James K Utterback

Nanocrystal folks: Join us at nanoGe MATSUS in Valencia, Oct 20-24 2025. The theme will be Emergent Properties in Nanomaterials. The invited speaker line-up is really exciting!
- Deadline for contributed talks: June 27
- Deadline for posters: Sept 22
www.nanoge.org/MATSUSFall25...

Inverted Thickness Dependence of Thermal Transport in Nanocrystal Supercrystals Down to the Monolayer Spatiotemporal thermoreflectance microscopy locally probes lateral thermal transport in ultrathin colloidal nanocrystal supercrystals. In stark contrast to typical materials, the thermal diffusivity ...

Paper #3 from the group!

We image thermal transport down to monolayer nanocrystal superlattices. In that regime ballistic phonon transport takes effect.

This was possible thanks to the beautiful samples from Florian Schulz.

advanced.onlinelibrary.wiley.com/doi/10.1002/...

Nano Letters Illustration of pump–probe spectroscopy of a colloidal semiconductor nanocrystal film, highlighting transient photoinduced heating effects. Heating following excitation above the band gap or at high fluences impacts transient spectra, relaxation kinetics, and carrier diffusivity measurements. The findings emphasize the importance of considering thermal contributions for accurate interpretation of spectroscopy measurements. View the article.

Now on the front cover of Nano Letters! @pubs.acs.org pubs.acs.org/toc/nalefd/2...

Simultaneous Electronic and Thermal Signatures in Pump–Probe Spectroscopy of Semiconductor Nanocrystal Films Thermal contributions are typically ignored in optical spectroscopy of semiconductor nanomaterials. However, such considerations are important for an accurate interpretation of spectroscopy measurements. Here, we identify signatures of transient photoinduced heating in optical pump–probe signals of colloidal semiconductor nanocrystal films. We find that lattice heating following excitation above the bandgap or at high fluences leads to a significant temperature-induced transient signal that impacts three aspects of pump–probe measurements: the transient spectra, relaxation kinetics, and spatiotemporally resolved carrier diffusivity. The effects are general across nanocrystal core material, appearing in both CdSe and PbS quantum dot films. This study proposes several methods for distinguishing simultaneous electronic and thermal contributions to transient measurements as well as guidelines for how to avoid misassignments. On the other hand, we discuss the ability to track both electronic and thermal transport as a largely missed opportunity that can be leveraged.

Very excited for the 2nd paper from my group to be out in Nano Letters ! We demonstrate how both charge carriers and heat contribute to pump-probe spectroscopy of nanocrystal films. doi.org/10.1021/acs....

Very cool work! Congrats.

Bravo! And corresponding author!

Nice work!

Anisotropic Thermal Transport in Tunable Self-Assembled Nanocrystal Supercrystals Realizing tunable functional materials with built-in nanoscale heat flow directionality represents a significant challenge that could advance thermal management strategies. Here we use spatiotemporally resolved thermoreflectance to visualize lateral thermal transport anisotropy in self-assembled supercrystals of anisotropic Au nanocrystals. Correlative electron and thermoreflectance microscopy reveal that nano- to mesoscale heat predominantly flows along the long-axis of the anisotropic nanocrystals, and does so across grain boundaries and curved assemblies while voids disrupt heat flow. We finely control the anisotropy via the aspect ratio of constituent nanorods, and it exceeds the aspect ratio for nanobipyramid supercrystals and certain nanorod arrangements. Finite element simulations and effective medium modeling rationalize the emergent anisotropic behavior in terms of a simple series resistance model, further providing a framework for estimating thermal anisotropy as a function of material and structural parameters. Self-assembly of colloidal nanocrystals promises an interesting route to direct heat flow in a wide range of applications that utilize this important class of materials.

Very excited to share the first publication of my independent group in ACS Nano! We control, model and visualize heat transport anisotropy
in supercrystals self-assembled from colloidal nanocrystals. Big thanks to the many collaborators! #matsky pubs.acs.org/doi/10.1021/...

Hello Bluesky! Joining this community to connect and share our group's research in #matsky #physics and #chemsky