arXiv subjects

David N. Seidman

Publications and source records attributed to David N. Seidman.

At least 19 recordsLinked to original sources

arXiv2026

Microstructural Characterization of Nb3Sn Thin Films Using FIB Tomography

The accelerating gradient of Nb3Sn superconducting radiofrequency (SRF) cavities is currently limited, and the underlying cause remains an open question in the field. One leading hypothesis attributes this limitation to the presence of tin-deficient regions within the Nb3Sn coating, which can suppress the superheating field. Due to the relatively large coherence length of Nb3Sn, defects near the surface may significantly interact with the RF field. However, these subsurface defects have proven difficult to characterize. This research aims to investigate the structure and distribution of subsurface Sn deficient regions to better understand their influence on cavity performance. We employ focused ion beam (FIB) tomography to analyze the subsurface microstructure of Nb3Sn thin films. This technique enables three-dimensional reconstruction of both the tin distribution and the grain structure within the film. By correlating Sn content with grain structure, we find that Sn deficient regions are more prevalent that previously thought. However, the Sn deficient regions are consistently located below the surface of the film where RF fields are strongly attenuated by supercurrent screening and are likely not a limiting factor for cavity performance.

cond-mat.mtrl-sci↗

arXiv2026

Oxygen distribution and segregation at grain boundaries in Nb and Ta-encapsulated Nb thin films for superconducting qubits

We report on atomic-scale analyses of oxygen distribution and segregation at grain boundaries (GBs) of Nb and Ta-encapsulated Nb (Ta/Nb) thin films for superconducting qubits using atom-probe tomography (APT) and transmission electron microscopy (TEM). We observe oxygen segregation at grain boundaries (GBs) relative to the oxygen concentration within the grains for both Nb and Ta-capped Nb thin films for superconducting qubits and find that higher oxygen concentration in the interior of Nb grains lead to greater oxygen segregation levels at GBs. This finding emphasizes that controlling oxygen impurities in Nb during film deposition and fabrication processing is important to reduce the level of oxygen segregation at GBs in Nb. The enrichment factor (Cgb/Cgrain) for oxygen segregation at GBs in Nb is 2.7 (error bar: 0.3) for Nb films, and Ta-capped Nb thin films exhibit slightly reduced Nb GB enrichment factors of 2.3 (error bar: 0.3) while GBs in the Ta capping layer itself possess higher enrichment factors of 3.0 (error bar: 0.3). We hypothesize that the Ta capping layer can trap oxygen and thereby affect oxygen in-diffusion and segregation at GBs in the underlying Nb thin films. Finally, we find that increases in the oxygen concentration in both Nb grains and GBs correlate with a suppression in the critical temperature for superconductivity (Tc). Together, our comparative chemical and charge transport property analyses provide atomic-scale insights into a potential mechanism contributing to decoherence in superconducting qubits.

cond-mat.supr-con↗

arXiv2025

Identifying Materials-Level Sources of Performance Variation in Superconducting Transmon Qubits

The Superconducting Materials and Systems (SQMS) Center, a DOE National Quantum Information Science Research Center, has conducted a comprehensive and coordinated study using superconducting transmon qubit chips with known performance metrics to identify the underlying materials-level sources of device-to-device performance variation. Following qubit coherence measurements, these qubits of varying base superconducting metals and substrates have been examined with various nondestructive and invasive material characterization techniques at Northwestern University, Ames National Laboratory, and Fermilab as part of a blind study. We find trends in variations of the depth of the etched substrate trench, the thickness of the surface oxide, and the geometry of the sidewall, which when combined, lead to correlations with the T$_1$ lifetime across different devices. In addition, we provide a list of features that varied from device to device, for which the impact on performance requires further studies. Finally, we identify two low-temperature characterization techniques that may potentially serve as proxy tools for qubit measurements. These insights provide materials-oriented solutions to not only reduce performance variations across neighboring devices, but also to engineer and fabricate devices with optimal geometries to achieve performance metrics beyond the state-of-the-art values.

quant-ph↗

arXiv2025

Analysis of Niobium Electropolishing Using a Generalized Distribution of Relaxation Times Method

Using electrochemical impedance spectroscopy, we have devised a method of sensing the microscopic surface conditions on the surface of niobium as it is undergoing an electrochemical polishing (EP) treatment. The method uses electrochemical impedance spectroscopy (EIS) to gather information on the surface state of the electrode without disrupting the polishing reaction. The EIS data is analyzed using a so-called distribution of relaxation times (DRT) method. Using DRT, the EIS data can be deconvolved into discrete relaxation time peaks without any a priori knowledge of the electrode dynamics. By analyzing the relaxation time peaks, we are able to distinguish two distinct modes of the EP reaction. As the polishing voltage is increased, the electrode transitions from the low voltage EP mode, characterized by a single relaxation time peaks, to the high voltage EP mode, characterized by two relaxation time peaks. We theorize that this second peak is caused by the formation of an oxide layer on the electrode. We also find that this oxide induced peak transitions from to a negative relaxation time, which is indicative of a blocking electrode process. By analyzing EPed samples, we show that samples polished in the low voltage mode have significantly higher surface roughness due to grain etching and faceting. We find that the surface roughness of the samples only improves when the oxide film peak is present and in the negative relaxation time region. This shows that EIS combined with DRT analysis can be used to predict etching on EPed Nb. This method can also be performed before or during the EP, which could allow for adjustment of polishing parameters to guarantee a smooth cavity surface finish.

cond-mat.mtrl-sci↗

arXiv2024

Effects of alloying elements on carbon diffusion in the austenite (f.c.c.) and ferrite (b.c.c.) phases

TThe effects of alloying elements on diffusion pathways and migration energies of interstitial carbon in austenite (f.c.c.) and ferrite (b.c.c.) are studied using density functional theory first-principles calculations. The binding energies between carbon and alloying elements are determined through 6th nearest-neighbor (NN) distances. The elements studied are Ni, Mo, V, Cr, Mn, Cu, Al, Ti, and Si, relevant to most high-strength steels. Nickel, Mn, Al, and Si have repulsive binding energies; Mo, V, Cr, Cu, and Ti have attractive binding energies in austenite and ferrite. Alloying elements at 1st NN sites of a C atom in an octahedral site introduce asymmetry into the minimum energy diffusion pathway, causing up to about 1 eV changes in saddle-point energies. This pathway goes from one octahedral site to another via intermediate energy states, differing for austenite and ferrite. We find that the elements with attractive binding energies increase the energy barrier for C migration resulting in decelerated carbon diffusion, while the elements with repulsive binding energies decrease the energy barrier for C migration leading to accelerated C diffusion. The magnitude of changes in C migration energies is proportional to the binding energies between C and alloying elements. Among the three austenite stabilizers, Ni and Mn are C diffusion accelerators, while Cu decelerates C diffusion in austenite. Among the four ferrite stabilizers, Si is a C diffusion accelerator, while V and Ti serve as C diffusion decelerators in ferrite. Aluminum has no significant effect on C's diffusivity, while Mo and Cr decelerate C diffusion.

physics.atom-ph↗

arXiv2024

Healing Gradient Degradation in Nb3Sn SRF Cavities Using a Recoating Method

Despite having advantageous superconducting properties, Nb3Sn superconducting radiofrequency (SRF) cavities still have practical challenges compared to Nb SRF cavities due to the brittle nature of Nb3Sn. Performance degradation can occur when a Nb3Sn SRF cavity experiences mechanical stresses such as during handling and tuning of the cavity. In this study, we present a potential treatment for SRF cavities that have experienced stress induced performance degradation that involves a recoating procedure. The degraded cavity is coated with a small amount of Sn using a single step vapor-diffusion methodology. Using this approach we can recover a significant portion of the lost performance of a Nb3Sn SRF cavity.

physics.acc-ph↗

arXiv2023

Improving Nb3Sn Cavity Performance Using Centrifugal Barrel Polishing

In this study we will show a new method of polishing for Nb3Sn cavities known as centrifugal barrel polishing (CBP). Using this method, Nb3Sn coated samples are polished to a surface roughness comparable to a traditional Nb cavity after electropolishing (EP). We also investigate different methods of cleaning the Nb3Sn surface after CBP to remove residual abrasive particles. The polished Nb3Sn surface is analyzed using confocal laser microscopy, and scanning electron microscopy (SEM) is used to image the surface and measure the surface roughness after polishing. Transmission electron microscopy (TEM) is also used for high resolution analysis of the surface after polishing. Finally, we show that centrifugal barrel polishing can improve the performance of a Nb3Sn SRF cavity.

physics.acc-ph↗

arXiv2023

Active Learning Sensitivity Analysis of $γ^\prime$(L1$_2$) Precipitate Morphology of Ternary Co-Based Superalloys

To better understand the equilibrium $γ^\prime$(L1$_2$) precipitate morphology in Co-based superalloys, a phase field modeling sensitivity analysis is conducted to examine how four phase-field parameters [initial Co concentration ($c_0$), double-well barrier height ($ω$), gradient energy density coefficient ($κ$), and lattice misfit strain ($ε_{\rm misfit}$)] influence the $γ^\prime$(L1$_2$) precipitate size and morphology. Gaussian Process Regression (GPR) models are used to fit the sample points and to generate surrogate models for both precipitate size and morphology. In an Active Learning approach, a Bayesian Optimization algorithm is coupled with the GPR models to suggest new sample points to calculate and efficiently update the models based on a reduction of uncertainty. The algorithm has a user-defined objective, which controls the balance between exploration and exploitation for new suggested points. Our methodology provides a qualitative and quantitative relationship between the $γ^\prime$(L1$_2$) precipitate size and morphology and the four phase-field parameters, and concludes that the most sensitive phase-field parameter for precipitate size and morphology is the initial Co concentration ($c_0$) and the double-well barrier height ($ω$), respectively. We note that the GPR model for precipitate morphology required adding a noise tolerance in order to avoid overfitting due to irregularities in some of the simulated equilibrium $γ^\prime$(L1$_2$) precipitate morphology.

cond-mat.mtrl-sci↗

arXiv2022

The effects of diffusional couplings on compositional trajectories and interfacial free energies during phase separation in a quaternary Ni-Al-Cr-Re model superalloy

The temporal evolution of ordered gamma-prime(L12)-precipitates and the compositional trajectories during phase-separation of the gamma(face-centered-cubic(f.c.c.)) and gamma-prime(L12)-phases are studied in a Ni-0.10Al-0.085Cr-0.02Re(mole-fraction) superalloy, utilizing atom-probe tomography, transmission electron microscopy, and the Philippe-Voorhees (PV) coarsening model. As the gamma-prime(L12)-precipitates grow, the excesses of Ni, Cr and Re, and depletion of Al in the gamma(f.c.c.)-matrix develop as a result of diffusional fluxes crossing gamma(f.c.c.)/gamma-prime(L12) heterophase interfaces. The coupling effects on diffusional fluxes was introduced (PV coarsening model) in terms of the diffusion tensor, D, and the second-derivative tensor of the molar Gibbs free energies, G", obtained employing Thermo-Calc and DICTRA calculations. The Gibbs interfacial free energies are (6.9 +- 1.4) mJ/m2 with all terms in D and G", which changes to (18.9 +- 2.1) mJ/m2, (37.7 +- 3.3) mJ/m2, and (-7.5 +- 1.2) mJ/m2 without including the off-diagonal terms in D, G", and both D and G", respectively. The experimental APT compositional trajectories are displayed and compared with the PV model in a partial quaternary phase-diagram, employing a tetrahedron. The compositional trajectories measured by APT exhibit curvilinear behavior in the nucleation and growth regimes, which become vectors, moving simultaneously toward the gamma(f.c.c.) and gamma-prime(L12) conjugate solvus-surfaces, for the quasi-stationary coarsening regime. The compositional trajectories are compared to the PV model with and without the off-diagonal terms in D and G". The directions including the off-diagonal terms in D and G" tensors are consistent with the APT experimental data.

cond-mat.mtrl-sci↗

arXiv2020

Analysis of Magnetic Vortex Dissipation in Sn-Segregated Boundaries in Nb$_3$Sn Superconducting RF Cavities

We study mechanisms of vortex nucleation in Nb$_3$Sn Superconducting RF (SRF) cavities using a combination of experimental, theoretical, and computational methods. Scanning transmission electron microscopy (STEM) image and energy dispersive spectroscopy (EDS) of some Nb$_3$Sn cavities show Sn segregation at grain boundaries in Nb$_3$Sn with Sn concentration as high as $\sim$35 at.\% and widths $\sim$3 nm in chemical composition. Using ab initio calculations, we estimate the effect excess tin has on the local superconducting properties of the material. We model Sn segregation as a lowering of the local critical temperature. We then use time-dependent Ginzburg-Landau theory to understand the role of segregation on magnetic vortex nucleation. Our simulations indicate that the grain boundaries act as both nucleation sites for vortex penetration and pinning sites for vortices after nucleation. Depending on the magnitude of the applied field, vortices may remain pinned in the grain boundary or penetrate the grain itself. We estimate the superconducting losses due to vortices filling grain boundaries and compare with observed performance degradation with higher magnetic fields. We estimate that the quality factor may decrease by an order of magnitude ($10^{10}$ to $10^9$) at typical operating fields if 0.03\% of the grain boundaries actively nucleate vortices. We additionally estimate the volume that would need to be filled with vortices to match experimental observations of cavity heating.

cond-mat.supr-con↗

arXiv2020

An integral method for the calculation of the reduction in interfacial free energy due to interfacial segregation

A method based on the Gibbs' adsorption isotherm is developed to calculate the decrease in interfacial free energy resulting from solute segregation at an internal interface, built on measured concentration profiles. Utilizing atom-probe tomography (APT), we first measure a concentration profile of the relative interfacial excess of solute atoms across an interface. To accomplish this we utilize a new method based on J. W. Cahn's formalism for the calculation of the Gibbs interfacial excess. We also introduce a method to calculate the decrease in interfacial free energy that is caused by the segregating solute atoms. This method yields a discrete profile of the decrease in interfacial free energies, which takes into account the measured concentration profile and calculated Gibbsian excess profile. We demonstrate that this method can be used for both homo- and hetero-phase interfaces and takes into account the actual distribution of solute atoms across an interface as determined by APT. It is applied to the case of the semiconducting system PbTe-PbS 12 mol.%-Na 1 mol.%, where Na segregation at the PbS/PbTe interface is anticipated to reduce the interfacial free energy of the {100} facets. We also consider the case of the nickel-based Alloy 600, where B and Si segregation are suspected to impede inter-granular stress corrosion cracking (IGSCC) at homo- (GB) and hetero-phase metal carbide (M7C3) interfaces. The concentration profiles associated with internal interfaces are measured by APT using an ultraviolet (wavelength = 355 nm) laser to dissect nanotips on an atom-by-atom and atomic plane-by-plane basis.

cond-mat.mtrl-sci↗

arXiv2019

Phase Segmentation in Atom-Probe Tomography Using Deep Learning-Based Edge Detection

Atom-probe tomography (APT) facilitates nano- and atomic-scale characterization and analysis of microstructural features. Specifically, APT is well suited to study the interfacial properties of granular or heterophase systems. Traditionally, the identification of the interface between, for precipitate and matrix phases, in APT data has been obtained either by extracting iso-concentration surfaces based on a user-supplied concentration value or by manually perturbing the concentration value until the iso-concentration surface qualitatively matches the interface. These approaches are subjective, not scalable, and may lead to inconsistencies due to local composition inhomogeneities. We propose a digital image segmentation approach based on deep neural networks that transfer learned knowledge from natural images to automatically segment the data obtained from APT into different phases. This approach not only provides an efficient way to segment the data and extract interfacial properties but does so without the need for expensive interface labeling for training the segmentation model. We consider here a system with a precipitate phase in a matrix and with three different interface modalities---layered, isolated, and interconnected---that are obtained for different relative geometries of the precipitate phase. We demonstrate the accuracy of our segmentation approach through qualitative visualization of the interfaces, as well as through quantitative comparisons with proximity histograms obtained by using more traditional approaches.

cond-mat.mtrl-sci↗

arXiv2018

A Correlative Four-Dimensional Study of Phase Separation at the Subnanoscale to Nanoscale of a Ni-Al Alloy

The temporal evolution of ordered gamma prime (L12)-precipitates precipitating in a disordered gamma(f.c.c.) matrix is studied in extensive detail for a Ni-12.5 Al at.% alloy aged at 823 K (550 oC), for times ranging from 0.08 to 4096 h. Three-dimensional atom-probe tomography (3-D APT) results are compared to monovacancy-mediated lattice-kinetic Monte Carlo (LKMC1) simulations, which include monovacancy-solute binding energies through 4th nearest-neighbor distances, for the same mean composition and aging temperature. The temporal evolution of the measured values of the mean radius, , number density, aluminum supersaturations, and volume fraction of the gamma prime(L12)-precipitates are compared to the predictions of a modified version of the Lifshitz-Slyozov-Wagner coarsening model due to Calderon, Voorhees et al. The resulting experimental rate constants are used to calculate the Gibbs interfacial free-energy between the gamma(f.c.c.)- and gamma prime(L12)-phases using data from two thermodynamic databases, and its value is compared to all extant values dating from 1966. The diffusion coefficient for coarsening is calculated utilizing the same rate constants and compared to all extant archival diffusivities, not determined from coarsening experiments, and is demonstrated to be the inter-diffusivity, , of Ni and Al. The monovacancy-mediated LKMC1 simulation results are in good agreement with our 3-D APT data. It is demonstrated that the compositional interfacial width, for the {100} interface, between the gamma(f.c.c.)- and gamma prime (L12)-phases, decreases continuously with increasing aging time and , for the 3-D APT results and monovacancy-mediated LKMC1 simulations, in disagreement with an ansatz intrinsic to the trans-interface diffusion-controlled coarsening model, which predicts the opposite trend for binary alloys.

cond-mat.mtrl-sci↗

arXiv2018

Morphological, nanostructural, and compositional evolution during phase separation of a model Ni-Al-Mo superalloy: Atom-probe tomographic experiments and lattice-kinetic Monte Carlo simulations

The details of phase separation of a Ni-6.5Al-9.9Mo aged at 978 K for aging times ranging from 0.125 to 1024 h are investigated by atom-probe tomography and lattice-kinetic Monte Carlo (LKMC) simulations. On the basis of the temporal evolution of the nanostructure, three experimental regimes are identified: (1) concomitant precipitate nucleation and growth (t less than 0.25 h); (2) concurrent coagulation and coalescence (t 0.25 to 16 h); and (3) quasi-stationary coarsening of gamma prime(L12)- precipitates (t 16 to 1024 h). The temporal dependencies of the mean precipitate radius and precipitate number density, Nv(t), are determined experimentally, 0.344 (0.012) and -0.95(0.02), respectively, following the predictions of quasi-stationary coarsening models. In this alloy aged at 978 K, Al partitions strongly to the gamma prime(L12)-phase with a partitioning coefficient 4.06(0.04), whereas Mo and Ni partition to the gamma(f.c.c.)-matrix with values of 0.61(0.01) and 0.90(0.01), respectively. In the quasi-stationary regime(t larger than 16h), the temporal exponents of the Al, Mo, and Ni supersaturations in both the gamma(f.c.c.)-matrix and gamma prime(L12)-precipitates are in reasonable agreement with a multi-component coarsening model's prediction of -0.33. Quantitative analyses of the edge-to-edge inter-precipitate distances demonstrate that coagulation and coalescence are consequences of the overlap of the diffusion fields surrounding the gamma prime(L12)-precipitates. Both 3-D APT and LKMC results demonstrate that the interfacial compositional width decrease with increasing values. And the interfacial compositional width at infinite ageing time are estimated to be 1.89(0.22) nm, 2.09(0.12) nm and 2.64(0.03) nm for Ni, Al and Mo, respectively.

cond-mat.mtrl-sci↗

arXiv2008

Composition Profiles within Al3Li and Al3Sc/Al3Li Nanoscale Precipitates in Aluminum

An Al-11.3Li-0.11Sc (at. %) alloy was double-aged to induce first alpha'-Al3Sc and then delta'-Al3Li precipitates. Atom-probe tomography revealed both single-phase delta'-precipitates and core-shell alpha'/delta'-precipitates (with respective average radii of 16 and 27 nm, and respective volume fractions of 12 and 9%) conferring a high strength to the alloy. Although the delta'-shells contain little Sc (~0.027 at. %), the alpha'-cores have a high Li content, with an average composition of Al0.72(Sc0.17 Li0.11). The Li concentrations within the delta'-phase and the Li interfacial excess at the delta'/alpha'-interface both exhibit wide precipitate-to-precipitate variations.

cond-mat.mtrl-sci↗

arXiv2007

Effects of a tungsten addition on the morphological evolution, spatial correlations, and temporal evolution of a model Ni-Al-Cr superalloy

The effect of adding 2 at.% W to a model Ni-Al-Cr superalloy on the morphological evolution, spatial correlations and temporal evolution of g'(L12)-precipitates at 1073 K is studied with scanning electron microscopy and atomic force microscopy. Adding W yields a larger microhardness, earlier onset of spheroidal-to-cuboidal precipitate morphological transition, larger volume fraction (from ~20 to 30%), reduction in coarsening kinetics by one third and a larger number density (Nv) of smaller mean radii ( ) precipitates. The kinetics of and interfacial area per unit volume obey t1/3 and t-1/3 relationships, respectively, which is consistent with coarsening driven by interfacial energy reduction. The Nv power law dependencies deviate, however, from model predictions indicating that a stationary-state is not achieved. Quantitative analyses with precipitate size distributions, pair correlation functions, and edge-to-edge interprecipitate distance distributions gives insight into 2D microstructural evolution, including the elastically driven transition from a uniform g'-distribution to one-dimensional <001>-strings to eventually clustered packs of g'-precipitates in the less densely packed Ni-Al-Cr alloy.

cond-mat.mtrl-sci↗

arXiv2007

Effects of solute concentrations on kinetic pathways in Ni-Al-Cr alloys

The kinetic pathways resulting from the formation of coherent L12-ordered y'-precipitates in the g-matrix (f.c.c.) of Ni-7.5 Al-8.5 Cr at.% and Ni-5.2 Al-14.2 Cr at.% alloys, aged at 873 K, are investigated by atom-probe tomography (APT) over a range of aging times from 1/6 to 1024 hours; these alloys have approximately the same volume fraction of the y'-precipitate phase. Quantification of the phase decomposition within the framework of classical nucleation theory reveals that the y-matrix solid-solution solute supersaturations of both alloys provide the chemical driving force, which acts as the primary determinant of the nucleation behavior. In the coarsening regime, the temporal evolution of the y'-precipitate average radii and the y-matrix supersaturations follow the predictions of classical coarsening models, while the temporal evolution of the y'-precipitate number densities of both alloys do not. APT results are compared to equilibrium calculations of the pertinent solvus lines determined by employing both Thermo-Calc and Grand-Canonical Monte Carlo simulation.

cond-mat.mtrl-sci↗

arXiv2007

Direct Measurement of 2D and 3D Interprecipitate Distance Distributions from Atom-Probe Tomographic Reconstructions

Edge-to-edge interprecipitate distance distributions are critical for predicting precipitation strengthening of alloys and other physical phenomena. A method to calculate this 3D distance and the 2D interplanar distance from atom-probe tomographic data is presented. It is applied to nanometer-sized Cu-rich precipitates in an Fe-1.7 at.% Cu alloy. Experimental interprecipitate distance distributions are discussed.

cond-mat.mtrl-sci↗