Gu et al. Nanoscale Research Letters 2011, 6:199 http://www.nanoscalereslett.com/content/6/1/199 Page 7 of 12 Figure 8 Illustration of the NSL process. Shown are the deposition of polystyrene spheres on the substrate, thermal evaporation of gold, and removal of polystyrene spheres leaving triangular gold NPs. Reproduced from [52]. Copyright The Royal Society of Chemistry, 2006. self-assembly into a hexagonally closely packed two- dimensional colloidal crystal that serves as a deposition mask, vacuum/electron beam deposition, and finally, removal of the nanosphere mask by ultrasonic treatment in an organic solution [55-57]. Different from EBL, the patterning is based on self-assembly rather than electron beam irradiation. Hence, the production cost is reduced because only a small amount of nanosphere solution is needed. In addition, the use of copper instead of Au, Ag, and Pt without degrading the NP properties can lead to further low production cost [58]. Other NSL-based tech- niques, for example, double-layer mask-based and angle- resolved NSL, allow more flexible tuning of the metallic NP optical response [59,60] and, consequently, enhance- ment in light emission. NSL has been utilized to fabricate metallic NPs to increase PL from Si nanocrystals and GaN light emitters [61,62]. However, on account of inherent restrictions such as difficulty to fabricate struc- tures other than triangles or quasi-triangles, this method has not been extended to produce LEDs. Using templates Using patterned templates, various nanostructures, both two- and three-dimensional, for example cylinders, squares grooves, and pyramids, can be easily fabricated. Frequently used templates are often produced from por- ous anodic alumina [PAA] or by lithography techniques [41,63,64]. The advantage of this method is avoidance of chemical peel-off, thus making incorporation of metallic NPs into EL LEDs possible. At present, only PAA-based templates have been applied to the fabrication of PL light emitters [41], and the bright future of using tem- plates to fabricate EL LEDs is to be explored. Other methods The fabrication techniques aforementioned are main- stream techniques that have been applied to NP fabrication to improve light emission efficiency. Nanoimprint lithography and chemical synthesis are alternatives and have been extensively studied [65-67]. However, these two techniques are too costly or diffi- cult to control, and so neither of them has been used successfully to produce NP arrays with improved light emission. More work is required in order to produce large-area, cost-effective, and easily tunable metallic NPs with enhanced light emission efficiency. One pro- mising proposal for achieving this goal is to use self- assembled nanorods, nanowires, or nanotubes because of the ease of production and high controllability [68-71]. Ag nanorods formed by heating of AgNO3 in pores of PAA template or oblique angle deposition, nanotubes by shadow evaporation, and Ag NPs on stacked carbon nanotube layers have already found intriguing applications in surface-enhanced Raman scattering, and we anticipate that these proposals may shortly be employed to LED efficiency enhancement with proper modifications. Applications LEDs have found major commercial applications in three areas: general lighting, flat panel displays, and optoelectronic chips. General lighting Advantages such as energy saving, low radiation, shock resistance, and spectral power tunability over fluorescent and incandescent light sources have propelled the com- mercialization of solid-state lighting devices containing semiconductors as the light emitters [72]. Specifically, recent realization of LEDs with fluorescent tube effi- ciency makes the prospect of solid-state lighting brighter. Some common strategies to make white light LEDs are illustrated in Figure 9. One method is to com- bine emitters with different colors in the device and adjust the spectral composition according to practical needs. Alternatively, phosphors and certain semiconduc- tor NCs such as CdSe/ZnS core/shell quantum dots are known to be capable of effectively converting high- energy photons to low-energy ones, and consequently, white light sources can be produced. In both strategies, the use of a blue or UV LED is indispensable. However, typical inorganic blue light emitters based on GaN/ InGaN QWs usually have a low IQE due to the rela- tively poor crystal quality. Since LSPR can introduce efficiency enhancement when the original IQE is low, there is big interest in using LSPR to increase the over- all efficiency of short-wavelength blue and green LEDs, as discussed in previous sections. The use of LSPR in fabricating white LEDs has been described by Yeh et al. [73]. Here, mixing of the red light converted from blue/green photons and residual