innovative research of electron microscopes -...

18. - 20. 5. 2011, Brno, Czech Republic, EU

INNOVATIVE RESEARCH OF ELECTRON MICROSCOPES - ANALY SE OF MAGNETIC PROPERTIES OF TECHNICALLY PURE FERRUM - BEHANIT

Martin MAREK a, Aleš FOLVARČNÝ a, Daniel PETLAK a, Regina HOLČÁKOVÁ a, Ladislav Jelen b, Jiří REŽNAR b

a) VŠB-Technical University of Ostrava, FEI, KAT410, Department of Power Electric Engineering, Laboratory of Magnetic Measurements and Applications, 17. listopadu 15, 708 33 Ostrava - Poruba, Czech Republic,

mail: [email protected], telefon: 00420-724-033-727

b) VÍTKOVICE - Research and Development - Technical Applications, Studentská 6202/17, 70800, Ostrava-Poruba, Czech Republic, mail: [email protected], telefon: 00420-775-113-433

Abstract

The paper deals with the basic goals and partial results of the project, which focuses on innovative research of the magnetic lenses and chambers of electron microscopes. This project and paper were created by financial support of state budget through the Ministry of Industry and Trade MPO-CR, project n. FR-TI1/334. This part contains the analysis of magnetic properties of the type steel which is designed for construction of lens and chamber of the electron microscopes.

Keywords: magnetic properties, magnetic measuring, electron microscope, magnetic lens, Behanit

1. INTRODUCTION

Electron microscopes are very powerful and useful apparatuses of the modern science, in metallurgy area itself as well as in other scientific and practical human branches. Currently, there is a number of basic and special types of electron microscopes varying in purpose and area of research. Design of selected types of modern electron microscopes is symbolically shown in Fig.1. Detailed description of the basic types and specific options is beyond the scope of this paper, more information can be found for example in reference [1], [2], [3], [4].

Fig.1. Examples of various types of electron

microscopes [3] Fig.2. Steels for parts of electron microscopes

2. MAGNETIC STEELS AND ALLOYS FOR CONSTRUCTION OF E LECTRON MICROSCOPES

Electron microscopes contain many various parts and components. The important parts made from magnetic steels and alloys include the lenses, objectives, chambers and shielding components. Each of these microscope parts has its own function and specific requirements. Symbolically, these parts are shown in Fig.2. From the view of the magnetic properties, the highest requirements are put on the steels for lenses and objectives.

The steels for these parts are designed specially for the conduction and forming of the magnetic field to the active area of lens, where magnetic field is acting on the electron beam. Therefore these steels must show high levels of magnetic saturation and permeability, and also have a narrow hysteresis loop and very small value of coercive force and remanent flux density. Similar situation is with the steels and alloys for the


shielding. The purpose of these materials and parts is shielding of external magnetic fields which can penetrate into the active area of lenses and cause optical defects. The steels for chambers construction have requirements primarily on the mechanical strength and vacuum tightness. It appears, however, that the magnetic properties of these steels may have a significant impact on the function and operation of the electron microscopes. Parameters of coercive force and remanent induction of these steels may reach relatively high values. With the respect to the large volume of chamber itself even a small remanent magnetization of the chamber steel may cause a relatively large and disturbing magnetic field at the various locations of the trajectories of electron beams and those can cause optical defects then. It is evident, that for the detailed formulation of these effects it is necessary to know the real magnetic properties of used materials. Therefore, the first part of the project solutions is devoted to a detailed analysis of the magnetic properties of types steels and alloys. The extensive range of steels and alloys has been tested.

3. MEASURING OF MAGNETIC PROPERTIES OF STEELS AND A LLOYS

The measurement of magnetic properties of steels and alloys was carried out on two measurement systems. These systems may be used to define both of the quasistationary and dynamic hysteresis and magnetization characteristics for various frequencies and limits of exciting magnetic field. The brief description of these measurement systems is given in the following section.

1.1 REMAGRAPH (DC characteristics)

This measuring system is designated for measuring of stationary BH characteristics of soft magnetic materials. The design of the measuring system is shown in the figure Fig.3. Measuring principle is given by general methods of measuring on toroidal samples. Signal processing and evaluation of induced voltage, by which is the magnetic induction in the sample is determined, is performed by electronic fluxmeter. More information can be found in reference [5], [6], [7].

1.1 REMACOMP (AC characteristics)

This measuring system is designated for the measuring of magnetic properties of soft magnetic materials in the dynamic magnetic fields with a frequency range 1Hz – 10 kHz. The Design and the principled scheme are shown in the following figure. Basic part of this measuring system is formed by linear four quadrants power amplifier. According to the set parameters and regulation there is given the value and shape of the excitation current. In this way there can be measured BH hysteresis characteristics or magnetizing amplitude characteristic for the required magnetic field parameters (frequency, amplitude of the magnetic flux density or intensity of magnetic field, wave shape, etc.). More information can be found in reference [4, 5, 6].

Fig.3. Implementation of the system Remagraph Fig.4. Implementation of the system Remacomp

4. ANALYSIS OF MAGNETIC PROPERTIES OF THE MATERIAL BEHANIT – PURE FERRUM

This chapter presents description of tested materials and basic results of the measuring of magnetic properties. There is described one selected material for construction of the lenses and objectives of electron microscopes. This material is technically pure ferrum.

This soft ferromagnetic material with trademark Behanit, grade number 19991, is characterized by the narrow BH hysteresis loop and is prepared by vacuum induction smelting technology with final operation process - forging and annealing. The purity of this material is 99,5% Fe. Material is manufactured in the shape of bar ingots of various sizes. For analysis of magnetic properties of this material there were prepared toroidal samples from two smelts. From each smelt there were prepared five samples with dimensions (d1=120mm, d2=100mm, h=10mm).


Fig.5. Example of Behanit Ingots Fig.6. Samples of Behanit for measuring magnetic properties

(pure samples and samples with winding)

The aim of this analysis was, firstly to find real magnetic properties of Behanit material, secondly to define magnetic homogeneity of material from one smelt, thirdly to define differences of materials from two smelts. The material for these samples was taken after forging process and before annealing process. For all samples there were measured BH hysteresis characteristics, stationary and dynamic, for various limits of magnetic field and various frequencies. Brief overview on the fundamental results is given in the next section. The quality of material homogeneity of ingot from one smelt is presented in fig.8. The differences of magnetic properties of samples, made from the ingot of one smelt, are practically zero. Images fig.9 and fig.10 follow to show the comparison of differences of magnetic properties of materials from two smelts. The chemical composition of material from both of smelts is practically the same, a small difference is in Mangan content (smelt no.1=0,15%, smelt no.2=0,31%). Shown graphs briefly present the quality and resulting magnetic properties of Behanit material after forging and before annealing process.

Fig.7. Behanit - stationary BH hysteresis characteristic,

Smelt no.1 (52618), Sample no.1, for Hmax= 8.000 (A/m)

Fig.8. Behanit - Comparison of stationary BH hysteresis characteristics, Smelt no.1 (52618), Samples no.1-2-3-4-5, for

Hmax= 8.000 (A/m)

Fig.9. Behanit - Comparison BH hysteresis characteristics,

Smelt n.1 x Smelt n.2, for Hmax= 8.000 (A/m) char.1,2 - Sample no.1,2 (Smelt no.1-52618) char.3,4 - Sample no.1,2 (Smelt no.2-56598)

Fig.10. Behanit - Comparison BH hysteresis characteristics, Smelt n.1 x Smelt n.2, for Hmax= 1.000 (A/m)

char.1,2 - Sample no.1,2 (Smelt no.1-52618) char.3,4 - Sample no.1,2 (Smelt no.2-56598)


5. METALOGRAPHIC DESCRIPTION

When analyzing the magnetic properties of the material Behanit there has been also performed the metallographic analysis to determine grain structure of the tested materials. Respective metallographic analysis was performed on one sample of smelt No.1 and also on one sample of smelt No.2.

Fig.11. Toroidal samples used for made of the metallographic samples

Fig.12. Samples of material Behanit after process scratch pattern preparing

Fig.12. Inverted metallographic microscope GX51 used for

metallographic analyses

Results of metallographic analyses and grain structure of the analyzed samples of material Behanit are presented in the next table and pictures.

Sample - smelt no.1 Sample - smelt no.2

Fig.17. sample of the radial direction of scratch pattern

zoom view X100 Fig.18. sample of the radial direction of scratch pattern

zoom view X100

Fig.19. sample of the radial direction of scratch pattern

zoom view X200 Fig.20. sample of the radial direction of scratch pattern

zoom view X200


6. CONCLUSION

The paper presents partial results of project solution. This part of solution is focused on the detailed analysis of magnetic properties of selected steels and alloys for magnetic lenses, chambers and other parts of electron microscopes. In this example there is shown the material of technically pure ferrum type – Behanit.

The detailed knowledge of real magnetic properties of used materials and other technology effects on the final magnetic properties of these materials provides new possibilities for design, optimalization and error correction of electron microscopes lenses.

7. ACKNOWLEDGEMENT

This project and paper was created by financial support of state budget through the Ministry of Industry and Trade of the Czech Republic, MPO-CR, project No. FR-TI1/334.

LITERATURA

[1.] DELONG, A., DRAHOŠ V.: Praktická elektronová mikroskopie. NCAV, Praha, 1958

[2.] DELONG, A., FRANK, L., KNOR, Z., KOLAŘIK, V.,: Metody analýzy povrchů, elektronová mikroskopie a difrakce. Academia, Praha, 1996

[3.] EGERTON, R. F.: Physical principles of electron microscopy: an introduction to TEM, SEM, and AEM. Springer, USA, 2005

[4.] Firms brochure and internet pages, FEI Company, Zeiss, Tescan, Delong Instruments,: http://www.fei.com, http://www.zeiss.de/nts, http://www.tescan.com, www.dicomps.com

[5.] MAREK. M.: Recognition methods of magnetic properties of the construction materials, specific examples of using and applications of the magnetic measuring., dissertation thesis, VŠB-TU Ostrava

[6.] VŠB-TU Ostrava, FEI, Laboratory of Magnetic Measurements and Applications: http://fei1.vsb.cz/kat453/www453/soubory/MAG_LAB/index.htm

[7.] DRAXLER, K., KAŠPAR, P, RIPKA, P.: Magnetické prvky a měření. CVUT-Praha, 1999

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