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Alf Mews

Publications and source records attributed to Alf Mews.

5 recordsLinked to original sources
PubMed2005

Synthesis and characterization of highly luminescent CdSe-core CdS/Zn0.5Cd0.5S/ZnS multishell nanocrystals.

We report on the preparation and structural characterization of CdSe nanocrystals, which are covered by a multishell structure from CdS and ZnS. By using the newly developed successive ion layer adhesion and reaction (SILAR) technique, we could gradually change the shell composition from CdS to ZnS in the radial direction. Because of the stepwise adjustment of the lattice parameters in the radial direction, the resulting nanocrystals show a high crystallinity and are almost perfectly spherical, as was investigated by X-ray diffraction and electron microscopy. Also, due to the radial increase of the respective valence- and conduction-band offsets, the nanocrystals are well electronically passivated. This leads to a high fluorescence quantum yield of 70-85% for the amine terminated multishell particles in organic solvents and a quantum yield of up to 50% for mercapto propionic acid-covered particles in water. Finally, we present experimental results that substantiate the superior photochemical and colloidal stability of the multishell particles.

Journal Article↗
PubMed2005

Photocurrent imaging of charge transport barriers in carbon nanotube devices.

The realization of high-performance electrical devices incorporating single-wall carbon nanotubes critically depends on the minimization of charge transport barriers in the tubes and at the contacts. Herein we demonstrate photocurrent imaging as a fast and effective tool to locate such barriers within individual metallic nanotubes contacted by metal electrodes. The locally induced photocurrents directly reflect the existence of built-in electric fields associated with the presence of depletion layers at the contacts or structural defects along the tubes.

Electric Impedance↗
PubMed2003

Semiconductor nanocrystals with multifunctional polymer ligands.

In this letter, we describe the preparation of a versatile polymer ligand, which can be attached to CdSe/ZnS semiconductor nanocrystals via a phase transfer reaction. The ligand is based on a chain of reactive esters, which can, in principle, be substituted by any compound containing amino-functionalities. The polymer/nanocrystal complexes are characterized in terms of structure and photostability.

Journal Article↗
PubMed2002

Fluorescence decay time of single semiconductor nanocrystals.

We present fluorescence decay measurements of single ZnS covered CdSe nanocrystals. It is shown that the fluorescence decay time is fluctuating during the investigation leading to a multiexponential decay even for a single nanocrystal. In combination with measurements of the fluorescence blinking behavior we find that a high fluorescence intensity is correlated with a long fluorescence decay time. This is consistent with a model of fluctuating nonradiative decay channels leading to variable dynamic quenching processes of the excited state.

Journal Article↗