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Three newly identified cross-slip mechanisms from atomistic simulations of fcc crystals, namely surface, bulk and intersection cross-slip types, were hierarchically informed into discrete dislocation dynamics simulations. The influence of each cross-slip type on the evolution of the dislocation microstructure in face-centered cubic microcrystals having different crystal sizes and initial dislocation densities was investigated. Dislocation pattern formation, surface slip localization and initial strain hardening were observed, in agreement with experimental observations, and possible explanations are given in the light of these simulations., Published in Acta Materialia, v85 p180-190, 2015. Sponsored in part by DARPA.

Twisted graphene is of particular interest due to several intriguing characteristics, such as its the Fermi velocity, van Hove singularities and electronic localization. Theoretical studies recently suggested the possible bandgap opening and tuning. Here, we report a novel approach to producing epitaxial twisted graphene on SiC (0001) and the observation of its intrinsic bandgap behaviour. The direct deposition of C60 on pre-grown graphene layers results in few-layer twisted graphene confirmed by angular resolved photoemission spectroscopy and Raman analysis. The strong enhanced G band in Raman and sp3 bonding characteristic in X-ray photoemission spectroscopy suggests the existence of interlayer interaction between adjacent graphene layers. The interlayer spacing between grapheme layers measured by transmission electron microscopy is 0.352 + or - 0.012 nm. Thermal activation behaviour and nonlinear current-voltage characteristics conclude that an intrinsic bandgap is opened in twisted graphene. Low sheet resistance (approximately 160 ohm square(exp1) at 10 K) and high mobility (approximately 2,000 cm(exp2)V 1s(exp1)1at 10 K) are observed., Published in Nature Communications, v6 n5677 p1-8, 6 January 2015. Prepared in collaboration with the Department of Physics at the University of Dayton, Dayton OH, the Department of Physics at Pusan National University, Republic of Korea and Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA.

This overall objective of this research task was to develop an alternative material system for use in VLWIR FPAs with the sensitivity required at 40K for long range sensing and discrimination of cold, dim targets. The alternative material system under development is based on thin alternating layers of indium arsenide and indium gallium antimonide creating a superlattice material capable of infrared detection out to 30 microns. A VLWIR detector adds detection range and discrimination to a space based platform. Operation at 40K provides significant reduction in size, weight and power for this application.

This overall objective of this research task was to push forward the state-of-the-art in utilizing semiconductor quantum dots in optical and optoelectronic devices of interest to the Air Force. The full potential of semiconductor quantum dots cannot be achieved by random formation and assembly processes. For narrow optical linewidths, suppressed thermal excitation, and tailored dot-to-dot interactions, the quantum dot size, composition and location needs to be precisely controlled to engineer the desired properties. Two complementary but distinct methods for fabricating uniform quantum dots with controlled dot/nanoparticle size, composition and location are proposed. 1) Nanopatterning and annealing of MBE grown planar InAs. 2) Synthesis of semiconductor nanocrystals by Supercritical Fluid CO2 process. In addition to the fabrication process development, a key objective is to model and characterize the fundamental physics and chemistry of these nanoscale heterostructures to provide the firm scientific basis for these materials to transition into advanced devices, such as detectors, lasers, optical communication and quantum computing.

The structures of Ca60Mg15Cu25, Ca60Mg20Cu20 and Ca60Mg25Cu15 metallic glasses have been investigated by neutron and X-ray diffraction. The correlation functions show a peak manifold in the region 2.2-4.5 , arising from the various atom pairs for these glasses. The results show clearly that there are contacts between the solute atoms (Cu and Mg) which agree with a simple estimate of the maximum solute atom fraction beyond which solute-solute contact becomes topologically necessary. The Cu-Mg and Cu- Ca distances are consistent with the sum of covalent radii, whereas all other interatomic distances are consistent with the sum of metallic radii. The neutron and X-ray diffraction correlation functions were simultaneously fitted with a series of symmetric peaks to obtain coordination numbers and interatomic distances, but only the results from the first two peaks, Cu-Cu and Cu-Mg, are of reasonable reliability. The Percus-Yevick approximation for binary hard sphere systems has been used to simulate the results. This shows that the results of fits to the Cu-Cu and Cu-Mg correlations give a reasonable description for atoms which are in close contact, but do not include an additional contribution at longer distance due to atoms which are almost in contact. The fits to the Cu-Ca peak are strongly affected by overlaps with both the longer distance peaks used in the fit, and the broad trailing edge in the distributions of interatomic distances that is not taken into account by fitting with symmetric peaks. Final results show that copper has a total of 6.5 neighbours which are in close contact, but has a total coordination number of about 12-13, when atoms which are almost in contact are included., Prepared in collaboration with Rutherford Appleton Laboratory, Didcot, UK, UES, Inc., Dayton, OH, and the Univ of Kent, Canterbury, UK. Published in Intermetallics, v19 p860-870, 2011.

Presented at ASETSDefense 2014: Sustainable Surface Engineering for Aerospace and Defense held at Fort Myer, VA on 18-20 Nov 2014.

Techniques employed in origami are of interest for the design of actuating structures with multiple defined geometric states. Most research in this area has focused on manipulating material chemistry or geometry to achieve folding, but crease development through full material thickness has not been studied in detail. Understanding creasing is crucial for establishing material selection guidelines in origami engineering applications. Identification of the precise failure mechanisms is critical for understanding the residual fold angle and selecting optimal materials for specific origami applications. To characterize crease formation and development, polymer films were folded using a modified parallel plate bending technique which was successfully modeled with Euler beam theory in the elastic regime. Fold angles measured after creasing provided a means to quantitatively describe a material's ability to retain a fold, and degree of plastic deformation incurred during folding. SEM micrographs of creased regions revealed tensile deformations on exterior crease surfaces while compressive deformations such as wrinkling occurred inside. Profilometry was performed on crease interiors to identify and measure wrinkle topology. It was found that increased dissipative plastic deformation led to retention of smaller fold angles. These characterization techniques can be used as a means of classifying and organizing polymers by potential usefulness in structural origami applications., Prepared in collaboration with UES Inc., Dayton, OH and University of Dayton, Dayton, OH.

To prepare cholesteric liquid crystalline nonlinear optical materials with ability to be vitrified on cooling and form long time stability cholesteric glasses at room temperature, a series of platinum acetylide complexes modified with cholesterol has been synthesized. The materials synthesized have the formula trans-Pt(PR3)(cholesterol (3 or 4)-ethynyl benzoate)(1-ethynyl-4- X-benzene), where R = Et, Bu or Oct and X = H, F, OCH3 and CN. A cholesteric liquid crystal phase was observed in the complexes R = Et, and X = F, OCH3 and CN but not in any of the other complexes. When X = CN, a cholesteric glass was observed at room temperature which remained stable up to 130 oC, then converted to a mixed crystalline/cholesteric phase and completely melted to an isotropic phase at 230 oC. When X = F or OCH3 the complexes were crystalline at room temperature with conversion to the cholesteric phase upon heating to 190 and 230 oC, respectively. In the series X = CN, OCH3 and F, the cholesteric pitch was determined to be 1.7, 3.4 and 9.0 , respectively., Prepared in collaboration with Centro de Investigacion en Quimica Aplicada (CIQA), Saltillo, Coahuila, Mexico, the Department of Chemistry, University of Dayton, Dayton, OH, and the Department of Physics, University of Colorado at Colorado Springs. Sponsored in part by AFOSR.

The effect of electric-current pulses on the evolution of microstructure and texture in cryogenically rolled copper was determined. The pulsed material was found to be completely recrystallized, and the recrystallization mechanism was deduced to be similar to that operating during conventional static annealing. The microstructural changes were explained simply in terms of Joule heating. A significant portion of the crystallization process was concluded to have occurred after pulsing; i.e., during cooling to ambient temperature. The grain structure and microhardness were shown to vary noticeably in the heat-affected zone (HAZ); these observations mirrored variations of temper colors. Accordingly, the revealed microstructure heterogeneity was attributed to the inhomogeneous temperature distribution developed during pulsing. In the central part of the HAZ, the mean grain size increased with current density and this effect was associated with the temperature rise per se. This grain size was slightly smaller than that in statically recrystallized specimens., Published in the Journal of Materials Research, v29 n22 p2727-2737, 28 Nov 2014.

Three two-photon absorption (2PA) dyes (donor-pi-donor DPA2F), donor-pi-donor acceptor (AF240), and acceptor-pi-acceptor (BT2F); specifically, D is Ph2N-, A is 2-benzothiazoyl, and the pi-linker is 9,9-diethylfluorene) are examined in a variety of aprotic solvents. Because the 2PA cross section is sensitive to the polarity of the local environment, this report examines the solvent-dependent linear photophysics of the dyes, which are important to understand before probing more complex solid-state systems. The symmetrical dyes show little solvent dependence; however, AF240 has significant solvatochromism observed in the fluorescence spectra and lifetimes and also the transient absorption spectra. A 114 nm bathochromic shift is observed in the fluorescence maximum when going from n-hexane to acetonitrile, whereas the lifetimes increase from 1.25 to 3.12 ns. The excited-state dipole moment for AF240 is found to be 20.1 D using the Lippert equation, with smaller values observed for the symmetrical dyes. Additionally, the femtosecond transient absorption (TA) spectra at time zero show little solvent dependence for DPA2F or BT2F, but AF240 shows a 52 nm hypsochromic shift from n-hexane to acetonitrile. Coupled with the solvatochromism in the fluorescence and large excited-state dipole moment, this is attributed to formation of an intramolecular charge-transfer (ICT) state in polar solvents. By 10 ps in AF240, the maximum TA in acetonitrile has shifted 30 nm, providing direct evidence of a solvent-stabilized ICT state, whose formation occurs in 0.85-2.71 ps, depending on solvent. However, AF240 in nonpolar solvents and the symmetrical dyes in all solvents show essentially no shifts due to a predominantly locally excited (LE) state. Preliminary temperature-dependent fluorescence using frozen glass media supports significant solvent reorganization around the AF240 excited state in polar solvents., Published in The Journal of Physical Chemistry A, v118 p5228-5237, 2014.

Both the global research community and federal governments are embracing a move toward more open sharing of the products of research. Historically, the primary product of research has been peer-reviewed journal articles and published technical reports. However, advances in information technology, new 'open access' business models, and government policies are working to make publications and supporting materials much more accessible to the general public. These same drivers are blurring the distinction between the data generated through the course of research and the associated publications. These developments have the potential to significantly enhance the value of both publications and supporting digital research data, turning them into valuable assets that can be shared and reused by other researchers. The confluence of these shifts in the research landscape leads one to the conclusion that technical publications and their supporting research data must be bound together in a rational fashion. However, bringing these two research products together will require the establishment of new policies and a supporting data infrastructure that have essentially no precedent in the materials community, and indeed, are stressing many other fields of research. This document raises the key issues that must be addressed in developing these policies and infrastructure and suggests a path forward in creating the solutions., Journal article published in Integrating Materials and Manufacturing Innovation 2014, 3:22.

Hafnium oxide (HfO2) films were grown by sputter-deposition by varying deposition temperature (Ts) in a wide range of 25?700?C. The deposited HfO2 films were characterized by studying their growth behavior, microstructure, and optical properties. Characterization of the films employing a wide range of analytical techniques indicate a clear functional relationship between processing conditions, structure, morphology, and optical properties. HfO2 films were amorphous at Ts 6 200?C, at which point a structural transformation occurs. HfO2 films grown at Ts200?C were nanocrystalline, stabilized in a monoclinic structure. The nanocrystalline HfO2 films exhibit a strong (111) texturing. The average crystallite size of HfO2 films increased from10 nm to 20 nm with increasing Ts. Electron and atomic force microscopy measurements also correlated with the crystalline behavior, as well as an evenly distributed network of spherical shaped crystallites for the nanocrystalline HfO2 films. Density (ƿ) of HfO2 films probed using X-ray reflectivity and ellipsometry data analysis indicate that the q values are strongly dependent on Ts; ƿ varied in the range of 7.36?9.14 g/cm3. The higher end of ƿ values were noted only for HfO2 films grown at relatively higher Ts indicating the crystalline nature accounts for the q improvement. The band gap values of the films varied in the range of 5.78?6.17(?0.03) eV for Ts = 25?700?C. Index of refraction at 550 nm increased from 1.80 to 2.09, which also correlates with the characteristic feature of improved structural order, packing density of HfO2 films with increasing Ts. Based on the observed results, a correlation between growth conditions, microstructure and optical constants is established., Published in Optic Materials v37 p621-628, 2014.

We report on the preparation of color-tunable mirrors based on electrically regulated bandwidth broadening of the circularly polarized reflection of polymer-stabilized cholesteric liquid crystals (PSCLCs). A number of improvements relating to the practical implementation of these materials are detailed including color and bandwidth stability, baseline optical properties, and response times. Experimentation reported herein focuses on the contribution of structural chirality, viscoelastic properties of the polymer network architecture, and electro-optic drive schemes. Through the examination of samples prepared in different conditions and compositions, we further elucidate the dominant role of structural chirality as well as the impact of cross-linking of the polymer stabilizing network on the threshold voltage and relative change in bandwidth per voltage (delta(delta wavelength)/V). Furthermore, the appearance of nonideal optical properties (scatter and haze) in some samples is shown to be correlated with the polymer/LC compatibility and effectiveness of structural templating. Due to the employment of an electromechanical displacement mechanism, the switching times of the PSCLCs are slower than mechanisms based on liquid crystal reorientation. However, a potential approach is identified to reduce the on and off switching times to approximately 1 s.

We studied the appearance of second- and third-order Bragg reflections in cholesteric liquid crystals (CLCs) in cells where the electric field was perpendicular to the helical axis. Second-order reflections with reflectance values as large as 80% of the first-order one were observed in the gap regions of alignment cells with interdigitated electrodes for CLC mixtures with pitches in the range 0.5-1.0 microns upon application of a field. The characterization was enabled by local probing of the CLC using a microspectrophotometer. LC cells that are transparent in the visible spectrum in the off-state and become colored upon application of a field due the second- or third-order reflection band appearance were demonstrated. The spectral position of the higher-order Bragg reflections can also be tuned by adjusting the magnitude of the electric field., Journal article published in Optics Express, v22 n13 p16510-16519, 30 Jun 2014. Prepared in collaboration with Azimuth Corp., Dayton, OH.

A dedicated experimental test program aimed to characterize the material behavior of seven different ceramic matrix composite (CMC) materials at room and elevated temperature for thermal protection systems is described. This report describes how to configure a furnace, set up a thermal profile, and conduct a thermal profile for testing CMCs at elevated temperatures up to 1300 deg C.

Coupled in situ alloying and nitridation of titanium--vanadium alloys, has been achieved by introducing reactive nitrogen gas during the spark plasma sintering (SPS) of blended titanium and vanadium elemental powders, leading to a new class of nitride reinforced titanium alloy composites. The resulting microstructure includes precipitates of the delta-TiN phase with the NaCl structure, equiaxed (or globular) precipitates of a nitrogen enriched hcp alpha(Ti,N) phase with a c/a ratio more than what is expected for pure hcp Ti, and fine scale plate-shaped precipitates of hcp alphi-Ti, distributed within a bcc Beta matrix. During SPS processing, the delta-TiN phase appears to form at a temperature of 1400 degrees C, while only hcp alpha(Ti,N) and alpha-Ti phases form at lower processing temperatures. Consequently, the highest microhardness is exhibited by the composite processed at 1400 degrees C while those processed at 1300 degrees C or below exhibit lower values. Processing at temperatures below 1300 degrees C, resulted in an incomplete alloying of the blend of titanium and vanadium powders. These delta-TiN precipitates act as heterogeneous nucleation sites for the alpha(Ti,N) precipitates that appear to engulf and exhibit an orientation relationship with the nitride phase at the center. Furthermore, fine scale alpha-Ti plates are precipitated within the nitride precipitates, presumably resulting from the retrograde solubility of nitrogen in titanium., Journal article published in Journal of Alloys and Compounds v617 p933 945, 15 Aug 2014. Prepared in collaboration with Center for Advanced Research and Technology and Department of Materials Science and Engineering, University of North Texas; X-ray Science Division, Advanced Photon Source, Argonne National Laboratory; and CMT Structural and Functional Metals Lab, GE Global Research Center. The original document contains color images.

Herein, we report on the two-absorption crosssection spectrum of trans-Pt(PBu3)2 (C C C6H4 C C C6H5)2 (PE2) platinum acetylide complex employing the femtosecond wavelength-tunable Z-scan technique. The PE2 complex can be visualized as two branches containing two phenylacetylene units, each one linked by a platinum center, completely transparent in the visible region. Because of this structure, large delocalization of -electrons allied to the strong intramolecular interaction between the branches is expected. The 2PA absorption spectrum was measured using the femtosecond wavelength-tunable Z-scan technique with low repetition rate (1 kHz), in order to obtain the 2PA spectrum without excited-state contributions. Our results reveal that PE2 in dichloromethane solution presents two 2PA allowed bands located at 570 and 710 nm, with cross section of about 320 and 45 GM, respectively. The first one is related to the strong intramolecular interaction between the molecule s branches due to the presence of platinum atom, while the second one is associated with the breaking of symmetry of the chromophore in solution due, most probably to a large twisting angle of the ligand s phenyl rings relative to the Pt core.

Manufacturing remains the essential core of the U.S. economy's innovation infrastructure and is critical to national defense. However, a gap exists between R&D activities and the deployment of technological innovations in the domestic production of goods and this gap could have long-term negative consequences for the defense industrial base. As global competition to manufacture advanced products intensifies, the performance of these innovation ecosystems must improve. Accelerating innovation and implementation of advanced manufacturing capabilities requires bridging a number of these gaps in the present U.S. innovation system. What is needed is for industry, academia, and government partners to leverage existing resources, collaborate, and co-invest to nurture manufacturing innovation and accelerate commercialization and defense production., Published in SAMPE Journal, v50 n5 p62-65, Sep-Oct 2014.

A new class of Ni-Ti-C-based metal-matrix composites has been developed using the laser-engineered net shaping(trade mark) process. These composites consist of an in situ formed and homogeneously distributed titanium carbide (TiC) phase reinforcing the nickel matrix. Additionally, by tailoring the Ti/C ratio in these composites, an additional graphitic phase can also be engineered into the microstructure. Serial-sectioning, followed by three-dimensional reconstruction of the microstructure in these composites, reveals homogeneously distributed primary and eutectic titanium carbide precipitates as well as a graphitic phase encompassing the primary carbides within the nickel matrix. The orphology and spatial distribution of these phases in three dimensions reveals that the eutectic carbides form a network linked by primary carbides or graphitic nodules at the nodes, which suggests interesting insights into the sequence of phase evolution. These three-phase Ni-TiC-C composites exhibit excellent tribological properties, in terms of an extremely low coefficient of friction while maintaining a relatively high hardness., Published as journal article in JOM: Journal of the Minerals, Metals & Materials Society, v66, n6 p935-942; published online 3 Apr 2014. Prepared in collaboration with Department of Materials Science and Engineering, University of North Texas, Denton, TX under contract FA8650-08-C-5226; Department of Materials Science and Engineering, The Ohio State University, Columbus, OH; and Institute of Advanced Composite Materials, Korea Institute of Science and Technology, Jeonbuk, Korea. The original document contains color images.

Toughness in continuous ceramic fiber reinforced ceramic matrix composites (CMCs) with dense matrices are dependent on the properties of the fiber coating or interphase that separate the fibers from the matrix. Multiple criteria have been proposed to describe the mechanism of crack propagation/deflection at the filament scale in brittle matrix continuous fiber reinforced composites; however, most of these criteria fail to account for the presence of an interphase of finite thickness or employ unrealistic boundary conditions. Recent simulations employing the extended finite element method (XFEM) have shown that variations in interphase thickness and strength relative to the fibers/matrix can have a significant influence on the mechanism of crack propagation/deflection. It is shown that primary crack deflection most often occurs when conditions favor secondary cracking in the interphase in front of an approaching matrix crack. Although this mechanism is similar to that argued by Cook and Gordon (Cook J, Gordon JE, Proc. Roy. Soc. A 1964; 28; 508-520), variations in the properties of the interphase are simulated to produce large deviations in the local crack growth behavior as a matrix crack grows into interphase., Presented at ECCM16 - 16th European Conference on Composite Materials, Seville, Spain 22-26 June 2014.

The microstructure, phase composition and mechanical properties of the AlMo0.5NbTa0.5TiZr and Al0.4Hf0.6NbTaTiZr high-entropy alloys are reported. The AlMo0.5NbTa0.5TiZr alloy consists of two body-centered cubic (bcc) phases with very close lattice parameters, alpha 1 = 326.8 pm and alpha 2 = 332.4 pm. One phase was enriched with Mo, Nb and Ta and another phase was enriched with Al and Zr. The phases formed nano-lamellae modulated structure inside equiaxed grains. The alloy had a density of rho = 7.40 g/cu cm and Vickers hardness Hv = 5.8 GPa. Its yield strength was 2000 MPa at 298 K and 745 MPa at 1273 K. The Al0.4Hf0.6NbTaTiZr had a single-phase bcc structure, with the lattice parameter alpha = 336.7 pm. This alloy had a density rho = 9.05 g/cu cm, Vickers microhardness Hv = 4.9 GPa, and its yield strength at 298 K and 1273 K was 1841 MPa and 298 MPa, respectively. The properties of these Al-containing alloys were compared with the properties of the parent CrMo0.5NbTa0.5TiZr and HfNbTaTiZr alloys and the beneficial effects from the Al additions on the microstructure and properties were outlined. A thermodynamic calculation of the solidification and equilibrium phase diagrams was conducted for these alloys and the calculated results were compared with the experimental data., Journal article published in Acta Materialia 68 (2014) 214-228. See also AFRL-RX-WP-TP-2014-0134, AFRL-RX-WP-JA-2014-0167, AFRL-RX-WP-JA-2014-0170, and AFRL-RX-WP-JA-2014-0177.

We demonstrate that argon ion bombardment of single crystal sapphire leads to the creation of substrates that support the growth of vertically aligned carbon nanotubes from iron catalysts with a density, height, and quality equivalent to those grown on conventional, disordered alumina supports. We quantify the evolution of the catalyst using a range of surface characterization techniques and demonstrate the ability to engineer and pattern the catalyst support through control of ion beam bombardment parameters., Journal article published in Nano Letters, v14 p4997-5003, 2014.

The width and energy of low-index interfacial boundaries (IFBs) in Ni?Ni3Al are calculated using first-principles methods for temperatures ranging from 0 to 1300 K. The low-temperature, coherent and chemically sharp (100), (110) and (111) IFBs are studied using conventional spin-polarized density functional methods. Cluster expansion methods, as implemented in the ATAT software suite, are used to estimate the interfacial excess free energies (IEFEs) and composition and long-range order profiles of these defects as a function of temperature. The simple face-centered cubic-based cluster expansion produces interfacial widths in the range of 1.5?3.0 nm at 1000 K. Interfacial widths double in size with an increase in temperature of 500 K. We also find that the IEFEs for the (100), (110) and (111) IFBs are strongly temperature dependent, decreasing by 90% as temperature increases from 0 to 1000 K. While vibrational and electronic entropic contributions were also considered, changes in free energy are dominated by the configurational entropy. The predicted high-temperature IEFE is approximately 10 mJ m-2 which is in excellent agreement with previous fits to experimentally measured coarsening rates.

Hierarchical superhydrophobic surfaces were constructed by growing various lengths of ZnO nanowires on microscale Si pyramids produced by chemical etching. The nano-size effect on wettability of nano/micro complex structures has been investigated by adjusting the ZnO nanowire length. As the nanowire length on the Si pyramid surface increases, a transition from the Wenzel state to the Cassie state occurs. A water contact angle as high as 169.1 , with a contact angle hysteresis less than 1.3 , was formed by growing ZnO nanowires of a suitable length on Si micro-pyramids. Compression and impact experiments further demonstrate the robust superhydrophobicity of ZnO nanowire Si pyramid hierarchical structures., The original document contains color images. Published in Journal of Materials Chemistry A, v2 p6180-6184, 2014.

High-resolution electron back-scatter diffraction (EBSD) analysis was employed to establish mircostructure evolution in heavily cold-rolled alpha-titanium. After thickness reductions of 75% to 96%, significant microstructure and texture changes were documented. The surface area of high-angle grain boundaries was almost tripled, thus giving rise to an ultra-fine microstructure with a mean grain size of 0.6 m. Moreover, orientation spread around typical split-basal rolling texture substantially increased. These effects were suggested to be related to the enhancement of pyramidal (c+a) slip., The original document contains color images. Published in Materials Science and Engineering A, v607 p145-154, 2014.

The overall research goal is to gain a detailed understanding of thermal transport through multilayered interfaces between dissimilar materials, using a combination of time-domain spectroscopy, physical modeling and materials processing. Specific goals for the overall project include; (i) investigate the structure, thickness and morphology of the copper-diamond interface for various processing conditions; (ii) assess the effect of interfacial morphology on bulk thermal conductivity, using appropriate models; (iii) publish the results of experimental investigations into bulk thermal properties of copper-diamond composites with various interfacial chemistries, including metallic and carbide layers, and; (iv) mimic the observed interface structure on a TDTR specimen by manipulating the various deposition techniques available to us experimentally., Prepared in collaboration with UES, Inc., Dayton, OH. Sponsored in part by AFOSR contract nos. F33615-04-D-5235, FA8650-10-D-5226 and FA8650-07-D-5800.

Segmenting materials images is a laborious and time-consuming process, and automatic image segmentation algorithms usually contain imperfections and errors. Interactive segmentation is a growing topic in the areas of image processing and computer vision, which seeks to find a balance between fully automatic methods and fully-manual segmentation processes. By allowing minimal and simplistic interaction from the user in an otherwise automatic algorithm, interactive segmentation is able to simultaneously reduce the time taken to segment an image while achieving better segmentation results. Given the specialized structure of materials images and level of segmentation quality required, we show an interactive segmentation framework for materials images that has three key contributions: (1) a multi-labeling approach that can handle a large number of structures while still quickly and conveniently allowing manual addition and removal of segments in real-time, (2) multiple extensions to the interactive toolswhich increase the simplicity of the interaction, and (3) a web interface for using the interactive tools in a client/server architecture., Published in Machine Vision and Applications, 2014.

Fatigue failure is a leading concern for many applications involving structures for transportation, manufacturing, medical devices, and electronic components. Recent advances in modeling and simulation, coupled with in situ experimental techniques, have enhanced the understanding required to distinguish and characterize mechanisms of fatigue crack formation and early growth at scales of underlying microstructure. In particular, microstructure substantially influences high cycle fatigue resistance and contributes to variability of the fatigue response. This paper reviews the confluence of recent experimental and modeling advances aimed at understanding and modeling of the formation and early growth of fatigue cracks with size on the order of dominant microstructure attributes., The original document contains color images. Prepared in collaboration with the Woodruff School of Mechanical Engineering and School of Materials Science & Engineering, Georgia Institute of Technology, Atlanta. Published in Current Opinion in Solid State and Materials Science, 2014.

The mechanical behavior of carbon nanotube (CNT) forests soaked in three solvents toluene, acetonitrile, and isopropanol is examined. Effective stiffness of the structure is evaluated in the dry and wet condition by micro-indentation using a 100 lm flat punch. With soaking of CNT forests in solvents, the stiffness decreases and deformation mechanism changes from buckling concentrated close to the bottom of the CNT forest to a distribution of local buckles along the height and global buckling of the entire length of CNTs. We use molecular dynamics simulations to relate the experimental observations to the reduced mechanical support from neighbor CNTs due to a decreased magnitude of van derWaals (vdW) interactions in the presence of solvents. Toluene, which produces the lowest average measured stiffness between the three solvents, produces the lowest vdW forces between individual CNTs. Furthermore, wet-dry cycling of CNT forests shows the reversibility and repeatability of change of stiffness by immersing in solvents. The results show that soaking CNT forests in solvents could be useful for applications such as interface materials where lower stiffness of CNT forests are needed and applications such as energy absorbing materials in which re-setting of stiffness is required., Published in Carbon, v69 p178-187, 7 Dec 2014. Sponsored in part by DARPA. Prepared in collaboration with the George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Universal Technology Corporation, Beavercreek, OH, the School of Mechanical and Materials Engineering, Washington State University, Pullman, and the School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta.

This report documents the final summation of a four-year in-house technical program on comprehensive materials development for organic, polymeric and carbonaceous composite and hybrid materials with combined structural loadbearing and other physical properties. The first three years of the four-year effort were comprised of tasks that were exclusively directed to fabrication, characterization and testing of multifunctional composite and hybrid materials for adaptive and shape-memory applications, and carbon fiber materials characterization and development. In the fourth and final year as the Composite and Hybrid Materials Exploratory Research Area (ERA), this bridge program incorporated portions of other areas such as thermal protective systems in extreme environments.

The Integrated Computational Model Development (ICMD) program worked to develop multiscale computational tools to predict material behavior based on its microstructure to: 1) accelerate materials development, 2) optimize the material and processes to ensure an optimal engineering design, and 3) enable optimized design using location-specific material properties.

In probabilistic design of materials for fracture-critical components in modern military turbine engines, a typical maximum design target risk (DTR) is 5 x 10 to the minus 8th power component failures/engine flight hour. This metric underscores the essential role of safety in a design process that simultaneously strives to achieve performance, efficiency, reliability, and affordability throughout the life cycle of the engine. Traditionally, the design and life management approaches for engine materials have typically relied on extensive testing programs to produce large databases of fatigue data, from which statistically based life limits are derived by extrapolation from the mean fatigue behavior. However, we have found that the statistical behavior of fatigue lifetimes under a given test condition often exhibits a bimodal form, and that the trends in mean vs. minimum fatigue lifetime typically respond differently to loading or to microstructural variables. Under such circumstances, the underlying life-limiting mechanisms appear to exhibit a probabilistic microstructural hierarchy in fatigue resistance that is controlled by susceptibility of local microstructural neighborhoods to early damage and the growth of small cracks. These findings suggest that significant opportunities may exist for reductions in uncertainty in materials life-cycle prediction and management, if such hierarchies can be understood and controlled. This paper explores the potential implications of these findings, and a number of possible approaches are suggested for incorporating the insights of life-limiting fatigue into methods of integrated computational materials engineering (ICME) to support optimized life-cycle design of materials and components in turbine engines., Prepared in collaboration with Universal Technology Corp., Dayton, OH and University of Dayton Research Institute, Dayton, OH. Published in International Journal of Fatigue, v57 p103-112, 2013.

A new computational method for characterizing the relationship between surface crystallography and electrical conductivity in anisotropic materials with low frequency electromagnetic techniques is presented. The method is discussed from the standpoint of characterizing the orientation of a single grain, as well as characterizing statistical information about grain ensembles in the microstructure. Large-area electron backscatter diffraction (EBSD) data was obtained and used in conjunction with a synthetic aperture approach to simulate the eddy current response of beta annealed Ti-6Al-4V. Experimental eddy current results are compared to the computed eddy current approximations based on electron backscatter diffraction (EBSD) data, demonstrating good agreement. The detectability of notches in the presence of noise from microstructure is analyzed with the described simulation method and advantages and limitations of this method are discussed relative to other NDE techniques for such analysis., Prepared in cooperation with the University of Dayton Research Institute, Dayton, OH, and the Southwest Ohio Council for Higher Education, Dayton, OH.

In this manuscript, we extend on our prior work to show that under certain conditions cross-slip nucleation is athermal and spontaneous with zero activation energy in FCC elemental metals such as Ni and Cu, and L12 intermetallic compounds such as Ni3Al. Using atomistic simulations (molecular statics), we show that spontaneous cross-slip occurs at mildly repulsive intersections. Further, the local Shockley partial dislocation interactions at such repulsive intersections are found to be attractive leading to junction formation. The line orientation of the intersecting dislocation determines whether the spontaneous cross-slip nucleation occurs from either the glide plane to the cross-slip plane or vice versa. Collectively, these results suggest that cross-slip should be preferentially observed at selected screw dislocation intersections in FCC-derviative metals and alloys., Published in Philosophical Magazine, v93 n22 p3012-3028, 2013. Sponsored in part by DARPA Contract no. N66001-12-1-4229.

Transparent and/or stretchable energy storage devices have attracted intense attention due to their unique optical and/or mechanical properties as well as their intrinsic energy storage function. However, it remains a great challenge to integrate transparent and stretchable properties into an energy storage device because the currently developed electrodes are either transparent or stretchable, but not both. Herein, we report a simple method to fabricate wrinkled graphene with high stretchability and transparency. The resultant wrinkled graphene sheets were used as both current collector and electrode materials to develop transparent and stretchable supercapacitors, which showed a high transparency \20157% at 550 nm\202 and can be stretched up to 40% strain without obvious performance change over hundreds of stretching cycles., Published in AC Nano, v8 n1 p1039-1046, 2014. Prepared in collaboration with the Center of Advanced Science and Engineering for Carbon (Case4Carbon) and Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, OH.

Autonomic materials are those that automatically respond to a change in environmental conditions, such as temperature or chemical composition. While such materials hold incredible potential for a wide range of uses, their implementation is limited by the small number of fully-developed material systems. To broaden the number of available systems, we have developed a post-functionalization technique where a reactive Ru Catalyst ink is printed onto a non-responsive polymer substrate. Using a succinimide-amine coupling reaction, patterns are printed onto co-polymer or biomacromolecular films containing primary amine functionality, such as polyacrylamide (PAAm) or poly-N-isopropyl acrylamide (PNIPAAm) copolymerized with poly-N-(3-Aminopropyl)methacrylamide (PAPMAAm). When the films are placed in the Belousov-Zhabotinsky (BZ) solution medium, the reaction takes place only inside the printed nodes. In comparison to alternative BZ systems, where Ru-containing monomers are copolymerized with base monomers, reactive printing provides facile tuning of a range of hydrogel compositions, as well as enabling the formation of mechanically robust composite monoliths. The autonomic response of the printed nodes is similar for all matrices in the BZ solution concentrations examined, where the period of oscillation decreases in response to increasing sodium bromate or nitric acid concentration. A temperature increase reduces the period of oscillations and temperature gradients are shown to function as pace-makers, dictating the direction of the autonomic response (chemical waves)., Published in Soft Matter, v10 p1329-1336, 2014.

Defects created during the manufacture of an oxide/oxide and two non-oxide (SiC/SiNC and MI SiC/SiC) ceramic matrix composites (CMCs) were categorized as follows: (1) Intra-yarn defects such as dry fibers, (2) Inter-yarn defects such as those at crossover points, matrix voids, shrinkage cracks and interlaminar separation, and (3) Architectural defects such as layer misalignment. Their impact on elastic properties was analytically investigated using a stiffness averaging approach considering the defects to have volumetric and directional influences. In-plane tensile and shear moduli as well as the through-thickness compressive modulus were experimentally evaluated. Results of analytical model were around 7% on average from the mean value of the experimental data. It was observed that interlaminar separation drastically reduced the through-thickness modulus by about 63% for the SiC/SiNC, 40% for the MI SiC/SiC and around 32% for the oxide/oxide composites. Shrinkage cracks in oxide/oxide composite reduced the in-plane tensile and shear moduli by 14% and 8.8%, respectively., Journal article published in Composites: Part B 55 (2013) 167-175. The original document contains color images.

We used residual gas analysis (RGA) to identify the species desorbed during field emission (FE) from a carbon nanotube (CNT) fiber. The RGA data show a sharp threshold for H2 desorption at an external field strength that coincides with a breakpoint in the FE data. A comprehensive model for the gradual transition of FE from adsorbate-enhanced CNTs at low bias to FE from CNTs with reduced H2 adsorbate coverage at high bias is developed which accounts for the gradual desorption of the H2 adsorbates, alignment of the CNTs at the fiber tip, and importance of self-heating effects with applied bias., Published in Applied Physics Letters, v103 article ID 053113, 31 Jul 2013. Prepared in collaboration with the Air Force Research Laboratory, Directed Energy Directorate, Kirtland AFB, NM. Prepared in cooperation with the Research Institute, University of Dayton, Dayton, OH, the Spintronics and Vacuum Nanoelectronics Laboratory, University of Cincinnati, Cincinnati, OH, and the Department of Chemical and Biomolecular Engineering and Department of Chemistry, The Smalley Institute for Nanoscale Science and Technology, Rice University, Houston, TX.

InAs/InGaSb superlattice (SL) materials are an excellent candidate for infrared photodiodes with cut-off wavelengths beyond 15 micrometer, i.e. in the very long infrared wavelength (VLWIR) range. There are relatively few options for high performance infrared detectors to cover wavelengths longer than 15 micrometer, especially for operating temperatures above 15K. There are a variety of possible superlattice designs that will cover the VLWIR wavelength range, including designs with and without indium alloying of the GaSb layers. Transport modeling has shown that alloy scattering should not be a dominant factor in these superlattices so our focus is on designs with 25% indium in the gallium antimonide to achieve energy band gaps less than 50 meV with a superlattice period on the order of 68 A. Similar to the work reported on InAs/GaSb LWIR and VLWIR superlattices, our designs employ InGaSb layers less than 7 monolayers in width. While the superlattice designs are strain balanced to the GaSb substrate, care was also taken to minimize strain spikes in the interfacial regions. High resolution transmission electron microscope images were analyzed to create strain mapping profiles of the SL layers and interfaces. By focusing on a narrow set of VLWIR SL designs, the deposition parameters for the molecular beam epitaxial SL growth could be carefully optimized., Prepared in collaboration with University of Dayton, Dept. of Physics, Dayton, OH.

The Composites Branch of the Air Force Research Laboratory?s Materials and Manufacturing Directorate (AFRL/RXCC) has observed anomalies in Q800 Dynamic Mechanical Analyzer (DMA) testing of fiber-reinforced polymer matrix composites related to both temperature dependence of the storage and loss moduli and to dependency of these data on specimen thickness using the dual-cantilever beam (DCB) clamp. Two factors are examined in detail: shear area factors used in the DCB stiffness calculations and coefficient of thermal expansion mismatch between the test specimen and the test frame. It is hoped this document will foster technical discussion with original equipment manufacturers of DMA instruments., Prepared in collaboration with University of Dayton Research Institute, Dayton, OH.

The effect of exposure at temperatures commonly used for wrought processing/heat treatment of nickel-base superalloys on the loss of alloying elements at the free surface has been determined. For this purpose, LSHR superalloy samples were exposed at 1408 K (1135 C) for 0.25 to 4 h in a vacuum or air furnace. Samples heat treated in the air furnace were either bare or enclosed in quartz capsules that had been evacuated or backfilled with argon. Following heat treatment, the alloy composition as a function of depth below the surface was determined by wavelength dispersive spectroscopy. Samples that had been heat treated in the vacuum furnace exhibited significant depletion of only chromium, a behavior explained on the basis of its high activity in nickel solid solution and corresponding rapid rate of evaporation. By contrast, samples heat treated in air exhibited an irregular scale at the surface and an underlying grain-coarsened, gamma-prime-depleted metal layer lean in aluminum, titanium, and chromium. A yet different behavior characterized primarily by aluminum loss at the surface was noted for samples that had been heat treated in evacuated or argon-backfilled capsules. These observations were interpreted in the context of a reaction between the quartz capsule and the aluminum evaporant.

A meeting of representatives from combined government, industry, and academia was held to evaluate the implications of Integrated Computational Materials Engineering (ICME) with respect to current export control regulations and identify recommendations for improvement. The meeting was held on 22-23 January 2013 in Dayton, OH and focused on structural materials for aerospace applications. The group arrived at a focused set of four recommended actions to overcome the friction points between ICME and export control: 1) Develop ICME case studies and export control decision trees to more fully explore the interaction of ICME with export control; 2) Create tailored and accessible export control training to educate the ICME community on export controls; 3) Implement proactive government policy to promote evaluation of export control issues at the beginning of external research efforts through contracting procedures; and, 4) Clarify export control definitions to aid determination of applicability of specific controls in an ICME environment.

Tailoring the efficiency of fluorescent emission via plasmon - exciton coupling requires structure control on a nanometer length scale using a high-yield fabrication route not achievable with current lithographic techniques. These systems can be fabricated using a bottom-up approach if problems of colloidal stability and low yield can be addressed. We report progress on this pathway with the assembly of quantum dots (emitter) on gold nanorods (plasmonic units) with precisely controlled spacing, quantum dot/nanorod ratio, and long-term colloidal stability, which enables the purification and encapsulation of the assembled architecture in a protective silica shell. Overall, such controllability with nanometer precision allows one to synthesize stable, complex architectures at large volume in a rational and controllable manner. The assembled architectures demonstrate photoluminescent enhancement (5x) useful for applications ranging from biological sensing to advanced optical communication., The original document contains color images.

We explore a new process for the formation of peptide nanotubes (PNTs) using plasma-enhanced chemical vapor deposition (PECVD). This state-of-the-art process allows coating of substrates with various peptides, while controlling the uniformity of the coating regardless of the substrate and with lower costs. In this study, a custom-built PECVD chamber (housed at AFRL/RX) has been modified to allow for the sublimation of solid monomers into the plasma stream and coat a variety of substrates held downstream from the plasma zone. The project was carried out in two stages; the first stage tested the feasibility of depositing diphenylalanine PNTs on activated carbon electrodes using PECVD in collaboration with AFRL. The second stage tested the quality of the deposited nanotubes and its effect on electrical capacitance and the contribution to the transfer of electrical cargo on activated carbon electrodes. Herein, we have demonstrated that surfaces such as activated carbon (both rough and smooth) can be coated with a layer of diphenylalanine peptide nanostructures. Coating rough carbon surfaces with peptides nanotubes can be inhomogeneous, but when these surfaces are treated with nitric acid, prior to the application of the peptides, the peptide coatings rearranged in homogenous forms of wires and tubes on the surface., The original document contains color images. Prepared in cooperation with Tel Aviv University, Israel.

Structural Health Monitoring (SHM) sensor systems have gained much interest in the aerospace community as potentially enabling technologies for reducing maintenance costs while maintaining flight safety of aging structures. Many candidate SHM technologies are essentially damage detection systems, i.e. variations of well-established NDI methods such as ultrasonics, electro-magnetic (eddy current), and acoustic emission. Still others employ displacement detection such as strain-sensing and dynamic vibration sensing. Unfortunately, the path for transition onto United States Air Force (USAF) weapon systems is not well defined. Before SHM technologies can be qualified for fleet-wide usage, these systems must demonstrate their capability to meet performance requirements in terms of detection capability, reliability, and safety while and providing an economic benefit. Ultimately the qualification program must be sufficiently robust to support an airworthiness certification decision. This document provides guidance for the demonstration and qualification of permanently mounted damage detection systems intended for use on USAF aircraft. More specifically, this document will a) focus on applications where damage tolerance principles are used to manage structural integrity, b) propose a task-based approach for system qualification, and c) identify existing Air Force policies that define the path for modification management and obtaining airworthiness certification approval.

Vapor phase growth of gold, nickel and titanium metal nanoparticles on multiwall carbon nanotube (MWCNT) buckypaper by sputtering was investigated. The size and distribution of nanoparticles was dependent on the intrinsic binding energy of the metal elements, but could be altered to mimic that of metals with different binding energies by in situ modification of the MWCNT surfaces by energetic metal ions or annealing of the buckypaper. A range of average gold particle diameters from approximately 5 30 nm could be produced depending on the intrinsic sputter process parameters (especially metal ion flux and kinetic energy) and defect density of the MWCNT surfaces, which could also be controlled by annealing prior to sputtering. The diameter of the MWCNTs had a significant influence on the geometry of the nanoparticles. Particles were elongated along the nanotube axis for tube diameters 30 nm. Remarkably strong alignment of the particles along the nanotube axis was observed, especially for MWCNTs with higher defect densities., Published in Carbon, v57 p274-281, 1 Feb 2013. Prepared in cooperation with the Department of Chemical and Materials Engineering and the University of Dayton Research Institute, University of Dayton, Dayton, OH, and the George W. Woodruff School of Mechanical Engineering and School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta.

This research effort involved studies on chemically synthesized quantum dots, epitaxially created quantum dots and graphene thin films. For this report we have gathered together seven research papers on chemically synthesized quantum dots that were published in the last two years. Titles are: Analysis of Thermal Band Gap Variations of PbS Quantum Dots by Fourier Transform Transmission and Emission Spectroscopy; Supercritical Fluid Deposition of Uniform PbS Nanoparticle Films for Energy-Transfer Studies; Lead Sulfide Quantum Dot Synthesis, Deposition, and Temperature Dependence Studies of the Stokes Shift; Fourier Spectroscopy on PbS Quantum Dots; PbS Nanoparticles: Synthesis, Supercritical Fluid Deposition, and Optical Studies; Emission of Precipitation Deposited PbS Quantum Dots on Polyethylen Terephthalate; Stability Studies of Lead Sulfide Colloidal Quantum Dot Films on Glass and GaAs Substrates.

Hydrophilic mercaptosuccinic acid (MSA) monolayer-protected gold nanorods (GNRs) were synthesized. The resulting GNRs encapsulated with biocompatible MSA molecules via covalent Au-S linkages were found to be able to self-aggregate through intermolecular hydrogen bonding. Interestingly, when the hybrid GNRs (MSA-GNR) were mixed with the hydrophilic fluorescent perylene diimide (PDI) molecules and carboxylic acid modified single-wall carbon nanotubes (CNT-COOH) respectively, their aggregation behaviors were pH- and temperature-dependent, which were investigated by UV-vis, fluorescence spectra, and TEM images. The aggregates of MSA-GNR with functional PDI and CNT-COOH were able to combine the properties of each component together through non-covalent interactions, providing insight in developing new multi-functional metal nanocomposites with properties tailored for their practical application., Published in the Journal of Physical Chemistry C, 7 Mar 2013. Prepared in cooperation with the Liquid Crystal Institute, Kent State University, Kent, OH, the Department of Chemistry, Mugla University, Mugla, Turkey, and Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, OH.

The physical state of the catalyst and its impact on the growth of single-walled carbon nanotubes (SWNTs) is the subject of a long-standing debate. We addressed it here using in situ Raman spectroscopy to measure Fe and Ni catalyst lifetimes during the growth of individual SWNTs across a wide range of temperatures (500 1400 C). The temperature dependence of the Fe catalyst lifetimes underwent a sharp increase around 1100 C due to a solidto- liquid phase transition. By comparing experimental results with the metal carbon phase diagrams, we prove that SWNTs can grow from solid and liquid phase-catalysts, depending on the temperature., Published in AC Nano, 2013. Prepared in cooperation with the National Research Council, Washington, D.C., the University of Dayton Research Institute, Dayton, OH, Duke University, Durham, NC, and the Honda Research Institute, Columbus, OH.

Broader applications of carbon nanotubes to real-world problems have largely gone unfulfilled because of difficult material synthesis and laborious processing. We report high-performance multifunctional carbon nanotube (CNT) fibers that combine the specific strength, stiffness, and thermal conductivity of carbon fibers with the specific electrical conductivity of metals. These fibers consist of bulk-grown CNTs and are produced by high-throughput wet spinning, the same process used to produce high-performance industrial fibers. These scalable CNT fibers are positioned for high-value applications, such as aerospace electronics and field emission, and can evolve into engineered materials with broad long-term impact, from consumer electronics to long-range power transmission., Published in Science, v 339 p182-186, 11 Jan 2013. Sponsored in part by AFRL. The original document contains color images.