Einzel Lens Research Articles

A capillaritron ion source as triode system coupled with an einzel lens

The capillaritron ion source consists of a fine capillary anode, with an orifice diameter of 25 μm. The capillary is fed with a gas, and is put on high potential. If the ignition voltage is reached, a self-sustaining plasma will originate at the capillary orifice from which ions are extracted by the applied high voltage. The construction as triode system allows to control ion energy and beam current independently. Capillaries are made of tungsten, but can be made of glass too, provided a thin conducting wire is inserted into the glass capillary enabling the high voltage to be applied. The ion source is followed by an einzel lens allowing to vary the spot size from about 20 (unfocused) to 0.3 mm (focused) at a distance of 40 mm. Smaller spot sizes should be attainable after improvement of the voltage stability of the einzel lens.

Size selection and focusing of neutral carbon clusters

A new method is proposed for producing a high-density beam of size-selected neutral clusters of metal or semiconductor materials. This method is based on photodetachment of negative cluster ions, size-selected and then tightly focused by two sets of einzel lens systems. This method was shown to focus the size-selected neutral cluster of C 10 beyond the limit of the “space charge” effect observed in the beam profile of C − 10.

Production of needle-type liquid-metal ion sources and their application in a scanning ion muscope

A tungsten wire is electrochemically etched in NaOH to produce tip radii of 4–10 μm for use in liquid-metal ion sources (LMIS). To ensure complete wetting of the needle with the liquid metal (Sn, Ga), the needle has to be annealed at 800–1000°C by electron bombardment in a vacuum. It is then immediately dipped into the liquid metal in the same vacuum chamber. An anode prepared in this way is part of a triode system, followed by an octupole stigmator, an electrostatic einzel lens and the scanning unit. Upon application of a high voltage the liquid metal will form a Taylor cone at the needle tip. In the resulting high electrical field ions are extracted through field evaporation. Typical beam current and spot size values during scanning ion muscope (SIM) operation are 2.5 μA and 10 μm respectively. An Everhart-Thornley detector and a quadrupole mass spectrometer are available to allow analysis of secondary particles emitted from the target.

Injection of high brightness H − beams into RFQ accelerators

The state of the art in low-energy beam transport (LEBT) of high brightness H − beams from the source to the RFQ accelerator using gas focusing and solenoid or quadrupole magnets is reviewed. Proposed advanced LEBT schemes with electric focusing elements presently under investigation avoid charge neutralization and hence the beam loss and emittance degradation inherent in gas focusing systems. Results of conceptual design studies for LEBT systems with electrostatic quadrupoles (ESQ) and einzel lenses are discussed.

Einzel lenses in atom probe designs

An electrostatic field and ion trajectory program has been used to characterise the focussing behaviour of simple einzel lenses used in linear flight-path atom probe designs. The focussing power and spot size obtained for two basic lens designs have been found as a function of applied voltage and lens size. A simple model for the beam convergence generated by such a lens has been used to calculate the time resolution and spatial focussing of a combined system including einzel lens and toroidal sector energy compensator. The results of these calculations agree well with the observed performance in a high resolution energy compensated atom probe. We find that the lens is able to improve the time resolution of a poorly focussed toroidal sector, but only on one side of the correct focussing condition. Under these conditions, accurate spatial focussing will not be achieved.

Performance of a reflectron energy compensating mirror

This paper describes the performance characteristics of a first order reflectron energy compensating mirror system on a voltage-pulsed atom probe. The performance of the instrument using the electrostatic mirror is compared to that obtained using the same electronics and a linear flight path, and the effect of an einzel lens on the performance is presented.

粉末粒子の静電加速による特殊加工法の研究（第６報） 帯電粉末粒子ビームの静電レンズによる集束

In order to realize a new method of powder particle beam machining, a fundamental approach to obtain a dense beam of powder particles was made with an Einzel lens designed from electron optical theories. The mechanism of forming well-focused beam is theoretically analyzed by a graphical method based on the electron optics, so that each of the particle trajectory and density distribution is represented as a function of the optical values and dimension of the lens. The validity of the theoretical analysis was proved by comparing the calculated density distribution with the measured beam spot on target material. Furthermore it became clear that the off-axis trajectories affected by spherical aberration remarkably contribute to the beam-spot formation and that the average beam density in the focused spot can be increased by about thirty times that of non-focused beam.

Design of a high-current-density focused-ion-beam optical system with the aid of a chromatic aberration formula

A 30-kV high-current-density focused-ion-beam optical system using a liquid metal ion source, has been designed for micromachining under the following restrictions: (1) all inter-electrode voltages are less than the acceleration voltage; (2) the sample and deflectors are not biased; (3) working distance is longer than 20 mm; and (4) the beam has an intermediate crossover. The design guidelines were obtained from an analysis of the chromatic aberration formula. The system has a tetrode condenser lens (zoom lens) and an einzel objective lens, each of which is made up of thin Butler-type lens electrodes. Both of the lenses are used in the deceleration mode. Calculated beam current density of the system is 1–10 A/cm2 in a wide range of beam diameters of 0.04−2 μm.

Performance Evaluation of a Novel Type of Low-Energy Electron Microscope

During the last few years the investigation of clean and adsorbate-covered solid surfaces as well as thin-film growth and molecular dynamics have given rise to a constant demand for high-resolution imaging microscopy with reflected and diffracted low energy electrons as well as photo-electrons. A recent successful implementation of a UHV low-energy electron microscope by Bauer and Telieps encouraged us to construct such a low energy electron microscope (LEEM) for high-resolution imaging incorporating several novel design features, which is described more detailed elsewhere.The constraint of high field strength at the surface required to keep the aberrations caused by the accelerating field small and high UV photon intensity to get an improved signal-to-noise ratio for photoemission led to the design of a tetrode emission lens system capable of also focusing the UV light at the surface through an integrated Schwarzschild-type objective. Fig. 1 shows an axial section of the emission lens in the LEEM with sample (28) and part of the sample holder (29). The integrated mirror objective (50a, 50b) is used for visual in situ microscopic observation of the sample as well as for UV illumination. The electron optical components and the sample with accelerating field followed by an einzel lens form a tetrode system. In order to keep the field strength high, the sample is separated from the first element of the einzel lens by only 1.6 mm. With a numerical aperture of 0.5 for the Schwarzschild objective the orifice in the first element of the einzel lens has to be about 3.0 mm in diameter. Considering the much smaller distance to the sample one can expect intense distortions of the accelerating field in front of the sample. Because the achievable lateral resolution depends mainly on the quality of the first imaging step, careful investigation of the aberrations caused by the emission lens system had to be done in order to avoid sacrificing high lateral resolution for larger numerical aperture.

A status report of the ISOL facility in Lanzhou

Abstract A new ISOL facility has been constructed for on-line use with the heavy-ion accelerator HIRFL in Lanzhou. The focal principle of ISOLDE-type separators is modified by including a quadrupole doublet lens in front of the magnet. The mass spectra of Ar and Xe isotopes were measured with a scanner inside the collection chamber in an off-line test. The resolving power is equal to 700–1200 by only using a single einzel lens.

An accel-mode einzel lens with through-lens energy analyzer for electron beam testing

An accel-mode einzel lens with through-lens energy analyzer is developed to apply a purely electrostatic optical column in low-voltage electron beam testers. A purely electrostatic optical column, enabling use of the accel-mode einzel lens as an objective lens, is also designed. Lens aberration is lowered by reducing focal length. Energy analyzer performance is improved by calculating secondary electron trajectories for the lens. The purely electrostatic optical column provides a 100 nm beam diam and a 0.23 eV energy resolution at beam voltage of 0.5 kV and beam current of 1 nA.

Solid state cesium ion guns for surface studies

Three cesium ion guns covering the energy range of 5–5000 V are described. These guns use a novel source of cesium ions that combine the advantages of porous metal ionizers with those of aluminosilicate emitters. Cesium ions are chemically stored in a solid electrolyte pellet and are thermionically emitted from a porous thin film of tungsten at the surface. Cesium supply to the emitting surface is controlled by applying a bias across the pellet. A total charge of 10.0 C can be extracted, corresponding to greater than 2000 h of lifetime with an extraction current of 1.0 μA. This source is compact, stable, and easy to use, and produces a beam with >99.5% purity. It requires none of the differential pumping or associated hardware necessary in designs using cesium vapor and porous tungsten ionizers. It has been used in ultrahigh-vacuum (UHV) experiments at pressures of <10−10 Torr with no significant gas load. Three different types of extraction optics are used depending on the energy range desired. For low-energy deposition, a simple space-charge-limited planar diode with a perveance of 1×10−7 A/V3/2 is used. Current densities of 10.0 μA/cm2 at the exit aperture for energies ≤20 V are typical. This type of source provides an alternative to vapor deposition with the advantage of precise flux calibration by integration of the ion current. For energies from 50 to 500 V and typical beam radii of 0.5 to 0.2 mm, a high perveance Pierce-type ion gun is used. This gun was designed with a perveance of 1×10−9 A/V3/2 and produces a beam with an effective temperature of 0.35 eV. For the energy range of 0.5 to 5 keV, the Pierce gun is used in conjunction with two Einzel lenses, enabling a large range of imaging ratios to be obtained. Beam radii of 60 to 300 μm are typical for beam currents of 50 nA to 1.0 μA. Results are presented and discussed for UHV studies of ion implantation, electronic surface changes induced by adsorbates, and negative secondary-ion mass spectrometry.

High-current deuteron ion source

A duoplasmatron ion source capable of delivering 20 mA of deuteron beam at an energy of 20 keV has been designed. This ion source will inject the beam into an RFQ accelerator, which is intended to be used as a 14-MeV neutron generator. In this design the emphasis is laid on the design of the plasma expansion cup and the extraction geometry. The space-charge beam dynamics through the ion source and the einzel lens is investigated with the help of a computer code iora developed by us. Almost all the components of the ion source have been made. The solenoid magnet and the intermediate electrode have been tested. The full assembly and the testing of the various parts is underway.

Solid state cesium ion guns for surface studies (abstract)

Three cesium ion guns covering the energy range of 5–5000 V are described. These guns use a novel source of cesium ions that combine the advantages of porous metal ionizers with those of aluminosilicate emitters. Cesium ions are chemically stored in a solid electrolyte pellet and are thermionically emitted from a porous thin film of tungsten at the surface. Cesium supply to the emitting surface is controlled by applying a bias across the pellet. A total charge of 10.0 C can be extracted, corresponding to greater than 2000 h of lifetime with an extraction current of 1.0 μA. This source is compact, stable, and easy to use, and produces a beam with >99.5% purity. It requires none of the differential pumping or associated hardware necessary in designs using cesium vapor and porous tungsten ionizers. It has been used in ultrahigh-vacuum (UHV) experiments at pressures of <10−10 Torr with no significant gas load. Three different types of extraction optics are used depending on the energy range desired. For low-energy deposition, a simple space-charge-limited planar diode with a perveance of 1×10−7 A/V3/2 is used. Current densities of 10.0 μA/cm2 at the exit aperture for energies ≤20 V are typical. This type of source provides an alternative to vapor deposition with the advantage of precise flux calibration by integration of the ion current. For energies from 50 to 500 V and typical beam radii of 0.5 to 0.2 mm, a high perveance Pierce-type ion gun is used. This gun was designed with a perveance of 1×10−9 A/V3/2 and produces a beam with an effective temperature of 0.35 eV. For the energy range of 0.5 to 5 keV, the Pierce gun is used in conjunction with two Einzel lenses, enabling a large range of imaging ratios to be obtained. Beam radii of 60 to 300 μm are typical for beam currents of 50 nA to 1.0 μA. Results are presented and discussed for UHV studies of ion implantation, electronic surface changes induced by adsorbates, and negative secondary-ion mass spectrometry.

Ion trajectories through the input ion optics of an inductively coupled plasma-mass spectrometer

A commercial program (MacSimion) has been used to model the einzel lens and bessel box input lens system of an inductively coupled plasma-mass spectrometer (ICP-MS). A number of plots are presented illustrating the effect of various lens voltages on ion trajectories. The trajectories are dependent on ion kinetic energy and since ion kinetic energy is mass dependent in ICP-MS, these plots clarify the mass dependence of ion lens voltage settings. Plots are also presented illustrating the interdependence of some lens voltage settings and how, in fact, different lens voltage settings can result in similar ion throughput. The model can be used to predict relative signal intensities for a range of ion masses as a function of lens potentials and these are shown to agree with experimentally measured data.

Compensation for non‐normal ejection of large molecular ions in plasma‐desorption mass spectrometry

AbstractBy introducing an Einzel lens in the field‐free region of a straight time‐of‐flight mass spectrometer, secondary ions of large mass can be detected more efficiently in plasma‐desorption mass spectrometry. This procedure compensates for the large radial velocities of large molecular ions recently observed experimentally. It is shown that large molecular ions like those of lysozyme can now be detected more efficiently, and larger molecular ions than observed before in plasma‐desorption mass spectrometry (like those of bovine ovalbumin, mol. wt 45 000) can now be studied.

Design study of a medical linac for neutron therapy

A 66 MeV proton linac for neutron therapy has been studied and conceptual designs for low energy beam transport (LEBT), a radio-frequency quadrupole (RFQ) and a drift tube linac (DTL) have been achieved. The machine is compact and simple enough to be operated in hospitals. The LEBT consists of two Einzel lenses and is 22 cm long. The 425 MHz RFQ is designed for 50 mA peak current at 60 Hz and is 1 m long. The 18-m-long DTL has the same frequency as the RFQ and uses permanent quadrupole magnets. Beam dynamics are very important for this compact and high-brightness machine. This paper emphasizes our investigation of the beam dynamics.

Intense metal ion beam formation by an impregnated-electrode-type liquid metal ion source

High current metal ion beams of several hundred μA for various single metal elements were obtained by single-point emission from an impregnated-electrode-type liquid metal ion source. For high efficiency ion beam transport, a double-lens system was designed, which consists of a physically asymmetric lens and an einzel lens, the former for suppressing large beam divergence just after the ion extractor and the latter for forming a suitable transport beam. Using this lens system, about 210 μA of lithium ion current was transported over a distance of 0.4 m within an optical column 2 cm in diameter. After mass separation, about 70 μA of Li + was obtained. To further intensify the metal ion current, a tip with three emission points in one dimension was developed. By three-point emission, 1.3 mA of germanium ion current was extracted. Based on these results, the impregnated-electrode-type liquid metal ion source is considered suitable as a multipurpose metal ion source.

A microwave ion source and injector system for a Van de Graaff accelerator

A compact and light weight injector system for a Van de Graaff accelerator has been developed. The system consists of a microwave ion source, an Einzel lens and a mass filter with crossed electrical and magnetic fields (Wien filter). The microwave ion source is a modified version of the source developed by Ishikawa [1]. The Wien filter of the injector system is a modified version of a Wien filter developed by Cleff and Schulte [2]. Typical beam currents are for example 100 μA of B + and 160 μA of Ar +. Other characteristics of the injector system are a stable beam current during at least eight hours even with reactive gases like oxygen, a lifetime of the antenna of at least 50 h, a small power consumption of the injector system of about 1 kW, including the ion source, and dimensions and weight which are small enough to mount the injector system in the terminal of a Van de Graaff accelerator.

Time-of-flight analyzer for ion end loss of a mirror plasma

A time-of-flight analyzer has successfully been used to measure the extracted charge-state distribution and impurity level of an ECRH mirror plasma. End-loss temperatures for each ion species have been determined from the rise time of the analyzer output pulses. Ions entering the line-of-sight device are first accelerated by a two-aperture lens and are then focused with an einzel lens. Electrostatic deflection plates chop the ion beam into short pulses which travel down a 1.20-m tube to an electron multiplier. Ion spectra are typically summed at a rate of 1 kHz using a hardware signal averager.