Volodymyr Yefremenko

Titanium nitride thin films are prepared using DC reactive magnetron sputtering at room temperature, with an RF bias applied to the substrate to systematically control film growth. By adjusting the substrate RF bias, the degree and length scale of disorder are tuned, leading to pronounced changes in film microstructure and superconducting properties. A dome-shaped dependence of the superconducting critical temperature, Tc, on RF bias is observed, accompanied by a minimum in the superconducting coherence length near the peak of the Tc dome. This correlated behavior reflects a controlled evolution from point-like disorder to a nanocrystalline microstructure that ultimately develops into well-ordered grains separated by electrically transparent grain boundaries. At intermediate RF bias, the films acquire an optimal grain size that enhances intragrain superconductivity while reducing the effective coherence length. This mesoscopic control of disorder and microstructure provides a pathway for engineering TiN films with superconducting properties that are desirable for applications requiring high normal-state sheet resistance in fully gapped superconductors, such as superconducting resonators and high-kinetic-inductance devices.

The South Pole Telescope Shirokoff Line Intensity Mapper (SPT-SLIM) experiment is a pathfinder for demonstrating the use of on-chip spectrometers for millimeter (mm) Line Intensity Mapping (LIM). We present spectral bandpass measurements of the SPT-SLIM spectrometer channels made on site using a Fourier Transform Spectrometer during the first deployment of SPT-SLIM in the 2024-2025 Austral summer season. We note the effect of FTS systematics on measurements of on-chip filterbank spectrometer resolutions and demonstrate a technique for measuring the narrow band passes of the SPT-SLIM filterbanks that improves beyond the intrinsic resolution of a Fourier Transform Spectrometer.

A Kinetic Inductance Phonon-Mediated Detector is a calorimeter that uses kinetic inductance detectors (KIDs) to read out phonon signals from the device substrate. We have established a consortium comprising university and national lab groups dedicated to advancing the state of the art in these detectors, with the ultimate goal of designing a detector with sub-eV threshold on energy deposited in the substrate, enabling searches for both light dark matter and low-energy neutrino interactions. This consortium brings together experts in kinetic inductance detector design, phonon and quasiparticle dynamics, and noise modeling, along with specialized fabrication facilities, test platforms, and unique calibration capabilities. Recently, our consortium has demonstrated a resolution on energy absorbed by the sensor of 2.1 eV, the current record for phonon-sensitive KIDs, though due to ∼ 1% phonon collection efficiency, the overall detector resolution was limited to 320eV. The current focus of the consortium is modeling and improving the phonon collection efficiency and implementing low-T_c superconductors, both of which serve to improve the overall energy resolution and threshold of the detectors. FNAL Report Number: FERMILAB-PUB-25-0652-ETD

The South Pole Telescope Shirokoff Line Intensity Mapper (SPT-SLIM) is a millimeter-wavelength line-intensity mapping experiment, which was deployed on the South Pole Telescope (SPT) during the 2024-2025 Austral summer season. This pathfinder experiment serves to demonstrate the on-sky operation of multi-pixel on-chip spectrometer technology. We report on the cryogenic performance of the SPT-SLIM receiver for the first year of commissioning observations. The SPT-SLIM receiver utilizes an Adiabatic Demagnetization Refrigerator (ADR) for cooling the focal plane of superconducting filterbank spectrometers to a temperature of 150 mK. We demonstrate stable thermal performance of the focal plane module during observations consistent with thermal modeling, enabling a cryogenic duty cycle above 80%. We also report on the receiver control system design utilizing the Observatory Control System (OCS) platform for automated cryogenic operation on the SPT.

Silicon-based dielectric is crucial for many superconducting devices, including high-frequency transmission lines, filters, and resonators. Defects and contaminants in the amorphous dielectric and at the interfaces between the dielectric and metal layers can cause microwave losses and degrade device performance. Optimization of the dielectric fabrication, device structure, and surface morphology can help mitigate this problem. We present the fabrication of silicon oxide and nitride thin film dielectrics. We then characterized them using Scanning Electron Microscopy, Atomic Force Microscopy, and spectrophotometry techniques. The samples were synthesized using various deposition methods, including Plasma-Enhanced Chemical Vapor Deposition and magnetron sputtering. The film's morphology and structure were modified by adjusting the deposition pressure and gas flow. The resulting films were used in superconducting resonant systems consisting of planar inductors and capacitors. Measurements of the resonator properties, including their quality factor, were performed.