Transport properties of mid-infrared colloidal quantum dot films

The transport and thermal properties of HgTe colloidal quantum dot films with cut-off wavelengths in the mid-IR are investigated. The cut-off wavelength of this material can be tuned over the 3-5 \mu m range, which makes it a promising alternative to existing high cost detectors. Post deposition processes such as ligand exchange and atomic layer deposition are investigated as a way to increase the carrier mobility.Comment: 7 pages, 7 figure

Characterizing Quantum-Dot Blinking Using Noise Power Spectra

Fluctuations in the fluorescence from macroscopic ensembles of colloidal semiconductor quantum dots have the spectral form of 1/f noise. The measured power spectral density reflects the fluorescence intermittency of individual dots with power-law distributions of "on" and "off" times, and can thus serve as a simple method for characterizing such blinking behavior

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Ultrafast resonant optical scattering from single gold nanorods: Large nonlinearities and plasmon saturation

We measure nonlinear optical scattering from individual Au nanorods excited by ultrafast laser pulses on resonance with their longitudinal plasmon mode. Isolating single rods removes inhomogeneous broadening and allows the measurement of a large nonlinearity, much greater than that of nanorod ensembles. Surprisingly, the ultrafast nonlinearity can be attributed entirely to heating of conduction electrons and does not exhibit any response associated with coherent plasmon oscillation. This indicates a previously unobserved damping of strongly driven plasmons.Comment: Revised tex

Viscoelastic Flows in Simple Liquids Generated by Vibrating Nanostructures

Newtonian fluid mechanics, in which the shear stress is proportional to the strain rate, is synonymous with the flow of simple liquids such as water. We report the measurement and theoretical verification of non-Newtonian, viscoelastic flow phenomena produced by the high-frequency (20 GHz) vibration of gold nanoparticles immersed in water-glycerol mixtures. The observed viscoelasticity is not due to molecular confinement, but is a bulk continuum effect arising from the short time scale of vibration. This represents the first direct mechanical measurement of the intrinsic viscoelastic properties of simple bulk liquids, and opens a new paradigm for understanding extremely high frequency fluid mechanics, nanoscale sensing technologies, and biophysical processes

Toward Bright Mid-Infrared Emitters: Thick-Shell n-Type HgSe/CdS Nanocrystals

A procedure is developed for the growth of thick, conformal CdS shells that preserve the optical properties of 5 nm HgSe cores. The n-doping of the HgSe/CdS core/shell particles is quantitatively tuned through a simple postsynthetic Cd treatment, while the doping is monitored via the intraband optical absorption at 5 μm wavelength. Photoluminescence lifetime and quantum yield measurements show that the CdS shell greatly increases the intraband emission intensity. This indicates that decoupling the excitation from the environment reduces the nonradiative recombination. We find that weakly n-type HgSe/CdS are the brightest solution-phase mid-infrared chromophores reported to date at room temperature, achieving intraband photoluminescence quantum yields of 2%. Such photoluminescence corresponds to intraband lifetimes in excess of 10 ns, raising important questions about the fundamental limits to achievable slow intraband relaxation in quantum dots

Osez l’optoélectronique (infrarouge) colloïdale !

International audienceLes dispositifs optoélectroniques basés sur les semi-conducteurs III-V et II-VI sont actuellement réalisés selon une approche top-down. En dépit de leurs performances, certaines de ces structures sont proches de leur limite quantique, ce qui rend l'optimisation de la couche active difficile. Une alternative intéressante à ces maté-riaux vient de l'approche colloïdale qui permet à la fois une réduction drastique des coûts tout en conservant un niveau de performance raisonnable. Ces matériaux sont actuellement utilisés du proche ultraviolet jusqu'au proche infrarouge en tant que marqueurs biologiques, diodes électroluminescentes ou pour le photo-voltaïque. L'utilisation de matériaux semi-métalliques tels le HgTe avec des longueurs d'onde de coupure dans la gamme 3 à 5 μm ouvre la voie à de nouvelles applications pour ces nanoparticules, en parti-culier en imagerie infrarouge. Dans cet article nous nous attachons à montrer que les principales objections à l'encontre des matériaux colloïdaux peuvent être réfu-tées grâce à un contrôle précis de la chimie de surface

Magnetoresistance of high mobility HgTe quantum dot films with controlled charging

Funding: We thank Christopher Melnychuk for very useful discussions. This work was supported by the National Natural Science Foundation of China under grant number 62105022, the University of Chicago Materials Research Science and Engineering Center, which was funded by the National Science Foundation under award number DMR1420709, and by the Department of Defense (DOD) Air Force Office of Scientific Research under grant number FA9550-18-1-0099.The magnetoresistance of HgTe quantum dot films, exhibiting a well-defined 1Se state charging and a relatively high mobility (1-10 cm2 V−1 s−1), is measured as a function of temperature down to 10 K and controlled occupation of the first electronic state. There is a positive-quadratic magnetoresistance which can be several 100% at low temperature and scales like x(1 − x) where x is the filling fraction of the lowest quantum dot state in the conduction band, 1Se. This positive magnetoresistance is orders of magnitude larger than the effect estimated from mobile carriers and it is attributed to the increased confinement induced by the magnetic field. There is also a negative magnetoresistance of 1-20% from 300 K to 10 K which is rather independent of the fractional occupation, and which follows a negative exponential dependence with the magnetic field. It can be empirically fit with an effective g-factor of ∼55 and it is tentatively attributed to the reduction of barrier heights by the Zeeman splitting of the 1Se state.Peer reviewe