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All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Flat-band-induced itinerant ferromagnetism in RbCo 2 Se 2

ACo 2 Se 2 (A=K,Rb,Cs) is a homologue of the iron-based superconductor, AFe 2 Se 2 . From a comprehensive study of RbCo 2 Se 2 via measurements of magnetization, transport, neutron diffraction, angle-resolved photoemission spectroscopy, and first-principle calculations, we identify a ferromagnetic order accompanied by an orbital-dependent spin-splitting of the electronic dispersions. However, we identify the ordered moment to be dominated by a d x 2 –y 2 flatband near the Fermi level, which exhibits the largest spin splitting across the ferromagnetic transition, suggesting an itinerant origin of the ferromagnetism. In the broader context of the iron-based superconductors, we find this d x 2 –y 2 flatband to be a common feature in the band structures of both iron chalcogenides and iron pnictides, accessible via heavy electron doping.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Materials Data on Cs3LiPb4 by Materials Project

Cs3LiPb4 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are two inequivalent Cs sites. In the first Cs site, Cs is bonded in a 2-coordinate geometry to eight Pb atoms. There are a spread of Cs–Pb bond distances ranging from 4.06–4.45 Å. In the second Cs site, Cs is bonded in a 1-coordinate geometry to seven Pb atoms. There are a spread of Cs–Pb bond distances ranging from 3.89–4.21 Å. Li is bonded in a distorted hexagonal planar geometry to six Pb atoms. There are two shorter (3.16 Å) and four longer (3.26 Å) Li–Pb bond lengths. There are two inequivalent Pb sites. In the first Pb site, Pb is bonded in a 2-coordinate geometry to five Cs, two equivalent Li, and three Pb atoms. There are two shorter (3.14 Å) and one longer (3.25 Å) Pb–Pb bond lengths. In the second Pb site, Pb is bonded in a 10-coordinate geometry to six Cs, one Li, and three Pb atoms. The Pb–Pb bond length is 3.10 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Expanding the Cage of 2D Bromide Perovskites by Large A-Site Cations

Two-dimensional (2D) halide perovskites have outstanding optoelectronic properties, and they feature a variety of organic cation spacers and cage A-site cations that can be incorporated into their structures. It has recently been reported that the Goldschmidt tolerance factor can be relaxed and expanded in iodide 2D perovskites. Bromide 2D perovskites, whose multilayer structures and optical properties are much less studied, provide a great platform for studying structure-property relationships for 2D perovskites with large Asite cations. Herein, we report the synthesis and structure of three new 2D bromide perovskites-(BA)(2)(MHy)(2)Pb3Br10 (BA, butylammonium; MHy, methylhydrazinium), (BA)(2)(EA)(2)Pb3Br10 (EA is ethylammonium), and (BA)(2)(DMA)Pb2Br7 (DMA is dimethylammonium). We compared them with other 2D perovskites with different A-site cations but with the same spacer and layer thickness. Single-crystal structures show that the Pb-Br bonds are elongated to accommodate the large A-site cations. Additionally, the octahedra in (BA)(2)(MHy)(2)Pb3Br10 and (BA)(2)(EA)(2)Pb3Br10 are highly distorted, and their different stacking patterns of the inner and outer layers lead to the formation of the n = 3 phases. Density functional theory calculations show that 2D perovskites with larger A-site cations (e.g., DMA, MHy, and EA) have smaller band dispersions and larger effective masses than those with Cs+ and MA. (BA)(2)(MHy)(2)Pb3Br10 also exhibits one of the largest Rashba splittings in the literature. Structures with large cage cations also exhibit high band gaps within the same n number and short photoluminescence (PL) lifetimes. Temperature- and power-dependent PL measurements reveal that the broad shoulder in the PL peak originates from the trap states.

Emission↗
DOE OSTI2022

Visualizing Light-Induced Microstrain and Phase Transition in Lead-Free Perovskites Using Time-Resolved X-Ray Diffraction

Metal halide perovskites have emerged as promising materials for optoelectronic applications in the last decade. A large amount of effort has been made to investigate the interplay between the crystalline lattice and photoexcited charge carriers as it is vital to their optoelectronic performance. Among them, ultrafast laser spectroscopy has been intensively utilized to explore the charge carrier dynamics of perovskites, from which the local structural information can only be extracted indirectly. Here, we have applied a time-resolved X-ray diffraction technique to investigate the structural dynamics of prototypical two-dimensional lead-free halide perovskite Cs 3 Bi 2 Br 9 nanoparticles across temporal scales from 80 ps to microseconds. We observed a quick recoverable (a few ns) photoinduced microstrain up to 0.15% and a long existing lattice expansion (~a few hundred nanoseconds) at mild laser fluence. Once the laser flux exceeds 1.4 mJ/cm 2 , the microstrain saturates and the crystalline phase partially transfers into a disordered phase. This photoinduced transient structural change can recover within the nanosecond time scale. Furthermore, these results indicate that photoexcitation of charge carriers couples with lattice distortion, which fundamentally affects the dielectric environment and charge carrier transport.

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

Abstract for CRADA between National Energy Technology Laboratory and Shell International Exploration & Production, Inc

Introducing CO₂ into geothermal systems as a working fluid in reservoirs can enhance geothermal conductivity, production, and pressure maintenance. A cross-disciplinary interaction of geothermal reservoir stimulation and CO₂ utilization satisfies renewable energy demands and operations that support sustainable energy infrastructure. Challenges to implementing CO₂-stimulated geothermal enhancement (CS-GE) include (1) accurately characterizing and imaging CO₂-stimulated geothermal reservoirs; (2) quantitatively inferring CS-GE evolution under current and future engineered conditions for cost effective operations; and (3) monitoring resources by improving observational methods to advance the understanding of complex geothermal systems for sweep efficiency and, ultimately, cost effectiveness. NETL and Shell will collaborate under this CRADA to develop software to image key features, including CO₂-stimulated fracture imaging, CO₂ fluid sweep imaging and heat transfer and exchange imaging by leveraging available datasets and applying advanced Artificial Intelligence/Machine Learning (AI/ML), multi-level data analytics and data/information fusion to better understand the comprehensive mechanisms of CO₂-stimulated geothermal systems.

15 GEOTHERMAL ENERGY↗
DOE OSTI2020

Materials Data on CsCa(SeO4)3 by Materials Project

CsCa(SeO4)3 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. Cs is bonded in a 9-coordinate geometry to thirteen O atoms. There are a spread of Cs–O bond distances ranging from 3.12–3.70 Å. Ca is bonded to seven O atoms to form distorted CaO7 pentagonal bipyramids that share corners with seven SeO4 tetrahedra. There are a spread of Ca–O bond distances ranging from 2.37–2.50 Å. There are three inequivalent Se sites. In the first Se site, Se is bonded to four O atoms to form SeO4 tetrahedra that share corners with three equivalent CaO7 pentagonal bipyramids. There are a spread of Se–O bond distances ranging from 1.67–1.69 Å. In the second Se site, Se is bonded to four O atoms to form SeO4 tetrahedra that share a cornercorner with one CaO7 pentagonal bipyramid. There are a spread of Se–O bond distances ranging from 1.65–1.69 Å. In the third Se site, Se is bonded to four O atoms to form SeO4 tetrahedra that share corners with three equivalent CaO7 pentagonal bipyramids. There are a spread of Se–O bond distances ranging from 1.66–1.71 Å. There are nine inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to two equivalent Cs and one Se atom. In the second O site, O is bonded in a bent 150 degrees geometry to one Ca and one Se atom. In the third O site, O is bonded in a distorted bent 120 degrees geometry to one Cs, one Ca, and one Se atom. In the fourth O site, O is bonded in a single-bond geometry to two equivalent Cs and one Se atom. In the fifth O site, O is bonded in a 3-coordinate geometry to one Cs, one Ca, and one Se atom. In the sixth O site, O is bonded in a distorted single-bond geometry to one Cs and one Se atom. In the seventh O site, O is bonded in a single-bond geometry to one Cs and one Se atom. In the eighth O site, O is bonded in a 2-coordinate geometry to one Cs, one Ca, and one Se atom. In the ninth O site, O is bonded in a 2-coordinate geometry to one Cs, one Ca, and one Se atom.

36 MATERIALS SCIENCE↗
NASA NTRS1994

CS multitransitional study of density distribution in star-forming regions. 2: The S140 region

The S140 molecular cloud was observed in five transitions of CS with resolutions of 11 to 45 arcsec. The data were analyzed with both the LVG and microturbulent models of radiative transfer to derive the density structure. It was found that the CS emission comes from three components of gas: a spherical component centered on the infrared cluster, an arc component along the ionization front between the S140 H II region and the dense molecular cloud core, and a high-velocity component from the dense part of a molecular outflow. The spherical component contributes most to the CS emission and was analyzed in more detail than the other components. Using a temperature distribution derived from an analysis of the dust emission from S140, we fit a power-law density distribution of n(r) = n(sub i)(r/r(sub i))(exp -alpha) to the spherical component. The best fit was for n(sub i) = 1.4 x 10(exp 6) (density at r(sub i) = 0.026 pc) and alpha = 0.8. The density (n(sub i)) was found to be greater than or equal to the density required to account for the dust emission, depending on the dust opacity laws adopted. The presence of optical emission (Dinerstein, Lester, & Rank 1979) suggests a clumpy structure for the dense gas. Considerations of the virial mass and the lowest amount of column density required to produce dust emission put the volume filling factor (f(sub nu)) of the dense gas at approximately 0.14-0.5. We compared S140 with other regions of star formation where the density structure has been derived from excitation analysis. Source-source variations in density gradients and clumpiness clearly exist, ranging from alpha = 2 and f(sub nu) approximately 1 in B335 to alpha approximately 0, f(sub nu) approximately 0.1 in M17. There is a tendency for more massive star-forming regions to have a flatter density distribution, a more clumpy structure, and a large number of young stars. The implications of this tendency are discussed.

Zhou, Shudong↗
DOE OSTI2020

Materials Data on Cs2B6NO2 by Materials Project

Cs2B6NO2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Cs sites. In the first Cs site, Cs is bonded in a 2-coordinate geometry to five B and two equivalent O atoms. There are a spread of Cs–B bond distances ranging from 3.48–3.74 Å. There are one shorter (3.15 Å) and one longer (3.27 Å) Cs–O bond lengths. In the second Cs site, Cs is bonded in a 2-coordinate geometry to seven B and two equivalent O atoms. There are a spread of Cs–B bond distances ranging from 3.51–3.66 Å. There are one shorter (3.24 Å) and one longer (3.32 Å) Cs–O bond lengths. There are six inequivalent B sites. In the first B site, B is bonded in a single-bond geometry to four B and one N atom. There are a spread of B–B bond distances ranging from 1.71–1.74 Å. The B–N bond length is 1.52 Å. In the second B site, B is bonded in a 7-coordinate geometry to three Cs and four B atoms. There are a spread of B–B bond distances ranging from 1.69–1.77 Å. In the third B site, B is bonded in a 7-coordinate geometry to three equivalent Cs and four B atoms. There is one shorter (1.70 Å) and one longer (1.73 Å) B–B bond length. In the fourth B site, B is bonded in a 4-coordinate geometry to four B atoms. Both B–B bond lengths are 1.73 Å. In the fifth B site, B is bonded in a 7-coordinate geometry to three equivalent Cs and four B atoms. The B–B bond length is 1.70 Å. In the sixth B site, B is bonded in a 7-coordinate geometry to three Cs and four B atoms. N is bonded in a trigonal planar geometry to one B and two O atoms. Both N–O bond lengths are 1.26 Å. There are two inequivalent O sites. In the first O site, O is bonded in a distorted single-bond geometry to two equivalent Cs and one N atom. In the second O site, O is bonded in a distorted single-bond geometry to two equivalent Cs and one N atom.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Colloidal Synthesis of Single-Layer Quasi-Ruddlesden–Popper Phase Bismuth-Based Two-Dimensional Perovskite Nanosheets with Controllable Optoelectronic Properties

Single- and few-layered two-dimensional (2D) nanomaterials have attracted intense research interest in the last two decades due to their unique electronic and optoelectronic properties leading to various potential applications. Herein, we report the colloidal synthesis of Bi-based 2D perovskite nanosheets (PEG6-NH 3 +) n Cs 3-n Bi 2 X 9 , where X = CI, Br, and I, through careful design of reaction conditions and selection of poly(ethylene glycol) (PEG6) surface passivating ligands. The 2D nanosheets are similar to 5 nm in thickness with micron-sized lateral dimensions and display composition-dependent band gap and work function modulation. Furthermore, small-angle X-ray scattering analysis substantiates that the individual inorganic crystal layer, Cs 3-n Bi 2 X 9 , is separated by the spacer, PEG6 ligand. Additionally, we determined that PEG6-NH 2 is an essential passivating ligand and spacer for the formation of Bi-based 2D nanosheets. Most importantly, controlled crystallization of the colloidal dispersion of nanosheets results in the formation of superlattice microstructures of the quasi-Ruddlesden-Popper phase. These microstructures can be exfoliated to ultrathin nanosheets by overcoming the van der Waals interaction between the organic passivating layers. The controlled synthesis of lead-free 2D perovskite nanosheets presented here can expand their utility to photocatalytic and optoelectronic applications with reduced toxicity.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CsDyN4O15 by Materials Project

CsDyN4O15 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Cs is bonded in a 3-coordinate geometry to ten O atoms. There are a spread of Cs–O bond distances ranging from 3.08–3.66 Å. Dy is bonded in a 9-coordinate geometry to nine O atoms. There are a spread of Dy–O bond distances ranging from 2.34–2.54 Å. There are four inequivalent N sites. In the first N site, N is bonded in a trigonal planar geometry to three O atoms. There are a spread of N–O bond distances ranging from 1.22–1.31 Å. In the second N site, N is bonded in a trigonal planar geometry to three O atoms. There are a spread of N–O bond distances ranging from 1.23–1.30 Å. In the third N site, N is bonded in a trigonal planar geometry to three O atoms. There are a spread of N–O bond distances ranging from 1.24–1.29 Å. In the fourth N site, N is bonded in a trigonal planar geometry to three O atoms. There are a spread of N–O bond distances ranging from 1.23–1.30 Å. There are fifteen inequivalent O sites. In the first O site, O is bonded in a distorted single-bond geometry to one Cs, one Dy, and one N atom. In the second O site, O is bonded in a 2-coordinate geometry to one Cs, one Dy, and one N atom. In the third O site, O is bonded in a single-bond geometry to one Cs and one N atom. In the fourth O site, O is bonded in a 1-coordinate geometry to one Cs, one Dy, and one N atom. In the fifth O site, O is bonded in a distorted L-shaped geometry to one Dy and one N atom. In the sixth O site, O is bonded in a distorted single-bond geometry to one Cs and one N atom. In the seventh O site, O is bonded in a water-like geometry to one Dy and one N atom. In the eighth O site, O is bonded in a distorted L-shaped geometry to one Dy and one N atom. In the ninth O site, O is bonded in a distorted single-bond geometry to one Cs and one N atom. In the tenth O site, O is bonded in a distorted single-bond geometry to one Cs, one Dy, and one N atom. In the eleventh O site, O is bonded in a single-bond geometry to two equivalent Cs and one N atom. In the twelfth O site, O is bonded in a 2-coordinate geometry to one Cs, one Dy, and one N atom. In the thirteenth O site, O is bonded in a bent 120 degrees geometry to two O atoms. There is one shorter (1.26 Å) and one longer (1.33 Å) O–O bond length. In the fourteenth O site, O is bonded in a water-like geometry to one Dy and one O atom. In the fifteenth O site, O is bonded in a single-bond geometry to one O atom.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Vibrational signatures of HNO 3 acidity when complexed with microhydrated alkali metal ions, M + ∙(HNO 3 )(H 2 O) n =5 (M = Li, K, Na, Rb, Cs), at 20 K

The speciation of strong acids like HNO 3 under conditions of restricted hydration is an important factor in the rates of chemical reactions at the air-water interface. Here we explore the trade-offs in play when HNO 3 is attached to alkali ions (Li + -Cs + ) with four water molecules in their primary hydration shells. This is achieved by analyzing the vibrational spectra of the M + ∙(HNO 3 )(H 2 O) 5 clusters cooled to about 20 K in a cryogenic photofragmentation mass spectrometer. The local acidity of the acidic OH group is estimated by the extent of the red shift in its stretching frequency when attached to a single water molecule. Here, the persistence of this local structural motif (HNO 3 -H 2 O) in all of these alkali metal clusters enables us to determine the competition between the effect of the direct complexation of the acid with the cation, which acts to enhance acidity, and the role of the water network in the first hydration shell around the ions, which acts to counter (screen) the intrinsic effect of the ion. Analysis of the vibrational features associated with the acid molecule as well as those of the water network reveal how cooperative interactions in the micro hydration regime conspire to effectively offset the intrinsic enhancement of HNO 3 acidity afforded by attachment to the smaller cations.

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

Materials Data on CsB9O13 by Materials Project

CsB9O13 crystallizes in the tetragonal P4_122 space group. The structure is three-dimensional. Cs is bonded in a 2-coordinate geometry to two equivalent O atoms. Both Cs–O bond lengths are 2.97 Å. There are five inequivalent B sites. In the first B site, B is bonded in a trigonal planar geometry to three O atoms. There are a spread of B–O bond distances ranging from 1.36–1.38 Å. In the second B site, B is bonded in a trigonal planar geometry to three O atoms. There is one shorter (1.34 Å) and two longer (1.40 Å) B–O bond length. In the third B site, B is bonded in a trigonal planar geometry to three O atoms. There is one shorter (1.32 Å) and two longer (1.41 Å) B–O bond length. In the fourth B site, B is bonded in a tetrahedral geometry to four O atoms. There is two shorter (1.46 Å) and two longer (1.48 Å) B–O bond length. In the fifth B site, B is bonded in a bent 120 degrees geometry to two O atoms. There is one shorter (1.33 Å) and one longer (1.43 Å) B–O bond length. There are seven inequivalent O sites. In the first O site, O is bonded in a distorted bent 120 degrees geometry to one Cs and two B atoms. In the second O site, O is bonded in a bent 120 degrees geometry to two equivalent B atoms. In the third O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the fourth O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the fifth O site, O is bonded in a distorted bent 150 degrees geometry to two B atoms. In the sixth O site, O is bonded in a bent 150 degrees geometry to two B atoms. In the seventh O site, O is bonded in a distorted bent 150 degrees geometry to two B atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CsMg6Zn by Materials Project

CsMg6Zn crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. Cs is bonded in a 2-coordinate geometry to eight Mg and two equivalent Zn atoms. There are a spread of Cs–Mg bond distances ranging from 4.25–4.39 Å. Both Cs–Zn bond lengths are 4.00 Å. There are four inequivalent Mg sites. In the first Mg site, Mg is bonded in a distorted single-bond geometry to one Cs, six Mg, and one Zn atom. There are a spread of Mg–Mg bond distances ranging from 3.10–3.29 Å. The Mg–Zn bond length is 2.81 Å. In the second Mg site, Mg is bonded in a 2-coordinate geometry to two equivalent Cs, six Mg, and two equivalent Zn atoms. There are a spread of Mg–Mg bond distances ranging from 2.90–3.31 Å. Both Mg–Zn bond lengths are 3.01 Å. In the third Mg site, Mg is bonded in a 8-coordinate geometry to eight Mg atoms. Both Mg–Mg bond lengths are 2.98 Å. In the fourth Mg site, Mg is bonded in a 10-coordinate geometry to two equivalent Cs and eight Mg atoms. Zn is bonded in a 8-coordinate geometry to two equivalent Cs and six Mg atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1990

CS in nearby galaxies: Distribution, kinematics, and multilevel studies

As a result of observations at the Institute for Radio Astronomy in the Millimeter Range (IRAM) 30-m telescope, maps of the distribution of the J = 2-1 transition of CS toward the galaxies IC 342 and NGC 253 are presented. The distribution of the CS emission from NGC 253 is consistent with the CO 1-0 line. The distribution of the CS emission from IC 342, however, resembles more that seen in the CO 3-2 line. For the first time, the detection of the isotopic substitution C-34S is reported toward an external galaxy: The C-34S 2-1 line has been detected toward NGC 253 and M 82 and the C-34S line has been detected tentatively toward M 82. Also for the first time, extragalactic CS has been observed in the 3-2 (toward NGC 253, IC 342 and M 82) and 5-4 (NGC 253 and IC 342) transitions.

Mauersberger, R.↗
DOE OSTI2024

The NanoSIMS-HR: The Next Generation of High Spatial Resolution Dynamic SIMS

The high lateral resolution and sensitivity of the NanoSIMS 50 and 50L series of dynamic SIMS instruments have enabled numerous scientific advances over the past 25 years. Here, in this study, we report on the NanoSIMS-HR, the first major upgrade to the series, and analytical tests in a suite of sample types, including an aluminum sample containing silicon crystals, microalgae, and plant roots colonized with a symbiotic fungus. Significant improvements have been made in the Cs + ion source, high voltage (HV) control, stage reproducibility, and other aspects of the instrument that affect performance. The modified design of the NanoSIMS-HR thermal-ionization Cs + source enables a 5 pA primary ion beam to be focused into a 100 nm spot, a ~2.5-fold increase compared to Cs + sources on previous instruments (~2 pA at 100 nm). The brightness of the new Cs + source enables an ultimate lateral resolution as high as 30 nm and improved detection limits for a given analysis area. Sample stage movement accuracy is higher than 500 nm, enabling many-fold higher throughput automated analyses. With the new HV control, the primary ion beam impact energy can be reduced from 16 to 2 keV, which enables higher depth resolution during depth profiling (a 2-fold improvement), albeit with a 5-fold decrease in lateral resolution. In the NanoSIMS-HR, the secondary ion column and detection system are identical to those used in the previous series, and the isotopic analysis performance is as precise as in previous NanoSIMS instruments.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Materials Data on CsZn3(PO4)3 by Materials Project

CsZn3(PO4)3 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. Cs is bonded in a 1-coordinate geometry to seven O atoms. There are a spread of Cs–O bond distances ranging from 3.07–3.49 Å. There are three inequivalent Zn sites. In the first Zn site, Zn is bonded to four O atoms to form ZnO4 tetrahedra that share corners with two equivalent ZnO4 tetrahedra and corners with four PO4 tetrahedra. There are a spread of Zn–O bond distances ranging from 1.91–2.02 Å. In the second Zn site, Zn is bonded to four O atoms to form ZnO4 tetrahedra that share corners with four PO4 tetrahedra. There are a spread of Zn–O bond distances ranging from 1.93–1.99 Å. In the third Zn site, Zn is bonded to four O atoms to form ZnO4 tetrahedra that share corners with two equivalent ZnO4 tetrahedra and corners with four PO4 tetrahedra. There are a spread of Zn–O bond distances ranging from 1.93–2.04 Å. There are three inequivalent P sites. In the first P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with five ZnO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.54–1.60 Å. In the second P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with four ZnO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.53–1.59 Å. In the third P site, P is bonded to four O atoms to form PO4 tetrahedra that share corners with three equivalent ZnO4 tetrahedra. There is one shorter (1.54 Å) and three longer (1.55 Å) P–O bond length. There are twelve inequivalent O sites. In the first O site, O is bonded in a distorted bent 120 degrees geometry to one Cs, one Zn, and one P atom. In the second O site, O is bonded in a distorted single-bond geometry to one Cs and one P atom. In the third O site, O is bonded in a single-bond geometry to one P atom. In the fourth O site, O is bonded in a distorted bent 120 degrees geometry to one Cs, one Zn, and one P atom. In the fifth O site, O is bonded in a trigonal planar geometry to two Zn and one P atom. In the sixth O site, O is bonded in a trigonal planar geometry to two Zn and one P atom. In the seventh O site, O is bonded in a 2-coordinate geometry to one Cs, one Zn, and one P atom. In the eighth O site, O is bonded in a bent 120 degrees geometry to one Zn and one P atom. In the ninth O site, O is bonded in a distorted bent 150 degrees geometry to one Zn and one P atom. In the tenth O site, O is bonded in a 2-coordinate geometry to one Cs, one Zn, and one P atom. In the eleventh O site, O is bonded in a 2-coordinate geometry to one Cs, one Zn, and one P atom. In the twelfth O site, O is bonded in a distorted bent 150 degrees geometry to one Cs, one Zn, and one P atom.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Harvesting electrons and holes from photodriven symmetry-breaking charge separation within a perylenediimide photosynthetic model dimer

Understanding how to utilize symmetry-breaking charge separation (SB-CS) offers a path toward increasingly efficient light-harvesting technologies. This process plays a central role in the first step of photosynthesis, in which the dimeric “special pair” of the photosynthetic reaction center enters a coherent SB-CS state after photoexcitation. Previous research on SB-CS in both biological and synthetic chromophore dimers has focused on increasing the efficiency of light-driven processes. In a chromophore dimer undergoing SB-CS, the energy of the radical ion pair product is nearly isoenergetic with that of the lowest excited singlet (S 1 ) state of the dimer. This means that very little energy is lost from the absorbed photon. In principle, the relatively high energy electron and hole generated by SB-CS within the chromophore dimer can each be transferred to adjacent charge acceptors to extend the lifetime of the electron–hole pair, which can increase the efficiency of solar energy conversion. To investigate this possibility, we have designed a bis-perylenediimide cyclophane (mPDI 2 ) covalently linked to a secondary electron donor, peri-xanthenoxanthene (PXX) and a secondary electron acceptor, partially fluorinated naphthalenediimide (FNDI). Upon selective photoexcitation of mPDI 2 , transient absorption spectroscopy shows that mPDI 2 undergoes SB-CS, followed by two secondary charge transfer reactions to generate a PXX •+ -mPDI 2 -FNDI •– radical ion pair having a nearly 3 µs lifetime. In conclusion, this strategy has the potential to increase the efficiency of molecular systems for artificial photosynthesis and photovoltaics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗