Radiation effects in bulk lithium- and aluminum-doped silicon
Co-60 gamma radiation and isochronal annealing temperature effects on minority carrier lifetime of Al and Li doped bulk silicon
Bass, R. F.↗
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Hole doping and electronic correlations in Cr substituted BaFe$_{2}$As$_{2}$
For a significant composition range, the suppression of the spin density wave transition temperature (T SDW ) in Cr- and Mn-substituted BaFe 2 As 2 (CrBFA and MnBFA, respectively) coincides as a function of Cr/Mn content, despite the distinct electronic effects of these substitutions. Additionally, for any Cr/Mn content superconductivity (SC) is absent and this topic is particularly less explored in the case of CrBFA. Here, in this work, we employ angle-resolved photoemission spectroscopy (ARPES) and combined density functional theory plus dynamical mean field theory (DFT+DMFT) to address the evolution of the Fermi surface (FS) and electronic correlations in CrBFA. Our findings reveal that incorporating Cr leads to an effective hole doping of the states near the FS, which is well described within the virtual crystal approximation (VCA). Moreover, analysis of the ARPES spectra of the bands with main d yz -orbital character reveals a fractional scaling of the imaginary part of self-energy as a function of the binding energy, a signature property of Hund's correlations. Our DFT+DMFT calculations support these experimental findings. We conclude that CrBFA is a correlated electron system for which the changes in the FS as a function of Cr are unrelated to the suppression of T SDW . In addition, we suggest that the absence of SC is primarily due to the competition between Cr local moments and the Fe-derived itinerant spin fluctuations.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Experimental Measurements of Soot and Soot Precursors of Sustainable Aviation Fuels
Sustainable Aviation Fuels (SAFs) are promising for decarbonizing the challenging-to-electrify aerospace sector and reducing yearly greenhouse gas emissions by thousands of tons. Developing predictive detailed chemical kinetic models for SAF (and traditional) fuel mixtures necessitates a robust experimental database to elucidate the intricate pyrolysis and oxidation chemistry of SAF fuel blend components. Two critical components of SAF surrogate mixtures are iso-dodecane isomers and trans-decalin. This report characterizes the structure of three slightly sooting, laminar, non-premixed, nitrogen-diluted Planar Mixing Layer Flames (PMLFs) fueled by either pure ethylene, ethylene doped with 1500ppm of either 2,2,4,6,6-pentamethyl-heptane or trans-decalin. The flames have the same stoichiometric mixture fraction and total mole fraction of fuels in the fuel stream (X F,F = X C2H4,F + X Dopant,F = 0.26), resulting in approximately the same maximum temperature (T max ≈ 1800 K) to highlight the effect of doping on soot and its gaseous precursors. The PMLF is unconfined and established between adjacent planar jets of the fuel and oxidizer streams surrounded by annular shielding nitrogen. The flow is stabilized by exhausting the hot buoyant flame products through a slot in a downstream plate onto which the cold flow impinges. Importantly, any horizontal cross-section of the PMLF has a self-similar thermochemical structure of a reactive boundary layer that grows at increasing Height Above the Burner (HAB). Therefore, the horizontal cross-sections of a PMLF can be modeled as a One-Dimensional Counterflow Flame (1D-CF) with very low strain rates which are unachievable in traditional CFs and yield a structure that is several millimeters thick. In brief, the PMLF is ideal for performing spatially resolved measurements with minimal effects of the sampling-induced perturbations, to develop and validate detailed chemical kinetic models on time scales of a few tens of milliseconds that are relevant in aviation applications. The horizontal profiles of C0-C18 gaseous species at HAB = 50 mm and soot volume fraction at 25 and 50 mm are measured using capillary sampling followed by GC-MS analyses and Laser Induced Emission Spectroscopy (LIES), respectively. Additionally, the Elastic Laser Light Scattering (E-LLS) coefficient is measured at HAB = 50 mm and 25 mm to determine the strain rates of the 1D-CFs equivalent to the characterized PMLF horizontal cross sections and the profile of the E-LLS equivalent diameter of soot. The comparison of the results in the base PMLF fueled only by ethylene with those in either doped PMLF in which 1500 ppm of ethylene are replaced with 2,2,4,6,6-pentamethyl-heptane or trans-decalin, reveals that the doping increases the mole fraction of several Polycyclic Aromatic Hydrocarbons (PAHs) at both HABs by a factor of approximately 2.5, and the soot volume fraction at both HABs by factors of ~1.5 for 2,2,4,6,6-pentamethyl-heptane and ~1.25 for trans-decalin doping, respectively. Conversely, doping causes a near doubling of the soot equivalent diameter only at HAB = 50 mm, without significant effects at 25 mm. The experimental results partially validate the tested state-of-the-art detailed chemical kinetic model and also point toward the further improvement of its predictive capabilities.
10 SYNTHETIC FUELS↗
Oxygen and carbon impurities and related defects in silicon
Oxygen and carbon are the predominant impurities in Czochralski-grown silicon. The incorporation of oxygen and carbon during crystal growth is reviewed and device effects are discussed. Methods for controlling oxygen and carbon incorporation during crystal growth are discussed and results supporting a segregation coefficient of k=0.5 for oxygen are presented. The nucleation and precipitation behavior of oxygen is complex. Temperature and doping level effects which add insight into the role of point defects in the nucleation process are highlighted. In general, precipitation is found to be retarded in N+ and P+ silicon. The types and quantities of defects resulting from the oxygen precipitates is of interest as they are technologically useful in the process called intrinsic gettering. A comparison is made between the available defect sites and the quantities of metallic impurities present in a typical wafer which need to be gettered. Finally, a discussion of the denuded-zone, intrinsic-gettered (DZ-IG) structure on device properties is presented.
Pearce, C. W.↗
Impurity-enhanced core valence luminescence via Zn-doping in cesium magnesium chlorides
Scintillators with faster timing capabilities are currently in high demand for use in radiation detection systems in the fields of nuclear and medical physics. The limited number of suitable materials that meet the performance criteria of next generation detection systems presents an opportunity for discovery of new fast scintillator materials. In this work, the effects of doping several ultrafast core-valence luminescent (CVL) scintillators with divalent Zn is explored. Three compounds are investigated – CsMgCl 3 , Cs 2 MgCl 4 , and Cs 3 MgCl 5 – and single crystals of each doped with 5 mol% Zn are grown via the Bridgman method. Additionally, mixing across the full range of concentrations (from 0 % to 100 % Zn) is explored in the Cs 2 Mg 1-x Zn x Cl 4 and Cs 3 Mg 1-x Zn x Cl 5 systems. For low concentrations of Zn, light yields of all three compounds are enhanced (by up to ~60 %) compared to the pure crystals, achieving what we believe to be the brightest known CVL, CsMgCl 3 :Zn 5 % (3400 ± 170 ph/MeV light yield). More importantly, Zn doping does not affect the ultrafast timing properties, with each composition maintaining a single-component decay time around 1–3 ns. A sub-100 ps coincidence time resolution (CTR) is also achieved with CsMgCl 3 :Zn 5 %. The results of this work reveal a new avenue towards obtaining brighter CVL materials, which could open up possibilities for more advanced ultrafast scintillators to be discovered moving forward.
36 MATERIALS SCIENCE↗
Manipulating high-temperature superconductivity by oxygen doping in Bi2Sr2CaCu2O8+δ thin flakes
Abstract Harnessing the fascinating properties of correlated oxides requires precise control of their carrier density. Compared to other methods, oxygen doping provides an effective and more direct way to tune the electronic properties of correlated oxides. Although several approaches, such as thermal annealing and oxygen migration, have been introduced to change the oxygen content, a continuous and reversible solution that can be integrated with modern electronic technology is much in demand. Here, we report a novel ionic field-effect transistor using solid Gd-doped CeO2 as the gate dielectric, which shows a remarkable carrier-density-tuning ability via electric-field-controlled oxygen concentration at room temperature. In Bi2Sr2CaCu2O8+δ (Bi-2212) thin flakes, we achieve a reversible superconductor–insulator transition by driving oxygen ions in and out of the samples with electric fields, and map out the phase diagram all the way from the insulating regime to the over-doped superconducting regime by continuously changing the oxygen doping level. Scaling analysis indicates that the reversible superconductor–insulator transition for the Bi-2212 thin flakes follows the theoretical description of a two-dimensional quantum phase transition. Our work provides a route for realizing electric-field control of phase transition in correlated oxides. Moreover, the configuration of this type of transistor makes heterostructure/interface engineering possible, thus having the potential to serve as the next-generation all-solid-state field-effect transistor.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
First principles based screen for identification of transparent conductors
We present methods for screening semiconductors as transparent conductors leading to a simple application dependent fitness function. We report a simple first principles based screen amenable to high throughput calculations for transparent conductors. These include the effects of doping on transparency, which can be important. In particular, doping leads to conduction accompanied by losses in transparency, both of which are materials dependent, but rarely considered in computational materials selection. We consider both the Drude contribution to optical conductivity, as well as new interband transitions that arise as a material is doped. This leads to a simple application dependent optical and electrical fitness function (OEF) that can be applied to semiconductors to identify materials that may be useful transparent conductors. The OEF goes beyond the frequently discussed criteria of suitable band gap and low effective mass. Finally, we illustrate this by application to a number of proposed p-type transparent conducting materials.
14 SOLAR ENERGY↗
Improved Superconducting Properties in Graphene-Doped MgB{sub 2} Prepared by Coating Method
The effects of graphene doping on the phase formation and superconductivity of MgB{sub 2} bulks synthesized with different process have been studied systemically. Considering the scattering structure of graphene, coating method was applied to enhance the uniformity of graphene doping. The graphene coated B addition was expected to improve the critical current density of MgB{sub 2} bulks. In our study, several experiments were performed to find out the suitable way for graphene doping. The coating method could enhance the critical current density of MgB{sub 2} from 1.9 × 10{sup 5} to 2.5 × 10{sup 5} A/cm{sup 2} at 20 K and 0 T, compared with that of the undoped sample. And the superconductivity of MgB{sub 2} prepared by coating method got obvious improvement at high field compared with that of pure graphene doping bulk. It can be concluded that the coating method could ensure the uniformity of graphene doping in MgB{sub 2} and refined the grain crystalline effectively.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Physi-sorption of H 2 on pure and boron-doped graphene monolayers: A dispersion-corrected DFT study
Carbon based materials are of interest as potential candidates for H 2 storage. Earlier work has been inconclusive on the effect of boron doping on the energy of H 2 binding. However, earlier work has been inconclusive on the definitive effect of boron doping on the energy of H 2 binding, i.e. isosteric heats of adsorption (Qst). In this work, we completed a systematic DFT study to evaluate this effect, and found that doping graphene with boron provides only minor enhancement in H 2 binding. More importantly, the presence of the electron deficient boron into a graphene ring introduces a defect, such as terminal hydrogen or distortion from planarity, which creates hydrogen adsorption sites with slightly increased Qst. The increase is from ~ 5 kJ/mol H 2 for the pure carbon matrix to ~6 - 7 kJ/mol for the boron doped system. The more strongly bond H 2 is located near the defect and shows little direct interaction with the boron. Most significant enhancement is found in systems where H 2 is confined between layers at a distance of about 7Å. In this case, the H 2 binding nearly doubles, to ~10 kJ/mol for both pure, undistorted graphene, and the 2% boron doped system, containing tetrahedral C atom distortion. Interestingly, at higher doping levels of boron, we found that the Qst decreases compared to the all carbon materials. These finding suggest that interplanar nanoconfinement may be more effective way to enhance H 2 binding than boron doping.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Competing magnetic fluctuations and orders in a multiorbital model of doped SrCo 2 As 2
We revisit the intriguing magnetic behavior of the paradigmatic itinerant frustrated magnet SrCo 2 As 2 , which shows strong and competing magnetic fluctuations yet does not develop long-range magnetic order. By calculating the static spin susceptibility Χ(q) within a realistic 16-orbital Hubbard-Hund model, we determine the leading instability to be ferromagnetic (FM). We then explore the effect of doping and calculate the critical Hubbard interaction strength U c that is required for the development of magnetic order. We find that U c decreases under electron doping and with increasing Hund's coupling J, but increases rapidly under hole doping. This suggests that magnetic order could possibly emerge under electron doping but not under hole doping, which agrees with experimental findings. We map out the leading magnetic instability as a function of doping and Hund's coupling and find several antiferromagnetic phases in addition to FM. We also quantify the degree of itinerant frustration in the model and resolve the contributions of different orbitals to the magnetic susceptibility. Lastly, we discuss the dynamic spin susceptibility Χ(q,ω) at finite frequencies, where we recover the anisotropy of the peaks at Q π = (π,0) and (0,π) observed by inelastic neutron scattering that is associated with the phenomenon of itinerant magnetic frustration. By comparing results between theory and experiment, we conclude that the essential experimental features of doped SrCo 2 As 2 are well captured by an itinerant Hubbard-Hund multiorbital model if one considers a small shift of the chemical potential towards hole doping.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Enhancing thermochemical energy storage density of magnesium‐manganese oxides
Abstract Three approaches for enhancing the energy density of magnesium‐manganese oxide porous reactive materials for thermochemical energy storage (TCES) are investigated: adjusting the mole ratio, lowering the oxygen partial pressure during thermal reduction, and transition metal oxide doping. The manganese‐to‐magnesium molar ratios are varied to determine the composition yielding maximal energy density. The increase in energy density by lowering the oxygen partial pressure during the reduction step is also studied. Volumetric oxygen exchange capacities are measured for every case considered. Finally, the effects of doping magnesium‐manganese oxide with cobalt oxide, iron oxide, zinc oxide, and nickel oxide on the TCES properties are examined. We found the optimal Mn/Mg ratio for maximum volumetric energy density is in the vicinity of 1/1, achieving 1813 ± 175, 2178 ± 204, and 2323 ± 281 MJ m −3 for oxygen partial pressures of 0.2, 0.05, and 0.01 atm during thermal reduction, respectively; lowering the oxygen partial pressure below atmospheric during thermal reduction enhances oxygen exchange capacities and improves the energy density between 10%‐42% and 24%‐55% for oxygen partial pressures of 0.05 and 0.01 atm, respectively, with the greatest increases observed for high manganese content samples; and, doped samples exhibit reduced oxygen exchange and questionable reactive stability, thus appearing to reduce energy density.
King, Keith↗
Potential for neutron and proton transmutation doping of GaN and Ga 2 O 3
As the potential applications of GaN and Ga 2 O 3 are limited by the inadequacy of conventional doping techniques, specifically when uniform selective area p-type doping is required, the potential for transmutation doping of these materials is analyzed. All transmuted element concentrations are reported as a function of time for several common proton and neutron radiation sources, showing that previously published results considered a small subset of the dopants produced. A 40 MeV proton accelerator is identified as the most effective transmutation doping source considered, with a 2.25 × 10 17 protons per cm 2 fluence yielding net concentrations of uncompensated p-type dopants of 7.7 × 10 15 and 8.1 × 1015 cm -3 for GaN and Ga 2 O 3 , respectively. Furthermore, it is shown that high energy proton accelerator spectra are capable of producing dopants required for magnetic and neutron detection applications, although not of the concentrations required for current applications using available irradiation methods.
36 MATERIALS SCIENCE↗
Nanotube/Quantum Dot-Polymer Solar Cells
Single wall carbon nanotubes used or this study were synthesized using the pulse laser vaporization technique. The as-produced SWNTs were collected from the condensed region on the quartz tube outside the furnace and purified by modification of the previously reported procedure. Preparation of the SWNT-P3OT composite solutions was performed using a series of mixing and sonication steps as previously demonstrated for other SWNT-polymer systems. Device fabrication involved the use of commercially-obtained, high quality (i.e., less than 10 W/sq.) ITO-coated polyethylene terapthalate (PET) substrates. Initially, an intrinsic layer of pristine P3OT is spray deposited (approx. 1-2 mL of the 15 mg/mL solution) onto the masked, 1 sq in. active area of the substrate. This is followed with spray deposition of the SWNT-P3OT composite solutions at similar volumes. As seen completion of the solar cell occurs when aluminum contacts (typical thicknesses of l000A) are applied to the IT0 and SWNT-P3OT composite film layers. The homogeneous distribution of SWNTs in a polymer matrix is dependent upon the ability of the polymer chain to associate with the SWNT superstructure. Stable composite dispersions of 0.1 % and 1.0% w/w SWNTs in P3OT were produced and analyzed in this study. Optical spectroscopy was conducted to observe the SWNT doping level effects on the absorption properties and infer potential electronic interactions between dopant and polymer. Shown is an overlay of these spectra where the pristine P3OT shows strong optical absorption at energies less than 2 eV. As expected, variation in absorption properties for the SWNT-P3OT composites is observed as the doping level increases. Through modification of the SWNT doping level in the polymer, it is possible to alter the absorption pattern of these composite materials. In fact, at these relatively low doping levels, the P3OT shows a significant enhancement in absorption through the near-IR and visible regions. The gray curve for purified SWNTs is offset from the other three for clarity, but indicates the typical complex pattern observed for this spectral range.
Bailey, Sheila G.↗
Prediction of orbital-selective Mott phases and block magnetic states in the quasi-one-dimensional iron chain Ce 2 O 2 FeSe 2 under hole and electron doping
The recent detailed study of quasi-one-dimensional iron-based ladders, with the 3d iron electronic density n=6, has unveiled surprises, such as orbital-selective phases. However, similar studies for n=6 iron chains are still rare. Here a three-orbital electronic Hubbard model was constructed to study the magnetic and electronic properties of the quasi-one-dimensional n=6 iron chain Ce 2 O 2 FeSe 2 , with focus on the effect of doping. Specifically, introducing the Hubbard U and Hund J H couplings and studying the model via the density matrix renormalization group, we report the ground-state phase diagram varying the electronic density away from n=6. For the realistic Hund coupling J H /U=1/4, several electronic phases were obtained, including a metal, orbital-selective Mott, and Mott insulating phases. Doping away from the parent phase, the competition of many tendencies leads to a variety of magnetic states, such as ferromagnetism, as well as several antiferromagnetic and magnetic “block” phases. In the hole-doping region, two different interesting orbital-selective Mott phases were found: OSMP1 (with one localized orbital and two itinerant orbitals) and OSMP2 (with two localized orbitals and one itinerant orbital). Moreover, charge disproportionation phenomena were found in special doping regions. We argue that our predictions can be tested by simple modifications in the original chemical formula of Ce 2 O 2 FeSe 2 .
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Metal ion-mediated structure and properties of α-Fe2O3 nanoparticles
Highlights: • Cu- and Zn-doped Fe{sub 2}O{sub 3} nanoparticles were successfully obtained by a simple solvothermal method. • The sizes and morphologies of the doped Fe{sub 2}O{sub 3} nanoparticles could be regulated by doping with divalent cations. • The doped Fe{sub 2}O{sub 3} nanoparticles showed enhanced remanent magnetization and coercivity. • The doped Fe{sub 2}O{sub 3} nanoparticles showed excellent catalytic activity toward thermal decomposition of ammonium perchlorate. • The enhanced catalytic activity could be attributed to the defect structure induced by doping with divalent cations. - Abstract: To assess the relationship between metal ion-mediated microstructures and the macro-performance, Cu- and Zn-doped α-Fe{sub 2}O{sub 3} nanoparticles were prepared via a solvothermal method. The morphologies of the as-synthesized nanoparticles were investigated by scanning electron microscopy and transmission electron microscopy. The results revealed that the sizes and morphologies could be regulated by doping with divalent cations. The structures of the as-synthesized nanoparticles were characterized by X-ray diffraction and Raman spectroscopy, indicating that Cu{sup 2+} and Zn{sup 2+} ions had diffused into the lattice of α-Fe{sub 2}O{sub 3} matrix. The magnetization behaviors of these nanoparticles were measured to analyze the effect of doping on α-Fe{sub 2}O{sub 3}. Furthermore, the catalytic activities of Cu- and Zn-doped α-Fe{sub 2}O{sub 3} nanoparticles demonstrated that the high-temperature decomposition temperature of ammonium perchlorate could be lowered by 115 °C and 107 °C, respectively, compared to that of ammonium perchlorate without catalyst. The enhanced catalytic activity could be attributed to the defect structure induced by doping with divalent cations.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Effect of Ti and Zn Doping on the Structural, Electric, and Magnetic Properties of GaFeO{sub 3}
Multidoped (Zn,Ti) gallium orthoferrite [GaFeO{sub 3} and Ga{sub 0.98}Zn{sub 0.02}Fe{sub 0.98}Ti{sub 0.02}O{sub 3}] ceramic was synthesized through a solid-state reaction. X-ray analysis of the prepared material provides its basic crystal data of a single-phase orthorhombic system. The scattered crystallite size and lattice strain of the material were estimated. Analysis of the micrograph of field emission scanning electron microscope shows uniform grain distribution in the sample, suggesting the formation of good quality of sample. Founded on the magnetic measurements, it is concluded that (Zn,Ti)-modified gallium ferrite has provided a reduction in the Curie temperature (T{sub C}); however, no significant changes in the magnetization values with Zn and Ti integration in GaFeO{sub 3} lattice. A noteworthy effect of substitution of multiple elements at the Ga and Fe sites on dielectric constant and tangent loss of GaFeO{sub 3} has been observed. Complete studies of temperature (180–400 K) and frequency (10–10{sup 7} Hz) dependence of dielectric constant and impedance have provided the effect of grains and grain boundaries on the conduction mechanism and dielectric relaxation of the material.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗