SU1118229A1 - Time-out-of-flight mass spectrometer - Google Patents

Abstract

TIME-FLIGHT MASS-SPECTROMETER, containing a pulsed ion source, an ion detector and a reflector located in front of the detector after the drift space, due to the fact that, in order to increase the sensitivity and accuracy of the measurement, the reflector is complete in the form of a torus located coaxially to the central axis a mass spectrometer, which also houses an ion detector, with an electrostatic deflection system of a toroidal configuration at the input of the reflector, and the drift space between the ion source and the reflector is bounded by two conical metal cones. (L (Ri.v.1

Description

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The invention relates to the field of scientific instrumentation, the main area of its use is elemental analysis of substances.

A device is known in which ionized by electron impact and accelerated to a certain energy, the ions of the gas after the passage of the first drift gap fall into the region of the decelerating electric field (reflector) and after reflection and passage of the second drift gap are recorded by a sensor.

Using a reflector instead of the direct burden of the drift tube significantly increases the resolution of the instrument and reduces its length. However, the ionizer used in the device is only suitable for gas and cannot be used for the analysis of substances in the solid phase.

The closest in technical essence and the achieved result to the proposed device is the time-of-flight mass spectrometer containing a pulsed ion source, drift space after which the reflector is located, and a detector in which the substance of the sample in the solid phase is evaporated and ionized radiation. Depending on the diameter of the spot and the specific power of the laser radiation, the ions are either accelerated additionally or moved in the free-flight mode.

However, when laser radiation interacts with the substance of the main mass of multiply charged ions, it is ejected perpendicularly to the target surface, which significantly reduces the accuracy of the measurements, since single-charge ions provide the main information. This is due to the fact that the peaks of multi-ion ions can be superimposed on the mass peaks of single-charged ions and lead to a significant distortion of the mass spectra of the substance. All the above difficulties lead to the fact that when working in a reflection configuration, reasonable results are obtained only in the free expansion mode. Work in this mode leads to a decrease in the number of ions that hit the sensor in comparison with the acceleration mode. Oblique incidence (usually below 5) of laser radiation on the sample leads to

forming a recess on its surface. If the sample is pressed from a powder, a few pulses are enough for the depth to exceed the crater diameter. In this case, the plasma formed by the action of radiation practically does not go outside (burying).

The aim of the invention is to increase the sensitivity of the device and the accuracy of measurement.

The goal is achieved by the fact that at a known time the passing mass spectrometer containing a pulsed ion source, a detector and a reflector located in front of the detector after the drift space, the reflector is made in the form of a torus

coaxially to the central axis of the mass spectrometer, which also contains an ion detector, with an electrostatic deflection system of a toroidal configuration at the input of the reflector, and the drift space between the ion source and the reflector is limited by two conical metal cones. FIG. 1 shows the proposed

mass spectrometer; in fig. 2 - the same cross section.

The proposed device contains a laser evaporator 1, a detector 2, a toroidal reflector 3, an electrostatic deflection system (EOS) 4, substrates 5 for the sample under study, an outer cone 6, an inner cone 7. The points indicate the area on which the ions are moving, the direction their movements. Pulsed laser radiation with a specific energy density, exceeding W 2-10 W / cm, when exposed to a sample, creates

 ions, which expands in a hemisphere with a center at the point of impact. G using external and internal cones from this flow, ions entering the deflection system enter the solid angle p – co (see Fig. 1). A radially directed electric field deflects ions, and they enter a toroidal reflector.

at an angle about The length of the reflector h, the distance d between the average circumference of the toroidal entrance and the center of the outlet, and the angle oi are chosen so that 3 ions enter detector 2 at a given voltage V on the reflector. The device can be approximately calculated using some formulas, for the calculation of two-dimensional reflex mass analyzers. Using these formulas, one can calculate one of the optimal examples of the implementation of the proposed device. The angle is calculated first. оС, if d 7.5 cm, В ,, ionization energy B; 150 eV, 2b.,, From. here about 5 °. I In order to ensure the entry of ions into the toroidal reflector at an angle of 5 ° when the sample is located at an oi distance of .60 cm, along the axis of symmetry from the output slit of the reflector, it is necessary to apply an E-Vgg, an aspis to the EOS 4 equal to, as shown by calculations , 100-200 V. If the detector is located oi cm away from the reflector in the internal cone, then, using the resolution formula of the device „oTpUi + Lil + cosoiE; h E; v ;; (L, -2hco5o6 294 for each of the above input parameters, we obtain a value of 100-120. With a laser radiation spot diameter of 10 µm or less, the device is able to operate in acceleration mode. In this case, at a distance of 1-3 cm From the target surface perpendicular to the line connecting the laser exposure area with the average circumference of the toroidal entrance, accelerator grids are installed and VOTP is fed between the sample and the grid. The invention increases the sensitivity of the device and increases the detection limit of small impurities by 20-40 times; The configurations of ion selection significantly reduce the number of multi-charge ions in the flow, which reduce the accuracy of the results, significantly simplify the process of manufacturing and setting up the device by switching to a circular configuration and reducing labor-intensive processes in the manufacture of the device in terms of machining and its adjustment. the device allows for normal incidence of the beam on the sample and thereby minimizes the undesirable effect of burrowing.

Claims (1)

TIME-SPAN MASS SPECTROMETER containing a pulsed ion source, an ion detector and a reflector located in front of the detector after the drift space, characterized in that, in order to increase the sensitivity and accuracy of measurement, the reflector is made in the form of a torus located coaxially with the central axis of the mass spectrometer, along which the ion detector is located, while at the entrance of the reflector there is an electrostatic deflecting system of the toroidal configuration, and the drift space between the ion source and the reflector torus bounded by two conical metal cones. e FI.G.1 QO er to co 1 11