Accelerating Lens System Research Articles

Ion Beam Simulation Using a Lens System for Acceleration and Deceleration of Low Energy Ion Beam

Ion Beam Simulation Using a Lens System for Acceleration and Deceleration of Low Energy Ion Beam The characteristics of electrostatic lens systems are studied with a view to applications in an ion-beam source. Rays are traced with the SIMION simulator, which offers a realistic description of space charge effects. Design of the lens system was done by using SIMION computer program. A parallel beam of singly charged nitrogen ions of diameter 10 mm with energy of 6 keV was started at a distance of 150 mm before entering the acceleration/ deceleration lens system. The lens system was optimized using the simulation data obtained with a SIMION computer program for calculating ion trajectories with and without space charge included. In order to design this lens system, we studied the two and three electrode lens systems with different parameters. Beam emittance as a function of the gap width of the deceleration lens system wasb studied for singly charged nitrogen ion trajectories downstream at 200 mm. Influence of the deceleration voltage on the deceleration electrode with different voltages of the four electrodes on the beam emittance was investigated with gap widths of 3, 5, 10, 15 and 21 mm. Deceleration lens system was used as an acceleration lens system by changing and optimising the voltage on each electroden of the lens system. Both the beam emittance and the beamb diameter were calculated at exit of the lens system at distance of 60 mm. The following calculations have been done with and without space charge.

Reaction dynamics of Mo + O2 → MoO + O studied by a crossed-beam velocity map imaging technique

The oxidation reaction dynamics of gas-phase molybdenum atoms by oxygen molecules was studied under a crossed-beam condition. The product MoO was detected by a time-of-flight mass spectrometer combined with laser multi-photon ionization. An acceleration lens system designed for the ion-velocity mapping condition, a two-dimensional (2D) detector, and a time-slicing technique were used to obtain the velocity and angular distributions of the products at three collision energies: 10.0, 17.8, and 50.0 kJ/mol. The angular distributions showed forward and backward peaks, whose relative intensities changed by the collision energy. While two peaks had similar intensities at low collision energies, the forward peak became dominant at the highest collision energy, 50 kJ/mol. The product kinetic energy distributions showed a good correlation with the initial collision energies, i.e., almost the same energy as the collision energy appeared as the product kinetic energy. These results suggested that the reaction proceeds via an intermediate complex, and the lifetime of the complex becomes shorter than its rotational period at high collision energy.

Design of a compact focusing lens system with short acceleration tube at 300 kV

A compact focusing lens system with high demagnification over 1500 was designed to form an ion nanobeam with 346keV energy by adding a short distance acceleration tube for beam acceleration and focusing downstream of the existing double acceleration lens system. The demagnification, focusing points and aberrations of the acceleration tube were studied using beam trajectory calculation. The acceleration tube was designed to have a length of 140mm and a demagnification of 2 at its acceleration tube voltage of 300kV, which resulted in a new compact focusing lens system with a total length of about 640mm. In addition, the maximum voltage and electric-field of the acceleration tube were confirmed experimentally on the built device to be 300kV and 30kV/cm, respectively. The final beam size formed by the system was estimated to be 130nm in diameter using the design parameters. The result suggests that an ion nanobeam of 346keV can be formed by an apparatus having the reasonable length of 2m, which permits us to develop a system for 1MV by elongating its tube length.

Time-sliced ion-velocity imaging study of the reaction Y + O2→ YO + O

The oxidation reaction dynamics of the gas-phase yttrium atoms by oxygen molecules was studied under crossed-beam conditions. The product YO was detected using a time-of-flight mass spectrometer combined with laser single-photon ionization. An acceleration lens system designed for the ion-velocity mapping conditions, a two-dimensional (2-D) detector, and a time-slicing technique were used to obtain the velocity and angular distributions of the products. Two ionization wavelengths were used for the internal (vibrational and/or electronic) energy selective detection of YO. The single photon of the shorter wavelength (202.0 nm) can ionize all states of YO(X (2)Σ, A' (2)Δ, and A (2)Π), while electronically excited YO(A' and A) are dominantly ionized at a longer wavelength (285.0 nm). Time-sliced images were converted to the velocity and angular distributions in the center-of-mass frame. The general features of the velocity distributions of YO, determined at two wavelengths, were well represented by those expected from the statistical energy disposal model. The forward-backward symmetry was also observed for two images. These results suggest that the reaction proceeds via long-lived intermediates, and that this mechanism is consistent with previous chemiluminescence/LIF studies.

Progress in submicron width ion beam system using double acceleration lenses

The submicron ion beam system has been developed for formation of tens keV H 2 + beam with 0.1 μm width using a duoplasmatron-type ion source and an acceleration lens system. The 33 keV H 2 + beam of 0.28 μm in width was obtained using plasma sheath acceleration in our previous study. In this study, the parallel ion beam extraction was newly introduced using the non-magnetic anode with a hole tapered with Pierce angle to minimize the beam divergence angle in the ion source without the plasma sheath acceleration. The 46 keV H 2 + beam of 0.16 H 2 + in width was obtained by this improvement.

Production of a Li− ion beam from a thermal contact–ionization plasma source

The beam source is composed of a thermal contact–ionization plasma source and an accelerating lens system. The plasma source is made of a rhenium-foil cylinder 5 mm in diameter and it can be heated up to about 3000 K. A Li+ beam current over 500 μA has been obtained with this source. For the production of a Li− beam, an additional reservoir is attached to the source to supply Cs vapor into the plasma. The ion species can be examined by the time-of-flight (TOF) technique. In the case of Li+ production, ions of alkaline impurities, Na and K, in the Li metal have been observed in the TOF spectra. In the case of Li− ion production, the current intensity of negative ions also changes with the passage of operating time from K−, Na− to H− or H−2. This is also attributable to alkaline impurities in Li metal. A negative ion beam, which has been observed after the evaporation of impurities amounting to 200 nA, is very likely attributable to the Li− beam, though the corresponding TOF signal is very noisy.

High current efficiency accelerating lens system of field emission scanning electron microscope

The current efficiency of the lens system for an accelerating lens composed of three anodes combined with an auxiliary magnetic lens in a field emission scanning electron microscope is described. In this system the spot size for the needed primary beam current can satisfactorily be minimized since the working distance can freely be changed and the auxiliary magnetic lens can be operated under the optimum condition. Current efficiency of one order higher than that of the accelerating lens composed of two anodes is obtained.

Determination of the Spot Size by Using the Intensity Distribution in the Accelerating Lens System of Scanning Electron Microscope

The intensity distribution on the specimen was computed by using the pupil function in terms of electron wave optics, and the spot size (defined as 80% of the total electron beam spread) was precisely obtained from this intensity distribution. From the computer simulation data the following results were obtained. (1) The spot size determined by the conventional method was generally over-estimated. (2) The difference in the optimum aperture size determined by the conventional method and by the electron wave optical method was of very small order of magnitude.

Three-anode accelerating lens system for field emission scanning electron microscopy (II)

The comparisons between the electronic computer data and the experimental results of the characteristics of a three-anode accelerating lens system for field emission scanning electron microscopy (FESEM) are described. Experimentally two characteristics were obtained. One of them is the relation between the accelerating voltages and the control voltages for the fixed working distance. The other is the variation of the current with the accelerating voltages. In comparison with the results of the electronic computer simulation, a close coincidence was found for the former case, but for the latter the experimental results are approximately half as large as those obtained theoretically.

Three-anode accelerating lens system for the field emission scanning electron microscope

The characteristics of an accelerating lens system composed of three anodes in the scanning electron microscope are described. The main advantages of this accelerating lens system are that the working distance can be changed freely or the accelerating voltage can be changed over a wide range (about 0.3–100 kV) without changing the working distance, by adjusting only the control voltage of the second anode. Some problems in the manufacturing and operating conditions are also discussed.

Analysis of accelerating lens system in field-emission scanning electron microscope

This paper is composed of five sections. Section III analyzes the Butler-type and flat-plate lenses of the accelerating lens system in the scanning electron microscope (SEM) using a field-emission gun. Section IV presents the result of an analysis of some new accelerating lens systems when three anodes are present. The lens systems described in sec. IV are designed particularly for the low-energy SEM. Their major advantage is that the accelerating voltages can freely be changed in a wide range (from 300 V to about 100 kV) by merely adjusting the control voltages between the tip and the second anode without changing the focal point, etc. The resolution of the system and the beam current on the specimen seem to have the possibility of reaching 1000 Å and 10−8 A respectively, at accelerating voltages higher than 3 kV. Therefore, these lens systems also seem appropriate for the scanning Auger electron microscope.