effect of surface preparation of copper on self-assembly
TRANSCRIPT
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Effect of Surface Preparation of Copper on Self-Assembly of Fullerene Molecules
Dongni Ma, Selene Sandoval, Krishna Muralidharan, Srini Raghavan
University of Arizona
Department of Materials Science and Engineering Department of Chemical and Environmental Engineering
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Objective
• Effect of surface preparation of copper on: Substrate mediated controllable self-assembly of fullerene rods
C60 buckyball C60 nano-rods
Ultimately enable high-aspect ratio molecular C60 wires as interconnects
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Background:
Conventional Methods for Fullerene Nanostructures
Template based self-assembly: longer processing time, expensive and broken nanotubes obtained—Porous alumina template to be infiltrated by fullerene solution.
Conventional synthesis techniques
Liquid-Liquid Interfacial Precipitation (LLIP): time consuming (a few hours - two weeks)—no substrate needed.
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Background: Surface mediated synthesis
Directed Air Stream: leads to fullerene rods
Self-assemblies size:
Length: ~2 µm
Width: ~500-700 nm
C60 dissolved in Toluene
2 psig
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Current Method: Spin coating based substrate mediated route
Substrates Solution Spin coating procedure Spin coating RPM
Cold rolled Cu
Fullerene dispersed in
Toluene (2mg/ml)
Repeated 1-4 procedure for total of 4 times.
200-500 RPMAnnealed Cu
Electropolished Cu
Graphene coated Cu
Overall processing
time: < 10 minutes
for one substrate of
size 𝟏 𝒄𝒎𝟐. 1) Dispense
2) Waiting
time
3) Ramp-up
spreading
4) 30 seconds
RPM. Drying
2. Wait for 1 minute.3. Spin substrate at a predetermined RPM.4. Spin for 30 seconds.
1. Dispense solution.
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Substrate Preparation
Cold rolled Cu (Contact angle of 72°)
Annealed Cu (Contact angle of 64°)
Graphene on Cu(Contact angle of 80°)
Electropolished Cu(Contact angle of 72°)
Organic impurities removal: IPA rinsed, DI water rinsed, and blown dry with nitrogen.
Annealed in a tube furnace (Lindberg Blue M) for 2 hours at 1050°C.
Graphene on Cu via chemical vapor deposition (CVD).
Acetic acid treatment:1) Immersed in 2M acetic acid solution at 60°C for 10 min. 2) DI water rinsed and blown dry with nitrogen.
Electropolishing procedure shown on next slide.
Copper foil (0.25 mm thick, 99.99% metals basis, Alfa Aesar Puratronic®)
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Preparation of Substrates: Electropolishing Procedure
Solution: 85% phosphoric acid.
Applied a constant potential of 1.5 V vs. SCE for 1 hour.
0 10 20 30 40 50 600
20
40
60
80
100
OCP:0.018 V
Three-electrode system
Working electrode: Cu
Counter electrode: Pt foil
Reference electrode: SCE (sat'd KCl)
Cu (250 m thickness)
Cu
rre
nt
de
nsity (
mA
/cm
2)
Time (min)
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Graphene grown via chemical vapor deposition (CVD)
CVD grown graphene shows characteristic ripple structure.
Raman
G
2D
CVD conditions: Pressure of 200 mTorrTemperature of 1050°C100 sccm Argon60 sccm Hydrogen20 sccm Methane
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SURFACE CHARACTERIZATION
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Cold rolled Cu (surface roughness rms : 15.5nm)
Electropolished Cu (surface roughness rms: 4.7nm)
Surface Roughness of
Cold Rolled Cu and Electropolished Cu
an AFM Analysis
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Surface Roughness of
Annealed Cu and Graphene Coated Cu
an AFM Analysis
Graphene Coated Cu (surface roughness rms: 41.5nm)
Annealed Cu (surface roughness rms: 53.3nm)
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Results and discussion
Substrates Solution
Cold rolled Cu
Fullerene dispersed in Toluene
(2mg/ml)
Annealed Cu
Electropolished Cu
Graphene coated Cu
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Uniform distribution of Rod-like C60 Self-Assemblies on
Cold Rolled Cu Substrate
Good control over size
and morphology of
fullerene rods at lower
rpm (next slide). Average length of fullerene self-assemblies (FSA) at 200 rpm: ~5 µm.
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Size Analysis : Projected Area and Length Distributions
of C60 rods on Cold Rolled Cu Substrate
0
0.02
0.04
0.06
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0.12
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Area of nanorods (µm2)
Projected Area
0
0.005
0.01
0.015
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0.025
0.03
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Area of nanorods (µm2)
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Length of nanorods (µm)
Length
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Length of nanorods (µm)
200 rpm 200 rpm
500 rpm 500 rpm
Best distribution of rods at 200 rpm.
Average length of fullerene self-assemblies at 200 rpm is ~5 µm.
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Results and discussions
Substrates Solution
Cold rolled Cu
Fullerene dispersed in Toluene
(2mg/ml)Annealed Cu
Electropolished Cu
Graphene coated Cu
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C60 Self-Assemblies on Annealed Cu Substrate:
larger variations in size and morphology
Less control over size and
morphology of fullerene rods at lower rpm.
Average length of FSA is ~5 µm.
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0
0.005
0.01
0.015
0.02
0 50 100 150 200 250
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Area of nanorods (µm2)
Projected Area
0
0.02
0.04
0.06
0.08
0.1
0.12
0 50 100 150 200 250
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Area of nanorods (µm2)
200 rpm
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0 10 20 30 40P
rob
abil
ity D
ensi
tyLength of nanorods (µm)
Length
0
0.05
0.1
0.15
0.2
0.25
0 10 20 30 40
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Length of nanorods (µm)
200 rpm
Size Analysis: Projected Area and Length Distribution of
C60 self-assemblies on Annealed Cu Substrate
500 rpm 500 rpm
Poor distribution at low and high spinning speeds.
Average length of 5 µm and projected area of 18 µm2 at 200 rpm.
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Results and discussions
Substrates Solution
Cold rolled Cu
Fullerene dispersed in Toluene
(2mg/ml)
Annealed Cu
Graphene coated Cu
Electropolished Cu
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C60 rods on Graphene Coated Cu Substrate:
Two distinct morphologies
Good control over distribution
and morphology of fullerene
nanorods at 200 rpm. average length ~ 5 µm.
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0
0.02
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0.06
0.08
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0.14
0 10 20
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Length (µm)
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0 20 40
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Area of nanorods (µm2)
Size distribution of larger rods: Projected Area and Length
Distribution on Graphene Coated Cu Substrate
Projected area of 10 µm2 with length of 5 µm.
200 rpm200 rpm
Projected Area Length
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Results and discussions
Substrates Solution
Cold rolled Cu
Fullerene dispersed in Toluene
(2mg/ml)Annealed Cu
Graphene coated Cu
Electropolished Cu
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Highly controllable synthesis of C60 rods on
Electropolished Cu Substrate
Excellent control over size
and morphology of fullerene nanorods at lower rpm.
Length of rod : ~10 µm
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C60 rods on Electropolished Cu (200 rpm)
by AFM Analysis
Length of nanorods is ~14 µm with diameter of ~1.5 µm.
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Size analysis: Projected Area and Length Distribution of rods on
Electropolished Cu Substrate
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0 100 200 300 400 500
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Area of nanorods (µm2)
Projected Area
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Area of nanorods (µm2)
500 rpm
0
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0 100 200 300
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Length of nanorods (µm)
Length
200 rpm
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Length of nanorods (µm)
500 rpm
200 rpm
Best distribution and morphology of rods at 200 rpm.
Length of fullerene self-assemblies is ~10 µm.
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Distinct Nanowire bundles in areas without C60 rods on electropolished Cu
C60 self-assemblies on electropolished Cu (200 rpm).
C60 rods
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In contrast,
No well-defined nanowires in Graphene Coated Cu (200 rpm)
Areas without nanorods are not well defined as one on EP Cu substrate.
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Discussion• It has been shown from DFT calculations that surface defects on Cu as well as
graphene corrugations serve as strong adsorption sites for C60 molecules
• Well defined adsorption sites on electropolished Cu and graphene on Cu lead to more control on size, shape, morphology of C60 rods
• Bigger rods are formed via nucleation and growth during the waiting time of 1 minute prior to ramp-up spreading
• The nanowires are formed after the ramp-up as a result of ‘coalescence’ between the remaining C60 molecules
• The coalescence is initiated due to C60-C60 interaction arising as a result of spinning
• The presence of intrinsic surface defects on annealed and cold-rolled Cu leads to less control of C60 morphology
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Conclusions and Future Outlook
• A simple, wet-chemistry based spin-coating method developed for obtaining c60 rods and nanowires in a controllable fashion
• The size, shape and morphology of the C60 structures are intimately linked to the substrate on which they are formed.
• The developed method provides a new avenue to achieve high aspect ratio C60 molecular wires based interconnects as well as devices with tunable electrical properties (see next slide)
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C60 milli-rods: electrical conductivity
Polycarbonate Glass
Electrical conductivity of millimeter long C60 rods (aspect ratio = 10:1) formed from CS2 solution within a glass/polycarbonate vial
16
60
1
)(10
)(1.0
cm
cm
filmC
rod
ITO
C60 rod
Silica substrate