Doctoral Defense - Tanvi Nikhar

About the Event

The Department of Electrical and Computer Engineering  

Michigan State University  

Ph.D. Dissertation Defense 

Thursday, February 20, 2025, 2:00 pm 

Civil and Environmental Engineering Conference Room EB 3546D and Zoom 

Contact Department or Advisor for Zoom Information

ABSTRACT

HIGHLIGHTING THE ROLE OF GAS-PHASE KINETICS IN CHEMICAL VAPOR DEPOSITION OF NANODIAMOND

BY: TANVI NIKHAR

ADVISOR: Dr. SERGEY BARYSHEV

The formation of nanodiamond through chemical vapor deposition (CVD) is a nuanced process and understanding the details of the physico-chemical processes involved in its synthesis can greatly enhance the capability of controlling the properties of the synthesized material. This work is geared towards developing a unified understanding of the gas phase and surface kinetics that can be universally applied across various CVD reactors for nanodiamond synthesis. 

Detailed structural and electrical properties of nanodiamond films grown in a H2/CH4 plasma were systematically studied as a function of reactor parameters. Such default deposition setup produced films that are a product of gas phase and surface processes combined. While diamond deposition is mostly understood in terms of surface kinetics, gas phase processes are not well analyzed. The deposition setup was altered to suppress surface kinetics by separating the plasma from the substrate. The collected sample, a product of gas phase kinetics, showed experimental proof of self-nucleation of nanodiamond in the gas phase, calling attention to the analysis of the plasma. 

Through plasma modeling, a hypothesis of nanodiamond nucleation and growth was formulated and compared with that of single crystal diamond growth. Gas temperature and CH3 radical distribution were identified to be the key determinants of the location of diamond formation in the plasma. To study this in greater detail, alternate reactor designs were attempted for compactness, portability and compatibility with plasma diagnostics. Radiofrequency and microwave flow-through plasma reactors were utilized to study the effect of gas temperature on carbon allotrope (sp2 vs sp3) formation. From this comparison, high gas temperature ~2000 K was proven to be necessary for sp3 phase (i.e. diamond) formation. Results from plasma simulations using the new reactor designs were in agreement with those for the industrial standard microwave chemical vapor deposition systems providing encouraging novel findings towards understanding the plasma engineering that universally apply to any microwave plasma CVD reactor. 

Persons with disabilities have the right to request and receive reasonable accommodation. Please call the Department of Electrical and Computer Engineering at 355-5066 at least one day prior to the seminar; requests received after this date will be met when possible.