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C 2015 American Chemical Society

A Conversation withProf. ZhongLinWang, EnergyHarvester

Imet with Prof. Zhong Lin Wang ofGeorgia Tech at the Beijing Friend-ship Hotel, during the Nano Energy and

Nano Systems meeting that he organizedand hosted in Beijing, China in December2014.

PSW: You started your research careerin electron microscopy and materialsstructure. How did you end up in energyharvesting, capture, and recycling?ZLW: My original training was in trans-

mission electron microscopy (TEM). My ad-visor told me, Why don't you start with asmall particle?At that time, it was not calleda nanoparticle, it was just a small particle.I was using TEM to look at the tiny littleparticles, looking at the surface oxidation ofcobalt particles.

PSW: With whom did you work andwhere?ZLW: My Ph.D. advisor was Prof. John

Cowley. He was the pioneer of modernhigh-resolution microscopy. He establishedthe theory for high-resolution microscopyback in the 1950s.14 Hewas the rst personto see atomic-resolution images with trans-mission electron microscopy, in 1969.5 Prof.Sumio Iijima610 was my advisor's post doc,years ago. He was a man who specializedin microscopy; he passed away in 2004, atage 81.

PSW: How did you nd your way into hislaboratory?ZLW:When I was a high school student, I

never dreamed of going to college. Thereason was that, college education wasbanned in China at that time; for poor kidslike me, there was no chance. The last yearof high school, they said there is a possibilityfor a college education and I said, Maybe Ishould try. I tried and I made it.

PSW: Where did you grow up?ZLW: My hometown, Gaoyang, is a two-

hour drive from Xian. It's a very little town,probably 3,000 people, farmland. Both myparents farmed for their whole life. They didnot even have a basic education, but theydid one thing right. They wanted their kid tohave the right education. This I appreciatefrom the bottom of my heartthey workedhard and supported me.

PSW: Are they still with you? Have theyseen your success?ZLW: My father passed away 25 years

ago; he did not see any of my success. Mymother passed away two years ago; she sawsome of my success.

PSW: You went to university in Xi'an?ZLW: I went to Xidian University in Xi'an;

now, it is got a new name [University ofElectronic Science and Technology at Xi'an].

I was 17 and I never studied English. Howcould I dream of studying in America? For-get about it, impossible. But, life changed.I put eort into studying English. I said,I want to do research, I want to knowEnglish. By the year I graduated, therewas a program called the US-China studentexchange in physics. It was for the top 100students in physics to study in America. Therst batch was in 1980, I think. I was in the

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Prof. Zhong LinWang of Georgia Tech discussesharvesting and recycling energy using nano-structures.

When I was a high school

student, I never dreamed of

going to college.Published online10.1021/acsnano.5b01581

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1983 group. I was lucky to pass the examand went to Arizona State University.

How did I end up at Arizona State? Atthat time, I had no knowledge aboutAmerican schools, which one is superior.I said, Okay, I'll choose one from A andI'll choose one from B and I'll choose onefrom C. A total of ve, no more. I choseA, Arizona State University; I thought,They have 40 faculty in physics, theymust be good. And I chose BrownUniversity. And ASU accepted me, so Iarrived on campus to study. This isgreat, just great. I was devoted 100% tostudying at that time. That is how I endedup in the U.S.

PSW: What about your independentcareer?ZLW: After I graduated, I continued to

do microscopy for years, fundamentalmicroscopy. When I got to Georgia Tech,the microscopy facility was not the best.In order to do microscopy, you have tohave the best equipment, multimilliondollar equipment. So I said, okay,maybe Ineed to do some measurements insidethe TEM. This was 1996, 1997, and I usedTEM to study the mechanical propertiesof individual carbon nanotubes.1114

We had the rst in situ measurements.Then, we measured the quantum trans-port of carbon nanotubes. Now, this hasevolved into a small eld.15

Then, I went to the (Georgia Tech)lawyer, and I said, I have a TEM speci-men holder; I want to apply for a USpatent.He askedme, Whenwill you getthis commercialized? I said, Probablythree to ve years. And he said, That'stoo long, anything that's not commercialwithin two years, we're not interested.Go away.

I didn't have a single patent when Istarted to make nanomaterials. Lookingback today, in 1999, I picked the rightmaterial, zinc oxide.16 Over the years,I worked on nanomaterials, I appliedfor various patents, and today, I have50 U.S. patents. In 2003, we madeall these devices, measured these gassensors, but how do we power this littlething? Can we make a power source todrive it instead of a battery? So, this wasthe original idea.

Let's see if the zinc oxide piezoelectriceect has anything to do with that. We

used AFM [atomic force microscopy] totest the individual wires.17 This wasthe starting point of all the researchthat followed, moving from single-wire devices to multi-wire devices, fromsmaller scales to large-scale power.Along the way, we invented piezotronicsand piezeophototronics, which wasrst published in ACS Nano (seeFigure 1),1829 and that has led me towhere I am today.

Also, an accident, which turned out tobe a good accident, was that when wemade the piezoelectric nanogenerator,we fabricated a device, but we did notpackage it very well and there was a littlegap. When we measured it, we had ahigh voltage output and so we asked,why is this? With piezoelectrics, if youhave a gap, you have no output, but wehad 5 V. At that time, the best we gotfrom piezoelectrics was a couple of volts.Why [was it] so large? We found that itwas due to the triboelectric eect. Thatled us to what we invent today.30

PSW: Can you dene each of thoseelds for us? Piezotronics, piezophoto-tronics, and triboelectric nanogenerators?ZLW: The rst one that we worked on

was nanoenergy: the energy required todrive sustainably, stably, and long lastingfor mobile electronics, sensor networks,those small electronics. More broadly, itis the use of nanomaterials for energysciences.

A nanogenerator is a device that uti-lizes piezoelectrics, triboelectrics, or para-electrics, or all three of them, to convertmechanical action, thermal action, or otheraction into electricity for powering smallelectronic devices, mostly by convertingmechanical energy.

Piezoelectronics utilize strain created ina piezoelectric semiconductormaterial asa gate voltage to tune, to control thecharge transport, separation, or recombi-nation processes.

Piezophototronics introduced opticalexcitation. We have semiconducting

piezoelectric coupling, but what happensif you introduce light? Piezophototronicshas three-way coupling; we use the piezo-potential to tune optoelectronic propertiesfor achieving optimized LEDs [light-emitting diodes], solar cells, or photo-detector eciencies.

A triboelectric nanogenerator (TENG,see Figure 2) utilizes the electrostaticcharge created due to the triboelectrica-tion process as a driving force for electronow to an external load. Using this processtoday, we can achieve 55%energy conver-sion eciency, the best so far; we alreadysubmitted a paper toACSNano.31Wehaveachieved a power density of 200 W/m2.That number is phenomenal and is close tosome commercial applications.

PSW: For each of these areas youhave put together a roadmap. Did youdo that with other people or did you dothat independently to try to move theeld forward?ZLW: I did that mostly by getting

my postdocs and students togetherto lay out the blueprint for the next20 years. Then, I brought this blueprintto a conference I organized in Juneand I said, Okay, what do you thinkabout this? I got some comments.I revised it, and nally I published thatroadmap.32

PSW: Even in your ACS Nano papers,we see many, many advances coming

Looking back today, I

picked the right material,

zinc oxide.

Figure 1. Studying the piezoelectric eect.Reprinted from ref 18. Copyright 2010American Chemical Society.

Along the way, we invented

piezotronics and

piezeophototronics.

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along;wind power, wave power,walking, driving, typing on keyboards,and so forth.3339 Do you have prio-rities for which ones wewill see aroundus rst and a path to get there?ZLW: We separated these into three

stages: near, middle, and long term.What's near term? Near term is utilizinga self-powered sensor. For example, webuild this as a security system.Webuild itunder the carpet and if somebody walksover it, we would detect it. No externalpower for the sensor. It generates thesignal itself on the door triggers, onsecurity locks; this can come rst be-cause it doesn't need that much power.

PSW: It's like the squeaky nightingaleoors at Nij-j in Kyoto, only electric?ZLW: Yes, electric. I think it's three

years away or so. Then, the middletermpowering cell phones, sensors,large-grid sensorsis ve years out.

Long term is major power. We makeindividual units, which give 1 mW. Yousay, it's not much, right? But, we willmake a 3D grid on 1 km2 of water surfacearea, to give 1 MW. This involves a lot ofissuesmaterial optimization, dielec-trics, surface wearability, durability, andalso triboelectric charge generation.Nano plays all roles in this one. Thematerials are so diverse. I wrote a reviewfor ACS Nano last year on this idea.40

PSW: Would commercialization bethrough licensing and collaboration,or are you trying to start a companyor companies?ZLW: How are we going to do it? I

think there are a number of ways. Num-ber one is somebody licenses the tech-nology and does it themselves. Thatwould be easier than for me to do it.

Number two is that we have a start-up. I have some students who started acompany; we have a couple companiesregistered. If somebody wants to licensea particular part of it, we'll license it tothem, but some parts, we want to tryourselves.

There is a lot of company interest;Samsung, Phillips, and LG;they alreadyhave a research group. Worldwide, wehave 40 groups working on triboelectricnanogenerators now. We have at leastve or six in the U.S., 15 in China, 20 inKorea, and ve or six in Europe.

I want to see impact on society andimpact on the quality of life, that we andour future generations will leave.

PSW: How robust in the environmentdo you imagine the ultimately pro-duced devices will be? Is there muchmore work to do? In terms of packa-ging, is that something that still re-quires a great deal of attention, or arethe basic materials going to be a goodstarting point for functional workingdevices?ZLW: The basic materials are a good

starting point. They already have sub-stantial durability. Let me give you oneexample. We do this kind of testing,rotation [rubbing hands]. We do this 10million times, there's no degradation inperformance. So conventional materials

work and work well. But for technologyapplications you can improve it drama-tically. There's work to do. What I antici-pate is that there are some hurdles wewill need to overcome because packa-ging people never thought about this.It's the eld they need to think aboutright now. I think those problems will besolved, but we can handle some applica-tions already.

PSW: What about in vivo applica-tions? You have started to explorethose in your laboratory. Do you seethose as viable?ZLW: We started in vivo in 2009; we

published the rst papers in 2010.41,42

We used a single wire on a heart-drivendevice. Today, we use the triboelectricgeneration and we stick [the device] tothe wall of the lung. When the lungcontracts, the breathing, the air com-pression, drives it. We use that [power]to drive a pacemaker now. This elddraws a lot of attention because if youcan drive a pacemaker, you can drive alot of in vivo biomedical devices. I thinkthere is a lot of research because wecan have self-powered in vivo medicalsystems.

PSW: Along those lines, is there built-inenergy storage in these devices? Theygeneratepower, but thensayyouneededto use the pacemaker. Presumably,one's heart would not be beating andthat would be the reason it needed toact.Howmuchpower can be stored, or isthat a separate part of the device?ZLW: That's why I call it a system;

we have an energy-generating deviceand we have a storage unit. This batterywill never drain out. It will keep chargingand then keep driving the pacemaker. Ifyou solely used a battery, it probablycould only last 3 to 5 years, but thissystem can buy you 10, 15 years, maybeeven longer. It is making a lifetime muchlonger and sustainable.

PSW: You have something like an al-ternator in a car that charges the bat-tery whenever your body is operating.ZLW: Yes.

PSW: What gives you the most plea-sure in this work?

We use that power to drive

a pacemaker now. If you

can drive a pacemaker, you

can drive a lot of in vivo

biomedical devices.

Figure 2. A triboelectric nanogenerator (TENG) uses electrostatic charge from motionand friction while in contact. Reprinted from ref 30. Copyright 2012 American ChemicalSociety.

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ZLW: Themost pleasure I get from thiswork is that I feel excited thatwhatwedotoday can impact the future of humancivilization, in a broad sense. Let's say 20,30, 50 years from now, when somebodyuses this technology, I'll feel very happyabout that. So that's why, just like you,we work day and night persistently.Hopefully, one day we can contributeto the large scope of energy require-ments and also solve part of the problemof sensor networks and the internet ofthings. Then, as nanoscience and nano-technology outcomes, I'll feel happy.

PSW: You have an enormous andgrowing effort in Chinawhere you haveset up a new institute here.43Where doyou see that going? How do you man-age your laboratories at Georgia Techand the institute here? There are a fewpeople that have this split life now andmany people are curious about how itis possible and how one does it,logistically.ZLW: I have two bases: one is at

Georgia Tech and the other is in Beijing.Georgia Tech is still my main base; myfamily is there. How I manage it is that Imake trips back to Beijing to take care ofbusiness, to supervise the students withface-to-face meetings, and also useSkype meetings, telephone, and email.Those let me interact eectively withstudents. I have 25 people at GeorgiaTech; I have 20 directly supervised peo-ple in Beijing. So, I have 45 directlyinterfacing withme and I also have someadministrative responsibilities.

I just try to do things eciently. Justlike you, there's no trick. Once it's in myhands, I process it right away, no waiting.Then, I utilizemodern communications tospeed up the interaction. I've found that itworks well and both sides eectivelymove forward. I think it adds a lot of me

for the travel. Even with jet lag, I think it'sworkingwell onboth sides and I think thiswill go on for some time, but we'll see.

PSW: How do you see the Beijinginstitute lling out? What will it looklike in a few years when it is set up?Right now, you are renting spacecanyou describe it?ZLW: The technology we develop, the

science we develop will have broad im-pact for environmental science, energyscience, sensor technology, and manyothers. I need a large team to do that,but the resources I have, the reducedfunding in the U.S., does not allow me todo it. In the U.S., I felt that I was a singlehorse rider. I love this country. I worryabout the U.S. and our educational sys-tem. Now, in Beijing, I have the re-sources. I want to use those resourcesto achieve my dream to advance thetechnology, to advance the science.Those are the goals I want to see [met].

What's the future? We started thisinstitute from scratchabsolute zero.We had the rst meeting with threepeople in a coee room about threeyears ago. Now, we have a total of250 peopleabout 150 students, 70 re-searchers, and 25 administrative sta.We're still in a rental place, but hopefullyin three years, we'll move to a new homethat's going to be beautiful. That's thebest estimate I have right now.

PSW: It's quite a large facility; youshowed a schematic of it at themeeting.ZLW: The estimated sizewill be 70,000

m2. This includes research labs, centralfacilities, administration, and also a stu-dent dormitory, entertainment, sports,all in one place. The anticipated invest-ment by the city of Beijing is aboutU.S. $100 million.

PSW: And the Chinese Academy ofSciences?ZLW: The Chinese Academy contri-

butes the research and operations bud-get. The city of Beijing is paying for theconstruction of the building.

PSW: When it's complete, how manypeople will be there? How will itoperate?

ZLW:We anticipate having about 700researchers, sta, and visiting research-ers. We anticipate having 500 of ourpeople that will be called researchers,including postdocs, assistant, associate,and full professors, and then an addi-tional 400 students. So, 1100 local peo-ple and 200300 visitors. We will haveinternational exchange programs forstudents, postdocs, and researchers.

PSW: Was this meeting that you areholding now part of the vision for theinstitute, for the eld?ZLW: This meeting has several objec-

tives. Number one is that we have thisinstitute, but we lack visibility becauseit's just too new; people don't know. Thismeeting will help us to promote theinstitute. Number two, it will also helpus to promote the eld we're interestedinnanoenergy and nanosystems arevery broad. We have brought distin-guished speakers from around the worldto this conference and that is very im-portant for us. At the same time, I thinkwe can use other means to promote ourinstitute and eld. This is the rst meet-ing. The second one will be in two years,then another one; it will continue foryears. As long as I can do it, it willcontinue.

PSW: The rooms were packed at thismeeting. At every session I attended,it was hard to nd a seat.ZLW: I took a lot away from the U.S. on

how to organize conferences. This time,we anticipated 300 people at the begin-ning and 600 turned out. I think nexttimewill be 1000, easily. I borrowed fromthe MRS [Materials Research Society]how to increase participation for posters.I said bring food, bring drinks. Peoplewere talking and discussing until thevery end. That's what happened yester-day. In China, most people leave beforethe posters. They don't ever look, butyesterday, it was full, packed.

PSW: Do you have any advice foryoung scientists, someone who wantsto do what you've done?ZLW: Over the years, my experience

has been, do what you love to do.Pick out the interest that you thinkyou can work on day and night and

The technology we develop

will have broad impact for

environmental science,

energy science, sensor

technology, and many

others.

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never get tired. This is the only drivingforce for you to advance. It's not for themoney; it's not a job requirement; it isinterest;I like it and I have a curiosity forit, number one.

Number two, for young people, dothings persistently. Success doesn'tcome in one day or even one year; youhave to be consistent in advances. In duecourse, people may question you, arguewith you about what you do, and some-times not believewhat you say, but if youbelieve in yourself, you will keep doingthe right thing. Let the data speak; even-tually, they'll accept you. Persistence isvery important. Be condent. If you be-lieve you're right, just work toward yourgoal, regardless of whatever other peo-ple say about you.

Number three, make sure to workhard. We have a lot of young people,smart and talented. There are a lot oftalented people in the world. Make sureyou work for it. If you don't work for it,your talent won't go very far.

For example, when I had the idea forpiezoelectronics, [people asked] what isthis? Could it be wrong? They didn't un-derstand it, and, I only had a vague idea.My denition was not as accurate veyears ago, when I started, as it is today.I felt that this is something emergent andI should dene it; I should give it a name.

Even at that time, you feel condentin what you do, but you don't haveenough data. I only published two orthree papersokay, this is a new phaseI should start. Over the years, you keepworking, publish 40 or 50 papers, andthen you form something substantial.Maybe people, at the beginning, don'tbelieve you. That's okay, just keepworking on your dream. And you'll bethere, some day.

PSW: Are your denitions still evolv-ing or have you now set where youthink these elds and devices aregoing? Not that you have exploredthem completely, but are you stillevolving your denitions now?ZLW: I think the denitions for nano-

generator, nanoenergy, piezotronics,piezophototronics are all done. I evenwrote a book three years ago.44 Thoseare well dened from fundamentalscience, physical pictures, even in poten-tial applications. We have many demon-strations. But, tribotronics (see Figure 3),which I just described in ACS Nano,45

is still at a very early phase, the ideais evolving. We can give a denitionfor tribotronics, but there are morespecics to be dened in the next fewyears. That's how exploration is beingadvanced.

PSW: We look forward to capturingthose advances and that evolution.ZLW: You know, Paul, ACS Nano

has been one of the major journalsto publicize those ideas. You trustme; you trust my understanding. Wetry to make the best contributions toscience, to educate younger genera-tions of scientists. They are the oneswho will work together with me in thefuture, and last a lot longer than me, toadvance the eld.

;Paul S. Weiss

Acknowledgment. We thank Ms. HollyBunje for help in preparing this Conversation.

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