Selective Dichroic Patterning by Nanosecond Laser Treatment of Ag Nanostripes

COMMUNICATION Juan R. Sanchez-Valencia , Johann Toude , * Ana Bo as, * Angel Ba anco , Ru h Lahoz , Ge man F. de la Fuen e , Fabian F u os , and Agus in R. Gonzalez-Elipe Selec i e Dich oic Pa e ning by Nanosecond Lase T ea men o Ag Nanos ipes D . J. R. Sanchez-Valencia, D . J. Toude , D . A. Bo as, D . A. Ba anco, P o . D . A. R. Gonzalez-Elipe Nano echnology on Su aces Labo a o y ICMSE: Ma e ials Science Ins i u e o Se ille CSIC-Uni e si y o Se ille A d. Ame ico Vespucio 49, 41092, Se illa, Spain E-mail: [email p o ec ed]; [email p o ec ed] D . R. Lahoz, P o . G. F. de la Fuen e Ma e ials Science Ins i u e o A agon CSIC-Uni e si y o Za agoza C/Ma ía de Luna 3, 50018, Za agoza, Spain D . F. F u os Applied Physics Depa men E.T.S. Ingenie ía In o má ica Uni e si y o Se ille A d. Reina Me cedes s/n, 41012 Se ille, Spain The s ong abso p ion o ligh [ 1 ] and he local ampli i ca ion o he elec omagne ic i eld [ 2 ] a he plasmon esonance o noble me al nanos uc u es ha e been he ocus o hund eds o s udies due o hei p ac ical applica ions o he ab ica ion o op ical de ices such as i l e s, non-linea op ical componen s, o Raman enhance s. [ 3,4 ] The con ol o he plasmon ea u es such as spec al wid h, [ 5 ] posi ion, [ 6 ] and shape [ 7 ] can be accom- plished by di e en physical deposi ion ou es [ 8–12 ] p o iding adequa e g owing condi ions o me al nanopa icles (MNPs). Pionee wo ks in he 1990s showed he op ical selec i i y o elonga ed Ag deposi s on SiO 2 wi h applica ions as op ical i l- e s o windows o con ol sola hea gain and gla e, among o he s. [ 13 ] Recen ly, assemblies o pa allel s ipes o MNPs ha e been ab ica ed on o p e o med su aces p esen ing a 1D pe iodic oughness [ 14 , 15 ] o bundled SiO 2 nanocolumns. [ 16 , 17 ] A signi i can mac oscopic op ical dich oism has been epo ed o hese sys ems ha can be use ul o he de elopmen o pola ized ligh emi e s o ma e ials wi h an enhanced IR lumi- nescence because o he exci a ion o wo dis inc plasmon esonances in he di ec ions pa allel (longi udinal mode) and pe pendicula ( ans e se mode) o he s ipes. [ 18 ] A chi ec u e con ol o he me al assemblies plays a de e minan ole in he unc ional p ope ies o he ma e ial. Fo his pu pose, he so - li hog aphic echniques p o ide means o accu a ely ailo he nanos uc u e o he ma e ials. [ 18–21 ] Lase scanning is a so - li hog aphic echnique widely used o modi y he shape and s uc u e o me al nanopa icles. [ 21–24 ] Su ace modi i ca ion can be easily achie ed by in si u [ 21 ] o ex si u [ 22–24 ] pulsed lase ea men in he case o andom sys ems o MNPs. In con as , no hing has been epo ed abou he e ec o a pulsed lase on he s uc u e and op ical dich oism o au oo ganized me al nanos uc u es. In his pape we show ha nanosecond (ns) lase i adia ion can be e ec i ely used o con ol he op ical dich oism o Ag s ipes suppo ed on SiO 2 nanocolumns (NCs). This dich oism can be e ec i ely ailo ed along he ull isible ange. Thus, we p opose he u iliza ion o he AgNPs/SiO 2 NCs s uc u es o w i ing dich oic pa e ns a he mic oscale wi h po en ial applica ions o enc yp ion and da a s o age pu poses. AgNPs/SiO 2 NCs i lms we e g own by a wo-s ep p ocess. [ 17 ] Fi s , SiO 2 hin i lms we e deposi ed by glancing angle apo deposi ion (GLAD) wi h a il ed columna nanos uc u e and ≈ 350 nm hickness (see Figu e S1a in he Suppo ing In o - ma ion and he Expe imen al Sec ion). [ 25 , 26 ] These s uc u es p esen an aniso opic su ace opog aphy known as “bun- dling”, [ 17 ] consis ing o he coalescence o he NCs along he x -di ec ion (Figu e S1b). The sil e nanopa icles we e hen g own by DC spu e ing a oom empe a u e. The “bundled” SiO 2 NCs ac as a empla e o he ab ica ion o Ag s ipes o med by me al NPs. [ 17 ] Nanosecond lase pos - ea men was hen pe o med a no mal incidence. The ene gy impinging on he sample su ace was con olled by a ying he ou pu lase powe ( P ) be ween 3.5 kW cm − 2 and 7.0 kW cm − 2 . Figu e 1 shows he scanning elec on mic oscopy (SEM) images o a i lm be o e (Figu e 1a,c,e ) and a e (Figu e 1b,d, ) lase ea men a 7.0 kW cm − 2 . The su ace o he o iginal i lm consis s o s ipes o densely packed MNPs ollowing he bun- dling di ec ion o he nanocolumns ( x -di ec ion) (Figu e 1a ). [ 17 ] These Ag-s iped nanos uc u es, sepa a ed om each o he a ound 30 nm in he y -di ec ion, co e 78% ac ion o he su ace (de i ned as he po ion o he image co esponding o MNPs) as ob ained by digi al pic u e analysis. Figu e 1c,e show ha he pa icles p esen a “ca pe -like” p ojec ed shape wi h a heigh ≈ 15–20 nm. A e lase ea men a 7.0 kW cm − 2 (Figu e 1b,d, ), he pa allel s ipes a e s ill p esen bu a e o med by con inuous and ex emely smoo h me al islands (see also a omic o ce mic oscopy (AFM) image in Figu e 2 ). In addi ion, hese islands appea o be mo e sepa a ed along he y -di ec ion. Indeed, while hei cen e - o-cen e dis ance emains unchanged, hei bo de - o-bo de dis ance has inc eased o 50 nm, wi h a su ace co e age o only 51%. The lase - ea ed me al s ipes p esen a unca ed ellipsoidal p ojec ed shape in he y – z plane (Figu e 1d, ). Thei es ima ed heigh o ≈ 30–40 nm is highe han be o e lase ea men . Fu he mo e, sepa a ed nanopa icles in he 10–20 nm ange appea on he la e al aces o he SiO 2 columns (Figu e 1e, and Figu e S2 in he Sup- po ing In o ma ion) in addi ion o he me al s ipes. Figu e 2 shows he AFM opog aphy pic u es o he as-g own sample (a) and he lase - ea ed samples a lase powe o 4.0 kW cm − 2 (b) and 7.0 kW cm − 2 (c). The su ace o he o iginal sample COMMUNICATION esul s can also be in e p e ed as he compa ison o he size dis ibu ions o he me al g ains in he su aces, showing ha he lase ea men induces a smoo hing in he me al nano- pa icles su ace as well as a sha pening in he size dis ibu- ion o he ea u es in he su - ace consis en wi h he enlon- ga ion o he Ag nano s ipes in he x -di ec ion. Mo eo e , i is also wo h men ioning ha he analysis o he AFM mic oscopy images by as Fou ie ans- o m in wo dimensions (2D- FFT) (see Expe imen al Sec ion o u he de ails) shows an inc ease o he aniso opy a e ea men a high lase powe . Figu e 3 (le ), which shows he SEM images o he samples, con- i ms ha he Ag nanos uc u es e ol e as a unc ion o he lase powe (see also Figu e S3, Sup- po ing In o ma ion). The com- pa ison be ween Figu e 3a (as- g own ma e ial) and Figu e 3b ( P = 4.0 kW cm − 2 ) con i ms he esul obse ed by AFM ha con inuous and smoo h me al s ipes al eady o m a in e me- dia e powe s. Fu he inc ease in he powe (Figu e 3c ; P = 7.0 kW cm − 2 ) p oduces a dec ease in he me al co e age ha is likely o be linked o an inc ease o he s ipe heigh . The consequences o he s uc u al changes p o oked by he lase ea men on he op ical esponse o he i lms we e s udied by ansmi ance measu emen s a no mal incidence wi h a collima ed and linea ly pola ized beam. Spec a in Figu e 3d we e acqui ed wi h he incoming elec ic i eld o ien ed along he s ipes ( x -pola iza ion) and hose in Figu e 3e wi h he i eld pe pendicula o he s ipes ( y -pola iza ion) o AgNPs/SiO 2 NCs i lms be o e and a e ea men a di e en lase ou pu powe s. The spec um o he o iginal sample p esen s abso p- ion bands peaking a 650 nm and 550 nm o x - and y - pola iza ion, espec i ely. This op ical dich oism mus esul om he exci a ion o dis inc plasmon esonances along he s ipes (longi udinal plasmon) and pe pendicula ly o hem ( ans e se plasmon), while he shi be ween he wo bands indica es ha he elec omagne ic coupling along he s ipes is s onge han be ween successi e s ipes. Upon lase ea men a mode a e powe ( P = 4.0 kW cm − 2 ), he longi udinal plasmon band (Figu e 3d ) becomes less in ense, b oadens, and shi s owa ds he in a ed. These ea- u es a e ypical o he o ma ion o con inuous me al s ipes in ag eemen wi h Figu e 3b . Inc easing he lase powe has a smalle e ec on his b oad band, which becomes p og essi ely (Figu e 2a ) is o med by densely packed nano pa icles, in ag ee- men wi h he SEM no mal iew mic oscopy image in Figu e 1a . The analysis o he AFM images shows ha hese Ag NPs ha e a wide size dis ibu ion anging om 20 o 100 nm. Such a high dispe sion in he Ag NPs sizes is known o p oduce a wide plasmon abso p ion band along he isible ange. [ 1–3 ] The AFM opog aphy pic u es o he lase ea ed sample a 4.0 kW cm − 2 does no e eal a subs an ial change in he size dis ibu ion o he Ag NPs al hough he pa icle edges a e now less de i ned. This indica es ha he MNPs ha e begun o pe cola e. Such a pe cola ion can be easily deduced om he de i a i e ep esen- a ion o he AFM opog aphic images shown in Figu e 2e . This ep esen a ion enhances he con as a he pa icle edges while he egions o a cons an slope a e shown wi h he same colo . Acco dingly, in he o iginal samples he Ag NPs p esen e y well de i ned bo de s, while in he sample ea ed a 4.0 kW cm − 2 lase powe he edges a e less de i ned. The mos ou s anding opog aphic change occu s o he lase ea ed sample a 7.0 kW cm − 2 (Figu e 2c, ). Fo his ea men he Ag NPs a e comple ely pe cola ed in e y smoo h and con inuous nano- s ipes in he x -di ec ion. Figu e 2g ep esen s he s a is ical analysis o he g ain bo de s o he ea u es in he su ace ob ained o he h ee modi i ed su aces in Figu e 2d– . The Figu e 1 . Su ace (a,b) and c oss-sec ion (c,d) SEM images o AgNPs/SiO 2 NCs i lms be o e (le ) and a e ( igh ) lase ea men a 7.0 kW cm − 2 ; e) and ) co espond o he backsca e ed elec on images o (c) and (d), espec i ely. o he sys em was modeled wi hin he dipole app oxi- ma ion. De ails a e gi en in Figu e S4 o he aniso opic e ec i e medium modeling [ 27 , 28 ] sec ion o he Suppo ing In o - ma ion. Despi e he simplici y o he model and he c ude app ox- ima ion o he s ipe mo pholo- gies (Figu e S4a, Suppo ing In o ma ion), he simula ions in Figu e S4b,c ep oduce quali a- i ely he measu ed e olu ion o he longi udinal and ans e se plasmon esonances upon bo h low and high powe lase ea - men s. Indeed, he b oadening and ed-shi o he longi udinal abso p ion band a e low powe ea men a e well- ep oduced by assuming a ansi ion om densely packed nanopa icles o con inuous s ipes (Figu e S4b). Meanwhile, he e e sal o he ans e se abso p ion band posi- ion and he loss o in ensi y o he longi udinal plasmon a e high-powe ea men s a e ep o- duced by assuming na owe s ipes wi h a highe aspec a io (Figu e S4c). Lase ea men o me als a low o mode a e powe s is gene ally known o a ec hei nanos uc u e h ough abla ion mechanisms [ 29 ] o by hea ing e ec s, p oducing an enhanced a omic su ace di usion o e en olume mel ing. [ 23 ] In ou expe imen a signi i can abla- ion o sil e can be disca ded because no emo al o sil e was obse ed, as es ima ed om he heigh o s ipes and he su ace co e age. Fo ns-lase annealing wi h pulse du a ions longe han he me al elec on–phonon elaxa ion ime, [ 23 , 30 ] hea accumula es in he me al. Fo con- inuous me al hin i lms deposi ed on SiO 2 /Si such localized annealing leads o mel ing and dewe ing o he me al. [ 31 , 32 ] Since he condi ions o ou expe imen (i.e., a ound 10 pulses wi h an a e age powe densi y o ≈ 7 kW cm − 2 pe pulse o he ea men a maximum powe eaching a pa icula zone o he sample su ace) a e compa able o hose used o pa ially dewe Ag hin i lms om SiO 2 /Si, [ 31 , 32 ] we p opose a wo s ep mechanism o accoun o he s uc u al e olu ion o he s ipes upon lase ea men . Fi s ly, he me al nanos uc u es accu- mula e hea up o hei mel ing empe a u e. Because o hei small size and he densely packed s a e in he o iginal i lms, hey mel apidly in o Ag d ople s, which acco ding o li e a u e less in ense. Unde y -pola iza ion (Figu e 3e ), he ans e se abso p ion band emains ela i ely na ow a e lase ea men bu shi s h ough he isible spec um as a unc ion o he lase powe (Figu e 3 ). T ea men a P = 3.5 kW cm − 2 esul s in a ed-shi om 650 o 750 nm, while u he inc easing he lase powe g adually shi s he band owa ds sho e wa eleng hs (a blue-shi up o 400 nm). Blue-shi s a e o en a ibu ed in he li e a u e o a ounding o he nanopa icles o o a weakening o he elec omagne ic coupling be ween hem. [ 10 , 11 ] Also no iceable in he x -pola ized spec a is he enhancemen o an addi ional abso p ion band a a ound 400 nm (Figu e 3d ) ha is al eady p esen be o e ea men . To in e p e he e olu ion o plasmon abso p ion bands as a unc ion o he lase powe , he op ical ex inc ion coe i cien Figu e 2 . AFM mic oscopy images o he AgNPs/SiO 2 NCs hin i lms be o e he lase ea men (a), a e ea men a P = 4.0 kW cm − 2 (b) and a P = 7.0 kW cm − 2 (c). Panels (d– ) show he co esponding de i a i e o he images in (a–c) in o de o enhance he bo de g ains be ween he sil e pa icles. g) Compa ison o he size dis ibu ion o he ea u es in he su ace calcula ed om (d– ). h) Compa ison o he 2D-FFT o he images in (a–c). possibili ies o op ical pa e ning and coding. Figu e 4 a shows a se ies o colo ed samples ob ained by ns-lase ea - men o AgNPs/SiO 2 NCs deposi ed on used silica sub- s a es. The pic u es we e acqui ed o samples illumina ed wi h whi e ligh h ough a linea pola ize (Figu e 4b ). Upon azimu hal o a ion o he samples, he illumina ion beam is oggled om x -pola ized o y -pola ized and pola iza ion modula ed colo s a e hen obse ed. In o he wo ds, hey display an op ical dich oism ha can be uned by a ying he lase powe . While x -pola ized exci a ion b ings ou a monoch oma ic image (g ey-blue ones) ha is li le a ec ed by he lase powe , a ansi ion om a blue o a yellow colo do no end o we he silica subs a e. [ 33 ] Secondly, hese d op- le s coalesce in he o m o con inuous and l a s ipes o med along he bundle s uc u e o he SiO 2 wi h NCs ac ing as a empla e. [ 34 ] Following he lase sho , he Ag NPs cool down, ec ys allize, and eeze p oducing an in e connec ed d ople shape s uc u e as shown by he SEM pic u es on Figu e 1b . As he lase powe inc eases, he s ipes unde go a pa ial dewe - ing. In all cases a esidual se o small Ag NPs emain a ached o he la e al aces o he SiO 2 NCs (see Figu e 1 and Figu es S2 and S3 in he Suppo ing In o ma ion). Among he possible applica ions o he lase w i ing echnique de eloped he e, we would like o highligh i s Figu e 3 . Le ) SEM images o AgNPs/SiO 2 NCs a) be o e lase ea men , b) ea ed a 4.0 kW cm − 2 , and c) ea ed a 7.0 kW cm − 2 . Righ ) T ansmi - ance spec a measu ed be o e and a e i adia ion a di e en lase powe s, as labeled o he incoming elec ic i eld o ien ed along d) he x -di ec ion and e) he y -di ec ion. The colo code is he same in bo h g aphs. Spec a o he o iginal sample and hose ea ed a 4.0 kW cm − 2 and 7.0 kW cm − 2 ha e been highligh ed o acili a e he compa ison wi h he co esponding SEM images (see also Figu e S3, Suppo ing In o ma ion). ) E olu ion o he spec al posi ion o he ans e se plasmon band as a unc ion o lase ou pu powe . COMMUNICATION Expe imen al Sec ion SiO 2 hin i lms wi h il ed nanocolumns we e g own by GLAD by placing he subs a es a a glancing angle o 70 ° wi h espec o he e apo a o . Ag was deposi ed a oom empe a u e on o he SiO 2 NCs by DC spu e ing a 400 V in an A (2 mba ) a mosphe e. Lase pos - ea men was pe o med a oom empe a u e wi h a 20 W diode-pumped Nd:YAG (Powe line E, Ro i n-Baasel Inc.) unpola ized lase emi ing a 1064 nm wi h an ≈ 100 ns pulse wid h and a 20 kHz epe i ion a e. [ 35 ] The samples we e scanned wi h an ≈ 0.5 mm spo a 1 m s − 1 speed. AgNPs/ SiO 2 NCs nanos uc u e was cha ac e ized by SEM wi h a Hi achi S5200 mic oscope. Op ical ansmi ance o he i lms was measu ed wi h a Ca y 100 spec opho ome e a no mal incidence and in he 300–900 nm ange wi h a 1-nm monoch oma o s ep. Noncon ac AFM cha ac e iza ion was ca ied ou wi h a Ce an es AFM sys em om NANOTEC and he 2D-FFT and u he analyses o he images pe o med wi h he WSXM so wa e. [ 36 ] Suppo ing In o ma ion Suppo ing In o ma ion is a ailable om he Wiley Online Lib a y o om he au ho . Acknowledgemen s Au ho s hank he P ojec s FUNCOAT CONSOLIDER-INGENIO CDS2008 – 0023, MAT2007 – 65764, MAT2010-18447, MAT2010-21228, CEN2007 – 2014, P09-TEP-5283, Domingo Ma inez Founda ion, and Juan de la Cie a G an Nº JCI-2009 – 05098 o J.T. depending on lase powe is seen unde y -pola ized illumina- ion. Op ical pa e ning wi h la e al esolu ion a he scale o he lase w i ing is a clea applica ion o his p ocedu e. An illus a ion a he mac oscale is shown in Figu e 4c whe e he le e s “CSIC” we e o med by iling a se ies o squa e pla es subjec ed o lase i adia ion wi h di e en powe s. Beyond his pola iza ion-dependen colo ing o pa e ns a he mac o- and mic oscales, he ma e ials and p ocedu e de el- oped he e migh be used o op ical enc yp ion by w i ing cha ac e s ha could only be ead wi h a gi en pola iza ion o he incoming ligh . Un o una ely he le e s “CSIC” can be dis inguished ega dless o he pola iza ion (Figu e 4c ). This beha io esul s om he weak dependence on lase powe o he x -pola ized ansmi ance o he i lms (Figu e 3d ). Howe e , in iew o da a enc yp ion applica ions, one can no e in Figu e 3d ,e ha he i lm ansmi ance a 490 nm is independen (s ongly dependen ) on lase powe when measu ed unde x -pola iza ion ( y -pola iza ion). Success ul dich oic enc yp ion migh hus be ob ained by deposi ing he AgNPs/SiO 2 NCs i lms on o a pho onic s uc u e ac ing as a 490-nm bandpass i l e . Main ad an ages o his p ocedu e wi h ega d o o he li hog aphic o mo e con en ional lase - based w i ing p ocedu es ely on i s easy implemen a ion (i.e., elec on, ion, o esis li hog aphy a e clea ly mo e com- plica ed me hods) and he ac ha enc yp ion and encoding e i ciency will no only depend on he size o he w i en pa - e ns bu also on he need o a gi en pola ized ligh o ead he in o ma ion. In his a icle, we ha e demons a ed ha i adia ion o Ag NPs deposi ed on o bundled SiO 2 nanocolumns wi h a com- me cial w i ing ns-lase enables a p ecise con ol o hei op ical dich oism, which is a ibu ed o he o ma ion o long ange o de ed sil e nanos ipes o med h ough 1D me al pe - cola ion and pa ial dewe ing along and pe pendicula o he bundling di ec ion o he SiO 2 NCs, espec i ely. We o esee ha hese esul s a e a i s s ep owa ds he use o AgNPs/ SiO 2 NCs o op ical nanopa e ning, enc yp ion, and da a s o age applica ions. Figu e 4 . a) Pic u es o a ≈ 3.5 × 2 cm 2 glass slide coa ed wi h AgNPs/SiO 2 NCs and subsequen ly ea ed by ns-lase . Pa e ning on he glass slide was achie ed applying di e en lase po we in each squa e zone. The ela ion be ween he appa en colo o he sample and he pe cen age o he lase powe is indica ed in he ske ch o he pic u e acquisi ion p ocedu e (b). Unde x -pola iza ion, he pixel colo emains monoch ome, whe eas a ull-colo ansi ion as a unc ion o he lase powe is seen unde y -pola iza ion. c) Example o dich oic cha ac e enc yp ion on glass slide coa ed wi h AgNPs/ SiO 2 NCs. The size o he pixels is ≈ 0.20 cm, bu i can be dec eased o he la e al esolu ion o he lase ( ≈ 100 μ m). [ 1 ] a) U. K eibig , M. Volme , Op ical p ope ies o me al clus e s , Sp inge , Be lin, Ge many 1995 ; b) W. A. Mu ay , W. L. Ba nes , Ad . Ma e . 2007 , 19 , 3771 . [ 2 ] H. Ibn El Ah ach , R. Bachelo , A. Vial , G. Lé ondel , J. Plain , P. Roye , O. Soppe a , Phys. Re . Le . 2007 , 98 , 107402 . [ 3 ] a) E. Hu e , J. H. Fendle , Ad . Ma e . 2004 , 16 , 1685 ; b) J. Toude , H. Fe nandez , D. Babonneau , S. Camelio , T. Gi a deau , J. Solis , Nano echnology 2009 , 20 , 475705 . [ 20 ] P. G eco , M. Ca allini , P. S olia , S. D. Qui oga , S. Du a , S. Zacchini , M. C. Iapalucci , V. Mo andi , S. Mili a , P. G. Me li , F. Bisca ini , J. Am. Chem. Soc. 2008 , 130 , 1043 . [ 21 ] T. Wenzel , J. Bosbach , A. Goldmann , F. S ie z , F. T äge , Appl. Phys. B 1999 , 69 , 513 . [ 22 ] M. Kaemp e , H. G aene , A. Kiesow , A. Heilmann , Appl. Phys. Le . 2001 , 79 , 1876 . [ 23 ] S. Link , M. El-Sayed , J. Phys. Chem. B 1999 , 103 , 8410 . [ 24 ] P. Zijls a , J. W. M. Chon , M. Gu , Na u e 2009 , 409 , 410 . [ 25 ] a) H. Van K anenbu g , C. Lodde , Ma e . Sci. Eng. 1994 , R11 , 295 ; b) J. R. Sanchez-Valencia , J. Toude , L. Gonzalez-Ga cia , A. R. Gonzalez-Elipe , A. Ba anco , Chem. Commun. 2010 , 46 , 4372 . [ 26 ] a) J. R. Sanchez-Valencia , A. Bo as , A. Ba anco , V. Rico , J. P. Espinos , A. R. Gonzalez-Elipe , Langmui 2007 , 24 , 9460 ; b) V. Rico , A. Bo as , F. Yube o , J. P. Espinos , F. F u os , A. R. Gonzalez-Elipe , J. Phys. Chem. C 2009 , 113 , 3775 . [ 27 ] E. D. Palik , Handbook o Op ical Cons an s , Academic P ess , New Yo k, USA 1985 . [ 28 ] A. Dakka , J. La ai , C. Sella , S. Be hie , M. Abd-Le dil , J. C. Ma in , M. Maaza , Appl. Op . 2000 , 39 , 2745 . [ 29 ] W. Hoheisel , U. Schul e , M. Vollme , R. Weidenaue , F. T äge , Appl. Su . Sci. 1989 , 36 , 664 . [ 30 ] S. J. Henley , J. D. Ca ey , S. R. P. Sil a , Phys. Re . B: Condens. Ma e Ma e . Phys. 2005 , 72 , 195408 . [ 31 ] J. T ice , D. Thomas , C. Fa azza , R. Su eshkuma , R. Kalyana aman , Phys. Re . B: Condens. Ma e Ma e . Phys. 2007 , 75 , 235439 . [ 32 ] H. K ishna , N. Shi a o , C. Fa azza , R. Kalyana aman , Phys. Chem. Chem. Phys. 2009 , 11 , 8136 . [ 33 ] K. S. Gad e , T. L. Al o d , J. Appl. Phys. 2003 , 93 , 919 . [ 34 ] F. A. Nichols , J. Appl. Phys. 1966 , 37 , 2805 . [ 35 ] A. Cas elo , D. Nie o , C. Bao , M. T. Flo es-A ias , M. V. Pe ez , C. Gomez-Reino , C. Lopez-Gascon , G. F. de la Fuen e , Op . Commun. 2007 , 273 , 193 . [ 36 ] I. Ho cas , R. Fe nandez , J. M. Gomez-Rod iguez , J. Colche o , J. Gomez-He e o , A. M. Ba o , Re . Sci. Ins um. 2007 , 78 , 013705 . [ 4 ] a) H. Y. Liang , Z. P. Li , W. Z. Wang , Y. S. Wu , H. X. Xu , Ad . Ma e . 2009 , 21 , 4614 ; b) A. Biswas , I. S. Baye , D. H. Dahanayaka , L. A. Bumm , Z. Li , F. Wa anabe , R. Sha ma , Y. Xu , A. S. Bi is , M. G. No on , E. Suhi , Nano echnology 2009 , 20 , 325705 . [ 5 ] H. Hö el , S. F i z , A. Hilge , U. K eibig , M. Vollme , Phys. Re . B: Condens. Ma e Ma e . Phys. 1993 , 48 , 18178 . [ 6 ] J. Gonzalo , R. Se na , J. Solis , D. Babonneau , C. N. A onso , J. Phys.: Condens. Ma e 2003 , 15 , 3001 . [ 7 ] J. S. Bi een , L. A. Swea lock , H. Me ens , N. S. Lewis , A. Polman , H. A. A wa e , J. Phys. Chem. C 2007 , 111 , 13372 . [ 8 ] J. P. Ba nes , A. K. Pe o d-Long , R. C. Doole , R. Se na , J. Gonzalo , A. Suá ez-Ga cia , C. N. A onso , D. Hole , Nano echnology 2002 , 13 , 465 . [ 9 ] B. Palpan , B. P e el , J. le me , E. Co ancin , M. Pella in , M. T eilleux , A. Pe ez , J. l. Vialle , M. B oye , Phys. Re . B: Condens. Ma e Ma e . Phys. 1998 , 57 , 1963 . [ 10 ] F. S ie z, Appl. Phys. A 2001 , 72 , 381 . [ 11 ] J. Toude , S. Camelio , D. Babonneau , M. F. Denano , T. Gi a deau , J.P. Espinós , P. Yube o , A. R. Gonzalez-Elipe , J. Appl. Phys. 2005 , 98 , 114316 . [ 12 ] L. Simono , D. Babonneau , S. Camelio , D. Lan ia , P. Gué in , B. Lamongie , V. An ad , Thin Solid Films 2010 , 518 , 2637 . [ 13 ] a) G. B. Smi h , S. Dliga ch , R. Sulli an , M. G. Hu chins , Sola Ene gy 1998 , 62 , 229 ; b) M. Suzuki , Y. Taga , J. Appl. Phys. 1992 , 71 , 2848 . [ 14 ] S. Camelio , D. Babonneau , D. Lan ia , L. Simono , F. Pailloux , Phys. Re . B: Condens. Ma e Ma e . Phys. 2009 , 80 , 155434 . [ 15 ] E. Fo , C. Ricolleau , J. Sau-Pueyo , Nano Le . 2003 , 3 , 65 . [ 16 ] M. Suzuki , W. Maeki a , K. Kishimo o , S. Te amu a , K. Nakajima , K. Kimu a , Y. Taga , J. Appl. Phys. 2005 , 44 , L193 . [ 17 ] J. R. Sánchez-Valencia , J. Toude , A. Bo as , C. Lopez-San os , I. O ega-Feliu , A. Ba anco , A. R. Gonzalez-Elipe , Plasmonics 2010 , 5 , 241 . [ 18 ] H. Me ens , A. Polman , Appl. Phys. Le . 2006 , 89 , 211107 . [ 19 ] M. Ca allini , C. Albone i , F. Bisca ini , Ad . Ma e . 2009 , 21 , 1043 .