S. K. Kulkarni

Dopant induced modifications in the physical properties of sprayed ZnO : In films

Indium-doped zinc oxide (IZO) films were prepared by the spray pyrolysis technique. The effect of gradual incorporation of indium cations on the structural, electrical, and compositional properties of IZO films was studied in detail. It was observed that even a small addition of indium modifies the preferred growth of IZO film from the [002] direction to the [101] direction. Such a modification in growth pattern is a result of more nucleating centers created by indium doping. Indium dopant improves the electrical properties of the films. The carrier concentration depends mainly on the indium dopant level while the mobility is affected by the changes in crystal orientation that take place due to addition of dopants. X-ray photoelectron spectroscopy results show that indium doping does not lead to any stoichiometric changes in the IZO films and the dopant incorporation in the film is linearly proportional to that in the solution.

Thiophenol-capped ZnS quantum dots

Free‐standing, stable, single‐sized, and highly pure ZnS nanosize particles or quantum dots are synthesized using a chemical route. The dimension of the quantum dots as estimated from x‐ray diffraction was about 7 and 15 A. The optical band gap for these particles was 5.2 and 4.8 eV, respectively, as compared with the bulk energy gap of 3.8 eV. These results are compared with the effective mass approximation. The observations indicate that only particular‐sized stable particles can be synthesized which should have minimum energy configuration. X‐ray photoelectron spectroscopy was utilized for examining stoichiometry and purity of the sample.

Superconductivity in Ni substituted Bi2Ca1Sr2Cu2−xNixOy

Abstract The effect of partial substitution of Ni in place of Cu in Bi 2 Ca 1 Sr 2 Ni x Cu 2− x O y has been systematically investigated for 0⩽ x ⩽0.2. The XRD of the samples confirms them to be of single phase. The superconducting critical temperature T c monotonically decreases with Ni concentration; the rate of T c decrease is around 2.5 K/% of the nominal substitution. All the samples have been subjected to XPS studies. The results show that Ni is incorporated in the lattice in the divalent state with Ni-O bonds substituting for the Cu-O bonds while keeping Bi-O, Sr-O and Ca-O bonds intact. Change in the Ni content does not seem to affect the valence state of Cu. The question of T c decrease with Ni substitution is examined.

Photoelectron spectroscopic studies on a silicon interface with Bi2Sr2CaCu2BO8+δ high Tc superconductor

X‐ray and ultraviolet photoelectron spectroscopies have been used to investigate the interaction between silicon and Bi2Sr2CaCu2O8+δ high Tc superconducting material. For low coverages, silicon adatoms disrupt CuO bonds and SrO bonds to form a complex Sr‐Si‐O phase. This interlayer efficiently prevents further reaction between silicon and the Bi2Sr2CaCu2O8+δ superconductor.

Photoemission and x-ray diffraction study of the Er/Si(111) interface

The Er-Si interface has been studied using XPS, UPS and glancing incidence XRD. Room temperature investigations of the evolving Er-Si interface reveal a two step reaction. Initially reacted clusters of silicon rich silicide form. At higher coverages, metal rich Er5Si3 formation takes place. High temperature annealing leads to stable disilicide formation at the interface.

Room‐temperature reaction of a Ni/Bi2Sr2CaCu2O8 interface

A Ni/Bi2Sr2CaCu2O8 reactive interface has been investigated by x‐ray and ultraviolet photoelectron spectroscopy.Nickel reacts with the substrate disrupting BiO bonds along with CuO bonds. This behavior has been explained on the basis of thermodynamics. A complex NiBiSrCaCuO phase formed at the interface, sets up the diffusion barrier for oxygen withdrawal from the substrate at a thickness of ∼10 A of nickel.

Reactivity and surface modification at a Bi/Bi2Sr2CaCu2O8 interface

Abstract The interface behaviour of the high-temperature superconductor Bi2Sr2CaCu2O8 with bismuth metal has been investigated by using X-ray and ultraviolet photoelectron spectroscopies. Weak reactivity and sharp interface formation were observed between the metal and the superconductor. This was inferred from the changes in the core level spectra of oxygen and bismuth. An explanation based on adatom ionic size has been proposed. A correlation between the changes in the width and satellite intensity of Cu 2p spectra to the adatom-induced distortions in Cu-O bonds are also suggested.

Photoelectron spectroscopic studies of the interface reactions between lead and the high-Tc Bi2Sr2CaCu2O8 superconductor

Abstract Interface characteristics between Pb and the Bi 2 Sr 2 CaCu 2 O 8 oxide superconductor were studied by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The core level results show the partial conversion of CU 2+ to the Cu 1+ state. Pb adatoms extract oxygen from the substrate, by disturbing Bi-O, Sr-O and Cu-O bonds and form an orthorhombic oxide. The interfacial reaction is compared within 40 A thickness.

Nonreactive Sb/Bi2Sr2CaCu2O8 interface

Abstract Interaction of antimony with Bi 2 Sr 2 CaCu 2 O 8 high T c superconductor has been investigated using X-ray Photoelectron and Ultraviolet Photoelectron Spectroscopy. Bi-O and more importantly Cu-O bonds remain unaffected. The unreactive nature of the interface could be explained on the basis of difference in the heat of oxide formation between Sb 2 O 5 and constituents. The results project the possibility of using antimony as a contact metal.

Chemical reactivity and band offset at the CdS/Si interface

Transport phenomena at heterojunctions are critically governed by chemical reactivity and the valence-band offset at the interface. Here we report our investigations carried out on the CdS/Si(111) interface using X-ray and ultraviolet photoelectron spectroscopy and glancing-incidence X-ray diffraction. Weak reactivity between CdS and Si(111) has been observed. A partial charge transfer interaction is suggested to explain the weak reactivity at the interface on the basis of the electronegativity difference. Hexagonal phase of CdS is preferentially grown at 700 K. The valence-band offsets obtained for the interfaces grown at 300 and 700 K are 1.6 and 1.3 eV, respectively. The effects of chemical reactivity and disorder are discussed.