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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

3rd harmonic magnetometry assessment of NbTiN-based SIS structures

In the quest for alternative superconducting materials to bring accelerator cavity performance beyond the bulk niobium (Nb) intrinsic limits, a promising concept proposes that superconductor-insulator-superconductor (SIS) thin film structures can delay magnetic flux penetration in accelerator cavities to higher fields [1]. NbTiN is a candidate superconductor for such structures. We have demonstrated high quality NbTiN and AlN deposited by reactive direct current magnetron sputtering (DCMS), both for individual layers and multilayers. Interface quality has been assessed for bi-layer stacks with various NbTiN and AlN thicknesses from 500 and 30 nm down to 3 and 1 nm. These SIS structures show continued sharp interfaces. The Hfp enhancement of the films was examined with 3rd harmonic magnetometry. The system was designed and built in an ongoing collaboration with CEA Saclay. It can measure 1? to 2? samples on a temperature controlled stage. This contribution presents the assessment of the first penetration field enhancement with 3rd harmonic magnetometry for standalone films and multilayer nanostructures.

Valente, Anne-Marie↗
DOE OSTI2021

SIS-AOP Cueing/Segmenting Algorithm (FOA_SIS-AOP) Using the Sandia FOA 4.0 Framework

For machine vision, one of the most important operations is fast and effective object cueing or segmentation. Sandia National Labs has a long history of development and implementation of very fast and effective cueing/segmentation algorithms. This report covers the history, motivation and implementation of evolving frameworks (Sandia FOA Frameworks) upon which this long legacy of successful algorithms are built. The report describes the innovative microprocessor implementation, enabling extremely fast morphological processing, combined with a novel adaptive quantization front - end and a feature - based backend that resulted in Sandia developing fast and effective cueing in a wide variety of applications, from defect detection to SAR ATR. The report covers evolution from Sandia FOA 1.0 Framework (1995) to current Sandia FOA 4.0 Framework (2021). Requirements for the cueing algorithm for SIS - AOP (FOA_SIS - AOP) that drove the Sandia FOA 4.0 Framework development are discussed, along with information on how to use the Sandia FOA Frameworks.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS2004

Development of Submillimeter SIS Mixers and Broadband HEMT Amplifiers

This is the final technical report for NASA grant NAG5-9493. entitled "Development of Submillimeter SIS Mixers and Broadband HEMT Amplifiers". The goal of this project was to develop and demonstrate a new generation of superconducting tunnel junction (SIS) receivers with extremely wide instantaneous (intermediate-frequency, or IF) bandwidths. of order 12 GHz. along with the wideband low-noise microwave HEMT (high electron mobility transistor) amplifiers which follow the SIS mixer. These wideband SIS/HEMT receivers would allow rapid submillimeter wavelength spectral line surveys to be carried out, for instance with the NASA airborne observatory SOFIA. and could potentially be useful for future submillimeter space missions such as SAFIR. In addition, there are potential NASA earth science applications. such as the monitoring of the distribution of chemical species in the stratosphere and troposphere using the limb-sounding technique. The overall goals of this project have been achieved: a broadband 200-300 SIS receiver was designed and constructed, and was demonstrated in the field through a test run at the Caltech Submillimeter Observatory on Mauna Kea. HI. The technical details are described in the appendices. which are primarily conference publications. but Appendix A also includes an unpublished summary of the latest results. The work on the SIS mixer design are described in the conference publications (appendices B and C). The "Supermix" software package that was developed at Caltech and used for the SIS design is also described in two conference papers, but has been substantially revised, debugged. and extended as part of the work completed for this grant. The Supermix package is made available to the community at no charge. The electromagnetic design of a radial waveguide probe similar to the one used in this work is described in a journal publication. Details of the novel fabrication procedure used for producing the SIS devices at JPL are also given in an upcoming journal article. Finally, details on the wideband HEMT amplifier design and noise characterization techniques are described in two publications.

Zmuidzinas, J.↗
NASA NTRS1988

Advances in SIS receiver technology

Significant advances in SIS receiver technology since the last Asilomar meeting include: superconductor materials, integrated inductive tuning elements, and planar mounting structures. The effect of these advances is to push the upper frequency operating limit from about 600 to 1500 GHz, and to enhance the feasibility of focal plane arrays of heterodyne receivers. A fundamental high frequency operating limit of SIS mixers is set by the superconducting energy gap. A practical limitation for high frequency operation of SIS junctions is their parasitic capacitance and resistance. The performance of the mixer will be degraded by the Resistor-Capacitor rolloff. Several designs were reported for inductive elements integrated on the same substrate as the SIS junctions to tune out the bulk junction capacitance. Most millimeter SIS-based heterodyne receivers have used waveguide coupling structures. Technology has advanced to the state where programs that have a high probability of success can be defined to produce arrays of SIS receivers for frequencies as high as 1500 GHz.

Frerking, M. A.↗
DOE OSTI2023

BaCu 2 SiS 4 : A New Member of the A II B I 2 M IV Q 4 Chalcogenide Family with a Chiral Crystal Structure

Abstract Noncentrosymmetric ternary and quaternary chalcogenides are studied as promising nonlinear optical (NLO) materials in the mid‐infrared region. Here, we report the synthesis of a new material BaCu 2 SiS 4 in the A II B I 2 M IV Q 4 family ( A =divalent metal; B =monovalent metal; M =tetrel, Q =chalcogen), and discuss its crystal structure, thermal stability, optical behavior, and electronic structure. BaCu 2 SiS 4 crystallizes in the noncentrosymmetric chiral space group P 3 2 21 with lattice parameters a =6.1440(3) Å, c =15.3542(8) Å, V =501.95(6) Å 3 , Z =3. The structure features helical channels formed by corner‐sharing [CuS 4 ] and [SiS 4 ] tetrahedral units. Synthesis was carried out in a molten salt flux, as opposed to a traditional solid‐state route from elements, to minimize the formation of a competing ternary phase, Ba 2 SiS 4 . BaCu 2 SiS 4 is a semiconductor with an experimentally‐determined direct bandgap of ~2.2 eV. The material exhibits second harmonic generation (SHG) activity, confirming the noncentrosymmetric nature of the structure. Analysis of reported A II B I 2 M IV Q 4 crystal structures pointed out a correlation among potential structure types and the radii of the constituent elements. Total energy calculations were carried out to explore the relative stability of several reported crystal structures in this family of compounds.

Sarkar, Arka↗
NASA NTRS1992

Embedding impedance approximations in the analysis of SIS mixers

Future millimeter-wave radio astronomy instruments will use arrays of many SIS receivers, either as focal plane arrays on individual radio telescopes, or as individual receivers on the many antennas of radio interferometers. Such applications will require broadband integrated mixers without mechanical tuners. To produce such mixers, it will be necessary to improve present mixer design techniques, most of which use the three-frequency approximation to Tucker's quantum mixer theory. This paper examines the adequacy of three approximations to Tucker's theory: (1) the usual three-frequency approximation which assumes a sinusoidal LO voltage at the junction, and a short-circuit at all frequencies above the upper sideband; (2) a five-frequency approximation which allows two LO voltage harmonics and five small-signal sidebands; and (3) a quasi five-frequency approximation in which five small-signal sidebands are allowed, but the LO voltage is assumed sinusoidal. These are compared with a full harmonic-Newton solution of Tucker's equations, including eight LO harmonics and their corresponding sidebands, for realistic SIS mixer circuits. It is shown that the accuracy of the three approximations depends strongly on the value of omega R(sub N)C for the SIS junctions used. For large omega R(sub N)C, all three approximations approach the eight-harmonic solution. For omega R(sub N)C values in the range 0.5 to 10, the range of most practical interest, the quasi five-frequency approximation is a considerable improvement over the three-frequency approximation, and should be suitable for much design work. For the realistic SIS mixers considered here, the five-frequency approximation gives results very close to those of the eight-harmonic solution. Use of these approximations, where appropriate, considerably reduces the computational effort needed to analyze an SIS mixer, and allows the design and optimization of mixers using a personal computer.

Kerr, A. R.↗
NASA NTRS2004

A Wide-Bandwidth, Low-Noise SIS Receiver Design for Millimeter and Submillimeter Wavelengths

In principle, millimeter and submillimeter heterodyne receivers using state-of-the-art SIS detectors are capable of extremely large instantaneous bandwidths with noise temperatures within a few Kelvin of the quantum limit. We are applying modem design tools, such as 3D electromagnetic simulators and Caltech's SuperMix SIS analysis package, to develop a new generation of waveguide SIS mixers with very broad RF and IF bandwidths. Our initial design consists of a double-sideband mixer targeted for the 180- 300 GHz band that uses a single SIS junction excited by a full bandwidth, fixed-tuned waveguide probe on a silicon substrate. The IF output band, limited by the MMIC low-noise IF preamplifier, is 6-18 GHz, providing an instantaneous RF bandwidth of 24 GHz (double-sideband). The SIS mixer conversion loss is predicted to be no more than 1-2 dB (single-sideband) with mixer noise temperatures across the band within 10 Kelvin of the quantum limit. The single-sideband receiver noise temperature goal is 70 Kelvin. The wide instantaneous bandwidth and low noise will result in an instrument capable of a variety of important astrophysical observations beyond the capabilities of current instruments. Lab testing of the receiver will begin in the summer of 2002, and a demonstration on the CSO should occur in the spring of 2003.

Sumner, Matthew↗
NASA NTRS1992

Slot antenna SIS mixers for submillimeter wavelengths

We are developing improved versions of a slot antenna SIS mixer which we have previously described. The initial work demonstrated a double sideband noise temperature of 420 K for a 500 GHz quasi-optical SIS mixer employing a twin-slot antenna on a quartz dielectric substrate. A quartz hyperhemispherical lens is used to focus the incoming radiation onto the twin-slot antenna. The advantages of a twin-slot antenna include a low impedance (35 omega) and a clean, symmetric beam pattern into the dielectric with a 70 percent efficiency. In our original mixer, the radiation was coupled from the two slot antennas onto superconducting microstrip lines which fed the SIS junction. By performing an impedance transformation using tapered lines and by feeding the radiation from the two slots to the junction in parallel, the effective (real) impedance seen by the junction was reduced to just 4 omega. This very low impedance allowed a junction area of 2.3 sq micron to be used at 500 GHz, which was manufactured using optical lithography. However, no attempt was made to tune out the junction capacitance. We estimate that this capacitance reduces the impedance coupling efficiency to eta(sub Z) approx. equals 0.23, for our junction with omega R(sub N) C = 5.3 at 500 GHz. The recent development of techniques using electron-beam lithography to manufacture junctions with very small areas (approx. equals 0.1 sq microns) now allows considerably more flexibility in the design of SIS mixer circuits. We have redesigned the slot-antenna mixer to take advantage of this possibility. In particular, we have included a novel circuit which allows the junction capacitance to be tune out over a broad bandwidth. For instance, mixers designed for 800 GHz using NbN/MgO/NbN junctions with realistic parameters achieve a 3 dB impedance bandwidth of nearly 400 GHz. Furthermore, our circuit uses only short lengths of microstrip and should be less sensitive to RF losses than other designs. The improved impedance match should give a large reduction in noise temperature as compared to our previous mixer. The new devices are currently under fabrication. Further details of the design and any available experimental results are discussed.

Zmuidzinas, Jonas↗
NASA NTRS1994

Observations of 13.5 micron rotation-vibration lines of SiS in IRC +10216

We report the first observations of the 13.5 micron fundamental band of SiS in the spectrum of the heavily obscured carbon star IRC +10216. The lines are formed in the inner region of the circumstellar envelope where the gas is accerlerating and where the temperature ranges from 800-500 K. We have carried out a detailed model of the observed line profiles. Our observations are best fit by a gradient in the abundance of SiS. We derive an abundance relative to molecular hydrogen of x(SiS) = 4.3 x 10(exp -6) at a distance of twelve stellar radii from the central star rising to x(SiS) = 4.3 x 10(exp -5) at a few stellar radii from the surface of the star.

Boyle, R. J.↗
NASA NTRS2000

A Low Noise NbTiN-Based 850 GHz SIS Receiver for the Caltech Submillimeter Observatory

We have developed a niobium titanium nitride (NbTiN) based superconductor- insulator-superconductor (SIS) receiver to cover the 350 micron atmospheric window. This frequency band lies entirely above the energy gap of niobium (700 GHz), a commonly used SIS superconductor. The instrument uses an open structure twin-slot SIS mixer that consists of two Nb/AlN/NbTiN tunnel junctions, NbTiN thin-film microstrip tuning elements, and a NbTiN ground plane. The optical configuration is very similar to the 850 GHz waveguide receiver that was installed at the Caltech Submillimeter Observatory (CSO) in 1997. To minimize front-end loss, we employed reflecting optics and a cooled beamsplitter at 4 K. The instrument has an uncorrected receiver noise temperature of 205K DSB at 800 GHz and 410K DSB at 900 GHz. The degradation in receiver sensitivity with frequency is primarily due to an increase in the mixer conversion loss, which is attributed to the mismatch between the SIS junction and the twin-slot antenna impedance. The overall system performance has been confirmed through its use at the telescope to detect a wealth of new spectroscopic lines.

Kooi, J. W.↗
DOE OSTI2025

Sequential Infiltration Synthesis (SIS) of In 2 O 3 -Based Porous Photoelectrodes for Molecular Sensitization

High-surface-area photoelectrodes are highly desirable for solar energy conversion applications, particularly in systems where surface-bound molecular chromophores are responsible for light absorption. To this end, porous Indium-Zinc-Oxide (IZO) frameworks are fabricated via Sequential Infiltration Synthesis (SIS) into poly(methyl methacrylate) (PMMA) films followed by air annealing. A more complete understanding of the multimetal infiltration process conditions and postannealing temperature allows for precise control of zinc (Zn) incorporation to afford porous, conductive, transparent, and amorphous photoelectrodes. Uniform incorporation of both indium (In) and Zn is found to require extended diethylzinc (DEZ) exposures to compensate for remarkably slow precursor diffusion in the presence of indium oxyhydroxide nuclei. SIS-fabricated IZO photoelectrodes are structurally robust, electrochemically active, and exhibit dye adsorption that suggest practical surface area enhancements greater than 100×. In conclusion, these attributes establish SIS as a rapid, scalable, and reproducible route to photoelectrodes for solar energy conversion and hybrid interface characterization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Self-Cleaning Highly Porous TiO 2 Coating Designed by Swelling-Assisted Sequential Infiltration Synthesis (SIS) of a Block Copolymer Template

Photocatalytic self-cleaning coatings with a high surface area are important for a wide range of applications, including optical coatings, solar panels, mirrors, etc. Here, we designed a highly porous TiO 2 coating with photoinduced self-cleaning characteristics and very high hydrophilicity. This was achieved using the swelling-assisted sequential infiltration synthesis (SIS) of a block copolymer (BCP) template, which was followed by polymer removal via oxidative thermal annealing. The quartz crystal microbalance (QCM) was employed to optimize the infiltration process by estimating the mass of material infiltrated into the polymer template as a function of the number of SIS cycles. This adopted swelling-assisted SIS approach resulted in a smooth uniform TiO 2 film with an interconnected network of pores. The synthesized film exhibited good crystallinity in the anatase phase. The resulting nanoporous TiO 2 coatings were tested for their functional characteristics. Exposure to UV irradiation for 1 h induced an improvement in the hydrophilicity of coatings with wetting angle reducing to unmeasurable values upon contact with water droplets. Furthermore, their self-cleaning characteristics were tested by measuring the photocatalytic degradation of methylene blue (MB). The synthesized porous TiO 2 nanostructures displayed promising photocatalytic activity, demonstrating the degradation of approximately 92% of MB after 180 min under ultraviolet (UV) light irradiation. Thus, the level of performance was comparable to the photoactivity of commercial anatase TiO 2 nanoparticles of the same quantity. Our results highlight a new robust approach for designing hydrophilic self-cleaning coatings with controlled porosity and composition.

36 MATERIALS SCIENCE↗
NASA NTRS1987

A study of System Interface Sets (SIS) for the host, target and integration environments of the Space Station Program (SSP)

System interface sets (SIS) for large, complex, non-stop, distributed systems are examined. The SIS of the Space Station Program (SSP) was selected as the focus of this study because an appropriate virtual interface specification of the SIS is believed to have the most potential to free the project from four life cycle tyrannies which are rooted in a dependance on either a proprietary or particular instance of: operating systems, data management systems, communications systems, and instruction set architectures. The static perspective of the common Ada programming support environment interface set (CAIS) and the portable common execution environment (PCEE) activities are discussed. Also, the dynamic perspective of the PCEE is addressed.

Mckay, Charles↗
NASA NTRS1992

Double dipole antenna SIS receivers at 100 and 400 GHz

Antenna patterns were measured between 95 and 120 GHz for a double dipole antenna / ellipsoidal lens combination. The structure produces a non-astigmatic beam with low side lobe levels over that whole band. A heterodyne SIS receiver based on this concept gave a best noise temperature of 145 K DSB at 98 GHz. Measurements were also made with a 400 GHz heterodyne SIS receiver, using a double dipole antenna in conjunction with a hyperhemispherical lens. The best noise temperature was 220 K DSB at 402 GHz. On-chip stubs were used to tune out the SIS junction capacitance.

Skalare, A.↗
NASA NTRS1997

Micromachined Millimeter- and Submillimeter-wave SIS Heterodyne Receivers for Remote Sensing

This is a progress report for the second year of a NASA-sponsored project. The report discusses the design and fabrication of micromachined Superconductor Insulator Superconductor (SIS) heterodyne receivers with integrated tuning elements. These receivers tune out the functional capacitance at desired frequencies, resulting in less noise, lower temperatures and broader bandwidths. The report also discusses the design and fabrication of the first monolithic 3x3 focal-plane arrays for a frequency range of 170-210 GHz. Also addressed is the construction of a 9-channel bias and read-out system, as well as the redesign of the IF connections to reduce cross talk between SIS junctions, which become significant a frequency of 1.5 GHz IF. Uniformity of the junction arrays were measured and antenna beam patterns of several array elements under operating conditions also were measured. Finally, video and heterodyne responses of our focal-plane arrays were measured as well. Attached is a paper on: 'Development of a 170-210 GHz 3x3 micromachined SIS imaging array'.

Hu, Qing↗
NASA NTRS1998

Development of SIS Mixers for 1 THz

SIS heterodyne mixer technology based on niobium tunnel junctions has now been pushed to frequencies over 1 THz, clearly demonstrating that the SIS junctions are capable of mixing at frequencies up to twice the energy gap frequency (4 Delta/h). However, the performance degrades rapidly above the gap frequency of niobium (2 Delta/h approx. 700 GHz) due to substantial ohmic losses in the on-chip tuning circuit. To solve this problem, the tuning circuit should be fabricated using a superconducting film with a larger energy gap, such as NbN; unfortunately, NbN films often have a substantial excess surface resistance in the submillimeter band. In contrast, the SIS mixer measurements we present in this paper indicate that the losses for NbTiN thin films can be quite low.

Zmuidzinas, J.↗
NASA NTRS2001

Low Noise 1.2 THz SIS Receiver

We present the development of a low noise superconductor insulator superconductor (SIS) mixer for the 1.1 - 1.25 THz heterodyne receiver of FIRST space radiotelescope. The quasi-optical SIS mixer has two NbTiN/AlN/Nb junctions with critical current density 30 kA/sq cm. The individual junction area is close to 0.65 square micrometers. The SIS junctions are coupled to the optical input beam through a planar double slot antenna and a Si hyperhemispherical lens. The minimum DSB receiver noise temperature is 650 K, about 12 hv/k.

Karpov, A.↗