Growth and Characterization of Co nanoparticles and nanowires 劉全璞國立成功大學材料科學及工程學系半導體奈米材料實驗室

Outline 1.Introduction : Nanoparticle; nanowire; and PVD 2.Co nanoparticle by magnetron sputtering 3.Co nanoparticle and nanotube by ion-beam deposition 4.Conclusions

Traditional PVDs for nanopaticle fabrication Clusters by free jet expansion Nanoparticle by low temperature deposition Quantum dot by epitaxial growth

Clusters by free jet expansion

Nanoparticle by low temperature deposition

Quantum dot by epitaxial growth Stranski-Krastanow growth mode What happen when together? Shape evolution

Traditional VLS for nanowire growth

Objectives Si substrate native SiO 2 Co nanoparticles These can be used for catalysts. Various types of CNT can be grown.

(a)(b)(c) (d) (e) (f) Deposition distance vs surface morphology AFM P W = 8 mtorr 、 P DC = 50 W 、 V bias = -100 V 、 t D = 10 sec 60mm70mm80mm 90mm100mm110mm Size =60-120nmSize = nm Size = nm

-50V (b) 0V (c) +250V (d) +525V (e) 0 nm 17.5 nm 35 nm -100V (a) 500 nm Substrate bias vs surface morphology AFM P W = 8 mtorr 、 P DC = 50 W 、 D T, Sub = 110 mm 、 t D = 10 sec

(b) Substrate bias vs size and height

Substrate bias vs island density positive V bias obvious particles uniform distribution

1μm100 nm Substrate bias vs surface morphology SEM plan view -100V -50V +250V

20 nm fcc structure BF DF Substrate bias vs nanoparticle microstructure TEM plan view

20 nm 100 nm 40 nm Substrate bias vs nanoparticle microstructure TEM cross sectionV sub = +250 V

Substrate bias – nanoparticle growth mechanism Coulomb force self-limited growth deposition e-e- e-e- crevice filling SiO 2 Si substrate repulsion deposition e-e- e-e- repulsion SiO 2 Si substrate island growth Si substrate deposition e-e- e-e- SiO 2

-100 V -50 V +525 V +250 V 0 V Substrate bias vs nanoparticle magnetic property

Growth time vs surface morphology AFM P W = 8 mtorr 、 P DC = 50 W 、 D T, Sub = 110 mm 、 t D = 10 sec 、 Vsub = +525 V (a) 20.1 ML (b) 39.8 ML (c) 59.6 ML 10 sec 20 sec30 sec

(a) 20 nm (b) 20 nm (a) 100 nm (c) 50 nm (b) 100 nm 20 sec fcc 30 sec fcc Growth time vs nanoparticle microstructure TEM cross sectionV sub = +250 V

1 ： ANODE grid 2 ： A/D grid 3 ： Ground grid solenoid coil P waveguide gas ECR zone E θ target water cooling Cu backing plate resputtered atom sputtered atom fast Ar substrate sputter voltage (positive bias) Mechanism of ion beam deposition

Co nanoparticle and wire by ion beam deposition SEM 2sec 、 RT2sec 、 400 ℃ ( c )( d ) 2sec 、 950 ℃

10 12 cm cm -2 5*10 8 cm -2 Co nanoparticle with various density

Co nanowire growth by ion beam deposition AFM 0.5  m Nucleation of Cobalt silicide nanowire On Si(001) 0.5  m Cobalt magnetic quantum dots on Si(001)

100nm Co nanowire growth by ion beam deposition TEM

Conclusions Nanoparticle can be formed under negative bias at suitable conditions, however, damaged. Due to Coulomb force self-limited growth, Co nanoparticle is of very uniform distribution without obvious damage. Co nanoparticle as small as 10nm can be prepared by sputtering and exhibit superparamagnetic property

Conclusions By IBS, the Co dot density can be varied by 1000 with very uniform size distribution EPitaxial Cobalt silicide nanowire can be fabricated by IBS

Acknowledgements 1.Students : 鍾秉憲 ; 王志欽 2. 國科會 NSC E