Suraface Analysis Applications
Many applications within the surface analysis community have been developed by the customers or by Applied Surface Technologies. The early papers by Sherman in 1990, 1991 and 1994 used XPS to study CO2 snow cleaning on surface chemistries of wafers, metals, ceramics, polymers, and glasses. The extent of contamination removal was measured on many different samples.
Since then applications within the surface analysis field have included further explorations on cleaning "clean" and contaminated samples and also the cleaning of the equipment used in surface analysis.
Cleaning "clean" samples, in order to reduce the adventitious hydrocarbon background on surface have been explored and used by many scientists. Hydrocarbon reductions have been observed on many sample classes. Generally reductions as large as 50% have been noted on certain surfaces. Other users have reported larger reductions. The extent of hydrocarbon reduction by CO2 snow cleaning is similar to those by use of high purity reagent grade solvents such as acetone, ethanol and freons. Cleaning standards for AFM, XPS, Auger, and FTIR is common.
The removal of inadvertent or intentional contamination without altering the base material is sometimes required by surface scientists who use surface analysis techniques. Here, residual contamination from handling, field tests, or just atmospheric exposure can interfere the analysis. Generally solvent cleaning in reagent or better grades of acetone or ethanol can remove most inadvertent contamination, but there are cases where solvent cleaning is inadequate. In these cases, ultrasonic solvent cleaning may take too long, or may not be able to remove or adequately reduce the residues. This has been the case for several users within the automotive and chemicals industry who have been interested in exploring the surfaces of test parts or field failures. Users of carbon dioxide snow cleaning can quickly clean these parts in under 15 seconds and removing enough residue to allow analysis. The cleaning is probably a combination of solvent action and freeze fracture.
In another study involving Auger spectroscopy on ceramics, J. Geller{1993} found not only surface cleaning but also NO surface charge build up during the analysis of ceramic insulators such as MgO.
Carbon dioxide snow cleaning has also been used to clean the equipment. Cleaning of electron guns, ion guns, dual plasmatron sources, X-ray anodes have all been done. One customer has automated the cleaning of X-ray anodes. The tests have shown that snow cleaning can remove particles and organic residues can be removed quickly without much disassembly necessary.
Cleaning of AFM samples can be found on another page: Atomic Force Microscopy and XPS data can be found at Applications
Vaccum Technologies
Many applications in vacuum technologies were developed including the cleaning of stainless steel vacuum components, cleaning of electron, ion and x-ray optics, cleaning of residual gas analyzers (RGA), bellows, and others. Cleaning of electropolished stainless steel parts appears to be as effective as high purity reagent grade solvents such as acetone and methanol. Snow cleaning can remove the machining oils, particle residues, and other debris from the stainless steel surfaces and even weld rods and tips before welding. This process has led to less staining near the weld zones and less weld defects during vacuum system or bellows fabrication. Please email for details.
Cleaning vacuum assemblies also works well to remove debris left from assembly. One example was given by Layden and Wadlow who investigated and compared CO2 snow cleaning to solvent cleaning for a special high pressure RGA. The RGA was designed to operate below 1 micron pressure, and initial pumpdown times proved to slow even after the first solvent cleaning. Solvent cleaning was done by total disassembly of the unit and ultrasonically cleaning in isopropanol. Repeated solvent cleaning led to an improved pumpdown time but still not as fast as needed. For CO2 cleaning, just the filament and beam aperture were removed. All parts were cleaned simultaneously. Pumpdown times now were under 30 minutes or less. Analysis of outgassing elements after solvent cleaning showed hydrocarbons and alkaline based contamination; and after CO2 snow cleaning, these peaks were reduced or eliminated. This simple test by Layden demonstrates the ability to clean complex vacuum equipment with CO2 snow cleaning.
One user in 1993 has remarked that CO2 Snow Cleaning a SIMS source after rebuilding led to reduced High Voltage arcing when the instrument is energized. This was attributed to reduced particle populations that can be sources of high voltage discharge. A similar result has been mentioned for tests done at William and Mary on SS surfaces for vacuum applications. These later results were taken and expanded for accelerator work at Jefferson Lab.
