Chemical Modulation On The Semiconductor Nanocrystal Superlattice And The Thermostability Study

The electronic, optical and magnetic properties of superlattice depend not only onthe intrinsic properties of individual nanocrystal, but also on the structure of thesuperlattice and the electronic/optical communication between the nanoparticles.Superlattice usually appeared the unique collective properties different from both bulkmaterials and single nanoparticles, because of the ordered stacking of nanocrystals. Bynow, the spherical nanocrystals, polyhedra, one-dimensional (1D) nanorods andtwo-dimensional (2D) nanodisks have been successfully used as the building blocks tofabricate the functional superstructures. Furthermore, the binary nanocrystalsuperstructures are also obtained by selecting two different types of nanocrystals withmatching shapes, sizes and surface stabilizers. Generally, such superstructures arespontaneously formed by taking advantage of different types of inter-nanocrystal forces,e.g., electrostatic interaction, van der Waals forces, charge-dipole and dipole-dipoleinteraction, or capillary force and so on. Recently, the external physical changes likepressure and temperature are recently found to have a large influence on thearrangement of nanocrystals, which considerably improve our ability to fabricate anduse these superstructures. In the chemistry community, an imperative question isnaturally raised: Could the chemical stimulations, for instance, chemical reactionsinside nanocrystals or chemical adsorption on nanocrystals, be used to tune thearrangement of superstructures? Besides, since the nanocrystal is thermo-instability, thethermo-stability of nanocrystals determines the structural stability of superlattice. Howabout the thermo-stability of superlattice? What are the key factors that affect thethermo-stability of the superlattice? This work mainly focused on studing the formationof Cu2S and Ag2S nanocrystal superlattice, and the modulation of their structure via thespecific chemical adsorption of anions on certain facetes. In addition, thethermo-stability property of superlattice and the related factors were also investigated.The dissertation mainly includes the following parts:1. A classic solventless thermolysis reaction of copper thiolate is used to preparethe Cu2S nanowires and the superlattice of Cu2S nanoparticles. Anions are found to playthe key role on arrangement of Cu2S nanocrystal superstructures. In the presence of Cl- ions, Cu2S nanowire arrays are prepared; otherwise the FCC superlattices of Cu2Snanoparticles are produced. The theoretical calculation confirmed that the difference ofthe adsorption energy of Cl-ions and MUA molecules on the different facets ofhexagonal Cu2S nanocrystals induced the different structure of Cu2S nanocrystalsuperlattice.2. Ag2S nanocrystal superlattice was fabricated by thermolysis the complex ofsilver acetate and octodecanthiol. Iodide ion was found to play the key role onarrangement of Ag2S nanocrystal superstructures. In the presence of I-ions, Ag2Snanowire arrays are prepared, otherwise the FCC superlattices of Ag2S nanoparticles areproduced. The results further confirmed that it is an effective pathway to modulate thestructure of the superlattice by anions.3. Cu2S nanocrystal FCC superlattice was fabricated by thermolysis the complex ofCu(acac)2and dodecanthiol. We found that the thermo-stability of Cu2S superlatticechanged with different ration of the Cu(acac)2and the dodecanthiol. Futher studyrevealed that acac influenced the thermo-stability of superlattice.