One dimensional metal nanowire grown by physical vapor deposition

DSL DÜNNSCHICHTLABOR One dimensional metal nanowire grown by physical vapor deposition Gunther Richter Max Planck Institute for Intelligent Systems (formerly MPI for Metals Research) Stuttgart, Germany MECANO Meeting, Ecole des Mines, Paris 30 th October 2012

Acknowledgment Universität Stuttgart/MPI für Intelligente Systeme Karla Hillerich Lisa Hofacker Matthias Kolb Matthias Schamel Carola Schopf Dominic Linsler Christian Kappel Vanessa Dörlich Friderike Baras Dominic Zug Horst P. Strunk Karlsruher Institut für Technologie Wenting Huang Andreas Sedlmeyr Reiner Mönig Oliver Kraft

Overview Motivation Examples in nature Artificial metal nanowhisker: - Microstructure - Growth Nucleation site Incorporation site - Mechanical properties - Composites Summary

Motivation 2 µm 2 µm FIB cutting top-down approach PVD growth bottom-up process for nano structuring Influence of FIB machining? Andreas Schneider

Historical Whisker: hair silver

Whisker 1574 AgS_Heizent.wmv Found in: Freiberg Schwarzwald Kupferberg Joachimsthal Kongsberg As long as I am talking about silver matte, I should for the sake of the eager reader tell something that is characteristic of its nature and behaviour. First: When silver matte is cast into an ingot, and while it is still hot, it can be hammered and shaped as you wish, just like lead. And further: It is possible to cats figures or coin medals from it which look like vitreous silver. When you have cast it into funny little decorative figures, lightly cut or scratch them with a knive and hold them over a gentle charcoal fire until they get hot, whereupon silver will sprout or grow out of them very delicately just as it grows in the mineral. This is amusing and very pretty to watch. I am telling this so that anybody who would like to do this for fun and play with it some more should know how it is done.

Old reviews

Whisker 1574 Vorkommen: Freiberg Schwarzwald Kupferberg Joachimsthal Kongsberg

arteficial Whisker Substrate: Silicon wafer, Tungsten foil + 30 nm Carbon by magnetron sputtering Growth parameters: UHV (2 10-10 mbar), Metal thermal evaporation, T S ~ 60% T M Cu growth: T S = 650 C 700 C, R = 0.05 nm / s Crystal morphology: needle / prismatic, diameter 20-200 nm, Length < 300 µm Isometric Copper islands grown on a clean Silicon surface

c z a x y b Microstructure c No defects as grain boundaries or dislocations the metallic whisker are perfect single crystalline [111] [011] [101] b Copper a 1.0 nm

Nano-whisker tip x [111]

HRTEM whisker axis HRTEM investigation: e-beam axis: - no edge dislocations detectable - no screw dislocation detectable - projected side facets flat - surface oxidized - no contaminations visible on surface e-beam axis: - 6-fold symmetry - no stacking faults - misfit dislocations in Ni - no dislocations in Cu whisker - Ni/Cu core-shell structure - Ni grows epitaxial by island growth 10 nm

Crystal shape Shape: - Low indexed {111}, {100} facets for surface - Low energy Wulff shape dominates geometry

Fe Nanowhisker [100] [001] [010] Substrate: Mo foil Temperature: 800 C α-fe Surface not defined by low surface energy {110} facet

Mathematical NW lengthening model Metal flux 5 min 120 min 120 min Ruth, V & Hirth, J.P., Kinetics of diffusion-controlled whisker growth, J. Chem. Phys. 41, 3139-3149 (1964)

Time [s] Substrate surface contribution 8000 7000 6000 5000 14 12 10 4000 8 Beta 3000 6 2000 1000 0 0,0E+00 2,0E-04 4,0E-04 6,0E-04 8,0E-04 1,0E-03 1,2E-03 1,4E-03 Whisker length [m] 4 2 0 100 200 300 Whisker radius (nm) 400 500 600 5 10 15 20 Diffusion length (µm) V l (m/s) w/d (1/m 2 ) ß X (µm) 4,4E-08 6,8E+06 10,6 380 1,3E-08 1,9E+07 57,2 230 2,2E-08 3,0E+07 0,5 180 2,0E-08 7,2E+06 9,2 370 1,8E-07 9,1E+08 0,7 33 Whisker growth: - NW growth by adatom diffusion on substrate surface - direct impingement on whisker facets - Adatom incorporation: tip or root

Substrate-Whisker interface Si substrate C layer Cu x Si Ni film Ni/Cu whisker Sabine Haag

C-Film Structuring Preferred nucleation in C holes

Länge [nm] Growth mechanism I Sequence of deposition steps: 30 nm C/Si(111) 10 min deposition @ 680 C SEM analysis 2400 2300 2200 2100 2000 1900 1800 0 10 20 30 40 50 Beschichtungszeit t [min] Secondary nucleation on NW side facets island growth No lengthening deactivation of atom incorporation

Growth mechanism II 50 nm Au colloids deposited by spin coating Artificial nucleation site 30 nm deposition steps @ 680 C Lengthening and structure rotation Incorporation site still active

Growth mechanism III TEM grid Fe-Cu-nanowhisker: 1. 180 nm Cu @ 680 C 2. 30 nm Fe @ 680 C substrate 30 nm/si(100) Miscibility gap Formation of second phase (Fe rich) at interface Nucleation and film growth on NW surface

Phenomenological growth model Suitable Substrate: - Si - metal surface Nucleation site: - Colloids - Defects in non-wetting layer Metal condensation Adatom diffusion Nucleation Nuclei growth Proto-whisker formation Nucleation and layer growth on facets Thickening Adatom incorporation at interface Lengthening

cyclic in situ bending

shear stress (GPa) y-koordinate in m bending stress (GPa) Results 8 Bending stress: - Lower limit of strength by curvature measurement - No diameter dependence Only small dislocation free volumes are tested 2 1 graphisch bestimmt berechnet (colmpare results from Bei and Pharr) Shear stress 0-2 -1 0 1 2 3 4 5 x-koordinate in m whisker axis <110> calculation of shear stress - Close to predicted value for partial dislocation (compare talk R. Mönig) 6 4 2 0 0 50 100 150 200 250 300 4 m=0.47 m=0.41 3 2 Frenkel Mckenzie diameter (nm) 1 0 0 50 100 150 200 250 300 diameter (nm)

Advanced microstructures: Au-Ag core shell structures Intensity (a.u.) A B C 10 µm 4 µm 2 µm D E E Ag L Au M 50 nm 0 1 2 3 4 5 6 Energy (kev)

Au-Ag core shell structures: Annealing A B C 10 µm 2 µm 1 µm D Measurement area and microscope type I Au Mα /I Ag Lα as deposited I Au Mα /I Ag Lα after annealing Film SEM Ag not detectable 11.9 0.5 Whisker SEM 0.4 0.1 12.2 2.8 Whisker TEM 0.5 0.1 13.9 1.3

Au(Ag)-Metallic nano-tubes - - 111-022 - 111 [011] [100] 200 nm [011] 2 nm

Tube formation: Model A B C D : Substrate and Au grain boundaries : Ag : Au Ag nano-whisker growth: - Si(100) substrate - R = 0.05 nm/s, T S = 800 C - Cooling to RT

Tube formation: Model A B C D : Substrate and Au grain boundaries : Ag : Au Au film deposition: - T S = RT no interdiffusion - R = 0.02 nm/s cube-on-cube epitaxy on Ag whisker polycrystalline Au film on substrate, columnar grains - grain diameter ~ 100 nm

Tube formation: Model A B C D : Substrate and Au grain boundaries : Ag : Au Au(Ag) nano-tube formation: - T S < 300 C activation of Ag diffusion - t = 70 h D = 2.7 10-25 m 2 /s L ~ Å D gb = 7.6 10-15 m 2 /s L gb ~ µm - Ag depletion by surface diffusion H. Mehrer, Ed., Landolt-Börnstein New Series, Group III: Crystal and Solid State Physics, Volume 26, Diffusion in Solid Metals and Alloys (Springer-Verlag Berlin 1990)

Tube formation: Model A B C D : Substrate and Au grain boundaries : Ag : Au Au(Ag) nano-tube: - wall thickness < 10 nm, length ~ 15 µm - single crystalline, dislocation free, stacking faults from wall formation - attached to substrate - no Kirkendall effect but lost-wax process H. Mehrer, Ed., Landolt-Börnstein New Series, Group III: Crystal and Solid State Physics, Volume 26, Diffusion in Solid Metals and Alloys (Springer-Verlag Berlin 1990)

Non Metal Nanowhisker Electron beam deposition of NaCl @ 250 C Evaporation of Na-Cl dimers Substrate: MgO, Al 2 O 3, Ge, W Growth direction: <100> 2 nd material deposition (e.g. V) Core shell structures without Kirkendall effect

Summary Nanowhiskers: - Unique microstructure Wulff-shape - Root growth Arrays of nanowhiskers by tuning nucleation site - 3D-substrate Advanced composites - Unique properties Theoretical mechanical strength limit reached

Acknowledgment Universität Stuttgart/MPI für Intelligente Systeme Karla Hillerich Lisa Hofacker Matthias Kolb Matthias Schamel Carola Schopf Dominic Linsler Christian Kappel Vanessa Dörlich Friderike Baras Dominic Zug Horst P. Strunk Karlsruher Institut für Technologie Wenting Huang Andreas Sedlmeyr Reiner Mönig Oliver Kraft Thank you for your attention!