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All sourcesNASA NTRSDOE OSTI
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Variable Pressure - Scanning Electron Microscopy (VP-SEM)

Variable Pressure (or Environmental) Scanning Electron Microscopy (VP-SEM) combined with Energy Dispersive X-ray Spectroscopy (EDS) is one of the most powerful methods for characterizing the sub-micron topography and chemical composition of uncoated samples. Terrestrially, VP-SEM is extensively used to non-destructively study geologic and manufactured materials with high spatial resolution (tens of nanometers) and large depth-of-field. An SEM offers a geologist a first survey of microscopic mineral phases via secondary electron imaging (SEI), which provides a topographic look at a sample, as well as backscattered electron (BEI) imaging, which contrasts the phases present based on their geochemistry (atomic number). A VP-SEM utilizes a gas in the sample chamber as a charge dissipation and signal amplification method, allowing analysis of a sample without preparation in the form of a conductive coating. A miniaturized VP-SEM operating in-situ on a lander or rover would be able to use the CO2-rich Martian atmosphere (e.g., Nier et al., 1976; Williams 2016) as an imaging medium for this purpose. Adaptation of a VP-SEM for in-situ Mars surface studies will provide a new imaging capability (via SEI) that is at least an order of magnitude higher resolution than the Mars Hand Lens Imager (MAHLI) on the Mars Science Laboratory (Williams et al., 2015), and equal to or better than the achieved resolution of the Atomic Force Microscope on the Phoenix Mars lander (Pike et al., 2011). In addition, the MVP-SEM is capable of BSI and simultaneous chemical analysis of the imaged region. In this sense, the MVP-SEM can be regarded as an instrument suite that will provide a new set of information not achievable by any other instrument. The Miniaturized Variable Pressure Scanning Electron Microscope (MVP-SEM) was designed, built, and benchtop tested by a team at NASA’s Marshall Space Flight Center and Jet Propulsion Laboratory (JPL), Jacobs Space Exploration Group, Applied Physics Technologies, Inc. (AP-Tech), and Creare LLC, working with a team of technical and science collaborators. Benchtop testing was successful, proving concept feasibility. To date, the MVP-SEM has achieved an imaging resolution of <100 nm in the lab, and with continued optimization, even better performance (~50 nm resolution) is possible. Use in-situ on the lunar or other planetary surfaces would require some redesign to optimize instrument performance, but such an instrument would be equally useful.

Variable Pressure Scanning Electron Microscopy↗
NASA NTRSDate not supplied

Miniature Variable Pressure - Scanning Electron Microscopy (MVP-SEM)

Variable Pressure (or Environmental) Scanning Electron Microscopy (VP-SEM) combined with Energy Dispersive X-ray Spectroscopy (EDS) is one of the most powerful methods for characterizing the sub-micron topography and chemical composition of uncoated samples. Terrestrially, VP-SEM is extensively used to non-destructively study geologic and manufactured materials with high spatial resolution (tens of nanometers) and large depth-of-field. An SEM offers a geologist a first survey of microscopic mineral phases via secondary electron imaging (SEI), which provides a topographic look at a sample, as well as backscattered electron (BEI) imaging, which contrasts the phases present based on their geochemistry (atomic number). A VP-SEM utilizes a gas in the sample chamber as a charge dissipation and signal amplification method, allowing analysis of a sample without preparation in the form of a conductive coating. A miniaturized VP-SEM operating in-situ on a lander or rover would be able to use the CO2-rich Martian atmosphere (e.g., Nier et al., 1976; Williams 2016) as an imaging medium for this purpose. Adaptation of a VP-SEM for in-situ Mars surface studies will provide a new imaging capability (via SEI) that is at least an order of magnitude higher resolution than the Mars Hand Lens Imager (MAHLI) on the Mars Science Laboratory (Williams et al., 2015), and equal to or better than the achieved resolution of the Atomic Force Microscope on the Phoenix Mars lander (Pike et al., 2011). In addition, the MVP-SEM is capable of BSI and simultaneous chemical analysis of the imaged region. In this sense, the MVP-SEM can be regarded as an instrument suite that will provide a new set of information not achievable by any other instrument. The Miniaturized Variable Pressure Scanning Electron Microscope (MVP-SEM) was designed, built, and benchtop tested by a team at NASA’s Marshall Space Flight Center and Jet Propulsion Laboratory (JPL), Jacobs Space Exploration Group, Applied Physics Technologies, Inc. (AP-Tech), and Creare LLC, working with a team of technical and science collaborators. Benchtop testing was successful, proving concept feasibility. To date, the MVP-SEM has achieved an imaging resolution of <100 nm in the lab, and with continued optimization, even better performance (~50 nm resolution) is possible. Use in-situ on the lunar or other planetary surfaces would require some redesign to optimize instrument performance, but such an instrument would be equally useful.

Variable Pressure Scanning Electron Microscopy↗
DOE OSTI2015

Efficiency of inhibitor for biocorrosion influenced by consortium sulfate reducing bacteria on carbon steel

The inhibition efficiency of benzalkonium chloride (BKC) in controlling biocorrosion on the carbon steel surfaces has been investigated. The carbon steel coupons were incubated in the presence of consortium SRB (C-SRB) with and without BKC for the difference medium concentration. The corrosion rate and inhibition efficiency have been evaluated by a weight loss method. The morphology of biofilm C-SRB on the steel surfaces were characterized with variable pressure scanning electron microscopy (VPSEM). The results revealed that BKC exhibits a low corrosion rate, minimizing the cell growth and biofilm development on the carbon steel surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Crystallization of fused silica surfaces by ultra-violet laser irradiation

In recent years, the increased use of high power lasers has created problems in optical elements due to laser damage. The International Organization for Standardization (ISO) describes in a publication ISO 11254 a laser-power resilience (LPR) test which we used to verify that by flattening the glass substrate of an optical element, we could improve the resistance to laser damage. We report on an evaluation of two types of samples of fused silica substrate whose surface roughness differed (R{sub a} = 0.20 nm and R{sub a} = 0.13 nm) using customized on-line laser damage testing. To induce laser damage to samples, we used the fifth harmonic generation from a Nd:YAG pulse laser (wavelength: 213 nm, pulse width: 4 ns, repetition frequency: 20 Hz). Results show that flattening reduced the progression of laser damage in the meta-phase laser damage phase by 1/3 of that without flattening. However, pro-phase laser damage which started at fluence 2.39 J/cm{sup 2} was unrelated to surface roughness. To analyze the pro-phase laser damage, we used x-ray diffraction (XRD), Raman spectroscopy, and variable pressure-type scanning electron microscopy (VP-SEM). From XRD data, we observed XRD patterns of cristobalite (111), cristobalite (102), {alpha}-quartz (111), and {beta}-quartz (102). Raman spectrum data showed an increase in the three-membered ring vibration (600 cm{sup -1}), four-membered ring vibration (490 cm{sup -1}), and many-membered ring vibration (450 cm{sup -1}, 390 cm{sup -1}, and 300 cm{sup -1}). We observed patchy crystallized areas on the sample surfaces in the VP-SEM images. Based on these experimental results, we believe that the dominant factors in pro-phase laser damage are their physical properties. Substrate and thin film material must be appropriately selected in producing an optical element with a high level of resilience to laser exposure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Non-Centrosymmetric Sr 2 IrO 4 Obtained Under High Pressure

Sr 2 IrO 4 with strong spin-orbit coupling (SOC) and Hubbard repulsion (U) hosts Mott insulating states. The similar crystal structure, magnetic and electronic properties, particularly the d-wave gap observed in Sr 2 IrO 4 enhanced the analogies to cuprate high-$T_c$ superconductor, La 2 CuO 4 . The incomplete analogy was due to the lack of broken inversion symmetry phases observed in Sr 2 IrO 4 . Here, under high pressure and high temperature conditions, we report a non-centrosymmetric Sr 2 IrO 4 . The crystal structure and its noncentrosymmetric character were determined by single crystal X-ray diffraction and high-resolution scanning transmission electron microscopy (HR-STEM). The magnetic characterization confirms the Ir 4+ with $\textit{S}$ = 1/2 at low temperature in Sr 2 IrO 4 with magnetic ordering occurred at around 86 K, where a larger moment is observed than the ambient pressure Sr 2 IrO 4 . Moreover, the resistivity measurement shows three-dimensional Mott variable-range hopping existed in the system. Further, this non-centrosymmetric Sr 2 IrO 4 phase appears to be a unique material to offer further understanding of high-$T_c$ superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Properties of polycarbonate containing BaTiO{sub 3} nanoparticles

The real part of the relative permittivity, ε′, and dielectric loss, tan δ, have been determined at audio frequencies at temperatures from about 5 K to 350 K for nano-composites composed of BaTiO{sub 3} nanoparticles and polycarbonate. The room temperature breakdown strength was also measured and thermal analysis, nuclear magnetic resonance and scanning electron microscopy studies were carried out. For some films the nanoparticles were surface-treated (STNP) while for others they were not (UNP). For concentrations of UNP greater than about 3.4 vol. %, ε′ is much larger than expected on the basis of laws of mixing. On the other hand, ε′ for materials made using STNP is well-behaved. Correspondingly, increased loss (ε″ or tan δ) in the vicinity of room temperature is observed for the materials made from UNP. The anomalously large values of relative permittivity and increased loss are attributed to the presence of large aggregates in the materials made using the UNP. For both UNP-and STNP-based materials, the breakdown strength is found to decrease as nanoparticle concentration increases. The breakdown strength for the materials made using STNP is found to be larger for all concentrations than for those containing UNP despite the presence of large aggregates in some of the STNP-based materials. This shows that breakdown is strongly affected by the nanoparticle surfaces and/or the interface layer. It is also found that the breakdown strength for materials made using UNP increases as particle size increases. Finally, variable temperature and pressure proton nuclear magnetic resonance relaxation measurements were made to assess the effect of nanoparticle inclusion on polymer motion, and the effects were found to be very minor.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Vertical and lateral morphology effects on solar cell performance for a thiophene–quinoxaline copolymer:PC 70 BM blend

The distribution of electron donor and acceptor in the active layer is known to strongly influence the electrical performance of polymer solar cells for most of the high performance polymer:fullerene systems. The formulation of the solution from which the active layer is spincoated plays an important role in the quest for morphology control. We have studied how the choice of solvent and the use of small amounts of a low vapour pressure additive in the coating solution influence the film morphology and the solar cell performance for blends of poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) and [6,6]-phenyl C 71 -butyric acid methyl ester (PC 70 BM). We have investigated the lateral morphology using atomic force microscopy (AFM) and scanning transmission X-ray microscopy (STXM), the vertical morphology using dynamic secondary ion mass spectrometry (d-SIMS) and variable-angle spectroscopic ellipsometry (VASE), and the surface composition using near-edge X-ray absorption fine structure (NEXAFS). The lateral phase-separated domains observed in films spincoated from single solvents, increase in size with increasing solvent vapour pressure and decreasing PC 70 BM solubility, but are not observed when 1-chloronaphthalene (CN) is added. A strongly TQ1-enriched surface layer is formed in all TQ1:PC 70 BM blend films and rationalized by surface energy differences. The photocurrent and power conversion efficiency strongly increased upon the addition of CN, while the leakage current decreased by one to two orders of magnitude. The higher photocurrent correlates with the finer lateral structure and stronger TQ1-enrichment at the interface with the electron-collecting electrode. This indicates that the charge transport and collection are not hindered by this polymer-enriched surface layer. Neither the open-circuit voltage nor the series resistance of the devices are sensitive to the differences in morphology.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Evolution of eggshell structure in relation to nesting ecology in non-avian reptiles

Amniotic eggs are multifunctional structures that enabled early tetrapods to colonize the land millions of years ago, and are now the reproductive mode of over 70% of all terrestrial amniotes. Eggshell morphology is at the core of animal survival, mediating the interactions between embryos and their environment, and has evolved into a massive diversity of forms and functions in modern reptiles. These functions are critical to embryonic survival and may serve as models for new antimicrobial and/or breathable membranes. However, we still lack critical data on the basic structural and functional properties of eggs, particularly of reptiles. Here, we first characterized egg shape, shell thickness, porosity, and mineralization of eggs from 91 reptile species using optical images, scanning electron microscopy, and micro computed tomography, and collected data on nesting ecology from the literature. We then used comparative analyses to test hypotheses on the selective pressures driving their evolution. We hypothesized that eggshell morphology has evolved to protect shells from physical damage and desiccation, and, in support, found a positive relationship between thickness and precipitation, and a negative relationship between porosity and temperature. Although mineralization varied extensively, it was not correlated with nesting ecology variables. Ancestral state reconstructions show thinning and increased porosity over evolutionary time in squamates, but the opposite in turtles and crocodilians. Egg shape, size, porosity and calcification were correlated, suggesting potential structural or developmental tradeoffs. This study provides new data and insights into the morphology and evolution of reptile eggs, and raises numerous questions for additional research.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Influence of Oxygen Partial Pressure Variation on Oxidation Resistance of Ti-46.7Al-1.9W-0.5Si at 750, 850 and 950 °C

γ-TiAl intermetallic alloys can be potentially employed as structural materials for many industries where high temperature and access of atmosphere with variable oxygen partial pressures are often met. Different partial pressures of oxygen may influence oxidation behavior and induce different oxide scale phase constitutes. This study investigated the influences of oxygen partial pressures on the oxidation resistance of a γ-TiAl alloy, Ti-46.7Al-1.9W-0.5Si (at.%), in Ar-O{sub 2} environments (5%O{sub 2}, 20%O{sub 2} and 80%O{sub 2}) at 750, 850 and 950 °C, respectively. The oxidation products were characterized using scanning electron microscopy, energy-dispersive x-ray analysis, x-ray diffraction and transmission electron microscopy. The oxidation kinetic results achieved by a discontinuous gravimetric method revealed that the alloy oxidized following a parabolic rate law. The oxidation resistance of the alloy was enhanced with increasing the oxygen partial pressures at all three experimental temperatures. Multilayered oxide scales of TiO{sub 2}/Al{sub 2}O{sub 3} were developed during the oxidation process. The enhancement of oxidation resistance was resulted from preferential generation of Al{sub 2}O{sub 3} and the reduction in defects in TiO{sub 2} with increasing the oxygen partials pressures.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Exploring Polarization Rotation Phase Instabilities in Super-Tetragonal BiFeO3 Epitaxial Thin Films and Their Technological Implications

Many functional properties of ferroelectrics are underlain by structural instabilities, which render these materials very susceptible to small alternating applied fields (electric, mechanical, etc.) through certain constitutive coupling relations, e.g., elastic compliance and piezoelectric response, and often such instabilities can be shifted by static applied fields thus meaning tunable dynamic properties. Structural instabilities are naturally accommodated on the brink of morphotropic phase boundaries (MPB s) where multiple phases of small energy difference coexist in different crystallographic forms. Canonical MPB is realized through compositional mixture, as is typically exemplified by Pb(Zr1-xTix)O3 solid solutions and relaxor ferroelectrics of (1-x)PbMg1/3Nb2/3O3-xPbTiO3. More recently, a strain-driven MPB has been discovered in BiFeO3 (BFO) thin films epitaxially grown on LaAlO3 (LAO) crystal substrates (which imposes about -4.5% in-plane strains). Such an MPB is in between a rhombohedral (R) phase that bulk BFO exhibits and a so-called super-tetragonal (T) phase, which name hints at its giant lattice axial ratio (c/a ~ 1.23) and accordingly high electric polarization (~1.5 C m-2). The discovery of an MPB in BFO has revealed another facet of this multiferroic system, further adding opportunities to its many exotic functionalities such as domain wall conduction, magnetoelectric and photovoltaic effects As with other MPB s, large electric-field induced strains as well as more underlying lattice softening effects are observed near this MPB promising piezoelectric-based applications. In addition, T-phase BFO itself shows distinct properties, e.g., electronic band gap and optical absorption, from the R-phase and the resultant switching effects between them may also be exploitable. However, unlike conventional ferroelectric oxides where the phases across an MPB usually have subtle difference caused by rotations of an ion off-centering polarization, the BFO system bears multiple structural degrees of freedom, in particular antiferrodistortive modes of oxygen octahedral tilt, and a multitude of structural transition paths are thereby facilitated. Moreover, since the MPB of BFO is driven by epitaxial strain, it is sensitive to the strain relaxation related to film thickness and growth conditions, and above some critical thickness the films appear in the form of a hierarchical mixed-phase microstructure involving several coexistent polymorphs with distinct lattice distortion (monoclinic phases) and tilts. Elastic and electrical heterogeneities are necessary consequences of such complex microstructure, which couple to the intrinsic order parameters and expectedly have profound influence on the structural dynamics and material properties. All these make it a demanding task to obtain a deep understanding of this MPB system on par with its application prospect. The thin-film material form also brings in experimental restrictions to the MPB phase transition studies of BFO since many pertinent techniques fail to operate at the nanoscale or suffer from formidably weak signals. Therefore, static structural characterizations using e.g. X-ray diffraction, electron microscopy and Raman scattering have prevailed thus far. Recently, we adapted band-excitation piezoresponse spectroscopy (BEPS) to probe the bias-induced R/T phase transition dynamics of BFO/SrTiO3 (STO) thin films, and revealed the soft-mode elastic behavior of the transition. The efficacy of our method, along with standard piezoresponse force microscopy (PFM), can be significantly leveraged by integrating a variety of local and/or global excitations, e.g., tip pressure (10 s GPa attainable), heating, photo-irradiation, available to modern scanning probe platforms. This can thus afford unique opportunities to survey the structural dynamics of ferroelectric materials coupled to those field variables, enabling rapid discovery or validation of their functional properties. In this study, we focus on the T-phase BFO/LAO system; we have examined its phase transition behavior not only due to local coaction of tip bias and loading force, but also under device-level global electric fields in a coplanar capacitor. The intrinsic elastic softening phenomena near the structural transitions are comprehensively revealed by BEPS and corroborated by phase-field modeling. Our findings may open a new pathway for technological utilization of the MPB phase instabilities of BFO.

BiFeO3↗
DOE OSTI2014

Polymorphs calcium carbonate on temperature reaction

Calcium carbonate (CaCO{sub 3}) has three different crystal polymorphs, which are calcite, aragonite and vaterite. In this study, effect of reaction temperature on polymorphs and crystallite structure of CaCO{sub 3} was investigated. X-ray powder diffraction (XRD), fourier transform infrared (FTIR), and variable pressure scanning electron microscope (VPSEM) were used to characterize the obtained CaCO{sub 3} particles. The obtained results showed that CaCO{sub 3} with different crystal and particle structures can be formed by controlling the temperature during the synthesis process.

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

Microstructural analysis of recycled concrete using X-ray microtomography

This paper reports an investigation of the recycled concrete (RC) microstructure using synchrotron microtomography (μCT) at the Advanced Light Source combined with Scanning Electron Microscopy analysis. The study evaluated the influence of 50% of recycled concrete aggregate (RCA) and its water absorption compensation on the RC microstructure. The following variables were studied: a) the compressive strength of the original concrete used to obtain the RCA (40 and 80 MPa) and b) the initial moisture condition of the RCA (Saturated Surface Dry and Oven Dry). The microtomographic images showed the mixtures cast with RCA in the dry condition developed an evident macropore network surrounding the RCA particle that was not observed in the mixtures using RCA in the SSD condition. SEM images confirmed the initial findings from μCT and showed that the thickness of the interfacial transition zone in RC is in the same order of magnitude as the reference concrete.

36 MATERIALS SCIENCE↗
NASA NTRS2024

Experimental Studies on the Effect of Impact Processes on the Formation and Evolution of Amino Acids

Introduction: A critical step in the emergence of life on Earth was the synthesis of larger organic molecules from simple building blocks such as NH3, CO2, H2O, and CH3OH. The presence of amino acids and other complex organics in comets and meteorites demonstrates that widespread organic synthesis likely occurred across the early solar system. Building on previous work [e.g., 1-3], we systematically explore impact-driven chemical evolution of exogenous organics and their precursors. Collisional processes may also have provided a source of energy for the formation of more complex organics from endogenous building blocks. The high flux of impactors to Earth immediately prior to and during the origins of life suggests that impacts could have played a critical role. Key Questions: 1. How are the formation and evolution of amino acids affected by the presence of a mineral matrix during cometary and asteroidal impacts onto the early Earth? 2. Do some minerals (e.g., phyllosilicates) provide a more robust protective framework or reactive surface site for amino-acid formation and/or polymerization? 3. Does the abundance of ices and/or amino acids relative to that of the mineral matrix affect the formation and evolution of amino acids? 4. Are there impact velocities/shock pressures at which formation or polymerization of amino acids is favored or precluded? Experimental Approach: This study systematically examines the conditions under which amino acids and other organic molecules can form, be polymerized, and/or be destroyed during impact events into particulate regolith simulants. Variable parameters include the modal composition of this regolith (silicate matrices, ratios of ices, silicates, and amino acids) and impact velocities/shock pressures. Impacts experiments were performed using the two-stage light-gas gun (LGG), vertical gun (VG), and flat-plate accelerator (FPA) in the Experimental Impact Lab at JSC. FPA experiments were performed over a range of shock pressures (11.3-31.5 GPa) using CM chondrite simulant mixed with amino acids at ratios of 0:10, 1:10, 1:103, and 1:106 (amino acid:host). Techniques for mixing cometary ices have been optimized and test runs have been performed using the LGG (see figure below). Analysis: Post-impact, samples are heated in water to extract amino acids and peptides. Extracts are characterized via liquid chromatography-mass spectrometry (LC-MS) and the mineralogies of solid residues are characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Additional LC-MS and mineralogical analyses are underway.

Eve L Berger↗
DOE OSTI2025

Overcoming Variability: A Reproducible Approach to SERS Detection of Nanodiamonds

Detonation nanodiamonds (DNDs) are formed at specific pressures and temperatures during explosions. Different explosives produce varied yields of DNDs within their detonation soot, with Composition B producing the highest yield. Raman spectroscopy (RS) is often used for the characterization of sp 2 - and sp 3 -hybridized carbon allotropes in carbonaceous materials because of distinct disorder and graphitic bands. Bulk diamond also gives a distinct Raman peak at 1332 cm –1 . Furthermore, as bulk diamond decreases in size to nanometer-sized species, the peak red-shifts and broadens, becoming increasingly difficult to detect with RS using visible excitations. Therefore, surface-enhanced Raman spectroscopy (SERS) was used to enhance the diamond peak of DNDs, enabling better detection and faster examination of DNDs within detonation soot. Previous literature of the SERS of DNDs delivered inconsistent results in spectral signatures and SERS substrates. Herein, refining of the methodology for the acquisition of SERS spectra of DNDs was achieved. Before any SERS experiments, the DNDs were first characterized with normal Raman (NR) and scanning electron microscopy. Two routes for SERS enhancement were evaluated: colloidal noble metal nanoparticles and evaporated silver films. Silver films produced the best signal enhancement of DNDs with the best signal-to-noise and peak enhancements observed at 20–30 nm thick silver films at 5% (∼300 μW) laser power. Consistent, reproducible SERS spectra were acquired of small aggregates of DNDs down to ∼500 nm. NR and SERS mapping analysis of DNDs before and after evaporation of silver films revealed the improvements in the detection capabilities of SERS compared with NR.

Carbon↗
DOE OSTI2013

Deposition and characterization of molybdenum thin films using dc-plasma magnetron sputtering

Molebdenum (Mo) thin films were deposited on well-cleaned soda-lime glass substrates using DC-plasma magnetron sputtering. In the design of experiment deposition was optimized for maximum beneficial characteristics by monitoring effect of process variables such as deposition power (100–200 W). Their electrical, structural and morphological properties were analyzed to study the effect of these variables. The electrical resistivity of Mo thin films could be reduced by increasing deposition power. Within the range of analyzed deposition power, Mo thin films showed a mono crystalline nature and the crystallites were found to have an orientation along [110] direction. The surface morphology of thin films showed that a highly dense micro structure has been obtained. The surface roughness of films increased with deposition power. The adhesion of Mo thin films could be improved by increasing the deposition power. Atomic force microscopy was used for the topographical study of the films and to determine the roughness of the films. X-ray diffractrometer and scanning electron microscopy analysis were used to investigate the crystallinity and surface morphology of the films. Hall effect measurement system was used to find resistivity, carrier mobility and carrier density of deposited films. The adhesion test was performed using scotch hatch tape adhesion test. Mo thin films prepared at deposition power of 200 W, substrate temperature of 23°C and Ar pressure of 0.0123 mbar exhibited a mono crystalline structure with an orientation along (110) direction, thickness of ∼550 nm and electrical resistivity value of 0.57 × 10{sup −4} Ω cm.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Development of an in situ ion irradiation scanning electron microscope

An in situ ion irradiation scanning electron microscope (I 3 SEM) has been developed, installed, and integrated into the Ion Beam Laboratory at Sandia National Laboratories. The I 3 SEM facility combines a field emission, variable pressure, scanning electron microscope, a 6 MV tandem accelerator, high flux low energy ion source, an 808 nm-wavelength laser, and multiple stages to control the thermal and mechanical state of the sample observed. The facility advances real-time understanding of materials evolution under combined environments at the mesoscale. As highlighted in multiple examples, this unique combination of tools is optimized for studying mesoscale material response in overlapping extreme environments, allowing for simultaneous ion irradiation, implantation, laser bombardment, conductive heating, cooling, and mechanical deformation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Tribological Performance of Duplex-Annealed Ti-6Al-2Sn-4Zr-2Mo Titanium Alloy at Elevated Temperatures Under Dry Sliding Condition

Ti-6Al-2Sn-4Zr-2Mo (Ti-6-2-4-2) is a typical near-α titanium alloy developed for high-temperature applications. It offers numerous enhanced properties like an outstanding strength-to-weight ratio, a low Young’s modulus and exceptional creep and corrosion resistance. On the other hand, titanium alloys are known for their weak resistance to wear. Ti-6-2-4-2 is mainly applied in aero engine component parts, which are exposed to temperatures up to 565 °C. Through an increasing demand on efficiency, engine components are exposed to higher combustion pressures and temperatures. Elevated temperature tribology tests were conducted on a pin-on-disk tribometer equipped with a heating chamber. The tests were carried out under dry conditions with a constant sliding distance of 600 m with a speed of 0.16 m/s at the ball point. The sliding partner was AISI E52100 steel ball with the hardness of 58HRC. The varied input variables are normal load and temperature. It can be concluded that the coefficient of friction (CoF) increases with increasing temperature, while the wear rate decreases to its minimum at 600 °C due to increasing adhesion and oxidation mechanisms. Wear track observations using a scanning electron microscope (SEM) including energy-dispersive x-ray spectroscopy (EDS) were used to determine the occurring wear mechanisms.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Probabilistic Analysis of Long-Term Degradation of Microwave Cavity Flow Sensor

We are investigating a microwave resonant cavity transducer for flow sensing in the vessel of a high temperature fluid advanced reactor (AR), such as a molten salt cooled reactor (MSCR) or a sodium fast reactor (SFR). This transducer is a hollow metallic cylindrical cavity, with the flat wall of the cylinder flexible enough to undergo microscopic deflection due to dynamic fluid pressure. Membrane deflection leads to a shift in the resonant frequency, which can be detected with a spectrum analyzer. We have performed a proof-of-concept experiment of flow sensing with the transducer in liquid sodium at 340°C in impinging liquid jet geometry. The transducer remained in liquid sodium for 70 days. After removal, no structural damage was observed, and the expected transducer response was verified in a water test. Because long-term (multi-year) experimental tests of transducer resilience to harsh environment are not practical, we have developed a probabilistic model of creep to estimate transducer resilience to the harsh environment. The probabilistic model considers diffusion creep under the condition of high temperature and low stress, where the stress and temperature are allowed to be random variables with Gaussian distributions. Using the probabilistic model, we estimate inelastic membrane deflections due to creep for several temperature ranges. We conclude that for temperatures less than 650°C, creep has negligible long-term effect on the transducer performance. Since a yellowish residue was observed on the transducer surface after 70 days of immersion in liquid sodium, we have investigated possible evidence of corrosion. Chromium depletion is a typical indicator of the corrosion process in stainless steel. Scraping off a residue from the transducer and performing scanning electron microscopy (SEM) with energy dispersive analysis (EDS) did not find any chromium in the residue. Approximately 60% of the residue consisted of copper, which can be attributed to contamination of sodium due to powder residue from machining of copper and brass components of the transducer.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗