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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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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
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
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
*
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).
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
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
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
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
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
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
CNTs results
O in the film
Carbon nanotubes grown by CVD, M. Morales,et al., JPhysD., Submitted, 2013
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
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
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
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
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
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
Low energy Ion bombardment nanostructuring Process
Fine control Deposition Parameters
• Ion Species and Ion Energy
• Impinging Angle
• Flux (Dose)
• Beam Size
• Substrate Temperature
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
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
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
Xe+ Patterning: Experiment
Cucatti & Alvarez, PSE 201222
•Substrate
•Ion gun
•Turbo•pump
Material: SS 316, Policrystal (austenite)
XPS
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)
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
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
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
Patterning effect on nitrogen diffusion
New Nitrided Phase
Small Precipitated
Needle Precipitated
Cucatti et al, DFA,IFGW,UNICAMP, 2013
Bombardment Effect
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+
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
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)
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
Near normal substrate ion bombardment
TiN Deposition: Ion Beam Deposition
Sputtering
gun
Turbo
pump
XPS
Carbon nanotubes grown by CVD, M. Morales,et al., JPhysD., Submitted, 2013
N2
The original pattern is conserved
Sculpted Si Perpendicularly Xe+ beam TiNxOy coated on sculpted Si
Patterned Si Substrate + Coating
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
•Self-organized 2-D Ni arrange
•Lattice constant of a x b
2-Fold Symmetry
ππππ
ππππ
+
AFM Image
• Lattice constants: |a|≈171 nm, |b|≈184 nm, 690
• Defects: missing row (“edge dislocations”)
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.
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
Ehrlich-Shhwoebel (E-S) barrier
λλλλ
Self - Organization
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