The effects of cation solvation and the volume change (Delta V) of reaction on the equilibrium and the morphology change in the cation-exchange reactions of metal chalcogenide nanocrystals, CdE --> M(x)E(y) (E = S, Se, Te; M = Pd, Pt), were investigated. Since the solvation of cations is an important controllable factor determining the free energy of the reaction, the effect of varying cation solvation conditions on the equilibrium of the reaction was examined. A two-phase solvent environment, where the cations involved in the exchange reaction were preferentially solvated in different phases by using selective cation complexing molecules, was particularly efficient in increasing the thermodynamic driving force. The effect of Delta V of reaction on the morphology of the product nanocrystals was also investigated. Depending on the stress developed in the lattice during the reaction, product nanocrystals underwent varying degrees of morphological changes such as void formation and fragmentation in addition to the preservation of the original morphology of the reactant nanocrystals. The knowledge of the effect of ion solvation and Delta V of reaction on the equilibrium and product morphology provides a new strategy and useful guides to the application of cation-exchange reactions for the synthesis of a broader range of inorganic nanocrystals.

Since September 2018, LAMOST starts a new 5-year medium-resolution spectroscopic survey (MRS) using bright/gray nights. We present the scientific goals of LAMOST-MRS and propose a near optimistic strategy of the survey. A complete footprint is also pro-

Quantum dots are an excellent resource for demonstrating quantum phenomena. Two new methods for synthesizing quantum dots are presented. Proceeding at relatively low reaction temperatures, these exercises are safe and easy to conduct in an undergraduate student laboratory. The quantum dots prepared from the first method exhibited visible luminescence across a broad range of colors. The size-dependent spectral properties of quantum dots were examined quantitatively in the second method. Following this procedure, students in an advanced chemistry laboratory course synthesized their own quantum dots and gained experience with these important nanomaterials.

Optically induced ultrafast demagnetization and its recovery in superparamagnetic colloidal iron oxide (Fe3O4) nanocrystals have been investigated via time-resolved Faraday rotation measurements. Optical excitation with near-infrared laser pulse resulted in ultrafast demagnetization in approximately 100 fs via the destruction of ferrimagnetic ordering. The degree of demagnetization increased with the excitation density, and the complete demagnetization reached at approximately 10% excitation density. The magnetization recovered on two time scales, several picoseconds and hundreds of picoseconds, which can be associated with the initial reestablishment of the ferrimagnetic ordering and the electronic relaxation back to the ground state, respectively. The amplitude of the slower recovery component increased with the size of the nanocrystals, suggesting the size-dependent ferrimagnetic ordering throughout the volume of the nanocrystal.

We present narrowband near-infrared images of a sample of 11 Galactic planetary nebulae (PNe) obtained in the H 2 2.122 μm and Brγ 2.166 μm emission lines and the K c 2.218 μm continuum. These images were collected with the Wide-field Infrared Camera on the 3.6 m Canada-France-Hawaii Telescope (CFHT); their unprecedented depth and wide field of view allow us to find extended nebular structures in H 2 emission in several PNe, some of these being the first detection. The nebular morphologies in H 2 emission are studied in analogy with the optical images, and indication of stellar wind interactions is discussed. In particular, the complete structure of the highly asymmetric halo in NGC 6772 is witnessed in H 2 , which strongly suggests interaction with the interstellar medium. Our sample confirms the general correlation between H 2 emission and the bipolarity of PNe. The knotty or filamentary fine structures of the H 2 gas are resolved in the inner regions of several ring-like PNe, also confirming the previous argument that H 2 emission mostly comes from knots or clumps embedded within fully ionized material at the equatorial regions. Moreover, the H 2 image of the butterfly-shaped Sh 1-89, after removal of field stars, clearly reveals a tilted ring structure at the waist. These high-quality CFHT images justify follow-up detailed morphokinematic studies that are desired in order to deduce the true physical structures of a few PNe in the sample.

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The role of surface spins in the relaxation of magnetization in optically excited Fe(3)O(4) nanocrystals has been investigated via time-resolved Faraday rotation measurements. The time scale of the magnetization recovery following the optically induced demagnetization increased from 250 to 350 ps as the size of the nanocrystals increased from 5 to 15 nm. From analysis of the data with a simple model relating the spin-lattice relaxation rate to the average spin-orbit coupling strength of the interior and surface spins, we estimated the relative efficiency of surface in spin-lattice relaxation with respect to the interior spins. Our analysis indicates that, in Fe(3)O(4) nanocrystals passivated with oleic acid, the surface is 3 times more efficient in spin-lattice relaxation than the interior.

The recent detection of fullerene (C 60 ) in space and the positive assignment of five diffuse interstellar bands to C + 60 reinforce the notion that fullerene-related compounds can be efficiently formed in circumstellar envelopes and be present in significant quantities in the interstellar medium. Experimental studies have shown that C 60 can be readily hydrogenated, raising the possibility that hydrogenated fullerenes (or fulleranes, C 60 H m , m = 1 − 60) may be abundant in space. In this paper, we present theoretical studies of the vibrational modes of isomers of C 60 H m . Our results show that the four mid-infrared bands from the C 60 skeletal vibrations remain prominent in slightly hydrogenated C 60 , but their strengths diminish in different degrees with increasing hydrogenation. It is therefore possible that the observed infrared bands assigned to C 60 could be due to a mixture of fullerenes and fulleranes. This provides a potential explanation for the observed scatter of the C 60 band ratios. Our calculations suggest that a feature around 15 µm due to the breathing mode of heavily hydrogenated C 60 may be detectable astronomically. A preliminary search for this feature in 35 C 60 sources is reported.