Electromagnetic Lens Research Articles

A transmission electron microscope for lecture demonstrations

A simple transmission electron microscope (TEM) suitable for lecture demonstrations is described. In this TEM electrons are created in a glow discharge between two parallel electrodes in air at a reduced pressure. The electrons are collimated by a small hole in the anode, focused by a solenoid that acts as an electromagnetic lens, and imaged on a thin layer of phosphor deposited inside an Erlenmeyer flask. An image of a biological sample placed between the source and the lens can be magnified about 20 times. The microscope uses inexpensive components that can be quickly assembled during a demonstration. The TEM provides a visual and memorable display that highlights phenomena such as mean-free-path, charged particle optics, electrical discharges, and cathodoluminescence.

シミュレーションによるＰｉｅｒｃｅ型電子銃の基本設計

Numerical simulation including the space charge effect was carried out to determine the basic parameters for a newly designed 100 kW (40 kV, 2.5 A) Pierce-type electron gun. It is required that the electron beam of 2.5 A could pass through the aperture hole without colliding with the electrode and lens assembly. Three models of electrode assembly, were examined, A) with a cone-shaped Wehnelt B) with a spherical Wehnelt, and C) same as B except a larger anode hole. The space charge limited current exceeds 2.5 A for model B and C. However, electron beams in model B collide with the anode inlet irrespective of the operating conditions. The model C was found to satisfy the requirement under an adequate operating condition of electromagnetic lens.

High Resolution Imaging with an Aberration Corrected JEOL 2200FS-AC STEM/TEM

A new JEOL 2200FS 200kV field emission STEM/TEM with a hexapole Cs-corrector (CEOS GmbH) for the probe-forming lens and an in-column Omega-type energy filter has recently been installed at the Advanced Microscopy Laboratory (AML) at Oak Ridge National Laboratory (ORNL). The microscope is intended primarily for high-resolution imaging of catalyst systems that are of interest to the U.S. Department of Energy for increased energy efficiency and energy security. In this paper we report on the high-resolution imaging characteristics of our microscope for both conventional high-resolution TEM and STEM imaging. The TEM Scherzer point resolution for our objective lens polepiece (C{sub s} = 0.5 mm) is 0.19 nm, but more significantly the information limit has been demonstrated to be better than 0.09 nm, as shown in Fig. 1. This figure shows a Young's fringe experiment carried out on an amorphous Ge specimen which was estimated to be 10 nm thick. The thickness of the sample damps out the Thon rings to some extent, but the information transfer to sub 0.1 nm resolution is clearly evident. The electron wave at the specimen exit surface with resolution out to the information limit of a microscope may be reconstructed via computational processing of amore » focal or tilt series of images. The extension of the TEM information limit to the sub-0.1 nm range in our microscope can be attributed primarily to the improved objective lens and high tension power supply stabilities provided by JEOL Co. to satisfy our instrument specifications. A contrast transfer function (CTF) calculated using the parameters for our microscope is shown in Fig. 2, computed at the alpha-null defocus condition used for FSR processing. The CTF closely matches the demonstrated Young's fringe pattern, indicating the ability of the microscope to achieve ultimate performance in TEM mode. Characterization of catalyst systems will be a primary focus of the aberration-corrected JEOL 2200FS and therefore high-resolution STEM high-angle annular dark field (HA-ADF) imaging will be applied to understand the atomic-scale arrangement of supported catalyst clusters. By correcting for the primary resolution-limiting aberration of a round electromagnetic lens - the third-order spherical aberration - smaller electron probes with greater probe current can be formed, with resulting improvements in both the point-to-point resolution for HA-ADF imaging and the signal-to-noise ratio. Both benefits are important for the study of the atomic arrangement of catalyst clusters. Figure 3 shows initial HA-ADF imaging images of very small Pt clusters on a 1.1 nm thick amorphous carbon film. Individual Pt atoms are clearly visible with a high signal-to-noise, as is shown in Fig. 4.« less

Magnetic lenses for neutron beams

PurposeTo provide information on magnetic lens design principles for neutron beam focussing and to characterize the efficiency of these devices.Design/methodology/approachMagnetostatic and neutron optical computations are presented for permanent magnet and electromagnetic hexapole lenses for neutron beam focusing. The numerical results are verified by magnetic and neutron beam measurements.FindingsNeutron lenses built from brick‐shaped permanent magnets approximating the six‐pole Halbach structure yield relatively high field constant for a relatively small useful diameter. Electromagnets are weaker, but allow field constant adjustment.Research limitations/implicationsThe main limitation of both presented solutions resides in the difficulty of obtaining high magnetic flux densities. Superconducting coils in hexapole configuration can overcome this limitation.Practical implicationsThe magnetic lenses can be used for beam focusing in scattering neutron instruments. The focused beam is also polarized.Originality/valueAnalytical formulae are supplied for the neutron path calculation in a six‐pole magnetic field. An electromagnet design with permanent magnet flux enforcement is provided.

A coherent positron beam for reflection high-energy positron diffraction

A 10 keV positron beam has been developed using coaxially symmetric electromagnetic lenses for reflection high-energy positron diffraction (RHEPD) experiments. The beam brightness is ∼107 e+/s/cm2/rad2/V which is comparable to that obtained using brightness enhancement technique. The beam parallel and normal coherence lengths are over 100 and 40 Å, respectively, which are long enough to observe diffraction patterns associated with large surface super-structures. RHEPD patterns from a Si(111)-(7×7) reconstructed surface have been successfully observed with a much better quality than previously reported.

Isotropic metamaterial electromagnetic lens

Several authors have recently exhibited the focusing activity in the domain of so-called electromagnetic lenses. These lenses are parallel-plate layers of metamaterials whose properties can be described in terms of negative index of refraction. Known works on this subject refer to 2D structures. This work is our first attempt to show the focusing effect by a parallel-plate layer of a 3D metamaterial, whose approximate analytical model was suggested before. The mini-band of propagation and the field distribution across the focal spot are in qualitative agreement with this previous theory.

Improved fifth-order geometric aberration coefficients of electron lenses

In this paper, fifth-order geometric aberrations of round electron lenses have been restudied. Improved analytical formulae of the aberration coefficients were derived by the computer algebra software—Mathematica—and their correctness verified by cross-checking with numerical integration and differential algebraic techniques for a given electromagnetic lens.

Differential algebraic description for third- and fifth-order aberrations of electromagnetic lenses

In this paper the modern map method is applied to the third- and fifth-order aberration analysis of electromagnetic lenses, focusing on the high order. It is also emphasized that there exist three types of differential algebraic (DA) descriptions for electron optical aberrations. The numerical results of third- and fifth-order aberrations of a given electromagnetic lens computed through the DA technique are shown to be in excellent agreement with those evaluated using electron optical aberration integrals. In conclusion, the DA technique is concise, efficient, and precise for electron optical aberration analysis and the code COSY INFINITY has been proved to be an excellent computer code for such purposes.

New Methods for Making the Qubits of a Solid-State Quantum Computer by Implantation of Single Highly Charged 31 P Ions

A step-and-repeat and a simultaneous method are proposed and evaluated for the implantation of single highly charged 31P ions into a Si/SixGe1 – x heterostructure with the aim of creating the qubits of a solid-state quantum computer. The capabilities of existing axially symmetric compound electromagnetic objective lenses and ion sources are examined in this context. The advantages of such lenses over electrostatic ones are shown. An electromagnetic objective lens of exceptionally small axial aberrations is designed. An optical system using the lens is proposed for a step-and-repeat implanter. The parameters of the implanter are identified that determine its performance. They are lateral ion-positioning tolerance, the chromatic-aberration coefficient of the objective lens, source brightness, and ion multiplicity. An equation is derived that relates the parameters. Requirements are stated on the ion source. Possible ways are discussed of improving the performance of the ion source and the ion-optical system.

Development of electromagnetic lenses for multielectron beam lithography system

High-throughput electron-beam (EB) lithography systems require high current. However, beam blur increases because of the individual Coulomb interaction among the electron beams. Isolating the electron beam into 4–16 perfectly independent beamlets is effective. As for the electromagnetic lens, many openings in the parallel flat plates can form the compound eye lens. This lens is called the lotus root lens (LRL). Simulations and experiments with the LRL were carried out. In the case of LRL of 4×4 openings with a 22 mm pitch, the uniformity of magnetic field along the axis was within 0.2%. The basic lens function between two openings separated by 44 mm in the LRL with 21 openings in the conventional column qualitatively evaluated. The LRL should be a potential platform for a multicolumn cell system that provides a multibeam direct-writing system that utilizes variable-shaped beam or character projection as unit-column optics.

First application of a spherical‐aberration corrected transmission electron microscope in materials science

One of the most challenging tasks for high-resolution electron microscopy is the investigation of the atomic structure of defects, interfaces, and grain boundaries. In particular, the application of thin films in electronic devices requires detailed knowledge of the microstructure, which can influence the electronic and optical properties. These tasks require a point resolution down to about 0.1 nm because this enables structure imaging for many semiconductors and metals. The resolution of transmission electron microscopes is limited, besides other parameters, by the spherical aberration coefficient C{sub s} of the objective lens and the wavelength {lambda} of the electrons. Commercial medium-voltage microscopes up to 400 kV offer only a point resolution of 0.16 nm due to the high spherical-aberration constant C{sub s} of the electromagnetic objective lens. Controlling the value of C{sub s} by a corrector lens system can offer the required resolution even at an acceleration voltage of 200 kV. Recently, a lens system for C{sub s}-correction, based on hexapole lenses, has been developed at the European Molecular Biology Laboratory in Heidelberg and incorporated in a commercial 200 kV instrument equipped with a field emission gun. This system allows the C{sub s}-value to be set between +2.0 mm and -0.05 mm.more » For the present investigation, we have adjusted a C{sub s}-value of 50 {mu}m in order to achieve optimum phase contrast, which improved the point resolution to 0.14 nm. Structure imaging can be performed down to atomic distances of 0.14 nm. A further unique advantage of C{sub s} correction is the reduction of contrast delocalization, which is a major obstacle in the interpretation of images of defects and interfaces. The influence of C{sub s} on contrast delocalization is demonstrated for a Si/CoSi{sub 2} interface. The unique combination of a low acceleration voltage and aberration-free imaging down to the information limit offers new prospects for the interpretation of non-periodic structures as defects and interfaces in crystalline materials.« less

磁界レンズを用いたエネルギー選別型β<SUP>+</SUP>-γ同時計測陽電子寿命測定装置

A β+-γ coincidence positron lifetime spectrometer equipped with two electromagnetic lenses was constructed. The electromagnetic lens was used to have energy-selected positron beam. It accomplished a time resolution of 385 ps (FWHM) for the total system with a Pilot U plastic scintillator. By using a silicon avalanche diode instead of Pilot U plastic scintillator to initiate start timing signals, the time resolution was improved to 345 ps (FWHM). With this method, in-situ positron lifetime measurements at high temperatures or under high stresses can be attained easily.

The use of controllable photonic band gap (CPBG) materials: An antenna application

In this paper, we theoretically and experimentally demonstrate the capability to realise controllable photonic band gap (CPBG) materials applied to the conformation of the radiation pattern of a planar antenna at 12 GHz. The CPBG materials studied are variable capacitance and conductance lattices fabricated with high frequency PIN diodes soldered along wires or metallic stripes on dielectric printed boards. Depending on the diode bias, the transmission factor of the lattice is controlled. Then, the emitted radiation of an antenna can be either transmitted or totally reflected by the material. In the transmission state, the antenna radiation is angular filtered by the CPBG material. In that case, it behaves like a controllable electromagnetic lens in the allowed frequency domain of the material.

Transmission of through-the-lens Auger spectroscopy in an electron microscope

In this paper, the transmission properties of through-the-lens Auger spectroscopy in an electron microscope using an electro-magnetic immersion lens are calculated. The effects of changes in acceptance angle and entrance slit of the spectrometer are discussed. It is shown that by including the effects of oscillations in final angle and radius, enhanced transmission is obtained under typical experimental conditions.

A simple quadrupole-octupole electromagnetic lens

Charged particle beam trajectories in a simple electromagnetic quadrupole-octupole lens are numerically calculated based on analytical expressions for the +potential distribution. Locations of the lens foci in the image space are determined over a wide range of initial conditions. Relationships between the electrostatic and magnetic lens components that provide correction for chromatic aberrations of off-axis beams, which are different from classical beams, are obtained. Phase contours at the lens exit are calculated for beams occupying the major part of the aperture, and conditions for transforming the phase contour with minimal distortions are found.

Analytical calculation of geometric and chromatic aberrations in a bi-potential electrostatic and bell-shaped magnetic combined lens

In the present paper, Gaussian optical property in the bi-potential electrostatic and the bell-shaped magnetic combined lens – a new theoretical model first proposed in electron optics – has been thoroughly studied. Meanwhile, based on electron optical canonical aberration theory, analytical formulas of third-order geometrical and first-order chromatic aberration coefficients and their computational results have first been derived for this bi-potential electrostatic and bell-shaped magnetic combined lens. It is to emphasized that this theoretical study can be used to estimate third-order geometric and first-order chromatic aberrations and to provide a theoretical criterion for numerical computation in a rotationally symmetric electromagnetic lens.

Incorporation of laser ablation into a proton probe system to study laser ablation of corrosion products, and enhance the probe's analytical capabilities

The Oxford University Scanning Proton Microprobe Unit has been responsible for many advances in the field of focused proton beams for analytical microscopy, including being the first to develop the optimized electro-magnetic lenses used to focus high-energy protons to the micron and sub-micron level. This has led to a revolution in using the proton microprobe as an analytical tool for the study of materials. Continuing the tradition of innovation at the Oxford SPM unit, the use of laser ablation to reduce the need for sampling or cleaning of art and archaeological objects, before analysis, is being investigated. Further, information on the makeup of corrosion layers and past conservation treatments is becoming available via this technique.

Electromagnetic quadrupole-octupole lens

A design is proposed for an electromagnetic quadrupole lens with correction for spherical chromatic aberration. This lens consists of eight electrodes, of which four are also the poles of the magnet.

Solution X-Ray Scattering-Based Estimation of Electron Cryomicroscopy Imaging Parameters for Reconstruction of Virus Particles

Structure factor amplitudes and phases can be computed directly from electron cryomicroscopy images. Inherent aberrations of the electromagnetic lenses and other instrumental factors affect the structure factors, however, resulting in decreased accuracy in the determined three-dimensional reconstruction. In contrast, solution x-ray scattering provides absolute and accurate measurement of spherically averaged structure factor amplitudes of particles in solution but does not provide information on the phases. In the present study, we explore the merits of using solution x-ray scattering data to estimate the imaging parameters necessary to make corrections to the structure factor amplitudes derived from electron cryomicroscopic images of icosahedral virus particles. Using 400-kV spot-scan images of the bacteriophage P22 procapsid, we have calculated an amplitude contrast of 8.0 ± 5.2%. The amplitude decay parameter has been estimated to be 523 ± 188 Å 2 with image noise compensation and 44 ± 66 Å 2 without it. These results can also be used to estimate the minimum number of virus particles needed for reconstruction at different resolutions.

First Application of a Spherical-Aberration Corrected Microscope Material Science

Abstract One of the most challenging tasks for high-resolution electron microscopy (HREM) is the atomistic investigation of defects and interfaces in thin films of semiconductors and ceramics. In particular, the application of these materials in electronic devices requires the understanding of the atomistic structure responsible for electronic and optical properties. The imaging of these structures requires a point resolution down to 0.1 nm. For example the smallest atomic spacing of GaAs in the (110) projection is 0.14 nm. According to Scherzer the point resolution of the TEM is proportional to spherical-aberration coefficient Cs1/4 and to the wave length λ3/4. Commercial medium-voltage microscopes up to 400 kV offer only a point resolution of 0.16 nm due to the high spherical-aberration constant Cs of the electromagnetic objective lens. Decreasing the wave length λ by increasing the electron energy improves the point resolution, but has the drawback of severe radiation damage and high costs.