Complex Nanostructures by Atomic Layer Deposition. Kornelius Nielsch.

Transcription

1 Complex Nanostructures by Atomic Layer Deposition Kornelius Nielsch Institute of Applied Physics, University of Hamburg (Germany)

2 Outline History and Principle Ferromagnetic Nanostructures Low-Temperature Processes and Biomaterials Novel Synthesis Approach and Nanostructures O u

3 Outline History and Principle Ferromagnetic Nanostructures Low-Temperature Processes and Biomaterials Novel Synthesis Approach and Nanostructures O u

4 History of Atomic Layer Deposition (ALD) originally Atomic Layer Epitaxy (ALE) ALD (ALE) was developed by Dr. T. Suntola for thin film electroluminescent (TFEL) displays First Finish patent 1974 and first U.S. patent 1977 First commercial use: Flat panel display based on ZnS films (from early 1980s). Todays main use: Deposition of high-k (high dielectric constant, e.g. HfO 2 ) thin films in microelectronic industry and research

5 Atomic Layer Deposition (ALD) Chemical vapor deposition (CVD): thermal decomposition on the substrate diffusion rate-limiting Atomic layer deposition (ALD): self-limited reaction with excess reactant layer-by-layer growth

6 ALD The Principle Four stages of one ALD cycle: a) Exposure of substrate to precursor 1 adsorption b) Purge with N 2 or Ar removal of excess precursor 1 c) Exposure of substrate with precursor 2 reaction d) Purge with N 2 or Ar removal of excess precursor 2 and reaction products Non-directed deposition method

7 Applications of ALD on Nanostructures Porous Alumina Silicon Trenches SiO 2 Nanoparticles M.S. Sander et al., Adv. Mater., 16, 2052 (2004) L.F. Hakim et al., Chem. Vap. Depos. 11, 420 (2005) Carbon Nanotubes Opal Structure Review Advanced Materials D.B. Farmer et al., Nano Letters, 6, 699 (2006) Mato Knez, Kornelius Nielsch, Lauri Niinistö (HUT, Finland) Advanced Materials 19, (2007). Synthesis and Surface Engineering of Complex Nanostructures by Atomic Layer Deposition D. Hausmann et al., Science, 298, 403 (2002) Summer 2007 J.S. King et al., Appl. Phys. Lett. 88, (2006)

8 Outline History and Principle Ferromagnetic Nanostructures Low-Temperature Processes and Biomaterials Novel Synthesis Approach and Nanostructures O u

9 65 nm-period Nickel Nanowire Array Areal Density: 176 Gbit/in 2 Patterned magnetic medium with perpendicular magnetisation single domain nanomagnets achievable areal density*: 700 Gb/in 2 *hexagonal array, lattice constant 33 nm 200 nm Nanowire diameter: ~ 25 nm, column length: ~ 800 nm

10 Chemical Approaches to ALD of Iron Oxides Chemical reaction Product Temperature accessible depth organic substrates Growth rate Precursor well-defined Fe 2 O 3 low-medium 4 μm yes 0.24 Å/cycle air-sensitive from collaboration ill-defined Fe 2 O 3 + Fe 3 O 4 high? no? air-stable commercial ill-defined Fe 2 O 3 medium-high 50 μm no ~0.2 Å/cycle air-stable commercial ill-defined? low? yes 0 Å/cycle air-sensitive commercial

11 Iron Oxide Nanotubes by ALD in Porous Alumina Scale bars: 100 nm 11 nm Fe 2 O 3 in Al 2 O 3 Fe 2 (O t Bu) 6 + H C D p = 50 nm, D int = 105 nm 42 nm Fe 3 O 4, isolated tube Fe 2 (O t Bu) 6 + H C D p = 160 nm, D int = 460 nm ZrO 2 / Fe 2 O 3 / ZrO 2 in Al 2 O 3 Fe 2 (O t Bu) 6 + H C D p = 160 nm, D int = 460 nm J. Bachmann et al., JACS 129, 9554 (2007). Highlighted in

12 Iron Oxide Nanotubes by ALD in Porous Alumina J. Bachmann et al., JACS 129, 9554 (2007).

13 Magnetism of Narrow Fe 3 O 4 Tubes 300 K, H // z Oxalic template: D p = 50(±10) nm D int = 105 (±20) nm

14 Magnetism of wider Fe 3 O 4 tubes 300 K, H // z Phosphoric template: D p = 160(±20) nm D int = 460 (±50) nm

15 Questions? D p = 50 nm (d w ) opt = 14 nm D p = 160 nm (d w ) opt = 8 nm Non-monotonic behavior Origin of H c decay Position of optimum

16 Interpretation: Modes of Magnetization Reversal Landeros, Appl. Phys. Lett. 2007, 90,

17 Quantitative Theoretical Modeling Non-monotonic behavior of H c (d w ) reproduced!!! Originates from crossover btw two different reversal modes Absolute values of H c too high

18 Effect of Stray Fields Interaction of each tube with its neighbors (stray field) decreases the magnetic field it effectively experiences Consequence: lower coercivity J. Escrig et al, PRB 77, (2008).

19 ALD Prozesses for Ferromagnetic Materials 1) Direct Reduction NiCp 2 + H 2 Ni 2) 3-Step Process NiCp 2 + H 2 O + H 2 Ni 3) After ALD-Reduction NiCp 2 + H 2 O NiO NiCp 2 H 2 x times NiCp 2 x times H 2 O NiCp 2 O 3 /H 2 0 x times H 2 Very Low Deposition Rates: <20 pm / cycle Very Granular Metallic Films Low Deposition Rates: 20 to 40 pm / cycle Very Granular Metallic Films H 2 Reduction NiO Ni High Deposition Rates: 0.2 to 0.3 Å / cycle Smooth Metallic Films

20 Nickel Nanotubes by ALD Method 1: Reduction during ALD process Three Step ALD Cycle: Ni(Cp) 2, H 2 0 and H 2 Pulse Method 2: Reduction after ALD process ALD Cycle: Ni(Cp) 2 and O 3 Pulse M. Daub et al, J. Appl. Phys. 101, 09J111 (2007).

21 Magnetic Properties of Nickel Nanotubes Tube diameter: 35 nm, wall thickness: nm 2 Co Nanotubes Applied field (Oe)

22 Outlook: Multilayer (Magnetic) Nanotubes 200 nm Single-Layer Nanotube Multi-Layer Nanotube 1000 nm 25 nm TiO2 (light), 30 nm Al2O3 (dark) and 35 nm TiO2

23 Calculations on Bi-Layer Magnetic Nanotubes Detailed Investigations on the magnetic behavior of nanotubes: e.g. potential Transitions: Parallel (β < 0.2) Curling (β = ) Parallel (β >0.8) Core-shell Nanotubes and Nanowires J Escrig, D Altbir, and K Nielsch, Nanotechnology 18, (2007).

24 Outline History and Principle Ferromagnetic Nanostructures Low-Temperature Processes and Biomaterials Novel Synthesis Approach and Nanostructures O u

25 Atomic Layer Deposition (ALD) Chemical vapor deposition (CVD): thermal decomposition on the substrate diffusion rate-limiting Atomic layer deposition (ALD): self-limited reaction with excess reactant layer-by-layer growth

26 ALD on a Complex Substrate

27 ALD on a Complex Substrate

28 Summary of low Temperature Processes M. Knez, K. Nielsch and L. Niinistö, Advanced Materials 19, (2007).

29 Tobacco Mosaic Virus (TMV) Length: 300 nm outer Ø : 18 nm inner Ø : 4 nm RNA T < 80 C 2.8 < ph < 8.5 pi = 3.5 hydrophilic hydrophobic

30 TiO 2 -deposition on TMV

31 ALD on Biomaterials M. Knez et al., Nano Lett. 6, 1172 (2006).

32 Outline History and Principle Ferromagnetic Nanostructures Low-Temperature Processes and Biomaterials Novel Synthesis Approach and Nanostructures O u

33 Development of ALD Processes: SiO 2 J. Bachmann et al. Angew. Chemie( 2008).

34 Laser Interference Lithography (LIL) Mirror Substrate θ Incoming Light P = λ / 2(sinθ ) Photoresist Substrate θ λ He-Cd Laser λ= 325 nm Rotation Stage Lloyd s Mirror Spatial Filter Limits: 175 nm (HeCd Laser), 140 nm (NdYAG Laser)

35 Nanoring Arrays by IL Lithography and ALD R. Ji et al., in preparation

36 ALD and Solid State Reactions ALD Kirkendall Effect: Material A Festkörperreaktion Solid State Material B Reaction Material A/B H.J. Fan, M. Knez et al., Nature Materials. 5, 627 (2006).

37 BMBF Nanotechnology Research Group: Multifunctional Nanowires and Nanotubes Team IAP Uni Hamburg Team MPI-Halle v Christy Chong Jana Sommerlatte Jongmin Lee Ren Bin Yang Financial support by Nachwuchswettbewerb Nanotechnologie : Bundesministerium für Bildung und Forschung (BMBF) German Federal Ministry for Education and Research