ACS Applied Materials Interfaces Research Article In general,the chemiresistor response transients were for supporting the preparation of graphical artwork.Mr.Adam characterized by a net increase in resistance,suggesting that Steiger is acknowledged for proofreading major parts of the swelling is the dominant component of the sensing mechanism. manuscript. For the more polar analytes,however,pronounced negative overshooting of the transients was observed after switching ■REFERENCES back from vapor atmosphere to carrier gas.In view of the activated tunneling model,this signature was assigned to slow (1)Terrill,R.H;Postlethwaite,T.A;Chen,C.-H.;Poon,C.-D. desorption of the analyte from voids. Terzis,A;Chen,A;Hutchison,J.E.;Clark,M.R;Wignall,G. By inducing 1%tensile strain,the sensitivity of the Londono,J.D.;Superfine,R;Falvo,M.;Johnson,C.S.,Jr.;Samulski chemiresistors was enhanced by ~30%,regardless of the E.T.;Murray,R.W.J.Am.Chem.Soc.1995,117,12537-12548. (2)Wuelfing,W.P.;Green,S.J.;Pietron,J.J.;Cliffel,D.E;Murray, analyte's polarity.We assigned this enhancement to reversible RW.J.Am.Chem.Soc.2000,122,11465-11472. rupture of the particle network and crack formation increasing (3)Wohltjen,H.;Snow,A.S.Anal.Chem.1998,70,2856-2859. the freedom of the films to swell in lateral direction during (4)Evans,S.D.;Johnson,S.R;Cheng,Y.L;Shen,T.J.Mater. analyte sorption.This explanation is supported by comparative Chem.2000,10,183-188. SEM measurements of the AuNDT-film in the relaxed state (5)Han,L;Daniel,D.R;Maye,M.M.;Zhong,C.-J.Anal.Chem. and under 3%tensile strain.Further,compressive strain also 2001,73,4441-4449. enhanced the chemiresistive response amplitudes,but the effect (6)Zamborini,F.P.;Leopold,M.C.;Hicks,I.F.;Kulesza,P.I.; was less pronounced than in the case of films under tensile Malik,M.A.;Murray,R.W.J.Am.Chem.Soc.2002,124,8958-8964. strain.Tentatively,we attributed this effect to a decreased void (7)Vossmeyer,T.;Guse,B.;Besnard,L;Bauer,R.E.;Muillen,K; Yasuda,A.Adv.Mater.2002,14,238-242. volume of the compressed film (8)Joseph,Y.;Besnard,L;Rosenberger,M.;Guse,B.;Nothofer,H. To study strain-induced structural changes in AuNP-films in G.;Wessels,J.M;Wild,U.;Knop-Gericke,A.;Su,D.;Schlogl,Ri more detail and to understand more quantitatively their impact Yasuda,A.;Vossmeyer,T.J.Phys.Chem.B 2003,107,7406-7413. on the conductivity and chemiresistive responses,we are (9)Steinecker,W.H.;Rowe,M.P.;Zellers,E.T.Anal.Chem.2007, currently focusing our research efforts on the preparation and 79,4977-4986. characterization of highly ordered nanoparticle films.Structural (10)Herrmann,J.;Muiller,K.-H;Reda,T.;Baxter,G.Ri Raguse,B.i changes in these materials can be studied with high resolution de Groot,G.J.J.B.;Chai,R;Roberts,M.;Wieczorek,L.Appl.Phys by various in situ scattering methods.For example,Siffalovic et Lett2007,91,183105(3pp). al7 demonstrated that in situ small-angle -ray scattering (11)Vossmeyer,T.;Stolte,C.;Ijeh,M;Kornowski,A.;Weller,H. (SAXS)is well-suited to investigating the increase in spacing of Adu.Funct.Mater.2008,18,1611-1616. non-cross-linked iron oxide nanoparticles when applying tensile (12)Briglin,S.M.;Gao,T.;Lewis,N.S.Langmuir 2004,20,299- 305. strain to the underlying substrate. (13)Peng,G.;Tisch,U.;Adams,O.;Hakim,M.;Shehada,N.;Broza Y.Y.;Billan,S.;Abdah-Bortnyak,R;Kuten,A.;Haick,H.Nat ■ASSOCIATED CONTENT Nanotechnol.2009,4,669-673. Supporting Information (14)Zhong,Q;Steinecker,W.H.;Zellers,E.T.Analyst 2009,134, TEM images of the gold nanoparticles,SEM images and 283-293. photographs of the gold nanoparticle films,IR spectra of the (15)Garcia-Berrios,E.;Gao,T.;Theriot,J.C.;Woodka,M.D.; HDPE substrate before and after plasma treatment,resistive Brunschwig,B.S.;Lewis,N.S.J.Phys.Chem.C 2011,115,6208- 6217. responses to tensile strain,response transients of the films (16)Im,J.;Sengupta,S.K.;Baruch,M.F.;Granz,C.D.;Ammu,S.; under strain to different vapors and with varying concentration, Langmuir-Henry fit parameters.This material is available free Manohar,S.K;Whitten,J.E.Sens.Actuators,B 2011,156,715-722. (17)Krasteva,N.;Fogel,Y.;Bauer,R.E;Millen,K;Joseph,Y.i of charge via the Internet at http://pubs.acs.org. Matsuzawa,N.;Yasuda,A.;Vossmeyer,T.Adv.Funct.Mater.2007,17, 881-888. AUTHOR INFORMATION (18)Joseph,Y.;Peic,A;Chen,X;Michl,J.;Vossmeyer,T.;Yasuda Corresponding Author A.J.Phys..Chem.C2007,111,12855-12859. *E-mail:tobias.vossmeyer@chemie.uni-hamburg.de (19)Zhang,H-L;Evans,S.D.;Henderson,J.R;Miles,R.E;Shen, T.-H.Nanotechnology 2002,13,439-444. Present Address (20)Ibanez,F.J.;Gowrishetty,U.;Crain,M.M.;Walsh,K.M.; Institute of Technical and Macromolecular Chemistry, Zamborini,F.P.Anal.Chem.2006,78,753-761. University of Hamburg,BundesstraBe 45,20146 Hamburg, (21)Garcia-Berrios,E.;Gao,T.;Woodka,M.D.;Maldonado,S.; Germany Brunschwig,B.S.;Ellsworth,M.W.;Lewis,N.S.I.Phys.Chem.C Author Contributions 2010,114,21914-21920. The manuscript was written through contributions of all (22)Ibanez,F.J.;Zamborini,F.P.Small 2011,8,174-202. (23)Farcau,C.;Moreira,H.;Viallet,B.;Grisolia,J.i Ciuculescu- authors.All authors have given approval to the final version of Pradines,D.;Amiens,C.;Ressier,L.J.Phys.Chem.C 2011,115 the manuscript 14494-14499. Notes (24)Farcau,C.;Sangeetha,N.M.;Moreira,H.;Viallet,B.;Grisolia, The authors declare no competing financial interest. J.;Ciuculescu-Pradines,D.;Ressier,L.ACS Nano 2011,5,7137-7143 (25)Radha,B.;Sagade,A.A.;Kulkarni,G.U.ACS Appl.Mater. ■ACKNOWLEDGMENTS Interfaces2011,3,2173-2178. The authors thank Mr.Jan H.Schroder and Mr.Sedat Dogan (26)Yin,J.;Hu,P.;Luo,J.;Wang,L.;Cohen,M.F.;Zhong,C.J ACS Nano2011,8,6516-6526. for technical assistance regarding the vapor deposition of gold (27)Leff,D.V.;Brandt,L.;Heath,J.R.Langmuir 1996,12,4723- electrodes.Mr.Andreas Kornowski is acknowledged for 4730. measuring the SEM images shown in Figures 1 and 3 and in (28)Shen,C.;Hui,C.;Yang,T.;Xiao,C.;Tian,J.;Bao,L.;Chen,S.; the Supporting Information.We thank Mr.Mateusz Olichwer Ding,H.;Gao,H.Chem.Mater.2008,20,6939-6944. 6160 dx.doLorg/10.1021/am301780bl ACS Appl.Mater.Interfoces 2012,4,6151-6161In general, the chemiresistor response transients were characterized by a net increase in resistance, suggesting that swelling is the dominant component of the sensing mechanism. For the more polar analytes, however, pronounced negative overshooting of the transients was observed after switching back from vapor atmosphere to carrier gas. In view of the activated tunneling model, this signature was assigned to slow desorption of the analyte from voids. By inducing 1% tensile strain, the sensitivity of the chemiresistors was enhanced by ∼30%, regardless of the analyte’s polarity. We assigned this enhancement to reversible rupture of the particle network and crack formation increasing the freedom of the films to swell in lateral direction during analyte sorption. This explanation is supported by comparative SEM measurements of the Au4 nmNDT-film in the relaxed state and under 3% tensile strain. Further, compressive strain also enhanced the chemiresistive response amplitudes, but the effect was less pronounced than in the case of films under tensile strain. Tentatively, we attributed this effect to a decreased void volume of the compressed film. To study strain-induced structural changes in AuNP-films in more detail and to understand more quantitatively their impact on the conductivity and chemiresistive responses, we are currently focusing our research efforts on the preparation and characterization of highly ordered nanoparticle films. Structural changes in these materials can be studied with high resolution by various in situ scattering methods. For example, Siffalovic et al.47 demonstrated that in situ small-angle X-ray scattering (SAXS) is well-suited to investigating the increase in spacing of non-cross-linked iron oxide nanoparticles when applying tensile strain to the underlying substrate. ■ ASSOCIATED CONTENT *S Supporting Information TEM images of the gold nanoparticles, SEM images and photographs of the gold nanoparticle films, IR spectra of the HDPE substrate before and after plasma treatment, resistive responses to tensile strain, response transients of the films under strain to different vapors and with varying concentration, Langmuir−Henry fit parameters. This material is available free of charge via the Internet at http://pubs.acs.org. ■ AUTHOR INFORMATION Corresponding Author *E-mail: tobias.vossmeyer@chemie.uni-hamburg.de. Present Address † Institute of Technical and Macromolecular Chemistry, University of Hamburg, Bundesstraße 45, 20146 Hamburg, Germany Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ■ ACKNOWLEDGMENTS The authors thank Mr. Jan H. Schrö der and Mr. Sedat Dogan for technical assistance regarding the vapor deposition of gold electrodes. Mr. Andreas Kornowski is acknowledged for measuring the SEM images shown in Figures 1 and 3 and in the Supporting Information. We thank Mr. Mateusz Olichwer for supporting the preparation of graphical artwork. Mr. Adam Steiger is acknowledged for proofreading major parts of the manuscript. ■ REFERENCES (1) Terrill, R. H.; Postlethwaite, T. A.; Chen, C.-H.; Poon, C.-D.; Terzis, A.; Chen, A.; Hutchison, J. E.; Clark, M. R.; Wignall, G.; Londono, J. D.; Superfine, R.; Falvo, M.; Johnson, C. 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