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Understanding the thermal transport properties of superlattice structures is relevant to a number of possible practical applications. Now, the scattering of phonons in oxide superlattices is shown to undergo a crossover from an incoherent to a coherent regime, which in turn strongly alters their thermal behaviour. Elementary particles such as electrons 1 , 2 or photons 3 , 4 are frequent subjects of wave-nature-driven investigations, unlike collective excitations such as phonons. The demonstration of wave–particle crossover, in terms of macroscopic properties, is crucial to the understanding and application of the wave behaviour of matter. We present an unambiguous demonstration of the theoretically predicted crossover from diffuse (particle-like) to specular (wave-like) phonon scattering in epitaxial oxide superlattices, manifested by a minimum in lattice thermal conductivity as a function of interface density. We do so by synthesizing superlattices of electrically insulating perovskite oxides and systematically varying the interface density, with unit-cell precision, using two different epitaxial-growth techniques. These observations open up opportunities for studies on the wave nature of phonons, particularly phonon interference effects, using oxide superlattices as model systems, with extensive applications in thermoelectrics and thermal management.

Nb-based circuits have broad applications in quantum-limited photon detectors, low-noise parametric amplifiers, superconducting digital logic circuits, and low-loss circuits for quantum computing. The current state-of-the-art approach for superconductor-insulator-superconductor (SIS) junction material is the Gurvitch trilayer process based on magnetron sputtering of Nb electrodes with Al-Oxide or AlN tunnel barriers grown on an Al overlayer. However, a current limitation of elemental Nb-based circuits is the low-loss operation of THz circuits operating above the 670 GHz gap frequency of Nb and operation at higher temperatures for projects with a strict power budget, such as space-based applications. NbTiN is an alternative higher energy gap material and we have previously reported on the first NbTiN/AlN/NbTiN superconducting-insulating-superconducting (SIS) junctions with an epitaxially grown AlN tunnel barrier. One drawback of a directly grown tunnel barrier compared to thermal oxidation or plasma nitridation is control of the barrier thickness and uniformity across a substrate, leading to variations in current density (Jc). Semiconductor barriers with smaller barrier heights enable thicker tunnel barriers for a given Jc. GaN is an alternative semiconductor material with a closed-packed Wurtzite crystal structure similar to AlN and it can be epitaxially grown as a tunnel barrier using the Reactive Bias Target Ion Beam Deposition (RBTIBD) technique. This work presents the preliminary results of the first reported high-quality NbTiN/GaN/NbTiN heterojunctions with underdamped SIS I(V) characteristics.

High quality Nb-based superconductor-insulator-superconductor (SIS) junctions with Al oxide (AlO\\(_x\\)) tunnel barriers grown from Al overlayers are widely reported in the literature. However, the thin barriers required for high critical current density (J\\(_c\\)) junctions exhibit defects that result in significant subgap leakage current that is detrimental for many applications. High quality, high-J\\(_c\\) junctions can be realized with AlN\\(_x\\) barriers, but control of J\\(_c\\) is more difficult than with AlO\\(_x\\). It is therefore of interest to study the growth of thin AlO\\(_x\\) barriers with the ultimate goal of achieving high quality, high-J\\(_c\\) AlO\\(_x\\) junctions. In this work, 100\\%\\ O\\(_2\\) and 2\\%\\ O\\(_2\\) in Ar gas mixtures are used both statically and dynamically to grow AlO\\(_x\\) tunnel barriers over a large range of oxygen exposures. In situ ellipsometry is used for the first time to extensively measure AlO\\(_x\\) tunnel barrier growth in real time, revealing a number of unexpected patterns. Finally, a set of test junction wafers was fabricated that exhibited the well-known dependence of J\\(_c\\) on oxygen exposure (E) in order to further validate the experimental setup.

The SALTUS Probe mission will provide a powerful far-infrared (far-IR) pointed space observatory to explore our cosmic origins and the possibility of life elsewhere. The observatory employs an innovative deployable 14-m aperture, with a sunshield that will radiatively cool the off-axis primary to <45K. This cooled primary reflector works in tandem with cryogenic coherent and incoherent instruments that span the 34 to 660 micron far-IR range at both high and moderate spectral resolutions.

As the Atacama Large Millimeter/submillimeter Array (ALMA) nears completion, 73 dual-polarization receivers have been delivered for each of Bands 3 (84-116 GHz) and 6 (211-275 GHz). The receivers use sideband-separating superconducting Nb/Al-AlOx/Nb tunnel-junction (SIS) mixers, developed for ALMA to suppress atmospheric noise in the image band. The mixers were designed taking into account dynamic range, input return loss, and signal-to-image conversion (which can be significant in SIS mixers). Typical SSB receiver noise temperatures in Bands 3 and 6 are 30 K and 60 K, resp., and the image rejection is typically 15 dB.

Cooperation among the churches of this country advanced visibly with the formation of the National Council of Churches in 1950.

God comes to us at Christmas; we do not go in search of Him! This we know when we believe that Christmas really happened. It Christ is Saviour and Lord, then Be is always coming to us, seeking us, reaching out to us. We have only to turn and open our hearts and there He is.

This work is focused on the development of a reliable fabrication technology for producing high quality Superconductor-Insulator-Superconductor (SIS) junctions for mixer applications in radio astronomy. SIS devices have recently superseded Schottky barrier devices as the technology of choice for low noise, high sensitivity applications below 115 GHz. There exists a growing interest in the exploration of SIS devices for operation at considerably higher frequencies. The advantages of this new technology are several. SIS mixers require a local oscillator power level several orders of magnitude lower than conventional devices. This advantage becomes even more important when designs for structures of arrays are considered. The potential for conversion gain and extremely low mixer noise temperatures has been realized by several experimentalists. In this dissertation, two SIS device technologies have been developed: (1) NbCN/PbBi edge and (2) Nb/Al-Al$\\sb2$O$\\sb3$/Nb trilayer technologies. Excellent SIS electrical characteristics have been obtained from these fabrication technologies.

Too many men and women, major breadwinners, find themselves with the wrong training, the wrong age, often in the wrong place and, tragically, often with the wrong color of skin.-- RAYMOND F. MALE, New Jersey State Commissioner of Labor and Industry.