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DOE OSTI2026

Dynamically tunable membrane metasurfaces for infrared spectroscopy and strong light-matter interactions

Mid-infrared spectroscopy enables biochemical sensing by identifying vibrational molecular fingerprints, but it faces limitations in instrumentation portability and analytical sensitivity. Optical metasurfaces with strong mid-infrared photonic resonances provide an attractive solution towards on-chip spectrometry and sensitive molecular detection, yet their static nature hinders their anticipated impact. Here, we introduce and demonstrate dynamically tunable silicon membrane metasurfaces exhibiting high-Q transmissive resonances in the fingerprint region. By harnessing silicon’s thermo-optical properties, we achieve continuous modulation of coupling-induced transparency (CIT) modes that emerge upon the interference of quasi-bound states in the continuum (q-BICs) and surface lattice modes (SLMs). We measure a spectral tuning rate of 0.06 cm −1 K −1 by continuously sweeping the sharp CIT resonances over a 23.5 cm −1 spectral range across a temperature range of 300–700 K. In the current proof‑of‑concept implementation, the dynamic transmission control enables non-contact chemical analysis of polymer films by detecting characteristic absorption bands of polystyrene (1450 and 1492 cm −1 ) and poly(methyl methacrylate) (1730 cm −1 ) without requiring conventional spectrometers. When analyte molecules fill the metasurface-generated photonic cavities, we demonstrate vibrational strong coupling between the poly(methyl methacrylate)’s carbonyl band and the CIT mode, manifested in a Rabi splitting of ~43 cm −1 . Our results establish a new photonic platform that unites spectral precision, strong field enhancement, and reconfigurability, offering diverse potential for compact mid-infrared spectroscopy, molecular sensing, and programmable polaritonic photonics.

74 ATOMIC AND MOLECULAR PHYSICS↗

NASA NTRS1996

Epitaxial Growth of beta-Silicon Carbide (SiC) on a Compliant Substrate via Chemical Vapor Deposition (CVD)

Many lattice defects have been attributed to the lattice mismatch and the difference in the thermal coefficient of expansion between SiC and silicon (Si). Stacking faults, twins and antiphase boundaries are some of the lattice defects found in these SiC films. These defects may be a partial cause of the disappointing performance reported for the prototype devices fabricated from beta-SiC films. The objective of this research is to relieve some of the thermal stress due to lattice mismatch when SiC is epitaxially grown on Si. The compliant substrate is a silicon membrane 2-4 microns thick. The CVD process includes the buffer layer which is grown at 1360 C followed by a very thin epitaxial growth of SiC. Then the temperature is raised to 1500 C for the subsequent growth of SiC. Since silicon melts at 1415 C, the SiC will be grown on molten Silicon which is absorbed by a porous graphite susceptor eliminating the SiC/Si interface. We suspect that this buffer layer will yield less stressed material to help in the epitaxial growth of SiC.

Mitchell, Sharanda L.↗

DOE OSTI2023

Semiconductor Thermal and Electrical Properties Decoupled by Localized Phonon Resonances

Abstract Thermoelectric materials convert heat into electricity through thermally driven charge transport in solids or vice versa for cooling. To compete with conventional energy‐conversion technologies, a thermoelectric material must possess the properties of both an electrical conductor and a thermal insulator. However, these properties are normally mutually exclusive because of the interconnection between scattering mechanisms for charge carriers and phonons. Recent theoretical investigations on sub‐device scales have revealed that nanopillars attached to a membrane exhibit a multitude of local phonon resonances, spanning the full spectrum, that couple with the heat‐carrying phonons in the membrane and cause a reduction in the in‐plane thermal conductivity, with no expected change in the electrical properties because the nanopillars are outside the pathway of voltage generation and charge transport. Here this effect is demonstrated experimentally for the first time by investigating device‐scale suspended silicon membranes with GaN nanopillars grown on the surface. The nanopillars cause up to 21% reduction in the thermal conductivity while the power factor remains unaffected, thus demonstrating an unprecedented decoupling in the semiconductor's thermoelectric properties. The measured thermal conductivity behavior for coalesced nanopillars and corresponding lattice‐dynamics calculations provide evidence that the reductions are mechanistically tied to the phonon resonances. This finding paves the way for high‐efficiency solid‐state energy recovery and cooling.

Spann, Bryan T.↗

NASA NTRS2020

Excess Heat Capacity in Mo/Au Transition Edge Sensor Bolometric Detectors

Excessheat capacity in a bolometric detector has the consequence of increasing or leading to multiple device time con-stants.The Mo/Au bilayer transition edge sensor (TES) bolo-metric detectors intended for the high resolution mid-infrared spectrometer (HIRMES) have two response time, one of which is a few times longer than that estimated from materials used in the design. The relative contribution of this settling time to the overall time response of the detectors is roughly proportional with the pixel area, which ranges between ~0.3 and 2.6 mm2.Use of laser ablation to remove sections of the silicon membranes comprising the pixels results in a detector response with a smaller contribution from the secondary time constant.Additional information about the nature of this excess heat capacity is gleaned from glancing in-cidence x-ray diffraction, which reveals the presence of molyb-denum silicides near the silicon surface from the bi-layer deposi-tion.Quantitative analysis of the concentration of excess molyb-denum, estimated with secondary ion mass spectroscopy, is com-mensurate to the additional heat capacity needed to explain the anomalous time response of the detectors.

HIRMES↗

NASA NTRS1992

Evolution of a phase separated gravity independent bioreactor

The evolution of a phase-separated gravity-independent bioreactor is described. The initial prototype, a zero head-space manifold silicone membrane based reactor, maintained large diffusional resistances. Obtaining oxygen transfer rates needed to support carbon-recycling aerobic microbes is impossible if large resistances are maintained. Next generation designs (Mark I and II) mimic heat exchanger design to promote turbulence at the tubing-liquid interface, thereby reducing liquid and gas side diffusional resistances. While oxygen transfer rates increased by a factor of ten, liquid channeling prevented further increases. To overcome these problems, a Mark III reactor was developed which maintains inverted phases, i.e., media flows inside the silicone tubing, oxygen gas is applied external to the tubing. This enhances design through changes in gas side driving force concentration and liquid side turbulence levels. Combining an applied external pressure of 4 atm with increased Reynolds numbers resulted in oxygen transfer intensities of 232 mmol O2/l per hr (1000 times greater than the first prototype and comparable to a conventional fermenter). A 1.0 liter Mark III reactor can potentially deliver oxygen supplies necessary to support cell cultures needed to recycle a 10-astronaut carbon load continuously.

Villeneuve, Peter E.↗

DOE OSTI2025

Enhanced biochemical sensing with high- Q transmission resonances in free-standing membrane metasurfaces

Optical metasurfaces provide solutions to label-free biochemical sensing by localizing light resonantly beyond the diffraction limit, thereby selectively enhancing light–matter interactions for improved analytical performance. However, high-Q resonances in metasurfaces are usually achieved in the reflection mode, which impedes metasurface integration into compact imaging systems. Here, we demonstrate a metasurface platform for advanced biochemical sensing based on the physics of the bound states in the continuum (BIC) and electromagnetically induced transparency (EIT) modes, which arise when two interfering resonances from a periodic pattern of tilted elliptic holes overlap both spectrally and spatially, creating a narrow transparency window in the mid-infrared spectrum. We experimentally measure these resonant peaks observed in transmission mode (Q ~ 734 at λ ~ 8.8 µm) in free-standing silicon membranes and confirm their tunability through geometric scaling. We also demonstrate the strong coupling of the BIC-EIT modes with a thinly coated PMMA film on the metasurface, characterized by a large Rabi splitting (32 cm -1 ) and biosensing of protein monolayers in transmission mode. Our new photonic platform can facilitate the integration of metasurface biochemical sensors into compact and monolithic optical systems while being compatible with scalable manufacturing, thereby clearing the way for on-site biochemical sensing in everyday applications.

Rosas, Samir [Univ. of Wisconsin, Madison, WI (Uni↗

NASA NTRS2017

Characterization of Si-Membrane TES Bolometer Arrays for the HIRMES Instrument

The High Resolution Mid-Infrared Spectrometer (HIRMES) instrument will fly onboard NASA's airborne Stratospheric Observatory for Infrared Astronomy (SOFIA) in 2019. HIRMES will provide astronomers with a unique observing window (25 122 Âµm) for exploring the evolution of protoplanetary disks into young solar systems, and the composition of our Solar System. There are two focal plane detector arrays for the instrument: a high-resolution (/ = 100,000) 8x16 detector array with a target noise-equivalent power, NEP 3x10-18 W/Hz; and a low-resolution (/ = 2,000 19,000) 16x64 detector array with a target NEP 2x10-17 W/Hz. The detectors for both of these arrays are superconducting Mo/Au bilayer transition edge sensor (TES) bolometers on thin suspended single-crystal silicon membranes. Here we present our characterization results for the detectors in both arrays, including measurements of thermal conductance with comparison to phonon transport models, saturation power, noise, and array uniformity.

Instrumentation and Photography↗

NASA NTRS2014

Precision Control of Thermal Transport in Cryogenic Single-Crystal Silicon Devices

We report on the diffusive-ballistic thermal conductance of multi-moded single-crystal silicon beams measured below 1 K. It is shown that the phonon mean-free-path is a strong function of the surface roughness characteristics of the beams. This effect is enhanced in diffuse beams with lengths much larger than, even when the surface is fairly smooth, 510 nm rms, and the peak thermal wavelength is 0.6 microns. Resonant phonon scattering has been observed in beams with a pitted surface morphology and characteristic pit depth of 30 nm. Hence, if the surface roughness is not adequately controlled, the thermal conductance can vary significantly for diffuse beams fabricated across a wafer. In contrast, when the beam length is of order, the conductance is dominated by ballistic transport and is effectively set by the beam cross-sectional area. We have demonstrated a uniformity of +/-8% in fractional deviation for ballistic beams, and this deviation is largely set by the thermal conductance of diffuse beams that support the micro-electro-mechanical device and electrical leads. In addition, we have found no evidence for excess specific heat in single-crystal silicon membranes. This allows for the precise control of the device heat capacity with normal metal films. We discuss the results in the context of the design and fabrication of large-format arrays of far-infrared and millimeter wavelength cryogenic detectors.

multi-moded single-crystal silicon beams↗

DOE OSTI2023

Vertical full-colour micro-LEDs via 2D materials-based layer transfer

Micro-LEDs (µLEDs) have been explored for augmented and virtual reality display applications that require extremely high pixels per inch and luminance. However, conventional manufacturing processes based on the lateral assembly of red, green and blue (RGB) µLEDs have limitations in enhancing pixel density. Recent demonstrations of vertical µLED displays have attempted to address this issue by stacking freestanding RGB LED membranes and fabricating top-down, but minimization of the lateral dimensions of stacked µLEDs has been difficult. Here we report full-colour, vertically stacked µLEDs that achieve, to our knowledge, the highest array density (5,100 pixels per inch) and the smallest size (4 µm) reported to date. This is enabled by a two-dimensional materials-based layer transfer technique that allows the growth of RGB LEDs of near-submicron thickness on two-dimensional material-coated substrates via remote or van der Waals epitaxy, mechanical release and stacking of LEDs, followed by top-down fabrication. The smallest-ever stack height of around 9 µm is the key enabler for record high µLED array density. We also demonstrate vertical integration of blue µLEDs with silicon membrane transistors for active matrix operation. Furthermore, these results establish routes to creating full-colour µLED displays for augmented and virtual reality, while also offering a generalizable platform for broader classes of three-dimensional integrated devices.

42 ENGINEERING↗

DOE OSTI2021

Quantitative agreement between dynamical rocking curves in ultrafast electron diffraction for x-ray lasers

Electron diffraction through a thin patterned silicon membrane can be used to create complex spatial modulations in electron distributions. By precisely varying parameters such as crystallographic orientation and wafer thickness, the intensity of reflections in the diffraction plane can be controlled and by placing an aperture to block all but one spot, we can form an image with different parts of the patterned membrane, as is done for bright-field imaging in microscopy. The patterned electron beams can then be used to control phase and amplitude of subsequent x-ray emission, enabling novel coherent x-ray methods. Furthermore, the electrons themselves can also be used for femtosecond time resolved diffraction and microscopy. As a first step toward patterned beams, we demonstrate experimentally and through simulation the ability to accurately predict and control diffraction spot intensities. We simulate MeV transmission electron diffraction patterns using the multislice method for various crystallographic orientations of a single crystal Si(001) membrane near beam normal. The resulting intensity maps of the Bragg reflections are compared to experimental results obtained at the Accelerator Structure Test Area Ultrafast Electron Diffraction (ASTA UED) facility at SLAC. Furthermore, the fraction of inelastic and elastic scattering of the initial charge is estimated along with the absorption of the membrane to determine the contrast that would be seen in a patterned version of the Si(001) membrane.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Visualizing plasmons and ultrafast kinetic instabilities in laser-driven solids using X-ray scattering

Ultra-intense lasers that ionize atoms and accelerate electrons in solids to near the speed of light can lead to kinetic instabilities that alter the laser absorption and subsequent electron transport, isochoric heating, and ion acceleration. These instabilities can be difficult to characterize, but X-ray scattering at keV photon energies allows for their visualization with femtosecond temporal resolution on the few nanometer mesoscale. Here, we perform such experiment on laser-driven flat silicon membranes that shows the development of structure with a dominant scale of 60 nm in the plane of the laser axis and laser polarization, and 95 nm in the vertical direction with a growth rate faster than 0.1 fs -1 . Combining the XFEL experiments with simulations provides a complete picture of the structural evolution of ultra-fast laser-induced plasma density development, indicating the excitation of plasmons and a filamentation instability. Particle-in-cell simulations confirm that these signals are due to an oblique two-stream filamentation instability. These findings provide new insight into ultra-fast instability and heating processes in solids under extreme conditions at the nanometer level with possible implications for laser particle acceleration, inertial confinement fusion, and laboratory astrophysics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2022

Density changes in amorphous silicon induced by swift heavy ions

For this study, pure and gold-doped amorphous silicon membranes were irradiated with swift heavy ions (75 MeV Ag or 1.1 GeV Au ions) and studied using small-angle x-ray scattering. The samples that were irradiated with 1.1 GeV Au ions produced a scattering pattern consistent with core-shell-type ion tracks of 2.0 ± 0.1 nm (core) and 7.0 ± 0.3 nm (total) radius irrespective of gold doping, consistent with radii previously observed. The density in the core is nearly 4% different from that of the surrounding material. The entire track (core + shell) is slightly less dense than the surrounding material, yielding an expansion or hammering constant A of 0.036 ± 0.003 nm 2 per ion track, consistent with the macroscopic “hammering” deformation. No tracks were found in samples irradiated with 75 MeV Ag ions, and no signature specific to the gold impurity doping could be observed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

X-Ray Performance of Critical-angle Transmission Grating Prototypes for the Arcus Mission

Arcus is a proposed Explorer Class soft X-ray grating spectrometer. It aims to explore cosmic feedback by mapping hot gases within and between galaxies and galaxy clusters and characterizing jets and winds from supermassive black holes and to investigate the dynamics of protoplanetary disks and stellar accretion. Arcus features 12 m focal-length grazing-incidence silicon pore optics (SPO) developed for the Athena mission. Critical-angle transmission (CAT) gratings efficiently disperse high diffraction orders onto CCDs. We report new and improved X-ray performance results for Arcus-like CAT gratings, including a record resolving power for two coaligned CAT gratings. Multiple Arcus prototype grating facets were illuminated by an SPO at the PANTER facility. The facets consist of 32 × 32.5 mm 2 patterned silicon membranes, bonded to metal frames. The bonding angle is adjusted according to the measured average tilt angle of the grating bars in the membrane. Two simultaneously illuminated facets show a minor broadening of the Al-K α doublet in the 18th and 21st orders with the best-fit record effective resolving power of ${R}_{G}\approx {1.3}_{-0.5}^{+\infty }\times {10}^{4}$ (3σ), about three to four times the Arcus requirement. We measured the diffraction efficiency of quasi-fully illuminated gratings at O-K wavelengths in orders 4–7 in an Arcus-like configuration and compare results with synchrotron spot measurements. After corrections for geometrical effects and bremsstrahlung continuum, we find agreement between full and spot illumination at the two different facilities, as well as with the models used for Arcus effective area predictions. We find that these flight-like gratings meet the diffraction efficiency and greatly exceed the resolving power Arcus requires.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1972

Evaluation of advanced bladder technology

Research conducted during this period is reported. Studies presented include: (1) diffusion and permeation of CO2, O2, N2, and NO2 through polytetra fluoroethylene; (2) diffusion, permeation and solubility of simple gases (CO2, O2, N2, CH4, C2H6, C3H8, and C2H4) through a copolymer of hexafluoro propylene and tetrafluoro ethylene (FEP); (3) viscous flow and diffusion of gases throug small apertures; (4) diffusion and permeation of O2, N2, CO2, CH4, C2H6, and C3H8 through nitroso rubber; and (5) results of gas transport studies with carborane siloxane, nitroso rubber, silicone membrane, krytox coating on teflon, and FEP coated glass cloth. Publications generated under this program are listed.

Christensen, M. V.↗

NASA NTRS1999

Some Aspects on the Mechanical Analysis of Micro-Shutters

An array of individually addressable micro-shutters is being designed for spectroscopic applications. Details of the design are presented in a companion paper. The mechanical design of a single shutter element has been completed. This design consists of a shutter blade suspended on a torsion beam manufactured out of single crystal silicon membranes. During operation the shutter blade will be rotated by 90 degrees out of the array plane. Thus, the stability and durability of the beams are crucial for the reliability of the devices. Structures were fabricated using focused ion beam milling in a FEI 620 dual beam machine, and subsequent testing was completed using the same platform. This allowed for short turn around times. We performed torsion and bending experiments to determine key characteristics of the membrane material. Results of measurements on prototype shutters were compared with the predictions of the numerical models. The data from these focused studies were used in conjunction with experiments and numerical models of shutter prototypes to optimize the design. In this work, we present the results of the material studies, and assess the mechanical performance of the resulting design.

Fettig, Rainer K.↗

NASA NTRS2002

The Stretched Lens Array (SLA): An Ultra-Light Photovoltaic Concentrator

A high-performance, ultralight, photovoltaic concentrator array is being developed for space power. The stretched lens array (SLA) uses stretched-membrane, silicone Fresnel lenses to concentrate sunlight onto triple-junction photovoltaic cells. The cells are mounted to a composite radiator structure. The entire solar array wing, including lenses, photovoltaic cell flex circuits, composite panels, hinges, yoke, wiring harness, and deployment mechanisms, has a mass density of 1.6 kg/sq.m. NASA Glenn has measured 27.4% net SLA panel efficiency, or 375 W/sq.m. power density, at room temperature. At GEO operating cell temperature (80 C), this power density will be 300 W/sq.m., resulting in more than 180 W/kg specific power at the full wing level. SLA is a direct ultralight descendent of the successful SCARLET array on NASA's Deep Space 1 spacecraft. This paper describes the evolution from SCARLET to SLA, summarizes the SLA's key features, and provides performance and mass data for this new concentrator array.

ONeill, Mark J.↗

NASA NTRS1992

Cell culture for three-dimensional modeling in rotating-wall vessels: an application of simulated microgravity

High-density, three-dimensional cell cultures are difficult to grow in vitro. The rotating-wall vessel (RWV) described here has cultured BHK-21 cells to a density of 1.1 X 10(7) cells/ml. Cells on microcarriers were observed to grow with enhanced bridging in this batch culture system. The RWV is a horizontally rotated tissue culture vessel with silicon membrane oxygenation. This design results in a low-turbulence, low-shear cell culture environment with abundant oxygenation. The RWV has the potential to culture a wide variety of normal and neoplastic cells.

Weightlessness Simulation↗

NASA NTRS2005

Making Wide-IF SIS Mixers with Suspended Metal-Beam Leads

A process that employs silicon-on-insulator (SOI) substrates and silicon (Si) micromachining has been devised for fabricating wide-intermediate-frequency-band (wide-IF) superconductor/insulator/superconductor (SIS) mixer devices that result in suspended gold beam leads used for radio-frequency grounding. The mixers are formed on 25- m-thick silicon membranes. They are designed to operate in the 200 to 300 GHz frequency band, wherein wide-IF receivers for tropospheric- chemistry and astrophysical investigations are necessary. The fabrication process can be divided into three sections: 1. The front-side process, in which SIS devices with beam leads are formed on a SOI wafer; 2. The backside process, in which the SOI wafer is wax-mounted onto a carrier wafer, then thinned, then partitioned into individual devices; and 3. The release process, in which the individual devices are separated using a lithographic dicing technique. The total thickness of the starting 4-in. (10.16-cm)-diameter SOI wafer includes 25 m for the Si device layer, 0.5 m for the buried oxide (BOX) layer, and 350 m the for Si-handle layer. The front-side process begins with deposition of an etch-stop layer of SiO2 or AlN(x), followed by deposition of a Nb/Al- AlN(x) /Nb trilayer in a load-locked DC magnetron sputtering system. The lithography for four of a total of five layers is performed in a commercial wafer-stepping apparatus. Diagnostic test dies are patterned concurrently at certain locations on the wafer, alongside the mixer devices, using a different mask set. The conventional, self-aligned lift-off process is used to pattern the SIS devices up to the wire level.

Kaul, Anupama↗