On-chip hybrid integration of silicon nitride microdisk with colloidal quantum dots

We report on the fabrication of on-chip freestanding silicon nitride microdisks hybridly integrated with embedded colloidal quantum dots. An efficient coupling of quantum dot emission to resonant disk modes in the visible range is demonstrated

Colloidal quantum dots enabling coherent light sources for integrated silicon-nitride photonics

Integrated photoniccircuits, increasingly based on silicon (-nitride), are at the core of the next generation of low-cost, energy efficient optical devices ranging from on-chip interconnects to biosensors. One of the main bottlenecks in developing such components is that of implementing sufficient functionalities on the often passive backbone, such as light emission and amplification. A possible route is that of hybridization where a new material is combined with the existing framework to provide a desired functionality. Here, we present a detailed design flow for the hybridization of silicon nitride-based integrated photonic circuits with so-called colloidal quantum dots (QDs). QDs are nanometer sized pieces of semiconductor crystals obtained in a colloidal dispersion which are able to absorb, emit, and amplify light in a wide spectral region. Moreover, theycombine cost-effective solution based deposition methods, ambient stability, and low fabrication cost. Starting from the linear and nonlinear material properties obtained on the starting colloidal dispersions, we can predict and evaluate thin film and device performance, which we demonstrate through characterization of the first on-chip QD-based laser

Homogeneously alloyed CdSe1-xSx QDs (0 ≤ x ≤ 1) : an efficient synthesis for full optical tunability

In the field of fluorescent semiconductor quantum dots (QDs), alloyed QDs open up new possibilities and opportunities. Indeed, these systems allow to tune the optical properties of the nanocrystals without changing their size. This is of particular interest for the integration of the QDs in devices such as LEDs or for their use as biological labels. We recently developed a novel method for the synthesis of CdSe and ZnSe binary QDs in colloidal solutions that is fast and highly efficient. This method is based on a heterogeneous Se-ODE precursor consisting of a simple dispersion of Se powder (200 mesh) in octadecene (ODE) and showing very high reactivity towards Cd precursor. In this contribution we will demonstrate that this method can be extended to the synthesis of CdSe1-xSx homogeneously alloyed QDs (0 ≤ x ≤ 1)

Bright and stable CdSe/CdS@SiO2 nanoparticles suitable for long term cell labeling

Semiconductor quantum dots (QDs) constitute very promising candidates as light emitters for numerous applications in the field of biotechnology, including cell labeling, in vivo imaging and diagnostics.[1] For such applications, semiconductor QDs represent an attractive alternative to classic organic fluorophores as they exhibit a higher brightness thanks to their large absorption cross-sections and high photoluminescence quantum yields. Nevertheless, QDs usually suffer from higly oxidative environments, such as water, which can cause a dramatic decrease of their photoluminescent quantum yield but also can result in the realease of toxic elements. In this contribution we present a new generation of QD@SiO2 nanoparticles based on newly developped core-shell QDs that mostly overcome these limitations, resulting in efficient nanoprobes for long term cell labeling. Among the numerous QDs being reported, core-shell heterostructures such as CdSe/CdS QDs with relatively thick CdS shells, are of particular interest as they offer several properties essential to biolabeling, including high photoluminescence quantum yields, low blinking behavior and robustness towards aggressive environments. We recently developed a new, fast and very efficient method for the synthesis of such QDs, denoted as ‘flash’ CdSe/CdS, which can feature up to 20 CdS monolayers after only 3 minutes of reaction.[2] They show state-of-the-art optical properties (sharp emission spectra, high photoluminescence quantum yields, low blinking behavior), and the CdS shell thickness can be easily controlled thanks to the full chemical yield of the reaction. These ‘flash’ CdSe/CdS QDs were encapsulated in silica nanoparticles through a water-in-oil microemulsion process, which allows a high control on the morphology of the resulting QD@SiO2 nanoparticles. All the nanoparticles contain one single QD located in its center (Fig. 1) and the thickness of the silica shell can be varied from only a few nanometers up to several tens of nanometers. The silica matrix provides the QDs with enhanced colloidal stability in polar solvents, but also with enhanced photo-physical and photo-chemical stability under continuous irradiation. More importantly, the QD@SiO2 nanoparticles based on ‘flash’ CdSe/CdS QDs fully retain their photoluminescence quantum yield even after a year of storage in water (Fig. 1), whereas QD@SiO2 nanoparticles based on ‘classical’ SILAR grown core-shell QDs typically lose their luminescence after a few weeks or even days. Thereafter, these ‘flash’ CdSe/CdS@SiO2 nanoparticles have proven to be very promising nanoprobes for bioimaging techniques. Indeed, the rapid uptake of high levels of these nanoparticles by live cells was evidenced by confocal fluorescence microscopy (Fig. 1). Furthermore, thanks to the high stability of their optical properties but also to their low toxicity after silica encapsulation, these nanoparticles are particularly appropriate for long term cell labeling, with up to 9 cell divisions being tracked. Thus, in this contribution we will report from the synthesis and characterization of these ‘flash’ CdSe/CdS@SiO2, all the way to the study of their toxicity and their application to cell labeling

Two-dimensional superstructures of silica cages

Despite extensive studies on mesoporous silica since the early 1990s, the synthesis of two-dimensional (2D) silica nanostructures remains challenging. Here, mesoporous silica is synthesized at an interface between two immiscible solvents under conditions leading to the formation of 2D superstructures of silica cages, the thinnest mesoporous silica films synthesized to date. Orientational correlations between cage units increase with increasing layer number controlled via pH, while swelling with oil and mixed surfactants increase micelle size dispersity, leading to complex clathrate type structures in multilayer superstructures. The results suggest that a three-dimensional (3D) crystallographic registry within cage-like superstructures emerges as a result of the concerted 3D co-assembly of the organic and inorganic components. Mesoporous 2D superstructures can be fabricated over macroscopic film dimensions and stacked on top of each other. The realization of previously inaccessible mesoporous silica heterostructures with separation or catalytic properties unachievable via conventional bulk syntheses is envisioned