Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “SILICONES”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Dual functionality of over-lithiated NMC for high energy silicon-based lithium-ion batteries

Owing to their high specific capacity and suitably low operating potential, silicon-based anodes are an attractive alternative to graphite in next-generation lithium-ion batteries. However, silicon anodes suffer from low initial coulombic efficiency and fast capacity decay, limiting their widespread application. Pre-lithiation strategies are highly appealing to compensate for irreversible active lithium loss and to boost the cell energy density. In this work, we maximize the cell energy density by direct pre-lithiation of the NMC (LiNi 0.5 Mn 0.3 Co 0.2 O 2 ) cathode to Li 1+x NMCO 2 without introducing inactive deadweight to either electrode. First, we demonstrate that Li 1+x NMCO 2 can be synthesized chemically, via reaction between NMC and lithium napthalide, and electrochemically. The NMC cathode is tolerant of a one-time over-lithiation up to 60 mA h g NMC -1 , giving capacity retention on par with untreated NMC in half cell electrochemical cycling. Using synchrotron X-ray absorption spectroscopy (ex situ) and diffraction (in situ), we demonstrate that higher amounts of over-lithiation lead to local structure distortion – driven by transition metal reduction to Jahn–Teller active Mn 3+ and Co 2+ – as well as bulk structural hysteresis during over-lithiation and layer “buckling” that increases the amount of lithium extracted from the structure in the charged state. The Li 1+x NMCO 2 with low-to-moderate over-lithiation capacity (23, 46, and 70 mA h g NMC -1 ) is proven to be a highly effective dual-purpose lithium source and cathode material in full cell tests with a commercially relevant Si–graphite anode. These cells show higher capacity, superior cycle life, and improved coulombic efficiencies when compared to those with stoichiometric NMC cathodes. Finally, this study introduces a new and simple method to pre-lithiate layered transition metal oxide cathodes, opening up new possibilities for the development of high energy density lithium-ion batteries with next-generation anodes.

25 ENERGY STORAGE↗
DOE OSTI2024

Elucidating the role of oxidation in two-dimensional silicon nanosheets

We report a synthetic protocol that yields hydrogen-terminated 2D silicon nanosheets with greatly reduced siloxane (e.g., Si–O–Si, O x Si) content. These nanosheets displayed weak, broad photoluminescence centered near 610 nm with a low absolute photoluminescence quantum yield (as low as 0.2%). By intentionally oxidizing the nanosheets, the photoluminescence peak emission wavelength blueshifted to 510 nm, and the quantum yield increased by more than an order of magnitude to 8.5%. These results demonstrate that oxidation of 2D silicon nanosheets modulates the material's bandgap and suggests that previously reported photoluminescence properties for this material resulted, in part, from oxidation.

Essner, Jeremy B. [Iowa State Univ., Ames, IA (Uni↗
DOE OSTI2020

High-field spatial imaging of charge transport in silicon at low temperature

We present direct imaging measurements of charge transport across a 1 cm × 1 cm × 4 mm-thick crystal of high purity silicon (~15 kΩ-cm) at temperatures of 5 K and 500 mK. We use these data to measure lateral diffusion of electrons and holes as a function of the electric field applied along the [111] crystal axis and to verify our low-temperature Monte Carlo software. The range of field strengths in this paper exceed those used in our previous study [R. A. Moffatt et al., Appl. Phys. Lett. 114, 032104 (2019)] by a factor of 10 and now encompass the region in which some recent silicon dark matter detectors operate [R. Agnese et al., Phys. Rev. Lett. 121, 051301 (2018)]. Finally, we also report on a phenomenon of surface charge trapping, which can reduce expected charge collection.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Thermal transport in nanoporous holey silicon membranes investigated with optically induced transient thermal gratings

In this study, we use transient thermal gratings—a non-contact, laser-based thermal metrology technique with intrinsically high accuracy—to investigate room-temperature phonon-mediated thermal transport in two nanoporous holey silicon membranes with limiting dimensions of 120 nm and 250 nm, respectively. We compare the experimental results with ab initio calculations of phonon-mediated thermal transport according to the phonon Boltzmann transport equation (BTE) using two different computational techniques. We find that the calculations conducted within the Casimir framework, i.e., based on the BTE with the bulk phonon dispersion and diffuse scattering from surfaces, are in quantitative agreement with the experimental data and thus conclude that this framework is adequate for describing phonon-mediated thermal transport in silicon nanostructures with feature sizes of the order of 100 nm.

Duncan, Ryan A. (ORCID:0000000328318099)↗
DOE OSTI2020

Epitaxial Er-doped Y 2 O 3 on silicon for quantum coherent devices

Rare-earth ions have incomplete 4f shells and possess narrow optical intra-4f transitions due to shielding from electrons in the 5s and 5p orbitals, making them good candidates for solid-state optical quantum memory. The emission of Er 3+ in the telecom C-band (1530 nm – 1565 nm) makes it especially attractive for this application. In order to build practical, scalable devices, the REI needs to be embedded in a non-interacting host material, preferably one that can be integrated with silicon. In this paper, we show that Er 3+ can be isovalently incorporated into epitaxial Y 2 O 3 thin films on Si (111). We report on the synthesis of epitaxial, single-crystalline Er:Y 2 O 3 on Si with a narrow inhomogeneous linewidth in the photoluminescence spectra, 5.1 GHz (<100 mK) and an optical excited state lifetime of 8.1 ms. The choice of Y 2 O 3 was driven by its low nuclear spin and small lattice mismatch with Si. Using photoluminescence (PL) and electron paramagnetic resonance, we show that Er 3+ substitutes for Y in the crystal lattice. The role of interfacial SiO x , diffusion of silicon into the film, and the effect of buffer layers on inhomogeneous PL linewidth are examined. We also find that the linewidth decreased monotonically with film thickness but surprisingly exhibits no correlation with the film crystalline quality as measured by the x-ray rocking curve scans suggesting other factors at play that limit the inhomogeneous broadening in Y 2 O 3 films.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Toward quantifying capacity losses due to solid electrolyte interphase evolution in silicon thin film batteries

To understand the origins of failure and limited cycle life in lithium-ion batteries (LIBs), it is imperative to quantitatively link capacity-fading mechanisms to electrochemical and chemical processes. This is extremely challenging in real systems where capacity is lost during each cycle to both active material loss and solid electrolyte interphase (SEI) evolution, two indistinguishable contributions in traditional electrochemical measurements. Here, we have used a model system in combination with (1) precision measurements of the overall Coulombic efficiency via electrochemical experiments and (2) x-ray reflectivity measurements of the active material losses. The model system consisted of a 515 Å thick amorphous silicon (a-Si) thin film on silicon carbide in half-cell geometry using a carbonate electrolyte with LiPF6 salt. This approach allowed us to quantify the capacity lost during each cycle due to SEI evolution. Combined with electrochemical analysis, we identify SEI growth as the major contribution to capacity fading. Specifically, the continued SEI growth results in increasing overpotentials due to increased SEI resistance, and this leads to lower extent of lithiation when the cutoff voltage is reached during lithiation. Our results suggest that SEI grows more with increased time spent at low voltages where electrolyte decomposition is favored. Finally, we extracted a proportionality constant for SEI growth following a parabolic growth law. Our methodology allows for the quantitative determination of lithium-ion loss mechanisms in LIBs by separately tracking lithium ions within the active materials and the SEI and offers a powerful method of quantitatively understanding LIB loss mechanisms.

25 ENERGY STORAGE↗
DOE OSTI2020

Atomistic study of silicon alloying in the spallation behavior of nanocrystalline aluminum systems

Here, the effect of concentration of the alloying element silicon (Si) on the shock and spall response of aluminum (Al) is studied using classical molecular dynamics (MD) simulations. Silicon is distributed as individual grains and as grain boundaries and the dynamic response under shock is studied for an impact velocity of 1000 m/s. A general trend observed here is that the spallation is almost exclusively intergranular and limited to Al-Si interfaces. The spall strengths are observed to a) decrease with an increase in alloying of Si as grains and b) show little increase for up to 50% grain boundary segregation. An increase in grain size of the whole system showed negligible differences in spall strength, highlighting the significance of concentration of the alloying species rather than its grain size. These results provide an atomistic understanding of light-weight metallic systems under shock compression and pave the way for designing multiphase metal matrix alloys and composites for defense/armor applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Diamond encapsulated silicon optical fibers synthesized by chemical vapor deposition

Semiconductor optical fibers encapsulated in a protective diamond coating can theoretically lead to immense power handling capabilities and infrared functionality. Here, silicon optical fibers are grown using high pressure chemical vapor deposition before being coated by 50 μm–300 μm of diamond by microwave plasma-assisted chemical vapor deposition. This coating extends conformally around the fiber cross section with diamond crystallites in the film on the order of several micrometers. Complete coating of high-quality diamond around the fiber is indicated by scanning electron microscopy and Raman measurements. The encapsulated silicon fibers are durable enough to survive the diamond deposition process, as demonstrated by their ability to guide infrared light.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Neural network potential from bispectrum components: A case study on crystalline silicon

In this article, we present a systematic study on developing machine learning force fields (MLFFs) for crystalline silicon. While the main-stream approach of fitting a MLFF is to use a small and localized training set from molecular dynamics simulations, it is unlikely to cover the global features of the potential energy surface. Additionally, to remedy this issue, we used randomly generated symmetrical crystal structures to train a more general Si-MLFF. Furthermore, we performed substantial benchmarks among different choices of material descriptors and regression techniques on two different sets of silicon data. Our results show that neural network potential fitting with bispectrum coefficients as descriptors is a feasible method for obtaining accurate and transferable MLFFs.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Examining normal modes as fundamental heat carriers in amorphous solids: The case of amorphous silicon

Normal mode decomposition of atomic vibrations has been used to provide microscopic understanding of thermal transport in amorphous solids for decades. In normal mode methods, it is naturally assumed that atoms vibrate around their equilibrium positions, and that individual normal modes are the fundamental vibrational excitations transporting heat. With the abundance of predictions from normal mode methods and experimental measurements now available, we carefully analyze these calculations in amorphous silicon, a model amorphous solid. We find a number of discrepancies, suggesting that treating individual normal modes as fundamental heat carriers may not be accurate in amorphous solids. Furthermore, our classical and ab initio molecular dynamics simulations of amorphous silicon demonstrate a large degree of atomic diffusion, especially at high temperatures, leading to the conclusion that thermal transport in amorphous solids could be better described starting from the perspectives of liquid physics rather than from crystalline solids.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Engineering local strain for single-atom nuclear acoustic resonance in silicon

Mechanical strain plays a key role in the physics and operation of nanoscale semiconductor systems, including quantum dots and single-dopant devices. In this report we describe the design of a nanoelectronic device, where a single nuclear spin is coherently controlled via nuclear acoustic resonance (NAR) through the local application of dynamical strain. The strain drives spin transitions by modulating the nuclear quadrupole interaction. We adopt an AlN piezoelectric actuator compatible with standard silicon metal–oxide–semiconductor processing and optimize the device layout to maximize the NAR drive. We predict NAR Rabi frequencies of order 200 Hz for a single 123Sb nucleus in a wide region of the device. Spin transitions driven directly by electric fields are suppressed in the center of the device, allowing the observation of pure NAR. Using electric field gradient-elastic tensors calculated by the density-functional theory, we extend our predictions to other high-spin group-V donors in silicon and to the isoelectronic 73Ge atom.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Silicon carbide fiber composite receiver tubes manufactured by PIP process

The performance of SiC fiber composites made by a polymer infiltration and pyrolysis (PIP) process was investigated. Two types of tubular composites were manufactured using Hi-Nicalon and Nicalon-CG silicon carbide fibers infiltrated with SMP10 silicon carbide matrix. The fiber content in both composites was about 25 vol.% with an average density of 2.39 g/cc. The tubular SiC composites showed stable solar absorptance and emittance of 0.97 and 0.91, respectively, at 800 °C. The composites were thermally shocked at 900, 1000, and 1100 °C with a waterjet simulating raindrops. As a result, the hoop tensile strength of the composites revealed no loss of mechanical strength due to the thermal shock experiments up to 1100 °C.

14 SOLAR ENERGY↗
DOE OSTI2024

Silicon x-ray backlighter improvement by targets with spike-like microstructures

In order to accurately probe high energy density matter states, it is vital to create powerful x-ray backlighters. One approach to create such x-ray sources is based on the usage of short-pulse, high-energy lasers, which greatly benefits from an optimization of the laser target coupling. Here, the spectral and temporal x-ray emission profiles of structured silicon targets with micron-sized spikes on the front surface are studied at laser intensities of 10 17 W cm -2 . The laser pulse length is varied between 1 and 20 ps with an energy of up to 1 kJ. The structured targets show an up to 13× enhancement of silicon He α emission compared to flat foils with a well-defined, sharp emission pulse profile. Furthermore, the performance of the microstructured targets is compared to targets with a CH shield as well as foils irradiated with a UV prepulse.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Observation of laser ablation of silicon as a function of pulse length at constant fluence via time-resolved x-ray spectroscopy

We investigate the ablation of silicon as a function of laser pulse length at a constant fluence using time-resolved x-ray spectroscopy data obtained from OMEGA EP experiments at the University of Rochester's Laboratory for Laser Energetics. Our targets consisted of three-layer planar structures composed of Si (50 μm), Cu (25 μm), and SiO 2 (500 μm) layers. The Si layer was irradiated by a 351-nm laser with varying pulse widths of 250 ps, 500 ps, 1 ns, and 10 ns while maintaining a constant fluence of ~27.9 kJ/cm 2 . Electron temperatures and densities of the ablated plasma were determined by analyzing the time-resolved x-ray spectroscopy data through a comparison of experimental measurements with synthetic results obtained from Si atomic calculations in a steady state and non-local thermodynamic equilibrium. These calculations were computed using PrismSPECT. Additionally, radiation-hydrodynamics simulations with FLASH are used to generate simulated plasma-density and plasma-temperature profiles, which are then compared with the experimental measurements. Our analyses reveal that increasing the laser pulse length at a constant fluence results in a decrease in electron temperatures and densities. Furthermore, the longer pulses with lower intensities lead to deeper ablation regions before reaching the peak ablation but lower ionization balances in the silicon layer. Furthermore, these findings emphasize the critical role of laser pulse length in plasma ablation and shock generation for laser-impulse studies.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Characterization of superconducting through-silicon vias as capacitive elements in quantum circuits

The large physical size of superconducting qubits and their associated on-chip control structures presents a practical challenge toward building a large-scale quantum computer. In particular, transmons require a high-quality-factor shunting capacitance that is typically achieved by using a large coplanar capacitor. Other components, such as superconducting microwave resonators used for qubit state readout, are typically constructed from coplanar waveguides, which are millimeters in length. Here, we use compact superconducting through-silicon vias to realize lumped-element capacitors in both qubits and readout resonators to significantly reduce the on-chip footprint of both of these circuit elements. We measure two types of devices to show that through-silicon vias are of sufficient quality to be used as capacitive circuit elements and provide a significant reduction in size over existing approaches.

Physics↗
DOE OSTI2024

Optical and microstructural characterization of Er 3+ doped epitaxial cerium oxide on silicon

Rare-earth ion dopants in solid-state hosts are ideal candidates for quantum communication technologies, such as quantum memories, due to the intrinsic spin–photon interface of the rare-earth ion combined with the integration methods available in the solid state. Erbium-doped cerium oxide (Er:CeO 2 ) is a particularly promising host material platform for such a quantum memory, as it combines the telecom-wavelength (~ 1.5 μm) 4f–4f transition of erbium, a predicted long electron spin coherence time when embedded in CeO 2 , and a small lattice mismatch with silicon. In this work, we report on the epitaxial growth of Er:CeO 2 thin films on silicon using molecular beam epitaxy, with controlled erbium concentration between 2 and 130 parts per million (ppm). We carry out a detailed microstructural study to verify the CeO 2 host structure and characterize the spin and optical properties of the embedded Er 3+ ions as a function of doping density. In as-grown Er:CeO 2 in the 2–3 ppm regime, we identify an EPR linewidth of 245(1) MHz, an optical inhomogeneous linewidth of 9.5(2) GHz, an optical excited state lifetime of 3.5(1) ms, and a spectral diffusion-limited homogeneous linewidth as narrow as 4.8(3) MHz. We test the annealing of Er:CeO 2 films up to 900 °C, which yields narrowing of the inhomogeneous linewidth by 20% and extension of the excited state lifetime by 40%.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Photovoltaic effect on silicon–alumina–ferromagnet tunnel junction providing insights about spin-dependent molecular spintronics solar cells

The study focuses on the observation of the photovoltaic (PV) effect on Si/AlOx/FM semiconductor–insulator–ferromagnetic metal (SIFM) structure. Utilization of ~10 nm NiFe film as the top ferromagnet (FM) layer was permeable for sufficient light radiation necessary for reaching the silicon substrate for the generation of electron–hole pairs upon photoexcitation. The effect of light intensity and magnetic field was studied on the SIFM’s PV response. We also investigated the role of silicon doping and the AlOx tunnel barrier between Si and FM in exploring suitable band bending necessary for separating the electron–hole pairs. Increasing the dopant density in Si and a damaged AlOx tunnel barrier quenched the PV effect. Ferromagnet/Insulator/Ferromagnet (FMIFM) was also studied to gain deeper mechanistic insights into the spin-dependent photovoltaic effect observed on FM/AlOx/FM tunnel junction-based molecular spintronics devices. Bridging of magnetic molecules between the Si and FM electrodes of SIFM increased the overall device current by establishing additional parallel conduction channels along with the AlOx tunnel barrier. However, SIFM with molecular conduction channels did not produce a PV effect. This study reported the PV effect on well-designed SIFM and opened possibilities for exploring new systems. More importantly, this paper provided insights into the role of molecule-induced exchange coupling in transforming an ordinary, cheap, and widely available ferromagnet into a semiconductor-like material capable of showing PV.

14 SOLAR ENERGY↗
DOE OSTI2024

Optical contrast analysis of α -RuCl 3 nanoflakes on oxidized silicon wafers

α-RuCl 3 , a narrow-band Mott insulator with a large work function, offers intriguing potential as a quantum material or as a charge acceptor for electrical contacts in van der Waals devices. In this work, we perform a systematic study of the optical reflection contrast of α-RuCl 3 nanoflakes on oxidized silicon wafers and estimate the accuracy of this imaging technique to assess the crystal thickness. Via spectroscopic micro-ellipsometry measurements, we characterize the wavelength-dependent complex refractive index of α-RuCl 3 nanoflakes of varying thickness in the visible and near-infrared. Building on these results, we simulate the optical contrast of α-RuCl 3 nanoflakes with thicknesses below 100 nm on SiO 2 /Si substrates under different illumination conditions. We compare the simulated optical contrast with experimental values extracted from optical microscopy images and obtain good agreement. Finally, we show that optical contrast imaging allows us to retrieve the thickness of the RuCl 3 nanoflakes exfoliated on an oxidized silicon substrate with a mean deviation of –0.2 nm for thicknesses below 100 nm with a standard deviation of only 1 nm. Our results demonstrate that optical contrast can be used as a non-invasive, fast, and reliable technique to estimate the α-RuCl 3 thickness.

2D materials↗