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Tool for surface studies
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
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