Mass analyzer, SIMS instrument

Figure 8 Atomika Dynamic In Depth Analyzer (ADIDA), quadrupole-based-imaging secondary ion mass spectrometry (SIMS) instrument.

In Dynamic Secondary Ion Ma s Spectrometry (SIMS), a focused ion beam is used to sputter material from a specific location on a solid surface in the form of neutral and ionized atoms and molecules. The ions are then accelerated into a mass spectrometer and separated according to their mass-to-charge ratios. Several kinds of mass spectrometers and instrument configurations are used, depending upon the type of materials analyzed and the desired results. 

The basic instrumental set-up for dynamic SIMS is the same as for SSIMS (Sect. 3.1.2). Depending on the intensity, beam diameter, and ion species needed, dif ferent ion sources are used. Several mass analyzers with different characteristics enable a broad field of applications. 

Apart from the quadrupole and TOP analyzers described in Sect. 3.2.2, the most important types of mass analyzer used in common dynamic SIMS instruments employ a magnetic-sector field. 

TOF analyzer it is critical for the mass resolution that the secondary ions are ejected at a precisely defined time. This means that the primary ion pulse should be as narrow in time as possible, preferably < 1 ns. At the same time maximum lateral resolution is desired. Unfortunately, there is a trade-off between these two parameters if the primary ion intensity is not to be sacrificed [122], Therefore, TOF-SIMS instruments have two modes of operation, high mass resolution and high lateral resolution. An advantage with the pulsed source is that an electron flood gun can be allowed to operate when the primary ion gun is inoperative. Thus, charge-compensation is effectively applied when analyzing insulating materials. 

The compatibility is excellent with continuous ion sources such as ESI, dynamic SIMS, CF-FAB, ICP, El, Cl, etc. Sector instalments are not well-suited for pulsed ionization methods, although there are examples where MALDI sources have been utilized [225-229]. Sector instruments are usually larger and more expensive than other mass analyzers, such as TOFs, quadrupole filters, and traps. 

Time of flight (TOF), 75 660-661 Time-of-flight (ToF) mass analyzers, 24 109 Time of flight diffraction (TOFD), 79 486 Time-of-flight instrumentation, in particle counting, 78 150—151 Time-of-flight-SIMS technique, 24 109 Time-resolved fluorimetry, 74 148-149 Time-resolved spectra, analysis of, 74 613 Time standards, 75 749—750 Time-temperature parameters (TTP), 73 471, 478, 479 creep properties and, 73 480 Time-temperature superposition, 27 746-747... 

Time of flight ion probes (TOF SIMS) have unique capabilities not found in other mass spectrometers. A pulsed ion beam, typically either cesium or gallium, ejects atoms and molecules from the sample. Ionized species are accelerated down the flight tube and the arrival time in the detector is recorded, giving the mass of the species (see discussion of time-of-flight mass analyzers above). TOF SIMS instruments used in cosmochemistry have spatial resolutions of <1 pm. They are used to determine elemental abundances in IDPs and Stardust samples. The spatial distribution of elements within a small sample can also be determined. TOF SIMS instruments can obtain good data with very little consumption of sample. 

A static calibration is used to accurately park the quadrupole mass analyzer on a specific mass of interest. If only a static calibration is performed, the instrument is calibrated for acquisitions where the quadrupoles are held at a single mass as in SIM or SRM. 

The time-of-flight secondary ion mass spectroscopy (ToF-SIMS) analysis was performed on a CAMECA ION-TOF Model IV spectrometer. This instrument was equipped with a reflection-type ToF mass analyzer and a pulsed 25 kV primary... 

Improvements in solid mass spectrometry after the Second World War focused on the development of several types of ion source and mass analyzers. For example, the fundamentals of secondary ion mass spectrometry had already been described by the observation of secondary ions by Thomson in 1910 5 T had the occasion.. . to investigate the secondary Canalstrahlen produced when primary Canalstrahlen strike against a metal plate. Significantly later in 1949, the first instrumental arrangement for secondary ion mass spectrometric measurements was reported by Herzog and Viehbock.43 The idea of applying secondary ions for surface analysis was developed in 1950 at the RCA Laboratories, Princeton, where Honig44 presented results of early SIMS studies. 

TOFSIMS analyses were performed on a Kratos PRISM instrument. It was equipped with a reflectron-type time-of-flight mass analyzer and a pulsed 25 kV liquid metal ion source of monoisotopic 69Ga ions with a minimum beam size of 500 A. Positive and negative spectra were obtained at a primary energy of 25 keV, a pulse width of 10-50 ns, and a total integrated ion dose of about 10" ions/cm2. This is well below the generally accepted upper limit of 5 x 1012 ions/cm2 for static SIMS conditions in the analysis of organic materials [12], The mass resolution at mass 50 amu varied from M/AM= 1000 at 50 ns pulse width to about 2500 at 10 ns pulse width. 

In 1967 Liebl reported the development of the first imaging SIMS instrument based on the principle of focused ion beam scanning [24]. This instrument, the ion microprobe mass analyzer, was produced by Applied Research Laboratories (Fig. 4.5). It used an improved hollow cathode duoplasmatron [25] ion source that eliminated filaments used in earlier sources and allowed stable operation with reactive gases. The primary ion beam was mass analyzed for beam purity and focused in a two-lens column to a spot as small as 2 pm. The secondary ions were accelerated from the sample surface into a double focusing mass spectrometer of Mattauch-Herzog geometry. Both positive and negative secondary ions were de-... 

In 1965 Long published a proposed ion microprobe analyzer [27]. Long s student, Drummond, began construction and in 1967 published secondary electron micrographs showing 0.5-pm resolution [28] using a primary beam column. This became the basis for the Associated Electrical Industries (AEI) Ltd. SIMS instrument [29]. This instrument utilized AEI s MS702R spark source mass spectrometer for secondary ion analysis and had a mass resolution of -5000. 

SIMS Analysis. The equipment and instrumental conditions have been described in detail (7.121. Mostly, a model 6300 Perkin Elmer spectrometer was used which was equipped with a 0-255 amu quadrupole mass analyzer. The primary beam of 4.5 keV Xe+ and 60 pA current was rastered in a 2x2 mm2 area. The total ion dose was not more than 3xl012 ions per cm2, which is considered a practical limit for static conditions (5rZ)- Charge neutralization was done by means of 500 eV electrons. Spectral optimization has been described (7.121. 

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