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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.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Understanding Photovoltage Deficits in Electrochemically Grown Tin Sulfide (SnS) Thin-Film Photovoltaic Devices

Tin­(II) sulfide (SnS) is an earth-abundant semiconductor with a direct optical bandgap of ca. 1.1 eV, which makes it a promising absorber material for thin-film photovoltaic (PV) devices. However, existing devices have significant photovoltage deficits, which may be related to the anisotropic structure of the layered Herzenbergite SnS crystal structure. Here, we explore electrochemical deposition as a near room temperature path to oriented SnS crystal films on Mo and FTO substrates and employ vibrating Kelvin probe surface photovoltage (SPV) spectroscopy and J–V measurements to identify conversion losses in them. According to grazing-incidence X-ray diffraction and SEM, the SnS films consist of crystalline microplates with preferred orientation in the [111] and [001] directions. The bare SnS films produce only small and irreversible surface photovoltage signals, due charge trapping and recombination at the SnS surfaces, but addition of a CdS buffer layer lowers the charge recombination rate by 2 orders of magnitude and increases both the photovoltage and its reversibility due to the formation of a p-SnS/n-CdS junction. According to SPV, the FTO/SnS back interface (but not the Mo/SnS interface) forms a detrimental p–n junction that hinders hole transfer. Additional shunting through the relatively open microcrystal SnS layers and a lower conductivity of the FTO substrate explain the low power conversion efficiencies of the final devices (0.18 and 0.10% for the Mo and FTO substrates). Altogether, this work establishes a low-temperature path for the fabrication of crystalline SnS film-based solar cells and identifies the bottlenecks that limit high photoconversion efficiency.

deposition↗
DOE OSTI2025

Dimensional Reduction Guides Electronic Structure Evolution in the A n Cu 4–n SnS 4 Semiconductor Series

The search for new functional materials with tunable properties remains a central challenge in chemistry, particularly for applications in energy and electronics. In this work, we present a framework for predictive crystal design in alkali metal chalcogenides that enables controlled dimensional reduction of a parent covalent motif, yielding a broad range of electronic structures, which systematically evolve from one parent to the other. We present 11 new members of the A n Cu 4–n SnS 4 family (A = alkali metal; n = 0–4), which reduce the three-dimensional (3D) covalent network of Cu 4 SnS 4 into various 3D, 2D, 1D, and 0D [Cu 4–n SnS 4 ] n− motifs through the substitution of Cu with alkali metals of various radii. The end members of the family set the range in achievable band gaps at 0.99 eV for fully covalent Cu 4 SnS 4 (n = 0) and 3.38 eV for K 4 SnS 4 (n = 4) with 0D [SnS 4 ] n− tetrahedra. As the dimensionality of [Cu 4–n SnS 4 ] n− systematically reduces within A n Cu 4–n SnS 4 (n = 1–3), a stepwise increase in band gap energy occurs through a gradual decrease in the energy of the valence band maximum and an increase in the conduction band minimum, with an increase in the effective masses of charge carriers. Furthermore, irrespective of the alkali metal, the thermal stability decreases with decreasing [Cu 4–n SnS 4 ] n− dimensionality within the quaternary members. Most importantly, we demonstrate that predictable crystal structure and property evolution for a given composition space is possible by deriving a general formula based on substituting the covalent metals of a parent structure with alkali metals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Power conversion in SnS photocathodes made by electrochemical growth is limited by recombination at (002) buried facets

Herzenbergite α-SnS is a promising p-type semiconductor for photovoltaic and solar fuel applications, but current devices are plagued by substantial photovoltage losses. Here we use vibrating Kelvin probe surface photovoltage for the first time to study the recombination losses in microcrystalline SnS photoelectrodes. α-SnS films of varied crystal orientation, size, and shape are obtained by electrochemical growth from aqueous tin( II ) chloride and sodium thiosulfate solutions near room temperature. After application of a CdS passivation layer, the films function as photocathodes for the methylviologen reduction reaction. Photoelectrochemical and surface photovoltage measurements reveal that the performance of these devices is sensitively controlled by mainly the SnS crystal orientation and to a lesser extent by the grain size. For example, the highest charge recombination rates of 8.97 × 10 14 s −1 cm −2 and lowest photocurrent (0.73 mA cm −2 ) and lowest photovoltage (0.12 V) occur for SnS films containing 500 nm crystals with irregular shapes and SnS lattices tilted away from the (001) orientation. On the other hand, the best performance (1.62 mA cm −2 , 0.16 V, 3.32 × 10 12 s −1 cm −2 ) is seen for 1100 nm fully (001) oriented SnS nanoplates. Furthermore, these findings agree with improved charge carrier mobility in the 001 direction and they also show that charge recombination in SnS films occurs mainly at dangling Sn–S bonds at buried (002) facets. Such buried interfaces need to be suppressed for optimized solar energy conversion with SnS.

Najaf, Zainab [University of California, Davis, CA↗
DOE OSTI2024

H - Ion Source RF Plasma Testing with 13 MHz and 27 MHz at the Spallation Neutron Source (SNS)

The baseline RF-driven H⁻ ion source configuration at the Spallation Neutron Source (SNS) facility uses a continuous wave (CW) 600 W 13 MHz RF system to ignite and maintain a low-density plasma inside the ion source vacuum chamber. After the continuous low-density 13 MHz plasma has been established, a pulsed (typical 1 ms pulse width and 60 Hz pulse repetition rate) 80 kW 2 MHz RF system is used to increase the plasma density to produce the pulsed H⁻ ion beam. Incremental upgrades and improvements to the SNS ion source systems have resulted in the ability to reliably operate an H⁻ ion source for SNS neutron production run cycles that can last up to four months. Conditions inside the SNS H⁻ ion source evolve throughout a four-month run cycle due to changes in impurity levels, sputtering, and erosion. As the internal ion source conditions change during the run cycle, there can also be changes in plasma stability and the 13 MHz RF power level required to ignite the plasma. This paper presents the preliminary results of testing performed on the SNS Ion Source Test Stand (ISTS) system where we looked at plasma ignition and plasma stability using 27 MHz RF in place of the baseline 13 MHz RF system.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Design improvements to the SNS ion source and diagnostics

The U.S. Spallation Neutron Source (SNS) is a state-of-the-art neutron scattering facility delivering the world's most intense pulsed-neutron beams to a wide array of instruments which are used to conduct investigations in many fields of science and engineering. The accelerator system is fed by an RF-driven, multicusp, H - ion source which nominally provides pulsed beam currents of 50-60 mA (1ms, 60Hz). This report provides a discussion of ongoing design improvements to the SNS ion source and Low Energy Beam Transport (LEBT) as well as diagnostic upgrades undertaken since the previous ICIS conference. These improvements include (i) simple mechanical modifications to the source outlet aperture which resulted in dramatically increased extracted beam current and comparable or lower emittance at similar beam currents, (ii) design improvements to the LEBT chopper target which will enable full power beam-dumping during physics studies, (iii) refinement of the SNS Allison emittance scanner that has enabled the first reliable LEBT beam measurements at full beam power (65kV, 50-100mA, 1ms, 60Hz) on the SNS ion source test stand and (iv) the implementation of a thermal imaging camera for the monitoring the LEBT electrode temperatures. (v) The design of an advanced Cs system, capable of more efficient Cs utilization with significantly lower Cs losses from the source is also presented. Mechanical details, computational simulations and experimental results are discussed within the context of these improvements.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

XY-like incommensurate magnetic order in Ce 2 ⁢SnS 5

We report the synthesis of single crystals of Ce 2 ⁢SnS 5 through a two-stage chemical vapor transport method. The Ce 2 ⁢SnS 5 system is a member of the orthorhombic Pbam (No. 55) space group and realizes a distorted trigonal tricapped prism (TTP) crystal field around each cerium site. We characterized the sample through orientation-dependent magnetization and heat capacity measurements to probe the magnetic anisotropy in the system characteristic of XY-like anisotropic Heisenberg model behavior. Ce 2 ⁢SnS 5 furthermore enters a zero-field ordered phase under 𝑇 𝑁 =2.4 K; powder neutron diffraction measurements reveal incommensurate magnetic order near 𝑇 𝑁 . Furthermore, the system then locks into a commensurate, two-𝑞 magnetic structure below approximately 1.2 K. This commensurate structure belongs to the Shubnikov group 𝑃⁢𝑏′⁢𝑎′⁢𝑚′ ⁡(MSG 55.359) and realizes the propagation vectors $\overrightarrow{𝑞}$ = (1/3, 0, 0) and $\overrightarrow{𝑞}$ = (0, 0, 0).

Antiferromagnetism↗
DOE OSTI2024

Proposed muon collider R&D at SNS

Generation of a muon beam at a Muon Collider requires relatively short, high-charge proton bunches. They are produced in a high-average-power proton driver by first accumulating a proton beam from a super-conducting linac, then bunching the beam and finally compressing and combining the bunches into a single high-intensity proton pulse. All of these beam formation stages involve handling of unprecedentedly high beam charges. Validation of these intricate beam manipulations requires better understanding of extreme space-charge effects and experimental demonstration. A facility perhaps most closely resembling the proton driver configuration and beam parameters is the Spallation Neutron Source (SNS) accelerator complex at Oak Ridge National Laboratory (ORNL). Considering the energy scaling of the space-charge parameters, many of the beam formation steps planned for the proton driver can be experimentally checked at the SNS at the relevant space-charge interaction levels. This paper discusses potential proton driver and other muon-collider-related R\&D at the SNS.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

15 years of spin-echo spectroscopy at SNS-NSE: Looking back and looking forward

High-resolution neutron spin echo (NSE) spectroscopy offers unique insights into the mobility of molecular (sub)structures excited by thermal fluctuations (i.e., Brownian motion) of “soft matter” as polymers in solution and in the melt, in biological matter (e.g., protein motions), membranes, and glasses. The ability to tag substructures using H, D contrast variation to resolve the relevant timescales of dynamics on selected molecular items in liquids, soft matter, and melts is a significant advantage of NSE. Also slow magnetic fluctuations on molecular length scales in the range of nanoseconds, e.g., in spin glasses or topological spin structures, can be accessed. This paper reviews the highlights and peculiarities of the SNS-NSE, based at the pulsed neutron source SNS, during its first 1.5 decades of operation. An outlook and perspectives of research in the domain of high-resolution spectroscopy is given.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Virtual to Physical: Reinforcement Learning to Optimize SNS Particle Accelerator Controls

Complex accelerators must have control systems that can handle dynamic nonlinear environments. This makes traditional control methods unsuitable as they can struggle to adapt to these uncertainties. This provides an ideal environment for reinforcement learning algorithms as they are adaptable and generalizable. We present a reinforcement learning pipeline that can effectively handle the dynamics of a complex accelerator. We test and prove our pipelines capabilities on multiple environments including the Spallation Neutron Source (SNS) and the Beam Test Facility (BTF) at Oakridge National Lab (ORNL). Due to the limited time available to train an online algorithm like reinforcement learning on a real accelerator, we utilize a virtual twin accelerator (VIRAC) developed by ORNL to pretrain the policy and show its ability to converge in the virtual environment. We then test the adaptability of the pretrained RL model by applying it on the real accelerator and comparing the results. Utilizing our Scientific Optimization and Controls Toolkit (SOCT) and open-source standards such as Gymnasium we create and solve for a MEBT orbit correction problem in the SNS and an emittance maximization problem in the BTF. We show how Twin Delayed Deep Deterministic Policy Gradient (TD3) can solve this optimization environment in the virtual accelerator and transfer this policy onto the real accelerator for inference and model retraining. We show how reinforcement learning can be utilized as a control system for complex accelerators and provide a model pipeline for how an implementation performs and can be adapted to new accelerator control problems.

Kasparian, Armen [Thomas Jefferson National Accele↗
DOE OSTI2025

Epitaxial Growth of 2D Core‐Crown SnS 2 /SnSe 2 Heterostructure Through Interfacial Modification with Polyvinylpyrrolidone

Abstract Developing generalized strategies for controlled synthesis of 2D heterostructures remains a significant challenge because the existing approaches often suffer from poor reproducibility and scalability. In this study, a solution synthesis approach for epitaxial core‐crown heterostructures with controlled band alignment, that overcomes these challenges is reported. Polyvinylpyrrolidone (PVP) is used as a structure‐directing agent to reduce lattice mismatch between SnS 2 and SnSe 2 (10‐10) surfaces and direct epitaxial growth of SnSe 2 crown on SnS 2 seed. Additionally, PVP adsorption to the basal plane prevents van der Waals stacking and stabilizes 2D heterostructures during synthesis. Driven by interfacial thermodynamics, the formation of the core‐crown heterostructure is highly reproducible and the size of the 2D heterostructure and relative areas of the core and the crown can be precisely controlled in a two‐step process by varying synthesis times for the seed and the crown. The identified growth pathway for 2D heterostructures can be generalized to other combinations of van der Waals materials to provide a platform for synthesizing micron‐size epitaxial heterostructures with a desired electronic structure for catalysis and microelectronics.

Liu, Lili [Physical and Computational Sciences Dir↗
DOE OSTI2025

Linear Dichroism of the Optical Properties of SnS and SnSe Van der Waals Crystals

Abstract Tin monochalcogenides SnS and SnSe, belonging to a family of Van der Waals crystals isoelectronic to black phosphorus, are known as environmentally friendly materials promising for thermoelectric conversion applications. However, they exhibit other desired functionalities, such as intrinsic linear dichroism of the optical and electronic properties originating from strongly anisotropic orthorhombic crystal structures. This property makes them perfect candidates for polarization‐sensitive photodetectors working in near‐infrared spectral range. A comprehensive study of the SnS and SnSe crystals is presented, performed by means of optical spectroscopy and photoemission spectroscopy, supported by ab initio calculations. The studies reveal the high sensitivity of the optical response of both materials to the incident light polarization, which is interpreted in terms of the electronic band dispersion and orbital composition of the electronic bands, dictating the selection rules. From the photoemission investigation the ionization potential, electron affinity and work function are determined, which are parameters crucial for the design of devices based on semiconductor heterostructures.

Chemistry↗
DOE OSTI2025

Modernization of PLC-Based Control Systems at SNS

When the SNS site was built around 20 years ago, the Conventional Facilities (CF) control systems were de-signed using 2 communication protocols to allow pro-grammable logic controllers (PLCs) to interface with motors, variable frequency drives (VFDs), and remote input and output (I/O) devices. The protocol chosen to control motors and VFDs is DeviceNet, a CANbus-based protocol developed by Allen-Bradley, a subsidiary of Rockwell Automation. The protocol chosen to communi-cate with remote I/O is ControlNet, another protocol developed by Allen-Bradley. Both of these protocols are obsolete and present reliability and maintainability is-sues, particularly DeviceNet. As the Control Systems Section at SNS is working to modernize control systems throughout the machine, a major goal for PLC-based systems is to remove the obsolete communication proto-cols in favor of standard, ubiquitous Ethernet. To this end, any new VFDs installed use Ethernet communica-tion. Many VFDs are currently being replaced in the Central Utilities Building (CUB) and the Central Exhaust Facility (CEF) and are being removed from DeviceNet in favor of Ethernet communication. Planning is underway to retrofit Eaton Intelligent Technology motor control centers (MCCs) in the Target Building to remove particu-larly troublesome DeviceNet adaptors and replace them with Ethernet adaptors for each motor starter. The Con-trolNet network in the CUB has been demolished, with I/O drops integrated into a local Ethernet network, im-proving sustainability and maintainability.

Beaushaw, Isaiah [ORNL]↗
DOE OSTI2024

Progress towards halo modeling at the SNS Beam Test Facility

The SNS beam test facility is a model of the SNS front end (source through medium-energy transport). On-going work at the BTF focuses on accurate modeling of the beam distribution to enable the prediction of halo losses (>100 parts per million). This presentation will discuss the latest progress towards this goal, including recent results after a reconfiguration of the test beamline. Good agreement within the 90% beam core is shown for a 30 mA beam at 2.5 MeV.

Ruisard, Kiersten↗
DOE OSTI2026

Spectral Flux Measurements on SNS Direct Geometry Spectrometers at IRP-2 End-of-Life

The Inner Reflector Plug (IRP) of the Spallation Neutron Source (SNS) was replaced during the SNS shutdown period beginning 25 November 2025. This IRP, IRP-2, was first placed in service in May 2018, and was in use for 42.5 GW-hrs of operation, somewhat longer than its original design life of 30 GW-hrs, or even a refined estimate of 33 GW-hrs for the water moderator poison plate and 39 GW-hrs on the decoupled-poisoned hydrogen moderator decoupler (Gallmeier, Lu, and Iverson 2018). The time-integrated power history for IRP-2 is tracked in Figure 1.

43 PARTICLE ACCELERATORS↗