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Alexander Eychmüller

Publications and source records attributed to Alexander Eychmüller.

11 recordsLinked to original sources
PubMed2006

Electrochemical observation of the photoinduced formation of alloyed ZnSe(S) nanocrystals.

Electrochemical studies of thiol-capped ZnSe nanocrystals in aqueous solution have demonstrated several distinct oxidation and reduction peaks in the voltammograms, with the peak positions being dependent on the size of the nanocrystals and their photoluminescence quantum efficiency. The evolution of the specific features in the cyclic voltammetric curves of ZnSe NCs as a function of their photochemical treatment is studied. The interpretation of the results based on the approaches previously developed for CdTe NCs is found to be in good correlation with the proposed mechanism of the ZnSe NCs phototreatment, i.e., the formation of a sulfur-enriched surface shell. By this, cyclic voltammetry has been demonstrated to be a powerful method for probing surface states of semiconductor NCs as well as for monitoring the evolution of these states during photochemical processing.

Journal Article↗
PubMed2006

Factors governing the quality of aqueous CdTe nanocrystals: calculations and experiment.

The aqueous synthesis of thiol-stabilized semiconductor CdTe colloidal nanocrystals has been revisited. We found optimal conditions for the synthesis of high-quality CdTe NCs through a study of the influence of the initial conditions (structure and concentration of Cd-thiol complexes) on the quality of the CdTe nanocrystals. A numerical calculation shows a clear correlation between the concentration of CdL (where L is (SCH(2)COO)(2-)) in the initial solution and the photoluminescence quantum efficiency of the CdTe nanocrystals.

Journal Article↗
PubMed2006

Designed fabrication of ordered porous au/ag nanostructured films for surface-enhanced Raman scattering substrates.

This article reports the designed preparation of two different kinds of novel porous metal nanostructured films, namely, an ordered macroporous Au/Ag nanostructured film and an ordered hollow Au/Ag nanostructured film. Different from previous reports, the presently proposed method can be conveniently used to control film structures by simply varying the experimental conditions. The morphology of these films has been characterized by scanning electron microscopy (SEM), and their performance as surface-enhanced Raman scattering (SERS) substrates has been evaluated by using rhodamine 6G (R6G) as a probe molecule. We show that such porous nanostructured films consisting of larger interconnected aggregates are highly desirable as SERS substrates in terms of high Raman intensity enhancement, excellent stability, and reproducibility. The interconnected nanostructured aggregate, long-range ordering porosity, and nanoscale roughness are important factors responsible for this large SERS enhancement ability.

Journal Article↗
PubMed2006

Comparative examination of the stability of semiconductor quantum dots in various biochemical buffers.

Due to their greater photostability compared to established organic fluorescence markers, semiconductor quantum dots provide an attractive alternative for the biolabeling of living cells. On the basis of a comparative investigation using differently sized thiol-stabilized CdTe nanocrystals in a variety of commonly used biological buffers, a method is developed to quantify the stability of such a multicomponent system. Above a certain critical size, the intensity of the photoluminescence of the nanocrystals is found to diminish with pseudo-zero-order kinetics, whereas for specific combinations of particle size, ligand, and buffer there appears to be no decay below this critical particle size, pointing out the necessity for thorough investigations of this kind in the view of prospect applications of semiconductor nanocrystals in the area of biolabeling.

Buffers↗
PubMed2005

Electrostatic and covalent interactions in CdTe nanocrystalline assemblies.

This paper focuses on the interactions between cysteamine-stabilized CdTe nanocrystals [CdTe(CA) NCs] and thioglycolic-acid-stabilized CdTe nanocrystals [CdTe(TGA) NCs]. These interactions were examined by the absorption, continuous, and time-resolved photoluminescence (PL) spectra of the electrostatically mixed and the covalently linked NCs assemblies comprised of the oppositely surface charged CdTe(CA) and CdTe(TGA) NCs and by a comparison with those of the corresponding pristine NCs. The CdTe(CA)-CdTe(TGA) coupling is dictated by the surfactant spacer, ranging between 0.93 and 1.14 nm and by electrostatic and covalent interactions, enabling a Förster resonance energy transfer (FRET) process among the NCs. The results revealed an excellent spectral overlap between the emission of the CdTe(TGA) NCs and the absorption of the CdTe(CA) NCs as well as a PL spectral red shift on the formation of electrostatic and covalent interactions. Furthermore, the measurements showed a lifetime ranging between 1.2 and 3 ns for the electrostatically mixed and the covalently linked assemblies, shorter than those of the pristine CdTe(CA) NCs and CdTe(TGA) NCs, both of which measured as approximately 5.5 ns. When CdTe(TGA) NCs performed as the most efficient donors, FRET rates of 10(10)-10(11) s(-1) were calculated for the electrostatically mixed NCs or covalently linked NCs.

Cadmium↗
PubMed2005

Size-dependent electrochemical behavior of thiol-capped CdTe nanocrystals in aqueous solution.

Electrochemical studies of thiol-capped CdTe nanocrystals in aqueous solution have demonstrated several distinct oxidation and reduction peaks in the voltammograms, with the peak positions being dependent on the size of the nanocrystals. While the size dependence of the reduction and one of the oxidation potentials can be attributed to altering the energetic band positions owing to the quantum size effect, an extraordinary behavior was found for the oxidation peak observed at less positive potentials. In contrast to a prediction based on the quantum size effect, this peak moves to more negative potentials as the nanocrystals' size decreases. Moreover, the contribution of the charge associated with this peak compared to the total charge passed during the nanocrystal oxidation correlates well with the photoluminescence (PL) efficiency of individual fractions of the CdTe nanocrystals. These experimental observations allow a peak to be assigned to the oxidation of Te-related surface traps. The intra-band-gap energy level assigned to these Te-related trap states shifts toward the top of the valence band as the nanocrystal size increases, thus allowing the higher photostability of the larger nanocrystals to be explained. At a certain nanocrystal size, the trap level can even move out of the band gap.

Cadmium Compounds↗