Tutorial_SIMS_questions_solutions.pdf

Secondary Ion Mass Spectrometry (SIMS) General knowledge questions 1. Describe how SIMS works. SIMS uses charged primary ions focused at a sample to sputter off atoms and molecules characteristic of the outermost atomic layers of the material. Common ion beams include Cs, Ar,...

Secondary Ion Mass Spectrometry (SIMS) General knowledge questions 1. Describe how SIMS works. SIMS uses charged primary ions focused at a sample to sputter off atoms and molecules characteristic of the outermost atomic layers of the material. Common ion beams include Cs, Ar, Ga, and Oxygen. 2. Describe at least three analytical features that differentiate SIMS from MALDI. Three of the following: Higher maximal spatial resolution, SIMS only analyzes top 50 nm of surface, SIMS needs no matrix coverage, SIMS mainly suited for small molecules and elements, SIMS does not ionize peptides/proteins, SIMS uses an ion beam instead of a laser to generate ions. 3. Is SIMS considered an ambient ionization technique? No, secondary ion ionization and emission from surfaces require high vacuum to take place 4. How does static SIMS instrumentally differ from Dynamic SIMS? The primary ion dose during SIMS measurements can be carefully controlled so that the damage to the surface is negligible and the technique is essentially considered as non-destructive; This is called Static SIMS. In Dynamic SIMS, conditions are arranged so that the surface is sputtered away during the experiment providing information as a function depth below the surface. 5. What is imaging SIMS? What type of information is obtained with Imaging SIMS? In imaging sims (also called scanning SIMS) the SIMS scans over the surface while obtaining secondary ion information. This provides a spatial image of surface composition. Similarly to static SIMS this is essentially non-destructive and only measuring the direct surface. 6. Rank the following ion beams in order of descending subsurface damage: a. Gallium ion beam b. Water cluster beam (H2O)28,000+ c. C60 molecular ion beam d. Argon cluster beam (Ar)1000+ e. Bi3+ ion beam The dimension of the cluster influences the amount of energy the ion carries. Ga (31), Bi (209), C60 (720), Ar (39000), H20 (54000). The correct answer is: a-e-c-d-b. Tutorial exercises 1. You are analyzing the surface of (i) polystyrene, (ii) polymethylmethacrylate, and (ii) a copolymer of the two polymers. Do you observe molecular ions of the polymers or fragments? Indicate which is which between the spectra below. Explain. No molecular ions are observed but only fragments as the ioniza on is more energe c than methods like ESI and Maldi. The residues indicate fragments from PS: PS main chain structure, such as C8H9+ (105) and 73 of MMA polymer. Thus a and c are the pure polymers and b the mixture of the two 1. You are analyzing the surface of a paint sample and an artificially aged paint. The two spectra are below. Do you think that the pigment is organic or inorganic? Which, in your opinion, is the original paint, and which is the aged sample? Explain. The original sample is the one above, as it shows residual faty acids presen ng double bonds. These were more quickly removed in the ar ficial aging process.