Characterization and Improvement of Ultra-Thin Carbon Foils for Space Instrumentation,

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Principal Investigators
Frédéric Allegrini
Dave McComas
David T. Young

Inclusive Dates:  07/01/03 - Current

Background - Ultra-thin carbon foils (approximately 5 nm) are critical nanotechnology components of many space instruments used for particle detection. As low energy (100s eV - 10s keV) ions and neutral atoms enter and exit the foils, they generate secondary electrons, which are often used to trigger coincidence or time-of-flight measurements. Further, charge exchange occurring at the exit of foils has been used to ionize neutral particles, thus allowing them to be electro-optically filtered and ultimately detected. Besides these useful properties of electron emission and charge exchange, however, the interaction also has unwanted effects like energy loss (straggling), and angular scattering of the particles, which are strong functions of particle species and energy as well as foil composition, thickness, cleanliness, and impact angle.

Approach - In this project, the research team proposes to quantify all these effects, both the wanted and the unwanted, as functions of the various foil and projectile parameters. These measurements will allow the team to understand better the physics of the interaction of particles with carbon foils and to develop significantly improved space instruments in the future. Finally, the team further proposes to examine enhancements to simple carbon foils by depositing extremely thin layers of different materials that have significantly different electronic interactions with the projectiles.

The main goal is to fully characterize and find improvements to the carbon foils used for space instruments. The objectives have been divided into three categories:

Objective 1. To make independent measurements with SwRI's sets of carbon foils and to fill in the lacking data in the literature.
Objective 2. To improve the charge conversion efficiency of carbon foils.

Accomplishments - The team set up an apparatus for measurements of the interaction of particles with carbon foils. The apparatus works in a high-vacuum chamber in the space instrument calibration facility at SwRI. The ion beam is produced by a duoplasmatron ion source. SwRI also has the capability to mount ultra-thin (down to 0.5 µg/cm2 or approximately 2.5 nm) carbon foils on fine nickel grids. Additionally the team has developed a technique for quantifying optically the percentage of damaged cells for ultra-thin carbon foils. SwRI has created a three-dimensional model of the apparatus with an electrostatic simulation software in support to the measurements. The team has measured the energy loss as a function of the particle's energy for different carbon foils and different projectile species.

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