MEEN 489/689:

Entrepreneurship & Nanomaterials for

Energy Applications

Lecture 6:

Diffusion & Failure at the Nanoscale

Synopsis of the Energy Sector

James Donnell, Andreas Polycarpou,

Tanil Ozkan, Haejune Kim

Fall 2015

19/8/2015

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How about nanoscale?

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You won’t be tested on the derivation but

should be able to explain why diffusion is

faster at the nanoscale.

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Is this kind of analysis still applicable at

the nanoscale?

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What can be done to avert mechanical

failure while keeping the process scalable?

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Application: Hard disk drives

R. Wood, J. Magn. Magn. Mater. (2008)

Nanotechnology 1:Ultra thin (and robust) films and super smooth (or structured) surfaces

Nanotechnology 2:Head-disk interface (nanometer level spacing and features) at 100 mph

A. Recent Thermal Flying Control technology shifted the interface interactions to smaller (nm) scales B. Proposed Heat Assisted Magnetic Recording possesses temperature challenges

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Hard disk drive (HDD) mechanics

D. Weller, Seagate

Slider

Magnetic disk

Slider

Original Flying Height Adjusted Flying Height

Protruded Pole Tip

)747(66.70

57.0

25.1

10)( Boeing

m

mm

mm

nmSlider =

< 1mm

Runway or road

Need reliable flying at 100 mph of few nm spacingHow to do it?Is small better?

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0 1 2 3 4 5 60

10

20

30

40

50

60

Separation, h (nm)

Ad

hes

ive

Fo

rces

(m

N)

Table 1: FvdwEq. (4): FIDMTEq. (1): FelEq. (16): Fel,roughEq. (17): Proposed Model

3 3.5 4 4.5 5 5.50

0.1

0.2

0.3

0.4

0.5

0.6

Separation, h (nm)

Ad

hes

ive

Fo

rces

(m

N)

Two flat parallel surfacesProposed (rough surface)

0 1 2 3 4 5 60

10

20

30

40

50

60

Separation, h (nm)

Ad

hes

ive

Fo

rces

(m

N)

Table 1: FvdwEq. (4): FIDMTEq. (1): FelEq. (16): Fel,roughEq. (17): Proposed Model

3 3.5 4 4.5 5 5.50

0.1

0.2

0.3

0.4

0.5

0.6

Separation, h (nm)

Ad

hes

ive

Fo

rces

(m

N)

Two flat parallel surfacesProposed (rough surface)

Roughness = 0.74 nm

Radius = 5.22 µm

Asperities = 9.33 µm-2

Total lube = 10 ÅMobile lube = 5 ÅContact Force = 0.151 N/m

Nominal contact = 300 um2

Adhesive Force Comparison (Flat-on-Flat vs. Rough

Surface)

The most important difference between idealistic smooth and “rough” cases is that the range of adhesive forces is LARGER when roughness is included

Rough surface model indicates rise of adhesion at higher flying-height

Suh and Polycarpou, JAP (2006)

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Areal Density Road Map

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Synopsis of the Energy Sector

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9/8/2015

Coal:

10,000 tons of coal per day

(1 freight train)

Nuclear:

100 tons of uranium per year

Hydroelectric:

60,000 tons of water per second

Comparison of power plants for 1 GW

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9/8/2015

Energy portfolio of industrialized nations

Although most of our energy originally comes from the Sun (except nuclear), only a

minuscule amount of solar energy is being used today.

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Supply and demand are far apart

Wind

Solar

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Electrical Storage

Chemical Storage

Storing energy

Energy/Weight

Energ

y/Volu

me

0

10

20

30

0 10 20 30 40

Energy Storage Density Gasoline

Batteries

Supercapacitors

• How do we store solar electricity overnight, wind electricity when calm ?

• The range of all-electric cars is short due to poor storage by batteries.

• Batteries have 30-50 times lower energy density than gasoline.

• Chemical energy is easy to store in fuel, but electricity is not.

Ethanol

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Electricity potential of our Sun (photovoltaics)

100×100 square kilometers of solar cells could produce all the

electricity for the US. But they are still too costly.

0.4 TW

US Electricity Consumption

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The required area of solar cells

1 kW/m2 (Incident solar power)

× 1/4 (Fraction of useful daylight)

× 0.16 (Efficiency of a solar cell ≅ 16%)

× 100×100 ·106 m2 (100×100 km2)

= 4 · 108 kW (Electric power generation in the US)

0.4 TW

US Electricity Consumption 16

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COMPANYPERCENT

SOLARIKEA 87%

GM 43%

VF Outdoor 33%

Johnson &

Johnson24%

REI 21%

Costco 17%

Kohl's 13%

Anheuser-

Busch 13%

Campbell's

Soup 12%

Hartz 11%

Walmart 5%

Macy's 5%

Whole Foods 5%

Bloomberg 4%

Tiffany's 3%

Safeway 3%

Commercial Users by Percent of Facilities with Solar PowerThe table below lists companies in order of the percentage of their facilities that are solar powered.This list provides another comparison for those companies that ranked highly in both installed capacity and number of installations. Note, this list is exclusively populated by companies surveyed for this report and does not include smaller companies that might otherwisebe considered to have higher ratios than presented below.

www.seia.org/researc

h-resources/solar-

means-business-2014-

top-us-commercial-

solar-users

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The efficiency keeps growing slowly

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How much would it cost to generate all

the electricity in the US by solar cells ?

1 $/W (Price of solar cells)

× 4 ·108 kW (Electric power generated in the US)

= 4 ·1011 $

= 400 Billion Dollars

The support structure adds substantial costs.20

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Solar thermal

Convert solar energy to steam, then to electricity

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Solar thermal (31% efficiency)

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Fuel from the Sun ?

• Photosynthesis

• Biofuels

• Split Water

Plants convert solar energy to chemical energy

but the efficiency is low (1%-2%)

Convert plants to fuel: Make ethanol, diesel fuel from

sugar, corn starch, plant oil, cellulose ...

Split water into hydrogen and oxygen using sunlight.

Use hydrogen as fuel. No greenhouse gases. (Futuristic)

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A little help from nanotechnology?

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Biofuels versus photovoltaics (PV)

How far could one drive a car with the energy produced by 100x100 m2 (2.5 acres) of land in a year ?

Biodiesel: 21 500 kmBioethanol 22 500 kmBiomass to liquid: 60 000 kmPhotovoltaics, electric car: 3 250 000 km

Solar cells are more efficient than photosynthesis.Electric motors are more efficient than combustion engines.

PHOTON International, April 2007, p. 106 (www.photon-magazine.com)25