[Todos] Lunes 29 de octubre - Seminario DQIAQF - INQUIMAE

[andrea en qi.fcen.uba.ar]

Seminarios DQIAQF - INQUIMAE, lunes 29 de octubre - 13 hs.

Aula de Seminarios INQUIMAE - DQIAQF
Facultad de Ciencias Exactas y Naturales
Ciudad Universitaria - Pab. 2  -  Piso 3

*Solution-based semiconductor nanowires*

Masaru Kuno
University of Notre Dame
Department of Chemistry and Biochemistry


In the first part of this talk, I will describe the development of a
low-cost, facile approach for making high quality semiconductor nanowires
(NWs). The developed solution-liquid- solid (SLS) growth exploits nearly
thirty year of work on colloidal syntheses for semiconductor nanocrystals
(quantum dots). In this manner, we have been able to produce various II-VI
and IV-VI nanowire systems, including ZnSe, CdSe, and PbSe. The
solution-approach is flexible and enables the growth of branched wires as
well as other complex morphologies such as core/ shell specimens.
Next, there has been significant work applying NWs to various applications.
This includes electronics. However, there has been significantly less work
on understanding their optical properties. This is especially puzzling
since optoelectronic applications are often invoked when talking about
nanowires. In the second part of my talk, I will therefore describe
extensive studies we have conducted on a model CdSe NW system to complement
analogous work on colloidal CdSe quantum dots.
Of particular interest is the absorption of the nanowires. In this regard,
molecules, nanoparticles and other nanostructures exhibit unique optical
properties such as emission intermittency (i.e. blinking) and spectral
wandering. These phenomena are only observable at the single molecule
level. Until more recently, single molecule detection has been mainly
restricted to fluorescent entities. But given that there are entire classes
of materials that are non-emissive (or which have negligible emission
quantum yields) there is a need to develop alternative approaches for
single molecule detection.
In the latter part of my talk, I will therefore present the use of a
spatial modulation absorption technique to obtain single CdSe NW extinction
spectra across the visible. Absorption spectra of single CdSe NWs have been
recorded from 500 nm to 750 nm along with their accompanying emission
spectra. Resulting data reveal structure in the extinction. These
measurements address the outstanding question as to whether the optical
properties of these (and other) 1D nanowires are excitonic or free carrier
in nature and is exactly the same question asked about the absorption of
analogous 1D carbon nanotubes.

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