The 204th MANA & 90th ICYS Joint Seminar
Dr. Lok Kumar Shrestha & Dr. Han Zhang
| Date | May 20, Friday |
| Time | 15:30-16:30 |
| Place | Seminar Room #431, 4F, MANA Bldg., NAMIKI, NIMS |
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15:30-16:00
C60 microcrystals with diverse morphologies via liquid-liquid interface
Bucky balls (fullerene C60) due to its unique structure and properties have become a promising material in versatile applications such as in semiconductors and optoelectrical devices. In particular, such applications utilize the C60 in a self-assembled one-dimensional (1-D) or two dimensional (2-D) structure that promotes its electronic and optical properties. Therefore studies on the self-assembled nanostructures of the C60 continue to attract attention. In this talk, a systematic synthesis and characterization of the C60 microcrystals having diverse morphologies will be discussed. Liquid-liquid interfacial precipitation method has been employed for the crystallization. Different alcohols and their mixtures have been used as antisolvents, whereas benzene and carbon tetrachloride (CCl 4), and their mixtures were considered as the main solvents. The 1-D and 2-D C60 microcrystals are possible to achieve depending on the type of alcohols, solvents, and their mixing fractions. Furthermore, following the strategy of mixing solvents meso-and macroporous 2-D C60 microcrystals are successfully obtained and it is the mixing fraction of solvents that determines the pore size distribution. Interestingly, the 3-D C60 microcrystals could be obtained upon incorporation of an inorganic salt under a special condition. It is suggested that the formation mechanisms are driven by the supersaturation of the C60 in organic solvents.
Speaker
Dr. Lok Kumar Shrestha, ICYS-MANA Researcher, MANA, NIMS
Chair
Dr. Katsuhiko Ariga, MANA PI, MANA, NIMS
16:00-16:30
LaB6 Field Emission Gun: Making a Decades Old Dream Come True with Nanotechnology
After the spherical aberration being corrected with the state-of-the art Cs-corrector technology, the remaining major factors limiting the resolving power and performance of an electron microscope are the chromatic aberration and the field emission source brightness. These two aspects can be significantly improved by reducing the work function of the field emitter material. While W, the conventional field emitter material, has a work function around 4.5eV, LaB6 exhibits only half that value in debt to its peculiar surface electric dipole arrangement. Though LaB6 has been recognized as the best electron emission material since 1950s, the research and development on using LaB6 as a field emission source, however, has made little progress. This is simply due to the fact that it is difficult to fabricate a LaB6 tip with nano-meter sharpness. In the year 2005, I developed a chemical method to grow LaB6 single crystalline nanowires, which is a natural form of sharp field emitter tips. The exploration about the possibility of LaB6 field emission gun has thus been revitalized. This talk will elucidate the following four key aspects of recent progresses that have made possible a LaB6 single nanowire field emitter: 1) the growth of clean LaB6 nanowires without contamination layer; 2) the accurate assembly of a field emitter with a single LaB6 nanowire; 3) an in-situ etching method to shape the desired tip cap geometry; 4) the formation of a nano-facet at the nanowire tip apex with La atoms as the outmost layer. While a complete characterization of the emission properties is still ongoing, the LaB6 field emitters’ unique feature of point electron emission localized through naturally low work function has already surpassed all other forms of field emission source candidate.
Speaker
Dr. Han Zhang, ICYS-Sengen Researcher, NIMS
Chair
Dr. Jie Tang, Group Leader, 1D Nanomaterials Group, Exploratory Materials Research Laboratory for Reliability and Safety, NIMS