148 research outputs found
Confined optical phonon modes in polar tetrapod nanocrystals detected by resonant inelastic light scattering
We investigated CdTe nanocrystal tetrapods of different sizes by resonant
inelastic light scattering at room temperature and under cryogenic conditions.
We observe a strongly resonant behavior of the phonon scattering with the
excitonic structure of the tetrapods. Under resonant conditions we detect a set
of phonon modes that can be understood as confined longitudinal-optical
phonons, surface-optical phonons, and transverse-optical phonons in a nanowire
picture.Comment: 12 pages, 4 figure
Insights into the Structure of Dot@Rod and Dot@Octapod CdSe@CdS Heterostructures
CdSe@CdS dot@rods with diameter around 6 nm and length of either
20, 27, or 30 nm and dot@octapods with pod diameters of ?15 nm and lengths of ?50
nm were investigated by X-ray absorption spectroscopy. These heterostructures are
prepared by seed-mediated routes, where the structure, composition, and morphology of
the CdSe nanocrystals used as a seed play key roles in directing the growth of the second
semiconducting domain. The local structural environment of all the elements in the
CdSe@CdS heterostructures was investigated at the Cd, S, and Se K-edges by taking
advantage of the selectivity of X-ray absorption spectroscopy, and was compared to pure
reference compounds. We found that the structural features of dot@rods are
independent of the size of the rods. These structures can be described as made of a
CdSe dot and a CdS rod, both in the wurtzite phase with a high crystallinity of both the
core and the rod. This result supports the effectiveness of high temperature colloidal
synthesis in promoting the formation of core@shell nanocrystals with very low
defectivity. On the other hand, data on the CdSe@CdS with octapod morphology suggest the occurrence of a core composed of
a CdSe cubic sphalerite phase with eight pods made of CdS wurtzite phase. Our findings are compared to current models
proposed for the design of functional heterostructures with controlled nanoarchitecture
Extraction of Accurate Biomolecular Parameters from Single-Molecule Force Spectroscopy Experiments
The atomic force microscope (AFM) is able to manipulate biomolecules and their complexes with exquisite force sensitivity and distance resolution. This capability, complemented by theoretical models, has greatly improved our understanding of the determinants of mechanical strength in proteins and revealed the diverse effects of directional forces on the energy landscape of biomolecules. In unbinding experiments, the interacting partners are usually immobilized on their respective substrates via extensible linkers. These linkers affect both the force and contour length (Lc) of the complex at rupture. Surprisingly, while the former effect is well understood, the latter is largely neglected, leading to incorrect estimations of Lc, a parameter that is often used as evidence for the detection of specific interactions and remodeling events and for the inference of interaction regions. To address this problem, a model that predicts contour length measurements from single-molecule forced-dissociation experiments is presented that considers attachment position on the AFM tip, geometric effects, and polymer dynamics of the linkers. Modeled data are compared with measured contour length distributions from several different experimental systems, revealing that current methods underestimate contour lengths. The model enables nonspecific interactions to be identified unequivocally, allows accurate determination of Lc, and, by comparing experimental and modeled distributions, enables partial unfolding events before rupture to be identified unequivocally
Formation of colloidal alloy semiconductor CdTeSe magic-size clusters at room temperature
Alloy magic-size clusters (MSCs) are difficult to synthesize, in part because so little is known about how they form. Here, the authors produce single-ensemble alloy CdTeSe MSCs at room temperature by mixing prenucleation-stage solutions of CdTe and CdSe, uncovering a formation pathway that may extend to the synthesis of other alloy MSCs
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