of NCM622 cathode material

The use of lithium-ion batteries (LIBs) has increased dramatically since its initial inception in the late 20th century. Such a surge in the LIB market and industry has resulted in a huge demand for mineral resources. Besides, the large scale of production will lead to massive amounts of waste batteries in the end. As such, recycling is seen as an end-of-pipe process to resolve sustainability and environmental concerns. The hydrometallurgical recycling is considered to be the most prominent method to recover cathode materials from spent LIBs owing to its high leaching efficiency and low energy costs. A series of procedures including pretreatment of the spent LIBs, acid leaching of the black mass, chemical co-precipitation of the hydroxide precursor, and sintering of the cathode active material need to be operated precisely. In this aspect, the impurities introduced during the process could pose a serious threat to the reaction stability as well as recycling consistency. Here, the impact of sulfide ions on recovered LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) cathode material with the method of hydrometallurgy is first investigated in detail. This study shows that hydrometallurgical process is not obviously influenced by sulfide impurity. No signs of secondary phase or impurity inclusion are spotted in synthesized cathodes. Under 5 at % sulfide concentration conditions, the obtained NCM622 cathode exhibits a capacity of 159.4 mAh/g after 100 cycles at 1/3C, which is at the same level as virgin benchmark. The difference in rate performance between cathodes with and without additional sulfide is less than 2 % or even smaller. In short, the results indicate a neutral status of sulfide ions in hydrometallurgical recycling.

25 ENERGY STORAGE↗
DOE OSTI2011

Characterization and photocatalytic activity of Fe- and N-co-deposited TiO{sub 2} and first-principles study for electronic structure

Titanium dioxide (TiO{sub 2}), co-deposited with Fe and N, is first implanted with Fe by a metal plasma ion implantation (MPII) process and then annealed in N{sub 2} atmosphere at a temperature regime of 400-600 deg. C. First-principle calculations show that the (Fe, N) co-deposited TiO{sub 2} films produced additional band gap levels at the bottom of the conduction band (CB) and on the top of the valence band (VB). The (Fe, N) co-deposited TiO{sub 2} films were effective in both prohibiting electron-hole recombination and generating additional Fe-O and N-Ti-O impurity levels for the TiO{sub 2} band gap. The (Fe, N) co-deposited TiO{sub 2} has a narrower band gap of 1.97 eV than Fe-implanted TiO{sub 2} (3.14 eV) and N-doped TiO{sub 2} (2.16 eV). A significant reduction of TiO{sub 2} band gap energy from 3.22 to 1.97 eV was achieved, which resulted in the extension of photocatalytic activity of TiO{sub 2} from UV to Vis regime. The photocatalytic activity and removal rate were approximately two-fold higher than that of the Fe-implanted TiO{sub 2} under visible light irradiation. - Graphical abstract: The electronic properties of (Fe, N) co-deposited TiO{sub 2} films determined by theoretical calculations is graphically shown; Fe and N preferentially substitute the Ti and O site, to form impurity level. Highlights: > The MPII produces a simple and low cost process for the fabrication of visible light photocatalysts. > Both theoretical and experimental approaches are used to discuss the relationship between band structure and photocatalysis. > The Fe and N preferentially substitute the Ti and O site, which generate additional Fe-O and N-Ti-O impurity levels for the TiO{sub 2} band gap. > A significant reduction of TiO{sub 2} band gap energy from 3.22 to 1.97 eV was achieved.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Doping in controlling the type of conductivity in bulk and nanostructured thermoelectric materials

Doping of materials for thermoelectric applications is widely used nowadays to control the type of conductivity. We report the results of ab-initio calculations aimed at developing the consistent scheme for determining the role of impurities that may change the type of conductivity in two attractive thermoelectric classes of materials. It is demonstrated that alloying of TiNiSn with Cu makes the material of n-type, and alloying with Fe leads to p-type conductivity. Similar calculations for PbTe with small amount of Na substituting for Pb leads to p-type conductivity, while Cl substituting for Te makes PbTe an n-type material. It is shown also that for nano-grained materials the n-type conductivity should be observed. The effect of impurities segregating to the grain boundaries in nano-structured PbTe is also discussed. - Highlights: • Bulk and nano-grained TE materials were analyzed by DFT. • The electronic effects on both PbTe and TiNiSn were demonstrated. • The role of impurities on the conductivity type was analyzed. • Interfacial states in nano-grained PbTe affect the conductivity type.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Atom probe study of grain boundary segregation in technically pure molybdenum

Molybdenum, a metal with excellent physical, chemical and high-temperature properties, is an interesting material for applications in lighting-technology, high performance electronics, high temperature furnace construction and coating technology. However, its applicability as a structural material is limited because of the poor oxidation resistance at high temperatures and a brittle-to-ductile transition around room temperature, which is influenced by the grain size and the content of interstitial impurities at the grain boundaries. Due to the progress of the powder metallurgical production during the last decades, the amount of impurities in the current quality of molybdenum has become so small that surface sensitive techniques are not applicable anymore. Therefore, the atom probe, which allows the detection of small amounts of impurities as well as their location, seems to be a more suitable technique. However, a site-specific specimen preparation procedure for grain boundaries in refractory metals with a dual focused ion beam/scanning electron microscope is still required. The present investigation describes the development and successful application of such a site-specific preparation technique for grain boundaries in molybdenum, which is significantly improved by a combination with transmission electron microscopy. This complimentary technique helps to improve the visibility of grain boundaries during the last preparation steps and to evidence the presence of grain and subgrain boundaries without segregants in atom probe specimens. Furthermore, in industrially processed and recrystallized molybdenum sheets grain boundary segregation of oxygen, nitrogen and potassium is successfully detected close to segregated regions which are believed to be former sinter pores. - Highlights: • First study of grain boundary segregation in molybdenum by atom probe • Site-specific preparation technique by FIB and TEM successfully developed • Grain boundary segregation of oxygen, nitrogen and potassium found • Segregation in former sinter-pores detected • Presence of grain boundaries without segregation evidenced.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Characterization of grain-boundary phases in Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12} solid electrolytes

Two types of Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12} (LLZ) pellets were prepared containing Al and Si impurities, and their grain boundaries characterized using scanning electron microscopy (SEM) with energy-dispersed X-ray (EDX) elemental mapping, transmission electron microscopy (TEM), selected-area electron diffraction (SAED), electron energy-loss spectroscopy (EELS), and high-resolution transmission electron microscopy (HRTEM). In the LLZ pellets containing a small amount of both Al and Si, the total conductivity and density were found to be greater than that of LLZ containing Al alone. Using EDX and TEM, the Al and Si were confirmed to accumulate predominantly at grain-boundary regions. EELS and SAED were used to determine the presence of crystallites of LiAl{sub 5}O{sub 8} and LiAlSiO{sub 4} in the Al-only and Si and Al containing specimens, respectively. HRTEM observations clarified that in the case of LiAlSiO{sub 4}, nano-sized particles exist within an amorphous phase matrix, with a microstructure similar to that in a glass-ceramic. The presence of grain-boundary phases is shown to greatly affect the grain boundary resistance, in the case of the LiAlSiO4 glass-ceramic-type phase resulting in a noticeable improvement of the total conductivity. - Highlights: • Total conductivity of LLZ improved by inclusion of Al and Si impurities • Presence of the impurities at grain boundaries detected using SEM and TEM • Structure of grain-boundary phases identified using SAED, EELS, and HRTEM • Improved conductivity correlated with formation of LiAlSiO{sub 4} in grain-boundary phase.

36 MATERIALS SCIENCE↗