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Using the two-modulator generalized ellipsometry microscope (2-MGEM), it is shown that it is possible to determine the direction of the optic axis of crystallites of the high birefringence materials calcite and dolomite. 2-MGEM measurements are performed in reflection at near-normal incidence, so sample preparation requires only an optically polished surface. For uniaxial materials, the 2-MGEM measures the direction of the fast axis and the diattenuation, which can then be related to the tilt angle of the optic axis with respect to the surface normal once the maximum diattenuation is known. The optical resolution of the present instrument is 4-6 μm, and areas as large as 1 cm2 can be measured without distortion. Additionally, the 2-MGEM measures the depolarization, which is a measure of the quality of the data. Using this information, an optical pole figure can be determined. The 2-MGEM results are compared with electron backscatter diffraction (EBSD) measurements on the same samples. Additional standard spectroscopic generalized ellipsometry measurements at a large angle of incidence were performed on single crystal calcite and dolomite to determine the spectroscopic ordinary and extraordinary refractive indices from 220 nm to 850 nm from which the maximum diattenuation can be determined.Using the two-modulator generalized ellipsometry microscope (2-MGEM), it is shown that it is possible to determine the direction of the optic axis of crystallites of the high birefringence materials calcite and dolomite. 2-MGEM measurements are performed in reflection at near-normal incidence, so sample preparation requires only an optically polished surface. For uniaxial materials, the 2-MGEM measures the direction of the fast axis and the diattenuation, which can then be related to the tilt angle of the optic axis with respect to the surface normal once the maximum diattenuation is known. The optical resolution of the present instrument is 4-6 μm, and areas as large as 1 cm2 can be measured without distortion. Additionally, the 2-MGEM measures the depolarization, which is a measure of the quality of the data. Using this information, an optical pole figure can be determined. The 2-MGEM results are compared with electron backscatter diffraction (EBSD) measurements on the same samples. Additional standard ...

The application of spectrum imaging multivariate statistical analysis methods, specifically principal component analysis (PCA), to atom probe tomography (APT) data has been investigated. The mathematical method of analysis is described and the results for two example datasets are analyzed and presented. The first dataset is from the analysis of a PM 2000 Fe-Cr-Al-Ti steel containing two different ultrafine precipitate populations. PCA properly describes the matrix and precipitate phases in a simple and intuitive manner. A second APT example is from the analysis of an irradiated reactor pressure vessel steel. Fine, nm-scale Cu-enriched precipitates having a core-shell structure were identified and qualitatively described by PCA. Advantages, disadvantages, and future prospects for implementing these data analysis methodologies for APT datasets, particularly with regard to quantitative analysis, are also discussed.

Erbium metal thin-films have been deposited on molybdenum-on-silicon substrates and then converted to erbium dideuteride (ErD{sub 2}). Here, we study the effects of deposition temperature ({approx}300 or 723 K) and deposition rate (1 or 20 nm/s) upon the initial Er metal microstructure and subsequent ErD{sub 2} microstructure. We find that low deposition temperature and low deposition rate lead to small Er metal grain sizes, and high deposition temperature and deposition rate led to larger Er metal grain sizes, consistent with published models of metal thin-film growth. ErD{sub 2} grain sizes are strongly influenced by the prior-metal grain size, with small metal grains leading to large ErD{sub 2} grains. A novel sample preparation technique for electron backscatter diffraction of air-sensitive ErD{sub 2} was developed, and allowed the quantitative measurement of ErD{sub 2} grain size and crystallographic texture. Finer-grained ErD{sub 2} showed a strong (1 1 1) fiber texture, whereas larger grained ErD{sub 2} had only weak texture. We hypothesize that this inverse correlation may arise from improved hydrogen diffusion kinetics in the more defective fine-grained metal structure or due to improved nucleation in the textured large-grain Er.

In this article, we use simulated and experimental data to explore how three operator-controllable parameters—(1) signal level, (2) detector resolution, and (3) number of factors chosen for analysis—affect quantitative analyses of scanning transmission electron microscopy–energy dispersive X-ray spectroscopy spectrum images processed by principal component analysis (PCA). We find that improvements in both signal level and detector resolution improve the precision of quantitative analyses, but that signal level is the most important. We also find that if the rank of the PCA solution is not chosen properly, it may be possible to improperly fit the underlying data and degrade the accuracy of results. Additionally, precision is degraded in the case when too many factors are included in the model.

Spectrum imaging (SI) methods are displacing traditional spot analyses as the predominant paradigm for spectroscopic analysis with electron beam instrumentation. The multivariate nature of SI provides clear advantages for qualitative analysis of multiphase specimens relative to traditional gray-scale images acquired with non-spectroscopic signals, where different phases with similar average atomic number may exhibit the same intensity. However, with the improvement in qualitative analysis with the SI paradigm has come a decline in the quantitative analysis of the phases thus identified, since the spectra from individual pixels typically have insufficient counting statistics for proper quantification. The present paper outlines a methodology for quantitative analysis within the spectral imaging paradigm, which is illustrated through X-ray energy-dispersive spectroscopy (EDS) of a multiphase (Pb,La)(Zr,Ti)O 3 ceramic in scanning transmission electron microscopy (STEM). Statistical analysis of STEM-EDS SI is shown to identify the number of distinct phases in the analyzed specimen and to provide better segmentation than the STEM high-angle annular dark-field (HAADF) signal. Representative spectra for the identified phases are extracted from the segmented images with and without exclusion of pixels that exhibit spectral contributions from multiple phases, and subsequently quantified using Cliff–Lorimer sensitivity factors. The phase compositions extracted with the method while excluding pixels from multiple phases are found to be in good agreement with those extracted from user-selected regions of interest, while providing improved confidence intervals. Without exclusion of multiphase pixels, the extracted composition is found to be in poor statistical agreement with the other results because of systematic errors arising from the cross-phase spectral contamination. The proposed method allows quantification to be performed in the presence of discontinuous phase distributions and overlapping phases, challenges that are typical of many nanoscale analyses performed by STEM-EDS.

Erbium dihydride Er(H,D,T)2 is a fluorite structure rare-earth dihydride useful for the storage of hydrogen isotopes in the solid state. However, thermodynamic predictions indicate that erbium oxide formation will proceed readily during processing, which may detrimentally contaminate Er(H,D,T)2 films. In this work, transmission electron microscopy (TEM) techniques including energy-dispersive x-ray spectroscopy, energy-filtered TEM, selected area electron diffraction, and high-resolution TEM are used to examine the manifestation of oxygen contamination in ErD2 thin films. An oxide layer ∼30–130 nm thick was found on top of the underlying ErD2 film, and showed a cube-on-cube epitaxial orientation to the underlying ErD2. Electron diffraction confirmed the oxide layer to be Er2O3. While the majority of the film was observed to have the expected fluorite structure for ErD2, secondary diffraction spots suggested the possibility of either nanoscale oxide inclusions or hydrogen ordering. In situ heating experiments combined with electron diffraction ruled out the possibility of hydrogen ordering, so epitaxial oxide nanoinclusions within the ErD2 matrix are hypothesized. TEM techniques were applied to examine this oxide nanoinclusion hypothesis.

Lead loss during processing of solution-derived Pb(Zr,Ti)O3 (PZT)-based thin-films can result in the formation of a Pb-deficient, nonferroelectric fluorite phase that is detrimental to dielectric properties. It has recently been shown that this nonferroelectric fluorite phase can be converted to the desired perovskite phase by postcrystallization treatment. Here, quantitative standard-based energy-dispersive x-ray spectrometry (EDS) in a scanning transmission electron microscope (STEM) is used to study cation distribution before and after this fluorite-to-perovskite transformation. Single-phase perovskite PbZr0.53Ti0.47O3 (PZT 53/47) and Pb0.88La0.12Zr0.68Ti0.29O3 (PLZT 12/70/30) specimens that underwent this treatment were found to be chemically indistinguishable from the perovskite present in the multiphase specimens prior to the fluorite-to-perovskite transformation. Significant Zr–Ti segregation is found in PLZT 12/70/30, but not in PZT 53/47. Slight La-segregation was seen in rapidly crystallized PLZT, but not in more slowly crystallized PLZT.

The high permittivity of Pb(Zr,Ti)O3 and (Pb,La)(Zr,Ti)O3—PZT and PLZT, respectively—thin films and the flexibility of chemical solution deposition (CSD) make solution-derived P(L)ZT thin films extremely attractive for integrated capacitor applications. However, Pb-loss or cation segregation during processing results in degraded properties of the final film. Here, we have extended the use of multivariate statistical analysis (MSA) of energy-dispersive spectroscopy (EDS) spectrum images (SIs) in scanning transmission electron microscopy (STEM) to allow the two-dimensional (2D) quantitative analysis of cation segregation and depletion in P(L)ZT thin films. Quantified STEM-EDS SIs allow high-resolution (< ≈10 nm) quantification of these cation distributions. Surface Pb depletion is found after crystallization and is replenished by a unique post-crystallization PbO overcoat+anneal processes. Zr/Ti and La segregation are found to develop in a decidedly nonplanar fashion during crystallization, especially in PLZT 12/70/30 material, highlighting the need for 2D analysis. Quantitative 2D chemical information is essential for improved processing of homogeneous P(L)ZT films with optimal electrical properties.

Chemical solution deposition has been used to fabricate continuous ultrathin lead lanthanum zirconate titanate (PLZT) films as thin as 20 nm. Further, multilayer capacitor structures with as many as 10 dielectric layers have been fabricated from these ultrathin PLZT films by alternating spin-coated dielectric layers with sputtered platinum electrodes. Integrating a photolithographically defined wet etch step to the fabrication process enabled the production of functional multilayer stacks with capacitance values exceeding 600 nF. Such ultrathin multilayer capacitors offer tremendous advantages for further miniaturization of integrated passive components.

This report details the findings of post-radiation mechanical testing and microstructural characterization performed on a series of model and commercial FeCrAl alloys to assist with the development of a cladding technology with enhanced accident tolerance. The samples investigated include model alloys with simple ferritic grain structure and two commercial alloys with minor solute additions. These samples were irradiated in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL) up to nominal doses of 7.0 dpa near or at Light Water Reactor (LWR) relevant temperatures (300-400 C). Characterization included a suite of techniques including small angle neutron scattering (SANS), atom probe tomography (APT), and transmission based electron microscopy techniques. Mechanical testing included tensile tests at room temperature on sub-sized tensile specimens. The goal of this work was to conduct detailed characterization and mechanical testing to begin establishing empirical and/or theoretical structure-property relationships for radiation-induced hardening and embrittlement in the FeCrAl alloy class. Development of such relationships will provide insight on the performance of FeCrAl alloys in an irradiation environment and will enable further development of the alloy class for applications within a LWR environment. A particular focus was made on establishing trends, including composition and radiation dose. Themore » report highlights in detail the pertinent findings based on this work. This report shows that radiation hardening in the alloys is primarily composition dependent due to the phase separation in the high-Cr FeCrAl alloys. Other radiation induced/enhanced microstructural features were less dependent on composition and when observed at low number densities, were not a significant contributor to the observed mechanical responses. Pre-existing microstructure in the alloys was found to be important, with grain boundaries and pre-existing dislocation networks acting as defect sinks, resulting in variations in the observed microstructures after irradiation. Dose trends were also observed, with increasing radiation dose promoting changes in the size and number density of the Cr-rich ' precipitates. Based on the microstructural analysis, performed tensile testing, and prior knowledge from FeCr literature it was hypothesized that the formation of the Cr-rich ' precipitates could lead to significant radiation-induced embrittlement in the alloys, and this could be composition dependent, a result which would mirror the trends observed for radiation-induced hardening. Due to the limited database on embrittlement in the FeCrAl alloy class after irradiation, a series of radiation experiments have been implemented. The overarching point of view within this report is the radiation tolerance of FeCrAl is complex, with many mechanisms and factors to be considered at once. Further development of the FeCrAl alloy class for enhanced accident tolerant applications requires detailed, single (or at least limited) variable experiments to fully comprehend and predict the performance of this alloy in LWRs. This report has been submitted as fulfillment of milestone M2FT-15OR0202321 titled, Summary report on the effect of composition on the irradiation embrittlement of Gen 1 ATF FeCrAl for the Department of Energy Office of Nuclear Energy, Advanced Fuel Campaign of the Fuel Cycle R&D program.« less

This document describes the installation, performance, and early results from the FCRD-funded acquisition of a new advanced analytical scanning / transmission electron microscopy (S/TEM) at the Oak Ridge National Laboratory Low Activation Materials Development and Analysis (LAMDA) facility.

Plasma-facing materials in the divertor of a magnetic fusion reactor have to tolerate steady state plasma heat fluxes in the range of 10 MW/m2 for ∼107 s, in addition to fusion neutron fluences, which can damage the plasma-facing materials to high displacements per atom (dpa) of ∼50 dpa. Materials solutions needed for the plasma-facing components are yet to be developed and tested. The material plasma exposure experiment (MPEX) is a newly proposed steady state linear plasma device designed to deliver the necessary plasma heat flux to a target for testing, including the capability to expose a priori neutron-damaged material samples to those plasmas. The requirements of the plasma source needed to deliver the required heat flux are being developed on the Proto-MPEX device which is a linear high-intensity radio-frequency (RF) plasma source that combines a high-density helicon plasma generator with electron- and ion-heating sections. The device is being used to study the physics of heating overdense plasmas i...

The equilibrium shape of 6H-SiC nanostructures and their surfaces were studied by analyzing nano-void (∼10 nm) shapes, which were introduced in monocrystalline 6H-SiC by high-temperature neutron irradiation, using transmission electron microscopy. The nano-voids were determined to be irregular icosahedrons truncated with six { 1 ¯ 100}, twelve { 1 ¯ 103}, one smaller top-basal, and one larger bottom-basal planes, which suggests that { 1 ¯ 100} and { 1 ¯ 103} are the next stable surface class after the basal planes. The relatively frequent absence of the { 1 ¯ 100} surface in the nano-voids indicated that the ( 1 ¯ 10 3 ¯ ) surface type is energetically rather stable. These non-basal surfaces were found not to be atomically flat due to the creation of nanofacets with half unit-cell height in the c-axis. The { 1 ¯ 100} and { 1 ¯ 103} surfaces were classified as two and four face types according to their possible nanofacets and surface termination, respectively. We also discuss the surface energy difference ...

Helium accumulation negatively impacts structural materials used in neutron-irradiated environments, such as fission and fusion reactors. Next-generation fission and fusion reactors will require structural materials, such as steels, that are resistant to large neutron doses yet see service temperatures in the range most affected by helium embrittlement. Previous work has indicated the difficulty of experimentally differentiating nanometer-sized cavities such as helium bubbles from the Ti–Y–O rich nanoclusters (NCs) in radiation-tolerant nanostructured ferritic alloys (NFAs). Because the NCs are expected to sequester helium away from grain boundaries and reduce embrittlement, experimental methods to study simultaneously the NC and bubble populations are needed. In this study, aberration-corrected scanning transmission electron microscopy (STEM) results combining high-collection-efficiency X-ray spectrum images (SIs), multivariate statistical analysis (MVSA), and Fresnel-contrast bright-field STEM imaging, have been used for such a purpose. Fresnel-contrast imaging, with careful attention to TEM-STEM reciprocity, differentiates bubbles from NCs. MVSA of X-ray SIs unambiguously identifies NCs. Therefore, combined Fresnel-contrast STEM and X-ray SI is an effective STEM-based method to characterize helium-bearing NFAs.

When will a small or low-contrast feature, such as an embedded second-phase particle, be visible in a scanning transmission electron microscopy (STEM) X-ray map? This work illustrates a computationally inexpensive method to simulate X-ray maps and spectrum images (SIs), based upon the equations of X-ray generation and detection. To particularize the general procedure, an example of nanostructured ferritic alloy (NFA) containing nm-sized Y2Ti2O7 embedded precipitates in ferritic stainless steel matrix is chosen. The proposed model produces physically appearing simulated SI data sets, which can either be reduced to X-ray dot maps or analyzed via multivariate statistical analysis. Comparison to NFA X-ray maps acquired using three different STEM instruments match the generated simulations quite well, despite the large number of simplifying assumptions used. A figure of merit of electron dose multiplied by X-ray collection solid angle is proposed to compare feature detectability from one data set (simulated or experimental) to another. The proposed method can scope experiments that are feasible under specific analysis conditions on a given microscope. Future applications, such as spallation proton–neutron irradiations, core-shell nanoparticles, or dopants in polycrystalline photovoltaic solar cells, are proposed.

A non-destructive neutron scattering method was developed to precisely measure the uptake of total hydrogen in nuclear grade Zircaloy-4 cladding. The hydriding apparatus consists of a closed stainless steel vessel that contains Zircaloy-4 specimens and hydrogen gas. By controlling the initial hydrogen gas pressure in the vessel and the temperature profile, target hydrogen concentrations from tens of ppm to a few thousands of ppm have been successfully achieved. Following hydrogen charging, the hydrogen content of the hydrided specimens was measured using the vacuum hot extraction method (VHE), by which the samples with desired hydrogen concentration were selected for the neutron study. Small angle incoherent neutron scattering (SAINS) were performed in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL). Our study indicates that a very small amount (≈ 20 ppm) hydrogen in commercial Zircaloy-4 cladding can be measured very accurately in minutes for a wide range of hydrogen concentration by a nondestructive method. The hydrogen distribution in a tube sample was obtained by scaling the neutron scattering rate with a factor, which is determined by calibration process with direct chemical analysis method on the specimen. This scale factor can be used for future test with unknown hydrogen concentration, thus provide a nondestructive method for absolute hydrogen concentration determination.

A single crystal of lead-zirconate-titanate (PZT), composition Pb(Zr0.80Ti0.20)O3, was studied by polarized-Raman scattering as a function of temperature. Raman spectra reveal that the local structure deviates from the average structure in both ferroelectric and paraelectric phases. We show that the crystal possesses several, inequivalent complex domain boundaries which show no sign of instability even 200 K above the ferroelectric-to-paraelectric phase transition temperature TC. Two types of boundaries are addressed. The first boundary was formed between ferroelectric domains below TC. This boundary remained stable up to the highest measurement temperatures, and stabilized the domains so that they had the same orientation after repeated heating and cooling cycles. These domains transformed normally to the cubic paraelectric phase. Another type of boundary was formed at 673 K and exhibited no signs of instability up to 923 K. The boundary formation was reversible: it formed and vanished between 573 and 673 K during heating and cooling, respectively. A model in which the crystal is divided into thin slices with different Zr/Ti ratios is proposed. The physical mechanism behind the thermal-stress-induced structural changes is related to the different thermal expansion of the slices, which forces the domain to grow similarly after each heating and cooling cycle. The results are interesting for non-volatile memory development, as it implies that the original ferroelectric state can be restored after the material has been transformed to the paraelectric phase. It also suggests that a low-symmetry structure, stable up to high-temperatures, can be prepared through controlled deposition of layers with desired compositions.

The alloy-design strategy of combining multiple elements in near-equimolar ratios has shown great potential for producing exceptional engineering materials, often known as 'high-entropy alloys'. Understanding the elemental distribution, and, thus, the evolution of the configurational entropy during solidification, is undertaken in the present study using the Al₁.₃CoCrCuFeNi model alloy. Here we show that, even when the material undergoes elemental segregation, precipitation, chemical ordering and spinodal decomposition, a significant amount of disorder remains, due to the distributions of multiple elements in the major phases. The results suggest that the high-entropy alloy-design strategy may be applied to a wide range of complex materials, and should not be limited to the goal of creating single-phase solid solutions.

The High and Thermal Magnetic Processing/Electro-magnetic Acoustic Transducer (HTMP/EMAT) technology has been shown to be an enabling disruptive materials processing technology, that can achieve significant improvements in microstructure and consequently material performance beyond that achievable through conventional processing, and will lead to the next generation of advanced performance structural and functional materials. HTMP exposure increased the reaction kinetics enabling refinement of microstructural features such as finer martensite lath size, and finer, more copious, homogeneous dispersions of strengthening carbides leading to combined strength and toughness improvements in bainitic steels. When induction heating is applied in a high magnetic field environment, the induction heating coil is configured so that high intensity acoustic/ultrasonic treatment occurs naturally. The configuration results in a highly effective electromagnetic acoustical transducer (EMAT). HTMP combined with applying high-field EMAT, produce a non-contact ultrasonic treatment that can be used to process metal alloys in either the liquid state resulting in significant microstructural changes over conventional processing. Proof-of-principle experiments on cast irons resulted in homogeneous microstructures in small castings along with improved casting surface appearance. The experiment showed that by exposing liquid metal to the non-contact acoustic/ultrasonic processing technology developed using HMFP/EMAT wrought-like microstructures were developed in cast components. This Energymore » Intensive Processes (EIP) project sponsored by the DOE EERE Advanced Manufacturing Office (AMO) demonstrated the following: (1) The reduction of retained austenite in high carbon/high alloy steels with an ambient temperature HTMP process, replacing either a cryogenic or double tempering thermal process normally employed to accomplish retained austenite transformation. HTMP can be described as a 'heat-free', heat treating technology. Lower residual stresses in HTMP treated materials are anticipated since no thermal strains are involved in inducing the transformation of retained austenite to martensite in high alloy steel. (2) The simultaneous increase of 12% in yield strength and 22% in impact energy in a bainitic alloy using HTMP processing. This is a major breakthrough in materials processing for the next generation of structural materials since conventionally processed materials show a reduction in impact toughness with an increase in yield strength. HTMP is a new paradigm to beneficially increase both yield strength and impact energy absorption simultaneously. (3) HTMP processing refined both the martensite lath population and the carbide dispersion in a bainitic steel alloy during Gausstempering. The refinement was believed to be responsible for the simultaneous increase in strength and toughness. Hence, HTMP significantly impacts nucleation and growth phenomenon. (4) HTMP processing developed comparable ultimate tensile strength and twice the impact energy in a lower cost, lower alloy content ({approx}8% alloy content) steel, compared to highly alloyed, (31% alloy elements involving Ni, Co, and Mo) 250-grade margining steel. Future low-cost HTMP alloys appear viable that will exceed the structural performance of highly alloyed materials that are conventionally processed. This economic benefit will enable U.S. industry to reduce cost (better more competitive worldwide) while maintaining or exceeding current performance. (5) EMAT processed cast iron exhibits significantly higher hardness (by 51% for a 9T condition) than a no-field processed sample. (6) EMAT produced microstructures in cast iron resulted in an unique graphite nodule morphology, a modified pearlite content, and unique carbide types, that formed during solidification and cooling. (7) EMAT processed nanoparticle dispersions in Mg resulted in a very fine, unagglomerated distribution of the nanoparticles in the magnesium matrix. This provides a breakthrough technology to make the next generation of nanocomposite reinforced metal matrix composites which can be tailored to exhibit higher strength and ductility combinations not only at ambient temperature but at elevated temperatures where enhanced creep resistance is observed. This technology can be extended to non-metallic systems as long as a conductive containment vessel is utilized that will convey the EMAT signal into the material of interest during processing. (8) Facilitation of HTMP/EMAT technology commercialization, throughout the course of the project. Two technology limitations were overcome that led to the first generation commercial prototype HTMP/EMAT system which was initially installed at ORNL. (9) During this project, a production-scale equipment design to enable commercialization of HMFP technology was conceptualized, designed, fabricated, and installed at ORNL as a commercial-scale prototype system.« less

CuIn x Ga 1−x Se 2 (CIGS) as an absorber material in solar cells is already known to present a less toxic alternative to current solar cells based on toxic elements such as CdTe. CIGS developed as nanoparticles in solution are ideal for non-vacuum deposition methods which help achieve lower-cost solar cells, compared to high vacuum deposition methods. This study investigates deposition, processing, and characterization of aqueous-based CIGS nanoparticles. The films are deposited via sono-deposition, spin coating method, and drop cast method. The as-deposited thin films are characterized via X-Ray Diffraction (XRD), Optical Microscope, and Scanning Electron Microscopy (SEM, and STEM). The films are then annealed via Pulsed Thermal Processing (PTP) technique, and post-PTP characterization shows change in the morphology of CIGS nanoparticles.

We report the nanojunction effect on nanocone based solar cell consisting of 5 μm thick CdTe thin film as a p-type absorption layer and n-type ZnO nanocones as a minority electron collector. The morphology of the nanojunction, with embedding depth ∼ 100 nm into CdTe matrix, was clearly revealed by transmission electron microscopy (TEM) and scanning TEM (STEM). The characteristics of nanojunction solar cell were compared with those of planar ZnO/CdTe structure in dark and under 100 mW (AM 1.5) illumination using a solar simulator. The nanojunction cell showed small reverse saturation current density in dark. Lower capacitance of the nanojunction from capacitance-frequency (C-f) measurement implies the existence of low defects at near the junction interfaces, which enables to lowerer junction recombination. The small junction area and low defects produces the higher open circuit voltage (V oc ) and fill factor (ff) than those of planar under light illumination. The fact that the performance of nanojunction based solar cell is not critically affected by interfacial defects will be very useful for polycrystalline or nanoparticle CdTe with many crystal defects. Our current conversion efficiency of ~ 3.2 % nanocone was achieved by decreasing CdTe grain size, which is different from planar polycrystalline solar cells.

Nanojunctions promise to provide higher charge transport efficiencies and less costly solar cell fabrication methods. We report a three-dimensional (3D) solar cell structure based on interdigitated nanojunctions formed with the tips of n-type ZnO nanocones embedded in a p-type polycrystalline (PX) CdTe film. This 3D nanocone tip-film cell, without optimization, enabled 3.2% power conversion efficiency, higher than that produced by a planar solar cell fabricated using the same materials. Reducing CdTe grain size and enriching the grain boundaries with chlorine improved the conversion efficiency for the tip-film structure. This higher conversion efficiency is attributable to improved charge transport in the nanojunction due to a combination of the high electric field generated in the CdTe and the utilization of the small junction area. The high field facilitates the extraction of minority carriers from the photoactive layer to the small junction region, while the use of the small junction area reduces the total electron recombination loss. The improved carrier transport in the nanocone tip-film junction implies that nanocone-based photovoltaic solar cells are capable of tolerating the imperfect materials produced using low-cost fabrication methods.

Multivariate statistical analysis (MVSA) methods, such as used in analytical electron microscopy and surface science, were applied to atom probe tomography (APT) data. It was found that MVSA methods allow fast and intuitive interpretation of APT data, where both spatial and spectral variance are described simultaneously in an unbiased manner. In this work, a FeCr-Al-Ti alloy (PM2000) subjected to different heat treatments was examined via APT. The different scale three-phase microstructures resulting from these heat treatments provided an interesting test of the capabilities and limits of the present MVSA methodology. Principal component analysis (PCA)-based MVSA identified the precipitate populations in all three samples, including ultrafine precipitates with the use of small (0.5 nm) voxel size, and high resolution (0.02 u) mass binning.

2 páginas, 3 figuras.-- Trabajo presentado al "Physical Sciences Symposia" celebrado en Oregon (USA) del 1 al 5 de Agosto de 2010., This research was supported by the Shared Research Equipment (SHaRE) User Program, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy and by the Laboratory Directed Research and Development Weinberg Fellowship Program at Oak Ridge National Laboratory.

We report measurements of the energy dependence of flux thresholds and incubation fluences for He-ion induced nano-fuzz formation on hot tungsten surfaces at UHV conditions over a wide energy range using real-time sample imaging of tungsten target emissivity change to monitor the spatial extent of nano-fuzz growth, corroborated by ex situ SEM and FIB/SEM analysis, in conjunction with accurate ion-flux profile measurements. The measurements were carried out at the multicharged ion research facility (MIRF) at energies from 218 eV to 8.5 keV, using a high-flux deceleration module and beam flux monitor for optimizing the decel optics on the low energy MIRF beamline. The measurements suggest that nano-fuzz formation proceeds only if a critical rate of change of trapped He density in the W target is exceeded. To understand the energy dependence of the observed flux thresholds, the energy dependence of three contributing factors: ion reflection, ion range and target damage creation, were determined using the SRIM simulation code. The observed energy dependence can be well reproduced by the combined energy dependences of these three factors. The incubation fluences deduced from first visual appearance of surface emissivity change were (2–4) × 1023 m−2 at 218 eV, and roughly a factor of 10 less at the higher energies, which were all at or above the displacement energy threshold. The role of trapping at C impurity sites is discussed.

Publisher Summary Cathodoluminescence (CL) is light emitted by a solid material because of irradiation by an electron beam. When the spectral distribution of light is studied, CL spectroscopy is performed. This chapter focuses on advances in CL instrumentation, theory, and application. CL is a valuable technique for studying the optical emission properties of semiconductor and insulating materials at a very fine spatial resolution. CL is an indispensable tool for the study of light emission from materials and the factors that improve or degrade it in the semiconductor and optoelectronic industries. CL is also heavily used in studies of mineralogy and geology. The basic physics that gives rise to the CL signal and the way the nature of the solid material under investigation changes the CL response is also presented in the chapter.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

To achieve high-efficiency polycrystalline CdTe-based thin-film solar cells, the CdTe absorbers must go through a post-deposition CdCl2 heat treatment followed by a Cu diffusion step. To better understand the roles of each treatment with regard to improving grains, grain boundaries, and interfaces, CdTe solar cells with and without Cu diffusion and CdCl2 heat treatments are investigated using cross-sectional electron beam induced current, electron backscatter diffraction, and scanning transmission electron microscope techniques. The evolution of the cross-sectional carrier collection profile due to these treatments that cause an increase in short-circuit current and higher open-circuit voltage are identified. Additionally, an increased carrier collection in grain boundaries after either/both of these treatments is revealed. The increased current at the grain boundaries is shown to be due to the presence of a space charge region with an intrinsic carrier collection profile width of ≈350 nm. Scanning transmission electron microscope electron-energy loss spectroscopy shows a decreased Te and increased Cl concentration in grain boundaries after treatment, which causes the inversion. Furthermore, each treatment improves the overall carrier collection efficiency of the cell separately, and, therefore, the benefits realized by each treatment are shown to be independent of each other.

We report results of measurements on the evolution of the surface morphology of a hot tungsten surface due to impacting low-energy (80 ? 12,000 eV) He ions, performed at the ORNL Multicharged Ion Research Facility (MIRF). Surface-morphology changes were investigated over a broad range of fluences, energies and temperatures for both virgin and pre-damaged W-targets. At low fluences, ordered coral-like and ridge-like surface structures are observed, with great grain-to-grain variability. At the largest fluences, individual grain characteristics disappear in FIB/SEM scans, and the entire surface is covered by a multitude of near-surface bubbles with a broad range of sizes, and disordered whisker growth, while in top-down SEM imaging the surface is virtually indistinguishable from the nanofuzz produced on linear plasma devices. These features are evident at progressively lower fluences as the He-ion energy is increased. In addition, simulations were carried out of damage caused by cumulative bombardment of 1 keV W self-atoms, using LAMMPS at the Kraken supercomputing facility of the University of Tennessee. The simulations show strong defect-recombination effects that lead to a saturation of the total defect number after a few hundred impacts, while sputtering and implantation lead to an imbalance of the vacancy and interstitial numbers.

We report results of measurements on the evolution of the surface morphology of a hot tungsten surface due to impacting low-energy (80?12?000?eV) He ions and of simulations of damage caused by cumulative bombardment of 1 and 10?keV W self-atoms. The measurements were performed at the ORNL Multicharged Ion Research Facility, while the simulations were done at the Kraken supercomputing facility of the University of Tennessee. At 1?keV, the simulations show strong defect-recombination effects that lead to a saturation of the total defect number after a few hundred impacts, while sputtering leads to an imbalance of the vacancy and interstitial number. On the experimental side, surface morphology changes were investigated over a broad range of fluences, energies and temperatures for both virgin and pre-damaged W-targets. At the lowest accumulated fluences, small surface-grain features and near-surface He bubbles are observed. At the largest fluences, individual grain characteristics disappear in focused ion beam/scanning electron microscopy (FIB/SEM)?scans, and the entire surface is covered by a multitude of near-surface bubbles with a broad range of sizes, and disordered whisker growth, while in top-down SEM imaging the surface is virtually indistinguishable from the nano-fuzz produced on linear plasma devices. These features are evident at progressively lower fluences as the He-ion energy is increased.

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008