Friction and wear of semiconductors in sliding contact with pure metals

Friction and wear of semiconductors in sliding contact with pure metals

Friction and wear of semiconductors in sliding contact with pure metals H MIshma* The frtct=on and wear of the semmonductors s)hcon and gallmm arsen~...

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Friction and wear of semiconductors in sliding contact with pure metals H MIshma*

The frtct=on and wear of the semmonductors s)hcon and gallmm arsen~de )n contact w~th pure metals was studied Frmtmon experiments were conducted at room temperature m a~r and m a vacuum of 2 0 x 10 -7 Pa Fwe transit=on and two nontransJt=on metals - t=tanmm, tantalum, mckel, palladmm, platinum, copper, and silver - were slid on a single crystal of silicon Four metals - mdmm, nmkel, copper, and silver - were shd on a single crystal of gallmm arsenide Furthermore, exper0ments on the wear of s=lmon m sliding contact with titamum, nmkel, and copper were conducted m a vacuum of 1 0 x 10 -s Pa The results =ndmated that the frmtion and wear of the semmonductors were dependent on the contacting metal The effect of the contact)ng metal on the frmtmn and wear was considered to arise from the )nteractmns at the metal-semmonductor interface Physmal and chemmal characteristics, espemally the Schottky bamer hmght at the metal-sere=conductor interface, are d~scussed w~th regard to the fr=ct~on behawour and wear behawour of the semmonductors Keywords fr/ct/on , wear, s e m i c o n d u c t o r - m e t a l contacts, s/hcon , gallium arson/de, S c h o t t k y barrier height

Introductmn Physical and chemical properties ot contacting materials play an important role in the mbologlcal phenomena of solids A considerable number of studies have been conducted for m e t a l - m e t a l contacts Melting point and crystal structure of metals affect their adhesmn behavIour 1 Mutual solublhty ot mating metals is closel:y related to the friction and wear phenomenon 2-4 However, only a few tnbologlcal experiments for semiconductors have been conducted Although the nature of surface fracture, filctton, and wear have been studied for slhcon and germamum in contact with metals s-8 , the elfects ol the physical properties of the metal semiconductor Interlace on trlbologlcal behaviour have not been addressed In a recent study an important characteristic relevant to the trxbologIcal behaviom of semiconductors was reported in the rubbing ofalumlnium and zinc 9 Although aluminlum and zinc are nontransltIon metals, where mild wear does not usually occur, in the rubbing of an alumlnxum and zinc couple mild wear appemed as a result of the formation of semlconductlng materials on the sliding surface Furthermore, the results of the wear experiments lor semiconductor silicon indicated that only mild wear occurred for silicon in shdmg contact with metals in air In the previous paper, tribologlcal behavlour was studied with regard to the occurrence of mild wear of a semiconductor, however, the basic trlbologlcal characteristics lor semiconductors were not discussed Many characteristics ot the surface chemistry and physics of semiconductors are generally caused by the electronic states which occur as excess *Fhe Institute oJ Ph vswal and Chemwal Research Htrosa~a, Wako sht Saltama 351-01 Japan

76

0301

679X/88/020076

electrons or positive holes in the atomic bondlngs In partlculal, in the case of contact with metals a Schottky barrlm is framed by a bending of the electronic band near the semiconductor surface when a semiconductor comes into contact with a metal 1°-12 These particular electronic states at the semiconductor surlace are expected to allecl the trlbologIcal behavlour ot semiconductors An example ol this property in relation to the hlctlon behavlour ol a semiconductor was reported by Buckley and Bralnald 6 According to the results ol trlction tests ol silicon, the lrlctlon behavlour was dependent on the type, P or N of the silicon semmonductor, made by doping with boron or phosphorus The noticeable point of this result is that the difference of electronic charges on the P-type or N-type semiconductor surfaces affects the hlCtlon ol the semiconductor in shdmg contact with metal Hence the mbological properties of semiconductors in contact with a metal are influenced by the electronic state at the interlace The same effects ol the contacting metals on the physical and chemical characteristics ol the semiconductor-metal interface have already been repolted as a relation with the Schottky barrier height 13-1s In this paper the eltects ol the physical properties ol the semlconductm were studied with regard to the tribologlcal behav]our ot semiconductors in shdmg contact with metals This report presents a study of the trlbologlcal behaviour of the two semiconductors silicon and gallium arsemde Since they are widely used in industry, they are easy to use This investigation determined the effect of contacting metals on the trlctlon behavlour and wear of these semiconductors m contact with pure metals m vacuum and In a i r

07 $3 00 © 1988 Butterworth & Co (Publishers) Ltd

Aprd 88 Vol 21 No 2

M/sh/na - f r i c t i o n a n d wear o f s e m i c o n d u c t o r s on p u r e metals

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was 0 1 N The semiconductor motion against the pin specimen created a single path with a 12 mm stroke on the semiconductor surface Sliding velocity was 0 2 mm/s The experiments were conducted at room temperature at a pressure of 2 0 x 10 -7 Pa

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Specimen cleaning

In the experiments In a high vacuum, the surface was cleaned by sputter bombardment by argon at 1000 V for a period at 30 mm Since the argon sputter bombardment of the galhum arsenlde produced changes m the initial surface composition 16-18, the method of cleaning galhum arsemde was different from that for silicon and metals a sputtering and anneahng method 18 was used The gallium arsenlde was annealed at 520 to 550°C for a period of 60 mln after argon sputter bombardment The specimen was heated m&rectly by resistance heating of the hafnium film coated on the ceramic block

force

Frmtlon experiments m air Fig l Frwtton apparatus m the vacuum system

Table 1 Coefficient of friction for metals in sliding contact with silicon at a load of 0,1 N in a vacuum of 2 0 x 1 0 - 7 Pa and in air Metal pin

Transition titanium tantalum n,ckel pallad)um platinum

In vacuum

In air

maximum

minimum

maximum

minimum

7 6 5 4 3

2 1 17 14 12 11

0 0 0 0 0

0 0 0 0 0

0 75 0 75

0 25 0 25

3 7 2 0 2

73 68 60 41 30

41 40 37 35 27

Nontransltton

copper sdver

30 3 1

<*-

For the frlcuon experiments in air a load from 0 1 to 1 0 N was applied as dead weight on the specimen pin in another pin-on-fiat apparatus described In Ref 8 A semiconductor specimen was mounted onto a stage which executed a reciprocating motion with a 10 mm stroke The maximum shdmg speed was 1 4 lnm/s In either direction In each experxment the pm specimen shd on the same 10 mm path of the semiconductor surface thirty t~mes in each dlrecUon The friction force was measured by strain gauges using an arm slmdar to that shown in Fig 1 The expermaents were conducted in a~r and at room temperature Wear experiments In vacuum

For the wear experiments a fiat-ended pin was pressed against a rotating silicon wafer with a rotating diameter of 20 mm xn a vacuum chamber The vacuum was achieved at a pressure of 1 0 × 10-s Pa by a turbomolecular pump system The normal load was 1 0 N, and the shdlng speed was 58 0 mm/s Wear of the specimen was determined by measulmg the weight of the pin and the wafer after each interval of shdlng distance All experiments were conducted at room temperature

Exper,mental method

Three different tnbometers were used m th~s investlgatmn Two were pro-on-flat devices which were used for the measurements at friction The other apparatus, used for the wear experiment, was a pro-on-rotating-disk

Matenals

F r i c t i o n apparatus in v a c u u m

The semiconductors used were slhcon and galhum arsenlde Slhcon was m the form of a single-crystal wafer ot (1 I 1 ) orlentauon Gallium arsemde was a single-crystal wafe~ o f ( 1 0 0 ) orientation Both at the specimens were pohshed and the roughness was less than 0 01 /~m Rrna\

The apparatus used for the friction experiments mvaL, uuln was enclosed m a vacuum chamber The chamber was evacuated by a conventional vacsorb mn-pulnp system capable of achlewng a pressure of 2 0 x 10 -7 Pa (1 5 x l0 -9 Torr) The friction dewce is shown m Fig 1 The semiconductor specimen was mounted on a cubic ceramic block The block was mounted on a mampulato) beam capable of three-dHnenslonal movement The surtace of the block to which the semiconductor specimen was mounted was coated with a hafnmm-sputtered film m order to achieve sputtering and heating of the semiconductor specimens The pin specmlen was fixed onto a beam which had two flats upon which strain gauges were mounted to measure load and friction Load was applied by advancing the block toward the pm The apphed load

l'he metals used as pin specimen wele pure (purity 99 9 7 99 999%) polycrystalhne titanium tantalum, nickel, palladmm, platinum indium copper, and silver In the friction experiments, hve transmon metals - T1, Ta, NI, Pd, and Pt - and two nontransltlon metals - Cu and Ag were shd on the SdlCOn ( 111 ) surface Four metals - In NI Cu, and Ag were slid on the gallium arsenlde (100) surface The &ameter at the pm specimen was 3 18 mm and the tip was hemispherical The sliding surfaces were pohshed with alumina powder In the wear experiments, only thlee metals - titanium, mckel, and copper - wele used for the pm specimen, with a diameter of 2 0 mm Both the pm and ware! specnnens were cleaned with ethyl alcohol or benzene in an ultrasonic bath before each e×perunenl

T R I B O L O G Y international

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the presence or absence of gas molecules in the environment The presence of surface films on the shdmg surface masked the true characterIsUcs of surtaces, therefore the influence of particular metals on the friction behavIour appeared weaker m a,r than in vacuum

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In the friction ot sihcon the most distinctive behavlour was the difference in filCtlon between the cases of transition metal contacts and nontransltlOn metal contat.ts Silicon ~s well known as a highly polarizable semiconductor, and, m particular, it has a strong chemical affinity for transmon metals Because ot this charactensUc the transition metals are expected to produce strong interracial bonds at.ross a metal-silicon interlace As a result of the strong bonding with slhcon the transition metals give relatively higher lrlctlon than nontransmon metals m sliding contact with silicon It is worthy of note that the value of 0 2 lor silver

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Fig 2 S t i c k - slip m o t i o n J o r s u t t o n m sliding c o n t a c t w i t h p l a t i n u m m a v a c u u m o 1 2 0 x 1(I -7 Pa h)ad P = 0 1 A shdlng s p e e d v = 0 2 n z m / s 08 To

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Results and discuss=on F n c t m n w i t h slhcon

T h e , a l u e s ot coefficient ol hictlon at a load of 0 1 N in a vacuum ot 2 0 × 10 -7 Pa and m an are summarized m Table I Sttck-shp motion was lound for all metals when the3, slid on sihcon except for the two nontlansitlon metals in air Fig 2 shows a t3,pical tiace ot the lnction fmce during shdIng lot platinum in shdmg contact with slhcon m vavuum In Table 1 the coethcients ot hlctlon listed are tire maximum and minimum ~alues cak.ulated In eacta hlction have as s h o w n l n Fig2 T h e c o ~ i e l a t i o n o t hictlon ~.oet h~aents w~th load lot seven metals shd on the StilL.On (111) ~urlat.e m an IS piesented m Fig 3 The ~.oelh~.ients ot hi~.tlon plotted m Fig 3 are the ma×lmum ~alues of the Illctlon lolce in each ht~.tlon trace because the stick of ~tl~.k slip tepiesents the bonding T h e i e s u l t s l n fable 1 and Fig 3 indicate that the hi,.lion on stilton was sensitive to the ~_ontactmg metal Titanmm caused the highest IilitlOn among the seven metals V~lth the othe~ fotll hans> non metals -- tantalum nickel palladium and platinum coeH~cients ol friction wele lowm than titanium The two nontransitton metals p~esented vmy tow lrtcUon In shdmg contact with sdtcon This influence of the natute of the contacting metal on the fncUon behaviotu did not change m vacuum and m air, although the dillerence ol the friction m the contacting metals was more pronounced in va~.uum than in au because of the absence of gas molecules in the environment to chemtsorb and/or torm sutlace films Since setmconductors and transition metals have a high activtty tor chemtsorptton o1 gas mole~.t, lea, the experimental iesults foz these matermls weJe greatl'~ altected by

78

f ) g 4 Wear trac h (m the sUu o n uofa~ e ariel ~hdmg , o t z t a c t with n t a / u u m m a z,acuum o / 2 0 × 1 0 - 7 Pa, P = 0 1 A v = 0 2 m m / s (a) S F M (h) Tt - h ~ m a p

A p r i l 88 V o l 21 No 2

M~shma - f r i c t i o n a n d wear o f s e m i c o n d u c t o r s on p u r e metals

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Fig 5 Correlation between coe/fictent of friction and S c h o t t k y barrier height ]or sthcon, P = 0 1 N, v = 0 2 m m / s tn vacuum (o) and 1 4 m m / s m air (~) Table 2 Coefflc,ent of fr,ctmn for metals m shdmg contact w,th gallium arsenlde at a load of 0 1 N m a vacuum of 2.0 × 1 0 - 7 Pa and m air

Metal pm

mdmm mckel copper silver

In vacuum

In a~r

mammum

mm,mum

maximum

ram,mum

32 13 10 0 91

12 0 7 0 51 0 50

0 0 0 0

0 30 *<<-

38 23 18 17

and copper in sliding contact with silicon is extremely low for frlctmn under dry shdmg conditions - the coefficient of friction for m e t a l - m e t a l contact is usually 0 4 - 1 2 under clean conditions One typical surface change during sliding is shown in Fig 4 Fig 4(a) shows a scanning electron mlcrograph of a wear t~ack on a slhcon surtace when the silicon slid on the ntanmm m vacuum Because of strong bonding at the Interlace ,ausmg a high coefficient of friction, many pamcles were removed from the surface and might be found on the weal tJack Fig 4(b) is a T I - K ~ map of such particles measured by energy dispersive X-ray analysis The observation Indicates that the debris on the wear track on silicon was not metallic tltanmm particles as expected, but silicon The debris had been initially removed from the original sd~con surface and then subsequently backtlanslerred to the slhcon surface The metal surface, in contrast sulfered httle damage, and a small amount of transfer ol slhcon was detected Similarly, silicon particles were observed on the wear track of the slhcon surface attel the slhcon contacted with other metals This characteristic of the sm lace changes on silicon was commonly observed m the wea~ expermlents for the rubbing of silicon and metals in an 7'8 It is especially lntelestlng that in the silicon metal contact, particles were preferentially removed from the covalently bonded sdlcon surface compared with the metal surface in vacuum and in air This is considered to be a result of the brittle character ol silicon and the strong adhesion occurring at the Interface

TR I BOLOGY international

Results in this investigation indicated that the friction o f sihcon m sliding contact with several metals is affected strongly by the contacting metal To determine the properUes characterizing the friction o f semiconductors in shdlng contact with metals, one physical property at the s e m i c o n d u c t o r - m e t a l interface shall be considered m this paper In the previous paper 9 the formatmn of semiconductmg materials on the surface was recognized by the measurement of a current-voltage characteristic on the surface ot a zinc disk after the rubbing ot an alummmm and zinc couple In that case, ohmic contact was made to give a diode character at the interface between the semlconductmg materials and metal If ohmic contact is made at the s e m i c o n d u c t o r - m e t a l interface during friction behavlour, the physical properties at the interface, especially Schottky barrier height, will be expected to have an Important effect on the friction behavlour when a metal shdes on the semiconductor As a typical effect of physical properties at the interface on the trlbological behavlour, the relation between the coefficients of friction at a load of 0 1 N m vacuum and air and the Schottky barrier height ~9-2i is shown in Fig 5 The relation between coefficient o f friction and Schottky barrier height appears to be divided Into two groups according to whether the contacting metal is transition metal or nontransltxon metal As discussed above, nontransmon metals have very weak affinity with silicon, hence the friction behavlour is very different from that o f transition metals, and the friction ol copper and silver is far lower than that of transmon metals As for the five transition metals used in this investigation, their chemical and metallurgical characteristics toward sihcon are, fortunately, qmte similar to each other le they have a eutecnc phase, and they form one or more compounds with slhcon 13,14 Hence, the friction behavmur ol these transition metals is considered to be simply dependent on the barrier height at the Interface The results indicate that metals wlth a higher barrier height on slhcon give lower friction Although some other physical and chemical properties at the s e m i c o n d u c t o r - m e t a l lnterthce will affect the friction of semiconductors, it ts assumed that the b a m e r height IS one of the most significant factors to characterize the friction behavlour of semiconductors It is reasonable that the coefficient of trlctlon is influenced by the barrier height at the interface, if the relation between the tormatlon energy of metal slhclde and the barrier height lor transition metals is considered ~3 That is, a high barrier height at the interface will prevent strong bonding of two materials, and hence it will result m low frlcuon Friction with gallium arsenide

The values o f coefficient of trzctzon for radium, nickel,

copper, and silver an shdlng contact with the gallium arsenlde (100) surface at a load of 0 1 N in a vacuum of 1 0 × 10 -7 Pa and in air are summarized in Table 2 Since a s t i c k - s l i p motion was observed in the lrlctlon trace for all metals in vacuum and for Indium in air, which IS similar to the observations for silicon (Fig 2), maximum and mlnunum values are listed ,n the table In Fig 6 the maximum values of coefficient of friction are plotted against load for the case ot metals sliding on gallium arsenide Ln air As In the case of slhcon, the friction behavlour of gallium a~senide depended on the contacting metal The coeffiment ot friction for mdmm was the highest among those of the four metals in vacuum and

79

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Ftg 8 Correlation between coeJjtctent oj ¢rtctton and S c h o t t k y barrter hetght f o r galhum arsentde, P = 0 1 N v = 0 2 m m / s m vacuum (o) and 1 4 m m / s m atr (*) in air With copper and sliver, the coefficients of friction were lowest and there was httle difference between the two The fncUon was even lower wxth all metals when less load was apphed m air The effect of the contacting metal on frlcUon for galhum arsemde in vacuum was similar to the results obtained in a~r A typical surface change of the galhum arsenlde during friction in vacuum when radium shd on the galhum arsemde is shown in Fig 7 The surface of gallium arsenlde was different from that of silicon On the wear track a large quantity of parUcles was found By energy dispersive X-ray analysis, shown m Fig 7(b), the pamcles were determined to be transfer particles from radium Since Indium is a very soft metal with low shearing force, the shear of the junctmns caused by the tnCtlOn force occurred preferentially within the indium, which was then transferred to the galhum arsenlde surface For the other three metals mckel, copper, and silver - m shdmg contact with galhum arsenlde, httle damage occurred to either surfaces of metals or gallium arsemde, because of weak lnterlaclal bonds

r

Ftg 7 Wear track on galhum arsentde surJace alter shdmg contact wtth mdtum m a vacuum oJ 2 0 x i 0 - 7 Pa, P = 0 1 N, v = 0 2 m m / s {a) SEM (b) hl-Kc~ map

80

As discussed for the friction behavlour of silicon the coeltlcxent o f friction of galhum arsemde was also examined in relaUon to the Schottky barrier height 22 The relation between the coefficient of friction and the Schottky b a m e r height is shown m Fig 8 for ~our metals shdlng on galhum arsemde at a load of 0 1 N in a vacuum of 1 0 x 10 -7 Pa and m air As shown In the figure, the coefficient ol friction for the galhum arsemde was dependent on the barrier height at the interface mdmm, with the lowest b a m e r height, gave the highest coefficient ot friction, and silver exhibited the lowest frlctmn as a result of its hagh barrier height It is important to note that the friction behavlour in Fig 8 is not dependent on the hardness of the pin metals but on the b a m e r height Although ttus tendency is quahtatlvely similar for sliding in vacuum and in air, the effect of the contacting metals appears more clearly in vacuum because of the absence ol surface films Since a chemical characteristic common to the four metals is not known, the relaUon shown in Fig 8 is not hnear as In the case for slhcon in shdmg contact with transition metals, shown in Fig 5 The gallium arsemde has a higher b a m e r height at the interlace than silicon, hence, it generally exhibited lower friction than the slhcon although gallium arsemde has a weaker mechamcal strength than silicon

Aprd 88 Vol 21 No 2

M~shma - f n c t t o n and wear of semtconductors on pure metals

IO

C

|SIhcon Jwofers

J~,-S, O4

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0

02

04 Shdm9d~stance,krn

06

Fzg 9 Wear-&stance curves for tttanmm-sfl~con, m c k e l sthcon, and c o p p e r - sthcon m a ~'acuum oJ 1 0 x l O - Spa, P = 1 ON, v = 5 8 O m m / s Table 3 Spec=flc wear rate and coefficient of fnctmn for metals m shdmg contact w~th s=l~con at a load of 1 0 N mavacuumoflOx 10-s Pa Metal pm

tttamum mckel copper

Spec~fm wear rate, mm3/N mm

Coeffm~ent of friction

pm

sdmon wafer

maximum

average

7 l x 10 -7 1 l x 1 0 -8 2 5 x 1 0 -~

4 9 x 10 -v 47x 10-' 2 3 x 1 0 -~

30 23 12

21 14 10

Wear w~th silicon

The wear experiment was conducted tor slhcon in shdlng contact with tltamum, mckel, and copper to determine the effect o f the contacting metals These three metals were selected on the basis of the results of the fnctmn experiments t~tanlum had the highest coefficient o f friction, copper had the lowest coelflcient of friction, and nickel was intermediate Fig 9 shows the wear-distance curves for the three metals, where each metal pin slid on the sihcon wafer at a load of 1 0 N in a vacuum ot 1 0 x 10 -s Pa

In a pro-on-disk shdlng system the wear o f the silicon wafer was larger than that of the metal pm in all couples although salmon is harder than the metals The wear of silicon increased hnearly along the shdmg distance The wear behavmurs of the metal pins were shghtly different from each other The wear rate of nickel and copper decreased along the sliding distance whereas titanium gradually increased as sliding continued In Table 3 the specific wear rates of pin and sihcon are summarized after a shdxng distance of 622 m in a vacuum of 1 0 x 10 -s Pa The klneUc coefflments of friction are also hsted in the table As shown in Fig 9 and Table 3 the wear of sdlcon was dependent on the pin material The wear o f sdlcon was largest in contact with tltamum, and lowest in contact with copper The wear of silicon m shdmg contact with mckel was very slightly less than that in contact with tltamum The influence of pm material on the wear of sdlcon was very slmdar to that on the fnctmn behavtour of silicon The wear of the metal pins did not show the same effect as that of the silicon water, however the difference m wear among the three metal pros was not so significant, because the wear volume ot the plns was much less than that of sihcon Fig 10 shows micrographs ot the shdmg surface ot the sthcon after the metal pins slid 622 m on the silicon wafer Mlcrographs el the shdmg surface of the metal pros are shown in Fig 11 According to the results of the w e a r distance curve in Fig 9 the surface change during the wear process was largest for the couple el uranium and silicon - large amounts o f transfer particles adhered to the surface ot the sdtcon and the titanium pin For the surfaces of the m c k e l - s l h c o n couple, slgmflcant transfer also occurred during wear Very smooth small transfer pamcles were observed for the c o p p e r - s i h c o n couple, corresponding to very low wear volume Considering the relation between wear and barrier hmght, it is assumed that the influence o f the contacting materials on the wear o f silicon ~s similar to that mferred from the friction experiments From these frlctmn and wear experiments on semlconductms in sliding contact with metals, the Schottky barrier height between the metal and the semiconductor is considered to be a s~gmhcant characteristic lor the t~ibologlcal behavlour of sem~conductms

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mUml Fig 10 Wear trat k on silicon surfa~es aJter shdlng ~onta~ t with (a) tztamum (b) nickel (c ) copper m a L,a~uum o] l O x lO-S pa, P= l ON, v = 5 8 0 m m / s

TR I B O L O G Y international

81

Mtshma - f r t c t t o n and wear o f semmonductors on pure metals

Fig 11 Wear track o n (a) t l t a m u m , (b) nickel, (~ ) c o p p e r p i n surlaces alter s h d m g ~ o n t a c t w i t h sth~on m a v a c u u m o] 1 0 × 10 -s Pa, P = 1 07¢. v = 5 8 0 m m / s

Conclusions The tH~tlon and wear ot the s e m i c o n d u c t o r s silicon and gallium a r s e m d e in c o n t a c t with pure metals were studied The results o f the e x p e r i m e n t s in air and m vacuum Indicated t h a t the p r o p e r t i e s o f the m e t a l - s e m i c o n d u c t o r interface i n f l u e n c e d the friction a n d wear behaviour The fr~ctlon and wear o f s e m i c o n d u c t o r s were sensitive to the nature of the c o n t a c t i n g metals The e l i e c t o f the c o n t a c t mg metals on the friction and wear ol the s e m i c o n d u c t o r s was assocmted with the chemical a f f i m t y and the S c h o t t k y barrier height b e t w e e n metal and s e m i c o n d u c t o r s

9

10 11

Mort N F The theory of crystalrectlhers Pro~ R Soc l o n d o n 1939, AI71 27

12

Bardeen J Surface state and rectlhCatlon at a metal semiconductor contact Phls Rev, 1947 71 (10) 717

13

Andrews J M and Phllhps J C ( hemlcal bonding and structure of metal-semiconductor interfaces Phvs Rev Lett 1975 35(1) 56

14

Ottavtam G , Tu K N and Mayer J W Interracial reaction and Schottkv barrier m metal-slhcon systems Phvs Rel l e t t 1980, 44 (4], 284

15

Ho P S Chemical bonding and Schottky barrier tormatlon at transition metal-siheon surfaces J t ac S~I Te~hnol 1983 AI (2), 745

16

McGmre G E Lttects ol ion sputtering on semiconductor surtaces Surf S~t, 1978 76, 130

17

Mark P , Planetta P , Lmdau I and Sptcer W E A comparison of I FI D intensity data trom chemically pohshed and cleaved (,aAs (110) surfaces Sur] Set 1977, 69 735

18

K u b l e r B , R a n k e W andJacobJK L L E D a n d A I S o l stolch]ometric and arsemde-rlch GaAs (110) surtace prepared by molecular beam epitaxy Sur] Sct 1980 92 519

References 1

Sikorskl M E The adhesion ot metals and tactors that lnfluent.e it Wear 1964 7 (2) 144

2

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MIshma H and Sasada T Mild wear occurr|ng in pure-metal/ semiconductor rubbings In Proc 25th Jpn Congr Mater Res, 1982, 139 Mishma H and Buckley D,H .friction behavior o] sth~on m contact with titanium, nickel sdver, and copper NASA TP 2362 1984

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8

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April 88 Vol 21 No 2