Oxidative chemical vapor deposition (oCVD) is a versatile technique that can simultaneously tailor properties (e.g., electrical, thermal conductivity) and morphology of polymer films at the nanoscale. In this work, we report the thermal conductivity of nanoscale oCVD grown poly(3,4-ethylenedioxythiophene) (PEDOT) films for the first time. Measurements as low as 0.16 W m⁻¹ K⁻¹ are obtained at room temperature for PEDOT films with thicknesses ranging from 50–100 nm. These values are lower than those for solution processed PEDOT films doped with the solubilizing agent PSS (polystyrene sulfonate). The thermal conductivity of oCVD grown PEDOT films show no clear dependence on electrical conductivity, which ranges from 1 S cm⁻¹ to 30 S cm⁻¹. It is suspected that at these electrical conductivities, the electronic contribution to the thermal conductivity is extremely small and that phonon transport is dominant. Our findings suggest that CVD polymerization is a promising route towards engineering polymer films that combine low thermal conductivity with relatively high electrical conductivity values.

The promise of using electromagnetic (EM) fields for low temperature materials synthesis is limited by our ability to structurally characterize these materials, which are often nanocrystalline or amorphous. Here we demonstrate that synchrotron X-ray radiation coupled with the recently developed thin film pair distribution function (tfPDF) analysis yields quantitative information about mixtures of crystalline and non-crystalline materials synthesized under EM excitation, which represents a new direction to study the chemical reactions and lattice ordering induced by EM fields. Our experiments demonstrate for the first time that ceramic oxide films of titanium dioxide (TiO₂) grown under microwave radiation (MWR) exposure contain a different phase composition and increased crystallinity compared to TiO₂ grown at similar temperatures without EM fields. Specifically, the field-assisted TiO₂ is composed of a mixed-phase structure consisting of long-range anatase TiO₂ phase with short-range amorphous components, while furnace-grown materials are amorphous with local ordering most resembling the brookite phase of TiO₂. The disordered component of MWR-grown TiO₂ results in a slightly narrower energy band gap relative to fully crystalline anatase, indicating enhanced light absorption in the visible spectrum. The impact of EM field-influenced atomic structure on resultant material properties creates the opportunity to utilize MWR-assisted synthesis as a novel method for rapid, single-step, low temperature synthesis of mixed ordered-disordered materials for potential use in photocatalysis, thermoelectrics, or lithium ion batteries.

Naturally occurring background radiation is a potential source of correlated decoherence events in superconducting qubits that will challenge error-correction schemes. In order to characterize the radiation environment in an unshielded laboratory representative of superconducting qubits’ environments, we performed broadband, spectroscopic measurements of background radiation events inside a millikelvin refrigerator. The spectrometer was designed to mimic the size and composition of a quantum circuit. Specifically, we measured the background radiation spectra in silicon substrates of two thicknesses, 500 and 1500 µm, and one area, 25 mm 2 . The observed spectra span energies from a few kilo-electron-volts up to nearly 10 MeV, are nearly featureless, and decrease in intensity by a factor of 40 000 between 100 keV and 3 MeV for the 500-µm substrate. We integrate the spectra to obtain the average event rates and deposited power levels. These quantities correspond to a rate of 0.023 events per second and a power of 4.9 keV s − 1 , when counting events that deposit at least 40 keV for the 500-µm-thick substrate. We find that the cryogenic measurements are in good agreement with predictions based on simple measurements of the terrestrial gamma-ray flux outside the refrigerator, published models of cosmic-ray fluxes, a crude model of the cryostat, and radiation-transport simulations. This model requires no free parameters to predict the background radiation spectra in the silicon substrates. The agreement between measurements and predictions demonstrates that the model we present can be used to assess the relative contributions of terrestrial and cosmic-ray sources to background radiation interactions in silicon substrates of varying thickness. These spectroscopic measurements are performed with a novel combination of superconducting microresonators located on micromachined silicon islands that define the interaction volume with background radiation. The resonators transduce deposited energy to a readily detectable electrical signal. Microresonator readout closely resembles dispersive superconducting qubit readout, so similar devices—with or without micromachined islands—are suitable for integration with superconducting quantum circuits as detectors for background radiation events. For our specific laboratory conditions, we find that gamma-ray emissions from radioisotopes are responsible for the majority of events that deposit E < 1 Me V . We present results demonstrating that the background radiation spectrum contains relevant contributions from cosmic-ray particles other than muons, particularly a tail of multi-mega-electron-volt events due to protons and neutrons. These observations suggest several paths to reducing the impact of background radiation on quantum circuits, supported by an empirically validated model for generating reliable predictions of radiation interactions with silicon substrates. Published by the American Physical Society 2024

In situpair distribution function analysis reveals that electromagnetic radiation exposure during SnO₂nanoparticle growth alters local atomic structure and the synthetic pathway compared to conventional hydrothermal synthesis routes.

We report on the 1,000-element transition-edge sensor (TES) x-ray spectrometer implementation of the TOMographic Circuit Analysis Tool (TOMCAT). TOMCAT combines a high spatial resolution scanning electron microscope (SEM) with a highly efficient and pixelated TES spectrometer to reconstruct three-dimensional maps of nanoscale integrated circuits (ICs). A 240-pixel prototype spectrometer was recently used to reconstruct ICs at the 130 nm technology node, but to increase imaging speed to more practical levels, the detector efficiency needs to be improved. For this reason, we are building a spectrometer that will eventually contain 3,000 TES microcalorimeters read out with microwave superconducting quantum interference device (SQUID) multiplexing, and we currently have commissioned a 1,000 TES subarray. This still represents a significant improvement from the 240-pixel system and allows us to begin characterizing the full spectrometer performance. Of the 992 maximimum available readout channels, we have yielded 818 devices, representing the largest number of TES x-ray microcalorimeters simultaneously read out to date. These microcalorimeters have been optimized for pulse speed rather than purely energy resolution, and we measure a FWHM energy resolution of 14 eV at the 8.0 keV Cu K $\alpha$ line.

Electromagnetic (EM) field exposure during materials synthesis offers the opportunity to engineer novel atomic structures and modify reaction kinetics beyond the capabilities of conventional routes. We demonstrate the first experimental evidence that even low energy EM fields can influence atomic structural arrangements, resulting in rapid low-temperature crystallization and phase transitions in ceramic oxides. Synchrotron X-ray characterization, coupled with first-principles calculations, show that phase stability is mediated by oxygen vacancy-induced structural distortions. These distortions are dependent on the local electric field intensity, validating a longstanding hypothesis that high local field strengths (exceeding 10⁶ V m⁻¹) act as a driving force in field-driven materials synthesis. This information linking field strength with atomic structure lays the foundation to deploy EM fields to explore regions of phase space and material properties not readily accessible in nature.