EmpaNews May 2011

Enzymes for industrialapplications 08

Transparent electrodes:flexible yet robust 07

Tracking traces ofpersistent toxins 12

Magazine for Research, Innovation and Technology TransferVolume 9 / Issue 33 / May 2011

EmpaNews

Chemistry everywhere 15

02 // Editorial

Developing fabricsTransparent electrodes:flexible yet robust 07

There’s a great dealof chemistry behindmaterials science

The United Nations General Assembly has de-clared 2011 the International Year of Chemistry(IYC2011) under the unifying theme “Chemistry –

our life, our future”. Truly a great topic because the en-tire world around us involves chemistry – in one way oranother. It’s hard to imagine what our daily lives – orour economy – would be like without the findings fromthis field and the knowledge we have gained about the

structure, behaviour and conversion ofmaterials. In everyday terms, just thinkabout products such as bread and wine orroutine processes such as cooking or start-ing an engine.

Chemical reactions also play a deci-sive role in the development of new mate-rials. Empa researchers attempt, for in-stance, to shed light on complex reactionmechanisms step by step by using a com-bination of experiments and simulations

to learn how to control them, say, with novel catalystsand in the end synthesise even better materials (seepage 20). Or, thanks to extremely sensitive analyticalmethods, they detect even the smallest traces of envi-ronmentally harmful substances in our various ecosys-tems (see page 12) – and whenever possible developsafer substitute materials. The current Focus section il-lustrates some exciting examples.

At the same time, IYC2011 is calling to mind the100th anniversary of the awarding of the Nobel Prize inChemistry to Marie Curie for the discovery of the chemi-cal elements radium and polonium. The first woman toreceive the Nobel Prize, she also gave a name to the sub-stances she investigated: radioactive, a term which hasrecently become extremely topical in a tragic manner.However, especially when it comes to energy, new typesof materials – such as those for high-performance batter-ies (see page 15) – are showing promise for a sustainable,safe energy supply. This is a topic about which we havereported extensively in past issues of EmpaNews andwhich we will certainly continue to cover in the future.

Enjoy your reading!

Michael HagmannHead Communications

Cover

Every material – just like every substance –is made up of chemical elements. It’sthus no wonder that chemists are hard atwork in many Empa laboratories. Oneexample is the Solid State Chemistry andCatalysis Laboratory where the applicationof perovskite metal oxides in batteries,catalysts and thermoelectric converters isbeing investigated.

Inhalt // 03

Building a wind tunnelHow nanoparticles moveabout in the atmosphere 22

Locating sourcesTracking traces ofpersistent toxins 12

Manufacturing biocatalystsEnzymes for industrialapplications 08

Research and development04 In atomic resolution

06 Medtech partners intensify collaboration

07 Plastic fabric for solar cells & co

08 Tracking down enzymes

Focus: International year of chemistry

10 Chemistry everywhere

12 Useful in the short-term, troublesome long-term

15 Design studio for new materials

20 Robust accelerant

22 Following the path of floating particles

Knowledge and technology transfer24 Into chemical depths

Science dialogue27 World Resources Forum 2011

28 Events

Imprint

PublisherEmpaÜberlandstrasse 129CH-8600 DübendorfSwitzerlandwww.empa.ch

Text & DesignCommunication section

ContactPhone +41 58 765 45 [email protected]

Published quarterly

ISSN 1662-7768

COC-100246 FSC Mix

04 // Research and development

For the first time scientists succeeded in determining the exact spatialarrangement of a single atom in a nanoparticle. The yellow spheresare the graphically depicted atoms that form the silver nanoparticle,which is about two nanometres in diameter. (Image: Empa/ETH Zürich)

Research and development // 05

In chemical terms, nanoparticles have different properties fromtheir “big brothers and sisters”: they have a large surface areain relation to their tiny mass and at the same time a small num-

ber of atoms. This can produce quantum effects that lead to alteredmaterial properties. Ceramics made of nanomaterials can suddenlybecome bendy, for instance, or a gold nugget is gold-colouredwhile a nanosliver of it is reddish.

New method developedThe chemical and physical properties of nanoparticles are determinedby their exact three-dimensional morphology, atomic structure and es-pecially their surface composition. In a study initiated by Rolf Erni,head of Empa’s Electron Microscopy Center, and ETH Zurich scientistMarta Rossell the 3D structure of individual nanoparticles has now suc-cessfully been determined on the atomic level. The new techniquecould help improve our understanding of the characteristics ofnanoparticles, including their reactivity and toxicity.

Gentle imaging processingFor their electron-microscopic study, which was published recent-ly in the journal “Nature”, Rossell and Erni prepared silvernanoparticles in an aluminium matrix. The matrix makes it easierto tilt the nanoparticles under the electron beam in different crys-tallographic orientations whilst protecting the particles from dam-age by the electron beam. The basic prerequisite for the study wasa special electron microscope that reaches a maximum resolutionof less than 50 picometres. By way of comparison: the diameter ofan atom measures about one Ångström, i.e. 100 picometres.

To protect the sample further, the electron microscope was setup in such a way as to also yield images at an atomic resolution witha lower accelerating voltage, namely 80 kilovolts. Normally, thiskind of microscope – of which there are only a few in the world –works at 200 – 300 kilovolts. The two scientists used a microscopeat the Lawrence Berkeley National Laboratory in California for theirexperiments. The experimental data was complemented with addi-tional electron-microscopic measurements carried out at Empa.

Sharper imagesOn the basis of these microscopic images, Sandra Van Aert fromthe University of Antwerp created models that “sharpened” the im-ages and enabled them to be quantified: the refined images madeit possible to count the individual silver atoms along different crys-tallographic directions.

For the three-dimensional reconstruction of the atomicarrangement in the nanoparticle, Rossell and Erni eventually en-listed the help of the tomography specialist Joost Batenburg fromAmsterdam, who used the data to tomographically reconstruct theatomic structure of the nanoparticle based on a special mathemat-ical algorithm. Only two images were sufficient to reconstruct thenanoparticle, which consists of 784 atoms. “Up until now, only therough outlines of nanoparticles could be illustrated using many im-ages from different perspectives”, says Marta Rossell. Atomicstructures, on the other hand, could only be simulated on the com-puter without an experimental basis.

“Applications for the method, such as characterising dopednanoparticles, are now on the cards”, says Rolf Erni. For instance,the method could one day be used to determine which atom config-urations become active on the surface of the nanoparticles if theyhave a toxic or catalytic effect. Rossell stresses that in principle thestudy can be applied to any type of nanoparticle. The prerequisite,however, is experimental data like that obtained in the study. //

For the first time, scientists from Empa and ETH Zurich have, incollaboration with a Dutch team, managed to measure the atomicstructure of individual nanoparticles. The technique, recentlypublished in “Nature”, could help better understand the propertiesof nanoparticles in future.

TEXT: Simone Ulmer*

In atomic resolution

Literature reference“Three-dimensional atomic imaging of crystalline nanoparticles”,S. Van Aert, K.J. Batenburg, M.D. Rossell, R. Erni & G. Van Tendeloo,Nature (2011), doi:10.1038/nature09741

* Simone Ulmer is editor at ETH Life.


Medtech partners intensify collaboration Empa and the St. Gallen Cantonal Hospital are stepping up theirpartnership. In addition to the existing collaboration in the area ofhuman stem cells, researchers from both institutions are hence-forth cooperating in nanosafety assessments, immunology and thedevelopment of medical implants. A number of new projects werekicked off at the beginning of 2011.

TEXT: Nadja Kröner

Within the scope of the new framework agreement figures, among other things, a project in which Empa researchers from the Materials-Biology Interactions Laboratory, together with their colleagues at

the Women’s Clinic and the Institute for Pathology at the St. Gallen CantonalHospital, are studying the exact transport mechanism of nanoparticles throughthe placenta along with their effects on placental tissue. A new perfusion ap-paratus for placental tissue is currently being set up at Empa, one that will keepthe mother and foetal circulatory system stable for several hours.

Nanosafety as a central issueWith nanotechnology, as is true for all new technologies, risks cannot be com-pletely ruled out. Thus, for several years Empa has been looking into possiblenegative effects, such as those on the unborn. For instance, last year re-searchers were able to demonstrate that nanoparticles with a diameter of lessthan 200 to 300 nanometres can make their way from the mother’s circulatorysystem through the placenta and into the foetal bloodstream.

Likewise, it is unknown to what extent the immune system is influencedby invading nanoparticles. Here, too, it is conceivable that nanomaterials couldbe used for diagnostic and therapeutic purposes in humans. Empa scientistsare investigating this possibility together with the Institute for Immunobiologyat the St. Gallen Cantonal Hospital.

Development of implants: an established collaborationAnother collaboration has being going on for some time at the hospital’s Clinicfor Orthopaedic Surgery and Traumatology. Each week, the clinic prepares bonemarrow samples for Empa scientists to allow them to test and optimise new ma-terials and surfaces such as those intended for implants. The question is whatproperties and conditions implant surfaces must exhibit so that stem cells candevelop “properly”, in other words, differentiate into the desired cell type, forexample into bone cells. This would, in turn, allow the implant to adhere to thebone in a stable manner and take over its function.

“Thanks to the collaboration with the Hospital, we’re in a position to con-siderably expand our activities in bio and medical technology. Through this,we’re taking an enormous step towards clinical applications of the materials andmethods we develop”, says Peter Wick, Co-head of Empa’s Materials-BiologyInteractions Laboratory, adding that further projects were already in develop-ment. //


Active layer Transparent fibre Metal wire

Plastic layer

Transparentelectrode

Light

Back electrode

Plastic fabric forsolar cells & coIn pliable thin-film solar cells, a transparent and flexible electrodecollects the light and conducts the electric current. Emparesearchers have developed a polymer-based fabric electrodewhich is now showing first promising results and presents analternative to indium tin oxide coatings.

TEXT: Rémy Nideröst

Shortages of raw materials along with increased con-sumption of rare earth metals are making electroniccomponents and equipment increasingly more expen-sive. These metals are used, for example, in transparentelectrodes for touch screens on mobile phones, in LCDs,organic light-emitting diodes and thin-film solar cells.The material of choice for such applications is indiumtin oxide (ITO), a conductive and largely transparentmixed oxide. However, because ITO is relatively expen-sive, it is not well suited for applications covering largeareas such as in solar cells.

The search for alternativesIndium-free transparent oxides do exist, but supply bot-tlenecks are becoming more frequent due to increasingdemand. Furthermore, fundamental disadvantages suchas brittleness and deformation remain an issue. As a re-sult, alternative transparent conductive coatings are be-ing researched intensely, examples being conductivepolymers, carbon nanotubes and graphenes. Carbon-based electrodes, however, generally have an excessive-ly high surface resistance and thus are insufficientlyconductive. If a metallic grid is integrated into an organ-ic layer, the resistance drops, but so does the mechani-cal stability; if a solar cell produced by this method wereto be bent, the layers would break and loose their con-ductivity. The challenge thus consists of manufacturingflexible yet stable conductive substrates, ideally in acost-effective industrial roll-to-roll process.

One solution: woven electrodes A very promising possibility turns out to be a transpar-ent, flexible polymer fabric. It was developed by Emparesearchers in the Functional Polymers Laboratory incooperation with the Swiss company Sefar AG and fi-nancially supported by the Swiss Commission for Tech-nology and Innovation CTI. Sefar, which specialises inprecision fabrics, is able to produce the fabric at an at-tractive price in large quantities using roll-to-roll pro-cessing similar to that in newspaper printing. Woven-inmetal wires provide the necessary electrical conductiv-ity. In a second step, the fabric is embedded in an inertplastic layer without covering the metal wires complete-ly and thus electrically insulating them. The resultingelectrode is transparent, stable and yet flexible. On topof it, Empa researchers applied a layered organic solarcell. Its efficiency is comparable to conventional ITO-based cells; moreover, the woven electrode is clearlymore stable during deformation than commerciallyavailable flexible plastic substrates, onto which ITO isdeposited as a thin, conductive layer. //

Literature reference“Flexible Mesh Electrodes: Woven Electrodes for Flexible OrganicPhotovoltaic Cells”, W. Kylberg, F. Araujo de Castro, P. Chabrecek,U. Sonderegger, B. Tsu-Te Chu, F. Nüesch and R. Hany, Adv. Mater. 8/2011,page 920, doi: 10.1002/adma.201190019

1Flexible precision fabricwhich was developedinto an electrode forthin-film solar cells incollaboration withSwiss company Sefar AG.(Photo: Sefar AG)

2Cross-section of a thin-filmsolar cell with a wovenelectrode. (Graphic: André Niederer)

1 2


Wood is a biomaterial. That’s whythere’s a good opportunity forcollaboration between Empa’s

Wood Laboratory and Biomaterials Labora-tory. Their common subject of research islaccase, an enzyme which is found in bac-teria, fungi and higher plants and acts as acatalyst for both the synthesis and decom-position of lignin, the main component ofwoody cells. Because the enzyme worksunder mild conditions – meaning in aque-ous solutions, at room temperature and un-der atmospheric pressure – and because itbuilds up no poisonous by-products, it isalso useful for industrial applications.

One example is the treatment of pulp forthe paper industry. The enzyme breaks downthe lignin which turns paper brown and thusacts as a biobleaching agent. Until now, paperhas been chemically bleached, but thatprocess pollutes the environment. Laccases,instead, are biodegradable, for instance inwastewater treatment plants. They are al-ready being used to bleach jeans because theycan break down the indigo dye typical in thatclothing. A further possible application wouldthus be the enzymatic processing of wastewater in the textile industry.

Interest in new, efficient and environ-mentally friendly processes has grownenormously in industry. And while laccasescan be put to use in many chemical-engi-neering processes, its widespread use is notpossible at this time. The enzyme cannotyet be produced at prices which would al-low its use on a large scale. In addition, thelaccases available today are partially notactive or stable enough to compete withchemical processes. There’s still a bit of de-velopment work ahead.

Wood research meets biomaterialsresearchFor quite some time, the Wood Laboratoryhas been doing research on the wood-decomposing effects of certain fungi whichare known as brown rot and white rotpathogens. Here the goal is, on the onehand, to find out what kind of damage thefungi cause and how various wood con-stituents can be decomposed. On the otherhand, the researchers are also investigatinghow these properties of fungi can be usedto change the material properties of wood.It’s been known for a long time that laccaseplays a decisive role particularly in the de-

1Laccase is an enzyme which in natureacts as a catalyst for both the synthesisand decomposition of lignin, the maincomponent of cells in plants. In industryit could prove to be quite useful as,for example, a biobleaching agent for thepulp used in the paper industry.

2Reaction of the laccase enzyme with acolour-forming substance on an agar plate(blue-green colouring).

3The filamentous fungi secrete the enzymelaccase into the culture medium.

Enzymes are environmental friendly and work under mild conditions.It’s no wonder that industry is interested in these “biocatalysts”.Empa researchers are investigating laccase, an enzyme that is ofparticular interest for the textile and wood-processing industries.Here, interdisciplinary cooperation is essential.

TEXT: Nadja Kröner / PHOTOS: iStock, Empa

Tracking down enzymes


composition of lignin. This is where the en-zyme specialists at the Biomaterials Labo-ratory came into the picture. In a commonproject, they proved that the build-up oflaccases varies quite widely in white rotfungi, and even among various strains andunder differing growth conditions. “Work-ing with filamentous fungi is somethingrather exotic for us, and that’s why collabo-ration with the experts from the Wood Lab-oratory makes so much sense”, says JulianIhssen from the Biomaterials Laboratory. Inaddition to laccases from fungi, other sim-ilar enzymes which occur in bacteria arebeing studied at Empa. Although bacteriallaccases can basically be produced biotech-nically more easily than those from fungi,there is still very little knowledge on theseenzymes.

For technical applications, it’s impor-tant that the properties of an enzyme areknown in the greatest possible detail.That’s because there’s also a variation inthe spectrum of molecules which can betransformed depending on the laccasesoriginating from different fungi or bacteria.Further, the optimal conditions for the re-action such as temperature, pH value or

solvents are different. Empa carried out re-lated experiments with the help of minia-turised enzyme tests based on changes incolour. If it turns out that the properties ofnaturally occurring laccases are inadequatefor industrial applications, there exist fur-ther possibilities to improve the enzyme inthe laboratory through directed evolution.This technique, which is becoming increas-ingly important in biotechnology, has beenestablished over the past two years in theBiomaterials Laboratory.

Every laccase has its optimal mediatorIn order to accelerate reactions with laccasesor to make these reactions possible at all,what are known as mediators are put to use.These are molecules that “mediate” be-tween laccase and the substance to be de-composed. In other words, the laccase reactswith the mediator, which in turn reacts forexample with lignin or dye, and in this wayit is retransformed into its original state,which means once again ready for the lac-case. In this way even large amounts of sub-stances or those which are hard to accesscan be efficiently decomposed. “The searchfor the right mediator for the right laccase

and for the right application is complex.Sometimes it’s just a matter of luck”, accord-ing to Empa wood expert Mark Schubert.

Empa is already recording its first suc-cesses. A very high yielding laccase pro-ducer, the white rot pathogen Heterobasid-ion annosum, was identified with the helpof a newly developed screening methodand was used to produce laccases. Further-more, they have been successful in usinggenetic-engineering methods to produce,purify and characterise an until now un-known thermostable bacterial laccase in E.coli.

Interested industrial partners havebeen identified in the areas of fine chemi-cals and wood processing, and further re-search in two projects financed by theSwiss Commission for Technology and In-novation CTI has been taking place sincethe end of 2010. The industrial applicationof laccases should not be far away. //

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Chemistry everywhereEvery material – just like every substance – is made up of chemicalelements. It’s no wonder, then, that a large number of chemists arehard at work at Empa. On the occasion of the “InternationalYear of Chemistry”, EmpaNews takes a peek into their laboratories.

TEXT: Beatrice Huber / PHOTO: iStock

UNESCO along with IUPAC (International Union of Pureand Applied Chemistry) have designated 2011 the Year ofChemistry. Under the unifying theme “Chemistry – our

life, our future”, the achievements of chemistry and its contribu-tions to the well-being of humankind are being highlighted. Ma-terials science is likewise tightly woven with chemistry. After all,every material ultimately consists of elements from the periodictable. And modern technologies use more and more of them, as isexemplified by the mobile phone: in its case there’s mostly carbon(in the form of a plastic) or aluminium; in the chip, silicon; in thecircuit board, gold; in the touchscreen, indium; and in the battery,lithium. And that’s just the start of the list – overall your averagecell phone contains 40 elements, give or take.

Chemists at Empa are looking into, among other things, newmaterials which are expected to be more effective, less expensiveand environmentally friendlier than those being used today (alsosee the article on page 15). For this, they are synthesising count-less as yet unknown materials and studying their properties. A fur-ther important area for chemistry is analytics. Empa researcherscan, for example, follow how long-lasting pollutants, some ofwhich have been banned for decades, can accumulate in variousecosystems (also see the article on the following page).

An appreciation for Marie CurieDuring the Year of Chemistry, the work of Maria SklodowskaCurie is also being honoured. This Polish-born scientist spent timein Paris investigating the phenomenon of radioactivity. Exactly100 years ago, Marie Curie received the Nobel Prize for Chemistryfor her discovery of the chemical elements radium and polonium,which are both radioactive. She was not only the first woman tobe awarded the Nobel Prize; she was also one of only four peopleto receive the Nobel Prize twice. In 1903, she had already receivedthe Nobel Prize for Physics together with Henri Becquerel and herhusband, Pierre Curie. //

The chemical elements are listed inthe periodic table according totheir atomic number. This figurecorresponds to the number of protonsin the nucleus. Modern technologies,such as are applied in telecommunicationsor transportation, use a large numberof still rather rare elements includinggold (Au), platinum (Pt), indium (In), andgallium (Ga).

Focus: International year of chemistry // 11

12 // Focus: International year of chemistry

Useful in the short-term,troublesome long-termMany substances used in industry persist in the environment, havea tendency to bioaccumulate and even decades later endangerthe health of people and animals. In order to show how and inwhich amounts poly- and perfluorinated compounds (PFC) as well aspolychlorinated biphenyls (PCB) are present, chemists at Empa aredeveloping custom-tailored, extremely sensitive analysis methods.

TEXT: Martina Peter / PHOTOS & GRAPHICS: Empa

Many chemical “refiners”, used byindustry to furnish materialswith desirable properties have a

severe drawback. Only very poorly dothese compounds decompose in the envi-ronment – if at all. They continue to showup in waterways, air and soil even decadesafter their production has been ceased,they accumulate to an undesirable extentin nature and present a serious threat forpeople and animals alike.

Persistent and surface active Consider the example of perfluorinatedcompounds (PFC), which are organic hy-drocarbon compounds in which all the hy-drogen atoms are replaced by fluorineatoms. PFC are extremely temperature re-sistant and chemically virtually indestruc-tible. Standard water-treatment plants failto handle them because PFCs cannot bedecomposed or filtered out.

Because they are simultaneouslygrease- and water-repellent, the textile andpaper industries use long-chain PFC to pro-duce dirt, grease and water-repellent mate-rials and packaging, for example, raincoatsand food wrappers, say, for hamburgers.PFC can also be contained in lubricants, im-pregnating agents and ski waxes.

PFC with hydrophilic end groups,known as perfluorinated tensides (PFT),reduce the surface tension of extinguish-ing foams. By almost completely coveringa kerosene fire, they build up a gas-tightfluid film between the combustible sub-stance and the foam and thus cut off theoxygen supply. Some of these PFT are alsovery popular in the electroplating indus-try. They prevent the formation of toxicmists during hard chrome plating in openmetal baths.

Until now, PFC have been “in service”without any restrictions. Only one of themost important PFT, perfluorooctane sul-fonate (PFOS), has had limited approvalfor industrial use since 2010, and there issome suspicion that it might be carcino-genic. Once taken up in the body, PFC bindto proteins and can be detected in theblood and especially in the liver, wherethey have been shown to cause cancer inanimal studies.

Verified in mountain lakes andpolar bear livers“We’re actually finding PFC everywhere inthe environment, even in polar bear liv-ers”, notes Claudia Müller. She’s a PhDstudent in Empa’s Analytical ChemistryLaboratory, writing her dissertation aboutthese problematic compounds under thesupervision of Konrad Hungerbühler, Pro-fessor for Safety and Environmental Tech-nology at ETH Zurich. “That wasn’t pre-dictable in the 1950s when we started touse them commercially.” It was only aboutten years ago that the problem came intofocus. In 2006 in Germany, groundwaterand drinking water was for the first timecontaminated with PFT. Farmers used a“bio fertiliser” which was incorrectly la-belled – it actually was industrial wastecontaining PFT – and which was washedout into rivers by rainfalls. The clean-upcosts are running into the multiple mil-lions of euros, and local residents havesince been examined regularly for toxicresidues. Even years after the scandal,negative effects are still being detected.

“But what’s the situation like inSwitzerland?” was a question posed by theFederal Office for the Environment(FOEN). PFC concentrations are generally

How do you detect substanceslike PCB which are poorlywater soluble? Passive collectorsmade of special silicon rubberwere attached to a pole andplaced in the water where theyremained for four weeks.


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low, but still too little is known about theirsources and how the substances spreadthroughout the environment. That’s be-cause the compounds are difficult to trackand can only be analysed with great effort.This is a challenge that excites Müller.“I’m interested above all in the intercon-nections. That is, questions like: Are per-fluorinated compounds more likely toarise in private households or in industrialprocesses? Are there large point sourcessuch as airports? How widespread are PFCproducts?” She took samples at 44 loca-tions all over Switzerland, from a varietyof rivers and lakes including a remotemountain lake as well as multiple possiblehot spots near airports and metal-workingfacilities, and determined the concentra-tion of 14 perfluorinated compounds.

Distribution of PFCs in SwitzerlandThe analysis proved to be anything butsimple. First of all, PFC are very surfaceactive and tend to stick to the sample con-tainers. Further, Müller had to pay veryspecial attention that the samples were not“contaminated”. That’s because even verysmall traces of PFC can be found virtuallyeverywhere, even in Empa’s laboratories.Together with her colleagues in the teamled by Empa researcher Andreas Gerecke,she developed a process to extract PFCfrom water samples and analyse them witha mass spectrometer. The result: the con-centrations of various substances weregenerally low, between 0.02 and 10nanogram per litre. In addition, she wasable to show that the level of pollution cor-relates well with the overall population.This indicates that the sources of PFCemissions are consumer products, such ascleaning agents, impregnated textiles orfurniture, rather than industrial processes.

So, can we issue an “all clear” signal?Not necessarily. “On the one hand,” cau-tions Müller, “the samples only represent asnapshot.” Therefore, FOEN is commission-ing a study intended to examine sewagesludge for PFC using new analytical meth-ods. “On the other hand, these substancescan accumulate in nature. That’s possibly adisadvantage for birds which feed on fish incertain rivers in Switzerland”, she adds.

CityPOP – emissions fromconstruction materialsNext, the Empa researchers are looking intohow and from where PFC manage to get intoremote mountain lakes. The first sampleswere recently collected within the scope ofthe newly initiated CityPOP project. For amonth, specially prepared foam filters were

exposed to air at 30 locations in the city ofZurich. This study, supported by the city andcanton of Zurich as well as FOEN, is designedto determine which chemical substances areemitted from construction materials in build-ings within the city.

Gerecke and ETH researcher ChristianBogdal are concentrating above all on per-sistent organic pollutants (POP) such asthe flame retardant HCBD (hexabromcy-clododecan). HCBD is used in polystyreneconstruction components, the light-blue orpink panels used for thermal insulation ofbuildings. This and other substances suchas plasticisers leak out of construction ma-terials even decades after being installed,and are thus a typical example of a “dirtylegacy” in the construction branch. Basedon their measurements, Gerecke and Bog-dal want to create a very special city mapof Zurich, one during the next few yearsthat shows neighbourhoods are contami-nated by POP emissions from constructionmaterials and to what extent. Their find-ings will then help to develop improvedemission-free construction materials.

Persistent and poisonous –polychlorinated biphenylAnother inherited pollution that hasemerged recently are polychlorinatedbiphenyl compounds (PCB), which wereutilised until the late 1980s. They wereused, for instance, as cooling and insulat-ing fluids in transformers and capacitors,as hydraulic oil and as plasticiser and flameretardant in wall coatings, sealants andplastics. There has been a total ban onthese toxic and carcinogenic substances inSwitzerland since 1986. Even so, largeamounts of PCB from previous applicationsstill linger today, such as approximately100 tonnes in joint sealing compounds inbuildings. Additional possible sources ofPCB include waste disposal sites, industrialbrownfields and metal recycling facilitities.

PCB can be released into the environ-ment from these “reservoirs” and, likePFC, bioaccumulate in the food chain. In2007, for instance, it was discovered thatfish from the Saane river in the canton ofFribourg and from the Birs river in the can-ton of Jura contained high levels of PCB.The highest concentration allowed in food-stuff is 8 picograms of toxic equivalents pergram of fresh weight, and this value was attimes exceeded by a factor of ten. Hobbyanglers were advised to limit their con-sumption of fish caught in said waters; forstretches of the rivers that were particular-ly contaminated, fishing was completelybanned.

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Innovative PCB collectors madeof siliconAt the same time, the cantons in chargewere working to identify PCB sources inthe drainage basin of the rivers in order toinitiate clean-up measures with thelandowners. The case for the Saane couldbe solved quickly: the source of PCB emis-sions is the former La Pila landfill, roughlyseven kilometres upstream from Fribourg.

In the Birs river just downstream fromthe village of Choindez, Empa scientists,working on behalf of the canton of Jura,had to take a far closer look. “That’s be-cause, for a chemist, fish are only a bio-in-dicator”, notes project manager MarkusZennegg. Fish are in constant motion, so ahighly contaminated fish caught in one lo-cation might not necessarily indicate theimmediate vicinity of the emission source.Thus, the Empa chemists, working with re-searchers from the Swiss Federal Instituteof Aquatic Science and Technology(Eawag), developed an analysis methodwhich, for the first time, detects even tinytraces of the dioxin-like PCB.

The “passive collector” consists of aspecial silicon rubber the size of a A5 sheetof paper. Akin to a flag, it is attached to apole and placed into the river. In two sam-pling periods, Zennegg and his colleaguesplaced the flags in two sessions, each timeputting 13 of them at various positions inthe course of the river. In each case, after

14 // Focus: International year of chemistry>>

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four weeks substances that are poorly wa-ter soluble accumulated on the silicon col-lectors' oil-like surface. “Just as a fish ab-sorbs toxins through its gills and skin, PCBdiffuse from the water phase into the plas-tic”, explains Zennegg.

By evaluating the data, it turned outthat the source had to be a factory down-stream from the village of Choindex, wheresteel had been produced since the mid-19thcentury and where, even today, steel con-tinues to be processed and recycled. Up-stream, no high PCB values were measured.The canton of Jura is currently working withthe operator of the manufacturing facility todetermine the origin of the PCB which madetheir way into the Birs, in order to be ableto sketch out measures to prevent future deposits in the waters. //

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1The analysis of the different poly-and perfluorinated substancesturned out to be a difficult taskbecause the compounds are, amongother things, very surface active.

2Water samples were also takenfrom the Aare river in theGrimsel region and checked for PFC.

3As the analysis of the passive collectorshowed, the largest amounts of PCBin the Birs were found downstreambetween Choindez and Courrendlin.


The variety of materials used in modern technology is virtu-ally limitless. Quite frequently, these materials contain notonly common chemical elements such as titanium, iron or

aluminium, but also very rare elements, for instance tellurium (forsolar cells) or rhodium (for catalytic converters).

Meanwhile, the search for new, improved materials proceedscontinuously. The goal is, on the one hand, to optimise the materialproperties and, on the other hand, to find replacements for materialconstituents which are disadvantageous in terms of scarcity (tellur-ium), price (precious metals) or environmental impact (cadmium).

Multi-talented perovskiteEmpa researcher Anke Weidenkaff has been working with col-leagues in her Solid State Chemistry and Catalysis Laboratory forquite some time on what are known as perovskite metal oxides.Perovskites are a class of compounds with the molecular formulaABO3, where A and B represent transition metals and O is oxygen.Due to their high temperature, pressure and oxidation stability theycan be put to use in a wide range of applications and are environ-mentally safe. In naturally occurring perovskite, A is calcium and B

Design studio fornew materialsEven everyday technologies such as catalytic convertersor rechargeable batteries for mobile phones and electricvehicles use “exotic”, meaning rare elements. Theyare expensive and also often poisonous. Chemists atEmpa are studying new materials based on readily available,affordable and environmentally friendly elements.

TEXT: Beatrice Huber / PHOTOS: Empa

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Chemists at Empa are working on perovskite metaloxides. Perovskites are a class of compounds with aflexible yet stable crystal structure, their chemicalcompositions can be varied widely and thereby thephysical properties, such as colour, can be modified.


is titanium. “Thanks to the perovskites’ flexible and yet stable crys-talline structure, their chemical composition can vary widely,”Weidenkaff describes their merits. “Moreover, the specific ex-change of both metal ions as well as oxygen enables us to optimisethe material’s physical properties, that is magnetic behaviour, elec-tric or thermal conductivity, colour and much more.” The under-lying idea is to synthesise new materials for various applicationsby using readily available, affordable and environmentally friendlyelements. Examples of use are rechargeable batteries in electric vehicles, catalytic converters and thermoelectrics, i.e. materialswhich convert heat directly into electricity.

Electricity storage as a key technologyThe major drawback of renewable energy sources such as solar ra-diation and wind is that they are not continuously available andthus cannot be used on demand. As a result, energy conversionand storage technologies are playing a key role in aligning supplyand demand and to leverage renewable energy sources. Researchprojects on polymer solar cells or solar water-splitting processesare further examples for activities in this field at Empa.

Batteries are the electrical energy storage systems of choice,especially for transportation purposes. Electricity is converted intochemical energy which can be easily stored. The reverse processreleases the electricity again, which can be used to power electricalvehicles or plug-in hybrid vehicles. Batteries have to fulfil three ba-sic requirements: they must be safe, reliable and affordable. Thesedemands on quality can be illustrated by a simple calculation. Infuture, the operational lifespan of batteries should correspond tothat of vehicles, i.e.15 years. Assuming daily recharging, a total ofapproximately 5500 charge/discharge cycles would arise. Today,only high-quality batteries, far too expensive for electrical vehicleapplication, can meet these standards.

Replacement for the “heavyweight” cobalt oxideAt present, lithium-ion batteries are considered as state-of-the-art,yet far from perfect. Cobalt contained in the frequently used cath-ode material lithium cobalt dioxide (LiCoO2) is heavy and thus re-sults in heavyweight batteries. What is more, cobalt is one of themost expensive transition metals due to its scarcity. Materials con-taining little if any cobalt but rather manganese, for example, arecurrently a hot research topic. Scientists at Empa are are even going beyond this. “We don’t just want to replace the cobalt”, explains Angelika Veziridis from Weidenkaff’s team. “We’researching for completely new materials, since the battery perform-ance in terms of energy density and reliability needs to be im-proved considerably.”

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1Laboratory experiments are notperformed simply by trial and error;Empa researchers deal intensively withthe relationship with the relationshipbetween crystal structure, composition,microstructure and material properties.

1


At room temperature, perovskite-type metal oxides exhibit a veryhigh lithium ion conductivity, making them interesting as alternativeelectrolytes but also as anode or cathode materials. Empa researchersare trying to even increase this conductivity by substituting of indi-vidual elements. This is not restricted to metal ions but also includesthe exchange of oxygen with nitrogen. The resulting oxynitrides exhibit an even higher lithium capacity and a better conductivity. In addition, they’re chemically and thermally more stable than pure oxides or nitrides.

The relationship between composition, structure and effectHowever, the chemists are not just acting upon the trial-and-errormethod but are rather trying to get to the bottom of how the com-position and thus the microstructure influences the material prop-erties. “Only if we have precise knowledge of the crystal structureor the locations where mobile ions are embedded or the oxidationstate of the transition metal, are we able to determine how thestructure influences the material properties”, Weidenkaff pointsout. In close collaboration with researchers from other laboratoriesat Empa and ETH Zurich, Weidenkaff’s team is synthesising vari-ous complex oxides and oxynitrides in order to investigate, amongother things, their application in batteries.

Less precious metal in catalystsIn the short term, efficient transportation can not be accomplishedwithout the use of fossil fuels. Among them, natural gas becomesincreasingly important as its combustion generates less NOx and CO2compared to petrol and diesel. However, the exhaust fumes fromnatural gas vehicles need a special treatment in order to removetraces of non-combusted methane which is a potent greenhouse gasand about 20 times more climate-damaging than CO2.

Until now, engineers simply adapted catalytic converters frompetrol-powered vehicles to the emission profile of natural gas ve-hicles. However, to ensure the removal of even small methane con-centrations, these converters contain at least three times as muchprecious metal. Within the scope of a national research programmeentitled “Intelligent Materials”, researchers from the Solid StateChemistry and Catalysis Laboratory are working together with en-gineers from the Internal Combustion Engines Laboratory on newtypes of catalytic converters for natural gas vehicles. They are sup-posed to have a long service life and require less precious metal.The Empa team wants to completely eliminate rhodium, which isone of the most prevalent constituents of conventional catalyticconverters but also one of the rarest and thus most expensive met-als of all. Instead, the researchers are taking advantage of a well-known property of perovskite-type metal oxides: in a reducing at-

mosphere precious metal atoms exit the crystal lattice and are dis-persed at the surface, while in an oxidising atmosphere they re-en-ter the structure. In this way, the precious metal particles can bestabilised and a constant catalytic activity is ensured.

The scientists are currently studying the catalytic efficiency ofvarious perovskite-type metal oxides by analysing both the structure and chemical composition as well as the reactivity in oxidation-reduction cycles typical of catalytic converters in auto-mobiles. First encouraging results have been achieved withLaFe0.95Pd0.05O3. The next step is to test those materials, whichhave shown promising results in the laboratory, in a natural gasengine.

A replacement for the “problem child” lead tellurideA sustainable supply of energy, however, can only be achieved bya more economic and efficient use of primary energy carriers. Tech-nical equipment and machines generate considerable amounts ofwaste heat, most of which simply dissipates unused – or even hasto be elaborately discharged. Thermoelectric generators can convertthis waste heat directly into electricity without any moving parts.Until now, however, such generators have been used only in nicheapplications such as space probes or buoys because inexpensive andefficient thermoelectric materials have not been available. Tellur-ium, for example, an integral constituent of today’s most commonthermoelectric materials, is scarce, expensive and also poisonous. Inaddition, the efficiency of these materials is modest and they are sta-ble only up to temperatures of 300°C.

The scientists in the Solid State Chemistry and Catalysis Labo-ratory strive to design perovskite-type metal oxides for thermoelec-tric applications, as well. Due to their high temperature stability inair, they’re well suited for an operating temperature range of up to1000°C. The researchers are looking for new thermoelectric mate-rials which are further optimised, for example, by nanostructuring.That way, the undesirable thermal conductivity is reduced while atthe same time the essential electrical conductivity is increased.

A nanostructured metal oxide (consisting of oxygen, calcium,manganese and niobium) has already been prepared. In contrastto oxides synthesised by conventional solid-state reaction meth-ods, the thermoelectric figure of merit ZT is twice as high makingit the best n-conducting perovskite-based thermoelectric materialat present. The figure ZT is a measure of quality of a thermoelectricmaterial. Today’s best thermoelectric materials have ZT values be-tween 0.8 and 1.1. ZT values between 1.2 and 1.5 along with agood thermal stability would be sufficient to cover the car’s de-mand for electricity by applying a thermoelectric generator in theexhaust gas system. //

2Not only the chemical composition butalso its microstructure influences thematerial properties. The picturesshow electron microscope images ofperovskite-type metal oxides.

1 μm 20 μm

2


When "corroding" implants are beneficial

In most cases, corrosion is undesirable. Sometimes, though, it canbe useful – for instance in biodegradable implants. Timing is, how-ever, critical; the degradation process should be carefully con-trolled to avoid dissolution of the implant before it has fulfilled itsfunction. Empa’s Analytical Chemistry Laboratory has developedan analytical setup, with which they measure local dissolutionprocesses. It is, for instance, possible to determine which ele-ments will preferentially dissolve out of an alloy and, throughautomated operation, to follow the dissolution process overtime. In collaboration with the Laboratory for Corrosionand Materials Integrity, this setup is currently used tostudy magnesium alloys, which are promising candi-dates for biodegradable implants because of their highbiocompatibility. Their corrosion behaviour is deter-mined, to a large extent, by the chemical composition ofthe alloys. Often impurities such as iron are kicking off lo-cal corrosion processes. In contrast, alloying componentsof the rare earth group such as yttrium seem to slow downthe dissolution rate of magnesium alloys. However, Empa re-searchers, in collaboration with ETH Zurich and partners from in-dustry, are still investigating their role.

The result of a master’s thesis: monocrystals withthermoelectric properties. (Photo: Empa)

Students at Empa

Knowledge transfer can’t get any more directthan this – each autumn semester, chemistry stu-dents from the University of Bern complete partof their inorganic chemistry trainings at the EmpaSolid State Chemistry and Catalysis Laboratory.It’s not really worthwhile to travel from Bern toDübendorf for just a few hours, so the trainingsare organised in two-day blocks. That, in turn,makes it possible to carry out extensive experi-ments in the laboratory. Objects of study includeperovskite compounds (ceramic oxide) for auto-mobile catalytic converters as well as thermoelec-tric converters for converting heat into electricity.The students synthesise the materials and inves-tigate them in great depth. In this way, they areintroduced to a variety of methods such as for theanalysis of elements and crystalline structures, orhow the morphology of materials can be studiedwith an electron microscope. These trainings also motivate students to contin-ue with their master’s thesis at Empa laborato-ries. Consider the current example of DavidMoser. Within the scope of the national researchfocal area MANeP (MAterials with Novel elec-tronic Properties), in his master’s thesis he is in-vestigating the manufacture of thermoelectricmonocrystals for studies using ARPES (angle re-solved photoemission spectroscopy). “Direct ac-cess to all the instruments needed for analysis,the interdisciplinary work and the large team are,from my viewpoint, the primary advantages com-pared to a classic university programme”, saysMoser. “Here I also get enough time to study andso I can grow into my assignments.” How is it possible to measure nanoparticles in a fluid medium such as the aerosol

from a spray can? Empa researchers have assembled an experimental setup forthis purpose. Here various spray products and their behaviour in the atmosphereare being investigated. (Photo: iStock)

Valve Pump

Micro-flow capillary

Metallic samples

Plasmamass

spectrometer

Electrochemicalsetup


Open house

A number of Swiss universities are tak-ing the Year of Chemistry as an occasionto open up their laboratories to the publicand provide a glimpse into the researchtaking place in chemistry. Most of theseevents will take place on Saturday, 18June. More details can be found at the Internet addresses provided below or atwww.chemistry2011.ch. Further informa-tion about the Year of Chemistry is avail-able at www.chemistry2011.org.

– University of BaselFest der MoleküleDepartment of Chemistrywww.fest-der-molekuele.ch

– University of BernOpen houseDepartment of Chemistryand BiochemistryAmong those giving presentationsis Anke Weidenkaff, EmpaLaboratory Head and Professorat the University of Bern.www.dcb.unibe.ch

– University of FribourgFest der ChemieDepartment of Chemistry

– University of Zurich/ETH ZurichKulturleistung ChemieUniversity of Zurich, Irchel Campus(“Farbstoffe, Duftstoffe,Kunststoffe”)ETH Zurich, Hönggerberg Campus (“Werkstoffe, Wirkstoffe, Naturstoffe”)www.kulturleistungchemie.ch

Nanoparticle release from spray products

Around the world, more than 1500 everyday products containing syntheticnanoparticles are already on the market. Among these are, for instance sprays,which contain silver nanoparticles for antibacterial applications. However, be-cause aerosols created during spraying can be easily inhaled and also becausenanoparticles can be easily absorbed, especially in the lungs, it’s important toknow if synthetic nanoparticles are released and how they subsequently behave.To investigate nanoparticles in solutions and aerosols in a reliable and repro-ducible manner, Empa’s Analytical Chemistry Laboratory has assembled a newexperimental setup. In cooperation with researchers from Empa’s AirPollution/Environmental Technology Laboratory and a group from ETH Zurichled by Konrad Hungerbühler, the team can determine the size, size distribution,chemical composition and morphology of the released nanoparticles.Their findings show that, especially in those applications involving a propellantgas dispenser, aerosols often contain particles smaller than 200 nanometres,which is a critical size for cell uptake. Furthermore, even a few minutes after theuse of the spray, these particles can still be detected. Whether airborne nano-particles are present or if they clump together into larger particles mainly dependson the type of spray container: in contrast to propellant gas dispensers, the useof a pump spray vessel shows no detectable nanoparticle release. But also thecomposition of the spray product has an influence on the released particles. Theseresults are establishing the fundamental data needed to model the behaviour ofsynthetic nanoparticles from spray products over an extended period of time, andthe ability to estimate the exposure of consumers to them.

Principle of the newly developed analytical setup: a thin capillary is placed onthe sample, and filled with a corrosive medium (e.g. a saline solution). Atdefined time intervals, a small amount of the solution is taken from the capillaryand sent to a plasma mass spectrometer to determine the different dissolutionrates of the individual elements.


These days, almost 80 per cent of all chemical prod-ucts result from processes which involve catalysts.In the manufacture of polymers, for instance, cat-

alysts initiate, accelerate and direct chemical reactions sothat the result is predominantly – or even sometimes ex-clusively – the desired product, for example the highlyfunctional thermoplastic polyethylene. The problem,though, is that base materials are often contaminated withtraces of acetylene. This “poisons” the catalysts, whichtypically consist of powdery palladium-silver alloys, suchthat the catalysts must be replaced regularly. Given aworldwide production of 60 million tonnes of polyethyl-ene each year, this entails considerable costs.

In order to develop durable catalysts with a long life-time, researchers at Empa are collaborating with theMax Planck Institute for Chemical Physics of Solids inDresden, the Fritz Haber Institute in Berlin and the Lud-wig Maximilian University (LMU) in Munich. In partic-ular, they are focusing on a palladium-gallium inter-metallic compound. This innovative catalyst, which incontrast to alloys has regular lattice structures, shouldbe able to suppress undesired side reactions and preventsegregation (the separation into different elements),thereby making the chemical processes on the catalystless complex. Palladium-gallium can withstand the “poi-son” by converting acetylene into ethylene through se-lective semi-hydrogenation.

Robust accelerant

It’s at the very top of the industrial wish list: a robust,long-lasting catalyst for the production of polyethylene.A novel palladium-gallium compound is a candidatewith great promise. In a European project, researchers arenow determining whether its future use makes economicsense. Empa scientists are, for instance, observing atthe atomic level how individual precursor moleculesbehave on the catalyst surfaces.

TEXT: Martina Peter / PHOTOS: Empa

1Photoelectron spectroscopy reveals the fact that the palladium-gallium monocrystal is chiral, that is, the front and back sidesare not identical but instead have a relationship to each othersimilar to an object and its mirror image.

2Front and rear view of a monocrystal: in a diagrammatic representationof crystals, the numbers (111) and (111), known as the Miller indices,serve to provide an unambiguous description of the crystal surface andthe planes of the crystal lattice.

Ga


However, because palladium-gallium is considerablymore expensive than existing catalysts, the researchershave to explore ahead of time in the laboratory whetherits future use would make economic sense. For industry,this innovative catalyst only becomes a viable option ifit is very selective, long-lived, highly effective, and dueto these factors, cost-effective.

Following chemical reactions step by stepIn a project sponsored by the Swiss National Science Foun-dation (SNSF), scientists from Empa’s nanotech@surfacesLaboratory are studying the catalyst’s surface structure.“While a chemist would focus on the actual reaction, wetake an atomic approach”, says project leader Roland Wid-mer. “We take an individual acetylene molecule and wantto find out exactly where it “sits” down on the palladium-gallium surface, what the hydrogen molecule does and ex-actly how the two react with each other.” Widmer’s goalis to follow the chemical reaction pathway step by step andto understand the reaction mechanism in detail. “So far,catalysts have been developed on a purely empirical basis.With our approach, we want to systematically contributeto improving their efficiency”, he says. The findingsshould lead to the ability to design and structure the sur-faces such that the catalytic process can proceed as effec-tively and inexpensively as possible while, at the sametime, preserving the environment and our natural re-sources to the largest possible extent.

For their work, the Empa team uses palladium-galliummonocrystals which are grown by their LMU colleaguesin Munich. These crystals have a homogeneous lattice,in which each atom sits in a defined location. Severallayers of the crystal lattice consist primarily of pallad-ium, others of a palladium-gallium mixture, and yet oth-ers primarily of gallium atoms. Depending on how thelayers are aligned and which surface energies they have,they function differently as catalytically active surfacesin the reaction between acetylene and hydrogen – some-times the catalyst is more efficient, sometimes less so.

Studying surfaces with different techniquesAt the moment, Widmer and his colleagues are studyingthe catalyst surfaces with a variety of different physicalmethods such as scanning tunnelling microscopy and X-ray photoelectron spectroscopy, supported by computermodelling. The researchers have already obtained someinitial results: the palladium-gallium monocrystal is chi-ral, that is, the front and back sides are not identical butinstead have a relationship to each other similar to an object and its mirror image. Whether or not this influ-ences the catalytic activities of the two mirror-image crys-tals is one of the questions the scientists want to examinein detail in the coming months. //

2

1

Pd

PdGa(111) PdGa(111)_ _ _

PdGa(111)_ _ _

PdGa(111)


Following the path offloating particlesThe newly appointed ETH professor and Empa researcher Jing Wangis investigating small and even the smallest particles floatingin the air. In order to study nano-sized particles, he set up a speciallaboratory at Empa, including a wind tunnel.

TEXT: Remy Nideröst / PHOTOS: Empa

Aroom, one filled with shiny ventilation ducts. That’s whatthe newest laboratory at Empa looks like. But what is thissetup used for? No, it’s not intended to make sure that re-

searchers and engineers at Empa are able to work in very comfort-able indoor conditions; rather it’s needed for scientific projects. Al-though a wind tunnel in the Building Technologies Laboratory wasjust dedicated in March, tests have already been running here on asecond such installation. “With it, though, we’ll be doing somethingcompletely different than the wind researchers in Building Tech-nologies,” explains Chinese-born Jing Wang who recently took uphis activities at Empa. “We’ll be investigating nanoparticles sus-pended in air.”

Jing Wang is taken with nanoparticles. Already his doctoral re-search at the University of Minnesota dealt with particles suspendedin fluids and gases like air. One example is that he dispersednanoparticles in polymer solutions to achieve new properties. “Inthis way we created new viscoelastic fluids” – and thus made it pos-sible to obtain usually high extensional viscosity. Since then, he hasprimarily studied fine airborne particles, known as aerosols. For in-stance, as Research Assistant Professor in Minnesota, where startingin 2007 he became the lab manager of the university’s Particle Tech-nology Laboratory.

After all, too coldAfter a total of ten years in the USA, his career has now brought JingWang to Switzerland. Last summer, he took on a position as Assis-tant Professor for industrial ecology and air-pollution control at theInstitute of Environmental Engineering at ETH Zurich; at the sametime he became Group Leader in the Analytical Chemistry Labora-tory at Empa.

On the one hand, he had enough of the climate in Minnesotawhere the winters are extremely cold and long. “Last winter inSwitzerland seemed like spring to me”, comments Wang with asmile. On the other hand, he was also attracted to Switzerland bythe professional opportunities available to him as a professor.“ETH Zurich is among the top universities in the world. For me,the combination of ETH and Empa is simply ideal”, comments

Wang, who raves about the excellent infrastructure and the envi-ronment offered to him at Empa for his research activities. The lab-oratory for the wind tunnel alone measures around 100 square me-tres. “That’s far larger than would have been available to me in theUSA.”

Everything is still being set up. One of the rooms has a bit offurniture, but otherwise it’s just about empty. In another a few in-struments are scattered about, some just having been unpacked.One of them produces nanoparticles which will be measured bythe others. An additional piece of equipment on the way is one thatWang developed himself. With it, nanoparticles or agglomerates ofthese tiny particles can be measured with high accuracy (primarysize, morphology, and agglomerate number, surface and volumedistributions). A prototype unit is already in use at the chemicalcompany BASF, which co-financed this development. It charac-terises the nanoparticles being produced there, for example titan-ium dioxide. This material serves as a catalyst in chemical process-es and has applications as a pigment in paints.

Previously, the morphology of nanoparticles produced in aflame reactor had to be analysed using a microscope. By the timeit was determined if their quality was adequate, tonnes of the par-ticles had already been produced. The test instrument Wang de-veloped, on the other hand, measures nanoparticles “online” – theresults are known within minutes. This time factor is a significantadvantage, and so for the instrument, called “universal nanoparti-cle analyser”, a patent is pending and the commercialisation is un-der way. “Then I’ll be sure to get one of those instruments for mywork”, jokes Wang.

Nanoparticles in the air – largely unexploredThere’s still too little known about exactly what happens to the air-borne particles. Therefore, workers often protect themselves pre-ventative with spacesuit-like clothing while cleaning productionfacilities. The wind tunnel is an excellent instrument for studyingnanoparticles under well-defined conditions. Thanks to fans, heat-ing and humidification, it is now possible to precisely control windspeed, temperature, humidity and other test parameters. In field

1


studies, these parameters are largely unknown. Wang’s team man-ufactures nanoparticles themselves and thus has precise knowl-edge about their size and nature. As soon as they are “set free” ina wind tunnel, they are very mobile and agile and remain in theair for a very long time; that’s in contrast to larger particles whichfall to the ground more quickly because they weigh more. “We in-vestigate how long they remain in the tunnel’s airstream under ex-actly defined conditions, how they propagate, whether they ag-glomerate and in this way change their size and whether they reactto each other chemically”, explains Wang. In addition, in the windtunnel we’ve installed measurement points at various spots, andour instruments then analyse the collected samples.”

In the tunnel, air-ventilation filters can also be tested so thatthe concentration of particles in front of the filter can be comparedto that behind it. Such devices can also filter out particles withnanometre dimensions, and new challenges are emerging withnew nanomaterials for filter manufacturers, with whom Wang isin very close contact, like 3M, which manufactures face masks, orBoeing for the filters installed inside aircraft interiors.

Collaboration with other research groupsAt Empa there’s a series of colleagues who deal with nanotech-nologies and are interested in Wang’s work. One of these is the In-ternal Combustion Engines Laboratory. Wang plans to collaboratewith that group to investigate the soot particles that come fromdiesel engines. Their findings could lead to better soot filters andcatalysts.

Furthermore, at ETH as well as at Empa, life cycle analyses(LCA) are being carried out. Until now, such analyses on productsthat contain nanoparticles have been somewhat imprecise becausethere’s hardly any experimental data available showing what hap-pens to nanoparticles when a given product is recycled or disposedof. It’s possible to make precise statements about the risks onlywhen the level of exposure and the behaviour in the environmentare known. Products could therefore not be evaluated accuratelyafterwards using a LCA; that’s a gap that will be filled thanks tothe future work of Wang and his group. //

1Empa researcher JingWang’s equipment:the wind tunnel forinvestigating nano-particles is an installationbuilt with externaldimensions of roughly3 x 13 metres.

2Jing Wang at hisintroductory lectureat ETH Zurich on30 March 2011.

3Nanofibre filters for removingparticles consist of multiplelayers. The fibres on the top layer,with a diameter around 100 to150 nanometres, can provideexcellent filtration performance.The fibres in the background,with diameters of about 10 to20 micrometres, providenecessary mechanical strength forthe composite filter.

310µm

2

26 // Im Dialog

With chemical depth profiles, it’s possible to analyse thin layers, suchas in solar cells, for their chemical composition from top to bottom.This lets scientists and engineers check whether the materials usedare present in the desired order and purity. Empa researchers havedeveloped an instrument which can create the chemical depth profileof very thin layers quickly and with high resolution.

TEXT: Beatrice Huber / PHOTOS & GRAPHIC: Empa

Layers at the micro- and nanoscale aregrowing in popularity in research andindustry thanks to their unique physi-

cal properties. They find applications, for in-stance, as polymer films in organic electron-ics, in food packaging and also in photo-voltaics. Experts at Empa and other researchinstitutes are designing prototypes of innova-tive solar cells made of various organic andinorganic materials. These cells are only afew micrometres thick but even so achievethe same or even better efficiency than con-ventional solar cells made of silicon. In addi-tion, thin-film solar cells are significantlylighter, which expands the number of placeswhere they can be used, and they require lessmaterial in their production.

To make sure that sunlight is convertedinto the largest amount of electricity, thefilms are generally very complex and builtup of a wide range of materials. Producingthese multilayer films precisely, reliablyand in a reproducible manner means thatthe design and chemical composition of theindividual layers must be checked on a reg-ular basis. Instruments which create achemical depth profile are thus required.Empa’s Mechanics of Materials and Nano-structures Laboratory in the city of Thunhas developed such an instrument.

Fast – and at the same time withhigh resolutionThe plasma profiler, as the instrument iscalled, combines mass spectrometry with aglow discharge. The latter uses a plasma inthe noble gas argon to release and ioniseatoms and molecules from the solid sampleunder analysis, and this at an ambient pres-sure of only a few millibar. The resulting ionsthen make their way into the mass spectrom-eter, which determines the chemical compo-sition of the thin layers.

“The combination of glow discharge andmass spectrometry isn’t really anythingnew”, remarks Empa researcher James Whit-by, who co-developed the instrument. “Thetime-of-flight mass spectrometer we use,however, enables a very fast measurementwithout the need for us to limit the massesover which we can measure. That’s some-thing which has been unavailable until to-day.” The importance is that the time-of-flightmass spectrometer analyses all the ions at thesame time including very large ones, for ex-ample those from polymers, even when thelayers are very thin. The depth resolution isapproximately five nanometres.

A development on the roadto marketabilityThe initial work on the plasma profilerstarted roughly eight years ago. Develop-ment of the instrument then continuedwithin the scope of a project financed bythe Swiss Commission for Technology andInnovation CTI. Besides Empa, Tofwerk AGwas involved. That company, headquar-tered in Thun, specialises in time-of-flightmass spectrometers. Further European uni-versities and industrial partners then joinedthe effort for a follow-up project which waspart of the EU 6th Framework Programme.In all, three prototypes were built. Besidesthe first instrument in Thun, today there isalso a plasma profiler at the University ofOviedo in Spain and another located at oneof the industrial partners, HORIBA JobinYvon SAS in Paris, which is also alreadymarketing the commercial version of the in-strument.

The Empa researchers in Whitby’steam have worked primarily on the funda-mental aspects. “We’ve invested a greatdeal of time in understanding and master-ing the instrument”, elaborates Whitby.“That’s because an analysis instrument isuseful only when we can correctly interpretits ‘output’.” How must the samples be pre-

Into chemical depths

24 // Knowledge and technology transfer

1

Surfacecontamination

Chromium layer(2 nm)

Traces ofphosphoric acid

Sign

al

Aluminiumoxide layer

Aluminium

C+

Al+

P+

O2+

Cr+

200150100Time (s)

500

0.001

0.01

0.1

1

10

Im Dialog // 27

pared? Which ambient pressures are opti-mal? At which frequencies must the plasmabe excited? Which materials leave which“fingerprints” in the mass spectrometer? Allthese questions need to be answered if theinstrument is to deliver reliable and repro-ducible results.

An instrument with many talentsThe plasma profiler offers a wide range ofadvantages, just one being pulsed excitation.Metastable argon atoms – which are espe-cially numerous in the plasma during the afterglow, in other words in the short timeafter the pulse – ionise the sample material“gently” and thus simplify the mass spec-trum from molecular materials. In addition,the pulsed excitation preserves the samplematerial so even substances such as glass,which would be damaged by continuous ex-citation, are now “analysable”. Even so, thisisn’t enough. Thanks to the time-of-flightmass spectrometer, the instrument not onlymeasures positively charged metal ions butalso negatively charged anions, for examplehalogens like fluorine and chlorine, some-thing not so easy when used in combinationwith other mass spectrometers. Because theplasma profiler employs radio-frequency ex-citation, non-conductive samples can also be

analysed. That’s something that until nowwas impossible with commercially availableinstruments which combine mass spectrom-etry with a glow discharge, but nonethelessis important when studying organic poly-mers.

Thus, this multi-talented machine has acorrespondingly wide range of applications.One example is the study of corrosionprocesses, such as on cultural assets but alsoin the automobile and aerospace industries.It’s also possible to perform chemical analy-ses with nanometre precision on coatings formedical implants and dielectric mirrors,which reflect only a portion of the light spec-trum and are used, for instance, in lasers.

Instrument for 3D profilesThe plasma profiler is on the road to com-mercialisation. The Empa team is alreadyworking on further projects. For example,they’re developing an instrument whichshows results at high resolution not only intothe depths of a sample but also laterally, thatis, to the side. With it they can create 3Dchemical maps of complex, multicomponentmaterials. //

Knowledge and technology transfer // 25

1Thin layers are studied for a variety of applica-tions such as in photovoltaics. Producingthem precisely, reliably and in a reproduciblemanner means that the design and chemicalcomposition of the individual layers must bechecked on a regular basis.

2The plasma profiler analyses samples andcreates chemical depth profiles even from verythin layers and does so with high resolution.The glow discharge takes place in the chamberat left in the photo (the sample holder isnot visible in this closed position); on the rightis the mass spectrometer (along with itspower supply).

3Depth analysis: an extremely thin chromiumlayer (violet, 2 nanometres thick) was embed-ded within an aluminium oxide layer (blue,230 nanometres thick). The peak shows withhigh resolution where the chromium layeris located. The strong signal at the start of themeasurement results from surface contamina-tion with carbon.

2

3

26 // Science dialogue

Wind tunnel inaugurated in Dübendorf

A typical city: row upon row of houses, asphalted roads, very few green areas.Cities built on this pattern warm up more strongly than their rural surround-ings, creating heat islands. The waste heat emitted by vehicles and machinery(such as air conditioning equipment) causes yet more heating, and even duringthe night the cities hardly cool down. The new wind tunnel, constructed by Empa together with ETH Zürich and in-augurated in March, is 26 m long and about 4 m high. In it, ideas for improvingthe "airing" of cities can be simulated, on a scale ranging from 1 to 50 to 1 to300. A ventilator with a diameter of 1.8 m powered by a 110 kW electric motorblasts air at up to 90 kilometres per hour through the tunnel. The researchersplan to investigate how air masses circulate around buildings, what velocitiesand turbulences occur and what effect does all this have in terms of energy,comfort and health. They would also like to know such things as whetherhouses can be cooled by the wind alone in summer (free of charge!), wheredraughts might cause problems – for example in street cafes – and whetherpollutants can be transported away by natural means.

Laser technology makes wind speeds visibleThe Empa wind tunnel has a sophisticated measuring instrumentation, whichincludes two high-speed cameras and a special high-performance laser.Whereas in other wind tunnels air mass movements must be inferred from aset of single measurements made at specific individual locations, "…we canmake the air currents visible almost in real time, even with all their fluctua-tions," says Victor Dorer, the Empa scientist responsible for the wind tunnel.In order to make the airflow “visible” to the two high-speed cameras, tiny par-ticles are injected, which are then lit up by a special laser producing a sheetof light. Pictures taken at millisecond intervals make the movements of theparticles visible. (Photo: Monika Estermann)

Laser Centre in Thun

In April 2011, the new Laser Centre wasdedicated in the presence of Empa DirectorGeneral Gian-Luca Bona and the Mayor ofThun, Raphael Lanz. It houses one of theworld’s most unique UV laser systems witha granite table measuring 4.5 x 2.5 metresand which was transported to Thun inOctober 2010 in a spectacular fashion.With the Laser Centre, Empa will workin close collaboration with CrealasGmbH to microstructure very large sur-faces. The system, under the manage-ment of Patrik Hoffmann, was created toaid in the development of innovative sur-faces. At the centre, industrial partnerswill manufacture unique types of largefilms using laser engraving with micro-and nanometre precision. The processingimparts the materials with new physical-mechanical properties. The microstruc-tures reduce friction, have a water-repel-lent effect and can inhibit fungal growth.Films for optical structures with light-controlling properties can also be manu-factured, whether for new types of light-ing, 3D screens or photovoltaics.

Science dialogue // 27

World Resources ForumBeing held for the second time, the World Resources Forum (WRF) will take place inDavos from 19 to 21 September 2011. The event aims to broaden the current focus on cli-mate change, because this is according to the organisers only a symptom of the biggerproblem: our current economic system needs too much natural resources. Global resourceproductivity has to be increased drastically in order to address the huge economic, envi-ronmental and social challenges the world faces. The WRF is an initiative of Empa; among the partners are UNEP’s International Panel forSustainable Resource Management, the Swiss Federal Office for the Environment FOEN, theFederal Environment Agency Germany UBA, the Swiss Agency for Development and Coop-eration SDC, the Swiss State Secretariat for Economic Affairs SECO as well as the SwissAcademy of Engineering Sciences (SATW). Registration: www.worldresourcesforum.org

“We want to present creativeapproaches for hot topics”

EmpaNews spoke with Xaver Edelmann, President of WRF andEmpa board member, about the goals and highlights of the event.

Mr Edelmann, what does the World Resources Forumwant to achieve?

The World Resources Forum wants to raise awareness of the “re-source problem”. It is both about rare-earth metals for high-tech prod-ucts and scarcity of natural resources in general. Besides “Peak Oil”,we already also speak about “Peak Minerals” or “Peak Metals”.

Whom do you address?On the one hand, of course, scientists who develop the knowl-

edge base to understand how to bring about sustainable use of resources, on the other hand politicians and government leaderswho have to take care of the political framework conditions. Wealso address the private sector which has to get ready for futurescenarios in terms of a “green economic system”, as well as thesociety in general, especially the young generation.

Why should we go to Davos?Because creative approaches for hot topics regarding natural re-

sources will be presented there. Furthermore the WRF is THE plat-form for resource productivity. I look forward to valuable ideas andproposals on how to implement a “green economic system”.

Could you tell us some of the highlights of the programme?Doris Leuthard, Federal Councillor and Swiss Minister for the

Environment, Achim Steiner, Executive Director of the UN Envi-ronment Programme (UNEP), as well as Janez Potocnik, EuropeanCommissioner for the Environment, have confirmed as speakers.Ashok Koshla, Co-president of the Club of Rome, will present thepoint of view of emerging and developing countries. The industryworkshop, a platform to highlight practical business cases, isamong the most promising events to me. And, hopefully, youngpeople from all around the world who participate at the same timein a multiday workshop will become a true highlight. I expect un-conventional and interdisciplinary discussions and suggestions inthis workshop.

What do you hope for the WRF?A constructive platform for dialogue between science, econo-

my, politics and the society. And, hopefully, a lot of innovativeoutput. The latter should be further worked on. We will expandthe World Resources Forum into a vivid information platform,also making use of the Internet and the social media, so that theWRF stays alive and kicking also after September 2011. //

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Events14, 21 and 28 June 2011A Holistic Approach to Fleet Management Fleet managers, environmental experts, vehiclesales staff, employees in the vehicle and fuel sectorsEmpa, Dübendorf

15 June 2011Ceramic Coatings and SurfacesEmpa /SVMT continuing education courseEmpa, Dübendorf

16 June 2011Analytics and Research for Your ProductDevelopmentFor industry professionalsEmpa, St. Gallen

24 June 2011Molecular Electronics: from Organic Electronicsto Single MoleculesFor researchers in the area of molecular electronicsEmpa, Dübendorf

14 to 18 August 2011Synthesis and Function of ThermoelectricMaterialsFor physicists, chemists, material scientistsand engineersVillars, Schweiz

23 August 2011Swiss Texnet Innovation Day 2011For the textile and clothing industries as well as theirsuppliersEmpa, Dübendorf

19 to 21 September 2011World Resources Forum WRFFor interested parties from science, politicsand businessDavos, Congress Centre

For details and further events: www.empa-akademie.ch

Your way to access Empa’s know-how:

The materials science at

Empa, especially in the

nano area, has been in a

rapid ascent for quite

some time. That's a great

thing for Switzerland

as a centre of research.

Prof. Dr Heinrich RohrerNobel Laureate in Physics

“

Opinion

Heinrich Rohrer

[email protected] +41 58 765 44 44www.empa.ch/portal”

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EmpaNews May 2011