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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Characterization of Two Positional Isomers of the Cs + Gly Complex Using Two-Color, IR–IR Photobleaching of the Cryogenically Cooled Ions

Metal ion binding to amino acid residues is an important interaction motif that controls the tertiary structures of oligopeptides. Analyses of the vibrational band patterns displayed by the amino acid scaffolds are commonly used to characterize the local docking motifs. Here we carry out two-color, IR-IR photobleaching measurements to obtain isomer-selective vibrational spectra of the Cs + Gly ion-molecule complex isolated in a cryogenically cooled, radiofrequency ion trap. The distinct band patterns of two non-interconverting isomers are observed and traced to different bidentate binding motifs between Cs + and the glycine scaffold. In one isomer, the ion attaches to the oxygen atoms of the carboxyl group whereas in the other it docks to the amino nitrogen and the carbonyl oxygen. Attachment to the acid head group yields a very diffuse absorption associated the OH group engaged in a strong intramolecular H-bond that closes a 5 membered ring. Furthermore, the band assignments, rearrangement pathways and electrostatic distortion of the electron density distributions in the glycine scaffold by the proximal ion are explored with electronic structure calculations and anharmonic theory.

Infrared spectroscopy↗
DOE OSTI2022

Systematic Characterization on Optical and Phonon Properties of Cs[Pb x Sn 1– x ]I 3 Alloyed Perovskites via First-Principles Modeling

Here, understanding the optical properties and phonon thermodynamic features of materials enables the determination of their viability for optoelectronic applications including optical-based gas sensors. Metal halide perovskites ABX 3 as well as their mixed alloys can be attractive in applications of this kind. In particular, the formation of alloyed perovskites A[B x B’ 1–x ]X 3 modulates the functional characteristics that can overtake the single-halide ABX 3 . To this end, we use the first-principles simulations to model the effect of B-site alloying on the optical and phonon properties of cubic Cs[Pb x Sn 1–x ]I 3 (x = 0.75, 0.50, and 0.25). We identified the systematic shifts of optical properties as a function of alloying concentration, such as dielectric constants, refraction indices, and absorption coefficients. It was also found that a linear correlation exists between the optical constants and the band gaps of these materials, which satisfies the Penn model. Modeling of phonons in Cs[Pb x Sn 1–x ]I 3 showed that dissipating the dynamically unstable phonons can be feasible at a carefully chosen alloying concentration, which are originally present in their single-halide Pb- and Sn-ends. Our findings pave a way to optimize the alloying conditions of the alloyed perovskite systems of interest for tuning their optical and phonon stability characteristics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Octahedral Distortion and Excitonic Behavior of Cs 3 Bi 2 Br 9 Halide Perovskite at Low Temperature

The metal halide ionic octahedron, represented as [MX 6 ] $n$- (M = metal cation, X = halide anion), serves as the basic structural unit in halide perovskites and plays a crucial role in determining their optoelectronic and chemical properties. Thus, it is possible to correlate the responses of metal halide perovskites to various environmental stimuli with the dynamic behaviors of the [MX 6 ] $n$- octahedra. In this study, with the temperature-dependent single-crystal X ray diffraction (SCXRD) measurements on Cs 3 Bi 2 Br 9 2D halide perovskites, we can identify two classes of distortions through the lowering of temperature: intraoctahedral distortion, which is the off-centering of Bi 3+ cation within a [BiBr 6 ] 3– octahedron due to the Bi 3+ 6s 2 lone pair electrons, and interoctahedral distortion, which is the collective misalignments among the [BiBr 6 ] 3– building blocks. Free exciton (FE) and self-trapped exciton (STE) models are used to study the relationship between the distortion of octahedra in Cs 3 Bi 2 Br 9 and the corresponding changes in its optoelectronic properties, which transform from dominating blue emission above 100 K to red emission at 4 K. In conclusion, this work provides new insights into the excitonic behaviors of perovskites and suggests a possibility that we can design and rationalize the optical properties of halide perovskites by regulating the environmental stimuli based on the knowledge of behaviors of the individual [MX 6 ] $n$- building blocks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

A Ba 6 Cu 31 Te 22 ( A = K, Rb, Cs) Featuring Polyanionic Copper–Telluride Frameworks with Ultralow Thermal Conductivity

In this study, hree polyanionic tellurides, ABa 6 Cu 31 Te 22 (A = K, Rb, Cs), were synthesized in salt flux. The isostructural tellurides crystallize in a new structure type, in the cubic Pa$\overline{3}$ space group with a Wyckoff sequence of d 10 c 2 b 1 and large unit cell volumes of over 5500 Å 3 . The structures feature a framework of [CuTe 4 ] tetrahedra and [CuTe 3 ] trigonal pyramids with disorder in the Cu sites. The polyanionic frameworks have large square antiprism and cuboctahedral voids where Ba and alkali metal cations are situated, forming [BaTe 8 ] and [ATe 12 ], respectively. The overall compositions are close to being charge balanced. The large [ATe 12 ] cuboctahedra allowed for significant anisotropic displacement of the A cations, as observed from both single crystal X-ray diffraction and heat capacity studies. Alkali cations rattling together with Cu atom displacement and disorder leads to the dispersion of phonons, thus softening the lattice and subsequently reducing the thermal conductivity. Evaluations of the electronic band structure revealed the occurrence of a narrow bandgap together with the presence of a flat band near the valence band maximum, giving rise to the high thermopower. The Cs and Rb analogues show a slope change in the temperature dependence of electrical resistivity around room temperature, which is typical for semimetals or degenerate semiconductors. For the as-synthesized and unoptimized materials, high values of the thermoelectric figure-of-merit of ~0.2 were observed at 623 K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Halide Perovskites Breathe Too: The Iodide–Iodine Equilibrium and Self-Doping in Cs 2 SnI 6

The response of an oxide crystal to the atmosphere can be personified as breathing-a dynamic equilibrium between O 2 gas and O 2– anions in the solid. We characterize the analogous defect reaction in an iodide double-perovskite semiconductor, Cs 2 SnI 6 . Here, I 2 gas is released from the crystal at room temperature, forming iodine vacancies. The iodine vacancy defect is a shallow electron donor and is therefore ionized at room temperature; thus, the loss of I2 is accompanied by spontaneous n-type self-doping. Conversely, at high I 2 pressures, I 2 gas is resorbed by the perovskite, consuming excess electrons as I 2 is converted to 2I – . Halide mobility and irreversible halide loss or exchange reactions have been studied extensively in halide perovskites. However, the reversible exchange equilibrium between iodide and iodine [2I – (s) ↔ I 2(g) + 2e – ] described here has often been overlooked in prior studies, though it is likely general to halide perovskites and operative near room temperature, even in the dark. An analysis of the 2I – (s) /I 2(g) equilibrium thermodynamics and related transport kinetics in single crystals of Cs 2 SnI 6 therefore provides insight toward achieving stable composition and electronic properties in the large family of iodide perovskite semiconductors.

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

Dynamic Behavior of Bound Interlayer Excitons in Interlayer-Doped Cs 3 Bi 2 Br 9 Vacancy-Ordered Perovskite

Interlayer doping of the vacancy-ordered 2D perovskite Cs 3 Bi 2 Br 9 (CBB) enables the formation of bound interlayer excitons (BIEs), a unique charge-transfer excited state within the layered solid. BIEs previously reported with silver (Ag + ) as an interlayer dopant exhibited bright broadband photoluminescence (PL) with prolonged lifetime at room temperature, offering potential applications in efficient white light emission, photocatalysis, and optoelectronics. However, the dynamic behavior of radiation and excited carriers remains poorly understood due to the limitations of ensemble spectroscopic measurements. Here, we investigate the temperature-dependent dynamics of Ag-doped Cs 3 Bi 2 Br 9 (Ag-CBB) using single-particle time-resolved PL spectroscopy and ultrafast transient absorption imaging. Single-particle PL measurements reveal three distinct emission regimes across temperature: (i) BIE-dominant emission at high temperatures, (ii) a mixture of radiation from BIEs and self-trapped excitons (STEs) at intermediate temperatures, and (iii) STE-dominant emission below 100 K. Rapid transient absorption mapping using Parallel Rapid Imaging with Spectroscopic Mapping (PRISM) reveals subpicosecond STE formation in pristine CBB and long-lived photoinduced absorption by BIEs, consistent with electron–hole separation and suppressed STE transfer. The spatial uniformity of these signals confirms homogeneous Ag doping across single crystals. These findings highlight the role of Ag interlayer dopants in governing the BIE dynamics.

bound interlayer exciton↗
DOE OSTI2021

Compositional heterogeneity in Cs y FA 1- y Pb(Br x I 1- x ) 3 perovskite films and its impact on phase behavior

Hybrid organic inorganic lead halide perovskite semiconductors of the form Cs y FA 1-y Pb(Br x I 1-x ) 3 are promising candidate materials for high-efficiency photovoltaics. Notably, cation and anion substitution can be used to tune the band gaps to optimize performance and improve stability. However, multi-component materials can be prone to compositional and structural inhomogeneity and the extent, length scale and impact of this heterogeneity on lead halide perovskite properties are not well understood. Here we use synchrotron X-ray diffraction to probe the evolution of crystal structure across the tetragonal-to-cubic phase transition for a series of Cs y FA 1-y Pb(Br x I 1-x ) 3 thin films with x = 0.05 to 0.3 and y = 0.17 to 0.40. We find that the transition occurs across a broad temperature range of approximately 40 °C, much larger than for pure compounds such as MAPbI 3 and MAPbBr 3 . Finally, we hypothesize that this smearing of the phase transition is due to compositional inhomogeneities that give rise to a distribution of local transition temperatures and we estimate the composition varies by about 10% to 15% with likely greater heterogeneity for the halide anion than the cation. This approach of mapping the transition is a simple and effective method of assessing heterogeneity, enabling evaluation of its impact.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Multichannel photodissociation dynamics in CS 2 studied by ultrafast electron diffraction

In this study, the structural dynamics of photoexcited gas-phase carbon disulfide (CS 2 ) molecules are investigated using ultrafast electron diffraction. The dynamics were triggered by excitation of the optically bright 1 B 2 ( 1 Σ u + ) state by an ultraviolet femtosecond laser pulse centred at 200 nm. In accordance with previous studies, rapid vibrational motion facilitates a combination of internal conversion and intersystem crossing to lower-lying electronic states. Photodissociation via these electronic manifolds results in the production of CS fragments in the electronic ground state and dissociated singlet and triplet sulphur atoms. The structural dynamics are extracted from the experiment using a trajectory-fitting filtering approach, revealing the main characteristics of the singlet and triplet dissociation pathways. Finally, the effect of the time-resolution on the experimental signal is considered and an outlook to future experiments provided.

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

3D printed water-stable Cd-doped Cs 4 MnBi 2 Cl 12 /polylactic acid perovskite/polymer composites for high-flux X-ray scintillation

Stable and efficient X-ray scintillators are crucial for medical diagnostics, industrial, and defense applications. However, conventional scintillator technologies face a trade-off between stability, optimal performance, and sustainability. Herein, we introduce 3D-printed Cs 4 MnBi 2 Cl 12 (Pero1) and Cs 4 Cd 0.68 Mn 0.32 Bi 2 Cl 12 (Pero2) perovskite microcrystals embedded within a polylactic acid (PLA) polymer composite as X-ray scintillators, combining efficiency, stability, and sustainability. The orange luminescent perovskite powder phosphors exhibited poor water stability, which was successfully addressed through incorporation into PLA via filament extrusion and fused deposition modeling (FDM) 3D printing. The resulting composite films demonstrated remarkable water stability while maintaining uniform orange emission throughout the polymer matrix, as confirmed by 3D topography scanning and X-ray fluorescence mapping. Structural characterization revealed minimal chemical interaction between the perovskite and PLA matrix, with the composites retaining their crystalline properties. The PLA-Pero2 composite exhibited superior optical properties, with a photoluminescence quantum yield of 47%, nearly 17 times higher than that of PLA-Pero1 (2.8%), attributed to the effective suppression of non-radiative decay pathways through Cd 2+ doping. Under hard X-ray irradiation at synchrotron beamlines, both composites exhibited excellent radioluminescence, with emission peaks at 605 nm, a linear response across a wide X-ray flux range, and remarkable radiation stability, showing less than 3% intensity degradation after 600 seconds of continuous high-dose exposure. The PLA-Pero2 composite achieved a spatial resolution of 5 line pairs per millimeter and a contrast ratio of 0.255. These performance metrics, combined with the polymer's biodegradability and scalability through additive manufacturing, position PLA-based composites as a more sustainable alternative to conventional petroleum-based polymer scintillators for next-generation medical imaging, radiation monitoring, and industrial radiography applications.

3D Printing↗
DOE OSTI2022

Transient vibration and product formation of photoexcited CS 2 measured by time-resolved x-ray scattering

Here, we have observed details of the internal motion and dissociation channels in photoexcited carbon disulfide (CS 2 ) using time-resolved x-ray scattering (TRXS). Photoexcitation of gas-phase CS 2 with a 200 nm laser pulse launches oscillatory bending and stretching motion, leading to dissociation of atomic sulfur in under a picosecond. During the first 300 fs following excitation, we observe significant changes in the vibrational frequency as well as some dissociation of the C–S bond, leading to atomic sulfur in the both 1 D and 3 P states. Beyond 1400 fs, the dissociation is consistent with primarily 3 P atomic sulfur dissociation. This channel-resolved measurement of the dissociation time is based on our analysis of the time-windowed dissociation radial velocity distribution, which is measured using the temporal Fourier transform of the TRXS data aided by a Hough transform that extracts the slopes of linear features in an image. The relative strength of the two dissociation channels reflects both their branching ratio and differences in the spread of their dissociation times. Measuring the time-resolved dissociation radial velocity distribution aids the resolution of discrepancies between models for dissociation proposed by prior photoelectron spectroscopy work.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Spinon excitations in the quasi-one-dimensional $S = \frac{1}{2}$ chain compound Cs 4 CuSb 2 Cl 12

The spin-$\frac{1}{2}$ Heisenberg antiferromagnetic chain is ideal for realizing one of the simplest gapless quantum spin liquids (QSLs), supporting a many-body ground state whose elementary excitations are fractional fermionic excitations called spinons. Here we report the discovery of such a one-dimensional (1D) QSL in Cs 4 CuSb 2 Cl 12 . Compared to previously reported $S = \frac{1}{2}$ 1D chains, this material possesses a wider temperature range over which the QSL state is stabilized. In this work, we identify spinon excitations extending at $\textit{T}$ > 0.8 K, with a large $\textit{T}$-linear contribution to the specific heat, γ = 31.5(2)mJ mol –1 K –2 , which contribute itinerantly to thermal transport up to temperatures as high as $\textit{T}$ = 35 K. At $\textit{T}$ = 0.7 K , we find a second-order phase transition that is unchanged by a $μ_0H = 5T$ magnetic field. Cs 4 CuSb 2 Cl 12 reveals new phenomenology deep in the 1D QSL regime, supporting a gapped QSL phase over a wide temperature range compared to many other experimental realizations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

$β$-delayed neutron emission studies of 137,138 I and 144,145 Cs performed with trapped ions

A detailed study of the β-delayed neutron emission properties of 137,138 I and 144,145 Cs has been performed by confining ions in the Beta-decay Paul Trap. The daughter ions following β decay emerge from the trapped-ion cloud with negligible scattering allowing reconstruction of the recoil-ion energy from the time of flight. From this information, the neutron-emission branching ratios and neutron-energy spectra were deduced. The results for the 137 I and 144,145 Cs decays are in agreement with previous results performed using direct neutron-detection techniques. In the case of 138 I, a branching ratio of 6.18(50)% is obtained, yielding a value consistent with the more recent results, which are a factor of two larger than measurements made prior to 1978.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Search for a light charged Higgs boson in $t \rightarrow H^{\pm } b$ decays, with $H^{\pm } \rightarrow cs$, in $pp$ collisions at $\sqrt{s}={13}\hbox { TeV}$ with the ATLAS detector

A search for a light charged Higgs boson produced in decays of the top quark, $t \rightarrow H^{\pm } b$ with $H^{\pm } \rightarrow cs$, is presented. This search targets the production of top-quark pairs $t\bar{t} \rightarrow WbH^{\pm } b$, with $W \rightarrow ℓv(ℓ = e, μ)$, resulting in a lepton-plus-jets final state characterised by an isolated electron or muon and at least four jets. The search exploits b-quark and c-quark identification techniques as well as multivariate methods to suppress the dominant $t\bar{t}$ background. The data analysed correspond to 140 fb -1 of $pp$ collisions at $\sqrt{s}$ = 13 TeV recorded with the ATLAS detector at the LHC between 2015 and 2018. Observed (expected) 95% confidence-level upper limits on the branching fraction $\mathscr{B}(t \rightarrow H^{\pm } b)$, assuming $\mathscr{B}(t \rightarrow Wb) + \mathscr{B}(t \rightarrow H^{\pm }(\rightarrow cs)b$, are set between 0.066% (0.077%) and 3.6% (2.3%) for a charged Higgs boson with a mass between 60 and 168 GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

A comprehensive final summary of the MCNP calculations performed concerning the UW 137 Cs release event

This document combines and supersedes earlier reports (e.g. LA-UR-19-32358 and LA-UR-20- 22216) that discussed MCNP-calculated conversion factors (count rate per unit activity per unit area) for collimated 2”x2” NaI detectors (Ludlum model 44-10 and Thermo model SPA3) in contact with various surfaces of interest to the University of Washington 137 Cs release event. These surfaces include: Exterior surface of round and rectangular ducts, Exterior surface of outdoor brick work, Exterior surface of cast iron pipes, Exterior surface of an O 2 filter assembly For each surface, the calculated conversion factors allowed inferences on 137 Cs activity on interior surfaces based on exterior contact measurements of the 662 keV photopeak count rate. The MCNP calculations included the effect of attached collimators (i.e. either a Pb/Sb-based Ludlum or a W-based “Rees” model) on detector response. As a consequence, the conversion factors only apply to the appropriate collimated 2”x2” NaI detector operated in pulse height analysis (PHA) mode. Other assumptions affecting the calculations and valid application of the conversion factors will be outlined below.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Carbon Storage Technical Viability Approach (CS TVA): An Integrated Approach for Feasibility and Data Resource Assessment

There is currently a poor understanding and lack of workflow to understand the technical viability of carbon storage spatially. To address this gap, the multi-faceted Carbon Storage Technical Viability Approach (CS TVA) is being developed to incorporate CO2 storage resources, environmental and socio-economic justice (EJ/SJ) factors to enable more comprehensive assessments. The CS TVA includes a (1) matrix framework, (2) an integrated and labeled database, (3) a data availability assessment workflow, and (4) spatial data availability assessment results. This approach leverages spatial and data science analytics to communicate data density, uncertainty, and gaps. The workflow can be applied in whole or in part, based on user needs.

Rodriguez, Neyda Cordero↗
DOE OSTI2020

Massive Stars in Molecular Clouds Rich in High-energy Sources: The Bridge of G332.809–0.132 and CS 78 in NGC 6334

Detections of massive stars in the direction of the H ii region CS 78 in NGC 6334 and of G332.809−0.132 are here presented. The region covered by the G332.809−0.132 complex coincides with the RCW 103 stellar association. In its core (40′ in radius), approximately 110 OB candidate stars (K {sub s} < 10 mag and 0.4 < A{sub K{sub s}} < 1.6 mag) were identified using 2MASS, DENIS, and GLIMPSE data. This number of OB stars accounts for more than 50% of the observed number of Lyman continuum photons from this region. Medium-resolution K-band spectra were obtained for seven early types, including one WN 8 star and one Ofpe/WN 9 star; the latter is located near the RCW 103 remnant and its luminosity is consistent with a distance of ≈3 kpc. The area analyzed encloses 9 of the 34 OB stars previously known in RCW 103, as well as IRAS 16115−5044, which we reclassify as a candidate luminous blue variable. The line of sight is particularly interesting, crossing three spiral arms; a molecular cloud at −50 (with RCW 103 in the Scutum-Crux arm) and another at −90 km s{sup −1} (in the Norma arm) are detected, both rich in massive stars and supernova remnants. We also report the detection of a B supergiant as the main ionizing source of CS 78, 2MASS J17213513−3532415. Medium-resolution H- and K-band spectra display H i and He i lines, as well as Fe ii lines. By assuming a distance of 1.35 kpc, we estimate a bolometric magnitude of −6.16, which is typical of supergiants.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Tests of Cs-Free Operation of the SNS RF H⁻ Ion Sources

Tests were performed at SNS in collaboration with visiting colleagues from ISIS, UK to evaluate the uncesiated beam performance of the SNS RF H⁻ ion sources. Two spare experimental sources, one with internal antenna and one with external antenna were used for the tests. The beam currents achieved with Cs-free operations accounted for about 1/3 to 1/2 of the beam currents produced with cesiated operations. ~17 mA uncesiated H⁻ current was demonstrated within the tested RF power range up to 65 kW with the internal antenna source and ~15 mA with up to 40 kW RF with the external antenna source. In Cs-free operations, the power supply for the electron dumping electrode was loaded down below its set voltage but was not too drastic to tamper the operation.

Han, Baoxi↗