Graduate Studies

 

First Advisor

Yongfeng Lu

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Electrical Engineering

Date of this Version

8-2024

Document Type

Dissertation

Citation

A dissertation presented to the faculty of the Graduate College of the University of Nebraska in partial fulfillment of requirements for the degree of Doctor of Philosophy

Major: Electrical Engineering

Under the supervision of Professor Yongfeng Lu

Lincoln, Nebraska, August 2024

Comments

Copyright 2024, Zhipeng Wu. Used by permission

Abstract

Application of diamond coatings on metallic substrates endows them with superior properties including mechanical robustness and corrosion resistance, rendering them highly adaptable for diverse industrial and technological applications. However, significant disparities in coefficients of thermal expansion (CTEs) result in pronounced residual stress near interfaces, causing delamination of the diamond coatings. Moreover, weak chemical bonding poses a concern for certain metallic substrates. Laser surface processing techniques show promise in enhancing adhesion by altering stress distribution and improving mechanical bonding. Therefore, the research efforts described in this dissertation mainly focus on femtosecond (fs) laser texturing for enhanced adhesion of diamond coatings on various metallic substrates including stainless steel 316 (SS 316) and copper (Cu). In addition, laser surface processing has been identified as an effective method for drying wafers.

Diamond coatings were deposited using combustion chemical vapor deposition (CVD) assisted by infrared-laser vibrational excitations of ethylene. Through fs laser texturing, adherent diamond coatings were achieved on SS 316 substrates. For Cu substrates, which exhibit low affinity with diamond, fs laser texturing was utilized in conjunction with nickel (Ni) interlayers to facilitate the firm coating of diamond. A comprehensive investigation was conducted into the influence of texture structures, taking both depth and shape into consideration. Furthermore, growth dynamics were analyzed by varying the deposition time.

Clean, dry silicon (Si) substrates can be obtained without any staining or damage through the usage of nanosecond (ns) laser pulses for laser-induced sub-surface evaporation. Time-resolved imaging was employed to investigate the drying dynamics following the interaction between laser pulses and substrates. Moreover, the influence of substrate conditions, including surface roughness, hydrophilicity, and material properties, on laser drying was thoroughly examined.

Advisor: Yongfeng Lu

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