Muhammad Bilal Khan

Hydrogen silsesquioxane resist stamp for replication of nanophotonic components in polymers

We investigate an affordable, accurate and large-scale production method to fabricate subwavelength grating structures by hot embossing replication in polycarbonate substrates. We use inorganic hydrogen silsesquioxane (HSQ), a high resolution, binary, negative electron beam resist, on silicon substrate to make a stamp for replication. The stamp is fabricated without any etching processes and with simple process steps. The process starts by spin coating an HSQ-resist layer on a silicon substrate. The desired film thickness is achieved by adjusting the spinning speed and time. The resist material is then subjected to e-beam writing and development followed by a heat treatment to enhance the hardness and to obtain hot embossing stamp material properties comparable with solid SiO2. A comparison with and without the silicon etching is also performed. We demonstrate that a high quality stamp for thermal nano-imprint lithography for optical gratings can be fabricated using an inexpensive process without an etching step. The process results in a uniform imprinting density over the entire grating surface and high imprint fidelity. The reflectance spectra of replicated grating structures are also shown to be in agreement with theoretical calculations.

Liquid exfoliated graphene smart layer for structural health monitoring of composites

Graphene nanosheets were exfoliated from graphite using liquid exfoliation method. Smart sensing layer was prepared by dispersing graphene nanosheets in thermoplastic polyurethane. The smart sensing layers thus obtained were pasted on to the glass fiber laminated composite specimens. The sensing layer due to its piezoresistivity was employed for detecting strains in the composite specimens. The results show that the smart sensing layer can be employed for strain sensing in the composite structures. The results hold promise for various applications of these sensors for structural health monitoring in composite parts.

Structural and optical properties of electrospun ZnO nanofibres applied to P3HT:PCBM organic photovoltaic devices

Electrospun ZnO nanofibres with a diameter in the range of 74–125 nm were synthesised by optimising various parameters. Zinc acetate was used as a precursor and optimised to obtain a homogeneous and interconnected porous ZnO nanofibres network. The ZnO/poly(vinylpyrrolidone) composite nanofibres were calcined at 450 °C for 2.5 h to obtain continuous nanofibres network. The morphology of the nanofibres was studied by scanning electron microscopy and imageJ software. The structural and optical properties of the synthesised nanofibres were studied by surface profiler, X-ray diffraction and ultraviolet–visible spectroscopy. The grain size increased while the bandgap was observed to decrease with increased precursor concentration. The effect of precursor concentration was also studied to improve the power conversion efficiency of ZnO nanofibres/poly(3-hexylthiophene) (P3HT): [6,6]-phenyl C61-butyric acid methyl ester (PCBM) photovoltaic device. The efficiency was improved from 0.896 ± 0.007% to 2.29 ± 0.03% by introducing the electrospun ZnO nanofibres.

Infiltration of Polymer Through the Pores of Electrospun Nanofibers and Performance of TiO2 Nanofibers/ P3HT Photovoltaic Devices

Metal oxide semiconductor nanofibers obtained by electrospinning are excessively used in organic-inorganic photovoltaic (PV) devices due to large surface area with low production cost. Performance of these devices depends upon the thickness of the active layer and polymer infiltration through the pores of nanofibers mat, which is controlled by electrospinning time. The parameters of hybrid photovoltaic devices, fabricated by poly (3-hexylthiophene) (P3HT) and TiO2/ Di-tetrabutylammonium cis-bis(isothiocyanato)bis(2,2�- bipyridyl-4,4�-dicarboxylato)ruthenium (II) (N719) composite nanofibers was analyzed by considering infiltration of polymer through the electrospun nanofibrous network. Power conversion efficiency (PCE) was improved from 0.13% to 0.93%. Open circuit voltage and short circuit current density were also improved to 0.61V and 3.64mA/cm 2 respectively. Longer electrospinning time resulted in an in- creased number of fiber layers, i.e. increased thickness of the active layer. This results in higher light absorption but reduced infiltration of polymer through the nanofibrous pores up to the lowest layer due to covering up by the top layers. These factors introduce defects and increased series resistance, contributing toward decrease in device efficiency.

DEPENDENCE OF ORGANIC/INORGANIC PHOTOVOLTAIC DEVICE PERFORMANCE ON PRECURSOR'S CONCENTRATION USED FOR ELECTROSPUN TiO2 NANOFIBERS

Electrospun TiO2 nanofibers were synthesized by optimizing various electrospinning conditions. The effect of the precursors concentration present in sol used for electrospinning was studied for the performance of hybrid photovoltaic devices. The synthesized nanofibers were characterized by XRD and UV-Vis absorption spectroscopy and morphology of the fibers were investigated by FE-SEM. The surface of fibers was modified, and these modified fibers were applied to P3HT/TiO2/ N719 composite nanofibers photovoltaic devices. The device performance was investigated by analysis of the incident photon to current conversion efficiency and a J–V characteristic under 1. 5G illuminations, which show that efficiency of the devices, can be improved from 0.13% to 0.83% by introducing TiO2 nanofibers synthesized by optimum precursors concentration.

Evaluating Mechanical Properties of Few Layers MoS2 Nanosheets-Polymer Composites

The reinforcement effects of liquid exfoliated molybdenum disulphide (MoS2) nanosheets, dispersed in polystyrene (PS) matrix, are evaluated here. The range of composites (0~0.002 volume fraction () MoS2-PS) is prepared via solution casting. Size selected MoS2 nanosheets (3~4 layers), with a lateral dimension 0.5~1 µm, have improved Young’s modulus up to 0.8 GPa for 0.0002 MoS2-PS as compared to 0.2 GPa observed for PS only. The ultimate tensile strength (UTS) is improved considerably (~×3) with a minute addition of MoS2 nanosheets (0.00002 ). The MoS2 nanosheets lateral dimension and number of layers are approximated using atomic force microscopy (AFM). The composites formation is confirmed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Theoretical predicted results (Halpin-Tsai model) are well below the experimental findings, especially at lower concentrations. Only at maximum concentrations, the experimental and theoretical results coincide. The high aspect ratio of MoS2 nanosheets, homogeneous dispersion inside polymer, and their probable planar orientation are the possible reasons for the effective stress transfer, resulting in enhanced mechanical characteristics. Moreover, the micro-Vickers hardness () of the MoS2-PS is also improved from 19 (PS) to 23 (0.002 MoS2-PS) as MoS2 nanosheets inclusion may hinder the deformation more effectively.

Investing in hydro power sector for Pakistan's energy security

Hydro power is currently the most widely used source of renewable energy in the world. It has a global installed capacity of more than 1000 GW (Giga Watts), and the capacity is expected to grow to 1680 GW by the year 2035, with non-OECD countries accounting for more than 90% of the said growth. This paper evaluates the historical account of the evolution of Pakistans power market, current market scenario, the key power market participants and presents the case for development of hydro-power projects to solve the cotemporary energy crises of the energy starved country. Furthermore, the paper looks into the investment opportunities in context of enforced regulations by the authorities including tariff setting mechanism and financial modeling for an independent hydro power producer.

Advance instrumentation and control of FTS-GTL facility by means of PLC-SCADA system

CES-NUST has installed Pakistans first GTL (Gas to Liquid) pilot plant based on Fischer Tropsch synthesis. SCADA (Supervisory Control and Data Acquisition) for Fischer Tropsch Synthesis (FTS) is concerned with the monitoring of the vital parameters of bench scale plant. In the present paper the physical parameters are obtained from sensors, processed and displayed by using graphical user interface at personal computer. Finally all the parameters are saved according to the user choice in form of .xls file. Arduino Mega controller along with integrated environment is used to achieve the task. The software and associated hardware is installed and fully functional. The paper highlights the development and architecture of the SCADA system applied to the FT synthesis process.

SWOT analysis of mobile telecommunications sector of Pakistan

This paper aims to perform SWOT analysis of the mobile telecom sector in Pakistan. Detailed study has been carried out by conducting surveys with subjects having different backgrounds and belonging to different professions, regions and age groups. A comparative study of the mobile networks presently operating in Pakistan has been performed. It is found that telecom sector has significant potential to further expand and establish itself in far flung regions of Pakistan. With the emergence of new technologies worldwide, telecom industry in Pakistan has a lot to benefit from and offer high quality services to mobile phone users. By adopting the proposed strategies, telecom industry can significantly increase its market share and establish itself as the primary means of communication.