National Institute of Laser and Optronics NILOP

Islamabad, Pakistan

National Institute of Laser and Optronics NILOP

Islamabad, Pakistan
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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.


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 | 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 | Iqbal A.,National Institute of Laser and Optronics NILOP | Zakria M.,National Institute of Laser and Optronics NILOP
Vacuum | Year: 2014

In this research article deep level green luminescence quenching, stability of ultraviolet excitonic emission and structural properties of composite (ZnO)1-x (Cr2O3)x (x = 0, 5, 10 and 15 mol%) are investigated. X-ray diffraction has demonstrated polycrystalline wurtzite structured ZnO and established proper incorporation of Cr3+ at most likely on the Zn lattice sites. More likely, the crystallite size and lattice constants (c, a) decrease while consequently the dislocation density is increased. A pronounced excitonic UV emission due to band-band transition and a weak deep level green emission caused by the oxygen vacancies are observed at peak-wavelengths (358-370) nm and (536-538) nm respectively. The UV luminescence shows a blue-shift and well-built stability up-to 10 mol% Cr2O 3; however for 15 mol% Cr2O3, both the UV and green emissions are completely suppressed while an orange emission appears at 640 nm. This emission is attributed to radiative recombination of a delocalized electron closed to the conduction band with deeply trapped hole in the oxygen interstitials (Oi- centers). Energy bandgap (Eg) is finely tuned from 3.35 eV to 3.46 eV. The exhibited blue shift in the energy bandgap is attributed to Burstein-Moss shift explained by the photon energy dependent measurements. The favorable assorted luminescence mechanisms are explained explicitly. © 2014 Published by Elsevier Ltd.


Khan T.M.,National Institute of Laser and Optronics NILOP | Zakria M.,National Institute of Laser and Optronics NILOP | Ahmad M.,National Institute of Laser and Optronics NILOP | Shakoor R.I.,National Institute of Laser and Optronics NILOP
Journal of Luminescence | Year: 2014

In principal, we described stability of the room temperature ZnSe thin films with thermal annealing deposited onto glass by pulsed laser deposition technique using third harmonic 355 nm of Nd: YAG laser beam. Optoelectronic analysis and stability with thermal annealing was described in terms of structural and optical properties. These properties were investigated via X-ray diffraction, atomic force microscope, scanning electron microscope, Raman, Fourier transform infrared and photoluminescence spectroscopies. From the strong reflection corresponding to the (1 1 1) plane (2θ=27.48) and the longitudinal optical "LO" phonon modes at 250 cm-1 and 500 cm-1 in the X-ray diffraction and Raman spectra, a polycrystalline zincblende structure of the film was established. At 300 and 350 C annealing temperatures, the film crystallites were preferentially oriented with the (1 1 1) plane parallel to the substrate and became amorphous at 400 C. Atomic force microscopic images showed that the morphologies of ZnSe films became smooth with root mean squared roughness 9.86 nm after annealing at 300 and 350 C while a rougher surface was observed for the amorphous film at 400 C. Fourier transform infrared study illustrated the chemical nature and Zn-Se bonding in the deposited films. For the as-deposited and annealed samples at 300 and 350 C, scanning electron micrographs revealed mono-dispersed indistinguishable ZnSe grains and smooth morphological structure which changed to a cracking and bumpy surface after annealing at 400 C. The physical phenomenon of annealing induced morphological changes could be explained in terms of "structure zone model". Excitonic emission at 456 nm was observed for both as-deposited and annealed film at 350 C. The transmission spectrum shows oscillatory behavior because of the thin film interference and exhibited a high degree of transparency down to a wavelength ~500 nm in the IR region. Energy band-gap was increased from 2.65 eV to 2.7 eV for the annealed crystalline film at 350 C which was further decreased to 2.56 eV for the annealed amorphous film at 400 C. The observed results manifested that room temperature pulsed laser ablated ZnSe thin film showed excellent structural, optical and morphological stability up 350 C for optoelectronic applications. © 2013 Elsevier B.V.


Khan T.M.,National Institute of Laser and Optronics NILOP | Mehmood M.F.,Federal Urdu University of Arts, Sciences and Technology Islamabad | Mahmood A.,National Institute of Laser and Optronics NILOP | Shah A.,National Institute of Laser and Optronics NILOP | And 3 more authors.
Thin Solid Films | Year: 2011

Zinc selenide (ZnSe) thin film on glass substrates were prepared by thermal evaporation under high vacuum using the quasi-closed volume technique at room temperature (300 ± 2 K). The deposited ZnSe properties were assessed via X-ray diffraction, atomic force microscope (AFM), UV-Vis specrophotometry, Raman spectroscopy, photo-luminescence, Fourier transform infrared spectroscopy (FT-IR) and spectroscopic ellipsometry. The X-ray diffraction patterns of the film exhibited reflection corresponding to the cubic (111) phase (2θ = 27.20°). This analysis indicated that the sample is polycrystalline and have cubic (Zinc blende) structure. The crystallites were preferentially oriented with the (111) planes parallel to the substrates. The AFM images showed that the ZnSe films have smooth morphology with roughness 6.74 nm. The transmittance spectrum revealed a high transmission of 89% in the infrared region (≥ 600 nm) and a low transmission of 40% at 450 nm. The maximum transmission of 89.6% was observed at 640 nm. Optical band-gap was calculated from the transmission data of specrophotometry, photo-luminescence and ellipsometry and was 2.76, 2.74 and 2.82 eV respectively. Raman spectroscopic studies revealed two longitudinal optical phonon modes at 252 cm -1 and 500 cm -1. In photoluminescence study, the luminescence peaks was observed at 452 nm corresponding to band to band emission. FT-IR study illustrated the existence of Zn-Se bonding in ZnSe thin film. The optical constants were calculated using spectroscopic ellipsometry and were determined from the best fit ellipsometric data in the wavelength regime of interest from 370-1000 nm. These results manifested excellent room temperature ZnSe synthesis and characteristics for opto-electronics technologies. © 2011 Elsevier B.V. All rights reserved.


Arslan M.,National University of Sciences and Technology | Maqsood A.,Center for Emerging science | Mahmood A.,National Institute of Laser and Optronics NILOP | Iqbal A.,National Institute of Laser and Optronics NILOP
Materials Science in Semiconductor Processing | Year: 2013

Thin films of Zn1-xCuxSe (0.00≤x≤0.20) have been prepared by the closed space sublimation technique. Various structural and optical properties have been investigated through X-ray diffraction (XRD), atomic force microscopy (AFM), spectrophotometry, spectroscopic ellipsometry (SE) and Fourier transform infrared spectroscopy (FTIR). The effect of Cu concentration has been observed on the physical properties of Zn 1-xCuxSe films for varying concentrations of copper. X-ray diffraction patterns show that the films are polycrystalline having preferential orientation along the (111) plane. Full width at half maximum (FWHM) values obtained by XRD show that FWHM decreases up to 10% copper concentration while an opposite trend has been observed beyond this concentration. RMS values calculated by AFM shows that the deposited films have smooth morphology; crystallinity improves with increasing Cu concentration and optimum results are shown with 10% Cu concentration. Various optical parameters i.e. absorption coefficient (α), extinction coefficient (k), reflectance (R), refractive index (n), optical conductivity (σop) and electrical conductivity (σel) have been determined using transmission spectra at different copper concentrations. From the reflection spectra it is observed that reflectance increases with the increase of copper concentration. The band gap energy has been determined using k spectra at various copper concentrations through spectroscopic ellipsometry. It is found that the band gap energy of the films decreases with the increase of copper concentration while dielectric constant increases. FTIR analysis revealed that the characteristic ZnSe bond stretching-vibrating mode occurs at 670.8 cm -1. © 2013 Elsevier Ltd.


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.


Shah A.,National Institute of Laser and Optronics NILOP | Mahmood A.,National Institute of Laser and Optronics NILOP | Aziz U.,National Institute of Laser and Optronics NILOP | Rashid R.,National Institute of Laser and Optronics NILOP | And 2 more authors.
Materials Chemistry and Physics | Year: 2016

In this paper, we report the structural and optical properties of Nb-doped TiO2 thin films deposited by e-beam evaporation technique. After post annealing in air at 500 °C for 1 h, the samples were characterized by various techniques such as X-ray diffraction (XRD), Raman spectroscopy, UV–Vis spectrophotometry and spectroscopic Ellipsometer. Both XRD and Raman analyses indicate that the films were crystallized into the polycrystalline anatase TiO2 structure. However it was observed that the crystallinity of the films decreases with the addition of Nb atoms and tends to become amorphous at 20% Nb content in TiO2 film. Moreover, no new phases such as Nb2O5, NbO2 or Nb metal were observed. The band gap energy was found to decrease with the increasing of Nb concentration which was verified by ellipsometric study. Ellipsomtric measurements also indicate that refractive index (n) of the films decreases while extinction coefficient (k) increases with the increasing of Nb content. All these analyses elucidate that the incorporation of Nb atom into TiO2 may tune the structural and optical properties of TiO2 thin films. © 2016 Elsevier B.V.


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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