Research Timothy Pennycook

Abstract

Defects such as dopants, vacancies and grain boundaries can dramatically alter the properties of 2D materials. Likewise new physical phenomena often emerge from interfaces between different materials. With 2D materials systems such interfaces can be laterally connected or stacked vertically, and exciting unexpected behaviors are emerging from both classes of interfaces. Understanding such systems requires knowledge of their local microscopic structure and composition. Electron ptychography and 4D STEM in general have recently experienced a renaissance as researchers realize the power of 4D STEM to provide local microscopic information that could not be directly accessed before. However 4D STEM, including ptychography, have previously been limited by the speed at which pixelated detectors could capture the required images, severely curtailing the speed at which 4D STEM could be performed. In this project we will overcome this limitation with our new 4D STEM detector which can operate hundreds of times faster than previous pixelated detectors. Using this breakthrough in speed we will develop superior means of not only imaging structure, but also atomic scale charge and field mapping, and extend such analysis into the third spatial dimension by combining 4D STEM with tomography and optical sectioning. Armed with these new tools we will enable a greater understanding of 2D material systems.

Researcher(s)

• Promoter: Pennycook Timothy

Research team(s)

• Electron microscopy for materials research (EMAT)

Project type(s)

• Research Project

Abstract

The salinity gradients that occur where fresh water flows into salty ocean water represent a very large and almost completely untapped source of clean, so called blue energy, based on osmosis. One reason blue energy remains untapped is the inefficiency of current methods to harvest it, mostly due to the poor performance of the membrane processes being used. A promising potential solution to this problem is to use atomically thin 2D materials with nanopores in them as the membranes. Proof of principle experiments with nanopores in 2D materials have demonstrated osmotic power densities up to six orders of magnitude better than conventional membranes. Charge buildup around the nanopores creates a filter that allows salt ions with only one sign of charge to be driven by the chemical potential gradient from a salty reservoir through the pores and into a fresh water reservoir. Much like in a battery, the resulting segregated charge build up creates an electrical potential difference that can be used for electrical power. However, in order to enable maximum efficiency power generation from blue energy, a better understanding of the nanopores is needed. At present even basic knowledge such as their atomic structures remains lacking. In this project we will determine the atomic structure of nanopores which have been characterised for blue energy performance and develop methods of probing the charge density and electric fields at and around the nanopores with electron microscopy. In conjunction with first principles theory we will use the correlations between blue energy performance and the findings of the microscopy experiments to understand the physics of osmotic power production with nanopores in different 2D materials. We will thus uncover what makes the best nanopore based membranes, facilitating the engineering of nanopores with optimal blue energy performance.

Researcher(s)

• Promoter: Pennycook Timothy
• Fellow: dos Santos Gomes José Nuno

Research team(s)

• Electron microscopy for materials research (EMAT)

Project type(s)

• Research Project

Abstract

Atomic resolution microscopy relies on beams of energetic electrons. These beams quickly destroy fragile materials, making imaging them a major challenge. I have recently developed a new approach that provides the greatest possible resolving power per electron. The method provides both double resolution and excellent noise rejection, via multidimensional data acquisition and analysis. Here I propose to couple the new method with breakthroughs in high speed cameras to achieve unprecedented clarity at low doses, almost guaranteeing major advances for imaging beam sensitive materials. Proof of principle will be achieved for biochemical imaging using the easy to handle, commercially available GroEL chaperone molecule. We will combine our enhanced imaging capabilities with the averaging methods recently recognized by the Nobel prize in chemistry for imaging biomolecules at ultra low doses. After proving our low dose capabilities we will apply them to imaging proteins of current interest at greater resolution. Similar techniques will be used for fragile materials science samples, for instance metal organic framework, Li ion battery, 2D, catalyst and perovskite solar cell materials. Furthermore the same reconstruction algorithms can be applied to simultaneously acquired spectroscopic images, allowing us to not only locate all the atoms, but identify them. The properties of all materials are determined by the arrangement and identity of their atoms, and therefore our work will impact all major areas of science, from biology to chemistry and physics.

Researcher(s)

• Promoter: Pennycook Timothy

Research team(s)

• Electron microscopy for materials research (EMAT)

Project type(s)

• Research Project