Nanofabrication using anodic alumina templates. IFIMUP and IN Institute of Nanoscience and Nanotechnology

Transcription

1 Nanofabrication using anodic alumina templates João Pedro Araújo IFIMUP and IN Institute of Nanoscience and Nanotechnology

2 Outline Template based nanofabrication Nanoporous alumina templates Template filling Physical/chemical/electrochemical process Antidots IBD Nanotubes Sol-Gel Nanowires Electrodeposition

3 Ordered porous formation 1st Anodization Volume expansion of aluminium (Al atomic density is smaller in the oxide form than in the metallic form) However the vertical growth hasn't Only occurs in the metal-oxide interface, creating got mechanical yet a good stress orientation! in the alumina barrier Aluminium No order at the surface! Pores begin to appear Repulsive forces between neighbour pores emerge allowing only their vertical growth 1 µm SEM surface

4 The two step anodization process For better order: 1 st Anodization Dissolution of Oxide Layer 2 nd Anodization Al 2 O 3 Aluminium Pattern formed 1 µm Better organization! 1 µm SEM surface SEM surface

5 Nanoporous alumina templates Oxalic acid Sulfuric acid Surface D ~ 100nm d ~ 30nm D ~ 50nm d ~ 15nm Phosphoric acid D ~ 500nm d ~ 150nm Secção Cross SEM Transversal section Dint ~ 15nm 40nm Dint ~ 40nm 100nm The dimensions of the pores can be adjusted Dint ~ 100nm 200nm The ability to control the dimensions Dint ~ 15nm 200nm Thickness ~ few nm to hundreds µm

6 Growth of nanostructures in porous alumina Nanoporous alumina templates Sputtering Sol-Gel Electrodeposition Antidots (Co, NiFe ) Silica Nanotubes Complex oxide Nanotubes Nanowires (Ni, Au, NiFe )

7 1 μm 1 μm t [Py] = 6.5 nm 35 t [Py] = 17.0 nm 250 Counts t [Py] = 33.2 nm μm The push to miniaturize computational high-density magnetic storage devices Pore Diameter (nm) Antidots (Co, NiFe) NiFe) Pore Diameter (nm) Pore diameter ~34 nm Interpore distance~100 nm Quasi-linear D[Pore] vs t[py] dependence Above a critical thickness the pores close (60 < t < 75 nm) Py film thickness (nm) 60 70

8 Transport characterization 35 Resistance R-R 0 (Ω) t [NiFe] = 63 nm t [NiFe] = 33 nm t [NiFe] = 17 nm t [NiFe] = 6.5 nm T (K) Linear behavior at high magnetic fields Origin: blocked magnetic domains due to the strong shape anisotropy Localization-like effects below ~65K? MR(%) Longitudinal Pore Diameter (nm) Magnetoresistance Transverso T=100K MR(%) t [Py] = 6.5 nm Py film thickness (nm) H (Oe) H (Oe)

9 Oxide nanotubes 60 %Transmitance FTIR Spectra 50 SNTs 40nm SNTs 80nm SNT D=80nm SNT D=30nm W avenumber (cm ) 2. Nanoporous alumina templates - Stretching mode: OH _ 3458cm-1 SiOH _ 976cm-1 SiOSi _ 830 and 1150cm-1 -Torsional mode: in-plane bending Si-O-H _ 670cm-1 Silica Manganite H=50 Oe Thermal Treatment 3. Alumina etching (NaOH) M(emu/g) 1. Percursor gel solution Tc=240K nm T (K) 300

10 Nanowires: electrodeposition Different regimes can be observed in the Deposition potencial(t): 1 st 2 nd 3 rd st :dendrite filling occurs nd : pore filling rd :nw coming out of the pores 1 μm The deposition was left in the 3 rd regime for a considerable time to obtain a good filling uniformity. The ratio of Ni:Fe was confirmed by EDS to be 80:20.

11 Magnetic and Transport Characterization of NiFe Nanowires M / M Sat T (K) HC (Oe) Field (Oe) Strong shape anisotropy 5 K (M Sat = 2.0 memu ) 20 K (M Sat = 2.0 memu ) 100 K (M Sat = 2.0 memu 50) 200 K (M Sat = 1.8 memu ) 300 K (M Sat = 1.7 memu ) 350 K (M Sat = 1.7 memu 40) Metallic behavior(dr/dt>0) R-R 0 (Ohm) /(R 300K -R 0 )*DR/DT V, I T (K) V, I Silver paint dendrites and the small tunnel barrier did not affect our transport measurements considerably T (K) Ni NiFe

12 Work in progress Towards Single Nanowires and Spin Torque Transport measurements ina single nanowire Chemical Etching Study of pseudo-spin-valve nanowires e-beam patterning Ion Milling + Al electrode deposition (e-beam evaporator + IBD deposition) V, I Spin torque, microwave generation and phase locking V, I Ion Milling + Al electrode deposition

13 Work in progress Silica NTs for Drug delivery - OH group contents determined by FTIR Sol- Gel Drug: % Tansmitance 100 Cancer/Inflamation Norma l SNT 120 ºC SNT 220 ºC SNT 350 ºC SNT 500 ºC Wavenumbers (cm -1 ) Electrodeposition Target: Folic acid Cancer/inflammation - Surface modification for drug functionalization Funcionalization in inner surface Second funcionalization 2515cm -1 and 2915cm -1 bands of carbonil group ( CH 2 ) 500nm 500nm

14 Acknowledgments João Bessa Sousa João Guilherme Correia João Ventura Armandina Lopes Diana Leitão Célia Sousa Mariana Proença André Pereira Paulo Freitas Susana Freitas Rita Macedo José Luís Costa Lima Salette Reis Marlene Lúcio Cláudia Nunes Manuel Vazquez Kleber Pirota The end

15 Anodization in 3 different electrolytes: Sulfuric, Oxalic and Phosphoric Acid Anodizing Conditions SEM surfaces after 2 nd anodization Current Density Transients during 1 st anodization 0.3M Sulfuric 25V, 12ºC D ~ 50nm d ~ 15nm 1min 0.3M Oxalic 40V, 10ºC D ~ 100nm d ~ 30nm 3min 0.1M Phosphoric 195V, 5ºC D ~ 500nm d ~ 150nm 80min