N. Sajid Babu

Bio: N. Sajid Babu is an academic researcher from University of Kerala. The author has contributed to research in topics: Nanocrystal & Thin film. The author has an hindex of 3, co-authored 7 publications receiving 38 citations.

Electrical properties of grain size tuned CdSe nanocrystal films for practical applications

Abstract: CdSe nanocrystal (NC) thin films of different NC sizes were synthesized using vacuum deposition technique. The films showed blue shift of band gap and the NC sizes calculated size using Brus equation were 9.40, 9.68 and 9.82 nm. DC conductivity and photoconductivity of as-deposited and annealed films increased and activation energy for conduction decreased with increase in the NC size. Also, both carrier concentration and mobility of the films increased with increase in the size of the NCs which was attributed to the increased electronic coupling between the NCs. The slow response part of photocurrent response pulse analyzed using power law: Iph ∞ tα gave larger values for α for larger NC size indicating stronger electronic coupling between grains in films of larger grain sizes. Charge transport in the CdSe NC films was akin to that of solid films of CdSe quantum dots, of sizes given by Brus equation, connected together by an outer shell of CdSe material where charge carriers had free movement. Additionally, measurement of the characteristics of the hetero-junction formed by the CdSe NC film with a similarly deposited Cu2Se film demonstrated usefulness of the CdSe NC films synthesized using the present technique for practical applications.

Deposition of nanocrystal thin films of Cu2Se and their optical and electrical characterization

Abstract: Cu2Se nanocrystal (NC) films of different nanocrystal sizes were synthesized using vacuum deposition technique. The structure of the films was analyzed using Grazing Incidence X-ray Diffraction (GIXRD) and High Resolution Transmission Electron Microscopy (HRTEM) analyses. Band gaps of the films were found to decrease with increase in grain size. Analysis of the Raman spectra of the Cu2Se NC films showed that the exciton-phonon coupling in the films could be tuned by varying the grain size. DC conductivity of the films was found to increase and the activation energy for conduction to decrease with increase in the grain size of the samples. The grain size dependent conductivity along with the optical properties of the Cu2Se NC films may find practical applications such as window material for solar cells.

Composite formation in CdSe:Cu2Se nanocrystal films, charge transport characteristics and heterojunction performance

Abstract: The use of nanocrystals as materials for potential technological applications depends on tailoring their properties through intentional doping with external impurities. We have used a new technique to synthesize nanocrystal thin films of CdSe:Cu2Se containing different weight percentages (wt%) of Cu2Se. The films were deposited on glass substrates at room temperature by co-evaporation of CdSe and Cu2Se powder in nitrogen gas at a pressure larger than that required for conventional thin film deposition. The films consisted of nanograins of CdSe doped with Cu2Se (i.e., nanograins of Cd1−xCu2(x)Se where x is the atom% of Cu2Se doped into CdSe) for lower wt% of Cu2Se, and nanocomposites of Cd1−xCu2(x)Se and Cu2Se for higher wt% of Cu2Se. An energy band diagram built using the Anderson model was used for discussing the heterojunction characteristics of the junction between nanograins of Cd1−xCu2(x)Se and Cu2Se. To investigate the usefulness of the nanocrystal thin films of CdSe:Cu2Se for practical applications, the I–V characteristics of p–p and p–n hetero-junctions formed by the films respectively with nanostructured films of similarly deposited Cu2Se and CdSe films were studied.

Linear and nonlinear optical properties of ZnS/Ag2S composite nanoparticles

Abstract: ZnS/Ag2S composite nanoparticles were synthesized by chemical precipitation method. The composite nanoparticles were characterized by X-ray diffraction and micro-Raman spectroscopy. The linear optical properties of the samples were investigated using UV–visible absorption spectroscopy. The nonlinear absorption of the samples was measured by Z-scan technique using nanosecond laser radiation of wavelength 532 nm. The observed nonlinear absorption was found to arise due to an effective three-photon process involving free-carrier absorption. Also, the samples behaved as efficient optical limiters.

Photoluminescent effect of Ag 2 S coated ZnS nanoparticles

Abstract: A controlled chemical precipitation technique was used to synthesize ZnS/Ag 2 S composite nanoparticles. The composite nanoparticles were characterized by X-ray diffraction. The presence of Ag 2 S in the ZnS/Ag 2 S composite nanoparticles of different concentration of Ag 2 S were compared using the XRD patterns. The room-temperature Photoluminescence spectra of the different samples were analyzed and the presence of Ag 2 S in the samples was investigated.

Impurity Conduction at Low Concentrations.

Abstract: The conductivity of an $n$-type semiconductor has been calculated in the region of low-temperature $T$ and low impurity concentration ${n}_{D}$. The model is that of phonon-induced electron hopping from donor site to donor site where a fraction $K$ of the sites is vacant due to compensation. To first order in the electric field, the solution to the steady-state and current equations is shown to be equivalent to the solution of a linear resistance network. The network resistance is evaluated and the result shows that the $T$ dependence of the resistivity is $\ensuremath{\rho}\ensuremath{\propto}\mathrm{exp}(\frac{{\ensuremath{\epsilon}}_{3}}{\mathrm{kT}})$. For small $K$, ${\ensuremath{\epsilon}}_{3}=(\frac{{e}^{2}}{{\ensuremath{\kappa}}_{0}}){(\frac{4\ensuremath{\pi}{n}_{D}}{3})}^{\frac{1}{3}}(1\ensuremath{-}1.35{K}^{\frac{1}{3}})$, where ${\ensuremath{\kappa}}_{0}$ is the dielectric constant. At higher $K$, ${\ensuremath{\epsilon}}_{3}$ and $\ensuremath{\rho}$ attain a minimum near $K=0.5$. The dependence on ${n}_{D}$ is extracted; the agreement of the latter and of ${\ensuremath{\epsilon}}_{3}$ with experiment is satisfactory. The magnitude of $\ensuremath{\rho}$ is in fair agreement with experiment. The influence of excited donor states on $\ensuremath{\rho}$ is discussed.

Absorption and intensity-dependent photoluminescence measurements on CdSe quantum dots : assignment of the first electronic transitions

Abstract: CdSe is used as a prototype to show the implications of valence-band degeneracy for the optical properties of strongly quantum-confined nanocrystals. Absorption spectra and photoluminescence spectra obtained under intermediate and strong pulsed excitation show the presence of new structures. The energy levels for the electron and the hole are calculated with the spherical confinement, the nonparabolicity of the conduction band, and the valence band degeneracy taken into account. The oscillator strengths of the dipole-allowed transitions are also calculated. This model is found to be in good agreement with the experimental observations, which originate mainly from the quantization of the energy spectrum of holes with due account given to valence-band degeneracy.

Effect of a CdSe Layer on the Thermo- and Photochromic Properties of MoO3 Thin Films Deposited by Physical Vapor Deposition

Abstract: The influence of a cadmium selenide (CdSe) layer on the thermochromic and photochromic properties of molybdenum trioxide (MoO3) thin films was studied. The films were deposited on glass substrates ...

Synthesis, modification and bioapplications of nanoscale copper chalcogenides

Abstract: Copper chalcogenides have a simple general formula, variable atomic ratios, and complicated crystal structures, which lead to their wealth of optical, electrical, and magnetic properties with great potential for wide applications ranging from energy conversion to the biomedical field. Herein, we summarize the recent advances in (1) the synthesis of size- and morphology tunable nanostructures by different methods; (2) surface modification and functionalization for different purposes; and (3) bioapplications for diagnosis and treatment of tumors by different imaging and therapy methods, as well as antibacterial applications. We also briefly discuss the future directions and challenges of copper chalcogenide nanoparticles in the biomedical field.