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Electron microscope specimen tilt stage
This content has been downloaded from IOPscience. Please scroll down to see the full text. 1975 J. Phys. E: Sci. Instrum. 8 265 (http://iopscience.iop.org/0022-3735/8/4/008) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 130.237.122.245 This content was downloaded on 01/10/2015 at 07:40
Please note that terms and conditions apply.
Apparatus and techniques used. This was not possible due to the failure of the CRT to give any current lower than this value. This can also be seen from figure 2 where the gain of the multiplier was highest for the lowest input currents used, and at the lower accelerating voltages. From the measured gains, values of the secondary electron emission ratio (y) were calculated and were found to be in reasonably good agreement with those of Bingham, namely, 1.67,1.82 and 2.01 (present study) and 1.5,2.0 and 2.3 (Bingham 1966) at dynode voltages of 100, 200 and 4OOV respectively. These discrepancies may be due to the differences in the two samples of aluminium used and in their surface conditions. Oxidation of the dynode surfaces was carried out by heating them to 170°C (limited by the PTFE) and cooling them gradually in the atmosphere, Gains obtained after this activation process showed an improvement of about 130 % under the same operating condition as can be seen from figure 3. From the above observations, it is obvious that aluminium can be successfully used as a cheap dynode material, especially when the availability of special materials or semiconducting layers that are used in modern multipliers is scarce. One most important advantage of this type of electron multipliers is that high gains are obtainable in spite of repeated exposure to the atmosphere. Acknowledgments The authors wish to thank Dr R P Wadhwa of Messrs Bharath Electronics Limited, Bangalore, for readily making available the CRT used in this study and to Professor H V Gopalakrishna for his interest in this work.
specimen plane. Tilt movements over a cylindrical bearing surface, coupled with a specimen rotation facility, permit tilt in any direction but result in excessive translation of images of specimen areas away from the specimen rotation axis, whilst the major difficulty with a spherical bearing surface seems to be to provide suitable drive mechanisms. The present application demanded a specimen tilt stage which would also permit in situ ion beam irradiation of the specimen. This requirement ruled out a tilt bearing in the specimen plane and the spherical bearing principle was instead adopted. This article describes the design of a permanently engaged drive mechanism which permits independant tilt about two orthogonal horizontal axes in the specimen plane. The stage was designed to fit the specimen chamber of the EM6G electron microscope using a front loading specimen change mechanism and also using a higher specimen position than standard to permit ion irradiation. 2 Design description A conical removable Cu specimen carrier rests in a s/s carriage, which in turn moves on a spherical brass bearing surface whose centre of curvature lies in the specimen plane. Figure 1 shows these three components in the upright and tilted positions. In the wall of the carriage are two holes forming seats for small ruby balls which are used to transmit the drive to the carriage.
References Allen J S 1947 Reo. Sci. Instrum. 18 73949 Bingham R A 1966 J. Sci. Instrum. 43 74-5 Narasimha Rao R 1973 MEng Thesis Indian Institute of Science, Bangalore, India Journal of Physics E: Scientific Instruments 1975 Volume 8 Printed in Great Britain 0 1975
Electron microscope specimen ti It stag e R Andrew Department of Electrical Engineering, University of Salford, Salford M5 4WT Received 30 October 1974 Abstract The principles of operation of an electron microscope specimen tilt stage are described. A stage using these principles has been constructed and permits tilt to an angle of 17.5" about any chosen axis in the specimen plane. 1 Introduction An electron microscope specimen tilt stage is normally required
to provide maximum tilt about any chosen axis in the specimen plane whilst causing minimal rotation or translation of the specimen and therefore image. It is also advantageous if this can be done in a reproducibly controllable manner, Commonly a bearing surface in the specimen plane is used whilst an alternative method is to employ a cylindrical or spherical bearing surface having its centre of curvature in the
Figure 1 Section showing juxtaposition of specimen holder H, carriage C and lower bearing L in (a) upright and (b) tilted position. Also indicated are ruby balls B, specimen position S and imaging electron beam E 265
Apparatus and techniques
Figure 3 Ball drive bridge showing semicylindrical grooves G in fixed arm F and sprung arm A
Figure 4 Complete specimen tilt stage
Figure 2 Plan view of carriage and lower bearing indicating motion to produce tilt about (a)axis XX' and (h) axis YY' (see text) Referring to the plan view of carriage and bearing in figure 2(a), tilt about the X X ' axis is achieved by moving the ruby balls equally in the direction shown. Since the balls remain at fixed distance from the specimen they must also be free to travel vertically as the carriage mOveS Over its spherical bearing, but they are constrained to the vertical planes through PQ and RS. The resultant motion of the balls, and hence the carriage and specimen to which they are attached, is that of rotation about the horizontal axis xX'in the specimen plane. To obtain tilt about the y y r axis the balls are moved as indicated in figure 2(6). Here again their vertical position will change as the carriage tilts and in addition the separation of the planes PQ and RS decreases slightly on tilting. Nevertheless, since the balls are constrained to the vertical plane through TU and are at fixed distancefrom the specimen their resultant motion, and that of the specimen, is that of rotation about the horizontal axis YY' in the specimen plane. In order then to achieve tilt about the axes XX'and YY' the balls must be driven horizontally in the directions shown whilst permitting freedom of vertical motion and small changes in horizontal centre separation. Figure 3 shows the ball drive bridge which surrounds the carriage. The balls sit in the vertical semicylindrical grooves in the fixed and sprung arms of 266
the bridge, the latter accommodating the changes in ball centre separation. Specimen tilt is now accomplished simply by horizontal motion of the bridge as indicated and conventional screw shifts are used for this purpose. The completed specimen stage is shown in figure 4. Appearing here are also small springs which prevent vertical lifting of the bridge and carriage during tilting. The cutaway section in various components which permit ion beam irradiation may ako be seen*
3 Appraisa' The maximum attainable tilt in any direction using this stage is 17.5" and preliminary tests have revealed negligible backlash in the model constructed. Tilt movements themselves are easily reproducible due to the permanent drive engagement* The maximum tilt angle is limited largely by the need to retain a reasonable area of bearing surface contact. The large conical cutaway in the lower bearing surface already results in only a crescent shaped area of bearing I X " t at high tilt although accurate machining has resulted in a stable seating wen in this condition. The ruby balls are available in English sizes from Insley Industrial Limited, Bracknell, Berkshire, and in metric sizes from Ernst Fr. Weinz Limited, 658 Idar-Oberstein 2, PO Box 2705, Germany. Journal of Physics E: Scientific Instruments 1975 Volume 8 Printed in Great Britain 0 1975
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Electron microscope specimen tilt stage
This content has been downloaded from IOPscience. Please scroll down to see the full text. 1975 J. Phys. E: Sci. Instrum. 8 265 (http://iopscience.iop.org/0022-3735/8/4/008) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 130.237.122.245 This content was downloaded on 01/10/2015 at 07:40
Please note that terms and conditions apply.
Apparatus and techniques used. This was not possible due to the failure of the CRT to give any current lower than this value. This can also be seen from figure 2 where the gain of the multiplier was highest for the lowest input currents used, and at the lower accelerating voltages. From the measured gains, values of the secondary electron emission ratio (y) were calculated and were found to be in reasonably good agreement with those of Bingham, namely, 1.67,1.82 and 2.01 (present study) and 1.5,2.0 and 2.3 (Bingham 1966) at dynode voltages of 100, 200 and 4OOV respectively. These discrepancies may be due to the differences in the two samples of aluminium used and in their surface conditions. Oxidation of the dynode surfaces was carried out by heating them to 170°C (limited by the PTFE) and cooling them gradually in the atmosphere, Gains obtained after this activation process showed an improvement of about 130 % under the same operating condition as can be seen from figure 3. From the above observations, it is obvious that aluminium can be successfully used as a cheap dynode material, especially when the availability of special materials or semiconducting layers that are used in modern multipliers is scarce. One most important advantage of this type of electron multipliers is that high gains are obtainable in spite of repeated exposure to the atmosphere. Acknowledgments The authors wish to thank Dr R P Wadhwa of Messrs Bharath Electronics Limited, Bangalore, for readily making available the CRT used in this study and to Professor H V Gopalakrishna for his interest in this work.
specimen plane. Tilt movements over a cylindrical bearing surface, coupled with a specimen rotation facility, permit tilt in any direction but result in excessive translation of images of specimen areas away from the specimen rotation axis, whilst the major difficulty with a spherical bearing surface seems to be to provide suitable drive mechanisms. The present application demanded a specimen tilt stage which would also permit in situ ion beam irradiation of the specimen. This requirement ruled out a tilt bearing in the specimen plane and the spherical bearing principle was instead adopted. This article describes the design of a permanently engaged drive mechanism which permits independant tilt about two orthogonal horizontal axes in the specimen plane. The stage was designed to fit the specimen chamber of the EM6G electron microscope using a front loading specimen change mechanism and also using a higher specimen position than standard to permit ion irradiation. 2 Design description A conical removable Cu specimen carrier rests in a s/s carriage, which in turn moves on a spherical brass bearing surface whose centre of curvature lies in the specimen plane. Figure 1 shows these three components in the upright and tilted positions. In the wall of the carriage are two holes forming seats for small ruby balls which are used to transmit the drive to the carriage.
References Allen J S 1947 Reo. Sci. Instrum. 18 73949 Bingham R A 1966 J. Sci. Instrum. 43 74-5 Narasimha Rao R 1973 MEng Thesis Indian Institute of Science, Bangalore, India Journal of Physics E: Scientific Instruments 1975 Volume 8 Printed in Great Britain 0 1975
Electron microscope specimen ti It stag e R Andrew Department of Electrical Engineering, University of Salford, Salford M5 4WT Received 30 October 1974 Abstract The principles of operation of an electron microscope specimen tilt stage are described. A stage using these principles has been constructed and permits tilt to an angle of 17.5" about any chosen axis in the specimen plane. 1 Introduction An electron microscope specimen tilt stage is normally required
to provide maximum tilt about any chosen axis in the specimen plane whilst causing minimal rotation or translation of the specimen and therefore image. It is also advantageous if this can be done in a reproducibly controllable manner, Commonly a bearing surface in the specimen plane is used whilst an alternative method is to employ a cylindrical or spherical bearing surface having its centre of curvature in the
Figure 1 Section showing juxtaposition of specimen holder H, carriage C and lower bearing L in (a) upright and (b) tilted position. Also indicated are ruby balls B, specimen position S and imaging electron beam E 265
Apparatus and techniques
Figure 3 Ball drive bridge showing semicylindrical grooves G in fixed arm F and sprung arm A
Figure 4 Complete specimen tilt stage
Figure 2 Plan view of carriage and lower bearing indicating motion to produce tilt about (a)axis XX' and (h) axis YY' (see text) Referring to the plan view of carriage and bearing in figure 2(a), tilt about the X X ' axis is achieved by moving the ruby balls equally in the direction shown. Since the balls remain at fixed distance from the specimen they must also be free to travel vertically as the carriage mOveS Over its spherical bearing, but they are constrained to the vertical planes through PQ and RS. The resultant motion of the balls, and hence the carriage and specimen to which they are attached, is that of rotation about the horizontal axis xX'in the specimen plane. To obtain tilt about the y y r axis the balls are moved as indicated in figure 2(6). Here again their vertical position will change as the carriage tilts and in addition the separation of the planes PQ and RS decreases slightly on tilting. Nevertheless, since the balls are constrained to the vertical plane through TU and are at fixed distancefrom the specimen their resultant motion, and that of the specimen, is that of rotation about the horizontal axis YY' in the specimen plane. In order then to achieve tilt about the axes XX'and YY' the balls must be driven horizontally in the directions shown whilst permitting freedom of vertical motion and small changes in horizontal centre separation. Figure 3 shows the ball drive bridge which surrounds the carriage. The balls sit in the vertical semicylindrical grooves in the fixed and sprung arms of 266
the bridge, the latter accommodating the changes in ball centre separation. Specimen tilt is now accomplished simply by horizontal motion of the bridge as indicated and conventional screw shifts are used for this purpose. The completed specimen stage is shown in figure 4. Appearing here are also small springs which prevent vertical lifting of the bridge and carriage during tilting. The cutaway section in various components which permit ion beam irradiation may ako be seen*
3 Appraisa' The maximum attainable tilt in any direction using this stage is 17.5" and preliminary tests have revealed negligible backlash in the model constructed. Tilt movements themselves are easily reproducible due to the permanent drive engagement* The maximum tilt angle is limited largely by the need to retain a reasonable area of bearing surface contact. The large conical cutaway in the lower bearing surface already results in only a crescent shaped area of bearing I X " t at high tilt although accurate machining has resulted in a stable seating wen in this condition. The ruby balls are available in English sizes from Insley Industrial Limited, Bracknell, Berkshire, and in metric sizes from Ernst Fr. Weinz Limited, 658 Idar-Oberstein 2, PO Box 2705, Germany. Journal of Physics E: Scientific Instruments 1975 Volume 8 Printed in Great Britain 0 1975
