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RISS 인기검색어
- 검색키워드
- 저자 : Khalid Mahmood (검색결과 57 건)
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Mahmood, Khalid,Swain, Bhabani Sankar,Han, Gill-Sang,Kim, Byeong-Jo,Jung, Hyun Suk American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.13
<P>The realization of arrays of high-aspect-ratio nitrogen-doped ZnO (NZO) nanorod is critical to the development of high-quality nanostructure-based optoelectronic and electronic devices. In this study, we used a solution-based method to grow arrays of vertically aligned high-aspect-ratio NZO nanorods on ZnO seed layer covered fluorine-doped tin oxide substrates. We investigated whether the diameters and aspect ratios of the nanorods were affected by the addition of polyethylenimine (PEI) to the precursor solution used as well as by variations in the growth temperature and the concentration of the precursor solution. The performances of dye-sensitized solar cells (DSSCs) in which the synthesized high-aspect-ratio NZO nanorods were used as the photoanode material were also studied. That the dopant, nitrogen, was introduced into the ZnO lattice was confirmed using X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy. It was seen that after the addition of PEI, the NZO and ZnO nanorod arrays increased in length and their diameters became smaller (i.e., their aspect ratios increased). This resulted in an increase in the amount of dye absorbed by them, leading to improvements in the DSSCs based on the nanorods. The structural, morphological, optical, and photovoltaic characteristics of ZnO and NZO nanorod arrays synthesized using different precursor concentrations and growth temperatures (160–190 °C) were also examined. We also investigated the effect of the use of PEI on these characteristics. The power conversion efficiency (PCE) of DSSCs fabricated using the NZO nanorod arrays was found to be significantly higher than that of DSSCs based on the pure ZnO nanorod arrays. This increase in efficiency could be attributed to the combined effects of the increase in the charge-carrier concentration, change in morphology, and increase in the Fermi energy levels of the nanorods, which resulted because of N doping. A PCE of 5.0% was obtained for a DSSC based on a film of arrays of NZO nanorods having an aspect ratio of ∼47 and synthesized using PEI.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-13/am500105x/production/images/medium/am-2014-00105x_0015.gif'></P>
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Khalid Mahmood,박승빈 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.2
Zinc oxide (ZnO) and Al-doped ZnO (AZO) thin films were prepared by electrostatic spray deposition method at atmospheric pressure followed by annealing. The effects of annealing and Al doping on the structural,electrical and optical properties of the films were investigated. The results show that films have random orientation with compact hexagonal wurtzite structure. It also implies that the annealing and the Al doping help to improve the electrical conductivity and optical properties as well. The minimum value of resistivity was 1.10 × 10−4 Ω cm for 0.5 at. % AZO film and transmittance was greater than 96% in the visible region. The present value of resistivity is comparable to the lowest values for AZO films reported in open literatures. All the films prepared by this method have a good crystalline structure and homogenous surface. We proposed that the substitution of Al in the ZnO lattice has positive effects in terms of increasing the free electron concentration. At atmospheric pressure, the electrospraying method was confirmed to be suitable for the preparation of AZO films with low resistivity and high transmittance.
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Khalid Mahmood Zia,Shahid Adeel,Fazal-ur- Rehman,Habiba Aslam,Muhammad Kaleem Khosa,Mohammad Zuber 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.77 No.-
The current research presents the exploration of coloring potential of neem bark under the influence ofultrasonic treatment. It is found that good color strength is obtained when tannin from bark is extractedin acidified methanol medium and is used to dye irradiated cotton fabric. New shades and good ratings offastness were obtained when optimal fabric was mordanted with herbal biomolecules where excellentrating has been obtained after bio-mordanting the fabrics under optimal conditions. It is concluded thatUS treatment being green tool in natural dyeing has a great potential to isolate colorants from plantsources under mild conditions.
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Mahmood, Khalid,Swain, Bhabani Sankar,Jung, Hyun Suk The Royal Society of Chemistry 2014 Nanoscale Vol.6 No.15
<P>In this paper, ZnO and Al-doped ZnO films were deposited using the electrospraying method and studied for the first time as photoanodes for efficient perovskite solar cells. Effects of substrate temperature, deposition time, applied voltage, substrate-to-nozzle distance and flow rate (droplet size) on the morphology of ZnO were studied with the help of FE-SEM images. The major factors such as the droplet size of the spray, substrate temperature and substrate-to-nozzle distance at deposition control the film morphology. Indeed, these factors determine the density of the film, its smoothness and the flow of solution over the substrate. The droplet size was controlled by the flow rate of the spray. The substrate-to-nozzle distance and flow rate will both regulate the solution amount deposited on the surface of the substrate. The most favorable conditions for a good quality ZnO thin film were a long substrate-to-nozzle distance and lower solution flow rates. In situ droplet size measurement shows that the size and dispersion of particles were narrowed. The method was shown to have a high deposition rate and efficiency relative to well-established thin film deposition techniques such as chemical and physical vapor deposition. In addition, it also allows easy control of the microstructure and stoichiometry of the deposits. The pure ZnO film produced under optimum conditions (440 nm thick) demonstrated a high power conversion efficiency (PCE) of 10.8% when used as a photoanode for perovskite solar cells, owing to its high porosity, uniform morphology and efficient electron transport. For thicker films a drastic decrease in PCE was observed due to their low porosity. We also observed that the open-circuit voltage increases from 1010 mV to 1045 mV and also the PCE increases from 10.8% to 12.0% when pure ZnO films were doped with aluminum (Al). Under atmospheric pressure, the electrospraying system produces the reasonably uniform-sized droplets of smaller size, so the films have a smooth surface and are highly suited for optoelectronic applications.</P>
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A Parametrical Study of Tunnel-Pile Interaction using Numerical Analysis
Khalid Mahmood,양형식,김원범 한국자원공학회 2011 Geosystem engineering Vol.14 No.4
The construction of shallow urban tunnels inevitably will affect the foundations of nearby structures due to the resulting settlement of the soil. This paper reports the results of a parametrical study that was conducted to assess the extent of the settlement problem near piles. The numerical model used in this assessment was FLAC 2D. In this study, the pile settlement results were studied by changing the rock parameters,such as elastic modulus, cohesion, tensile strength and friction angle where the pile is situated. We also studied the effects of changing the vertical and lateral distances between the piles and tunnel. From this numerical study, it was concluded that rock parameters, such as elastic modulus, affect the settlement results. Cohesionaffected the settlement results when it was lowerthan a certain fixed value, while other parameters had no effect. Changes in the lateral and vertical distances of the plies from crown of the tunnel affected the settlement results. Various parameters related to tunnel construction were used to develop a descriptive matrix. The construction of the matrix was based on Rock Engineering System(RES), and the parameters included the dimensions of the tunnel, overburden, and the lateral and vertical offsets of the piles. Further research is needed to determine the numerical values for each matrix term.
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Enhancement of thermoelectric properties of MBE grown un-doped ZnO by thermal annealing
Khalid, Mahmood,Asghar, Muhammad,Ali, Adnan,Ajaz-Un-Nabi, M.,Arshad, M. Imran,Amin, Nasir,Hasan, M.A. Techno-Press 2015 Advances in energy research Vol.3 No.2
In this paper, we have reported an enhancement in thermoelectric properties of un-doped zinc oxide (ZnO) grown by molecular beam epitaxy (MBE) on silicon (001) substrate by annealing treatment. The grown ZnO thin films were annealed in oxygen environment at $500^{\circ}C-800^{\circ}C$, keeping a step of $100^{\circ}C$ for one hour. Room temperature Seekbeck measurements showed that Seebeck coefficient and power factor increased from 222 to $510{\mu}V/K$ and $8.8{\times}10^{-6}$ to $2.6{\times}10^{-4}Wm^{-1}K^{-2}$ as annealing temperature increased from 500 to $800^{\circ}C$ respectively. This observation was related with the improvement of crystal structure of grown films with annealing temperature. X-ray diffraction (XRD) results demonstrated that full width half maximum (FWHM) of ZnO (002) plane decreased and crystalline size increased as the annealing temperature increased. Photoluminescence study revealed that the intensity of band edge emission increased and defect emission decreased as annealing temperature increased because the density of oxygen vacancy related donor defects decreased with annealing temperature. This argument was further justified by the Hall measurements which showed a decreasing trend of carrier concentration with annealing temperature.
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Mahmood, Khalid,Kang, Hyun Wook,Park, Seung Bin,Sung, Hyung Jin American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.8
<P>Upright-standing nanoporous nanosheets of iodine-doped ZnO (ZnO:I) nanocrsytallites were grown hydrothermally at low temperature and studied as dye-sensitized solar-cell electrodes. The highest overall energy-conversion efficiency of ∼6.6% was achieved with the film consisted of nanosheets of ZnO:I nanocrystallites. This efficiency was significantly improved than the 3.2% achieved for ZnO:I films only including nanosized crystallites, and higher than the 2.4% for undoped ZnO nanosheet film. The nanosheets of ZnO:I nanocrsytallites were proven to be positive in causing light scattering in a broad wavelength region and, therefore, enhancing the light harvesting capability of the photoelectrode film and thus, promotes the solar cell performance. The fabricated cells exhibited highly durable cell performances, even after a month under atmospheric conditions. Electrochemical impedance spectroscopy (EIS) data confirmed that iodine doping was helpful to lower the recombination resistance and prolonged electron lifetime of the ZnO:I cells, hence diminishing the recombination process. The efficiency achieved for the best DSSC in this work was much better than ever reported for a ZnO-based DSSC.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-8/am303272g/production/images/medium/am-2012-03272g_0011.gif'></P>
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