14. visions for the future · 14. visions for the future 3.optical reflection of all incoming...

14. Visions for the future

What kind of advanced materials are going to be needed in the future?

Very difficult to predict!

F i t did

needed in the future?

For instance, did anyone predict that super-conductors would have largest application in medicine?

Or that there would beOr that there would be lasers & computers in every household?

But before attempting to predict the future, let’s begin with brief update on recent course-related advances:


“Complete” metallic behavior in ‘conducting polymers’ finally observed (~30 years after discovery)y y)

3 typical metal attributes:

1. High conductivity1. High conductivity

Original polyacetylene: σ ~105 S/cm in doped state (similar to ordinary metals; e.g. σ(Cu) ≈ 6*105 S/cm!

2. Monotonic decrease in σ with increasing T, since valence electrons “free” particles in conventional metals (remember Drude’s free-electron model) and it is rate ith hich electrons are scattered that limits cond cti itis rate with which electrons are scattered that limits conductivity

Because dominant source of electron scattering is phonons (which increase with increasing T): conductivity of metal decreases with increasing Tg ) y g

Monotonic dσ/dT < 0 not observed in ‘conducting polymers’ until…


…Lee et al., in recent issue of Nature, report designed synthesis of unprecedented high-qualitydesigned synthesis of unprecedented high quality polyaniline, using self-stabilized dispersion polymerization in two-phase solvent

Finally: monotonic increase in resistivity (= decrease in conductivity) with increasing T observed!


3. Optical reflection of all incoming photons below plasma frequencyω ≤ ω = ( 2/ε )1/2 d t i f i id t h t i ll ti

Conventional metals: high concentration

ω ≤ ωp = (ne2/εm)1/2, due to screening of incident photons via collective motion of (plasma of) conduction electrons

gof conduction electrons (n) → ωp positioned in UV range and material appears shinyappears shiny

‘Conducting polymers’: n significantly smaller, since polymer repeat unit significantly larger than metal atom →

ωp should be positioned in IR range, as is i d d b d i hi h litindeed observed in new high-quality polyaniline (ωp ≈ 1.4 eV)

14. Visions for the futureAlso Thin Film Electronics (Swedish company) developed sophisticated 3D memory with ‘conducting polymers’ as active material…

… now changed concept from extremely high-capacity, fast 3D polymer/Si hybrid memory to “simpler” and slower 2D all-y ppolymer memory that stores only 100 Bits!

Why? Simple printing of small flexible memories fits many emerging large-quantitymemories fits many emerging large quantity and low-end applications, e.g. marking and tracking of food containers, tickets, smart cards

Overall, organic electronics predicted to take off in near future, partly because it offers low-cost and flexible designcost and flexible design

But can this function only be attained with organic materials?


Traditional production of Si-based electronics requires complicated -- andelectronics requires complicated and expensive -- processing in clean rooms using:

(i)(i) vacuum

(ii) poisonous chemicals

(iii) energy intensive processes at very high(iii) energy intensive processes at very high T → excluding use of flexible substrates

But recent report by Furusawa et al (inBut recent report by Furusawa et al (in Nature) demonstrates that it is possible to perform simple solution-processing of Si → possibility to print Si based microelectronicpossibility to print Si-based microelectronic devices, e.g. field-effect transistors (FETs), on flexible substrates!?

14 Visions for the future14. Visions for the future

Furusawa et al. used Si-based liquid (cyclo-pentasilane) dissolved in organic solvent as Sipentasilane) dissolved in organic solvent as Si-containing solution

(1) slight UV-polymerization to make solution(1) slight UV polymerization to make solution viscous (→)

(2) deposition of film on substrate (by printing or spin coating), (3) heat treating film at modest T, (4) exposure with high power (excimer) UV-laser to transform film into poly-crystalline Si, as seen in TEM image (←)

14 Vi i f h f14. Visions for the future

With this approach, authors managed to prepare FET i h l i d i i lFETs with solution-processed active materials

Resulting FETs had very good performance ( i ll i d fil ) l i h(especially spin coated film), almost on par with traditional chemical vapor deposition (CVD) prepared FETsp p

14. Visions for the future14. Visions for the future

Strong emergence of printable electronics (organic or possibly silicon-based) very(organic or possibly silicon-based) very likely in near future, since versatility, bio-compatability, flexibility & simplicity will allow for new types of desirableallow for new types of desirable applications

“Traditional” high-performance g pelectronics will also continue to develop (remember Moore’s law); and emergence of bottom-up nanotechnology expected to p gy pplay important rule

Critical issues to address with nanotechnology: gy(i) controlled production, (ii) scaling up of production, (iii) quantum effects, and (iv) safety


Opportunities with nanotechnology enormous, notnanotechnology enormous, not only in nano-electronics but also in:

•medicine

• biotechnology

• and for development of more efficient & functional energy systems e g :systems, e.g.:

• solar cells

th l t i d i• thermoelectric devices

• energy-storage devices…

14 Visions for the future14. Visions for the future

Let’s finish by speculating about “biggest challenge of mankind” where development ofchallenge of mankind , where development of advanced materials will play significant role:

The reformation of the energy system!

Total worldwide power consumption ≈15 TW

Projected to increase significantly to ~50 TW in 2100 (partly because of economic development of large-population nations, e.g. India, China)

≥80 % of world’s energy comes from fossil fuels,≥80 % of world s energy comes from fossil fuels, which in not-too-distant future will run out (~50-200 years)

G d id i i i f f il f l liGood idea to minimize use of fossil fuels earlier, because of serious concerns regarding effects of global warming


Grand problem: (i) we need more energy, (ii) it should be produced in environmentally sound way and (iii) we have to give up our biggest energyenvironmentally sound way, and (iii) we have to give up our biggest energy source!

So what to use?

Well, Earth-based renewable sources, such as hydroelectricity, wind, tides, geothermal, biomass, y y, , , g , ,all expected to contribute but also to fall significantly short of our total demand

Only the sun -- hits us with 165,000 TW of power -- can supply the large amount of power that is expected to be required in the future (~50 p q (TW/year 2100)


Currently strong push worldwide to convert to a ”Hydrogen economy”:

3 key components – production, storage, and utilization of hydrogen fuel cells –and utilization of hydrogen fuel cells –each with its own special challenges

1. Production of hydrogen (current status)y g ( )

•H2 not naturally occurring

• Current produced amount only fractionCurrent produced amount only fraction of required amount

• Current production stems in large parts p g pfrom reforming of fossil fuels (= not renewable!)


1. Production of hydrogen (future vision)

Decentralized system of integrated units (in individual houses!), which via photovoltaic conversion of sunlight (absorbed on roof), co ve s o o su g t (abso bed o oo ),produces H2 (and O2) from H2O safely and cheaply by electrolytic process (in basement)

H d i ffi i l ?How to do it efficiently?

No one knows, but (i) nanotechnology and (ii) bioscience expected to provide assistance!bioscience expected to provide assistance!

Examples: (i) optimization of catalytic particles at electrode interfaces: size, shape & composition, (ii) controlled bio-systems performing similar processes but with higher efficiency: artificial photosynthesis


2. Storage of produced hydrogen:

Gas, liquid, physisorption (within porous carbon network), or chemisorption (in metal hydrides)?y )

Critical that energy cost of storing (via compression or cooling) and/or accessing hydrogen (breaking of physical or chemical bonds) not significant in comparison to hydrogen energy contenty g gy

Nanoscience again expected to play key role in providing, e.g., nano-structured

i l i h l f dmaterials, with large surface area and optimized binding sites

14. Visions for the future3. Utilization of hydrogen fuel cells:

Status: Currently in small scale use & intrinsicStatus: Currently in small-scale use, & intrinsic energy conversion efficiency higher (currently ~60 %) than in internal combustion engines (~35 %), since heat not necessary intermediate stateheat not necessary intermediate state

A number of key areas need to be addressed:

•More efficient and cheaper catalysts to speed upMore efficient and cheaper catalysts to speed up reactions at electrode interfaces (nanotechnology!)

• Optimized electrode-electrolyte surfaces that allow f t t h l f i i 3 diff tfor easy transport channels of species in 3 different phases – gases (H2/O2 & H2O), ions (H+/O2-) in ion-conducting electrolyte, and electrons in metallic wires to/from common reaction point coated withwires – to/from common reaction point coated with (reducing or oxidizing) catalyst (more nanotechnology!!)


Predicted evolution of hydrogen economy

Small steps forward can be taken by improvement/employment of currently available and functional technology:gy

Production of hydrogen via reformation of fossil fuels, storage via compressed gas (or cooled liquid), and energy conversion via “conventional” internal combustion engines

But to gain true benefits of hydrogenBut to gain true benefits of hydrogen economy, breakthroughs in basic science and development of advanced materials b l l !absolutely necessary!


Flexible solar-battery device

European researchers integrated thin-film solar cell with ultraslim Li-polymer battery → “first” device combining energy generation & storage and capable of g gy g g pself-recharging under natural or indoor light

Organic solar cell (Konarka): {conducting polymer + fullerene} mixture

Li-polymer battery (Warta): recharged > 1000 times, relatively high energy density. Used in Apple's iPod nano

fullerene} mixture

pp

Solar-battery device: m = 2 g; thickness < 1 mm; cut or produced in desired shapes and printed on a roll-to-roll machine at low temperature → cheap and flexible device

Lots of applications for portable self-rechargeable power supplies: Watches, toys, RFID tags, smart cards, sensors, remote controls, digital cameras, mobile phones etc.


Undergraduates develop dirt-powered microbial fuel cells for lighting

~ 75 % of Sub Saharan Africans (550 million people) lack access to electricity & many~ 75 % of Sub-Saharan Africans (550 million people) lack access to electricity & many rely upon dangerous kerosene lamps and candles for illumination

Team of Harvard students & alumni developed microbial fuel cell (MFC) based lighting systems and established company dedicated to solving lighting crisis in Africa

MFCs capture energy produced by naturally occurring microbial metabolism and generate electricity frommicrobial metabolism and generate electricity from organic-rich materials (e.g. soil, manure, or food scraps)

Advantages: Unlike other renewable energy h l i ( l d i d ) MFC ktechnologies (e.g. solar and wind power) MFCs work

day or night, rain or shine - and are markedly less expensive. Also safe and reliable

First field study Kilimanjaro, Tanzania; then test & distribution of refined prototypes in Namibia


Many exciting challenges remain…

14. visions for the future · 14. visions for the future 3.optical reflection of all incoming...

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