Cylindrical Mirror Analyzer Research Articles

Development of a cylindrical mirror analyser electron spectrometer and associated data acquisition system to study inner shell electron emission following ion-atom collision

In this paper we report on the development and performance of a cylindrical mirror analyser electron spectrometer for ion atom collision experiments. A low cost data acquisition system using Arduino microcontroller has also been developed and tested. We have measured the Auger emission spectra for various gaseous targets in collision with 1 MeV proton beams. Relative total Auger emission cross sections have also been measured for N2 molecular target as a function of incident proton energy. The projectile energy dependence agrees well with earlier reported measurements.

Quantification in high-energy resolution Auger electron spectroscopy; Proposal of a reference target convolution technique for direct spectra

Currently, high-energy resolution Auger electron spectroscopy (AES) is utilized for chemical-state qualitative analysis, such as x-ray photoelectron spectroscopy. It is highly desirable to perform quantitative analysis using the high-energy resolution direct spectra used for qualitative analysis. However, AES analysis parameters, such as relative sensitivity factors (RSFs), derived from conventional-energy resolution differentiated spectra cannot be adopted for high-energy resolution direct spectra. Furthermore, for quantification by high-energy resolution direct spectra, there is no established method for determining peak intensity, and no database of RSFs is available in surface analysis communities. Therefore, we tasked ourselves with investigating the use of the analysis parameters obtained from conventional-energy resolution-differentiated spectra obtained with a cylindrical mirror analyzer (CMA)-type AES instrument for high-energy resolution direct spectra measured with a spherical capacitor analyzer (SCA)-type AES instrument. The convolution technique proposed here is achieved by using a conventional-energy resolution spectral dataset obtained with CMA-AES as a target. By applying the convolution with the window function of the convoluted function of the Gaussian function and rectangular function, high-energy resolution direct spectra containing the inherent nature of fine structures are converted to the similar shapes of conventional-energy resolution direct spectra after the Shirley type background subtraction [Watanabe et al., J. Vac. Sci. Technol. A 41, 043209 (2023)]. Results revealed that for all spectra of conventional-energy resolution spectra taken with CMA-AES, as well as high-energy resolution spectra taken with SCA-AES with various energy resolutions, the ratios of the background-subtracted direct peak areas and the differentiated peak-to-peak intensities were well-aligned along the identical parabolic curve as a function of the kinetic energy (KE). Experimental results also revealed that the generalized conversion function f(KE;ΔE)=IareacmaIareaconv.sca(KE;ΔE), which is the ratio of the conventional-energy resolution spectral area (Iareacma) and the convoluted high-energy resolution spectral area (Iareaconv.sca), which can transform differentiated intensities of convoluted high-energy resolution spectra, such that they are similar to those of conventional-energy resolution spectra obtained using the CMA-AES instrument, being a function of KE and the energy resolution ΔE. By applying the conversion function, the historically accumulated AES analysis parameters for conventional-energy resolution differentiated spectra can be adopted to differentiated high-energy resolution spectra. Finally, the results revealed the sufficiency of the conversion function obtained by the actual measurements of the four reference specimens for the practical quantification of high-energy resolution AES direct spectra.

Mechanistic and Kinetic Measurements of Elementary Surface Reactions Using Temperature-Programmed X-ray Photoelectron Spectroscopy.

This paper describes a method by which surface-reaction kinetics can be measured by slowly and precisely ramping up the surface temperature at a constant rate while simultaneously collecting X-ray photoelectron spectra (XPS). This approach results in the collection of a large amount of data over relatively small temperature steps to produce quasi-continuous kinetic data. The method is illustrated for the desorption and reaction of diethyl disulfide (DEDS) on a Au(111) substrate in ultrahigh vacuum, where the results can be compared with previous conventional temperature-programmed desorption (TPD) data from Au(111). Experiments were carried out using a double-pass cylindrical-mirror analyzer with a channeltron detector to demonstrate how this approach can be implemented in a routine, multitechnique vacuum chamber. The approach will be even more effective in a more modern, specialized XPS apparatus with high-transmission hemispherical analyzers with multichannel array detectors, which will enable the spectra of several elements to be measured simultaneously. The results yielded an activation energy for multilayer desorption of DEDS of 41 ± 1 kJ/mol, with a pre-exponential factor of 8 ± 7 × 1012 s-1, an activation energy of 53 ± 6 kJ/mol and pre-exponential factor of 9 ± 8 × 1013 s-1 for monolayer desorption and an activation energy of 90 ± 6 kJ/mol with a prefactor of 1.0 ± 0.3 × 1015 s-1 for the reaction of adsorbed ethyl thiolate species to adsorbed DEDS. While these results were collected for a system for which the kinetic data could have been obtained using conventional TPD, this method can be more usefully applied to those surface reaction processes that do not rely on the formation of desorption products. This system, having been previously studied by TPD, facilitates a comparison with results obtained by conventional methods.

Peak intensities in Auger electron spectroscopy for quantification: Relationship between differentiated spectral intensities and direct peak areas

In Auger electron spectroscopy, qualitative analyses are performed by using high-energy resolution direct spectra with a spherical capacitor analyzer (SCA). Although it is used to carry out quantitative analyses with differentiated spectra, high-energy resolution spectra measured with an SCA differ from those obtained with conventional energy resolution measurements using a cylindrical mirror analyzer. When we attempt quantitative analyses by applying direct spectra, this does not allow the use of previously accumulated analytical parameters for differentiated spectra, such as relative sensitivity factors. Therefore, we clarified the relationship between Auger direct spectral intensities and differentiated spectral intensities, and we defined a correction factor enabling the use of the analytical parameters given by differentiated spectra to direct spectra. To estimate the direct spectral area contributing to a quantitative analysis, the background of the direct spectrum is subtracted by the Shirley method, similar to the spectral treatment used in x-ray photoelectron spectroscopy. The correction factor is expressed as the ratio of the normalized peak area and normalized differentiated peak-to-peak intensity, which is actually measured and determined in every laboratory and with any instrument.

Compact 2D electron analyzer CoDELMA: Simultaneous wide reciprocal and real space analysis using wide-angle deceleration lens, CMA and projection lens

A compact wide-acceptance angle (around ± 50°) high-energy-resolution 2D electron analyzer CoDELMA (Compact DELMA) is proposed, constructed and tested. CoDELMA is composed of a recently-proposed variable-deceleration-ratio wide-acceptance-angle electrostatic lens (VD-WAAEL), a cylindrical mirror analyzer (CMA) and a projection lens. After a brief review of VD-WAAEL, the use of a plane grid in the lens is presented as a new design option, which allows keeping the focusing angle almost constant irrespective of the deceleration ratio. A detailed consideration is given to the combination of CMA and a projection lens, which allows simultaneous analysis of wide reciprocal ( ± 8°) and real space ( ± 5 mm) at the entrance of CMA. CoDELMA is the successor to the previously developed DELMA instrument including a concentric hemispherical analyzer. The whole system of CoDELMA becomes much more compact than that of DELMA owing to the use of VD-WAAEL and CMA, and this results in considerable reduction of the production cost. Results of test measurement of energy spectrum and angular distribution using an electron gun as an excitation source confirmed that the energy resolution and the acceptance angle are almost the same as the designed values.

Optimization of cylindrical mirror analyzer

In this paper, we show that the energy resolution of a classical one-step cylindrical mirror analyzer can be made three times better by adjusting its geometrical parameters.

Surface and Bulk Plasmon Excitation on Aluminum Surface at Small to High Grazing Angles

We present a series of spectra measured by reflected electron energy loss spectroscopy on an aluminum sample using a cylindrical mirror analyzer. The measurements were performed in the energy range between 250 eV and 2000 eV and with various incident angles, including the grazing geometry of an 88° incident angle. The observed spectra were evaluated and decomposed for surface and bulk excitation. The determined surface plasmon excitations were compared to the elastic peak and to the bulk excitation. We found a slight surface plasmon energy shift with altering glancing angles. We show that this shift exists independently from the bulk plasmon interference.

SE OF COLLIMATION REGIME OF CHARGED PARTICLE BEAM FOR EXPAND THE FUNCTIONAL CAPABILITIES OF CORPUSCULAR OPTICAL SYSTEMS

The approach for the modeling of corpuscular-optical systems for the analysis of charged particle flows is considered. For all the methods considered and used earlier, the condition of spatial focusing of the particle beam was required. However, this strict condition is not always feasible in combination with other requirements. When a cylindrical electrostatic mirror analyzer is used as the main element, spatial focusing ofthe beam is incompatible with focusing in time of flight in terms of energy. In the paper the possibility of using the collimation regime of charged particle beam is considered, thereby eliminating the need to fulfill the focusing condition.

90°-deflection imaging electron analyzer for measuring wide 2D angular distribution and perpendicular spin texture

A 90°-deflection imaging electron analyzer for measuring wide 2D angular distribution and perpendicular spin texture is proposed. This analyzer, which we call “right-angle-deflection imaging analyzer (RADIAN)”, provides electrostatic 90°-deflection and 2D focusing of an electron beam. Here a large acceptance angle comparable to that of cylindrical mirror analyzer (CMA) is achieved without using a grid, while CMA uses grids at the entrance and the exit of an electrostatic field. The 90° deflection allows measuring spin polarization not only in the in-plane direction, but also in the surface-normal direction. Basic properties of RADIAN, calculated by ray tracing, are shown in comparison with those of the most widely used electron energy analyzer, i.e., concentric hemispherical analyzer (CHA). RADIAN has a much higher 2D focusing capability than CHA and allows a much larger acceptance angle for 2D imaging. Moreover, the high focusing capability of RADIAN allows us to obtain high energy resolution comparable to that obtained in CHA. A simple and effective way to achieve higher energy resolution is to combine two or more RADIANs in tandem. Double-pass and triple-pass analyzers in this combination are taken into account. For a practical application, we consider a combination of RADIAN with the recently proposed ±90° omnidirectional photoelectron acceptance lens. RADIAN can be suitably used to develop a wide-angle 2D imaging analyzer, and can also be used to develop a spin-resolved 2D imaging analyzer that can perform perpendicular-spin-texture imaging.

Modification of a Cylindrical Mirror Analyzer for High Efficiency Photoelectron Spectroscopy on Ion Beams

An existing cylindrical mirror analyzer (CMA) that was initially equipped with eight channeltrons detectors has been modified to install large micro-channel plate detectors to perform parallel detection of electrons on an energy range corresponding to ~12% of the mean pass energy. This analyzer is dedicated to photoelectron spectroscopy of ions ionized by synchrotron radiation. The overall detection efficiency is increased by a factor of ~20 compared to the original analyzer. A proof of principle of the efficiency of the analyzer has been done for Xe5+ and Si+ ions and will allow photoelectron spectroscopy on many other ionic species.

Data-driven computational method for determining accurate analytical field solutions on arbitrary-geometry spectrometers

Not all workable spectrometer systems can be represented by an exact analytical field; furthermore, while traditional design methods typically involve approximating known analytical fields with appropriate electrode/magnet configurations, modern simulation-based approaches do away with analytical representations altogether. Nonetheless, analytical solutions offer several advantages, including the ease of accurately evaluating focusing properties, and the prospect of optimization through mathematical analysis. In this paper, we propose an original and novel data-driven computational method for determining highly-accurate analytical field solutions, applicable to energy analyzers of arbitrary geometry and electrode/magnet configuration. The method encompasses a statistical analysis on a sample numerical field, from which appropriate eigenvalue bases are identified for the construction of an approximate series solution. The proposed method is demonstrated on three instruments—the parallel radial mirror analyzer, radial mirror analyzer, and parallel cylindrical mirror analyzer—illustrating its excellent versatility and accuracy in both the derived analytical fields ( < 1% mean error) and relative energy resolution predictions. We also demonstrate the potential application of automated optimization on the analytical fields through an adaptive Levenberg-Marquardt algorithm, exploiting the dimension-reducing properties of the method to aid in efficiency. Our proposed method is general enough to be applied across other fields of applications.

A hybrid genetic-Levenberg Marquardt algorithm for automated spectrometer design optimization

Advancements in computational tools have driven increasingly automated, simulation-centric approaches in the design and optimization of spectroscopic electron-optical systems. These augmented methodologies accelerate the optimization process, and can yield better-performing instruments. While classical gradient-based methods had been explored, modern alternatives such as genetic algorithms have rarely been applied. In this paper, we propose a novel fully-automated hybrid optimization method for use on electron-optical systems. An adaptive switching scheme between a Levenberg–Marquardt and a genetic sub-algorithm enables the simultaneous exploitation of the computational efficiency of the former and the robustness of the latter. The hybrid algorithm is demonstrated on two test examples—the parallel cylindrical mirror analyzer, and the first-order focusing parallel magnetic sector analyzer—and is found to outperform both the Levenberg–Marquardt and genetic algorithms individually. Our work is significant as a versatile tool for parallel energy spectrometer design, and can greatly aid the development of mechanically-complex parallel energy analyzers, which are expected to be of utility to the semiconductor industry in the near future.

The zero gap conjecture

The conjecture asserts that one electron optical device modeled having no gaps and another in which there are arbitrarily small gaps between the contacting elements are equivalent. It is verified using as an example a high resolution cylindrical mirror analyzer having contacting elements at different potentials. The verification proceeds by showing the equivalence between an air gap separating the elements and that of a small segment separating the elements at voltage V. Next use is made of this small segment at ever decreasing lengths in order to complete the assertion. Lastly the net charge located in the vicinity of the contact point is numerically calculated and it is found that this net charge becomes vanishingly small as the mesh point density surrounding the contact point becomes increasingly large. Thus there is no net charge in the contact region that can affect trajectories, a result consistent with the conjecture itself.

Lithium analysis in Li‐ion battery materials via a scanning electron microscopy‐based approach

We performed Li analysis by reflection electron energy loss spectroscopy (REELS) with a scanning electron microscopy‐based apparatus. It was possible to distinguish between Li compounds containing different transition metal elements spatially, via the spectrum imaging scheme of REELS spectra. We also acquired the Li spectrum for an Li‐inserted graphite negative electrode. REELS measurements with hemispherical analyzer were performed to obtain high‐quality spectra with sufficient energy resolution and compared with those from cylindrical mirror analyzer measurements; the former provided a more detailed chemical state evaluation of Li.

Optical properties and excitation energies of iridium derived from reflection electron energy loss spectroscopy spectra

We present the combined experimental and theoretical investigations of optical properties and excitation energies of metallic iridium. The reflected energy loss spectroscopy (REELS) spectra of polycrystalline Ir were measured with a cylindrical mirror analyzer in UHV conditions at primary energies of 500, 1000 and 2000 eV. The energy loss function (ELF) and thereby the refractive index n and the extinction coefficient k were calculated from these REELS spectra in the loss energy range of 2–200 eV by applying our reverse Monte Carlo method. The high accuracy of the obtained results is justified with the ps- and f-sum rules. Using the derived ELF the inelastic mean free paths of Ir were calculated from 1 eV up to 10 keV. Moreover, we identified for the first time in the optical data the 5p3/2, 4f5/2 and 4f7/2 shell excitations of the solid Ir sample.

Accurate trajectory tabulations for benchmark electrostatic geometries

The lack of accurate data on trajectories that originate from or pass through equipotential surfaces as in the hemispherical deflector or cylindrical mirror analyzers is apparent. This absence of trajectory data is remedied in this report by defining a set of benchmark geometries and determining accurate intercept values for selected rays through these geometries. Accurate tables of intercept values have been thus created and are presented allowing the testing of any simulation software against these trajectory solutions. In addition preliminary studies using a generic BEM for both the centric HDA and SC have found that the trajectory intercept data for a given number of segments in BEM is similar to an order 2 FDM solution using an equivalent mesh spacing. The implication is that BEM seems to be an order 2 process when considering trajectory errors in these geometries.

Recommended Practice for Use of Electrostatic Analyzers in Electric Propulsion Testing

Electrostatic analyzers are used in electric propulsion to measure the energy per unit charge distribution of ion and electron beams: in the downstream region of thrusters, for example. This paper serves to give an overview of the most fundamental, yet most widely used, types of electrostatic analyzer designs. Analyzers are grouped into two classifications: 1) mirror-type analyzers, and 2) deflector-type analyzers. Common mirror-type analyzers are the parallel-plate mirror analyzer and the cylindrical mirror analyzer. For deflector-type analyzers, a generalized toroidal type is first described and the commonly used cylindrical deflector and spherical deflector analyzers are discussed as special cases. The procedure for energy resolution calculations of electrostatic analyzers is described, which is a common way of comparing analyzers. Ion energy distributions from a spherical deflector analyzer are presented, comparing variations in 1) particle energy, 2) particle angle, 3) the entrance and exit geometry of the analyzer, and 4) sector angle using numerical calculations.

Improving the performance of the cylindrical mirror analyzer II: Reducing the dependence of energy resolution on sample position

Electrode segmentation of the cylindrical mirror analyzer has been shown to significantly improve the resolution of the standard instrument. The high precision solution which had been found for the 42.3 device is shown in this report to exist in fact for an extended set of input angles or equivalently for a range of sample positions. This has allowed a significant limitation of the CMA, namely the critical dependence of instrument performance on sample position, to be largely overcome. In addition by placing the sample at the minimum in the curve of resolution vs sample position, a base width resolution of ∼.00005 has been obtained for a ±6° bundle an improvement of a factor of ∼40 over the standard spectrometer. Thus electrode segmentation has been found not only to significantly improve the device performance, but in fact to enable its high precision to be realized.

Cylindrical mirror energy analyzer with the input of charged particles through end-surface diaphragm

Computer simulation is used to study electron-optical properties of a cylindrical mirror analyzer with the input of charged particles through the end-surface diaphragm. Regimes with double crossing of the optical axis (two-stage analyzer) are considered to increase the linear dispersion. The external electrode of the electron-optical system under study can be divided into several insulated parts with independently controlled potentials. Such an approach allows the second-order tuning of focusing and wide-range variation in the dispersion. Optimal working regimes make it possible to increase the linear dispersion by a factor of 3–4 in comparison with the one-stage regime.

The segmented cylindrical mirror analyzer (CMA)

The standard cylindrical mirror analyzer (CMA) has been modified by dividing the inner and outer electrodes into segments and setting the voltages on these segments to obtain the best value for the energy resolution. It has been found that dividing both the inner and outer electrodes using only one segment has resulted in an energy resolution of 0.017% for entrance angles of 42.3±6°. This corresponds to more than an order of magnitude improvement in the resolution over that of the standard instrument.