Dynamically mechanical and nano-impact (fatigue) analysis of touch screen thin films deposited on polyethylene terephthalate substrate

Nano-scale touch screen thin film have not been thoroughly investigated in terms of dynamic impact analysis under various strain rates. This research is focused on two different thin films, Zinc Oxide (ZnO) film and Indium Tin Oxide (ITO) film, deposited on Polyethylene Terephthalate (PET) substrate for the standard touch screen panels. Dynamic Mechanical Analysis (DMA) was performed on the ZnO film coated PET substrates. Nano-impact (fatigue) testing was performed on ITO film coated PET substrates. Other analysis includes hardness and the elastic modulus measurements, atomic force microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR) and the Scanning Electron Microscopy (SEM) of the film surface.
Ten delta of DMA is described as the ratio of loss modulus (viscous properties) and storage modulus (elastic properties) of the material and its peak against time identifies the glass transition temperature (Tg). Thus, in essence the Tg recognizes changes from glassy to rubber state of the material and for our sample ZnO film, Tg was found as 388.3 K. The DMA results also showed that the Ten delta curve for Tg increases monotonically in the viscoelastic state (before Tg) and decreases sharply in the rubber state (after Tg) until recrystallization of ZnO takes place. This led to an interpretation that enhanced ductility can be achieved by negating the strength of the material.
For the nano-impact testing using the ITO coated PET, the damage started with the crack initiation and propagation. The interpretation of the nano-impact results depended on the characteristics of the loading history. Under the nano-impact loading, the surface structure of ITO film suffered from several forms of failure damages that range from deformation to catastrophic failures. It is concluded that in such type of application, the films should have low residual stress to prevent deformation, good adhesive strength, durable and good resistance to wear.

Comparing gold nano-particle enhanced radiotherapy with protons, megavoltage photons and kilovoltage photons: a Monte Carlo simulation

Gold nanoparticles (GNPs) have shown potential to be used as a radiosensitizer for radiation therapy. Despite extensive research activity to study GNP radiosensitization using photon beams, only a few studies have been carried out using proton beams. In this work Monte Carlo simulations were used to assess the dose enhancement of GNPs for proton therapy. The enhancement effect was compared between a clinical proton spectrum, a clinical 6 MV photon spectrum, and a kilovoltage photon source similar to those used in many radiobiology lab settings. We showed that the mechanism by which GNPs can lead to dose enhancements in radiation therapy differs when comparing photon and proton radiation. The GNP dose enhancement using protons can be up to 14 and is independent of proton energy, while the dose enhancement is highly dependent on the photon energy used. For the same amount of energy absorbed in the GNP, interactions with protons, kVp photons and MV photons produce similar doses within several nanometers of the GNP surface, and differences are below 15% for the first 10 nm. However, secondary electrons produced by kilovoltage photons have the longest range in water as compared to protons and MV photons, e.g. they cause a dose enhancement 20 times higher than the one caused by protons 10 μm away from the GNP surface. We conclude that GNPs have the potential to enhance radiation therapy depending on the type of radiation source. Proton therapy can be enhanced significantly only if the GNPs are in close proximity to the biological target.

Competing anisotropies in exchange biased nano-structured thin films

The magnetic anisotropies of a patterned, exchange biased Fe50Mn50/Ni80Fe20 system are studied using ferromagnetic resonance, supplemented by Brillouin light scattering experiments and Kerr magnetometry. The exchange biased bi-layer is partially etched into an antidot geometry so that the system approximates a Ni80 Fe20 layer in contact with antidot structured Fe50 Mn50 . Brillouin light scattering measurements of the spin wave frequency dependence on the wave vector reveal a magnonic band gap as expected for a periodic modulation of the magnetic properties. Analysis of the ferromagnetic resonance spectra reveals 8-fold and 4-fold contributions to the magnetic anisotropy. Additionally, the antidot patterning decreases the magnitude of the exchange bias and modifies strongly its angular dependence. Softening of all resonance modes is most pronounced for the applied magnetic field aligned within 10◦ of the antidot axis, in the direction of the bias. Given the degree to which one can tailor the ground state, the resulting asymmetry at low frequencies could make this an interesting candidate for applications such as selective/directional microwave filtering and multi-state magnetic logic.

Interface-mediated ferroelectric patterning and Mn valency in nano-structured PbTiO3/La0.7Sr0.3MnO3

We employed a multitechnique approach using piezo-force response microscopy and photoemission microscopy to investigate a self-organizing polarization domain pattern in PbTiO3/La0.7Sr0.3MnO3 (PTO/LSMO) nanostructures. The polarization is correlated with the nanostructure morphology as well as with the thickness and Mn valence of the LSMO template layer. On the LSMO dots, the PTO is upwards polarized, whereas outside the nanodots, the polarization appears both strain and interface roughness dependent. The results suggest that the electronic structure and strain of the PTO/LSMO interface contribute to determining the internal bias of the ferroelectric layer.

Studies on betanin natural dye incorporated ZnO composites at nano and micro scale for photonic device applications

Green energy and Green technology are the most of the quoted terms in the context of modern science and technology. Technology which is close to nature is the necessity of the modern world which is haunted by global warming and climatic alterations. Proper utilization of solar energy is one of the goals of Green Energy Movement. The present thesis deals with the work carried out in the eld of nanotechnology and its possible use in various applications (employing natural dyes) like solar cells. Unlike arti cial dyes, the natural dyes are available, easy to prepare, low in cost, non-toxic, environmentally friendly and fully biodegradable. Looking to the 21st century, the nano/micro sciences will be a chief contributor to scienti c and technological developments. As nanotechnology progresses and complex nanosystems are fabricated, a growing impetus is being given to the development of multi-functional and size-dependent materials. The control of the morphology, from the nano to the micrometer scales, associated with the incorporation of several functionalities can yield entirely new smart hybrid materials. They are special class of materials which provide a new method for the improvement of the environmental stability of the material with interesting optical properties and opening a land of opportunities for applications in the eld of photonics. Zinc oxide (ZnO) is one such multipurpose material that has been explored for applications in sensing, environmental monitoring, and bio-medical systems and communications technology. Understanding the growth mechanism and tailoring their morphology is essential for the use of ZnO crystals as nano/micro electromechanical systems and also as building blocks of other nanosystems.

Greffage d’un film mince de nano-TiO2 sur les fibres naturelles cellulosiques pour le renforcement de biocomposites polymériques

Abstract : Natural materials have received a full attention in many applications because they are degradable and derived directly from earth. In addition to these benefits, natural materials can be obtained from renewable resources such as plants (i.e. cellulosic fibers like flax, hemp, jute, and etc). Being cheap and light in weight, the cellulosic natural fiber is a good candidate for reinforcing bio-based polymer composites. However, the hydrophilic nature -resulted from the presence of hydroxyl groups in the structure of these fibers- restricts the application of these fibers in the polymeric matrices. This is because of weak interfacial adhesion, and difficulties in mixing due to poor wettability of the fibers within the matrices. Many attempts have been done to modify surface properties of natural fibers including physical, chemical, and physico-chemical treatments but on the one hand, these treatments are unable to cure the intrinsic defects of the surface of the fibers and on the other hand they cannot improve moisture, and alkali resistance of the fibers. However, the creation of a thin film on the fibers would achieve the mentioned objectives. This study aims firstly to functionalize the flax fibers by using selective oxidation of hydroxyl groups existed in cellulose structure to pave the way for better adhesion of subsequent amphiphilic TiO[subscript 2] thin films created by Sol-Gel technique. This method is capable of creating a very thin layer of metallic oxide on a substrate. In the next step, the effect of oxidation on the interfacial adhesion between the TiO[subscript 2] film and the fiber and thus on the physical and mechanical properties of the fiber was characterized. Eventually, the TiO[subscript 2] grafted fibers with and without oxidation were used to reinforce poly lactic acid (PLA). Tensile, impact, and short beam shear tests were performed to characterize the mechanical properties while Thermogravimetric analysis (TGA), Differential Scanning Calorimetry (DSC), Dynamic mechanical analysis (DMA), and moisture absorption were used to show the physical properties of the composites. Results showed a significant increase in physical and mechanical properties of flax fibers when the fibers were oxidized prior to TiO[subscript 2] grafting. Moreover, the TiO[subscript 2] grafted oxidized fiber caused significant changes when they were used as reinforcements in PLA. A higher interfacial strength and less amount of water absorption were obtained in comparison with the reference samples.

Cyto- and Genotoxicity assessment of manufactured nano cerium dioxide in the A549 cell line

In the past decades the growing application of nanomaterials (NMs) in diverse consumer products has raised various concerns in the field of toxicology. They have been extensively used in a broad range of applications and cover most of the industrial sectors as well as the medicine and the environmental areas. The most common scenarios for human exposure to NMs are occupational, environmental and as consumers and inhalation is the most frequent route of exposure, especially in occupational settings. Cerium dioxide NMs (nano-CeO2) are widely used in a number of applications such as in cosmetics, outdoor paints, wood care products as well as fuel catalysts. For such reason, nano-CeO2 is one of the selected NMs for priority testing within the sponsorship program of the Working Party of Manufactured Nanomaterials of the OECD. In this context, the aim of this study is to assess the safety of nano-CeO2 (NM-212, Joint Research Center Repository) through the characterization of its cytotoxicity and genotoxicity in a human alveolar epithelial cell line. A dispersion of the NM in water plus 0.05% BSA was prepared and sonicated during 16 minutes, according to a standardized protocol. DLS analysis was used to characterize the quality of the NM dispersion in the culture medium. To evaluate the cytotoxicity of nano-CeO2 in the A549 cell line, the colorimetric MTT assay was performed; the capacity of cells to proliferate when exposed to CeO2 was also assessed with the Clonogenic assay. The genotoxicity of this NM was evaluated by the Comet Assay (3 and 24h of exposure) to quantify DNA breaks and the FPG-modified comet assay to assess oxidative DNA damage. The Cytokinesis-Block Micronucleus (CBMN) assay was used to further detect chromosome breaks or loss. The nano-CeO2 particles are spherical, displaying a diameter of 33 nm and 28 m2/g of surface area. The results of the MTT assay did not show any decreased in cells viability following treatment with a dose-range of nano-CeO2 during 24h. Nevertheless, the highest concentrations of this NM were able to significantly reduce the colony forming ability of A549 cells, suggesting that a prolonged exposure may be cytotoxic to these cells. Data from both genotoxicity assays revealed that nano-CeO2 was neither able to induce DNA breaks nor oxidative DNA damage. Likewise, no significant micronucleus induction was observed. Taken together, the present results indicate that this nano-CeO2 is not genotoxic in this alveolar cell line under the tested conditions, although further studies should be performed, e.g., gene mutation in somatic cells and in vivo chromosome damage (rodent micronucleus assay) to ensure its safety to human health.

The influence of nano-scale second-phase particles on deformation of fine grained calcite mylonites

Grey and white carbonate mylonites were collected along thrust planes of the Helvetic Alps. They are characterised by very small grain sizes and non-random grain shape (SPO) and crystallographic preferred orientation (CPO). Presumably they deformed in the field of grain size sensitive flow by recrystallisation accommodated intracrystalline deformation in combination with granular flow. Both mylonites show a similar mean grain size, but in the grey mylonites the grain size range is larger, the grain shapes are more elongate and the dynamically recrystallised calcite grains are more often twinned. Grey mylonites have an oblique CPO, while the CPO in white mylonites is symmetric with respect to the shear plane. Combustion analysis and TEM investigations revealed that grey mylonites contain a higher amount of highly structured kerogens with particle sizes of a few tens of nanometers, which are finely dispersed at the grain boundaries. During deformation of the rock, nano-scale particles reduced the migration velocity of grain boundaries by Zener drag resulting in slower recrystallisation rates of the calcite aggregate. In the grey mylonites, more strain increments were accommodated by individual grains before they became refreshed by dynamic recrystallisation than in white mylonites, where grain boundary migration was less hindered and recrystallisation cycles were faster. Consequently, grey mylonites represent ‘deformation’ microfabrics while white mylonites are characterised by ‘recrystallisation’ microfabrics. Field geologists must utilise this different deformation behavior when applying the obliquity in CPO and SPO of the respective mylonites as reliable shear sense indicators.

Is there any imprint of the wind variability on the Atlantic Water circulation within the Arctic Basin?

The Atlantic Water (AW) layer in the Arctic Basin is isolated from the atmosphere by the overlaying surface layer, yet observations have revealed that the velocities in this layer exhibit significant variations. Here analysis of a global ocean/sea ice model hindcast, complemented by experiments performed with an idealized process model, is used to investigate what controls the variability of AW circulation, with a focus on the role of wind forcing. The AW circulation carries the imprint of wind variations, both remotely over the Nordic and Barents Seas where they force the AW inflow variability, and locally over the Arctic Basin through the forcing of the wind-driven Beaufort Gyre, which modulates and transfers the wind variability to the AW layer. The strong interplay between the circulation within the surface and AW layers suggests that both layers must be considered to understand variability in either.

Heat dissipation from carbon nano-electronics

The incorporation of graphitic compounds such as carbon nanotubes (CNTs) and graphene into nano-electronic device packaging holds much promise for waste heat management given their high thermal conductivities. However, as these graphitic materials must be used in together with other semiconductor/insulator materials, it is not known how thermal transport is affected by the interaction. Using different simulation techniques, in this thesis, we evaluate the thermal transport properties - thermal boundary conductance (TBC) and thermal conductivity - of CNTs and single-layer graphene in contact with an amorphous SiO2 (a-SiO2) substrate. First, the theoretical methodologies and concepts used in our simulations are presented. In particular, two concepts are described in detail as they are necessary for the understanding of the subsequent chapters. The first is the linear response Green-Kubo (GK) theory of thermal boundary conductance (TBC), which we develop in this thesis, and the second is the spectral energy density method, which we use to directly compute the phonon lifetimes and thermal transport coefficients. After we set the conceptual foundations, the TBC of the CNT-SiO2 interface is computed using non- equilibrium molecular dynamics (MD) simulations and the new Green-Kubo method that we have developed. Its dependence on temperature, the strength of the interaction with the substrate, and tube diameter are evaluated. To gain further insight into the phonon dynamics in supported CNTs, the scattering rates are computed using the spectral energy density (SED) method. With this method, we are able to distinguish the different scattering mechanisms (boundary and CNT-substrate phonon-phonon) and rates. The phonon lifetimes in supported CNTs are found to be reduced by contact with the substrate and we use that lifetime reduction to determine the change in CNT thermal conductivity. Next, we examine thermal transport in graphene supported on SiO2. The phonon contribution to the TBC of the graphene-SiO2 interface is computed from MD simulations and found to agree well with experimentally measured values. We derive the theory of remote phonon scattering of graphene electrons and compute the heat transfer coefficient dependence on doping level and temperature. The thermal boundary conductance from remote phonon scattering is found to be an order of magnitude smaller than that of the phonon contribution. The in-plane thermal conductivity of supported graphene is calculated from MD simulations. The experimentally measured order of magnitude reduction in thermal conductivity is reproduced in our simulations. We show that this reduction is due to the damping of the flexural (ZA) modes. By varying the interaction between graphene and the substrate, the ZA modes hybridize with the substrate Rayleigh modes and the dispersion of the hybridized modes is found to linearize in the strong coupling limit, leading to an increased thermal conductance in the composite structure.