Improved Carbon Analysis with Evactron Plasma Cleaning

Abstract

Analyzing carbon in an electron microscope by EDS is difficult, since the pollution by hydrocarbons is responsible for a fast growing C peak when the beam is positioned in spot mode. Hydrocarbons from the chamber surfaces, vacuum pumps and sample surface migrate, react with the electron beam and form a black spot rich in carbon where the analysis is conducted. The analytical difficulty extends to N, which peak is partially overlapped by the growing adjacent C peak and strongly absorbed by the carbon layer that builds up at the surface.The Evactron Anti-Contaminator (A-C) removes Hydrocarbons from the SEM vacuum and from the sample surface [1]. The Evactron A-C is a small RF plasma device mounted on a chamber port and produces Oxygen radicals to oxidize off the hydrocarbons. Although a full clean-up of a dirty microscope chamber use for years cannot be expected in a few minutes, the following results show that the Evactron A-C makes low level carbon analysis possible just after installation.To test the improvement on removing C pollution, a pure Cu polished sample has been used. The microscope was a Gemini 982, fitted with a Noran thin window EDS. The sample had been prepared using the best standard procedure recognized by the operator to give the smallest pollution: polishing, ultrasonic cleaning and final cleaning with pure ethanol. Spectra have been acquired at 15 kV and the EDS system used to measure net intensity peaks on the elements found: C and Cu La. The spot was left static for 15 minutes, and spectra were run for 50 s. The first spectrum was acquired immediately and then three other after 3, 6 and 15 minutes. Results:The first series of spectra has been acquired before Evactron A-C cleaning. The spectrum shows immediately a C peak, and this carbon peak quickly grows up from a relative C/ CuLa intensity ratio of 0.76 % to 5.06 % after 15 minutes of static beam, as it can be seen on the spectrum in Figure 1. The Evactron A-C was then run 4 minutes to remove the hydrocarbons. The first spectrum acquired after cleaning still showed a small carbon peak ratio of 0.61 % that grew up to 1.39 % after 15 minutes. This improvement was impressive but not enough: you cannot expect to clean a sample and a large chamber that had been used for several years in 4 minutes. So a second 4 minutes cleaning was done and a third one two hours later. This gave time to the trapped hydrocarbons to diffuse back and be converted to H 2 O, CO and CO 2 by oxygen radicals from the Evactron A-C. After the third run, the EDS system did not find any carbon in the spectrum for the spectra acquired immediately and after 3 minutes. The spectrum acquired after 6 minutes and 15 minutes showed a small increase of the C intensity that allowed the software to detect C.

Surface deterioration and elemental composition of retrieved orthodontic miniscrews

“…The carbon quantification was excluded from this study because of the technical limitation of the EDX in an electron microscope. 20 Elements with lower atomic masses such as carbon (atomic number 6 and lower) are difficult to distinguish from each other using EDX. The carbon x-rays have low energy and are easily absorbed by the x-ray detector windows.…”

“…Hydrocarbons from the chamber surfaces, vacuum pumps, and sample surface migrate and react with the electron beam to form a black spot that is rich in carbon. 20 After elemental analysis with the EDX, the retrieved MSIs were subjected to a cleaning cycle of 30 minutes in an ultrasonicator, completely immersed in enzymatic detergent (Cidezyme; ASP: a Johnson and Johnson company, Irvine, Calif) so that organic debris would be removed and the surface topography of the MSIs could be fully observed under the microscope. 16 After cleaning, they were again mounted on carbon stubs and kept in a dessicator for 24 hours, and surface images were taken with SEM (Leo 435VP; SEMTech Solutions, Cambridge, United Kingdom).…”

Windowless, Silicon Nitride window and Polymer window EDS detectors: Changes in Sensitivity and Detectable Limits

“…Plasma cleaners have become common accessories to modern SEMs as they help reduce sample and chamber contamination, and they have even been shown to improve light element sensitivity in EDS measurements (3). However, there is still debate about to which extent cleaning is compatible with x-ray windows.…”

Study of biomechanical behavior of the all ceramic dental crown

“…The K line X-ray carbon is easily absorbed only from the surface of the specimen. Significant carbon background signals and hydrocarbon interfere with the quantitative analysis and can be responsible for a fast growing C peak [55]. Nevertheless, the latter explanation does not seem sufficient to explain these high concentrations.…”

“…For glass ceramic reconstructions, the two elements are assembled by an adhesive system (54). In the literature, these reconstructions are defined as Resin Bonded All Ceramic crowns (RBCs) (55).…”