Prof. William A Tisdale

Research in the Tisdale Lab is focused on the basic science and engineering of energy transport phenomena in nanostructured materials. We care about the mechanisms by which excitons, free charges, phonons (heat), and reactive chemical species are converted to more useful forms of energy, and how we can leverage this understanding to guide materials design and process optimization. We are actively engaged in the synthesis of colloidal nanoparticles, the investigation of methods for assembling these nanoscale building blocks into functional thin films, and the development of spectroscopic tools for interrogating their properties. We maintain close collaborative relationships with industrial partners, and our perspectives and ambitions are shaped by real engineering needs.

Specific areas of focus include:

COLLOIDAL QUANTUM DOTS
Colloidal quantum dots (QD) are semiconductor crystallites just a few nanometers in size. They exhibit electronic and optical properties that may be adjusted simply by changing the physical size of the nanocrystal. Colloidal QD dispersions are prepared via wet chemistry techniques carried out at moderate temperatures, suggesting a feasible path toward scalable implementation of QD materials in next-generation renewable energy technologies like solar power, high efficiency lighting, and thermal energy scavenging.

We synthesize our own QDs, but we also work closely with industrial partners to evaluate the capabilities of the next generation of commercial grade QD materials.

MOLECULAR ENGINEERING OF NANOCRYSTAL SURFACES
A salient feature of colloidal QD materials is the presence of organic ligands coating each nanocrystal facet. By rationally tuning the surface chemistry, we can control the rate and mechanism of energy transport within QD ensembles. For instance, these ligands determine whether QD excited states move as free charges or as excitons, and they likely play a central role in regulating heat transport.

NANOMATERIALS PROCESS ENGINEERING
If nanostructured materials are to make an impact in meeting global energy needs, nanomaterials processing methods must be amenable to low-cost manufacturing on a global scale. This means using earth-abundant elements, environmentally friendly solvents, and bottom-up approaches to nanofabrication.

NEAR-FIELD SCANNING OPTICAL MICROSCOPY (NSOM)
The spatial resolution of an optical microscope is fundamentally limited â?? by the wavelength of light â?? to a few hundred nanometers. By introducing a sharp scanning probe tip into the optical field near the sample surface, spatial resolution may be improved to a few tens of nanometers or less. An additional advantage of this approach is the simultaneous acquisition of structural and spectroscopic information.

We employ a variety of NSOM modalities in our lab, including tip-enhanced fluorescence, tip-enhanced Raman scattering (TERS), optical second harmonic generation (SHG), and time-resolved variants thereof.

ULTRAFAST SPECTROSCOPY
Excited state electron dynamics are central to the operation of the most promising futuristic solar cells. Important dynamic events typically occur on picosecond or sub-picosecond time scales â?? faster than the capabilities of present-day electronics. To probe such processes, the use of femtosecond (1 fs = 10-15 s) pulsed lasers is required. Currently, we are using femtosecond second harmonic generation (SHG) to investigate excited state dynamics at organic and inorganic nanostructured materials interfaces. For an example of the capabilities of this approach, see Tisdale et al., Science 328, 1543 (2010).

COHERENT NONLINEAR OPTICAL IMAGING
Recent advances in high-repetition rate pulsed laser technology and ultrahigh frequency signal acquisition electronics have enabled a new generation of high-sensitivity low power laser imaging methods. While these techniques have already made an impact in the biomedical sciences, the deployment of such tools to address questions in chemical and materials engineering has been comparatively limited.


(summary updated 8/2013)