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12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Micromachined Thermoelectric Sensors and Arrays and Process for Producing

Linear arrays with up to 63 micromachined thermopile infrared detectors on silicon substrates have been constructed and tested. Each detector consists of a suspended silicon nitride membrane with 11 thermocouples of sputtered Bi-Te and Bi-Sb-Te thermoelectric elements films. At room temperature and under vacuum these detectors exhibit response times of 99 ms, zero frequency D* values of 1.4 x 10(exp 9) cmHz(exp 1/2)/W and responsivity values of 1100 V/W when viewing a 1000 K blackbody source. The only measured source of noise above 20 mHz is Johnson noise from the detector resistance. These results represent the best performance reported to date for an array of thermopile detectors. The arrays are well suited for uncooled dispersive point spectrometers. In another embodiment, also with Bi-Te and Bi-Sb-Te thermoelectric materials on micromachined silicon nitride membranes, detector arrays have been produced with D* values as high as 2.2 x 10(exp 9) cm Hz(exp 1/2)/W for 83 ms response times.

Foote, Marc C.↗
DOE OSTI2022

Large Exchange Coupling Between Localized Spins and Topological Bands in MnBi 2 Te 4

Magnetism in topological materials creates phases exhibiting quantized transport phenomena with potential technological applications. The emergence of such phases relies on strong interaction between localized spins and the topological bands, and the consequent formation of an exchange gap. However, this remains experimentally unquantified in intrinsic magnetic topological materials. Here, this interaction is quantified in MnBi 2 Te 4 , a topological insulator with intrinsic antiferromagnetism. This is achieved by optically exciting Bi-Te p states comprising the bulk topological bands and interrogating the consequent Mn 3d spin dynamics, using a multimodal ultrafast approach. Ultrafast electron scattering and magneto-optic measurements show that the p states demagnetize via electron-phonon scattering at picosecond timescales. Despite being energetically decoupled from the optical excitation, the Mn 3d spins, probed by resonant X-ray scattering, are observed to disorder concurrently with the p spins. Together with atomistic simulations, this reveals that the exchange coupling between localized spins and the topological bands is at least 100 times larger than the superexchange interaction, implying an optimal exchange gap of at least 25 meV in the surface states. Here, by quantifying this exchange coupling, this study validates the materials-by-design strategy of utilizing localized magnetic order to manipulate topological phases, spanning static to ultrafast timescales.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Quasi-two-dimensional ferromagnetism and anisotropic interlayer couplings in the magnetic topological insulator MnBi 2 Te 4

MnBi 2 Te 4 (MBT) is a promising van der Waals layered antiferromagnetic (AFM) topological insulator that combines a topologically nontrivial inverted Bi-Te band gap with ferromagnetic (FM) layers of Mn ions. Here, the inelastic neutron scattering on single crystals reported here describes rather complex magnetism in MBT. The magnetic anisotropy that controls the bulk and surface magnetic field response of MBT is found to have contributions from both single-ion and interlayer two-ion terms. A description of the quasi-two-dimensional intralayer FM spin waves requires long-range, competing FM and AFM interactions and anomalous damping. While this might suggest carrier-mediated magnetic coupling, abinitio calculations in insulating MBT also find long-range interactions, and classical spin dynamics simulations suggest that magnetic vacancies are at least partially responsible for observations of anomalous damping near the zone boundary.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2001

Progress towards high-performance thermopile imaging arrays

The purpose of this present work is to improve thermopile 2-D arrays substantially by combining Bi-Te and Bi-Sb-Te thermoelectric materials with a unique pixel structure and low-noise readout circuitry.

detector thermopile infrared uncooled array imagin↗
NASA NTRS2003

Surface-Micromachined Planar Arrays of Thermopiles

Planar two-dimensional arrays of thermopiles intended for use as thermal-imaging detectors are to be fabricated by a process that includes surface micromachining. These thermopile arrays are designed to perform better than do prior two-dimensional thermopile arrays. The lower performance of prior two-dimensional thermopile arrays is attributed to the following causes: The thermopiles are made from low-performance thermoelectric materials. The devices contain dielectric supporting structures, the thermal conductances of which give rise to parasitic losses of heat from detectors to substrates. The bulk-micromachining processes sometimes used to remove substrate material under the pixels, making it difficult to incorporate low-noise readout electronic circuitry. The thermoelectric lines are on the same level as the infrared absorbers, thereby reducing fill factor. The improved pixel design of a thermopile array of the type under development is expected to afford enhanced performance by virtue of the following combination of features: Surface-micromachined detectors are thermally isolated through suspension above readout circuitry. The thermopiles are made of such high-performance thermoelectric materials as Bi-Te and Bi-Sb-Te alloys. Pixel structures are supported only by the thermoelectric materials: there are no supporting dielectric structures that could leak heat by conduction to the substrate.

Foote, Marc C.↗
DOE OSTI2020

Materials Data on BiTe by Materials Project

BiTe is MAX Phase-derived structured and crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of two BiTe sheets oriented in the (0, 0, 1) direction. there are three inequivalent Bi2+ sites. In the first Bi2+ site, Bi2+ is bonded to six Te2- atoms to form a mixture of edge and corner-sharing BiTe6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (3.11 Å) and three longer (3.28 Å) Bi–Te bond lengths. In the second Bi2+ site, Bi2+ is bonded to six Te2- atoms to form a mixture of edge and corner-sharing BiTe6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (3.09 Å) and three longer (3.29 Å) Bi–Te bond lengths. In the third Bi2+ site, Bi2+ is bonded in a 3-coordinate geometry to three equivalent Te2- atoms. All Bi–Te bond lengths are 3.70 Å. There are three inequivalent Te2- sites. In the first Te2- site, Te2- is bonded in a 3-coordinate geometry to three equivalent Bi2+ atoms. In the second Te2- site, Te2- is bonded to six Bi2+ atoms to form a mixture of distorted edge and corner-sharing TeBi6 octahedra. The corner-sharing octahedral tilt angles are 4°. In the third Te2- site, Te2- is bonded to six Bi2+ atoms to form a mixture of edge and corner-sharing TeBi6 octahedra. The corner-sharing octahedral tilt angles are 4°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Bi4Te3 by Materials Project

Bi4Te3 is MAX Phase-derived structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three Bi4Te3 sheets oriented in the (0, 0, 1) direction. there are two inequivalent Bi+1.50+ sites. In the first Bi+1.50+ site, Bi+1.50+ is bonded to six Te2- atoms to form a mixture of edge and corner-sharing BiTe6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (3.11 Å) and three longer (3.29 Å) Bi–Te bond lengths. In the second Bi+1.50+ site, Bi+1.50+ is bonded in a 3-coordinate geometry to three equivalent Te2- atoms. All Bi–Te bond lengths are 3.66 Å. There are two inequivalent Te2- sites. In the first Te2- site, Te2- is bonded to six equivalent Bi+1.50+ atoms to form a mixture of edge and corner-sharing TeBi6 octahedra. The corner-sharing octahedral tilt angles are 5°. In the second Te2- site, Te2- is bonded to six Bi+1.50+ atoms to form a mixture of distorted edge and corner-sharing TeBi6 octahedra. The corner-sharing octahedral tilt angles are 5°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Bi2Te3 by Materials Project

Bi2Te3 is MAX Phase-derived structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three Bi2Te3 sheets oriented in the (0, 0, 1) direction. Bi3+ is bonded to six Te2- atoms to form a mixture of corner and edge-sharing BiTe6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (3.10 Å) and three longer (3.29 Å) Bi–Te bond lengths. There are two inequivalent Te2- sites. In the first Te2- site, Te2- is bonded in a 6-coordinate geometry to three equivalent Bi3+ atoms. In the second Te2- site, Te2- is bonded to six equivalent Bi3+ atoms to form edge-sharing TeBi6 octahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BiTe3 by Materials Project

BiTe3 crystallizes in the trigonal R3m space group. The structure is three-dimensional. Bi5+ is bonded to six Te+1.67- atoms to form edge-sharing BiTe6 octahedra. There are three shorter (3.18 Å) and three longer (3.22 Å) Bi–Te bond lengths. There are three inequivalent Te+1.67- sites. In the first Te+1.67- site, Te+1.67- is bonded in a 6-coordinate geometry to six Te+1.67- atoms. There are three shorter (3.27 Å) and three longer (3.30 Å) Te–Te bond lengths. In the second Te+1.67- site, Te+1.67- is bonded in a 6-coordinate geometry to three equivalent Bi5+ and three equivalent Te+1.67- atoms. In the third Te+1.67- site, Te+1.67- is bonded to three equivalent Bi5+ and three equivalent Te+1.67- atoms to form distorted edge-sharing TeBi3Te3 octahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Bi2Te3 by Materials Project

Bi2Te3 is trigonal omega-like structured and crystallizes in the trigonal R3m space group. The structure is two-dimensional and consists of three Bi2Te3 sheets oriented in the (0, 0, 1) direction. there are two inequivalent Bi3+ sites. In the first Bi3+ site, Bi3+ is bonded in a distorted T-shaped geometry to three equivalent Te2- atoms. All Bi–Te bond lengths are 3.14 Å. In the second Bi3+ site, Bi3+ is bonded in a distorted T-shaped geometry to three equivalent Te2- atoms. All Bi–Te bond lengths are 3.13 Å. There are three inequivalent Te2- sites. In the first Te2- site, Te2- is bonded to three equivalent Bi3+ and three equivalent Te2- atoms to form a mixture of corner and edge-sharing TeBi3Te3 octahedra. The corner-sharing octahedral tilt angles are 0°. All Te–Te bond lengths are 3.28 Å. In the second Te2- site, Te2- is bonded to six Te2- atoms to form edge-sharing TeTe6 octahedra. All Te–Te bond lengths are 3.28 Å. In the third Te2- site, Te2- is bonded to three equivalent Bi3+ and three equivalent Te2- atoms to form a mixture of corner and edge-sharing TeBi3Te3 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BiTe by Materials Project

BiTe is Molybdenum Carbide MAX Phase-like structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Bi2+ is bonded to six equivalent Te2- atoms to form a mixture of edge and corner-sharing BiTe6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Bi–Te bond lengths are 3.25 Å. Te2- is bonded to six equivalent Bi2+ atoms to form a mixture of edge and corner-sharing TeBi6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗