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The effect of carbon ion implantation on the nucleation of diamond on Ti-6Al-4V alloy
Surface and Comings Technolngy, 51 0992) 307-312
307
The effect of carbon ion implantation on the nucleation of diamond on Ti-6A1-4V alloy D. K. Sood Microelectronics and Mat erials Technology Centre. Royal Melbourne lnstitu/e ~" Techmdogy. Melbourne, 3(~)i (Australia /
W. R. Drawl and Russell Messier Materials Research Luix~ratory, Pennsyl~'ania State Unh;ersity, University Park, P A 168¢)2 (USA)
Akstcact The hetexogencous nucleation of diamond particles during the early stages of diamond film formation on non-diamond substrates is not well understond, In this work, we used ion implantation as a pretreatracnt process, to control the nucleation of diamond particles, The well known surgical alloy Ti-6AI-4V ("mirror" polished) was used as the substrate. Carbon ions at 30 keV energy were implanted at room temperature into masked regions on the samples, up to doses of 1 xl0=~-Txl0 I' ions cm -z. At the high doses, carbon concentrations up to 80 at,% were generated as shown by Rutherford baekseattering ~ t r o m e t r y (RBS), After ion implantation, diamond depositions were conducted at MRL utilizing a Toshiba microwave chemical vapour deposition (CVD) system, Operating conditions were 12kPa total system pressure, I% methane in hydrogen at a total flow of 100 standard cm "~rain -=, substrat¢ temperature of 1000 >C, deposition time 5 h, The deposited films were studied by scanning electron microscopy, microfocus Raman scattering and RBS, The results indicate (a) a reduction in nucleation density up to 8 times with increasing ion dose, Ib) near perfect diamond particles (Raman scatteringl and (el large internal stresses leading to partial flaking when the film becomes continuous. The role of a possible "carbided layer" formed by ion implantation is discussed.
1. Imcoductiea Recent developments [I, 2] in numerous low cost, low pressure methods of making diamond particles and coatings from the vapour phase have aroused many expectations for several applications. The diamond films grown by most of the chemical vapour deposition (CVD) methods consist of micrometre-sized randomly oriented particles of diamond which nucleate sparsely and grow three-dimensionally until they impinge on their neighbouring crystallites. The nucleation of diamond (particles) during early stages of film formation on nondiamond substrates is not well understood, Several techniques have been reported in the literature [I, 2] to enhance nucleation, The most popular pretreatment process employs surface abrasion with fine powder or paste of diamond or boron carbide particles. This poorly understood technique usually results in higher nucleation density of diamond on most non-diamorKl substrates. However, good control and not just enhancement of nucleation density is highly desirable for several practical applications of diamond films, Ion bombardment is a well established process for improving and controlling the nucleation of met~lic films on a variety of substrates [3], We believe that it could be successfully applied to the growth of diamond films, Indeed, recent studies on
0257-8972/92/$5,00
selective nucleatiort of diamond particles [4-6] on silicon, have employed argon ion bombardment to reduce nucleation. The aim of the present work was to use ion implantation as a pretreatment process to achieve such control of nucleation of diamond phase on non-diamond substrates, Carbon was selected as the implant species, since carbide phases are believed to he precursors to diamond formation [2], High dose implantation of carbon ions at low enough energy could lead to the formation of surface precipitates of carbides which could then promote diamond nucleation. The well known surgical alloy Ti-6AI-4V was chosen as the substrate, This alloy is extensively used for making prosthetic devices such as artificial hip joints, knees, knuckles etc., which are surgically implanted inside the human body. Diamond film may he a useful protective coating for ,such prosthetic devices to provide lower friction, wear and corrosion inside the human body, leading to greatly prolonged useful life of the device.
2. Exl~qmemM detMls Discs I mm thick were spark cut from a rod of high quality Ti-6AI-4V alloy, The discs were annealed at
~ 1992 - - Elsevier Sequoia, All rights reserved
.111,~
I), [
.'l,,.d ~'l ~lt.
,\'ltcl~'all, m t~! ,hllltll.lll'
700 (" for 2 h in a vacuum of a l ~ u l (i.13 Pa. M¢¢hanicai polishing was dont: to obtahl a mirror linish by tixing diamond pasl¢ of 0.25 pin raling as lh~ Iinal slag¢. Ion implantation was pcrfornlctl with the R M I T inlplanit:r. using carbon ions tit 30 keV io doses b¢lwct:n I , Ill TM and 7×1(i I~ ions~nl -~ til ¢urrcnl d¢ilsiiics of tlboul liitl liA ¢nl -~. The substl'aics Wt:l'¢ iiiotlnlctl on ti copper heal sink phtt¢ hdd tit roon~ l¢ll/pt:r;.ilur¢. Ion bcanl healin t could htiv¢ product:d ;.i Icnlper~lltir¢ of tip Io 15i) (7". Plirl of the sample surftice was nlaxkctl off' io provki~ a control uiliil/planlcd Ivirghll region on ¢adi sanlpI¢..~tlll~ samples had inore than o11¢ tlos¢ i'cgion to avokt any difti:rcnct:s in dianlond lilnl growth t:nvirollmcnt or substrat¢ fronl the sludv of dost: t:ll~:c'is. Al'It:r ion iinplanlalitm, diamond dcposilioil.~ wt:rt: conducted at M I L utilizing a Toshiba microwavt: ( ' V I ) system. Operating conditions were 12 k Pa lolai s)'slt:ill pressure. I°~i~ nlclhan¢ ill hydrogcn al a lolal IIo~v of 10() seem. substrai¢ temperature of Ill01) C. dcpoxilion tirol: 5 h. "Fkcst: arc Ih¢ growth ~ondilions oplinlizt:d previously (by the M R L groupi for prothi¢ing s~lei'tll nli¢l'onlctrc thick ¢ontintlotis tlianlond Iilnls till silicon, The deposited tilms were studied by su-annhlg ¢1¢¢11"on
.ll "1i ~> I~ JI
illicros¢Ol~y (St']M)and Raman ,¢ailcring using an INA l~inlanor t l-100ti nlicroftlcus sric¢lronl¢lcr, I~anl;all ¢ondilion,~ were a laser ~avelt:llgih of 514,532 IIIII. ill a pov, cr of .~{I nlli~.'. alid it spot tlianiclcr of aboul 2 .~ lilil. Rulhcrford backs~xitlcring sr~¢ir~,nlch" ) (P.,B~) WtlS used Io ¢xlinlale ¢al'h~ql tlt:plh proliles of s~nlc high thls¢ ,n~iillpl¢~.
3. Results l l ~ ~ . ~ k m R I]S anal)sis o1" high dose speoinml.~ dcai'k sllm,~¢d lhal Ctll'holl ¢onct:lllrtlliOns of tip to RIP',I \vt:i'¢ prt:,,~t:nl oil iht: ~,ul'fat't:, Thus, T i ( ' or V(" could fit., I'~ll'lllt2tl on lilt: Sul'fa¢¢ held al Illllli (' dul'illg Ih¢ lil/ile hlcubalion D:riod Ib¢l'~li't: Iht: tlianlond nuclei siabiliz¢i hi Ilk." M W P ( ' V I ) rcachlr, ('alt:tilillions b), T R I M sllo~v lhat flit: pro.letted I'~illgt: of .~(IkeV carbon ionx ill a 1 i (~AI 4 V larg¢l is (~ iinl ~ilh a sli'aggliilg ~ k i t h of .~(I IIlll, All lh¢ Xalllrilcs tVCl't: ,~ludit:tl iii d¢lail I~) SI:M aild nli~l'ofocun ranlan xcall¢l'iilg, ,~ttlllt: s¢lt:clctl rcxulls al'¢ sliowli ill t"ig, I, Tht: dialllond liinl grown on a tii'ghi
Diamond ¢>
1,000
0.800 O
- ~ 0,600
0,400
0,200
400,0 I"ig. Ilal
600,0
800,0
1000,0
1200,0
R (cm -1)
1400,0
1600,0
D, K, Sood et al, : Nucleation o f diamond on Ti 6 A I - 4 V
309
0
8,000
6,400, A
W
4.8OO,
Non-dlamond
(sp2)
3,200,
1,600, Ii
400,0
600,0
800,0
1000,0
Fig, l(bl
sample which was not implanted at all, was a continuous film (Fig. I(a), SEM image). The Raman spectrum obtained from this film (also shown in Fig. i(a)), is nearly as good as a spectrum obtained from natural diamond exhibiting a sharp line at 1330 cm -~, This is to be compared with the Raman line from natural diamond characterized by its phonon at 1331 c m i with a band width at half intensRy less than 1.8 cm- 1 For natural diamonds of different origins, the frequency varies from 1331 to 1 3 3 6 c m ~ and the half lyand width from i.8 to 3 cm i [7]. There is no evidence of any significant amount of non-diamond contamination. Figures I(b) and I(c) show the results for diamond growth observed on samples implanted with 2 and 7 × I 0,!~ C ions cm- 2. No continuous film is obtained. Instead, isolated crystallites of facetted diamond are observed by SEM, having sizes of up to 4 IJm across. Microfocus Raman scattering obtained from one such crystallite shows the characteristic diamond line, and a significant non-diamond (sp 2 binding) contribution having a plateau at 1537 cm[8]. The non-diamond contribution appears to increase systematically with the carbon ion dose (Figs. I(a)-I(c)). This could be due to either a possible "creeping" of
1200,0
R (¢m")
1400,0
1600,0 (continued)
implamed carbon into the growing diamond crystallites or the presence of a residual amount of implamed carbon at the diamond-substrate interface. A Raman spectrum taken "off crystal" (Fig. I(c)) shows complete absence of both diamond or non-diamond carbon. Detailed SEM studies (not presented here) reveal considerable etching of the alloy surface ("off crystal"). From a SEM image. the diamond nucleation density is determined by counting the number of diamond crystals over a known area. The dose dependence of such nucleation density is shown in Fig. 2. Carbon ion implantation produces a reduction in nucleation density by a factor of eight. Even at the lowest dose studied, there is a marked reduction. Carbon implantation is therefore acting as an effective deterrent to diamond nucleation. Since TiC would certainly be produced under post-implamation heating in the plasma reactor, we can conclude that the formation of TiC does not appear to be conducive to nucleation of diamond on Ti-6AI-4V alloy under the present conditions of diamond growth. The extent of "poisoning" caused by implamation induced damage could be quite significant as shown by the large reduction in nucleation density at the lowest dose of 1 ×i016 ions c.m -a, Further work
D, K, Sood el al,
3111
Nm'h,ution o l'diamond on Ti ¢~,,11 4 1 o.
2,000
1,600
0
IP-
>¢
.•W
1.200
0,800
o
I Off
""..
crystal (xS)
I
%.
0,400
400,0
600,0
800.0
1000.0
1200,0
1400.0
11600,0
R (cm") I'ig, 1, A ~.nquem.'e o f R a m a r t ,~caltering a n d S E M rcst|ll,,; frortl d i a m o n d g r o w n o n (al a n u n i m p l a n t e d (virginl s a m p l e , (hi a ,xmuple i m p l a n t e d with 2 ~ I() I - (" ions c m ", (el a s a m p l e i m p l a n t e d with 7 × Ill t'~ (" ions c m ' , R;itnl:.ln SlX;ctra " o f f c r y s t a l " a r e a l s o s h o w n ,
25
•
20
10
0
• 0
i , 0,1 0,8 Ced)on Ion 0 0 ~
, , 2.0 5,0 ( x 1E17 i o n ~ o m 2 )
, 7,0
Fig. 2. Nucleation density of diamond crystals rs, carbon ion dose, schematic histograms,
is in progress (at much lower doses and by implantation with self ions of titanium), to study the role of ion damage, An alternative explanation could be offered as foUows, if the nucleation of diamond on Ti-6AI-4V were due to the homoepitaxial growth on diamond particles embedded into the surface during polishing with dia-
mond paste impregnated cloth and papers. During carbon ion implantation, the diamond ".'seeMs" embedded on the surface could be transformed to non-nucleating graphite, amorphized diamond, or ~ m e other form of carbon. During their recent study of ion irradiated diamond powders, Wong et al, [9] have indeed found that the 1332 cm x sharp line (obtained on the unirradiated diamond), after implantation with krypton (3 MeVj at It) ions nm 2 became broad and decreased in intensity dramatically, and another peak appeared around 1600 cm i, corresl~nding to non-diamond carbon (see Fig, 4 of ref. 9). Further work is in progress to test this hypothesis, by (i) implantation with krypton ions and (ii) by preparing samples without using any diamond particles during polishing. Nearly continuous diamond films were observed on the masked unimplanted regions of all implanted samples. These films suffered from acute delamination problems resulting from poor adhesion to the underlying substrate. Large areas were denuded producing flakes of "curled up" film, A Raman spectrum taken from a region of the continuous film still adherent to the unimplanted region of a substrate (implanted with
D, K. Sood et ai. / Nucleaticm ¢~"diamond on T i - 6 A I - 4 V
311
?,OOQ
6,000 (= ,p-
X W S,O00
~ 4,000
(.)
400,0
600.0
IO0,O
1O~O.O
1200,0
R (cm')
i
!
1400,0
1600,0
Q,
1,200
1,000
x~ m
O,4QO
0.200
I III,. . . . . .
~,0
(b)
(mO,O
I1~,0
1~0,0
1"200,0
I 14~0.0
) 1600,0
R (cm~)
FiB, 3, Raman spectra obtained from the film deposited onto the unimplanted (masked) resion of a ~ n p l ¢ implanted with 5 × I0 I~ C :ons cm-=: (a) region of continuous film still attached to the substrate, (b) a small "curled-up" flake i~olated from the near vicinity of (a).
312
D. K. Sood "el al.
Nm'h'atio, ol diamo,d o , "l'i 6-11 4 1
5 × I0 TM C ions cm 21, is shown in Fig, 3(al, The characteristic diamond line was considerably broadened, shiftu~d to a much higher wave number and split into a doublet itx:at'ed at 1338 and 1348em ~, However. the Raman spectrum taken from a small detached flake fi'om the same film. shows (Fig. 31b)l a sharp line at 1331 cm and marked disap~arance of the broadening, shift or the doublet observed in Fig, Ilal. This indicates that the broadening, shift and doublet hmnation are a result of internal stresses present in the film. This stress is relieved after delamination from the substrate and the fihn curls up, The isolated flake also exhibits a small non-diamond contamination {shown by the background rising from about 81,1(IIt+ 16IX)cm i) in the diamond crystal. Since the lilm {Fig. Ilal) on the completely unimplanted Ivirginl region is free from such background, we can speculate that the implanted carbon "creeps" into the growing diamond crystals, When diamond films are deposited onto non-diamond substrates, stress can occur in tbe films owing to lattice mismatch and/or difli~rences in coefficient of tbermal expansion between diamond and the substrate material, Furthermore. lateral variations in grain size, density, or impurities incorporated during the lilm growth process can lead to stress. This stress is known usually to build up with increasing film thickness, The stress can be either tensile or compressive, In general a material which is in tensile strain will exhibit a Raman peak which is shifted to lower frequency while the Raman peak of a material undergoing a compressive strain is shifted to higher frequency [10, II]. Since the shift in Fig. 3{a) is towards higher wave numbers, the diamond film must be under a compressive stress, The broadening of the Raman i i ~ can result from a reduction in domain size [10] or from an increase in disorder within the diamond crystal [7], However. it is very unlikely that these two features woukt relax back in an opposite manner upon delamination of the film, At present, we have no plausible explanation for the broadening and doublet formation in Fig, 3{a) and their absence in Fig, 3(b), after delaminalion. However. it is clear that this behaviour is related to delamination or stress relief in the fihn,
4, (7omcl~kms
Ill Carlxm ion implantation can be very effective in
controlling (reducing) the nucleation of diamond on Ti 6AI 4V alloy, 12) Nucleation density for diamond formation shows a strong dependence on ion dose, 13) 1"he I'ormation of carbides at the growth surface does not appear to be important tbr diamond nucleation on Ti 6AI 4V alloy. Instead, ion damage to the substrafe, or to the diamond "seeds" embedded into the surface during mechanical polishing, could be resl~msible for the observed reduction in nucleation. (41 Some of the implanted carbon is either incorporated into the growing diamond crystals, or is present at the diamond substrate interface, (5) ('ontinuous diamond lilm forms on the unimplanted surface but displays large internal compressive stresses and exhibits poor adhesion, }-'urthcr work needs to be done to remedy these problems befi~rc the diamond lilms dci'msited onto the Ti 6Ai 4V can be of a m possible use for prosthetic applications,
Ackmm4ed~,mems
We thank Dianne Knight for Raman scattering measurements, Sue Lane for alloy sample preparation, Darrdl Duckworth and Vimxl N~.lth for ion implantation, Veena ~ m d for SEM, and Zhou Wei for RBS measurements. D, K, S. thanks Russ Messier tot kind hospitality and support during his slay at MRI..
References I P.K. Bachman and R. Mes...ier. ¢hem E , ~ . . \ ' c ~ . . Ixlax I~x~j~ 2 K. I. Sl"~.:+ill'+_3..111'I. ( ¢r~llll. So~.. +~ ll"hR")l I':I l'll 3 M, Marillov. +hill Solid I"ih+ln. -/6 ( I'4R?I 26". 4 K. I lirabayashi. Y. "l'aniguchi. (). Takamal.~u. 1. Ikcda. K. Ikoma and N. Iwasaki-Kurihara. APPI. Phys la+ll...';3 I I~)SRI I.M5. J. S. Ma. H. Kawarada. 1". Yonehara. J. Suzuki. J. Wei. Y Yokol~t and A. Hiraki...tPPI. I*hvx. I.elt. 55 I Dt~91 1(171. h J.S. Ma. H. Ka~arada. T. Yonehara..I. St|/t|ki. Y. ¥okol;.I and A. Hiraki. ,I. ('rvsl. Growg~, 99 11~+9111 1206 1210 7 P. V. Huollg. Ditmlo,d Re/at. l+hlwr.. I t10911 33 s I). S. Knight artd W. R White. ,I. ,Xhl/cr, Re,'<. 4 I 1'+•91 3x5, t+ M . S . Wong. I:.(i. Kariori.,, and I. ('ariz. Sl~rl, t',,,a. I+echn.I, 43 44 ! 19t~ll 6~. IO Y. M, Lel.iri,.'c. R. J. Nemanich..I. 1. (ila,x,x. ~, H. Lee. R. A. Rudder and R . K . M a r k u n a s , Ala/cr. Rex. Sot.. Syrup, I+r,,~., le,2 119901 219, II H. Bt~ppart..I. Van .~lraal¢l+t al~d 1. I-. ~ihcra. l-'hl.~. Nov. B, 3.'. 11t~,~51 1423.
307
The effect of carbon ion implantation on the nucleation of diamond on Ti-6A1-4V alloy D. K. Sood Microelectronics and Mat erials Technology Centre. Royal Melbourne lnstitu/e ~" Techmdogy. Melbourne, 3(~)i (Australia /
W. R. Drawl and Russell Messier Materials Research Luix~ratory, Pennsyl~'ania State Unh;ersity, University Park, P A 168¢)2 (USA)
Akstcact The hetexogencous nucleation of diamond particles during the early stages of diamond film formation on non-diamond substrates is not well understond, In this work, we used ion implantation as a pretreatracnt process, to control the nucleation of diamond particles, The well known surgical alloy Ti-6AI-4V ("mirror" polished) was used as the substrate. Carbon ions at 30 keV energy were implanted at room temperature into masked regions on the samples, up to doses of 1 xl0=~-Txl0 I' ions cm -z. At the high doses, carbon concentrations up to 80 at,% were generated as shown by Rutherford baekseattering ~ t r o m e t r y (RBS), After ion implantation, diamond depositions were conducted at MRL utilizing a Toshiba microwave chemical vapour deposition (CVD) system, Operating conditions were 12kPa total system pressure, I% methane in hydrogen at a total flow of 100 standard cm "~rain -=, substrat¢ temperature of 1000 >C, deposition time 5 h, The deposited films were studied by scanning electron microscopy, microfocus Raman scattering and RBS, The results indicate (a) a reduction in nucleation density up to 8 times with increasing ion dose, Ib) near perfect diamond particles (Raman scatteringl and (el large internal stresses leading to partial flaking when the film becomes continuous. The role of a possible "carbided layer" formed by ion implantation is discussed.
1. Imcoductiea Recent developments [I, 2] in numerous low cost, low pressure methods of making diamond particles and coatings from the vapour phase have aroused many expectations for several applications. The diamond films grown by most of the chemical vapour deposition (CVD) methods consist of micrometre-sized randomly oriented particles of diamond which nucleate sparsely and grow three-dimensionally until they impinge on their neighbouring crystallites. The nucleation of diamond (particles) during early stages of film formation on nondiamond substrates is not well understood, Several techniques have been reported in the literature [I, 2] to enhance nucleation, The most popular pretreatment process employs surface abrasion with fine powder or paste of diamond or boron carbide particles. This poorly understood technique usually results in higher nucleation density of diamond on most non-diamorKl substrates. However, good control and not just enhancement of nucleation density is highly desirable for several practical applications of diamond films, Ion bombardment is a well established process for improving and controlling the nucleation of met~lic films on a variety of substrates [3], We believe that it could be successfully applied to the growth of diamond films, Indeed, recent studies on
0257-8972/92/$5,00
selective nucleatiort of diamond particles [4-6] on silicon, have employed argon ion bombardment to reduce nucleation. The aim of the present work was to use ion implantation as a pretreatment process to achieve such control of nucleation of diamond phase on non-diamond substrates, Carbon was selected as the implant species, since carbide phases are believed to he precursors to diamond formation [2], High dose implantation of carbon ions at low enough energy could lead to the formation of surface precipitates of carbides which could then promote diamond nucleation. The well known surgical alloy Ti-6AI-4V was chosen as the substrate, This alloy is extensively used for making prosthetic devices such as artificial hip joints, knees, knuckles etc., which are surgically implanted inside the human body. Diamond film may he a useful protective coating for ,such prosthetic devices to provide lower friction, wear and corrosion inside the human body, leading to greatly prolonged useful life of the device.
2. Exl~qmemM detMls Discs I mm thick were spark cut from a rod of high quality Ti-6AI-4V alloy, The discs were annealed at
~ 1992 - - Elsevier Sequoia, All rights reserved
.111,~
I), [
.'l,,.d ~'l ~lt.
,\'ltcl~'all, m t~! ,hllltll.lll'
700 (" for 2 h in a vacuum of a l ~ u l (i.13 Pa. M¢¢hanicai polishing was dont: to obtahl a mirror linish by tixing diamond pasl¢ of 0.25 pin raling as lh~ Iinal slag¢. Ion implantation was pcrfornlctl with the R M I T inlplanit:r. using carbon ions tit 30 keV io doses b¢lwct:n I , Ill TM and 7×1(i I~ ions~nl -~ til ¢urrcnl d¢ilsiiics of tlboul liitl liA ¢nl -~. The substl'aics Wt:l'¢ iiiotlnlctl on ti copper heal sink phtt¢ hdd tit roon~ l¢ll/pt:r;.ilur¢. Ion bcanl healin t could htiv¢ product:d ;.i Icnlper~lltir¢ of tip Io 15i) (7". Plirl of the sample surftice was nlaxkctl off' io provki~ a control uiliil/planlcd Ivirghll region on ¢adi sanlpI¢..~tlll~ samples had inore than o11¢ tlos¢ i'cgion to avokt any difti:rcnct:s in dianlond lilnl growth t:nvirollmcnt or substrat¢ fronl the sludv of dost: t:ll~:c'is. Al'It:r ion iinplanlalitm, diamond dcposilioil.~ wt:rt: conducted at M I L utilizing a Toshiba microwavt: ( ' V I ) system. Operating conditions were 12 k Pa lolai s)'slt:ill pressure. I°~i~ nlclhan¢ ill hydrogcn al a lolal IIo~v of 10() seem. substrai¢ temperature of Ill01) C. dcpoxilion tirol: 5 h. "Fkcst: arc Ih¢ growth ~ondilions oplinlizt:d previously (by the M R L groupi for prothi¢ing s~lei'tll nli¢l'onlctrc thick ¢ontintlotis tlianlond Iilnls till silicon, The deposited tilms were studied by su-annhlg ¢1¢¢11"on
.ll "1i ~> I~ JI
illicros¢Ol~y (St']M)and Raman ,¢ailcring using an INA l~inlanor t l-100ti nlicroftlcus sric¢lronl¢lcr, I~anl;all ¢ondilion,~ were a laser ~avelt:llgih of 514,532 IIIII. ill a pov, cr of .~{I nlli~.'. alid it spot tlianiclcr of aboul 2 .~ lilil. Rulhcrford backs~xitlcring sr~¢ir~,nlch" ) (P.,B~) WtlS used Io ¢xlinlale ¢al'h~ql tlt:plh proliles of s~nlc high thls¢ ,n~iillpl¢~.
3. Results l l ~ ~ . ~ k m R I]S anal)sis o1" high dose speoinml.~ dcai'k sllm,~¢d lhal Ctll'holl ¢onct:lllrtlliOns of tip to RIP',I \vt:i'¢ prt:,,~t:nl oil iht: ~,ul'fat't:, Thus, T i ( ' or V(" could fit., I'~ll'lllt2tl on lilt: Sul'fa¢¢ held al Illllli (' dul'illg Ih¢ lil/ile hlcubalion D:riod Ib¢l'~li't: Iht: tlianlond nuclei siabiliz¢i hi Ilk." M W P ( ' V I ) rcachlr, ('alt:tilillions b), T R I M sllo~v lhat flit: pro.letted I'~illgt: of .~(IkeV carbon ionx ill a 1 i (~AI 4 V larg¢l is (~ iinl ~ilh a sli'aggliilg ~ k i t h of .~(I IIlll, All lh¢ Xalllrilcs tVCl't: ,~ludit:tl iii d¢lail I~) SI:M aild nli~l'ofocun ranlan xcall¢l'iilg, ,~ttlllt: s¢lt:clctl rcxulls al'¢ sliowli ill t"ig, I, Tht: dialllond liinl grown on a tii'ghi
Diamond ¢>
1,000
0.800 O
- ~ 0,600
0,400
0,200
400,0 I"ig. Ilal
600,0
800,0
1000,0
1200,0
R (cm -1)
1400,0
1600,0
D, K, Sood et al, : Nucleation o f diamond on Ti 6 A I - 4 V
309
0
8,000
6,400, A
W
4.8OO,
Non-dlamond
(sp2)
3,200,
1,600, Ii
400,0
600,0
800,0
1000,0
Fig, l(bl
sample which was not implanted at all, was a continuous film (Fig. I(a), SEM image). The Raman spectrum obtained from this film (also shown in Fig. i(a)), is nearly as good as a spectrum obtained from natural diamond exhibiting a sharp line at 1330 cm -~, This is to be compared with the Raman line from natural diamond characterized by its phonon at 1331 c m i with a band width at half intensRy less than 1.8 cm- 1 For natural diamonds of different origins, the frequency varies from 1331 to 1 3 3 6 c m ~ and the half lyand width from i.8 to 3 cm i [7]. There is no evidence of any significant amount of non-diamond contamination. Figures I(b) and I(c) show the results for diamond growth observed on samples implanted with 2 and 7 × I 0,!~ C ions cm- 2. No continuous film is obtained. Instead, isolated crystallites of facetted diamond are observed by SEM, having sizes of up to 4 IJm across. Microfocus Raman scattering obtained from one such crystallite shows the characteristic diamond line, and a significant non-diamond (sp 2 binding) contribution having a plateau at 1537 cm[8]. The non-diamond contribution appears to increase systematically with the carbon ion dose (Figs. I(a)-I(c)). This could be due to either a possible "creeping" of
1200,0
R (¢m")
1400,0
1600,0 (continued)
implamed carbon into the growing diamond crystallites or the presence of a residual amount of implamed carbon at the diamond-substrate interface. A Raman spectrum taken "off crystal" (Fig. I(c)) shows complete absence of both diamond or non-diamond carbon. Detailed SEM studies (not presented here) reveal considerable etching of the alloy surface ("off crystal"). From a SEM image. the diamond nucleation density is determined by counting the number of diamond crystals over a known area. The dose dependence of such nucleation density is shown in Fig. 2. Carbon ion implantation produces a reduction in nucleation density by a factor of eight. Even at the lowest dose studied, there is a marked reduction. Carbon implantation is therefore acting as an effective deterrent to diamond nucleation. Since TiC would certainly be produced under post-implamation heating in the plasma reactor, we can conclude that the formation of TiC does not appear to be conducive to nucleation of diamond on Ti-6AI-4V alloy under the present conditions of diamond growth. The extent of "poisoning" caused by implamation induced damage could be quite significant as shown by the large reduction in nucleation density at the lowest dose of 1 ×i016 ions c.m -a, Further work
D, K, Sood el al,
3111
Nm'h,ution o l'diamond on Ti ¢~,,11 4 1 o.
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R (cm") I'ig, 1, A ~.nquem.'e o f R a m a r t ,~caltering a n d S E M rcst|ll,,; frortl d i a m o n d g r o w n o n (al a n u n i m p l a n t e d (virginl s a m p l e , (hi a ,xmuple i m p l a n t e d with 2 ~ I() I - (" ions c m ", (el a s a m p l e i m p l a n t e d with 7 × Ill t'~ (" ions c m ' , R;itnl:.ln SlX;ctra " o f f c r y s t a l " a r e a l s o s h o w n ,
25
•
20
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0
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i , 0,1 0,8 Ced)on Ion 0 0 ~
, , 2.0 5,0 ( x 1E17 i o n ~ o m 2 )
, 7,0
Fig. 2. Nucleation density of diamond crystals rs, carbon ion dose, schematic histograms,
is in progress (at much lower doses and by implantation with self ions of titanium), to study the role of ion damage, An alternative explanation could be offered as foUows, if the nucleation of diamond on Ti-6AI-4V were due to the homoepitaxial growth on diamond particles embedded into the surface during polishing with dia-
mond paste impregnated cloth and papers. During carbon ion implantation, the diamond ".'seeMs" embedded on the surface could be transformed to non-nucleating graphite, amorphized diamond, or ~ m e other form of carbon. During their recent study of ion irradiated diamond powders, Wong et al, [9] have indeed found that the 1332 cm x sharp line (obtained on the unirradiated diamond), after implantation with krypton (3 MeVj at It) ions nm 2 became broad and decreased in intensity dramatically, and another peak appeared around 1600 cm i, corresl~nding to non-diamond carbon (see Fig, 4 of ref. 9). Further work is in progress to test this hypothesis, by (i) implantation with krypton ions and (ii) by preparing samples without using any diamond particles during polishing. Nearly continuous diamond films were observed on the masked unimplanted regions of all implanted samples. These films suffered from acute delamination problems resulting from poor adhesion to the underlying substrate. Large areas were denuded producing flakes of "curled up" film, A Raman spectrum taken from a region of the continuous film still adherent to the unimplanted region of a substrate (implanted with
D, K. Sood et ai. / Nucleaticm ¢~"diamond on T i - 6 A I - 4 V
311
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FiB, 3, Raman spectra obtained from the film deposited onto the unimplanted (masked) resion of a ~ n p l ¢ implanted with 5 × I0 I~ C :ons cm-=: (a) region of continuous film still attached to the substrate, (b) a small "curled-up" flake i~olated from the near vicinity of (a).
312
D. K. Sood "el al.
Nm'h'atio, ol diamo,d o , "l'i 6-11 4 1
5 × I0 TM C ions cm 21, is shown in Fig, 3(al, The characteristic diamond line was considerably broadened, shiftu~d to a much higher wave number and split into a doublet itx:at'ed at 1338 and 1348em ~, However. the Raman spectrum taken from a small detached flake fi'om the same film. shows (Fig. 31b)l a sharp line at 1331 cm and marked disap~arance of the broadening, shift or the doublet observed in Fig, Ilal. This indicates that the broadening, shift and doublet hmnation are a result of internal stresses present in the film. This stress is relieved after delamination from the substrate and the fihn curls up, The isolated flake also exhibits a small non-diamond contamination {shown by the background rising from about 81,1(IIt+ 16IX)cm i) in the diamond crystal. Since the lilm {Fig. Ilal) on the completely unimplanted Ivirginl region is free from such background, we can speculate that the implanted carbon "creeps" into the growing diamond crystals, When diamond films are deposited onto non-diamond substrates, stress can occur in tbe films owing to lattice mismatch and/or difli~rences in coefficient of tbermal expansion between diamond and the substrate material, Furthermore. lateral variations in grain size, density, or impurities incorporated during the lilm growth process can lead to stress. This stress is known usually to build up with increasing film thickness, The stress can be either tensile or compressive, In general a material which is in tensile strain will exhibit a Raman peak which is shifted to lower frequency while the Raman peak of a material undergoing a compressive strain is shifted to higher frequency [10, II]. Since the shift in Fig. 3{a) is towards higher wave numbers, the diamond film must be under a compressive stress, The broadening of the Raman i i ~ can result from a reduction in domain size [10] or from an increase in disorder within the diamond crystal [7], However. it is very unlikely that these two features woukt relax back in an opposite manner upon delamination of the film, At present, we have no plausible explanation for the broadening and doublet formation in Fig, 3{a) and their absence in Fig, 3(b), after delaminalion. However. it is clear that this behaviour is related to delamination or stress relief in the fihn,
4, (7omcl~kms
Ill Carlxm ion implantation can be very effective in
controlling (reducing) the nucleation of diamond on Ti 6AI 4V alloy, 12) Nucleation density for diamond formation shows a strong dependence on ion dose, 13) 1"he I'ormation of carbides at the growth surface does not appear to be important tbr diamond nucleation on Ti 6AI 4V alloy. Instead, ion damage to the substrafe, or to the diamond "seeds" embedded into the surface during mechanical polishing, could be resl~msible for the observed reduction in nucleation. (41 Some of the implanted carbon is either incorporated into the growing diamond crystals, or is present at the diamond substrate interface, (5) ('ontinuous diamond lilm forms on the unimplanted surface but displays large internal compressive stresses and exhibits poor adhesion, }-'urthcr work needs to be done to remedy these problems befi~rc the diamond lilms dci'msited onto the Ti 6Ai 4V can be of a m possible use for prosthetic applications,
Ackmm4ed~,mems
We thank Dianne Knight for Raman scattering measurements, Sue Lane for alloy sample preparation, Darrdl Duckworth and Vimxl N~.lth for ion implantation, Veena ~ m d for SEM, and Zhou Wei for RBS measurements. D, K, S. thanks Russ Messier tot kind hospitality and support during his slay at MRI..
References I P.K. Bachman and R. Mes...ier. ¢hem E , ~ . . \ ' c ~ . . Ixlax I~x~j~ 2 K. I. Sl"~.:+ill'+_3..111'I. ( ¢r~llll. So~.. +~ ll"hR")l I':I l'll 3 M, Marillov. +hill Solid I"ih+ln. -/6 ( I'4R?I 26". 4 K. I lirabayashi. Y. "l'aniguchi. (). Takamal.~u. 1. Ikcda. K. Ikoma and N. Iwasaki-Kurihara. APPI. Phys la+ll...';3 I I~)SRI I.M5. J. S. Ma. H. Kawarada. 1". Yonehara. J. Suzuki. J. Wei. Y Yokol~t and A. Hiraki...tPPI. I*hvx. I.elt. 55 I Dt~91 1(171. h J.S. Ma. H. Ka~arada. T. Yonehara..I. St|/t|ki. Y. ¥okol;.I and A. Hiraki. ,I. ('rvsl. Growg~, 99 11~+9111 1206 1210 7 P. V. Huollg. Ditmlo,d Re/at. l+hlwr.. I t10911 33 s I). S. Knight artd W. R White. ,I. ,Xhl/cr, Re,'<. 4 I 1'+•91 3x5, t+ M . S . Wong. I:.(i. Kariori.,, and I. ('ariz. Sl~rl, t',,,a. I+echn.I, 43 44 ! 19t~ll 6~. IO Y. M, Lel.iri,.'c. R. J. Nemanich..I. 1. (ila,x,x. ~, H. Lee. R. A. Rudder and R . K . M a r k u n a s , Ala/cr. Rex. Sot.. Syrup, I+r,,~., le,2 119901 219, II H. Bt~ppart..I. Van .~lraal¢l+t al~d 1. I-. ~ihcra. l-'hl.~. Nov. B, 3.'. 11t~,~51 1423.