Aqueous solution-processed nanocrystals

In contrast to the dry methods, there are other conventional methods related to post heat treatment from precipitates from the aqueous solutions. The ambient aqueous routes and the hydrothermal methods at elevated temperature usually lead to rare earth precipitates like hydroxides, carbonates, instead of oxides. In fact, the hydrothermal treatment of rare earth oxide powders results in a hydration process to form hydroxides. Subsequently, the precursor could be used to produce rare earth oxide nanocrystals with post annealing at varied temperatures and in appropriate atmosphere. 

Devices Processed from Nanocrystals in Aqueous Solutions... 

Maghemite and Magnetite Nanocrystals One of the first syntheses of magnetite nanocrystals employed aqueous solutions of FeCl2 and FeCfi, and was reported by Massart [95]. The chemical reaction leading to the Fe304 phase occurred at pH 8-14 under airless conditions the process can be expressed as ... 

Other groups have achieved CNT forest assemblies by electrostatic SWNT-COO / Fe interactions also starting with shortened CNTs. The assembly process involves sequential substrate dipping in dilute Nafion and aqueous FeCl3 solutions followed by DMF-assisted precipitation of the nafion-adsorbed Fe to produce thin FeO(OH)/FeOCl nanocrystals. Subsequent immersion into a DMF disperse nanotube suspension produces the forest assembly that is driven by acid-base neutralization [12, 61, 121[. 

The hydrothermal method has been used to prepare monodispersed ZnS (6 nm) [10] and CdS nanocrystals (16 nm) [11]. By hydrothermal polymerization and simultaneous sulfidation processes, nanocomposites CdS/poly(vinyl acetate) nanorods [12] and nanospheres [13] were synthesized. In aqueous hydrazine solutions, nonstoichiometric metal telluride nanocrystallites such as Cu2.86Te2, CuyTes, Cuy-xTe, and Ag7Te4 [14], and cubic CogSg were hydrothermally synthesized [15]. Other transition metal chalcogenides, such as single-molecular-layer M0S2 [16] and MoSey [17] were also prepared under hydrothermal conditions. 

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