**3. Conclusions**

542 Recent Advances in Nanofabrication Techniques and Applications

Fig. 8. AFM images (1×1 um2) of (a) pit-pattern with a periodicity of 200 nm, (b) pit-pattern after Si buffer layer growth, (c) ordered GeSi nano-islands after deposition of 10 monolayers

distributed GeSi nano-islands grown under the same conditions on a flat Si (001) substrate.

Ge by molecular beam epitaxy on a pit-patterned Si (001) substrate, (d) Randomly

The unit of height bar is nm.

A scalable approach to fabricate periodic nanopatterning in a large-scale area with controllable periodicity using nanospheres, so called NSL, has been developed. The NSL generally started with self-assembling monolayer of PS spheres on the substrates, which can be obtained by various methods. One potential routine to obtain ordered monolayer of PS spheres is via self-assembling PS spheres at the interface between water and air. Such a regular arrangement of monolayer PS spheres in a hexagonal lattice resulted from the balance between an electrostatic repulsion among adjacent spheres and a capillary attraction due to the deformation of liquid meniscus by electrostatic stresses. An external electrical field perpendicular to the water surface, which affected the interaction between PS spheres, could efficiently improve the ordering of PS spheres, particularly of small PS spheres. The interplay among PS spheres can also be affected by changing the surface chemistry of PS spheres or the electrostatic environment of the water-air interface, which can be readily realized by mixing some electrolytes, such as solution of H2SO4 or NaCl. In addition, it was found that the ordering of PS spheres was improved on the water of ~ 4 oC mainly due to the increase of water surface tension and the suppression of the Brownian motion of the PS spheres and dust clusters in the water. This ordered monolayer PS spheres could be transferred onto the substrate placed previously inside water by draining off the water. This method facilitates large-area highly ordered monolayer of PS spheres on substrates,which can act as a mask or a template for subsequent lithography to obtain ordered nano-wires or nano-pits, or for subsequent growth of desired nanostructures. Two-dimensionally ordered nanopattern with a periodicity equal to the diameter of PS spheres in the range of several micrometers to less than 100 nm could be readily obtained. The geometrical profiles of the nanopattern could be modulated by controlling the etching conditions. NSL has been exploited in fabricating ordered nano-wires and nano-dots. This technique was characterized by its low-cost,high throughput, and easy manipulation for producing largescale periodic patterns. More interestingly,NSL can be applied to obtain nanostructures of various materials on many kinds of substrates, which will facilitate the production of varieties of ordered nanostructures.
