Large-area dielectric and metallic freestanding gratings for midinfrared optical filtering applications
Fabrication process of large-area dielectric (H1) and metallic (H2) freestanding gratings. (a) -thick (100)-Si substrate. [(b) and (c)] Deposition of and layers on the front and back sides of the substrate. (d) Nickel grating obtained by UV contact lithography and lift-off, deposition of an additional protection layer. (e) Optical lithography and subsequent etching of the layer (definition of the membrane surface). (f) Etching of the Si substrate in a TMAH solution. (g) Membrane drilling by reactive ion etching. (H1) Ni removal by chemical etching and critical point drying technique (see the text). (H2) Multidirectional gold deposition on the grating.
SEM images of -thick SiC freestanding gratings showing bar sticking due to the drying process after liquid immersion. (a) Period , bar width . (b) Period , bar width .
SEM images of -thick (a) SiC and (b) freestanding gratings obtained by critical point drying. (a) Period , bar width . (b) Period , bar width .
SEM images of a gold-coated freestanding grating (period , slit width , and thickness ). The core of the grating is made of to ensure the rigidity of the structure.
Experimental (solid curves) and calculated (dashed curves) optical transmission spectra of two freestanding -thick gold-coated gratings, for TM polarization (magnetic field parallel to the slits) and normal incidence. Grating G1 (dark): period , slit width . Grating G2 (red): period , slit width .
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