Following and controlling nanoscale formation and function of bottom-up assembled materials
Speaker: Prof. Naomi S. Ginsberg (University of California, Berkeley & Lawrence Berkeley National Laboratory)
Talk title: Following and controlling nanoscale formation and function of bottom-up assembled materials
Time: 2024/11/04 (Mon.) 14:30-15:30
Place: NCTS Physics Lecture Hall, 4F, Chee-Chun Leung Cosmology Hall, NTU
Abstract:
Short-range-interacting particles can in principle crystallize via so-called non-classical pathwaysinvoking a metastable liquid intermediate, yet non-equilibrium gelation often occurs before a
metastable liquid can form. Using in situ X-ray scattering, we nevertheless watch electrostatically
stabilized colloidal semiconducting nanocrystals self-assemble into long-range-ordered
superlattices via this non-classical pathway and show how the pathway increases the rate of
crystallization over that of direct crystallization from the colloidal phase. Furthermore, by
mapping the phase behavior and kinetics as a function of nanocrystal density and electrostatically
tuned driving force for assembly, we demonstrate a highly unusual degree of control of a
nanoscale system. This control is exemplified by varying the self-assembly rate by over three
orders of magnitude, along with predictive control of superlattice yield, size, and crystallinity.
Most strikingly, we reveal that this non-classical pathway increases crystallinity of the superlattice
simultaneously with the crystallization rate. To further elucidate the elusive nature of the short-
range interactions at the nanoscale, we also study the microscopic fluctuations of colloidal
suspensions and liquid droplets of the nanocrystals via free-electron laser MHz X-ray photon
correlation spectroscopy (XPCS). We discover suppressed nanocrystal self-diffusion in the liquid
state, which we attribute to the explicit attractive interactions that are not captured by typical
charged particle hydrodynamic models. The combined results suggest design rules for the shape
of interaction potentials not only to leverage liquid intermediates in crystallization processes but
also to avoid gelation for better control of phase behaviors.
Energy transport in these and other materials is an important emergent property to also
characterize at the nanoscale, especially since the solids created often still contain nanoscale
heterogeneities. I will therefore also share recent advances in detecting, tracking, and discerning
the spatiotemporal evolution of charge carriers, excitons, heat and ions as they interconvert and
explore emerging materials’ structure and heterogeneity on multiple scales. I will share our
development of sub-picosecond and single-digit nanometer sensitivity stroboscopic optical
scattering microscopy (stroboSCAT) through a series of examples of increasing complexity,
ranging from solution-processed semiconductors to transition metal oxide photoelectrodes for
artificial photosynthesis to the most direct measurements to-date of exciton transport in natural
photosynthesis.
For a bio, please page to the bottom of the following URL (photo is at the top):
http://www.cchem.berkeley.edu/nsggrp/ginsberg.html
