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Surface Engineering Nanostructures Low energy Ion bombardment nanostructuring Process Fernando Alvarez Instituto de Física "Gleb Wataghin", Unicamp, 13083-970, Campinas, SP, Brazil Collaborators M. Morales, E. A. Ochoa, S. Cucatti, R. Droppa, R. B. Merlo Equipamentos e Processos Equipamentos e Processos

Engenharia de nanoestruturas de superfície

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Arquivo do seminário apresentado pelo professor Fernando Alvarez, pesquisador da seção Unicamp do Instituto Nacional de Engenharia de Superfícies, no dia 20 de agosto de 2013, na seção UCS do Instituto, para um público de 30 estudantes e professores de cursos de graduação e pós-graduação.

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Page 1: Engenharia de nanoestruturas de superfície

Surface Engineering Nanostructures

Low energy Ion bombardment nanostructuring Process

Fernando Alvarez

Instituto de Física "Gleb Wataghin", Unicamp, 13083-970, Campinas, SP, Brazil

Collaborators

M. Morales, E. A. Ochoa, S. Cucatti, R. Droppa, R. B. Merlo

Equipamentos e ProcessosEquipamentos e Processos

Page 2: Engenharia de nanoestruturas de superfície

Surface Engineering Nanostructures: An Introduction

• Top Down : photo lithographic, micro-contact printing and catalyst growth, masks, writing (electron beam), molds

• Bottom Up: Surface Functionalization, Self Organized Nano-Porous Lattice, supramolecular structures (from atomic to mesosopic scales)

Self Organization by Ion Beam Treated Surfaces

a) Sculpted Substrate By Ion Beam Bombarded

b) Self – Organized Structures Obtained By Ion Sputtering

• Coclusions

Page 3: Engenharia de nanoestruturas de superfície

Flat panels (CNT-FED) Project CANADIS

Top Down Fabrication: Nanostructured Regular Patterns

Nano-Lithography (Project NANOLITH)

Cold cathode for hyper-frequency devices (> 30 GHz) Propjet CANVADS

Standard Photo-Lithography Electron Beam PatterningReactive Plasma Etching

Page 4: Engenharia de nanoestruturas de superfície

*

Carbon nanotubes grown by CVDM. Morales,et al., JPhysD., 2013, IFGW-UNICAMP

Top Down Fabrication: Nanostructured Regular

Patterns

Single Carbon nanotubes between triple-layer catalyst (Al~10 nm/Fe~1 nm!/Mo~0.2 nm) Lacerda et al. APL, 84,269, 2004

Single Carbon nanotubes between two electrodes

Tans, S., et al., Nature 394, 761–764 (1998).

Page 5: Engenharia de nanoestruturas de superfície

EDS

EDS

Bottom Up Fabrication: Mesoporous Patterned Silica

Amphiphilic: from the Greek αµφις, amphis: both and φιλíα, philia: friendships, EDS: Energy Dispersive X-ray Spectroscopy

Pm3n Cubic Symmetry

Cross Section TEM

• Mesoporous (Pm3n) films (dip coating) combining polycondensation of silicate speciesand organization of amphiphilic mesophases

• Temperature Evaporation-induced self-assembly of the mesoporous film

• Decorated with iron-based nanoparticles in iron aqueous solution (0.2M FeSO4.7H2O)

M. C. Marchi, C. Figueroa, and F. Alvarez, J. Nanosc. Nanotechn., 8, 448, 2008 , IFGW, UNICAMP

Evaporation-induced self-assembly

Page 6: Engenharia de nanoestruturas de superfície

Bottom Up Fabrication: Mesoporous Patterned Silica

J.J.S. Acuña, M.C. Marchi, C. Figueroa, F. Alvarez , Thin Solid Films 519 (2010) 214–217

• Silica Based Thin Film (Im3m) cubic symmetry

• 7 nm cavities sizes separated by ~1.8 nm walls

• CVD Carbon Nanotubes Growth

TEM-Cross Section SEM-Top ViewSEM-Top View

Page 7: Engenharia de nanoestruturas de superfície

Si

Nanotubes growth:Sequential process

Carbon nanotubes grown by CVD, M. Morales,et al., JPhysD., Submitted, 2013

IBD-TINxOy

Nickel Particles

CVD-CNTs IBD

Si

Si

+ Annealing

Barrier layer

Page 8: Engenharia de nanoestruturas de superfície

TiNx Buffer Layers Thin Films Preparation

� 500°C

Sputtering

gun

Turbo

pump

XPS

IBD-TINxOy

� H2 Flux 0,1,2,3,4 sccm

Oxygen Containing Control

Si

Carbon nanotubes grown by CVD, M. Morales,et al., JPhysD., Submitted, 2013

Page 9: Engenharia de nanoestruturas de superfície

Si

Catalyst Ni Particles: Ion Beam

Deposition

Sputtering

gun

Turbo

pump

XPS

Nickel Particles

� 750°C

� 1.5 min deposition

� 5 min annealing

Carbon nanotubes grown by CVD, M. Morales,et al., JPhysD., Submitted, 2013

Page 10: Engenharia de nanoestruturas de superfície

CNTs analysis

6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5

20

40

60

80

100

0612 18 24

[H2]/[N2+Ar], %

Nu

mb

er

of

CN

Ts

/ µµ µµm

2

Oxygen Concentration, at.%6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5

26

28

30

32

34

36

38

D

iam

ete

r M

od

e C

NT

s (

nm

)Oxygen Concentration, at.%

06

[H2]/[N2+Ar], %12 18 24

•Carbon nanotubes grown by CVD, M. Morales,et al., JPhysD., Submitted, 2013

Page 11: Engenharia de nanoestruturas de superfície

CNTs results

O in the film

Carbon nanotubes grown by CVD, M. Morales,et al., JPhysD., Submitted, 2013

Page 12: Engenharia de nanoestruturas de superfície

CNTs analysis

12

6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5

20

40

60

80

100

0612 18 24

[H2]/[N2+Ar], %

Nu

mb

er

of

CN

Ts

/ µµ µµm

2

Oxygen Concentration, at.%

Oxygen

Presence

Inhibit

Ostwald

ripening

6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5

26

28

30

32

34

36

38

D

iam

ete

r M

od

e C

NT

s (

nm

)Oxygen Concentration, at.%

06

[H2]/[N2+Ar], %12 18 24

Original

Number

particles

Smaller

Si

TiNxOy

NiNi

Si

TiNxOy

NiSmaller ΦΦΦΦ

CNTs

More

Density CNTs

Ostwald

ripening

Page 13: Engenharia de nanoestruturas de superfície

1W. K. Burton, N. Cabrera and F. C. Frank, Royal Soc., 243, 1950; D. Walton in Nucleation, Edited by A. Z. Zettlemoyer, Marcel Dekker, INC. NY, 1969; W. K. Burton , N. Cabrera. And F. C, Frank, Phil. Trans. Roy Soc., London, A243, 302, 1951

Surface Structuring: a brief introduction

• Atoms deposited from the vapor phase

• Self-Organizing: Mean Way between kinetic and thermodynamic phenomenon (non-equilibrium)

• Surface diffusion on a flat surface (terrace): primary mechanism (activated process)

• Mean displacement adatom λλλλ: distance before remains immobilized or detaching to the vapor1

λλλλ=λλλλ0exp [ (εεεεs-us)/2kT]

εεεεs : evaporation energies (from the surface to the vapor phase)

us : jumping activation energy between two neighboring equilibrium positions distant λλλλ0 each other

λλλλ

Jumping

Detaching

F

• D/F>>1 Process Governed by Thermodynamic

(Near Equilibrium)

• D/F<<1 Process Governed by Kinetic

D= Diffusion Coefficient

Page 14: Engenharia de nanoestruturas de superfície

Lagally and Zhang, nature, 417, p907, 2002

Thin Films Growth: Surface Phenomenon

Potential Barriers•Along a Terrace

Crossing

• 3D-Barrier

• 2D-Barrier

• 1D-Barrier

Ehrlich & Schwoebel Barrier

Page 15: Engenharia de nanoestruturas de superfície

Surface Structuring: Continuation• Interlayer mass transport: control vertical uniformity

• Controlled by energetic barriers at the step

Ehrlich & Schwoebel Barrier (E-S) : Scale with local coordination

Ehrlich &Schwoebel Barrier

Page 16: Engenharia de nanoestruturas de superfície

S. J. Liu et al. Appl. Phys. Lett., Vol. 80, No. 18, 6 May 2002

{111}{111}

Top View

Diffusing along the terrace

Eb~ 0.45 eV

Page 17: Engenharia de nanoestruturas de superfície

S. J. Liu et al. Appl. Phys. Lett., Vol. 80, No. 18, 6 May 2002

{111}{111}

Top View

Instability: Piling up along the terrace

Eb~ 0.45 eV

Page 18: Engenharia de nanoestruturas de superfície

Low energy Ion bombardment nanostructuring Process

Fine control Deposition Parameters

• Ion Species and Ion Energy

• Impinging Angle

• Flux (Dose)

• Beam Size

• Substrate Temperature

Page 19: Engenharia de nanoestruturas de superfície

Campinas Sky, SP, Brazil

Snow Ripples

Las Leñas, Argentina

Atacama Desert, Chile

Ion Beam Sputtering

Si (110) Xe, 1keV, PerpendicularMorales, Merlo, Droppa, and Alvarez, 2013. DFA, IFGW, UNICAMP

Page 20: Engenharia de nanoestruturas de superfície

Topography Accident: Sand and Snow

Sand(Snow) Dunes: At the hill or depression, Different Velocities

Clouds: ripples between the dry, cool air above and the moist, warm air below

Less Velocity

Αννννεµος: Wind God

Page 21: Engenharia de nanoestruturas de superfície

Nano-Structures on Gallium Antimonide: Ar+ Ion Sputtering

Facsko et al., Science 285,1999, p1551

Hexagonal Symmetry

4x1017 cm-2, 40 s 2x1018 cm-2, 200 s 4x1018 cm-2, 200 s

500nm 500nm 500nm

GaSb

Fluences:5.2x1031/nm2;Tempo: 90 min and λλλλ=37–43 nm

Au

ΘΘΘΘ~730Dual Ion Beam Sputtering, 2keV

Page 22: Engenharia de nanoestruturas de superfície

Xe+ Patterning: Experiment

Cucatti & Alvarez, PSE 201222

•Substrate

•Ion gun

•Turbo•pump

Material: SS 316, Policrystal (austenite)

XPS

Page 23: Engenharia de nanoestruturas de superfície

Xe+ Patterning

Fixed parameters:• Room temperature (~25ºC)

• Time: 30 min

• Energy: 1 KeV

• Current density: 0.37 mA/cm²

• Power: 0.4W/cm²

• Dosis: 2.2 x 1018

• Working pressure: 1.4 x 10-3 mbar

•23 •PSE 2012 S. Cucatti Sep 12

� Different impinging angles

β = 0º, 15º, 30º, 45º, 60º

Austenitic Stainless Steel 316LMirror-polished samples (roughness < 1.5 nm)

Page 24: Engenharia de nanoestruturas de superfície

Xe+ Bombardment (SS 316L)

β =15º β = 45º β = 60º

Patterns depend on crystalline orientation

Diffusion regime: time to reach equilibriumCucatti , Morale, Alvarez, DFA, IFGW, UNICAMP, 2013

SEM-FEG

Page 25: Engenharia de nanoestruturas de superfície

SEM-FEG images from AISI 316L using (Xe+, 1 keV)

•25 •PSE 2012 S. Cucatti Sep 12

� Crystalline grains evidenced

� Patterns within the crystalline grains

15º

Pattern

Page 26: Engenharia de nanoestruturas de superfície

Xe+ Bombardment SS 316L- Roughness

PSE 2012 S. Cucatti Sep 12

• Competition between the diffusion and erosive regime ³

• Lower angle increasing sputtering

• Pattern: direction of the beam

Increase of impinging angle

0 15 30 45 600

5

10

15

20

25

RM

S R

ou

gh

nes

s (

nm

)

Impinging angle ββββ (degrees)

Only polished (<1.5 nm)

•[3U. Valbusa, C. Boragno, F. Buatier de Mongeot, J. Phys.: Condens. Matter 14 (2002) 8153-8175

Page 27: Engenharia de nanoestruturas de superfície

Patterning effect on nitrogen diffusion

New Nitrided Phase

Small Precipitated

Needle Precipitated

Cucatti et al, DFA,IFGW,UNICAMP, 2013

Page 28: Engenharia de nanoestruturas de superfície

Bombardment Effect

Page 29: Engenharia de nanoestruturas de superfície

Experimental: Ion Beam

Energy

(nominal): 20 – 1200 eV

PO2 <10-8 mbCurrent

(nominal): ~1mA/cm2

TARGET

ION GUN 1

UHV

XPS

SUBSTRATE

T Controlled

ION GUN 2

TURBO

PUMP

NG+

Ion gun

(Kaufman)

Noble gases Bombardment (NG +): Ar +, Kr, + Xe +Noble gases Bombardment (NG +): Ar +, Kr, + Xe +

Ar, Xe+

Page 30: Engenharia de nanoestruturas de superfície

Ion-driven patterning: Bradley & Harper Model

ConvexConcave

M. Bradley and J. M. E. Harper, J. Vac. Sci. Technol. A, 6,4, 1988

Closer: More Energy in ΘΘΘΘ´ Faster Erosion

ΘΘΘΘ´

ΘΘΘΘ

Page 31: Engenharia de nanoestruturas de superfície

Ripples Wavelength: Diffusive Regimen

λλλλ=2ππππ (2K/||||vi||||)1/2

i=x,y directions and vi, the largest velocity

Erosion Regimen• Strong Sputtering preventing accommodation by diffusion

• The surface nanostructure is forced to following the direction of the ions

• Increasing roughness with impinging sputtering angles.

• The erosion is mild and diffusion “fast”

• The Ripples align along the crystalline direction (thermodynamically equilibrium)

Page 32: Engenharia de nanoestruturas de superfície

Self-organized 2-D Ni particles deposited on titanium nitride

(a) Near normal substrate ion bombardment

(b) Pattern formed after bombardment

(c) Thin film of TiNxOy on the patterned substrate

(d) Self-organized nickel particles deposited on the template

M. Morales, R. B. Merlo, R. Droppa Jr, and F. Alvarez, submitted, 2013 , IFGW, UNICAMP

Sequential steps in the growing process of the nickel particles self-assembling

Page 33: Engenharia de nanoestruturas de superfície

Near normal substrate ion bombardment

Page 34: Engenharia de nanoestruturas de superfície

TiN Deposition: Ion Beam Deposition

Sputtering

gun

Turbo

pump

XPS

Carbon nanotubes grown by CVD, M. Morales,et al., JPhysD., Submitted, 2013

N2

Page 35: Engenharia de nanoestruturas de superfície

The original pattern is conserved

Sculpted Si Perpendicularly Xe+ beam TiNxOy coated on sculpted Si

Patterned Si Substrate + Coating

Page 36: Engenharia de nanoestruturas de superfície

TiN + Ni Particles Ion Beam Deposition

Sputtering

gun

Turbo

pump

XPS

Carbon nanotubes grown by CVD, M. Morales,et al., JPhysD., Submitted, 2013

Si

Nickel Particles

� 750°C

� 1.5 min deposition

� 5 min annealing

Page 37: Engenharia de nanoestruturas de superfície

•Self-organized 2-D Ni arrange

•Lattice constant of a x b

2-Fold Symmetry

ππππ

ππππ

+

Page 38: Engenharia de nanoestruturas de superfície

AFM Image

• Lattice constants: |a|≈171 nm, |b|≈184 nm, 690

• Defects: missing row (“edge dislocations”)

Page 39: Engenharia de nanoestruturas de superfície

Adatoms: diffusion and coalescence

•The Ni particles diffuse on the surface until incorporated at a nucleation center.

•Adatoms diffuse a mean displacement λλλλ constrained to move on the crest due to the Ehrlich-Shhwoebel barrier,

λλλλ= λλλλ0 exp [ (εεεεs-us)/2kT]

εεεεs Evaporation energies from the surface to the vapor phase

us Jumping energy between two equilibrium positions distant λλλλ0 each other

•The adatom diffuses along the top of the hill until meeting a second atom

• A particle sink and depleted surrounding neighborhood start.

Page 40: Engenharia de nanoestruturas de superfície

S. J. Liu et al. Appl. Phys. Lett., Vol. 80, No. 18, 6 May 2002

{111}{111}

Top View

Instability: Piling up along the terrace

Eb~ 0.45 eV

Page 41: Engenharia de nanoestruturas de superfície

Ehrlich-Shhwoebel (E-S) barrier

λλλλ

Self - Organization

Page 42: Engenharia de nanoestruturas de superfície

Conclusions• Process generating organized nanostructures: top down, bottom up and

ion driven

• Different possibilities generating nanostructures by bombarding

• Ion driven patterning can generate regular patterns

• Self-organized metallic nano-particles on coated patterned silicon

• Self-organization: Irregularities still important (Improving process necessary)

• Lack of general theoretical understanding of the general process

of self-organization