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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Mitigation of hot-electron preheat from the two-plasmon-decay instability using silicon-doped plastic shells in direct-drive implosions on OMEGA

Hot electrons generated by the two-plasmon-decay (TPD) instability in laser-direct-drive implosions preheat the fuel and degrade performance. The mitigation of preheat using silicon-doped ablators (i.e., preheat is reduced by a factor of 1.40 ± 0.04) while decreasing the ratio of the laser spot diameter to the target diameter (⁠R b /R t⁠ ) to mitigate cross-beam energy transfer has been demonstrated on the OMEGA laser for quarter-critical laser intensities of 4.1 x 10 14 W/cm 2 ⁠, equivalent to an incident laser intensity of 8.3 x 10 14 W/cm 2 ⁠. The silicon dopant increases the electron temperature of the ablation plasma, which raises the intensity threshold for the onset of the TPD instability. These results show that implosion designs utilizing higher drive intensities can be used to achieve higher shell velocities, which are currently inaccessible with plastic ablators due to excessive preheat.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Direct integration of atomic precision advanced manufacturing into middle-of-line silicon fabrication

Atomic precision advanced manufacturing (APAM) dopes silicon with enough carriers to change its electronic structure and can be used to create novel devices by defining metallic regions whose boundaries have single-atom abruptness. Incompatibility with the thermal and lithography process requirements for gated silicon transistor manufacturing have inhibited exploration of both how APAM can enhance CMOS performance and how transistor manufacturing steps can accelerate the discovery of new APAM device concepts. In this work, we introduce an APAM process that enables direct integration into the middle of a transistor manufacturing workflow. We show that a process that combines sputtering and annealing with a hardmask preserves a defining characteristic of APAM, a doping density far in excess of the solid solubility limit, while trading another, the atomic precision, for compatibility with manufacturing. The electrical characteristics of a chip combining a transistor with an APAM resistor show that the APAM module has only affected the transistor through the addition of a resistance and not by altering the transistor. This proof-of-concept demonstration also outlines the requirements and limitations of a unified APAM tool, which could be introduced into manufacturing environments, greatly expanding access to this technology and inspiring a new generation of devices with it.

Chemical vapor deposition↗
DOE OSTI2020

Characterization of silicon drift detectors with electrons for the TRISTAN project

Sterile neutrinos are a minimal extension of the standard model of particle physics. A promising model-independent way to search for sterile neutrinos is via high-precision β-spectroscopy. The Karlsruhe tritium neutrino (KATRIN) experiment, equipped with a novel multi-pixel silicon drift detector focal plane array and read-out system, named the TRISTAN detector, has the potential to supersede the sensitivity of previous laboratory-based searches. In this work we present the characterization of the first silicon drift detector prototypes with electrons and we investigate the impact of uncertainties of the detector’s response to electrons on the final sterile neutrino sensitivity.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Scintillation and cherenkov photon counting detectors with analog silicon photomultipliers for TOF-PET

Objective. Standard signal processing approaches for scintillation detectors in positron emission tomography (PET) derive accurate estimates for 511 keV photon time of interaction and energy imparted to the detection media from aggregate characteristics of electronic pulse shapes. The ultimate realization of a scintillation detector for PET is one that provides a unique timestamp and position for each detected scintillation photon. Detectors with these capabilities enable advanced concepts for three-dimensional (3D) position and time of interaction estimation with methods that exploit the spatiotemporal arrival time kinetics of individual scintillation photons. Approach. In this work, we show that taking into consideration the temporal photon emission density of a scintillator, the channel density of an analog silicon photomultiplier (SiPM) array, and employing fast electronic readout with digital signal processing, a detector that counts and timestamps scintillation photons can be realized. To demonstrate this approach, a prototype detector was constructed, comprising multichannel electronic readout for a bismuth germanate (BGO) scintillator coupled to an SiPM array. Main Results. In proof-of-concept measurements with this detector, we were able to count and provide unique timestamps for 66% of all optical photons, where the remaining 34% (two-or-more-photon pulses) are also independently counted, but each photon bunch shares a common timestamp. We show this detector concept can implement 3D positioning of 511 keV photon interactions and thereby enable corrections for time of interaction estimators. The detector achieved 17.6% energy resolution at 511 keV and 237 ± 10 ps full-width-at-half-maximum coincidence time resolution (CTR) (fast spectral component) versus a reference detector. We outline the methodology, readout, and approach for achieving this detector capability in first-ever, proof-of-concept measurements for scintillation photon counting detector with analog silicon photomultipliers. Significance. The presented detector concept is a promising design for large area, high sensitivity TOF-PET detector modules that can implement advanced event positioning and time of interaction estimators, which could push state-of-the-art performance.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2021

Full configuration interaction simulations of exchange-coupled donors in silicon using multi-valley effective mass theory

Abstract Donor spins in silicon have achieved record values of coherence times and single-qubit gate fidelities. The next stage of development involves demonstrating high-fidelity two-qubit logic gates, where the most natural coupling is the exchange interaction. To aid the efficient design of scalable donor-based quantum processors, we model the two-electron wave function using a full configuration interaction method within a multi-valley effective mass theory. We exploit the high computational efficiency of our code to investigate the exchange interaction, valley population, and electron densities for two phosphorus donors in a wide range of lattice positions, orientations, and as a function of applied electric fields. The outcomes are visualized with interactive images where donor positions can be swept while watching the valley and orbital components evolve accordingly. Our results provide a physically intuitive and quantitatively accurate understanding of the placement and tuning criteria necessary to achieve high-fidelity two-qubit gates with donors in silicon.

Joecker, Benjamin (ORCID:0000000302635440)↗
DOE OSTI2023

Energetics of silicon in the bulk and near surfaces of tungsten: a first-principles study

Abstract Siliconization of the tokamak walls is a candidate method to improve plasma confinement in fusion tokamaks containing tungsten plasma facing components (W PFCs). To understand the interactions of silicon (Si) with W, the Si behavior in bulk W, and near three low-index W surfaces ((100), (110) and (111)) has been investigated using first-principles density functional theory. In bulk W, Si interstitial atoms have a low solution ability and high mobility, and Si atoms can be strongly trapped by W vacancies. The interaction between two Si adatoms is responsible for the stability of adatom superstructures on W surfaces, consistent with previous experimental observation (Tsong and Casanova 1981 Phys. Rev. Lett. 47 113). Although the coverage dependence of Si adsorption and diffusion energetics on surfaces is related to surface orientation, the W(110) surface has lower Si adsorption affinity and higher Si diffusivity than either the W(111) or W(100) surfaces. The most stable Si adatom superstructure on W surfaces is: square c(2 × 2) pattern on W(100) covered with 0.5 ML Si; rectangular c(4 × 2) pattern on W(110) with 0.25 ML Si; and rhombus p(1 × 1) pattern on W(111) with 1 ML Si. The coverage dependence of Si mobility on/toward W surfaces is generally related to the stability of the Si superstructures as a function of coverage on each surface. Interestingly, Si adatoms prefer to transport below the surface and into W subsurface by an exchange mechanism with W atoms, indicating the likelihood of epitaxial growth of W silicide layers on W surfaces during the operation of W PFCs.

Yang, L. (ORCID:0000000322166071)↗
DOE OSTI2021

Magnetic triggering — time-resolved characterisation of silicon strip modules in the presence of switching DC-DC converters

Modules for the ATLAS Inner Tracker (ITk) strip tracker include a DC-DC converter circuit glued directly to the silicon sensor which converts the 11 V supplied to the module to the 1.5 V required for the operation of the readout chips. The DC-DC converter unit, consisting of a copper solenoid and custom ASIC, is located directly above the silicon strip sensor and therefore needs to be shielded to protect the sensor from EMI noise created during the operation of the circuit. Despite dedicated shielding, consisting of an aluminium shield box with continuous solder seams encompassing the surface components and a copper layer in the PCB beneath it, module channels connected to sensor strips located beneath the converter circuit were found to show a noise increase. While the DC-DC converter unit causing the underlying EMI noise operates at a frequency of 2 MHz, module characterisation measurements for ITk strip tracker modules are typically performed asynchronously to the DC-DC switching and are therefore averaged over the full range of time bins with respect to the converter frequency. In order to investigate the time dependence of the noise injection relative to the DC-DC switching frequency, a dedicated setup to understand the time-resolved performance change in modules was developed. By using a magnetic field probe to measure the field leaking through the shield box and triggering on its rising edge, data taking could be synchronised with the DC-DC switching. This paper illustrates the concept and setup of such time-resolved performance measurements using magnetic triggering and presents results for the observed effects on signal and noise for ATLAS ITk strip modules from both laboratory and beam tests.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Reflectivity of VUV-sensitive silicon photomultipliers in liquid Xenon

Silicon photomultipliers are regarded as a very promising technology for next-generation, cutting-edge detectors for low-background experiments in particle physics. This work presents systematic reflectivity studies of Silicon Photomultipliers (SiPM) and other samples in liquid xenon at vacuum ultraviolet (VUV) wavelengths. A dedicated setup at the University of Münster has been used that allows to acquire angle-resolved reflection measurements of various samples immersed in liquid xenon with 0.45° angular resolution. Four samples are investigated in this work: one Hamamatsu VUV4 SiPM, one FBK VUV-HD SiPM, one FBK wafer sample and one Large-Area Avalanche Photodiode (LA-APD) from EXO-200. Here, the reflectivity is determined to be 25–36 % at an angle of incidence of 20° for the four samples and increases to up to 65 % at 70° for the LA-APD and the FBK samples. The Hamamatsu VUV4 SiPM shows a decline with increasing angle of incidence. The reflectivity results will be incorporated in upcoming light response simulations of the nEXO detector.

(pin diodes, APDs, SiPMs, G-APDs, CCDs, EBCCDs, EM↗
DOE OSTI2023

Specifications and pre-production of n + -in-p large-format strip sensors fabricated in 6-inch silicon wafers, ATLAS18, for the Inner Tracker of the ATLAS Detector for High-Luminosity Large Hadron Collider

Abstract The ATLAS experiment is constructing new all-silicon inner tracking system for HL-LHC. The strip detectors cover the radial extent of 40 to 100 cm. A new approach is adopted to use p-type silicon material, making the readout in n + -strips, so-called n + -in-p sensors. This allows for enhanced radiation tolerance against an order of magnitude higher particle fluence compared to the LHC. To cope with varying hit rates and occupancies as a function of radial distance, there are two barrel sensor types, the short strips (SS) for the inner 2 and the long strips (LS) for the outer 2 barrel cylinders, respectively. The barrel sensors exhibit a square, 9.8 × 9.8 cm 2 , geometry, the largest possible sensor area from a 6-inch wafer. The strips are laid out in parallel with a strip pitch of 75.5 μm and 4 or 2 rows of strip segments. The strips are AC-coupled and biased via polysilicon resistors. The endcap sensors employ a “stereo-annulus” geometry exhibiting a skewed-trapezoid shapes with circular edges. They are designed in 6 unique shapes, R0 to R5, corresponding to progressively increasing radial extents and which allows them to fit within the petal geometry and the 6-inch wafer maximally. The strips are in fan-out geometry with an in-built rotation angle, with a mean pitch of approximately 75 μm and 4 or 2 rows of strip segments. The eight sensor types are labeled as ATLAS18xx where xx stands for SS, LS, and R0 to R5. According to the mechanical and electrical specifications, CAD files for wafer processing were laid out, following the successful designs of prototype barrel and endcap sensors, together with a number of optimizations. A pre-production was carried out prior to the full production of the wafers. The quality of the sensors is reviewed and judged excellent through the test results carried out by vendor. These sensors are used for establishing acceptance procedures and to evaluate their performance in the ATLAS collaboration, and subsequently for pre-production of strip modules and stave and petal structures.

Instruments & Instrumentation↗
DOE OSTI2023

Conceptual study of a two-layer silicon pixel detector to tag the passage of muons from cosmic sources through quantum processors

Abstract Recent studies in quantum computing have shown that quantum error correction with large numbers of physical qubits are limited by ionizing radiation from high-energy particles. Depending on the physical setup of the quantum processor, the contribution of muons from cosmic sources can constitute a significant fraction of these interactions. As most of these muons are difficult to stop, we perform a conceptual study of a two-layer silicon pixel detector to tag their hits on a solid-state quantum processor instead. With a typical dilution refrigerator geometry model, we find that efficiencies greater than 50% are most likely to be achieved if at least one of the layers is operated at the deep-cryogenic (<1 K) flanges of the refrigerator. Following this finding, we further propose a novel research program that could allow the development of silicon pixel detectors that are fast enough to provide input to quantum error correction algorithms, can operate at deep-cryogenic temperatures, and have very low power consumption.

Instruments & Instrumentation↗
DOE OSTI2025

Operation and performance of the CMS silicon strip tracker with proton-proton collisions at the CERN LHC

Salient aspects of the commissioning, calibration, and performance of the CMS silicon strip tracker are discussed, drawing on experience during operation with proton-proton collisions delivered by the CERN LHC. The data were obtained with a variety of luminosities. The operating temperature of the strip tracker was changed several times during this period and results are shown as a function of temperature in several cases. Details of the system performance are presented, including occupancy, signal-to-noise ratio, Lorentz angle, and single-hit spatial resolution. Saturation effects in the APV25 readout chip preamplifier observed during early Run 2 are presented, showing the effect on various observables and the subsequent remedy. Studies of radiation effects on the strip tracker are presented both for the optical readout links and the silicon sensors. The observed effects are compared to simulation, where available, and they generally agree well with expectations.

47 OTHER INSTRUMENTATION↗
DOE OSTI2026

Silicon pinhole strip defects and their impact on ATLAS Inner Tracker HV current measurement

In preparation for the High-Luminsity LHC (HL-LHC) [1], the ATLAS detector will undergo major detector upgrades, including the replacement of the current Inner Detector with the new all-silicon Inner Tracker (ITk) [2]. The ITk consists of a pixel detector close to the beamline surrounded by a large-area strip detector. During detector production, the electrical properties of silicon sensors and readout electronics must be characterized through a series of quality control (QC) and quality assurance tests. These tests ensure any defect is captured at the earliest possible stage. One such defect, callled a pinhole, occurs when the strip implant and the metal readout electrode are shorted through the intermediary dielectric layer. Notably, the introduction of pinholes during module assembly and pinhole effects on completed modules, especially on leakage current measurement circuitry, have never been studied. In this paper, we investigate the effect of such connections on the sensor leakage current measurements of completed modules and introduce new ways to locate pinholed strips. Here, with minor modifications to testing procedures, such defects are shown not to impede module testing or performance.

FOS: Physical sciences↗
DOE OSTI2021

Bound States in the Continuum on a Silicon Chip with Dynamic Tuning

Expanding bound states in the continuum (BIC) beyond photonic crystal systems may enable broader applications benefiting from the unique properties of BIC states. We use photonic integrated circuit to realize a Fabry-Pérot BIC on a silicon chip. The devices consist of cascaded ring resonators with tunable resonance frequencies and phase delays. As a result, the BIC state is dynamically tuned with electrical I/O. We analyze the mechanism of the formation of BIC states in this waveguide system and point out the fundamental differences between the BIC states and electromagnetically induced transparency states in integrated photonics. The high transmission protected by the BIC state enables versatile optical filters, which are capable of independent control over switching, peak position, and quality factor. We also demonstrate the scalability of this platform. As a result, this integrated silicon photonic platform brings opportunities for practical BIC applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Radiation-Induced Dark Counts for Silicon Single-Photon Detectors in Space

Single-photon detectors operating on satellites for use in a quantum communications network can incur large dark-count-rate increases from the natural radiation environment of space. Displacement damage to the material lattice of a detector from the ionizing radiation can result in a permanent dark-count increase in the detector. In this work, we analyze the radiation-induced dark-count rate of a silicon single-photon avalanche diode onboard a satellite at different orbiting altitudes, as well as, the additional radiation from a nuclear-disturbed environment caused by a high-altitude nuclear explosion. For detectors on low Earth orbit satellites, protons are the biggest source of radiation damage and are best mitigated by choosing an orbit that minimizes exposure when passing through the South Atlantic Anomaly and Polar Cusps. Detectors on medium Earth orbit and geostationary orbit satellites, if shielded by more than 10 mm of aluminum, provide the best platform in terms of the least amount of radiation damage to the detectors. In the event of a high-altitude nuclear explosion, the artificial radiation belts produced by the explosion will cause too much damage to silicon single-photon detectors on low Earth orbit satellites and render them unfit for quantum communications in less than a day. Higher orbit satellites will only suffer minor dark-count-rate increases from the artificial radiation belts.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Temperature Mapping of Stacked Silicon Dies from X-Ray-Diffraction Intensities

Increasing power densities in integrated circuits have led to an increased prevalence of thermal hotspots in integrated circuits. Tracking these thermal hotspots is imperative to prevent circuit failures. In three- dimensional (3D) integrated circuits, conventional surface techniques like infrared thermometry are unable to measure the 3D temperature distribution, and optical and magnetic resonance techniques are difficult to apply due to the presence of metals and large current densities. X-rays offer a high penetration depth and can be used to probe 3D structures. We report a method utilizing the temperature dependence of x-ray-diffraction intensity via the Debye-Waller factor to simultaneously map the temperature of individual silicon dies in a stack. Here, utilizing beamline 1-ID-E at the Advanced Photon Source (Argonne), we demonstrate, for each individual silicon die, a temperature resolution of 3 K, a spatial resolution of 100 × 400 μm 2 , and a temporal resolution of 20 s. Utilizing a sufficiently high-intensity laboratory source, e.g., from a liquid-anode source, this method can be scaled down to laboratories for noninvasive temperature mapping of 3D integrated circuits.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Shock-compressed silicon: Hugoniot and sound speed up to 2100 GPa

In this work, the high-pressure equation of state and isentropic sound speed of fluid silicon were studied using laser-driven shock waves. Principal Hugoniot measurements to 2100 GPa were performed using impedance matching to an α-quartz reference. Sound speed was determined by time correlating imposed shock-velocity perturbations in both the sample (Si) and reference material (α-quartz). A change in shock velocity versus particle velocity (u s –u p ) slope on the fluid silicon principal Hugoniot was detected at 200 GPa. Density functional theory-based quantum molecular dynamics simulations suggest that an increase in ionic coordination and 50% increase in average ionization is coincident with the experimentally observed change in slope.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Diffusion coefficients predicting facet-dependent crystallization in amorphous silicon nitride

Amorphous silicon nitride is a common material in microelectronics devices, which acts as an insulating barrier. Extended annealing times at elevated temperature can initiate crystallization of α-Si 3 ⁢ N 4 , which does not possess the same barrier properties. Molecular dynamics can resolve the fundamental mechanism for α-Si 3 ⁢N 4 crystallization and the influence of local environments. Here, we compare two interatomic potentials and conclude that these models predict structural features (e.g., angular distributions and densities) which span the range of experimental measurements. We confirmed these models reproduce experimental estimates of activation energy and leveraged these models to identify crystallization drivers. We conclude that near-T g , facet-dependent silicon nitride crystal growth rates can be predicted directly by either bulk or interfacial diffusion properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Unraveling the intrinsic atomic physics behind x-ray absorption line shifts in warm dense silicon plasmas

Here, we present a novel free-energy density functional theory (DFT)-based methodology for optical property calculations of warm dense matter to cover a wide range of thermodynamic conditions and photon energies including the entire x-ray range. It uses Mermin–Kohn–Sham density functional theory with exchange-correlation (XC) thermal effects taken into account via a fully temperature dependent generalized gradient approximation XC functional. The methodology incorporates a combination of the ab initio molecular dynamics (AIMD) snapshotted Kubo–Greenwood optic data with a single-atom in simulation cell calculations to close the photon energy gap between the L and K edges and extend the K-edge tail toward many-keV photon energies. This gap arises in the standard scheme due to a prohibitively large number of bands required for the Kubo–Greenwood calculations with AIMD snapshots. Kubo–Greenwood data on snapshots provide an accurate description of optic properties at low photon frequencies slightly beyond the L-edge and x-ray absorption near edges structure (XANES) spectra, while data from periodic calculations with single atoms cover the tail regions beyond the edges. To demonstrate its applicability to mid-Z materials where the standard DFT-based approach is not computationally feasible, we have applied it to opacity calculations of warm dense silicon plasmas. These first-principles calculations revealed a very interesting phenomon of red-to-blue shift in K–L (1s → 2p) and K-edge absorptions along both isotherm and isochore, which are absent in most continuum-lowering models of traditional plasma physics. This new physics phenomenon can be attributed to the underlying competition between the screening of deeply bound core electrons and the screening of outer-shell electrons caused by warm-dense-plasma conditions. We further demonstrate that the ratio of 1s → 2p to the K-edge x-ray absorptions can be used to characterize warm-dense-plasma conditions. Eventually, based on our absorption calculations, we have established a first-principles opacity table (FPOT) for silicon in a wide range of material densities and temperatures.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗