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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 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Malignant transformation of colonic epithelial cells by a colon-derived long noncoding RNA

Highlights: •Non-coding RNAs are found in the colonic crypt progenitor compartment. •Colonocytes transformed by ncNRFR are highly invasive and metastatic. •ncNRFR has a region similar to the miRNA, let-7 family. •ncNRFR expression alters let-7 activity as measured by reporter construct. •ncNRFR expression upregulates let-7b targets. -- Abstract: Recent progress has been made in the identification of protein-coding genes and miRNAs that are expressed in and alter the behavior of colonic epithelia. However, the role of long non-coding RNAs (lncRNAs) in colonic homeostasis is just beginning to be explored. By gene expression profiling of post-mitotic, differentiated tops and proliferative, progenitor-compartment bottoms of microdissected adult mouse colonic crypts, we identified several lncRNAs more highly expressed in crypt bottoms. One identified lncRNA, designated non-coding Nras functional RNA (ncNRFR), resides within the Nras locus but appears to be independent of the Nras coding transcript. Stable overexpression of ncNRFR in non-transformed, conditionally immortalized mouse colonocytes results in malignant transformation, as determined by growth in soft agar and formation of highly invasive tumors in nude mice. Moreover, ncNRFR appears to inhibit the function of the tumor suppressor let-7. These results suggest precise regulation of ncNRFR is necessary for proper cell growth in the colonic crypt, and its misregulation results in neoplastic transformation.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Long-term low-dose α-particle enhanced the potential of malignant transformation in human bronchial epithelial cells through MAPK/Akt pathway

Highlights: • Multi-exposures of 25 mGy α-ray enhanced cell proliferation, adhesion, and invasion. • MAPK/Akt but not JNK/P66 was positively correlated with cell invasive phenotypes. • LDR of α-irradiation triggers cell malignant transformation through MAPK/Akt. - Abstract: Since the wide usage of ionizing radiation, the cancer risk of low dose radiation (LDR) (<0.1 Gy) has become attractive for a long time. However, most results are derived from epidemiologic studies on atomic-bomb survivors and nuclear accidents surrounding population, and the molecular mechanism of this risk is elusive. To explore the potential of a long-term LDR-induced malignant transformation, human bronchial epithelial cells Beas-2B were fractionally irradiated with 0.025 Gy α-particles for 8 times in total and then further cultured for 1–2 months. It was found that the cell proliferation, the abilities of adhesion and invasion, and the protein expressions of p-ERK, p-Akt, especially p-P38 were not only increased in the multiply-irradiated cells but also in their offspring 1–2 months after the final exposure, indicating high potentiality of cell malignant transformation. On opposite, the expressions of p-JNK and p-P66 were diminished in the subcultures of irradiated cells and thus may play a role of negative regulation in canceration. When the cells were transferred with p38 siRNA, the LDR-induced enhancements of cell adhesion and invasion were significantly reduced. These findings suggest that long-term LDR of α-particles could enhance the potential of malignant transformation incidence in human bronchial epithelial cells through MAPK/Akt pathway.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Phase transformations at interfaces: Observations from atomistic modeling

Here, we review the recent progress in theoretical understanding and atomistic computer simulations of phase transformations in materials interfaces, focusing on grain boundaries (GBs) in metallic systems. Recently developed simulation approaches enable the search and structural characterization of GB phases in single-component metals and binary alloys, calculation of thermodynamic properties of individual GB phases, and modeling of the effect of the GB phase transformations on GB kinetics. Atomistic simulations demonstrate that the GB transformations can be induced by varying the temperature, loading the GB with point defects, or varying the amount of solute segregation. The atomic-level understanding obtained from such simulations can provide input for further development of thermodynamics theories and continuous models of interface phase transformations while simultaneously serving as a testing ground for validation of theories and models. They can also help interpret and guide experimental work in this field.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Mineralogical transformations in polymetallic nodules and the change of Ni, Cu and Co crystal-chemistry upon burial in sediments

Polymetallic nodules from the Clarion and Clipperton Zone of the equatorial Pacific Ocean were studied using X-ray diffraction, X-ray absorption, Fourier-transformed infrared spectroscopy and transmission electron microscopy. Here, this study includes nodules found at the sediment surface as well as subsurface (14–16 cm sediment depth) and deeply buried (530–985 cm sediment depth) nodules. The surface and subsurface nodules are currently under oxic conditions whereas the deeply buried nodules are under suboxic conditions. Surface nodules consist mainly of turbostratic phyllomanganates (7 Å and 10 Å vernadite and Fe-vernadite); todorokite is a minor phase, if present at all. In contrast, subsurface and especially deeply buried nodules predominantly consist of todorokite, which increases in abundance with depth in the sediment. Thus, upon burial of nodules within the shallow sediment, phyllomanganates transform to todorokite, probably through the combined action of time and change in the ambient chemical conditions. Nodules from deeper sediment depth (>500 cm) consist primarily of todorokite and additionally show signs of dissolution. The transformation of phyllomanganates to todorokite and their further dissolution upon nodule burial under suboxic conditions induces modifications in the crystal-chemistry of Ni, Co, and Cu. In surface nodules, Ni and Co are incorporated in the octahedral sheets of phyllomanganates, whereas Cu mainly is located at the edges of those phyllomanganate sheets. In buried nodules Cu and to a lesser extent Ni are incorporated in todorokite by forming outer-sphere complexes within the tunnels. However, Ni is predominantly incorporated within the octahedra of the newly formed todorokite structure. Co is also enriched in the octahedra of todorokite as a result of dissolution of hydrogenetic vernadite and re-incorporation in the more stable Mn-phase formed during the diagenetic transformation. Co enrichment under suboxic conditions after burial within the sediments is noteworthy since Co in surface nodules is characteristic for oxic conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Phase transformations and selective growth in YMnO{sub 3} films

An irreversible phase transformation from amorphous to crystalline orthorhombic YMnO{sub 3} (o-YMO) phase takes place in Y–Mn–O films deposited by pulsed-injection metal organic chemical vapor deposition (MOCVD) on Si(100) substrate. This phase transformation was studied through ex-situ and in-situ thermal annealings and the corresponding structural changes were analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. It was shown that it takes place at an almost constant temperature (∼700 °C) and in a short period of time (∼min) and that the o-YMO phase thus obtained is stable at least up to 900 °C. We also demonstrate that the selective growth of amorphous, orthorhombic or hexagonal films is made possible by adapting the MOCVD temperature according to the temperature stability region of the different phases. - Graphical abstract: Temperature-dependent Raman spectra of an amorphous as-deposited Y–Mn–O film in the temperature range RT – 900 °C. The red spectrum marks the crystallization of the amorphous phase into the o-YMnO{sub 3} phase. - Highlights: • Phase transformations and selective growth in YMnO{sub 3}/Si(100) MOCVD films are studied. • Transformation from amorphous to crystalline orthorhombic YMnO{sub 3} occurs. • It takes place at an almost constant temperature (∼700 °C). • The orthorhombic YMnO{sub 3} phase thus obtained is stable at least up to 900 °C. • A selective growth is made possible by adapting the MOCVD temperature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Structural transformation and photoluminescence behavior during calcination of the layered europium-doped yttrium hydroxide intercalate with organic-sensitizer

Graphical abstract: Calcination of organic sensitizer intercalated layered europium-doped yttrium hydroxide displayed tunable luminescent performance dependent on calcined temperatures. The 200 °C-calcined sample revealed an optimal fluorescence behavior with respect to TA-LYH:Eu composite and the as-transformed oxide. - Highlights: • We report the calcinations process of organic/LYH:Eu nanocomposite materials. • We study structural transformation and fluorescence behavior of the calcined samples. • Calcined samples displayed tunable luminescent performance dependent on temperatures. • The optimal fluorescence was found in 200 °C-calcined sample. • This material can provide valuable guide for developing tunable luminescent materials. - Abstract: We report, for the first time, structural transformation and photoluminescence behavior by calcination of layered europium-doped yttrium hydroxide (LYH:Eu) intercalate with organic sensitizer terephthalate (TA). The calcined samples displayed tunable luminescent performance dependent on calcined temperatures. Calcination under low temperatures (200 and 300 °C) retained layered structure, while high temperatures (>400 °C) yielded oxide phase. The optimal fluorescence occurred in 200 °C-calcination, possibly resulting from an optimal arrangement of TA. Above 200 °C, the luminescence intensity was first weakened and then enhanced, due to gradual departure of TA and following occurrence of oxide phase. The energy transfer presented an intrinsic transition from TA-to-Eu{sup 3+} in the organic intercalate to O{sup 2−}-to-Eu{sup 3+} charge transfer in as-transformed oxide. The predominant luminescence property of the hybrid material can provide valuable guide for developing tunable luminescent materials, especially flexible materials resulting from the containing organic component.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Kinetics of the transformation of n-propyl gallate and structural analogs in the perfused rat liver

n-Propyl gallate and its analogs are used in foods and other products to prevent oxidation. In the liver the compound exerts several harmful effects, especially gluconeogenesis inhibition. The mode of transport and distribution of n-propyl gallate and its kinetics of biotransformation have not yet been investigated. To fill this gap the transformation, transport and distribution of n-propyl gallate and two analogs were investigated in the rat liver. Isolated perfused rat liver was used. n-Propyl gallate, methyl gallate, n-octyl gallate and transformation products were quantified by high pressure-liquid chromatography coupled to fluorescence detection. The interactions of n-propyl gallate and analogs with the liver presented three main characteristics: (1) the hydrolytic release of gallic acid from n-propyl gallate and methyl gallate was very fast compared with the subsequent transformations of the gallic acid moiety; (2) transport of the esters was very fast and flow-limited in contrast to the slow and barrier-limited transport of gallic acid; (3) the apparent distribution volume of n-propyl gallate, but probably also of methyl gallate and n-octyl gallate, greatly exceeded the water space in the liver, contrary to the gallic acid space which is smaller than the water space. It can be concluded that at low portal concentrations (< 50 μM) the gallic acid esters are 100% extracted during a single passage through the liver, releasing mainly gallic acid into the systemic circulation. For the latter a considerable time is required until complete biotransformation. The exposure of the liver to the esters, however, is quite prolonged due to extensive intracellular binding. - Highlights: • The liver binds very strongly n-propyl gallate and releases basically gallic acid. • n-propyl gallate and analogs undergo concentrative flow-limited distribution. • Gallic acid undergoes barrier-limited distribution and is slowly transformed. • The long residence time of n-propyl gallate and analogs increases toxicity.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Nickel-induced HIF-1α promotes growth arrest and senescence in normal human cells but lacks toxic effects in transformed cells

Nickel is a human carcinogen that acts as a hypoxia mimic by activating the transcription factor HIF-1α and hypoxia-like transcriptomic responses. Hypoxia and elevated HIF-1α are typically associated with drug resistance in cancer cells, which is caused by increased drug efflux and other mechanisms. Here we examined the role of HIF-1α in uptake of soluble Ni(II) and Ni(II)-induced cell fate outcomes using si/shRNA knockdowns and gene deletion models. We found that HIF-1α had no effect on accumulation of Ni(II) in two transformed (H460, A549) and two normal human cell lines (IMR90, WI38). The loss of HIF-1α also produced no significant impact on p53-dependent and p53-independent apoptotic responses or clonogenic survival of Ni(II)-treated transformed cells. In normal human cells, HIF-1α enhanced the ability of Ni(II) to inhibit cell proliferation and cause a permanent growth arrest (senescence). Consistent with its growth-suppressive effects, HIF-1α was important for upregulation of the cell cycle inhibitors p21 (CDKN1A) and p27 (CDKN1B). Irrespective of HIF-1α status, Ni(II) strongly increased levels of MYC protein but did not change protein expression of the cell cycle-promoting phosphatase CDC25A or the CDK inhibitor p16. Our findings indicate that HIF-1α limits propagation of Ni(II)-damaged normal cells, suggesting that it may act in a tumor suppressor-like manner during early stages of Ni(II) carcinogenesis. - Highlights: • HIF-1α enhances growth arrest and senescence by Ni(II) in normal human cells. • HIF-1α is important for upregulation of the cell cycle inhibitors p21 and p27 in Ni(II)-treated normal cells. • Apoptotic responses and clonogenic toxicity by Ni(II) in transformed human cells are HIF-1α independent. • HIF-1α does not affect Ni(II) accumulation in normal or transformed human cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Defect-Driven Oxide Transformations and the Electrochemical Interphase

The redox reaction pathway is crucial to the sustainable production of the fuels and chemicals required for a carbon-neutral society. Our society is becoming increasingly dependent on devices using batteries and electrolyzers, all of which rely on a series of redox reactions. The overall properties of oxide materials make them very well suited for such electrochemical and catalytic applications due to their associated cationic redox properties and the static site-adsorbate interactions. As these technologies have matured, it has become apparent that defect-driven redox reactions, defect-coupled diffusion, and structural transformations that are both time- and rate-dependent are also critical materials processes. This change in focus, considering not only redox properties but also more complex, dynamic behaviors, represents a new research frontier in the molecular sciences as they are strongly linked to device operation and degradation and lie at the heart of various phenomena that take place at electrochemical interfaces. Fundamental studies of the structural, electronic, and chemical transformation mechanisms are key to the advancement of materials and technological innovations that could be implemented in various electrochemical systems. In this Account, we focus on recent studies and advances in characterizing and understanding the dynamic redox evolution and structural transformations that take place in model perovskites and layered oxides under reactive conditions and correlate them with degradation mechanisms and operations in electrolyzers and batteries. We show that the dynamic evolution of oxygen vacancies and cationic migration in the surface or bulk occurs at the solid-liquid interface, using a combination of different synchrotron-based Xray spectroscopies and scattering probes. Detailed redox-structure-reactivity correlation studies show how defects and diffusion processes can be tailored to drive various physical and chemical transformations in electrolyzers and batteries. We also highlight a strong correlation between oxygen redox reactivity and structural reorganization in both model thin films and particles, helping to bridge the gap between fundamental studies of the reaction mechanism and device applications. Finally, on the basis of these findings, we discuss strategies to probe and tune the redox reactivity and structural stability of the redox-active oxide interphase toward devising efficient pathways for energy and chemical harvesting.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Phase Transformation Mechanism of Amorphous Calcium Phosphate to Hydroxyapatite Investigated by Liquid-Cell Transmission Electron Microscopy

Crystallization via phase transformation of a metastable precursor is a ubiquitous and effective strategy used by living systems to direct the growth of crystalline nanomaterials with remarkable functional properties. However, determining the exact process by which transformation occurs at the nanoscale is a difficult challenge. In this work, the recrystallization process of amorphous calcium phosphate (ACP) to hydroxyapatite (HAP) is explored by liquid-cell transmission electron microscopy. The effect of confinement in the liquid-cell is found to increase the size of ACP nanoparticles. In the presence of Mg 2+ , these large ACP nanoparticles transform to HAP by first dissolving from the interior to create a hollow structure, after which HAP forms preferentially on the surface and then subsequently in the bulk solution. We propose that the preferential dissolution within ACP particles is due to a change in the structure and/or chemistry of the ACP surface, likely associated with dehydration before crystallization of HAP. These results imply an important role of the confined environment of the liquid-cell in regulating the size of ACP particles, which then affects the surface structure and the detailed dissolution–recrystallization pathway. Moreover, we stress the key role of Mg 2+ in controlling HAP formation by stabilizing ACP via reduction in ACP solubility. This work provides a better understanding of the roles of additives and confinement during the phase transformation of ACP to HAP through dissolution and recrystallization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Transformation of Gibbsite to Boehmite in Caustic Aqueous Solution at Hydrothermal Conditions

Phase transformations among aluminum (oxyhydr)oxide minerals play important roles across a wide range of natural and industrial settings. In highly caustic aqueous solutions, uncertainty persists regarding whether solid-state or dissolution-reprecipitation pathways dominate. We explored transformation of gibbsite [a Al(OH)3] to boehmite (? AlOOH) in caustic NaOH solution at hydrothermal conditions as a function of temperature, Al(III) and NaOH concentrations, and reaction time. Comparison of detailed structural and morphological solids characterization by XRD, SEM/TEM, AFM, Raman spectroscopy, and high field 27Al MAS NMR to predictions from equilibrium thermodynamics calculations suggests the critical importance of dissolution-reprecipitation across our range of system conditions. The yield and physical properties of the boehmite product was found to be sensitive to the hydrothermal treatment temperature and the Al/OH- ratio, controlled by the loading of gibbsite with respect to NaOH. Experiments at lower Al/OH- ratios (e.g., 0.64) indicate that the dissolution of the gibbsite reaches an aqueous aluminate saturation state sufficient to overcome the nucleation barrier for boehmite. Higher Al/OH- ratios (e.g., 3.2) are found to slow the phase transformation, leaving residual unreacted gibbsite in the final product. Higher temperatures appear to improve the phase transformation rate, but also typically yield smaller sized boehmite particles. Particle morphological analyses compared to thermodynamic expectations suggest an important role of kinetics at mineral/solution interfaces, both in the gibbsite dissolution rate as well as the growth rate of boehmite nanocrystals.

Zhang, Xin↗
DOE OSTI2020

Structural Transformation and Chemical Stability of a Shock-Compressed Insensitive High Explosive Single Crystal: Time-Resolved Raman Spectroscopy

Despite the considerable interest in insensitive high explosives (IHE) as a safer alternative to conventional high explosives, a good understanding of the low sensitivity of IHEs to shock initiation is lacking. In particular, real-time measurements to directly probe the molecular-level response of shock compressed IHE single crystals constitute an important need. To address this need, plate impact experiments were conducted to determine time-resolved changes in the Raman spectra of 1,1-diamino-2,2-dinitroethene (FOX-7) single crystals – a representative IHE crystal – shock compressed up to 20 GPa longitudinal stress. The Raman measurements examined vibrational frequencies from 800 cm-1 to 1500 cm-1 with 15 nanosecond time resolution and were conducted at several peak stresses. At 4 – 6 GPa, two new Raman peaks appeared, in addition to the original peaks, consistent with onset of the α' – ε structural transformation reported previously in static compression work. The measured spectra indicated completion of the transformation at 10 GPa. Raman data to 20 GPa showed neither additional transformations nor any indication of chemical decomposition. This finding, though consistent with recent continuum measurements, is in marked contrast to the chemical decomposition observed at lower stresses in shock compressed conventional high explosive single crystals. Our Raman results support the previous suggestion that strengthening of intra- and inter-molecular bonds, due to the α' – ε structural transformation, plays a significant role in the insensitivity of FOX-7 single crystals to shock initiation. In conclusion, the present work, in conjunction with previous static compression studies, provides the first experimental insight into the molecular-level response of a shock compressed IHE single crystal and can serve as a bench mark for theoretical studies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Transformation of an Embedded Five-Membered Ring in Polycyclic Aromatic Hydrocarbons via the Hydrogen-Abstraction–Acetylene-Addition Mechanism: A Theoretical Study

Five-membered rings are constituents of many polycyclic aromatic hydrocarbons (PAHs) and their presence on the edges of large PAHs has been repeatedly observed experimentally. However, modern kinetic combustion models often do not consider the growth of PAHs through the transformation of the five-membered rings. Here, in connection with the above, we carried out a theoretical study of the mechanism of Hydrogen-Abstraction-aCetylene-Addition (HACA) transformation of an embedded five-membered ring on the armchair PAH edge to a six-membered ring, considering cyclopenta[d,e,f]phenanthrene (4,5-methylenephenanthrene) as a prototype system for this process. The potential energy surface for the reactions of cyclopenta[d,e,f]phenanthrenyl radicals produced by direct H abstractions from cyclopenta[d,e,f]phenanthrene with acetylene has been compiled at the G3(MP2,CC)//B3LYP/6-311G(d,p) level of theory including zero-point vibrational energy corrections. The computed energies and molecular parameters were then used to solve the Rice-Ramsperger-Kassel-Marcus Master Equation (RRKM-ME) in order to calculate reaction rate at various pressures and temperatures, which were fitted to modified Arrhenius equation for further kinetic modeling. The results show that the HACA transformation of the embedded five-membered ring to a six-membered ring is possible, albeit slow. The most viable reaction mechanism involves the R2 + C 2 H 2 reaction, where the acetylene molecules adds to a σ-radical in the six-membered ring adjacent to the five-membered ring via a low entrance barrier. The predominant product of R2 + C 2 H 2 is predicted to be 3 ethynyl 4H cyclopenta[def]phenanthrene Pr5 via immediate H elimination from the initial addition complex. Next, Pr5 undergoes H-assisted isomerization to 4aH-pentaleno[4,3,2,1-cdef]phenanthrene Pr4, and the latter adds an H atom eventually forming the 1-pyrenylmethyl radical Pr3: R2 + C 2 H 2 ⇌ 3 ethynyl 4H cyclopenta[def]phenanthrene (Pr5) + H ⇌ 4aH-pentaleno[4,3,2,1-cdef]phenanthrene (Pr4) + H Pr5 + H ⇌ Pr4 + H Pr4 + H → 1-pyrenylmethyl (Pr3) This HACA sequence may be competitive with the methyl radical addition to the R1 radical formed by H abstraction from the CH 2 group in the five-membered ring of cyclopenta[d,e,f]phenanthrene, which provides a pathway to pyrene following two H atom losses. Relative contributions of the two mechanisms of the five- to six-membered ring transformation would strongly depend on the branching ratios of the R1 and R2 radicals produced by the H abstractions and the available concentration of C 2 H 2 vs. CH 3 and hence differ in different flames.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Atomic Insight into the Layered/Spinel Phase Transformation in Charged LiNi 0.80 Co 0.15 Al 0.05 O 2 Cathode Particles

Layered LiNi 0.80 Co 0.15 Al 0.05 O 2 (NCA) holds great promise as a potential cathode material for high energy density lithium ion batteries. However, its high capacity is heavily dependent on the stability of its layered structure, which suffers from a severe structure degradation resulting from a not fully understood layered → spinel phase transformation. Using high-resolution transmission electron microscopy and electron diffraction, we probe the atomic structure evolution induced by the layered → spinel phase transformation in the NCA cathode. We show that the phase transformation results in the development of a particle structure with the formation of complete spinel, spinel domains, and intermediate spinel from the surface to the subsurface region. The lattice planes of the complete and intermediate spinel phases are highly interwoven in the subsurface region. The layered → spinel transformation occurs via the migration of transition metal (TM) atoms from the TM layer into the lithium layer. Incomplete migration leads to the formation of the intermediate spinel phase, which is featured by tetrahedral occupancy of TM cations in the lithium layer. Finally, the crystallographic structure of the intermediate spinel is discussed and verified by the simulation of electron diffraction patterns.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Crystal Morphology and Phase Transformation of LiAlO 2 : Combined Experimental and First-Principles Studies

Layered α-LiAlO 2 matrix often suffers from detrimental structural and morphological changes during its lifetime, especially under H 2 containing fuel inlet environments of molten carbonate fuel cell systems. However, the underlying mechanism of this phase and morphological transformations has rarely been explored. In this study, transmission electron microscopy (TEM) techniques were used to determine the changes in structure and morphology of LiAlO 2 samples lifted by a focused ion beam (FIB). In accordance with X-ray diffraction (XRD) analysis, TEM images show that under H-rich conditions the rhombohedral α-LiAlO 2 transforms to tetragonal γ-LiAlO 2 phase with the appearance of the (101) terminated octahedral shaped γ-LiAlO 2 crystallites. We further support, and plausibly rationalize, the observed transformations using density functional theory (DFT) calculation. The DFT computed surface energies of γ-LiAlO 2 reveal that the {101} surface becomes the lowest energy surface upon H-adsorption, thus leading to formation of observed octahedral geometry. Contrary to stabilization of γ-LiAlO 2 surfaces upon H passivation, DFT revealed H-adsorption on α-LiAlO 2 surfaces to be energetically unfavorable. Furthermore, this contrasting behavior of α-LiAlO 2 and γ-LiAlO 2 under H-rich environments could be a potential driving force for the observed α-LiAlO 2 to γ-LiAlO 2 phase transformation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Combinatorial Exploration and Mapping of Phase Transformation in a Ni–Ti–Co Thin Film Library

Combinatorial synthesis and high-throughput characterization of a Ni–Ti–Co thin film materials library are reported for exploration of reversible martensitic transformation. The library was prepared by magnetron co-sputtering, annealed in vacuum at 500 °C without atmospheric exposure, and evaluated for shape memory behavior as an indicator of transformation. Composition, structure, and transformation behavior of the 177 pads in the library were characterized using high-throughput wavelength dispersive spectroscopy (WDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and four-point probe temperature-dependent resistance (R(T)) measurements. A new, expanded composition space having phase transformation with low thermal hysteresis and Co > 10 at. % is found. Unsupervised machine learning methods of hierarchical clustering were employed to streamline data processing of the large XRD and XPS data sets. Through cluster analysis of XRD data, we identified and mapped the constituent structural phases. Finally, composition–structure–property maps for the ternary system are made to correlate the functional properties to the local microstructure and composition of the Ni–Ti–Co thin film library.

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

Reversible Phase Transformation of Colloidal 2D Lead Halide Perovskite Platelets under Photoirradiation

The photostability of lead halide perovskites is an important criterion for their utilization in light harvesting applications. Colloidal two-dimensional mixed halide perovskites offer a convenient approach to probe photoinduced transformations using spectroscopy tools. We employed suspensions of colloidal 2D methylammonium lead halide perovskite platelets with butylammonium and octylammonium as organic spacer cations. Upon irradiation of the mixed halide perovskite (BAOAMAPb 2 (Br 3.5 I 3.5 )) colloidal platelet suspension, we observe a phase transformation, as seen from the formation of bromide rich domains (BAOAMAPb 2 Br 7 ) and an iodide complex (PbI 3 – ). Unlike in the case of 3D mixed halide films, we did not observe the formation of iodide rich domains as part of the photoinduced phase segregation process. Instead, we observed the dissociation of the BAOAMAPb 2 I 7 to form an iodide complex, PbI 3 – . Interestingly, this photoinduced phase transformation was reversible, as the products which were confined in the colloidal core restored the original mixed halide phase upon storage in dark. The spectroscopic measurements that characterize excited states of different colloidal methylammonium lead halide perovskites and kinetics of photoinduced transformation and their dark recovery are presented. Furthermore, these new phototransformations of colloidal perovskite platelets provide new insights into the processes that dictate their overall photostability.

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

Real-Time Diagnostics of 2D Crystal Transformations by Pulsed Laser Deposition: Controlled Synthesis of Janus WSSe Monolayers and Alloys

Energetic processing methods such as hyperthermal implantation hold special promise to achieve the precision synthesis of metastable two-dimensional (2D) materials such as Janus monolayers; however, they require precise control. Here, we report a feedback approach to reveal and control the transformation pathways in materials synthesis by pulsed laser deposition (PLD) and apply it to investigate the transformation kinetics of monolayer WS 2 crystals into Janus WSSe and WSe 2 by implantation of Se clusters with different maximum kinetic energies (<42 eV/Se-atom) generated by laser ablation of a Se target. Real-time Raman spectroscopy and photoluminescence are used to assess the structure, composition, and optoelectronic quality of the monolayer crystal as it is implanted with well-controlled fluxes of selenium for different kinetic energies that are regulated with in situ ICCD imaging, ion probe, and spectroscopy diagnostics. First-principles calculations, XPS, and atomic-resolution HAADF STEM imaging are used to understand the intermediate alloy compositions and their vibrational modes to identify transformation pathways. The real-time kinetics measurements reveal highly selective top-layer conversion as WS 2 transforms through WS 2(1–x) Se 2x alloys to WSe 2 and provide the means to adjust processing conditions to achieve fractional and complete Janus WSSe monolayers as metastable transition states. The general approach demonstrates a real-time feedback method to achieve Janus layers or other metastable alloys of the desired composition, and a general means to adjust the structure and quality of materials grown by PLD, addressing priority research directions for precision synthesis with real-time adaptive control.

2D materials↗