Magnet neto-pl plasmonic asmonic Au/ u/Tb Tb 18 18 Co Co 82 82 - PowerPoint PPT Presentation

Magnet neto-pl plasmonic asmonic Au/ u/Tb Tb 18 18 Co Co 82 82 nano nano-ring ring res esona onator tors s Initial patterning and update by Agn ė Čiučiulkaitė Uppsala University

Motivation  Fabricate magneto-plasmonic nano-antenna arrays for all-optical switching of magnetization via focusing circularly polarised light  Possible geometry for focusing circularly polarised light – nano-ring 14/09/2018 Uppsala University 2

Tb 18 Co 82 amorphous layers  Magnetron sputtering of AlO x (2 nm)/Tb 18 Co 82 (18 nm)/AlO x (2 nm) on fused silica/Au(20 nm) Co Al 2 O 3 Tb Figure 1. Faraday rotation measured at 600 nm wavelength of incident light for the hybrid structure film 14/09/2018 Uppsala University 3

Patterning e-beam exposure PMMA L=400 nm Writing of a disc Spin-coating of PMMA (or ring) pattern R=120 nm via electron beam lithography Ar + Al O R in R out =120 nm Development and removal of exposed L=400 nm PMMA Resulting disc or ring square arrays Ar milling through after Ar + milling Electron-beam an Al 2 O 3 mask through Al 2 O 3 mask evaporation of remaining after Al 2 O 3 mask resist removal 14/09/2018 Uppsala University 4

Characterization  Scanning electron microscopy (SEM)  Optical transmission measurements  Spectroscopic Faraday rotation measurements 14/09/2018 Uppsala University 5

Scanning electron microscopy (SEM) (a) Disc (b) Thick rings (c) Thin Rings Figure 2. SEM micrographs of EBL patterned (a) disc, (b) donut and (c) ring arrays. Nominal radius* Actual radius** Sample R out , nm R in , nm R out , nm R in , nm 125 ± 5 a 40 0 126 ± 5 30 ± 5 b 60 120 123 ± 5 60 ± 5 c 80 Broken “Broken” “Broken” 100 rings*** *Nominal radius  from the patterning file **Actual radius  dimensions measured from SEM micrographs ***Not shown, can be found in Additional information 14/09/2018 Uppsala University 6

Optical transmission measurements Figure 3. Optical transmission measurements of nano- arrays shown in Fig.2. 14/09/2018 Uppsala University 7

Spectroscopic Faraday rotation measurements: Schematics µ 0 H p-polarized light M Rotation and Ellipticity λ =550-850 nm Figure 4. Schematic of polar MOKE measurement geometry. Measured arrays fabricated from Tb 18 Co 82 alloy, exhibit out-of-plane magnetization M . External field magnetic field µ 0 H was applied out-of-plane. 14/09/2018 Uppsala University 8

Spectroscopic Faraday rotation measurements: Results (a) (b) x10 x10 Figure 5. Spectroscopic magneto-optical measurements of nano-arrays shown in Fig. 2: (a) Faraday rotation and (b) ellipticity. 14/09/2018 Uppsala University 9

Magneto-Optic measurements (a) Disc Compare to: (a) Discs (b)Donuts (b) Thick rings Figure 1. Faraday rotation measured at 600 nm wavelength of incident light for the hybrid structure film (c) Thin Rings (c) Rings Figure 6. Magnetic Faraday rotation measurements 14/09/2018 10 at 600 nm wavelength of nano-arrays.

Summary  Patterning ring structures via EBL and Ar + milling results in expansion of structures, namely, outer diameter becomes slightly larger while the inner – smaller, resulting in thicker rings than expected from the design.  Aiming for 80 nm thick rings with 120 nm outer radius resulted into what appears as closed discs;  Aiming for 20 nm thick rings with 120 nm outer radius, resulted into broken rings and lost magnetization of the sample;  Pattern appears to be uniform throughout the entire area of 3x3 mm 2  Spectroscopic Faraday effect measurements show broad resonances extending to IR region for three magnetic arrays of discs, thick and thin rings. 14/09/2018 Uppsala University 11

Outlook  Modify the EBL designs in order to shift resonances to a visible range  reduce dimensions from 120 nm outer radius to …  Fabricate identical structures using the following stuctures:  Au(40nm)/AlOx(20nm)/Au(40nm) (cap structure with AlOx since EBL worked on Au/AlOx/TbCo/AlOx multilayer);  AlOx/TbCo;  Au/AlOx/TbCo/AlOx;  ... 14/09/2018 Uppsala University 12

Additional information SEM images, optical transmission measurements 14/09/2018 Uppsala University 13

SEM 14/09/2018 Uppsala University 14

Array 1: Discs 14/09/2018 Uppsala University 15

Array 1: Discs 14/09/2018 Uppsala University 16

Array 2: Thick rings 14/09/2018 Uppsala University 17

Array 2: Thick rings 14/09/2018 Uppsala University 18

Array 3: Thin rings 14/09/2018 Uppsala University 19

Array 3: Thin rings 14/09/2018 Uppsala University 20

Array 4: Broken rings 14/09/2018 Uppsala University 21

Array 4: Broken rings 14/09/2018 Uppsala University 22

Optical transmission 14/09/2018 Uppsala University 23

Optical transmission: comparison of all arrays Patch 1 – 40 nm: Discs Patch 2 – 60 nm: Thick rings Patch 3 – 80 nm: Thin rings Patch 4 – 100 nm: Broken rings 14/09/2018 Uppsala University 24

Optical transmission: Discs 14/09/2018 Uppsala University 25

Optical transmission: Thick rings 14/09/2018 Uppsala University 26

Optical transmission: Thin rings 14/09/2018 Uppsala University 27

Optical transmission: Broken rings 14/09/2018 Uppsala University 28