Persistence of magic cluster stability in ultra-thin semiconductor nanorods

Abstract

The progression from quasi zero-dimensional (Q0D) nanoclusters to quasi one-dimensional (Q1D) nanorods, and, with increasing length, to nanowires, represents the most conceptually fundamental transition from the nanoscale to bulk-like length scales. This dimensionality crossover is particularly interesting, both scientifically and technologically, for inorganic semiconducting (ISC) materials, where striking concomitant changes in optoelectronic properties occur.(1,2) Such effects are most pronounced for ultra-thin(3) ISC nanorods/nanowires, where the confining and defective nature of the atomic structure become key. Although experiments on ISC materials in this size regime have revealed especially stable (or "magic") non-bulk-like Q0D nanoclusters,(4,5) all ISC Q1D nanostructures have been reported as having structures corresponding to bulk crystalline phases. For two important ISC materials (CdS and CdSe) we track the Q0D-to-Q1D transition employing state-of-the-art electronic structure calculations demonstrating an unexpected persistence of magic cluster stability over the bulk-like structure in ultra-thin nanorods up to >10 nm in length. The transition between the magic-cluster-based and wurtzite nanorods is found to be accompanied by a large change in aspect ratio thus potentially providing a route to nano-mechanical transducer applications.

Correlated barrier hopping in CdS nanoparticles and nanowires

“…33 Polaronic states in IIÀVI semiconductor quantum dot were also studied previously. [35][36][37] The energy states of neutral, positively and negatively charged dangling bonds in tetrahedrally bonded materials, are denoted by T 3 0 (D 0 ), T 3 þ (two holes localized on a bond) and T 3 À (two electrons localized on a dangling bond), respectively, where the subscript denotes the coordination number and superscript, the charge state. Different from the four fold coordination in the bulk solid the Zn/Cd and S atoms on the surface of wurtzite ZnS and CdS nanostructures are twofold and/or threefold coordinated.…”

Reduced ceria nanofilms from structure prediction

“…the O-Ce-O-Ce-O unit found in the vertical stacking of atomic layers in A-type Ce 2 O 3 (001) is counted as 2 ML. We employed the simulated mechanical annealing (SMA) technique [20][21][22] for searching the space of low energy film structures. Following the experimental observation of structural relaxation via application of mechanical stress (termed as mechanical annealing 23 ) in submicrometre atomic systems, the SMA method consists of cyclically gradually compressing and stretching the simulated Ce 2 O 3 nanofilms laterally (by up to ±30%) in a step-wise fashion.…”

Quantum Dot-Doped Glasses and Fibers: Fabrication and Optical Properties

“…Since the CdSe QDs were first demonstrated to be available in the visible optical amplification (Klimov et al, 2000), nowadays, the wavelength of optical amplification have explored from visible to infrared. For infrared broadband PL semiconductor QDs, the research system is mainly about PbS, InAs, PbSe, HgTe, and so forth (Steiner et al, 2004;O'Connor et al, 2005;Sukhovatkin et al, 2005). Among them, PbS QDs with a large Bohr exciton radii (~18 µm) and a moderate band gap at near/mid-infrared Comparison of normalized emission spectra produced using low (blue) and high (red) pump intensities (inset), which are dominated by spontaneous PL and ASE, respectively, shows the ASE as a spectrally narrowed, red-shifted band (Schaller et al, 2003).…”