Nanocrystal formation

Fortner JD, Lyon DY, Sayes CM, Boyd AM, Falkner JC, Hotze EM, Alemany LB, Tao YJ, Guo W, Ausman KD, Colvin VL, Hughes JB (2005) C in water Nanocrystal formation and microbial response. Environ. Sci. Technol. 39 4307 1316. 

The production of such tailor-made nanomaterials by electrochemical procedures is advantageous because the two crudal steps in nanocrystal formation -nudeation and growth of nudei - can be controlled by physical (current, voltage, time, temperature) and chemical (grain refiners, complex formers) parameters during the deposition process [42, 43]. 

Cen L, Neoh KG, Kang ET (2005) Gold nanocrystal formation on viologen-fimctionalized polymeric nanospheres. Adv Mater 17 1656-1661... 

SiGe NANOCRYSTAL FORMATION IN PECVD GROWN SiOx/Si/Ge/Si/SiOx MULTILAYERS... 

Fig. 1 demonstrates sample structure used in this study. A series of samples have been deposited with 200 seem Ge into Si02 and annealed at different temperatures to study the effects of dose and annealing temperature on the nanocrystal formation. Supersaturated Ge precipitates into crystallites in amorphous Si02 upon annealing. To demonstrate the effect of annealing temperature, Raman spectrum of these multilayer annealed samples are shown in Fig. 2. For these multilayer samples, 4 peaks are observed around 295, 400, 485 and 521cm ( Fig. 2). These peaks are assigned to the Ge-Ge, Si-Ge, nanocrystalline Si-Si and crystalline Si-Si vibrations, respectively.

A dynamics of nanocrystals formation has been also investigated. The luminescence spectra of colloidal solutions were registered during the reaction. Luminescence was excited by He-Cd laser with the wavelength of 325 nm. Fig. 1 shows the luminescence spectra of CeP04 Tb (15 mol.%) colloidal solution depending on the synthesis time. After 1 h of synthesis, the luminescence spectrum consists of the single intensive broad band with maximum at 370 nm, which corresponds to the luminescence of amorphous cerium phosphate particles. Only after 2 h of synthesis the narrow luminescence bands associated with the Af intrastate transitions of Tb were observed. The Tb ions are not... 

SiGe nanocrystal formation in PECVD grown SiOj/Si/Ge/Si/SiOx multilayers.77... 

The influence of phosphorus doping on the PL of ion-implantation-produced Si02 nc-Si is demonstrated in Fig. 1 [1,2,9,11]. The positive role of phosphorus can be explained by the action of the mechanisms (2), (5) and (6). The contribution of the mechanism (4) seems to be not probable because the order of annealing (nanocrystals formation) and P implantation in this case does no affect the degree of the impurity-induced enhancement. Note that the role of the Auger recombination (mechanism (7)) is not apparently revealed. It should be mentioned that the influence of the Auger recombination was considered only for impurity-free QD. For QD with donor atoms this consideration can occur to be not valid. 

It was demonstrated recently [6,7] that on SiO2/Si surfaces patterned by a focused ion beam, a high density of laterally ordered Ge nanocrystals may be grown. Under certain fabrication conditions, nanocrystal formation on the nanopatterned oxidized surface driven by surface diffusion or surface minimization leads to the dot growth only inside the holes. Ordering is in this case possible by appropriate design of the corresponding pattern. 

In the synthesis of the nanocrystals, a homogeneous iron-oleate solution prepared at room temperature is heated to 320°C, which is the thermal decomposition temperature of iron-oleate complex, and held at that temperature (24). As shown in Figure 6.13, the curve for the reaction extent of the thermal decomposition of iron-oleate complex in the solution shows a sigmoidal shape, which is typical of autocatalytic reactions. Interestingly, there is a time lag between the onset of the reaction extent curve and the initiation of the nanocrystal formation. As shown in the right of the figure, when the solution temperature just reaches 320°C, there is a trace amount of nanocrystals in the solution while about half of the iron-oleate complex has already been decomposed. This implies that iron oxide crystal is not a direct product of the thermal decomposition of iron-oleate complex. Rather, when iron-oleate complex is thermally... 

Historically, QDs were first synthesized in glass matrices where the slow difiusion of precursors provided some measure of size control. In the last couple of decades, colloidal techniques have advanced to the point that parameters such as precursor reactivity, temperature, surfactants etc. can be independently tuned to control and regulate nanocrystal formation. This enables the synthesis of high quality solvent dispersible particles that may be further processed using simple wet-chemical methods. Qne of the earliest techniques employed to achieve this is known as the arrested precipitation method where the semiconductor growth is arrested after the... 

The slow 1D growth of TiOa nanocrystals from the resin-bound precursor, [Ti(02> (0H)(H20) ] or Ti(lV), in the absence of any other coexisting ions has been reported. The ID morphology of the nanocrystal formation takes place in the presence of coexisting ions and is also affected by the reaction rate regardless of the crystal phases. 

S. Kim, H. S. R5fu, H. Shin, H. S. Jung and K. S. Hong, In Situ Observation of Hydroxyapatite Nanocrystal Formation from Amorphous Calcium Phosphate in Calcium-rich Solutions, Mater. Chem. Phys., 2005,91, 500-506. 

First, the effects of pH on the pseudohoehmite nanocrystal formation were examined. Hydrochloric acid and sodium hydroxide were used for pH control. From FE-SEM observations of the surface, the nanocrystals formation on the surface was confirmed for pH of 5.5-8.0. For pH < 5 or pH > 8.0, the alumina gel films are dissolved during the hot water treatment because alumina is an amphoteric oxide. Therefore, pseudohoehmite nanocrystals were obtained in neutral conditions (pH = 5.5-8.0) by the hot water treatment of alumina gel films. 

Gurin VS (1998) Observation and simulation of PbS nanocrystal formation at the initial steps. Macromol Symp 136 13-16... 

Semiconductor particles can also be used advantageously in coating applications to provide specific optical response to the material. As an example, Kumacheva et al. recently described the synthesis of monodisperse nanocomposite particles with inorganic CdS nanocrystals sandwiched between a PMMA core and a P(MMA-co-BA) outer copolymer shell layer. The particles are prepared by emulsion polymerization in three steps (Fig. 4.21) [144]. In a first step, polymer latexes are used as host matrices for CdS nanocrystals formation [145,146]. To do so, monodisperse poly(methyl methacrylate-co-methacrylic acid) (PMMA-PMAA) latex particles were ion-exchanged with a Cd(Cl04)2 solution. The Cd + ions thus introduced into the electrical double layer were further reduced into CdS nanoclusters by addition of a Na2S solution. The CdS-loaded nanocomposite particles were subsequently recov-... 

H. Yao, Y. Takada, N. Kitamura, Electrolyte effects on CdS nanocrystal formation in chelate polymer particles, Langmuir 199S, 14,595-601. 

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