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Laser Induced Surface Structuring of Metals Correlated With Breakdown Spectroscopy and Field Emission Properties

Thesis Info

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Author

Mahreen Akram

Program

PhD

Institute

Government College University

City

Lahore

Province

Punjab

Country

Pakistan

Thesis Completing Year

2018

Thesis Completion Status

Completed

Subject

Physics

Language

English

Link

http://prr.hec.gov.pk/jspui/bitstream/123456789/11295/1/Mahreen%20Ikram_Phy_2018_GCU%28L%29_PRR.pdf

Added

2021-02-17 19:49:13

Modified

2024-03-24 20:25:49

ARI ID

1676726576747

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In this dissertation three important aspects of laser-matter interaction for four selected metals i.e. Zinc (Zn), Copper (Cu), Molybdenum (Mo) and Tungsten (W) are addressed. These aspects include: (1) Understanding of physical processes involved in laser ablation and surface structuring, (2) The role of two important laser induced plasma parameters i.e. electron temperature (Te) and electron number density (ne) for the growth of various surface structures and (3) Applications of these surface structures for enhancing the field emission properties of the selected metals.The laser induced surface structuring is performed by employing both nanosecond (ns) and femtosecond (fs) i.e. Nd:YAG (1064 nm, 10 ns , 10 Hz) and Ti: sapphire (800 nm, 30 fs , 1kHz) laser irradiation. The crater depth is investigated using optical microscope analysis. The surface morphology is explored by Scanning Electron Microscope (SEM) analysis. For the estimation of plasma parameters Laser Induced Breakdown Spectroscopy (LIBS) analysis is employed. The field emission properties are explored by using the self-designed and fabricated set-up in a diode configuration under ultrahigh vacuum condition. The whole dissertation is divided into three parts.Part A deals with the laser induced surface structuring of metals and its correlation with the plasma parameters at various irradiances ranging from 6 GW/cm2 to 50 GW/cm2.The irradiation is carried out for three metals i.e. Zn , Mo and W with low, moderate and high melting points. SEM analysis of laser ablated Zn reveals the formation of microscale ripples, wave-like ridges with cones and cavities. For Mo, large sized grains along with cavities and conical interiors, dense ridges with droplets are seen. For W, the formation of grains with pronounced cracking and large sized cones are observed. The evaluated values of Te explored by LIBS analysis vary from 5973 K to 6240 K for Zn, 6526K to 9305 K for Mo and 7800 K to 16383 K for W. Similarly The values of ne vary from 1.35861×1018 cm-3 to 1.44331×1018 cm-3 for Zn, 0.58,878 × 1018 cm-3 to 0.72,067 × 1018 cm-3for Mo and 0.46,085 × 1018 cm-3 to 0.69,679 × 1018 cm-3 for W.It is found that surface structuring of selected metals strongly depend on the laser irradiance and plasma parameters. Part B and C of the dissertation are independent and deal with ns and fs laser induced surface structuring of selected metals for the enhancement of FE properties. The part B deals with the investigation of FE properties of the ns laser irradiated Cu and W metals at four laser irradiances ranging from 13 GW/cm2to 50 GW/cm2. SEM analysis revealed the formation of ridged protrusions, localized melt pools, cones and pores for Cu, whereas, cones, grains and mounds covered with porous structures are observed for W. The Fowler-Nordheim (FN) plots are found to be linear and confirm the quantum mechanical tunneling phenomena for the structured metals. The values of turn-on field, field enhancement factor and maximum current density rangefrom 5 V/ μm to 8.5 V/ μm , 1380 to 2730and 147 μ A / cm2 to 375 μ A / cm2 for Cu and 5 V/μm to 8.5 V/μm,1300to 3490 and 107 μA/cm2 to 350 μA/cm2 for W respectively. Part C deals with the investigation of FE properties of fs laser irradiated W carried out at six different irradiances ranging from 0.2 × 1014 W/cm2 to 6.9 × 1014 W/cm2. The SEM analysis revealed particulates, grains and nanoscale ripples formation. The values of turn on field, field enhancement factor and maximum current density range from 7 to 15 V/μm, 460 to 6120 and 134 μA/cm2 to 341 μA/cm2 respectively. The obtained FE parameters are well correlated with the surface morphology and comparable to the previously reported values.Overall dissertation presents the idea that both laser irradiance and plasma parameters can provide a better control over micro/nano structuring of metals which make them potential candidate for the enhancement in the FE properties as well as other applications.
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ہمیں معلومات سے زیادہ حکمت چاہیے

ہمیں معلومات سے زیادہ حکمت چاہیے
نحمدہ ونصلی علی رسولہ الکریم امّا بعد فاعوذ بااللہ من الشیطن الرجیم
بسم اللہ الرحمن الرحیم
معزز اساتذہ کرام اور میرے ہم مکتب ساتھیو!
آج مجھے جس موضوع پر لب کشائی کا موقع دیا گیا ہے وہ ہے:’’ہمیں معلومات سے زیادہ حکمت چاہیے‘‘
صدرِذی وقار!
علم ایک خزانہ ہے، ہر ایک اس خزانے سے اپنی تجوریوں کو بھرنا چاہتا ہے، علم جستجو سے حاصل ہوتا ہے ،علم کے حصول کے لیے محنت شاقہ کی ضرورت ہے، علم کی تگ و دو میں زندگیاں صرف ہو جاتی ہیں۔ معلومات حاصل کرتے کرتے ایّام زیست گزر جاتے ہیں۔ معلومات جیسی بھی ہوں جہالت کے گھٹا ٹوپ اندھیروں کا خاتمہ کر دیتی ہیں۔
جنابِ صدر!
معلومات کا خزانہ اس وقت متمتع اور کار آمد ثابت ہوتا ہے، جب اس خزانے کے صحیح مصارف معلوم ہوں، ان معلومات کے لیے صحیح استعمال سے آشنائی حاصل ہو، معلومات کے مطابق زندگی کے ڈھنگ ہر صاحب علم کی دسترس میں ہوں۔ دنیا بھر کی معلومات ہیں لیکن وہ صرف اپنی ذات کی حد تک محدود ہیں تو وہ نہ ہونے کے برابر ہیں۔
جنابِ صدر!
جب کسی کام میں حکمت شامل ہو جاتی ہے تو اس کے حسن کو دوبالا کر دیتی ہے، اس کی خوبصورتی میں اضافہ ہو جاتا ہے، اس کی دھنک کے رنگ نمایاں ہو جاتے ہیں، اس کی اہمیت دوبالا ہو جاتی ہے، اس کی شان نرالی ہو جاتی ہے۔ دانائی اور حکمت سے معمور کام انفرادیت کا حامل ہوتا ہے، اس علم صفت کے حامل طفلان خودمعا ملہ نہیں ہوتے بلکہ زیرک و فطین لوگ ہوتے ہیں۔
صدرِذی وقار!
حکمت کے پھول کاغذی پھول نہیں ہوتے، گلشن حکمت و دانائی میں چلنے والی ہوا حیات بخش جھونکوں سے معمور ہوتی ہے، جس جگہ پر حکمت ہوتی ہے...

Muatan Konten Lokal pada Materi Pelajaran Bahasa Inggris di SMP Negeri 5 Sigi

Based on the 2013 curriculum 2016’s revision, there are subject materials that demand about local content in English subjects at the level of SMP Class VII. Teachers need many researches and practices integrating and implementating these subjects. Basically,   it needs to be done in-depth study in the form of content analysis. This research was conducted on content and learning English in SMP Negeri 5 Sigi. This study aims to find out 1) how many percentage of local content in English lesson material Class VII SMP in the curriculum 2013 revision 2016; 2) how to integrate local content in English subject matter in SMP Negeri 5 Sigi; 3) how the implementation of material with local content in English learning in SMP Negeri 5 Sigi, and; 4) how to integrate local content in effective and efficient English lessons in SMP Negeri 5 Sigi. The study used a qualitative descriptive approach with the method of collecting document studies, interviews, and observation. The research results are 1) the proportion of local content that can be integrated into English language learning material SMP is 95%; 2) the integrity of local content in English learning materials in SMP Negeri 5 Sigi can be found in the lesson plan; 3) implementation of materials with local content in English learning attached to KTSP, Syllabus, lesson plan and learning resources enrichment book.

Fixed Frequency Sliding Mode Control for Power Electronic Converters

In the modern era of industrialization, power electronic converters have gained key importance due to their wide range of applications such as; use in arc furnaces, in duction heating systems, variable speed drives of motors, power supplies of various electronic systems, fluorescent lamps, elevators and cooling systems. Furthermore, the low-cost proliferation of power electronic devices due to the technological de velopments in the semiconductor industry has made them an attractive choice for integrating renewable energy resources. They are the essential and integral part of the systems providing solutions to issues like voltage sag, swell, frequency reg ulation, current sharing among different renewable energy resources, power factor correction and voltage regulation in different types of micro-grids. In all the above-mentioned applications, the robustness of the system under dif ferent load and line conditions depend upon the control algorithm of the power electronic converters. This is why the research in the field of power electronics has been focused on the control of power converters during the last decade. Among different types of control techniques, Sliding Mode Control (SMC) is renowned for its disturbance rejection and parameter invariant nature which makes it an irre sistible choice for controlling such systems. However due to physical constraints of the switching components, ideal condition of infinite frequency cannot be sat isfied. This causes the system to operate at finite but time varying switching frequency which is a serious issue for power electronic converters as they consist of passive components whose size and value depends upon the switching frequency. Moreover, the time varying switching frequency degrades the power quality and causes electromagnetic interference (EMI) issues in case of grid connected power converters. In the first phase of this research, a fixed frequency sliding mode controller uti lizing an integral sliding manifold is designed to improve the dynamic response of the power converter regulating the grid voltage, in the presence of unknown x load condition and uncertain network parameter of the micro-grid. A special purpose test rig is designed to experimentally validate the results in comparison with conventional PI controllers. In the second phase of the research, the power quality issues regarding DC micro grids are addressed. Power quality issues have been widely discussed regarding AC power systems but discussion regarding DC power quality in micro-grids is rare in research community because in past power transmission was carried out using AC systems only. However, in the recent years DC grids and transmission has emerged as an attractive solution to integrate renewable energy resources. Hence, to enhance the power quality, a fixed frequency SMC is proposed with harmonic cancellation and chattering reduction, using a PI type sliding manifold. Experimental results are presented to validate the theoretical derivations using the test rig. Finally, a new method based upon filter extraction of the equivalent control is proposed to fix the switching frequency in power converters controlled by SMC. The technique is implemented on a boost converter and the results are presented in comparison with PWM-SMC. Rigorous mathematical analysis is provided along with experimental results to validate the proposed technique.