Integrated Calendar

Abstract

With the advent of novel fabrication techniques in the 1980s and 1990s, it became possible to explore many physical phenomena at the nanoscale. Since then, a lot of progress has been done in the understanding of the electronic transport, mechanical, and optical properties of nanoscale devices. However, thermal transport in these systems has remained relatively unexplored because of the experimental difficulty to measure the flow of heat and energy at this small scale. In this talk, I will review our theoretical and experimental efforts to establish the fundamental laws that govern nanoscale thermal transport by using atomic and molecular junctions as a playground. In particular, I will discuss basic phenomena such as Joule heating and Peltier cooling in molecular junctions [1,2] and quantized thermal transport in atomic-size contacts [3].

References

[1] W. Lee, K. Kim, W. Jeong, L.A. Zotti, F. Pauly, J.C. Cuevas, P. Reddy, Nature 498, 209 (2013).
[2] L. Cui, R. Miao, K. Wang, D. Thompson, L.A. Zotti, J.C. Cuevas, E. Meyhofer, P. Reddy, Nature Nanotechnology 13, 122 (2018).
[3] L. Cui, W. Jeong, S. Hur, M. Matt, J.C Klöckner, F. Pauly, J.C. Cuevas, E. Meyhofer, P. Reddy, Science 355, 1192 (2017).

A new type of transmission electron microscopes operating at electron energies between 80keV and 20keV has been developed to obtain structural and electronic properties of advanced low-dimensional material at the atomic scale. It allows to undercut most of the materials knock-on damage thresholds and enables sub-Angstroem resolution in an 4000x4000 pixels, single-shoot image down to 40keV by correcting not only the geometrical aberrations of the objective lens but also its chromatic aberration. During the imaging process, the interaction of the beam electrons with the low-dimensional material can, nevertheless, results in changes of the atomic structure due to ionization and radiolysis, and sophisticated sample preparation methods are employed to reduce these effects. In this talk, we briefly outline key instrumental and methodological developments and report on structural properties of low-dimensional materials. We not only determine the structure of the pristine material but also use the electron beam to engineer defined properties. Thus, we show for instance the dynamics of extended defects in MoTe2 and WS2 and the creation of a commensurate charge density wave (CDW) in a monolayer 1T-TaSe2, as well as properties of MnPS3, and moreover the dynamics and bond order changing of dirhenium molecule in single-walled carbon nanotubes. Finally we intercalate bilayer graphene by lithium and study in-situ lithiation and delithiation between bilayer graphene, identify single Li atoms as well as the structure of the new high density crystalline Li- phase.

Over a century ago, various experiments both in gravitropism and phototropism, revealed that plants respond to an integrated history of stimuli rather than responding instantaneously. Particularly, experimental observations have shown that plants respond identically to different combinations of stimuli - intermittent in time or with reciprocal ratios of intensity and duration - as long as the total dose of these stimuli is the same. Current mathematical descriptions of the kinematics of tropic
responses are instantaneous and limited to constant stimuli. In this work we adopt the well-established approach of response theory, which describes the non-trivial input-output relationship of a signal transducer, in this case a plant turning an external stimulus into a growth response. This model is experimentally tractable, allowing a quantitative description of the ability of plants to integrate stimuli over time, laying the foundation for an understanding of decision-making in plant tropisms.