Naughty Paul

Performing time-tagged, time-correlated, single-photon-counting studies on individual colloidal nanocrystal quantum dots (NQDs), the evolution of photoluminescence (PL) intensity-fluctuation behaviors in near-infrared (NIR) emitting type II, InP/CdS core-shell NQDs is investigated as a function of shell thickness. It is observed that Auger recombination and hot-carrier trapping compete in defining the PL intensity-fluctuation behavior for NQDs with thin shells, whereas the role of hot-carrier trapping dominates for NQDs with thick shells. These studies further reveal the distinct ramifications of altering either the excitation fluence or repetition rate. Specifically, an increase in laser pump fluence results in the creation of additional hot-carrier traps. Alternately, higher repetition rates cause a saturation in hot-carrier traps, thus activating Auger-related PL fluctuations. Furthermore, it is shown that Auger recombination of negatively charged excitons is suppressed more strongly than that of positively charged excitons because of the asymmetry in the electron-hole confinement in type II NQDs. Thus, this study provides new understanding of how both NQD structure (shell thickness and carrier-separation characteristics) and excitation conditions can be used to tune the PL stability, with important implications for room-temperature single-photon generation. Specifically, the first non-blinking NQD capable of single-photon emission in the near-infrared spectral regime is described.

Single-dot spectroscopy studies of near-infrared emitting type II, InP/CdS core–shell nanocrystals reveal that Auger recombination and hot-carrier trapping compete in defining the PL intensity-fluctuation behavior at thin shells, whereas the role of hot-carrier trapping dominates for thick shells. Additionally, a strong potential is demonstrated for the use of the g-NQDs in room-temperature single-photon generation.

A thorough study of direct InSb nanocrystal formations on patterned InAs (111)B substrates is provided. These nanostructures are created without the use of Au catalysts or initial InAs segments. Under the growth conditions generally used for selective-area, catalyst-free epitaxy, a wide range of InSb nanocrystal morphologies are observed. This is because the low-energy InSb surfaces, studied by first-principles calculations, are the {111} facets as opposed to the {110} facets. By controlling the V/III ratio during growth, different InSb nanostructures can be achieved. Using low V/III growth conditions, In droplets start to form and InSb nucleation takes place at the droplet–semiconductor interface only, resulting in vertical, self-catalyzed InSb nanopillars.

The morphology of Au-free InSb nano­crystals is extremely sensitive to growth conditions. By controlling the V/III ratio during growth, different InSb nanostructures can be achieved. Using low V/III growth conditions, In droplets start to form and InSb nucleation takes place at the droplet–semiconductor interface only, resulting in vertical, self-catalyzed InSb nanopillars.

In the hunt for ultimately thin electronic devices, atomically thin layers of group VI transition metal dichalcogenides (TMDCs) are recognized as ideal 2D materials after the success of graphene. Monolayer TMDCs feature nonzero but contrasting Berry curvatures and valence-band spin splitting with opposite sign at inequivalent K and K′ valleys located at the corners of the 1st Brillouin zone. These features raise the possibility of manipulating electrons' valley and spin degrees of freedom by optical and electric means, which subsequently makes monolayer TMDCs promising candidates for spintronics and valleytronics applications.

Atomically thin transition metal dichal­cogenides (TMDCs) feature degenerate but inequivalent valleys and strong spin-orbit coupling. These features raise the possibility of quantum manipulation of the spin and valley degrees of freedom, which are the focused topics in spintronics and valleytronics. In this Research News article, experimental progress in the field is discussed, including valley polarization by optical pumping and spin-valley coupling.

Controlling synthesis of near-infrared emitting quantum rods (QRs) for in vivo imaging is a major challenge in the fabrication of multifunctional nanoprobes. Here, a reliable synthetic approach for CdTe_x Se_1–x /ZnS alloy nanocrystals to achieve highly bright (quantum yields up to 80%) with controllable rod-shape and near-infrared (650–870 nm) emission is developed. Aspect ratio and emission of QRs are correlated with composition, which can be easily tuned by changing Te and Se mole ratio. It illustrates that the content of Se plays an important role in maintaining the rod-shape, while Te has a significant impact on emitting of the nanorods. Besides exhibiting great stability over a broad range of pH (4–10) and ion strength (up to 2 mol L^-1 NaCl solution), these hydrophilic QRs display good photo stability and storage stability. In particular, the specially absorbing of paramagnetic gadolinium ions on the QRs lead to a versatile method to engineer multimodal imaging nanoprobes, which are applied for in vivo lymph node dual-modal imaging (fluorescence and magnetic resonance imaging). These results suggest a promising strategy for engineering multifunctional imaging nanoprobes with the stable near-infrared QRs.

Near-infrared quantum rods (QRs) with tunable emission and aspect ratio are synthesized as nano-platforms for engineering multifunctional nanoprobes. The as-prepared QRs exhibit great stability and little nonspecific binding. Paramagnetic gadolinium ions can be easily assembled on the QRs to produce multi­functional contrast agents for in vivo lymph node fluorescence and magnetic resonance dual-modal imaging. It provides a general method for designing rod-shape multifunctional nanostructure.