MTL Annual Report

Figure 1: Confocal raster scan of a dilute InAs/CdSe nanocrystal film. The pixel size is 1 μm, and the emission was collected with 50-ms bin-times.

The study of colloidal nanocrystals (NCs) that are optically active in the near-infrared is of great importance, from both a fundamental and a technological perspective ^[1].  Photoluminescence (PL) intermittency from single NCs has yet to be observed in materials that emit past 1 μm, largely due to the lack of single-photon-counting detectors in that wavelength regime.  Similarly, an efficient room-temperature single-photon source at telecom wavelengths does not exist but remains highly desirable to many communities ^[2].

To meet these challenges, we have pursued studies on single core/shell indium arsenide (InAs)/cadmium selenide (CdSe) NCs whose photoluminescence can be tuned through the infrared ^[3].  Our motivation for choosing this system is two-fold: a) InAs PL lifetimes are relatively short, resulting in large single-photon bandwidths, and b) the shell improves the photostability of the single photon source by passivating defects on the surface of the core NC.

We have succeeded in imaging single or small-number clusters of InAs/CdSe NCs (Figure 1).  NC emission was measured using a novel superconducting nanowire photo-detector capable of single-photon-counting with high efficiency ^[4], while scanning the sample position in the x-y plane to create a raster image.  Preliminary PL intensity-versus-time traces of a single “feature” do not display blinking, but this phenomenon is most likely due to more than one NC being in the observation volume.  An antibunching (g(2) intensity autocorrelation) experiment would confirm the presence of >1 NCs, and we are working towards this measurement on our apparatus.

1. E. H. Sargent, “Infrared quantum dots,” Advanced Materials, vol. 17, pp. 515-522, March 2005. [↩]
2. B. Lounis and M. Orrit, “Single photon sources,” Reports on Progress in Physics, vol. 68, pp. 1129-1179, May 2005 [↩]
3. A. A. Guzelian, U. Banin, A. V. Kadavanich, X. Peng, and A. P. Alivisatos, “Colloidal chemical synthesis and characterization of InAs nanocrystal quantum dots,” Applied Physics Letters, vol. 69, pp. 1432-1434, Sept. 1996. [↩]
4. X. Hu, T. Zhong, J. E. White, E. A. Dauler, F. Najafi, C. H. Herder, F. N. C. Wong, and K. K. Berggren, “Fiber-coupled nanowire photon counter at 1550 nm with 24% system detection efficiency,” Optics Letters, vol. 34, pp. 3607-3609, Dec. 2009. [↩]