Drop-casting

Figure 4.17 A Steel crucible with Al20 liner used for drop casting of niobium.

Despite facile formation of p-type ZnTe from the precursor, films of ZnTe formed from a drop cast precursor solution had a small grain structure (using conditions that we have so far explored), which limited prospective TFT device performance. Note that we expect a similar chemistry to that for ZnTe to also be operative for selected other metal telluride precursors. In contrast to the ZnTe films, well-crystallized films of In2Te3 have been formed using... 

For cases in which the NPs are not soluble in the supporting electrolyte in which they will be examined, it is possible to solvent-cast a thin film of the NPs on the electrode surface followed by evaporation [44] or to directly apply an insoluble gel containing the NPs [45]. In a related approach, films of anionic Prussian Blue NPs that had been synthesized in a solution containing chitosan (a cationic glucosamine polymer) were drop-cast onto glassy carbon surfaces, giving very stable... 

Zhao et al. prepared magnetite (FesO nanoparticles modified with electroactive Prussian Blue [44]. These modified NPs were drop-cast onto glassy-carbon electrodes. They observed the redox processes commonly observed for PB (similar to that seen in Figure 4.8), and also demonstrated that the Prussian White material produced by PB reduction at 0.2 V served as an electrocatalyst for Fi202 reduction. They also prepared LbL films in which PB NPs and glucose oxidase were alternated between PD DA layers [99]. These were demonstrated to act as electrocatalysts for Fi202 reduction. Based on the ability to sense the product of the enzymatic reaction, these structures were shown to act as glucose sensors. 

Perhaps the most simple way of obtaining small single crystals, albeit in an uncontrolled way, is the drop casting teclmique. This method consists in the deposition of a drop of a saturated solution of a soluble material on a clean substrate prior to the evaporation of the solvent in air, usually at RT. Some interesting examples are shown next. 

The simple drop casting crystallization method, discussed in Section 3.1, has also shown its validity in the determination of hole mobilities at least for the TTF-derivatives DTTTF (Mas-Torrent et al, 2004), EDT-TTF-(CONHMe)2 (Colin et al, 2004) and DBTTE (Mas-Torrent et al, 2005). In all cases, 1 cm s In this case the formation of high-quality organic/insulating interfaces is a matter of serendipity (see the discussion on the formation of nanovolcanoes at the surfaces of drop-cast single crystals in Section 3.1). 

Other applications use self-assembling fibers to coat materials. For example, preassembled peptide amphiphiles have been covalently immobilized on titanium implant surfaces via a silane layer (Sargeant et al., 2008). Primary bovine artery endothelial cells or mouse calvarial preosteoblastic cells spread on these coated surface and proliferated to a far greater extent than on samples where the peptide amphiphiles had been drop cast onto the metal surface. This study therefore suggests that covalent attachment is required in order to prevent fibers lifting from the coated surface and to encourage maximal cell growth. 

In this context, solutions of octaalkoxy substituted CuPcs drop-casted on silica surfaces give rise to the formation of highly homogeneous, 1-D (in the case of the octa(n-butoxy) CuPc) or 2-D (in the case of the octa(n-octyloxy) CuPc) aggregates [208], Density functional computations have revealed that a combination of in-plane interactions and displaced parallel stacking for Pcs are responsible for the different self-assembled structures. 

More recently, another example of a Pc-based system (31) (Fig. 27a) able to self-organize on HOPG and graphite-like surfaces by drop-casting technique was reported. AFM studies revealed that the covalently linked Pc-C6o fullerene conjugate 31 is able to form nanostructured fibers and films (Fig. 27b) [48],... 

Benoit et al. (41) obtained electrically conductive nanocomposites by dispersing SWCNT and PMMA in toluene, followed by drop casting the mixture on substrates. Thin films of SWCNT-PMMA composites for different CNT concentration were produced by spin casting by Chapelle et al. (54) and Stephan et al. (55). They characterized these nanocomposites by Raman spectroscopy to study interactions between nanotubes and PMMA and found that PMMA tends to intercalate between the CNTs thereby increasing the distance between the nanotubes in the film. 

Fig. 1. Illustration of microcapillary capabilities of PDMS stamp, where a composite suspension of lipid tubules was drop casted onto a glass substrate (a-c). Once the lipid tubules were assembled into the PDMS channels, their confinement was confirmed through transmission mode optical microscopy. Reprinted with permission from ref. 14. Copyright 2008 American Chemical Society.

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