arXiv subjects

Arkaprava Das

Publications and source records attributed to Arkaprava Das.

5 recordsLinked to original sources

arXiv2019

Orbital hybridization induced band offset phenomena in NixCd1-xO thin films

We present the cationic impurity assisted band offset phenomena in NixCd1-xO (x= 0, 0.02, 0.05, 0.1, 0.2, 0.4, 0.8, 1) thin films and further discussed in the light of orbital hybridization modification. Compositional and structural studies revealed that cationic substitution of Cd2+ by Ni2+ ions leads to a monotonic shift in (220) diffraction peak, indicating the suppression of lattice distortion while evolution of local strain with increasing Ni concentration mainly associated to the mismatch in electro-negativity of Cd2+ and Ni2+ ion. In fact, Fermi level pinning towards conduction band minima takes place with increasing Ni concentration at the cost of electronically compensated oxygen vacancies, resulting modification in the distribution of carrier concentration which eventually affects the band edge effective mass of conduction band electrons and further endorses band gap renormalization. Besides that, the appearance of longitudinal optical (LO) mode at 477 cm-1 as manifested by Raman spectroscopy also indicate the active involvement of electron-phonon scattering whereas modification in local coordination environment particularly anti-crossing interaction in conjunction with presence of satellite features and shake-up states with Ni doping is confirmed by X-ray absorption near-edge and X-ray photoelectron spectroscopy studies. These results manifest the gradual reduction of orbital hybridization with Ni incorporation, leading to decrement in the band edge effective mass of electron. Finally, molecular dynamics simulation reflects 13% reduction in lattice parameter for NiO thin film as compared to undoped one while projected density of states calculation further supports the experimental observation of reduced orbital hybridization with increasing Ni concentration.

cond-mat.mtrl-sci↗

arXiv2019

High temperature induced B1 to B2 phase transformation in Cd doped ZnO nanocomposite thin films

In this paper, we report the high temperature mediated structural phase transformation from B1 to B2 phase in solgel derived Cd0.2Zn0.8O nanocomposite thin film for the temperature range of 700 to 900 degree centigrade. Xray diffraction pattern provides a direct and unambiguous indication of phase evolution with increase in annealing Temperature from 700 to 900 degree centigrade along with coexistence of wurtzite phase throughout the whole transformation regime. In fact, significant reduction in lattice parameters in case of transformed B2 phase, extracted by Rietveld refinement provides a direct indication of chemical pressure inducement inside the lattice owing to anticipated mismatch in thermal expansion coefficient which leads to facilitate such phase transformation. Raman spectrum for 900 degree centigrade annealed ones, moreover, shows a distinguishable phonon mode at 866 centimeter inverse, suggesting the formation of B2 phase at higher temperature, consistent with XRD results. Scanning electron microscopy reveals the agglomeration of nanocrystallites followed by distinct void formation, indicating the evolution of chemical pressure inside the lattice. Soft Xray absorption measurement reflects a deviation of the inflection point of the absorption edge which implies Fermi level pinning with transforming phase.

cond-mat.mtrl-sci↗

arXiv2019

Semiconductor to metal transition for Ni doped CdO thin films

In the present investigation resistivity Vs temperature measurements have been performed for solgel prepared pure and Ni doped CdO (NDO) thin films. The semiconducting behavior i.e. negative temperature coefficient of resistivity (TCR) of pure CdO thin film through-out the whole temperature range can be attributed mainly due to concentration dependent thermally activation mechanism of the carriers. The semiconductor to metal transition (SMT) for NDO thin films has been elucidated via combined effect of involved grain boundaries, ionic impurities, phonon scattering and carrier activation.

cond-mat.mtrl-sci↗

arXiv2019

Tailoring superhydrophobic ZnO nanorods on Si pyramids with enhanced visible range antireflection property

Simultaneous superhydrophobic and visible range antireflective properties are demonstrated in hydrothermally grown ZnO nanorods on chemically textured Si surfaces. A drastic transformation of Si micro pyramids from hydrophobic to superhydrophobic is observed by securing the formation of polycrystalline ZnO nanorods at surfaces, showing an increment of apparent contact angle from 102 degree to 157 degree and further explained in the light of a decrease in solid fractional surface area, according to the Cassie Baxter model. Moreover, wurtzite phase of ZnO NRs is confirmed by the X ray diffraction and Raman analysis. Such hierarchical structures further exhibit a large visible range antireflection, 5 percentage, and correlated it to the variation in aspect ratio of Si pyramids in conjunction with the formation of graded refractive index. The combined superhydrophobic and large antireflection phenomenon in the present dual scale structures is believed to be useful for Si based photovoltaic applications.

physics.app-ph↗

arXiv2019

High temperature mediated rocksalt to wurtzite phase transformation in cadmium oxide nano-sheets and their theoretical evidence

In the paper, high temperature induced phase transformation in chemically grown CdO thin films has been demonstrated whereas their corresponding electronic origin is further investigated by density functional theory. In particular, cubic rocksalt to hexagonal wurtzite PT in 900 degree centigrade annealed CdO thin films is confirmed by Xray diffraction , consistent with High Resolution Transmission Electron Microscopy. Such high temperature treatment also leads to significant enhancement in optical band gap from 2.2 to 3.2 eV as manifested by UV-Visible spectroscopy. Moreover, atomic force microscopy and scanning electron microscopy clearly evidence the structural evolution via formation of nano-sheet network in wurtzite phased CdO films. Furthermore, Xray Absorption spectra at oxygen k edge revealed a notable shift in inflection point of absorption edge while X-ray Photoelectron spectroscopy of Cd 3d and O 1s suggested the gradual reduction in CdO2 phase with increasing annealing temperature. In addition, different complementary techniques including Rutherford Backscattering, Raman Spectroscopy have also been exploited to understand the aforementioned PT and their structural correlation. Finally, molecular dynamics simulation along with density functional theory calculations suggest that symmetry modification at Brillouin zone boundary provides a succinct signature for such PT in CdO thin film.

cond-mat.mtrl-sci↗