14. Visions for the future

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1 What kind of advanced materials are going to be needed in the future? Very difficult to predict! For instance, did anyone predict that superconductors would have largest application in medicine? Or 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:

2 Complete metallic behavior in conducting polymers finally observed (~30 years after discovery) 3 typical metal attributes: 1. High conductivity Original polyacetylene: σ ~10 5 S/cm in doped state (similar to ordinary metals; e.g. σ(cu) 6*10 5 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 with which electrons are scattered that limits conductivity cti it Because dominant source of electron scattering is phonons (which increase with increasing T): conductivity of metal decreases with increasing T Monotonic dσ/dt < 0 not observed in conducting polymers until

3 Lee et al., in recent issue of Nature, report designed 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!

4 3. Optical reflection of all incoming photons below plasma frequency ω ω =( p (ne 2 /εm) 1/2, due to screening of incident id photons via collective motion of (plasma of) conduction electrons Conventional metals: high concentration of conduction electrons (n) ω p positioned in UV range and material appears shiny Conducting polymers : n significantly smaller, since polymer repeat unit significantly larger than metal atom ω p should be positioned in IR range, as is indeed dobserved din new high-quality h polyaniline (ω p 1.4 ev)

5 Also 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- polymer memory that stores only 100 Bits! Why? Simple printing of small flexible memories 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 design But can this function only be attained with organic materials?

6 Traditional production of Si-based electronics requires complicated -- and expensive -- processing in clean rooms using: (i) vacuum (ii) poisonous chemicals (iii) energy intensive processes at very high T excluding use of flexible substrates But 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 microelectronic devices, e.g. field-effect transistors (FETs), on flexible substrates!?

7 Furusawa et al. used Si-based liquid (cyclo- pentasilane) dissolved in organic solvent as Sicontaining 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 ( )

8 14. Visions i for the future With this approach, authors managed to prepare FETs with solution-processed active materials Resulting FETs had very good performance (especially spin coated film), almost on par with traditional chemical vapor deposition (CVD) prepared FETs

9 Strong emergence of printable electronics (organic or possibly silicon-based) very likely in near future, since versatility, biocompatability, flexibility & simplicity will allow for new types of desirable applications Traditional high-performance electronics will also continue to develop (remember Moore s law); and emergence of bottom-up nanotechnology expected to play important rule Critical issues to address with nanotechnology: gy (i) controlled production, (ii) scaling up of production, (iii) quantum effects, and (iv) safety

10 Opportunities with nanotechnology enormous, not only in nano-electronics but also in: medicine biotechnology and for development of more efficient & functional energy systems, e.g.: solar cells thermoelectric t devices energy-storage devices

11 Let s finish by speculating about biggest challenge 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, which in not-too-distant future will run out (~ years) G did i i i ff il f l li Good idea to minimize use of fossil fuels earlier, because of serious concerns regarding effects of global warming

12 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 energy source! So what to use? Well, Earth-based renewable sources, such as hydroelectricity, y, wind, tides, geothermal, biomass, 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 TW/year 2100)

13 Currently strong push worldwide to convert to a Hydrogen economy : 3 key components production, storage, and utilization of hydrogen fuel cells each with its own special challenges 1. Production of hydrogen (current status) H 2 not naturally occurring Current produced amount only fraction of required amount Current production stems in large parts from reforming of fossil fuels (= not renewable!)

14 1. Production of hydrogen (future vision) Decentralized system of integrated units (in individual houses!), which via photovoltaic conversion o of sunlight (absorbed bed on roof), produces H 2 (and O 2 ) from H 2 O safely and cheaply by electrolytic process (in basement) How to do it efficiently? No one knows, but (i) nanotechnology and (ii) 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

15 2. Storage of produced hydrogen: Gas, liquid, physisorption (within porous carbon network), or chemisorption (in metal hydrides)? 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 content Nanoscience again expected to play key role in providing, e.g., nano-structured materials, with large surface area and optimized binding sites

16 3. Utilization of hydrogen fuel cells: Status: Currently in small-scale scale use, & intrinsic energy conversion efficiency higher (currently ~60 %) than in internal combustion engines (~35 %), since heat not necessary intermediate state A number of key areas need to be addressed: More efficient and cheaper catalysts to speed up reactions at electrode interfaces (nanotechnology!) Optimized electrode-electrolyte surfaces that allow for easy transport t channels of species in 3 different phases gases (H 2 /O 2 & H 2 O), ions (H + /O 2- ) in ion-conducting electrolyte, and electrons in metallic wires to/from common reaction point coated with (reducing or oxidizing) catalyst (more nanotechnology!!)

17 Predicted evolution of hydrogen economy Small steps forward can be taken by improvement/employment of currently available and functional technology: 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 hydrogen economy, breakthroughs in basic science and development of advanced materials absolutely l necessary!

18 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 self-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 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.

19 Undergraduates develop dirt-powered microbial fuel cells for lighting ~75%of Sub-Saharan SubSaharan 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 from organic-rich materials (e.g. soil, manure, or food scraps) Advantages: Unlike other renewable energy technologies (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

20 Many exciting challenges remain