Joshi, Mihir J

Raval, Amit H

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bdianl Pkys. 68A(1), 113-116 (1994)UP AliateiMliiiqaljoiinialStudy at dislocation etch pits in antimony single crystals by etching in citric acid containing etchantsAmit H Raval and Mihir J JoshiSolid State Physics, and Materials Science Laboratory«Department of Physics, SauFBshtra University, Rajkot-360 005, IndiaReceived 28 April 1993, accepted 1J August 1993Abstract : The (111) cleavages of antimony single crystals were etched in etchants containing 10 parts citric acid, 3 parts fuming nitric acid and 1 part distilled water. The etchant exhibited well-defined triangular etch pits at the sites of dislocations. The reactivity at line defects for lateral motion of ledges in the etch-pits and the frequency factor have been calculated for this etchant.Keywords : Dislocations, etchants, etch-pits, activation energy, frequency factor. PACS Not. : 61.70. Jc, 61.72. FfChemical etching is a valuable tool in revealing dislocations in crystals. Etching of antimony crystals have been attempted by many workers [1-7]. The earlier work was reported by Wemick etal {!] on antimony by etching in CP4, which had been used by Vogel etal [8] to show dislocations on the (100) and (1 11) planes of germanium. The Dash etchant [9], which is a modified CP4 etch was found to be a polishing agent for antimony without producing etch-pits. However, there are only few standard etchants available to etch antimony cleavages. In the present communicationanetchant has been developed consisting of aqueous mixtures of citric acid and mtric acid, which is found to be a fairly good etchant to reveal dislocations.Single crystals of antiinony were grown by Chahner's technique [10], which has been extensively discussed elsewhere by Thakar and Sfiah [11]. The metal of 5N purity obtained from Nuclw Fuels Complex* Hyderabad, India, was used. Several crystals were grown€>1994IACS114 Amit H  Ram i and M ihirJJoshiunder temperature gradient of 92° C/cm and growth velocity of 1.5 cm/hr. The cryshds were cleaved at Uquid nitrogen ten^terature in conventional manner.The etchant used to reveal etch-pits at the sites of dislocations consisted of 10 parts citric acid, 3 pans fuming nitric acid and one part distilled water. The etdumt produced Uiangular, crystallographically oriented etch pits, which revealed dislocations of the (111) [lOT] type. High temperature etching was performed by raising the temperature of the samples and etdtants to the required temperatures befoie etdiing. The etching uras carried out from room temperature to 55°C. It was confirmed through various tests suggested by Amelinckx [12] that this etchant reveals dislocation etch pits. Figure 1 is a photoipiciogi^h showing the types of etch pits obtained at 40“C for etching time of 30 seconds. Whereas, the Figures 2 and 3 are photomicrographs exhibiting* the etch pits at 45“C and 50°C.'From these photomicrographs one can see that the size of etch pits increases with the tempe^ture. Figure 4 shows the histogram indicating distribution of different size of etch pits anp their numbers at 40“C.Ca01E4 5 6Width of Etch Pit inF l i i t r c  4 . H istogram  show ing  di$tiibution o f  differen t size o f  e tch  p its in  the  observed  a m  on (111) cleavage plane o f  antim ony crystal a t 40^C .The activation energy for lateral motion of ledges were obtained by using an Airhenius type lawSttidy at dislocation etch pits etcPlat t  /Figure 1. Type of etch pits observed by etching (III)  cleavages of antimony at 40”C for 30 seconds.Figure2i T y p e  o f e tc h  p its  re v e a le d  by e tc h in g  (111) c leav ag es  o f an tim o n y  a t  45*C fo r  30 seconds*Amit H Raval and Mihir J JoshiHate IIFlgm  3. The large size etch pits exhibited on (111) plane of antim ony by etching at S0*’C for liO second.Wm Aex.p {-E/kT)where ly is the average width of etch piu, T the absolute temperature, k the Boltzmann constant, A fbt frequency factor related to the collisional frequency and steric factor and £the activation energy. Figure 5 shows the Arrhenius plot of log W versus l/T  and the acUvation energy, which is calculated from the plot, is found to be 0.41 cV. The frequency factor calculated udng eq. (1) is found to he 5.4 x 10* cm/sec.Study at dislocation etch pils etc ]J5V|*k’3-0<t 3-06 3-oe 3-10 3-12 3>U 3-16 34S 3>19Xl^F ig u re  5. A piot of togaiithin of average width of etch pits versus reciprocal of absolute temperatim.Wemick etai fl] used CP4 etchent containing 3 parts HF, 5 parts HNOa, 3 parts CH3COOHand 1 part & 2  to etch (111) cleavages of antitnony. While the Desh reagent, which contaiitt 1 part HF, 3 pam HNO3 . and 12 parts CHjCOOH, was found to be good polishing agISiit. The snjieroxQl reagent, which consists of 1 pans 30^6 HjOj, 1 part 48%116 Amit H Raval and Mihir J JoshiHF, and 4 parts H^O [13J, is used as a crystallographic etch for germanium. Theuerer (13] found that the amplification characteristics of germanium transisters were improved by etching of the face upon which two point electrodes were applied. However, the modified form of the superoxol reagent brought out spiral terraces in shallow etch pits in antimony [1]. Koscvich [2] had also etched (111) plane of antimony with CP4 etchant He studied etch patterns on the faces of blocks, slip tines, and elastic and stable twinned layers. He had also modified the CP4 etchant by using composition of 28 parts glacial CHjCOOH, S parts HNOt, 4 parts HF and 3 parts Brj. Shigeta etal [4] used the etchant comprising of 10 gms FeCU, 30 cc HCI and 120 cc H2O to etch (111) plane of antimony. Pandya and Bhatt [5] and Pandya and Balasubramanian [6] have tried a solution of tartric acid and nitric acid for the purpose of revealing dislocations. The surface remained bright after prolonged etching. Thakar [7] carried out in detail the chemical and thermal etching of antimony cry/stals. A systematic study of the relative merits of various etchants had been made and it is found that the purity of metal and reagent composition of the etchants were very sensitive par^eters. Pile-ups had also been observed by the author [7] which supports the view that the etlph pits were formed at the sites of dislocations. \In conclusion, the etch pits were observed, using the developed etchant, at the sites of dislocations. The activation energy for the lateral motion of ledges was found to be 0.41 eV. Also, the frequency factor was found to be 5.4 x 10  ^cm/sec. Further work is in progress.AcknowledgmentAuthors are highly thankful to Prof. B S Shah for useful discussions and Praf. R G Kulkami for his keen interest.References[ I ] J H Wcmick, J N Hobsteticf, L C Lovell and D Dorsi 1958 /  A p p i  Phys, 29 1013 [21 V M Kosevich 1961 Sov, P hys.-C rysta llogr. 5 715[3] V M Kosevich 1961 P hys.-C rysta llogr  6 379(4) J Shigeta and M Hiramaisu 1958 J. Phys. Soc. Jpn, 13 1404[.5] N S Pandya and V P Bhatt 1961 Current Sci. 30 293[6] N S Pandya and A P Balasubramanian 1963 Indian  J. Pure A p p i Phys. 1 277[7] B B Thakar 1967 PhD  Thesis (M S University of Baroda, India)[8] F L Vogel, W 0  Pfann, H E Corey and E E Thomas 1953 Phys. Rev. 90 489 [91 W C Dash 1956 J. A p p i Phys. 27 1193110] n Chalmers 1953 Canad. J. Phy.s. 31 132[11] B B Thakar and B S Shah 1986 Cryst. Res. T e c h n o i 21 189[12] S Amelinckx 1964 The D irect Observation o f  D islocations ( New York : Academic) p 2 1[13] H C Theuerer 1951 U S  P atent to Bell telephone Laboratory Inc. N o. 2 > 54 2^ 7 27

Study at Dislocation etch Pits in Antimony Single Crystals by Etching in Citric Acid Containing Etchants-Amith H Raval and Mihir J Joshi

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Study at Dislocation etch Pits in Antimony Single Crystals by Etching in Citric Acid Containing Etchants-Amith H Raval and Mihir J Joshi

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