MSE Department Seminar

This seminar covers our group’s recent work on novel 2D nanomaterials development and mechanical energy harvesting device innovations. In the first half, I will present an ionic layer epitaxy (ILE) technique that uses surfactant monolayers to serve as soft templates guiding the nucleation and growth of 2D nanomaterials in large area beyond the limitation of van der Waals solids. Through this approach, 1 to 2 nm thick, single-crystalline free-standing ZnO nanosheets with sizes up to tens of microns were synthesized at the water-air interface.

The incompatibility of the energy of a solar photon and the absorption band of a chemical bond prevents the use of light to activate the chemical bond for interesting chemical reactions directly. This presentation will focus on a strategy that enables the efficient coupling of photon energy into chemical bonds to selectively promote the desired chemical reactions.

Phononic band gaps – the analogous to electronic band gaps in semiconductors – are frequencies ranges for which vibrations are not allowed to propagate in periodic structures. In contrast to well-understood electronic and photonic band gaps, being able to achieve forbidden frequency ranges for thermal phonons has been more challenging. In this talk, I discuss recent developments to understand and control the transport of thermal vibrations by wave interference and band gaps.

Chirality is fundamental to many physical, chemical, and biological systems, impacting processes as diverse as pharmaceutical-cell interactions to the evolution of species. Measuring molecular chirality is especially important to synthesize chiral compounds, study enzymatic interactions, and understand dynamic protein folding and DNA hybridization. Current methods to measure molecular chirality rely on ensemble techniques such as circular dichroism spectroscopy. However, these techniques require large analyte concentrations and relatively long integration times.

High heat fluxes and increased temperatures have led to major road blocks in the advancement of materials and technologies. For example, high frequency devices and optical links, energy storage and conversion devices, and high power laser systems have all demonstrated thermal failures that prevent functional material composites from reaching their full theoretical potential. These composites devices rely on a multitude of thin film materials with varying levels of dopants and defects in addition to a high density of material interfaces.

Strength is one of the most important material properties in engineering applications. With the advanced design of nano-materials and nano-structures, the corresponding computational and theoretical modeling techniques are required in order to optimize the structure design and predicate the enhanced material properties.

Two-dimensional (2D) layered crystals are a promising class of materials for post silicon electronics. Due to their atomic thinness, flexibility, and versatile electrical properties (i.e. conductors, semiconductors, and insulators), we can envision future ultra-small, flexible computers completely comprised of various 2D materials. For this application, lateral heterostructures of 2D materials play a major role, as they are the fundamental elements in a circuit, such as p-n junctions and metal-semiconductor contacts.

Point defects may act as compensating centers, charge traps, or radiative or nonradiative recombination centers. In addition, unintentional impurities often play an equally detrimental role; for instance, carbon that is unavoidably incorporated during growth can act as a recombination center in nitrides, or as a charge trap in oxide dielectrics.  Theoretical advances now enable us to calculate the electronic and optical properties as well as radiative and nonradiative carrier capture coefficients with unprecedented accuracy.