CdS nanopartides

Yonemura, H Yoshida, M Mitake, S. and Yamada, S. (1999) Magnetic field effects on photocurrent responses from modified electrodes with CdS nanopartides. Electrochemistry, 67, 1209-1210. 

Nakanishi, T, Ohtani, B. and Uosaki, K. (1998) Fahrication and characterization of CdS-nanopartide mono- and multilayers on a self-assemhled monolayer of alkanedifhiols on gold, f Phys. Chem. B, 102, 1571-1577. 

For example, when silica-coated photoconductive CdS nanopartides were used as inorganic partides, the resultant materials were shown to retain the photolumi-nescent properties of the core. However, no mention was made about the colloidal stability of these systems. 

Reaction System This example describes the synthesis of CdS nanopartides based on the precipitation reaction at room temperature according to the procedure reported by Su and Chang [128]. The synthesis of CdS nanopartides via a continuous-flow microreactor based on a simple precipitation reaction in aqueous phase at room temperature [29-32,130,131] or in nonaqueous phase at a higher temperature [132] has been reported in the literature. The ligand (L)-capped CdS nanopartide formation mechanism could be described according to the following basic steps [29] ... 

Lai, C.Y., Trewyn, B.G., Jeftinija, D.M., Jeftinija, K., Xu, S., Jeftinija, S. et al. (2003) A mesoporous silica nanosphere-based carrier system with chemically removable CdS nanopartide caps for stimuli-responsive controlled release of neurotransmitters and drug molecules. Journal of the American Chemical Society, 125(15), 4451-9. 

More complex optical devices can be of the form electro-optical or magneto-optical responses. An electro-optical touch sensor was made up of alternating layers of metal Au and semiconduaing CdS nanopartides separated by dielectric... 

Size affects the stmcture of nanopartides of materials such as CdS and CdSe, and also their properties such as the melting point and the electronic absorption spectra. In Figures 1.4 and 1.5, we show such size effects graphically. It should be noted that even metals show nonmetallic band gaps when the diameter of the nanocrystals is in the 1-2 nm range. Hg dusters show a nonmetallic band gap which shrinks with increase in cluster size. It appears that around 300 atoms are necessary to dose the gap. It is also noteworthy that metal partides of 1-2 nm diameter also exhibit unexpected catalytic activity, as exemplified by nanocatalysis by gold particles. 

Henglein and Weller made significant progress [14-16] using CdS colloids prepared by controlled predpitation methods [17-22]. However, to obtain highly monodispersed nanopartides, post-preparative separation techniques such as size exdusion chromatography [20] and gel electrophoresis have been employed [21]. Gel electrophoresis was found to be superior to other separation techniques. 

In a metathetic reaction, two compounds AB and CD, exchange species to give two new compounds AC and BD. Such routes have been explored in the preparation of nanopartides. Arnal et al. [62] have reported two non-hydrolytic routes to sol-gel metal oxides, particularly of titanium. The first route involves the reaction of a metal halide with a metal alkoxide ... 

The sonoelectrochemical deposition of CdSe nanopartides is carried out from an aqueous solution of CdS04, complexed with potassium nitrilotriacetate (N(CH2C02K)3) NTA as a source for Cd, and a selenosulfate solution, (Na2SeS03), as source for Se. The CdSe crystal size could be varied from X-ray amorphous up to 9 nm by controlling the various electrodeposition and sonic parameters. The effects of various electrodeposition and sonic parameters on the properties of CdSe nanopartides are presented in Table 6.3. 

The en molecules play an important role in controlling the nucleation and growth of the CdS nanorods. As a bidentate ligand, en molecules may react with Cd + ions and form relatively stable complexes. Under appropriate solvothermal conditions, the complexes become unstable and decompose, which results in the formation of CdS nanorods [lOOj. A mono-dentate ligand, n-butylamrne, was found to be a shape controller for nanorods of CdS and MSe (M = Zn, Cd or Pb) [101]. Similarly, the precursor of ZnE(en)o.s (E = S, Se) could also form in en which then is converted to ZnSe nanopartides via pyrolysis in solvothermal conditions [102]. The coordinating ability of the solvent was found to play an important role in the nucleation and growth of nanocrystallites [103]. 

During the past two decades, the synthesis or preparation of II-VI semiconductor nanopartides has experienced an enormous development, to the point where the pubhshed material related to the topic has become virtually unmanageable. Nevertheless, the aim of this chapter is to provide a chronological overview of some of the major historical lines in this area, starting with the earliest studies with CdS nanocrystals prepared in aqueous solution. At several points in the story - mostly when successful preparations are first described - the chapter branches into evolving sub-fields, leading to Sections 3.2.1.2 and 3.2.I.3. The remainder of the review then relates to matters distinct from these preparational approaches. More complicated nanoheterostructures, in which two compounds are involved in the build-up of spherically layered particles, are detailed in Sections 3.2.1.4 and 3.2.1.5. 

The self-organization phenomena in colloids of magnetic nanopartides (ferro-fluids) induced by external magnetic fields has attracted considerable attention on the basis of importance from both fundamental and applied perspectives [31]. However, the lack of systematic investigations, combined with some contradictory findings, have led to these materials remaining a relative novelty. Wirtz et cd. [32] have suggested that the formation of macroscopic 1-D periodic patterns composed of... 

One of the first hints that gold nanopartides (AuNPs) could be deposited in an ordered manner was provided by Schiffrin et cd. [35], whenS run gold partides, which had been prepared in a two-phase liquid-liquid system and stabilized by dithiols [36], provided crosslinked assemblies for which the quality of ordering was rather limited compared to recent results. Nonetheless, these preliminary findings confirmed that 2-D self assembled arrays could be produced. 

The first work on the self-assembly of gold colloid particles capped with alkanethiols was done by Brust and coworkers [Netzer, L, 1983]. This routine has been adopted by other scientists for the deposition of self-assembled monolayers of different colloid nanopartides (e.g., Ag, CdS, CdSe, and ZnS), which were prepared using mercapto-alcohols, mercaptocarboxylic acids, and thiophenols as capping agents. Self-assembled nanopartides usually show well-ordered lateral structures, proved by numerous observations with SEM, STM, and AFM [Collier. C, 1997, Lover. T, 1997, Rogach. A. L, 1999 and Vogel. W, 2000]. 

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