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At least 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Nitrification in a completely stirred tank reactor treating the liquid phase of digestate: The way towards rational use of nitrogen

Highlights: • Nitrification of digestate liquid phase was simulated in a laboratory scale. • The attention was paid mainly to rationale use of nitrogen. • Nitrate was produced immediately after the process initiation. • Ammonia oxidation rate reached up to 0.59 kg/(m{sup 3} d). • The operation of the system was effectively optimized by pH control. - Abstract: The nitrification of the liquid phase of digestate (LPD) was conducted using a 5 L completely stirred tank reactor (CSTR) in two independent periods (P1 – without pH control; P2 – with pH control). The possibility of minimizing nitrogen losses during the application of LPD to the soil as well as during long-term storage or thermal thickening of LPD using nitrification was discussed. Moreover, the feasibility of applying the nitrification of LPD to the production of electron acceptors for biological desulfurization of biogas was assessed. Despite an extremely high average concentration of ammonia and COD in LPD reaching 2470 and 9080 mg/L, respectively, nitrification was confirmed immediately after the start-up of the CSTR. N-NO{sub 3}{sup −} concentration reached 250 mg/L only two days after the start of P1. On the other hand, P1 demonstrated that working without pH control is a risk because of the free nitrous acid (FNA) inhibition towards nitrite oxidizing bacteria (NOB) resulting in massive nitrite accumulation. Up to 30.9 mg/L of FNA was present in the reactor during P1, where the NOB started to be inhibited even at 0.15 mg/L of FNA. During P2, the control of pH at 7.0 resulted in nitrogen oxidation efficiency reaching 98.3 ± 1.5% and the presence of N-NO{sub 3}{sup −} among oxidized nitrogen 99.6 ± 0.4%. The representation of volatile free ammonia within total nitrogen was reduced more than 1000 times comparing with raw LPD under these conditions. Thus, optimum characteristics of the tested system from the point of view of minimizing the nitrogen losses as well as production of electron acceptors for the desulfurization of biogas were gained in this phase of reactor operation. Based on the results of the experiments, potential improvements and modifications of the tested system were suggested.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Targeted Quantification of Phosphorylation Dynamics in the Context of EGFR-MAPK Pathway

Large-scale phosphoproteomics with coverage of over 10,000 sites of phosphorylation have now been routinely achieved with advanced mass spectrometry (MS)-based workflows. However, accurate targeted MS-based quantification of phosphorylation dynamics, an important direction for gaining quantitative understanding of signaling pathways or networks, has been much less investigated. Herein, we report an assessment of the targeted workflow in the context of signal transduction pathways, using the epidermal growth factor receptor (EGFR)–mitogen-activated protein kinase (MAPK) pathway as our model. 43 phosphopeptides from the EGFR–MAPK pathway were selected for the study. The recovery and sensitivity of a workflow consisted of two commonly used enrichment methods, immobilized metal affinity chromatography (IMAC) and titanium oxide (TiO2), combined with selected reaction monitoring (SRM)-MS, were evaluated. The recovery of phosphopeptides by IMAC and TiO2 enrichment was quantified to be 38 ± 5% and 58 ± 20%, respectively, based on internal standards. Moreover, both enrichment methods provided comparable sensitivity from 1-100 g starting peptides. Robust quantification was consistently achieved for most targeted phosphopeptides when starting with 25-100 g peptides. However, the numbers of quantified targets significantly dropped when peptide samples were in the 1-25g range. Finally, IMAC-SRM was applied to quantify signaling dynamics of EGFR-MAPK pathway in Hs578T cells following 3 ng/mL EGF treatment. The kinetics of phosphorylation clearly revealed early and late phases of phosphorylation, even for very low abundance proteins. These results demonstrate the feasibility of robust targeted quantification of phosphorylation dynamics for specific pathways, even starting with relatively small amounts of protein.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2019

Cu-Catalyzed Synthesis of CdZnSe–CdZnS Alloy Quantum Dots with Highly Tunable Emission

Fabrication of quantum dots (QDs) with emission covering a wide spectral region has been persistently intriguing because of their potentials in a range of practical applications such as biological labeling and imaging, solar cells, light-emitting diodes, and next-generation displays. We report the synthesis of CdZnSe–CdZnS core–shell alloy QDs through a Cu-catalyzed solid solution alloying strategy starting from CdSe–CdS core–shell QDs. The resulting CdZnSe–CdZnS alloy QDs exhibit emission profiles covering a wide wavelength range of 470–650 nm while maintaining high photoluminescence quantum yields. In addition, high morphological uniformity of the starting CdSe–CdS QDs can be largely retained in the final alloy QDs. We attribute this alloying process to the high mobility nature of Cu cations in Cd-chalcogenide crystals at elevated reaction temperatures, which allows Cu cations to act as transporting agents to transfer a Zn component into the CdSe–CdS QDs while maintaining the particle integrity. We show that this unique alloying strategy is independent of the shape of the starting QDs and can also be applied to the synthesis of CdZnSe–CdZnS nanorods. We anticipate that our study will instigate the synthesis of various high-quality alloy QDs and other alloy nanocrystals beyond what can be achieved currently.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Energetics of Ag Adsorption on and Adhesion to Rutile TiO 2 (100) Studied by Microcalorimetry

The adsorption and adhesion energies of vapor-deposited Ag on rutile TiO 2 (100) films have been measured using single crystal adsorption calorimetry (SCAC) and He + low energy ion scattering spectroscopy (LEIS). Ag grows as three-dimensional (3D) nanoparticles at 300 and 100 K. The saturation particle density is 8 × 10 16 particles/m 2 at 300 K and 2.5 × 10 17 particles/m 2 at 100 K. The differential heat of adsorption starts low, increases with Ag coverage, and finally approaches the sublimation enthalpy of Ag at both 300 and 100 K. At 300 K, the differential heat of adsorption starts from 208 kJ/mol and rises rapidly to 265 kJ/mol by 1 ML. At 100 K, Ag grows nanoparticles with smaller particle size on the terraces, while at 300 K, the Ag nanoparticles have bigger particle size and grow on step edges with stronger binding strength to the nanoparticles. Thus, the heat of Ag adsorption at 100 K starts at 141 kJ/mol (near the monomer size limit on terrace sites) and remains lower than that at 300 K until 1.5 ML. Here, the adhesion energy of Ag(solid) to rutile TiO 2 (100) is found to be large (~2.44 J/m 2 ), supporting a trend of decreasing adhesion energy with the enthalpy of oxide reduction.

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

Heterologous Gene Expression of N -Terminally Truncated Variants of LipPks1 Suggests a Functionally Critical Structural Motif in the N -terminus of Modular Polyketide Synthase

Streptomyces genomes have a high G + C content and typically use an ATG or GTG codon to initiate protein synthesis. Although gene-finding tools perform well in low GC genomes, it is known that the accuracy in predicting a translational start site (TSS) is much less for high GC genomes. LipPks1 is a Streptomyces-derived, well-characterized modular polyketide synthase (PKS). Here, using this enzyme as a model, we experimentally investigated the effects of alternative TSSs using a heterologous host, Streptomyces venezuelae. One of the TSSs employed boosted the protein level by 59-fold and the product yield by 23-fold compared to the originally annotated start codon. Interestingly, a structural model of the PKS indicated the presence of a structural motif in the N-terminus, which may explain the observed different protein levels together with a proline and arginine-rich sequence that may inhibit translational initiation. Lastly, this structure was also found in six other modular PKSs that utilize noncarboxylated starter substrates, which may guide the selection of optimal TSSs in conjunction with start-codon prediction software.

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

WUS256: An Adjoint Waveform Tomography Model of the Crust and Upper Mantle of the Western United States for Improved Waveform Simulations

Abstract We report a new model (WUS256) of radially anisotropic seismic wavespeeds of the crust and upper mantle of the western United States (WUS) obtained from adjoint waveform tomography for the purpose of improving synthetic waveform fits to observed data. WUS256 is based on inversion of over 94,000 waveforms from 72 earthquakes recorded by nearly 3,400 stations. We started with the SPiRaL global model (Simmons et al., 2021, https://doi.org/10.1093/gji/ggab277 ) and waveforms in the period band of 50–120 s. We followed a conservative multiscale inversion approach with eight stages and 256 total inversion iterations which enabled monotonic misfit reduction to 20‐s minimum‐period waves. WUS256 relied on time‐frequency (TF) phase misfits and a trust region limited memory Broyden–Fletcher–Goldfarb–Shanno (L‐BFGS) optimization. Hessian‐vector products were used to qualitatively assess model resolution. Results indicate that WUS256 has good coverage of the continental regions to depths of about 150 km and is able to resolve features on lateral scales of about 200 km. We quantify waveform fits by the reduction in TF and normalized amplitude difference misfits between WUS256 and the SPiRaL starting model. WUS256 significantly improves waveform fits with misfit reduction 64% for both inversion and validation data sets compared to the SPiRaL starting model and shows even better fits compared to other models. Waveform fits illustrate that WUS256 reproduces body‐waves, fundamental mode surface waves as well as late arriving dispersed and/or scattered short period surface waves. The improvement in waveform fit indicates that WUS256 can be used to reproduce path effects on regional complete waveforms and moment tensor inversions.

58 GEOSCIENCES↗
DOE OSTI2024

The Influence of Climate Variability and Future Climate Change on Atlantic Hurricane Season Length

Abstract Atlantic hurricane season length is important for emergency management preparation, motivating the need to understand its variability and change. We investigated the influence of ocean variability on Atlantic hurricane season length in observations and a future climate simulated by the Energy Exascale Earth System Model (E3SM). We found that multiple factors influence hurricane season length, through their influence on season start and end. Warm western subtropical Atlantic sea‐surface temperature anomalies (SSTAs) during boreal spring (before the official hurricane season start) drive early starts to the hurricane season, and vice versa for cool SSTAs. Meanwhile, La Niña in autumn (before the official hurricane season end) drives late ends to the hurricane season, and vice versa for El Niño. E3SM projects a 27‐day increase in future Atlantic hurricane season length given La Niña and warm northern tropical Atlantic SSTAs. This research documents sources of predictability for Atlantic hurricane season length.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

The Remarkable 2024 North Atlantic Mid‐Season Hurricane Lull

Abstract The 2024 North Atlantic (hereafter Atlantic) hurricane season started quickly, with the earliest Category 5 on record (Beryl) and three hurricanes forming through 14 August. Following Ernesto's dissipation on 20 August, the Atlantic hurricane season became extremely quiet during the climatological peak of hurricane season, with only one Category 2 hurricane (Francine) and one tropical storm through 23 September. Several environmental factors likely contributed to this unexpected, prolonged lull. During mid‐to‐late August, subseasonal conditions were broadly favorable for Atlantic hurricanes, but a northward shift in African easterly wave emergence latitude yielded fewer tropical cyclone seed disturbances that also traversed unfavorably cool ocean water. During early‐to‐mid September, subseasonal variability driven by the Madden‐Julian oscillation was less conducive to hurricane activity, with several bouts of increased vertical wind shear across the central Atlantic. Throughout most of the lull, the tropical Atlantic was anomalously dry and subsident, suppressing hurricane formation chances. Plain Language Summary The 2024 North Atlantic (hereafter Atlantic) hurricane season was anticipated to be extremely active, with seasonal forecasts calling for a potentially historic season. Following a busy start including the earliest Category 5 Atlantic hurricane on record (Beryl), the season became very quiet between 20 August–23 September, with only one Category 2 hurricane (Francine) and one tropical storm forming. Following the lull, the Atlantic became extremely busy again, with seven hurricanes forming from 25 September through the end of the season–the most on record for this period. This paper focuses on the surprising lull and attributes it to several different factors, including a late‐August northward shift in African easterly wave tracks (organized thunderstorm complexes spanning thousands of kilometers that often serve as Atlantic hurricane seeds). This northward shift brought these systems out over colder water and into a drier airmass, suppressing their hurricane formation chances. During the first 3 weeks of September, a large‐scale tropical phenomenon known as the Madden‐Julian oscillation, resulted in increased sinking motion, drier mid‐levels and increased vertical wind shear–all of which typically reduce Atlantic hurricane activity. Overall, the lull demonstrates how seed disturbances and other environmental factors can strongly modulate aggregate seasonal tropical cyclone activity. Key Points Following an active start, the 2024 Atlantic hurricane was quiet during the climatological peak with only 1 tropical storm and 1 hurricane The lull was not anticipated by seasonal forecasting agencies, which called for an extremely active 2024 Atlantic hurricane season Factors reducing storm count included a northward shift in African easterly waves, broad‐scale subsidence, and reduced mid‐level moisture

Klotzbach, P J↗
DOE OSTI2017

Dominant role of plant physiology in trend and variability of gross primary productivity in North America

Annual gross primary productivity (GPP) varies considerably due to climate-induced changes in plant phenology and physiology. However, the relative importance of plant phenology and physiology on annual GPP variation is not clear. In this study, a Statistical Model of Integrated Phenology and Physiology (SMIPP) was used to evaluate the relative contributions of maximum daily GPP (GPP max ) and the start and end of growing season (GS start and GS end ) to annual GPP variability, using a regional GPP product in North America during 2000-2014 and GPP data from 24 AmeriFlux sites. Climatic sensitivity of the three indicators was assessed to investigate the climate impacts on plant phenology and physiology. The SMIPP can explain 98% of inter-annual variability of GPP over mid- and high latitudes in North America. The long-term trend and inter-annual variability of GPP are dominated by GPP max both at the ecosystem and regional scales. During warmer spring and autumn, GS start is advanced and GS end delayed, respectively. GPP max responds positively to summer temperature over high latitudes (40-80°N), but negatively in mid-latitudes (25-40°N). This study demonstrates that plant physiology, rather than phenology, plays a dominant role in annual GPP variability, indicating more attention should be paid to physiological change under futher climate change.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

D 5h [PhSiO 1.5 ] 10 synthesis via F – catalyzed rearrangement of [PhSiO 1.5 ] n . An experimental/computational analysis of likely reaction pathways

We describe here in this paper the synthesis and analysis of the reaction pathways leading to formation of the rare D 5h decaphenylsilsesquioxane (SQ) [PhSiO 1.5 ] 10 via F – catalyzed rearrangement of [PhSiO 1.5 ] n n = 8, 12, and oligomers initially synthesized from PhSi(OEt) 3 . Isolated yields of ~50% [PhSiO 1.5 ] 10 are obtained via rearrangement of all starting materials. The recovered starting materials can be re-equilibrated using catalytic F – to generate similar yields in second batches. These yields arise because [PhSiO 1.5 ] 10 exhibits higher solubility and better energy stabilization (10 kcal mol –1 theory) in CH 2 Cl 2 compared to [PhSiO 1.5 ] 8 or [PhSiO 1.5 ] 12 . Reaction intermediates were identified using time dependent 19 F NMR and MALDI-ToF mass spectrometry eventually equilibrating to form the 8: 10 : 12 cages in a 1 : 3 : 1.3 equilibrium in CH 2 Cl 2 . Experimental results coupled with modeling using the Gamess computational package provide multiple reasonable pathways for SQ rearrangements to [RSiO 1.5 ] 10 , starting from [RSiO 1.5 ] 8 . Heats of reaction for interconversion of the model intermediates [HSiO 1.5 ] x determined computationally, were used to select the most reasonable reaction pathways. The findings support a mechanism involving activation and cleavage of a T 8 cage corner by F – attachment, followed by the corners stepwise removal as [ i.e. RSi(OH) 3 ], followed thereafter by reinsertion forming [RSiO 1.5 ] 9 –OH followed by, insertion of another corner to form [RSiO 1.5 ] 10 –(OH) 2 and finally condensation to give [RSiO 1.5 ] 10 . The most enthalpically favorable path (–24 kcal mol –1 ) involves a hybrid mechanism.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Status of the 1 MeV Accelerator Design for ITER NBI

The beam source of neutral beam heating/current drive system for ITER is needed to accelerate the negative ion beam of 40A with D{sup -} at 1 MeV for 3600 sec. In order to realize the beam source, design and R and D works are being developed in many institutions under the coordination of ITER organization. The development of the key issues of the ion source including source plasma uniformity, suppression of co-extracted electron in D beam operation and also after the long beam duration time of over a few 100 sec, is progressed mainly in IPP with the facilities of BATMAN, MANITU and RADI. In the near future, ELISE, that will be tested the half size of the ITER ion source, will start the operation in 2011, and then SPIDER, which demonstrates negative ion production and extraction with the same size and same structure as the ITER ion source, will start the operation in 2014 as part of the NBTF. The development of the accelerator is progressed mainly in JAEA with the MeV test facility, and also the computer simulation of beam optics also developed in JAEA, CEA and RFX. The full ITER heating and current drive beam performance will be demonstrated in MITICA, which will start operation in 2016 as part of the NBTF.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Phase stability and property evolution of biphasic Ti-Ni-Sn alloys for use in thermoelectric applications

Thermoelectric properties and phase evolution have been studied in biphasic Ti–Ni–Sn materials containing full-Heusler TiNi 2 Sn embedded within half-Heusler thermoelectric TiNiSn. Materials, prepared by levitation induction melting followed by annealing, were of the nominal starting composition of TiNi 1+x Sn, with x between 0.00 and 0.25. Phases and microstructure were determined using synchrotron X-ray diffraction and optical and electron microscopy. The full-Heusler phase is observed to be semi-coherent with the half-Heusler majority phase. Differential thermal analysis was performed to determine melting temperatures of the end-member compounds. The thermal conductivity is reduced with the introduction of a dispersed, full-Heusler phase within the half-Heusler material. This leads to an increased thermoelectric figure of merit, ZT, from 0.35 for the stoichiometric compound to 0.44 for TiNi 1.15 Sn. Beyond x = 0.15 ZT decreases due to a rise in thermal conductivity. Density functional theory calculations using hybrid functionals were performed to determine band alignments between the half- and full-Heusler compounds, as well as comparative energies of formation. The hybrid functional band structure of TiNiSn is presented as well.

Douglas, Jason E.↗
DOE OSTI2014

Synchrotron radiation, pair production, and longitudinal electron motion during 10-100 PW laser solid interactions

At laser intensities above 10{sup 23} W/cm{sup 2}, the interaction of a laser with a plasma is qualitatively different to the interactions at lower intensities. In this intensity regime, solid targets start to become relativistically underdense, gamma-ray production by synchrotron emission starts to become an important feature of the dynamics and, at even higher intensities, electron-positron pair production by the non-linear Breit-Wheeler process starts to occur. In this paper, an analysis is presented of the effects of target density, laser intensity, target preplasma properties, and other parameters on the conversion efficiency, spectrum, and angular distribution of gamma-rays by synchrotron emission. An analysis of the importance of Breit-Wheeler pair production is also presented. Target electron densities between 10{sup 22} cm{sup −3} and 5 × 10{sup 24} cm{sup −3} and laser intensities covering the range between 10{sup 21} W/cm{sup 2} (available with current generation laser facilities) and 10{sup 24} W/cm{sup 2} (upper intensity range expected from the ELI facility are considered. Results are explained in terms of the behaviour of the head of the laser pulse as it interacts with the target.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Search for 0ν2β of {sup 100}Mo by NEMO-3 and status of SuperNEMO

The NEMO-3 experiment was devoted to the research of the neutrinoless double beta decay and the precise measurement of the two-neutrino double beta decay of seven isotopes. The detector took data in the Laboratoire Souterrain de Modane (LSM) from 2003 to 2011. The unique combination of a 3D-tracker and a calorimeter allowed to fully reconstruct the double beta decay events topology and strongly reduces the backgrounds. This feature also permitted to characterize the remaining backgrounds in independent analysis channels. With an exposure of 34.7 kg·y of {sup 100}Mo no evidence for the 0ν2β signal has been found, yielding a limit for the light Majorana neutrino mass mechanism of T{sub 1/2}(0ν2β) > 1.1 10{sup 24} years (90 % C.L.) once both statistical and systematic uncertainties are taken into account. Depending on the Nuclear Matrix Elements this corresponds to an upper limit on the Majorana effective neutrino mass of |m{sub ββ}| < 0.3 − 0.9 eV (90 % C.L.). Constraints on other lepton number violating mechanisms of 0ν2β decays are also given. Searching for high-energy double electron events in all suitable sources of the detector, no event in the energy region [3.2-10] MeV is observed for an exposure of 47 kg·y. The next generation experiment, SuperNEMO, will use the same experimental technique to extend the sensitivity on the neutrinoless double beta decay search. Several aspects have been improved compared to NEMO-3: choice of the isotope, energy resolution, energy losses… but the main challenge is the background reduction. All the detector materials have been selected for their low natural radioactivity contaminations through High Purity Germanium (HPGe) gamma spectroscopy. The double beta sources after enrichment are being prepared with extreme care and the ultimate contaminations will be characterized by the most sensitive BiPo detector. External radon tightness and internal radon emanation have been studied to ensure a very low level in the tracker with very sensitive complementary detectors: diffusion apparatus, concentration line and emanation tanks. The construction of the first detector, called the demonstrator, has started in 2012. Studying 7 kg of {sup 82}Se, the demonstrator will reach the NEMO-3 sensitivity in only 5 months and improve it by at least a factor 6 in 2.5 years. Underground installation will start fall 2014 and physics data taking should start by summer 2015.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Recent performance and ignition tests of the pulsed SNS H{sup −} source for 1-MW neutron production

After acquiring several reliable spare targets, SNS ramped the beam power from 850 kW to 1.4 MW, which required an increase in H{sup −} beam pulse length from 0.88 to 1.0 ms at 60 Hz. This increase initially produced slow 2-MHz power ramp-ups and, after several weeks of uninterrupted operation, it produced plasma outages every time the pulse length was raised above ∼0.95 ms. Similar outages were previously observed towards the end of long service cycles, which were believed to indicate that the breakdown voltage of the high purity hydrogen started to exceed the induced electric fields. In 2011 the RF was reconfigured to start with 10 cycles of 1.96 MHz, which yielded the shortest H{sup −} beam rise times and apparently eliminated those plasma outages. The new, pulse-length dependent outages were eliminated by increasing the initial frequency to 1.985 MHz. However, careful frequency studies are unable to justify this frequency. In addition, the paper discusses the issues and solutions for the electron-dump voltage, which starts to sag and become unstable after several weeks of high current operation. At the request of the authors and the Proceedings Editor this article has been updated to include References 3–13, which were present in the author’s original submission but were lost during manuscript processing in the Proceedings Editor's office. The updated article was published on 5 May 2015.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

A systematic benchmark of the ab initio Bethe-Salpeter equation approach for low-lying optical excitations of small organic molecules

The predictive power of the ab initio Bethe-Salpeter equation (BSE) approach, rigorously based on many-body Green’s function theory but incorporating information from density functional theory, has already been demonstrated for the optical gaps and spectra of solid-state systems. Interest in photoactive hybrid organic/inorganic systems has recently increased and so has the use of the BSE for computing neutral excitations of organic molecules. However, no systematic benchmarks of the BSE for neutral electronic excitations of organic molecules exist. Here, we study the performance of the BSE for the 28 small molecules in Thiel’s widely used time-dependent density functional theory benchmark set [Schreiber et al., J. Chem. Phys. 128, 134110 (2008)]. We observe that the BSE produces results that depend critically on the mean-field starting point employed in the perturbative approach. We find that this starting point dependence is mainly introduced through the quasiparticle energies obtained at the intermediate GW step and that with a judicious choice of starting mean-field, singlet excitation energies obtained from BSE are in excellent quantitative agreement with higher-level wavefunction methods. The quality of the triplet excitations is slightly less satisfactory.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

A modular reactor design for in situ synchrotron x-ray investigation of atomic layer deposition processes

Synchrotron characterization techniques provide some of the most powerful tools for the study of film structure and chemistry. The brilliance and tunability of the Advanced Photon Source allow access to scattering and spectroscopic techniques unavailable with in-house laboratory setups and provide the opportunity to probe various atomic layer deposition (ALD) processes in situ starting at the very first deposition cycle. Here, we present the design and implementation of a portable ALD instrument which possesses a modular reactor scheme that enables simple experimental switchover between various beamlines and characterization techniques. As first examples, we present in situ results for (1) X-ray surface scattering and reflectivity measurements of epitaxial ZnO ALD on sapphire, (2) grazing-incidence small angle scattering of MnO nucleation on silicon, and (3) grazing-incidence X-ray absorption spectroscopy of nucleation-regime Er{sub 2}O{sub 3} ALD on amorphous ALD alumina and single crystalline sapphire.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Lieb-Liniger-like model of quantum solvation in CO-{sup 4}He{sub N} clusters

Small {sup 4}He clusters doped with various molecules allow for the study of “quantum solvation” as a function of cluster size. A peculiarity of quantum solvation is that, as the number of {sup 4}He atoms is increased from N = 1, the solvent appears to decouple from the molecule which, in turn, appears to undergo free rotation. This is generally taken to signify the onset of “microscopic superfluidity.” Currently, little is known about the quantum mechanics of the decoupling mechanism, mainly because the system is a quantum (N + 1)-body problem in three dimensions which makes computations difficult. Here, a one-dimensional model is studied in which the {sup 4}He atoms are confined to revolve on a ring and encircle a rotating CO molecule. The Lanczos algorithm is used to investigate the eigenvalue spectrum as the number of {sup 4}He atoms is varied. Substantial solvent decoupling is observed for as few as N = 5 {sup 4}He atoms. Examination of the Hamiltonian matrix, which has an almost block diagonal structure, reveals increasingly weak inter-block (solvent-molecule) coupling as the number of {sup 4}He atoms is increased. In the absence of a dopant molecule the system is similar to a Lieb-Liniger (LL) gas and we find a relatively rapid transition to the LL limit as N is increased. In essence, the molecule initially—for very small N—provides a central, if relatively weak, attraction to organize the cluster; as more {sup 4}He atoms are added, the repulsive interactions between the identical bosons start to dominate as the solvation ring (shell) becomes more crowded which causes the molecule to start to decouple. For low N, the molecule pins the atoms in place relative to itself; as N increases the atom-atom repulsion starts to dominate the Hamiltonian and the molecule decouples. We conclude that, while the notion of superfluidity is a useful and correct description of the decoupling process, a molecular viewpoint provides complementary insights into the quantum mechanism of the transition from a molecular cluster to a quantum solvated molecule.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗