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Surface Acoustic Wave Response to Optical Absorption by Graphene Composite Film Venkata S. Chivukula, Member, IEEE, Daumantas Čiplys, Member, IEEE, Jin Ho Kim, Romualdas Rimeika, Jimmy M. Xu, Fellow, IEEE, and Michael S. Shur, Fellow, IEEE Abstract—Propagation of surface acoustic waves in YZ LiNbO3 overlaid with graphene flakes has been investigated and its optical response to illumination by 633-nm light from a He-Ne laser was studied. The heating of the sample surface caused by optical absorption by the graphene led to a downshift in the transmitted SAW phase caused by the wave velocity’s dependence on temperature. The proposed simple model based on optothermal SAW phase modulation was found to be in good agreement with the experimental results.
I. Introduction
G
raphene is an extraordinary material with outstanding electrical, mechanical, and thermal properties [1]–[3]. Being a single layer of carbon atoms arranged in honeycomb lattice, it allows the entire volume to be exposed to surface interactions. Recent developments in material synthesis and fabrication technology enabled growth of graphene flakes with variable sheet resistance (on the order of several ohms to kilohms) by varying the layer thickness [4]. SAWs, being sensitive to surface perturbations, are an effective tool to probe the physical change in surface properties of material. Experimental investigations of SAW propagation and interaction in graphenebased structures are still scarce, even though theoretical studies predict interesting physical effects [5]. Surface acoustic wave sensors incorporating graphene sheets have been demonstrated for sensing hydrogen, carbon monoxide, carbon dioxide, and ambient humidity [6]–[9]. In spite of this impressive progress, studies on optical interaction with SAWs in graphene are still not present in literature. This is mainly because of the weak optical response from graphene and graphene nanoribbons. The optical absorption studies on graphene from terahertz to visible light have revealed an absorption coefficient of less than 3%, mainly resulting from vanishing of density of states near the Fermi energy and relatively small inter-band transi-
Manuscript received January 25, 2011; accepted November 17, 2011. This work was supported primarily by the Engineering Research Centers Program (ERC) of the National Science Foundation under NSF Cooperative Agreement No. EEC-0812056, and in part by New York State under NYSTAR contract C090145 and at Brown University by the Air Force Office for Scientific Research. V. S. Chivukula and M. S. Shur are with the Department of Electrical Engineering, Rensselaer Polytechnic Institute, Troy, NY (e-mail: [email protected]). D. Čiplys and R. Rimeika are with the Department of Radiophysics, Vilnius University, Vilnius, Lithuania. J. H. Kim and J. M. Xu are with the Department of Engineering, Brown University, Providence, RI. Digital Object Identifier 10.1109/TUFFC.2012.2186 0885–3010/$25.00
tion amplitudes [10], [11]. To date, this has been a major obstacle in development of graphene structures for optoelectronics and photonics. Surface acoustic waves have been shown to be effective for studies of light interaction with matter and optical sensing [12], [13]. In the present paper, we demonstrate the possibility of using surface acoustic waves for sensing optical power absorbed by graphene flakes by exploiting the extraordinary thermal properties of graphene at room temperature. Supported graphene layers have thermal conductivities on the order of ~600 W·m−1·K−1, which is about 2.4 times higher than the thermal conductivity of copper thin films at room temperature [14], [15]. We report on the effect of 633-nm light from a He-Ne laser on the propagation of surface acoustic waves in piezoelectric lithium-niobate substrate covered with a graphene composite film that is formed of randomly stacked graphene flakes. To explain this effect, the simple model of optothermal SAW phase modulation is proposed. II. Experimental Technique The sample configuration is shown in Fig. 1(a). The interdigitated transducers (IDTs) for SAW excitation and detection were fabricated on YZ LiNbO3 substrate by standard photolithography, and the graphene composite film was deposited on the SAW propagation path between the IDTs. Graphene flakes were prepared from an aqueous solution of graphene oxide. The graphene oxide was synthesized from purified natural graphite by Hummer’s method [16], [17] and colloidal dispersions of individual graphene oxide sheets in water at the concentration of 3 mg·mL−1 were prepared using ultrasound. The graphene oxide paper was prepared by filtration of the resulting colloid through an Anodisc membrane filter (Whatman plc, Maidstone, UK), followed by air drying and peeling from the filter. A scanning electron microscopy image of the fabricated film of graphene flakes is shown in Fig. 1(b). Graphene films with various average thickness values ranging from 200 to 900 nm, as estimated from the atomic force microscopy measurements, were prepared. The sheet resistances of the layers measured using the four-probe technique was in the range from 1 to 42 kΩ, the lower resistance corresponding to the thicker layer. The SAW transmission parameter S12 was measured using a network analyzer (4396B, Agilent Technologies Inc., Santa Clara, CA). A He-Ne laser with a beam diameter of 2 mm and the power 6.7 mW was used for sample illumination. The
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Fig. 1. (a) Schematics of the experiment and (b) scanning electron microscopy image of graphene flakes.
Fig. 3. Transmitted SAW phase shift under illumination as a function of light spot position.
Fig. 2. SAW transmission (curves 1) without and (curve 2) with 200-nm graphene overlay at the acoustic wavelengths (a) 60 μm and (b) 32 μm.
optical power was measured with a PD300-UV-SH photodiode (Ophir Optronics Ltd., Jerusalem, Israel). III. Experimental Results A. SAW Transmission The SAW transmission characteristics in YZ LiNbO3, measured before and after graphene layer deposition, are shown in Fig. 2 for two SAW wavelengths, 60 and 32 μm, the IDT edge-to-edge spacing being 16 and 12 mm, respectively. The 200-nm-thick graphene overlay between the IDTs had dimensions 5 × 4 mm, with the longer side in the SAW propagation direction. As seen from Fig. 2(a), the transmission loss on the free substrate surface was 17 dB at 60 μm wavelength (IDT center frequency 57 MHz), and it remained unchanged even after the 200-nm-thick graphene layer was deposited. In contrast, a significant additional loss of 10 dB due to the same graphene layer was observed at shorter wavelength of 32 μm [IDT center frequency 108 MHz, Fig. 2(b)]. The trend of graphene-layer loss at shorter wavelengths was confirmed by measurements in other samples. In particular, in the 900 nm thick graphene layer, the transmission loss at 54 μm wavelength increased by only 1 dB with respect to the free-substrate value, whereas an increase
as large as 28 dB was observed for 400-nm thickness at the wavelength 36 μm. Such a strong dependence of graphene-induced transmission loss on acoustic wavelength is consistent with the Rayleigh scattering caused by nonuniform graphene flakes, which is inversely proportional to the fourth power of wavelength [18]. A 633-nm He-Ne laser beam (diameter 2 mm) was scanned along the SAW propagation path on the sample surface, and the transmitted SAW phase was measured as a function of the beam position, as shown in Fig. 3. As seen, illumination of the SAW propagation path away from graphene did not affect the SAW phase. In contrast, when the laser spot was on the graphene overlay, the decrease in the SAW phase was observed. For a given laser power, the downshift was 2°. We attribute this shift to the change in SAW velocity as a result of the increase in surface temperature resulting from optical energy absorbed in the graphene layer. To find the amount of absorbed energy, we measured the laser light reflection and transmission in our sample. B. Evaluation of Absorbed Optical Power The optical power reflected from the sample surface and transmitted through the sample was measured by scanning the laser spot on free and graphene-coated surfaces of the substrate as shown in Fig. 4. During the measurements, the incident light was slightly inclined (by ~2° off surface normal to the substrate). The LiNbO3 substrate being transparent to visible light, most of the light passed through when shining on the free surface. The sharp perturbations of light reflection and transmission seen in the IDT regions are due to light diffraction from the metal gratings, which are not considered here. The light transmitted through the sample after two reflections from both of the sample surfaces has the power PT = (1 − R)2Pi, where Pi is the incident light power, and the optical re-
chivukula et al.: SAW response to optical absorption by graphene composite film
Fig. 4. Dependencies of reflected and transmitted optical power on incident light spot position on sample surface. The locations of the interdigitated transducers (IDT) are indicated below the curves.
flectance from the crystal–air interface is R = (n − 1)2/ (n + 1)2, n being the refractive index of the crystal. For LiNbO3, the ordinary refractive index at 633 nm is 2.286 [19], and R = 0.15. At the given reflectance value, the contribution of the transmitted beam power from multiple light reflections in the plate can be neglected. At the incident light power of 6.7 mW, the transmitted power PT = 4.8 mW, in excellent agreement with the measured value. As seen from Fig. 4, the light transmission and reflection were strongly reduced in the region covered by graphene flakes, which is attributed to light absorption in the graphene overlay. The absorbed optical power can be expressed as Pa = Pi − PR′ −
PT′ , (1) 1−R
where PR′ and PT′ are the optical power reflected from graphene and the optical power transmitted through the entire structure, respectively. With the measured values of PR′ = 0.48 mW and PT′ = 0.7 mW, one obtains the absorbed optical power Pa = 5.4 mW, i.e., 80% of the incident power. C. Temperature Change When the surface of the substrate, which is treated as a semi-space, is heated by the uniform constant power source for a time 0 < t < τ, the time-dependent distribution of temperature variation ΔT into the substrate depth, neglecting any thermal exchange with the ambient environment, can be expressed as
∆T (x, t) =
{
F δ ierfc(x /δ) t ≤τ (2) κ δ ierfc(x /δ) − δ1ierfc(x /δ1) t > τ,
where δ = (4χt)1/2, δ1 = [4χ (t − τ)]1/2 and τ is the maximum heating time [20]. The thermal diffusivity is ex-
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Fig. 5. (a) Calculated temperature distribution in the LiNbO3 substrate at different surface heating durations normalized to heating power density of 1 mW/mm2. (b) Time dependencies of the magnitude of SAW phase change calculated without lateral heat spreading by the graphene film at (1) 1.7 mW/mm2 and (2) 0.27 mW/mm2; dots: experimental values of phase change magnitude from Fig. 6.
pressed as χ = κ/cρ, where κ, c, and ρ are the thermal conductivity, specific heat, and mass density of the substrate material, respectively. The heat flow is F = Pa/S, where Pa is the absorbed optical power and S is the heated surface area. The following parameters of LiNbO3 substrate were used in the calculations: κ = 4.18 W(m·K)−1, c = 628 J(kg·K)−1, ρ = 4.65 g/cm3 [19], yielding the thermal diffusivity χ = 1.43 × 10−6 m2·s−1. The temperature variation with distance from the substrate surface for different durations of surface heating is shown in Fig. 5(a). The heating power density was assumed to be 1 mW/mm2. As seen, the temperature variation with depth is relatively weak, and at a given time moment, can be approximated by a constant value over the entire SAW confinement region, which is on the order of the acoustic wavelength. D. Phase Modulation The change in temperature ΔT of SAW propagating medium causes changes in SAW velocity and a very small change in the propagation distance. This results in SAW delay time variation resulting from change in velocity which is much larger than the change in propagation distance resulting from thermal expansion. The SAW delay time variation is expressed as
∆τ D/τ D = TCD ⋅ ∆T, (3)
where TCD is the temperature coefficient of delay for SAW propagation. The delay time τD = L/V, where L is the length of the SAW propagation path subjected to temperature change, and V is the SAW velocity. The change in transmitted SAW phase is then expressed as
∆φ deg = −360
L TCD ⋅ ∆T , (4) Λ
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Fig. 6. Dependencies of SAW phase shift on time upon illumination with chopped light. Noisy curves: experiment; smooth curves: theory.
where Λ = V/f is the acoustic wavelength and f is the SAW frequency. For SAWs propagating in YZ LiNbO3, the temperature coefficient of delay TCD = 94 · 10−6K [21]. We considered two limiting cases: no lateral heat spreading and ideal heat spreading by graphene. In the first case, the heating area was equal to the area of light spot, S1 = 3.1 mm2, and the length of the SAW propagation path with increased temperature was equal to the spot diameter, L1 = 2 mm. In the second case, the heating area was equal to the graphene area, S2 = 20 mm2, and the SAW propagation path subjected to elevated temperature was equal to length of the graphene overlay, L2 = 5 mm. The heating power densities, respectively, are F1 = 1.7 mW/ mm2 and F2 = 0.27 mW/mm2. The temperature at the distance 16 μm from the substrate surface corresponding to half of the acoustic wavelength was used as an approximation for the temperature of the SAW propagation medium. With these assumptions, the time dependencies of the absolute value of SAW phase change were calculated as a function of illumination duration for both cases. They are shown in Fig. 5(b). The time characteristics of the SAW phase response were investigated by illuminating the sample with light beams modulated at different frequencies. The laser beam was modulated using a mechanical chopper at frequencies of 16 Hz and 50 Hz and the corresponding SAW phase variations were measured, as shown in Fig. 6. The magnitude of these variations is plotted in Fig. 5(b). As the chopper frequency increased, the SAW phase response decreased in accordance with lower temperatures attained during the light pulse. The experimental values of phase modulation amplitude are in good agreement with calculations based on the assumption that there is no lateral heat spreading. We interpret this result as being caused by poor lateral heat transfer between graphene flakes. It must also be taken into account that the heat penetration depths under consideration are smaller by two orders of magnitude than the lateral dimensions of the graphene layer.
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The calculations of the dynamic SAW phase response were performed using (2) and (4) with the parameters given in the approximation of no lateral heat spreading. With no heat loss to the ambient environment, the calculation from (2) yields a slow drift of average temperature. This drift was compensated by adding the linear term ΔTloss = −at, where constant a was selected so that the temperature change recovered to zero value after a single light-on and light-off cycle. At the given optical power density, the calculation predicts the phase variations in the range of 0.1° to 0.2°, depending on heating time of the pulse. One can see that the experimentally measured phase modulation amplitudes lie in the same range of magnitudes, and the same trend of amplitude decrease with the increase in light chopping frequency is observed. Using (4), the temperature variations in the proximity of the sample surface could be extracted. The corresponding temperature scale is also shown in Fig. 6. As seen from Fig. 5(b), it takes about 3 s to achieve the experimentally observed stationary phase shift of 2° as shown in Fig. 3, corresponding to the rise in temperature of about 1°C. This result can be treated only as a reasonable estimation, because for such long heating times, the semi-space model is no longer valid for the sample of finite thickness (1 mm in our case). The calculated temperature and phase shift exhibit constant growth with time because no thermal exchange with ambient environment has been taken into account in the calculations, whereas the stationary value of temperature and phase change is established in the experiment because of the thermal balance. IV. Conclusion We have demonstrated the response of surface acoustic waves to optical irradiation of graphene composite film consisting of randomly stacked flakes deposited on a surface of piezoelectric substrate. The SAW phase change under illumination from He-Ne laser is attributed to the sample heating resulting from optical power absorbed by the graphene layer. Our research reveals possibilities of optothermal spectroscopy of graphene films using surface acoustic waves. Acknowledgments This work was supported primarily by the Engineering Research Centers Program (ERC) of the National Science Foundation under NSF Cooperative Agreement No. EEC0812056, and in part by New York State under NYSTAR contract C090145 and at Brown University by the Air Force Office for Scientific Research. References [1] A. H. Castro Neto, F. Guinea, N. M. R. Peres, K. S. Novoselov, and A. K. Geim, “The electronic properties of graphene,” Rev. Mod. Phys., vol. 81, no. 1, pp. 109–162, 2009.
chivukula et al.: SAW response to optical absorption by graphene composite film [2] A. Balandin, S. Ghosh, W. Bao, I. Calizo, D. Teweldebrhan, F. Miao, and C. N. Lau, “Superior thermal conductivity of single-layer graphene,” Nano Lett., vol. 8, no. 3, pp. 902–907, 2008. [3] C. Lee, X. Wei, J. W. Kysar, and J. Hone, “Measurement of the elastic properties and intrinsic strength of monolayer graphene,” Science, vol. 321, no. 5887, pp. 385–388, 2008. [4] S. Banerjee, M. Sardar, N. Gayathri, A. K. Tyagi, and B. Raj, “Enhanced conductivity in graphene layers and their edges,” Appl. Phys. Lett., vol. 88, no. 6, art. no. 062111, 2006. [5] P. Thalmeier, B. Dora, and K. Ziegler, “Surface acoustic wave propagation in graphene,” Phys. Rev. B, vol. 81, no. 4, art. no. 041408(R), 2010. [6] R. Arsat, M. Breedon, M. Shafiei, K. Kalantar-zadeh, W. Wlodarski, S. Gilje, R. B. Kaner, and F. J. Arregui, “Graphene-like nanosheets/36° LiTaO3 surface acoustic wave hydrogen gas sensor,” in Proc. IEEE Sensors Conf., 2008, pp. 188–191. [7] R. Arsat, M. Brendon, M. Shafiei, P. G. Spizziri, S. Gilje, R. B. Kaner, K. Kalantar-zadeh, and W. Wlodarski, “Graphene-like nano-sheets for surface acoustic wave gas sensor applications,” Chem. Phys. Lett., vol. 467, no. 4–6, pp. 344–347, 2009. [8] V. Chivukula, S. Kritzinger, F. Yavari, D. Čiplys, N. Koratkar, and M. Shur, “Detection of CO2 absorption in graphene using surface acoustic waves,” in Proc. Int. Utrason. Symp., 2010, pp. 257–260. [9] D. Čiplys, R. Rimeika, V. Chivukula, M. S. Shur, J. H. Kim, and J. M. Xu, “Surface acoustic waves in graphene structures: Response to ambient humidity,” in Proc. IEEE Sensors Conf., 2010, pp. 785–788. [10] A. B. Kuzmenko, E. van Heumen, F. Carbone, and D. van der Marel, “Universal optical conductance of graphite,” Phys. Rev. Lett., vol. 100, no. 11, art. no. 117401, 2008. [11] J. M. Davlaty, S. Shivaraman, J. Strait, P. George, M. Chandrasekhar, F. Rana, M. S. Spencer, D. Veksler, and Y. Chen, “ Measurement of the optical absorption spectra of epitaxial graphene from terahertz to visible,” Appl. Phys. Lett., vol. 93, no. 13, art. no. 131905, 2008. [12] A. Wixforth, “Interaction of surface acoustic waves, electrons, and light,” Int. J. High Speed Electron. Syst., vol. 10, no. 4, pp. 1193– 1227, 2000. [13] V. Chivukula, D. Ciplys, M. Shur, and P. Dutta, “ZnO nanoparticle surface acoustic wave UV sensor,” Appl. Phys. Lett., vol. 96, no. 23, art. no. 233512, 2010. [14] R. Prasher, “Graphene spreads the heat,” Science, vol. 328, no. 5975, pp. 185–186, 2010. [15] J. K. Viljas and T. T. Heikkila, “Electron-phonon heat transfer in monolayer and bilayer graphene,” Phys. Rev. B, vol. 81, no. 24, art. no. 245404, 2010. [16] D. A. Dikin, S. Stankovich, E. J. Zimney, R. D. Piner, G. H. B. Dommett, G. Evmenenko, S. T. Nguyen, and R. S. Ruoff, “Preparation and characterization of graphene oxide paper,” Nature, vol. 448, no. 7152, pp. 457–460, 2007. [17] V. C. Tung, M. J. Allen, Y. Yang, and R. B. Kaner, “High-throughput solution processing of large scale graphene,” Nat. Nanotechnol., vol. 4, no. 1, pp. 25–29, 2009. [18] V. N. Chukov, “Rayleigh wave scattering by statistical arbitrary form roughness,” Solid State Commun., vol. 149, no. 47–48, pp. 2219–2224, 2009. [19] Crystal Technology Inc. (2010, Dec.) Lithium niobate/lithium tantalate acoustic crystals. [Online]. Available: http://crystaltechnology.com/docs/LN_LTAppNote.pdf [20] H. C. Carslow and J. C. Jaeger, Conduction of Heat in Solids. Oxford, UK: Clarendon Press, 1959. [21] C. K. Campbell, Surface Acoustic Wave Devices for Mobile and Wireless Communications. San Diego, CA: Academic Press, 1998.
Venkata Chivukula obtained the Ph.D. degree in electrical engineering from Rensselaer Polytechnic Institute (RPI) in 2010 and B.E and M.S. degrees in electrical engineering from Nagpur University, India, and Louisiana Tech, Ruston, LA, in 1999 and 2005, respectively. Dr. Chivukula is an author of more than 20 journal publications and conference proceedings. He has received a number of awards and scholarships to recognize his accomplishments: RPI Founders Award of Excellence (2009), Best Student Paper finalist at the International Ultrasonics Symposium, Rome, Italy
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(2009), Graduate Teaching and Research Scholarships from RPI (2006) and Louisiana Tech (2004), Merit Award for top undergraduate student (1997, 1998, and 1999). He is the publicity chair and GOLD representative for the IEEE Sensors Council. He is a member of the American Society for Engineering Education and the IEEE EDS and UFFC societies.
Daumantas Čiplys (M’11) was born in Vilnius, Lithuania. He received the Diploma (Hon) in physics from Vilnius University, Vilnius, Lithuania, in 1967, and the Ph.D. degree in physics from the A. F. Ioffe Institute of Physics and Technology, St. Petersburg, Russia, in 1974, and completed the habilitation procedure at Vilnius University in 2005. He is a Professor in the Department of Radiophysics and the Senior Scientist at the Laboratory of Physical Acoustics at Vilnius University. During the period from 1999 to 2010, he also periodically worked at Rensselaer Polytechnic Institute, Troy, NY, as a Visiting Scholar. His scientific interests include surface acoustic waves, guided optical waves, and acousto-optic interaction. He has published (with coauthors) more than 70 scientific papers and coauthored a book on surface acoustic waves and acousto-optic effects in nitrides and a textbook on guided wave optics. Prof. Čiplys became a member of IEEE and the UFFC Society in 2011. He is a member of the Editorial Board of the Ultrasound Journal (Kaunas, Lithuania) and a member of the Lithuanian Acoustic Society.
Jin H. Kim received B.S., M.S., and Ph.D. degrees in chemistry in 1991, 1993, and 2000, respectively, from Pohang University of Science and Technology (POSTECH), Pohang, GyeongBuk, South Korea. He joined Jimmy Xu’s Laboratory, Engineering, Brown University, in 2003 as a post-doctoral fellow and now is senior research scientist in the same group.
Romualdas Rimeika received the Ph.D. degree in physics from Vilnius University, Vilnius, Lithuania, in 1993. He is an associate professor in the Department of Radiophysics and a senior scientist at the Laboratory of Physical Acoustics, both of Vilnius University. His scientific interests include surface acoustic waves, guided optical waves, acousto-optic interaction, and their applications for sensing and signal control.
Jimmy Xu is the Charles C. Tillinghast ’32 University Professor of Engineering and Physics at Brown University, Providence, RI. Prior to coming to Brown in 1999, he was the James Ham Professor of Optoelectronics and the Nortel Professor of Emerging Technology at the University of Toronto. He served as Director of the Nortel Institute of Telecommunication, as Editor (compound semiconductors) of the IEEE Transactions on Electron Devices, and on Advisory Boards of several institutions and companies, including the National Research Council of Canada. He received several prizes and awards including the 1995 Steacie Prize of Canada, the 1996 FCCP Award of Merit, the Conference Board of Canada–NSERC Best Industrial-University R&D Prize, and a Guggenheim Fellowship, and is a Fellow of the Institute of Physics, the American Association for the Advancement of Science, IEEE, and the American Physical Society.
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Michael S. Shur (M’79–SM’83–F’89) received the M.S.E.E. degree (with honors) from St. Petersburg Electrotechnical Institute, St. Petersburg, Russia, and the Ph.D. and Dr. Sc. degrees from A. F. Ioffe Institute, St. Petersburg. He has been at Ioffe, Cornell, Oakland University, the University of Minnesota, and the University of Virginia. He is now Patricia W. and C. Sheldon Roberts Professor, Co-Director of the National Science Foundation Industry/University Cooperative Research Centers, and Acting Director of the Center for Integrated Electronics at Rensselaer Polytechnic Institute (RPI), Troy, NY. He is the author or coauthor of many technical papers and books and holds more than 50 patents. Prof. Shur is a Fellow of the American Physical Society, the Electrochemical Society, the World Innovation Foundation, the American Association for Advancement of Science, and a member of Eta Kappa Nu, Tau Beta Pi, the Materials Research Society, the American Society for Engineering Education, Elected Member and former Chair of the US Commission D, former member of the National Research Council Union of Radio Science International, and Life Member of the IEEE Microwave Theory and Technique Society, Sigma Xi, and the Humboldt Society. He is the
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Editor-in-Chief of the International Journal of High Speed Electronics and Systems and a book series on electronics and systems, Regional Editor of Physica Status Solidi, Member of the Honorary Board of Solid State Electronics and the Journal of Semiconductor Technology and Science International Advisory Committee, Vice President for Publications of the IEEE Sensor Council, Distinguished Lecturer of the IEEE Electron Device Society, and former Associate Editor of the IEEE Transactions on Electron Devices. He is Co-Founder and Vice President of Sensor Electronics Technology, Inc. He has been involved with many IEEE conferences. His awards include a Saint Petersburg Technical University Honorary Doctorate, 2008, Technical Achievement Award from the IEEE Sensors Council, 2007 IEEE Donald Fink Best Paper Award, 2007 IEEE Kirchmayer Award, the Gold Medal of the Russian Education Ministry, Best Paper awards, van der Ziel Award, Senior Humboldt Research Award, Pioneer Award from Compound Semi, RPI Engineering Research Award, Commendation for Excellence in Technical Communications, and several Best Paper Awards from different national and international conferences. He is listed by the Institute of Scientific Information as Highly Cited Researcher. In 2009, he was elected Foreign Member of the Lithuanian Academy of Sciences.
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Surface Acoustic Wave Response to Optical Absorption by Graphene Composite Film Venkata S. Chivukula, Member, IEEE, Daumantas Čiplys, Member, IEEE, Jin Ho Kim, Romualdas Rimeika, Jimmy M. Xu, Fellow, IEEE, and Michael S. Shur, Fellow, IEEE Abstract—Propagation of surface acoustic waves in YZ LiNbO3 overlaid with graphene flakes has been investigated and its optical response to illumination by 633-nm light from a He-Ne laser was studied. The heating of the sample surface caused by optical absorption by the graphene led to a downshift in the transmitted SAW phase caused by the wave velocity’s dependence on temperature. The proposed simple model based on optothermal SAW phase modulation was found to be in good agreement with the experimental results.
I. Introduction
G
raphene is an extraordinary material with outstanding electrical, mechanical, and thermal properties [1]–[3]. Being a single layer of carbon atoms arranged in honeycomb lattice, it allows the entire volume to be exposed to surface interactions. Recent developments in material synthesis and fabrication technology enabled growth of graphene flakes with variable sheet resistance (on the order of several ohms to kilohms) by varying the layer thickness [4]. SAWs, being sensitive to surface perturbations, are an effective tool to probe the physical change in surface properties of material. Experimental investigations of SAW propagation and interaction in graphenebased structures are still scarce, even though theoretical studies predict interesting physical effects [5]. Surface acoustic wave sensors incorporating graphene sheets have been demonstrated for sensing hydrogen, carbon monoxide, carbon dioxide, and ambient humidity [6]–[9]. In spite of this impressive progress, studies on optical interaction with SAWs in graphene are still not present in literature. This is mainly because of the weak optical response from graphene and graphene nanoribbons. The optical absorption studies on graphene from terahertz to visible light have revealed an absorption coefficient of less than 3%, mainly resulting from vanishing of density of states near the Fermi energy and relatively small inter-band transi-
Manuscript received January 25, 2011; accepted November 17, 2011. This work was supported primarily by the Engineering Research Centers Program (ERC) of the National Science Foundation under NSF Cooperative Agreement No. EEC-0812056, and in part by New York State under NYSTAR contract C090145 and at Brown University by the Air Force Office for Scientific Research. V. S. Chivukula and M. S. Shur are with the Department of Electrical Engineering, Rensselaer Polytechnic Institute, Troy, NY (e-mail: [email protected]). D. Čiplys and R. Rimeika are with the Department of Radiophysics, Vilnius University, Vilnius, Lithuania. J. H. Kim and J. M. Xu are with the Department of Engineering, Brown University, Providence, RI. Digital Object Identifier 10.1109/TUFFC.2012.2186 0885–3010/$25.00
tion amplitudes [10], [11]. To date, this has been a major obstacle in development of graphene structures for optoelectronics and photonics. Surface acoustic waves have been shown to be effective for studies of light interaction with matter and optical sensing [12], [13]. In the present paper, we demonstrate the possibility of using surface acoustic waves for sensing optical power absorbed by graphene flakes by exploiting the extraordinary thermal properties of graphene at room temperature. Supported graphene layers have thermal conductivities on the order of ~600 W·m−1·K−1, which is about 2.4 times higher than the thermal conductivity of copper thin films at room temperature [14], [15]. We report on the effect of 633-nm light from a He-Ne laser on the propagation of surface acoustic waves in piezoelectric lithium-niobate substrate covered with a graphene composite film that is formed of randomly stacked graphene flakes. To explain this effect, the simple model of optothermal SAW phase modulation is proposed. II. Experimental Technique The sample configuration is shown in Fig. 1(a). The interdigitated transducers (IDTs) for SAW excitation and detection were fabricated on YZ LiNbO3 substrate by standard photolithography, and the graphene composite film was deposited on the SAW propagation path between the IDTs. Graphene flakes were prepared from an aqueous solution of graphene oxide. The graphene oxide was synthesized from purified natural graphite by Hummer’s method [16], [17] and colloidal dispersions of individual graphene oxide sheets in water at the concentration of 3 mg·mL−1 were prepared using ultrasound. The graphene oxide paper was prepared by filtration of the resulting colloid through an Anodisc membrane filter (Whatman plc, Maidstone, UK), followed by air drying and peeling from the filter. A scanning electron microscopy image of the fabricated film of graphene flakes is shown in Fig. 1(b). Graphene films with various average thickness values ranging from 200 to 900 nm, as estimated from the atomic force microscopy measurements, were prepared. The sheet resistances of the layers measured using the four-probe technique was in the range from 1 to 42 kΩ, the lower resistance corresponding to the thicker layer. The SAW transmission parameter S12 was measured using a network analyzer (4396B, Agilent Technologies Inc., Santa Clara, CA). A He-Ne laser with a beam diameter of 2 mm and the power 6.7 mW was used for sample illumination. The
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Fig. 1. (a) Schematics of the experiment and (b) scanning electron microscopy image of graphene flakes.
Fig. 3. Transmitted SAW phase shift under illumination as a function of light spot position.
Fig. 2. SAW transmission (curves 1) without and (curve 2) with 200-nm graphene overlay at the acoustic wavelengths (a) 60 μm and (b) 32 μm.
optical power was measured with a PD300-UV-SH photodiode (Ophir Optronics Ltd., Jerusalem, Israel). III. Experimental Results A. SAW Transmission The SAW transmission characteristics in YZ LiNbO3, measured before and after graphene layer deposition, are shown in Fig. 2 for two SAW wavelengths, 60 and 32 μm, the IDT edge-to-edge spacing being 16 and 12 mm, respectively. The 200-nm-thick graphene overlay between the IDTs had dimensions 5 × 4 mm, with the longer side in the SAW propagation direction. As seen from Fig. 2(a), the transmission loss on the free substrate surface was 17 dB at 60 μm wavelength (IDT center frequency 57 MHz), and it remained unchanged even after the 200-nm-thick graphene layer was deposited. In contrast, a significant additional loss of 10 dB due to the same graphene layer was observed at shorter wavelength of 32 μm [IDT center frequency 108 MHz, Fig. 2(b)]. The trend of graphene-layer loss at shorter wavelengths was confirmed by measurements in other samples. In particular, in the 900 nm thick graphene layer, the transmission loss at 54 μm wavelength increased by only 1 dB with respect to the free-substrate value, whereas an increase
as large as 28 dB was observed for 400-nm thickness at the wavelength 36 μm. Such a strong dependence of graphene-induced transmission loss on acoustic wavelength is consistent with the Rayleigh scattering caused by nonuniform graphene flakes, which is inversely proportional to the fourth power of wavelength [18]. A 633-nm He-Ne laser beam (diameter 2 mm) was scanned along the SAW propagation path on the sample surface, and the transmitted SAW phase was measured as a function of the beam position, as shown in Fig. 3. As seen, illumination of the SAW propagation path away from graphene did not affect the SAW phase. In contrast, when the laser spot was on the graphene overlay, the decrease in the SAW phase was observed. For a given laser power, the downshift was 2°. We attribute this shift to the change in SAW velocity as a result of the increase in surface temperature resulting from optical energy absorbed in the graphene layer. To find the amount of absorbed energy, we measured the laser light reflection and transmission in our sample. B. Evaluation of Absorbed Optical Power The optical power reflected from the sample surface and transmitted through the sample was measured by scanning the laser spot on free and graphene-coated surfaces of the substrate as shown in Fig. 4. During the measurements, the incident light was slightly inclined (by ~2° off surface normal to the substrate). The LiNbO3 substrate being transparent to visible light, most of the light passed through when shining on the free surface. The sharp perturbations of light reflection and transmission seen in the IDT regions are due to light diffraction from the metal gratings, which are not considered here. The light transmitted through the sample after two reflections from both of the sample surfaces has the power PT = (1 − R)2Pi, where Pi is the incident light power, and the optical re-
chivukula et al.: SAW response to optical absorption by graphene composite film
Fig. 4. Dependencies of reflected and transmitted optical power on incident light spot position on sample surface. The locations of the interdigitated transducers (IDT) are indicated below the curves.
flectance from the crystal–air interface is R = (n − 1)2/ (n + 1)2, n being the refractive index of the crystal. For LiNbO3, the ordinary refractive index at 633 nm is 2.286 [19], and R = 0.15. At the given reflectance value, the contribution of the transmitted beam power from multiple light reflections in the plate can be neglected. At the incident light power of 6.7 mW, the transmitted power PT = 4.8 mW, in excellent agreement with the measured value. As seen from Fig. 4, the light transmission and reflection were strongly reduced in the region covered by graphene flakes, which is attributed to light absorption in the graphene overlay. The absorbed optical power can be expressed as Pa = Pi − PR′ −
PT′ , (1) 1−R
where PR′ and PT′ are the optical power reflected from graphene and the optical power transmitted through the entire structure, respectively. With the measured values of PR′ = 0.48 mW and PT′ = 0.7 mW, one obtains the absorbed optical power Pa = 5.4 mW, i.e., 80% of the incident power. C. Temperature Change When the surface of the substrate, which is treated as a semi-space, is heated by the uniform constant power source for a time 0 < t < τ, the time-dependent distribution of temperature variation ΔT into the substrate depth, neglecting any thermal exchange with the ambient environment, can be expressed as
∆T (x, t) =
{
F δ ierfc(x /δ) t ≤τ (2) κ δ ierfc(x /δ) − δ1ierfc(x /δ1) t > τ,
where δ = (4χt)1/2, δ1 = [4χ (t − τ)]1/2 and τ is the maximum heating time [20]. The thermal diffusivity is ex-
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Fig. 5. (a) Calculated temperature distribution in the LiNbO3 substrate at different surface heating durations normalized to heating power density of 1 mW/mm2. (b) Time dependencies of the magnitude of SAW phase change calculated without lateral heat spreading by the graphene film at (1) 1.7 mW/mm2 and (2) 0.27 mW/mm2; dots: experimental values of phase change magnitude from Fig. 6.
pressed as χ = κ/cρ, where κ, c, and ρ are the thermal conductivity, specific heat, and mass density of the substrate material, respectively. The heat flow is F = Pa/S, where Pa is the absorbed optical power and S is the heated surface area. The following parameters of LiNbO3 substrate were used in the calculations: κ = 4.18 W(m·K)−1, c = 628 J(kg·K)−1, ρ = 4.65 g/cm3 [19], yielding the thermal diffusivity χ = 1.43 × 10−6 m2·s−1. The temperature variation with distance from the substrate surface for different durations of surface heating is shown in Fig. 5(a). The heating power density was assumed to be 1 mW/mm2. As seen, the temperature variation with depth is relatively weak, and at a given time moment, can be approximated by a constant value over the entire SAW confinement region, which is on the order of the acoustic wavelength. D. Phase Modulation The change in temperature ΔT of SAW propagating medium causes changes in SAW velocity and a very small change in the propagation distance. This results in SAW delay time variation resulting from change in velocity which is much larger than the change in propagation distance resulting from thermal expansion. The SAW delay time variation is expressed as
∆τ D/τ D = TCD ⋅ ∆T, (3)
where TCD is the temperature coefficient of delay for SAW propagation. The delay time τD = L/V, where L is the length of the SAW propagation path subjected to temperature change, and V is the SAW velocity. The change in transmitted SAW phase is then expressed as
∆φ deg = −360
L TCD ⋅ ∆T , (4) Λ
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Fig. 6. Dependencies of SAW phase shift on time upon illumination with chopped light. Noisy curves: experiment; smooth curves: theory.
where Λ = V/f is the acoustic wavelength and f is the SAW frequency. For SAWs propagating in YZ LiNbO3, the temperature coefficient of delay TCD = 94 · 10−6K [21]. We considered two limiting cases: no lateral heat spreading and ideal heat spreading by graphene. In the first case, the heating area was equal to the area of light spot, S1 = 3.1 mm2, and the length of the SAW propagation path with increased temperature was equal to the spot diameter, L1 = 2 mm. In the second case, the heating area was equal to the graphene area, S2 = 20 mm2, and the SAW propagation path subjected to elevated temperature was equal to length of the graphene overlay, L2 = 5 mm. The heating power densities, respectively, are F1 = 1.7 mW/ mm2 and F2 = 0.27 mW/mm2. The temperature at the distance 16 μm from the substrate surface corresponding to half of the acoustic wavelength was used as an approximation for the temperature of the SAW propagation medium. With these assumptions, the time dependencies of the absolute value of SAW phase change were calculated as a function of illumination duration for both cases. They are shown in Fig. 5(b). The time characteristics of the SAW phase response were investigated by illuminating the sample with light beams modulated at different frequencies. The laser beam was modulated using a mechanical chopper at frequencies of 16 Hz and 50 Hz and the corresponding SAW phase variations were measured, as shown in Fig. 6. The magnitude of these variations is plotted in Fig. 5(b). As the chopper frequency increased, the SAW phase response decreased in accordance with lower temperatures attained during the light pulse. The experimental values of phase modulation amplitude are in good agreement with calculations based on the assumption that there is no lateral heat spreading. We interpret this result as being caused by poor lateral heat transfer between graphene flakes. It must also be taken into account that the heat penetration depths under consideration are smaller by two orders of magnitude than the lateral dimensions of the graphene layer.
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The calculations of the dynamic SAW phase response were performed using (2) and (4) with the parameters given in the approximation of no lateral heat spreading. With no heat loss to the ambient environment, the calculation from (2) yields a slow drift of average temperature. This drift was compensated by adding the linear term ΔTloss = −at, where constant a was selected so that the temperature change recovered to zero value after a single light-on and light-off cycle. At the given optical power density, the calculation predicts the phase variations in the range of 0.1° to 0.2°, depending on heating time of the pulse. One can see that the experimentally measured phase modulation amplitudes lie in the same range of magnitudes, and the same trend of amplitude decrease with the increase in light chopping frequency is observed. Using (4), the temperature variations in the proximity of the sample surface could be extracted. The corresponding temperature scale is also shown in Fig. 6. As seen from Fig. 5(b), it takes about 3 s to achieve the experimentally observed stationary phase shift of 2° as shown in Fig. 3, corresponding to the rise in temperature of about 1°C. This result can be treated only as a reasonable estimation, because for such long heating times, the semi-space model is no longer valid for the sample of finite thickness (1 mm in our case). The calculated temperature and phase shift exhibit constant growth with time because no thermal exchange with ambient environment has been taken into account in the calculations, whereas the stationary value of temperature and phase change is established in the experiment because of the thermal balance. IV. Conclusion We have demonstrated the response of surface acoustic waves to optical irradiation of graphene composite film consisting of randomly stacked flakes deposited on a surface of piezoelectric substrate. The SAW phase change under illumination from He-Ne laser is attributed to the sample heating resulting from optical power absorbed by the graphene layer. Our research reveals possibilities of optothermal spectroscopy of graphene films using surface acoustic waves. Acknowledgments This work was supported primarily by the Engineering Research Centers Program (ERC) of the National Science Foundation under NSF Cooperative Agreement No. EEC0812056, and in part by New York State under NYSTAR contract C090145 and at Brown University by the Air Force Office for Scientific Research. References [1] A. H. Castro Neto, F. Guinea, N. M. R. Peres, K. S. Novoselov, and A. K. Geim, “The electronic properties of graphene,” Rev. Mod. Phys., vol. 81, no. 1, pp. 109–162, 2009.
chivukula et al.: SAW response to optical absorption by graphene composite film [2] A. Balandin, S. Ghosh, W. Bao, I. Calizo, D. Teweldebrhan, F. Miao, and C. N. Lau, “Superior thermal conductivity of single-layer graphene,” Nano Lett., vol. 8, no. 3, pp. 902–907, 2008. [3] C. Lee, X. Wei, J. W. Kysar, and J. Hone, “Measurement of the elastic properties and intrinsic strength of monolayer graphene,” Science, vol. 321, no. 5887, pp. 385–388, 2008. [4] S. Banerjee, M. Sardar, N. Gayathri, A. K. Tyagi, and B. Raj, “Enhanced conductivity in graphene layers and their edges,” Appl. Phys. Lett., vol. 88, no. 6, art. no. 062111, 2006. [5] P. Thalmeier, B. Dora, and K. Ziegler, “Surface acoustic wave propagation in graphene,” Phys. Rev. B, vol. 81, no. 4, art. no. 041408(R), 2010. [6] R. Arsat, M. Breedon, M. Shafiei, K. Kalantar-zadeh, W. Wlodarski, S. Gilje, R. B. Kaner, and F. J. Arregui, “Graphene-like nanosheets/36° LiTaO3 surface acoustic wave hydrogen gas sensor,” in Proc. IEEE Sensors Conf., 2008, pp. 188–191. [7] R. Arsat, M. Brendon, M. Shafiei, P. G. Spizziri, S. Gilje, R. B. Kaner, K. Kalantar-zadeh, and W. Wlodarski, “Graphene-like nano-sheets for surface acoustic wave gas sensor applications,” Chem. Phys. Lett., vol. 467, no. 4–6, pp. 344–347, 2009. [8] V. Chivukula, S. Kritzinger, F. Yavari, D. Čiplys, N. Koratkar, and M. Shur, “Detection of CO2 absorption in graphene using surface acoustic waves,” in Proc. Int. Utrason. Symp., 2010, pp. 257–260. [9] D. Čiplys, R. Rimeika, V. Chivukula, M. S. Shur, J. H. Kim, and J. M. Xu, “Surface acoustic waves in graphene structures: Response to ambient humidity,” in Proc. IEEE Sensors Conf., 2010, pp. 785–788. [10] A. B. Kuzmenko, E. van Heumen, F. Carbone, and D. van der Marel, “Universal optical conductance of graphite,” Phys. Rev. Lett., vol. 100, no. 11, art. no. 117401, 2008. [11] J. M. Davlaty, S. Shivaraman, J. Strait, P. George, M. Chandrasekhar, F. Rana, M. S. Spencer, D. Veksler, and Y. Chen, “ Measurement of the optical absorption spectra of epitaxial graphene from terahertz to visible,” Appl. Phys. Lett., vol. 93, no. 13, art. no. 131905, 2008. [12] A. Wixforth, “Interaction of surface acoustic waves, electrons, and light,” Int. J. High Speed Electron. Syst., vol. 10, no. 4, pp. 1193– 1227, 2000. [13] V. Chivukula, D. Ciplys, M. Shur, and P. Dutta, “ZnO nanoparticle surface acoustic wave UV sensor,” Appl. Phys. Lett., vol. 96, no. 23, art. no. 233512, 2010. [14] R. Prasher, “Graphene spreads the heat,” Science, vol. 328, no. 5975, pp. 185–186, 2010. [15] J. K. Viljas and T. T. Heikkila, “Electron-phonon heat transfer in monolayer and bilayer graphene,” Phys. Rev. B, vol. 81, no. 24, art. no. 245404, 2010. [16] D. A. Dikin, S. Stankovich, E. J. Zimney, R. D. Piner, G. H. B. Dommett, G. Evmenenko, S. T. Nguyen, and R. S. Ruoff, “Preparation and characterization of graphene oxide paper,” Nature, vol. 448, no. 7152, pp. 457–460, 2007. [17] V. C. Tung, M. J. Allen, Y. Yang, and R. B. Kaner, “High-throughput solution processing of large scale graphene,” Nat. Nanotechnol., vol. 4, no. 1, pp. 25–29, 2009. [18] V. N. Chukov, “Rayleigh wave scattering by statistical arbitrary form roughness,” Solid State Commun., vol. 149, no. 47–48, pp. 2219–2224, 2009. [19] Crystal Technology Inc. (2010, Dec.) Lithium niobate/lithium tantalate acoustic crystals. [Online]. Available: http://crystaltechnology.com/docs/LN_LTAppNote.pdf [20] H. C. Carslow and J. C. Jaeger, Conduction of Heat in Solids. Oxford, UK: Clarendon Press, 1959. [21] C. K. Campbell, Surface Acoustic Wave Devices for Mobile and Wireless Communications. San Diego, CA: Academic Press, 1998.
Venkata Chivukula obtained the Ph.D. degree in electrical engineering from Rensselaer Polytechnic Institute (RPI) in 2010 and B.E and M.S. degrees in electrical engineering from Nagpur University, India, and Louisiana Tech, Ruston, LA, in 1999 and 2005, respectively. Dr. Chivukula is an author of more than 20 journal publications and conference proceedings. He has received a number of awards and scholarships to recognize his accomplishments: RPI Founders Award of Excellence (2009), Best Student Paper finalist at the International Ultrasonics Symposium, Rome, Italy
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(2009), Graduate Teaching and Research Scholarships from RPI (2006) and Louisiana Tech (2004), Merit Award for top undergraduate student (1997, 1998, and 1999). He is the publicity chair and GOLD representative for the IEEE Sensors Council. He is a member of the American Society for Engineering Education and the IEEE EDS and UFFC societies.
Daumantas Čiplys (M’11) was born in Vilnius, Lithuania. He received the Diploma (Hon) in physics from Vilnius University, Vilnius, Lithuania, in 1967, and the Ph.D. degree in physics from the A. F. Ioffe Institute of Physics and Technology, St. Petersburg, Russia, in 1974, and completed the habilitation procedure at Vilnius University in 2005. He is a Professor in the Department of Radiophysics and the Senior Scientist at the Laboratory of Physical Acoustics at Vilnius University. During the period from 1999 to 2010, he also periodically worked at Rensselaer Polytechnic Institute, Troy, NY, as a Visiting Scholar. His scientific interests include surface acoustic waves, guided optical waves, and acousto-optic interaction. He has published (with coauthors) more than 70 scientific papers and coauthored a book on surface acoustic waves and acousto-optic effects in nitrides and a textbook on guided wave optics. Prof. Čiplys became a member of IEEE and the UFFC Society in 2011. He is a member of the Editorial Board of the Ultrasound Journal (Kaunas, Lithuania) and a member of the Lithuanian Acoustic Society.
Jin H. Kim received B.S., M.S., and Ph.D. degrees in chemistry in 1991, 1993, and 2000, respectively, from Pohang University of Science and Technology (POSTECH), Pohang, GyeongBuk, South Korea. He joined Jimmy Xu’s Laboratory, Engineering, Brown University, in 2003 as a post-doctoral fellow and now is senior research scientist in the same group.
Romualdas Rimeika received the Ph.D. degree in physics from Vilnius University, Vilnius, Lithuania, in 1993. He is an associate professor in the Department of Radiophysics and a senior scientist at the Laboratory of Physical Acoustics, both of Vilnius University. His scientific interests include surface acoustic waves, guided optical waves, acousto-optic interaction, and their applications for sensing and signal control.
Jimmy Xu is the Charles C. Tillinghast ’32 University Professor of Engineering and Physics at Brown University, Providence, RI. Prior to coming to Brown in 1999, he was the James Ham Professor of Optoelectronics and the Nortel Professor of Emerging Technology at the University of Toronto. He served as Director of the Nortel Institute of Telecommunication, as Editor (compound semiconductors) of the IEEE Transactions on Electron Devices, and on Advisory Boards of several institutions and companies, including the National Research Council of Canada. He received several prizes and awards including the 1995 Steacie Prize of Canada, the 1996 FCCP Award of Merit, the Conference Board of Canada–NSERC Best Industrial-University R&D Prize, and a Guggenheim Fellowship, and is a Fellow of the Institute of Physics, the American Association for the Advancement of Science, IEEE, and the American Physical Society.
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Michael S. Shur (M’79–SM’83–F’89) received the M.S.E.E. degree (with honors) from St. Petersburg Electrotechnical Institute, St. Petersburg, Russia, and the Ph.D. and Dr. Sc. degrees from A. F. Ioffe Institute, St. Petersburg. He has been at Ioffe, Cornell, Oakland University, the University of Minnesota, and the University of Virginia. He is now Patricia W. and C. Sheldon Roberts Professor, Co-Director of the National Science Foundation Industry/University Cooperative Research Centers, and Acting Director of the Center for Integrated Electronics at Rensselaer Polytechnic Institute (RPI), Troy, NY. He is the author or coauthor of many technical papers and books and holds more than 50 patents. Prof. Shur is a Fellow of the American Physical Society, the Electrochemical Society, the World Innovation Foundation, the American Association for Advancement of Science, and a member of Eta Kappa Nu, Tau Beta Pi, the Materials Research Society, the American Society for Engineering Education, Elected Member and former Chair of the US Commission D, former member of the National Research Council Union of Radio Science International, and Life Member of the IEEE Microwave Theory and Technique Society, Sigma Xi, and the Humboldt Society. He is the
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Editor-in-Chief of the International Journal of High Speed Electronics and Systems and a book series on electronics and systems, Regional Editor of Physica Status Solidi, Member of the Honorary Board of Solid State Electronics and the Journal of Semiconductor Technology and Science International Advisory Committee, Vice President for Publications of the IEEE Sensor Council, Distinguished Lecturer of the IEEE Electron Device Society, and former Associate Editor of the IEEE Transactions on Electron Devices. He is Co-Founder and Vice President of Sensor Electronics Technology, Inc. He has been involved with many IEEE conferences. His awards include a Saint Petersburg Technical University Honorary Doctorate, 2008, Technical Achievement Award from the IEEE Sensors Council, 2007 IEEE Donald Fink Best Paper Award, 2007 IEEE Kirchmayer Award, the Gold Medal of the Russian Education Ministry, Best Paper awards, van der Ziel Award, Senior Humboldt Research Award, Pioneer Award from Compound Semi, RPI Engineering Research Award, Commendation for Excellence in Technical Communications, and several Best Paper Awards from different national and international conferences. He is listed by the Institute of Scientific Information as Highly Cited Researcher. In 2009, he was elected Foreign Member of the Lithuanian Academy of Sciences.
