Organic conductors and superconductors go nano Eun Sang Choi, Florida State University, DMR 1309146

[1] D. de Caro et al., Four Molecular Superconductors Isolated as Nanoparticles, Eur. J. Inorg. Chem., DOI:10.1002/ejic.201402007.[2] L. E. Winter et al., Spin density wave and superconducting properties of nano-particle organic conductor assemblies , to be submitted to Phys. Rev. B.

Fig. 1. (a) HR-TEM of a nanoparticle (dashed outline) of (TMTSF)2ClO4 showing the 3 to 4 nm sized single crystal sub-structure (scale bar = 5 nm). (b) Field and temperature dependent susceptibility of (TMTSF)2PF6 below the SDW transition. (c and d) Diamagnetic shielding effects of (TMTSF)2ClO4 below the SC transition, and critical field effects in (TMTSF)2ClO4 for two temperatures in the SC phase. Dashed lines are comparisons with bulk single crystal data.

(c)(d)

Recently dispersed nanoparticles (~ 30 nm NPs) of donor-acceptor (DA) organic conductors have been realized by either oxidation or electrocrystallization in the presence of stabilizing agents acting as growth inhibitors, and refinements of the synthesis conditions have produced a number of DA organic superconductors where strong correlations between the spectroscopic and crystallographic properties of the bulk materials and the nanoparticles have been established, and with our group, superconductivity[1]. Since then, we have begun a more detailed investigation to determine in detail the low temperature thermodynamic ground states of the nanoparticle species. Our recent studies have focused on the spin density wave state (SDW; TSDW = 12 K) in (TMTSF)2PF6 and superconductivity (SC; Tc = 1.2 K) in (TMTSF)2ClO4. Some of the results, soon to be submitted for publication[2], are shown in Fig. 1. We find that remarkably, even at the nano-size scale, the NPs retain to a large extent the ground state properties of bulk crystalline systems. Further work is underway to consider the effects of smaller-sized NPs less than coherence length scales, and ways to probe individual NP entities by tunneling spectroscopy or other means.

(a)(b)

The PI believes in bringing the lab into the classroom and vice versa, having the goal of “proof of concept” for activities, and showing the students the “real thing”. Presented here are some aspects of this summer’s nanoscience workshop under the auspices of the FloridaLearns STEM Scholars program, which focuses particularly on gifted and talented students from small, rural areas in the Florida Panhandle. The students spend 3 lab/classroom days doing hands-on activity challenges with construction materials, chemical and physical materials, and measuring instruments, and one day at Florida State University where they visit facilities where nanomaterials are made and characterized. The PI’s NSF-supported students help prepare demonstrations and operate high level instruments used for instruction (i.e. AFM, etc.).

Nano goes to schoolEun Sang Choi, Florida State University, DMR 1005293

Nanoscience Challenge for Florida Panhandle Gifted and Talented High School Students: Use the materials available to build a working model of an Atomic Force Microscope (AFM), and use it to produce an image of a model epitaxial thin film, all in 1 ½ hours.

Figure 1. Photos: Students with their AFM model, detail of a square lattice epitaxial film, and image of the film produced by the model instrument (pencil marks, outlined by circles, represent high regions of the film topology). Actual scanned images: left, AFM image of a DVD surface; right: SEM image of a carbon nanotube rope.