Surface image analysis SIMS used

Imaging SIMS, used for spatially resolved elemental analysis. A focussed ion beam is rastered over the surface so that each point on the target is individually bombarded in turn, so that secondary ion emission is localized. The intensity of a particular secondary ion is monitored for each position of the primary beam and the result shown at the corresponding point of a synchronized oscilloscope display or computerized data system. In this way, pixel by pixel across the sample surface and in depth as the material is removed, three-dimensional information on the sample composition may be obtained. 

It is a remarkable feature of secondary ion mass spectrometry (SIMS) that considerable chemical information is accessible through the procedurally simple physical technique of sputtering. SIMS--espec ia 11 y under low primary ion flux conditions ("static SIMS," a 1 s o known as "molecular SIMS" when applied to compounds)—provides information on molecular weight and molecular structure and allows isotopic analysis. The surface sensitivity of SIMS permits its use in imaging, in monitoring of surface... 

There are basically three variations of the SIMS experiment. Static SIM.S is used for elemental analysis of sub-monolayers on surfaces. Although SIMS is basically a destructive technique, static conditions maintain the surface integrity during the lime scale of the experiment. Dynamic SIMS is used to obtain compositional information as a function of depth below the surface, nic dynamic SIMS experiment takes advantage of the destructive nature of SIMS to oblain information on various layers of materials. Imaging SIMS. also called scanning SIMS, is used to provide spatial images of surfaces. 

Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is a surface analysis technique used to analyze mass and image constituents that are present on the surface of materials. The equipment (Figure 12.47) uses a pulsed primary ion beam to desorb and ionize species from the sample surface. The resulting secondary ions are accelerated into a mass spectrometer and analyzed by measuring the ToF from the sample surface to the deteetor. The location and distribution of the species on the surface can be identified and an image shown at the detector. The composition is determined from the mass spectrum. Many different primary sources can be used for ionization ... 

The capability to directly obtain the spatial distribution of organic molecules with high surface sensitivity is one advantage of imaging SIMS analysis. SIMS imaging of polymers was used to solve a variety of polymer... 

Samples, one half coated with SiOa and the other half with Ti02, were used for quantitative surface analysis after each of the siuface treatment steps (cleaning, self-assembly, and polymer and protein adsorption, section 2). These samples exhibit material contrast on a macroscopic scale and are discussed in section 3.1. Micropat-temed surfaces were subjected to identical siuface modification procedures and characterized qualitatively by imaging ToF-SIMS (section 3.2) and fluorescence microscopy (section 3.3) and were used in the cell experiments (section 3.4). In both types of samples, material contrast (on a macroscopic or microscopic scale, Figure la) is converted into contrast with respect to protein adhesion (Figure Ic) via a series of surface modification steps (self-assembly of DDP, adsorption of PLL-g-PEG section 2). 

In addition to data obtained using the spectral mode of analysis, it is often important to know the location of a particular chemical group or compound on the sample surface. Such information is achieved by static SIMS chemical mapping—a procedure in which a specific chemical functionality on the material is imaged, providing information as to its lateral distribution on the surface. 

SIMS has superb surface sensitivity since most of the secondary ions originate within a few nanometers of the surface and since high detection efficiency enables as little as 10 " of a monolayer to be detected for most elements. Because of its very high surface sensitivity, SIMS can be used to obtain depth profiles with exceptionally high depth resolution (<5 nm). Since the beam of primary ions can be focused to a small spot, SIMS can be used to characterize the surface of a sample with lateral resolution that is on the order of micrometers. Elements with low atomic numbers, such as H and He, can be detected, isotope analysis can be conducted, and images showing the distribution of chemical species across... 

Valuable results with Tof-SIMS imaging have been obtained e.g., with paper samples. The distribution of papermaking chemicals on the surface of coated and uncoated papers is very important for its further treatment, such as printing. Figure 16 [70] is an example of use of the technique for chemical microscopy analysis of paper surfaces. 

Figure 13.7. The image of a fingerprint taken from a glass sheet surface (10,000 x 10,000 j,m). (Reprinted from Szynkowska, M. I. et al., 2007. Preliminary Studies Using Scanning Mass Spectrometry (TOF-SIMS) in the Visualisation and Analysis of Fingerprints, Imaging Sci. J., 55 180-187. With permission from Maney Publishing.) (See color insert.)...

---