Vacuum news

Barium titanate thin lilm material A new grade of barium titanate of 99.99 per cent purity, claimed to be the highest com- mercially available, has been developed by Materials Research Company Ltd speci- fically for the preparation of ferroel&tric thin films. Films of MRC BaTiOa have been prepared with dielectric constants in excess of-1 500 and consistently controllable reoroducibilitv which has traditionally been hampered by i-mpurities commonly fo&d in materials that are only 98 per cent pure. The material may also be produced to contain a selective addition of other titanates, stannates, zirconates, etc, as may be requir- ed in the development of barium thin film devices of various characteristics. These compounds would be custom-manufactured in accordance with device specifications as to what additions are to be incorporated in the svnthesis while the 99.99 ner cent nuritv is maintained. The MRC b&urn titanate is available in the form of powder, evapora- tion slugs and sputtering targets. Materials Research Co Ltd, 303 Ballards Lane, London, N12 8NP.

Spanning the gap between optical and con- ventional electron microscopes The JEOL JSM-Sl is a recently developed scanning microscope, first introduced at the International Conference on Electron Microscopy, Grenoble, and exhibited in the UK for the first time at Micro 70.

Combining high performance with the competitive price, ihe JSM-Sl has been designed for a wide range of industrial and laboratory applicatio& in materials science, semiconductor technology, quality control, biology, etc. The guaranteed reso- lution is 250 AU. and the magnification range x 19 to x 100,000 in standard mode and x 63 to x 10.000 in TV mode (high speed scan). Acceldrating voltages are 4 kV and 10 kV.

The instrument is particularly easy to use and all controls are grouped compactly in the ergonomically designed console. Solid state electronics are used throughout for maximum reliability and simplified servic- ing.

The great depth of focus enables observa- tions of thick sections and rough-surfaced specimens to be made and eliminates much of the time generally required for the pre- paration of replicas. No alignment of the column is necessary. The automatic vacuum is controlled by pneumatic valves and changes of specimen can be made rapidly, without breaking the column vacuum. The universal goniometer stage enables precise specimen movements X-Y linear, rotation through 360” and tilting through 50” (-5” to + 45”).

Photographic facilities include manual and electronic synchronised shutters and exposure meter. The instrument may also be adapted for videotape recording. Jeolco (UK) Ltd, Jeolco House, Grove Park, London, NW9 OJN.

Development of the Torvac Metallizing plant M E Boston, MA, Joint Managing Director

The new JEOL JSM-SI scanning microscope.

of Torvac gave a paper entitled “Critical considerations in the design of semi- continuous olant” at the First International Conference bn Vacuum Coating in London on February 11 th. Cambridge Conference Services have issued the following report of this paper.

Reviewing twenty years of work on vacuum metallizing, Mr Malcolm Boston, Joint Managing Director of Torvac of Cambridge discussed developments with which he had been directly concerned in the evolution of metallizing machines and a widening range of application of the tech- nique.

During the years 1947-58 work was con- centrated on achieving higher rates of evaporation of aluminium from more

reliable sources with longer life. Research on resistance heated materials culminated in the discovery and development of com- posites. Malcolm Boston, Paul Alexander and Alex Baxter were the pioneer workers in this field.

Carbon rods were used, and other grades of carbon machined to special shapes; on these were fired in vacua carbides (titanmm, zirconium, hafnium). Much time was spent evolving better end contacts and bus bars to carry the current with minimum reactance to allow thermal expansion of the heater itself. A number of patents were applied for during this period, but most were super- seded before oublication. Further develoo- ment along these lines was transferred to the USA with the termination of the

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Vacuum news

One of the many uses of Torvacs metallized polyester film.

The new Torvac 21124 Vacuum metallizer now available ensures high output at low operating cost. Metallizing speeds up to 1000 ft per min (20,000 metres per hour) are attainable, with winding speeds up to 50 per cent higher. The chamber will take jumbo rolls up to 21 in. (535 mm) dia. This picture shows the machine open readyfor loading.

Malcolm Boston (R) joint Managing Director of Torvac of Cambridge, with Syd Hamon (L) his Production Manager, inspecting the latest 24121 vacuum metallizer, being built under contract to an electronics manufacturer in Belgium.

partnership in 1951. Construction developed during this

period: early machines had open spans and multiple cooled rollers were introduced. Mechanical boosters were introduced in 1954, to give more powerful vapour pumps, making it possible to increase the speed and efficiency of pump-down.

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Early machines had one or two rows of evaporating boats placed beneath an un- supported horizontal web. In 1952 rotating d&is were introduced to convey the web; these were cooled, and later chilled. The form of feeder introduced at that time is now universally used: this involves two driven gears nipping the wire and feeding it

into a directed tube. During the 1950’s the basis of the present

machines was developed. This entailed access to machines at both ends for clean- ing, replenishing the evaporation system, and reloading, and to give best access to the drive system and pumps. A stationary chamber with both ends opening full aper- ture permitted large pumping ports for the high capacity pumps and large diameter flat bulkheads mounted on wheeled pedes- tals running on rails gave good access to the mechanical parts as well as accessi- bility to each of the separate sections. The winding system is wholly cantilevered on an accurate frame on one end, the evapora- tion system wholly on the other. The pedes- tal frame made it possible to mount the very heavy current power transformers avoiding the need for flexible or demount- able connections. At the same time the circular vessel was displaced by a rectangu- lar tank, giving substantially more usable space for a given volume, and more space above the median plane for larger pay-off and take-up reels.

introduction of polyester film. The intro- duction of polyester film in the USA in 1952 -the first high temperature resistant polymer-and the rapid increase in com- mercial demand for metallized yarn acted as a stimulant to the development of metal- lizing plant. Machines were built with the capacity to handle web widths up to 66 inch with reel diameter of 27 inch. The Christmas decoration and packaging trades were interested, but this could not be developed due to the cost of polyester at the time.

In the United States in 1956 a serious attempt was made to develop a metallized paper for packaging. The best-known result of this work is on an acetate film: the Ever- Ready battery label. Reverse-printed and back-metallized, this product remained unique and played a significant part in the

Vacuum news

sales of the battery-largely on eye-appeal. DeveloDment of plastic film for caoacitors.

In 1958 interest in Europe focused on the use of polyester and polystyrene as di- electrics, and thence towards polycarbonate. A machine was developed to metallize very thin grades uniformly without pinholes or creases and free of surface charges: man- datory specifications for capacitor grade work. The optimum width in this produc- tion was established at 12 inches. A single capstan roller, accurately aligned with reduced spans, was installed and produced tolerable film at greater speed: 6 micron film became easy to produce, then 3 micron, and finally 2 micron after removing polariz- ing charges on the surface. By the adoption of carrier techniques it became possible to metallize down to 9 micron, but this was not a commercial proposition.

Capacitor metallizing requires film with a very accurate resistance, or with graded resistance; material must be margined, and possibly slit and metallized in one opera- tion. Margining was originally attained by silhouette with curved water-cooled hollow bars close to the film surface; but other methods include slow or fast moving tapes.

Winding system design. The use-of sen- sitive and thin mastic film calls for a verv precise winding system with accurately balanced rollers, carefully aligned, free running and with hardened surfaces of minimum inertia mounted in a rigid frame. A prerequisite for crease free handling is minimum unsupported spans and wind-up on the take-up reel in contact with the last roller. This is achieved by means of a roller on a shaft keyed to two pinions at each end, running in a rack. This rolls against the take-up reels and is displaced along the rack as it increases in diameter. While an alternative system, the pivoted cluster, offers advantages, it is by comparison a cumbersome device.

To avoid telescoping during wind-up controllable torque was introduced and this is used today. An essential feature of the winding system is a drive which oper- ates without snatch and responds quickly to changes.

Control of metal vapour deposits. The interior surfaces of metallizers coated with aluminium and alumina crust absorb moisture and atmospheric gases very fast and desorb them under vacuum environ- ment of 1 to 10 microns and better. This slows pump-down significantly and too early metallizing results in further deposi- tion. This factor has been minimized by introducing water-cooled shields surround- ing the vapour sources so that the lining of the machine can be renewed progressively. It is now possible, with care, to begin heat- ing the metallizing boats in about 2 minutes and metallizing within 5 minutes, com- pared with the hour’s pump-down time accepted in practice a few-years ago.

‘Two chamber’ design. The material to be metallized will outgas during pump-down time from the exposed surface and the edges, as fresh surface is exposed, and at the instant of metallizinu. Evolution of eas from the cardboard cores used to reel The supply material is also significant: most film makers are now ready to overcome this.

The problem has been overcome by pro- viding a dividing diaphragm across the centre of the vacuum tank, to maintain a pressure ratio of 1O:l across it. While it might be desirable to improve the fit further, it would probably not be practic- able beyond 200 or 300: 1. The introduction of the dividing diaphragm and other features have reduced pump-down to the expected 3 minutes.

Many problems still unsolved. Malcolm Boston ended by posing questions for the future: What is the mechanism involved in the erosion of the composite boats- thermal, electrochemical, diffusion? If this erosion could be reduced it would cut down the largest cost factor in the whole produc- tion operation. He suggested that a renewed look at this problem could be rewarding. Might it be possible to generate a metallic arc, or to direct the metal vapour as in electrostatic spraying? Could very high speed running of the film past the vapour overcome diffusion of moisture on the sur- face? What is the mechanism of nucleation and adhesion? He invited discussion of these questions from the floor.

High capacity electron beam evaporator

A new Electron Beam Source and associ- ated Power Supply has been introduced by G V Planer Ltd to satisfy the current demand for vacuum evaporators with large capacity for production coating purposes. A special feature of the equipment is the readily interchangeable water-cooled copper hearth and graphite crucible recep- tacles for the evaporant.

The equipment is rated at 5 kW, opera- ting at voltages continuously variable to 10 kV and currents to 500 mA, the LT fila- ment supply being 16V/25A. The power supply has appropriate surge and overload protection and is fully interlocked.

This equipment extends the Planer range

New high capacity ejectron beam source.

of lower powered Electron Beam Evapor- ators,being particularly designed for use in applications where relatively large areas of substrates have to be coated to a high degree of uniformity. To this end, the source is arranged to provide for a large cone angle of evaporation (approx 90”) and utilizes an evaporant receptacle of nomin- ally 40 mm diameter.

The water-cooled copper hearth con- figuration may be used for the deposition of a wide range of high melting metals, in- cluding for instance tantalum, molyb- denum, titanium, etc, as well as refractory materials, such as zirconia, alumina, ceria, etc; the interchangeable special graphite crucible, also of large capacity, is advan- tageously employed in the evaporation of special glass compositions, as well as silica and the like, used as dielectrics or protec- tive layers.

The source and associated power supply are designed to allow ready incorporation in standard vacuum coating plants, being a low-cost adjunct to such systems for small or large scale production coating processes. G V Planer Ltd, UK, Windmill Road, Sunbury-on-Thames, Middx

New equipment from Edwards at Labex

Edwards High Vacuum (Plant) introduced a number of items on Stand G23 at the Laboratory Equipment Exhibition at Earls Court on March 29th to Aoril 2nd. These included a new freeze dryer-and equipment for preparing electron microscope speci- mens. The EF3 series of freeze dryers con- sists of two basic models: a manifold dryer for handling pre-frozen materials in bulk containers, and a shelf dryer for handling vials or small specimens, they can be supplied with a single condenser of 3 kg ice capacity or double condensers can be fitted where continuous working is required, each operating alternately while the other is defrosted. The manifold freeze dryer EF301 provides 10 l-inch connectors which can accommodate flasks, drying tubes or special containers. Alternatively a tray attachment in a lightweight chamber can be substituted for the manifold. A thermo- statically controlled freezing bath can be supplied for pre-freezing material down to minus 35°C. The shelf freeze dryer EF302 can be supplied with one, two, or three shelfs of 273 x280 mm area and can also handle bulk vessels of up to 2 litres volume. Among the optional extras available are a vial stoppering device, a shelf refrigerator (to provide a controlled rate of cooling or maintain a constant low temperature), a cam controller and a six point recorder. Also on display was an Edwards EF03 centrifugal freeze dryer, fitted with a refrigerated condenser of 1 litre ice capacity, this model can handle ampoules and flasks (bv the use of an additional manifold) and can also be fitted for solvent extraction, providing fast evaporation of liquids with- out frothing or contamination. The Edwards E12E series of coating units com- prises models specifically for the prepara- tion of electron microscope specimens, and a number of new accessories was shown for the first time at Labex. The scanning elec-

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