On the RISE APPLICATION NOTE. Correlative Confocal Raman and Scanning Electron Microscopy. WITec GmbH, Lise-Meitner-Str. 6, Ulm, Germany

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1 APPLICATION NOTE On the RISE Correltive Confocl Rmn nd Scnning Electron Microscopy WITec GmH, Lise-Meitner-Str. 6, Ulm, Germny fon +49 (0) , fx +49 (0)

Introduction Correltive imging techniques gin more nd more importnce in mny fields of pplictions due to the fct tht more chrcteristics of specimen cn e nlyzed with one instrument.

2 Introduction Correltive imging techniques gin more nd more importnce in mny fields of pplictions due to the fct tht more chrcteristics of specimen cn e nlyzed with one instrument. The efficient workflow of correltive microscopy techniques is n dditionl dvntge tht sves time nd money. In this ppliction note we present correltive RISE microscopy: The first instrument comining fully loded SEM with confocl Rmn microscope including white light microscopy. RISE: Rmn Imging nd Scnning Electron Microscopy Scnning electron microscopy (SEM) uses the interction of electrons with the investigted mteril to revel the highest lterl resolution imges of specimen structure. The sme focused electron em cn e used to generte energy dispersive X-ry spectr (EDX) for otining informtion on the chemicl elements of the mtter. This technique, though very powerful, cnnot extrct detils of the onding of toms, which would disclose the nture of the molecules in smple. This tsk cn e chieved y fusing SEM with non-destructive Rmn imging. Rmn imging relies on the interction of photons with smple. The tremendous importnce of the Rmn effect is sed on the inelstic scttering of photons with molecules cused y the excittion or nnihiltion of specific moleculr virtion nd is chrcteristic for the type nd coordintion of the molecules involved in the scttering process. Thus Rmn imging revels the moleculr/chemicl composition of the sustnce. This powerful comintion is relized in one instrument for Rmn Imging nd Scnning Electron (RISE) microscopy. Due to n intelligent positioning system the instrument enles for the first time diffrction limited confocl Rmn imging from exctly the sme smple re s the SEM imge. Info Box: RISE Microscopy RISE Microscopy is the comintion of confocl Rmn Imging nd Scnning Electron Microscopy. It incorportes the sensitivity of the non-destructive, spectroscopic Rmn technique long with the tomic resolution of electron microscopy. Rmn Imging enles the identifiction of molecules, their llotropes nd polymorphs, the determintion of their orienttion, purity nd crystllinity, nd the detection of strin sttes. SEM llows for the imging of surfce structures on the nnometer scle. RISE comines the dvntges of oth, thus fcilitting the most in-depth chrcteriztion of the smple. RISE microscopes consist of WITec confocl Rmn microscope comined with n SEM (TESCAN or ZEISS).

RISE imging of geologicl smples A minerl phses of rock section from drill core ws nlyzed in the next exmple. The dominnt rock type is Diorite.

This reduces the risk of contmintion of the surfce, which is of gret importnce not only for geologicl drill cores ut lso for ojects derived from the deep se. Fig.

The distriution of elementl groups indictes the presence of three distinct minerls. Single Rmn spectr could e cquired from the three different res (Fig.

Rmn spectr of the three primry minerls were evluted using cluster nlysis.

3 RISE imging of geologicl smples A minerl phses of rock section from drill core ws nlyzed in the next exmple. The dominnt rock type is Diorite. The smple hd no need to e treted or vporized ut ws only sectioned with dimond sw under wter. This reduces the risk of contmintion of the surfce, which is of gret importnce not only for geologicl drill cores ut lso for ojects derived from the deep se. Fig. 1 shows the SEM imge of smll smple re using the ck-scttered electron detector of the SEM. The sme re ws nlyzed using EDX (Fig. 1). The distriution of elementl groups indictes the presence of three distinct minerls. Single Rmn spectr could e cquired from the three different res (Fig. 1c) three of which show the chrcteristic Rmn nds for qurtz, epidote nd plgioclse. This is in good greement with the elementl composition otined y EDX. Rmn spectr of the three primry minerls were evluted using cluster nlysis. In ddition to these spectr, four others were detected, two of which could indicte different grin orienttions within the phses of epidote nd plgioclse respectively. The sptil distriution of the minerls is shown in the color coded RISE imge (Fig. 1d) where the colors of the Rmn imge mtch the colors of the spectr. Not only minerl phse distriution could e detected ut lso smll grins within minerl phse. Fig. 1e shows the white light imge cquired from the sme smple re s the SEM imge. It clerly emphsizes tht high resolution opticl imges require proper focusing, wheres SEM is completely insensitive to surfce roughness, which is why it is difficult to retrieve the smple re when using two stnd-lone instruments. RISE imging of non-conductive orgnic mterils Non-conductive compounds cn e exmined with modern SEMs without specific pretretment y using low vcuum c e d Fig. 1: A minerl phse of diorite rock section. () SEM imge () overly of SEM nd EDX imge. Three element groups could e distinguished with EDX: Si, O: ornge; C, Fe, Al: grey-purple; N; green. (c) Rmn single spectr cquired from the three distinct regions with the chrcteristic Rmn nds of qurtz (rown), epidot (red) nd Plgioclse (green). (d): Rmn spectrl imge overlid with the SEM imge. (e) light-microscopy imge from the sme smple re. Imge prmeters: 100 x 100 µm 2, 150 x 150 pixels = 22,500 spectr, integrtion time 0.08 sec per spectrum. Smple courtesy y Christine Heim, Geoscience Centre GZG, Dept. Geology, University of Göttingen, Germny. mode tht prevents the mteril from eing electriclly chrged. Imging polymer lends or iologicl mterils in this wy cn revel contrst in the SEM imges, though without giving ny clue regrding the chemicl composition of the vrious phses. A film of polymer lend consisting of polystyrene (PS) nd polymethylmethcrylte (PMMA) ws nlyzed y RISE Microscopy. Both polymers re comprised only of the elements cron, oxygen nd hydrogen. With EDX these elements cn e identified without reveling how the elements re comined into molecules. Tht is however precisely the strength of Rmn imging s the spectr shed light on the chemicl nture (structurl units, type nd degree of rnching, end groups, dditives), conformtionl order (physicl rrngement of the polymer chin), stte

Fig 2: () PMMA (red) nd PS (green) show chrcteristic, distinguishle Rmn spectr. () Bsed on the spectr Rmn imge of PMMA-PS emulsion ws tken nd overlid with SEM picture.

of the order (crystlline, mesomorphous, nd morphous phses), nd orienttion (type nd degree of polymer chin nd side group lignment in nisotropic mterils). Fig.

4 Fig 2: () PMMA (red) nd PS (green) show chrcteristic, distinguishle Rmn spectr. () Bsed on the spectr Rmn imge of PMMA-PS emulsion ws tken nd overlid with SEM picture. Imge prmeters: 50 x 50 µm 2, 300 x 300 pixels = 90,000 spectr, integrtion time sec per spectrum. of the order (crystlline, mesomorphous, nd morphous phses), nd orienttion (type nd degree of polymer chin nd side group lignment in nisotropic mterils). Fig. 2 shows n overly of color coded RISE imge of the PS (green) - PMMA (red) mixture. The SEM imge revels the fine structure of the two polymeric phses, wheres the chemicl identifiction of the polymeric phses is provided y the confocl Rmn imge. The Rmn spectr of PMMA nd PS re shown in Fig. 2. Due to their different hydrophilic properties the two compounds do not mix ut form dispersion of seprted eds. RISE imging of hmster rin tissue In this ppliction exmple RISE Microscopy ws performed on microtome slide of hmster rin tissue. In the SEM imge the white nd gry rin mtter cn e distinguished y their structurl differences. Both tissues cn e lso chemiclly distinguished y their typicl Rmn spectr (figure 3). Overlying the SEM with the color-coded Rmn imge revels more precise view of the distriution of the gry nd white mtter (figure 3). Fig. 3: ) The Rmn spectr of hmster rin tissue smple revel the different spectrl chrcteristics of the white nd gry rin mtter. ) Rmn-SEM imge overly. In the color-coded Rmn imge the white rin mtter is shown in Green nd the gry rin mtter in Red. 100 x 100 μm 2, 300 x 300 pixels = 90,000 spectr, integrtion time: 50 ms/spectrum

c RISE nlysis of cron nno-mterils Thin-lyered or single lyer mterils, defined s 2D mterils, hve recently ttrcted enormous reserch interest due to their specil electronic nd opticl properties which

4 the SEM () nd RISE () imges of CVD grphene sheet deposited on Si/SiO 2 sustrte re presented. The SEM imge ws cquired with low ccelertion voltge (2 kv) using the secondry electron (SE) detector.

The colors used represent single lyer (lue, drk green) with different grde of defects nd more thn one lyer (light green, red).

The specil properties of cron nnotues such s high therml conductivity mke them interesting for pplictions in electronics, nnotechnology, optics nd mterils science.

5 c RISE nlysis of cron nno-mterils Thin-lyered or single lyer mterils, defined s 2D mterils, hve recently ttrcted enormous reserch interest due to their specil electronic nd opticl properties which differ significntly from tht of their ulk precursors. Grphene is one of the most populr mterils extensively studied in this context. In Fig. 4 the SEM () nd RISE () imges of CVD grphene sheet deposited on Si/SiO 2 sustrte re presented. The SEM imge ws cquired with low ccelertion voltge (2 kv) using the secondry electron (SE) detector. This imging mode of the SEM is very surfce sensitive, thus reveling the fine structure of the CVD grphene sheet. The colors used represent single lyer (lue, drk green) with different grde of defects nd more thn one lyer (light green, red). The RISE imge highlights the lrge mount of defects in the lue re, in good greement with the high resolution SEM imge. The specil properties of cron nnotues such s high therml conductivity mke them interesting for pplictions in electronics, nnotechnology, optics nd mterils science. Single-wll cron nnotues (SWCNTs) consist of single tom thick, curved sheet of cron. Their unique electronic nd mechnicl properties mke them ttrctive for electronics friction. The Rmn spectrum identifies SWCNTs s single-wlled y the presence of their chrcteristic RBM (rdil rething mode) nds t low wvenumers (fig. 5). The RISE imge (fig. 5c) of SWCNTs emedded in polyethylene (PE) ws generted y merging the Rmn imge (fig 5) with the SEM imge. c Fig. 4: () SEM imge of grphene smple. () SEM imge overlid with the color-coded confocl Rmn imge. The colors disply the grphene lyers nd wrinkles. Imge prmeters: 20 x 20 µm 2, 150 x 150 pixels = 22,500 spectr, integrtion time: 0.05 s/ spectrum, 1 lyer (lue, drk green), > 1 lyer (light green, red), Si (yellow). Fig. 5: () Chrcteristic Rmn spectr of SWCNTs nd PE. () color-coded Rmn imge. (c) RISE imge. Imge Prmeters: 150 x 150 µm 2 scn rnge, 80 x 80 pixels = spectr, integrtion time: 60 ms/spectrum, PE (red), SWCNTs (green), SEM imge (grey).

To explore the 3D structure of the SWCNTs smple, 16 Rmn imges were tken in the z-direction intervls of 1 µm (fig. 6). From these dt 3D imge ws compiled.

6 Volume scns re vlule tool in providing informtion out the dimensions of ojects or the distriution of certin compound throughout the smple. In order to generte 3D imges, confocl 2D Rmn imges of different focl plnes re cquired y scnning throughout the smple in the z-direction. The 2D imges re then comined into 3D imge stck. To explore the 3D structure of the SWCNTs smple, 16 Rmn imges were tken in the z-direction intervls of 1 µm (fig. 6). From these dt 3D imge ws compiled. It illustrtes tht the SWCNTs lie on top of the PE mtrix (fig. 6). RISE microscopy of MoS 2 Inspired y progress in grphene reserch, other mono-lyered mterils such s hexgonl oron nitride (h-bn) nd trnsition metl dichlcogenides (TMDs) hve lso received widespred ttention. Recent work hs shown tht exfolited monolyer molydenium disulfide (MoS 2 ) is 2D direct ndgp semiconductor indicting tht the mteril is suitle for optoelectronics nd energy hrvesting. Bulk MoS 2 however is n indirect ndgp semiconductor. Thus detiled knowledge of the structures nd fetures of grins nd grin oundries re essentil for understnding nd exploring the mterils properties nd its further pplictions. Here we present with MoS 2 tht RISE microscopy revels structure s well s crystlline nd exciton dynmics of thin-lyered TMDs. CVD grown monolyers of TMDs form tringulr two dimensionl crystls. Twin crystls of MoS 2 on SiO 2 /Si pper in the SEM imge s str-shped forms (fig. 7). The Rmn spectr of these 2D crystls show the chrcteristic E2g nd A1g Rmn nd modes of MoS 2 (fig. 7c). With n incresing numer of lyers the two Rmn nds drift prt due to inter-lyer nd in-plne virtions. At the grin oundries the Rmn nds not only show shifts, ut dditionl nds lso pper (green spectr), indicting defects or misligned 2D crystls. Fig 6: 3D imging of SWCNTs on PE film. For 3D imge of the SWCNTs on PE smple 16 equidistnt Rmn imges were tken while the focus ws shifted y 1 µm for ech imge. The individul imges re displyed s RISE imges in (). The compiled 3D Rmn imge of the nlyzed smple re shows the SWCNTs locted on the top of the PE filter (). Imge prmeters: 200 x 200 µm 2 scn rnge, 70 x 70 pixels = 4,900 spectr, integrtion time: s/ spectrum. PE (red), SWCNTs (green), SEM imges (grey).

c Fig. 7: () SEM imge of MoS 2 twin crystls () Rmn spectr of MoS 2 monolyers (red), two or more lyers (green) nd silicon (purple).

Imge prmeters: 22 x 17 µm 2 scn rnge, 65 x 50 pixels = 3,250 spectr, integrtion time: 0.037 s/spectrum. They proly result from djcent crystls colliding out t their oundries.

The overlpping oundries identified y Rmn imging correlte perfectly with the drk edges visile in the SEM imge.

7 c Fig. 7: () SEM imge of MoS 2 twin crystls () Rmn spectr of MoS 2 monolyers (red), two or more lyers (green) nd silicon (purple). (c) corresponding color-coded Rmn imge derived from the spectrl informtion overlid on the SEM imge to give the RISE imge. Imge prmeters: 22 x 17 µm 2 scn rnge, 65 x 50 pixels = 3,250 spectr, integrtion time: s/spectrum. They proly result from djcent crystls colliding out t their oundries. The spectrl informtion ws used to crete Rmn imge which ws overlid on the SEM imge (fig. 7). The overlpping oundries identified y Rmn imging correlte perfectly with the drk edges visile in the SEM imge. RISE nlysis of polymorphs: Correlting structure with chemicl phses With SEM it is possile to identify mterils consisting of different toms using common comintion with EDX (energy-dispersive X-ry spectroscopy). It cnnot however distinguish etween different modifictions of chemiclly identicl mterils (polymorphs). As the mnner of tomic onding gretly influences the structure nd properties of mteril, visulizing not only morphology ut lso identifying its moleculr rchitecture is importnt. RISE microscopy ccomplishes oth of these tsks s demonstrted with the nlysis of TiO 2 polymorphs (fig. 8). TiO 2 is studied intensively ecuse of its interesting chemicl nd opticl properties nd is widely employed in photo-ctlysis, electrochemistry, photovoltics nd chemicl ctlysis. It is lso used s white pigment in tooth pste, sun screen nd wll pint nd s node mteril for lithium-ion tteries. Depending on the ppliction, one crystlline form or the other gins in importnce. TiO 2 occurs in eight modifictions, two of which ntse nd rutile were exmined. For RISE microscopy n SEM imge tken of 1:1 ntse/rutile powder mixture (fig. 8) The corresponding confocl Rmn imge from the sme smple re ws merged with this SEM imge (fig. 8). It ws demonstrted tht though the elementl compositions of the modifictions ntse nd rutile re identicl, they cn e distinguished from one nother y their chrcteristic Rmn spectr t reltive wvenumers etween 300 nd 800 cm -1 (fig. 8c). Both phses were comined in gglomertes, in which rutile ccumulted in lrger prticles thn ntse. c Figure 8: Two modifictions of TiO2, ntse nd rutile, were mixed 1.1, ground, dissolved in wter nd imged with n SEM () nd confocl Rmn microscope. () SEM nd Rmn imges overlid. (c) In the Rmn spectrum ntse (lue) cn e esily distinguished from rutile (red). Imge prmeters: 12 x 12 µm 2 scn rnge, 150 x 150 pixels = 22,500 spectr, integrtion time: s/spectrum.

a * a (2,1) 1,1 0,1 1,1 2,1 hkl 1,0 1,0 2,0 O 2,1 0,1 1,1 0,2 1,2 2,2

a * a (2,1) 1,1 0,1 1,1 2,1 hkl 1,0 1,0 2,0 O 2,1 0,1 1,1 0,2 1,2 2,2 18 34.3 The Reciprocl Lttice The inverse of the intersections of plne with the unit cell xes is used to find the Miller indices of the plne. The inverse of the d-spcing etween plnes ppers in expressions