Transfer lens

When the whole sample surface is irradiated by the exciting X-rays, an image can be obtained in a different way The spot accepted by the transferring lens system in front of the input of the CHA is rastered by introducing deflector plates in front of the lens system. Again, only electrons of a characteristic energy can pass the analyzer. This technique is realized with the Axis series. 

Turner et al. [114] described an ICP-MS with a hexapole transfer lens (Fig. 3.12a) in a tube that allows the pressure to be maintained. The cell was initially reported to contain He, although it is likely that H2 or H20 vapor was also in the cell and is now purposely added to the cell [115]. Ar2+, ArCl+, ArO+, and Ar+ signals were reduced relative to Se+, As+, Fe+, and Ca+, respectively. Detection limits for Fe, Ca, K, Se, and As near 10 parts per trillion (ppt) have been reported [115]. Recently, Beaty and Liezers [116] also described a collision-reaction cell at a pressure of 30 mtorr that reduced the ion kinetic energy spread as well as continuum ICP-MS background to less than 1 count/sec. Previously, Douglas and French had described the use of an rf-only quadrupole for collisional focusing and reduction of the ion kinetic energy spread [117]. 

Micromass has applied this new hexapole technology to a fast scanning magnetic sector multiple-collector instrument (Fig. 8.6). The source is at ground potential so most of the lens system and analyzer float at —6 kV. The ions are extracted into the hexapole through a sample cone with a 1.1-mm orifice, a 0.8-mm orifice skimmer cone, and finally a 2-mm orifice transfer lens held at —400 V. The hexapole is inclined to prevent line-of-sight transmission and damage to the detectors from the source. A lens system transfers the ions into the mass analyzer. 

The light from the source, in this case a laser diode, is transferred to the fibre input cross section by a transfer lens system. The first lens is the laser collimator, with a focal length, fl, which is normally a few mm. If the collimated beam is focused into a fibre by a lens of a longer focal length, 12, all aberrations in the laser beam profile are magnified by a factor M = 12 / fl. This requires a fibre of a eorrespondingly large diameter. However, the NA of the beam coupled into the fibre, and eonsequently the pulse dispersion in the fibre, is reduced by the same ratio. 

The msgority of commercial instrumentation consists of a flood x-ray or uv photon source and an energy analyzer equipped with an energy retardation transfer lens. The analysis spot size in this instrumentation is limited by the image the entrance slit of the analyzer makes on the sample surface in the analysis position. Materials studies are thus limited to model structures or large area surfaces (at least a few millimeters in size). Because semiconductor device structures generally consist of features which are on the order of micrometer dimensions, the trend in modem instmmentation is towards smaller analysis spot size Small analysis spot size permits investigators to employ photoelectron spectroscopy on real devices rather than model device structures. 

The first approach used to decrease the analysis spot size was to design the electron transfer lens so that it effectively demagnifies the... 

Figure 9.6 shows a schematic of an ion mobility MS called the Synapt, the only low-pressure IMS-MS that is commercially available. Known as the TW-IMS, this mobility cell is embedded in a Q-TOF-type MS with multiple capabilities. The figure depicts the ions traveling from left to right. On the far left is the ESI source, which introduces aqueous samples from a high-performance liquid chromatographic (HPLC) instrument or by direct infusion. As the electrosprayed ions enter the MS, they are bent in a Z manner to eliminate the solvent and focus the ions into a traveling wave ion transfer lens. From here, the ions enter a QMS, where a mass can... 

After mobility separation, ions are transferred to a third traveling wave cell similar to the first cell of the triwave assembly and operating as an ion transfer lens or as a CID cell. Finally, the ions are transferred into a high-resolution TOF-MS. Thus, many types of analyses can be performed with this single instrument. It can operate simply as an IMS-TOF or a Q-TOF, but it can also operate as a Q-IMS-TOF or, in its most powerful mode, as a Q-IMS-CID-TOF. 

Ion Source Drift Tube Transfer Lens System TOF - MS 12 3... 

Another approach to form a lens directly in the substrate material is to form first a lens in photoresist deposited onto the substrate using some of the above procedures. After that reactive-ion etching (fast, but relatively small choice of materials) or ion milling (slower, more materials) is used to transfer lens into the substrate... 

In an extension of the idea of Yates and West, above. Seah and Smith [62] introduced a scanning system inside the analyzer input lens, between the specimen and the transfer lens, to raster the virtual image of the analysis area. The spatial resolution available depends of course on the size of the aperture at the entrance to the CHA. The instrumental arrangement is shown in Fig. 20, from Ref. 6.. It forms the basis for the AXIS system marketed by Kratos Analytical. 

The advantage of a CMA is its relatively high sensitivity due to its large y however, this is at the expense of resolution. Fitting a hemispherical analyzer with a high transmission electron transfer lens makes the sensitivity of this type of analyzer comparable to that of a CMA, with the added advantage of high resolution. 

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