Joshi, Mihir J

Raval, Amit H

Shah, B S

IACS Institutional Repository

Indian J. Phys. 70A (5), 569-573 (1996)I J P  A— an international journalT h e  e ffe c t  o f  co m p o sit io n  o f  e tch a n ts  on  rea ctiv ity  at lin e  d e fe c ts  in  a n tim o n yA m it H R avai, M ihir J Joshi and B S ShahSolid State Physics & Materials Science Lahnmtniy. Department of Physics, Saurashtru University, Rajkot-360 005, Gujaiai, IndiaReceived 15 January 1996 accepted 12 Februai v !996Abstract : The (111) cleavages of antimony single ciystals were etched in the etchants containing citric acid, nitric acid and distilled water Two different types of etching solutions were selected, in one type of etchant, the composition of citric acid was increased systematically, whereas in the othei type of etchant, the composition of citric acid was increased and at the same tune the composition of nitric acid was decreased correspondingly to maintain the total composition constant The values of activation energy and frequency factor were calculated using Arrhenius law The activation energy and the frequency factor vaiy in a different manner in both types of etchants The results are explainedKeywords : Etchants, liiie defects, activation eneigy PACSNo. : 61 12 P1 . I n t r o d u c t i o nConsiderable interest has been shown by various experimentalists to study the dislocationetching on ( 111)  c le a v a g e s  o f  antim ony [ J-3J. R ecently . Ravai and Joshi [4] studied theetch ing  o f  an tim ony c le a v a g e s  in citric acid  conta in ing  etchants and Ravai e t a l  [ 5 1 withdextro tartaric and iev o  tartaric acid contain ing etchants. It is usually d ifficu lt to d evice anysim ple c la ss if ica tio n  for the com p on en ts in the d islocation  etchants. Broadly speaking, theetch in g  so lu tio n  can  be o f  the fo llo w in g  nature : (1 ) T he prim ary requirem ent is ano x id is in g  s y s te m  to provide a therm odynam ic ‘driving force' to d isso lve  metal. The drivingforce is measured I v the oxidation potential and which can he controlled by various ways,such as, the choice and on ‘nuation o f the oxident and concentration ol the auxiliaryreagents, /.<\, com p lex  ing agents. (2 ) V arious factors can influence differently the e ficct olthe ox id a tiv e  driv ing  force  on d ifferent reg ion s o f  the surface by controlling the activationen erg ies o f  d sso lu tio n . D ifferen tia l adsorption  is an important factor and the ch o ice  ofsubstances used  in the o x id is in g  system  w ill depend on fheir adsorption behaviour.(c; 1996 1 ACS570 Am it H Raval, Mihir J Joshi and B S ShahIn this study, the authors have chosen various concentrations o f  nitric acid and citric acid in the etchant in order to study the role o f  different com ponents in the etchants.2. Experimental techniques and resultsS in g le  crystals o f  antim ony w ere grow n hy m odified  C halm er’s technique w hich is described in detail elsew here [61. M etal o f  99.999%  purity w as obtained from Nuclear Fuels C om plex, Hyderabad, India. Many crystals were grown under temperature gradient o f  92° C /cm  and growth velocity  o f  1.5 cm/hr. The crystals were cleaved at liquid nitrogen temperature in conventional way.T w o different sets o f etchants w ere selected . In Etchants f A h  the com position  of nitric acid and distilled water was kept constant and citric acid com position w as increased;V0Vd\ C o m p to n  Vte cYctotvv tev* WMWUHVV yVk citric acid com position was increased and at the same tim e, vYie m u te  compowwon wasOicv^ y c a s c v N \ u  c e \ u a \  a m o u n V  M \  \Y v c  c V c Y v a n V S  p r o d u c e d  U V A W ^ u V & Y  C T ^ S V d W o v i t ; \ p \ \ \ C A \ \ \oiicntcd etch pits revealing (1 11) [ 1()T| type dislocations. Table I shows the composition of etchants used.Tabic 1. The values of activation energy and frequency factor for different ctchanisComposition Etching Activation f-ri i|Etchant ol etchants time energy hktinseconds eV niiAtx8 c c Citnc Acid + 75 1 16 1 XX X 10"A Ic c  HNO^ +1 c c distilled H 2O9 c c Citnc Acid + 105 0 73 7 70 a 10s3 c c  HNOi *t e c  distilled H2O10 cc  Citric Acid + 3 0 0.46 4 42 x 10-U c UNO*+1 c c  d is ti l le d  H 209 c c. Citric Acid + 105 0 73 7.70 x I053 c C. HNO3 +1 c c distilled H2O9.5 c c Citric Acid + 26 0.63 1.77 x 10s2.5 cx HNO^ +1 c c distilled H2O10 c.c. Citric Acid + 75 0.74 8.84 x I062 c.c. HNO3 +l c c distilled H >()T h e  e f f e c t  o f  c o m p o s i t i o n  o f  e t c h a n t s  o n  r e a c t i v i t y  e t cPlate IFigure 1. Photomicrograph showing the type of etch-pits produced on (111) cleavage plane of antimony single crystals by etching in the etchant containing 8 parts citric acid, 3 parts nitric acid and 1 part distilled water at 45°C for 75 sec. etching time.The etching was carried out from room temperature to 55°C. It was also confirmed through various tests that these etchants revealed dislocations |7|. Figure I shows the typeof etch pits produced by etching in the etchant containing 8 parts citric acid + 3 pans nitric- acid and I part distilled water at 45°C.The activation energy for lateral motion of ledges and the frequency factor can he found out by Arrhenius law [4]. Figure 2 shows the plot of logarithm of average width of etch pits W, versus the reciprocal of absolute temperature 1 IT, for the etchant containing 8 parts citric acid, 3 parts nitric acid and 1 part distilled water. The values of activation energy and frequency factor are listed in Table 1 for different etchants.3. DiscussionO&S I^J experimentally confirmed the conclusions of James and Turnstall [9] that the unit rhomb of antimony is 6.20 A. The structure consists of two interpenetrating face-centered lattices. The shortest distances between the centres of the two atoms was found to be 2.92 A.. Lamport and Rcichclt [ 10] described the crystal lattice of antimony having point groupEtchont: 8 Citric dcid+3HN03«* IH2OThe effect o f composition o f etchants on reactivity etc 5 7 13*10 3-12 3 *U 3*16 3*18Figure 2. A plot of logarithm of average width of etch pit W \cr \u \ 1/7' foi the etchant containing 8 parts citric acid, 3 parts nitric acid and I part dnrtilled watet572 Amit H Raval, Mihir J Joshi and B S ShahR 3m  and it is isomorphous to arsenic. They have illustrated the rhombohedral and hexagonal unit cell of antimony with the lattice consisting of double layers of atoms vertical to the [111] directions. Each atom has three next neighbours in its own double layer and three second next neighbours in the adjacent layers. Atoms within the hexagonal plane are third next neighbours. Within the double layers, the bonds between the antimony atoms are mainly covalent, whereas between neighbouring double layers. Van der Waal bonds prevail.The growth and dissolution of crystal is due to advance or retreat of monomolecular steps on the surface of the crystal 111]. The active sites are the places along the steps where single molecular rows end. These are known as ‘kinks’, where individual molecules can be deposited or removed. When a perfect face is exposed to a solvent, dissolution probably starts by the nucleation of unit pit of one molecular depth. These unit pits grow as steps retreat across the crystal through the action of kinks. This process is discussed in detail by Gilman e ta l[  12].Rosenblatt and Lee [13] and Rosenblatt 114] reported the vapourization behaviour of antimony and found that the vapour of antimony is composed of mainly Sb4. The rate of antimony vapourization was found to be limited by the rale of kink initiation in straight­edge segments, but where the kink initiation rate was rapid enough compared to the rate oi the kink motion and to the length of the ledges so that the number of kinks initiated along a given length of the ledge was proportional to the length of that ledge. Angus and Dyble [ 15] proposed an etching model for (111) diamond surface, which includes the ‘multiple kink mechanism’. Results of Lampert and Reichelt [10] corresponds to that of Rosenblatt and Lee [ T3].I Table 1 shows that in Etchants (A), as the composition of citric acid increases in the etchants* the values of activation energy and the frequency factor decrease. The activation energy can be thought of as a barrier to the reaction, therefore, the greater is the activation energy, slower is the rate of reaction. Hence, the increase in the composition of citric acid suggests faster rate of reaction. The values of the activation energy and frequency factor differ from the earlier cited values [4] due to non-consideration of. etch pits not corresponding to dislocations.From Table 1, it is seen that in Etchants (B), the total composition of the etchants is maintained constant, i.e., as the citric acid composition is increased, the composition of nitric acid is decreased accordingly. Increasing the concentration of citric acid decreases the activation energy and the frequency factor, thereafter again the values of activation energy and frequency factor increase with citric acid composition. This indicates the presence of a critical point which shows a deviation in the normal trend of reaction. This behaviour was reported in bismuth by Shah et al [16,17] and recently by Raval et al [5] in antimony. The nitric acid is serving as an oxidising agent in the composition of the etchants [18|, the variation in its composition seems to modify the kink kinetics in the ledges within theetch-pits which has been reported earlier by Shah et al [16], responsible for deviation in thenormal trend in Etchants (B).4. Conclusions(1) All the etchants reveal dislocations of (111) [lOl] type.(2) Increasing the composition of citric acid in the etchants (Etchants-A), the activation energy and the frequency factor decrease suggesting a lower barrier to be surmounted to form products and hence higher the reaction rate.(3) Increasing the composition of citric acid and decreasing the composition of nitric acid in the constant composition of etchants (Etchants-B), a critical point is observed where a deviation in normal behaviour is observed which corresponds to the earlier results in bismuth and antimony. This suggests that a specific composition of nitric acid is responsible for this behaviour with comparison to Etchants-A. This further suggests a modification in kink kinetics in die ledges within the etch pits.A cknow ledgm entThe authors are thankful to Prof. R G Kulkarni for his keen interest.T h e  e f f e c t  o f  c o m p o s i t io n  o f  e tc h a n ts  o n  r e a c tiv i ty  e tc  573References111 J H Wcrmk, J H Hobstetter, L C Lovell and D Dorsi J. Appl. Phys. 29 1013 (1958)[21 V M Koscvich Sov Phys Crystalloxr 5 715 (1961)131 R Vijayavallis and R Kruse J. Electrochem. Soc (India) 22(4) 343 (1973)|4] AH Raval and M J Joshi Indian J Phys 68A 113 (1994)|S| AH Raval, M J Joshi and B S Shah Cryst Res Techno! 30 1003 (1995)|6| B B Thaker and B S Shah ( n s t AYs, Tec final 21 189(1986)17] S Amehnckx The Pi eu  Ol'\c vanon aj Dislocations (New York Academic) p 21 (1964)[S’ AOw P I u l  Man 42 lMiF>2L,[c I R W James and N T\install Pntl Man 40 p 233 (1920)110] B Lampert and K Reichclt J Crvst Growth 51 213 (1981)111! W K Burton, N Cabrera and F C Frank Phil Trans Roy Soc (London) A234 299 (1951)1121 J J Ci;lman, W G Johnston and G W Sears J Appl Phys. 29 747 (1958)113] Ci M Rosenblatt and P K Lee J Chem Phys. 52 1454 (1970)114] G M Rosenblatt 'Surface and Defect Properties of Solids' Vol 5 eds. M W Roberts and J M Thomas (TheChemical Society, London) p 36 (1976)I > 5] J C Angus and T J Dyble 50 157 (1975)116J B S Shah, M J Joshi and L K Maniar Latin Am J. Met. Mat 7 48 (1987)117] B S Shah, M J Joshi and L K Mamar Cryst. Uitt Dej Amorph. Mat 17 417 (1988)118] J W Faust (Jr.) Reactivity of Solids' eds. J W Mitchell et al (New York . John Wiley) p 337 (1909)

The Effect of Composition of Etchants on Reactivity at Line Defects in Antimony

http://arxiv.iacs.res.in:8080/jspui/bitstream/10821/4994/1/The%20Effect%20of%20Composition%20of%20Etchants_%20By%20Amit%20H%20Raval.pdf

The Effect of Composition of Etchants on Reactivity at Line Defects in Antimony

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