“Will Carbon Replace Silicon as the Top Engineering Material? ”

Dr. Marc Madou Chancellor’s Professor UC Irvine UC Irvine, Tuesday 24 January 2006

Table of Content

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Fractals in Nature and Electrochemistry

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Why Carbon and What is C-MEMS?

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Applications:

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Battery

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Molecular Switches

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Wash-line DNA Sensors

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Conclusions

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An Indian Tale

Fractals in Nature

  The fundamental equation that describes scaling of various variables with relation to body mass is an allometric equation of the form : V=aM b The empirical observation that has perplexed scientists is the fact that the exponents (b) of many variables including cellular metabolism (b=-1/4), heartbeat (b=-1/4), maximal population growth (b=-1/4), life-span (b=1/4), blood circulation (b=1/4), metabolic rates of entire organisms (b=3/4), and cross-sectional areas of tree trunks (b=3/4) are multiples of 1/4 instead of 1/3.

Fractals in Nature

 Pure geometric scaling of area ( 2 ) and volume ( 3 ) leads to a scaling constant of 2/3, but as Max Kleiber discovered in the early 1930s, the metabolic rates of entire organisms (which should scale with area) scales with respect to body mass (which should scale with volume) with a scaling constant of 3/4.

to as Kleiber's law.

This relationship is now referred

Fractals in Nature

  Why not S/V = 0.67? One of the more inspiring explanations for Kleiber’s law came from ecologists Enquist and Brown and physicist West in 1997. These authors explain that the generic principle underlying Kleiber’s law is that nutrient supply networks in animals and plants form a branching fractal network  to reach all cells in an organism. By modeling the cardiovascular system as a fractal-like network that ends in terminal units (capillaries) of the same size, they have shown that minimizing the work that the heart performs in pulsatile systems leads to the proper scaling constants that are empirically observed (see also West et al 2005).

• G. B. West and J. H. Brown, (2005) Journal of Experimental Biology, 208 , 1575-1592

Fractals in Electrochemistry

 Fractals are an optimal geometry for minimizing the work lost due to the transfer network while maximizing the effective surface area. In many electrochemical systems, it is advantageous to have a large surface to volume ratio, while needing to transfer the signal or power effectively to an electrical network.

Electrochemical energy conversion devices such as fuel cells and some types of batteries as well as sensors such as glucose sensors examples of such applications.

are

With Mr. Ben Park

Fractals in Electrochemistry

 when scaling isometrically and with R ~ V -1 (b) (2) when scaling area.

 The resistance R of a bulk material scales with R ~ V -1/3 (a) (1) The surface area and the scaling of the surface to volume ratios are as follows (assuming t<<< l ): A V  l 2 l 3 A V  l 2 l 2 = 1 l   (3)   (4) 

With Mr. Ben Park

Fractals in Electrochemistry

 As can be seen in eqns (1), (2), (3), and (4), 2D scaling from a small  in lower internal resistance and higher effective area compared to an isometric 3D scaling approach. Indeed, commercial Li-ion batteries and fuel cells are composed of many layers of anode, cathode, and electrolyte that are rolled, folded, or stacked on top of each other Impossible in MEMS Highest k = s = 2, highest N k = n s = N s = 4 Fractals

   With Mr. Ben Park

Fractals in Electrochemistry

I total  N s (5) R total  1 N s (6) R total  1 V 0 (7) A total V 0  constant (8)     The total current is proportional to the number of the smallest elements within the fractal network.

Maximizing the number of small elements within a fractal structure is desired.

The total resistance is the inversely proportional to the number of small elements and ensures that current is maximized, while the internal resistance is minimized.

Comparing eq 7 to eq 2, it can be concluded that the resistance of fractal electrodes scale similar to a thinly layered structure, not to an isometrically scaled volumetric geometry.

Comparing eq 8 to eq 4, the surface to volume ratio of a fractal electrode does not change as the volume changes, again he fractal geometry scales more like a layered film than a volumetric electrode.

What is C-MEMS?

C-MEMS

Why Carbon?

          Polymerizes better than Si All types of forms: amorphous, graphite, nanotubes, etc Wide electrochemical stability window Biocompatibility Low cost Chemically inert Easy to derivatize Well known for its battery and sensor application Carbon nanotubes connect via C-MEMS?

Carbon is nature ’ s building bloc!

What is C-MEMS?

Yoke Khin Yap QuickTime™ and a Sorenson Video 3 decompressor are needed to see this picture.

Positive photoresist Negative photoresist

Bae et al Chemistry Letters Vo.33, No,4, 2005

What is C-MEMS?

 Photoresists pyrolyzed are patterned (e.g, using an photolithography) and in an inert environment (e.g., vacuum) to yield carbon films and 3D microstructures.

N 2 Vacuum or forming gas Ceramic tube (a) WEBB #40 vacuum furnace Quartz tube (b) Inert gas furnace Exhaust gas

Positive photoresist Negative photoresist TEM images

What is C-MEMS?

Sheet Resistance (Ohm/square)

450 400 350 300 250 m l m 200 150 100 l l 50 l 0 m m l m l m 600 C 700 C

Temperature (°C)

800 C 900 C 1000C 1100C

Sheet resistance vs temperature of heat treatment for AZ-4330 and OCG-825 resists

l m AZ-4330 OCG-825

S.Rnaganathan, M.Madou et.al, ”Photoresist derived carbon for microelectromechanical systems”

What is C-MEMS?

  In earlier work we demonstrated that photoresist derived carbon electrodes exhibit kinetics comparable to glassy carbon for selected electrochemical reactions in aqueous and nonaqueous electrolytes Later we found that the these carbon electrodes could also be charged discharged with Li

Applications

    Energy: micro-fuel cell, micro battery, super capacitor, micro-biofuel cell Microswitches Electronics: stable molecular switches for rectification, memory, conductance switching, etc, C-MEMS bridges the gap from nano to microworld and macro: current collectors, contacts, microswitches, etc 100nm 300nm 400nm 500nm

Applications

  Better electrochemical sensors: electronic DNA arrays, DNA hybridization sensors and glucose sensors as first target, nano-arrays Biocompatibility of nano-porous carbon

Battery

• • • C-MEMS film in 1 M LiClO 4 in a 1:1 volume mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC).

Measured 0.070 mAh cm -2 the second and subsequent cycles (against Li foil). for For a fully dense film, this corresponds to ~ 220 mAh g -1 , which is within the range of reversible capacities reported for coke.

Battery

  Lithium-based secondary batteries - high values of practical specific energies (150 Whkg -1 ) and energy densities (220 WhL -1 )-- vs. gasoline (3000 Whkg -1 ). Reported values of energy density are generally based on the performance of larger cells with capacities of up to several ampere-hours. For small microbatteries the achievable power and energy densities are diminished because the packaging and internal hardware determines the size and mass of battery  New manufacturing methods and new materials are needed.

Battery

SU-8 SU-8 SU-8

Battery

3 rd level 2 nd level 1 st level

Electronic Switches

Silicon carbon carbon Rick McCreery, OSU metal Silicon molecular monolayer

V

NO 2 N N NO 2 N N NO 2 N N metal top contact molecular layer Carbon substrate

DNA Wash-Line Sensors

V 100nm 300nm 400nm 500nm Non-Hybridization Hybridization V : DC bias

DNA Wash-Line Sensors

 Fast-Heating CVD:   Offers the control of orientation of the CNTs. Is characterized by “Kite Mechanism” and tip-growth.

Chiang, I. W., B. E. Brinson, R. E. Smalley, J. L. Margrave, and R. H. Hauge.

J. Phys. Chem. B

2001,

105,

1157 1161. “Purification and Characterization of Single-Wall Carbon Nanotubes.”

Conclusions

     Carbon 3D STRUCTURES especially fractals are an interesting and potentially very important research topic Electrochemical tests demonstrate that C-MEMS electrodes can be charged/discharged with Li. A C MEMS battery approach has the potential to solve both manufacturing and materials problems plaguing current battery scaling issues By careful control of processing parameters and heating conditions, a variety of complex 3D C-MEMS structures, such as suspended carbon wires, bridges, plates, self organized bunched posts (carbon flowers) and networks, are possible Combining C-MEMSA with nanotubes might make the needed bridge between the macro and nanoworld And,…

India, December 2005

NSF Project: USA-INDIA

     2 to 3 UCI students stay in India IIT’s for 3 months 3 months stay:   Joint Research Cultural Experience Trip and living expenses paid P.I. Madou, NSF Program Manager South Asia: Marjorie Lueck Choosing next 2-3 students (MEMS classes grades + desire to go)

DST-Project: India-US

 

PI: Suman Chackraborty Travel for PI’s and senior researchers

INDO-US

UCI URBANA-CHAMPAIGN Northwestern IIT Kanpur-Sanjay Dhande IIT Kharagpur-A.Gosh

Shiv Kapoor Kory Ehmann Jian Cao

QuickTime™ and a Motion JPEG OpenDML decompressor are needed to see this picture.

Dank u wel