Multifunctional super-flat vertically aligned-carbon nanotubes (VA ...
Graduate Category: Engineering and Technology Degree Level: PhD Abstract ID# 1230
Multifunctional super-flat vertically aligned-carbon nanotubes (VA-CNTs) film; towards high static friction, low adhesion, and applications such as a dry adhesive and a nanoparticle assembly Sanghyun Hong*, Troy Lundstrom, Ranajay Ghosh, Hamed Abdi, Ji Hao, Ashkan Vaziri, Nader Jalili and Yung Joon Jung Department of Mechanical and Industrial Engineering, Colleage of Engineering, Northeastern University, Boston MA 02115, USA * presenter
Conclusion
Abstract
Multi-functional super-flat VA-CNTs film has been fabricated by multi-step transfer processes. Unlike asgrown VA-CNTs that have a non-uniform surface, randomly entangled CNTs crust layer on top, and weak interface between CNTs and substrates, this super-flat VA-CNTs film has high friction behavior in a shear direction (the coefficient of static friction (COF) 40 under a small preloading of 0.2N/cm2 with CNTs 500µm in length), and extremely low adhesion force in a tension direction (near zero adhesion force under a preloading of 11mN/cm2 and maximum 100µm displacement in a piezo-scanner). As one of the applications, we considered a high friction brush. High static friction between CNTs and nanoparticles overcomes the adhesion between the nanoparticles and the substrate. Then nanoparticles were clearly brushed. One layer of 200nm nano-particles was successfully placed in 400nm height patterns without loss and contaminations.
In this study, we fabricated the super-flat surface of VA-CNTs which has the nanometer level flatness over a large area avoiding the densification of CNTs by the adhesive polymer fluid and random entanglements on the top layer typically found as-grown CNTs, through our transfer process. As a result, high pressure is not necessary for a uniform contact over a surface. Dry adhesive and nanoparticle cleaning applications were successfully demonstrated. This anisotropic properties, high static friction and low adhesion, have the potential applications such as an end effector for a robot, a reusable tape, MEMs, and also increasing the mobility in space 1. In order to fabricated super-flat surface the combination of continuous metal layer and viscose polymer layer were employed for our unique transfer process 2. Engineered VA-CNT surface shows ultimate static friction and zero adhesion behavior with a small loading 3. Nanoparticles were cleaned and assembled by a simple brushing of superflat VA-CNT film
Background
Sample preparation
• Different friction and adhesion forces for various applications High friction + high adhesion “adhesive” Low friction + low adhesion “separator” Low friction + high adhesion “lubricant” High friction + low adhesion “end effector”, “break pad”, “MEMs”
An example of high friction and low adhesion in nature ; Gecko foot
Vertically Aligned CNTs growth Cobalt nano-particle catalyst
C2H2 SiO2/Si wafer
Transfer process for super-flat surface
Synthesis of VA-CNTs by CVD (Chemical vapor Al/Al2O3 buffer layer deposition) method. Length control by reaction time.
CVD temperature 800°C
The optical and scanning electron microscopy (SEM) images of VA-CNTs
Schematics of the transfer process of the super-flat surface CNT film
Surface morphology change
Nanoparticle assemblies by simple brushing A 6mm × 6mm CNT forest films are observed by SEM; before, after metal deposition and transfer. SEM images of VA-CNTs; the cross-sectional view of (A,D) as grown VA-CNTs and (C,F) transferred VACNTs. Insets; optical photos in cross-sectional view.
Space b/w CNTs ; 10-15nm
As-grown VA-CNTs film has a curved surface. And initially grown CNTs grow random directions because of the low density. Deposited metal layer infused into the body and held the crust layer. This Before metal layer also played a role of protecting the body brushing from the polymer adhesive. The other side of VACNTs film has the atomic level flatness.
COF measurement setup COF of as-grown VA-CNTs
Adhesion force measurement
Fluorescence microscope image
SEM images
After brushing
(A) approach (manually)
Time (sec)
preloading COF of transferred VA-CNTs
displacement
(C)
4
3
2
approach
detached
2.25m/s 4.50m/s 9.00m/s m/s
Adhesion force (mN)
(B) Adhesion force (mN)
Results
Static friction coefficient
Contact between CNTs and a nanoparticle
1
4
PDMS transferred VA-CNTs film 3
2
1
Fadh 0
0 -1
40
60
80
Time (sec)
PDMS is represented high friction (sticky) materials.
The angle friction method for the static COF measurement. As-grown VA-CNTs broke with multiple tests, because the interface between CNTs and a growth substrate is weak. Transferred VA-CNTs film shows high COF, and close to the sticky polymer film, PDMS.
100
-60
-40
-20
0
Displacement ( m)
(A) Adhesion measurement setup, scheme of piezo device and test diagram. (B) Multiple measurements with different pulling speeds show near zero adhesion force. (C) Comparison of PDMS and transferred VA-CNTs film For the precise sensing of adhesion force, we used the piezo device. Adhesion force can be measured by bending of adhesion load cell. The time scale (s) is same meaning as the displacement (µm) in the test diagram.
20
(A) The contact behavior of VA-CNTs on both a flat surface and a 200nm diameter nanoparticle was simulated by 3DS MAX. The ways how CNTs contact the surface are similar, because CNTs are densely packed, and the spacing is just 10-15nm. The generated static friction force between CNTs and a nanoparticle overcame the adhesion force between a nanoparticle and a substrate. Then, nanoparticles stayed in VA-CNTs (H,I). On the other hand, it means the particles were cleaned on the substrate (E-G). (B-G) Dispersed 200nm fluorescence silica particles on patterned substrate assembled in the holes has 400nm depth. Super-flat surface of VA-CNTs didn’t touch the particles in the holes and just cleaned particles on top surface.
Multifunctional super-flat vertically aligned-carbon nanotubes (VA-CNTs) film; towards high static friction, low adhesion, and applications such as a dry adhesive and a nanoparticle assembly Sanghyun Hong*, Troy Lundstrom, Ranajay Ghosh, Hamed Abdi, Ji Hao, Ashkan Vaziri, Nader Jalili and Yung Joon Jung Department of Mechanical and Industrial Engineering, Colleage of Engineering, Northeastern University, Boston MA 02115, USA * presenter
Conclusion
Abstract
Multi-functional super-flat VA-CNTs film has been fabricated by multi-step transfer processes. Unlike asgrown VA-CNTs that have a non-uniform surface, randomly entangled CNTs crust layer on top, and weak interface between CNTs and substrates, this super-flat VA-CNTs film has high friction behavior in a shear direction (the coefficient of static friction (COF) 40 under a small preloading of 0.2N/cm2 with CNTs 500µm in length), and extremely low adhesion force in a tension direction (near zero adhesion force under a preloading of 11mN/cm2 and maximum 100µm displacement in a piezo-scanner). As one of the applications, we considered a high friction brush. High static friction between CNTs and nanoparticles overcomes the adhesion between the nanoparticles and the substrate. Then nanoparticles were clearly brushed. One layer of 200nm nano-particles was successfully placed in 400nm height patterns without loss and contaminations.
In this study, we fabricated the super-flat surface of VA-CNTs which has the nanometer level flatness over a large area avoiding the densification of CNTs by the adhesive polymer fluid and random entanglements on the top layer typically found as-grown CNTs, through our transfer process. As a result, high pressure is not necessary for a uniform contact over a surface. Dry adhesive and nanoparticle cleaning applications were successfully demonstrated. This anisotropic properties, high static friction and low adhesion, have the potential applications such as an end effector for a robot, a reusable tape, MEMs, and also increasing the mobility in space 1. In order to fabricated super-flat surface the combination of continuous metal layer and viscose polymer layer were employed for our unique transfer process 2. Engineered VA-CNT surface shows ultimate static friction and zero adhesion behavior with a small loading 3. Nanoparticles were cleaned and assembled by a simple brushing of superflat VA-CNT film
Background
Sample preparation
• Different friction and adhesion forces for various applications High friction + high adhesion “adhesive” Low friction + low adhesion “separator” Low friction + high adhesion “lubricant” High friction + low adhesion “end effector”, “break pad”, “MEMs”
An example of high friction and low adhesion in nature ; Gecko foot
Vertically Aligned CNTs growth Cobalt nano-particle catalyst
C2H2 SiO2/Si wafer
Transfer process for super-flat surface
Synthesis of VA-CNTs by CVD (Chemical vapor Al/Al2O3 buffer layer deposition) method. Length control by reaction time.
CVD temperature 800°C
The optical and scanning electron microscopy (SEM) images of VA-CNTs
Schematics of the transfer process of the super-flat surface CNT film
Surface morphology change
Nanoparticle assemblies by simple brushing A 6mm × 6mm CNT forest films are observed by SEM; before, after metal deposition and transfer. SEM images of VA-CNTs; the cross-sectional view of (A,D) as grown VA-CNTs and (C,F) transferred VACNTs. Insets; optical photos in cross-sectional view.
Space b/w CNTs ; 10-15nm
As-grown VA-CNTs film has a curved surface. And initially grown CNTs grow random directions because of the low density. Deposited metal layer infused into the body and held the crust layer. This Before metal layer also played a role of protecting the body brushing from the polymer adhesive. The other side of VACNTs film has the atomic level flatness.
COF measurement setup COF of as-grown VA-CNTs
Adhesion force measurement
Fluorescence microscope image
SEM images
After brushing
(A) approach (manually)
Time (sec)
preloading COF of transferred VA-CNTs
displacement
(C)
4
3
2
approach
detached
2.25m/s 4.50m/s 9.00m/s m/s
Adhesion force (mN)
(B) Adhesion force (mN)
Results
Static friction coefficient
Contact between CNTs and a nanoparticle
1
4
PDMS transferred VA-CNTs film 3
2
1
Fadh 0
0 -1
40
60
80
Time (sec)
PDMS is represented high friction (sticky) materials.
The angle friction method for the static COF measurement. As-grown VA-CNTs broke with multiple tests, because the interface between CNTs and a growth substrate is weak. Transferred VA-CNTs film shows high COF, and close to the sticky polymer film, PDMS.
100
-60
-40
-20
0
Displacement ( m)
(A) Adhesion measurement setup, scheme of piezo device and test diagram. (B) Multiple measurements with different pulling speeds show near zero adhesion force. (C) Comparison of PDMS and transferred VA-CNTs film For the precise sensing of adhesion force, we used the piezo device. Adhesion force can be measured by bending of adhesion load cell. The time scale (s) is same meaning as the displacement (µm) in the test diagram.
20
(A) The contact behavior of VA-CNTs on both a flat surface and a 200nm diameter nanoparticle was simulated by 3DS MAX. The ways how CNTs contact the surface are similar, because CNTs are densely packed, and the spacing is just 10-15nm. The generated static friction force between CNTs and a nanoparticle overcame the adhesion force between a nanoparticle and a substrate. Then, nanoparticles stayed in VA-CNTs (H,I). On the other hand, it means the particles were cleaned on the substrate (E-G). (B-G) Dispersed 200nm fluorescence silica particles on patterned substrate assembled in the holes has 400nm depth. Super-flat surface of VA-CNTs didn’t touch the particles in the holes and just cleaned particles on top surface.
