Gu et al. Nanoscale Research Letters 2011, 6:199 http://www.nanoscalereslett.com/content/6/1/199 Page 6 of 12 Figure 5 AFM images of Ag NPs deposited on an n-GaN layer before and after annealing. (a) Before annealing and (b) after annealing. After deposition, the particle size is significantly enlarged for better enhancement. AFM, atomic force microscopy. Reproduced from [33]. Copyright WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2008. different structures [36,37,47] and Si-based LEDs [48] have been produced by the sputtering-annealing process. Electron beam lithography EBL is often used to fabricate sub-100-nm monodis- persed metallic NPs. Current state-of-the-art equipment boasts a resolution of < 10 nm that is small enough for LSPR-enhanced LEDs. The general procedures to pro- duce metallic NPs are illustrated in Figure 6, and more details can be found elsewhere [49-52]. EBL can be uti- lized to produce metallic NPs exhibiting enhanced light emission efficiency. For example, metal-enhanced fluor- escence has been reported by Pompa et al. [53]. Here, EBL is used to fabricate highly ordered 100- to 200-nm- wide triangular gold prisms on planar substrates, and pictures of one representative sample are depicted in Figures 7a,b,c. Uniform CdSe/ZnS core/shell nanocrys- tals [NCs] dispersed in a polymethylmethacrylate Figure 6 General procedure of EBL. Reproduced from [50]. Copyright American Chemical Society, 1997. Figure 7 Typical example of a highly regular gold nanopattern by EBL: (a) SEM image of a triangular gold array. (b) High- resolution SEM image of a single nanotriangle. (c) AFM image of the single nanostructure. (d) Comparison between fluorescence with and without Au NPs. SEM, scanning electron microscopy. Reproduced from [53]. Copyright Nature Publishing Group, 2006. [PMMA] matrix to control the distance between the NCs and gold NPs are spin-coated onto the substrate, and the resulting enhancement is as high as 30-fold, as demonstrated by a comparison of the fluorescence with and without Au NPs in Figure 7d. Besides CdSe/ZnS NCs, luminescence from Si QDs increases by a factor of 7 [54]. After cleaning the Si QD-doped quartz in a 5:1:1 H2O/H2O2/NH4OH solution, EBL is used to pattern 100 × 100-μm circular arrays on two layers of PMMA cov- ered by Ge. After removing the Ge and developing the resist, the Si and Ag layers are deposited by vacuum deposition, and following lift-off of the remaining PMMA, only Ag islands are left on the quartz. Although EBL has some benefits over other fabrication methods, for instance, the high resolution and the ability to produce NPs with different shapes, it has disadvan- tages. For instance, large-area fabrication is difficult. The NPs produced are only two-dimensional and the equip- ment is expensive. Another disadvantage is that the acet- one lift-off process harms the electron or hole transport layer. Future research needs to focus on introducing some protection during patterning of the metallic NPs. Nanosphere lithography Traditional NSL, as illustrated in Figure 8, involves dropping a suspension of nanospheres onto a substrate,