Molecular Depth Profiling and Chemical Imaging with Cluster ToF-SIMS

Open Access

Author:

Shen, Kan

Graduate Program:

Chemistry

Degree:

Doctor of Philosophy

Document Type:

Dissertation

Date of Defense:

July 10, 2015

Committee Members:

• Nicholas Winograd, Dissertation Advisor
• Nicholas Winograd, Committee Chair
• Barbara Jane Garrison, Committee Member
• Christine Dolan Keating, Committee Member
• Yingwei Mao, Committee Member

Keywords:

• ToF-SIMS
• molecular depth profiling
• chemical imaging

Abstract:

The work presented in this dissertation is concentrated on improving the fundamental understanding of molecular depth profiling and chemical imaging associated with time-of-flight secondary ion mass spectrometry (ToF-SIMS) equipped with cluster ion sources, mainly C60 and argon gas cluster ion beams (Ar-GCIBs). A gold-cholesterol hybrid system is used to elucidate the reasons for the difficulties of depth profiling of heterogeneous thin film structures. The model study provides mechanistic insight into depth profiling of hybrid materials and offers an appropriate strategy for improving the quality of the depth profiles. Depth profiling of trehalose thin films is investigated under different Ar-GCIBs bombardment conditions to elucidate the influence of cluster size and kinetic energy on the formation of molecular ions. The study provides insight into selecting optimal Ar-GCIBs characteristics for molecular depth profiling of organic materials. Finally, room temperature ionic liquids (ILs) are employed in mass spectrometry imaging experiments. The surface and the internal structure of microspheres synthesized in ILs are investigated by the high spatial resolution imaging and depth profiling capabilities of cluster ToF-SIMS. The study introduces a new type of matrix for imaging mass spectrometry and provides insight into the key drivers and restraints behind ToF-SIMS three-dimensional (3D) molecular analysis. Overall, the thesis work is of great value for the fundamental understanding cluster ion-solid interactions in ToF-SIMS analysis and is beneficial for the advancement of the technique.