Multi-chromatic silicon nanocrystals.

Silicon nanocrystals (SiNCs) have great potential to become environmental friendly alternatives to heavy-metal containing nanocrystals for applications including medical imaging, lighting and displays. SiNCs exhibit excellent photostability, non-toxicity and abundant resources, but their often reported inefficient and spectrally limited light emission seriously impair their applications. Here we demonstrate a new method that converts SiNCs into an efficient and robust multi-chromatic phosphor.

Strong Absorption Enhancement in Si Nanorods.

We report two orders of magnitude stronger absorption in silicon nanorods relative to bulk in a wide energy range. The local field enhancement and dipole matrix element contributions were disentangled experimentally by single-dot absorption measurements on differently shaped particles as a function of excitation polarization and photon energy. Both factors substantially contribute to the observed effect as supported by simulations of the light-matter interaction and atomistic calculations of the transition matrix elements.

Spectroscopy of carrier multiplication in nanocrystals.

Carrier multiplication in nanostructures promises great improvements in a number of widely used technologies, among others photodetectors and solar cells. The decade since its discovery was ridden with fierce discussions about its true existence, magnitude, and mechanism. Here, we introduce a novel, purely spectroscopic approach for investigation of carrier multiplication in nanocrystals.

Exciton lifetime measurements on single silicon quantum dots.

We measured the exciton lifetime of single silicon quantum dots, fabricated by electron beam lithography, reactive ion etching and oxidation. The observed photoluminescence decays are of mono-exponential character with a large variation (5-45 μs) from dot to dot, even for the same emission energy. We show that this lifetime variation may be the origin of the heavily debated non-exponential (stretched) decays typically observed for ensemble measurements.

Surface concentration dependent structures of iodine on Pd(110).

We use photoelectron spectroscopy, low energy electron diffraction, scanning tunneling microscopy, and density functional theory to investigate coverage dependent iodine structures on Pd(110). At 0.5 ML (monolayer), a c(2 × 2) structure is formed with iodine occupying the four-fold hollow site.

Blinking statistics of silicon quantum dots.

The blinking statistics of numerous single silicon quantum dots fabricated by electron-beam lithography, plasma etching, and oxidation have been analyzed. Purely exponential on- and off-time distributions were found consistent with the absence of statistical aging. This is in contrast to blinking reports in the literature where power-law distributions prevail as well as observations of statistical aging in nanocrystal ensembles.

Coexistence of 1D and quasi-0D photoluminescence from single silicon nanowires.

Single silicon nanowires (Si-NWs) prepared by electron-beam lithography and reactive-ion etching are investigated by imaging optical spectroscopy under variable temperatures and laser pumping intensities. Spectral images of individual Si-NWs reveal a large variability of photoluminescence (PL) along a single Si-NW. The weaker broad emission band asymmetrically extended to the high-energy side is interpreted to be due to recombination of quasi-free 1D excitons while the brighter localized emission features (with significantly variable peak position, width, and shape) are due to localization of electron-hole pairs in surface protrusions acting like quasi-0D centers or quantum dots (QDs).

Controlled fabrication of individual silicon quantum rods yielding high intensity, polarized light emission.

Elongated silicon quantum dots (also referred to as rods) were fabricated using a lithographic process which reliably yields sufficient numbers of emitters. These quantum rods are perfectly aligned and the vast majority are spatially separated well enough to enable single-dot spectroscopy. Not only do they exhibit extraordinarily high linear polarization with respect to both absorption and emission, but the silicon rods also appear to luminesce much more brightly than their spherical counterparts.