NSF Award
2214998
NON-TECHNICAL SUMMARY<br/><br/>This Major Research Instrumentation (MRI) award will develop a secondary ion mass spectrometer with higher sensitivity than current commercial instruments and also with better depth resolution. Secondary ion mass spectrometry is used for chemical analysis of the surface layer of solids with up to part per million sensitivity and nanometer depth resolution. In this chemical analysis method, an ion beam is used to remove material from the outermost surface of the sample. This beam is referred to as the primary ion beam. Some of the removed materials lose electrons forming secondary ions that escape the surface of the studied material along with neutrals. These secondary ions are then analyzed to find their mass which yields the material composition. An increase in the ratio of secondary ions to neutrals increases the detection sensitivity and resolution. Current commercial secondary ion mass spectrometers use singly-charged ions to remove molecules from the surface of the sample. In this project, multicharged ions from laser ablation will be used as the primary ions, which can enhance the ratio of secondary ions to neutrals from the studied sample and, correspondingly, increase chemical detection sensitivity and resolution. The developed instrument will enable the chemical analysis of ultrathin layers used in nanoelectronics for high-speed computers, advanced electronic devices, and sensors. The instrument will also enable fundamental studies to better understand the interaction of multicharged ions with materials, therefore, advancing the use of multicharged ions in nanofabrication. At least three Ph.D. students will be involved in the development of the instrument, while many faculty and graduate and undergraduate students will utilize the instrument once it is commissioned. Also, over the duration of the project, 20‒24 Old Dominion University undergraduate students will participate in the project as part of their engineering and physics senior projects, and 2‒4 University of California-Berkeley undergraduate students will participate in the simulation of the ion beam components of the instruments.<br/> <br/><br/>TECHNICAL SUMMARY<br/><br/>This project will develop a secondary ion mass spectrometer (SIMS) with higher sensitivity than current commercial SIMS and also with better depth resolution. The key technological improvement is the use of multicharged ion (MCI) pulses generated from a compact laser ion source as the primary beam. Current commercial SIMS uses singly-charged ions or clusters for the primary beam, which causes secondary ion ejection by collisional sputtering from the surface of a sample. Multicharged primary ions with high potential energy cause potential energy sputtering in addition to collisional sputtering, in which the ionization fraction for the secondary beam can be two-to-three orders of magnitude higher than for singly-charged ions or clusters. The higher ionization fraction results in a corresponding increase in SIMS sensitivity and depth resolution. A pulsed laser will be used to ablate bismuth or gold targets, producing an intense source of MCIs. These ion pulses will be accelerated and shortened to a few nanoseconds. Then, a specific charge will be selected and incident on the sample to be analyzed. A time-of-flight ion spectrometer will be built to identify the mass of the secondary ions. The instrument sensitivity, mass resolution, and depth and lateral resolutions will be tested under static and dynamic SIMS. The MCI-SIMS will enable elemental depth profiling of shallow-implanted dopants, identification of the composition of the surface region of thin films and ultrathin layers with much reduced pre-equilibrium region and mixing effects, and nanoscale ion implantation for implantation-based quantum devices. The instrument will enable further research on MCI interaction with surfaces and the study of synergy between MCI-surface interaction and laser surface excitation. At least three Ph.D. students will be involved in the development of the MCI-SIMS, while many faculty and graduate and undergraduate students will utilize the instrument once it is commissioned. Also, over the four years, 20‒24 Old Dominion University undergraduate students will participate in the project as part of their engineering capstone senior design and physics senior thesis, and 2‒4 University of California-Berkeley undergraduate students will be introduced to particle-in-cell simulation as undergraduate research.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
