Nanocrystal Patterning

Creating patterns of nanocrystals on surfaces has attracted wide attention. Such patterned substrates can act as templates to grow nanowires, etch masks to grow nanopillars and quantum dots [154-156]. Other than the layer-by-layer technique mentioned before, simple techniques such as spin coating have been employed to create a nanocrystalline pattern on surfaces [157]. 

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FIG. 2. Contact AFM images of y-Fe2Oj nanocrystal patterns drawn (a) on mica along with (b) its surface plot, (c) on silicon with the native SiOr layer (arrows point to closely-drawn patterns) and (d) on etched silicon. 

Curri, M.L., Comparelli, R., Striccoli, M., Depalo, N., Fanizza, E., 2013. Inorganic nanocrystals patterning and assembling. Encyclopedia Inorg. Chem. 

Figure C2.17.6. Transmission electron micrograph and its Fourier transfonn for a TiC nanocrystal. High-resolution images of nanocrystals can be used to identify crystal stmctures. In tliis case, tire image of a nanocrystal of titanium carbide (right) was Fourier transfonned to produce tire pattern on tire left. From an analysis of tire spot geometry and spacing, one can detennine that tire nanocrystal is oriented witli its 11001 zone axis parallel to tire viewing direction [217].

Figure C2.17.7. Selected area electron diffraction pattern from TiC nanocrystals. Electron diffraction from fields of nanocrystals is used to detennine tire crystal stmcture of an ensemble of nanocrystals [119]. In tliis case, tliis infonnation was used to evaluate the phase of titanium carbide nanocrystals [217].

MicrocrystalUne zeolites such as beta zeolite suffer from calcination. The crystallinity is decreased and the framework can be notably dealuminated by the steam generated [175]. Potential Br0nsted catalytic sites are lost and heteroatoms migrate to extra-framework positions, leading to a decrease in catalytic performance. Nanocrystals and ultrafine zeolite particles display aggregation issues, difficulties in regeneration, and low thermal and hydrothermal stabilities. Therefore, calcination is sometimes not the optimal protocol to activate such systems. Application of zeolites for coatings, patterned thin-films, and membranes usually is associated with defects and cracks upon template removal. 

To determine if the resonance peak is due to self-organization, optical spectra of disorganized nanocrystals (see TEM pattern inset Fig. 8) are recorded under v- and p-polar-ization. Under v-polarization, the optical spectrum obtained at 0 = 60° (Fig. 8A) shows one resonance peak at 2.7 eV. This is attributed to the surface plasmon parallel to the substrate. 

On the other hand, in.the case of the nonionic surfactants C-15, NP-15 and 0-15 (the nonionic surfactant/cyclohexane system), mono-dispersed silicalite nanocrystals were obtained as shown in Fig. 1(c), 1(d) and 1(e), respectively. The X-ray diffraction patterns of the samples showed peaks corresponding to pentasile-type zeolite. The average size of the silicalite nanocrystals was approximately 120 nm. These results indicated that the ionicity of the hydrophilic groups in the surfactant molecules played an important role in the formation and crystallization processes of the silicalite nanocrystals. 

Figure 8.2 XRD patterns of (a) CoOOH and (b) Ce02. (c) TEM image of Ceo.g4Bio.16Oi 92 nanocrystals. Reprinted with permission from [18, 19] (2011) American Chemical Society and Wiley-VCH GmbH Co. KG a A.

Figure 10.10. (a) Optical absorption spectrum of a colloidal solution of 8-nm PbSe nanocrystals, (b) TEM image of an array of 8-nm PbSe nanocrystals, (c) GISAXS pattern of a PbSe nanocrystal film. The appearance of well-resolved reflections confirms both in-plane and vertical ordering of the PbSe nanocrystals. Reproduced from Ref. 68, Copyright 2005, with permission from the A A AS. 

Figure 3. (a)Beam movement in a TEM after applying conical dark field/precession mode (b)electron diffraction (ED) pattern of a LixMn204 nanocrystal in (111) orientation, with no application and after application of precession mode as it can be observed dynamical contribution to all reflections is greatly reduced. 

Figure 2. Formation of nanocrystals with bcc-Fe(Co) lattice from amorphous (Fe3Co2)73Nb7Si5B15 annealed at 840K/800min with the corresponding XRD and electron diffraction patterns (right). Vertical hues and indices indicate the positions of the bcc-Fe(Co) peaks higher order reflections not measured by XRD are easily identifiable on the electron diffraction pattern with sufficient intensity.

Figure 3. Foimation of tiny nanocrystals of bcc -Fe(Mo) from the amorphous matrix in FcyaMogCuiBis aUoy (a - sample annealed at 823K/1 hour), followed by formation of additional irregular phase with fee lattice (b - sample annealed at 923K/1 hour) and (c) recrystallization after annealing at 973K/1 hour into polyhedral grains with the same lattice parameters. The insets show the corresponding XRD patterns.

Cui Y, Bjork MT, Liddle JA, Sonnichsen C, Boussert B, Alivisatos AP (2004) Integration of colloidal nanocrystals into lithographically patterned devices. Nano Lett 4 1093-1098... 

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