32 



M. E. MAINE AND R. S. PAGE 



Breite dient fiir Ubersichtsbilder) einzustellen. Zur 

 Registrierung von Versuchsdaten dienen auf dem 

 Rand des Films aufzubringende Lichtmarken. Zum 

 Anbau an das Mikroskop (s. Abb. 2) wird das 

 vorstehend beschriebene Gerat einfachgegendasden 

 Mechanismus fiir den Pkittentransport dienende 

 Bauteil der normalen PkUtenschleuse ausgetauscht. 

 Zum Gesamtaufbau des Cerates sei bemerkt, daB 

 die Einspeisung der Hochspannungsanlage durch 

 einen stabilisierten Rohrengenerator (125 Hz) er- 

 folgt. Die auf Kathodenpotential liegenden Hilfs- 

 spannungen warden iiber HF-Sender erzeugt. 



Bine ausfiihrliche Publikation, die auch auf die 

 konstruktiven Einzelheiten eingeht, erscheint in der 

 Zeitschrift Optik. 



LiTERATUR 



1. Bethge, H., Optik 10, 137 (1953). 



2. BoERSCH, H., Ann. Physik 11, 75 (1936). 



3. BoETTCHER, A. uiid Thun, R., Physik. Verhandltingen 3, 



115 (1953); Optik 11, 22 (1954)'. 



4. Heise, F., Optik 9, 139 (1952). 



5. Rang, O., Optik 5, 518 (1949). 



A New Universal Electron Microscope of High Resolving Power: 



Metro-Vick Type EM6 



M. E. Haine and R. S. Page 



Metropolitan-Vickers Electrical Co. Ltd (R. S. P.) and A. E. I. Research (M. E. H.) 



In the course of the last few years research and 

 development work at Aldermaston and Manchester 

 has led to new conceptions in the design of electron 

 microscopes. Some of this work has already been 

 reported at earlier conferences or in published papers 

 and a number of features have been in operation in 

 experimental microscopes and in the Metro-Vick 

 Type EM3A. A new instrument has now been 

 designed and the prototype, which is the subject of 

 this paper, has been in operation for several months. 

 The principal objects in the new design have been 

 the reliable attainment of a high resolving power 

 coupled with ease of operation and versatility in 

 application. 



The most important components of an electron 

 microscope, the electron gun, and the lenses have 

 been the subjects of special attention. In order to 

 provide sufficient illumination for focussing at high 

 magnification it is necessary to operate the electron 

 gun at a brightness approaching the theoretical limit 

 (2) and, more important, to be able to maintain this 

 performance without internal adjustments. A simple 

 method of checking and adjusting the gun for 

 optimum performance has been adopted which 

 allows this operation to be carried out in a few sec- 

 onds without dismantling. 



The work of Liebmann (3) and Mulvey (4) has 

 enabled lenses to be designed with the required 

 focal characteristics which are free from undesirable 

 characteristics such as tilting of the magnetic axis 

 with change of excitation. It is now possible to align 

 the image forming lenses using preset controls know- 

 ing that the alignment will be maintained over the 

 full range of lens excitation. Other new features of 

 the microscope will appear in the following descrip- 

 tion. 



The instrument uses conventional principles in 

 respect of the electron optical parts with a column 

 mounted vertically on a wide desk, the power supplies 

 being kept in a separate cabinet. This arrangement 

 allows greater flexibility in installation than the 

 single unit construction and provides more freedom 

 of choice in the selection of suitably rated components 

 for the power supplies since magnetic fields and heat 

 from valves are well removed from the microscope. 



The electron gun is of rugged and simple construc- 

 tion with the h.t. cable permanently sealed into the 

 porcelain insulator. The upper half of the earthed 

 anode cylinder is hinged to provide access to the 

 cathode assembly which is removable, by a bayonet 

 catch, from the end of the insulator. When replacing 

 a filament, the cathode assembly is removed and 

 the new filament tip centred in the cathode shield 

 aperture by means of three adjusting screws. Cen- 

 tering the filament tip in the 1 mm diameter aperture 

 by visual estimation provides sufficient accuracy of 

 alignment. The anode aperture is adjustable by 

 means of two screw controls outside the vacuum 

 wall. It is this feature which allows the beam to be 

 easily aligned with the condenser lenses to provide 

 maximum gun brightness. This operation is further 

 simplified by means of a current collecting probe 

 which can be inserted into the beam below the con- 

 denser lens aperture. The current collected by this 

 probe is a direct measure of the gun brightness which 

 is adjusted using the anode aperture alignment, bias 

 voltage and filament heating current. The anode 

 aperture plate can be removed for cleaning as also 

 can contamination screens through the bores of the 

 condenser lenses. 



Two condenser lenses, built as a single unit, are 

 used to provide a small illumination spot size down 



