Research Interests
Chemistry and physics share tremendous potential at the nanoscale. This is where chemistry excels and where physics predicts that many properties can be tuned. For example, quantum states, charging, spin, phonons, and plasmons show dramatic effects at this scale. Colloidal synthesis enables the construction of nanostructures by chemical precipitation. Our research is therefore driven by physical concepts and enabled by synthesis.
Much of our work involves nanocrystals of semiconductor materials. These show very strong quantum confinement effects, and controlling their size leads to exquisite tuning of energy levels. Our group works on the effect of small additions of charges, i.e., quantum dot ions, on the optical, magnetic, and electronic properties. We synthesize semiconductor nanocrystals to control their sizes and their surfaces. We then use microscopy and nonlinear spectroscopy to study basic aspects of electron dynamics and interaction in such strongly confined structures. Aspects of general interest are the doping of nanocrystals, their unusual infrared response, their electrochromic effects, as well as the potentially novel electrical transport properties in films made of these artificial atoms.
Alongside basic studies, we explore potential applications in infrared detection and emission. We are particularly interested in the infrared above 3 microns wavelength. This is where objects slightly warmer than room temperature emit more light than they scatter.It is also the spectral range of molecular vibrational spectroscopy. In particular, the high cost of existing detection technologies prevents widescale applications such as infrared cameras for autonomous vehicles or compact infrared spectrometers. Starting from a zero-gap semiconductor and using a single chemistry to vary the size of nanoparticles allows to tune the absorption edge anywhere in the infrared. We then explore films of such quantum dots for infrared detection and emission. The goal of achieving fast and sensitive thermal infrared photodetection is also an interesting challenge that forces us to refine the understanding of non-radiative processes in the quantum dots, of transport across nanoparticles, and of carrier doping at the nanoscale.
Selected References (Google Scholar)
Dual-Band Imaging Using Stacked Colloidal Quantum Dot Photodiodes, Nature Photonics 13 (4), 277 (2019)
Fast and Sensitive Colloidal Quantum Dot Mid-Wave Infrared Photodetectors, ACS Nano 12, 7264 (2018)
Auger Suppression in n-Type HgSe Colloidal Quantum Dots, ACS Nano 13, 9 (2019)
Quantum dot solids showing state-resolved band-like transport, Nature Materials 19, 323–329 (2020)
Colloidal quantum dots intraband photodetectors, ACS nano 8, 11707 (2014)
Mid-infrared HgTe colloidal quantum dot photodetectors, Nature Photonics 5, 489 (2011)
Slow Electron Cooling in Colloidal Quantum Dots, Science 322, 929 (2008)
Conducting n-type CdSe Nanocrystal solids, Science 300, 1277 (2003)
N-type colloidal semiconductor nanocrystals, Nature, 407, 981 (2000).
Synthesis and characterization of strongly luminescing ZnS-Capped CdSe nanocrystals, J. Phys. Chem. 100, 468 (1996).