- Email: [email protected]
New apparatus
Micron, 1981, Vol.: 12, lap. 147-152.
0047-7206/81/020147-06502.00[0
Pergamon Press Ltd. Printed in Great Britain
NEW
APPARATUS
PHILIPS SCANNING ELECTRON MICROSCOPE--SEM 505 MAJOR FEATURES
lens condenser system, or new single crystal LaBe source; (iii) unrestricted access to whole specimen mounting stage, also allows quick exchange of" substages and special holders for applications such as bulk specimens.
(1) New high-sensitivity fast-response detectors with interchangeable elements for backscattered electrons or cathodoluminescence. (2) Fibre optics link of new detectors to INNOVATIVE DETECTORS AND external photomultiplier/pre-amplifier avoids SYSTEM INTEGRATION MAKE THE limitation in performance of any other detector. SCANNING ELECTRON MICROSCOPE (3) TV-rate in all imaging modes--secondary, A COMPREHENSIVE ANALYTICAL backscattered and transmitted electron, specimen INSTRUMENT current and cathodoluminescence. (4) Advanced image manipulation and video Innovative detectors with flexible fibre optics facilities include automatic data registration, linkage to external photomultiplier/pre-amplifier split-screen imaging, signal mixing and subtrac- combinations have produced dramatic advances tion. in image analysis for the new Philips scanning (5) Unique Data Link provides parallel con- electron microscope, SEM 505. The sensitivnection of all control modules; interchange, up- ity of the detectors in backscatter mode is such dating or expansion is quick and simple. that when used for image analysis improved (6) EDAX PV 9100 energy dispersive and levels of atomic number resolution are attained. Microspec WDX-2A wavelength dispersive X- Further, the space created by the compactness of ray spectrometers always have optimum the system allowed the designers to develop a nogeometry. compromise geometry for both wavelength- and (7) WEDAX option co-ordinates energy dis- energy-dispersive X-ray spectrometers. persive and wavelength dispersive X-ray analysis. Automation and integration of these systems (8) Omnicon Sigma 200R provides on-line has been developed to such an extent that the SEM image analysis, and can be integrated with total potential of the SEM 505 has yet to be fully the energy dispersive X-ray spectrometer. explored. (9) Analytical multi-sample holder movements may be joystick controlled through motor Image analysis drives, facilitating rapid accurate switching from The new detector system is used for either standard to sample and relocation of specific backscattered electrons or cathodoluminescence. points-of-interest. There are four multi-function detectors grouped (10) EDAX PV 9100 control of analytical beneath the final lens, and each can act in either multi-sample holder allows for automatic analysis mode. Conversion from one to the other is quick of pre-located points. and simple. (11) Latest circuit technology, top quality When used in the backscatter mode for image components and computer aided design have analysis, resolution of atomic number provides provided numerous further benefits. These sufficient contrast that a copper/nickel interface includeshows a contrast difference of four grey levels for (i) easy operation ensured by functionally an atomic number difference of one. This opens related layout of control module panels; the way to image analysis of metallurgical phases. (ii) high quality illumination from unique The SEM 505 can be equipped with the OmniPhilips tungsten mini-gun and optimised double 'con Sigma 200R for on-line image analysis. This 147
148
New Apparatus
Fig. I. Philips' new scanning electron microscope, the SEM 505, which has the innovative multi-function detectors that give greatly improved detection of backscattered electrons and cathodoluminescence, without interference with any of the other detection systems. provides digital scan generation, a detection module with control facility, plus a minicomputer with print-out terminal and optional floppy disc system. Integration of this system with the energydispersive X-ray spectrometer creates an interestingly versatile analytical system.
X-ray analysis The energy-dispersive X-ray spectrometer, EDS, functions at both eucentric positions of the goniometer, providing take-off angles of 16 and 26 °. Detector specimen distance is adjustable for optimisation of the solid angle. The EDAX PV 9100 EDS used gives rapid simultaneous elemental analysis over the range sodium to uranium. A special detector with removable window is availab!e for light element detection, down to carbon. Automatic peak identification simplifies analysis of major components. Elemental distribution or relative distribution of elements and background can be mapped and related to other
images of the same area, e.g. backscattered or secondary-electron images. Line scans or elemental maps can be stored for up to four elements at a time. A special slow-line-scan facility of the SEM 505 provides high quality statistics. F R A M E C or COR 2 ZAF correction methods provide high quality quantitative results. The Microspec WDX-2A wavelength-dispersive spectrometer, WDS, provides fully automated qualitative and quantitative analysis of all elements down to beryllium. It has a microprocessor based integrated digital control system. Programmable operation allows automatic selection of wavelength position, with reproducibility 0.00l nm LiF equivalent and eight selectable scan speeds for each of a choice of four crystals mounted on a rotating turret. Slit size in 0.01 mm steps up to 2.5 mm, and slit position, for precise alignment with respect to the diffracted beam, are also automatically selected.
New Apparatus
149
Fig. 2. The new Philips scanning electron microscope, SEM 505, showing the wavelengthdispersive X-ray spectrometer,immediatelybehind the column.The display-screenand operatingkeyboardfor the energy dispersive X-ray spectrometer are visible in the background. The control panel is fitted with a second viewingmonitor and, at the right-hand-side,a videoscope.
All analysis parameters are programmable in selected step intervals, including amplifier gain, analyser lower level and window, counter and timer operation, ratemeter output ranges and time constants, and detector high voltage supply. The spectrometer operates in four modes: manual; scan, over a pre-set wavelength range; element, measuring a given set of elements from a storage capacity of 90; and external, where control is by an external automated system. WEDAX
Simultaneous operation of the two X-ray analytical systems, in combination is possible with the aid of an external automated control system, WEDAX 3. A special geometric configuration of the energy dispersive detector provides the same take-off angle as the wavelength dispersive spectrometer (35°), it also allows operation at the same beam current. This, combined with the arrangement of the WDS so that its focussing is height insensitive, ensures that the output of the two spectrometers is truly compatible and can be fully automated. The combination offers the superior trace element performance and light element detection
of the WDS with the heavy element detection and convenient simultaneity of the EDS, all centrally controlled. The speed and convenience of the system is further enhanced by the analytical specimen holder. This provides accommodation for a selection of standard and metallurgical mounts. Stage motor drives for X, Y and rotation movements are joystick controlled. Any point on any of the specimens can be relocated, with an accuracy of 2/zm and any specimen reselected within 4 see, with no need to re-open the chamber. Thus allowing for rapid comparisons of standards and unknowns. Automation
Optical identification of points-of-interest in specimens with insufficient electron interaction contrast, and their subsequent analysis is laborious and occupies an expensive installation for a simple task. The anomaly is increased when low versatility, limited operation built-in optical microscopes are used. In the SEM 505 centralised control through the WEDAX system enables the user to examine specimens under an independent top-quality
150
New Apparatus
optical microscope and register co-ordinates of points for analysis in the memory of the EDAX PV 9100. The sample is then fitted into the electron microscope and orientated. Relocation of all registered co-ordinates and analysis proceeds automatically. The co-ordinates of points for analysis on a further sample can be recorded as this analysis continues, thus the installation need never be under utilised.
High quality illumination High quality illumination is obtained from the unique Philips tungsten filament mini-gun and optimised double-lens condenser system. This is a further contribution to the excellent TV rate imaging of the SEM 505. Gun brightness is 2 × 105Acm -2 sr at 30kV, and the plug-in Wehnelt cylinder has facilities for varying the filament-Wehnelt distance and the Wehnelt aperture diameter for special applications. An optional single crystal LaBe source gives up to a ten-fold increase in gun brightness and extended lifetime. The source has a simple plugin mounting making it interchangeable with the standard gun. Advantages include high quality analysis, improved image definition and higher scanning rates.
Flexible imaging The four backscattered electron or cathodoluminescence detectors are connected in pairs to
two photomultipliers outside the chamber. Optical switches enable the images to be mixed or isolated as required. Because of their compactness the new detectors do not interfere in the excellent performance of the secondary-electron detector. A similar arrangement of detector, optical fibre linkage and photo-multiplier pre-amplifier combination is used beneath the stage for transmitted electrons. Signals from any two of these detectors plus the specimen current can be mixed, and/or inverted. Extensive video-handling capacity in the SEM 505 includes enhancement of fine detail, splitscreen imaging and automatic data registration. All control modules are connected in parallel to a unique Data Link which carries all information relevant to adjustment of microscope parameters. This system permits interchange of modules, up-dating or expansion, quickly and simply in response to changing needs. Thus in the SEM 505 Philips has achieved, for the first time in scanning electron microscopy, optimisation of all modes visual and analytical, with no compromises. The SEM 505 also represents a significant improvement in price performance ratio. These features combine with Philips' application support, worldwide service network and long-term guarantee of spares availability to provide the value for money only obtainable from a world leader in scientific instrumentation.
Fig. 3. Four of the innovative multi-function detectors, from the new Philips SEM 505 scanning electron microscope, surround a sample. Signals are transmitted from the detectors using fibre optics bundles.
New Apparatus FIBRE OPTICS AND ADVANCED VIDEO CONTROL GIVE THE SCANNING ELECTRON MICROSCOPE UNEQUALLED VERSATILITY Dramatically increased sensitivity of backscattered electron and cathodoluminescence detection have been achieved by Philips in the design of the new scanning electron microscope, the SEM 505. These increases have been achieved without any reduction in performance of the secondary-electron detector or X-ray spectrometers. Combined with a unique Data Link for modular units and extensive capacity for image manipulation, this produces a simple-to-operate instrument with unprecedented versatility in imaging modes and excellent analytical capability.
New detectors and fibre optics Four compact detectors beneath the final lens are used for either backscattered electrons or cathodoluminescence. Conversion from one mode to the other is quick and simple, and the specially developed scintillator for the detection of backscattered electrons lasts the lifetime of the instrument. The signals from the detectors are carried, in two pairs, using flexible fibre optics, to two photomultiplier pre-amplifier combinations outside the evacuated specimen chamber. Optical switches allow rapid changeover from one detector to another, for instance switching mode from backscatter to cathodoluminescence, or signal mixing. This system, which is the subject of a patent application, is so sensitive that detection of backscattered electrons and cathodoluminescence has been improved two-hundred fold over the standard of the previous detectors. The flexibility of fibre optics allows each detecting element to be placed in an ideal position for any function, without the limitations of fixed constructions or precise port locations. The availability of four elements mounted under the final lens makes it possible to simulate either point source or diffuse illumination and to rotate this source around a stationary specimen. The same arrangement, with fibre optics and a photomultiplier, is used for the transmitted electron detector, operating in conjunction with a suitable aperture to give bright or dark-field images. The SEM 505 has as standard a secon-
151
dary-electron detector and facilities for measuring specimen current thus providing comprehensive imaging capabilities. The fast response of the fibre optics system permits TV-rate images to be produced in all detection modes, even at low kV values. Hence output can also be through closed circuit TV monitors or for video recording. An optional module enables the operator to select and mix any two of all the available signals, with inversion facilities if required. The mix can be varied continuously from 100% of one signal to 100.%oof the other.
Data Link The modular control units of the SEM 505 are all connected in parallel via a unique Data Link system. The Data Link carries all information relevant to the control of the microscope, enabling automatic adjustment of compensating circuits and readout for any selection of operating parameters. Control modules on the Data Link can be interchanged easily, so siting of modules can be arranged according to user preference. This provides for fast simple adaptation in response to changing requirements. Also, additional modules can be added to give convenient upgrading. Video control The comprehensive video control facilities of the SEM 505 include enhancement of fine detail by mixing of the differentiated video signal with the unprocessed signal. Extra information can be gained from dark areas by applying variable gamma amplification to the video signal. Switching between the processed and unprocessed image is simplified by an independent black level control which allows the original detector settings to remain unaltered. A single module provides facilities for splitscreen imaging. This can be used to compare images differentially magnified (up to eight times difference), images from two different detection sources or subjected to two different processing conditions, or to produce a stereo pair obtained at two different angles of tilt. The same module also supplies automatic registration of factors such as image scale, kV value, magnification, detectors in use, as a continuously displayed alphanumeric code along the lower edge of the image. Additionally, it allows scan rotation up to 360 ° and tilt correction,
152
New Apparatus
eliminating dimensional foreshortening of the image, up to 70 °. A logical system has been developed for routing of video signals, preventing the SEM 505 from reacting to any 'illegal' instructions.
Easy operation Easy operation is ensured by the control module panels which have been carefully designed to give a functionally related layout. For example the focussing control most used is placed immediately above the desk for easy locatiOn and relaxed adjustment. Simple optimisation and recording of images is obtained through the provision of independent contrast and brightness controls for viewing and photographic channels, and the high speed response video level indicator. The photographic sequence is automatic. Maximum use of the available contrast and accurate calibration of photographic systems is achieved using an internally generated greyscale. High-quality illumination High-quality illumination is obtained from the unique Philips tungsten filament mini-gun and optimised double-lens condenser system. This is a further contribution to the excellent TV-rate imaging of the SEM 505. Gun brightness is 2 x 105A cm -2 sr at 30kV, and the plug-in Wehnelt cylinder has facilities for varying the filament-Wehnelt distance and the Wehnelt aperture diameter for special applications. Variable Wehnelt biasing provides an additional dimension for control of emission. An optional single crystal LaB~ source can give a ten-fold increase in gun brightness and extended lifetime. It has a simple plug-in mounting making it interchangeable with the standard gun. Advantages include high quality analysis, improved image definition and higher scanning rates. Stable reliable electronics and optics Latest circuit technology, top quality components and computer aided design provide excellent electronic stability and reliability. The versatile electron optical configuration allows almost all tasks to be carried out without the need to change the aperture. Accurate alignment of the complete electron optical system can be achieved in seconds using electromagnetic fine controls. Centering of the
final aperture is never required, due to precision manufacture and assembly. Focussing is fully compensated for changes in high tension and spot size. Spot sizes range from 4 nm to 1000 nm with seven precision switched values and continuous variation between steps. A resolution of 6 nm is guaranteed with 5 nm attainable. Astigmatism correction is made easy by the provision of discrete focussing steps and superb TV-rate imaging. The electron optics are fully isolated from the exceptionally clean high quality vacuum, in the order of 1.3 × 10-4pa, (10-6Torr).
Eucentric goniometer The eucentric goniometer stage provides six independent specimen movements. Fast precise orientation is obtained by the use of back-lash free goniometer drives. The simple design gives fully eucentric specimen tilting at two precisely defined working distances. Up to 90 ° tilt is available. Excellent reproducibility of positioning is ensured by the following performance characteristics, routinely achieved: (i) accuracy of eucentricity is such that specimen detail is retained on screen over a wide range of tilt, for magnifications up to 10,000x; (ii) flatness of the X-Y movement is better than 2 tzm over the whole table; (iii) drift of the specimen with respect to the optical axis is better than 20 nm 10 min -1 in the iV- Y plane. The specimen chamber is designed for unrestricted access to the whole specimen mounting stage. This also allows quick exchange of substages and special holders for applications such as bulk specimens. Analysis The SEM 505 can also function as a powerful X-ray analytical instrument. Accepting both wavelength and energy dispersive spectrometers simultaneously, it provides excellent qualitative and quantitative analyses. The memory of the EDAX PV 9100 60 system can be programmed independently, for automatic relocation of points for analysis. Further Information from: Tony Gooda.._ll, Pye Unicam Ltd., York Street, Cambridge CB1 2PX. Tel. : (0223) 358866, Ext. 368.
0047-7206/81/020147-06502.00[0
Pergamon Press Ltd. Printed in Great Britain
NEW
APPARATUS
PHILIPS SCANNING ELECTRON MICROSCOPE--SEM 505 MAJOR FEATURES
lens condenser system, or new single crystal LaBe source; (iii) unrestricted access to whole specimen mounting stage, also allows quick exchange of" substages and special holders for applications such as bulk specimens.
(1) New high-sensitivity fast-response detectors with interchangeable elements for backscattered electrons or cathodoluminescence. (2) Fibre optics link of new detectors to INNOVATIVE DETECTORS AND external photomultiplier/pre-amplifier avoids SYSTEM INTEGRATION MAKE THE limitation in performance of any other detector. SCANNING ELECTRON MICROSCOPE (3) TV-rate in all imaging modes--secondary, A COMPREHENSIVE ANALYTICAL backscattered and transmitted electron, specimen INSTRUMENT current and cathodoluminescence. (4) Advanced image manipulation and video Innovative detectors with flexible fibre optics facilities include automatic data registration, linkage to external photomultiplier/pre-amplifier split-screen imaging, signal mixing and subtrac- combinations have produced dramatic advances tion. in image analysis for the new Philips scanning (5) Unique Data Link provides parallel con- electron microscope, SEM 505. The sensitivnection of all control modules; interchange, up- ity of the detectors in backscatter mode is such dating or expansion is quick and simple. that when used for image analysis improved (6) EDAX PV 9100 energy dispersive and levels of atomic number resolution are attained. Microspec WDX-2A wavelength dispersive X- Further, the space created by the compactness of ray spectrometers always have optimum the system allowed the designers to develop a nogeometry. compromise geometry for both wavelength- and (7) WEDAX option co-ordinates energy dis- energy-dispersive X-ray spectrometers. persive and wavelength dispersive X-ray analysis. Automation and integration of these systems (8) Omnicon Sigma 200R provides on-line has been developed to such an extent that the SEM image analysis, and can be integrated with total potential of the SEM 505 has yet to be fully the energy dispersive X-ray spectrometer. explored. (9) Analytical multi-sample holder movements may be joystick controlled through motor Image analysis drives, facilitating rapid accurate switching from The new detector system is used for either standard to sample and relocation of specific backscattered electrons or cathodoluminescence. points-of-interest. There are four multi-function detectors grouped (10) EDAX PV 9100 control of analytical beneath the final lens, and each can act in either multi-sample holder allows for automatic analysis mode. Conversion from one to the other is quick of pre-located points. and simple. (11) Latest circuit technology, top quality When used in the backscatter mode for image components and computer aided design have analysis, resolution of atomic number provides provided numerous further benefits. These sufficient contrast that a copper/nickel interface includeshows a contrast difference of four grey levels for (i) easy operation ensured by functionally an atomic number difference of one. This opens related layout of control module panels; the way to image analysis of metallurgical phases. (ii) high quality illumination from unique The SEM 505 can be equipped with the OmniPhilips tungsten mini-gun and optimised double 'con Sigma 200R for on-line image analysis. This 147
148
New Apparatus
Fig. I. Philips' new scanning electron microscope, the SEM 505, which has the innovative multi-function detectors that give greatly improved detection of backscattered electrons and cathodoluminescence, without interference with any of the other detection systems. provides digital scan generation, a detection module with control facility, plus a minicomputer with print-out terminal and optional floppy disc system. Integration of this system with the energydispersive X-ray spectrometer creates an interestingly versatile analytical system.
X-ray analysis The energy-dispersive X-ray spectrometer, EDS, functions at both eucentric positions of the goniometer, providing take-off angles of 16 and 26 °. Detector specimen distance is adjustable for optimisation of the solid angle. The EDAX PV 9100 EDS used gives rapid simultaneous elemental analysis over the range sodium to uranium. A special detector with removable window is availab!e for light element detection, down to carbon. Automatic peak identification simplifies analysis of major components. Elemental distribution or relative distribution of elements and background can be mapped and related to other
images of the same area, e.g. backscattered or secondary-electron images. Line scans or elemental maps can be stored for up to four elements at a time. A special slow-line-scan facility of the SEM 505 provides high quality statistics. F R A M E C or COR 2 ZAF correction methods provide high quality quantitative results. The Microspec WDX-2A wavelength-dispersive spectrometer, WDS, provides fully automated qualitative and quantitative analysis of all elements down to beryllium. It has a microprocessor based integrated digital control system. Programmable operation allows automatic selection of wavelength position, with reproducibility 0.00l nm LiF equivalent and eight selectable scan speeds for each of a choice of four crystals mounted on a rotating turret. Slit size in 0.01 mm steps up to 2.5 mm, and slit position, for precise alignment with respect to the diffracted beam, are also automatically selected.
New Apparatus
149
Fig. 2. The new Philips scanning electron microscope, SEM 505, showing the wavelengthdispersive X-ray spectrometer,immediatelybehind the column.The display-screenand operatingkeyboardfor the energy dispersive X-ray spectrometer are visible in the background. The control panel is fitted with a second viewingmonitor and, at the right-hand-side,a videoscope.
All analysis parameters are programmable in selected step intervals, including amplifier gain, analyser lower level and window, counter and timer operation, ratemeter output ranges and time constants, and detector high voltage supply. The spectrometer operates in four modes: manual; scan, over a pre-set wavelength range; element, measuring a given set of elements from a storage capacity of 90; and external, where control is by an external automated system. WEDAX
Simultaneous operation of the two X-ray analytical systems, in combination is possible with the aid of an external automated control system, WEDAX 3. A special geometric configuration of the energy dispersive detector provides the same take-off angle as the wavelength dispersive spectrometer (35°), it also allows operation at the same beam current. This, combined with the arrangement of the WDS so that its focussing is height insensitive, ensures that the output of the two spectrometers is truly compatible and can be fully automated. The combination offers the superior trace element performance and light element detection
of the WDS with the heavy element detection and convenient simultaneity of the EDS, all centrally controlled. The speed and convenience of the system is further enhanced by the analytical specimen holder. This provides accommodation for a selection of standard and metallurgical mounts. Stage motor drives for X, Y and rotation movements are joystick controlled. Any point on any of the specimens can be relocated, with an accuracy of 2/zm and any specimen reselected within 4 see, with no need to re-open the chamber. Thus allowing for rapid comparisons of standards and unknowns. Automation
Optical identification of points-of-interest in specimens with insufficient electron interaction contrast, and their subsequent analysis is laborious and occupies an expensive installation for a simple task. The anomaly is increased when low versatility, limited operation built-in optical microscopes are used. In the SEM 505 centralised control through the WEDAX system enables the user to examine specimens under an independent top-quality
150
New Apparatus
optical microscope and register co-ordinates of points for analysis in the memory of the EDAX PV 9100. The sample is then fitted into the electron microscope and orientated. Relocation of all registered co-ordinates and analysis proceeds automatically. The co-ordinates of points for analysis on a further sample can be recorded as this analysis continues, thus the installation need never be under utilised.
High quality illumination High quality illumination is obtained from the unique Philips tungsten filament mini-gun and optimised double-lens condenser system. This is a further contribution to the excellent TV rate imaging of the SEM 505. Gun brightness is 2 × 105Acm -2 sr at 30kV, and the plug-in Wehnelt cylinder has facilities for varying the filament-Wehnelt distance and the Wehnelt aperture diameter for special applications. An optional single crystal LaBe source gives up to a ten-fold increase in gun brightness and extended lifetime. The source has a simple plugin mounting making it interchangeable with the standard gun. Advantages include high quality analysis, improved image definition and higher scanning rates.
Flexible imaging The four backscattered electron or cathodoluminescence detectors are connected in pairs to
two photomultipliers outside the chamber. Optical switches enable the images to be mixed or isolated as required. Because of their compactness the new detectors do not interfere in the excellent performance of the secondary-electron detector. A similar arrangement of detector, optical fibre linkage and photo-multiplier pre-amplifier combination is used beneath the stage for transmitted electrons. Signals from any two of these detectors plus the specimen current can be mixed, and/or inverted. Extensive video-handling capacity in the SEM 505 includes enhancement of fine detail, splitscreen imaging and automatic data registration. All control modules are connected in parallel to a unique Data Link which carries all information relevant to adjustment of microscope parameters. This system permits interchange of modules, up-dating or expansion, quickly and simply in response to changing needs. Thus in the SEM 505 Philips has achieved, for the first time in scanning electron microscopy, optimisation of all modes visual and analytical, with no compromises. The SEM 505 also represents a significant improvement in price performance ratio. These features combine with Philips' application support, worldwide service network and long-term guarantee of spares availability to provide the value for money only obtainable from a world leader in scientific instrumentation.
Fig. 3. Four of the innovative multi-function detectors, from the new Philips SEM 505 scanning electron microscope, surround a sample. Signals are transmitted from the detectors using fibre optics bundles.
New Apparatus FIBRE OPTICS AND ADVANCED VIDEO CONTROL GIVE THE SCANNING ELECTRON MICROSCOPE UNEQUALLED VERSATILITY Dramatically increased sensitivity of backscattered electron and cathodoluminescence detection have been achieved by Philips in the design of the new scanning electron microscope, the SEM 505. These increases have been achieved without any reduction in performance of the secondary-electron detector or X-ray spectrometers. Combined with a unique Data Link for modular units and extensive capacity for image manipulation, this produces a simple-to-operate instrument with unprecedented versatility in imaging modes and excellent analytical capability.
New detectors and fibre optics Four compact detectors beneath the final lens are used for either backscattered electrons or cathodoluminescence. Conversion from one mode to the other is quick and simple, and the specially developed scintillator for the detection of backscattered electrons lasts the lifetime of the instrument. The signals from the detectors are carried, in two pairs, using flexible fibre optics, to two photomultiplier pre-amplifier combinations outside the evacuated specimen chamber. Optical switches allow rapid changeover from one detector to another, for instance switching mode from backscatter to cathodoluminescence, or signal mixing. This system, which is the subject of a patent application, is so sensitive that detection of backscattered electrons and cathodoluminescence has been improved two-hundred fold over the standard of the previous detectors. The flexibility of fibre optics allows each detecting element to be placed in an ideal position for any function, without the limitations of fixed constructions or precise port locations. The availability of four elements mounted under the final lens makes it possible to simulate either point source or diffuse illumination and to rotate this source around a stationary specimen. The same arrangement, with fibre optics and a photomultiplier, is used for the transmitted electron detector, operating in conjunction with a suitable aperture to give bright or dark-field images. The SEM 505 has as standard a secon-
151
dary-electron detector and facilities for measuring specimen current thus providing comprehensive imaging capabilities. The fast response of the fibre optics system permits TV-rate images to be produced in all detection modes, even at low kV values. Hence output can also be through closed circuit TV monitors or for video recording. An optional module enables the operator to select and mix any two of all the available signals, with inversion facilities if required. The mix can be varied continuously from 100% of one signal to 100.%oof the other.
Data Link The modular control units of the SEM 505 are all connected in parallel via a unique Data Link system. The Data Link carries all information relevant to the control of the microscope, enabling automatic adjustment of compensating circuits and readout for any selection of operating parameters. Control modules on the Data Link can be interchanged easily, so siting of modules can be arranged according to user preference. This provides for fast simple adaptation in response to changing requirements. Also, additional modules can be added to give convenient upgrading. Video control The comprehensive video control facilities of the SEM 505 include enhancement of fine detail by mixing of the differentiated video signal with the unprocessed signal. Extra information can be gained from dark areas by applying variable gamma amplification to the video signal. Switching between the processed and unprocessed image is simplified by an independent black level control which allows the original detector settings to remain unaltered. A single module provides facilities for splitscreen imaging. This can be used to compare images differentially magnified (up to eight times difference), images from two different detection sources or subjected to two different processing conditions, or to produce a stereo pair obtained at two different angles of tilt. The same module also supplies automatic registration of factors such as image scale, kV value, magnification, detectors in use, as a continuously displayed alphanumeric code along the lower edge of the image. Additionally, it allows scan rotation up to 360 ° and tilt correction,
152
New Apparatus
eliminating dimensional foreshortening of the image, up to 70 °. A logical system has been developed for routing of video signals, preventing the SEM 505 from reacting to any 'illegal' instructions.
Easy operation Easy operation is ensured by the control module panels which have been carefully designed to give a functionally related layout. For example the focussing control most used is placed immediately above the desk for easy locatiOn and relaxed adjustment. Simple optimisation and recording of images is obtained through the provision of independent contrast and brightness controls for viewing and photographic channels, and the high speed response video level indicator. The photographic sequence is automatic. Maximum use of the available contrast and accurate calibration of photographic systems is achieved using an internally generated greyscale. High-quality illumination High-quality illumination is obtained from the unique Philips tungsten filament mini-gun and optimised double-lens condenser system. This is a further contribution to the excellent TV-rate imaging of the SEM 505. Gun brightness is 2 x 105A cm -2 sr at 30kV, and the plug-in Wehnelt cylinder has facilities for varying the filament-Wehnelt distance and the Wehnelt aperture diameter for special applications. Variable Wehnelt biasing provides an additional dimension for control of emission. An optional single crystal LaB~ source can give a ten-fold increase in gun brightness and extended lifetime. It has a simple plug-in mounting making it interchangeable with the standard gun. Advantages include high quality analysis, improved image definition and higher scanning rates. Stable reliable electronics and optics Latest circuit technology, top quality components and computer aided design provide excellent electronic stability and reliability. The versatile electron optical configuration allows almost all tasks to be carried out without the need to change the aperture. Accurate alignment of the complete electron optical system can be achieved in seconds using electromagnetic fine controls. Centering of the
final aperture is never required, due to precision manufacture and assembly. Focussing is fully compensated for changes in high tension and spot size. Spot sizes range from 4 nm to 1000 nm with seven precision switched values and continuous variation between steps. A resolution of 6 nm is guaranteed with 5 nm attainable. Astigmatism correction is made easy by the provision of discrete focussing steps and superb TV-rate imaging. The electron optics are fully isolated from the exceptionally clean high quality vacuum, in the order of 1.3 × 10-4pa, (10-6Torr).
Eucentric goniometer The eucentric goniometer stage provides six independent specimen movements. Fast precise orientation is obtained by the use of back-lash free goniometer drives. The simple design gives fully eucentric specimen tilting at two precisely defined working distances. Up to 90 ° tilt is available. Excellent reproducibility of positioning is ensured by the following performance characteristics, routinely achieved: (i) accuracy of eucentricity is such that specimen detail is retained on screen over a wide range of tilt, for magnifications up to 10,000x; (ii) flatness of the X-Y movement is better than 2 tzm over the whole table; (iii) drift of the specimen with respect to the optical axis is better than 20 nm 10 min -1 in the iV- Y plane. The specimen chamber is designed for unrestricted access to the whole specimen mounting stage. This also allows quick exchange of substages and special holders for applications such as bulk specimens. Analysis The SEM 505 can also function as a powerful X-ray analytical instrument. Accepting both wavelength and energy dispersive spectrometers simultaneously, it provides excellent qualitative and quantitative analyses. The memory of the EDAX PV 9100 60 system can be programmed independently, for automatic relocation of points for analysis. Further Information from: Tony Gooda.._ll, Pye Unicam Ltd., York Street, Cambridge CB1 2PX. Tel. : (0223) 358866, Ext. 368.