Amorphous films of lead oxyfluorosilicate were prepared with a rf-sputtering technique, and the distribution profiles of the component elements and chemical states of the fluoride ions were analyzed with an X-ray photoelectron spectrometer. Si atoms with an expanded coordination, O(4)Si-F, were present near the surface, and O(3)Si-F units were present in the deeper part of the films. Electrical resistance indicated transition to a
conduction state for the films containing fluoride ions, while the films were crystallized to precipitate low quartz by the irradiation of He-Ne laser of 3 mW up to 1 sec

Kawamura, Haruyuki

Miura, Yoshinari

Osaka, Akiyoshi

Okayama University Scientific Achievement Repository

Memoirs of the Faculty of Engineering,Okayama University'vo1.28, No.2, pp.77-84, March 1994 215Chemical States of Fluorine Atoms and Laser-Induced Crystallizationin rf-Sputtered Thin Films of Amorphous Lead FluorosilicateAkiyoshi OSAKA*~, Haruyuki KAWAMURA*t, and Yoshinari MIURA*(Received January 8 , 1994)SYNOPSISAmorphous films of lead oxyfluorosilicate were prepared with arf-sputtering technique, and the distribution profiles of thecomponent elements and chemical states of the fluoride ionswere analyzed with an X-ray photoelectron spectrometer. Siatoms with an expanded coordination, 04Si-F, were present nearthe surface, and 03Si-F units were present in the deeper part ofthe films. Electrical resistance indicated transition to aconduction state for the films containing fluoride ions, while thefilms were crystallized to precipitate low quartz by theirradiation of He-Ne laser of 3 mW up to 1 sec.1. INTRODUCTIONIn the processes of preparing thin films such as plasma CVD and rf-sputtering gas phase particles of high kinetic energy states lose drastically theirenergy to be quenched to a solid state. The resulted films therefore may exhibitstructures and properties different from those of corresponding bulk solids. Thefilms are also capable of a phase transition between amorphous state andcrystalline state induced by laser irradiation and thus capable of giving a new*~tDepartment ofApplied ChemsitryNow at Department of Bioengineering ScienceNowat Nippon Sheet Glass Company77216 Akiyoshi OSAKA, Haruyuki KAWAMURA and Yoshinari MIURAmicroscopic composite structure. A laser beam irradiation of strong intensitymay draw series of pits or lines on the films. Therefore, promising materials aresuch thin films of oxyhalide glasses[l] that have lower melting temperatures andhigher halide ion conductivity since (a) they are applicable to photomemoriestaking advantage of the photoinduced phase transitions between an amorphousstate and a crystalline one, (b) they may exhibit increased ionic conductivity dueto interaction between ion-conductive matrix and precipitated insulatorpartic1es[2], and since (c) such fast-ion conductive channels may even be formedthough they are impossible under ordinary conditions. It is thus interesting toinvestigate laser interaction of such oxyhalide thin films and to discusssuitability for optoelectronic materials.In the present experiment, we prepared thin films of the F-O-Pb-Si systemwith an rf-sputtering technique and examined film compositions, chemical statesof fluorine atoms, and fluoride ion conductivity as well as we observed laserinduced a phase transition of the films.Table 1. Sputtering conditions100WAr0.006 Torr45 minNa-Ca slide glassrfpowerSputtering gasPressureSputtering timeSubstrate2. EXPERIMENTALReagent grade Si02, PbO, and PbF2 were weighed so as to give 100g mixturesof a molar ratio 30:40:30. A few drops of 2-butanol were added to the batchesbefore they were mixed well and pressed into a disc of 10cm in diameter. Thediscs were served as the target material for the rf-sputtering (Shinku Riko SBR-11) after being dried in an air bath for 12 hat 100·C. Slide glasses were used asthe substrate. The sputtering conditions are summarized in Table 1. Filmcompositions were determined X-ray photoelectron spectra (XPS) and F, °and Sidepth profiles were measured (Shimadzu ESCA-750). The binding energy for FIs and ° 15 core electrons was calibrated with assuming Si 2p=110.0 eV.Electrical resistance was measured with a two-electrode method and wasconverted to conductivity with measured film thickness. The phase transition ofthe films were observed under ascanning electron microscope afterirradiating 3 mW He-Ne laser beam(0.2 mm in diameter, and the wavelength=632.8nm) for 1/500, 1160,118, and 1/1sec.78Laser Induced Crystallization ofrf-Sputtered Fluurosilicate Thin Films 2173. RESULTSANDDISCUSSIONFig. 1 (top) and Fig. 2(bottom) Depthprofilesofcomponent elements for films F1(top) andF5(bottom).F1F5o 15Pb4f.r--..__._.._ .._. ._---.._ .. ._M_._6 O.60.20._ 40.dPttl(j)~.0: 2 O.;; 4 O.3.1 XPS depth profiles and chemical states of fluoride ionsThe thin films contained black precipitation that was supposed to be colloidparticles of metallic lead when the films were sputtered with newly preparedtargets or under a high rf power. However, all the sputtered films were X-rayamorphous, irrelevant to the sputtering conditions. A preliminary experimenthad shown that fluoride ion content in the fIlms decreased when sputtering wasconducted in a longer period on a target. Thus it was suggested that the fluorideion content was controllable. Figs. 1 and 2 show the depth profiles of theelements composing fIlms F1 and F5, respectively, where the former fIlm had alarger fluoride ion content than the latter. It is evident that each element inboth films is uniformlydistributed in the bulk rangedeeper than the outermostsurface layer (<2 min in Ar ion(~- 015 etching time). It should be/r-'-'-'-"-"-"-"---"Pb4f-"-'-'-'-"-"-"-'-' mentioned that chloride ionsf were detected for all the\ C1s Si2p samples. Those ionsC12p ..{-.--.-.---.-.-.--.-.---.--.-.-.--t?:-.'"::::::::::::.::::::::::::.:::::::::.:::::::~~:::.::::::::::::::::::::.:::::::::.::::::::::::.-----supposedly were introduced aso. -'----0-+.~;:.,.;..,....,.,...-;:.,:--;";:-;:":-I-;';:'O~M-'--;..,.,..,......-.-r~~20".~~"""""'~""';3o. an impurity from hydrochloricEtching time (min) acid solutions employed forcleaning the slide glasssubstrates. Presence of sodiumions and protons wereaccordingly expected but theywere not detected by XPS.Figure 3 shows the XPS of F Is,.'--·--·-·-·--·--~iZ;------·- core electrons for film F1 atC12p .', C1 5 various etching times. Two.,o. -'----:-+.....~:...""':-;..;:"M-'':-;;._,:;.-...,::-",.--,.:;:;:;:;:;.:--;;;.::''''~~-.-~---~._--;:;;;- i¥-~;:;;:-:'1;;;:;5;:r:_;;;:.;::;;,_-~_""~.",~~._~.",~,,,;;;:;:;:,::j peaks were observed: theo. 10. 20. 30Etching time (min) . stronger one at 692 eVand theweaker one at 695 eVeAccording to Osaka et ale [1],the former peak is assigned to79218 Akiyoshi OSAKA, Haruyuki KAWAMURA and Yoshinari MIURA7 ........,.....---.........,.1013---...---... 3.2 Oxygen 1s spectraXPS of 0 1s electrons for films F1 and F5 at each"----'"' etching time were exhibited in Figs. 4 and 5,16 respectively. The spectra consist of a main peak20 .................--...1 near 538 eVand a shoulder near 540 eVe Those25 peaks can be assigned to a non-bridging oxygen~3:.:::0,.........~.-f"'-,.........,.........~~~ atom (NBO) and bridging one (BO), respectively,700 696 692 688Binding energy (eV) on the basis of the XPS study on bulk silicateFig. 3. F1s sprectra for film glasses [3-5]. In both series of the spectra, peakF1 at various etching times. position seemed to shift with etching time.However, when the peaks were deconvoluted intol"'-h.u.......................lu-............................................""I the fluoride ions of high ionicity, surrounded byF 1 5 lead ions, and the latter to those of high(Si2p=110eV)Etcing time covalency, bonded to Si atoms. The chemical,0:;...--(_m_i~n",,)-,,",--..r'.r"'JI~,_...--..........., states of the fluoride ions in film F5 could not1 referred to because the peaks were so weak due-....,.--" to small fluoride ion contents.015(Si2p=110eV)0 1--------13c:: 5·M..§. 7Ql.~ 10.j..l0' 13c:::E 16utj 202530 .......,.,....~"li'"""'_"1'"""'"l'""'...-,....................""""r""""'lF1015(Si2p=110eV)0r--- -""1c: 3.~ 5Ql 7e:;j 100'13c:::8 16()~ 202530 1-..........'I"'""'~"1"""'"1"'""~...,.........,........,;::..""i'm'...j548 544 540 536 532Binding energy (eV~548 544 540 536 532Binding energy (eV)Fig. 4 (left) and 5 (right) ..0 1s spectra for films F1(left) and F5(right) at variousetching times.80Laser Induced Crystallizatian ofrf-Sputtered Fluorosilicate Thin Films 219two Gaussian peaks, the position ofeach component peak remained unchanged.Thus the apparent shift in the position was accounted for by varied relativeintensity of the two component peaks.0.6 ~---------.., 1.0 ~----------.F1 F530•0 0.8[QEo[Q 0.60.0o0 0.4[Qa[Q 0.2, 0.4L-----L_~-........._....L__.L..___110 '20 30 0 10 20Etching time (min) Etching time (min)Figs. 6(a)(left) and (b)(right) The ratio of the fractions of bridging oxygen (BO)and non-bridging oxygen (NBO) as a function of etching time.3.3 Constitutions of the filmsThe ratio BO/NBO in the total amount of oxygen atoms can be represented bythe peak area ratio of the both 0 1s components, and the ratio (F-Si)/(F-Pb) canbe evaluated in a similar way based on the F 1s XPS peak area. The ratio BO/NBO was plotted in Figs. 6(a) and (b) for films F1 and F5, respectively, as afunction of etching time. It is reasonable that F1 shows a larger ratio BO/NBO ateach depth than F5, because F1 has a greater content of fluoride ions asdiscussed later~ In the bulk range of the films deeper than 2 min etching, theratio BO/NBO slightly decreased in F1 from 0.3 to 0.2, while it showed a slightincrease in F5 from 0.5 to 0.7. On the other hand, the ratio of the fluoride ions(F-Si)/(F-Pb) plotted in Fig. 7 increased with a distance from the surface,indicating that the fraction of the covalent fluoride ions increased at the expenseof the ionic fluoride ions.With the results indicated above, continuity of an Si-O network in the filmscan be correlated with the changed ratio (F-Si)/(F-Pb). We should first reconfirmthat (a) the content ratios of the component atoms like F/Si or O/Si are constantas shown in Figs. 1 and 2 and (b) the binding energies of 0 1s electrons remainunchanged in Figs. 4 and 5. However, the ratio BO/NBO decreases in the inner81220 Akiyoshi OSAKA. Haruyuki KAWAMURA and Yoshinari MIURAF1soo0.6.0 0.4a-Li..:::::enIu. 0.2part of film Fl, indicating the increasein the fraction of NBO. That is, averagesize of the network is greater near thesurface whereas worse continuityhappens in the deeper part of the films.Then a problem arises whether thechange in the network size has beenbrought by the introduced fluoride ionsor not.Two kinds of Si-F bonds are10 20 30 illustrated in Fig. 8: (a) is the case of SiEtching time (min) atoms offour-fold coordination, and (b)Fig. 7 The ratio of the fractions of is for those with an expandedfluride ions covalently bonded to Si(F-Si) and those sorrounded by lead coordinationofS. ThefractionofNBO(F-Pb). increases with formation of Si atoms oftype (a), whereas it remains unchanged with formation of type (b). It is evidentthat the fraction of covalent fluoride ions decreased as the ratio BO/NBOincreased. Consequently, the present results can be interpreted as showing (1)Si atoms of type (b) are predominant near the surface; (2) the fraction of type (a)increases in deeper range of the films and the network is gradually broken,accompanying increase in the fraction of the fluoride ions with more ionicity.3.3 Electrical conductivity and laserinduced phase changesElectrical conductivity (T of film Flis plotted in Fig. 10 as a function oftemperature where the film thicknesswas 0.9/lm. The conductivity of film FSexceeded the lower limit of themeasuring system. (J for film Flfollowed an Arrhenius type equation (1)(a) .. Si-0-Si = + F- ..... "" Si-O- + F-Si==(b) == Si-Q-Si = + F- ..... (= Si-O-Si=)-IFFig. 8 Two types of Si-F bonds arepossible. Coordination ofSi in (a)remeains 4 but is expanded to 5 in (b).(T = (TO exp (AE/kT) (1)where Lill is an apparent activation energy of conduction, k and T bear universalmeaning. Fl had M3= 106Skj/mol, 1.2 times as large as M3 for a bulk glass of82Laser Induced Crystallization ofrf-Sputtered Fluorosilicate Thin Films 221IllsIIBs-lO/JIDcomposition 3.2PbF2-68.7PbO-28.1Si02 (<1E= 91.4kJ/mol) [6] and3 times for a fast ion conductive1/60sLowIHH~HighDegree of crysrtallization3Fig. 10. Schematical illustration of laser inducedphase transition region. Laser beam: He-Ne, 3mW,0.2mm.• F1• BulkglassM:=106.5kJ/mol21000KfT-2 r-..--~-----------,-6-4-8-10-12-14 L.-_.L--_.L--_.L--_.L...-_.LJIl-----'1Fig. 9 Electrical conductivity of film Flshows an Arrhenius type dependence ontemperature. that of a bulk glass of compo-sition 3.2PbF2-68.7PbO- 28.1Si02 [6] is alsoshown.PbF2 crystal (<1E=35.8kJ/mol) [6].Schematically illustrated in Fig.11 is a phase transitioned regionof films induced by irradiation of3 mW He-Ne laser for 1/500, 1/60, 1/8, and 1 sec. A 1/500 secirradiation induced a high phasetransition in the area of about 11}lm in diameter as well as an area4of 18 }lm for weaker degree oftransition. That phase transitionwas known to be crystallization ofa-quartz with the XRD patterns ofthe irradiated films, as shownlater. Both area grew from 11 to17 }lm and 18 to 30 /..1m after 1/60 sec irradiation. After 1/8 sec, the size of the both area grew little though itseemed the degree of crystallization increased slightly. After 1 sec irradiationthe size of the center regiongrew to 19 /..lffi and thesurrounding area of aweaker crystallizationdegree grew to diameter ofabout 34 11m. The reasonfor the apparent differenceof the two area in theI/SOOsdegree of crystallization isnot understood yet, but itmay be related to intensitydistribution of theemployed laser beam. Fig.11 shows X-ray diffractionprofiles for film Fl after83zzz Akiyoshi OSAKA, Haruyuki KAWAMURA and Yoshinari MIURAbeing irradiation up to 1 sec. Only a diffraction was observed near 26.2° fromlow-quartz. It seems strange that a spot with area of only 30 11m in diametergives a diffraction peak of over 1 kcps. Film F5 showed similar phase transitions,precipitated phase, and diffraction pattern or intensity.--.dcd-• : Low-quartz •1/1 s~1/8 s-'1/60 sj/\.~1/500 s.",.20 22 24 2626 (CuKu)28 30Fig. 11 X-ray diffraction profiles of film F1after being irradiated by the laser for1/500, 1160, 118, and 1I1s.AcknowledgmentFinancial support of Grant-in-Aid for Scientific Research (04650705) is gratefully acknowledged.REFERENCES1] A. Osaka, Y-H. Wang, Y. Miura, and T. Tsugaru, J. Mat. Sci., 26 (1991)2778-82.2] K. Shahi and J.B. Wagner, Jr., J. Electrochem. Soc., 128 (1981) 6.3] R. Bruckner, H-U. Chun, and H. Goretzki, Glastechn. Ber., 51 (1978) 1-7.4] B.M.J. Smets and T.P.A. Lommen, J. Non-Cryst. Solids, 46 (1981) 21-32.5] B.M.J. Smets andD.M. Krol, Phys. Chern. Glasses, 25 (1984) 113-18.6] Y-H. Wang, K. Kobayashi, A. Osaka, Y. Miura, and K. Takahashi, J. Am.Ceram. Soc., 71 (1988) 564-68.84

Chemical States of Fluorine Atoms and Laser-Induced Crystallization in rf-Sputtered Thin Films of Amorphous Lead Fluorosilicate

Abstract

Similar works

Full text

Available Versions

Okayama University Scientific Achievement Repository