Nanoscience and Nanotechnology Commons^™

Trailer Mounted Bursting Energy Absorption System, John D. Reid, John R. Rohde, Dean L. Sicking

Department of Mechanical and Materials Engineering: Faculty Publications

A portable crash attenuation System having a trailer frame and an energy absorption mechanism attached thereto. The absorption mechanism has a first Stage pivotably connected to a Second Stage and the Second Stage is pivotably connected to the frame. By pivoting the Stages about hinges the attenuation System may be folded from an extended, deployed position or mode to a shortened transit mode for easy relocation of the entire attenuation System.

Solid-Like Dynamics In Ultrathin Films Of Polymeric Liquids, Gaurav Singh, Ravi F. Saraf, Yves Martin

Papers in Nanotechnology

In this letter, we demonstrate that, at mesoscales, nonferroelectric liquid films of polydimethyl siloxane. exhibit significant electrostriction not present in the corresponding bulk state. Remarkably, the observed electrostrictive effect has a response time ,20 ms in contrast to .5 ms recorded in conventional bulk ~ferroelectric polymers. The emergence of this fast electrostrictive strain in thin films is explained in terms of the amalgamation of two contrasting dynamic features—the influence of a highly mobile, viscous layer ~at the air/film interface. on the less-mobile, but fast responding, solid-like layer at the film/substrate interface. The effect is observed for thickness below 200 nm.

Manufacturing Of Novel Continuous Nanocrystalline Ceramic Nanofibers With Superior Mechanical Properties, Yuris A. Dzenis, Ruqiang Feng, Gustavo F. Larsen, Joseph Turner, Xiao Cheng Zeng

Papers in Nanotechnology

This project is in the area of nanomanufacturing of advanced nanostructured materials. Nanostructured materials (NSMs) with unusual and extreme properties will play a key role in many emerging technologies. However, manufacturing of NSMs with the desired properties is highly complex and currently is over-reliant on empirical data. In this project, a novel manufacturing process producing a new class of ceramic materials, i.e. continuous ceramic nanofibers, is addressed. The novel sol-gel electrospinning technique (patents pending), invented recently by two of the PI’s (Dzenis and Larsen), produces ceramic fibers of submicron diameters with potentially extreme thermomechanical properties. This technique is being analyzed …

Atomic Force Acoustic Microscopy Methods To Determine Thin-Film Elastic Properties, D.C. Hurley, K. Shen, N.M. Jennett, Joseph A. Turner

Nebraska Center for Materials and Nanoscience: Faculty Publications

We discuss atomic force acoustic microscopy (AFAM) methods to determine quantitative values for the elastic properties of thin films. The AFAM approach measures the frequencies of an AFM cantilever’s first two flexural resonances while in contact with a material. The indentation modulus M of an unknown or test material can be obtained by comparing the resonant spectrum of the test material to that of a reference material. We examined a niobium film (d=280±30 nm) with AFAM using two separate reference materials and two different cantilever geometries. Data were analyzed by two methods: an analytical model based on conventional …

Elastic Wave Propagation And Scattering In Solids With Uniaxially Aligned Cracks, Liyong Yang, Joseph A. Turner

Nebraska Center for Materials and Nanoscience: Faculty Publications

In this article, elastic wave propagation and scattering in a solid medium permeated by uniaxially aligned penny-shaped microcracks are studied. The crack alignment refers to the case in which the unit normals of all cracks are randomly oriented within a plane of isotropy. The analysis is restricted to the limit of the noninteraction approximation among individual cracks. Explicit expressions for attenuations and wave speeds of the shear horizontal, quasilongitudinal, and quasishear vertical waves are obtained using stochastic wave theory in a generalized dyadic approach. The ensemble average elastic wave response is governed by the Dyson equation, which is solved in …

Optically Transparent, Scratch-Resistant, Diamond-Like Carbon Coatings, Xiao-Ming He, Deok-Hyung Lee, Michael A. Nastasi, Kevin C. Walter, Michel G. Tuszewski

Department of Mechanical and Materials Engineering: Faculty Publications

A plasma-based method for the deposition of diamond-like carbon (DLC) coatings is described. The process uses a radio-frequency inductively coupled discharge to generate a plasma at relatively low gas pressures. The deposition process is environmentally friendly and scaleble to large areas, and components that have geometrically complicated surfaces can be processed. The method has been used to deposit abherent 100-400 nm thick DLC coatings on metals, glass, and polymers. These coatings are between three and four times harder than steel and are therefore scratch resistant, and transparent to visible light. Boron and silicon doping of the DLC coatings have produced …

Method For Producing Fluorinated Damond-Like Carbon Films, Marko J. Hakovirta, Michael Nastasi, Deok-Hyung Lee, Xiao-Ming He

Department of Mechanical and Materials Engineering: Faculty Publications

Fluorinated, diamond-like carbon (F-DLC) films are produced by a pulsed, glow-discharge plasma immersion ion processing procedure. The pulsed, glow-discharge plasma was generated at a pressure of 1 Pa from an acetylene (CH) and hexafluoroethane (CF) gas mixture, and the fluorinated, diamond-like carbon films were deposited on silicon <100>Substrates. The film hardness and wear resistance were found to be strongly dependent on the fluorine content incorporated into the coatings. The hardness of the F-DLC films was found to decrease considerably when the fluorine content in the coatings reached about 20%. The contact angle of water on the F-DLC coatings was found …

Jecp/Ed — A Computer Program For Simulation Of Selected-Area And Precession Electron Diffraction Patterns, Xingzhong Li

Nebraska Center for Materials and Nanoscience: Faculty Publications

Crystal structure determination by electron crystallography has been very successful in many fields, ranging from organic to inorganic materials. Collection of electron diffraction data is still a crucial step in electron crystallography. The curvature of the Ewald sphere limits the data available in each electron diffraction pattern. The dynamical multi-scattering effect of electron diffraction increases the complexity of the structure determination procedure.

A precession method (Vincent & Midgley, 1994) has been used to solve the crystal structure of AlmFe by Gjonnes and coworker (Berg et al., 1998; Gjonnes et al., 1998). The advantages of precession electron diffraction are (i) the …

Scattering Of Elastic Waves In Damaged Media, Liyong Yang, Joseph A. Turner

Nebraska Center for Materials and Nanoscience: Faculty Publications

The scattering of elastic waves in a medium with damage from microcracking is discussed. The influence of damage from penny-shaped microcracks within a homogeneous medium is considered. The microcracks are assumed to be randomly oriented and uniformly distributed. Explicit expressions are derived for the attenuation of longitudinal and shear elastic waves in terms of the damage parameter and the effective elastic moduli of the medium. A generalized tensor-based approach is used such that the results are coordinate free. The derivation is based upon diagrammatic methods. The problem is formulated in terms of the Dyson equation, which is solved for the …

Multiscale Modeling Of Hysteretic Phenomena In Magnets „(Invited), Vladimir P. Antropov, Kirill D. Belashchenko

Nebraska Center for Materials and Nanoscience: Faculty Publications

Methodology of multiscale modeling of hysteretic phenomena in magnets is discussed. A practical combination of first-principles, micromagnetic, and microstructural calculations is constructed which allows one to study the hysteretic phenomena in hard magnets. Advantages and shortcomings of this approach are discussed. Multiscale nature of coercivity in CoPt type magnets is elucidated. Two sources of coercivity in polytwinned CoPt type magnets developing at different length scales, domain wall pinning at antiphase boundaries and splitting at twin boundaries, are illustrated for a realistic microstructure

Stability Of Order In Solvent-Annealed Block Copolymer Thin Films, Sanjun Niu, Ravi F. Saraf

Papers in Nanotechnology

ABSTRACT: One way to produce high order in a block copolymer thin film is by solution casting a thin film and slowly evaporating the solvent in a sealed vessel. Such a solvent-annealing process is a versatile method to produce a highly ordered thin film of a block copolymer. However, the ordered structure of the film degrades over time when stored under ambient conditions. Remarkably, this aging process occurs in mesoscale thin films of polystyrene-polyisoprene triblock copolymer where the monolayer of vitrified 15 nm diameter polystyrene cylinders sink in a 20 nm thick film at 22 °C. The transformation is studied …

Alloy States In Dilute Gaas1-XNX Alloys (X<1%), X. D. Luo, Jinsong Huang, Z. Y. Xu, C. L. Yang, J. Liu, W. K. Ge, Y. Zhang, A. Mascarenhas, H. P. Xin, C. W. Tu

Department of Mechanical and Materials Engineering: Faculty Publications

A set of GaAs_1-xN_x samples with small nitrogen composition (x<1%) were investigated by continuous-wave photoluminescence (PL), pulse-wave excitation PL, and time-resolved PL. In the PL spectra, an extra transition located at the higher-energy side of the commonly reported N-related emissions was observed. By measuring the PL dependence on temperature and excitation power, the PL peak was identified as a transition of alloy band edge-related recombination in GaAsN. The PL dynamics further confirms its intrinsic nature as being associated with the band edge rather than N-related bound states.

Multiscale Nature Of Hysteretic Phenomena: Application To Copt-Type Magnets, Kirill D. Belashchenko, Vladimir P. Antropov

Nebraska Center for Materials and Nanoscience: Faculty Publications

We suggest a workable approach for the description of multiscale magnetization reversal phenomena in nanoscale magnets and apply it to CoPt-type alloys. We show that their hysteretic properties are governed by two effects originating at different length scales: a peculiar splitting of domain walls at twin boundaries and their strong pinning at antiphase boundaries. We emphasize that such multiscale nature of hysteretic phenomena is a generic feature of nanoscale magnetic materials.

Rectangular Bursting Energy Absorber, John D. Reid, John R. Rohde, Dean L. Sicking

Department of Mechanical and Materials Engineering: Faculty Publications

A bursting energy absorber System having an impact head, and energy absorption mechanism. The energy absorbing mechanism has a generally rectangular mandrel for rupturing cooperating thin-walled generally rectangular tubes in a controlled rupture to absorb impact forces for a colliding vehicle. A frame may be used to mount the System to a truck, trailer, guardrail, median barrier end treatment, or a crash cushion. Stress concetrators such as saw cuts or scoring may be incorporated into the absorption tubes to selectively control rupturing and energy dissipation. The mandrels may be tapered, rectangulary shaped with beveled edges to reduce frictional forces along …

In Situ Corrosion Studies On The Battleship Uss Arizona, John D. Makinson, James D. Carr, Matthew A. Russell, David L. Conlin, Larry E. Murphy

Department of Mechanical and Materials Engineering: Faculty Publications

U.S. National Park Service Submerged Resources Center archaeologists and University of Nebraska-Lincoln metallurgists are assessing hull corrosion by drilling through accumulated concretions and measuring pH and corrosion potentials. Concretion samples are being analyzed to determine the role of microbes in the corrosion process, identify chemical species, and measure electrical and physical properties. The lowest values of pH and E corr occur at the metal/concretion interface. Analysis suggests a variable corrosion rate supported by hydrogen discharge and/or oxygen reduction inside the concretion.

Spontaneous Planarization Of Nanoscale Phase Separated Thin Film, Ravi F. Saraf, Sanjun Niu, Eric Stumb

Papers in Nanotechnology

Structure of complex fluid at mesoscales is influenced by interfacial effects. We describe the dynamic response in such films to sudden change in interfacial tension. In a self-assembled block copolymer film, the monolayer of 15 nm diam cylindrical discrete phases close to the surface commence to sink at an average rate of 0.16 nm/day in response to the interfacial tension change. Surprisingly, this spontaneous planarization occurs, even though the cylinders are covalently stitched to the matrix. A simple model explains the observed behavior. The observation may lead to approaches to tailor the structure of mesoscale thin films of complex fluids …

Structure Of Macrodomain Walls In Polytwinned Magnets, Kirill D. Belashchenko, Vladimir P. Antropov

Nebraska Center for Materials and Nanoscience: Faculty Publications

We propose a microscopic approach to the studies of magnetic configurations in hard magnets which may be conveniently used for nanoscale systems; the microstructure of the magnet is easily and naturally included in the calculations. This approach is applied to find the structure of macrodomain walls in polytwinned magnets of the CoPt family. Magnetostatic fields are small compared to the anisotropy field in these magnets; direct simulation shows that in this case the macrodomain wall is not continuous, but rather comprised of segments held together by relatively small magnetostatic forces. This segmentation is expected to have a strong effect on …

Magnetization Reversal Of Individual Nanowires With Controlled Defects, Andrei Sokolov, Renat F. Sabirianov, W. Wernsdorfer, Bernard Doudin

Nebraska Center for Materials and Nanoscience: Faculty Publications

Low temperature magnetization reversal measurements were performed on individual permalloy nanowires of diameters between 30 and 60 nm. During the electrochemical growth of the wire, a defect was induced by a short pulse in the deposition potential modifying locally the microstructure and composition. Magnetic measurements performed with micro-superconducting quantum interference devices were performed. The angular dependence of switching field revealed significant deviations from classical predictions. For specific angles, magnetization curves indicate a reversal occurring in two steps.

Characterization Of Crbn Films Deposited By Ion Beam Assisted Deposition, S.M. Aouadi, F. Namavar, E. Tobin, N. Finnegan, R.T. Haasch, R. Nilchiani, Joseph A. Turner, S. L. Rohde

Nebraska Center for Materials and Nanoscience: Faculty Publications

This article reports on the growth and analysis of CrBN nanocrystalline materials using an ion beam assisted deposition process. In addition, this article addresses the utilization of spectroscopic ellipsometry for in situ analysis of ternary nitrides. Coatings, with a total thickness of 1.5 ±0.2 μm, were deposited at low temperatures (<200 °C) on silicon substrates using ion beam assisted deposition. These coatings were characterized postdeposition using x-ray diffraction (XRD), atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), visible-light spectroscopic ellipsometry (VIS-SE), infrared spectroscopic ellipsometry (IR-SE), and nanoindentation. The primary phases in the films were investigated using XRD. The surface morphology and nanocrystalline nature of the coatings (grain size of 5–7 nm) were deduced using AFM. The elemental composition and phase composition of the samples were determined from XPS and AES measurements and were subsequently deduced from the analysis of the VIS-SE data, and these correlated well. XPS, AES, and IR-SE revealed the crystal structure of the BN phase in the ternary compounds. The correlation of the results from these various techniques indicates that in situ SE may be a potential technique to control the growth of ternary nitride coatings in the future. The mechanical properties of the coatings were evaluated using nanohardness testing. The hardness and elastic modulus were measured to be 19–22 GPa and 250–270 GPa, respectively.

Prediction Of Soakout Time Using Analytical Models, B. Chakravarthy, H. P. Cherukuri, R. G. Wilhelm

Department of Mechanical and Materials Engineering: Faculty Publications

In precision manufacturing enterprises, machine parts at nonstandard temperatures are often soaked to standard temperature prior to making any dimensional measurements. The soakout times are usually determined using lumped heat-transfer models where the part temperatures are assumed to be uniform. This article discusses conditions under which lumped model assumptions are valid by comparing lumped analyses for various shapes and materials with the more general finite element results. In addition, the effect of ambient temperature cycling on part response is also studied.

Boron Carbide/N-Silicon Carbide Heterojunction Diodes, Shireen Adenwalla, P. Welsch, A. Harken, Jennifer I. Brand, A. Sezer, Brian W. Robertson

Nebraska Center for Materials and Nanoscience: Faculty Publications

The fabrication, initial structural characterization, and diode measurements are reported for a boron carbide/silicon carbide heterojunction diode. Current–voltage curves are obtained for operation at temperatures from 24 to 351 °C. Plasma-enhanced chemical-vapor deposition (PECVD) -deposited undoped boron carbide material is highly crystalline and consists of a variety of polytypes of boron carbide (BC) with crystal sizes as large as 110 nm. Crystal phases are similar to those for PECVD BC on Si but only partially match known boron and boron-rich BC phases.

Hybrid Transient-Parametric Method And System To Distinguish And Analyze Sources Of Acoustic Emission For Nondestructive Inspection And Structural, Health Monitoring, Yuris Dzenis

Department of Mechanical and Materials Engineering: Faculty Publications

A nondestructive evaluation (NDE) technique for inspecting or health monitoring of Structures and/or Specimens by analyzing acoustic emission (AE) signals emitted by the Structures and/or specimens. The method and System ana lyzes acoustic emission (AE) signals emitted by structures and/or Specimens. AE Signals emitted by the Structures and/or Specimens are parametrically filtered as a function of parametric filters corresponding to characteristic waveforms of transient AE classes of predefined AE signals. In para metric analysis, the filtering may be pre- or post-recording. In transient AE analysis, the filtering may be prior to transient recording of the transient signals.

Crash Attenuation System, John D. Reid, John R. Rohde, Dean L. Sicking

Department of Mechanical and Materials Engineering: Faculty Publications

A crash attenuation system having an impact head, and energy absorption mechanism. The energy absorbing mechanism has a mandrel for rupturing thin-walled tubes in a controlled rupture to absorb impact forces from a colliding vehicle. A frame may be used to mount the system to a truck, trailer, guardrail, median barrier end treatment, or a crash cushion. Stress concentrators may be incorporated into the tubes and the mandrels to selectively control rupturing and energy dissipation.

Anisotropy Of Conducting P States And 11B Nuclear Spin-Lattice Relaxation In Mg1-XAlXB2, Kirill D. Belashchenko, Vladimir B. Antropov, S.N. Rashkeev

Nebraska Center for Materials and Nanoscience: Faculty Publications

We calculated the nuclear spin-lattice relaxation rate in the Mg_1-xAl_xB₂ system and found that the orbital relaxation mechanism dominates over the dipolar and Fermi-contact mechanisms in MgB₂, whereas in AlB₂ due to a smaller density of states and strong anisotropy of boron p orbitals the relaxation is completely determined by Fermi-contact interaction. The results for MgB₂ are compared with existing experimental data. To validate the theory, nuclear resonance experiments for the studied diboride alloy system are needed.

Coexistence Of Covalent And Metallic Bonding In The Boron Intercalation Superconductor Mgb2, Kirill D. Belashchenko, Mark Van Schilfgaarde, Vladimir P. Antropov

Nebraska Center for Materials and Nanoscience: Faculty Publications

Chemical bonding and electronic structure of MgB₂, a boron-based newly discovered superconductor, is studied using self-consistent band-structure techniques. Analysis of the transformation of the band structure for the hypothetical series of graphite–primitive graphite–primitive graphitelike boron–intercalated boron, shows that the band structure of MgB₂ is graphitelike, with π bands falling deeper than in ordinary graphite. These bands possess a typically delocalized and metallic, as opposed to covalent, character. The in-plane σ bands retain their two-dimensional (2D) covalent character, but exhibit a metallic hole-type conductivity. The coexistence of 2D covalent in-plane and three-dimensional (3D) metallic-type interlayer conducting bands is …

Delamination Resistant Composites Prepared By Small Diameter Fiber Reinforcement At Ply Interfaces, Youris A. Dzenis, Darrell H. Reneker

Department of Mechanical and Materials Engineering: Faculty Publications

A fiber reinforced composite material comprising a resin matrix and primary reinforcement fibers and further comprising secondary, smaller diameter, reinforcement fibers at one or more ply interfaces, or portion thereof, provides improved interlaminar toughness, strength, and delamination resistance and without substantial increase in weight. In one embodiment, the small fibers are attached to one side of a conventional prepreg prior to lamination. The small fibers are flexible and are expected to conform to the shape and distribution of the primary reinforcing fibers at the interface.

Energy Absorbing Breakaway Steel Guardrail Post, John R. Rohde, John D. Reid, Dean L. Sicking

Department of Mechanical and Materials Engineering: Faculty Publications

An improved breakaway steel guardrail post for use in dissipation of impact energy upon impact of the post having an upper post member and a lower post member, a connecting joint, and a mechanism connected to the upper and lower post members for controlling the energy dissipation of the guardrail post about the connecting joint at a predetermined rate. A first embodiment utilizes a cable restraint lopped through openings in he guardrail posts. Other embodiments included straps and fasteners disigned to distort or fail at predetermined rates or strengths and combinations thereof.

Controlled Buckling Breakaway Cable Terminal, John D. Reid, John R. Rohde, Dean L. Sicking

Department of Mechanical and Materials Engineering: Faculty Publications

A crash attenuation apparatus for use with a guardrail system having rail posts and rail elements. An impact head has a buffer nose section and a rail post breaking beam system. The post breaking beam system has upper and lower breaking beams attached to the head. A guide tube is attached to the side of the head. A strut member extends from a first attachment point on the rail element to a second point downstream. Upon impact by a vehicle, the head breaks the first rail post, before impacting the strut and buckling the rail element downstream.

Superconductivity Of Metallic Boron In Mgb2, J. Kortus, I.I. Mazin, Kirill D. Belashchenko, Vladimir P. Antropov, L.L. Boyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

Boron in MgB₂ forms stacks of honeycomb layers with magnesium as a space filler. Band structure calculations indicate that Mg is substantially ionized, and the bands at the Fermi level derive mainly from B orbitals. Strong bonding with an ionic component and considerable metallic density of states yield a sizable electron-phonon coupling. Together with high phonon frequencies, which we estimate via zone-center frozen phonon calculations to be between 300 and 700 cm^-1, this produces a high critical temperature, consistent with recent experiments. Thus MgB₂ can be viewed as an analog of the long sought, but still …

Scattering Of Elastic Waves In Heterogeneous Media With Local Isotropy, Joseph A. Turner, Phanidhar Anugonda

Nebraska Center for Materials and Nanoscience: Faculty Publications

The scattering of elastic waves in heterogeneous media is discussed. Explicit expressions are derived for the attenuation of longitudinal and transverse elastic waves in terms of the statistics of the density and Lame´ parameter fluctuations. The derivation is based upon diagrammatic methods with the problem posed in terms of the Dyson equation. The Dyson equation is solved for the mean field response. The results are given here in a straightforward manner, in which the attenuations reduce to simple integrals on the unit circle. The medium is assumed statistically homogeneous and statistically isotropic. This model, with assumed local isotropic properties, is …