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Electro-optics and laser international '82
I"
Grinding Universal Grinding Wheel Company have produced a 90 page manual about grinding wheel application and selection entitled 'Grinding Technology'. This application manual provides background information on grinding wheel technology and some 1000 applications. It is designed to provide the practical engineer with information on selection of wheels for major grinding applications. The recommendations are based on practical experience and assume that normal operating conditions apply. Universal Grinding Wheel Company Ltd, Doxey Road, Stafford, UK, ST16 l E A
Tool for surface studies 'Tunnelling' of electrons through a thin vacuum is the basis of an experiment on the wave nature of electrons, an experiment that has eluded physicists for fifty years, and has been accomplished at the IBM Research Laboratory in Zurich, Switzerland. Quantum mechanics recognises both the wave and particle properties of such particles as electrons. As waves, when they encounter a barrier such as a vacuum, they are not deflected, but penetrate a short distance into the barrier. If the barrier is thin enough, some part of the wave penetrates it and appears on the other side as an electric current. This is called tunnelling. Tunnelling was observed in thin barriers in solids as early as 1957, and has been studied extensively because it provides detailed scientific information about the behaviour of electrons in materials. In addition to its scientific interest, electron tunnelling in solids is the basis of a number of high-performance electronic devices such as the tunnel diode. The Zurich experiments have, for the first time, shown unequivocally tunnelling through a vacuum between two electrodes, one a tungsten needle probe and the other a flat platinum sample. Tunnelling through a vacuum is difficult to observe because it occurs only over a few atomic diameters. The slightest vibration can ruin such an experiment. (Earlier vacuum tunnelling
172
experiments, notably at the National Bureau of Standards and at IBM's Yorktown, NY, research laboratory were plagued by vibration problems, and produced somewhat ambiguous results.) The Zurich researchers have reduced vibrations to a sufficiently low level in two stages. Vibrations from the building are filtered out by placing the experimental vacuum chamber on a heavy stone slab mounted on what amounts to a set of inner tubes. Other vibrations are filtered out by magnetically levitating the apparatus within the vacuum chamber. Within the levitated apparatus, high precision positioning of the probe, both of its distance from the sample and its position along the sample surface, is accomplished by applying a voltage to piezoelectric blocks on which the sample is mounted. The sensitivity of the piezoelectric mounts is about 0.1 nm V -I , permitting the relative positions of needle and target to be controlled easily to within 0.1 nm. Thus, it becomes possible to perform a process called tunnelling microscopy. Tunnelling microscopy can give very precise information about the topography of a surface into which electrons are tunnelling, because the tunnelling current is an exponential function of the distance between needle and surface. For example, a change in the distance of a single atomic diameter (about 0.3 nm) changes the tunnelling current by a factor of up to a thousand. Topographic pictures with clearly resolved monatomic steps have already
been obtained for metal and semiconductor surfaces. This corresponds to a resolution up to hundred times better than possible with conventional scanning electron microscopes. For other scientific studies, vacuum tunnelling has the advantage of providing the simplest experimental situation. It depends only on the surfaces and composition of the two electrodes. The tunnelling barrier, a vacuum, is much better characterized than the oxide or semiconductor junction barriers used in previous tunnelling experiments. This makes vacuum tunnelling particularly interesting for study of inter-atomic forces of molecules adsorbed on surfaces by measuring the energy lost by tunnelling electrons (inelastic tunnelling spectroscopy). Even more interesting, the high spatial resolution of vacuum tunnelling should yield information on preferential adsorption of atoms and molecules at special surface characteristics such as atomic steps. Growth of ultra-thin insulating layers on metals and semiconductors is of increasing technological importance. Monatomic insulating layers drastically change the tunnel barrier and thus the tunnelling current. With vacuum tunnelling, many important features of the growth and behaviour of such layers can be investigated with spatial resolution on the atomic scale. The first experiments are reported in the 15 January 1982 issue. of Applied Physics Letters in a paper by G. K. Binnig, H. Rohrer, C. Gerber and E. Weibel of the Zurich laboratory.
Conference reports 23-25 March 1982, Brighton, UK
Electro-Optics and Laser Internalional '82 Developments in Electro-Optical and Infra-Red Devices The seventh electro-optical and laser conference to be held in England focussed attention on new design techniques and applications of electrooptical systems through a series of parallel technical sessions and professional advancement courses. Fibreoptic systems in telecommunications, photo-detectors, image sensors and
intensifiers, flat-panel displays, infrared and laser applications were all discussed in considerable detail. The exhibition of new products, by more than 240 companies, included a wide range of equipment from the suppliers of special glassesand fibres, modulators, thermal imaging systems and holographic devices.
J U L Y 1982 V O L 4
NO 3
rR=¢|s W.J. Murray of British Telecomshort distance applications, are difficult munications said that the idea of using to focus and often fail over longer glass fibre as a transmission medium was distances. Infra-red laser beam devices given serious consideration during the do not meet the exacting requirements 1960's and subsequent research and for remote and unattended security development had led to practiCal systems when year-long operation must systems for short and long distances. A be guaranteed whatever the weather major contributory factor has been the conditions in hot sunshine or cold new technology for making glass fibres night. The beam must detect a human having low attenuation over relatively form but not insects, animals, or broad bandwidths. Multimode gradientnatural air shimmer. The source which index fibres operating in the 850 nm has proved to be the most reliable is a to 1500 nm wavelength region have an small hot filament pulsed light bulb attenuation of 3 dB per km to 1.5 dB associated with a photo-transistor per km respectively, whilst monomode receiver in a telescope system. A minifibre can have an attenuation of 0.5 dB mum of four beams, around a periper km, enabling regenerators to be meter, are essential for security and placed only every 30 km. A gradientsensitivity is enhanced by automatic index optical glass has a refractive index compensation for background or variwhich varies radially or along the axis able light conditions which overcome so a rod may be pulled into a fibre and the possibility of wilful interference. used for high bandwidth telecomProfessor C. Hilsum of the Royal Signals and Radar Establishment, in a munications. Lasers, edge emitting professional advancement course, prodiodes and light emitting diodes are vided very interesting details concernused for various applications and waveing front panel electronic displays length windows in conjunction with PIN field effect transistor hybrid which are compatible with microelecmodule detectors. Significant economic tronic systems now being developed. and reliability benefits are predicted These new devices exploit solids, from optical-fibre systems, using high liquids, gases and vacua for signs, flow capacity digital links, compared to diagrams, numeric data on calculators copper cable equivalents. and cash registers, bar-graphs on cars Little and Wright of the Central and radio, alphabetic characters on Electricity Generating Board lectured word processors and directories, graphs on the inspection of contaminated on computers or radar, wall displays nuclear reactor fuel elements by holoon destination indicators, and pictorial graphy. The techniques provided on television. A critical feature of the remote safe reconstruction, high resodisplay is its appearance and attractivelution and depth of focus, large aperness for user-appeal legibility but the ture, accessibility of a real image, and cost, including the drive electronics, is the ability to make a series of repeated crucial for consumer electronics. measurements of the width of fuel For the purpose of addressing a pins. The advantage of this method is display, the area of the panel is divided safety in remote measurement but into a number of pixels which can range there is no improvement in accuracy, from 10 in a mimic diagram to over a compared with the use of a vernier million in a high resolution wall disinstrument, because of problems assoplay. A number can be presented as ciated with edge resolution, blemishes, seven bars but the Roman alphabet is speckle and location techniques. usually constructed by a fixed dot forR.E.G. Keon of R.K. Industries mat, with a minimum of 35 dots, in a discussed long range all-weather infra7 x 5 pattern for each character. The red perimeter security barriers for display of a small message can require power stations, warehouses, water activating a large number of pixels. In reservoirs and other remote sites. For order to address a complex panel a reliable all-weather security there are matrix of X lines on one side and an difficulties in penetrating thick snow orthogonal matrix of Y" lines on the or sand with infra-red systems over a other side join pixels at the cross minimum of 200 m. Solid-state infrapoints. With 2 n connections, n 2 pixels red sources, which are suitable for can be addressed but techniques other
PRECISION ENGINEERING
than electronic excitation can be used such as temperature dependent physical phenomena or time-variant funktions. Some displays work by emitted light and others modulate ambient light by control of transmission, absorption, reflection or scattering. Light emitters are inefficient and subtractive displays, which are best seen in bright light, are usually economic in power consumption but require a source of illumination when used under low-light conditions. Light emitting diodes are good indicator lamps but, when used in large numbers, are expensive and may be unreliable. Electroluminescent devices are probably the lowest cost emitters for multiplexed panel displays. Subtractive displays are likely to be based on liquid crystals using a twisted nematic cell. Low voltage, low frequency and low power consumption at a speed better than 100 m s-1 make this technique attractive, using dyes which have been developed since 1980. Professor J.N. Butters of Loughborough University of Technology discussed coherent optical sensor¢, in a professional advancement course, and emphasised the need for non-contacting measurement of components during processing or quality control. Optical devices usually make use of the total intensity of light available by sensing the position of a beam. The capability can be increased when coherent light is used, by not only varying intensity but also wavelength and phase as carriers of information. Diffraction and interference incorporate the fundamentals of a coherent optical system which may use gratings, holograms or electronic speckle pattern interferometry as a means for surface texture monitoring. The exhibition of equipment reflected the growth of multi-layer thin films, emitters and detectors, fibre-optic sources,and connectors. and aspheric optical surfaces including micro-surface generating with single crystal diamond tools. Uses for the near and middle infra-red wavebands are likely to increase in importance as improved materials and new devices become commercially available. D.F. Home
173
Grinding Universal Grinding Wheel Company have produced a 90 page manual about grinding wheel application and selection entitled 'Grinding Technology'. This application manual provides background information on grinding wheel technology and some 1000 applications. It is designed to provide the practical engineer with information on selection of wheels for major grinding applications. The recommendations are based on practical experience and assume that normal operating conditions apply. Universal Grinding Wheel Company Ltd, Doxey Road, Stafford, UK, ST16 l E A
Tool for surface studies 'Tunnelling' of electrons through a thin vacuum is the basis of an experiment on the wave nature of electrons, an experiment that has eluded physicists for fifty years, and has been accomplished at the IBM Research Laboratory in Zurich, Switzerland. Quantum mechanics recognises both the wave and particle properties of such particles as electrons. As waves, when they encounter a barrier such as a vacuum, they are not deflected, but penetrate a short distance into the barrier. If the barrier is thin enough, some part of the wave penetrates it and appears on the other side as an electric current. This is called tunnelling. Tunnelling was observed in thin barriers in solids as early as 1957, and has been studied extensively because it provides detailed scientific information about the behaviour of electrons in materials. In addition to its scientific interest, electron tunnelling in solids is the basis of a number of high-performance electronic devices such as the tunnel diode. The Zurich experiments have, for the first time, shown unequivocally tunnelling through a vacuum between two electrodes, one a tungsten needle probe and the other a flat platinum sample. Tunnelling through a vacuum is difficult to observe because it occurs only over a few atomic diameters. The slightest vibration can ruin such an experiment. (Earlier vacuum tunnelling
172
experiments, notably at the National Bureau of Standards and at IBM's Yorktown, NY, research laboratory were plagued by vibration problems, and produced somewhat ambiguous results.) The Zurich researchers have reduced vibrations to a sufficiently low level in two stages. Vibrations from the building are filtered out by placing the experimental vacuum chamber on a heavy stone slab mounted on what amounts to a set of inner tubes. Other vibrations are filtered out by magnetically levitating the apparatus within the vacuum chamber. Within the levitated apparatus, high precision positioning of the probe, both of its distance from the sample and its position along the sample surface, is accomplished by applying a voltage to piezoelectric blocks on which the sample is mounted. The sensitivity of the piezoelectric mounts is about 0.1 nm V -I , permitting the relative positions of needle and target to be controlled easily to within 0.1 nm. Thus, it becomes possible to perform a process called tunnelling microscopy. Tunnelling microscopy can give very precise information about the topography of a surface into which electrons are tunnelling, because the tunnelling current is an exponential function of the distance between needle and surface. For example, a change in the distance of a single atomic diameter (about 0.3 nm) changes the tunnelling current by a factor of up to a thousand. Topographic pictures with clearly resolved monatomic steps have already
been obtained for metal and semiconductor surfaces. This corresponds to a resolution up to hundred times better than possible with conventional scanning electron microscopes. For other scientific studies, vacuum tunnelling has the advantage of providing the simplest experimental situation. It depends only on the surfaces and composition of the two electrodes. The tunnelling barrier, a vacuum, is much better characterized than the oxide or semiconductor junction barriers used in previous tunnelling experiments. This makes vacuum tunnelling particularly interesting for study of inter-atomic forces of molecules adsorbed on surfaces by measuring the energy lost by tunnelling electrons (inelastic tunnelling spectroscopy). Even more interesting, the high spatial resolution of vacuum tunnelling should yield information on preferential adsorption of atoms and molecules at special surface characteristics such as atomic steps. Growth of ultra-thin insulating layers on metals and semiconductors is of increasing technological importance. Monatomic insulating layers drastically change the tunnel barrier and thus the tunnelling current. With vacuum tunnelling, many important features of the growth and behaviour of such layers can be investigated with spatial resolution on the atomic scale. The first experiments are reported in the 15 January 1982 issue. of Applied Physics Letters in a paper by G. K. Binnig, H. Rohrer, C. Gerber and E. Weibel of the Zurich laboratory.
Conference reports 23-25 March 1982, Brighton, UK
Electro-Optics and Laser Internalional '82 Developments in Electro-Optical and Infra-Red Devices The seventh electro-optical and laser conference to be held in England focussed attention on new design techniques and applications of electrooptical systems through a series of parallel technical sessions and professional advancement courses. Fibreoptic systems in telecommunications, photo-detectors, image sensors and
intensifiers, flat-panel displays, infrared and laser applications were all discussed in considerable detail. The exhibition of new products, by more than 240 companies, included a wide range of equipment from the suppliers of special glassesand fibres, modulators, thermal imaging systems and holographic devices.
J U L Y 1982 V O L 4
NO 3
rR=¢|s W.J. Murray of British Telecomshort distance applications, are difficult munications said that the idea of using to focus and often fail over longer glass fibre as a transmission medium was distances. Infra-red laser beam devices given serious consideration during the do not meet the exacting requirements 1960's and subsequent research and for remote and unattended security development had led to practiCal systems when year-long operation must systems for short and long distances. A be guaranteed whatever the weather major contributory factor has been the conditions in hot sunshine or cold new technology for making glass fibres night. The beam must detect a human having low attenuation over relatively form but not insects, animals, or broad bandwidths. Multimode gradientnatural air shimmer. The source which index fibres operating in the 850 nm has proved to be the most reliable is a to 1500 nm wavelength region have an small hot filament pulsed light bulb attenuation of 3 dB per km to 1.5 dB associated with a photo-transistor per km respectively, whilst monomode receiver in a telescope system. A minifibre can have an attenuation of 0.5 dB mum of four beams, around a periper km, enabling regenerators to be meter, are essential for security and placed only every 30 km. A gradientsensitivity is enhanced by automatic index optical glass has a refractive index compensation for background or variwhich varies radially or along the axis able light conditions which overcome so a rod may be pulled into a fibre and the possibility of wilful interference. used for high bandwidth telecomProfessor C. Hilsum of the Royal Signals and Radar Establishment, in a munications. Lasers, edge emitting professional advancement course, prodiodes and light emitting diodes are vided very interesting details concernused for various applications and waveing front panel electronic displays length windows in conjunction with PIN field effect transistor hybrid which are compatible with microelecmodule detectors. Significant economic tronic systems now being developed. and reliability benefits are predicted These new devices exploit solids, from optical-fibre systems, using high liquids, gases and vacua for signs, flow capacity digital links, compared to diagrams, numeric data on calculators copper cable equivalents. and cash registers, bar-graphs on cars Little and Wright of the Central and radio, alphabetic characters on Electricity Generating Board lectured word processors and directories, graphs on the inspection of contaminated on computers or radar, wall displays nuclear reactor fuel elements by holoon destination indicators, and pictorial graphy. The techniques provided on television. A critical feature of the remote safe reconstruction, high resodisplay is its appearance and attractivelution and depth of focus, large aperness for user-appeal legibility but the ture, accessibility of a real image, and cost, including the drive electronics, is the ability to make a series of repeated crucial for consumer electronics. measurements of the width of fuel For the purpose of addressing a pins. The advantage of this method is display, the area of the panel is divided safety in remote measurement but into a number of pixels which can range there is no improvement in accuracy, from 10 in a mimic diagram to over a compared with the use of a vernier million in a high resolution wall disinstrument, because of problems assoplay. A number can be presented as ciated with edge resolution, blemishes, seven bars but the Roman alphabet is speckle and location techniques. usually constructed by a fixed dot forR.E.G. Keon of R.K. Industries mat, with a minimum of 35 dots, in a discussed long range all-weather infra7 x 5 pattern for each character. The red perimeter security barriers for display of a small message can require power stations, warehouses, water activating a large number of pixels. In reservoirs and other remote sites. For order to address a complex panel a reliable all-weather security there are matrix of X lines on one side and an difficulties in penetrating thick snow orthogonal matrix of Y" lines on the or sand with infra-red systems over a other side join pixels at the cross minimum of 200 m. Solid-state infrapoints. With 2 n connections, n 2 pixels red sources, which are suitable for can be addressed but techniques other
PRECISION ENGINEERING
than electronic excitation can be used such as temperature dependent physical phenomena or time-variant funktions. Some displays work by emitted light and others modulate ambient light by control of transmission, absorption, reflection or scattering. Light emitters are inefficient and subtractive displays, which are best seen in bright light, are usually economic in power consumption but require a source of illumination when used under low-light conditions. Light emitting diodes are good indicator lamps but, when used in large numbers, are expensive and may be unreliable. Electroluminescent devices are probably the lowest cost emitters for multiplexed panel displays. Subtractive displays are likely to be based on liquid crystals using a twisted nematic cell. Low voltage, low frequency and low power consumption at a speed better than 100 m s-1 make this technique attractive, using dyes which have been developed since 1980. Professor J.N. Butters of Loughborough University of Technology discussed coherent optical sensor¢, in a professional advancement course, and emphasised the need for non-contacting measurement of components during processing or quality control. Optical devices usually make use of the total intensity of light available by sensing the position of a beam. The capability can be increased when coherent light is used, by not only varying intensity but also wavelength and phase as carriers of information. Diffraction and interference incorporate the fundamentals of a coherent optical system which may use gratings, holograms or electronic speckle pattern interferometry as a means for surface texture monitoring. The exhibition of equipment reflected the growth of multi-layer thin films, emitters and detectors, fibre-optic sources,and connectors. and aspheric optical surfaces including micro-surface generating with single crystal diamond tools. Uses for the near and middle infra-red wavebands are likely to increase in importance as improved materials and new devices become commercially available. D.F. Home
173