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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Dynamic Ligand Surface Chemistry of Excited PbS Quantum Dots

The ligand shell around colloidal quantum dots mediates the electron and energy transfer processes that underpin their use in optoelectronic and photocatalytic applications. In this work, we show that the surface chemistry of carboxylate anchoring groups of oleate ligands passivating PbS quantum dots undergoes significant changes when the quantum dots are excited to their excitonic states. Additionally, we directly probe the changes of surface chemistry using time-resolved mid-infrared spectroscopy that records the evolution of the vibrational frequencies of carboxylate groups following excitation of the electronic states. The data reveal a reduction of the Pb-O coordination of carboxylate anchoring groups to lead atoms at the quantum dot surfaces. The dynamic surface chemistry of the ligands may increase their surface mobility in the excited state and enhance the ability of molecular species to penetrate the ligand shell to undergo energy and charge transfer processes that depend sensitively on distance.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Evidence of Skewness and Sub-Gaussian Character in Temperature-Dependent Distributions of One Million Electronic Excitation Energies in PbS Quantum Dots

Obtaining statistical distributions by sampling a large number of conformations is vital for an accurate description of temperature-dependent properties of chemical systems. However, constructing distributions with 105??106 samples is computationally challenging because of the prohibitively high computational cost of performing rst-principles quantum-mechanical calculations. In this work, we present a new technique called the Eective Stochastic Potential Conguration Interaction Singles (ESP-CIS) method to obtain excitation energies. The ESP-CIS method uses random matrix theory for the construction of an eective stochastic representation of the Fock operator and combines it with linear-response theory. Here, we perform excitation calculations on PbS quantum dots (0.75-1.75 nm) at temperatures of 200-400 K. Results from a total of 15 million excitation energy calculations (1 million samples for each of the three dots at ve dierent temperatures) revealed the distributions to be sub-Gaussian in nature with negative skewness. The distributions progressively became red-shifted with increasing temperature. The study shows that random distortions in structure from the minimum-energy geometry of these quantum dots are more likely to lower the excitation energies.

Scher, Jeremy A.↗
DOE OSTI2024

PBS_UTILS

SF-24-051 PBS_Utils is a collection of tools and libraries for administrating a PBSPro/OpenPBS system.

Pershey, Eric↗
NASA NTRS1980

An airborne short wave infrared /SWIR/ pushbroom imaging system using a 64-element PbS detector array

Research evidence indicates that data in the short wave infrared (SWIR) spectral region will greatly improve the information content of remotely sensed data. Bands are required in the 1.55-1.75 micron and 2.08-2.35 micron spectral regions for a variety of agricultural and geological investigations. It is anticipated that future Landsat sensors will use pushbroom linear array technology to obtain high resolution, improved sensitivity and increased system reliability. To obtain early laboratory and field data, an airborne pushbroom image system has been designed for operation in the short wave infrared spectral region. The system uses a 64-element staggered PbS array and is operated at 195 K; the instrument has been designed to operate in an aircraft and will view a 19 degree swath width with a 5.8 mrad IFOV. The spectral bandwidth of each channel is .05 micron and the noise equivalent reflectivity in the order of .2% is provided. The requirements for more advanced detector arrays for use in future NASA spacecraft remote sensing instruments are also discussed.

Husain-Abidi, A. S.↗
NASA NTRS1983

Fundamental linewidth in solitary, ultranarrow output PbS(1-x)Se(x) diode lasers

The fundamental, quantum phase noise limited Lorentzian linewidth was directly measured from the beat-note spectra generated by heterodyning PbS(1-x)Se(x) diode lasers with a stable CO gas laser. The experimental results were matched by calculated theoretical line profiles. Linewidths as narrow as 22 kHz full width at half-maximum power were observed.

Freed, C.↗
DOE OSTI2020

Materials Data on Ni3(PbS)2 by Materials Project

Ni3Pb2S2 crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Ni is bonded in a distorted linear geometry to four Pb and two equivalent S atoms. There are two shorter (2.82 Å) and two longer (2.84 Å) Ni–Pb bond lengths. Both Ni–S bond lengths are 2.18 Å. There are two inequivalent Pb sites. In the first Pb site, Pb is bonded in a hexagonal planar geometry to six equivalent Ni atoms. In the second Pb site, Pb is bonded to six equivalent Ni and two equivalent S atoms to form corner-sharing PbNi6S2 hexagonal bipyramids. Both Pb–S bond lengths are 3.16 Å. S is bonded in a 3-coordinate geometry to three equivalent Ni and one Pb atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ni3(PbS)2 by Materials Project

Ni3Pb2S2 crystallizes in the cubic I2_13 space group. The structure is three-dimensional. Ni is bonded in a distorted linear geometry to four equivalent Pb and two equivalent S atoms. There are two shorter (2.85 Å) and two longer (2.91 Å) Ni–Pb bond lengths. Both Ni–S bond lengths are 2.16 Å. Pb is bonded in a 7-coordinate geometry to six equivalent Ni and one S atom. The Pb–S bond length is 3.17 Å. S is bonded in a 3-coordinate geometry to three equivalent Ni and one Pb atom.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Combining Clinical and Dosimetric Features in a PBS Proton Therapy Cohort to Develop a NTCP Model for Radiation-Induced Optic Neuropathy

Radiation-induced optic neuropathy (RION) is a rare, yet severe complication following radiation therapy for brain, head and neck, or skull-base tumors. Although several risk factors, such as age, metabolic syndrome, and delivered dose, have been identified, we aimed at expanding the understanding of the mechanisms of interplay regarding dosimetry and patient variables leading to the onset of RION with a focus on proton therapy.

62 RADIOLOGY AND NUCLEAR MEDICINE↗