Publications

We report a new and highly versatile approach to artificial layered materials synthesis which borrows concepts of molecular beam epitaxy, self-assembly, and graphite intercalation compounds. It readily yields stacks of graphene (or other two-dimensional sheets) separated by virtually any kind of "guest" species. The new material can be "sandwich like", for which the guest species are relatively closely spaced and form a near-continuous inner layer of the sandwich, or "veil like", where the guest species are widely separated, with each guest individually draped within a close-fitting, protective yet atomically thin graphene net or veil. The veils and sandwiches can be intermixed and used as a two-dimensional platform to control the movements and chemical interactions of guest species.

Semiconductor nanocrystals were prepared for use as fluorescent probes in biological staining and diagnostics. Compared with conventional fluorophores, the nanocrystals have a narrow, tunable, symmetric emission spectrum and are photochemically stable. The advantages of the broad, continuous excitation spectrum were demonstrated in a dual-emission, single-excitation labeling experiment on mouse fibroblasts. These nanocrystal probes are thus complementary and in some cases may be superior to existing fluorophores.

Die Autoren dieser Zuschrift möchten darauf hinweisen, dass im oberen Teil von Abbildung 1 B die x-Achsen von Diagramm und Einschub um 80 nm verschoben wiedergegeben wurden: Die x-Achse des Diagramms muss von 420 nm bis 670 nm reichen und nicht von 500 nm bis 750 nm. Diagramm und Einschub mit den korrekten x-Achsen sind hier gezeigt. Alle weiteren Resultate und Schlussfolgerungen des Beitrags sind von diesem Versehen nicht betroffen. […︁] B) Photoluminescence spectra of CdS nanorods (top), […︁] obtained from hot injection (red), cation exchange (green), and post-change purification (blue). […︁] Inset of B: Normalized photoluminescence showing similarity in the photoluminescence peak positions between samples obtained from the three different methods. […︁]

The ability of cancer cells to migrate and metastasize is known to be directly related to tumor cell motility. Therefore, assaying the level of tumor cell motility is an excellent indicator of metastatic potential. We have developed an efficient and sensitive two-dimensional cell motility assay to image the phagokinetic uptake of colloidal CdSe/ZnS semiconductor nanocrystals (quantum dots [QDs]). As cells move across a thin, homogeneous layer of QDs, they engulf and uptake the nanocrystals and leave behind a fluorescent-free trail. By measuring the ratio of trail area to cell area we have discovered that it is possible to distinguish between noninvasive and invasive cancer cells lines. This technique has, therefore, the potential to be used as a rapid, robust, and quantitative in vitro measure of metastatic potential. Because the technique only relies on fluorescence detection, requires no significant data processing, and is used with live cells, it is both rapid and straightforward.

Abstract Abstract Pressure-induced structural phase transitions have been studied in CdSe, CdS, InP and Si semiconductor nanocrystals. Nanocrystals transform via single nucleation of the phase transition with a kinetic barrier that increases in increasing cluster size. The structural transition path causes a shape change in the nanocrystals, which dictates the surface energy and thus the kinetic and thermodynamic stability of the transformed nanocrystal. These finite size effects can be used to tune the metastability of the nanocrystals versus pressure. Enhanced metastability allows structural and optical measurements in a regime inaccessible to the bulk solid, as well as possible recovery of the dense high pressure phase to atmospheric pressure. Key Words: MetastabilityNanocrystalPhase transitionHigh pressureKinetics

The structure and composition of core–shell CuCo nanoparticles were found to change as a result of cleaning pretreatments and when exposed to syngas (CO + H2) at atmospheric pressure. In situ X-ray absorption and photoelectron spectroscopies revealed the oxidation state of the particles as well as the presence of adsorbates under syngas. Transmission electron microscopy was used for ex situ analysis of the shape, elemental composition, and structure after reaction. The original core–shell structure was found to change to a hollow CuCo alloy after pretreatment by oxidation in pure O2 and reduction in pure H2. After 30 min of exposure to syngas, a significant fraction (5%) of the particles was strongly depleted in cobalt giving copper-rich nanoparticles. This fraction increased with duration of syngas exposure, a phenomenon that did not occur under pure CO or pure H2. This study suggests that Co and Cu can each individually contribute to syngas conversion with CuCo catalysts.

Water-soluble, highly fluorescent, silanized semiconductor nanocrystals with different surface charges were synthesized. To covalently attach the nanocrystals to biological macromolecules with a variety of mild coupling chemistries, the outermost siloxane shells were derivatized with thiol, amino, or carboxyl functional groups. Single- or double-stranded DNA was coupled to the nanocrystal surfaces by using commercially available bifunctional cross-linker. Conjugation had little effect on the optical properties of the nanocrystals, and the resulting conjugates were more stable than previously reported systems. By using the strategies developed in this study, most biomolecules can be covalently coupled to semiconductor nanocrystals. These nanocrystal-DNA conjugates promise to be a versatile tool for fluorescence imaging and probing of biological systems.

We report controllable anisotropic light emission of photons originating from vertically aligned transition dipole moments in spun-cast films of CsPbBr₃ nanocubes. By depositing films of nanocrystals on precoated substrates we can control the packing density and resultant radiation pattern of the emitted photons. We develop a technical framework to calculate the average orientation of light emitters, i.e., the angle between the transition dipole moment vector (TDM) and the substrate. This model is applicable to any emissive material with a known refractive index. Theoretical modeling indicates that oriented emission originates from an anisotropic alignment of the valence band and conduction band edge states on the ionic crystal lattice and demonstrates a general path to model the experimentally less accessible internal electric field of a nanosystem from the photoluminescent anisotropy. The uniquely accessible surface of the perovskite nanoparticles allows for perturbation of the normally isotropic emissive transition. The reported sensitive and tunable TDM orientation and control of emitted light will allow for applications of perovskite nanocrystals in a wide range of photonic technologies inaccessible to traditional light emitters.

Accident of CPB is a reality. It is important to be prepared for discussion with the family, with the hospital administration, eventually with the justice. But we have also to support perfusionnist and anesthetic team in charge of the patient during accident.

Luminescence excitation spectra are employed to study the electronic states of CdSe nanocrystals ranging in size from 9 to 26 Å radius at 77 K. These studies show that all samples have, in addition to the discrete manifold of quantum confined electronic excitations, a threshold for continuum absorption. Absorption into this continuum results in substantially reduced luminescence efficiency.