High resolution solid state NMR experiments were carried out on several compounds, to see how this technique can now be used to investigate in detail the surface structure of different biomaterials. First, because the surface of titanium implants can be functionalized by phosphonic acids, for instance to prevent bacterial adhesion,17O NMR experiments were performed on model TiO2 surfaces functionalized by 17O enriched phosphonic acids, to look at the mode of grafting of these coupling agents. Results bring clear evidence of the formation of Ti-O-P bridges and of the presence of residual P=O and P-OH groups. Second, given that calcium phosphates are widely present in biological hard tissues and synthetic biomaterials, 43Ca correlation experiments were performed on 43Ca enriched materials (hydroxyapatite and calcium benzoate), to see how the proximities between this nucleus and neighbouring atoms can be analyzed. Results show that both Ca…C and Ca…H proximities can be evidenced, and could thus help elucidate interface structures. All in all, these studies should pave the way to future investigations of biomaterials, and in particular of the structure of organic-inorganic interfaces.

In order to perform a systematic study of the interaction between grain boundaries (GBs) and dislocations using molecular dynamics (MD), several tools need to be available. A combination of computational geometry and MD was used to build the foundations of what we call a virtual laboratory. First, an algorithm to generate GBs on face-centered cubic bicrystals was developed. Two crystals with different orientations are placed together. Then, by applying “microscopic” rigid body translations along the GB plane to one of the crystals and removing overlapping atoms, a set of initial configurations is sampled and a minimum energy configuration is found. Second, to classify the geometry of the GBs a local symmetry type (LST) describing the angular environment of each atom is calculated. It is found that for a given relaxed GB the number of atoms with different LSTs is not very large and that it is possible to find unique geometrical patterns in each GB. For instance, the LSTs of two GBs having the same “macroscopic” configuration but different “microscopic” degrees of freedom can be dissimilar: the configurations with higher GB energy tend to have a higher number of atoms with different LSTs. Third, edge dislocations are introduced into the bicrystals. We see that full edge dislocations split into Shockley partials. Finally, by loading the bicrystals with tensile stresses the edge dislocations are put into motion. Various examples of dislocation-GB interactions in Cu are presented.

Due to the advantages of low production cost, flexibility and low temperature fabrication, much effort has been devoted to the development of organic electronic devices such as light emitting diodes, photovoltaics and transistors. Organic thin film transistors have several important applications such as switching devices for active-matrix OLED displays, smart cards, identification tags and sensors [1-3]. However, the low carrier mobility in organic materials and the difficulty of integrating organic devices into inorganic processing procedures have hindered the development of organic transistors that are comparable to traditional transistors [4]. Much effort has been devoted to develop new organic materials with higher carrier mobility, while retaining the same conventional inorganic metal-oxide-semiconductor structures.

Lithium fluoride (LiF) has the largest band gap and the largest negative electron affinity of any solid, [5] making it a superb candidate for use in the insulating layer of transistors. Using LiF as the gate dielectric layer can facilitate the organic transistor fabrication. In this work, thin film transistors based on pentacene and PTCDI-C8 (N,N′-Dioctyl-3,4,9,10-perylenedicarboximide) as organic semiconductor layers and LiF as gate dielectrics are studied. The electrical properties of these devices have been investigated in atmospheric conditions and under variable light exposure. Output and transfer characteristics of several photo-responsive thin film transistors using different organic materials but with the same insulating layer will be presented and the increase of drain-source current upon illumination will be discussed based on the photoconduction properties of the transistor active layer.

Recently, thermoelectric (TE) is ignited by enhancement of nano-science and engineering that uncovers the possibility of increasing of figure of merit (ZT). As a candidate for thermoelectric materials, metal could not be considered because of their high thermal conductivity. However, according to other research, it is feasible to decrease thermal conductivity of also metal without much degradation of the electrical conductivity, which strongly implies that nanoscale metal can be utilized to improve thermoelectric properties of devices, especially power factor. Semiconductor-semiconductor superlattice nanowire structure has been studied as one of the best candidates for thermoelectric devices, because of their photon scattering characteristics at the interfaces. In this research, instead of semiconductor-semiconductor superlattice structure, metal-semiconductor superlattice structure was synthesized, and its microstructure and electrical properties are investigated. With this structure, improvement of electrical conductivity as well as degradation of thermal conductivity with phonon scattering would be anticipated. Metal-semiconductor superlattice nanowires were acquired with electrochemical displacement method, which can exchange the material which has low reduction potential with more noble materials in aqueous electrolyte. To achieve this, Ni-Ag superlattice structure was firstly prepared as metal-metal superlattice structure. The electrolyte for the electrodeposition of Ni-Ag segmented nanowries was consisted of 0.3 mol/L C6H5Na3O7, 0.7mol/L NiSO4 and AgNO3. Electrodeposition was performed galvanostatically in two electrode cell configuration with anodized aluminum oxide(AAO) template. Cu layer was deposited at the one side of AAO template as a working electrode, platinum coated titanium stripe as counter electrode. The composition of electrodeposits could be controlled by applied potential which is directly related the applied current density. Ni-rich phase could be obtained when the applied current density was over 10mA/cm2 and Ag-rich phase at 0.5mA/cm2. After acquiring Ni-Ag segmented nanowire structure, we synthesized the metal-semiconductor segemented nanowries (Ag-BiTe segmented nanowire) by using galvanic-displacement method. Because standard reduction potential energy of nickel is more negative (-0.25V) than that of BiTe in Bi ion and Te ion contained bath, it is possible to make displacement of Ni with BiTe using galvanic displacement. The morphology was investigated by SEM and composition profile was observed by EDS. In conclusion, nanoscale metal-semiconductor segmented nanowires were synthesized by electrodeposition and electrochemical displacement method. Their structural characteristics and electrical properties were investigated to understand the possibility of this segmented nanowires as a thermelectrical materials.

The corrosion resistance of biocompatible materials in body fluids is one of the essential factors in the determination of the lifetime of medical implants. Therefore, it is of great relevance to understand the interface processes that occur when a surface is exposed to body fluids. To this end, amorphous titanium and niobium oxide films were deposited on medical grade stainless steel using a magnetron sputtering system. The biocompatibility of the films was evaluated by adhesion and viability/proliferation assays using human cells, showing non-toxic response. The electrochemical response of the films was evaluated by poteontiodynamic polarization and electrochemical impedance spectroscopy (EIS) as a function of time, up to 500 hrs, using three different simulated body fluids; the NaCl solution and Hartman (Ringer's + Lactate) and Gey's (Ringer's + Phosphates + Glucose) solution. The results indicated that the chemical composition of the solution was very important since different electrochemical behavior was observed for each case. For example, NbOx showed a better resistance than the TiOx films in the Hartman's solution but it failed when Gey's solution was used. Meanwhile TiOx showed a well passivated response for both NaCl and Gey's solution.

Amyloid fibrils aggregation is a key pathological feature of many severe degenerative disorders including Alzheimer’s disease and clinical dementia. Moreover, amyloids have been classified as intriguing molecules due to their exceptional strength, sturdiness and elasticity. However, physical models that explain the structural basis of these properties remain largely elusive, preventing the description of the link between their hierarchical structure and physical properties. Here we present an atomistic-based multiscale analysis based on computational materiomics, utilized to predict the structure of the two known polymorphous Alzheimer’s Aβ(1–40) amyloid fibers. We report an analysis of the energies, structural changes and H-bonding for varying amyloid fibril lengths, elucidating their size dependent properties. We also propose an explanation for the different stability of the two morphologies. A structural model of amyloid fibers with lengths of hundreds of nanometers at atomistic resolution is obtained. It predicts the formation of twisted amyloid microfibers in close agreement with experimental results. The approach used here provides a link between the fibril geometry, the chemical interactions and the most stable configuration, and resolves the issue of missing atomistic structures for long amyloid fibers.

Large shift of localized surface plasmon resonance (LSPR) spectrum of gold nanoparticles was attained by electrochemical oxidation of the nanoparticle surface. This oxidation occurred in a cell consisting of a pair of indium tin oxide (ITO) electrodes with water medium between the electrodes. On one side of the ITO electrode, the gold nanoparticles were adsorbed. The LSPR spectrum was moved consecutively to the red by increasing the applied positive voltage. By the application of 5 V to the cell, the spectrum shift as large as 55 nm was obtained. Though the spectrum shift has already been observed by changing liquid crystal (LC) orientation surrounding gold nanoparticles, the amount of the shift was not large (11 nm). That was because the variation of the effective refractive index of LC was rather small. Our large shift due to electrochemical oxidation resulted from the large refractive index of Au-O. The upper limit of the LSPR spectrum shift by our method is estimated to be 138 nm.

Rotations of a single spin-qubit are demonstrated using only electrical gates. The results of simulations are presented for a typical gated quantum-well structure based on the strong spin-orbit semiconductor InSb, showing typical length and time scales for Hadamard and NOT operations. Approximate analytic expressions are derived for the spin transformations that give excellent agreement with the numerical results and demonstrate the generality of the method.

The effective medium approximation (EMA) approach to calculating the macroscopic properties of disordered materials from an average of microscopic interactions is logically divided into two parts. First, an expression based on the microscale physics of constituents embedded in the effective medium is derived. Second, a configurational average of some sort over is performed, leading to an equation for an effective parameter, which is then solved. Based on this division, we present a numerical approach to the EMA in which the effective parameter ?e satisfiesg(ξe) = <f(σ,ξe)> = ∫ f(σ,ξe)ρ(σ)dσ = 0. Here, σ represents possible configurations of the system, i.e. some variable of the physical formulation with respect to which we have knowledge of both i) microscale interactions and ii) the distribution of constituents; f represents our knowledge of the microscale interactions as a function of σ; and ρ represents our knowledge of the distribution of the configurations/constituents with respect to σ. Then g is the expectation of f. The equation says that the average of the microscale interactions embodied in f, which is a function of the effective parameter ξe, over the possible configurations of the system represented by ρ(σ), is zero. This equation allows us to determine the effective parameter ξe, which, for example, we can compare to experiment, or use in a drift/diffusion type of macroscopic simulation. A key point is that our explicit formulation allows specifying ρ and f numerically (e.g. via Monte Carlo simulation).

We present both simple illustrative examples, as well as a realistic application to hopping transport in organic photovoltaics simulation. Preliminary results from this numerical EMA match experimental data remarkably well.

Conducting polymers can act as actuators when an electrochemical stimulus causes the materials to undergo volumetric changes. Ion flux into the polymer causes volumetric expansion and ion outflow causes contraction. Polypyrrole is an attractive actuator material due to its ability to generate up to 30 MPa active stress and 10% to 26% maximum strain with voltage supply lower than 2 V. The polymer’s mechanical performance depends upon the solvent used and the dominating ion species. In this study, we used 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6) to characterize the effect of temperature increase on ion flow and how it contributes to strain and maximum strain rate of polypyrrole. In this solvent, the cation BMIM+ diffuses in and out of the polymer under applied voltage to cause strain changes. For approximately each increment of 10°C from 27°C to 83°C, isotonic tests were done with +/-0.8 V square pulses, using a custom built device that is capable of performing temperature controlled dynamic mechanical analyses and electrochemistry simultaneously. Results showed that, independent of voltage polarity, from 27 to 83°C the strain increased from 0.4% to 2.0%. Both the maximum charge and strain rate rates increased with temperature, and were higher at positive voltage than at negative voltage throughout the same temperature range. Positive voltage caused the maximum strain rate to increase exponentially from 0.1 %/s to 0.67 %/s, while negative voltage caused it to increase more linearly from 0.06 %/s to 0.23 %/s. The results suggest that the increase in strain resulted from the charge delivered to the polymer in higher quantities at higher temperature. Furthermore, BMIM+ ions are expelled faster than those being attracted in to the polymer, perhaps due to the ions preferentially remaining in the bulk solution. As the temperature increased, the ionic mobility increased and as a result, BMIM+ ions are expelled back into the solvent even faster.

A straightforward ambient temperature route to the fabrication of surface silver-metallized polyimide films is described. Silver(I) trifluoromethane sulfonate and a polyimide, derived from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and an equimolar amount of 4,4'-oxydianiline (ODA) and 3,5-diaminobenzoic acid (DABA), were dissolved together in dimethylacetamide. Silver(I)-doped films were prepared at thicknesses of 25-50 microns and depleted of solvent by evaporation. The silver(I)-containing films were then treated with aqueous reducing agents, which brought forth silvered films exhibiting conductivity on the order of bulk polycrystalline silver and good specular reflectivity.

We report on the growth and properties of nanocrystalline Si superlattice solar cells. The solar cells consisted of a stack of alternating layers of amorphous and nanocrystalline Si. The thickness of each of the two layers in the superlattice structure was varied independently. It was found that when the nanocrystalline layer thickness was low, increasing the thickness of the amorphous layer in the superlattice systematically reduced the <220> grain size, while the <111> grain size remained essentially invariant. This fact shows that by interposing an amorphous layer between two nanocrystalline layers forces the nano grains to renucleate and regrow. It was also found that when the amorphous Si layer was too thick, there were significant problems with hole transport through the device. Measurements of defect densities and effective diffusion lengths showed that there was an optimum thickness of the amorphous layer (about 10 nm) for which the defect density was the lowest and the diffusion length was the highest. We also show that the absorption coefficient in nano Si depends upon the grain size and can be increased significantly by increasing the grain size.

Ferroelectric random access memory (FeRAM) is believed to be the most promising candidate for the next generation non-volatile memory due to its fast access time and low power consumption. Fabrication technologies of FeRAM can be divided into two parts: CMOS technologies for circuits which are standard and can be shared with traditional IC process line, and process relating to ferroelectric which is separated with CMOS process and defined as backend module. This paper described technologies for integrating ferroelectric capacitors into standard CMOS, mainly about modeling of ferroelectric capacitors and backend fabrication technologies. Hysteresis loop of the ferroelectric capacitor is the basis for FeRAM to store data. Models to describe this characteristic are the key for the design of FeRAM. A transient behavioral ferroelectric capacitor model based on C-V relation for circuit simulation is developed. The arc tangent function is used to describe the hysteresis loop. “Negative capacitance” phenomenon at reversing points of applied voltage is analyzed and introduced to the model to describe transient behaviors of the capacitor. Compact equivalent circuits are introduced to integrate this model into HSPICE for circuit simulation. Ferroelectric materials fabrication, electrodes integration and etching are the main technologies of FeRAM fabrication process. An metal organic chemical vapor deposition (MOCVD) process is developed to fabricate high quality Pb(Zr1-xTix)O3 (PZT) films. Pt is known to cause the fatigue problems when used as electrodes with PZT. Ir is used as electrodes to improve the fatigue property of PZT based capacitors, and mechanism of the fatigue is analyzed. Hard mask is used to reduce the size of the capacitors and damage caused in etching process. In our process, Al2O3 is developed as hard mask, which simplifies the FeRAM backend integration process.

The Women in Materials (WIM) program is an on-going collaboration between Simmons College and the Cornell Center for Materials Research (CCMR). Beginning in 2001, during the initial four years of the project, materials-related curricula were developed, a new joint research project was begun, and nearly 1/2 of Simmons College science majors participated in materials-related research during their first two years as undergraduates. We have previously reported the student outcomes as a result of this initial stage of the project, demonstrating a successful partnership between a primarily undergraduate women's college and a federally funded Materials Research Science and Engineering Center. Here, we report the evolution and impact of this project over the last three years, subsequent to the initial seed funding from the National Science Foundation. The Women in Materials project is now a key feature of the undergraduate science program at Simmons College and has developed into an organizing structure for materials-related research at the College. Initially, three faculty members were involved and now eight faculty members from all three laboratory science departments participate (biology, chemistry, and physics). The program now involves research related to optoelectronics, polymer synthesis, biomaterials, and green chemistry, and each semester about 80% of the students who participate in these projects are 1st and 2nd year science majors. This structure has led to enhanced funding within the sciences, shared instrumentation facilities, a new minor in materials science, and a spirit of collaboration among science faculty and departments. It has also spawned a new, innovative curricular initiative, the Undergraduate Laboratory Renaissance, now in its second year of implementation, involving all three laboratory science departments in incorporating actual, on-going research projects into introductory and intermediate science laboratories. Most importantly, the Women in Materials program has embedded materials-related research into our science curriculum and has deepened and broadened the educational experience for our students; the student outcomes speak to the program's success. Approximately 70% of our science majors go on to graduate school within two years of completing their undergraduate degree. Our students also have a high acceptance rate at highly competitive summer research programs, such as Research Experience for Undergraduates (REU) programs funded by the National Science Foundation.

ZnO nanowire arrays are grown on carbon fiber to enhance the interface strength of a polymer matrix composite without degrading the base fiber and in-plane strength of the composite. The morphology of the nanowire array is controlled during growth to create nanowires with different aspect ratios to elucidate the structure-property relations of the interphase. Nanowires are shown to double the composite interfacial shear strength at an intermediate nanowire length, indicating that an optimal point exists and the interface can be engineered to maximize the interfacial enhancement. Furthermore, the observed effect of the morphology on interface strength indicates that the bond between the ZnO nanowire array and the carbon fiber is quite strong, more than twice as strong as the interaction between the matrix and control fiber.

Kinetics of formation of intrinsic colloids by tetravelent metal ions, namely, Th(IV), Hf(IV) and Pu(IV) have been studied using the dynamic light scattering technique. The milli-molar solutions of Hf(IV) and Th(IV) were prepared at varying pH (2-4) and ionic strength (0-0.01 M) and the samples were subjected to dynamic light scattering measurements at regular intervals for few days. The results showed that the size of intrinsic colloids varies with pH and ionic strength. In the case of Pu(IV) the concentration of aqueous solutions was 4.5×10−5 M.

We present a multiscale method for the modeling of dynamics of crystalline solids. The method employs the continuum elastodynamics model to introduce loading conditions and capture elastic waves, and near isolated defects, molecular dynamics (MD) model is used to resolve the local structure at the atomic scale. The coupling of the two models is achieved based on the framework of the heterogeneous multiscale method (HMM) and a consistent coupling condition with special treatment of the MD boundary condition. Application to the dynamics of a brittle crack under various loading conditions is presented. Elastic waves are observed to pass through the interface from atomistic region to the continuum region and reversely. Thresholds of strength and duration of shock waves to launch the crack opening are quantitatively studied and related to the inertia effect of crack tips.

The effect of the external magnetic field on the dispersion of the effective permittivity in arrays of parallel CoFe-based amorphous wires is demonstrated by measuring S-parameters in free space in the frequency band of 0.9-17 GHz. The magnetic field is applied along the wires sensitively changing their magnetization and high frequency impedance. Based on the measurements of magneto-impedance in a single wire and transmission/reflection spectra of composites in free space, we show the correlation between magneto-impedance and the field dependence of the effective permittivity.

The high temperature phases of BiFeO3 have courted much controversy with many conflicting structural models reported, in particular for the paraelectric β-phase. High temperature powder neutron diffraction (PND) experiments indicate that the ferroelectric (R3c) α-phase transforms to the paraelectric β-phase at approximately 820 °C via a first order phase transition. We demonstrate that this phase is unambiguously orthorhombic, adopting the GdFeO3 structure-type with a space group Pbnm. On further heating BiFeO3 undergoes another first order phase transition (β-γ) at approximately 930 °C which is marked by a discontinuous decrease in cell volume consistent with an insulator-metal transition. Close inspection of the PND data show no evidence of any symmetry change, with the postulated γ-phase remaining orthorhombic Pbnm. In addition we present PND and impedance spectroscopy data for BiFeO3 which suggest that the so-called ‘Połomska’ transition observed by some authors at approximately 185 °C is not intrinsic.

The unique material characteristics of silicon carbide (SiC) and nanocrystalline diamond (NCD) present solutions to many problems in conventional MEMS applications and especially for biologically compatible devices. Both materials have a wide bandgap along with excellent optical, thermal and mechanical properties. Initial experiments were performed for NCD films grown on 3C-SiC using a microwave plasma chemical vapor deposition (MPCVD) reactor. It was observed from the atomic force microscopy (AFM) analysis that the NCD films on 3C-SiC possess a more uniform grain structure, with sizes ranging from approximately 5 – 10 nm, whereas on the Si surface, the NCD has large, non-unioform inclusions of grains ≈1 μm in size. The in vitro biocompatibility performance of NCD/3C-SiC was measured utilizing 2 immortalized neural cell lines: H4 human neuroglioma (ATCC #HTB-148) and PC12 rat pheochromocytoma (ATCC #CRL-1721). MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay was used to measure viability of the cells for 96 hours and live/ fixed cell. AFM was performed to determine the general cell morphology. The H4 cell line shows a good biocompatibility level with hydrogen treated NCD as compared with the cell treated polystyrene control well, while the PC12 cells show decreased viability on the NCD surfaces.