Suparna Sen Gupta

Low voltage electrodeposition of diamond-like carbon films

Abstract Diamond-like carbon (DLC) films were deposited by electrodeposition technique onto SnO 2 -coated glass substrates by using a mixture of acetic acid and water as electrolyte. The applied voltage between the electrodes was mere 2.1 V. The films have rough surface and distinct broad characteristic peaks at ∼1336 and ∼1601 cm −1 dominated the Raman spectra. Band gap and refractive index of the films varied between 2.3–2.65 eV and 1.25–1.3, respectively. Photoluminscence studies indicate excitonic transition at ∼2.62 eV.

Etching Studies of Gel-Grown Crystals: (100) Faces of Potassium Dihydrogen Orthophosphate

Microscopic observations of the chemically etched prismatic (100) faces of single crystals of KDP (KH2PO4), grown from modified double diffusion gel technique, revealed the presence of hillocks and etch spirals. Both edge and screw dislocations were clearly identified with suitable etchants. Influence of various alcohols and acid concentration on the pit morphology has also been observed. The features have been presented and discussed mainly from examination of optical micrographs.

A study of the deformation characteristics of solution—grown mixed crystals of ammonium–potassium sulphate

Abstract Mixed crystals of ammonium sulphate (AS) and potassium sulphate (PS), [(NH 4 ) 1− x K x ] 2 SO 4 were grown by slow evaporation technique at room temperature. Mechanical characterization was done by studying the variation of microhardness with applied load on (100) faces of mixed AS–PS system for several compositions. Vickers hardness numbers, H v were found to increase primarily with increase in load and then become load independent. Meyer indices, n were found to be always greater than two showing soft material characteristics. Some hardness related parameters such as crack length, fracture toughness were also calculated and interpreted. Fracture toughness increases with higher K + concentration.

Compositional dependence of lattice constants in solution grown crystals of mixed ammonium–potassium sulphate by X-ray diffraction

X-ray diffraction studies have been carried out on solution grown mixed crystals of ammonium–potassium sulphate (AS–PS) over the entire range of composition. Lattice parameters a, b and c are experimentally determined using Computer program POWD and have been found to obey Vegards law of linear dependence with a constant deviation. Results are analysed in the light of packing consideration of the individual atoms.

Revelation of dislocation etch pits in mixed crystals of ammonium-potassium sulphate, [K1−x(NH4)x]2SO4

Defect configurations in as-grown mixed crystals of ammonium-potassium sulphate have been revealed by chemical etch technique with greater details for the first time. Interesting features like symmetrical pyramidal pits, circular terraced pits, row of closely spaced pits forming low angle tilt boundary indicating branching of dislocations etc. were clearly observed using aqueous solutions of various inorganic salts (etchants) applied for different timings. It is found that addition of a salt generally promotes the formation of good pits. The results are briefly interpreted in the light of Cabreras thermodynamic theory of dislocation etch pit formation. The optical and scanning micrographs show a good correspondence between formation of etch pits and dislocations.

Growth and Defect Characterisation in Single Crystals of Ferroelectric Ammonium Sulphate

Some observations of growth hillocks, growth spirals and layers on the chemically etched as-grown (100) faces of ammonium sulphate, (NH4)2SO4 crystals obtained at 26°C from aqueous solutions of different pH are reported and discussed for the first time with greater details. Optical and scanning electron microscopy show a good correspondence between etch pits and dislocation behaviour.

Etching studies of solution-grown crystals : (100) Faces of mixed crystals of potassium dihydrogen orthophosphate and ammonium dihydrogen orthophosphate (KDP-ADP)

We have critically examined the growth conditions to obtain transparent and moderate single crystals of K1-x (NH4)x H2PO4 over the entire range of composition by several tests. Defect configurations of as-grown mixed crystals have been studied by chemical etch technique with greater details. Various interesting patterns like growth hillocks, pyramids, trisection of boundaries and branching of dislocations were clearly observed on the etched surfaces of mixed crystals. Optical and scanning electron micrographs show a good correspondence between etch pits and dislocations.