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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 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

ROSAT-IUE observations of symbiotic stars. The x ray morphology of high latitude associations

The purposes of this grant included: to provide for continuing investigations of the x-ray properties of a class of interacting binaries known as symbiotic stars through analysis of their detection statistics in the ROSAT All-Sky Survey and simultaneous IUE observations; and to obtain and analyze ROSAT images of selected high latitude OB star associations, in order to permit multi-wavelength dissection of their contents and energetics. The first study is expected to result in enhanced information on mass transfer and accretion in such systems, and provide a more quantitative basis for interpretation of the spectra of these and similar stellar and extragalactic systems. This particular effort represents NASA support for an approved collaboration between the PI and the ROSAT Team at MPE Garching. In the second study, we seek to correlate the strength with which the diffuse clouds have been shocked and the recent star formation triggered, namely, the O and B stars of the Association, as well as nearby T Tauri stars. The large scale X-ray emission in deep ROSAT PSPC images will be compared with the optical, infrared, and radio topology of nearby supernova remnants, molecular clouds, and the distribution of massive stars in the regions. This should enable us to test whether the star formation triggering shocks originate from in the galactic plane (nearby supernovae) or from the collision of infalling matter with the disk material (galactic fountain dynamics).

Stencel, Robert E.↗
DOE OSTI2023

How does your gyroid grow? A mesoatomic perspective on supramolecular, soft matter network crystals

We propose and describe a framework to understand the structure of supramolecular network crystals formed in soft matter in terms of mesoatomic building blocks, collective groupings of amphiphilic molecules that play a role analogous to atomic or molecular subunits of hard matter crystals. While the concept of mesoatoms is intuitive and widely invoked in crystalline arrangements of spherelike or cylinderlike (micellelike) domains, analogous notions of natural and physically meaningful building blocks of triply periodic network (TPN) crystals, like the double-gyroid or double-diamond structures are obscured by the complex, bicontinuous domain shapes and intercatenated topologies of the double networks. Focusing on the specific example of diblock copolymer melts, we propose generic rules for decomposing TPN crystals into a unique set of mesoatomic building blocks. Based on physically motivated principles, the combination of symmetries and topologies of these structures point to mesoatomic elements associated with the nodal connections, leading to mesoatomic volumes that are nonconvex and bound by smoothly curved faces, unlike the more familiar Voronoi polyhedral shapes associated with spherelike and cylinderlike mesoatoms. We analyze the shapes of these mesoatoms, their internal structure, and importantly, their local packing with neighbor mesoatomic units. Importantly, we hypothesize that mesoatoms are kinetically favored intermediate structures whose local shapes and packing template network crystal assembly on long time scales. We propose and study a minimal energetic model of mesoatom assembly for three different cubic double-network crystals, based on local shape packing, which predicts a detailed picture for kinetics of intercatenation and surface growth. Based on these analyses, we discuss several possible extensions and elaborations of the mesoatomic description of supramolecular soft matter network crystals, most notably the implications of mesoatomic malleability, a feature that distinguishes soft matter from hard matter crystals. We describe experimental observations of malleable mesoatomic units in the precursor sponge phase as well as in ordered cubic networks and suggest possibilities for observing mesoatoms in primordial, precrystalline states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2005

Operational Aspects of Space Radiation Analysis

Minimizing astronaut's short and long-term medical risks arising from exposure to ionizing radiation during space missions is a major concern for NASA's manned spaceflight program, particularly exploration missions. For ethical and legal reasons, NASA follows the "as low as reasonably achievable" (ALARA) principal in managing astronaut's radiation exposures. One implementation of ALARA is the response to space weather events. Of particular concern are energetic solar particle events, and in low Earth orbit (LEO), electron belt enhancements. To properly respond to these events, NASA's Space Radiation Analysis Group (SRAG), in partnership with the NOAA Space Environment Center (SEC), provides continuous flight support during U.S. manned missions. In this partnership, SEC compiles space weather data from numerous ground and space based assets and makes it available in near real-time to SRAG (along with alerts and forecasts), who in turn uses these data as input to models to calculate estimates of the resulting exposure to astronauts. These calculations and vehicle instrument data form the basis for real-time recommendations to flight management. It is also important to implement ALARA during the design phase. In order to appropriately weigh the risks associated with various shielding and vehicle configuration concepts, the expected environment must be adequately characterized for nominal and worst case scenarios for that portion of the solar cycle and point in space. Even with the best shielding concepts and materials in place (unlikely), there will be numerous occasions where the crew is at greater risk due to being in a lower shielded environment (short term transit or lower shielded vehicles, EVAs), so that accurate space weather forecasts and nowcasts, of particles at the relevant energies, will be crucial to protecting crew health and safety.

Weyland, M. D.↗
DOE OSTI2020

Ultrafast terahertz spectroscopy provides insight into charge transfer efficiency and dynamics in artificial photosynthesis

Terahertz (THz) spectroscopy provides a noncontact method to measure the ultrafast dynamics and photoconductivity of mobile carriers in semiconducting materials. This has proven useful in studying artificial photosynthesis devices which use semiconductor photoelectrodes. In this work, we present a brief introduction to optical-pump THz-probe (OPTP) spectroscopy, a technique that provides unique and useful insight into interfacial electron transfer (from the surface-attached dye to the conduction band of the semiconductor) in dye-sensitized photoelectrochemical cells. Compared with more familiar methods like visible transient absorption spectroscopy, OPTP spectroscopy stands out in offering both sub-picosecond time resolution as well as sensitivity to mobile carriers (electrons and holes) in the semiconductor portion of artificial photosynthesis devices. The mobile carriers are crucial to device performance as only they pass to the other half cell to complete the reaction. In order to highlight these advantages and illustrate the types of questions OPTP spectroscopy can address, we discuss three case studies. In the first, OPTP spectroscopy is used to measure the injection rates from a set of six different dyes, revealing the effect of the energetics and lifetimes of the dye excited states on interfacial electron transfer. The subsequent case studies investigate the influence of varying the moieties which bind to the surface (anchors), as well as the moieties that connect the chromophore with these anchors (linkers). OPTP spectroscopy was used to measure the interfacial electron transfer rate as these moieties were varied.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Defect passivation in nanostructured silica for stable birefringence in polarization optics

Nanostructured materials with anisotropic microstructure exhibit direction-dependent refractive index, known as form birefringence. One of the main advantages of these nanostructured materials is that the ease of fabrication significantly reduces the cost of production. However, their birefringence is affected by humidity as well as time. The hypothesis is that defects, particularly silanols, are responsible. Here, in this work, we present the use of hexamethyldisilazane (HMDS) vapor as a passivation strategy. Using spectroscopic ellipsometry and Raman scattering, the data show that HMDS successfully passivates silanol groups and promotes O-Si-O bond formation, resulting in improved stability. The results demonstrate a simple method to enhance the reliability of all-silica polarization optics offering potential advancements for high-power laser components.

Mireles, Marcela [Univ. of Rochester, NY (United S↗
DOE OSTI2026

A Transferable Force Field for Simulating Adsorption in Metal–Organic Frameworks with Open Metal Sites Based on the 12–6–4 Lennard-Jones Potential

Metal−organic frameworks (MOFs) that contain coordinatively unsaturated open metal sites (OMSs) provide strong host− guest interactions, making them promising sorbents for low-concentration gas adsorption applications such as direct air capture and atmospheric water harvesting. However, accurately modeling host−guest interactions involving OMSs remains challenging for classical force fields (FFs) based on the 12−6 Lennard−Jones (LJ) potential, as the polarization effect of the guest molecule induced by the positively charged OMS is not considered. Here, we introduce an FF based on the 12−6−4 LJ potential, which incorporates charge−induced dipole interactions and is parametrized against a diverse set of host−guest potential energy surfaces (PESs) obtained from density functional theory (DFT). The resulting FF, trained on a generic trimetallic cluster, performs well in both host−guest binding energetics and gas adsorption isotherms across different OMS-containing MOFs, including MOF-74 series and Cu-BTC. These results highlight the excellent transferability of our approach and its potential to enhance the accuracy and robustness of high-throughput MOF discovery workflows, particularly for gas adsorption and separation in large and diverse MOF databases.

36 MATERIALS SCIENCE↗
DOE OSTI2024

HIGH BURNUP FUEL-COOLANT INTERACTION ANALYSIS SUPPORTING FUEL SAFETY TESTING AT IDAHO NATIONAL LABORATORY

In the near future, experiments on HBu fuel under loss-of-coolant accident (LOCA) and reactivity-initiated accident (RIA) conditions will be performed within the Transient Reactor Test Facility (TREAT) at Idaho National Laboratory (INL). These experiments will be performed using the Transient Water Irradiation System for TREAT (TWIST) experiment vehicle. To support these experiments, analysis of fuel-coolant interaction (FCI) energetics is underway. This paper discusses FCIs in the context of light water reactor (LWR) safety, differentiating between the severe accident focus of commercial reactors and experimental RIA test programs where FCIs have occurred. However, it is highlighted that as the nuclear industry aims for increased burnup limits, the FCI events observed in RIA test programs may become relevant to commercial LWR safety analysis. The paper then presents developments to the UW-FCI computer program to enable simulation of FCIs initiated by solid fuel particles dispersing into the coolant during RIAs.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

High-Level Reverse Intersystem Crossing and Molecular Rigidity Improve Spin Statistics for Triplet–Triplet Annihilation Upconversion

The structural factors affecting triplet−triplet annihilation (TTA) at the molecular level are not well-understood. Here, our steady-state photoluminescence and transient absorption results demonstrate that the spin statistical factor, η, decreases from 0.60 to 0.46 and 0.14 going from 9,10-diphenylanthracene (DPA) to the 1,5-DPA and 2,6-DPA isomers, respectively, during photon upconversion with a platinum octaethylporphyrin sensitizer. Density functional theory (DFT) shows that η depends on the energetics of hot triplet states and molecular rigidity. The significantly high conical intersection energy between the S 0 and T 1 states for 9,10-DPA gives its longer triplet lifetime. Time-dependent DFT calculations show that 9,10-DPA and 1,5-DPA can undergo high-level reverse intersystem crossing from their T 2 and T 3 states, respectively, to the bright S 1 state, increasing the limit of the spin statistical factor. Both factors ultimately serve to enhance the TTA efficiency. Furthermore, this work provides insight into designing molecules for efficient light-emitting and photon upconversion applications.

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

Improving and Understanding the Hydrogen Evolving Activity of a Cobalt Dithiolene Metal–Organic Framework

Despite the promising previous reports on the development of electrocatalytic dithiolene-based metal–organic frameworks (MOFs) for the hydrogen evolution reaction (HER), these materials often display poor reproducibility of the HER performance because of their poor bulk properties upon integration with electrode materials. In this work, we demonstrate an in-depth investigation of the electrocatalytic HER activity of a cobalt 2,3,6,7,10,11-triphenylenehexathiolate (CoTHT) MOF. To enhance the durability and charge transport properties of the constructed CoTHT/electrode architecture, CoTHT is deposited as an ink composite (1) composed of Nafion and carbon black. We leverage here the well-established use of catalyst inks in the literature to increase adhesion of the catalyst to the electrode surface and to improve the overall electrical conductivity of the integrated catalyst/electrode. The utilization of the composite 1 leads to a significant improvement in the overpotential (η) to reach a current density of 10 mA/cm 2 (η = 143 mV) compared to prior reports, resulting in the most active MOF-based electrocatalyst for the HER that contains only earth-abundant elements. Extensive density functional theory (DFT) calculations were applied to understand the structure of CoTHT and the mechanistic pathways of the HER. The computational results suggest that an AB stacking geometry is energetically favorable, where one layer is slipped by 1.6 Å relative to the neighboring one along the a and b vectors. Additionally, the DFT calculations indicate that the catalytic cycle likely involves a Volmer discharge step to generate a cobalt hydride, followed by a Heyrovsky step to form a cobalt–H 2 intermediate, and finally the dissociation of H 2 .

DFT calculations↗
NASA NTRS2007

Laboratory Measurements of Charging of Apollo 17 Lunar Dust Grains by Low Energy Electrons

It is well recognized that the charging properties of individual micron/sub-micron size dust grains by various processes are expected to be substantially different from the currently available measurements made on bulk materials. Solar UV radiation and the solar wind plasma charge micron size dust grains on the lunar surface with virtually no atmosphere. The electrostatically charged dust grains are believed to be levitated and transported long distances over the lunar terminator from the day to the night side. The current models do not fully explain the lunar dust phenomena and laboratory measurements are needed to experimentally determine the charging properties of lunar dust grains. An experimental facility has been developed in the Dusty Plasma Laboratory at NASA Marshall Space Flight Center MSFC for investigating the charging properties of individual micron/sub-micron size positively or negatively charged dust grains by levitating them in an electrodynamic balance in simulated space environments. In this paper, we present laboratory measurements on charging of Apollo 17 individual lunar dust grains by low energy electron beams in the 5-100 eV energy range. The measurements are made by levitating Apollo 17 dust grains of 0.2 to 10 micrometer diameters, in an electrodynamic balance and exposing them to mono-energetic electron beams. The charging rates and the equilibrium potentials produced by direct electron impact and by secondary electron emission processes are discussed.

Abbas, Mian M.↗
NASA NTRS2016

The Rate of Dielectric Breakdown Weathering of Lunar Regolith in Permanently Shadowed Regions

Large solar energetic particle events may cause dielectric breakdown in the upper 1 mm of regolith in permanently shadowed regions (PSRs). We estimate how the resulting breakdown weathering compares to meteoroid impact weathering. Although the SEP event rates measured by the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on the Lunar Reconnaissance Orbiter (LRO) are too low for breakdown to have significantly affected the regolith over the duration of the LRO mission, regolith gardened by meteoroid impacts has been exposed to SEPs for approx.10(exp 6 yr. Therefore, we estimate that breakdown weathering's production rate of vapor and melt in the coldest PSRs is up to 1.8−3. 5 ×10(exp −7) kg/sq m/yr, which is comparable to that produced by meteoroid impacts. Thus, in PSRs, up to 10-25% of the regolith may have been melted or vaporized by dielectric breakdown. Breakdown weathering could also be consistent with observations of the increased porosity ("fairy castles") of PSR regolith. We also show that it is con- ceivable that breakdown-weathered material is present in Apollo soil samples. Consequently, breakdown weathering could be an important process within PSRs, and it warrants further investigation.

Meteoroid↗
DOE OSTI2022

Entrapped Molecule‐Like Europium‐Oxide Clusters in Zinc Oxide with Nearly Unaffected Host Structure

Abstract Nanocrystalline ZnO sponges doped with 5 mol% EuO 1.5 are obtained by heating metal–salt complex based precursor pastes at 200–900 °C for 3 min. X‐ray diffraction, transmission electron microscopy, and extended X‐ray absorption fine structure (EXAFS) show that phase separation into ZnO:Eu and c ‐Eu 2 O 3 takes place upon heating at 700 °C or higher. The unit cell of the clean oxide made at 600 °C shows only ≈0.4% volume increase versus undoped ZnO, and EXAFS shows a ZnO local structure that is little affected by the Eu‐doping and an average Eu 3+ ion coordination number of ≈5.2. Comparisons of 23 density functional theory‐generated structures having differently sized Eu‐oxide clusters embedded in ZnO identify three structures with four or eight Eu atoms as the most energetically favorable. These clusters exhibit the smallest volume increase compared to undoped ZnO and Eu coordination numbers of 5.2–5.5, all in excellent agreement with experimental data. ZnO defect states are crucial for efficient Eu 3+ excitation, while c ‐Eu 2 O 3 phase separation results in loss of the characteristic Eu 3+ photoluminescence. The formation of molecule‐like Eu‐oxide clusters, entrapped in ZnO, proposed here, may help in understanding the nature of the unexpected high doping levels of lanthanide ions in ZnO that occur virtually without significant change in ZnO unit cell dimensions.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Iron dopant energy levels in β-Ga 2 O 3

The energetic positions of the two Fe dopant levels in the bandgap of β-Ga 2 O 3 are determined to be at 3.05(±0.05) and 3.85(±0.05) eV below the conduction band minimum from transmission measurements employing a sub-picosecond tunable ultraviolet laser radiation source. A further measurement of the quantum efficiency of photoelectron emission from the Fe:Ga 2 O 3 (010) photocathode is consistent with the obtained absorption data and a dominant optical phonon assisted Franck–Condon emission mechanism, while also providing an estimate of 100 ps for the conduction band electron lifetime.

24 POWER TRANSMISSION AND DISTRIBUTION↗
NASA NTRS2014

NASA's Asteroid Redirect Mission: A Robotic Boulder Capture Option for Science, Human Exploration, Resource Utilization, and Planetary Defense

NASA is examining two options for the Asteroid Redirect Mission (ARM), which will return asteroid material to a Lunar Distant Retrograde Orbit (LDRO) using a robotic solar electric propulsion spacecraft, called the Asteroid Redirect Vehicle (ARV). Once the ARV places the asteroid material into the LDRO, a piloted mission will rendezvous and dock with the ARV. After docking, astronauts will conduct two extravehicular activities (EVAs) to inspect and sample the asteroid material before returning to Earth. One option involves capturing an entire small (~4 - 10 m diameter) near-Earth asteroid (NEA) inside a large inflatable bag. However, NASA is also examining another option that entails retrieving a boulder (~1 - 5 m) via robotic manipulators from the surface of a larger (~100+ m) pre-characterized NEA. The Robotic Boulder Capture (RBC) option can leverage robotic mission data to help ensure success by targeting previously (or soon to be) well- characterized NEAs. For example, the data from the Japan Aerospace Exploration Agency's (JAXA) Hayabusa mission has been utilized to develop detailed mission designs that assess options and risks associated with proximity and surface operations. Hayabusa's target NEA, Itokawa, has been identified as a valid target and is known to possess hundreds of appropriately sized boulders on its surface. Further robotic characterization of additional NEAs (e.g., Bennu and 1999 JU3) by NASA's OSIRIS REx and JAXA's Hayabusa 2 missions is planned to begin in 2018. This ARM option reduces mission risk and provides increased benefits for science, human exploration, resource utilization, and planetary defense. Science: The RBC option is an extremely large sample-return mission with the prospect of bringing back many tons of well-characterized asteroid material to the Earth-Moon system. The candidate boulder from the target NEA can be selected based on inputs from the world-wide science community, ensuring that the most scientifically interesting boulder be returned for subsequent sampling. In addition, the material surrounding the boulder can be collected from the surface, thus providing geological contextual information and additional samples of NEA regolith. The robotic manipulators used for capturing the boulder will ensure some of the surface remains undisturbed and that the boulder will retain its structural integrity, which will preserve the context of any samples collected by the astronauts and ensure a high level of science return. Human Exploration: Due to the coherent nature of the boulder that will be collected, entire encapsulation of the asteroid material is not required. This facilitates exploration and sample collection of the boulder by astronauts in a variety of ways. The total time for EVA during the crew portion of the mission is very limited. Current estimates are that each of the two EVAs will only last four hours. The RBC option will allow crew members to have good situational awareness of the work site and quickly identify sample sites of interest. In addition, the samples to be collected can be readily accessed without having to deal with removal of an encapsulation system, which adds extra complexity and risk for the astronauts during EVA. Resource Utilization: One of the most crucial aspects for resource utilization is the identification and collection of appropriate materials (e.g., volatiles, organics, metals, etc.) that contain components of interest. Prior characterization of NEAs is required in order to increase the likelihood that appropriate materials will be returned. Ground-based observations of small (<10 m) NEAs are challenging, but characterization efforts of larger targets have demonstrated that NEAs with volatiles and organics have been identified. Two potential targets for the RBC option (Bennu and 1999 JU3) have been previously identified as potentially rich in resources, and both are already targets of currently planned robotic missions that will characterize their physical properties in great detail. Planetary Defense: The RBC option involves interaction with a well- characterized potentially hazardoussized NEA that would enable NASA to conduct one or more planetary defense demonstrations. The primary method would use the collected boulder to augment the mass of the ARV and perform an Enhanced Gravity Tractor (EGT) demonstration on the NEA. Additionally, other approaches could be demonstrated during the mission, such as Ion Beam Deflection (IBD) and/or observation of a Kinetic Impactor (KI). The relative effectiveness of a slow push-pull method such as the EGT or IBD could be directly compared and contrasted with the results of the more energetic KI method on the target NEA. Conclusions: This boulder option for NASA's ARM can leverage knowledge of previously characterized NEAs from prior robotic missions, which provides more certainty of the target NEA's physical characteristics and reduces mission risk. This increases the return on investment for NASA's future activities with respect to human exploration, resource utilization, and planetary defense.

Abell, P.↗
DOE OSTI2026

Atomic‐Scale Surface Imaging of Bulk Epitaxial CsPbBr 3 Perovskite Single Crystals on Mica Using Light Assisted Scanning Tunneling Microscopy at Low‐Temperature (80 K)

Epitaxial single-crystalline CsPbBr 3 perovskite films on mica, prepared ex situ, are explored using a low-temperature scanning tunneling microscope (STM) by probing the unoccupied electronic states of their surface in ultra-high vacuum (UHV) at 80 K. Light-assisted STM measurements under a broadband illumination with visible light were employed to enhance and stabilize surface conductivity. STM imaging across the surface of macroscopic bulk CsPbBr 3 films reveals large flat terraces characterized by a specific type of surface reconstruction, consisting of parallel rows of U-shaped atomic nanostructures. These structures are spaced by 12 Å and exhibit an internal feature size of 5.1 Å. Density functional theory (DFT) calculations reproduce the experimental observations and reveal a competition between different orthorhombic CsPbBr 3 (110) surface reconstructions: a Cs-rich structure, identified as the most energetically stable, and three alternative Pb–Br-rich reconstructions, which are slightly higher in energy yet remain consistent with the STM data. Additional analyses that explicitly account for the mica substrate exclude the cubic CsPbBr 3 phase and other orthorhombic surface orientations, while showing that variations in the mica surface termination do not alter the preferred CsPbBr 3 (110) reconstruction. In conclusion, this combined approach thereby confirms our assignment and resolves previous STM interpretations of CsPbBr 3 .

36 MATERIALS SCIENCE↗
DOE OSTI2023

Giant Magnetic and Optical Anisotropy in Cerium-Substituted M-Type Strontium Hexaferrite Driven by $4f$ Electrons

By performing density-functional calculations, we find a giant magnetocrystalline anisotropy (MCA) constant in abundant element cerium $\mathrm{Ce}$ substituted M-type hexaferrite, in the energetically favorable strontium site, assisted by a quantum confined electron transfer from $\mathrm{Ce}$ to a specific iron $\mathrm{2a}$ site. Remarkably, the calculated electronic structure shows that the electron transfer leads to the formation of $\mathrm{Ce}^{3+}$ and $\mathrm{Fe}^{2+}$ at the $\mathrm{2a}$ site producing an occupied $\mathrm{Ce}$$(4f^1)$ state below the Fermi level that adds a significant contribution to MCA and magnetic moment. A half $\mathrm{Ce}$ substitution forms a metallic state, while a full substitution retains the semiconducting state of the strontium hexaferrite (host). In the latter, the band gap is reduced due to the formation of charge-transferred states in the gap region of the host. The optical absorption coefficient shows an enhanced anisotropy between light polarization in parallel and perpendicular directions. Calculated formation energies, including the analysis of probable competing phases, and elastic constants confirm that both compositions are chemically and mechanically stable. With successful synthesis, the $\mathrm{Ce}$ hexaferrite can be an alternative high-performing critical-element-free permanent magnet material adapted for use in devices such as automotive traction drive motors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Growth of topological insulator Bi 2 Se 3 particles on GaAs via droplet epitaxy

The discovery of topological insulators (TIs) and their unique electronic properties has motivated research into a variety of applications, including quantum computing. It has been proposed that TI surface states will be energetically discretized in a quantum dot nanoparticle. These discretized states could then be used as basis states for a qubit that is more resistant to decoherence. In this work, prototypical TI Bi2Se3 nanoparticles are grown on GaAs (001) using the droplet epitaxy technique, and we demonstrate the control of nanoparticle height, area, and density by changing the duration of bismuth deposition and substrate temperature. Within the growth window studied, nanoparticles ranged from 5 to 15 nm in height with an 8–18 nm equivalent circular radius, and the density could be relatively well controlled by changing the substrate temperature and bismuth deposition time.

Materials Science↗