愛総研・研究報告 創刊号平成11年
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MBE Method
分子線エピタキシ}法により
KBr
基板上作製された
パナジノレフタロシアニン薄膜
Akinori MAEDA+， Norihiro OKUl'v任JRA++，Hiroytuci NAKANO++ラ
Hideo FURUHASHI→→+， Toshio YOSHlKAWA++++ヨYoshiyukiUC回DA+++ラ
Kenzo KOJIMA+ラAsaoOHASHI+フToru Imura++++， Shizuyasu OCHIAI+ and
Masayuki IEDA+ Abstraci 前田昭徳、十・奥村典弘+・中野寛之+・古橋秀夫++・吉川俊夫+件。内田悦行++・小嶋憲三+・ 大橋朝夫+・井村 徹++++・落合鎮康+・家田正之+ 11 Nonlinear optical materials are important in developing optical devices such as optical switch、 modulation and m巴mory. Therefore， they have recently a杭ractedmuch aitention. Vanadyl -Phthalocyanine (VOPc) is one of them. In this paper， we investigated not only the morphologies of VOPc thin自1mprepared on KBr substrate by molecular beam epitaxy (MBE) but also the conditions to prep紅edlarge single crystals. A lSnmthick VOPc thin film prepared on a KBr substrat巴witha substrate temperature (Ts : 80oC)， evaporating tempera加re(T巴 :300oC)and de -positing time (t :10 min.) has a uniform surface image of scanning巴lectronmicroscopy (SEM). The film has an optical absorption peak at 810nm in the visible and infrared region. Itwas epitaxially grown. A VOPc thin film prepared on a KBr with another condition of Ts : 2000C and Te 3000C and t 60 min. has discrete single crystals. Their av巴ragesize ar巴 about lxO.5x0.1μm. The single crystal is 3x3R4So type andItwas ep抗axiallygrown judging from the images of SEM， atomic force microscoy (AFM)， r巴flectionhigh en巴rgyelectron diffraction
(RHEED)叩dせlespectra measured with a UV NIS sp巴ctroscopy. A VOPc thin film prepared
on a KBr substrate with Ts・2500Cand Te : 3000C shows the absorption peak around 830nm. Therefore， the shi立ofthe optical absorption p巴akfor the single crystal to a longer wavel巴ngth may be related to disorder in a film epitaxially grown andJor may be due to a phase transition under a high substrate temperature. 瓦eywards:Vanadyl-Phthalocyanine single crystal， Epitaxy growth， KBr substrate， Molecular beam epitaxy + 愛知工業大学電気工学科 (豊田市) H 愛知工業大学 情報通信工学科(豊田市) +++愛知工業大学 総合技術研究所(豊田市) ++++愛知工業大学機械工学科 (豊田市) 1.Introduction Many research巴rs have reported仕lat VOPc thin films prepared on alkali halide sub -strates by the molecular beam epitaxy w巴rea
12 Vanadyl Phtha!ocyanine Thin Film Prepared on a KBr Substrate by~ν1BE Method .創刊号・平成11年 epitaxial grown. The VOPc thin film prepared on a KBr (100) substrate forms a sin -gle domain square lattice on the KBr substrate. Itwas named 3x3R450type [1]. The distance k制reenneighboring molecules is about 14A [1]. The AIPcCl (Chloroaluminum回 phthalocyanine) thil1film evaporated on a NaCl subs回teby1¥侶Emethod forms the tetragonal (SEM)， atomic force microscopy (AFM)， Xray diffraction (XRD) and refl巴ctionhigh energy eleciron diffraction (RHEED)ι This work was selected a main pr句ect企om and was supported in part by the help from Research institute for industrial technology in Aichi institute of technology phase. Its predominant phas巴 onth巴 NaCl 2.E五perimentaland Results (100) was a bidirectionally oriented tetragonal phase with f13xf13R土110. The phase of Material used is VOPc powder supplied
AIPcCl/KCl and AIPcClIKBr were企om Eastman Kodak company. Figure 1
bidir巴ctionally oriented tetragonal phase with shows the molecular structure of VOPc. The fl0xfl0R:!:270 on KCl and with fl0xfl0R:l270 molecule has the size of 1.4 nrn in diameter on KBrフrespectively. The predominant phase and 0.20 nm for the b axis. The main cham -ofAlPcClIKI was an unidirectionally oriented ber of恥侶Eis at about 10.7Pa. After VOPc tetragonal phase on KI (100) with 3x3R450• The phase of VOPc/KCl was bidirectinally ori -ented tetragonal phase on KCl with
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1 Ox [10土270[2]守 Hoshiet a.lhav巴 S印diedthe thickness dependence of the crystal struc加reof a VOPc film epitaxially grown on KBr(100) by optical absorption spectra and pointed out that 社lecrystal struc旬rechanges around 64 nm in thickness. The VOPc thin film was an epitaxially grown film below 64 nm but not above 64 nm. The epitaxially grown filll1ι
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b Fig.l Mol巴clllarstructllre of VOPc. showed a s巴condharmonic generation and the Tabl巴1: Conditions to prepare VOPc film film with a bulk monoclinic phase did not [3]. on KBr substrat巴 Therefore， th巴 epitaxiallygrown filll1is very ill1portant for a second harmonic generation. Morphologies of VOPc films on alkali halide substrates are important for their optical appli圃 cations. However， there are some unknown things. VOPc thin films have not been prepared at a substrate temperature above 100O
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on alkali halide substrates so that there are few optical studies on them. Moreoverラthe growth mechanism of a single crystal on an al個 kali halaide is not stiU clear enough. Hereラ we investigated the substrate temp巴ra旬rede -pendence of VOPc thin film prepared on a cleaved KBr substrate by恥侶E. The VOPc film prepared on the substrate of KBr kept at 800C had a domain crystal and a large single crystal above 100oC. Morphologies of single crystals were studied by optical absorption spectroscopyラ scanning electron microscopy S.l S.l S.3 SA S-5 S司6 S.7 S.8 S・9 S困10 S.ll S・12 S.13 S.14 S・15 TsCC) t(min) 80 10 80 60 80 120 100 10 100 60 100 120 150 10 150 60 150 120 200 10 200 60 200 120 250 10 250 60 250 120 d(nm) 15 40 80 ー. .13 Vanadyl Phtha10cyanin巴ThinFilm Prepared on a KBr Substrate by MBE Method Fig. 4 FT.IR spectra of S.1， 5， 8 and 11. powder is inserted into a Knudsen.ce，1lit is preheated at 3000C for two hours. The sub -strate of KBr isc1eaved just before setting to a holder. After the main chamber of MBE be -comes about 10'7pa，吐leKBr substrate is pre -h巴atedat 1500C for one hour. The evaporat・ ing te凶pera旬reis 300O
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Table 1 shows吐le conditions to prepare VOPc films on KBr suか strate. Symbols of Te， Ts， t and d express an evaporating temp.， substrat巴temp.，巴vaporating time and thickness， respectively. Figure 2 shows the XRD specむaof KBr alone (V)， S.1 and VOPc powder (A)， respectively. The spectra of S.1 and KBr a10ne have a peak at 2 B = 270 which does not exist in the spectrum of VOPc powder.Moreover，せ1巴peakint巴，nsity of S・1is larger than白紙ofKBr a1one. This revea1s V ~-
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D A [ 切 J Z z g h 恥 岡 ﹄ 一 三 円 四 ﹄ 帽 ︺ 弘 一 = m z ω 一 自 己 目 30 20 10 旬 E E A n δ ε ' A O ρ し W CB a u m M 官 μ ロ δ戸 、
d pb T r 1.5 ( d・ 5 u u ロ 胃 七 o m ﹄ 司 2 B (de，
reel Fig. 2 XRD spectra ofKBr alone (V)， S.1 and VOPc powd巴r(A) respectively. WaveJength(目前 Fig. 6 Optica1absorption spectra of S・1，S.2 andS・3respectively. Fig. 3 AFM image of S・1.Vanadyl Phthalocyanine Thin Film Prepared on a KBr Substrate bylIIffiE Method.創刊号・平成11年 14 that VOPc molecules pile with the interval of 0.33 nm. Therefore， this also indicates th呂t VOPc molecules pile along the b axis of molecule normal to a substrate becaus巴 the diameter of molecule is 14A. The XRD spectra of S.1 to 10 show a similar pa社E印 so that VOPc molecules under oth巴rproducing conditions pile up with the b axis normal to the substrate白 Figure3 shows the AFM image of S.I. Multi開layersare observed at叩 edgeon the film so that the film shows the layer growth守 Figure4 shows theFTIR spectra of S.I， 5， 8組d 11， resp巴ctivly. The FT・IR spectra were measured with the incid巴ncenor司 mal to samples. A VOPc molecule has a V固
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stretching mode at 1000 cm田1 Samples measured have no absorption peak at 1000 cm'l. This m巴 阻s that VOPc molecules in出e VOPc/KBr pile up with the b axis normal to a substrate. Figure 5 shows the SEM image of S.1. The film is an uniform film with small grains. Figt田 6shows the optical absorption spectra of S.I， S・2and S.3， respectivelyιThe optical absorption Fig. 9 SEM叩dAFM imag巴sof S圃 8. SEM image of S. 5. 叩 叩耐 印 h t 叩 e 叩 山 4 w m Fig. 7 1.5 ( . 3 3 ω υ ロ ロ f c m a ︿ Fig. 10 SEM and AFM images S.9. Fig. 8 Optical absorption spectra of S-4to 6.15 RHEED pa抗ernsof S.8 and KBr alone. The RHEED pattern of S・8shows thecrystal growth of 3x3R450 冒 Asd巴scribedabove， the type of crystal growth depends upona substrate temp巴r -ature. This indicates that molecules on the substrate kept for the long time at a high tem幽 perature (S剛7to 9) ar巴possibleto migrat，巴 This explains that misfitted molecules disap -p巴arin the film of S'8. Figure 13 shows the SEM image of S.11. The crysta1s on KBr substrate are lxO.5μ m square crystals and their average thickness is about 0.1μ m from the AFM image. Figure 14 shows the SEM image of S.12. Crystals紅巴 much smal1er than those of S.11. The unidirectional ori開 園 tation is disturbed at the crystal boundary. as compared with S圃12. Remarkable crystal boundaries app巴arin S・12 as shown Fig. 15 since strains between crysta1s may suppress the 巴pitaxia1 Vanadyl Phthalocyanine Thin Film Prepared on a KBr Subsirat巴by1¥侶EMethod spectrum of S.1 shows an absorption peak at 810 nm. Other samples show an absorption peak at 780 nm. This m巴ansthat only film of S.1 is epitaxially grown[3]. The films of S.2 and S・3have a monoclinic s仕ucture[3]. Figure 7 shows th巴SEMimage of S・5. The film is nonuniform with unidirectionally oriented grains. Figure 8 shows the optical absorption spectra of S-4to 6. Each sampJe has a dominant absorption peak at 780 nm. This suggests that the films of S-4to 6 have a monoclinic structure [4]. 1.5 ( . コ 同 ) ω υ ロ B H C ω ﹄ ︿ 0.5 h Ji¥__" 0' 200 300 400 500 600 700 800 900 Wavelength (nm) KBr ( 100 ) alone 12 RHEED patt巴rns of di旺巴rent places of VOPc film of S.8 and KBr a10n巴. VOPc thIn film VOPc thin film VOPc thin film Fig. Fig. 11 Optical absorption spectra of S圃7to 9. This indicates that VOPc molecules misfit with the substrate at 1000C (S-4to 6). Figure 9 shows the SEM and AFM images of S.8. The film is non.uniform with unidirectionally orient巴dcrystals from SEM imag巴andit is the 3x3R450 type from AFM image. Figure 10 shows出巴 SEMand AFM images S町9. Crys -tals are much larger than those of S・8. How国 巴ver‘theunidir巴ctionalorientation is disturbed at the crystal bound紅y，as compared with S.8. Th巴 crystal boundary may depend upon the properties of a cl巴avedKBr substrate. The film thickness is about 60 nm from th巴AFM imag巴 Figure 11 shows the optical absorption spectra of S.7 to 9. Each sample has the absorption shoulder at 810 nm. This suggests that the films of S.7 to 8 are mixed with epitaxially grown and monoclinic one [3] The optica1absorption spectrum of S幽9shows the absorption peak at 780 nm， suggesting a monoclinic structure. Figure 12 shows the
Vanadyl Phthalocyanine Thin Film Prepared on a KBr Substrate by MBE Method .創刊号。平成 11年 16 -p (200'C， 120min) -.N(200'C，60min) -M (200'C， 10min) ￨￨￨Illi--:!Jj14 よ ∞ 、 ﹂ -目 白 、 、 -L i 、 -i 1 l i t z -s
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A 円 lis-lili--tf'N ︹ M ↓ 側 1 5 3 2 t z f l J l / 一 3 2 1 ' t e f ノ -， d -0 ・ ・ 戸 -ー 一 o f / / 一 7 3 7 ， ， ﹃ E f l ， d F ) / ー / ' / 一 omi
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' 〆 戸 -n b r、 ， ιシ - 一 h μ = 一 日 罰 一 ニ ム n u m 川 i、 こ 5 e ; -l : 苧 3 j ﹃ t L A -ぃ 一 三 ¥ -D V i i -L ︺ a -t 電l a i -? パ e ︺ 引 W ! f ︻ l i i t ， . J t i -， i f 司 f l i e d f -唱 t j l ¥ L E I -I J 1 l 3 l i t -a 、 1 1 l i l t -! 、 ー ー ι E 1 3 i I F 1.5 0.5 2385 官 。 m A ︿ SEM image of S.11. Fig目 13 Optical absorption spectra of S.10 to 12. Fig. 16 VOPc出nfilm SEM image of S.12. Fig. 14 VOPc thin film Fig. 17 RHEED patterns at different plac巴S of VOPc film of S.11 VOPc thin film SEM imag巴ofS・14. Fig. 18 AFM image of S・12. growth. Figure 16 shows the optical absorp圃 tion spectra of S.10 to 12. Th巴optIcalab圃 sorptlOn spectra of S.1 0 to 11 show the absorp -tion peak at 810 nm inthe Q band region ands
・12 has the absorption peak at 780nm. These suggest the epitaxial growth Fig. 1517 ( tric1inic crysta1structure). The triclinic crysta1has a higher third harmonic generation coe宜icient than the monoclinic crysta1[1]. Therefore， films with large triclinic crystals are important for由e出irdharmonic generation de -Vlces. Vanadyl Phthalocyanine Thin Film Prepared on a KBr Substrate by 1'v1BE Method 1.5 3. Conclusions (1) Fi1ms prepared on a KBr substrate tempera -飢reat 800C are uniform and layer growth. (2) Fi1ms prepared on a KBr substrate above 1000C are nonuniform. 2 . 3 8 5 f 自 宅 (3) Crystals on a KBr substrate at a high tem同 perature ( Ts : 150
0
C ) or ( Ts : 200O
q
are 3x3R450 grown epitaxia11y. (4) Crysta1s on a KBr substrate of a high tem -perature ( Ts : 2500q
are a roof.like type and 白ephase transition from a monoc1inic to a tri -c1inic crysta1s的lctureoccours町1. M. Hosodaヲ T. Wada， A.Yamad，a A.F.
Garito and H. Sasabe: Jpn.J.App.1Phys. 30 ( 1991) L.1486. 2.H. Tad，a K. Saikai andA.Koma: Jpn. J App.1Phys. 30 ( 1991)L.306. 3.H. Hoshi and Y. Maruyama:J.App.1Phys. 69 ( 1991) 3046 4. H. Hoshi， K. Hamamoto， T. Yamada， K. Ishikawa， H. Takezoe， A.Fukuda， S. Fang， K. Kohama andY.Maruyama: Jpn. J. App.1Phys. 33 ( 1994) 1.1555. 5. C. H. Griffiths， M. S. Wa1ker and P. Gold -stein: Mo.1Crys.tLiq. Cryst.33 ( 1976 ) 149. 6. Masahiro Hosod，a Tatsuo Wada， Akira Yamadぇ A nthony F. Garito andHiroyuki Sasabe: Jpn.J.App P.l hys. 3 (1991) 11486. Rferences Fig. 19 Optical absorption spectra of S・13 to 15. for S・10and11[4]叩dthe monoclinc growth for S.12. Figure 17 shows也巴 RHEEDpat -terns of S.l1， suggesting也ecrysta1grow也of 3x3R450 目 Thissuggests that misfitted mole田 cules completely disappear in社lefilm of S.l1. Figure 18 shows the SEM image of S・14. The crystals on KBr substrate are a roof.like 匂rpe，社leirsize is above 1μm squ紅e，about 0.15μm in the thickness from an atomic force microscopy. Figure 19 shows the optical ab圃 sorption spec仕aof S.13 to 14. The optica1 absorption spec仕aof S.13， 14 and 15 show the absorption peaks at 810， 830 and 860nm in也e
