Search NASA⌕ Search

SEARCH · Search NASA

Results for “surface morphology”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

High-efficiency single-junction p-i-n GaAs solar cell on roll-to-roll epi-ready flexible metal foils for low-cost photovoltaics

We demonstrate the fabrication and characterization of high-efficiency, single-junction p-i-n GaAs solar cells, on flexible metal foil with epi-ready buffer via roll-to-roll fabrication. Single-junction p-i-n GaAs solar cells were fabricated using metal–organic chemical vapor deposition (MOCVD). Furthermore, an efficiency greater than 13% was obtained at 1 sun, which is the highest reported efficiency on GaAs photovoltaics directly deposited on metal tapes. This exceeds our previously reported study showcasing 11.5% efficiency on single-junction p-n solar cell structure. Improved morphology of p-i-n structure compared with p-n is explained by atomic force microscopy (AFM), scanning electron microscopy (SEM), and helium ion microscopy (HIM) measurements. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis showed reduced Zn diffusion in p-i-n cell compared with the p-n cell. We attribute the improvement in efficiency of p-i-n cells on flexible metal tapes to the quality of the junction, surface morphology, controlled diffusion of species within the active layers, and increase in absorption due to the optimized intrinsic layer thickness.

14 SOLAR ENERGY↗
DOE OSTI2016

Growth features and spectroscopic structure investigations of nanoprofiled AlN films formed on misoriented GaAs substrates

Nanostructured aluminum-nitride films are formed by reactive ion-plasma sputtering onto GaAs substrates with different orientations. The properties of the films are studied via structural analysis, atomic force microscopy, and infrared and visible–ultraviolet spectroscopy. The aluminum-nitride films can have a refractive index in the range of 1.6–4.0 at a wavelength of ~250 nm and an optical band gap of ~5 eV. It is shown that the morphology, surface composition, and optical characteristics of AlN/GaAs heterophase systems can be controlled using misoriented GaAs substrates.

36 MATERIALS SCIENCE↗
NASA NTRS2016

Diverse Eruptions at Approximately 2,200 Years B.P. on the Great Rift, Idaho: Inferences for Magma Dynamics Along Volcanic Rift Zones

Compositionally and morphologically diverse lava flows erupted on the Great Rift of Idaho approximately 2.2 ka (kilo-annum, 1000 years ago) during a volcanic "flare-up" of activity following an approximately 2 ky (kiloyear, 1000 years) hiatus in eruptions. Volcanism at Craters of the Moon (COTM), Wapi and Kings Bowl lava fields around this time included primitive and evolved compositions, separated over 75 kilometers along the approximately 85 kilometers-long rift, with striking variability in lava flow emplacement mechanisms and surface morphologies. Although the temporal associations may be coincidental, the system provides a planetary analog to better understand magma dynamics along rift systems, including that associated with lunar floor-fractured craters. This study aims to help bridge the knowledge gap between ancient rift volcanism evident on the Moon and other terrestrial planets, and active rift volcanism, e.g., at Hawai'i and Iceland.

RIFT ZONEs↗
DOE OSTI2016

Fundamentals of ultrafast laser–material interaction

Short pulse laser irradiation has the ability to bring a material into a state of strong electronic, thermal, phase, and mechanical nonequilibrium and trigger a sequence of structural transformations leading to the generation of complex multiscale surface morphologies, unusual metastable phases, and microstructures that cannot be produced by any other means. In this article, we provide an overview of recent advancements and existing challenges in the understanding of the fundamental mechanisms of short pulse laser interaction with materials, including the material response to strong electronic excitation, ultrafast redistribution and partitioning of the deposited laser energy, the peculiarities of phase transformations occurring under conditions of strong superheating/undercooling, as well as laser-induced generation of crystal defects and modification of surface microstructure.

Materials Science↗
DOE OSTI2014

Multicycle rapid thermal annealing optimization of Mg-implanted GaN: Evolution of surface, optical, and structural properties

The first step of a multi-cycle rapid thermal annealing process was systematically studied. The surface, structure, and optical properties of Mg implanted GaN thin films annealed at temperatures ranging from 900 to 1200 °C were investigated by Raman spectroscopy, photoluminescence, UV-visible spectroscopy, atomic force microscopy, and Nomarski microscopy. The GaN thin films are capped with two layers of in-situ metal organic chemical vapor deposition -grown AlN and annealed in 24 bar of N{sub 2} overpressure to avoid GaN decomposition. The crystal quality of the GaN improves with increasing annealing temperature as confirmed by UV-visible spectroscopy and the full widths at half maximums of the E{sub 2} and A{sub 1} (LO) Raman modes. The crystal quality of films annealed above 1100 °C exceeds the quality of the as-grown films. At 1200 °C, Mg is optically activated, which is determined by photoluminescence measurements. However, at 1200 °C, the GaN begins to decompose as evidenced by pit formation on the surface of the samples. Therefore, it was determined that the optimal temperature for the first step in a multi-cycle rapid thermal anneal process should be conducted at 1150 °C due to crystal quality and surface morphology considerations.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Bio‐based glycerol plasticizers for flexible poly(vinyl chloride) blends

Abstract A series of glycerol‐based compounds were investigated for their application as plasticizers for flexible poly(vinyl chloride) (PVC) blends. The effect of plasticizer chemical structure on the performance, migration behavior, and blend morphology were evaluated and compared to blends produced using the commercial plasticizer dioctyl terephthalate (DOTP). Blends containing 40 phr (parts per hundred rubber) of glycerol‐based plasticizer showed a considerable reduction (between 54 to 86°C) in glass transition temperature ( T g ) relative to neat PVC ( T g ~ 80°C). Tensile testing of samples prepared with the glycerol analogs demonstrated higher ductility (elongation at break values of up to 97%) than DOTP (elongation at break value of 75%) at identical plasticizer loadings. The surface morphologies showed excellent incorporation of the glycerol plasticizers functionalized with alkyl chains longer than four carbons in length into the PVC matrix, whereas droplet formation was observed in blends with shorter chain glycerol derivatives. Leaching behavior of the plasticized samples were evaluated into different media and showed that plasticizers comprised of branched, or longer alkyl chains produced 2‐ to 4‐fold lower migration rates compared to those with shorter alkyl chains into polar solutions.

Halloran, Matthew W.↗
DOE OSTI2014

Thickness dependent structural, optical and electrical properties of CuIn{sub 0.8}Ga{sub 0.2}Se{sub 2} thin films deposited by pulsed laser deposition

CuIn{sub 0.8}Ga{sub 0.2}Se{sub 2} (CIGS) polycrystalline thin films have been deposited on soda lime glass substrate at different deposition time by pulsed laser deposition. The effect of thickness on structural, surface morphological, optical and electrical properties of thin films were investigated by X-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM), atomic force microscopy (AFM), UV-Vis-NIR spectrophotometer and electrical measurement unit. XRD study reveals that all deposited films are polycrystalline in nature and have tetragonal phase of CIGS. Crystallinity of CIGS films has been found to improve with increase in thickness of CIGS films as evidenced by sharp XRD peaks for (112) orientation. Grain size and rms surface roughness of CIGS films have been found to be increased with increase in thickness. All the deposited CIGS films exhibit direct band gap semiconducting behaviour with ∼10{sup 6} cm{sup −1} absorption co-efficient. Optical band gap and resistivity of CIGS films have been found to decrease with increase in thickness.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Study on copper phthalocyanine and perylene-based ambipolar organic light-emitting field-effect transistors produced using neutral beam deposition method

The neutral cluster beam deposition (NCBD) method has been applied to the production and characterization of ambipolar, heterojunction-based organic light-emitting field-effect transistors (OLEFETs) with a top-contact, multi-digitated, long-channel geometry. Organic thin films of n-type N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide and p-type copper phthalocyanine were successively deposited on the hydroxyl-free polymethyl-methacrylate (PMMA)-coated SiO{sub 2} dielectrics using the NCBD method. Characterization of the morphological and structural properties of the organic active layers was performed using atomic force microscopy and X-ray diffraction. Various device parameters such as hole- and electron-carrier mobilities, threshold voltages, and electroluminescence (EL) were derived from the fits of the observed current-voltage and current-voltage-light emission characteristics of OLEFETs. The OLEFETs demonstrated good field-effect characteristics, well-balanced ambipolarity, and substantial EL under ambient conditions. The device performance, which is strongly correlated with the surface morphology and the structural properties of the organic active layers, is discussed along with the operating conduction mechanism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Direct measurement of thermal Knudsen forces in rarefied gas environments

At micro- and nanoscales, momentum transfer between surfaces is influenced by various physical mechanisms, including quantum fluctuations, electromagnetic interactions, electric charges, and the dynamics of (rarefied) gases. Under non-isothermal conditions, rarefied gases give rise to thermal Knudsen forces whose magnitudes strongly depend on the gas species and surface characteristics. Knudsen forces are particularly relevant in nanotechnology, optical manipulation, and aerospace systems, where gas rarefaction occurs due to highly confined geometries, sub-micrometer length scales, and reduced particle densities. Despite their significance, predictive modeling of Knudsen forces is limited by a lack of comprehensive experimental data across diverse materials and surface morphologies. Here, in this work, we present a highly sensitive and adaptable measurement platform capable of directly quantifying Knudsen forces using a suspended, interchangeable micro-cantilever within controlled rarefied helium and nitrogen environments. The system integrates optical fiber interferometry to precisely capture out-of-plane displacements at sub-micrometer resolution, driven by Knudsen forces. From the empirical data, we derive a robust correlation linking the magnitudes of Knudsen forces to energy accommodation coefficients, offering deeper insights into the underlying gas–surface interaction mechanisms.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Two-phase flow numerical analysis of electrode geometry for alkaline water electrolyzers

Hydrogen is a promising component of a future energy-secure and efficient economy, but its competitiveness depends on reducing production costs. One strategy is to operate alkaline water electrolyzers at higher current densities to increase output. However, this intensifies performance losses due to gas bubble accumulation, which blocks transport pathways and deactivates electrochemically active surfaces. Enhancing bubble evacuation through electrode design is therefore essential. Previous studies have explored various approaches — such as modifying surface morphology, applying sonication or pressure modulation, and introducing surfactants — but these efforts have addressed a limited range of conditions due to the complexity of two-phase flow and electrode geometries. Experiments have also largely been focused on either cell level improvements, which lack the information necessary to isolate each contributing factor, or on modified geometries that are not relevant to practical cell operation. From a modeling perspective, conventional Eulerian multiphase models do not track the complex gas–liquid interfacial dynamics and often neglect surface tension and contact angle effects, reducing their predictive accuracy. To provide insights on the effects of different electrode geometries on the performance of alklaine water electrolyzers this work employs an immersed boundary volume-of-fluid method to simulate bubble behavior in 3D porous electrodes. Multiple base electrode geometries, typically used in practice, with varying porosity are evaluated under a constant surface gas generation rate. Simulation data is analyzed to quantify electrode gas coverage, bubble size dynamics and other relevant metrics. Results show that porosity strongly influences bubble accumulation on electrode surfaces, with higher porosity reducing gas coverage, and its not strictly dependent on the electrode geometry. However, the electrode’s base geometry significantly affects gas accumulation at the separator gap, independent of porosity. A foam electrode geometry resulted in the lowest gas coverage of all electrodes with a median volumetric gas coverage of 11%, but at the cost of a 70% reduction in active area compared with the largest surface area electrode, while gyroid electrodes showed the best trade-off between gas coverage, particularly at the separator surface, and electrochemically active area. In conclusion, the results highlight the need for holistic electrode design strategies.

Alkaline↗
DOE OSTI2021

Pretreatment of Biomass by Selected Type-III Deep Eutectic Solvents and Evaluation of the Pretreatment Effects on Hydrothermal Carbonization

Hydrothermal carbonization (HTC) is a novel thermochemical conversion that converts wet biomass into energy dense solid fuel. Residual moisture under subcritical conditions reacts with a lignin-cellulose-hemicellulose matrix with the major reactions being identified as dehydration and decarboxylation. Among other reaction parameters (e.g., temperature, time, pressure), biomass morphology often plays a key role in HTC. The hypothesis of this study was enhancing the porous structure of biomass without significantly affecting biopolymer composition would augment hydrothermal carbonization (HTC). To prove the hypothesis, two type-III deep eutectic solvents (DESs), namely choline chloride:urea (ChCl:Urea, 1:2 mol/mol) and methyltriphenylphosphonium bromide:ethylene glycol (MTPB:EG, 1:4 mol/mol), were studied to pretreat loblolly pine at room temperature and ambient pressure for 1 h. DES pretreatment shows swelling of the biomass, increasing the surface fiber-to-fiber gap length by 52% and 185% for ChCl:Urea and MPTB:EG pretreatments, respectively. The total pore volume remained intact (2.6 × 10 –3 cm 3 /g), although new small pores evolved, and existing pores were abated with DES pretreatment. Hydrochars prepared from DES pretreated loblolly pine showed a high O/C and H/C ratio resulting in a significant increase of energy content (up to 42%) and a decrease of mass yield (up to 50 wt %), indicating an enhancement of HTC severity due to the alteration of surface morphology by DES. Finally, a preliminary process economics revealed that integrated DES pretreatment-HTC would increase fixed capital investment but decrease the cost of operation and manufacturing than the standalone HTC process.

09 BIOMASS FUELS↗
DOE OSTI2016

Structural and magnetic analysis of Cu, Co substituted NiFe{sub 2}O{sub 4} thin films

In the present work we prepared NiFe{sub 2}O{sub 4}, Ni{sub 0.95}Cu{sub 0.05}Fe{sub 2}O{sub 4} and Ni{sub 0.94}Cu{sub 0.05}Co{sub 0.01} Fe{sub 2}O{sub 4} thin films by metallo-organic decomposition method (MOD) using spin coating technique. The thin films were analyzed by X-ray diffractometer (XRD) and Atomic force microscope (AFM) for structural studies. The XRD patterns confirmed the ferrite phase of thin films. From AFM, we analyzed surface morphology, calculated grain size (GS) and root mean square roughness (RMSR). Room temperature magnetic properties were investigated by vibrating sample magnetometer (VSM).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Bi2O2(OH)NO3/AgI heterojunction with enhanced UV and visible-light responsive photocatalytic activity and mechanism investigation

Highlights: • Bi{sub 2}O{sub 2}(OH)NO{sub 3}/AgI heterojunction is obtained by in-situ crystallization method. • It shows a higher degradation activity than Bi{sub 2}O{sub 2}(OH)NO{sub 3} and AgI under UV light. • It shows a higher catalytic activity than Bi{sub 2}O{sub 2}(OH)NO{sub 3} and AgI under visible light. • Enhanced charge separation is responsible for the enhanced degradation activity. - Abstract: Fabricating heterojunction between a wide-band-gap semiconductor and a narrow-band-gap semiconductor has become an important strategy to simultaneously improve the photoabsorption and charge separation. In this work, a new heterojunction photocatalyst Bi{sub 2}O{sub 2}(OH)NO{sub 3}/AgI was prepared through a facile in-situ crystallization method under ambient atmosphere. The crystal morphology, surface structure and element distribution were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) mapping and X-ray photoelectron spectroscopy (XPS). Compared with the pristine Bi{sub 2}O{sub 2}(OH)NO{sub 3} and AgI, Bi{sub 2}O{sub 2}(OH)NO{sub 3}/AgI shows much enhanced degradation performance for eliminating MO regardless of UV or visible light. Photocurrent, electrochemical impedance spectra (EIS) and photoluminescence (PL) demonstrated that the enhanced photocatalytic activity is ascribed to the greatly promoted charge separation and transfer resulted from the matchable band energy levels of Bi{sub 2}O{sub 2}(OH)NO{sub 3} and AgI, favoring the formation of heterojunction. In addition, according to the active species trapping experiment, the main active species are superoxide radicals (O{sub 2}{sup −}) and holes (h{sup +}) during the degradation process.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

TiO 2 Nanocoatings with Controllable Crystal Type and Nanoscale Topography on Zirconia Implants to Accelerate Bone Formation

In dentistry, zirconia implants have emerged as a promising alternative for replacing missing teeth due to their superior aesthetic performance and chemical stability. To improve the osseointegration of zirconia implants, modifying their surface with hierarchical micro/nanotopography and bioactive chemical composition are two effective ways. In this work, a microscale topography was prepared on a zirconia surface using hydrofluoric acid etching, and then a 50 nm TiO 2 nanocoating was deposited via atomic layer deposition (ALD). Subsequently, an annealing treatment was used to transform the TiO 2 from amorphous to anatase and simultaneously generate nanoscale topography. Various investigations into the coating surface morphology, topography, wettability, and chemical composition were carried out using scanning electron microscopy, white light interferometry, contact‐angle measurement, X‐ray diffraction, and X‐ray photoelectron spectroscopy. In addition, in vitro cytocompatibility and osteogenic potential performance of the coatings were evaluated by human bone marrow mesenchymal stem cells (hBMSCs), and in vivo osseointegration performance was assessed in a rat femoral condyle model. Moreover, the possible mechanism was also investigated. The deposition of TiO 2 film with/without annealing treatment did not alter the microscale roughness of the zirconia surface, whereas the nanotopography changed significantly after annealing. The in vitro studies revealed that the anatase TiO 2 coating with regular wavelike nanostructure could promote the adhesion and proliferation of osteoblasts and further improve the osteogenic potential in vitro and osseointegration in vivo. These positive effects may be caused by nanoscale topography via the canonical Wnt/ β ‐catenin pathway. The results suggest that using ALD in combination with annealing treatment to fabricate a nanotopographic TiO 2 coating is a promising way to improve the osteogenic properties of zirconia implants.

Li, Nan (ORCID:0000000255156737)↗
NASA NTRS2004

Lunar and Planetary Science XXXV: Asteroids, Meteors, and Comets

The session "Asteroids, Meteors, and Comets" contained the following reports:Ejecta Generation and Redistribution on 433 Eros: Modeling Ejecta Launch Conditions; Macroscopic Voids in Small Asteroids: Effects of Cohesion; The Seismic Effect of Impacts on Asteroid Surface Morphology: Early Modeling Results; Photometric Studies of Eros from NEAR Data; Quantitative Aspects of Space Weathering: Implications for Regolith Breccia Meteorites and Asteroids; Diversity of Types of Hydrated Minerals on C-Class Asteroids; Mineralogical Variations Among High Albedo E-Type Asteroids: Implications for Asteroid Igneous Processes; Multi-Wavelength Observations of 2100 Ra-Shalom: Radar and Lightcurves; What are the P-type Asteroids Made Of?; Sodium Overabundance in Meteoroids from Meteor Spectroscopy; Migration Processes and Volatiles Inventory to the Inner Planets; Characterization of the Surface Properties of MUSES-C/Hayabusa Spacecraft Target; Asteroid 25143 Itokawa; and Sample Return Science by Hayabusa Near-Earth Asteroid Mission.

Source record↗
DOE OSTI2012

Au-coated ZnO nanostructures for surface enhanced Raman spectroscopy applications

Thin ZnO nanostructured films were produced by pulsed laser deposition (PLD) for surface enhanced Raman spectroscopy (SERS) studies. The experimental conditions used for preparation of the samples were chosen to obtain different types of ZnO nanostructures. The Raman spectra of rhodamine 6G (R6G) were measured at an excitation wavelength of 785 nm after coating the ZnO nanostructures with a thin Au layer. The influence of the surface morphology on the Raman signal obtained from the samples was investigated. High SERS signal enhancement was observed from all Au-coated ZnO nanostructures.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

The growth of ubiquitous ZnO rods on PMMA-coated substrate by solution-immersion method at different annealing temperatures

In this work, solution-immersion method was used to grow ZnO rods on PMMA-coated substrate. For this purpose, 0.15 M of zinc nitrate hexahydrate (Zn(NO{sub 3}){sub 2}.6H{sub 2}O) and hexamethylenetetramine (C{sub 6}H{sub 12}N{sub 4}) were used to growth of ZnO films at different annealing temperatures (room temperature, 80, 100, 120 and 140 °C). The morphology of the films was investigated by Scanning Electron Microscope (SEM) and optical properties were studied by Ultraviolet (UV-Vis) Spectroscopy. SEM analysis showed ubiquitous growth of ZnO rods that became better aligned and more closely-packed as the annealing temperature increased. As the annealing temperature exceeds 100 °C, the rods tend to merge to adjacent particles and the UV absorption decreased for the sample at higher temperatures (120 °C and 140 °C). Good absorption and better orientation of ZnO was obtained for the sample annealed at 100 °C due to the film possess better distribution and these improved orientation of particles caused the light to be effectively scattered on the sample. Both surface morphology and UV was significantly affected by the change in annealing temperatures thus thermal effect played a dominant role in shaping and improving the orientation of ZnO rods on PMMA-coated and its UV absorption.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Effect of Surface Texture on Pinhole Formation in SiO x -Based Passivated Contacts for High-Performance Silicon Solar Cells

High-efficiency silicon solar cells rely on some form of passivating contact structure to reduce recombination losses at the crystalline silicon surface and losses at the metal/Si contact interface. One such structure is polycrystalline silicon (poly-Si) on oxide, where heavily doped poly-Si is deposited on a SiO x layer grown directly on the crystalline silicon (c-Si) wafer. Depending on the thickness of the SiO x layer, the charge carriers can cross this layer by tunneling (<2 nm SiO x thickness) or by direct conduction through disruptions in the SiOx, often referred to as pinholes, in thicker SiO x layers (>2 nm). In this work, we study structures with tunneling- or pinhole-like SiO x contacts grown on pyramidally textured c-Si wafers and expose variations in the SiOx layer properties related to surface morphology using electron-beam-induced current (EBIC) imaging. Using EBIC, we identify and mark regions with potential pinholes in the SiO x layer. We further perform high-resolution transmission electron microscopy on the same areas, thus allowing us to directly correlate locally enhanced carrier collection with variations in the structure of the SiO x layer. Our results show that the pinholes in the SiO x layer preferentially form in different locations based on the annealing conditions used to form the device. With greater understanding of these processes and by controlling the surface texture geometry, there is potential to control the size and spatial distribution of oxide disruptions in silicon solar cells with poly-Si on oxide-type contacts; usually, this is a random phenomenon on polished or planar surfaces. Such control will enable us to consistently produce high-efficiency devices with low recombination currents and low junction resistances using this contact structure.

14 SOLAR ENERGY↗