Synthesis of Inorganic Quantum-Confined Nanomaterials

The solvothermal method is more efficient and permits wide range of reaction temperature due to high boiling point of the organic solvents. The most common method rmder solvothermal is hot-injection method compared to heating-up method used for colloidal synthesis of nanocrystals. 

Synthesis of colloidal III-V, IV-VI nanocrystals and some ternary and quaternary systems has been tabulated in Table 3.1. 

HI = hot-injection method, HU = heating-up method, RT = room temperature, CdMe = dimethyl cadmium, ZnEt = diethylzinc, TMS = trimethlsilyl, (BDMSj Te = his tert-butyldimethylsilyljteUuride, TDPA = tetradecylphosphonic acid, ODPA = octadecy-Iphosphonic acid, SA = stearic acid, LA = lauric acid, MA = myristic acid, OA = oleic acid, ac = acetate, acac = acetylacetonate, st = stearate, hdx = hexadecylxanthate, ex = ethylxanthate, dx = decylxanthate, TOPO = trioctylphosphine, HDA = hexadecylamine, DDA = dodecylamine, ODA = octadecylamine, TOP = trioctylphosphine, TBP = tribu-tylphosphine, ODE = 1-octadecene, HH = hexadecylhexadecanoate, BP = benzophenone, TOA = trioctylamine, OAm = oleylamine, DPE = diphenylether, TAA = thioacetamide TEA = triethanolamine, DDT = dodecanethiol, dedc= diethyldithiocarbamate. 

Most reliable and popular technique being followed for synthesizing highly stable core-shell semiconducting nanocrystals is Successive Ion Layer Adsorption and Reaction better known as SILAR [109]. The shell is formed by growing one monolayer at a time over the core nanocrystal s surface. In a typical synthesis, the cationic and anionic precursors are alternately added and made to adsorb on the cores surface followed by reaction. This way of adding cationic and anionic precursors in separate injections prevents the otherwise possible homogenous nucleation of shell material. 

In SILAR technique, reaction temperature plays a crucial role for the growth of shell onto the core nanocrystal. Too high growth temperature lead to Ostwald ripening of the core and core-shell nanocrystals as well as formation of new nuclei, whereas at too low temperature intended NC phase formation does not occur. Therefore, required phase, size and optoelectronic properties are obtained only at optimum temperature. For example, for growing ZnS shell onto CdSe nanocrystal, the optimum growth temperature is around 200-240°C. 

---