Arun K. Pal

Bio: Arun K. Pal is an academic researcher from Indian Association for the Cultivation of Science. The author has contributed to research in topics: Band gap & Thin film. The author has an hindex of 21, co-authored 90 publications receiving 1301 citations. Previous affiliations of Arun K. Pal include State University of New York System & Indian Institute of Technology Bombay.

Morphology of thin silver film grown by dc sputtering on Si(001)

Abstract: The morphology and growth mechanism of silver films approximately 150 A in thickness on Si(001) substrates have been studied by atomic force microscopy and x-ray reflectivity. The thin films prepared by dc sputtering at room temperature are composed of islands of silver. The shape and size distribution of these islands are studied using these two complementary measurement techniques.

Nano-diamond films produced from CVD of camphor

Abstract: Nano-diamond films were deposited by chemical vapour deposition (CVD) of camphor (C 10 H 16 O) and hydrogen (∼ 75 vol.%) on glass (at 523–623 K) and quartz/Si substrate (at 523–713 K). The films had low values of surface roughness (∼ 17 nm on quartz) along with high values of hardness and band gap. IR studies of the films deposited on Si substrate indicated the films to be transparent in the IR region. Optical properties of the films deposited on quartz (fused silica) and glass (Corning) substrates were studied. The absorption data in the below band gap region were utilized to estimate the strain (2–12 × 10 −3 ), stress (1.9–8.4 GPa) and hardness (47–62 GPa) in the films. The FTIR studies of the films did not show absorption around 2900 cm −1 , while the Raman spectra indicated a sharp peak (with FWHM ∼8 cm −1 ) at 1337 cm −1 corresponding to good quality diamond films.

Optical properties of nanocrystalline ZnS films prepared by high pressure magnetron sputtering

Abstract: Nanocrystalline ZnS films with different thickness (10–40 nm) were deposited onto quartz and NaCl substrates by magnetron sputtering of a ZnS target in argon plasma. All the films showed a zinc blende structure and the photoluminescence peak positions depended on the surface to volume ratio of the films. The optical absorption in these films could be explained by the combined effects of phonon and inhomogeneity broadening along with optical loss due to light scattering at the nanocrystallites.

The Triplet-Singlet Gap in the m-Xylylene Radical: A Not So Simple One.

Abstract: Meta-benzoquinodimethane (MBQDM) or m-xylylene provides a model for larger organic diradicals, the triplet–singlet gap being the key property. In the present work this energy difference has been the object of a systematic study by means of several density functional theory-based methods including B3LYP, M06, M06-2X, HSE and LC-ωPBE potentials and a variety of wave function-based methods such as complete active space self consistent field (CASSCF), Multireference second-order Moller–Plesset (MRMP), difference dedicated configuration interaction (DDCI), and Multireference configuration interaction (MRCI). In each case various basis sets of increasing quality have been explored, and the effect of the molecular geometry is also analyzed. The use of the triplet and broken symmetry (BS) solutions for the corresponding optimized geometries obtained from B3LYP and especially M06-2X functionals provide the value of the adiabatic triplet–singlet gap closer to experiment when compared to the reported value of Wentho...

Synthesis of diamond-like carbon film by novel electrodeposition route

Abstract: Diamond-like carbon films were deposited by electrodeposition technique onto SnO 2 -coated glass substrates by using a mixture of acetic acid and water as electrolyte. The films are compact with quite smooth surface. Raman spectra showed two distinct broad characteristic peaks at ∼1350 and ∼1600 cm −1 . Shift in the peak position was found to depend on the microstructure of the films. XRD spectrum of the films indicated strong peaks for (1 1 1) and (2 2 0) planes located at 2θ=43.9° and 75.2°, respectively. Band gap and refractive index of the films deposited at different voltage varied between 2.87–3.08 and 1.55–1.61 eV, respectively.

Metal Oxide Semi-Conductor Gas Sensors in Environmental Monitoring

Abstract: Metal oxide semiconductor gas sensors are utilised in a variety of different roles and industries. They are relatively inexpensive compared to other sensing technologies, robust, lightweight, long lasting and benefit from high material sensitivity and quick response times. They have been used extensively to measure and monitor trace amounts of environmentally important gases such as carbon monoxide and nitrogen dioxide. In this review the nature of the gas response and how it is fundamentally linked to surface structure is explored. Synthetic routes to metal oxide semiconductor gas sensors are also discussed and related to their affect on surface structure. An overview of important contributions and recent advances are discussed for the use of metal oxide semiconductor sensors for the detection of a variety of gases—CO, NOx, NH3 and the particularly challenging case of CO2. Finally a description of recent advances in work completed at University College London is presented including the use of selective zeolites layers, new perovskite type materials and an innovative chemical vapour deposition approach to film deposition.

Tin doped indium oxide thin films: Electrical properties

Abstract: Tin doped indium oxide (ITO) films are highly transparent in the visible region, exhibiting high reflectance in the infrared region, and having nearly metallic conductivity. Owing to this unusual combination of electrical and optical properties, this material is widely applied in optoelectronic devices. The association of these properties in a single material explains the vast domain of its applicability and the diverse production methods which have emerged. Although the different properties of tin doped indium oxide in the film form are interdependent, this article mainly focuses on the electrical aspects. Detailed description of the conduction mechanism and the main parameters that control the conductivity is presented. On account of the large varieties and differences in the fabrication techniques, the electrical properties of ITO films are discussed and compared within each technique.

Theory of the linear and nonlinear optical properties of semiconductor microcrystallites

Abstract: We analyze theoretically the optical properties of ideal semiconductor crystallites so small that they show quantum confinement in all three dimensions [quantum dots (QD's)]. In the limit of a QD much smaller than the bulk exciton size, the linear spectrum will be a series of lines, and we consider the phonon broadening of these lines. The lowest interband transition will saturate like a two-level system, without exchange and Coulomb screening. Depending on the broadening, the absorption and the changes in absorption and refractive index resulting from saturation can become very large, and the local-field effects can become so strong as to give optical bistability without external feedback. The small QD limit is more readily achieved with narrow-band-gap semiconductors.

Identifying active surface phases for metal oxide electrocatalysts: a study of manganese oxide bi-functional catalysts for oxygen reduction and water oxidation catalysis

Abstract: Progress in the field of electrocatalysis is often hampered by the difficulty in identifying the active site on an electrode surface. Herein we combine theoretical analysis and electrochemical methods to identify the active surfaces in a manganese oxide bi-functional catalyst for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). First, we electrochemically characterize the nanostructured α-Mn2O3 and find that it undergoes oxidation in two potential regions: initially, between 0.5 V and 0.8 V, a potential region relevant to the ORR and, subsequently, between 0.8 V and 1.0 V, a potential region between the ORR and the OER relevant conditions. Next, we perform density function theory (DFT) calculations to understand the changes in the MnOx surface as a function of potential and to elucidate reaction mechanisms that lead to high activities observed in the experiments. Using DFT, we construct surface Pourbaix and free energy diagrams of three different MnOx surfaces and identify 1/2 ML HO* covered Mn2O3 and O* covered MnO2, as the active surfaces for the ORR and the OER, respectively. Additionally, we find that the ORR occurs through an associative mechanism and that its overpotential is highly dependent on the stabilization of intermediates through hydrogen bonds with water molecules. We also determine that OER occurs through direct recombination mechanism and that its major source of overpotential is the scaling relationship between HOO* and HO* surface intermediates. Using a previously developed Sabatier model we show that the theoretical predictions of catalytic activities match the experimentally determined onset potentials for the ORR and the OER, both qualitatively and quantitatively. Consequently, the combination of first-principles theoretical analysis and experimental methods offers an understanding of manganese oxide oxygen electrocatalysis at the atomic level, achieving fundamental insight that can potentially be used to design and develop improved electrocatalysts for the ORR and the OER and other important reactions of technological interest.