CPM Seminar

Chemically synthesized CdSe quantum nanowires: Correlations between structural, optical, and electronic properties

Tobias Kipp

Department of Chemistry
Universität Hamburg

Individual CdSe quantum nanowires (QNWs) with diameters below about 15 nm and lengths up to several micrometers synthesized by the so-called solution-liquid-solid method are investigated by confocal time-, energy-, and space-resolved photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM), and electrostatic force microscopy (EFM).

By correlating room-temperature PL measurements with TEM studies on the same individual QNWs we established a detailed relationship between structural and optical properties [1], which is mainly dictated by confinement effects in radial direction. By combining confocal optical methods with simultaneous EFM measurements, we showed that photo-generated charge carriers or excitons diffuse in axial direction [2] and can be separated in band-gap engineered QNW heterostructures [3]. By actively charging isolated CdSe QNWs with a biased AFM tip, the PL emission can either be enhanced or reversibly or irreversibly quenched [4]. Recent low-temperature PL investigations revealed fundamentally new features of QNWs that are hidden at room temperature. In particular we observed a multitude of sharp excitonic emission peaks arranged in two different emission bands (see Figure at left), which exhibit a complex blinking behavior, each on a different time scale, as well as different phonon couplings. [5]

In this talk, I will summarize the main aspects of above-mentioned experiments. I will then try to draw a comprehensive picture of the structural, optical, and electrical properties of CdSe-based QNWs that will include effects from different diameters, crystal lattice modifications, the dielectric surrounding, as well as from defects, like charged donors and acceptors, or surface trap states. Finally; I will give an example of using QNWs as active elements in photodetector devices. [6]

[1] ACS Nano 10, 7920 (2011).
[2] Nano Lett. 11, 2672 (2011).
[3] APL 100, 022110 (2012).
[4] PRL 107, 137403 (2011).
[5] Nano Lett. 14, 6655 (2014).
[6] ACS Appl. Mater. Interfaces 7, 12184 (2015)