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Synthesis and Fragmentation of Carbon Clusters and Nanotubes

Thesis Info

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Author

Javeed, Sumera

Program

PhD

Institute

Pakistan Institute of Engineering and Applied Sciences

City

Islamabad

Province

Islamabad

Country

Pakistan

Thesis Completing Year

2014

Thesis Completion Status

Completed

Subject

Physics

Language

English

Link

http://prr.hec.gov.pk/jspui/bitstream/123456789/2189/1/2753S.pdf

Added

2021-02-17 19:49:13

Modified

2024-03-24 20:25:49

ARI ID

1676727470943

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A detailed study of the formation and fragmentation patterns of sp2 bonded carbon nano and micro structures has been carried out. Nanotubes and graphite are the extended and composite structures formed by the curved and flat sheets of graphene. Their structural stabilities and subtle differences have shown to be responsible for their characteristic fragmentation patterns under different forms of irradiations. Various techniques were employed for imparting energy to these structures. These include arc discharge, magnetron sputtering, energetic ion induced sputtering, and ablation with electronic and ionic pulses. Emission spectroscopy as well as the velocity and momentum analyzers was employed for the identification of the fragments. Arc discharge and magnetron sputtering of graphite delivered C1, C2, C3 and higher clusters which subsequently coalesced to form two types of thin films. Raman, Fourier transform infra red spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses relates the sp2 character of these two types of films to the relative ratios of C2 versus all these clusters used in their respective formation. C2 is shown to be the essential component of formation as well as fragmentation of the sp2-bonded structures. Detailed mass spectrometric investigations were performed on Cs+ irradiated SWCNTs, MWCNTs and graphite as a function of Cs+ energy (E(Cs+)) ranging from few tens of eV to 5000 eV. C2, C3 and C4 emission are shown to be the main fragmentation channels for irradiated and pristine single and MWCNTs while C1 shows a linearly increasing relative number density as a function of E(Cs+) thus indicating C1 to be the by-product of the dissociation of C2 and C3. Relative stability of C2 and C3 in energetic collisions with N2 demonstrates that C2 and C2+ dissociate at relatively small collision energies as compared with C3 which has superior survival probabilities even at much higher energies. Sputtering of C2, C3 and C1 under broad energy ranges and doses of Cs+ has been modeled to visualize the breaking of multiple bonds in direct and secondary recoils. The prevalence of C2 among the sputtered species from the irradiated SWCNTs, MWCNTs and graphite targets identify the dominant role that recoil sputtering plays, where a double bonded pair of carbon breaks its four single bonds with four C2 neighbors on sp2– bonded surface.
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سید عبدالرحمن تھنگل

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Contemporary Debate on Peace, Politics and Religion: A Quranic Perspective

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Laser Ablation Studies of Metal Alloys Using Libs and Time of Flight Mass Spectrometry

Laser ablation is a versatile technique used for the investigations of technological advanced and industrially important materials. In this technique, the interaction of a short and intense laser pulse forms a plasma plume. The laser produced plasma plume consists of radiation which arises due to transitions of electrons from the excited states of atoms and ions. The aim of this thesis is the fabrication of the laser ablation time of flight mass spectrometer (LA-TOF-MS) with an improved resolution and to compare the compositional results of mass spectra from LA-TOF-MS with the emission spectra obtained from laser induced breakdown spectroscopy (LIBS). The compositional analysis using calibration free (CF-LIBS) techniques is based on the observed emission spectra of the laser produced plasma plume whereas, the elemental composition analysis using laser ablation time of flight mass spectrometer (LA TOFMS) is based on the mass spectra of the ions produced by laser ablation. We have successfully designed and locally fabricated an improved version of the laser ablation time-of-flight mass spectrometer (LA-TOF-MS) for isotope mass analysis and elemental analysis of materials. This system is coupled with a Q-switched Nd: YAG laser, which is capable of delivering the energy of about 850 mJ at 1064 nm and 500 mJ at 532 nm. The resolution of system has been improved by adjusting spatial and space focusing, and optimizing other parameters. The capability of the system has been exploited by the isotopic analysis and compositional analysis of different alloy samples, having certified composition. The laser ablation time of flight mass spectrometer complementary with Laser induced breakdown spectroscopy has xxi been used for the quantitative determination of constituents of certified samples; different Karats of gold (18K, 19K, 20K, 22K, 24K), Brass alloy (Cu 62%, Zn 38%) and Cu-Ni Alloy (75% Cu, 25% Ni). Moreover, the samples with the unknown compositions such as different brands of the cigarette available in Pakistan have also been investigated using LIBS and LA-TOF-MS techniques. Initially five Karats of gold alloys, 18K, 19K, 20K, 22K and 24K having certified composition of gold as 75%, 79%, 85%, 93% and 99.99% were selected and their precise elemental compositions were determined by LIBS and LA-TOF-MS. Here internal reference line self-absorption correction laser induce breakdown spectroscopy (IRSAC-LIBS) technique have been utilized for the quantitative determination of constituents present in different Karats. Elemental compositions of these gold alloys were also determined using a Laser Ablation time of flight mass spectrometer (LA-TOF-MS). The quantitative analysis of brass alloy has been studied using Laser Induced Breakdown Spectroscopy (LIBS), Energy Dispersive X-ray Spectroscopy (EDX) and Laser Ablation Time of Flight Mass Spectrometry (LA-TOF-MS). The emission lines of copper (Cu I) and zinc (Zn I) are used to calculate the plasma parameters. Here we have compared the elemental composition obtained by SCF-LIBS and IRSAC-LIBS with LA-TOF-MS and EDX. After utilizing SCF-LIBS and IRSAC-LIBS for quantitative analysis, we have compared the composition for Cu-Ni alloy using three calibration free LIBS techniques other than IRSAC-LIBS, and also compared the results with laser ablation LA-TOF-MS. For the quantitative determination of constituents of Cu-Ni Alloy (Pakistani five rupee coin of year 2004) of known composition (Cu 75%, Ni 25%), we have utilized one line calibrations-free (OL-CF xxii LIBS), self-calibration free (SCF-LIBS), and algorithm based calibration free (AB-CF LIBS) techniques. Results obtained by these LIBS based techniques have also been compared with LA-TOF-MS. The samples of fourteen different brands of cigarettes available in Pakistan have also been analyzed using the above mentioned techniques. We have also performed compositional analysis of the trace elements in different brands of tobacco available in Pakistan using one line calibration free (OLCF-LIBS) and Laser ablation Time of Flight Mass Spectrometer (LA-TOFMS). The results obtained by (CF-LIBS) are comparable with (LA-TOF-MS). The compositional results obtained by OL-CF-LIBS, SCF-LIBS, IRSAC-LIBS and algorithm based AB-CF LIBS are in agreement with that of LA-TOF-MS and other standard techniques. The analysis of different industrial important alloys and different brands of cigarettes demonstrates that LIBS complemented with LA-TOF-MS are powerful techniques for the elemental analysis of the major and trace elements in any solid samples.