The 295th MANA & the 128th ICYS Joint Seminar
Dr. Martin Hollamby & Dr. Songlin Li
| Date | November 2, Friday |
| Time | 15:30-16:30 |
| Place | Seminar room #811, 8F, Central Bldg, SENGEN Site, NIMS |
Download PDF file for seminar info.
15:30-16:00
Hydrophobic amphiphilicity – from micelles to larger assemblies
Electronically-active organic molecules usually contain an aromatic part from which the functions derive. The precise organization and orientation of these active centres strongly influences material properties.1 Typically, assemblies are grown out of solution by carefully triggering crystallization and/or annealing in the condensed phase.2,3 However, this process can be difficult to control and different products are often formed upon slight changes in external conditions. Equilibrium solution assemblies, such as lyotropic liquid crystals, could exploit the potency while providing tunability, reproducibility and stability. Additionally, they provide other opportunities e.g. control by external stimuli.
My work investigates a new concept in soft matter science of fully hydrophobic functional amphiphiles. These alkyl-aromatic molecules self-assemble into small micelle-like aggregates in alkane solvents, despite possessing no hydrophilic group common to conventional amphiphiles (e.g. surfactants). They have a high aromatic content and are extremely soluble in organic solvents. The assembly is driven by both the associative strength and solvophobicity of the aromatic part and can be easily controlled. Recently, using these principles, highly ordered lyotropic gel-like phases have been identified at a loading of < 5 wt%. In this phase, the C60 content is thought to be isolated into columnar assemblies. In this talk, this new finding will be presented, alongside efforts to align the phases using an externally applied magnetic field.
References
- Altoe, V.; Martin, F.; Katan, A.; Salmeron, M.; Aloni, S. Nano Lett. 2012, 12, 1295–1299.
- Sathish, M.; Miyazawa, K.; Hill, J. P.; Ariga, K. J. Am. Chem. Soc. 2009, 131, 6372–6373.
- Park, C.; Yoon, E.; Kawano, M.; Joo, T.; Choi, H. C. Angew. Chem. Int. Ed. 2010, 49, 9670–9675.
Speaker
Dr. Martin Hollamby, ICYS-Sengen Researcher, NIMS
Chair
Dr. Takashi Nakanishi, Principal Researcher, Polymer Materials Unit, NIMS
16:00-16:30
Rapid thickness identification and electronic transport in MoS2 atomic sheets
Abstract: Two-dimensional semiconductors are promising for the ultimate atomic field-effect transistor (FET) technology after silicon because of their unique atomic-scale thickness and flatness. In this talk, I will firstly demonstrate a rapid and nondestructive layer counting technique for the atomic layers on insulating substrates by using an interference Raman spectroscopy. As an example, atomically thin MoS2 sheets with discrete numbers of layers from 1 to 20 are obtained. Based on the accurate information on sample layers, we also performed combined experimental and theoretical studies and employed the channel thickness as a unique clue to clarify the underlying scattering mechanisms in atomic FETs. It is found that the carrier mobility changes by two orders of magnitude, increasing from ~1 to 100 cm2/Vs, as channel increases from monolayer to bulk. A careful comparison with theoretical calculation indicates that Coulomb impurities dominate the scattering events for channels thicker than 3 layers, while strong interfacial roughness like scatterings, arising from surface ripple and lopsided carrier distribution, stand out for channels as thin as 1-2 layers. The understanding highlights the critical role of substrate roughness and provides direct guidance in performance improvement in atomic-scale FETs, which are essential for the ultimate post-silicon nanoelectronics.
Speaker
Dr. Songlin Li, ICYS-MANA Researcher, MANA, NIMS
Chair
Dr. Kenjiro Miyano, Managing Director, ICYS, NIMS