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SIMS: Secondary Ion Mass Spectrometry
Published in Terrance E. Conners, Sujit Banerjee, Surface Analysis of Paper, 2020
Lisa D. Detter-Hoskin, Kenneth L. Busch
If secondary ions are to be sputtered from insulating surfaces, a residual charge can accumulate on the surface that prevents further ion sputtering. Charge compensation is accomplished by using a low energy electron (< 10 eV) flood gun placed near the surface. An essentially neutral surface is maintained through a balance of the arrival of positive ions, the creation and capture of low energy electrons, and the departure from the surface of sputtered ions and electrons. The ion extraction optics of a SIMS instrument vary with the intended use and resolution required. Quadrupole-based SIMS instruments provide low resolution mass spectra, and can achieve moderate spatial resolution. Sector-based instruments can provide higher resolution mass spectral data, and dynamic emittance matching is used in a sophisticated ion optical system to maintain congruous transmission of ions into the mass analyzer from a small surface area. In an ion microscope, secondary ions from a relatively large irradiated surface area pass through the instrument optics in such a way that the image of the surface is preserved. An ion microprobe uses a scanning approach in which the position of the primary ion beam on the surface is rastered, and the ions that pass through the extraction optics to the detection system at any specified time are referenced to the surface position of the rastered beam.
Photo/Electromagnetic Sources
Published in Peter E. J. Flewitt, Robert K. Wild, Physical Methods for Materials Characterisation, 2017
Peter E. J. Flewitt, Robert K. Wild
Bombarding a surface with photons and ejecting electrons causes the surface to become positively charged. This will cause the photoelectron peaks to move to a lower kinetic energy, which could result in an erroneous chemical state identification. There are many practical ways to reduce or eliminate surface charging. Either an electron flood gun is used to fire a wide beam of low-energy electrons onto the surface to neutralise the charge or a monolayer of conducting material, such as gold, is deposited onto the surface to provide paths for charge leakage. These methods are not always satisfactory for many insulating materials. It is, however, possible to utilise the difference in the change in the energy of an Auger peak and equivalent photoelectron peak to determine the chemical state, and this is independent of charging. The difference between the Auger and photoelectron chemical shifts results from the difference in final-state relaxation energies between the chemical states (Briggs and Seah 1990). A parameter, the Auger parameter αA, can be defined such that (Wagner 1975) () αA=EAuger−Ephotoelectron. In practical terms, this is the difference between the most intense Auger transition and the most intense photoelectron peak. αA can have negative values, and to overcome the problem, Wagner et al. (1979a) defined a ‘modified’ Auger parameter, α*, where () α∗=αA+hv=EAuger(kinetic)+Ephotoelectron(binding energy).
Thermodynamic and kinetic investigation of heavy metals sorption in packed bed columns by recycled lignocellulosic materials from olive oil production
Published in Chemical Engineering Communications, 2019
Andrea Petrella, Danilo Spasiano, Vito Rizzi, Pinalysa Cosma, Marco Race, Nicoletta De Vietro
These findings were confirmed by X-Ray Photoelectron Spectroscopy (XPS) analysis. XPS detections were performed using a Thermo Electron Theta Probe spectrometer (Thermo Fisher Scientific Inc., USA) equipped with a monochromatic Al Ka X-ray source (1486.6 eV) operating at a spot size of 300 μm corresponding to a power of 70 W. Survey (0–1400 eV) and high resolution (C1s, O1s, N1s) spectra were recorded in FAT (fixed analyzer transmission) mode at pass energy of 200 and 100 eV, respectively. All spectra were acquired at a take-off angle of 37° with respect to the sample surface. Charge compensation was accomplished by a low energy electron flood gun (1 eV). Charge correction of the spectra was performed by taking the hydrocarbon (C–C, C–H) component of the C1s spectrum as internal reference (binding energy, BE = 285.0 eV). Atomic percentages were calculated from the high resolution spectra using the Scofield sensitivity factors set in the ThermoAvantage V4.87 software (Thermo Fisher Corporation, USA) and a non-linear Shirley background subtraction algorithm. The best-fitting of the high-resolution XPS spectra was performed using mixed Gaussian–Lorentzian peaks after a Shirley background subtraction; a maximum relative standard deviation of 10% was estimated on the area percentages of the curve-fitting components, while the determined standard deviation in their position was ±0.2 eV.