Synthesis and Energy Applications of Mesoporous Titania Thin Films

The optical and electronic properties of TiO2 thin films provide tremendous opportunities in several applications including photocatalysis, photovoltaics and photoconductors for energy production. Despite many attractive features of TiO2, critical challenges include the innate inability of TiO2 to absorb visible light and the fast recombination of photoexcited charge carriers. In this study, mesoporous TiO2 thin films are modified by doping using hydrogen and nitrogen, and sensitization using graphene quantum dot sensitization. For all of these modifiers, well-ordered mesoporous titania films were synthesized by surfactant templated sol-gel process. Two methods: hydrazine and plasma treatments have been developed for nitrogen and hydrogen doping in the mesoporous titania films for band gap reduction, visible light absorption and enhancement of photocatalytic activity. The hydrazine treatment in mesoporous titania thin films suggests that hydrazine induced doping is a promising approach to enable synergistic incorporation of N and Ti3+ into the lattice of surfactant-templated TiO2 films and enhanced visible light photoactivity, but that the benefits are limited by gradual mesostructure deterioration. The plasma treated nitrogen doped mesoporous titania showed about 240 times higher photoactivity compared to undoped film in hydrogen production from photoelectrochemical water splitting under visible light illumination. Plasma treated hydrogen doped mesoporous titania thin films has also been developed for enhancement of visible light absorption. Hydrogen treatment has been shown to turn titania (normally bright white) black, indicating vastly improved visible light absorption. The cause of the color change and its effectiveness for photocatalysis remain open questions. For the first time, we showed that a significant amount of hydrogen is incorporated in hydrogen plasma treated mesoporous titania films by neutron reflectometry measurements. In addition to the intrinsic modification of titania by doping, graphene quantum dot sensitization in mesoporous titania film was also investigated for visible light photocatalysis. Graphene quantum dot sensitization and nitrogen doping of ordered mesoporous titania films showed synergistic effect in water splitting due to high surface area, band gap reduction, enhanced visible light absorption, and efficient charge separation and transport. This study suggests that plasma based doping and graphene quantum dot sensitization are promising strategies to reduce band gap and enhance visible light absorption of high surface area surfactant templated mesoporous titania films, leading to superior visible-light driven photoelectrochemical hydrogen production. The results demonstrate the importance of designing and manipulating the energy band alignment in composite nanomaterials for fundamentally improving visible light absorption, charge separation and transport, and thereby photoelectrochemical properties

Kinetics of Length Scale Dependent Deformation of Gold Microspheres and Micropillars

In this thesis length and time scale dependence of the operative plastic deformation mechanisms in Au is studied. Uniaxial compression tests were performed at various loading rates on FIB-milled Au micropillars and single-crystalline Au microspheres of diameter ranging from 0.8 to 6.0 µm to investigate the incipient and bulk plasticity events. Constant-load ambient-temperature creep tests were performed on the micropillars to study the time-dependent plasticity at very slow strain rates. Uniaxial compression tests were also performed on coated Au microspheres to study the effect of extrinsic constraint on the deformation mechanisms. During uniaxial compression, both the Au micropillars and microspheres displayed strain jumps, the frequency of which decreased with increasing sample diameter and increasing resolved shear stress. The bulk flow stress, corresponding to 5% – 20% average compressive strain, was dependent upon both the strain rate and the specimen diameter. Analysis of the apparent activation volume, V*, and energy, Q*, of the deformation process indicated that the operative deformation mechanism for the small 0.8 µm diameter pillars and spheres was characteristic of a mechanism limited by surface nucleation of dislocations while larger diameter samples displayed values indicative of the more common dislocation-obstacle interaction limited deformation mechanism. The deformation-rate dependence of incipient plastic deformation of the Au micropillars and microspheres was also dependent upon the strain rate and sample diameter. For the smallest, sub-micrometer size, samples the incipient plasticity was controlled by heterogeneous dislocation nucleation events, while a dislocation-obstacle interaction limited glide process was found to be operative in the larger specimens. In the extrinsic constraint study, Au microspheres that were coated with a 40 – 80 nm thick Ni layer displayed a slightly increased flow stress compared to similar size uncoated microspheres. The estimated V* and Q* values for the coated microspheres suggest that the mechanism responsible for the initiation of first dislocation motion is essentially the same regardless of the presence of a constraining coating

Terceiras Sesióis d'Estudio del Occidente (A Caridá (El Franco), 19 y 20 de octubre de 2012)

The study explored the attitude and behavior of general people towards suicide with particular focus on role of counseling for suicide prevention in Bangladesh. Seventeen national newspapers were reviewed to look at the extent of suicide in Bangladesh and opinion of 50 people from different age, sex and profession was collected through Focus Group Discussions and an individual questionnaire. The analysis of reported news revealed that women committed suicide 5.68 times higher than men did; married people committed suicide more than unmarried people did. The data also revealed that the number of suicide is highest at age range of 16 to 20 years and family conflict is the number one cause of suicide in Bangladesh. Hanging from the ceiling and poison are the most popular method for committing suicide. Focused group discussions revealed a common belief of suicide as a sin and considered not as a right decision. All the participants undoubtedly believed that counseling is helpful in preventing suicidal behavior. The result of personal questionnaire showed that 20% of the participants thought about ending their life in their lifetime

First-order melting of a weak spin-orbit Mott insulator into a correlated metal

The electronic phase diagram of the weak spin-orbit Mott insulator (Sr(1-x)Lax)3Ir2O7 is determined via an exhaustive experimental study. Upon doping electrons via La substitution, an immediate collapse in resistivity occurs along with a narrow regime of nanoscale phase separation comprised of antiferromagnetic, insulating regions and paramagnetic, metallic puddles persisting until x~0.04. Continued electron doping results in an abrupt, first-order phase boundary where the Neel state is suppressed and a homogenous, correlated, metallic state appears with an enhanced spin susceptibility and local moments. As the metallic state is stabilized, a weak structural distortion develops and suggests a competing instability with the parent spin-orbit Mott state.Comment: 5 pages, 4 figure

Measuring topic network centrality for identifying technology and technological development in online communities

Online communities are a rapidly growing knowledge repository that provides scholarly research, technical discussion, and social interactivity. This abundance of online information increases the difficulty of keeping up with new developments difficult for researchers and practitioners. Thus, we introduced a novel method that analyses both knowledge and social sentiment within the online community to discover the topical coverage of emerging technology and trace technological trends. The method utilizes the Weibull distribution and Shannon entropy to measure and link social sentiment with technological topics. Based on question-and-answer and social sentiment data from Zhihu, which is an online question and answer (Q&A) community with high-profile entrepreneurs and public intellectuals, we built an undirected weighting network and measured the centrality of nodes for technology identification. An empirical study on artificial intelligence technology trends supported by expert knowledge-based evaluation and cognition provides sufficient evidence of the method's ability to identify technology. We found that the social sentiment of hot technological topics presents a long-tailed distribution statistical pattern. High similarity between the topic popularity and emerging technology development trends appears in the online community. Finally, we discuss the findings in various professional fields that are widely applied to discover and track hot technological topics