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ELECTRON SPECTROMETER FOR MÖSSBAUER SPECTROSCOPY
T. Toriyama, K. Saneyoshi, K. Hisatake
To cite this version:
T. Toriyama, K. Saneyoshi, K. Hisatake. ELECTRON SPECTROMETER FOR MÖSS- BAUER SPECTROSCOPY. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-14-C2-16.
�10.1051/jphyscol:1979203�. �jpa-00218461�
JOURNAL DE PHYSIQUE
Collogue C2, supplement au n° 3, Tome 40, mars 1979, page C2-14
ELECTRON SPECTROMETER FOR MOSSBAUER SPECTROSCOPY
T. Toriyama, K. Saneyoshi and K. Hisatake
Department of Applied Physios, Tokyo Institute of Technology, Ohokayama, Megw?o-ku, Tokyo, Japan
Résumé.- On a construit un nouveau spectromètre d'électrons à champ retardé pour détecter les électrons de conversion interne émis par effet Mossbauer. Ce spectromètre est intéressant pour étudier les propriétés de surface des solides. Le domaine d'énergie observable est compris entre 0 et 20 keV, avec une résolution de 0,1 % pour une transmission de 1 % des électrons émis par un
filament chauffé. Cette résolution est plus mauvaise, par un ordre de grandeur, pour les électrons de conversion issus d'une source radioactive. Le système complet qui est décrit comporte le spec- tromètre d'électrons un évaporateur et un spectromètre Mossbauer.
Abstract.- A new retarding-field electron spectrometer has been constructed to detect internal conversion electrons emitted in the Mossbauer effect. This spectrometer is useful to investigate the surface properties of solids. The energy range of the spectrometer is from 0 to 20 keV. The transmission of 1 J at 0.1 2 resolution was obtained for electrons emitted from a hot filament, but for conversion electrons from a radioactive source the transmission was so far found to be one order worse. The whole system, which is the combination of the electron spectrometer with .a vacuum evaporator and a Mossbauer spectrometer, is also described.
1. Introduction.- The Mossbauer spectrum can be taken by detecting internal conversion electrons emitted from the absorber. This method is especially useful for the investigation of the surface properties of solids since the electron spectrum measured gives the information of the depth from the surface. Se- veral preliminary studies have been made with this method /1-4/, but a complete work has not yet been performed due to either low energy resolution or low detection efficiency of the electron spectrome- ter used.
In order to resolve these problems of an elec- tron spectrometer, we have constructed a new retarding- field spectrometer, whose energy resolution is ai- med to be 0.1 % at the transmission of 1 X. Some retarding-field spectrometers designed for ESCA experiment /5-8/ seem to nearly meet the present purpose but the workable energy ranges are limited to at most 4 keV; for the Mossbauer study the ener- gy range of up to 20 keV is desirable if one wants to study both iron and tin. The present spectrome- ter can be worked up to 20 keV, but the final reso- lution and transmission have not yet attained to the aimed values.
2. The electron spectrometer.- The present electron spectrometer can analyze electron energy with three pairs of grids; that is, retarding grids, reflec- ting grids and supressing grids, as are illustrated in figure 1. This design is similar to ones used for ESCA /5-8/, but for the present one we adopted a confocal ellipsoid of revolution for the reflec-
ting grids to get a high transmission.
Fig. 1 : The whole system of the Mossbauer spectro- meter combined with an electron spectrometer.
1 Mossbauer source 1 2 absorber 1 3 retarding grids 4 reflecting grids 5 suppressing grids
6 channeltron 7 Pb shield 8 evaporator and annealing system 9 transducer 10 Mossbauer source 2 11 absorber 2 12 Nal (2 mmt) scintil- lator.
Between these three pairs of grids are applied the retarding voltage V_ (= 0 1^20 kV), the reflecting voltage V_ (= -30 %-300 V) and the suppressing vol- tage V„ (= -40 %-80 V ) , respectively. The last one is for suppressing secondary electrons. The elec- trons passing through the suppressing grids are de- tected with a channeltron, whose potential is 300 V relative to the suppressing grid. The grids are mesh of 50 urn wire of SUS 32, 500 ym apart. The geometrical transmission of the mesh is 81 %. Since the incident solid angle of the retarding grids is 43 % of 4 ir, the maximum transmission passing through the six grids is estimated to be 43 x (0.81)6 X = 12 %.
In order to investigate the resolution and
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979203
transmission of the spectrometer, a hot filament was set at the source position of the spectrometer.
forthe collection of the analyzed electron beam, a brass rod was set in place of the channeltron. A typical result of the investigation is given in figure 2, where the collected current is shown as a function of an incident beam energy with a parameter of the reflecting voltage VF.
7
Collected Current(rA) VI=-4000 v VF-80v
I
Acceleration Voltage
experiment. In the figure are also shown the data of the INS (Institute for Nuclear Study, University of Tokyo) iron-f ree magnetic 8-spectrometer with 'CO source for comparison.
Resent spectro- 0"
meter wlth f lament -sP
electrons ,w. "'
.
-
,,A' INS alr core
,I spectrometer
,P' -.a*'
.
with-
p sourcea ,
_ -
,e'* .-a-
,'
-
d .Q Present spectrometer
<.0*
,
-
with % p sourceFig. 4 : The relation between energy resolution and transmission for the electron spectrometer with
at
different electron-sources and detectors.
Fig. 2 : Typical Performance of the electron spec-
Data of INS iron-free magnetic spectrometer is also trometer by use of a hot filament as an electron
shown for comparison.
source.
-@..
-
--,* ,-I I 1 1 1 , 1 1 1 I 6 1 11, , , I 1 1 1 1 1 1 1 t 1 .
From the figure the relation between the energy reso- lution (AE/E) and the transmission can be obtained.
The result is shown in figure 3 together with those of other experiments. The obtained maximum transmis- sion was found to be 12 %, which is just as large as the expectation mentioned above.
0.0 I 0.1 1.0 I 0
Energy Resolut~on AE/E (%I
Fig. 3 : Electron spectrum of 5 7 ~ o taken with the pqesent electron spectrometer. The instrumental resolution was set as 1.5 % at 7.3 KeV.
By setting a 5 7 ~ o source in place of the filament, we measured the internal conversion and Auger elec- trons. The spectrum taken with the instrumentalreso- lution AE/E of 1.5% at 7.3 KeV is shown in figure 4.
The relation between the resolution and the transmis- sion for "CO source is shown in figure 3. The transmission in this case was found to be smaller by one order than in the case of the filament
We suppose that the cause for the poor transmission of the present spectrometer was the low detection efficiency of the channeltron; it was found by an independent experiment that the channeltron used had the efficiency of more than 50 % but the sensi- tive area was much smaller than the cone area of the detector. To get higher transmission the field form near the channeltron should be improved for the electrons to hit the sensitive area of the detector.
3. The whole system.- The whole system consists of an electron spectrometer, a vacuum evaporator and a Miissbauer spectrometer, as is shown in figure 1 . The first two are contained in a vacuum chamber of stainless steel, which is evacuated with a combina- tion of a sputter- ion pump with a titanium-getter and a sorption pumps. The vacuum is maintained as low as 1 x lo-' torr. The sample to be investigated can be prepared in the evaporator and be moved to the source .position of the electron spectrometer without breaking vacuum.
The ~Gssbauer spectrometer is a conventional one with a feedback system. There are two assbauer sources at both ends of the driving rod, as is shown in figure 1. One (source 1 ) is for taking the M6ss- bauer spectrum detected with electrons and the other (source 2) is for the check of the motion of the transducer.
The function generator of the transducer and the retarding voltage of the electron spectrometer are controlled by a microcomputer of TK-80 type of
3
c2- 16
JOURNAL DE PHYSIQUENEC with 8K RAM and 4K ROM. The data acquisition is References also performed with the microcomputer. In figure 5
/3/ Toriyama, T., Kigawa, M., Fujioka, M. and Hisa- take, K., Japan J. Appl. Phys. Suppl.2 (1974) 733.
141 Bonchev, Tsv., Minkova, A., Kushev, G. and Groz- danov,M., Nucl. Instr. Meth. 4,lJ (1977) 481.
/5/ Huchital, .D.A. and Rigden, J.D., J. Appl. Phys.
43 (1972) 2291.
-
161 Staib, P., J. Phys. E
5
(1972) 484.is shown the Massbauer spectrum thus taken.
/I/ Bonchev, Zv., Jordanov, A. and Minkova, A., Nucl.
Instr. Meth.
70
(1969) 38.7 7 6 5 n. 3 2 t 0 -1 -2 -3 -4 -5 -6 -7 -8
Doppler Velocity (mrn/s
ifon
1
/7/ Lee, J.D., Rev. Sci. Instrum.64
(1973) 893./ 2 / Bzverstam, U., Bohm, C., Ringstram, B. and Ekdahl, T., Nucl. Instr. Meth.
108
(1973) 439.mo-
I
/8/ Staib, P., J. Phys. E10
(1977) 914.n
Fig. 5 : ~zssbauer spectrum of iron film taken with the present system. The energy of electrons was set as the peak position of the 14.4-K of 5 7 ~ e . The electron energy was set at the peak position of the K conversion of the 14.4 keV transition of 5 7 ~ e . The signal-to-noise ratio of the spectrum is not as good as expected due to the low efficiency and the high background of the electron spectrometer.
These problems are now under study.
The authors are indebted to Prof. Fujioka and Mr Kigawa for their contributions in the early stage of the study.
