Issue No. 3, December

Abstract

Developing a photocatalysis system to generate hydrogen from water is a topic of great interest for fundamental and practical importance. In this study, hydrogen production by a new Z-scheme photocatalysis water splitting system was examined over Rh modified K₄Nb₆O₁₇ nanosheets and Pt/WO₃ photocatalysts for H₂ evolution and O₂ evolution with I-/IO₃ - electron mediator under UV light irradiation. The H₂ evolution photocatalyst, Rh/K₄Nb₆O₁₇ nanosheets with a slit like framework, was prepared by exfoliation of and proton exchange reaction. Pt/WO₃ prepared by incipient-wetness impregnation method was used as O₂ evolution photocatalyst. The catalysts were characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy analysis (XPS), and ultraviolet-visible spectroscopy (UV-vis). These catalysts characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible spectroscopy (UV-Vis). In this study, we developed a facile method of preparing K₄Nb₆O₁₇ nanosheets containing Rh nanoparticles. Our results show that I- concentration and pH of reaction solution have significant influences on the photocatalytic activity. The combination of Rh modified K₄Nb₆O₁₇ nanosheets with Pt/WO₃ achieves a very high photoactivity (H₂: 4240 O₂: 1622 (μmol g^-1 h^-1)).

Abstract

The main aim of this study was to electrochemically synthesize and characterise bismuth vanadate (BiVO₄) photoelectrodes for photoelectrochemical (PEC) water splitting. The influence of annealing temperature on the nanostructured semiconductor BiVO₄ thin film structure was studied systematically. This was followed by advanced characterisation of the BiVO₄ photoelectrodes by using field emission-scanning electron microscopy (FE-SEM), Raman spectroscopy, photoluminescence and PEC properties measurements. When the electrochemically synthesized BiVO₄ thin films were subjected to different annealing temperatures, phase transitions occurred for tetragonal BiVO₄ at 300 oC and monoclinic BiVO₄ at 400 oC. Through this study, it was found that the annealing treatment at 400 oC resulted in the highest photocurrent density (i.e. photoactivity) of 1.23 mA/cm² at 0.6 V vs. Ag/AgCl. Finally, the BiVO₄/CuO heterojunction photoelectrode was also fabricated in order to further enhance its photoactivity under visible light irradiation.

Abstract

Grafting TiO₂ on PMMA was studied by atom-transfer radical-polymerization (ATRP). Each step in grafting process was monitored by fourier transform infrared spectroscopy (FT-IR), ¹H NMR and ¹³C NMR spectra. The glass temperature of grafted-PMMA film was determined by using differential scanning calorimetry (DSC). The morphology and bulk composition were characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEMEDX). The surface composition was characterized by X-ray photoelectron spectroscopy (XPS). As results, a novel method of grafting TiO₂ on PMMA was successfully grafted and confirmed in various techniques. The photocatlytic activity was evaluated under UV and visible light irradiation. The reusability of TiO₂-g-PMMA films was studied in details.

Abstract

TiO₂ films of varying mineralogical and microstructural characteristics were fabricated on sand-blasted Ti₆Al₄V plates by anodisation in 2 M sulphuric acid (H₂SO₄) and 2 M phosphoric acid (H₃PO₄) at 120 V and 300 mA/cm² for 10 min and 15 min, respectively. The film formed by anodisation in H₂SO₄ consisted of both anatase and rutile while the film formed by anodisation in H₃PO₄ consisted only of rutile. This inconsistency is attributed to the presence of anatase below the level of detection in the sample anodised in the H₃PO₄, which consisted of a thinner TiO₂ anodised film. SEM images demonstrated that H₂SO₄ resulted in arcing and resultant porosity while H₃PO₄ did not. Profilometry revealed that the former was rougher than the latter and that the latter was nearly the same roughness as the sand-blasted plate. These observations are consistent with the conclusion that H₃PO₄ formed a thinner anodised film and that the greater thickness from H₂SO₄ resulted in asperity formation, which enhanced arcing and densification. Although the anataserutile mixture and the greater roughness of the sample anodised in H₂SO₄ could be expected to have yielded superior performance, the fact that it did not is attributed to the greater bulk density and associated lower surface area of the TiO₂ matrix. Preliminary cell culture tests showed that human osteoblast-like cells (MG63) were attached effectively on smooth anodised films (on polished plates) after 4 h of incubation while cell proliferation was confluent after 2 days. The major finding of the present work is that X-radiation in clinical doses (<200 cGy) is sufficient to cause degradation of organic species via photocatalysis.

Abstract

This contribution revisits recent results regarding the selective detection of the trace gases hydrogen sulfide, nitrogen oxide, and nitrogen dioxide using cupric oxide (CuO). It demonstrates how the variation of the surface temperature may be used to learn about basic material parameters as well as control the surface reactions. In contrast to commonly employed modulation schemes that continuously vary the temperature we use a steady-state approach in order to extract information about gas matrices. Our results highlight the potential for incorporating laboratory results regarding surface processes in pattern recognition schemes to improve the performance of these algorithms. We propose to implement the findings into temperature modulation schemes in order to allow for adding highly gas specific elements to the algorithms deployed.

Abstract

SnO₂-based sensor has many advantages such as low cost, small size, high reliability, and long operating life, but selectivity has been a major obstacle on the application for discriminating gas species in mixture of multi-reduction gases. To resolve the problem in this work, the pure SnO₂ and NiO-, CuO- and Pt-modifying SnO₂ as sensing materials were prepared by sol-gel method, the sensor cells were fabricated and characteristics of sensitivity and selectivity of the sensor cells to CO and H₂ at 400oC were investigated. The results showed that the response of CO was improved obviously by doping 20mol%NiO or 5mol%CuO into the SnO₂, while the response of H₂ was changed no more, and the responses of CO and H₂ both were enhanced dramatically by bearing 1mol%Pt into the SnO₂. On the basis of empirical equation (R=1+kCn), two sensor cells with different selectivity were introduced to assemble a novel SnO₂-based sensor, and proposed a potential method to detect the concentrations of CO and H₂ in multi-component gases, in which the parameters of k and n for sensor cells were obtained and feasibility of the method was demonstrated.

Abstract

Six different ZnO nanomorphologies were synthesized trough wet chemical routes starting from a water solution of zinc nitrate hexahydrate, obtaining two types of morphologies: bidimensional nanocrystals and nanoparticles aggregates. Powders and films characterizations have been carried out by means of TG–DTA, SEM, and X-ray diffraction analysis. Finally, electrical measurements were performed with the aim to compare conductive properties of the thick films, surface barrier heights and gas sensing features, mainly versus acetone and other VOCs related to the breath gas analysis. Among the different morphologies tested, it turned out that the samples constituted by nanoparticle aggregates exhibited the best performances versus all gases, but especially toward acetone at sub-ppm level.
 

Abstract

In this research work, a very simple, low cost eco-friendly method is presented for the synthesis of silver nanoparticles to be used in colorimetric optical sensors based on localized SPR (LSPR) measurement for gas ammonia. Silver nitrate salts are reduced using gaur gum which acts as a capping and reducing agent. Commonly used reducing agents such as trisodium citrate or sodium borohydride are replaced by a more environmental friendly natural polysaccharide. Nanocomposite films of ~ 1.5 μm thicknesses were fabricated using Gaur Gum and silver nanoparticles. The uniformity of nanoparticles size was measured by SEM and TEM, while face centred cubic structure of crystalline silver nanoparticles was characterized using the X-ray diffraction technique. The optical properties of the composite film were tested by UV-VIS Spectroscopy. The formation of Gaur Gum/silver nanocomposite films was confirmed using SEM images. Also the resistivity of nanocomposite thin film was measured which could be then used for gas sensing application.

Abstract

Several approaches to improve H₂ sensing properties of TiO₂-based diode-types sensors have been investigated. Those include the adoption of a Pd-Pt alloy electrode instead of using a pure Pd electrode, formation of a polymer coating atop the Pd-Pt alloy electrode and an Au coating on the Pd-Pt alloy electrode. The advantages of the using of the Pd-Pt alloy electrode, the polymer or Au coatings are demonstrated.

Abstract

We study the structure of nonstoichiometric HfO_x films with variable composition using methods of XPS, spectroscopic ellipsometry, and ab initio calculations. According to XPS and optical absorption experiment data HfO_x consists of metal Hf and 10-15% of nonstoichiometric hafnium suboxide HfO_y (y < 2). HfO_y can be placed between HfO₂ and Hf, inside HfO₂, inside Hf. According to this model space fluctuations of chemical composition cause space fluctuations of bandgap in HfO_x. We found that transport in such electronic systems is described by percolation theory. This approach can be applied to explain LRS transport of HfO_x-based RRAM.

Abstract

Lithium (0, 1.0 and 10 at.%)-doped ZnO (LiZnO) polycrystalline thin films were deposited on Pt/SiO₂, LaB₆/Al₂O₃, Au/SiO₂ and 20 at.% fluorine-doped SnO₂(FTO)/glass substrates by an e-beam evaporation method. Metal/LiZnO/Metal sandwich structures were constructed by depositing different top electrodes (Ag, Al and Au) to find memristive characteristics depending on the lithium content and electrode materials. Compared with undoped and 1%Li-doped ZnO devices, the 10 at.%Li-doped ZnO (10LiZnO) device exhibits resistive switching memory. The Ag/10LiZnO/Pt and Ag/10LiZnO/LaB₆ memory devices exhibit unipolar resistive switching behavior while bipolar resistive switching in Ag/10LiZnO/FTO, Au/10LiZnO/FTO and Al/10LiZnO/LaB₆ structures is revealed. The dominant conduction mechanisms are explained in terms of Ohmic behavior, space charge limited current (SCLC) and Schottky emission for the URS and BRS behaviors.

Abstract

A Magnetic Random Access Memory (MRAM) device was successfully embedded into TowerJazz’s 130nm CMOS platform. The fabricated devices are stand-alone 4Mbit and 1Mbit MRAM memories and Multi-MLU magnetic sensors. This paper will describe the process development challenges in adapting a standard 130nm Cu BEOL to incorporate the magnetic cell element, and the device sensitivities to processing.
The main process challenges to be discussed are 1) formation of shallow damascene Cu contacts to the lower electrode; 2) patterning of the 150nm magnetic cell both lithography and etching of the magnetic stack; 3) planarization of the topography from the magnetic cell; 4) formation of dual damascene VIA’s to both the magnetic cell upper electrode and to the CMOS.
Some electrical yield results of the stand-alone MRAM memory and magnetic sensors will be presented.
This project was a collaborative effort between TowerJazz and Crocus Technology