ZnO nanorod-arrays as photo-(electro)chemical materials: strategies designed to overcome the material's natural limitations

The urgent need for clean and storable energy drives many currently topical areas of materials research. Among the many materials under investigation zinc oxide is one of the most studied in relation to its use in photo-(electro)chemical applications. This study aims to give an overview of some of the main challenges associated with the use of zinc oxide for these applications: the high density of intrinsic defects which can lead to fast recombination, low visible light absorption and the occurrence of photo-corrosion. Employing simple low-temperature solution based methods; it is shown how defect-engineering can be used to increase the photo-electrochemical performance and how doping can strongly increase the visible light absorption of zinc oxide nanorod-arrays. Furthermore the deposition of ultra-thin titanium dioxide layers using atomic layer deposition is investigated as possible route for the protection of zinc oxide against photo-corrosion

Atomic layer deposition of metals: Precursors and film growth

The coating of complex three-dimensional structures with ultrathin metal films is of great interest for current technical applications, particularly in microelectronics, as well as for basic research on, for example, photonics or spintronics. While atomic layer deposition (ALD) has become a well-established fabrication method for thin oxide films on such geometries, attempts to develop ALD processes for elemental metal films have met with only mixed success. This can be understood by the lack of suitable precursors for many metals, the difficulty in reducing the metal cations to the metallic state, and the nature of metals as such, in particular their tendency to agglomerate to isolated islands. In this review, we will discuss these three challenges in detail for the example of Cu, for which ALD has been studied extensively due to its importance for microelectronic fabrication processes. Moreover, we give a comprehensive overview over metal ALD, ranging from a short summary of the early research on the ALD of the platinoid metals, which has meanwhile become an established technology, to very recent developments that target the ALD of electropositive metals. Finally, we discuss the most important applications of metal ALD

Colloidal co-crystallization: A new route for production of three-dimensional metallodielectric photonic crystals

Growth of three-dimensional (3D) photonic crystals is most interesting research in new and enhancing devices performance ranging from sensor, optoelectronic, photovoltaic and also surface enhance Raman scattering. Co-crystallization with bottom up technique was introduced in producing 3D photonic crystals with metal properties or so called as metallodielectric photonic crystals and also its inverse structure. In this study, poly(methyl methacrylate) (PMMA) particles, acid-hydrolyzed tetraethylorthosilicate solution and pre-formed gold nanoparticles was combined followed by the removal of PMMA template. Relatively large (10 s of mm), robust and crack-free films with thickness of approximately below 20 deposition layers was successfully produced by this simple yet effective route. Its morphology, particle size and optical properties were characterized by scanning electron microscopy (SEM), optical bench set-up

Atomic layer deposited V2O5 coatings: a promising cathode for Li-ion batteries

A modified, thermal atomic layer deposition process was employed for the pulsed chemical vapour deposition growth of vanadium pentoxide films using tetrakis (dimethylamino) vanadium and water as a co-reagent. Depositions were carried out at 350 °C for 400 pulsed CVD cycles, and samples were subsequently annealed for 1hour at 400 °C in air to form materials with enhanced cycling stability during the continuous lithium-ion intercalation/deintercalation processes. The diffusion coefficients were estimated to be 2.04x10-10 and 4.10x10-10 cm2 s-1 for the cathodic and anodic processes, respectively. These values are comparable or lower than those reported in the literature, indicating the capability of Li+ of getting access into the vanadium pentoxide framework at a fast rate. Overall, it presents a specific discharge capacity of 280 mA h g-1, capacity retention of 75 % after 10000 scans, a coulombic efficiency of 100 % for the first scan, dropping to 85 % for the 10000th scan, and specific energy of 523 W h g-1

(2+1)-dimensional photonic crystals from Langmuir-Blodgett colloidal multilayers

Angle-resolved transmission spectra of multilayers of two-dimensional colloidal crystals prepared by the Langmuir-Blodgett technique have been studied. In contrast to the light diffraction in three-dimensional colloidal crystals, optical spectra revealed only very weak correlation between layers in the Langmuir-Blodgett multilayers. Two reasons for the observed transmission minima have been identified: the diffraction at a stack of layers and the scattering of the incident beam by guided modes of the two-dimensional colloidal crystals. (c) 2006 American Institute of Physics. (DOI:10.1063/1.2234568

Atomic vapor deposition of bismuth titanate thin films

c-axis oriented ferroelectric bismuth titanate (Bi4Ti 3O12) thin films were grown on (001) strontium titanate (SrTiO3) substrates by an atomic vapor deposition technique. The ferroelectric properties of the thin films are greatly affected by the presence of various kinds of defects. Detailed x-ray diffraction data and transmission electron microscopy analysis demonstrated the presence of out-of-phase boundaries (OPBs). It is found that the OPB density changes appreciably with the amount of titanium injected during growth of the thin films. Piezo-responses of the thin films were measured by piezo-force microscopy. It is found that the in-plane piezoresponse is stronger than the out-of-plane response, due to the strong c-axis orientation of the films

Piezoresponse force microscopy investigations of Aurivillius phase thin films

The sol-gel synthesis and characterization of n≥3n≥3 Aurivillius phase thin filmsdeposited on Pt/Ti/SiO2–SiPt/Ti/SiO2–Si substrates is described. The number of perovskite layers, nn, was increased by inserting BiFeO3BiFeO3 into three layered Aurivillius phase Bi4Ti3O12Bi4Ti3O12 to form compounds such as Bi5FeTi3O15Bi5FeTi3O15 (n=4)(n=4). 30% of the Fe3+Fe3+ ions in Bi5FeTi3O15Bi5FeTi3O15 were substituted with Mn3+Mn3+ ions to form the structureBi5Ti3Fe0.7Mn0.3O15Bi5Ti3Fe0.7Mn0.3O15. The electromechanical responses of the materials were investigated using piezoresponse force microscopy and the results are discussed in relation to the crystallinity of the films as measured by x-ray diffraction

The structural and piezoresponse properties of c-axis-oriented Aurivillius phase Bi5Ti3FeO15 thin films deposited by atomic vapor deposition

The deposition by atomic vapor deposition of highly c-axis-oriented Aurivillius phase Bi 5Ti 3FeO 15 (BTFO) thin films on (100) Si substrates is reported. Partially crystallized BTFO films with c-axis perpendicular to the substrate surface were first deposited at 610°C (8 excess Bi), and subsequently annealed at 820°C to get stoichiometric composition. After annealing, the films were highly c-axis-oriented, showing only (00l) peaks in x-ray diffraction (XRD), up to (0024). Transmission electron microscopy (TEM) confirms the BTFO film has a clear layered structure, and the bismuth oxide layer interleaves the four-block pseudoperovskite layer, indicating the n 4 Aurivillius phase structure. Piezoresponse force microscopy measurements indicate strong in-plane piezoelectric response, consistent with the c-axis layered structure, shown by XRD and TEM

Room temperature electromechanical and magnetic investigations of ferroelectric Aurivillius phase Bi5Ti3(FexMn1−x)O15 (x = 1 and 0.7) chemical solution deposited thin films

Aurivillius phase thin films of Bi5Ti3(FexMn1−x)O15 with x = 1 (Bi5Ti3FeO15) and 0.7 (Bi5Ti3Fe0.7Mn0.3O15) on SiO2-Si(100) and Pt/Ti/SiO2-Si substrates were fabricated by chemical solution deposition. The method was optimized in order to suppress formation of pyrochlore phase Bi2Ti2O7 and improve crystallinity. The structuralproperties of the films were examined by x-ray diffraction, scanning electron microscopy, and atomic force microscopy. Optimum crystallinity and pyrochlore phase suppression was achieved by the addition of 15 to 25 mol. % excess bismuth to the sols. Based on this study, 17.5 mol. % excess bismuth was used in the preparation of Bi2Ti2O7-free films of Bi5Ti3FeO15 on SrTiO3(100) and NdGaO3(001) substrates, confirming the suppression of pyrochlore phase using this excess of bismuth. Thirty percent of the Fe3+ ions in Bi5Ti3FeO15 was substituted with Mn3+ ions to form Bi2Ti2O7-free thin films of Bi5Ti3Fe0.7Mn0.3O15 on Pt/Ti/SiO2-Si, SiO2-Si(100), SrTiO3(100), and NdGaO3(001) substrates. Bi5Ti3FeO15 and Bi5Ti3Fe0.7Mn0.3O15thin films on Pt/Ti/SiO2-Si and SiO2-Si(100) substrates were achieved with a higher degree of a-axis orientation compared with the films on SrTiO3(100) and NdGaO3(001) substrates. Room temperature electromechanical and magnetic properties of the thin films were investigated in order to assess the potential of these materials for piezoelectric,ferroelectric, and multiferroic applications. Vertical piezoresponse force microscopy measurements of the films demonstrate that Bi5Ti3FeO15 and Bi5Ti3Fe0.7Mn0.3O15thin films are piezoelectric at room temperature. Room temperature switching spectroscopy-piezoresponse force microscopy measurements in the presence and absence of an applied bias demonstrate local ferroelectric switching behaviour (180°) in the films. Superconducting quantum interference device magnetometry measurements do not show any room temperature ferromagnetic hysteresis down to an upper detection limit of 2.53 × 10−3 emu; and it is concluded, therefore, that such films are not mutiferroic at room temperature. Piezoresponse force microscopy lithography images of Bi5Ti3Fe0.7Mn0.3O15thin films are presented

Cu nanodendrite foams on integrated band array electrodes for the nonenzymatic detection of glucose

We demonstrate the successful electrodeposition of Cu nanodendrite foams (CuFoams) onto a series of lithographically formed gold band array electrodes at negative overpotentials in an acidic environment. The nanodendrite foams were deposited onto two different integrated microelectrode arrays fabricated using standard lithographic techniques. Each electrode consisted of 17 gold band electrodes deposited onto a silicon wafer substrate, labeled BA5 (with a width of 5 μm and a length of 250 μm) and BA10 (with a width of 10 μm and a length of 500 μm). Prior to Cu deposition the gold electrodes were characterized by scanning electron microscopy (SEM) in order to evaluate the morphology of each design and by cyclic voltammetry (CV) in order to investigate their diffusion profiles. After Cu deposition the resulting 3D foam structures were studied using SEM, XPS, and EDX. The CuFoam/Au microelectrodes were then used for the electrocatalytic detection of glucose via oxidation at a potential of +0.45 V vs Ag/AgCl in an alkaline medium. It was found that both types of electrode arrays used showed excellent analytical performance in terms of sensitivity, reproducibility, and stability in comparison with the best performances reported in the literature. In particular, the BA5-CuFoam electrode exhibited an outstanding sensitivity of 10,630 μA mM–1 cm–2 toward glucose with a wide linear range up to 22.55 mM, while the BA10-CuFoam electrode showed a sensitivity of 4,437 μA mM–1 cm–2. The performance of the proposed electrochemical sensor is attributed to a combination of the use of the very high surface area Cu nanodendrite foam and the enhanced radial distribution profile associated with the use of the smaller band microfabricated electrodes. Additionally, both sensors also showed a strong resistance to the poisoning effects of chlorine ions and excellent stability over a period of three months