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Usman A.,University of Engineering and Technology Lahore | Rafique M.S.,University of Engineering and Technology Lahore | Khaleeq-Ur-Rahman M.,University of Engineering and Technology Lahore | Siraj K.,University of Engineering and Technology Lahore | And 6 more authors.
Materials Chemistry and Physics | Year: 2011

The structure and surface morphology of Ni-incorporated diamond like carbon (Ni:DLC) films have been investigated. These films were deposited on Si substrates using pulsed laser deposition (PLD) technique. A KrF Excimer laser (λ = 248 nm) was used for co-ablation from multi component Ni-graphite target. The concentration of Ni was varied by ablating the Ni part of the target with various numbers of laser pulses. The SEM and AFM analysis reveals that the surface is composed of segregates of Ni which increases with the increase in Ni content during the growth process. The structural investigations by XRD and Raman spectroscopy provided information about the orientation of the incorporated constituent and the ordering of the carbon species. Maximum height of the nano structures which were observed on the surface was ∼50 nm. The G-peak of the graphite was shifted towards higher wave number due to enhancement in SP2 sites which have been increased due to the increase in the Ni concentration. A small change in the surface roughness ranging from 7.78 nm to 13.1 nm due to increased Ni concentration was also observed. © 2010 Elsevier B.V. All rights reserved.

Khan S.,Pakistan Institute of Engineering and Applied Sciences | Ahmed I.,Quaid-i-Azam University | Shah A.,National Institute of Laser and Optronics NILOP
Applied Surface Science | Year: 2014

Thin films of monoclinic titanium oxide phase (β-TiO2) have been grown on glass substrate using DC magnetron sputtering technique. The effect of oxygen conditions on the films stoichiometry, growth rate, structure, molecular mode of vibration and optical properties has been investigated. An improvement in stoichiometric ratio (O/Ti) has been observed with the increase of oxygen content in the synthesized chamber. XRD patterns demonstrated the polycrystalline nature of the deposited films with (2¯11) preferential orientation of β-TiO2 phase. In the FTIR analysis, a dominant peak at 868 cm-1 wavenumbers corresponding to the longitudinal optical (LO) mode of monoclinic TiO2 phase was observed at 10% oxygen condition. It shifted to 880 cm-1 wavenumbers at higher oxygen fractions, illustrated the rise of oxygen concentration in the grown films. The influence of various oxygen conditions on transmittance/extinction coefficient, band gap and refractive index of TiO2 (B) phase is reported. © 2014 Elsevier B.V. All rights reserved.

Khan T.M.,National Institute of Laser and Optronics NILOP | Bibi T.,University of Peshawar
Chinese Physics B | Year: 2012

We report the room temperature synthesis of zinc selenide (ZnSe) nano crystalline thin film on quartz by using a relatively simple and low cost closed space sublimation process (CSSP). The compatibility of the prepared thin films for optoelectronic applications was assessed by X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM), Raman spectroscopy, photoluminescence, and Fourier transform infrared spectroscopy (FT-IR). The XRD confirmed that the films were polycrystalline with the preferential orientation along the (111) plane corresponding to the cubic phase (2θ = 27.28°). The AFM indicated that the ZnSe film presented a smooth and compact morphology with RMS roughness 19.86 nm. The longitudinal optical phonon modes were observed at 247 cm -1 and 490 cm -1 attributed to the cubic structured ZnSe. The Zn - Se stretching band was confirmed by the FT-IR. The microstructure and compositional analysis was made with the SEM. The grain size, dislocation density, and strain calculated were co-related. All these properties manifested a good quality, high stability, finely adhesive, and closely packed structured ZnSe thin film for optoelectronic applications. © 2012 Chinese Physical Society and IOP Publishing Ltd.

Khan S.,Pakistan Institute of Engineering and Applied Sciences | Mehmood M.,Pakistan Institute of Engineering and Applied Sciences | Ahmad I.,Quaid-i-Azam University | Ali F.,Pakistan Institute of Engineering and Applied Sciences | Shah A.,National Institute of Laser and Optronics NILOP
Materials Science in Semiconductor Processing | Year: 2015

Zirconium nitride (ZrN) thin films were grown on glass and aluminum substrates using a dual cathodic arc ion deposition technique. The effects of various negative bias voltages and flow ratios of N2/Ar on the stoichiometric ratio of nitrogen to zirconium (N/Zr), deposition rate, structure, surface morphology and electrical resistivity of the ZrN layer were investigated. Rutherford backscattering spectroscopy measurements indicated a drop in the deposition rate and a slight increase in stoichiometric ratio (N/Zr) with the increase of bias voltage up to -400 V, although the latter still remained slightly less than unity (∼0.92). Deposition rate of the film showed an increase with the argon addition. X-ray diffraction patterns depicted mostly polycrystalline nature of the films, with preferential orientation of (2 0 0) planes in the -100 V to -300 V bias voltage range. For 70-50% nitrogen and at a bias voltage of -400 V, the (1 1 1) orientation of ZrN film predominated. The films were smoother at a lower bias of -100 V, while the roughness increased slightly at a higher bias voltage possibly due to (increased) preferential re-sputtering of zirconium-rich clusters/islands. Changes in the resistivity of the films were correlated with stoichiometry, crystallographic orientation and crystalline quality. © 2014 Elsevier Ltd.

Khan T.M.,National Institute of Laser and Optronics NILOP | Khan T.M.,Trinity College Dublin | Irfan M.,University of Peshawar
Applied Physics A: Materials Science and Processing | Year: 2014

This paper reports on the use of phonon spectra obtained with laser Raman spectroscopy for the uncertainty concerned to the optical phonon modes in pure and composite ZnO1−x (Cr2O3)x. Particularly, in previous literature, the two modes at 514 and 640 cm−1 have been assigned to ZnO are not found for pure ZnO in our present study. The systems investigated for the typical behavior of phonon modes with 442 nm as excitation wavelength are the representative semiconductor (ZnO)1−x (Cr2O3)x (x = 0, 5, 10 and 15 %). Room temperature Raman spectroscopy has been demonstrated polycrystalline wurtzite structure of ZnO with no structural transition from wurtzite to cubic with Cr2O3. The incorporation of Cr3+ at most likely on the Zn sub-lattice sites is confirmed. The uncertainty of complex phonon bands is explained by disorder-activated Raman scattering due to the relaxation of Raman selection rules produced by the breakdown of translational symmetry of the crystal lattice and dopant material. The energy of the E2 (high) peak located at energy 53.90 meV (435 cm−1) due to phonon–phonon anharmonic interaction increases to 54.55 meV (441 cm−1). A clear picture of the dopant-induced phonon modes along with the B1 silent mode of ZnO is presented and has been explained explicitly. Moreover, anharmonic line width and effect of dislocation density on these phonon modes have also been illustrated for the system. The study will have a significant impact on the application where thermal conductivity and electrical properties of the materials are more pronounced. © 2014, Springer-Verlag Berlin Heidelberg.

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