Nanoscale Sciences
NEMS
TAMS
Nanocontacts
Magnetic Studies
Engineered Biomotors
Tools Research
AIMS
SEM/AFM
Nanomanipulator
3D Force Microscope
Mixing Model/Experiment
Biomedical Research
Cystic Fibrosis
Fibrin And Blood Clotting
Gene Therapy and Viruses
DNA
Cell Division
Bacterial Motility
Molecular Motors
Project Groups:
CISMM
(Computer Integrated
Systems for Microscopy
and Manipulation)
; Nanoscale Education
; NCCNM
(North Carolina
Center for Nanoscale
Materials)
TAMS : Thermally Actuated Mobile System
Nanotube Cantilever Actuator/Sensor
Cantilever Actuator/Sensor:
Bilayer cantilever is an actuator/sensor device which has two layers with different thermal stress or intrinsic stress between two materials. Depending on stress change, its curvature can be controlled. Our nanotube cantilever device uses thermal stress to bend itself.
Bilayer cantilevers became important devices in MEMS(Micro-ElectroMechanical System) because of high sensitivity in detecting several physical quantities like energy, pH as well as chemical or biological molecule, photon detector. Following continuous trend of miniaturization, cantilevers fabricated have been based on atomic force microscope tip with reactive material to target properties.
Surface stress transducer using complementary DNA fragments recognition, Fritz, 2000
It is possible to reduce the device size if we can use carbon nanotube as one of bilayer. Carbon nanotube has many promising properties. Carbon nanotube is cylindrical and hollow tube shape carbon material. If number of shell is just one it is called single-wall nanotube(SWNT). If it has several shells concentrically it is called multi-wall nanotube(MWNT). Depending on how carbon atoms are arranged with respect to tube axis, there are many kind of chiral tubes. We note mechanical and thermal properties of nanotube for cantilever. It has high resilience to mechanical strains such as bending, bending or bucking and it shows thermal expansion under temperature change.
Bending and Buckling of Nanotube, Falvo, 1997
Carbon Nanotube Actuator:
Our goals are:
- Demonstrate that Metal-MWNT cantilever can be fabricated.- Show that it can change its curvature by temperature change and find optimum thickness ratio of metal-MWNT thickness.
- Measure thermal expansion coefficient, aMWNT, and surface stress, sMWNT.
- Show that it can change its curvature by laser light induced heating.
Metal(Aluminum) is deposited on multi-wall nanotube by thermal evaporator on top of cold sample holder. Then we get double-layered structure. The amount of bending can be controlled by temperature change, length of cantilever, and thickness ratio of the two materials. If the thickness of metal is too shallow or deep, it will not bend much, then there should be optimum thickness ratio. In case of Aluminum and multiwall nanotube it is when Aluminum is thicker be 1.7 than MWNT.
Various double-layered cantilevers with different thickness ratio
Thermal bending experiments were done inside SEM with heating plate prepared in it. Below images are from one example. This proves that we can have thermally actuated cantilever.
Bending experiment were done with various thickness ratio cantilevers, and maximum bending was found at 1.7 which is expected by theory.
Right is a graph showing prediction and data. Horizontal axis is thickness ratio and vertical axis is curvature.
Theoretical curv was drawn with assumptions that cantilever length is 1mm and its cross section is stack of rectangles. For thermal expansion ratios, Aluminum bulk and graphite is used.
For data points, thickness of each layers and curvatures are measured from digital images using software tool.
Summary and Next Step:
- It was demonstrated that we can get double-layered cantilever on MWNT.
- It changed its curvature under temperature change, so it works as we wanted it as actuator.
- Best bending happens at thickness ratio 1.7 (= tAl / tMWNT )
- Next step is to control nanotube actuator by laser heating.
Below images show that MWNTs adsorbs light energy selectively depending on light polarity. In first image, both MWNTs (A and B) are dark, adsorbing energy. In second and third images, only B and A are adsorbing. Green arrows are displaying polarizations of laser light. We will use this to actuate nanotube cantilever thermally.
