Polypyrrole (pPy) conducting polymer films embedded with MnO2 nanoparticles have been synthesized by electrochemical polymerization and anodic oxidation processes. MnO2 nanoparticles coexist in the hydrated Mn(II) and Mn(IV) states and undergo valence state change along side pPy anion doping-dedoping contributing to the system pseudocapacitance. Increased density of sequestered MnO2 nanoparticles in pPy significantly improves charge storage properties as shown by increased electrodic specific capacitance from 200 to 620 Fg-1 based on cyclic voltammetry studies. MnO2 nanoparticle dispersion in open porous pPy microstructure is affected by current density in excess of 4 mA.cm-2 used in synthesis and results in MnO2 particle agglomeration that excludes open surface access reducing specific capacitance. Charge-discharge studies show stable capacitance retention for ∼1000 cycles. The redox performance of MnO2-pPy composite electrodes is suitable for application in the high energy density supercapacitors.

In the work presented here, Ce0.97Cu0.03O2 nanoparticles were synthesized by a microwave-assisted hydrothermal method under different synthesis temperatures. The obtained nanoparticles were tested as catalysts in preferential oxidation of CO to obtain CO-free H2 (PROX reaction). The samples were characterized by X-ray diffraction, transmission electron microscopy (TEM), electron paramagnetic resonance spectroscopy (EPR) and temperature-programmed reduction (TPR). X-ray diffraction measurements detected the presence of pure cubic CeO2 for all synthesized samples. TEM images of the Ce0.97Cu0.03O2 nanoparticles revealed that samples synthesized at 80°C are composed mainly of nanospheres with an average size of 20 nm. The formation of some nanorods with an average diameter of 8 nm and 40 nm in length, and the size reduction of the nanoparticles from 20 to approximately 15 nm is observed with increasing synthesis temperature. EPR spectra indicated that copper is found well dispersed in sample synthesized at 160°C, located predominant in surface sites of ceria. For samples synthesized at 80 and 120°C, the species are less dispersed than in the other one, resulting in the formation of Cu2+−Cu2+ dimmers at the surface of ceria. TPR profiles presented two reduction peaks, one below 400°C attributed to the reduction of different copper species and a second peak around 800°C attributed to the reduction of Ce4+→ Ce3+ species located in the volume of the nanoparticles. The peak related to the reduction of copper species shifts to lower temperatures with increasing synthesis temperature, i.e., the sample synthesized at 160°C is more easily reduced than the ones synthesized at 120 and 80°C. The nanoparticles showed active as catalysts for the CO-PROX reaction. The microwave-assisted method revealed efficient for the synthesis of Ce0.97Cu0.03O2 nanoparticles with copper species selective for the CO-PROX reaction, which reaches CO conversions up to 92% for the sample synthesized at 160°C.

The photovoltaic materials in solar cells take multiple tasks including absorbing lights, separating the light-induced electron-hole pairs, and consequently transport charges to the corresponding metallic electrodes. These tasks, however, are often mutually conflicting. In particular, a thick PV layer is desired to absorb enough light for creating sufficient light-induced charges, while a thin PV layer is also desired to shorten the charge transport path length insider the PV layer in order to suppress recombination. Using dye-sensitized solar cells as an exploratory platform, this dilemma is mitigated using a non-traditional 3-dimensional (3-D) highly doped fluorinated SnO2 (FTO, core)-TiO2(shell) nanostructured photoanodes. The FTO core serves as conductive core for low-resistance and drift-assisted electron extraction. The thin, conformal and low-doped TiO2 shell layer is coated by atomic layer deposition, which provides a large area for anchoring dyes and maintains a large resistance against recombination.

Our ability to fabricate multipodal and multilayer TiO2 nanotube arrays enables us to increase performance and functionality in light harvesting devices such as excitonic solar cells and photocatalysts. Using a combination of simulations and experiments, we show that multilayer nanotube arrays enable photon management in the active toward enhancing the absorption and utilization of incident light. We show that the simultaneous utilization of TiO2 nanotubes with large (∼450 nm) and small (∼80 nm) diameters in stacked multilayer films increased light absorption and photocurrent in solar cells. Such enhanced light absorption is particularly desirable in the near-infrared region of the solar spectrum in which most excitonic solar cells suffer from poor quantum efficiencies and for blue photons at the TiO2 band-edge where significant room exists for improvement of photocatalytic quantum yields. Under AM 1.5 one sun illumination, multilayer nanotube arrays afforded us an approximately 20% improvement in photocurrent over single layer nanotube array films of the same thickness for N-719 sensitized liquid junction solar cells. Also, the possibility of multipodal TiO2 nanotube growth with different electrolyte recipes is presented.

Bismuth ferrites crystallites were synthesized by a polyvinyl alcohol (PVA) modified hydrothermal method. X-ray diffraction (XRD) analysis indicated that the pure phase of Bi25FeO40, BiFeO3 and Bi2Fe4O9 were synthesized with initial Bi/Fe ratio of 1:1 at the temperature of 200°C for 24 h, using NaOH concentration of 2, 5 and 10 M, respectively. With addition of PVA, the individual Bi-Fe oxides could be existed in a more wide range of processing parameters. The phase evolution of bismuth ferrites in the process of hydrothermal reactions was discussed. Moreover, photocatalytic properties of the bismuth ferrites crystallites were explored. The results showed that they possessed band gaps of about 2.0 eV and performed good degradation effect at visible light region.

Inkjet printing provides an interesting technology for electronic devices, as it is a versatile minimum-waste cost-effective technique for direct writing on almost every surface without need of masks or sacrificial layers. Among the fields in which it has been tested, transparent and flexible electronics offer a variety of applications ranging from large-area roll-toroll (such as OLEDs for lighting or solar cells) to small low-consumption biocompatible devices such as biosensors.

This work aims to present some advances in the field of semiconductors synthesized by sol-gel and patterned by inkjet printing. Chemical routes are used to obtain suitable inks, based on salts of Ga, In, Zn, Cu and Sn and solvents as methoxyethanol. Inkjet printing provides thin layers 20-300nm thick, with morphology strongly depending on the materials. Different thermal treatments are tested, and some chemical and optical characterization of the obtained layers allows optimizing the technology for each material.

The effectiveness of the inks and the technique is demonstrated by the electronic behavior of thin-film transistors fabricated by the proposed technology. The different devices are compared, suggesting the properties of the different materials analyzed, as a step ahead in the development of a complete logic for such promising applications of the flexible electronics.

The cubic perovskite SrTiO3 is an important semiconductor oxide with a band gap of 3.2 eV. It has a wide variety of applications such as: dielectric materials, photoluminescent devices, and in photocatalysis. It is conventionally obtained by the classic solid state synthesis (SS), in which TiO2 and SrCO3 react for several hours at temperatures as high as 1200 °C. Besides the high energy demand, SS is not useful for the control of physical characteristics, such as particle size and morphology, which has become essential for some of its applications. It is known that many soft and green routes can produce SrTiO3. Among them, the hydrothermal (HT) and sol-precipitation (SP) methods, as well as the molten salt synthesis (MS) are interesting not only due to their low cost and energy use, but also because of the possibility of particle size and shape control. This study compares the size and morphology of the SrTiO3 particles obtained by these three synthetic pathways. Scanning electron microscopy (SEM) was used to compare particle size and morphology, and X-ray diffraction (XRD) was used to confirm the perovskite formation as well as to determine the Scherrer’s particle size.

Metal ferrite nanoparticles are of considerable technological and theoretical interest. Magnetic response of these systems is a function of various system properties like saturation magnetization, growth orientation, average particle size and size distribution, volume concentration, etc. [1]. This preliminary study investigates the magnetization dynamics (and thereby the Verdet constant) of aqueous Fe3O4 nanoparticle solutions through precision AC measurements of the Faraday Rotation (FR) at 633 nm for three different Fe3O4 nanoparticle solutions that are all prepared to have the same average particle size (∼10 nm) but differing saturation magnetization values. For each of these nanoparticle solutions precision measurements for FR are carried out over a given range of volume concentrations. The study shows simple linear dependence of FR on volume concentration and a more involved dependence on saturation magnetization. Some preliminary results relating to the frequency dependence of Verdet constants are also presented. Future directions for this work are also discussed. It is hoped that that these results will help in the development of better models to characterize response of these technologically and fundamentally useful systems.

The percolation threshold in a ceramic composite depends on the processing conditions used to fabricate them along with the size and shape of the filler. In this study, borosilicate glass microspheres were used as the matrix material and nanosized antimony tin oxide (ATO) particles were used as the filler. The microsphere/ATO composites were fabricated by hot pressing around the glass transition temperature in order to control the viscosity. The pressure and temperature applied allowed the ATO to be confined to the spaces between certain glass particles, forming percolating networks at low volume fractions of the ATO. The electrical properties were examined using ac impedance spectroscopy. The impedance, electric modulus, and tan δ were studied which allowed for valuable insights in structure-property-processing relationships in these materials, along with determination of the percolation behavior in these composites. This analysis on samples right before percolation indicated that there was a highly resistive component affecting long range conductivity which is likely due to porosity at the triple points while the dielectric response is affected by the clusters of ATO nanoparticles. Based on this, the percolation of ATO should reduce down to lower concentrations if the processing conditions are improved to reduce this porosity and further segregate the ATO.

Yttrium titanate belongs to a family of compounds called pyrochlores with significant properties such as ionic conduction, optical non-linearity and radiation tolerance that have resulted in applications thermal barrier coatings, high-permittivity dielectrics, and materials for safe disposal of actinide-containing nuclear waste, and hydrogen storage material. The application of these materials in ODS ferritic steels, photocatalytic water splitting and a more efficient host material than TiO2 for Er3+ luminescence have been evaluated. ErxY2-xTi2O7 has tremendous applications in fiber amplifiers, integrated optical devices and selective emitters for thermophotovoltaic applications. Since 1-D nanostructures are deemed to be important building blocks for future optical and optoelectronic nanodevices, we have used electrospinning methods to synthesize nanofibers and freestanding, non-woven nanofibers membranes of single phase yttrium titanate and ErxY2-xTi2O7 (Er/(Ti+Er) at. ratio= 0 -15 %) with diameters less than 150 nm and have characterized the physical, thermal and optical properties of these nanofibers.

The oscillatory change in the optical absorbance of NiO-TiO2 film containing Au nanoparticles in the presence of H2S gas are investigated. The oscillatory phenomena could be monitored by looking at the variation of the surface plasmon resonance peak of the Au nanoparticles embedded in the TiO2-NiO matrix. Au nanoparticles act as optical probes in the detection of H2S, while the oxide matrix is responsible for the catalytic oxidation of H2S. To the best of our knowledge, it is the first time that oscillatory phenomena are monitored by optical spectroscopy.

We report on preliminary studies of low (14 at.%) and high (53at.%) concentration Mn doped MgO films deposited by co-sputtering from metallic Mn and Mg targets. The structural, surface morphologies and magnetic properties of the films of different thickness were studied. All the as grown films are found to be amorphous and film surfaces are found to be flawless and homogeneous. We observe at room temperature robust ferromagnetic loops with a saturation magnetization value that is a function of film thickness reaching a maximum of ∼38.5 emu/cm3 in the Mn0.53Mg0.47O film at a thickness of ∼92 nm. In thicker films room-temperature ferromagnetic ordering is suppressed and eventually at a thickness around 120nm the expected diamagnetism of the bulk appears. The origin of ferromagnetism may be attributed to cation defects at the Mg-site.

Commercially available antimony tin oxide (ATO) nanoparticles were dispersed in water using tetramethylammonium hydroxide (TMAH) as a dispersing agent and deposited onto glass substrates by spin coating. Films of one to five layers were made. These thin films were characterized using impedance spectroscopy and ultraviolet-visible spectroscopy to obtain their sheet resistances and optical transmittance, respectively. The films displayed sheet resistances around 105-106 kΩ/☐ and optical transmittance in the near infrared to near ultraviolet range above 95%. Films were then made using a higher concentration ATO solution and found to achieve sheet resistances on the order of 102 kΩ/☐ but had decreased transmittance as low as 65% at some wavelengths. Impedance measurements, along with optical micrographs, were taken at different locations on the films. These experiments demonstrated that films of more than one layer showed greater uniformity. Additional sets of films were also produced with varying substrate preparation and dispersion deposition parameters. Aside from dispersion concentration, high humidity during film measurement was found to be the most crucial parameter for achieving low sheet resistances.

Recently, there has been much interest in the creation of 3D networks of nanowires. One possible way to do this is to encase the nanowires inside transparent polymer matrices since there is also a demand for obtaining conducting transparent composites. If the filler of the composite is made from a strongly conducting material, the degree of connectivity of the networked nanowires can be tested by measuring its conductivity. Though much work has been done with ITO (Tin-doped indium oxide), little has been done with the chemically similar, but cheaper, ATO (Antimony-doped tin oxide). In this study, ATO nanoparticles were added into a polystyrene matrix and simultaneously pressed and heated so that a 3D network of the nanoparticles would form. The effecti veness of the conducting pseudo-nanowire networks was measured as the concentration of ATO in polystyrene was varied. Another variable utilized was the temperature at which the samples were pressed. The optical transmittance of the composites was also measured in order to quantify their transparency. It was found that, once the nanowire networks had percolated at a concentration of about 1.25 PHR, the conductivity and, consequently, the coherence of the networks increased at a decreasing rate as the concentration was increased. The effect of the pressing temperature was complex and required many additional sets of specimens to understand. Samples pressed at the highest temperature had the least coherent networks, as the polystyrene became too fluid and disrupted the ATO networks while at lower temperatures the opposite occurred. The optical transmittance dropped sharply as the concentration of ATO reached and surpassed 1.0 PHR. Nanowire networks were, indeed, formed through this process using these materials, but use as a conducting transparent composite in the visible range is unlikely as the percolation threshold occurs at a concentration greater than that of the optical transmittance drop, creating a trade-off between conductivity and transparency. The resistivity did drop as much as six orders of magnitude and may be useful for other applications.

Multilayer structures of Nb2O5/Ag/Nb2O5 have been deposited onto flexible substrates by sputtering at room temperature to develop indium free composite transparent conductive electrodes. The optical and electrical properties of the multilayers are measured by UV–Visible spectroscopy, Hall measurement and four point probe and the effect of Ag thickness has been studied. The critical thickness of Ag to form a continuous conducting layer is found to be 9.5 nm and the multilayer stack has been optimized to obtain a sheet resistance of 7.2 Ω/sq and an average optical transmittance of 86 % at 550 nm. The Haacke figure of merit (FOM) has been calculated for the films, and the multilayer with 9.5 nm thick Ag layer has the highest FOM with 31.5 x 10-3 Ω/sq, which is one of the best FOM reported till date for room temperature deposition on flexible substrates. The multilayered samples are annealed in vacuum, forming gas, air and O2 environments and the optical and electrical properties are compared against the as-deposited samples.

In this study, we have developed a constant current method for fabrication of AAO membranes with a large interpore distance in order to avoid the burning phenomenon. From our preliminary results, the average growth rate of AAO membranes could increase up to 6 μm/hr with an applied current density of 6 mA/cm2 and the burning phenomenon could be totally avoided at a relatively high anodizing voltage of 175 V. The effect of current density on the growth rate and burning phenomenon was also investigated.

Nanocoral ZnO structures are fabricated by means of reactive magnetron sputtering with post deposition annealing. The films are polycrystalline with highly developed surfaces. Their application for biosensing is presented in the extended-gate FET approach where a nanocoral gate electrode is used to sense the pH of the solution and then the presence of BSA molecules.

A versatile and powerful new lithographic fabrication method has been used to fabricate a number of nano-architectured ordered 2-D indium tin oxide (ITO) and silver (Ag) electrodes. By careful tuning of the dimensions of the nanofeatures in the electrodes, the surface area can be enhanced as desired, in-turn changing resistivity and free carrier concentrations accordingly. Absorption spectra of the samples show the existence of a new optical bandgap, in addition to the bulk bandgap, that is smaller. Nanostructured electrodes show enhanced transparency compared to their planar counterparts and demonstrate typical surface plasmon characteristics. The resonance frequency can be tuned as well by changing the dimensions of the nanofeatures in the electrodes.

The well-known high irradiation resistance of fluorite-structured oxides is examined on the nanoscale by focused electron beam irradiation of ceria nanoparticles. It is found that ceria is amongst the nanomaterials most resistant to electron beam perforation with mainly swelling and amorphisation damage observed, along with grain reorientation effects. A comparison to reference nano-materials, shows that cubic zirconia behaves similarly resistant but that ultra-fine holes can be drilled, unlike for ceria, while SiC on the other hand can be perforated easily. Ablation of carbon films around electron beam impact zones is found accelerated in ceria, as compared to SiC, and discussed as a potential catalytic effect.