Bimodal growth mode of Fe/ cc(110) ; cc=(W,Mo) Application to the - PowerPoint PPT Presentation

Bimodal growth mode of Fe/ cc(110) ; cc=(W,Mo) Application to the self-organization of thick stripes O.Fruchart, Laboratoire Louis Néel (CNRS), Grenoble I CCG1 4 – Aug. 2 0 0 4 Laboratoire Laboratoire Louis Néel. Louis Néel. Laboratoire Louis Néel. http:/ / lab http:/ / lab- neel.grenoble.cnrs.fr/ them es/ couches/ ext/ neel.grenoble.cnrs.fr/ them es/ couches/ ext/ http:/ / lab- neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Outline Evidence for bim odal grow th Application to self-organized thick stripes Extend versatility of self-assem bly Discussion of results from the literature Olivier Fruchart – ICCG14 – Aug. 2004 – p.2 Laboratoire Laboratoire Louis Néel Louis Néel Laboratoire Louis Néel http:/ / lab http:/ / lab- neel.grenoble.cnrs.fr/ them es/ couches/ ext/ neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Growth of Fe/ W-Mo(110) systems Grow th processes • Motivation : model system for 2D magnetism (no alloying, pseudomorphic, layer-by-layer) • Grow th : • Pseudomorphic 1st layer, then Stranski-Krastanov • Kinetic roughness along [ 001] at room temperature • Progressive increase of temperature for flat films • Dots at high temperature • Substrate : quanlitatively (if not quantitatively) similar results for W(110) and Mo(110). Self- organization • Step-decoration of vicinal surfaces: 0.5ML, 1.5ML. Curie temperature < 300K Key references • Pioneering : Gradmann82, Tikhov-Bauer90 • Follow ing : Elm ers-Gradmann90, Albrecht-Gradmann93, Bethge95 • Stripes : Hauschild-Gradmann98, Bode-Wiesendanger00 Olivier Fruchart – ICCG14 – Aug. 2004 – p.3 Laboratoire Louis Néel Laboratoire Louis Néel Laboratoire Louis Néel http:/ / lab- neel.grenoble.cnrs.fr/ them es/ couches/ ext/ http:/ / lab neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Fe/ Mo(110) – the surface Ex-situ AFM P ULSED L ASER D EPOSITION, UHV 10 x 10 µ m T HE S URFACE Nd:YAG Single crystalline Mo(110) surface, Pulsed Laser with atomic steps : (110)//(11-20) cc(110) / Al 2 O 3 (11-20) 150nm-500nm Target Mo cc=Mo, W, Nb, etc. +/- 0.1° 1 0 nm Al 2 O 3 STM- 600x600 nm STM- 750x750 nm 45° from [001] // [001] cc(110) surface : 200nm 150nm Mo[001] Mo[1-11] Mo[1-10] Buffer layer growth : O. Fruchart, S. Jaren, J. Rothm an, Appl. Surf. Sci. 1 3 5 , 2 1 8 ( 1 9 9 8 ) MBE versus PLD : J. .Shen et al., Surf. Sci. Rep., 5 2 , 1 6 3 ( 2 0 0 4 ) Olivier Fruchart – ICCG14 – Aug. 2004 – p.6 Laboratoire Louis Néel Laboratoire Louis Néel Laboratoire Louis Néel http:/ / lab- neel.grenoble.cnrs.fr/ them es/ couches/ ext/ http:/ / lab neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Fe/ Mo(110) – bimodal growth ? [1-10] (110) [1-10] (110) e nom = 0.7 nm ~ 3.5ML 50% Vol. 3D [001] [001] Ts = 700K Fe h=1.2nm Flat Mo(110) 50% Vol. AFM, 3 µ m x 2.8 µ m Bimodal Stranski-Krastanov growth e nom = 8 nm ~ 40ML 8nm 3D 90% Vol. 8 Volume per unit 3D 6 surface (nm) 0.7nm 4 h=1.2nm 2 Flat Flat 10% Vol. 0 AFM, 3.6 µ m x 3.6 µ m 0 2 4 6 8 Mean coverage (nm) P.- O.Jubert et al. , JMMM 2 2 6 , 1 8 4 2 ( 2 0 0 1 ) P.- O.Jubert et al. , PRB6 4 , 1 1 5 4 1 9 ( 2 0 0 2 ) Olivier Fruchart – ICCG14 – Aug. 2004 – p.9 Laboratoire Louis Néel Laboratoire Louis Néel Laboratoire Louis Néel http:/ / lab- neel.grenoble.cnrs.fr/ them es/ couches/ ext/ http:/ / lab neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Self-assembly : shape of dots W ulff’s theorem W ulff Kaishev’s theorem Free crystal Supported crystal (growth on surfaces) γ i γ i h i h i h int h j γ j No facets with high surface energy Truncated crystal Olivier Fruchart – ICCG14 – Aug. 2004 – p.10 Laboratoire Louis Néel Laboratoire Louis Néel Laboratoire Louis Néel http:/ / lab- neel.grenoble.cnrs.fr/ them es/ couches/ ext/ http:/ / lab neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Self-assembly – more versatility Based on Wulff’s construction I nterface energy deduced from m easurem ents 0.5 0.4 3 Vertical ratio η = H / W Lateral ratio r = L / W 0.3 2 0.2 w Mo 1 0.1 0 0.0 0.0 0.5 1.0 1.5 -2 ) − 2 Interfacial energy (J.m − = ± ( Fe Mo ) 0 . 65 0 . 15 J.m E int − 2 − = ± ( Fe W ) 0 . 15 0 . 1 J.m E int Micron -size dots: Includes interfacial dislocation energy � Effective interface energy Olivier Fruchart – ICCG14 – Aug. 2004 – p.11 Laboratoire Louis Néel Laboratoire Louis Néel Laboratoire Louis Néel http:/ / lab- neel.grenoble.cnrs.fr/ them es/ couches/ ext/ http:/ / lab neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Fe/ Mo(110) – metastable critical thickness 25°C growth + 450°C Annealing - Ex-situ AFM 2.5AL, 5 x 5 µ m 3AL, 5 x 5 µ m 3.75AL, 5 x 5 µ m 5.75AL, 5 x 5 µ m 6.5AL, 10 x 10 µ m 7.25AL, 10 x 10 µ m 8.25AL, 10 x 10 µ m � t<7AL : 7AL metastable patches � t>7AL : patches are ‘sucked’ � 3D dots more stable than 7AL patches. Olivier Fruchart – ICCG14 – Aug. 2004 – p.12 Laboratoire Louis Néel Laboratoire Louis Néel Laboratoire Louis Néel http:/ / lab- neel.grenoble.cnrs.fr/ them es/ couches/ ext/ http:/ / lab neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Fe/ Mo(110) – why stripe nucleation along steps ? Step 1 : layer-by-layer grow th at 1 5 0 ° C ~ 2AL ~ 2.5AL ~ 3.25AL Fe films grown at 150°C STM, 600nm x 600nm Step 2 : annealing at 5 0 0 ° C -- > stripes along steps STM, 750nm x 750nm Fe Mo Al 2 O 3 O. Fruchart et al. , APL 8 4 , 1 3 3 5 ( 2 0 0 4 ) Olivier Fruchart – ICCG14 – Aug. 2004 – p.13 Laboratoire Louis Néel Laboratoire Louis Néel Laboratoire Louis Néel http:/ / lab- neel.grenoble.cnrs.fr/ them es/ couches/ ext/ http:/ / lab neel.grenoble.cnrs.fr/ them es/ couches/ ext/

1nm-thick stripes – orientation Fe[ 0 0 1 ] 3.5x3.5 µ m 10x10 µ m 5x5 µ m Fe[ 1 - 1 0 ] (Slightly too high temperature for this sample… ) � 7ML stripes (instead of 1-2ML usually) � Tunable orientation � To be optimized for better quality Olivier Fruchart – ICCG14 – Aug. 2004 – p.14 Laboratoire Louis Néel Laboratoire Louis Néel Laboratoire Louis Néel http:/ / lab- neel.grenoble.cnrs.fr/ them es/ couches/ ext/ http:/ / lab neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Fe(110) stripes – stripes with increased height Sapphire\ W ( 8 nm ) \ Fe( 1 5 0 ° C + 4 5 0 ° C annealing) [ 1.8nm ] [ 1.2nm ] [ 3.0nm ] [ 2.4nm ] Stripe = 4.0nm Stripe height = 5.5nm Stripe height = 5.5nm Stripe = 5.0nm � Stripes for Fe/W(110) � Increased height : 5.5nm (significant advancement compared with existing literature) Olivier Fruchart – ICCG14 – Aug. 2004 – p.15 Laboratoire Louis Néel Laboratoire Louis Néel Laboratoire Louis Néel http:/ / lab- neel.grenoble.cnrs.fr/ them es/ couches/ ext/ http:/ / lab neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Fe(110) stripes – stripes remanence and coercivity at 300K Coercivity and rem anence at 3 0 0 K Sapphire \ W \ Fe(3nm) \ Mo 1.0 10 µ m 100 K 200 K 0.5 300 K H//[001] M/M s 0.0 [1-10] -0.5 -1.0 -100 0 100 Applied field (mT) [001] 1.0 100 K 200 K 0.5 300 K H//[1-10] 0.0 M/M s � Coercivity and high remanence at 300K -0.5 � Weak temperature dependence > behaves like a conventional material -1.0 -100 0 100 Applied field (mT) O. Fruchart et al. , APL 8 4 , 1 3 3 5 ( 2 0 0 4 ) Olivier Fruchart – ICCG14 – Aug. 2004 – p.16 Laboratoire Louis Néel Laboratoire Louis Néel Laboratoire Louis Néel http:/ / lab- neel.grenoble.cnrs.fr/ them es/ couches/ ext/ http:/ / lab neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Fe(110) stripes – other systems for thick stripes ? STM, 80x70 nm 3 ML Fe 65 Ni 35 / Cu(111)-vic 1.2° � Grooves along steps General phenomenon that may be exploited ? S. Cherifi et al. , PRB 6 4 ( 2 0 0 1 ) 1 8 4 4 0 5 Olivier Fruchart – ICCG14 – Aug. 2004 – p.19 Laboratoire Louis Néel Laboratoire Louis Néel Laboratoire Louis Néel http:/ / lab http:/ / lab- neel.grenoble.cnrs.fr/ them es/ couches/ ext/ neel.grenoble.cnrs.fr/ them es/ couches/ ext/

Explaining the magical height Quantum confinem ent Evidence for ‘magic’ heights have been reported for several syst ems: Pb/ Cu( 1 1 1 ) : 6,8,11,15,17,20 ML. R. Otero et al., PRB6 6 , 1 1 5 4 0 1 ( 2 0 0 2 ) Ag/ GaAs : A.R. Smith et al., Science 2 7 3 , 2 2 6 ( 1 9 9 6 ) Ag/ Si( 1 1 1 ) : L. Gavioli et al., Phys. Rev. Lett. 8 2 , 1 2 9 ( 1 9 9 9 ) L. Huang et al., Surf. Sci. 4 1 6 , L1 1 0 1 ( 1 9 9 8 ) Pb/ Si( 1 1 1 ) : V. Yeh et al., Phys. Rev. Lett. 8 5 , 5 1 5 8 ( 2 0 0 0 ) W . B. Su et al., Phys. Rev. Lett. 8 6 , 5 1 1 6 ( 2 0 0 1 ) Au/ Fe( 0 0 1 ) : 5ML, D. A. Luh et al., Science 2 9 2 , 1 1 3 1 ( 2 0 0 1 ) However, several magical heights would be expected… � Under investigation Olivier Fruchart – ICCG14 – Aug. 2004 – p.20 Laboratoire Louis Néel Laboratoire Louis Néel Laboratoire Louis Néel http:/ / lab- neel.grenoble.cnrs.fr/ them es/ couches/ ext/ http:/ / lab neel.grenoble.cnrs.fr/ them es/ couches/ ext/