Stress reduction in a-C:H coatings through the addition of nitrogen to the feed gas

S ess educ ion in a-C:H coa ings h ough he addi ion o ni ogen o he eed gas F. Rabbani a, *, R. Escoba Galindo b , W.M. A noldbik c , S. an de Zwaag d , A. an Veen b, F , H. Schu b a Depa men o Ma e ials Science, Del Uni e si y o Technology, Ro e damsweg. 137, 2628 AL Del , The Ne he lands b In e acul y Reac o Ins i u e, Del Uni e si y o Technology, Mekelweg. 15, 2629 JB Del , The Ne he lands c Su aces, In e aces and De ices, Debye Ins i u e, U ech Uni e si y, P.O. Box 80.000, 3508 TA, U ech , The Ne he lands d Facul y o Ae ospace Enginee ing, Del Uni e si y o Technology, Kluy e weg. 1, 2629 HS Del , The Ne he lands Abs ac In insic s ess in amo phous hyd ogena ed ca bon (a-C:H) coa ings was educed h ough addi ion o 10–20 sccm N 2 o he eed gas. The comp essi e s esses obse ed in his s udy we e in he ange 0.91 o 1.6 GPa. App oxima ely 2–3 a .% ni ogen was inco po a ed in o he coa ings as de e mined using elas ic ecoil de ec ion (ERD). Raman spec oscopy shows ha he G peak o samples made wi h ni ogen is shi ed o highe wa e numbe s, and ha he e is a mo e p onounced ‘shoulde ’ a he D peak posi ion. I is hypo hesized ha ni ogen addi ion o he eed gas a a low a e o 20 sccm enhances he o ma ion o a oma ic ings associa ed wi h he D peak. The s ess educ ion no ed o ni ogen addi ion a 10 sccm was con ibu ed o a educ ion in he mean coo dina ion numbe o he ne wo k. Posi on beam analysis (PBA) was used o show ha in a high empe a u e deposi ion he in e ace o he ni ogen-con aining coa ing has mo e open space. This phenomenon can con ibu e o a educ ion o he comp essi e s ess by educing he in e acial s ess. Annealing es s we e pe o med o moni o his open olume using Raman and PBA analysis. Keywo ds: Amo phous hyd ogena ed ca bon; Vib a ional p ope ies cha ac e iza ion; De ec cha ac e iza ion 1. In oduc ion Some o he a ac i e p ope ies o amo phous hyd o- gena ed ca bon (a-C:H) coa ings a e hei low coe icien o ic ion, good wea a e, chemical ine ness and low su ace ene gy. A p oblem in he manu ac u e o hese coa ings is hei high in insic s ess, which esul s in coa ing ailu e. In his esea ch he adhesion o a-C:H coa ings on o s eel and Si subs a es was no ed o imp o e wi h he addi ion o ni ogen o he gas plasma. O he esea che s ha e also epo ed be e adhesion and/o a educ ion o he coa ing s ess wi h ni ogen inco po a ion [1–6]. The ollowing sys ema ic s udy was unde aken o in es iga e he educ- ion in he in insic s ess o a-C:H coa ings deposi ed on o Si wa e s wi h ni ogen in he gas eed a 10 and 20 sccm low a es. These a-C:H coa ings we e p oduced by a non- con en ional p ocess: he decomposi ion o a eac i e plasma was achie ed in a PVD chambe by applying a DC-bias ol age o he subs a e able while gases we e in oduced in o he e acua ed chambe a se low a es. The gas composi ion was a ied om pu e CH 4 ,CH 4 +A , o CH 4 +H 2 , in each case a sample was also deposi ed wi h ni ogen in he gas eed. I was seen ha addi ion o 10 sccm ni ogen had some e ec bu no as much as 20 sccm in educing he in insic s ess. This s ess was in all he cases comp essi e and in he ange o s esses epo ed o hese coa ings in he li e a u e [7]. As he deposi ion empe a u e is also a a iable ha a ec s ilm g ow h, wo samples we e made a 300 jC o isola e he e ec o ni ogen addi ion. In all cases, he comp essi e s ess in he coa ings dec eased wi h he addi ion o ni ogen. In depo- * Co esponding au ho . Tel.: +31-1527-89518; ax: +31-1527-86730. E-mail add ess: . abbani@ nw. udel .nl (F. Rabbani). F Deceased 3 Janua y 2004. si ions whe e hea ing was no applied o he p ocess, he elas ic modulus was also educed wi h ni ogen addi ion a 20 sccm. In he case o he high empe a u e deposi ions, he educ ion in he elas ic modulus was no ed o bo h samples. The s ess in he coa ings was de e mined h ough adius o cu a u e measu emen s made on he Si subs a e be o e and a e deposi ion. The mechanical p ope ies o he coa ings such as he elas ic modulus and ha dness we e measu ed using nano-inden a ion es ing. Elas ic ecoil de ec ion yielded in o ma ion on he composi ion o he ilms and show ha 2–3 a .% ni ogen is inco po a ed. This esea ch uses posi on beam analysis (PBA) and Raman spec oscopy as complemen a y echniques o s udy a-C:H coa ings. As hyd ogen p esen a oids essen ially masks hese de ec s o PBA de ec ion [8], a se ies o annealing es s we e ca ied ou o ‘isola e’ open space a e ou di usion o hyd ogen. Unique o his s udy is he inding ha he D peak becomes mo e p onounced, signi - ican o augmen a ion in size o numbe o a oma ic ing s uc u es. 2. Expe imen al A Hauze PVD machine was used o gene a e a eac i e glow made om he decomposi ion o a ange o gas mix u es wi h and wi hou N 2 , whe e CH 4 was he ca bon con aining gas. E en hough a PVD chambe was used he p ocess is unique in ha a ge spu e ing was no employed. The PVD chambe was i s pumped down o a acuum o app oxima ely 10 4 Pa. P io o he coa ing p ocedu e an e ch s ep was included using A gas o emo e he su ace oxide laye on he Si subs a e. The plasma was gene a ed h ough he applica ion o a bias ol age o 550 V-DC o a o a ing subs a e able, while he gases we e in oduced a speci ic low a es high enough o gene a e a glow dis- cha ge. The coa ings we e deposi ed on o Si (100) single c ys al subs a es, o a deposi ion ime o 1 h. Du ing deposi ion he p ocess empe a u e ises g adually o some equilib ium alue less han 300 jC due o he hea gene a ed by ion bomba dmen . Two samples we e made wi h em- pe a u e egula ion, i.e. he deposi ion was s a ed a 300 jC and his empe a u e was main ained du ing he es by applying ex e nal hea ing no gene a ed by he plasma i sel . The annealing es s we e conduc ed a 150, 300, 400, 500 and 600 jC in a acuum o 10 5 Pa o 30-min in e als. PBA and Raman spec oscopy we e used o moni o he changes ha occu ed in he coa ings be ween each anneal- ing expe imen . 2.1. S ess measu emen s S ess measu emen s we e made by de e mining he adius o cu a u e o he Si wa e be o e and a e depo- si ion, using a bending lase beam me hod. De ails o he expe imen al se -up can be ound in Re . [9]. The s ess was calcula ed using a modi ied S oney equa ion [10]: ¼½ESi=ð1mSiÞð 2 Si=6 cÞð1=Rc1=RSiÞð1Þ whe e is he s ess in he coa ing, E Si he elas ic modulus o he Si wa e , m Si he Possion’s a io o he Si wa e , Si he hickness o he Si wa e , c he hickness o he coa ing (de e mined by weigh gain measu emen s and assuming a densi y o he a-C:H coa ing o 2.010 +3 kg m 3 ). R Si is he adius o cu a u e o he Si subs a e be o e deposi ion and R c he adius o cu a u e a e deposi ion. 2.2. Nano-inden a ion es ing The elas ic modulus and ha dness o he coa ings we e measu ed wi h a Hysi on T iboScope R nanomechanical es ins umen equipped wi h a Be ko ich diamond ip. The so wa e calcula es he elas ic modulus by aking he linea po ion o he unloading cu e. Simul aneously, ha dness is calcula ed by sub ac ing he elas ic displacemen om he load-displacemen da a [11]. 2.3. Raman A Renishaw Raman mic oscope sys em 2000, using he 514.5 nm line o an A ion lase was used o he spec os- copy analysis. The measu emen s we e made a a lase powe se ing o 2 mW, and he sys em was calib a ed wi h a Si specimen. G ams 32 so wa e was applied o sub ac a linea backg ound om he spec a and o i wo cu es o a mix Gaussian–Lo en zian unc ion in he egion 1000– 1750 cm 1 . All he i pa ame e s such as linewid h, posi ions and a eas we e allowed o a y. The G peak is due o he ela i e s e ching mo ion o sp 2 ca bon a oms in ings o chains; and he D peak is due o he b ea hing modes o a oma ic ings [12]. The I d /I g a io was de e mined based on peak a eas. 2.4. PBA The PBA expe imen s we e pe o med wi h he Del Va iable Ene gy Posi on beam (VEP) [13]. The posi ons we e injec ed in he samples wi h ene gies uned be ween 100 eV and 30 keV. The maximum implan a ion ene gy co esponds o a ypical mean implan a ion dep h o 4Am in ma e ials wi h a densi y o 3gcm 3 . All expe imen s we e ca ied ou a oom empe a u e unde a acuum o app oxima ely 10 6 Pa. PBA esul s a e desc ibed in e ms o wo pa ame e s desc ibing he Dopple b oadening o he 511 keV annihila ion pho o-peak. The Spa ame e indica es he ac ion o posi ons ha annihila e wi h low momen um elec ons (small Dopple b oadening) such as alence o conduc ion elec ons. This pa ame e is ela ed o he open olume de ec s p esen in he sample such as acancy clus e s and/o in e aces wi h mis i . Sinc eases as he open- olume de ec s in a ma e ial inc ease, and la ge alues o Sindica e ha he ma e ial has mo e open- olume de ec s [8].TheWpa ame e indica es he ac ion o posi ons ha annihila e wi h high momen um elec ons (co e elec ons) and hus cause la ge Dopple b oadening. This pa ame e is ela ed o he chemical en i onmen whe e he annihila ion akes place. Bo h pa ame e s can be com- bined in SWmaps whe e he di e en annihila ion si es can be dis inguished. The da a we e analyzed wi h he VEPFIT p og am [14]. The Sand Wpa ame e s o he Si subs a e we e used o no malize he da a (as hese alues a e iden ical o all samples, i allows o compa isons o be made be ween coa ings and among annealing es s). Al- hough posi on annihila ion si es can occu a he su ace, in he bulk o he coa ing, a he coa ing-subs a e in e ace, and in he silicon subs a e, only he coa ing and he in e ace alues a e o in e es in his s udy. These annihi- la ion si es can be dis inguished by selec ing he posi on implan a ion ene gy. 2.5. ERD The elas ic ecoil de ec ion [15] (ERD) measu emen s we e ca ied ou employing 50 MeV Cu 8+ ions p oduced by he 6 MV EN Tandem an de G aa accele a o a U ech Uni e si y. These ions can p o ile all elemen s om hyd ogen o silicon o a dep h o a ew hund ed nanome e in one single measu emen . Howe e , in he case o la ge hyd ogen concen a ions, hyd ogen ends o deso b om he laye s unde hea y ion i adia ion [16]. The e o e, he hyd ogen concen a ion was de e mined in a sepa a e, sho , measu emen using a la ge opening angle. Du ing his measu emen he hyd ogen con en in he ilm was moni o ed as a unc ion o ion dose, and his cu e is ex apola ed o i s ini ial alue o de e mine he hyd ogen con en . Fo he hyd ogen measu emen s a solid-s a e de ec o a an angle o u=30jwi h he beam di ec ion was used. A 29 Am Myla abso be oil p e en s pa icles o he han hyd ogen om en e ing he de ec o . The inci- dence angle be ween he ion beam and he sample su ace was se o 20j. Subsequen ly, he o he elemen s we e measu ed unde he same geome y, using a DE-Eioniza- ion chambe wi h a F isch g id as he pa icle de ec o . No A was de ec ed in he coa ings using ene gy dispe si e X- ay spec oscopy analysis. 3. Resul s 3.1. Nano-inden a ion es ing and adius o cu a u e measu emen s Table 1 summa izes he gas composi ions and low a es ha we e used o gene a e he plasma, wi h he co esponding alues o elas ic modulus (E), ha dness (H), coa ing hickness ( ) and comp essi e s ess o he esul an coa ings. The samples we e gi en a code symbolizing he di e ences in he gas plasmas: R, N2, A , A N2, A 2N2, H2, H2N2 (whe e R is he e e ence plasma consis ing o CH 4 gas only). Nano-inden a ion es ing was used o a i e a he Eand H alues, and as desc ibed in he expe imen al sec ion, s ess in he coa ings was de e mined by he adius o cu a u e me hod. As he a e age pa icle ene gy o he impinging ions o neu als is di ec ly p opo ional o he e m V B /P 1/2 [17], he de elopmen o comp essi e s ess is associa ed wi h he gas p essu e ( P) and he bias ol age applied (V B ). In his s udy, V B was kep cons an and Pwas a ied be ween 7.7 and 12 Pa, howe e , no ela ionship be ween hese a iables and he s ess in he ilm was obse ed. Di e en gas composi ions p oduce coa ings wi h di e en s ess le els, and he only end in s ess educ ion was ela ed o he addi ion o ni ogen. Fig. 1 shows ha in all cases, he measu ed s ess in he coa ings is lowe wi h ni ogen Table 1 Sample e e ences co esponding wi h se p ocess a iables ha p oduce a-C:H coa ings wi h he gi en coa ing hickness ( ), Eand H alues, and comp essi e s ess Sample P essu e (Pa) T ange (jC) (nm) E(GPa) H(GPa) S ess (GPa) 100 sccm CH 4 9.6 50–145 582 125.5F2.3 14.3F0.6 1.4 N2 100 sccm CH 4 +20 sccm N 2 12 53–226 441 115.3F2.6 14.4F0.6 1.1 A 50 sccm CH 4 +30 sccm A 7.8 103–180 345 132.1F2.9 15.5F0.8 1.6 A N2 50 sccm CH 4 +30 sccm A +10 sccm N 2 7.8 105–134 365 121.1F3.2 15.3F1.0 1.3 A 2N2 50 sccm CH 4 +30 sccm A +20 sccm N 2 8.3 108–180 335 109.5F4.3 13.0F0.9 0.91 H2 50 sccm CH 4 +50 sccm H 2 7.7 300–300 182 106.4F5.1 9.7F2.2 1.5 H2N2 50 sccm CH 4 +50 sccm H 2 +20 sccm N 2 8.3 300–300 122 109.8F4.4 9.7F3.0 1.2 addi ion, wi h mo e p onounced e ec s occu ing a 20 sccm low a e. In he case o deposi ions made a empe - a u es lowe han 300 jC, he e is a concu en educ ion in he elas ic modulus wi h ni ogen addi ion, bu a clea end does no eme ge o a educ ion in he ha dness alues. A high p ocess empe a u e, i.e. 300 jC, he e is li le di e - ence be ween he Eand H alues o he ni ogen con aining coa ings and he con ol, howe e , compa ed o he low empe a u e deposi ions hese a iables a e g ea ly educed. The s ess educ ion associa ed wi h ni ogen inclusion is also e iden o his es . 3.2. ERD The composi ional a ia ion o he a-C:H coa ings wi h and wi hou ni ogen inclusion has been de e mined wi h ERD and he esul s a e summa ized in Table 2. I can be seen ha all he samples made wi h ni ogen in he plasma a e doped, including he sample made a a ni ogen low a e o 10 sccm. The ni ogen inco po a ion a ies app oxima e- ly be ween 2 and 3 a .%, and he ela ionship be ween ni ogen con en and s ess educ ion is displayed in Fig. 2. The e is a 5–8 a .% dec ease in hyd ogen con en o coa ings con aining ni ogen as compa ed wi h he con ol coun e pa s; he g ea es e ec is obse ed o he deposi- ions a lowe empe a u es. ERD shows ha a e annealing o 600 jC, he hyd ogen con en has dec eased by 50–58% o i s o iginal alue. 3.3. Raman spec oscopy o as deposi ed coa ings The Raman spec a o he as deposi ed coa ings, (no including he high empe a u e deposi ion), a e shown in Fig. 3. The e is a mo e dis inc ‘shoulde ’ in he spec a o samples made wi h 20 sccm ni ogen. These esul s a e summa ized in Table 3 o all coa ings and include he G and D peak posi ions, he G and D peak line wid hs (measu ed a ull wid h hal maximum (FWHM)), I d /I g a ios, and app oxima e sp 3 con en . In amo phous ca bons, he de elopmen o a D peak indica es o de ing, and I d /I g is p opo ional o he numbe and clus e ing o ings [12]. The in ensi y maximum o he D peak ela i e o he G peak is di ec ly ela ed o he exis ence o six- old a oma ic ings, while a b oadening o he D peak can be co ela ed wi h ing o de s o he han six [12]. The wid h o he G peak is p opo ional o bond-angle diso de a sp 2 si es [12].Fig. 4 is a plo o he G peak line- wid h as a unc ion o he measu ed s ess o coa ings made wi hou ni ogen, and wi h ni ogen a a low a e o 20 sccm in he gas eed. I can be seen om his igu e and he da a in Table 3 ha he line wid h o he G peak dec eases when ni ogen is included a a low a e o 20 sccm ela i e o he gas composi ion wi hou ni ogen. This is indica i e o less bond angle diso de a sp 2 si es which in u n means ha he sys em is less cons ained and, he e o e unde less s ess. Schwan e al. [18] show ha as he in insic s ess inc eases Table 2 Composi ional a ia ion o he samples as measu ed wi h ERD including he ni ogen o ca bon a io (N/C) Sample H (a .%) N (a .%) N/C R 27 0.07 0.001 N2 (20 sccm N 2 ) 19 2.1 0.026 A 27 0.18 0.002 A N2 (10 sccm N 2 ) 21 2.2 0.029 A 2N2 (20 sccm N 2 ) 22 2.9 0.038 H2 31 0.42 0.006 H2N2 (20 sccm N 2 ) 26 2.9 0.041 H2 a e inal anneal 12 – – H2N2 (20 sccm N 2 )13 – – A e inal anneal Fig. 1. Ba g aphs showing he educ ion in he comp essi e s ess wi h he addi ion o ni ogen o di e en se s o gas composi ions used o gene a e he plasma. Fig. 3. Raman spec a o as deposi ed coa ings wi h and wi hou ni ogen addi ion. (a) Raman spec a o coa ings R and N 2 showing de elopmen o enhanced ‘shoulde ’ wi h he addi ion o ni ogen, (schema ic o he i ed D and G peaks ha e been included). (b) Samples A , A N2 and A 2N2 compose he se ies made wi h CH 4 /A , wi h 10 and 20 sccm ni ogen inclusion-a b oadening o he ‘shoulde ’ only occu s wi h 20 sccm ni ogen addi ion. Fig. 2. Rela ionship be ween he comp essi e s esses measu ed o he a-C:H coa ings and hei ni ogen con en . (Un illed symbols co espond o coa ings made wi h ni ogen in he gas plasma). he G peak line wid h inc eases; he e o e coa ings unde lowe in insic s ess ha e a smalle G peak line wid h. The a ia ion in he D peak wid h be ween coa ings made in a plasma con aining ni ogen as compa ed wi h i s co esponding coun e pa con aining no ni ogen was only signi ican o samples R and N2, ( he di e ences among he o he se s we e oo close o he e o in he peak i analysis o es ablish conclusi e indings). The wid h o he D peak is g ea e o he coa ing deposi ed using a me hane/ ni ogen (N2) mix u e as compa ed wi h he pu e me hane plasma (R), indica ing ha he coa ing con ains a g ea e di e si y o a oma ic ing o de s [12]. The da a in Table 3 illus a e ha wi h ni ogen addi ion he G peak shi s o highe wa e numbe s, and he I d /I g a io inc eases. I has been shown using EELS spec oscopy ha sp 2 bonding inc eases as a unc ion o ni ogen con en o ilms o a-C:H [19]. As i was no possible o do EELS spec oscopy in his s udy, an sp 3 ac ion was app oxima ed using he analysis o Robe son and Fe a i [12] based on he G peak posi ion and he I d /I g a io. They ob ained a ela ionship be ween sp 3 con en and hese Raman pa am- e e s o as deposi ed a-C:H, by i ing a line o he expe imen ally ob ained da a o sp 2 con en and op ical gap [12]. In his s udy, his analysis was u he ex ended o es ima ing an sp 3 con en o he doped coa ings since he ni ogen con en in he ilms was oo low o es ablish he p esence o a CN phase, and any changes obse ed in he op ical gap we e a ibu ed o a ia ion in he sp 2 con en . This es ima e shows ha he sp 3 con en is lowe o samples made wi h 20 sccm ni ogen. In addi ion, he high empe a u e deposi ion a 300 jC (H2) also has a lowe sp 3 con en o highe sp 2 con en han con ol coa ings made a lowe empe a u es. The clus e diame e o in-plane co ela ion leng h o a oma ic clus e s, L a , was calcula ed based on he ollowing ela ion: Id=Ig¼CVkðÞL2 að2Þ Whe e CV(514 nm)=0.0055 (A ˚ 2 ) (Al hough his equa- ion is used o a i e a L a o coa ings s udied in his esea ch, he compa ison is compa a i e, i.e. he alue o L a is mos likely o e es ima ed as sugges ed by Schwan e al. [18]). The esul ing L a alues a e included in Table 3. The plo o L a agains he G peak posi ion and G peak wid h is illus a ed in Fig. 5. I can be seen ha in gene al L a is bigge (e.g. H2N2) and/o ha he e a e mo e a oma ic clus e s (e.g. N2) wi h ni ogen inclusion, and as he alue o L a Table 3 G and D peak posi ion, line wid hs, I d /I g a ios, sp 3 ac ion and clus e diame e (L a ) o a-C:H coa ings made wi h and wi hou N 2 Sample Ni ogen low G peak Line wid h D peak Line wid h I d /I g App oxima e L a (sccm) (cm 1 ) o G peak (cm 1 ) o D peak sp 3 con en (A ˚) (cm 1 ) (cm 1 ) (%) [12] R 0 1552 154 1389 364 1.5 35 16.5 N2 20 1564 131 1407 399 3.0 25 23.3 A 0 1554 156 1396 380 1.7 30 17.6 A N2 10 1553 155 1394 386 1.8 30 18.1 A 2N2 20 1562 142 1404 382 2.5 25 21.3 H2 0 1566 142 1410 384 2.4 25 20.9 H2N2 20 1574 126 1412 374 3.1 25 23.7 Fig. 4. Changes in G peak line wid h as a unc ion o s ess o coa ings made wi h a ious plasma composi ions wi h and wi hou ni ogen addi ion a 20 sccm. (The do ed line was a bi a ily d awn o show he dema ca ion in s ess le el be ween coa ings made wi h ni ogen and hose made wi hou ni ogen). inc eases he G peak posi ion mo es o highe wa e numbe s and he wid h dec eases. The la e obse a ion, i.e. dec ease in wid h o he G peak, has been linked wi h s ess educ ion [18]. As no ed be o e om he a ia ion in he D peak wid h, sample N2 has a la ge di e si y o a oma ic ing o de s so he la ge alue o L a in his case is a ibu ed o an inc ease in numbe o clus e s. The la ge alue o L a o H2N2 co esponds wi h an inc ease in he six-membe ed a oma ic clus e size as he D peak wid h has no inc eased and he G peak has shi ed o highe wa e numbe s. 3.4. Annealing s udy: using Raman spec oscopy and posi on beam analysis 3.4.1. Raman spec oscopy Two samples we e made a he egula ed and ele a ed empe a u e o 300 jC, o isola e he e ec o ni ogen on s ess de elopmen a high empe a u es. Tha is, o obse e i a high empe a u e deposi ion, which may be conduci e o he gene a ion o a highe he mal s ess componen , is in luenced by he p esence o ni ogen in he gas plasma. As seen in Table 1, he s ess is educed wi h ni ogen inclusion and he Raman spec a show ha al hough bo h samples ha e a ‘shoulde ’, he sample manu ac u ed wi h 20 sccm ni ogen has a mo e p onounced ‘shoulde ’. Fig. 6 displays he Raman spec a o he as deposi ed coa ings and hei inal e olu ion a e annealing o 600 jC. As men ioned be o e, he annealing expe imen s we e pe o med o iden- i y open olume in he samples. The e olu ion o he G and D peak posi ions, and he changes in hei line wid hs, as a unc ion o annealing empe a u e is lis ed in Table 4. The g aphi iza ion p ocess is unde way a 300 jC o he ni ogen-con aining sample, H2N2, as he G peak posi ion is a 1580 cm 1 . Howe e , o he coa ing made wi hou ni ogen, H2, 300 jC ma ks he s a o he p ocess as seen by he mo emen o he G peak o highe wa e numbe s. This beha io is linked wi h he ac ha he as deposi ed coa ing wi h ni ogen in he gas plasma has a G peak ha is shi ed o highe wa e numbe s, 1574 cm 1 as compa ed Fig. 5. Changes in he clus e size wi h ni ogen inclusion: (a) Shows a ia ion o clus e size wi h G peak posi ion o samples wi h and wi hou ni ogen. (b) Illus a es ha as he clus e size inc eases, he G peak wid h dec eases. (Un illed symbols ep esen samples made wi h ni ogen in he plasma.) wi h he G peak o he me hane/hyd ogen mix u e which is a 1566 cm 1 . The ans o ma ion o a g aphi ic s uc u e wi h annealing has been linked o he elease o bounded hyd ogen be ween 400 and 600 jC[20]. In his empe a u e ange sp 3 ca bon bonds a e ans o med o sp 2 bonds [21]. As seen be o e, he wid h o he G peak is less o he ni ogen con aining samples— he e o e, less bond angle diso de a sp 2 si es. A gene al end o dec easing bond angle diso de wi h inc easing annealing empe a u e is eco ded o bo h samples. The e is a shi o he D peak posi ion wi h anneal- ing empe a u e o lowe wa eleng hs. The wa eleng hs 1353 and 1598 cm 1 a e associa ed wi h small c ys al- li es o g aphi e, and in he p oximi y o 1353 cm 1 i can be concluded ha he c ys alli es o med a e h ee- old coo dina ed [22]. A ine-g ained polyc ys alline s uc u e eme ges as he coa ing becomes mo e g aphi ic in na u e, i.e. he clus e s will lose hei molecula like p ope ies [19]. The changes in he D peak wid h wi h annealing empe a u e shows ha o de ed clus e s o six-membe ed ings (c ys alli es) domina e as he sample is hea ed. These ans o ma ions can also be seen in he PBA da a. 3.4.2. PBA The posi on beam analysis da a (Table 5) show ha he open olume, as seen in he alue o he Spa ame e is g ea e a he in e ace o bo h coa ings as compa ed wi h Table 4 Shi o he G and D peaks and changes in peak wid hs as a unc ion o annealing empe a u e TG peak posi ion G peak line wid h D peak posi ion D peak line wid h (jC) (cm 1 ) (cm 1 ) (cm 1 ) (cm 1 ) H2N2 H2 H2N2 H2 H2N2 H2 H2N2 H2 As deposi ed 1574 1566 126 142 1412 1410 374 384 150 1573 1565 123 142 1419 1409 406 381 300 1580 1571 115 131 1411 1403 365 375 400 1580 1576 109 120 1401 1405 352 366 500 1587 1590 103 103 1372 1375 333 310 600 1585 1585 107 101 1355 1349 316 314 Fig. 6. Raman spec a o he high empe a u e deposi ions: (a) As deposi ed a-C:H ilms (H2N2 con ains ni ogen); (b) Shows he inal e olu ion o he Raman spec a a e successi e annealing p ocedu es o 600 jC. he bulk. The Wpa ame e is also signi ican ly di e en a he in e ace sugges ing he exis ence o a mixed laye , which is c ea ed du ing he sub-plan a ion o he ions du ing deposi ion. The changes in he Wpa ame e wi hin he coa ing show ha he chemical en i onmen is changing wi h annealing. Bo h he Sand Wpa ame e s ha e al e ed a e he inal anneal: he open olume has dec eased, and he alue o he Wpa ame e has inc eased. The change in he Wpa ame e o he coa ing o H2, ( he sample made wi hou ni ogen), is signi ican ly g ea e han H2N2. A 600 jC PBA shows ha he e is ‘delamina ion’ o bo h coa ings as he Sand Wpa ame e s ake on he alue o he su ace. Fig. 7 shows he changes in he Sand Wpa ame e s wi h annealing, and i becomes ob ious ha he e a e acancy de ec s a he in e ace (Fig. 7a) o he ni ogen- con aining sample (H2N2) since he Spa ame e is high and he Wpa ame e low [23]. Du ing he annealing p ocedu e o 400 jC, he Spa ame e inc eases. This ise in he alue o he Spa ame e can be seen mo e clea ly in Fig. 8a, coincides wi h emo al o physiso bed hyd ogen [8]. Howe e , a app oxima ely 500 jC he gas eleased du ing he annealing is no only he elease o ‘unbound’ hyd ogen, bu also he H bounded a e ahed al si es o ca bon, hen he e is a need o in e nal es uc u ing o he ‘la ice’, hence he dec ease in he alue o Sa he in e ace. The chemical en i onmen wi hin he coa ings, and a hei in e ace, change wi h empe a u e as can be no ed in he a ia ion o he Wpa ame e (Fig. 8b). Also e iden in he plo o Fig. 8a is ha he Spa ame e o he ni ogen con aining coa ing, H2N2, is gene ally la ge han ha o he e e ence sample indica ing ha o e all his coa ing has mo e open olume which is cha ac e is ic o a doped laye . Fig. 7. S–Wmaps o he coa ings made a high empe a u e, H2N2 and H2 showing he e ec s o annealing: (a) in e ace (b) coa ing. (No e: Fig. 7a and b a e no o he same scale). Table 5 VEPFIT esul s o samples s udied a oom empe a u e and a e annealing o 600 jC(S Si =1, W Si =1). (The e o s a e DS 0.002 and DW 0.03) Sample Be o e annealing A e annealing S coa W coa S in e W in e S coa W coa S delam W delam H2N2 0.932 1.40 0.964 1.33 0.929 1.48 0.906 1.68 H2 0.931 1.30 0.946 1.43 0.919 1.54 0.907 1.67