Fig. 4
a i Smooth metallic (silver; Ag) film-coated dielectric (silicon-dioxide; SiO2) atomic force microscope (AFM) tip. a ii SEM image of a Ag-coated AFM tip. After Ag coating by thermal evaporation, a thin granular Ag layer is deposited onto the tip. b i, Rough Ag-nanoparticle-coated SiO2 AFM tip. b ii SEM image of rough Ag-grain-coated SiO2 AFM tip formed during the thermal evaporation process. c i Single Ag nanoparticle attached to the apex of a SiO2 AFM tip. c ii SEM image of an AFM tip after photoreduction to selectively fabricate an Ag nanoparticle at the tip apex. d i Ag-coated SiO2 AFM tip with a focused ion beam (FIB) milled gap. d ii SEM image of antenna fabricated by FIB milling of annular ring and subsequent Ag thermal evaporation from under the tip. The mushroom shape shadows the annular ring from Ag coating. e i Illustration of side illumination TERS for surface plasmon polariton (SPP) nanofocusing. OBJ, objective. e ii Schematic of the tip structure for SPP nanofocusing which is composed of a SiO2 pyramidal structure (AFM tip) and a Ag film on the surface. The incident light is coupled to the surface by the FIB-fabricated grating nanostructure. e iii SEM image of a Ag-coated SiO2 tip with a FIB-fabricated grating structure. a i, b i and ii, c i reproduced from Ref. [198] with permission from The Royal Society of Chemistry. (ref.). a ii reprinted with permission from [86]. c ii Reprinted from [199] with permission from IOP. d i Adapted from [200]. d ii Reprinted from [200] with permission from IOP. e i Adapted from [201]. e ii and iii reproduced from Ref. [201] with permission from The Royal Society of Chemistry