Nanoscience and Nanotechnology Commons^™

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 …

Microstructure And Electrochemical Characteristics Of The Anodic Film Formed On Aluminum Surface, Jeng-Kuei Chang, Chi-Min Liao, Chih-Hsiung Chen, Wen-Ta Tsai

Journal of Electrochemistry

The thickness, morphology, chemical composition, and crystallinity of the anodized film formed on aluminum were examined in a transmission electron microscope (TEM). Thin foil for TEM analysis was prepared by ultramicrotomy. The relationship between the microstructure and the electrochemical characteristics of the alumina film forming on the pure aluminum was discussed in this investigation. At the forming voltage less than 100V, the anodized films formed at 85 ℃in aqueous ammonium adipate electrolyte was amorphous in nature. Although the film resistance was increased with the forming voltage, its dielectric constant was not changed significantly. As the forming voltage exceeded 100V, crystalline …

Study Of Marine Biocorrosion Using Afm And Molecular Techniques, Herbert H.P.Fang, Lichong Xu, Tong Zhang

Journal of Electrochemistry

Biofilm is ubiquitous in nature.However,corrosin caused by biofilm is still by and large overlooked. This presentation is to demonstrate the applications of several newly developed analytical techniques in chemisrty and microbiology for the study of marine biocorrosion on steel. AFM(atomic force microscopy) was applied to investigate the initial formation mechanism of biofilm and the degree of corrosion of steel in polluted seawater. DNA/RNA-related molecular techniques were used to analyze the microbial composition corrosive biofilm. Results showed that microbial corrosion began within six days, and the corroded volume in the increased as a power function of time with an index 2.83. …

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 …

Microstructural Study Of Nanoprecipitates In Rra Treated Al-7075 T6 Using Afm/Ufm/Stem, Samuel J.M. Kuhr, Margaret Pinnell, Daniel Eylon

Mechanical and Aerospace Engineering Faculty Publications

7075 T651 aluminum alloy is frequently used in aircraft applications for its high strength to weight ratio. However, aircraft parts made of this alloy have been plagued by stress corrosion cracking (SCC). Retrogression and re-aging (RRA) is a post T651 two-stage heat treatment that provides improved SCC resistance with minimal loss in tensile strength. In this study, various forms of microscopy and mechanical testing are used to investigate how the RRA process affects the microstructure.

The microscopic observations in this paper show that the precipitates in the aluminum alloy coarsen and that the grain boundary regions are depleted of copper …

In Situ Measurements Of Solution Conductivity In Microwave Field, Yong-Qing Su, Chun-Peng Liu

Journal of Electrochemistry

The curves of the conductivity as a function of temperature for 24 kinds of solutions have been in situ measured both in the microwave field and in absence of microwave field. The results indicated that the relationship between the conductivity in microwave field (L_w) and temperature (T) can be expressed by an equation L_w=a′+b′T+c′T² , similar to the one that is valid in absence of the microwave field L_n=a+bT+cT². Conductivity in the absence and presence of microwave field can be linked by the equation lnL_w=A+BL_n+CL²_{n …}

Pure Iron Electrolyzed From Scrap Iron Chips And Its Corrosion Characteristics, Wei-Min Cao, Ren-He Yin, Hui-Ceng Yan, Zhi-Qiang Ye

Journal of Electrochemistry

The high purity electrolytic iron was made from scrap iron chips. Electrolytic conditions of pure iron were determined in chloride baths and the highest purity was 99.983% by chemical analysis. Pure iron had very compact texture and high mechanical strength by SEM figures of cross section. In deaerated 0.5 kmol·m^-3 H₂SO₄ and 0.5 kmol·m^-3 NaCl solutions, the corrosion rate of iron decreased with increasing purity.

Study For The Cathodic Behavior Of Active Chlorine On 316l Ss Electrode Surface, Hui Yu, Ming-Xian Sun, Yan Ma, Xiao-Bin Wang

Journal of Electrochemistry

The cathodic reducing reactions of active chlorine on 316 L SS electrode surface have been investigated by electrochemical techniques. The open circuit potential shifted positively and the limited diffusion current density increased significantly with the increasing content of active chlorine in the 3.5% sodium chloride solution. The two cathodic reduction processes of HClO and ClO^- exhibited on the surface of electrode with the active chlorine added to the 3.5%sodium chloride solution and the corresponding potentials of the two reducing reactions were confirmed. The linear relationship of the mass transport-limited Faradaic current, Id vs. the square root of the angular …

The Effect Of Processing Conditions On Varistors Prepared From Nanocrystalline Zno, Suresh Pillai, Declan Mccormack, John Kelly, Ramesh Raghavendra

Articles

Nanoparticles of ZnO were prepared by the reaction of ethanolic solutions of zinc acetate and oxalic acid
followed by drying (80 uC) and calcination (500 uC). Subsequently varistor materials were fabricated from this
nanoparticular ZnO via two separate routes:- a) from a ‘‘core shell’’ material using metal salts as additives; b)
by using a conventional solid state mixing of metal oxides. Sintering (1050 uC) and subsequent electrical studies
were carried out for each of these samples and they were compared with commercial varistor samples prepared
under similar conditions. ‘‘Core shell’’ type varistor material showed considerably higher breakdown voltage
(Vc ~ …

Ultrafine Nife2o4 Powder Fabricated From Reverse Microemulsion Process, Jiye Fang, Narayan Shama, Le Duc Tung, Eun Young Shin, Charles J. O'Connor, Kevin L. Stokes, Gabriel Caruntu, John B. Wiley, Leonard Spinu, Jinke Tang

Physics Faculty Publications

NiFe2O4 ultrafine powder with high crystallinity has been prepared through a reverse microemulsion route. The composition in starting solution was optimized, and the resulting NiFe2O4 was formed at temperature of around 550–600 °C, which is much lower than that observed from the solid-state reaction. Magnetic investigation indicates that samples are soft-magnetic materials with low coercivity and with the saturation magnetization close to the bulk value of Ni ferrite.

Self-Assembly Of Fept Nanoparticles Into Nanorings, Weilie L. Zhou, Jibao He, Jiye Fang, Tuyet-Anh Huynh, Trevor J. Kennedy, Kevin L. Stokes, Charles J. O'Connor

Physics Faculty Publications

The application of nanoparticles as quantum dots in nanoelectronics demands their arrangement in ordered arrays. Shape controlled self-assembly is a challenge due to the difficulties of obtaining proper self-assembling parameters, such as solvent concentration, organic ligands, and nanoparticle size. In this article, hard magnetic FePt nanoparticles were synthesized using a combination approach of reduction and thermal decomposition. The nanoparticles are about 4.5 nm and appeared as truncated octahedral enclosed by the

{100} and {111}

crystal facets of fcc structure. The nanoparticles are of hexagonal close packing and orient randomly in the self-assembly nanoarrays.  By diluting the solution for large-area self-assembly, …

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.

Detection And Analysis Of Sec1 Immunological Reaction By Afm And Electrochemical Method, Sa-Ying Dong, Hong-Ren Wang

Journal of Electrochemistry

The goals of this work were to demonstrate the ability of atomic force microscopy (AFM) to detect various immunological processes between antibodies and antigens.A sensor was designed by covalently linking the antibody of staphylococcal enterotoxin Cl (SEC1) on the self-assembled gold surface. This sensor permitted detection of antibody-antigen recognition events which were highly correlated with the topography under different conditions. The statistic data of AFM were analysed. As control experiments, nonspecific antigens and lower concentration SEC1 antigens were directly observed. In addition, an acidic solution was used to break the antigen-antibody pair and made the sensor reuse. Electrochemical evidence was …

Preparation And Electrochemical Lithium Intercalation Performance Of Different Shaped Carbon Nanotube, Mao-Hui Chen, Zhen-Cai Huang, Guo-Tao Wu, Jin-Kua You, Zu-Geng Lin

Journal of Electrochemistry

In the present work, different shaped carbon nanotubes were produced by the general CVD and the template method at different temperature (600 ℃,700 ℃) with the reaction gas of acetylene. The morphology, structure and the electrochemical lithium intercalation performance were comparatively studied and characterized by TEM, HRTEM, SEM, XRD, Raman techniques and Charge/Discharge Test. It was found that the different preparation methods and temperatures all had an obvious effect on these properties of carbon nanotubes. In our samples, with the increase of preparation temperature, the degree of crystallinity decreased, and the reversible specific capacity increased respectively.

Nano-Sized Cobalt-Based Oxides As Negative Electrode For Lithium-Ion Batteries, Feng Huang, Zheng-Yong Yuan, Yun-Hong Zhou, Ju-Tang Sun

Journal of Electrochemistry

Nanosized cobalt-based oxide (Co₃O₄, CoB_1.36O_2.8 and CoB_0.5Al_0.1O_1.5) samples were prepared by rheological phase method and were tested as anodes in secondary lithium batteries. The cells were cycled between 0.01V and 3.00 V. The best electrochemical performance was obtained from the Co₃O₄ cell, which retained 95% of its initial capacity (931 mAh/g) after 30 cycles. The doping of B, Al reduced the reversible capacity during the first discharge/charge cycle, and the quantity of reversible capacity reduced with B, Al increasing. The modifying structures at difference …

Electrochemical Preparation And Reaction Mechanism Of Nanocrystalline Nio, Jia-Shan Gu, Ai-Jie Han, Xing-Fu Zhou, Dao-Bao Chu, Chang-Jian Lin

Journal of Electrochemistry

Metallic nickel was electrochemically dissolved in absolute ethanol and acetylacetone mixed solutions and in the presence of Bu₄NBr (as an electron-conductive additive). The electrolyte solution containing the precursor was then directly hydrolyzed to obtain nanocrystalline NiO. The precursor was characterized by FTIR, HNMR, Raman spectra and the nano-powder was characterized by XRD and TEM. The results showed that the NiO powder after calcined at 450 ℃ had formed the cubic NaCl structure and the nanocrystalline NiO prepared by this method had narrow size distribution of 10～15 nm. Moreover, the product yield could be improved by controlling temperature below …

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.

Facilitated K+ Ion Transfer By Db18c6 Across The Micro Liquid/Liquid Interface, Dong-Ping Zhan, Bing-Liang Wu

Journal of Electrochemistry

A novel microcavity Ag|AgCl electrode was fabricated to construct the micro-interface of two immiscible electrolyte solutions(ITIES). The transfer reactions of K⁺ ion facilitated by DB18C6 across the water/1,2-DCE interface was investigated with the three-electrodes system. The corresponding reaction parameters were derived from the voltammetric data. The results showed that the microcavity electrode would be a useful and efficient tool to investigate the charge transfer reactions at ITIES.

Pure Hap Film Prepared By Direct Electrodepositing On Metallic Surface And Its Mechanism, Hao-Bing Hu, Chang-Jian Lin, Fei Chen, Ren Hu, Ming Guo

Journal of Electrochemistry

In controlling concentration of Ca²⁺ and PO₄^3- in electrodeposition solution, the HAP film on Ti alloy has been deposited directly. Using XRD and SEM we have learned that prepared HAP is intact in crystal and equal in dimension. Thermodynamic calculation indicated that the HAP is easer formation of than that TCP of. With the XRD, SEM analyses and thermodynamic calculation, the electrodeposition mechanism has been discussed. It was proved that electrodepositon is a two-stage process and formation of HAP is a direct process from solution ions to HAP crystal without precursor.

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 …

Syntheses And Photoluminescence Of Zinc Oxide Polyaniline Coaxial Nanowires And Their Array, Zhi-Xin Zheng, Yan-Yan Xi, Ping Dong, Huai-Guo Huang, Jian-Zhang Zhou, Lin-Lin Wu, Zhong-Hua Lin

Journal of Electrochemistry

A novel nanomaterial, zinc oxide (ZnO) and polyaniline (PANI) coaxial nanowires and their array in the template, was synthesized using anodic aluminum oxide (AAO) membrane as template. The morphology of these coaxial nanowires was observed with transmission electron microscope (TEM). The experiments on photoluminescence (PL) of coaxial nanowires and their array in AAO membrane show that the visible emission band of ZnO shifts from 530 nm to 400 nm and the luminescence is enhanced for the coaxial nanowires array in AAO membrane,and the visible emission band shifts to a lower wavelergth (385 nm) for coatial nanowires in NaOH solution. Possible …

The Preparation And Characterization Of Growing Preferentially Cds Nanopartile Film, Huai-Guo Huang, Yan-Yan Xi, Zhi-Xin Zheng, Jia-Wei Yan, Jian-Zhang Zhou, Ling-Ling Wu, Zhong-Hua Lin

Journal of Electrochemistry

CdS nanoparticle films were prepared on the PANI film, PATP film, Au film and ITO respectively by constant current deposition or current impulse method, and their structure and character were also studied. The results show that the substrates influence the structure and character of CdS particle film.

Nanofatigue Studies Of Ultrathin Hard Carbon Overcoats Used In Magnetic Storage Devices, Xiaodong Li, Bharat Bhushan

Faculty Publications

A technique to perform nanofatigue experiments was developed. This technique utilizes a depth-sensing nanoindenter with harmonic force. The nanofatigue behavior of 20 nm thick amorphous carbon coatings was studied. The contact stiffness was monitored continuously throughout the test. The abrupt decrease in the contact stiffness indicates fatigue damage has occurred. The critical load amplitude, below which no fatigue damage occurs, was identified. It was found that the filtered cathodic arc coating exhibits longer fatigue life than a direct ion beam coating. Failure mechanisms of the coatings during fatigue are also discussed in conjunction with the hardness,elastic modulus, and fracture toughness, …