15:30-16:00

Your Nanostructure Exposed! A Thorough Look at Nanostructural Characterization with Small-Angle Scattering.

"What does the nanostructure in my material look like", is a question often posed by the materials synthesizing crowd to microscopists and small-angle scatterers. Unfortunately, small-angle scattering cannot answer this question. Once the scientist is done looking at his structure under a microscope, however, that is where small angle scattering comes in. If you need numbers, high-quality, reliable values, maybe you should try… Small-angle scattering!

Small-angle scattering is a technique to measure the quantifiable details of the nanostructure, such as structural dimensions, volume fractions and orientation on many samples. More specifically, small-angle scattering is a technique that promises statistically significant structural parameters, measured over non-negligible quantities of material, with a minimum of sample preparation. As such, it should be an ideal technique for structural characterization. With that as a lure, it has had many a scientist salivating at the prospect of actually obtaining such parameters for their materials.

While the measurements are relatively easy (but not as straightforward as many researchers think), the real stumbling block lies at the processing and analysis of the measurements. As such, the analysis of small-angle scattering patterns has been a hot topic since the technique emerged almost 100 years ago. With the advent of ubiquitous computing power, less cumbersome analysis methods have started to develop.

One of these novel analysis methods are methods based on Monte-Carlo (Trial-and-Error) approaches. In the ongoing research, this has been shown to be applicable to scattering from unoriented systems, allowing for the extraction of scatterer size distributions as well as the uncertainties on those numbers. This, then, is one of the few techniques which indicates how far you can trust the values you got (which may be more important than the actual value!).

Very recently, this approach has been applied to oriented structures, in particular to study aligned nanovoids in fibres. Given the additional dimensionality of the data, more information than usual can be inferred from the small-angle scattering, providing information on sizes as well as orientation.

This talk will discuss the developed small-angle scattering methodology and the progress in analysis of materials, and will highlight some steps of the methodology towards obtaining reliable high-quality nanostructural parameters. The construction of a new (Bonse-Hart) SAXS instrument at NIMS will be highlighted as well, which is scheduled to become operable late 2012.

Speaker

Dr. Brian Richard Pauw, ICYS-Sengen Researcher, NIMS

Chair

Dr. Kenjiro Miyano, Managing Director, ICYS, NIMS

16:00-16:30

Graphene "Dopant": Ambipolar Engineering of Graphitic Carbon Nitride

Graphene is a fascinating material not only for electronic applications, but also as a dispersible aromatic platform for chemical reactions or as a carrier for catalysts. However, graphene is not merely interesting in itself. Here we show graphene was used as a dopant for semiconductors in band-structure engineering. Like the union of tetrathiafulvalene (TTF) with tetracyanoquinodimethane (TCNQ) through π-π stacking forming a new molecule, we stacked graphene with its analogue, graphitic carbon nitride (g-C₃N₄) sheet. Our results showed that by doping with reduced graphene oxide (rGO, ≤1wt %) the band structure of g-C₃N₄ was modulated between more “n-type” and more “p-type”. Consequently, a significant increase of either anodic or cathodic photocurrent from g-C₃N₄ was obtained (e.g., when biased at 0.4 V vs. Ag/AgCl, the anodic photocurrent was 300% higher after doping). Moreover, the host semiconductors are feasibly extended to other layered semiconductors; therefore, graphene would be promising as a general intercalating dopant. Meanwhile, it also implicated the rational combination of any other two-dimensional materials towards new properties.

References

[1] K. Geim and K. S. Novoselov, Nature Mater., 2007, 6, 183-191.

[2] V. Lightcap, T. H. Kosel and P. V. Kamat, Nano Lett., 2010, 10, 577-583.

[3] X. Dong, D. Fu, W. Fang, Y. Shi, P. Chen and L. J. Li, Small, 2009, 5, 1422-1426.

[4] P. W. Anderson, P. A. Lee and M. Saitoh, Solid State Commun., 1973, 13, 595-598.

[4] Y. Zhang, T. Mori, L. Niu and J. Ye, Energy Environ. Sci., 2011, 4, 4517.

Speaker

Dr. Yuanjian Zhang, ICYS-MANA Researcher, MANA, NIMS

Chair

Dr. Jinhua Ye, MANA Principal Investigator, MANA, NIMS