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All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

An APFIM/AEM Study of Phase Decompositions in Fe-Ni Alloys at Low Temperatures

A combined atom probe field ion microscopy and analytical electron microscopy characterization has been performed on laboratory aged martensitic and austenitic specimens of FeNi and FeNiP alloys. These techniques revealed that the martensitic 24.1 and 28.6 at.% Ni alloys decomposed during aging for 1 year at 300 C to form face centered cubic precipitates of approx. 56 at.% Ni in a body centered cubic matrix containing approx. 20 at.% Ni. Some thin platelets were observed in the field ion micrographs of the austenitic Fe-42.9 at. % Ni alloy and the Fe-43.2 at.% Ni-0.44 at.% P alloy after aging at 400 and 350 C. Atom probe analysis revealed phosphorus clustering in the ternary alloy aged at 300 C.

Zhang, J.↗
NASA NTRS1994

A Microgravity Helium Dilution Cooler

We are developing a He-3-He-4 dilution cooler to operate in microgravity. It uses charcoal adsorption pumps and heaters for its operation; it has no moving parts. It currently operates cyclically to well below 0.1 K and we have designed a version to operate continuously. We expect that the continuous version will be able to provide the long-duration cooling that many experiments need at temperatures down to 0.040 K. More importantly, such a dilution cooler could provide the precooling that enables the use of adiabatic demagnetization techniques that can reach temperatures below 0.001 K. At temperatures below 0.002 K many fascinating microgravity experiments on superfluid He-3 become possible. Among the possibilities are: research into a superfluid He-3 gyroscope, study of the nucleation of the B-phase of superfluid He-3 when the sample is floating out of contact with walls, study of the anisotropy of the surface tension of the B-phase, and NMR experiments on tiny free-floating clusters of superfluid He-3 atoms that should model the shell structure of nuclei.

Roach, Pat R.↗
NASA NTRS1991

The use of transition heights for the representation of ion composition

Several characteristic transition heights can be found in ionospheric ion-composition profiles. These are the boundaries between the regions dominated by light ions, atomic oxygen ions, molecular ions, and cluster ions, respectively. Ion-composition modeling can benefit from the use of these transition heights. Special emphasis is given to the 'upper' transition height H sub T (light ions to atomic oxygen) and to the 'lower' transition height h sub t (atomic oxygen to molecular ions). Transition-height models deduced from rocket and satellite measurements are compared with the heights predicted by the International Reference Ionosphere. Considerable discrepancies are found between the different models as well as between the models and independent measurements.

Bilitza, Dieter↗
DOE OSTI2023

Bonding and Acidity of the Formal Hydride in the Prototypical Au 9 (PPh 3 ) 8 H 2+ Nanocluster

Abstract The role of hydrogen atoms as surface ligands on metal nanoclusters is of profound importance but remains difficult to directly study. While hydrogen atoms often appear to be incorporated formally as hydrides, evidence suggests that they donate electrons to the cluster's delocalized superatomic orbitals and may consequently behave as acidic protons that play key roles in synthetic or catalytic mechanisms. Here we directly test this assertion for the prototypical Au 9 (PPh 3 ) 8 H 2+ nanocluster, formed by addition of a hydride to the well‐characterized Au 9 (PPh 3 ) 8 3+ . Using gas‐phase infrared spectroscopy, we were able to unambiguously isolate Au 9 (PPh 3 ) 8 H 2+ and Au 9 (PPh 3 ) 8 D 2+ , revealing an Au−H stretching mode at 1528 cm −1 that shifts to 1038 cm −1 upon deuteration. This shift is greater than the maximum expected for a typical harmonic potential, suggesting a potential governing cluster‐H bonding that has some square‐well character consistent with the hydrogen nucleus behaving as a metal atom in the cluster core. Complexing this cluster with very weak bases reveals a redshift of 37 cm −1 in the Au−H vibration, consistent with those typically seen for moderately acidic groups in gas phase molecules and providing an estimate of the acidity of Au 9 (PPh 3 ) 8 H 2+ , at least with regard to its surface reactivity.

Hernández, Hanna Morales↗
DOE OSTI2020

Materials Data on Sn4H26(Br4O5)3 by Materials Project

(SnH5(OBr)3)4(H2O)3 crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of six water molecules and four SnH5(OBr)3 clusters. In two of the SnH5(OBr)3 clusters, there are two inequivalent Sn4+ sites. In the first Sn4+ site, Sn4+ is bonded to three O2- and three Br1- atoms to form distorted edge-sharing SnBr3O3 octahedra. There are a spread of Sn–O bond distances ranging from 2.12–2.18 Å. There are two shorter (2.55 Å) and one longer (2.66 Å) Sn–Br bond lengths. In the second Sn4+ site, Sn4+ is bonded to three O2- and three Br1- atoms to form distorted edge-sharing SnBr3O3 octahedra. There are a spread of Sn–O bond distances ranging from 2.10–2.22 Å. There are a spread of Sn–Br bond distances ranging from 2.55–2.64 Å. There are ten inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.03 Å) and one longer (1.54 Å) H–O bond length. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the third H1+ site, H1+ is bonded in a distorted linear geometry to two O2- atoms. There is one shorter (1.01 Å) and one longer (1.68 Å) H–O bond length. In the fourth H1+ site, H1+ is bonded in a distorted single-bond geometry to one O2- atom. The H–O bond length is 1.01 Å. In the fifth H1+ site, H1+ is bonded in a distorted single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the eighth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the ninth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the tenth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to one Sn4+ and two H1+ atoms. In the second O2- site, O2- is bonded in a distorted single-bond geometry to two Sn4+ and one H1+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to two Sn4+ and one H1+ atom. In the fourth O2- site, O2- is bonded in a distorted water-like geometry to one Sn4+ and two H1+ atoms. In the fifth O2- site, O2- is bonded in a water-like geometry to three H1+ atoms. In the sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to three H1+ atoms. There are six inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a distorted single-bond geometry to one Sn4+ atom. In the second Br1- site, Br1- is bonded in a single-bond geometry to one Sn4+ atom. In the third Br1- site, Br1- is bonded in a single-bond geometry to one Sn4+ atom. In the fourth Br1- site, Br1- is bonded in a single-bond geometry to one Sn4+ atom. In the fifth Br1- site, Br1- is bonded in a single-bond geometry to one Sn4+ atom. In the sixth Br1- site, Br1- is bonded in a single-bond geometry to one Sn4+ atom. In two of the SnH5(OBr)3 clusters, Sn4+ is bonded to three O2- and three Br1- atoms to form edge-sharing SnBr3O3 octahedra. There are two shorter (2.12 Å) and one longer (2.20 Å) Sn–O bond lengths. There are a spread of Sn–Br bond distances ranging from 2.56–2.62 Å. There are five inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the third H1+ site, H1+ is bonded in a distorted linear geometry to two O2- atoms. There is one shorter (1.02 Å) and one longer (1.63 Å) H–O bond length. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted water-like geometry to three H1+ atoms. In the second O2- site, O2- is bonded in a distorted water-like geometry to one Sn4+ and two H1+ atoms. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Sn4+ and one H1+ atom. There are three inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a single-bond geometry to one Sn4+ atom. In the second Br1- site, Br1- is bonded in a single-bond geometry to one Sn4+ atom. In the third Br1- site, Br1- is bonded in a single-bond geometry to one Sn4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Computational studies of structural, energetic, and electronic properties of pure Pt and Mo and mixed Pt/Mo clusters: Comparative analysis of characteristics and trends

The added technological potential of bimetallic clusters and nanoparticles, as compared to their pure (i.e., one-component) counterparts, stems from the ability to further fine-tune their properties and, consequently, functionalities through a simultaneous use of the “knobs” of size and composition. The practical realization of this potential can be greatly advanced by the knowledge of the correlations and relationships between the various characteristics of bimetallic nanosystems on the one hand and those of their pure counterparts as well as pure constituent components on the other hand. Here, in this study, we present results of a density functional theory based study of pure Pt n and Mo n clusters aimed at revisiting and exploring further their structural, electronic, and energetic properties. These are then used as a basis for analysis and characterization of the results of calculations on two-component Pt n-m Mo m clusters. The analysis also includes establishing relationships between the properties of the Pt n-m Mo m clusters and those of their Pt n-m and Mo m components. One of the particularly intriguing findings suggested by the calculated data is a linear dependence of the average binding energy per atom in sets of Pt n-m Mo m clusters that have the same fixed number m of Mo atoms and different number n-m of Pt atoms on the fractional content (n-m)/n of Pt atoms. We derive an analytical model that establishes the fundamental basis for this linearity and expresses its parameters—the m-dependent slope and intercept—in terms of characteristic properties of the constituent components, such as the average binding energy per atom of Mo m and the average per-atom adsorption energy of the Pt atoms on Mo m . The conditions of validity and degree of robustness of this model and of the linear relationship predicted by it are discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2003

Iron catalyst chemistry in modeling a high-pressure carbon monoxide nanotube reactor

The high-pressure carbon monoxide (HiPco) technique for producing single-wall carbon nanotubes (SWNTs) is analyzed with the use of a chemical reaction model coupled with flow properties calculated along streamlines, calculated by the FLUENT code for pure carbon monoxide. Cold iron pentacarbonyl, diluted in CO at about 30 atmospheres, is injected into a conical mixing zone, where hot CO is also introduced via three jets at 30 degrees with respect to the axis. Hot CO decomposes the Fe(CO)5 to release atomic Fe. Then iron nucleates and forms clusters that catalyze the formation of SWNTs by a disproportionation reaction (Boudouard) of CO on Fe-containing clusters. Alternative nucleation rates are estimated from the theory of hard sphere collision dynamics with an activation energy barrier. The rate coefficient for carbon nanotube growth is estimated from activation energies in the literature. The calculated growth was found be about an order of magnitude greater than measured, regardless of the nucleation rate. A study of cluster formation in an incubation zone prior to injection into the reactor shows that direct dimer formation from Fe atoms is not as important as formation via an exchange reaction of Fe with CO in FeCO.

Evaluation Studies↗
DOE OSTI2020

Materials Data on H5BrO2 by Materials Project

(H2O)2HBr crystallizes in the triclinic P1 space group. The structure is zero-dimensional and consists of two (H2O)2HBr clusters. In one of the (H2O)2HBr clusters, there are fifteen inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the second H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.14 Å) and one longer (1.29 Å) H–O bond length. In the third H1+ site, H1+ is bonded in a single-bond geometry to one O2- and one Br1- atom. The H–O bond length is 1.01 Å. The H–Br bond length is 2.18 Å. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one O2- and one Br1- atom. The H–O bond length is 1.02 Å. The H–Br bond length is 2.15 Å. In the sixth H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.11 Å) and one longer (1.34 Å) H–O bond length. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one O2- and one Br1- atom. The H–O bond length is 1.01 Å. The H–Br bond length is 2.17 Å. In the eighth H1+ site, H1+ is bonded in a single-bond geometry to one O2- and one Br1- atom. The H–O bond length is 1.00 Å. The H–Br bond length is 2.26 Å. In the ninth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the tenth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the eleventh H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the twelfth H1+ site, H1+ is bonded in a single-bond geometry to one O2- and one Br1- atom. The H–O bond length is 0.99 Å. The H–Br bond length is 2.29 Å. In the thirteenth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the fourteenth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the fifteenth H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.14 Å) and one longer (1.29 Å) H–O bond length. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a trigonal non-coplanar geometry to three H1+ atoms. In the second O2- site, O2- is bonded in a trigonal non-coplanar geometry to three H1+ atoms. In the third O2- site, O2- is bonded in a trigonal non-coplanar geometry to three H1+ atoms. In the fourth O2- site, O2- is bonded in a trigonal planar geometry to three H1+ atoms. In the fifth O2- site, O2- is bonded in a trigonal planar geometry to three H1+ atoms. In the sixth O2- site, O2- is bonded in a trigonal planar geometry to three H1+ atoms. There are three inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a distorted single-bond geometry to one H1+ atom. In the second Br1- site, Br1- is bonded in a 1-coordinate geometry to one H1+ atom. In the third Br1- site, Br1- is bonded in a 1-coordinate geometry to three H1+ atoms. In one of the (H2O)2HBr clusters, there are five inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- and one Br1- atom. The H–O bond length is 1.02 Å. The H–Br bond length is 2.10 Å. In the third H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.13 Å) and one longer (1.31 Å) H–O bond length. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a trigonal non-coplanar geometry to three H1+ atoms. In the second O2- site, O2- is bonded in a trigonal planar geometry to three H1+ atoms. Br1- is bonded in a distorted single-bond geometry to one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Bonding and Acidity of the Formal Hydride in the Prototypical Au 9 (PPh 3 ) 8 H 2+ Nanocluster

The role of hydrogen atoms as surface ligands on metal nanoclusters is of profound importance but remains difficult to directly study. While hydrogen atoms often appear to be incorporated formally as hydrides, evidence suggests that they donate electrons to the cluster's delocalized superatomic orbitals and may consequently behave as acidic protons that play key roles in synthetic or catalytic mechanisms. Here we directly test this assertion for the prototypical Au 9 (PPh 3 ) 8 H 2+ nanocluster, formed by addition of a hydride to the well-characterized Au 9 (PPh 3 ) 8 3+ . Using gas-phase infrared spectroscopy, we were able to unambiguously isolate Au 9 (PPh 3 ) 8 H 2+ and Au 9 (PPh 3 ) 8 D 2+ , revealing an Au–H stretching mode at 1528 cm –1 that shifts to 1038 cm –1 upon deuteration. This shift is greater than the maximum expected for a typical harmonic potential, suggesting a potential governing cluster-H bonding that has some square-well character consistent with the hydrogen nucleus behaving as a metal atom in the cluster core. Complexing this cluster with very weak bases reveals a redshift of 37 cm –1 in the Au–H vibration, consistent with those typically seen for moderately acidic groups in gas phase molecules and providing an estimate of the acidity of Au 9 (PPh 3 ) 8 H 2+ , at least with regard to its surface reactivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Local atomic environment analysis of short and long-range solute-solute interactions in a symmetric tilt grain boundary

We develop an efficient molecular-statics algorithm for predicting local solute-solute interaction effects on grain-boundary segregation. This algorithm is applied to the segregation and interaction of Ni and Cu solutes in a Σ9 (221) symmetric tilt grain boundary in Ag. It is found that the strength of interaction between two solutes directly correlates with the change of average segregation energy in the local atomic environment of a fixed grain-boundary solute. It is shown that local interaction effects at grain boundaries can be either attractive or repulsive wherein long-range attractive effects increase the propensity for solute cluster nucleation. This study underscores the atomic nature of grain-boundary solute segregation and provides a tool that could yield meaningful insight into heterogeneous solute segregation phenomena in polycrystalline alloys beyond their dilute limit.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Si3BiH27(C5Cl)2 by Materials Project

Si3BiH27(C5Cl)2 is Silicon tetrafluoride-derived structured and crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of four Si3BiH27(C5Cl)2 clusters. In two of the Si3BiH27(C5Cl)2 clusters, there are three inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There are a spread of Si–C bond distances ranging from 1.88–1.94 Å. In the second Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.93 Å) Si–C bond length. In the third Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There are a spread of Si–C bond distances ranging from 1.88–1.94 Å. There are ten inequivalent C4- sites. In the first C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. In the second C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. In the third C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form corner-sharing CSiH3 tetrahedra. There is one shorter (1.09 Å) and two longer (1.10 Å) C–H bond length. In the fourth C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. In the fifth C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form distorted corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. In the sixth C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. In the seventh C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. In the eighth C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. In the ninth C4- site, C4- is bonded to three Si4+ and one Bi3+ atom to form corner-sharing CSi3Bi tetrahedra. The C–Bi bond length is 2.34 Å. In the tenth C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form distorted corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. Bi3+ is bonded in a trigonal non-coplanar geometry to one C4- and two Cl1- atoms. There are one shorter (2.51 Å) and one longer (2.52 Å) Bi–Cl bond lengths. There are twenty-seven inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the second H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the third H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the eighth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the ninth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the tenth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the eleventh H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twelfth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the thirteenth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the fourteenth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the fifteenth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the sixteenth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the seventeenth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the eighteenth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the nineteenth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twentieth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twenty-first H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twenty-second H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twenty-third H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twenty-fourth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twenty-fifth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twenty-sixth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twenty-seventh H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. There are two inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Bi3+ atom. In the second Cl1- site, Cl1- is bonded in a single-bond geometry to one Bi3+ atom. In two of the Si3BiH27(C5Cl)2 clusters, there are three inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There are a spread of Si–C bond distances ranging from 1.88–1.93 Å. In the second Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.93 Å) Si–C bond length. In the third Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There are a spread of Si–C bond distances ranging from 1.88–1.94 Å. There are ten inequivalent C4- sites. In the first C4- site, C4- is bonded to three Si4+ and one Bi3+ atom to form corner-sharing CSi3Bi tetrahedra. The C–Bi bond length is 2.34 Å. In the second C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form distorted corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. In the third C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. In the fourth C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. In the fifth C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. In the sixth C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. In the seventh C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form corner-sharing CSiH3 tetrahedra. There is one shorter (1.09 Å) and two longer (1.10 Å) C–H bond length. In the eighth C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. In the ninth C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. In the tenth C4- site, C4- is bonded to one Si4+ and three H1+ atoms to form distorted corner-sharing CSiH3 tetrahedra. All C–H bond lengths are 1.10 Å. Bi3+ is bonded in a trigonal non-coplanar geometry to one C4- and two Cl1- atoms. There are one shorter (2.51 Å) and one longer (2.52 Å) Bi–Cl bond lengths. There are twenty-seven inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the second H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the third H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the eighth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the ninth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the tenth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the eleventh H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twelfth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the thirteenth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the fourteenth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the fifteenth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the sixteenth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the seventeenth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the eighteenth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the nineteenth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twentieth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twenty-first H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twenty-second H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twenty-third H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twenty-fourth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twenty-fifth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twenty-sixth H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. In the twenty-seventh H1+ site, H1+ is bonded in a single-bond geometry to one C4- atom. There are two inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Bi3+ atom. In the second Cl1- site, Cl1- is bonded in a single-bond geometry to one Bi3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2026

H I Depletion Begins Well Beyond the Virial Radius: A FAST Stacking Study of 36 Galaxy Clusters to 5 × R 200

Abstract We present a stacking study of the neutral atomic hydrogen (H i ) content in and around 36 local galaxy clusters at z < 0.07, using a combination of the FAST All Sky H i survey (FASHI) and the extensive spectroscopic catalog mainly from the Dark Energy Spectroscopic Instrument (DESI). We employ spectral stacking techniques to probe the average H i mass and HI-to-stellar mass ratio ( M HI / M * ) for member galaxies down to stellar masses of M * ∼ 10 9 M ⊙ , spanning a projected cluster-centric distance of up to 5 R 200 . Our analysis reveals a pronounced environmental effect; both M HI and M HI / M * decrease steadily toward the cluster center, dropping by ∼0.5 dex on average from the outskirts to the core. Crucially, we find that M HI / M * of galaxies remain lower than the field galaxies even at the 5 R 200 . This provides direct, statistical evidence for substantial gas stripping and preprocessing in the cluster outskirts, likely occurring in infalling groups and large-scale filaments. By further splitting the sample by g − r color, we show that the H i deficiency persists at fixed galaxy color; even the bluest cluster members exhibit ∼0.5 dex lower M HI / M * than field galaxies of similar color, reflecting environmental effects on the cold gas reservoir prior to full optical transformation. The total H i mass within clusters and their outskirts agrees broadly with predictions from cosmological simulations. Our results underscore the critical role of the extended cluster environment in quenching galaxies by depleting their cold gas reservoirs well before they enter the dense cluster core.

Cheng, Cheng [Chinese Academy of Sciences South Am↗
DOE OSTI2025

Evidence for Ga clusters in β-Ga 2 O 3 from Raman spectroscopy and density functional theory

Monoclinic gallium oxide (β-Ga 2 O 3 ) single crystals have a Raman mode at ∼250 cm −1 that is strongly correlated with free-electron density. Prior work attributed this peak to an electronic excitation of a shallow donor impurity band. However, heavily n-type thin films grown by metalorganic chemical vapor deposition or molecular beam epitaxy do not have the peak. In the present work, an alternate model is proposed: the 250 cm −1 Raman peak arises from Ga clusters, defined as two or more Ga atoms that form Ga–Ga bonds. Raman mapping reveals variations in the frequency that are consistent with a distribution of cluster sizes. The intensity of the peak decreases as the temperature is raised, attributed to melting of the Ga clusters. First-principles calculations indicate that the 250 cm −1 mode is due to Ga–Ga bond-stretching vibrations. As the Fermi energy is raised, the formation of Ga–Ga dimers becomes energetically favorable, explaining the correlation between n-type conductivity and the appearance of the Raman peak.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A family of ionic supersalts with covalent-like directionality and unconventional multiferroicity

Ionic crystals composed of elemental ions such as NaCl are non-polar due to directionless ionic bonding interactions. Here, we show that these can develop polarity by changing their building blocks from elemental ions to superalkali and superhalogen cluster-ions, which mimic the chemistry of alkali and halogen atoms, respectively. Due to the non-spherical geometries of these cluster ions, corresponding supersalts form anisotropic polar structures with ionic bonding, yet covalent-like directionality, akin to sp 3 hybridized systems. Using density functional theory and extensive structure searches, we predict a series of stable ferroelectric/ferroelastic supersalts, PnH 4 MX 4 (Pn = N, P; M = B, Al, Fe; X = Cl, Br) composed of superalkali PnH 4 and superhalogen MX 4 ions. Unlike traditional ferroelectric/ferroelastic materials, the cluster-ion based supersalts possess ultra-low switching barrier and can endure large ion displacements and reversible strain. In particular, PH 4 FeBr 4 exhibits triferroic coupling of ferroelectricity, ferroelasticity, and antiferromagnetism with controllable spin directions via either ferroelastic or 90-degree ferroelectric switching.

36 MATERIALS SCIENCE↗
NASA NTRS1989

Theoretical investigations of the structures and binding energies of Be(sub n) and Mg(sub n) (n = 3-5) clusters

Researchers determined the equilibrium geometries and binding energies of Be and Mg trimers, tetramers and pentamers using single and double excitation coupled cluster (CCSD) and complete active space self-consistent-field (CASSCF) multireference configuration interaction (MRCI) wave functions in conjunction with extended atomic basis sets. Best estimates of the cluster binding energies are 24, 83 and 110 kcal/mole for Be3, Be4 and Be5; and 9, 31 and 41 kcal/mole for Mg3, Mg4 and Mg5, respectively. A comparison of the MRCI and CCSD results shows that even the best single-reference approach (limited to single and double excitations) is not capable of quantitative accuracy in determining the binding energies of Be and Mg clusters.

Lee, Timothy J.↗
DOE OSTI2025

Characterizing the surface compositions of supported bimetallic PtSn clusters: Effects of cluster-support interactions and surface adsorbates

PtSn bimetallic clusters on TiO2(110) and highly oriented pyrolytic graphite (HOPG) surfaces have been characterized by scanning tunneling microscopy, low energy ion scattering (LEIS), Xray photoelectron spectroscopy, and temperature programmed desorption (TPD); density functional theory (DFT) calculations have also been performed to better understand adsorption of CO and D2 on the PtSn surfaces. On TiO2 at coverages of 2 ML of Pt and 2 ML of Sn, exclusively bimetallic clusters are formed for both orders of deposition because clusters of the first metal completely cover the surface such that all atoms of the second metal are incorporated into the existing clusters. In contrast, on HOPG, the high mobility and weak cluster-support interactions on HOPG result in much larger 2 ML monometallic clusters (~30 Å high) that do not completely cover the surface, and deposition of the second metal produces larger clusters as well as smaller ones. Despite the difference in cluster morphologies for the different orders of deposition and supports, the LEIS experiments demonstrate that in all cases, the PtSn clusters are rich in Sn at the surface, as expected based on the lower surface free energy for Sn compared to Pt. Furthermore, the +0.2 eV shift in the Sn(3d5/2) binding energy observed on all surfaces in the presence of Pt is consistent with PtSn alloy formation. Deposition of 2 ML of Sn on TiO2 produces two-dimensional clusters with oxidation of Sn and reduction of titania at the clustersupport interface, but addition of Pt to the Sn clusters causes Sn to diffuse away from this interface, leaving Sn in the metallic state. TPD experiments on 2 ML Pt/TiO2 with increasing coverages of Sn show that the number of adsorption sites for D2 sharply decreases to nearly zero at 0.5 ML, while CO adsorption decreases to zero only at much higher Sn coverages of 2 ML. DFT studies for Sn modified Pt surfaces and bulk structures demonstrate that for CO adsorption at low Sn coverages (<0.25 ML), the strong Pt-CO interactions induce diffusion of Pt to the cluster surface and the formation of a bulk Pt3Sn alloy, whereas D2 adsorption does not lead to interactions with the Pt surface that are strong enough to induce alloy formation. A single Sn adatom prevents D2 adsorption on four neighboring Pt atoms via site-blocking and the donation of electron density to Pt.

Li, Fangliang↗
DOE OSTI2026

Vapor-Phase Heteroatom Incorporation into Semiconductive Molecular-Scale Magic-Size Clusters

Magic-size metal chalcogenide clusters of molecular size exhibit well-defined structure and unique properties that might be further expanded with the incorporation or substitution of a second metal. Here, we report the postmodification of magic-size clusters synthesized in polymer thin films via exposure to volatile metal organic precursors commonly utilized for atomic layer deposition. Exposure of In 6 S 6 (CH 3 ) 6 clusters to dimethylcadmium results in exposure-dependent incorporation of Cd 2+ , which extends the optical absorbance of the clusters into the visible spectrum. The mechanism for Cd 2+ incorporation is consistent with Cd 2+ replacement of In 3+ that includes methyl ligand removal to maintain charge neutrality. Even for clusters embedded in a polymer matrix, ligand loss leads to sintering and transformation into larger nanoscale aggregates with zinc blende-type structure. The extent of Cd incorporation can be modulated by varying the process temperature and volatile metal organic exposure as well as the choice of volatile metal organic precursor. A computational thermodynamic analysis of heteroatom incorporation for several metals and chemistries reveals that both the stability of the substituted cluster and the favorability of reaction byproducts jointly determine the favorability of cation incorporation.

atomic layer deposition↗