CNT Composites for MEMS CNT Composites for MEMS Mechanical Structural Applications : Mechanical Structural Applications :

A Systems ApproachA Systems Approach

Ranga Komanduriand

Satish BukkapatnamOklahoma State University

Stillwater, OK

Workshop onResearch Challenges for Nanomanufacturing Systems

National Science FoundationArlington, VA

February 11-12, 2008

GRAPHENE SHEET, SWNT AND GRAPHENE SHEET, SWNT AND MWNTMWNT

Unique Mechanical Properties of CNTUnique Mechanical Properties of CNT

– Quite stiff, exceptionally strong, and resilient.Young’s modulus of SWNT is ~0.75 TPaStrength of SWNT is ~37 GPaCNT are extremely flexible under large elastic strains and resist failure under repeated bending. Small diameter CNT can be extended elastically to ~ 5.8% before breaking

– Low density (1.1 to 1.5 g/cm3), hallow structure, large aspect ratio, nanometric dimensions

– Density normalized modulus and strength of typical SWNT are ~19 and ~56 times that of steel wire, respectively

– Very high damping coefficient

CNT before and after nanoindentationCNT before and after nanoindentation

EngineerEngineer’’s Dream Materials Dream Material

They can be considered as engineer’s dream material as no material to date has such unique combination of desirable properties.

The mechanical properties alone make CNTs, a unique material as they are stiff at the same time highly flexible, strong yet highly deformable. They perform much better in compression than carbon fibers and do not fracture easily. SWNTs can be bent, twisted, flattened and can be made into small circles without breaking. We have also observed that CNTs do not undergo any permanent deformation when indented with an AFM probe.

FeaturesFeatures

An engineer’s approach for the synthesis of CNT composites for MEMS mechanical structural applications with high stiffness and damping. Can also be used for structural health monitoring, for CNT can also be used as sensors. The focus is not on composites with pure SWCNTs but on composites with highly-aligned bundles of MWCNTs with the ends closed and the catalyst sealed inside the tubes for structural composite applications. The focus is not on macro structural applications, such as hydrogen storage batteries for automobile, aerospace structural applications, it will focus on micro structural applications, such as MEMS components, power supply. This way, the high cost and large volume requirements will not be factors in their application to MEMS.

ApproachApproach

Develop CTC composites with highly aligned CNT bundles for structural applications with significant increase in stiffness/damping for potential MEMS mechanical structural applications.

There are numerous MEMS applications where this approach would be more than adequate and the conventional approaches would not be cost effective.

The analogy would be instead of considering composites for aerospace applications, where quality is a prime requisite, our approach will be tantamount to considering reinforced concrete for structural applications (e.g. roads, buildings, bridges) where the requirements are not as stringent but used extensively all around the world.

ApproachApproach

Also, instead of applications requiring large volumes of CNTs (macro), the research work will focus on micro (MEMS) systems. Consequently, the cost or volume requirements of CNTs will be a minor issue similar to platinum coating on razor blades.

Significant cost reductions can accrue from using the as-grown, highly-aligned multiwalled CNT bundles for advanced composite applications as subsequent processing costs are minimal and large quantities of CNTs are not required.

Mechanical StructuresMechanical StructuresCast Iron– Easy to cast complicated structures– Believed to have “high” damping– Inexpensive– Low elastic modulus (10 x 106 psi) or stiffnessWelded steel– High elastic modulus (30 x 106 psi) or stiffness– Low damping– More expensiveGranite-epoxy: machine tools for HSM– Low modulus– More dampingCeramic structures for UPM– High modulus– High precision– Thermally more stable– Low damping

CNT Composites for Structural CNT Composites for Structural ApplicationsApplications

High modulusHigh stiffnessHigh dampingBuilt-in sensors for structural health monitoringIdeal for MEMS structural applicationsReasonable cost

EXCIMER LASER PLD SETUPEXCIMER LASER PLD SETUP

Schematic of PLD setup Photograph of PLD setup

MICROWAVE CVD SYSTEM FOR MICROWAVE CVD SYSTEM FOR SYNTHESIS OF SYNTHESIS OF CNTsCNTs

TANGLED CARBON NANOTUBESTANGLED CARBON NANOTUBES

TEM OF CNTTEM OF CNT

100 μm

100 μm

THANK YOUTHANK YOU