Search NASA⌕ Search

SEARCH · Search NASA

Results for “Surface structures”

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 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Laser-Generated Proton Beams for High-Precision Ultra-Fast Crystal Synthesis

We present a method for the synthesis of micro-crystals and micro-structured surfaces using laser-accelerated protons. In this method, a solid surface material having a low melting temperature is irradiated with very-short laser-generated protons, provoking in the ablation process thermodynamic conditions that are between the boiling and the critical point. The intense and very quick proton energy deposition (in the ns range) induces an explosive boiling and produces microcrystals that nucleate in a plasma plume composed by ions and atoms detached from the laser-irradiated surface. The synthesized particles in the plasma plume are then deposited onto a cold neighboring, non-irradiated, solid secondary surface. We experimentally verify the synthesizing methods by depositing low-melting-material microcrystals - such as gold - onto nearby silver surfaces and modeling the proton/matter interaction via a Monte Carlo code, confirming that we are in the above described thermodynamic conditions. Morphological and crystallinity measurements indicate the formation of gold octahedral crystals with dimensions around 1.2 μm, uniformly distributed onto a silver surface with dimensions in the tens of mm 2 . This laser-accelerated particle based synthesis method paves the way for the development of new material synthesis using ultrashort laser-accelerated particle beams.

Science & Technology - Other Topics↗
DOE OSTI2023

Synthesis of a novel multifunctional organic–inorganic nanocomposite for metal ions and organic dye removals

In this study, we used solvent assisted mechano-synthesis strategies to form multifunctional organic–inorganic nanocomposites capable of removing both organic and inorganic contaminants. A zeolite X (Ze) and activated carbon (AC) composite was synthesized via state-of-the-art mechanical mixing in the presence of few drops of water to form Ze/AC. The second composite (Ze/L/AC) was synthesized in a similar fashion, however this composite had the addition of disodium terephthalate as a linker. Both materials, Ze/AC and Ze/L/AC, were characterized using scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), Powdered X-ray diffraction (P-XRD), Fourier-transform infrared spectrometry (FTIR), Accelerated Surface Area and Porosimetry System (ASAP), and thermal gravimetric analysis (TGA). The SEM–EDS displayed the surface structure and composition of each material. The sodium, oxygen and carbon contents increased after linker connected Ze and AC. The P-XRD confirmed the crystallinity of each material as well as the composites, while FTIR indicated the function groups (C=C, O–H) in Ze/L/AC. The contaminant adsorption experiments investigated the effects of pH, temperature, and ionic strength on the adsorption of methylene blue (MB) and Co(II) for each material. In MB adsorption, the first-order reaction rate of Ze/L/AC (0.02 h -1 ) was double that of Ze/AC (0.01 h -1 ). The reaction rate of Ze/L/AC (4.8 h -1 ) was also extraordinarily higher than that of Ze/AC (0.6 h -1 ) in the adsorption of Co(II). Ze/L/AC composite achieved a maximum adsorption capacity of 44.8 mg/g for MB and 66.6 mg/g for Co(II) ions. The MB adsorption of Ze/AC and Ze/L/AC was best fit in Freundlich model with R 2 of 0.96 and 0.97, respectively, which indicated the multilayer adsorption. In the Co(II) adsorption, the data was highly fit in Langmuir model with R 2 of 0.94 and 0.92 which indicated the monolayer adsorption. These results indicated both materials exhibited chemisorption. The activation energy of Ze/L/AC in MB adsorption (34.9 kJ mol -1 ) was higher than that of Ze/L/AC in Co (II) adsorption (26 kJ mol -1 ).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Identification of Au–S complexes on Au(100)

In this study, using a combination of scanning tunneling microscopy and density functional theory (DFT) calculations, we have identified a set of related Au–S complexes that form on Au(100), when sulfur adsorbs and lifts the hexagonal surface reconstruction. The predominant complex is diamond-shaped with stoichiometry Au 4 S 5 . All of the complexes can be regarded as combinations of S–Au–S subunits. The complexes exist within, or at the edges of, p(2 × 2) sulfur islands that cover the unreconstructed Au regions, and are observed throughout the range of S coverage examined in this study, 0.009 to 0.12 monolayers. A qualitative model is developed which incorporates competitive formation of complexes, Au rafts, and p(2 × 2) sulfur islands, as Au atoms are released by the surface structure transformation.

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

Dissolution, migration, and deposition of transition metal ions in Li-ion batteries exemplified by Mn-based cathodes – a critical review

Unlike the revolutionary advances in the anodes of lithium-ion batteries from Li intercalation materials to Li alloy and/or conversion reaction materials, the development of the cathode is still dominated by the Li intercalation compounds. Transition metal ions are essential in these cathodes as the rapid redox reaction centers, and one of the biggest challenges for the TM-based cathodes is the capacity and power fading especially at an elevated temperature, which is directly associated with the dissolution–migration–deposition (DMD) process of TMs from the cathode materials. This process not only alters the surface structure of the cathode materials, but more importantly, changes the SEI composition at the anode side. There is no doubt that the TM-DMD issue should be addressed thoroughly to unlock the potential of these compounds to enable a prolonged battery lifetime. This review article mainly focuses on research activities with regard to the DMD process in TM-based cathode materials. In the first four sections, we choose Mn-based cathodes as an example to discuss how Mn DMD relates to the capacity fade of the cell, and what possible approaches might suppress the DMD process by modification of the electrode or electrolyte. In the fifth section, we discuss the TM DMD process in Ni-, Co-, Fe- and V-containing cathode materials. Furthermore, this article reviews the frontier electrochemical research on TM-based cathodes and summarizes the progress and challenges, thereby helping to advance future R&D of LIBs.

25 ENERGY STORAGE↗
DOE OSTI2019

Crystalline Nickel, Cobalt, and Manganese Antimonates as Electrocatalysts for the Chlorine Evolution Reaction

The chlorine-evolution reaction (CER) is a common, commercially valuable electrochemical reaction, and is practiced at industrial scale globally. A precious metal solid solution of RuO 2 or IrO 2 with TiO 2 is the predominant electrocatalyst for the CER. Herein we report that materials comprised only of non-precious metal elements, specifically crystalline transition-metal antimonates (TMAs) such as NiSb 2 O x , CoSb 2 O x , and MnSb 2 O x , are moderately active, stable catalysts for the electrochemical oxidation of chloride to chlorine under conditions relevant to the commercial chlor-alkali process. Specifically, CoSb2Ox exhibited a galvanostatic potential of 1.804 V vs. NHE at 100 mA cm –2 of Cl 2 (g) production from aqueous pH = 2.0, 4.0 M NaCl after 250 h of operation. In this work, studies of the bulk and surface of the electrocatalyst and the composition of the electrolyte before and after electrolysis indicated minimal changes in the surface structure and intrinsic activity of CoSb 2 O x as a result of Cl 2 (g) evolution under these conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

The role of atomic carbon in directing electrochemical CO (2) reduction to multicarbon products

Electrochemical reduction of carbon-dioxide/carbon-monoxide (CO (2) R) to fuels and chemicals presents an attractive approach for sustainable chemical synthesis, but it also poses a serious challenge in catalysis. Understanding the key aspects that guide CO (2) R towards value-added multicarbon (C 2+ ) products is imperative in designing an efficient catalyst. Herein, we identify the critical steps toward C 2 products on copper through a combination of energetics from density functional theory and micro-kinetic modeling. We elucidate the importance of atomic carbon in directing C 2+ selectivity and how it introduces surface structural sensitivity on copper catalysts. Overall, this insight enables us to propose two simple thermodynamic descriptors that effectively identify C 2+ selectivity on metal catalysts beyond copper and hence it defines an intelligible protocol to screen for materials that selectively catalyze CO (2) to C 2+ products.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

A mathematical model of solid-state dewetting of barium thin films on W (112)

Solid state dewetting occurs when a thin solid film is heated. The temperature of dewetting depends on the thickness of the film; dewetting can be observed in the range of 1/3 to 1/2 of the bulk melting temperature. While remaining solid, the film behaves in a manner similar to liquids dewetting and agglomerating to forming islands or droplets. One of the possible mechanisms is the conversion of a metastable thin film geometry into a more stable form. Heating the metastable film gives the film atoms higher mobility, and the films retract, dewetting the surface. This atomic motion can be restricted due to surface anisotropy. Herein we present in situ emission microscopy observations of barium thin films deposited onto W (112) by thermal evaporation. From the modeling viewpoint, the evolution of the film in this system could be divided in four stages: (i) the nucleation and growth of the thin film as a simply connected region; (ii) formation of droplets/islands/hillocks; (iii) nucleation of holes; (iv) evolution of the components of the disconnected film to their equilibrium state. We present a continuum model that is qualitatively consistent with the evolution of the film observed at the initial stage of the experiment and discuss the later stages of the evolution of surface structures.

36 MATERIALS SCIENCE↗
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

Size effect on transfection and cytotoxicity of nanoscale plasmid DNA/polyethyleneimine complexes for aerosol gene delivery

Nanoscale plasmid DNA (pDNA)/polyethyleneimine (PEI) complexes were fabricated in the aerosol state using a nebulization system consisting of a collison atomizer and a cool-walled diffusion dryer. The aerosol fabricated nanoscale complexes were collected and employed to determine fundamental properties of the complexes, such as size, structure, surface charge, and in vitro gene transfection efficiency and cytotoxicity. The results showed that mass ratio between pDNA and PEI should be optimized to enhance gene transfection efficiency without a significant loss of cell viability. These findings may support practical advancements in the field of nonviral gene delivery.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Jumping-droplet electrostatic energy harvesting

Micro- and nanoscale wetting phenomena have been an active area of research due to its potential for improving engineered system performance involving phase change. With the recent advancements in micro/nanofabrication techniques, structured surfaces can now be designed to allow condensing coalesced droplets to spontaneously jump off the surface due to the conversion of excess surface energy into kinetic energy. In addition to being removed at micrometric length scales (~10 μm), jumping water droplets also attain a positive electrostatic charge (~10–100 fC) from the hydrophobic coating/condensate interaction. In this work, we take advantage of this droplet charging to demonstrate jumping-droplet electrostatic energy harvesting. The charged droplets jump between superhydrophobic copper oxide and hydrophilic copper surfaces to create an electrostatic potential and generate power during formation of atmospheric dew. We demonstrated power densities of ~15 pW/cm 2 , which, in the near term, can be improved to ~1 $μ$W/cm 2 . This work demonstrates a surface engineered platform that promises to be low cost and scalable for atmospheric energy harvesting and electric power generation.

42 ENGINEERING↗
DOE OSTI2015

Equivalent ambipolar carrier injection of electrons and holes with Au electrodes in air-stable field effect transistors

Carrier injection from Au electrodes to organic thin-film active layers can be greatly improved for both electrons and holes by nano-structural surface control of organic semiconducting thin films using long-chain aliphatic molecules on a SiO{sub 2} gate insulator. In this paper, we demonstrate a stark contrast for a 2,5-bis(4-biphenylyl)bithiophene (BP2T) active semiconducting layer grown on a modified SiO{sub 2} dielectric gate insulator between two different modifications of tetratetracontane and poly(methyl methacrylate) thin films. Important evidence that the field effect transistor (FET) characteristics are independent of electrode metals with different work functions is given by the observation of a conversion of the metal-semiconductor contact from the Schottky limit to the Bardeen limit. An air-stable light emitting FET with an Au electrode is demonstrated.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Investigation of micro-structure and micro-hardness properties of 304L stainless steel treated in a hot cathode arc discharge plasma

We have established a hot cathode arc discharge plasma system, where different stainless steel samples can be treated by monitoring the plasma parameters and nitriding parameters independently. In the present work, a mixture of 70% N{sub 2} and 30% H{sub 2} gases was fed into the plasma chamber and the treatment time and substrate temperature were optimized for treating 304L Stainless Steel samples. Various physical techniques such as x-ray diffraction, energy dispersive x-ray spectroscopy and micro-vickers hardness tester were employed to determine the structural, surface composition and surface hardness of the treated samples.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Studies on linear, nonlinear optical and excited state dynamics of silicon nanoparticles prepared by picosecond laser ablation

We report results from our studies on the fabrication and characterization of silicon (Si) nanoparticles (NPs) and nanostructures (NSs) achieved through the ablation of Si target in four different liquids using ∼2 picosecond (ps) pulses. The consequence of using different liquid media on the ablation of Si target was investigated by studying the surface morphology along with material composition of Si based NPs. The recorded mean sizes of these NPs were ∼9.5 nm, ∼37 nm, ∼45 nm and ∼42 nm obtained in acetone, water, dichloromethane (DCM) and chloroform, respectively. The generated NPs were characterized by selected area electron diffraction (SAED), high resolution transmission microscopy (HRTEM), Raman spectroscopic techniques and Photoluminescence (PL) studies. SAED, HRTEM and Raman spectroscopy data confirmed that the material composition was Si NPs in acetone, Si/SiO{sub 2} NPs in water, Si-C NPs in DCM and Si-C NPs in chloroform and all of them were confirmed to be polycrystalline in nature. Surface morphological information of the fabricated Si substrates was obtained using the field emission scanning electron microscopic (FESEM) technique. FESEM data revealed the formation of laser induced periodic surface structures (LIPSS) for the case of ablation in acetone and water while random NSs were observed for the case of ablation in DCM and chloroform. Femtosecond (fs) nonlinear optical properties and excited state dynamics of these colloidal Si NPs were investigated using the Z-scan and pump-probe techniques with ∼150 fs (100 MHz) and ∼70 fs (1 kHz) laser pulses, respectively. The fs pump-probe data obtained at 600 nm consisted of single and double exponential decays which were tentatively assigned to electron-electron collisional relaxation (<1 ps) and non-radiative transitions (>1 ps). Large third order optical nonlinearities (∼10{sup −14} e.s.u.) for these colloids have been estimated from Z-scan data at an excitation wavelength of 680 nm suggesting that the colloidal Si NPs find potential applications in photonic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2016

ZnS nanostructured thin-films deposited by successive ionic layer adsorption and reaction

ZnS thin films were grown on glass substrate using successive ionic layer adsorption and reaction (SILAR) technique at room temperature. Aqueous solutions of ZnCl{sub 2} and Na{sub 2}S were used as precursors. The X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Raman spectroscopy and optical absorption measurements were applied to study the structural, surface morphology and optical properties of as-deposited ZnS thin films. The X-ray diffraction profiles revealed that ZnS thin films consist of crystalline grains with cubic phase. Spherical nano grains of random size and well covered on the glass substrate were observed from FESEM. The average grain size were found to be 77 nm, 100 nm and 124 nm for 20 cycles, 40 cycles and 60 cycles samples respectively. For 60 cycle sample, Raman spectra show two prominent peaks at 554 cm{sup −1} and 1094 cm{sup −1}. The optical band gap values were found to be 3.76 eV, 3.72 eV and 3.67 eV for 20 cycle, 40 cycle and 60 cycle samples respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Amorphous indium gallium zinc oxide thin film grown by pulse laser deposition technique

Highly electrically conducting and transparent in visible light IGZO thin film were grown on glass substrate at substrate temperature of 400 C by a pulse laser deposition techniques. Structural, surface, electrical, and optical properties of IGZO thin films were investigated at room temperature. Smooth surface morphology and amorphous nature of the film has been confirmed from the AFM and GIXRD analysis. A resistivity down to 7.7×10{sup −3} V cm was reproducibly obtained while maintaining optical transmission exceeding 70% at wavelengths from 340 to 780 nm. The carrier densities of the film was obtain to the value 1.9×10{sup 18} cm{sup 3}, while the Hall mobility of the IGZO thin film was 16 cm{sup 2} V{sup −1}S{sup −1}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Growth and passivation of individual carbon nanoparticles by C2H2 addition at high temperatures: Dependence of growth rate and evolution on material and size

Absolute kinetics for reactions of C2H2 with a series of ∼60 individual carbon nanoparticles (NPs) from graphite, graphene, graphene oxide, carbon black, diamond, and nano-onion feedstocks were measured for temperatures (TNP) ranging from 1200 to 1700 K. All the NPs were observed to gain mass by carbon addition under conditions that varied with feedstock but with large variations in initial growth rate. Long reaction periods were studied to allow the evolution of growth rates over time to be observed. Diamond NPs were found to passivate against C2H2 addition if heated above ∼1400 K, and the highly variable initial reactivity for carbon nano-onions was found to depend on the presence of non-onion-structure surface carbon. For graphitic and carbon black NPs, three distinct growth modes were observed, correlated with the initial NP mass (Minitial). Smallest graphitic and carbon black NPs, with masses <∼25 MDa, initially grew rapidly but also passivated quickly after adding <4% of Minitial. NPs in the 20–50 MDa range also passivated but only after multiple waves of fast growth separated by periods of low reactivity, with up to ∼11% total mass gain before passivation. The largest carbon black and graphitic NPs, with Minitial >50 MDa, grew rapidly and continuously, adding up to ∼300% of Minitial with no sign of rate slowing as long as C2H2 was present. The efficiencies for C2H2 addition and etching by O2 are strongly correlated, but the correlation changes as the NPs passivate. Growth and passivation mechanisms are discussed.

Chemistry↗
DOE OSTI2024

Matrix-formation dynamics dictate methyl nitrite conformer abundance

Methyl nitrite has two stable conformational isomers resulting from rotation about the primary C–O–N–O dihedral angle: cis-CH 3 ONO and trans-CH 3 ONO, with cis being more stable by ∼5 kJ/mol. Here, the barrier to rotational interconversion (∼45 kJ/mol) is too large for isomerization to occur under ambient conditions. This paper presents evidence of a change in conformer abundance when dilute CH 3 ONO is deposited onto a cold substrate; the relative population of the freshly deposited cis conformer is seen to increase compared to its gas-phase abundance, measured by in situ infrared spectroscopy. We observe abundance changes depending on the identity of the bath gas (N 2 , Ar, and Xe) and deposition angle. The observations indicate that the surface properties of the growing matrix influence conformer abundance—contrary to the widely held assumption that conformer abundance in matrices reflects gas-phase abundance. We posit that differences in the angle-dependent host-gas deposition dynamics affect the growing surfaces, causing changes in conformer abundances. Quantum chemistry calculations of the binding energies between CH 3 ONO and a single bath-gas component reveal that significant energetic stabilization is not observed in 1:1 complexes of N 2 :CH 3 ONO, Ar:CH 3 ONO, or Xe:CH 3 ONO. From our results, we conclude that the growing surface plays a significant role in trapping cis-CH 3 ONO more effectively than trans-CH 3 ONO, likely because cis-CH 3 ONO is more compact. Taken together, the observations highlight the necessity for careful characterization of conformers in matrix-isolated systems, emphasizing a need for further study into the deposition dynamics and surface structure of chemically inert matrices.

Hockey, Emily K.↗
DOE OSTI2015

Deposition of zinc films by laser method

Conditions of laser irradiation of a zinc target under which large droplets of a laser target material are not formed in the erosion plume are found, and zinc nanofilms with a minimum number of large particles on the surface are produced. The surface structure, thickness and optical characteristics of zinc films are determined as functions of the power density of laser radiation falling on a zinc target. The evaporation threshold for a zinc target irradiated by nanosecond laser pulses is found. (laser technologies)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗