The presence of small quantities of sulfanilamide in a highly purified acidic CuSO4 electroplating bath alters the growth habit of Cu on a single-​crystal Cu(110) plane.  At a given c.d. a transition from a ridge type of growth to broken ridgesand then to polycryst. growth was obsd. with increasing sulfanilamide concn. andthis mechanism was discussed using η vs. log i curves.  These effects were attributed to complex formation, decomplexation and the adsorption of sulfanilamide

Nageswar, S.

Subramanian, K.

ePrints@Bangalore University

Surface Technology, 11 (1980) 83 - 90 83 ( Elsevier Sequoia S.A, Lausanne Printed m the Netherlands THE EFFECT OF SULPHANILAMIDE ON THE ELECTRO- CRYSTALLIZATION OF COPPER ON A SINGLE-CRYSTAL Cu(ll0) PLANE K SUBRAMANIAN and S NAGESWAR Department of Chemtstry, Central College, Bangalore Umverstty, Bangalore 560001 (India) (Received October 11, 1979) Summary The presence of small quantit ies of su lphamlamide m a highly purified acidic copper sulphate e lectrop latmg bath alters the growth habit  of copper on a single-crystal Cu(110) plane At a given current  density a t rans l tmn from a ridge type of growth to broken ridges and then to po lycrysta lhne growth is observed with increasing su lphamlamlde concentratmn.  The mech- amsm of the deposltmn process m the presence of su lphamlamide is dis- cussed using ~ versus log z curves. These effects are attr ibuted to complex formation, decomplexatmn and the adsorpt ion of su lphamlamlde 1. Introduct ion The mechamsm of e lectrocrystal l izat lon has been made general ly more comprehensible by the theoret ical  and exper imental  invest igat ions of recent years (e.g. by Gerlscher [1] and Bockrls [2]) The study of the mechanism of crystal  growth under e lectrocrysta lhzat lon condit ions can be divided into two stages. The first stage deals with the kinetics of deposit ion when the surface of the substrate is not changing, z.e when only a monolayer  of metal  is de- posited. Conway and Bockr~s [3] have suggested that  metal  electrodeposlt lon occurs in three steps. (1) charge transfer  to give part ia l ly  hydrated adlons, (i0 surface diffusion of the adions; (hi) the incorporat ion of the adions into the cathode surface at k ink sites. It  has been shown [4] that  when copper ~s deposited onto a copper surface the rate-determining step is surface dlf fusmn at low current  dens~tles and charge transfer  at higher current  denslhes. The rate equatmn for the charge transfer  process is then z--Zo exp -~T] -exp[  RT  ]~ (1) 84 For ~7/> 50 mV eqn. (1) becomes [3~ F~I =z oexp-  RT (2) wh;ch is the Tafel equation -~l = a+b logz where fi, F, q, R and T have the usual meanings. The second stage ;s the study of crystal  growth dur ing prolonged deposition, ~.e. e lectrocrystal l izat lon Damjanovlc  et al [5] have shown that  the rate-determining step does not change dur ing the prolonged deposit ion of copper onto copper single-crystal faces from a highly purified bath and also that  the rate equation (eqn (1)) holds good Addit ion agents added to e lect rop latmg baths to give enhanced physl- cal propert ies (brightness, smoothness, internal  stress etc.) usual ly increase cathodic polarization. We can therefore evaluate the kinetic parameters  from the Tafel relat ion If  the kinetic data are correlated with the result ing crystal  morphology it may be possible to understand the role of the addlUon agent  in crystal  growth at the cathode Barnes [6] and Turner  and Johnson [7] have invesUgated the effect of addl tmn agents (sulphur compounds) on the klnet;cs of electrodeposit ion and the morphology of electrodeposits. in the present invest igat ion we studied the effect of su lphamlamlde on the morphology and klneUc parameters  of copper deposited from an acidic copper sulphate bath onto a single-crystal Cu(l l0) face. We observed a tran- s;t lon from mdges to broken ridges and then to a po lycrysta lhne deposit 2. Exper imenta l  A single-crystal Cu(110) plane grown m the [110] or ientat ion was used. The omentat ion was confirmed by etching techniques. A single-crystal cop- per cathode was fixed in Tygon tubing so that  only the (110) face of the crystal  was exposed. The (110) plane was first mechanica l ly  pohshed to- gether with the Tygon tubing using 3/0 and 4/0 emery papers with ethanol  as lubricant. It  was cleaned with ethanol,  was washed with running dlstdled water  and was e lectropohshed 18] in a 50% orthophosphor lc  acid bath at 1.2 V for 30 mm with a large copper cathode. The crystal  was removed from the acid soluUon w;thout switching off the current,  was washed first with 10% orthophosphor lc  acid and then with tr iply d;stflled water and was immediately t ransferred to the deposit;on cell !9] An AnalaR copper foil with an area 40 Umes greater  than that  of the cathode was used as the anode. A freshly prepared copper electrode was used as a reference lectrode. The bath consisted of highly pumfied 0.25 M CuSO4 and 0.1 M H2SO 4 to which a known amount  of sulphanl lamlde was 85 added as required, and deposit ion was carr ied out at 2, 5, 10 and 15 mA cm-2 to a copper thickness of 3.6 ~m with a coulombic charge of 10 C cm-2 on the copper single-crystal  (110) plane. The cathodic overpotent la l  dur ing the deposit ion was accurate ly  measured using an Elico digital pH meter  with an accuracy to + 5 mV. The surface morphology of the copper deposit on the single crystal  was examined by phase contrast  microscopy at a magni f icatmn of 625×, and microphotographs were taken. 3. Results  3 1. Surface morphology 3.1.1. At 2 mA cm-2 As reported by earl ier workers [10], ridges al igned m the [100] direction were observed when copper was deposited onto the (110) face from pure solut ion (Fig 1). When the concentrat ion of sulphanl lamlde m the bath was 10 -12 mol 1 1 distorted ridges al igned in the [110] direct ion were obtained (Fig. 2). An increase in the concentrat ion to 10 10 mol 1-1 produced broken ridges (Fig. 3). At 10-s mol 1-1 small thread-l ike broken ridges were obser- ved (Fig. 3) which at 10 7 mol 1 i were becoming polycrystal l ine (Fig. 4). At 10-6 mol 1 1 po lycrysta lhne growth was observed (Fig. 5). Fig. 1. A ridge type of growth depos,ted onto Cu(ll0) from pure acidm copper sulphate solution at 2 mA cm-2 (Magmfication, 500 × ) Fig 2. A distorted mdge type of growth deposited onto Cu(ll0) In the presence of 10 12 tool l- 1 sulphamlamlde at 2 mA cm 2 (MagnlficaUon, 500 × ) 3.1.2. At  5 mA cm 2 A fine ridge type of growth al igned in the [100] direct ion was observed at 5 mA cm -2 in the pure acidic copper sulphate bath (Fig. 6). At a con- centrat ion of 10 12 mol 1-1 sulphani lamide broken ridges al igned in the [100] direct ion were obtained (Fig. 7) and on increasing the concentrat ion to 10-1° mol 1 '-1 small thread-l ike ridges appeared (Fig. 8). At 10 s mol 1-1 larger i r regular  ridges with pyramids were observed (Fig. 9). A further  m- crease in the concentrat ion to 10 7 mol 1 1 produced large broken ridges 86 Fig 3 Thread-hke  broken  mdges  depomted onto  Cu( l l0 )  m the presence  of  10 8 mol 1 su lphamlamlde  at 2 mA cm 2 (Magmf icat lon ,  500 × ) F ig 4 The  rMges  chang ing  to a po lycrys ta lhne  growth  on Cu( l l0 )  m the presence  of  10 mol 1 ~ su lphamlamMe at 2 mA cm 2 (Magmf icatmn 500× ) F ig 5 A po lycrys ta lhne  depomt  grown on Cu( l l0 )  m the presence  of  10 6 mol 1 1 su lpha-  mlamlde  at  2 mA cm 2. (Magmf icat lon ,  500 × ) F ig  6 A mdge type of  g rowth  depomted onto  Cu(110) from pure acidic copper  su lphate  so lu t ion  at 5 mA cm 2 (Magn l f i ca tmn,  500 × ) F ig  7 Broken  r idges ahgned m the  [100] d i rect ion  grown on Cu( l l0 )  m the presence  of  10 12 tool 1 1 su lphamlamlde  at 5 mA cm 2 (Magmf icat lon ,  500× ) F ig  8 Smal l  th read-hke  mdges  depomted onto  Cu( l l0 )  in the  presence  of 10 ~ mol l  su lphamlamlde  at 5 mA cm 2 (Magmf ieat lon ,  500 × ) 87 (Fig.  10). A t  10-  ~ mol  1 1 the  broken  r idges  were  becoming  po lycrys ta lhne  (cf. Fig.  4) and  at  10 5 mol  1 1 a fu l ly  po lycrys ta l l ine  depos i t  was  observed  (cf. Fig.  5). Fig 9 Large irregular idges grown on Cu(110) m the presence of 10- 8 mol 1 1 sulphaml- amlde at 5 mA cm 2 (Magmficatmn, 500 × ) Fig 10 Larger broken ridges grown on Cu(ll0) m the presence of 10 7 mol 1 ~ sulphaml- amlde at 5 mAcm 2 (Magnlficatmn, 500 × ) 3.1.3. At 10 mA cm-2 In  pure  so lu t ion  a r idge  type  of g rowth  m the  [110] d i rec t ion  was  obser-  ved. When the  concent raUon of su lphamlamide  was 10 12 mol  1 1 there  was no  change in  the  growth  habxt.  On  increas ing  the  concent ra t ion  t  10 11 mol  1 1, s l ight ly  b roken  r idges  were  obta ined  (Fig.  11) wh ich  were  com- p le te ly  b roken  at  a concent ra t ion  of  10 10 mol i  1 su lphan i lamide  (Fig.  12). A t  10 s tool 1-1 a la rge  number  of rec tangu lar  pyramids  were  observed  (Fig.  13). An  increase  in  the  concent ra t ion  t  10 6 tool 1 -1 produced la rger  b roken  r idges  (F ig  14). A t  10 5 mol  l -  1 the  depos i t  was  po lycrys ta l l lne  (cf. F~g. 5). Fig 11 Shghtly broken r,dges grown on Cu(ll0) m the presence of 10 11 mol 1-1 sulpha- mlamlde at 10 mA cm-2 (Magmficatlon, 500 × ) Fig 12 Broken ridges grown on Cu(110) m the presence of l0 x0 mol 1 I sulphamlamlde at 10 mA cm 2 (MagmficaUon, 500 × ) 88 F~g 13 A large number of rectangular pyramids depomted onto Cu(110) m the presence of 10 s mol 1 ~ sulphamlam~de at 10 mA cm ~ (Magmficatmn, 500 x ) F~g 14 Larger broken ridges grown on Cu(l l0) m the presence of 10 " tool 1 ' sulphanll- amMe at 10 mA cm -~ (Magmficatmn, 500 × ) 3.1.4. A t  15 mA cm ~ In  pure  so lu tmn r idges  ahgned m the  1110] d~rect lon  were  observed .  There  was  no change m the  growth  hab i t  w i th  the  add l tmn of  10 '~ too! 1 su lphamlamide  to the  bath .  On  increas ing  the  concent ra t ion  t  10 '~ mol  1 l, shght ly  b roken  r idges  were  observed  (cf F ig  11) There  was  no mgm-  f i cant  change m the  growth  hab i t  for  a concent ra tmn of  10 " mo l  1 ~ but  at  10 s mo l  1 ~ broken  mdges  were  obta ined  (F;g.  15) An  inc rease  m the  concent ra tmn to 10 : mo l  1 ' p roduced  a th read-hke  depomt  (F~g. 16) A t  10 e mo l  1 1 the  r idges  gave  way  to po lycrys ta lhne  growth ,  and  at  10 ~ mol  1 ~ the  depos i t  was  po lycrys ta l l ine .  Fig 15 Broken mdges grown on Cu(110) m the presence of 10 s mol 1 i sulphamlamlde at 15 mA cm 2 (Magmficanon, 500x ) F~g 16 A thread-hke growth depomted onto Cu(110) m the presence of 10 7 mol 1 sulphamlamlde at 15 mA cm 2 (Magnification, 500 x ) 3.2. Overpotent ia l  The overpotent la l  on  the  (110) p lane  did not  change  w i th  t ime when copper  was  depos i ted  e i ther  f rom pure  so lu t ion  or  in the  presence  o f  a low concent ra t ion  of  su lphamlamlde  (10- 12 - 10 le mo l  1 ' )  at  a l l  cur rent  den-  s l t les  At  h igher  concent ra t ions  of  su lphamlamlde  (above  10 " mol  1 ')  89 there  was some increase  m the  overpotent ia l  at  al l  cur rent  dens i t ies  but  when the  concent ra t ion  of  su lphan i lamide  was h igher  than  10-s  mol  1 i the  change was not  regu lar .  In  pure  so lu t ion  the  s lope of  the  ~ versus  log i curve  was found to be 120_+ 5 mV and the  exchange cur rent  dens i ty  was 2.0 mA cm-2 .  A hnear  versus  logz re la t ion  was found at  lower  concent ra t ions  (10 -12 - 10 6 mol  1 1) of  su lphamlamide  (Fig. 17) and the exchange cur rent  dens i t ies  and the s lopes were around 1.7 mA cm 2 and 140 ± 5 mV respecUve ly .  However ,  at  very  h igh  concent ra tmns  (above 10 5 mol 1 ~) th is  re la tmn no longer  he ld  200 lOO ~ , ~  ,,- -~ lO ~ (a) c i  od 0 "" lO C urrent J 1 o 2 I o 1o2 (b) J , / "  ~o z 10 Density (mAlcm 2) (c) (d) F*g. 17. ~/ vs.  log 1 for copper deposited onto Cu(ll0) from an acidic copper sulphate bath containing various concentraUons of sulphamlamlde' (a) pure solution, b = 132 9 mV, to = 2.0 mA cm-2, (b) copper sulphate solution containing 10 ~2 mol 1 i sulphamlamlde, b = 142.9 mV, to = 1.7 mA cm- 2, (c) copper sulphate solution containing 10 ~o mol l  1 sulphanllamlde, b = 140 mV, l o = 1 7 mA cm 2 ; (d) copper sulphate soluhon containing 10 ~mol l  1 sulphamlamade, b=139mV,  z 0=17mAcm 2 4. D iscuss ion  The l inear  t /versus  log i re la t ion  ho lds  for low concent ra t ions  (10 12 _ 10 -6 mol  1-1) of  su lphan i lamide  in the bath ,  ind icat ing  that  charge  t rans fer  is the  ra te -determin ing  s tep  (Fig. 17). However ,  at  h igh  concent ra t ions  ofsu lphan i lamide  (above 10 s mol  1-1) the  Tafe l  behav iour  does not  ho ld  because  the  Tafel  l ines  do not  ref lect  the  ac t ive  t rans fer .  I t  is known [11] that  su lphur  compounds  are  spec i f i ca l ly  adsorbed  on the  sur face,  and  the  character i s tm morpho log ica l  changes  i  copper  depos i t s  can  be exp la ined  w i th  the  lp  of  F i scher ' s  adsorpt ion  theory  [12]. I t  has  been found [13] that  copper( I I )  forms a complex  (1:2) w i th  su lphan i lamlde  and  that  su lphan i lamide  is not  readaly  hydro lysed  by t reatment  w i th  bo i l ing  ac id  so lu t ions  [14]. Hence  the  su lphan i lamlde  forms a complex  in the  ac id ic  copper  su lphate  bath ,  and complexat ion  occurs  th rough the  amine  group  of  su lphamlamlde .  90 The formation of a copper su lphanl lamlde complex with copper ~ons suggests the non-ava i lab i l i ty  of su lphamlamlde  for adsorpt ion,  but dur ing the process of charge transfer  the metal  1on has to be freed from the hgands before it enters the tuner Helmholtz plane. At low current  densit ies there may be complexat lon and decomplexatmn near  the outer Helmholtz  plane but at h igher  current  densmes the complex may be adsorbed at the elec- trode. At lower concentrat ions  the deposmon process ~s fac ihtated,  however the complex may be prec ip i tated in the interface regmn at h~gher con- centrat lons  In pure solunon,  on the (110) plane the incorporat ion  of adlons along the [100] d l recnon requires less energy than the lncorporatmn of adlons along the [110] d l recnon 115] since the [100] row is less densely packed. At current  densit ies of 10 mA cm 2 and 15 mA cm 2 the overpotentxal is in- creased and the growth direct ion changes to [110]. This trend is mainta ined at lower concentrat ions  of su lphamlamlde  but at h igher  concentrat ions  random nuc leat ion  takes place, resul t ing m po lycrys ta lhne  growth. Acknowledgments The authors  wish to express thei r  grat i tude to Dr. J W. Young, Oak Ridge Nat iona l  Laboratory ,  Oak Ridge, Tennessee, U.S.A,  for the gift of the copper single crysta ls  and to the Univers i ty  Grants  Commission, New Delhi, for f inancial  ass istance The authors  are also grateful  to Professor G K N Reddy for his kind encouragement  and to Messrs. R L Sarma and G. Roopkumar  for helpful discussions References 1 H Genscher, Electrochtm Acta, 2 (1960) 1 2 J O'M Bockns, m E Yeager (ed), Trans Syrup on the Electrodeposmon Proce~, Wiley. New York, 1959, p 161 3 B E Conway and J O'M Bockrls, Proc R Soc London, 248 (1958)394 4 E Mattson and J O'M Bockns, Trans Faraday Soc,  55 (1959) 1586 5 A Damjanovlc, T H V Setty and J O'M. Bockns, J Electrochem Soc,  113 (1966) 429 6 S C Barnes, Electrochzm. Acta, 79 (1961) 169 7 D R Turner and G R. Johnson, J Electrochem Soc,  109 (1962) 798 8 P A Jacquet, Met Rev,  1 (1956) 157 9 S Nageswar and T H V Setty, Proc Indtan Acad Scl ,  Sect A, 67(1968)178 10 S Nageswar and T H V Setty, Curr Scz, 39 (1970)483 11 B S Sheshadn and T H V Setty, Indtan J Chem, 8 (1970) 162 12 H Fischer, Z Elektrochem, 54 (1950) 459 13 K K Narang and J K Gupta, Indtan J Chem, 13 (1975) 705 14 N L Allport, Q J Pharm. Pharmacol ,  9 (1936) 360 15 R Plontelh, Recherches ur l'Electrochtmte des Monocr~staux Metalltques, Conf h l 'Unwerslte Lzbre de Bruxelles, January 19, 1966, accord culturel Italo-Belge 

The effect of sulfanilamide on the electrocrystallization of copper on a single crystal copper (110) plane

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The effect of sulfanilamide on the electrocrystallization of copper on a single crystal copper (110) plane

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