Multifunctional Hybrid Nanocrystal-Carbon Nanotube Structures :Junhong Chen Multifunctional Hybrid Nanocrystal-Carbon Nanotube Structures Junhong Chen, Associate Professor Plasma Processing and Nanotechnology Lab (PPNL) Department of Mechanical Engineering University of Wisconsin-Milwaukee July 25, 2008


Motivation :Junhong Chen Motivation Functionalization of CNTs with nanoparticles - hybrid nanostructures with enhanced functionality Guided one-dimensional assembly of nanoparticles Rich interfacial science Applications: e.g., nanomanufacturing and nanodevices


Electrostatic Force Directed Assembly (ESFDA) of NPs onto CNT Surfaces :Junhong Chen Electrostatic Force Directed Assembly (ESFDA) of NPs onto CNT Surfaces J. H. Chen and G. H. Lu, Nanotechnology 17 (12), 2891-2894, 2006.


MWCNTs before Assembly (TEM) :Junhong Chen MWCNTs before Assembly (TEM)


MWCNTs Coated with NPs (TEM) :Junhong Chen MWCNTs Coated with NPs (TEM)  Nanoparticles are assembled onto external surface of CNTs - a generic/material independent approach Ag SnO2


HRTEM Images of Coated MWCNTs (I) :Junhong Chen HRTEM Images of Coated MWCNTs (I)  Both nonagglomerated entity and crystallinity of NPs are preserved. Ag SnO2


HRTEM Images of Coated MWCNTs (II) :Junhong Chen HRTEM Images of Coated MWCNTs (II)  Lots of nanoparticles are coated on the CNT tip.  Coating CNTs with nanoparticles of multiple materials.


HRTEM Images of Coated SWCNTs :Junhong Chen HRTEM Images of Coated SWCNTs  SWCNTs can be coated with nanoparticles using the same technique.


Hybrid Nanoparticle-Nanorod-CNT Structures :Junhong Chen Hybrid Nanoparticle-Nanorod-CNT Structures Liu et al., Nanotechnology 19(26), No. 265705, 2008.


Intrinsic Nanoparticle Size Selection :Junhong Chen Intrinsic Nanoparticle Size Selection  Smaller nanoparticles with a narrower size distribution on CNTs. Before assembly After assembly SnO2


Nanoparticle Size Selection Mechanism :Junhong Chen Nanoparticle Size Selection Mechanism  NPs reaching substrate are selected through their electrical mobility.  Shorter residence time and lower electric field result in a smaller cut-off size.


Control of NP Size on CNTs by Flow :Junhong Chen Q = 5.15 lpm Control of NP Size on CNTs by Flow  Larger flow rate leads to smaller nanoparticle size on CNTs. Q = 2.15 lpm


Control of NP Packing Density on CNTs :Junhong Chen Control of NP Packing Density on CNTs t = 5.5 min t = 2.75 min  Nanoparticle packing density can be controlled by the assembly time.


Slide 14:Junhong Chen ESFDA of Nanocrystals onto CNT Array Lu et al., J. Phys. Chem. C. 111(48), 17919-17922, 2007.


Vertically Aligned CNT Array :Junhong Chen Vertically Aligned CNT Array  CNT diameter: ~150 nm and CNT length: ~10 μm, provided by Prof. Ren @ Boston College.


CNT Array Coated with Ag NPs :Junhong Chen CNT Array Coated with Ag NPs  Ag nanoparticles are coated onto CNT array quite uniformly.


TEM and HRTEM Images of CNT Coated with Ag Nanocrystals :Junhong Chen TEM and HRTEM Images of CNT Coated with Ag Nanocrystals  Larger and denser Ag nanocrystals close to the tip portion of the CNT.


Isolated CNT Coated with Ag NPs :Junhong Chen Isolated CNT Coated with Ag NPs  The isolated CNT is coated with NPs from tip to root.  NP packing density is higher and the particles are larger at the tip.


Electric Field Distribution near CNT :Junhong Chen Electric Field Distribution near CNT  Field enhancement monotonically increases from root to tip.  Field is much weaker for the 4-tube array due to shielding effect. Single isolated CNT Four-CNT array Root Tip


Slide 20:Junhong Chen Coating CNTs with Colloidal Nanocrystals Mao et al., Nanotechnology 19(45), No. 455610, 2008.


Slide 21:Junhong Chen CNT Coated with Colloidal CdSe QDs


Slide 22:Junhong Chen CNT Coated with Colloidal Au NCs


Slide 23:Junhong Chen XPS Spectrum of Ag NPs + MWCNT


Slide 24:Junhong Chen Cover Feature: Ripening of Silver Nanocrystals on Carbon Nanotubes Zhu et al., NANO 2(3), 149-156, 2007.


Ripening of Ag NPs :Junhong Chen Ripening of Ag NPs


Summary :Junhong Chen Summary An efficient and material-independent dry route has been developed to coat CNTs with nanoparticles. In addition to an intrinsic nanoparticle size selection, the packing density and the final nanoparticle size distribution on CNTs can be controlled during the assembly. The new method enables in-situ and multicomponent coating of CNTs with nanoparticles. Ag nanoparticle-CNT interaction: van der Waals


Acknowledgements :Junhong Chen Acknowledgements PPNL members: Dr. G. H. Lu, P. X. Wang, S. Mao, M. Liu Collaborators Prof. R. Ruoff, UT-Austin Prof. D. Dikin, Northwestern University Prof. Z. Ren, Boston College Prof. K. Kuno, University of Notre Dame UWM HRTEM Lab Prof. M. Gajdardziska-Josifovska Mr. D. Roberson UWM Advanced Analysis Facility Dr. S. Hardcastle NSF funding CBET-0604079, CMMI-0609059


Thank you! :Junhong Chen Thank you!