Acharya, H N

Gartia, R K

Mathur, B K

Samantaray, B K

English

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142 A ch arya , S a m a rta ra y , M athur and G a rtiaR efeeencesA['ai'wal V. J-), & Gupta K. C. 1974 Im liaii J . Phy», 48, 2\)1.AKiirwal H. C. & Gupta R. C. 1974 Indian J .  Phyft. 48. 302.A)p(!j‘t N. L. 1919 rhya, Tlcv, 75, .‘19S.Alul^ o^ \ K. K. & Eadufn 11. CJ. 1953 Pror. PhyN. Sov. A66, 415.floaidon J. A & Walls N. M. 1951 Per. 81, 73.nJot'niOurL^ f'ii N., Pound R. V. & PliicoII JO. C. 1918 Phys. I\cv. 73, 079.Giaoomollow ({., Li(jiuu’i A. M. & Rayjamnnii A. 1956 177, 944.(iiiUnVKky H. S. & G. K. 1950 ./. Chcin> tdnjs. 18. 102 Aloskak'v A". V. J902 Pov. Jdnjft, .Solid .StaU 3, 2218.Sinilh G. VV. 1965 ./. Chem. Phys, 42, 4229.Sinitli G. VV'. 1909 J .  (Jhrm. Pliyfi. 50, 3595.Van Vlo(*k J. II. 1948 Phys. Pen. 74, 1168.Indian J. Phya. 51A, 142-144, (1977)1Study of island growth in vapour deposited lead sulphide filn\s by optical diffraction from the electron micrograph.H. N. Arhara a^ , B. K Samantakay, J3. K. Matiittr and R. K. GartiaDvpfviinml of Phy.sics, Indian InslUute of Technology, Kharagpvr(tlcccivcd 27 January 1970. revised. 14 June 1970 and 111 Hepfewber 1970)Study ()1‘ tlu^  projMU't ios of vapour dopositod load sulpliide filmn is ol' importa/nce lxu^ aus(‘ ot tlirir applioalious in dovicos as infra-iod dotoctors, Siiu.'o most ol 11k‘ riuijauotic, idoctrioai and optical proportic^s of poly(*rystalljne liJms depend oiitically on tlu^  i.l)iakncss and niiciostriu^ ure, a study of the. structiual eliaraclcristies ol tli(^  iilrus tA^ ould 1k  ^ highly usol’ul, Tln^  use of small angle X-ray scattering and small angle eltxdron diffraetion foi‘ determining the particle sizes and size-distribn- tions is well known (Guinier Ar- Foiirnet 1955, Ferrier 1909). Beeston et al  (1972) have reviewed the various studies on the optical diffract.ion fiom electron iniero- gi'aphs and have emphasised its uses in obtaining structural information. Hence in i he present investigation, tlu^  island sizes liav(‘ been determined by the optical diffraetion trom tli(^  okudron micrographs and also by the eouventional tecluiiqne. Pr(d’ei’ied orientation and the sizes of llio ct>herently diffracting ciystallites have been dettuniiiied. by X-iay line broadening method.Thin films of different iJiickness were deposited on glass substrates kept at' I’oom temperatim^ using an EdAvards Vacuimi coating unit under a vacuum of 10~ t-orr. The t hickness of the tilnis was estimat ed by the loss of‘ mass method. The surface structim'S of the PbS films used in tlie present investigation were studied by the earbon replica leeliniqne. For obtaining better contrast tlieH. N. A oh akya  et ahliiiliajj J. l>JiyH. A ol CAA No. I97';!•)\ ri',.. . V . * .   ^ -iW m i9^ %' I P '  1f»’ •vw ."’■s I. Jilortron ...i<^o.Kmpl. <,C2:;i-;o A lluck l'!,S  (il,„ a,„l i(s oj,!,ral ,|iri,a.'(,.„, (,„ ||„. „,hhI).Study o f  growth in  vapour deposited lead sulphide film s 143roplicas wore shadowed with an alloy of ^^ >ld and palladiiiui. The inicrogi aphs wore obtained with the help of mi A.E.l. EM (> olcctrou niicj'osoope. The ojitical diffraction patterns were obtained wi(h a laser diffractometer eoustnicted in the laboratory using I mW Kpeelra Physics He-Ne laser (A = <5328 A.U.) as the source. It is similar to the one described by Bcoston et al (1972). A typical electron micrograph obtained in the present investigation 1ms been shovm in figure 1 with its optical transform in the insist. The intensities umo obtained from the photographs with the help of a recording microphot ometer.From Debye-Ualoigh theory ol' scattering of light by si>herical particles, the relative intensity of scattered light at. an angle 0 is given by (Debye 1947)3whwroU = 2DA Sin (I)(1)(2)where D iB the diameter oftlie Rcattering parti el A is ih(' wavelength of the light and 0 is the scattering angle. Eep (1) is valid for the case of in 1, where m is the ratio of the refractive index oCthe scattcihig particles and lhaf of the medium. Eq. (1) has first minimum and maximum of intensity at 4-4924 andIJ — 5-7G17 j’adians respectively. For othei' values of m, the (ioiTCsiiomling value of U for different minima and maxiimi can be obtained from Mie theory calculations (Maron et al 19GU). The angular positions of the- minima and maxima are given byD . lOi\ . ..Am ( 2 ) - CDwhore ht oj‘ Ki correspond to d.h minima and iik maxima respeotiv(4y. Valutas of Ici and Ki have been ealculat.cd by many workers for difterent eascis (IVIaJon et al 196If, Nakagaki & Heller 1900 and Kerker et al 1994). The above method has been apifiied by Handlikei* (1950), Dezolic &> Kratohvil (J9(il), Maron & Ekhu’ (1963) and others for determination of particle sizc^  and the results ar(^  in good agreement with the electron microscopic data.In the present investigation the island sizes were measured from the positions of the maxima and minima of the scattered intensity and by using eq, (3). The island sizes wore also measured from the electron micrographs by the usual method.X-ray diffraction profiles of the films were recorded vdth the help of a Norolco X-ray diffractometer and the crystallite sizes wer(.‘ obtained from the. line profiles by using the method of integral width (Williamson & Hall 1953).It is observed tliat in initial stages of deposition the islaxids show an irregular structure. These islands however become almost circular in shape for films ofthjsknoHs. It jk fiJsu obyorvocl that initially the increase in island size with the thick]loss is very slow. However for grcfiter tiiiclaiesses the rate of incronso iu tli(^  isJaud size is much greatcu’. The optical diffraction patterns for most of the micJ (jgrapli.s show broad circular inrerfcreuce maxima, thus indicating (leiiae packing and uniform sliapo of the isiaJids. Typical results lor some of the films have boon showji in table 1.Table 1. Structural paramotei s of load sulphide films.144 Acharya, Samantaray, Mathur and GartiaTliifdoioss in AUiHlaxifl Hizo from (‘loftiron micrographs in (A II.)OpticalCon von tio n al di ff roc tion toohniqiio technique■taoufmParticle size from X-ray analysiB in A II( 111 ) (200)150017602350450020026020010003003002001100•57■60•64300 100 350 120 GOO 300It is clear lieiu table 1 that at the initial stages of the groAvth there is an increase in tlw^  number of the islands with little increase in their size. Homo i.imes even tlieie is an imaease ixi the niimbei’ of islands at the cost of the size. X»L’ay analysis of the various films shmv that the ratio of the intensities is (d‘ the order of ()'(k thus indiciating a profci caitial growth of the eiystallites with 111 |)lan(^ s parallel to the substrates J\1easiircnient of tU(^  ^ erysiaUHe sizo per­pendicular to the i l l  and 200 pianos shows tliat the crystallite size in the 111 direction is larger than that in the 200 direetion. It is also observed that the anisotropy in the crystallito size docroasos with the increase in tliickness.R eferencesUooyluii 11. K. V , lJuriu'K. VV. iV Markluiiu K. ,1972 Practical MctJi4)ds in Elrdron Microf(co2yy,Vol. 1, lid. M. G. Lauberl. North Bollaiid Pub. Co. Daudlikor W. H. 1950 J , Am. Chan. Soc. 72, 5110.Dobyo 1». 1947 J .  Fhijs. & Golloif Chem. 51, 18.Do/,('lie G. & Knithovil ,1. P. 1961 J .  Colloid iSci. 16, 561.Korrior H. P. 1959 Advances in Op ical and dec ran microscopy^  Vol. 3, Ed. K. Barrier & V. E.(Josalot, Academic Press.Guinior v\. Foiirnot G. 1955 angle scaettring of X-rays, Wiley, Now York.Korkor M., Faroiio W. A., Smith L. B & Matijovic E, 1964 J . Colloid Sci. 19, 193.Ataroii S. IL & Elder M. E. 1963 J .  Colloid Sci. 18, 107.Maroii 8. i l . ,  J^ iooio P. E. & Elder E. 1963 J .  Colloid Sci. 18, 391.Nakagaki M, Holler W, 1060 J ,  Chem. Phys. 32, 835

Study of Island Growth in Vapour Deposited Lead Sulphide Films by Optical Diffraction from the Electron Micrograph

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Study of Island Growth in Vapour Deposited Lead Sulphide Films by Optical Diffraction from the Electron Micrograph

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