*2.6.2. Merits*



**Table 7.** Hierarchical TiO<sup>2</sup> nanostructures produced via dot patterning/photolithography.

• Chemical vapor deposition (CVD) • Physical vapor deposition (PVD)

tions can be controlled by these processes.

Flipin et al. [76] grew hierarchical TiO<sup>2</sup>

Multistacked nanotrees composed of TiO<sup>2</sup>

Yoshitake et al. [77] prepared hierarchical TiO<sup>2</sup>

**(m2 g−1)**

Flipin et al. [76] Anatase — 50–120 Below 100 (for

**Reference Phase Surface area** 

**Table 8.** Hierarchical TiO<sup>2</sup>

via these processes.

*2.7.1. Examples*

Very little work has been done by these techniques to grow TiO<sup>2</sup>

we can grow hierarchical structures. The film cost, thickness, source material and composi-

In CVD process, precursors are introduced in the reaction chamber and flow of molecules is regulated by control values. The precursor molecules get deposited over the surface of substrates after chemical reactions take place. Heat energy is provided for chemical reactions to take place. While in PVD, deposition occurs by various routes like evaporation, sputtering and molecular beam epitaxy (MBE). **Table 8** shows different characteristics of HNSs prepared

sition technique. Porphyrins and phthalocyanines were used as cost-effective precursor molecules. First of all, seed layer was grown by polycrystalline anatase films for highly dense and homogenous organic nanowires. Physical vacuum deposition was done to grow organic nanowires (ONWs) of phthalocyanine molecules with sublimation temperature of 250°C. As a result, tunable ONWs in the range between 1 and 30 μm and diameters between 50 and

as shown in **Figure 27**. These nanotubes were grown as 1D structures provide maximum electron percolation as compared to 0D nanoparticles due to less grain boundaries. These structures were then employed for DSSCs to evaluate their efficiency for current production.

sopropoxide (TTIP) was used as a precursor material. About 40 g of water was added to 8 g of TTIP with 2.6 g of dodecyl amine at 273 K. The mixture was stirred with 0.1 M HCl and was kept overnight for aging. The reaction mixture was transferred to autoclave at 373 K for

> **Crystallite size (nm)**

all structures)

120 nm were produced. Then, PECVD was done to cap ONWs with TiO<sup>2</sup>

4 days. The powder obtained was washed with methanol and dry ethyl ether.

**Particle size (diameter) (nm)**

Yoshitake et al. [77] Anatase 518 3.03 3.30 Worm-like spherical

nanostructures produced via vapor deposition processes.

HNSs. By these techniques,

31

http://dx.doi.org/10.5772/intechopen.74525

nanotubes by plasma-enhanced chemical vapor depo-

Hierarchical Nanostructures of Titanium Dioxide: Synthesis and Applications

nanowires were grown as a result of this synthesis

structures by CVD method. Titanium tetrai-

Nanoforest composed of nanowires

agglomerated structures

shells.

**Morphology Application**

DSSCs

—

**Figure 26.** Hierarchical flower-like structures produced by dot patterning [48].
