Electrostatic Immersion Lens Research Articles

Deceleration Cylindrical Electrostatic Lens Using the Charge Density Method

With the aid of the integrated charge density method, Laplace’s equation is solved to calculate the axial potential distribution of the electrostatic immersion lens consisting of equi-diameter cylindrical electrodes separated by a specified distance. The potential and electric fields can be calculated directly outside the poles by the charge density on the poles. The solution is obtained by solving the integral equation using the bisection method. The optical properties of the decelerating lens determined under finite, zero and infinite magnification mode with no space-charging effects.

Concept for an electrostatic focusing device for continuous ambient pressure aerosol concentration

Abstract. We present a concept for enhancing the concentration of charged submicron aerosol particles in a continuous-flow stream using in situ electrostatic focusing. It is proposed that electrostatic focusing can enable the continuous, isothermal concentration of aerosol particles at ambient pressure, without altering their chemical composition. We model this approach theoretically and demonstrate proof of concept via laboratory measurements using a prototype. The prototype design consists of a nozzle-probe flow system analogous to a virtual impactor. The device was tested in the laboratory using submicron, monodisperse stearic acid particles. Particles were charged using a unipolar charger then concentrated using a cylindrical electrostatic immersion lens to direct the charged submicron particles into the sample probe. Under applied lens voltages ranging from 0 V to 30 kV, aerosol concentration increased up to 15 %. Observed particle enrichment varied as a function of voltage and particle diameter. These results suggest that an imposed electric field can be used to increase aerosol concentration in a continuous flow. This approach shows promise in increasing the effective enriched size range of virtual impactors or other continuous-flow methods of collection.

Effect of the Electrode Angle on the Optical Properties of Electrostatic Immersion Lens

Effect of the Electrode Angle on the Optical Properties of Electrostatic Immersion Lens

Developments in low‐voltage microscopy instrumentation

Low-voltage microscopy can produce high-resolution, high-contrast images of nanometer-scale surface features. Several techniques exist for low-energy electron generation, but most successful in current instrumentation is the combination of a magnetic lens with an electrostatic immersion lens. This compound lens allows the low-voltage column to maintain high potential in the column while independently controlling the landing energy on the sample. Aberration coefficients decrease linearly with the immersion ratio leading to larger optimum semiconvergent angle on the sample and improvement in spot size and beam current. Most recently highly scaled miniature electron beam columns have shown promising low-voltage performance from all electrostatic lenses operating only at low potential. This article explores the current design of low-voltage columns, including variations on compound lenses and miniature lenses, and from a system level, discusses the strength and weaknesses of each design.

DESIGN OF AN ELECTROSTATIC IMMERSION LENS USING THE CHARGE DENSITY METHOD

A computational investigation has been carried out in the field of non-relativistic chargedparticle optics using the charge density method as a boundary value problem with the aid of a personal computer under the absence of space-charge effects. This work has been concentrated on designing a two-electrode electrostatic immersion lens whose electrodes are cylindrical in shape separated by an air gap. The variable parameters of the two electrodes are the applied voltage ratio and the radii of the two cylindrical electrodes. The axial potential distribution of an electrostatic immersion lens has been computed by taking into consideration the distribution of the charge density due to the voltages applied on the two cylindrical electrodes. Potentials have been determined anywhere in space by using Coulomb s law. The optical properties of the immersion lens have been investigated under finite and zero magnification conditions.

Immersion probe-forming system as a way to the compact design of nuclear microprobe

The paper discusses the feasibility of constructing a compact nuclear microprobe combining ion acceleration and ion probe formation. In the design proposed a mass-separator, object-and angular collimators are placed at the accelerating tube entrance. Immediately behind the accelerating tube a quadruplet of magnetic quadrupole lenses is positioned to provide final ion probe formation at the target. Using the accelerating tube, which is an extended electrostatic immersion lens with axial symmetry together with magnetic quadrupole lenses to form an ion microprobe, it is possible to find conditions permitting the total aberration level to be reduced. Numerical optimization of the probe-forming system was performed involving the maximum emittance method developed by the authors in earlier papers. The calculations show that with a 3MeV accelerator, the design proposed would allow generation of a H+ ion beam with a 0.4μm spot size and 3.15μm2mrad2MeV normalized emittance. The total length of the facility is about 4m.

Low energy large scan field electron beam column for wafer inspection

A swing objective retarding immersion lens (SORIL) column for wafer inspection is designed and constructed based on SOIL concept. The column consists of a compound retarding electrostatic and magnetic immersion lens and five electrostatic deflectors. The retarding electrostatic and magnetic immersion lens has small spherical and chromatic aberration coefficients for low landing energy. All electrostatic deflectors have a cylindrical duodecapole structure. One deflector is accommodated between the polepiece of the magnetic lens and the specimen surface, and operated at high voltage to fulfill SOIL condition. An on-axis annular semiconductor detector with a small opening in the center is employed to collect signal electrons. The annular detector achieves high collection efficiency over a large scan field. Experimental results show that the SORIL column has accomplished a 600μm×600μm scan field with 0.1μm maximum spot size in a wide landing energy range (from 200to2000eV) without dynamic aberration correction or dynamic focusing. Resolution of 15nm is achieved in a 50μm×50μm scan field. The probe beam current delivered by the SORIL column is from a few nA to more than 100nA because of the specially designed bright electron gun. The SORIL column has been installed onto HMI’s electron beam wafer inspection tool, eScan™ 300. The SORIL’s optical performances enable eScan™ 300 to be a powerful electron beam wafer inspection and in-line process monitoring tool.

Analytical and numerical analysis of third-order geometric and first-order chromatic aberrations in a bi-potential electrostatic lens

Glaser and Robl (Z. Angew. Math. Phys. 2 (1951) 444) first proposed a theoretical model for a bi-potential electrostatic lens, whose axial potential distribution satisfies the law of electrostatics and whose paraxial trajectory equation is soluble. In this paper, the Gaussian optical property in the bi-potential electrostatic lens has been thoroughly studied. Meanwhile, based on electron optical canonical aberration theory, analytical formulas of third-order geometrical and first-order chromatic aberration coefficients have first been derived and their computational results obtained for this bi-potential electrostatic lens. It is to be 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 electrostatic immersion lens.

Focusing properties of micron‐sized immersion lenses

We report here on the focusing properties of a two‐electrode electrostatic immersion lens of micron dimensions that is combined with the electron point source. Depending on the mode of operation of the lens, the resulting focused electron beam can have an energy as low as 15 eV if the lens is used in the decelerating mode, or an energy of typically 200 eV if the lens is used in the accelerating mode. We will also present results of using the focused beam in a TEM setup as well as in the scanning mode.

Wave-vector imaging photoelectron spectrometer

We have developed an imaging photoelectron spectrometer based on a simple electrostatic immersion lens with the capability of measuring photoemission intensity as a function of the parallel component of electron wave vector throughout the Brillouin zone. The image is a simple rectilinear mapping of the k∥ component of the wave vector in reciprocal space. Using a retarding field-energy selection system, it is possible to energy select and image the various states below the Fermi energy. We obtain an energy resolution of 0.3 eV and a k∥ resolution of 0.04 Å−1. The distribution of photocurrent is amplified onto a phosphor screen by a channel electron multiplier array. The image on the screen is then picked up with a charge-coupled device (CCD) camera so that the digitized image can be both position and energy analyzed. The performance of the system is demonstrated by imaging the photoelectron distribution from a Cu(001) single crystal. We find that the intensity distribution of emission in k space reflects the dispersion of the projected bulk energy band structure.

Photostimulated Exoelectron Emission from Slip Lines—A New Microscopy of Metal Deformation

Plastic deformation of metals enhances photoelectron emission, an effect known as photostimulated exoelectron emission. It has been proposed that the electrons are emitted from microcracks produced in the oxide. We have observed this phenomenon directly in a photoemission electron microscope (PEM) and shown conclusively that such emission does indeed originate from cracks in the oxide at slip lines.The PEM consists essentially of two magnetic and one electrostatic immersion lens. The sample is illuminated with ultraviolet radiation, and the photoemitted electrons are imaged on a fluorescent screen. A Channeltron Electron Multiplier Array provides image intensification. The sample is deformed in situ by bending to produce tensile deformation of the surface under study.

Rigorous Treatment of the Electrostatic Immersion Lens Whose Axial Potential Distribution Is Given by: φ(z)=φ0e K arctan z

Investigations have shown that the electrostatic immersion lens, given by the axial potential distribution φ(z)=φ0 exp(K arctan z), is the simplest electrostatic lens for which Newton's image equations are satisfied throughout the field. The general solution of the paraxial ray differential equation is derived. Based on this solution and the fact that Newton's image equations are satisfied, exact expressions are derived for all important optical quantities such as the focal lengths, the location of the four cardinal points, magnification, the object-image relation, and the spherical and chromatic aberration for any object position. The optimum positions of an object are determined so that the chromatic and spherical aberrations are reduced to a minimum. All quantities are represented graphically. A plot of the equipotential lines in space is given for a special value of the voltage ratio.