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Dr Alex Robertson

Research interests

My group uses operando transmission electron microscopy (TEM) imaging to understand the dynamic structural and chemical changes that nano and energy materials undergo under application relevant conditions. This includes looking at how two dimensional materials behave while under electrical biasing, or the electrochemical processes that occur at a battery electrode.

I am currently recruiting for PhD projects! Check my personal site or the Department project list for project descriptions, and please contact me if you are interested and would like to discuss the project details.


An atomic resolution image of monolayer MoS2, with a line defect running through its centre

Atomic resolution scanning-mode TEM image of a line defect in monolayer MoS2, alongside a corresponding atomic model calculated by density functional theory (DFT). High-angle annular dark field (HAADF) images like this can be interpreted directly, as pixel intensity correlates with the atomic number; i.e., the Mo atoms look bright, S atoms look faint, and the two S atoms atop one another are intermediate intensity. We can see the central band consists of a single S atom per site, rather than S2 pairs. This is a line defect assembled from multiple S vacancies formed at high temperature within the TEM, and has been modelled to have interesting electrical properties. Dopant atoms, highlighted in blue in the DFT model and visible as fainter sites in the image, are Cr atoms that have substituted for Mo, and will further alter the material properties. 10.1021/acsnano.6b05674.

Flow diagram of an operando liquid-cell TEM holder.

The operando liquid-cell TEM holder and some example TEM images, which we can use for safely studying specimens in liquid environments while under the high vacuum environment of the TEM. (a) A photo of the holder, and (b) magnified view of the tip assembly that houses the cell. (c) Removing the cap reveals the o-ring and silicon chips that form the liquid-cell. (d) The two small silicon chips are held in place and sealed by the circular o-ring (coin for scale!). Each chip has an ultra-thin (30 nm) membrane in its centre that acts as an impermeable viewing window into the cell. (e) Liquid-cell TEM images of gold nanoparticles moving in a thin layer of water. (f) Magnified view showing the faint resolution of the gold crystal lattice. 10.1021/acsami.8b03688 and 10.1098/rsos.191204.

A graphene nanopore image

Atomic resolution TEM images of sub-nanometre pores in graphene, alongside DFT calculated atomic models. Our TEM images were used as the foundational data for an 'isomer cataloguing' algorithm (developed by collaborators) that could predict the relative probabilities of the perimeter atomic structure of graphene pores of various sizes. These graphene pore structures are of interest in applications that require molecular filtering - like the desalination of salt water. 10.1038/s41563-018-0258-3.

Calcium metal dendrites forming during electrochemical cycling of a new calcium-ion battery electrolyte

Electrochemical deposition of calcium onto a working electrode imaged in real time by operando liquid-cell TEM. As we reach the limits of what is possible with conventional lithium-ion batteries, new chemistries are being explored for alternative rechargeable batteries. Multivalent calcium-ions promise greater stability and higher abundance than lithium, yet remain relatively under-studied. We studied a promising prototype calcium-ion electrolyte, Ca(BH4)2 dissolved in THF, to better understand the charging conditions under which adverse electrode structures may form. 10.1021/acsenergylett.0c01153.

TEM images and atomic models showing a graphene defect changing via a mediator atom

Sequential TEM images showing the evolving atomic structure of a defect in graphene, alongside computationally modelled atomic structures. The TEM images show the positions of individual carbon atoms, with each black dot corresponding to a carbon atom. The regular hexagonal grid of perfect graphene is disturbed in the centre, showing the tail-end of a two-dimensional partial dislocation. This changes between the first and second image. We worked with modelling experts at Seoul National University to develop a new framework for understanding how these defects can evolve; so-called 'mediator atoms' that are weakly bound to the crystal are able to facilitate low-energy bond breaking and forming, allowing for rapid changes in defect configuration. 10.1126/sciadv.aba4942.

Snapshot image of lithium metal electroplating onto an electrode in liquid-cell TEM. Our current Li-ion batteries utilise graphite as the anode, with lithium able to safely store between the graphene layers. However, chemically the graphite does not contribute to energy storage, and so represents a weight overhead for the cell. Replacing graphite with a lithium metal electrode would be optimal, however lithium's reactivity preclude this, as over several charge-discharge cycles dangerous lithium dendrites form. Controlling the reactivity problem of the lithium metal anode by tailoring the electrolyte chemistry is one option for preventing this. We investigated the influence of this strategy by capturing the lithium deposition process as it occurred by TEM, revealing how electrolyte makeup controls the lithium morphology dynamics during charge and discharge. 10.1002/aenm.202003118.

Group

I currently supervise four PhD students who are working on understanding and controlling the electrochemistry of rechargeable battery electrolytes, and have previously hosted a post-doc and a summer student in my group.

Teaching

I currently teach a Physics undergraduate tutorial group.

Alex Robertson

Dr Alex W Robertson

Assistant Professor
Microscopy Group


Personal site: Robertson Group

Google Scholar: Publication list


Write to:

Department of Physics,
University of Warwick,
Coventry, CV4 7AL


Contact Details:

Office: P1.26
E-Mail:
Alex dot W dot Robertson at warwick dot ac dot uk

Links:

Microscopy Group