P.K. Ghosh

Jadavpur University, Kolkata, Bengal, India

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Publications (22)44.08 Total impact

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    P. K. Ghosh · K. K. Chattopadhyay
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    ABSTRACT: Nanoparticles of ZnS have been synthesized via radio frequency magnetron sputtering technique. Selected area electron diffraction patterns confirmed the nanocrystalline cubic phase of ZnS. TEM micrographs of the thin films revealed the manifestation of ZnS nanoparticles (3.00 - 5.83 nm). UV-VIS-NIR spectrophotometric measurements showed that the films are highly transparent ~ 90 % with a blue shift of absorption edge. The particle size calculated from the shift of direct bandgap (3.89-4.44 eV) due to quantum confinement of nanoparticles lying in the range 3.23 - 5.60 nm, which well support the TEM results. The photoluminescence spectra of the films showed sulfer vacancy in the films and the EDX results also supported these results.
    Preview · Article · Jun 2013
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    N.S. Das · P.K. Ghosh · M.K. Mitra · K.K. Chattopadhyay
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    ABSTRACT: Nanocrystalline cadmium sulfide thin films were deposited by the radio frequency magnetron sputtering technique on Si and glass substrates with different particle sizes and thicknesses by varying deposition time. X-ray diffraction and transmission electron microscopic studies confirmed the nanocrystalline cubic CdS phase formation. TEM micrographs of the films revealed the manifestation of nano-CdS phase with average particle size of 3.6–7.3 nm for different films. These nanocrystalline films were analyzed by spectroscopic ellipsometry. The optical constants and the fitting constants were obtained by fitting the ellipsometric parameter del and psi data using Forouhi and Bloomer models in the wavelength range 248–825 nm. The optical band gaps of the films were also measured by spectrophotometric studies. It was found that the energy band gap decreased from 3.28 to 2.54 eV when the film thickness increased from 153 to 205 nm.
    Full-text · Article · Jun 2010 · Physica E Low-dimensional Systems and Nanostructures
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    ABSTRACT: Ni nanoclusters in silica matrix have been synthesized via sol–gel process for different percentage of Ni in the matrix. Transmission electron microscopic studies showed that the particle size of nickel was in the range 6–8.5nm for a variation of Ni content in the silica matrix 5–15%. Selected area electron diffraction patterns confirmed that these nanoparticles are cubic Ni and XRD studies of the composite powder also supported the presence of metallic Ni. It was observed that with the increase of nickel percentage in the silica matrix, the particle size increased, and stress decreased. ac conductivity, dielectric constant and complex permittivity spectrum have been studied over a wide range of frequency for different percentage of Ni content in the samples at room temperature. ac conductivity (σac) measurements indicated σac increased in the lower frequency region (below 12–14kHz), but becomes nearly constant in the high frequency range. In the Cole–Cole plot two semicircular arcs appeared which indicated polydispersive nature of the dielectric properties of the Ni–silica nanocomposite. It was also observed that the dielectric properties of the Ni–silica nanocomposite not only depended on frequency but also changes with the grain size.
    Full-text · Article · Apr 2008 · Journal of Alloys and Compounds
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    P.K. Ghosh · Sk.F. Ahmed · B. Saha · K.K. Chattopadhyay
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    ABSTRACT: Nanocrystallites of cadmium sulfide (CdS) thin films have been deposited by radio frequency magnetron sputtering technique. XRD and TEM diffraction patterns have confirmed the nanocrystalline cubic CdS phase formation. The intensity of XRD peaks also increases with the increase of deposition time that implies that better crystallinity takes place at higher deposition time. TEM micrographs of the films have revealed the manifestation of nano CdS phase with average particle size lying in the range 2.00 nm to 5.36 nm. UV-VIS spectrophotometric measurement showed high transparency of the film with a blue-shift of the absorption edge. The direct optical bandgap values of the films increased with the increase of deposition time and lie in the range from 3.06 - 3.94 eV.
    Full-text · Conference Paper · Jan 2008
  • P.K. Ghosh · Sk.F. Ahmed · S. Jana · K.K. Chattopadhyay
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    ABSTRACT: Nanoparticles of ZnS:Mn have been grown by radio frequency magnetron sputtering technique on glass and Si substrates at a substrate temperature 300 K. X-ray diffraction patterns and selected area electron diffraction patterns confirmed the nanocrystalline cubic ZnS phase formation. TEM micrographs of the films revealed the manifestation of ZnS:Mn nanoparticles with an average size ∼6 nm. UV–Vis–NIR spectrophotometric measurement showed that the films are highly transparent (∼90%) in the wavelength range 400–2600 nm. From the measurements of transmittance spectra of the films the direct allowed bandgap values have been calculated and they lie in the range 3.89–4.12 eV. The bandgap decreased with the increase of Mn concentration in the films. The Mn concentrations in the films have been varied from 0% to 8.9% and was measured by energy dispersive X-ray analysis. The photoluminescence of the Mn doped ZnS nanoparticles was measured. The intensity of the PL peaks at first increased with the increase of Mn concentration in the films up to 3.8% of Mn doping and at a Mn concentration higher than this, the intensity of PL peak decreased. Nanocrystalline ZnS:Mn showed good field emission property with a turn on field lying in the range 5.26–6.78 V/μm for a variation of anode to sample distance from 60 μm to 100 μm.
    No preview · Article · Aug 2007 · Optical Materials
  • P.K. Ghosh · S. Jana · S. Nandy · K.K. Chattopadhyay
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    ABSTRACT: Nanocrystalline ZnS thin films have been synthesized by radio frequency magnetron sputtering technique on glass and Si substrates at a substrate temperature 300 K. X-ray diffraction and selected area electron diffraction studies confirmed the formation of nanocrystalline cubic phase of ZnS in the films, although the target material was hexagonal ZnS. The particle size, calculated from the XRD patterns of the thin films was found in the range 2.06–4.86 nm. TEM micrographs of the thin films revealed the manifestation of ZnS nanoparticles with sizes in the range 3.00–5.83 nm. UV–vis–NIR spectrophotometric measurements showed that the films were highly transparent (∼90%) in the wavelength range 400–2600 nm with a blue shift of the absorption edge. The direct allowed bandgaps have been calculated and they lie in the range 3.89–4.44 eV. The particle size, calculated from the shift of direct bandgap, due to quantum confinement effect lying in the range 3.23–5.60 nm, well support the TEM results. The room temperature photoluminescence spectra of the films showed two peaks centered around 315 and 450 nm. We assigned the first peak due to bandgap transitions while the latter was due to sulfur vacancy in the films. The composition analysis by energy dispersive X-rays also supported the existence of sulfur deficiency in the films. The dielectric property study showed high dielectric constant (85–100) at a higher frequency (>5 kHz).
    No preview · Article · Mar 2007 · Materials Research Bulletin
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    ABSTRACT: Nanostructured ZnS thin films have been synthesized by radio frequency magnetron sputtering technique. X-ray diffraction and selected area electron diffraction studies confirmed the formation of nanocrystalline cubic phase of ZnS in the films. The particle size calculated from the XRD patterns of the thin films was found in the range 2.06-4.86 nm. TEM micrographs of the thin films revealed the manifestation of ZnS nanoparticles with sizes lying in the range 3.00-5.83 nm. UV-Vis-NIR spectrophotometric measurements showed that the films are highly transparent (-90 %) in the wavelength range 500-2600 nm. The absorption edge showed a blue shift. The direct allowed bandgaps was found in the range 3.89-4.44 eV. The room temperature photoluminescence spectra of the films showed two peaks centered around 315 nm and 450 nm. We assigned the first peak due to bandgap, transitions while the letter due to sulfur vacancy in the films. The composition analysis by energy dispersive X-rays also supported the existence of sulfur deficiency in the films. The thicknesses of the films were in the range 260-350 nm depending on the deposition time.
    No preview · Article · Jan 2007
  • U.N. Maiti · P.K. Ghosh · S. Nandy · K.K. Chattopadhyay
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    ABSTRACT: Zn1−xMnxO sub-micron fibrous thin films were synthesized by a simple sol–gel dip-coating technique. XRD pattern confirmed the hexagonal wurtzite structure of the synthesized material. Expansion of the c-axis lattice parameter has been observed with the increase of manganese content in the films. Manganese content (x) in the films varied from 0.0098–0.0568 and was determined by energy-dispersive X-ray analysis. The average diameter of the ZnO fibers were ∼700 nm whereas the length was several hundred micro-meters and hence the aspect ratio was quite large (>150). Branching and uneven growth occurred with the increase of manganese content as is evident from SEM analysis. Optical transmittance spectra showed absorption band due to characteristic d–d transition of Mn2+ ions nearly at 3 eV. The band gap, as determined from the transmittance spectra, decreased to 3.28 eV for x=0.0287 and then increased upto 3.38 eV for x=0.0568 as compared with the undoped film for which the band gap is 3.31 eV. Photoluminescence spectra of Zn1−xMnxO fibrous thin films on glass substrate for different doping levels were also studied which showed a broad UV band at ∼397 nm, a narrow blue–green band at ∼466 nm and another broad peak at ∼526 nm. Mn doping causes a large reduction in the intensity of the UV emission and small reduction in green emission intensity of the PL spectra.
    No preview · Article · Jan 2007 · Physica B Condensed Matter
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    ABSTRACT: We have observed low-macroscopic field electron emission from wide bandgap nanocrystalline Al doped SnO2 thin films deposited on glass substrates. The emission properties have been studied for different anode-sample spacings and for different Al concentrations in the films. The turn-on field and approximate work function were calculated and we have tried to explain the emission mechanism from this. The turn-on field was found to vary in the range 5.6–7.5V/μm for a variation of anode sample spacing from 80–120μm. The turn-on field was also found to vary from 4.6–5.68V/μm for a fixed anode-sample separation of 80μm with a variation of Al concentration in the films 8.16–2.31%. The Al concentrations in the films have been measured by energy dispersive X-ray analysis. Optical transmittance measurement of the films showed a high transparency with a direct bandgap ∼3.98eV. Due to the wide bandgap, the electron affinity of the film decreased. This, along with the nanocrystalline nature of the films, enhanced the field emission properties.
    No preview · Article · Dec 2006 · Applied Physics A
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    ABSTRACT: Thin films of cadmium doped zinc oxide rod like microstructure have been synthesized by a very simple sol-gel dip coating technique. Sols were prepared from hydrated zinc oxide precursor and 2-methoxyethanol solvent with monoethanolamine as a sol stabilizer. XRD pattern confirmed the hexagonal wurtzite structure of the deposited ZnO films. Surface morphologies of the films have been studied by a scanning electron microscope and an atomic force microscope, which confirmed that the films are composed of densely packed randomly oriented nano/submicron rods with diameter in the range 300–400nm having various lengths. We proposed a possible growth mechanism for this rodlike structure. X-ray photoelectron spectroscopic study was used to determine the binding energies and the Zn 2p3/2, Cd 3d5 and O 1s peaks in the XPS spectra were located at 1021.08eV, 404.6eV and 529.8eV respectively, which confirmed the Cd doping in ZnO. Cadmium content in the film was estimated both from energy dispersive X-ray analysis and XPS measurement. Band gap energy determined from optical transmittance spectra systematically varied from 3.28eV to 3.15eV for 0% to 5.6% of Cd doping. Urbach parameter determined from the band tail of the transmittance spectra showed that it increased with doping percentage and this parameter for a fixed cadmium doping level decreased with increase of temperature.
    No preview · Article · Dec 2006 · Journal of Sol-Gel Science and Technology
  • P.K. Ghosh · U.N. Maiti · S. Jana · K.K. Chattopadhyay
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    ABSTRACT: The field emission property of zinc sulphides nanorods synthesized in the thin film form on Si substrates has been studied. It is seen that ZnS nanorod thin films showed good field emission properties with a low-macroscopic turn-on field (2.9–6.3 V/μm). ZnS nanorods were synthesized by using radio frequency magnetron sputtering of a polycrystalline prefabricated ZnS target at a relatively higher pressure (10−1 mbar) and at a lower substrate temperature (233–273 K) without using any catalyst. Transmission electron microscopic image showed the formation of ZnS nanorods with high aspect ratio (>60). The field emission data were analysed using Fowler–Nordhiem theory and the nearly straight-line nature of the F–N plots confirmed cold field emission of electrons. It was also found that the turn-on field decreased with the decrease of nanorod's diameters. The optical properties of the ZnS nanorods were also studied. From the measurements of transmittance of the films deposited on glass substrates, the direct allowed bandgap values have been calculated and they were in the range 3.83–4.03 eV. The thickness of the films was ∼600 nm.
    No preview · Article · Nov 2006 · Applied Surface Science
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    ABSTRACT: Transparent conducting Cd1−xSnxS thin films have been synthesized by radio frequency magnetron sputtering technique on glass and Si substrates for various tin concentrations in the films. X-ray diffraction studies showed broadening of peaks due to smaller crystal size of the Cd1−xSnxS films, and SEM micrographs showed fine particles with average size of 100 nm. Sn concentration in the films was varied from 0% to 12.6% as determined from energy-dispersive X-ray analysis. The room-temperature electrical conductivity was found to vary from 8.086 to 939.7 S cm−1 and corresponding activation energy varied from 0.226 to 0.076 eV. The optimum Sn concentration for obtaining maximum conductivity was found to be ∼9.3%. The corresponding electrical conductivity was found to be ∼939.7 S cm−1, and the mobility ∼49.7 cm2 V−1 s−1. Hall measurement showed very high carrier concentrations in the films lying in the range of ∼8.0218×1018–1.7225×1020 cm−3. The conducting Cd1−xSnxS thin films also showed good field emission properties with a turn on field 4.74–7.86 V μm−1 with variation of electrode distance 60–100 μm. UV–Vis–NIR spectrophotometric studies of the films showed not needed the optical band gap energy increased from 2.62 to 2.80 eV with increase of Sn concentration in the range 0–12.6%. The optical band gap was Burstein–Moss shifted, and the corresponding carrier concentration obtained from the shift also well matched with that obtained from Hall measurement.
    No preview · Article · Oct 2006 · Solar Energy Materials and Solar Cells
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    P. K. Ghosh · S. Jana · U. N. Maity · K. K. Chattopadhyay
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    ABSTRACT: The field-emission property of transparent nanocrystalline CdS thin films, grown by chemical bath deposition (CBD) within the pores of polyvinyl alcohol (PVA) on Si and glass substrates, has been studied. X-ray diffraction and transmission electron microscopy studies confirmed the nanocrystalline nature of the CdS particles with sizes lying in the range 6–12 nm. The Fowler–Nordhiem plots of the emission current from the nano-CdS/PVA thin films are almost straight line. The turn-on fields of the grown nano-CdS/PVA thin films are found to be in the range of 3.6–6.6 V/μm. The turn-on field decreases with the decrease of particle size. Only PVA thin film and bulk CdS/PVA composite thin film grown on Si substrates have not showed field-emission property under the same conditions.
    Preview · Article · Oct 2006 · Physica E Low-dimensional Systems and Nanostructures
  • P.K. Ghosh · U.N. Maiti · K.K. Chattopadhyay
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    ABSTRACT: CdS nanofibers have been prepared by direct current-sputtering technique without using any catalyst or matrix. X-ray diffraction patterns and selected area electron diffraction patterns confirmed the cubic CdS phase formation in the thin films, although the initial target material was hexagonal CdS powder. TEM micrographs have confirmed the nanofiber formation with diameters in the range 2–4.3 nm and length of a few microns. XRD patterns showed the crystal size increased with the increase of deposition time. UV–Vis spectra of the films have showed nearly 90% transparency in the visible range and the bandgap is higher compared to that of the bulk material. The direct bandgap increased from 3.06 to 3.56 eV with decrease of deposition time from 20 to 7 min. The crystallite sizes have also been determined from the shift of the direct bandgap with that of bulk CdS and they lie in the range 2.82–3.65 nm.
    No preview · Article · Oct 2006 · Materials Letters
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    ABSTRACT: Al doped SnO2 thin films have been synthesized by a sol-gel dip coating technique with different percentages of Al on glass and silicon substrates. X-ray diffraction studies confirmed the proper phase formation in the films and atomic percentage of aluminium doping in the films was obtained by energy dispersive X-ray studies. SEM studies showed the particle sizes lying in the range 100–150nm for the undoped films and it decreased with increase of Al doping. Optical transmittance spectra of the films showed high transparency (∼80%) in the visible region and the transparency increases with the increase of Al doping in the films. The direct allowed bandgap of the films have been measured for different Al concentration and they lie within the range of 3.87–4.21eV. FTIR studies depicted the presence of Sn–O, Al–O, bonding within the films. The room temperature electrical conductivities of the films are obtained in the range of 0.21Scm−1 to 1.36Scm−1 for variation of Al doping in the films 2.31–18.56%. Room temperature Seebeck coefficients, SRT of the films were found in the range +56.0μVK−1 to −23.3μVK−1 for variation of Al doping in the films 18.56–8.16%. It is observed that the Seebeck coefficient changes its sign at 12.05% of Al in the films indicating that below 12.05% of Al doping, SnO2:Al behaves as an n-type material and above this percentage it is a p-type material.
    No preview · Article · Sep 2006 · Journal of Sol-Gel Science and Technology
  • K.K. Chattopadhyay · P.K. Ghosh
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    ABSTRACT: Preparations of nanometer size crystallites have opened up the opportunity of observing the evolution of physical properties of materials with sizes. With the reduction of size the bulk properties of a material change remarkably and provide the possibility of observing novel behaviors such as size dependent structural, optical and electrical properties. In recent years, a rapid and remarkable progress in the field of nanostructured material in general and II-VI semiconductors in particular, has been achieved. Interest in this group of semiconducting materials stems from the favorable properties they have and also from the expectations that at reduced dimensions most of the properties will be improved. These materials have possible applications in practical field such as in transparent windows, photoluminescence devices, photocathode in photo electrochemical cells, sensors, solar cells, protective coatings, etc. II-VI semiconducting oxide such as CdO and ZnO are widely used as transparent conducting oxides and other II-VI semiconductors such as CdS and ZnS are widely used in luminescent devices and in photovoltaics. The luminescence property also enhances with the decrease of sizes (i.e. in the nanostructured form) and some unconventional and interesting properties like electron field emission, large changes in dielectric constants etc. can also be observed. Nanostructures of some important II-VI semiconductors (mainly CdS and ZnS) have been synthesized using rf-magnetron sputtering of a pre-fabricated polycrystalline target of respective material at different depositions conditions. Effect of variation of deposition parameters, such as inter-electrode distance, rf-power and gas pressure on the structural and optical properties of the above nanocrystalline II-VI semiconductor thin films were investigated in detail. Structural characterizations were performed using X-ray diffractions and transmission electron microscopy. Detail study indicated a size dependent structural phase transition from hexagonal to cubic phase for this class of semiconductors. Nanocrystallites with different morphologies and shapes like nanotubes, nanorods and nanoparticles were achieved by properly optimizing the deposition conditions. Optical properties of the above different nanostructures were studied in detail. All the structures showed blue-shift of fundamental absorption edge due to quantum confinement effect. Different optical constants like bandgap energies, refractive indices, absorption coefficients and extinctions coefficients were determined from the above study. Their variations with particle sizes and correlation of these variations with deposition conditions were established.
    No preview · Article · Jan 2006
  • P. K. Ghosh · S. Das · K. K. Chattopadhyay
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    ABSTRACT: Nanocrystallites of cadmium oxide (CdO) thin films were deposited by sol–gel dip coating technique on glass and Si substrates. XRD and TEM diffraction patterns confirmed the nanocrystalline cubic CdO phase formation. TEM micrograph of the film revealed the manifestation of nano CdO phase with average particle size lying in the range 1.6–9.3 nm. UV–Vis spectrophotometric measurement showed high transparency (nearly 75% in the wavelength range 500–800 nm) of the film with a direct allowed bandgap lying in the range 2.86–3.69 eV. Particle size has also been calculated from the shift of bandgap with that of bulk value for the films for which the particles sizes are comparable to Bohr exitonic radius. The particle size increases with the increase in annealing temperature and also the intensity of XRD peaks increases which implies that better crystallinity takes place at higher temperature.
    No preview · Article · May 2005 · Journal of Nanoparticle Research
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    ABSTRACT: Thermoelectric and electrical properties of transparent p-type CuAlO2 thin films deposited by dc-sputtering method have been studied in detail. Postdeposition annealing in excess oxygen is a necessary precondition of obtaining enhanced p-type conduction in the films. The effect of postdeposition annealing time in excess oxygen on electrical and thermoelectric properties was studied. Thermoelectric measurements of the films, showed considerable high values of room-temperature Seebeck coefficients ranging from 230 to 120 μV K−1, for annealing times of 90 to 30 min, respectively. Natural layered-structure materials, having an effective two-dimensional carrier density, showed an enhanced thermoelectric figure-of-merit. CuAlO2, having a natural superlattice structure, showed very good thermoelectric properties, and it may become a good thermoelectric material for future applications.
    Full-text · Article · Mar 2005 · Thin Solid Films
  • P.K. Ghosh · R Maity · K K Chattopadhyay
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    ABSTRACT: Nanocrystallites of CdS have been grown by chemical bath deposition within the pores of poly(vinyl alcohol) (PVA) on glass and Si substrates. The CdS-PVA composite films are transparent in the visible region. XRD and TEM diffraction patterns confirmed the nanocrystalline CdS phase formation. TEM study of the film revealed the manifestation of nano CdS phase formation and the average particles size was varied in the range 5-12 nm. UV-vis spectrophotometric measurement showed high transparency (nearly 80% in the wavelength range 550-900 nm) of the films with a direct allowed band gap lying in the range 2.64-3.25 eV. Particle sizes have also been calculated from the shift of band gap with respect to that of bulk value and were found to be in the range 3.3-6.44 nm. The high dielectric constant (lies in the range 120-250 at high frequency) of PVA/CdS nanocomposite compared to that of pure PVA (-28) has been observed. The dielectric constant decreases with increase of dispersibility of the CdS nanoparticles within PVA. The nanocrystalline PVA/CdS thin films have also showed field emission properties with a turn-on field of approximately 6.6 V/microm, whereas only PVA thin film and bulk CdS on PVA have shown no field emission.
    No preview · Article · Mar 2005 · Journal of Nanoscience and Nanotechnology
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    P. K. Ghosh · S. Das · S. Kundoo · K. K. Chattopadhyay
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    ABSTRACT: Highly conducting fluorine doped n-type cadmium oxide thin films have been synthesized by sol–gel dip coating process on glass and Si substrates for various fluorine concentrations in the films. X-ray diffraction pattern confirmed the cubic CdO phase formation and SEM micrograph showed fine particles of CdO with size ~0.3 m. F concentration in the films was varied from 1.8% to 18.7% as determined from energy dispersive X-ray analysis (EDX). The resistivity of the CdO films decreased with increase of F doping and increase of temperature below 14.6% of F, as usual for semiconductors. Above this F concentration the resistivity increased with increase of temperature like metals. Hall measurement showed very high carrier concentrations in the films lying in the range of ~2.93 1020 cm–3 to 4.56 1021 cm–3. UV-VIS-NIR spectrum of the films showed the optical bandgap energy increased with increase of F doping and corresponding carrier concentrations obtained from Burstein-Moss shift also support the Hall measurement results.
    Full-text · Article · Jan 2005 · Journal of Sol-Gel Science and Technology